Asbestos is the generic term for a group of naturally occurring fibrous minerals with high tensile strength, flexibility, and resistance to thermal, chemical and electrical conditions. Asbestos fibers are of high-tensile strength, flexible, heat and chemical resistance, and good frictional properties. Cement is the most essential raw material in any kind of construction activity. Ceramics also known as fire clay is an inorganic, non-metallic solid article, which is produced by the art or technique of heat and subsequent cooling. Limestone is a sedimentary rock, mainly composed of calcium carbonate (CaCO3). It is the principal source of crushed stone for construction, transportation, agriculture, and industrial uses.
Emerging applications in commercial sectors such as asbestos, cement and ceramic are poised to fuel demand in the coming years. Growing demand for limestone in the production of cement as well as in several other chemicals that are used in the production of high-value every-day products offers significant opportunities for growth. Global Limestone consumption is projected to reach 5.7 billion tons and expected to grow at an average annual rate of 4–5% in coming years. Presently, cement production is 330 million tonnes and expected to double to reach almost 550 million tonnes in future.
The major contents of the book are asbestos, monitoring and identification of air-borne asbestos, asbestos in industrial applications, asbestos – cement products, non – occupational asbestos emissions and exposures, cements, mortars and concrete, raw materials, additives and fuels for cement, processes of manufacturing of cement, cement based on natural and artificial pozzolanas, fast-setting cements, special portland cements, packing of cement, storages of cement, ceramics, lime & limestone, glass & glass ceramics etc. It describes the manufacturing processes and photographs of plant & machinery with supplier’s contact details.
It will be a standard reference book for professionals, entrepreneurs, those studying and researching in this important area and others interested in the field of these industries.
Properties and Composition
Method of Analysis
Crocidolite and Amosite
Monitoring and Identification of Air-borne Asbestos
Membrane Filter Method
I. Outline Technique
II. Definitions of Fibre which are evaluated
III. Membrane Filter
V. Transportation of Filters
VI. Mounting of the Filters
VII. Microscopical Evolution
VIII. Accuracy of the Membrane Filter Method
IX. Recent Developments in Fibre Evalution
Determination of Very Low Asbestos Concentrations
Direct - Reading Dust Monitoring Equipment
II. The Thermal Precipitation
III. The Konimeter
IV. Owens Jet Counter
V. The Impinger
Identification of Air-borne Asbestos Fibres
II. Optical Techniques
III. Electron Microscopical Techniques
IV. Physical and Chemical Analysis
Alternatives to Asbestos in Industrial Applications
I. Thermal Properties
II. Mechanical Properties
III. Other Properties
IV. Price and Availability
Industrial Applications of Asbestos Products
I. Asbestos Textiles
1. Fire and Heat Protection Clothes
2. Fire Blankets, Curtains and Aprons
3. Electrical Insulators
5. Ropes, Yarns, Tapes etc
6. Other Applications
II. Thermal Insulations and High Temperature Applications
1. Dry Asbestos Packings
2. Asebstos Jointings
4. Lining and Insulating Blocks
5. Ceramic and Mineral Fibres
6 Vermculite and Perlite
7 Solid Ceramics
8 Further information
III. Asbestos millboard
IV. Industrial applications of asbestos-cement
VI. Friction materials
1. Substitutes for asbestos in friction materials
V. Dry-rubbing bearings
1 Substitutes for asbestos-reinforced thermosets
in bearing applications
VI Electrical insulation
1 Substitutes for asbestos products in
2 Substitute electrical insulants at high temperatures
VII Asbestos composites (not including frictional,
bearing, and electrical applications)
1 Alternatives to asbestos composites
VIII Miscellaneous applications
Health hazards of substitute materials
Methods of Manufacture
Methods of Analysis
Non-Occupational Asbestos Emissions and Exposures
Asbestos emissions from natural sources
Asbestos emissions from human-created sources
Redistribution and fate of asbestos in the environment
(i) Redistribution by air
(ii) Redistribution by water
(iii) Ultimate fate of asbestos fibres
Exposure to airborne asbestos
(i) Exposure from ambient air
(ii) Exposure from air near asbestos industrial facilities
1 Asbestos mining, milling, and product manufacture
2 Transportation of materials containing asbestos
3 Estimated atmospheric concentration and exposures
(iii) Exposure from asbestos manufactured products
1 Automotive friction materials
2 Spray asbestos
(iv) Exposures from disposal of asbestos products and wastes
(v) Exposures of asbestos workers’ families
Exposure to asbestos in drinking water
(i) Asbestos content of drinking water supplies
(ii) Elevated asbestos levels
(iii) Estimated asbestos consumption from water
Exposure to asbestos in foods and drugs
Appendix, calculation of atmospheric asbestos
concentrations in the vicinity of major U.S. Asbestos
Cements, Mortars and Concrete
Methods of Analysis
Determination of Compound Composition
Determination of major components
Rapid Procedures for Major Components
Raw Materials, Additives and Fuels for Cement
1. Raw Materials for Making Cement
2. Constituents of Raw Mix and their proportioning
2.2 Silica and Alumina
2.3 Iron Oxide
3. Proportioning Constituents
3.1 Correcting Materials
4. Composition of Clinker
5. Quality Control
5.1 Commonly Found Proportions
6. Blended Cements
8. Fuel in Shaft Kilns
9. Fuels for Rotary Kilns
10. Coals as Fuel
10.1 Preparation of Coal for Firing
10.2 Preparation of Oil for Firing
11. Costs of Fuels
12.1 Typical Compositions of Coal and Coke are
12.2 Typical Composition of Coal Ash is
13. Calorific Value of Fuels
15. Gas as Fuel
16. Specific Fuel Consumption Obtainable using Different Fuels
17. Requirements of Raw Materials and Fuel
Processes of Manufacturing of Cement
1. Process of Making Cement
2. Predominance of Wet Process
3. Marginal grade Limestone and Froth Flotation
3. Dry and Semi Dry Processes
3.1 Semi Dry Process
5. Dry Grinding and Blending
6. Semi Wet Process
7.1 Lepol Grate Preheater
7.2 Suspension Preheater
8. Clinker Coolers
8.1 Rotary and Planetary Coolers
8.2 Grate Coolers
9. Increase in Size of the Cement Plant – Large Kilns
11. Technical Collaborations
12. Various Processes, Machinery and Size of Cement Plant
Cements based on Natural and Artificial Pozzolanas
1 Fly Ash based Cements
1.1 Composition and properties of fly ashes
1.2 Lime-activated fly ash binder
1.3 Portland-fly ash cement and fly ash concrete
1.4 High-volume fly ash concrete
1.5 Alkali-activated fly binder
2. Cements made with fluidized bed ashes
3. Binders containing natural pozzolanas and related products
4. Microsilica-modified Portland cement
5. Rice Husk ash based cement
1. Control of Portland Cement setting by
the use of chemical admixtures
2. Fast-setting gypsum-free portland cement
3. Fast-setting cements containing the phases
C11A7.CAF2 or C12A7
4. Fast-setting cements containing the phase tetracalcium
5. Fast-setting blends of portland cement and calcium aluminate
6. Fast-setting magnesium phosphate cement
7 Fast-setting glass cement
8 Miscellaneous fast-setting cements
Special Portland Cements
1. Constituents and Composition of Portland Cements
1.1 Tricalcium silicate (3CaO.SiO2, abbreviation C3S)
1.2 Dicalcium silicate (2CaO.SiO2. abbreviating C2S)
1.3 Tricalcium Aluminate (3CaO.Al2O3, abbreviation C3A)
1.4 The ferrite phase [calcium alumiate ferrite,
2CaO(Al2O3, Fe2O3)[ abbreviation C2(A,F)]
1.5 Calcium sulfate
1.6 Free Calcium oxide (free lime, Cao)
1.7 Free Mangness oxide (periclase, MgO)
1.8 Alkali sufates
1.9 Composition of Portland clinker and Portland cement
2. The Hydration of Portland Cement
3. High-C3S Portland Cement
4. Portland Cement with Elevated C2S content
5. High-C3A Portland Cement
6. C3A Portland Cement
7. Low-Iron (White) Portland Cement
8. High-Iron Portland Cement
9. High-Mgo Portland Cement
10. Low-Alkali Portland Cement
11. Mineralized Portland Cement
12. High Specific Surface Area Portland Cement
13. Low Specific Surface Area Portland Cement
13. Limestone-Modified Portland Cement
15. Portland Cement Modified with Chemical Agents
16. Gypsum-Free Portland Cements
16.1 Low-porosity cement
17. Special Approaches in Portland Cement Manucacture
18. Special Approaches in Cement Processing
Packing of Cement
1. Packing Cement for Despatches
2. Packing Machines
2.1 Rotary Packing Machines
3. Paper and HDPE/Jute Bags
Storages of Cement
2. Daily requirements of Various Materials
3. Conventions in Storing various materials
4. Factors Governing Storages
5. Storages of Semi Finished and Finished products
6.3 Stack Reclaimer
6.4 Raw Mill and Blending
6.5 Preheater – Calciner – Kiln and cooler
7. Storage After Expansion
8. Storage of Coal
10. Space for storages
Clay Products, Whitewares, and Porcelains
Enamels and Glazes
Glass and Glass Ceramics
Methods of Analysis
Determination of the Chemical Composition
Lime and Limestone
Methods of Analysis
Sampling and Handling Precautions
Glass and Glass Ceramics
Constitution of Glasses
Method of Analysis
Chemical Methods for Individual Constiluents
Redox State Determinations
Electron Microprobe Analysis
broad term applied to a number of fibrous mineral silicates found in
natural state throughout the world. The most extensive deposits are
Canada in the province of Quebec. Some thirty varieties of asbestos
only six of these are of economic importance. For the purpose of this
only three of the six will be considered: chrysotile,
or white asbestos;
blue asbestos; and amosite.
Chrysotile is a fibrous variety of serpentine, a hydrous magnesium
mineral. Crocidolite and amosite are member of a group known as
and amosite are iron silicates of solid-strip structure. The former is
ferroso-ferric silicate found mainly in South Africa and, to the lesser
in Australia and Bolivia. The latter is a ferrous magnesium silicate
in South Africa.
fibers, because of their
great strength, are used as a reinforcement with other raw materials.
combined with Portland cement to form a variety of structural building
materials that are outstanding for their strength and durability.
resistant asbestos-cement pipe is also produced and can contain a blend
asbestos fibers in combination with Portland cement. Asbestos fiber can
combined with plastics to form floor tiles which are noted for their
Asbestos is also used as reinforcement in lime silica and magnesia
high-temperature insulations. The flexibility of asbestos fibers
to be woven into yarns, cloths, and ropes. Such asbestos fabrics are
proof, rotproof, and capable of withstanding high temperatures.
also can be combined with metal, rubber, resins, and other impregnants
binders to form brake linings, packings, and gaskets.
and chemical properties of three varieties of asbestos are summarized
1(3). The chemical compositions are shown in Table 2. It should be
that compositions vary and that different sources report different
Electron microscope pictures of the
three type of asbestos
fibres chrysotile appears to be a tabular structure with amorphous
the outside and inside of the tubes. Crociodolite appears to be in
needles. Amosite molecules seem to form straight flat sheets.
The gravimetric method for
silica involves fusion with sodium carbonate solution in hydrochloric
dehydration of the silica, and volatilization with hydrofluoric acid.
1.0000 g of ignited
sample into a clean, tared platinum crucible. Add approximately 5 g of
anhydrous sodium carbonate and mix well. Cover the crucible and heat
fusion is complete. The heat should be gradually increased at first
action ceases and then the full heat of the burner can be employed.
30-60 min is required for complete fusion. Using platinum-tipped tongs,
to cover and carefully swirl the contents to spread the melt around the
of the crucible. Allow to cool and then place the crucible and the
cover into a
clean, 600-ml Pyrex beaker containing approximately 150 ml of 1:6
acid. Cover the beaker and carefully heat on a hot plate until the melt
completely digested. Remove the crucible and the cover the scrub to
adhering insolubles. Crush all siliceous lumps thoroughly. No gritty or
matter should remain at this point. Should unfused matter be present,
fusion must be repeated. Evaporate to dryness on a steam bath. This
requires several hours. Place the beaker containing dry residue on the
plate to insure complete removal of all hydrochloric acid. Cool, add 10
concentrated hydrochloric acid to the residue and then add 100 ml of
Heat on the hot plate until all salts dissolve. Filter the precipitated
using No. 41 Whatman filter paper or equivalent and wash with hot 5% by
hydrochloric acid. Finally wash with hot water. Scrub the beaker to
adhering silica. Transfer the clear filtrate to the original beaker and
the dehydration directly on the hot plate. Exercise care to avoid
as the volume decreases. Bake the residue carefully to remove all acid
continue baking on an asbestos pad for 1 hr to dehydrate completely the
traces of silica. Cool, dissolve salt as previously indicated, and
No. 40 Whatman paper or equivalent. Wash as previously indicated, and
beaker to recover all silica. Save the filtrate for separation of
hydroxide group. Place both filter papers containing the silica in the
crucible used in fusion and heat in a muffle furnace at 800oF
to char the filter paper. Raise the temperature to 1000oF
until all the carbon is removed and the silica residue is white. Then
constant weight at 1800oF.
Obtain the total weight of the
crucible and contents. The residue represents impure silica.
manganese is present in the
<0.01% quantity, it is not normally removed prior to
calcium and magnesium. However, if the need arises, manganese can be
precipitated from the filtrate remaining after removal of the R2O3 group.
This separation is required in the analysis of amosite fiber and will
discussed under the amphiboles. In the analysis of chrysotile asbestos,
manganese can be determined colorimetrically by periodate oxidation.
% acid-soluble sulfate is obtained by digesting the original sample
hydrochloric acid and precipitating the sulfate with barium chloride
3-5 g of the original
sample to a 400-ml beaker. Add 100 ml of 10% hydrochloric acid and boil
mixture for 1 hr. Filter using vacuum, and wash the residue with hot
the filtrate to a 400-ml
beaker and reduce the acidity to 1-3% by using concentrated ammonium
Heat to boiling and slowly add 25 ml of 10% barium chloride solution.
Heat on a
hot plate until the precipitate settles. Cool and filter on Whatman No.
filter paper. Wash the precipitate free of chlorides with cold water.
the precipitate to a tared platinum crucible and ignite at 800oF, 1000oF,
and finally at 1800oF
to constant weight.
Calculate the acid-soluble sulfates from the weight of the barium
chloride may be determined by the Volhard method described below.
water-soluble chloride be desired, an aqueous extraction of a 10%
slurry of the
fiber in a water-immiscible solvent can be made. Chloride can be
the filtrate by any one of several methods suited to this low
dioxide from carbonates is usually very low in quantity in chrysotile
However, as previously indicated, fibers such as Arizona, California
(Coalinga), and Rhodesia may contain several % of carbonate impurity.
method of choice follows.
determined by the Smith extraction procedure followed by flame
photometry. If a
flame photometer is not available, the alkalies must be separated and
determined gravimetrically by suitable techniques.
of Traces. Organic
matter is determined by extracting a very large sample of the original
with an appropriate solvent, evaporating to dryness, and drying to
weight. Magnetite content of chrysotile asbestos varies considerably
source of the sample. The Arizona asbestos samples contain virtually no
magnetite and some Canadian grades (fines or short fibers) may contain
as 5% or more. For quantitative determination of magnetite, the Shell
may be used. The fluoroborate procedure may also be used but allowances
made for the solubility of magnetite in the method.
estimate of the magnetite
content can be made by the method described by ASTM for determining the
magnetic rating of asbestos used for electrical purposes. Nickel is
gravimetrically. Chromium is determined colorimetrically.
general, the methods given
under chrysotile asbestos may be applied to crocidolite and amosite
or no change.
of the changes involve
differences in simple weights or in aliquots taken because of the
levels of concentration of the constituents. For example, chrysotile
much less iron then crocidolite or amosite. Accordingly, smaller
used for the total iron determination by potassium permanganate
Likewise, a smaller sample size, 0.5 g instead of 1-2, g is used for
of iron in crocidolite or amosite. Inspection of Table 2 will aid in
selection of the proper sample size.
In the analysis of amosite, manganese must be removed gravimetrically
separation of calcium and magnesium. The procedure follows.
After removal of the R2O3 precipitate, add 5 ml of
liquid bromine to the filtrate. Place the solution on a ceramic ring on
bath. Overlay with approximately 125 ml of concentrated ammonium
solution and allow the reaction to proceed slowly for 1 hr. If the
become too violent, remove from the steam bath and allow to stand for a
minutes at room temperature before replacing on the steam bath. After
is entirely expelled, allow the brown manganese dioxide precipitate to
coagulate over open steam for approximately 1 hr. Filter using No. 41
paper or equivalent and wash with 1% ammonium hydroxide solution.
precipitate in the platinum crucible to 1800oF.
Fuse the ignited precipitate with 1-2 g of potassium pyrosulfate.
clear melt in 5% nitric acid. Pour the solution into a 100-ml
and dilute to volume with water. Use an appropriate aliquot and
asbestos dust is
usually monitored for one of three reasons. Firstly, large numbers of
are taken to check compliance with legislation. As part of the
by most controlling authorities recommended methods are described by
monitoring should be done. Secondly, within the asbestos industry
sampling is carried out to determine the efficiency of dust suppression
equipment. Here it is frequently necessary to know only the relative
dust present, and direct-reading dust monitoring instruments play a key
Finally, an increasing number of samples are taken for epidemiological
purposes. For this it is essential that standard methods be used which
related to one another, and which remain constant over many years. This
includes monitoring the exposure of people outside the asbestos
may involve measuring extremely small amounts of asbestos.
The measurement of the airborne
fibre number concentration
is normally preferred in most countries. This avoids some of the
and uncertainties of mass monitoring by using a microscopical method to
separate out only those particles thought to be potentially harmful
from a sample
of all the dust from the air. The results obtained, however, depend
microscopical magnification and technique used and also upon any
placed upon the type of particle counted. Some early attempts to
exposure of asbestos workers recorded all the particles thought to be
respirable, but most present methods involve counting only those fibres
a limited size and shape range. One advantage of this method is that,
the mass standard, the 2 fibres/ cm3 British Standard for
(which has been adopted by several other countries), is based upon an
epidemiological study. This type of measurement is also likely to
basis of any revised standard within the foreseeable future.
The Membrane Filter Method
This is now the most widely used
method for monitoring
asbestos dust in industry. In 1972 a report to the World Health
International Agency for Research on Cancer recommended that
trials be carried out, so that this method could be standardized.
(i) Outline technique
Measurements are taken by drawing a
known volume of air
through a membrane filter. This filter is then made transparent, and
of fibres fitting a standard definition of size and shape which are in
deposit are counted using a phase-contrast microscope. The mean fibre
concentration during the sampling period can be calculated. Where fibre
Identification is needed, different types of sampling filters and
techniques may be required.
Definition of the
Fibres which are evaluated
The membrane filter method was
developed by the British
Asbestosis Research Council in order to try to monitor only those
thought to be capable of causing lung damage. At the time of its
asbestos or ferruginous bodies were thought to play a major role in the
development of asbestosis. These bodies are fibres surrounded by
iron frequently found in the sputum of asbestos workers. These fibres
normally longer than 10mm
and it was therefore concluded that it was necessary to
evaluate only the longer fibres.
(iii) The membrane filter
Cellulose ester filters are
normally used for asbestos
fibre monitoring. The Asbestosis Research council in the U.K.
use of 0.8-5.0 mm
pore size filters, whereas the Australian code of practice suggests
that only a
pore size of 0.8 mm
should be used. Although many asbestos fibres have diameters much less
this, they are in fact captured by the filter and the optical fibre
not affected by penetration.
filter is placed in a
holder, where it is supported by a gauze or thick pad, which helps in
controlling the distribution of air through the filter. The 25 mm
is normally used with the filter surface completely exposed. The 37-mm
Millipore holder can also be used in this way, or alternatively the
may be left in place and the small plug removed.
Transportation of filters
Once the sample has been taken, the
open end of the filter
holder should be covered with a cap to prevent contamination, and the
removed and mounted in a clean atmosphere away from the sampling
Some codes of practice suggest that the dust deposit should be fixed on
membrane surface while the filter is in the sampling head. Two methods
Mounting of the filter
filter must now be made
transparent so as to enable the sample to be examined by transmission
microscopy. Most filter samples are mounted on standard 25×76 mm
slides. The 25-mm filters can be mounted whole, but the larger 37-mm
filters must be divided into sectors.
Although the filter is now
transparent, many of the fibres
themselves cannot be seen when using a normal transmission optical
because the refractive index of the background medium is very close to
the asbestos. The effect is therefore equivalent to looking for a glass
in a tank of water, and very few fibres are visible. The light which
through the fibre, however, has a small change of phase relative to
goes through the background alone.
Accuracy of the membrane filter method
Errors can occur both in sampling
and evaluating the dust
samples. Sampling differences are difficult to determine as it is not
to maintain stable standard dust clouds. The errors are probably
those found when sampling spherical dust, and similar precautions
taken, e.g. the use of isokinetic sampling heads in high-velocity air
The effects of electrostatic charges, filter pore size, and sampling
are not yet fully understood, however. These errors, on the other hand,
probably small compared with those in the microscopical evaluation.
developments in fibre evaluation
Microscope counting of fibres is
not only prone to error,
but is also very tedious and time consuming. Methods have therefore
developed either to try to aid the microscopist, or to automate the
Statistical methods have been used to try to reduce the time required
Determination of very low asbestos
accumulated over the past decade indicates that asbestos is found in
of most city dwellers and the need to measure the concentration in the
environment has therefore arisen. The methods described so far are
monitor accurately the extremely small amount of asbestos present. In
obtain sufficient fibres for analysis, the dust must be collected from
large volumes of air. Asbestos, however, constitutes only a very small
proportion of the particulate matter present, and any fibres present
obscured by other material.
to Asbestos in Industrial Applications
The numerous applications of
asbestos are a consequence of
its desirable physical and chemical properties, combined with a low
cost. It is this unique combination that makes the replacement of
difficult in many applications.
Some of the properties of asbestos
are summarized in Table
2, together with the comparable properties of some of the synthetic
materials that have been suggested as replacements for asbestos in some
applications. Some of these properties require further comment.
(i) Thermal properties
(ii) Mechanical properties
Industrial Applications of asbestos
fibre forms the
basic raw material for almost all of the activities of the asbestos
industry. The length of flexibility of the longer grades of chrysotile
that spinning into yarn and cloth weaving are possible. Two basic types
are produced: plain, possibly braced with an organic fibre; and
which incorporate either wire or another yarn such as nylon, cotton, or
polyester. The wire-reinforced yarns and textiles can retain their
properties at temperatures up to 600oC.
Recently developed textiles
combined with resins and ceramic binders have successfully withstood
exposure to temperatures up to 2200oC.
The main applications of asbestos
textiles are represented in Figure 1. Some of the applications and
alternatives are considered in other sections as indicated.
(ii) Thermal insulations and
The use of asbestos for insulation
three main areas: asbestos insulation board, asbestos spray, and
lagging in high-temperature applications. For most high-temperature
applications chrysotile fibre is the basic constituent because it
properties of resilience, strength as a reinforcement, flexibility, and
resistance. In some cases amosite fibres are used, such as in the shaped block-type
lagging that can be
applied to high-temperature pipes, in which a lime/silica binder is
(i). 1 Dry asbestos packings
(ii). 3 Gaskets
(ii). 4 Linings and
(ii). 5 Ceramic and mineral
(iv) Industrial applications
Asbestos composites (not including frictional, bearing,
Health hazards of substitute materials
If it is required to replace
asbestos on health grounds,
then it is sensible to ascertain whether or not the suggested
itself constitutes a health hazard. Some of the suggested synthetic
replacements for asbestos in specific applications are listed in Table
details of fibre lengths and diameters.
these observations in
mind, examination of the fibre diameters in Table 2 suggests that the
synthetic refractory type fibrous materials that can be used to
asbestos in elevated temperature applications may themselves constitute
health hazard. A mean fibre diameter in the range 2-3mm is quoted for
all of these
fibres, suggesting that a significant proportion of them have diameters
than the 2mm
level thought to be significant in the production of asbestosis.
have also been
performed on vermiculite that suggests that it has no tendency towards
carcinogenicity or the production of fibrosis in the lungs.
Expanded Perlite can generate
airborne dust. This has been
examined as a possible health hazard, and is thought to cause no
except for nuisance. Experience in the U.S.A. going back nearly 30
indicated no related disease pattern with the use of Perlite.
products have become well established in industrial and domestic
Siding and roofing shingles are manufactured in many attractive colors
designs. Pressure pipe is used in water distribution systems in many
municipalities and in industry for conveying water, process liquids,
slurries. The non-pressure pipe is installed in sewage collection
in main trunk lines and laterals.
products are manufactured by two different processes, normal and steam
cure. A normal-cured
product is made with Portland cement and water and is
reinforced with one
or more varieties of asbestos fiber, usually only chrysotile. The
product is prepared for use by exposure to specified humidity
curing or setting the Portland cement.
product is composed of Portland cement, silica flour
(quartz), and water,
and is also reinforced by one or more varieties of asbestos fiber.
this type of product is both precured and autoclaved at prescribed
of time and temperature. The hydrothermal reactions resulting from the
autoclaving produce a product which is stronger, more resistant to
agents, and dimensionally more stable. Susceptibility to efflorescence
color fading are also diminished by steam curing.
product is more alkaline because of the unreacted lime remaining from
hydration of the Portland cement. In steam curing, the lime reacts with
silica to form a calcium silicate gel which in turn improves the binder
characteristics and chemical resistance of the product.
Products (Short Procedure). If
time is a factor in obtaining
analysis required for composition calculations, the following shortened
procedure can be used for normal-cure chrysotile-Portland cement
1,000 g of a finely ground sample with 5 g of sodium carbonate in a
the clear melt in 50 ml
of 1:2 hydrochloric acid in a 250-ml beaker. Disintegrate all siliceous
and examine for evidence of any incomplete fusion. When the sample is
completely digested, add 6 drops of bromine water and boil to destroy
bromine and then neutralize using 1:1 ammonium hydroxide with 1-2 drops
methyl red indicator. If the indicator color fades rapidly, excess
not been destroyed.
the neutralized sample to a 1-liter flask, adjust to the volume with
mix well. Let the precipitate settle. The precipitate is a combination
silica and R2O3.
Pipet two 50-ml aliquots of the
supernatant liquid into separate 250-ml Erlenmeyer flasks. Proceed with
titrations of calcium and magnesium as outlined in analysis of these
for chrysotile asbestos. If experienced with EDTA titrations, known
calcium and magnesium should be titrated to recognize the end points.
to pH recommendations is important. See asbestos.
calcium oxide and % magnesium oxide as follows:
of Additional Fibers in Asbestos-Cement Products. Calculation
the composition of asbestos-cement products can be complicated by the
use of an
additional fiber, crocidolite (blue), amosite asbestos, or wood fiber.
asbestos fibers are encountered, the only analytical approach would be
the iron content. Both amosite and crocidolite have approximately 40%
If the iron content of the remaining
furnish can be estimated, the balance is attributed to amosite or
asbestos. If the fiber blend is known, the amount of the second fiber
determined based on the calculated chrysotile value.
Fiber in Asbestos–Cement Products. Wood
fiber in asbestos-cement products
may be determined by wet oxidation of organic matter by chromic acid,
absorption, and weighing of the carbon dioxide formed, and correction
carbon dioxide from inorganic carbonates.
Asbestos Emissions and Exposures
significant exposures of humans to asbestos occur in the workplace.
persons not employed in asbestos-related occupations are also exposed
asbestos fibres that originate from natural sources or from man-created
such as the manufacture and use of asbestos products. Such asbestos may
inhaled-as, for example, in an office building in which the air is
by asbestos insulation-or it may be ingested with water, food, and
inadvertently, parenterally inoculated). These exposures, termed
‘non-occupational’, are the subject of this chapter.
emissions from natural sources
distribution of ultrabasic and metamorphic rock formations in the
that could possibly contain asbestos is shown in Figure 1. It can be
the primary areas of source rock are Minnesota, New England, and many
Western and Southeastern states (especially in the vicinity of the
Mountains). Because of high population density, the most critical areas
emissions from natural sources appear to be Eastern Pennsylvania,
New York, Southwestern Connecticut, and greater Los Angeles and San
emissions from human-created sources
sources of non-occupational exposures to asbestos include the mining
milling of asbestos, the transportation of asbestos materials and
manufacture, installation, use, and demolition of asbestos products,
disposal of wastes.
and fate of asbestos in the environment
is exceptionally resistant to thermal and chemical degradation, it
the environment and can be widely redistributed by both natural forces
human means. The magnitude of this redistribution is governed by an
extraordinary complex set of factors which include the height of the
source, the rates of air and water flow, fibre diameter, rain, thermal
inversions, electrostatic forces, agglomeration of particles, and the
of vehicular traffic on asbestos-containing landfill, to name only a
(i) Redistribution by air
Redistribution by water
Ultimate fate of asbestos fibres
to airborne asbestos
expect, airborne asbestos can be found in the vicinity of asbestos
mills, manufacturing facilities, and waste dumps. However, elevated
also be found near concentration of braking vehicles, in buildings in
asbestos spray products have been used, and in the cars and homes of
workers who have contaminated them with dust brought from the work area
clothing, body, or equipment. Asbestos may be inhaled by persons who
their own asbestos roofing or flooring, or who repair such items as
brakes and clutches, home hearing and plumbing systems, wires for
waffle irons, or the walls of their homes.
Mortars and Concrete
general sense, is a substance that joins or bonds materials. Hydraulic
cement refers to a material that will harden under water and
is capable of
uniting particles or masses of other solid matter into a compact whole.
purposes of this article, discussion will usually be limited to
cements, and will generally refer only to those cements whose strength
achieved through the formation of various calcium silicate and
hydrates. In the United States most of the hydraulic cement used in
construction is Portland cement. The analytical methods given were
primarily for Portland cement, but may generally be applied to the
use of lime mortars by the Greeks and Romans, the production of
material has played an important role in the development civilization.
invention of Portland cement, probably by Aspdin in 1824, and the
development of modern concrete led to a present world cement production
about two and a half billion barrels a year. In the United States, the
now over four hundred million barrels a year, over 90% of which is
are produced by
the partial or complete dehydration of gypsum, usually to the plaster
or hemihydrate stage. They often contain added accelerators, retarders,
workability agents. Gypsum plasters are distinguished by their low
workability and expansion upon setting. Gypsum plaster is not usually
considered to be a cement, and this article does not cover the usual
chemistry and properties of such a material; see gypsum.
ground mixtures of a cementitious material, usually Portland cement,
hydrated lime, slag, and limestone, or other fillers. Often organic
proofing agents such as calcium stearate and air entrainers, such as
abietate, are added. Masonry cements are used for mortars, and as such
characterized by their plasticity or workability and their water
of Compound Composition
Individual hydraulic cements
can be identified
by determination of their compound compositions, generally through the
an x-ray diffractometer or a petrographic microscope. Such analysis are
required, but the reader who is confronted with this task will find
microscopic data on cement compounds given below or the x-ray and
data given by Taylor or Yang an x-ray pattern of a typical Portland
less complete x-ray data in Lea and Desch may also prove of value.
preparations and thin section techniques are used with the petrographic
A micrograph of a thin section of Portland cement clinker . For
incident light, polished sections etched with a suitable reagent that
differentiate compounds present are convenient. Etchants commonly used
dilute solutions of nitric acid, which attack the silicates, and
hydroxide, which attacks the aluminates. A very practical etchant is
a pH between 6.8 and 7.0, which attacks differently. The ferrite phase
brightest reflectance and is readily identifiable.
of major components
physical properties of most cements have been reported to be almost
due to the major components of the cements. The analytical chemistry of
has thus been concerned primarily with those elements present in major
Recent investigation, however, indicates that some elements present in
qualities in cement may have important effects out of proportion to
given below, applicable to the more common hydraulic cements are
producing great accuracy for the elements or oxides described, provided
the effect of the more common interferences are recognized. Usual
caused by the presence of trace or rare elements, or by application of
methods to unusual products, can only be detected by analyzing each
can best be determined by gravimetric, colorimetric, or x-ray
methods. A method for the determination of free silica is available.
gravimetric method is the referee method and is described in detail
molybdic acid colorimetric is included as part of the rapid procedure
Weigh 0.5000g of the sample
into a 100-ml
platinum evaporating dish. Add 10 ml of cold water and swirl to
solids in the water. While still swirling the sample, add 10 ml of
hydrochloric acid. Warm the platinum dish on a steam bath until
complete. Any lumps remaining should be broken up by using a
policeman. Evaporate the solution to dryness on a steam bath. Remove
from the steam bath and cool.
difference between this weight and weight of the crucible plus the
silicon dioxide previously obtained represents the amount of silicon
present in the sample. Calculate % silicon dioxide to the nearest 0.01%
multiplying the weight, in g, of silicon dioxide, less the weight of
oxidized forms, is usually determined by volumetric or colorimetric
Methods for metallic iron and ferrous iron are available. Titration
potassium dichromatic is the classical procedure for ferric oxide and
described below. A colorimetric method is given in the rapid procedure
determined by the usual gravimetric methods, generally includes
given weight of strontium oxide in the final ignited precipitate would
reported as the same weight of calcium oxide. It is believed that
not separated prior to the precipitation of calcium, contaminates the
precipitate and leads to slightly high results. There have been some
the literature that do not support this belief.
can be determined by gravimetric and EDTA complexometric titration
Flame photometric and atomic absorption techniques are also applicable.
is best determined by colorimetric procedures such as the one described
Some cements may have quantities of vanadium sufficient to interfere
colorimetric determination of titanium. Blaine et al.found that less
than 5% of
nearly 100 portland cements contained as much as 0.1% vanadium. Slag or
portland blast-furnace slag cements, however, may contain appreciable
of vanadium. When its presence is suspected, a sodium carbonate fusion
to remove vanadium.
Procedures for Major Components
product control purposes, a cement plant chemist often requires an
the raw mix, clinker, or cement as soon as possible after sampling.
gravimetric methods for cement analysis are time consuming. Even when
reducing short cuts are used, such methods require 4 hr or more to
Spectrophotometric (colorimetric) and complexometric titration methods,
recently developed, permit more rapid analyses.
methods for determining the major oxides in cement and silicates were
Hedin in 1947. Since then a number of other investigators have
methods for the analysis of cement, silicate rock, and related
gives detailed procedures for the complete analysis (major and minor
cements, raw mix, and related material, using colorimetric and
Fineness. A finely ground cement
hydrates quickly and
gains strength faster than a coarse cement of the same chemical
Primarily, because of the demand by the construction industry for
great early strength, there has been a trend toward the production of
increasingly finer cements. Fineness may be measured by sieving the
through exceptionally small sieves by the Wagner turbidimeter or by air
Although a sieve analysis
for portland cement
is seldom required, the amount of material passing a certain sieve may
part of specification for other cements. A specific procedure may be
for acceptance purposes, but normal sieving procedures, carefully
generally give equivalent information.
and mortar properties, such as strength and time of set, depend on the
consistency, or plasticity, of the mixture. The consistency in turn is
function of the water content of the paste or mortar and will vary
cements. A consistency test of a paste or mortar is made to determine
requirements of a particular cement and, in addition, to provide a neat
paste, or a mortar, of a desired consistency so that it can be used to
test specimens for time of set, strength, and air content
As cement paste
sets, or hardens, it stiffens slowly from a liquid slurry form to one
hardness. The rate at which a cement hardens is usually controlled at
cement mill by adding an appropriate % gypsum to the cement clinker
final grinding of the cement. Infrequently, the % of gypsum admixture
incorrect for a particular purpose, or the cement has been ground at
too high a
temperature. This can cause the concrete to stiffen prematurely,
placing and consolidation of the concrete. Test procedures have been
detect and evaluate premature stiffening, or false setting, of cement
and mortars. False setting is an abnormal cement property that can be
in manufacture or controlled by appropriate adjustments of the mixing
Problems similar to those
false setting are encountered if the normal setting time of a nonfalse
cement is too short. Ideally, the cement paste shoule unergo little
during the first hour or so after mixing so that the concrete can be
compacted without using an undesirably large proportion of mix water,
excess mix water weakens concrete and decreases its durability.
of a cement paste depends upon the original water-cement ratio of the
the paste temperature, and the drying conditions to which the paste is
Therefore, all times of set are run on pastes of normal consistency,
closely controlled temperature and humidity conditions.
Compressive Strengths. The
strength of the cement component is a factor
affecting the strength of a concrete structure made with the cement.
strength depends upon cohesion between cement grains, strength of
and adhesion between particles of cement and aggregate. Job
nearly always include strength requirements for both the cement and the
concrete. Ordinarily, however, the strength of a neat cement paste is
determined. Instead, to compensate somewhat for the strength effects
aggregates, mortars incorporating the cement and a standard silica sand
aggregate are tested for tensile and compressive strengths.
materials made with portland cement should ideally be dimensionally
the cement has hardened. Actually, a small amount of shrinkage with
resultant microcracking is virtually unavoidable. It is, however,
by appropriate construction procedures involving proper placement and
of contraction joints. Normally the tendency of a concrete to expand
setting is undesirable.
reaction between cement and water is exothermic.
The heat generated by
the hydrating cement in a concrete specimen that is being cured
may increase the concrete temperature by nearly 50oC.
However, a cement’s heat of hydration
is usually of concern only in mass structures such as bridge piers or
which are too large to permit the heat to escape quickly from the
additives to cement may act as foaming agents and cause, during the
process, the formation of appreciable volumes of small air bubbles in
concrete. Proprietary organic aids to cement grinding, for example, can
such air in concrete. The presence of excessive entrained air will
Additives and Fuels for Cement
Raw Materials for Making Cement
of Cements and their properties were seen. Cement concrete is
made up by processing raw materials like limestone, clayey materials
ferrugineous materials in proportions that would yield clinker of
quality – after going through processes like calcining and sintering.
Constituents of Raw Mix and their proportioning
mentioned above, limestone, and clay,
sand and iron ore or laterite are usual components of raw materials
added in suitable proportions and ground produce ‘raw mix’.
to arrive at
these proportions is decided by following certain norms and applying
yardsticks. These yardsticks are:
Hydraulic Modulus or Lime Saturation
Composition of Clinker
also have, complex compounds, that are formed during the process of
in certain proportions to obtain desired strengths in cement; they are C3S
clinker should also be limited to less than 1.5%. Burnability factor is
yardstick which furnishes information on temperatures to be maintained
burning zone to limit free lime to desired values.
in manufacture of cement is a highly specialized field and is not the
of this book. It is touched upon to highlight their impact on design of
and machinery in a cement plant.
blended cements compositions of fly ash and slag should be known so
what proportions they could be added to clinker could be worked out to
Pozzolana and Slag Cements respectively. Up to 65% slag can be added to
slag cement; up to 30% fly ash can be added to make pozzolana cement.
heat energy required to make clinker from raw mix. Solid fuels like
have ash in proportions varying from 10 to 40% also influence the
Fuel in Shaft Kilns
require low volatile coals. Presently coke breeze is used as fuel in
volatile content is negligible. Coke breeze is ground with raw
suitable proportion. Ground raw meal is made into nodules for feeding
Fuels for Rotary Kilns
use all types of fuels – solid i.e., coals, lignite and petcoke; liquid
oil and also gas.
fired in pulverized form. Liquid fuels are atomized and fired through
burners. They need to be heated to obtain correct viscosity to
atomization. Gas – commonly natural gas is used – can be fired most
Coals as Fuel
principal properties like calorific value and ash content from place to
or even in the same place. They are more difficult to burn and quality
clinker produced needs to be watched closely as ash in coal gets almost
absorbed in clinker formed – affecting its composition thereby. As a
to maintain uniform quality of clinker, raw meal composition has to be
to counteract effect of coal ash.
Manufacturing of Cement
Process of Making Cement
is a good
example of developments in manufacturing processes used to make a
which by itself has not changed much.
processes of manufacture of cement are reflections of the needs of the
such as scale of production, product quality and specific consumption
thermal and electrical energy to produce it.
Predominance of Wet Process
country like America persisted for a long time (compared to Europe)
wet process of manufacture of cement because of :
aggregates that were used in Construction Industry in America.
requirements of manpower.
Marginal grade Limestone and Froth Flotation
when cement plants were few and high quality limestones were readily
marginal grade limestones was sought to be used to make cement by
them. The ‘froth flotation’ process used to enrich limestone, removed
from limestone and thus increased the carbonate content. This process
‘slurry’ with moisture content of 36-38%. The slurry was agitated and
in cells with additions of doses of chemicals that removed ‘silica’ in
Dry and Semi Dry Processes
evolved with time. The first cement was produced by dry process. While
were produced by dry process. Initially dry process kilns were long
chain systems like wet process kilns. Chains had to be of heat
Dry Grinding and Blending
two developments became necessary:
Drying and Grinding of Raw materials in
‘Dry Grinding’. This was not difficult as coal mills and cement mills
already dry grinding mills. Hence, same ball mills could be used to
Blending Dry – As a result of dry
grinding it became necessary to blend dry ground fine powders.
‘fluidization’ techniques resulted in ‘Airmerge blending’ systems –
‘batch’ systems and then ‘continuous’ systems.
Dry process or semi dry
process became a
reality after dry blending and pneumatic conveying was developed.
Semi Wet Process
Fertilizer plants produced calcium carbonate sludge as byproduct. It
used to make cement with small corrections for composition and
next stages in development were :
out of the kiln had to be cooled to temperatures at which it could be
by the then available conveying equipment like pan, drag chain
conveyors and by
even belt conveyors.
Increase in Size of the Cement Plant – Large Kilns
this point it
was realized that kilns larger than this diameter had shorter brick
gain in capacity tended to be lost due to lesser number of working days.
another epoch making development- that of ‘calciner’ – took place.
carried out the process of calcination outside the kiln almost up to
kiln was thus liberated from the task of calcination and hence the same
could achieve 2-2 ½ times more production. The total fuel was divided
kiln and calciner; kiln receiving only 40-50% and calciner receiving
Technical Collaborations with World’s leading Process designers and
Manufacturers of Cement Plants since early Sixties. But rate of
‘Know how’ was rather slow in the decades of sixties to eighties. After
due to policies of liberalization, the rate of transfer of technology
Natural and Artificial Pozzolanas
pozzolanic materials, are defined as siliceous and aluminous materials
their own possess little or no cementitious value, but which will – if
in finely divided form and in the presence of moisture – react
calcium hydroxide at ordinary temperature to form compounds possessing
cementitious properties (ASTM C 619-89).
natural and artificial materials that differ in their chemical
mineralogical nature, and geological origin exhibit pozzolanic
Chemically they are rich in SiO2 and - to a lesser extent in
both oxides being present as constituents of a reactive (glassy or
phase. The CaO content of pozzolanic materials is low. Sometimes they
contain limited amounts of chemically bound water. Some pozzolanic
may also contain non-pozzolanic constituents side by side with those
conventional cements preserve their plasticity for
several hours before setting and hardening.
Such a plastic stage is necessary so that it is possible to produce a
concrete/mortar mix of the desired consistency, transport it to the
it is to be applied, and compact it after placing. In some special
applications, however, cements with very short setting times are
Examples of such applications are various repair works (repairs of
for example) and emergency measures (such as plugging of leaks to
leakage of water or other liquids).
Control of Portland Cement
setting by the use
of chemical admixtures
alkaline chemicals, such as alkali metal hydroxides, carbonates,
aluminates, cause of significant shortening of the setting time of
cement. They act by increasing the pH of the liquid phase, and thus
accelerating the hydration of the tricalcium aluminate present in the
If alkali silicates are used, soluble SiO2 is immediately available to
react with the
calcium hydroxide formed in the simultaneous hydration of tricalcium
and additional amounts of the C-S-H phase are also formed. At moderate
of the additives the resulting strengths are increased, but at high
rapid setting caused by the added alkali silicate results in a more
structure and a lower strength.
Fast-setting gypsum-free portland cement
Portland cements contain limited amounts of calcium sulfate (in the
anhydrite or gypsum), interground with Portland clinker, to control
Under these conditions the tricalcium aluminate of the clinker reacts
sulfate and water, to yield ettringite (Aft phase, C6AS3H32).
This phase precipitates at the
surface of the cement grain as a thin layer, which does not adversely
the rheology of the cement suspension. The cement paste sets after
hours, owing to the hydration of the tricalcium silicate present and
formation of the C-S-H phase.
cements containing the phases C11A7.CAF2 or C12A7
contain the calcium fluoroaluminate phase (11CaO.7Al2O3.CaF2)
in combination with calcium sulfate
exhibit a very fast setting and initial strength development, owing to
formation of the ettrringite phase. In alite-fluoroaluminate cements
fluoroaluminate is combined with tricalcium silicate, whereas the
cements dicalcium silicate, but no tricalcium silicate, is present.
Fast-setting cements containing the phase tetracalcium trialuminate
contain the phase tetracalcium trialuminate sulfate (C4A3S)
in combination with calcium sulfate exhibit fast setting and fast early
strength development. Such binders include sulfobelite cement,
cement, calcium sulfoaluminate modified Portland cement, and
cement. The setting and initial strength development are brought about
rapid formation of ettringite in a reaction between C4A3 and calcium sulfate in these
blends of portland cement and calcium
ordinary Portland cement (OPC) and calcium aluminate cement (CAC)
very fast setting over a wide range of OPC/CAC ratios. Figure 1 shows a
example of such behavior, but the exact setting time will also depend
on the characteristics of the individual cements employed, and on the
water/solid ratio of the mix. After setting, the OPC + CAC blend
strength development, and measurable strength values may be achieved
less than 1 hour. The final strengths, however, are lower than those of
the Portland cement or the calcium aluminate cement alone. Figure 2
typical strength development of OPC + CAC as a function of their
Fast-setting magnesium phosphate cement
magnesia (MgO) in combination with diammonium hydrogen phosphate [(NH4)2HPO4]
or some other water-soluble phosphates
yields a fast-setting binder that sets within minutes and yields
strengths within less than half an hour.
Fast-setting glass cement
the system CaO-Al2O3-SiO2,
if ground to a high fineness, yield cements called glass cements, which
very fast setting and hardening. The main product of hydration in such
in the hydrogarnet phase. Fast-setting glass cements
must have a low SiO2 content, as at higher
contents of this oxide
strätlingite rather than hydrogarnet is formed in the hydration, and
results in an extension of the setting time. Glass cements yielding the
hydrogarnet phase as hydration product exhibit a very short setting
fast early strength development, but only very moderate strength grows
are inorganic binders obtained by
grinding to a high fineness Portland clinker alone or – most commonly –
with calcium sulfate, acting as a set regulator. The ASTM standard C
define Portland cement as “a hydraulic cement produced by pulverizing
Portland-cement clinker, and usually containing calcium sulfate.” The
standard ENV 197-1requires for Portland cement a clinker content of
a content of “minor additional constituents” of no more than 5%, in
limited amounts of calcium sulfate.
Portland clinker is
a product of burning a raw mix
containing the oxides CaO, SiO2,
and Fe2O3 (plus
other oxides in smaller amounts) to temperatures of partial melt
Under these conditions calcium oxide, originally present in the form of
first converts to free CaO and then react with the remaining
the raw mix to yield clinker minerals. The most important phase
produced in the
burning process, and the one characteristic for Portland clinker, is
silicate (3CaO.SiO2 or Ca3SiO5,
The other main phases present in Portland
clinker are dicalcium silicate (2CaOSiO2 or Ca2SiO4,
tricalcium aluminate (3CaO.Al2O3 or Ca3Al2O6 abbreviation C3A)
aluminate ferrite [ferrite phase, 2CaO(Al2O3,
sometimes also described as C4AF].
In industrial cements these phases are not present as pure chemical
but contain variable amounts of foreign ions in their crystalline
1. Packing Cement
produced in bulk and stored in cement silos or large capacities. It is
market in general and to individual customers in bags of specific
in the cement plant.
dispatches of cement in bulk has been common in developed countries but
India it is catching up only now.
in bags of specific weight required packing or bagging machines which
pack large quantities accurately. Packing machines were developed to
this need. In developed countries paper bags are being used. In India
and durable and reusable material was jute. Hence till now cement used
packed in jute bags. Jute has now been replaced by high density
were developed to carry out the operation of filling each bag with
weight with a tolerance of + 0.5%.
a bag was eliminated by making bags with a self closing valve. Bag to
was slipped on a spout of the packing machine. It rested on supports
tilted when bag was full and allowed to slip it off the spout. Pressure
cement closed the valve.
mechanism similar to a weighing scale with a fixed weight of 50 kgs on
and the bag being filled on the other side of the arm was used for many
to ensure correct weighing of bags. This mechanism is now replaced by
electronic weight scales.
mechanism similar to a weighing scale with a fixed weight of 50 kgs on
and the bag being filled on the other side of the arm was used for many
to ensure correct weighing of bags. This mechanism is now replaced by
electronic weigh scales.
Rotary Packing Machines
packing machines, spouts were arranged on a rotating bin complete with
for the bags. Operator slipped bags on successive spouts as they were
positioned in front of him for the purpose. Bags got filled as machine
and dropped at another point. One operator was sufficient for
capacities up to
capacities rotating machines with two loading and two dropping off
Paper and HDPE/Jute Bags
considerable difference in handling paper bags and jute or polythene
Handling is easier and faster with paper bags. There is no spillage.
are more prone to get stuck and spillage is more.
feeding machines have been developed for paper bags. Either rolls of
or bags in a stack are fed to the packing machine by mechanical
dispatching operations with paper bags have been fully automated in
stocks of materials to be maintained in between one part of the process
another to maintain continuity of operation in the event of a breakdown
materials i.e., limestones and additives
like clay, iron ore, gypsum and blending materials fly ash and slag.
Daily requirements of Various Materials
a large plant
of 3000 tpd capacity, the daily consumption/production of various
Conventions in Storing various materials
Factors Governing Storages
governing storages to be maintained for materials bought from outside
distance over which these items are
brought, time taken in processing the order and actual receipt of
site have to be taken into account.
factor, reliability of sources.
or weather factor, like
differences in moisture content in dry and wet seasons and necessity to
maintain stocks dry.
Storages of Semi Finished and Finished products
governing storages of semi finished products and finished products
plant are :
and duration of break downs in
requirements like blending
operations, which influence quantity to be stored.
in productions for long
periods for brick lining of kilns changing and grading of grading media
lining plates, roller liners etc. for ball and vertical mills.
6. Storage in
shovel/dumper can cause disruption in supply of stone to crusher; but
3 shifts are available per week for maintenance; normally standby units
also provided. Therefore no stock of uncrushed stone is normally
breakdown will stop quarrying operations will disrupt milling
there is a stock of crushed stone. Often crushes are far from the
Maintenance jobs like changing hammers, liners etc., can take longer
available per week. Therefore 7 days’s stocks are normally maintained
crusher and raw mill.
reclaimer system design depends on degree of blending required. It
number of layers in the stock pile, which in turn are decided by
stone in stockpiles.
Raw Mill and Blending
does not receive raw meal when raw mill stops. Kiln stops when raw meal
of raw mill for change of lining plates, rollers, grading of grinding
take – 2-3 days or 6-9 shifts (normally
such jobs will be ‘planned’ in advance to coincide with stoppage of
for maintaining running of kiln, raw meal stocks of 2-2½ days are
blending like stacker reclaimer depends for blending effect on no. of
formed and broken during extraction.
blending silo, is never emptied to contain less than 40% of its
is also a factor which decides size and capacity of raw meal storage.
Storage After Expansion
be applied to other storages also to reduce costs of storages as shown
Storage of Coal
fuel consumption be 750 kcal/kg and useful calorific value of coal be
Storage of Clinker
will normally be stored under a covered shed. It is a semi-finished
Weathering (without getting wet) improves grindability.
would be advisable to have separate stockpiles of clinker for each
can however be a common stock pile for under burnt clinker and spill
Space for storages
storages requires heavy investments also considerable space. In a way
unproductive investment. Out of it helps ensuring production and sales
desirable for keeping down the investment, to keep storages to a
also not advisable to cut things too fine. Stoppage in production due
of storage facilities would cause direct loss of revenue.
a wide variety of inorganic materials having diverse chemical
physical properties, and structures. Many ceramic bodies are derived
the term ceramic is applied to high-temperature silicates but since
II most high-temperature, inorganic, nonmetallic materials have been
ceramics. The American Ceramic Society defines a ceramic as “any of a
inorganic, nonmetallic products which are subjected to high temperature
manufacture or use. Typically, but not exclusively, a ceramic is a
oxide, boride, carbide, or nitride, or a combination or mixture of such
materials. High temperature usually means a temperature above barely
red, about 540oC
classified as ceramics are used as industrial abrasives because of
hardness, toughness, chemical inertness, thermal shock resistance, and
thermal conductivity. Many important abrasives are obtained both in
by synthesis. Moreover,
natural abrasives have compositions very similar to other ceramic
with the definition of ceramics, those abrasive materials which may
be classed as ceramics include carbides, diamonds, nitrides, silicides,
certain synthetic oxides. About 45% of bonded abrasive grinding wheels
composites bonded with a ceramic, such as glass or porcelain.
sintering a mixture of natural raw materials such as calcium carbonate
form of limestone or chalk, and aluminum silicate materials such as
shale. During sintering, chemical reactions produce nodules or clinkers
are composed principally of calcium silicates and aluminates. A blend
pulverized clinker and a small amount of gypsum is portland cement.
mixtures of portland cement with masonry, slag, or pozzolan cements.
cements include iron ore and bauxite, high-alumina, and magnesium
Products, Whitewares, and Porcelains
clay products are
produced by conditioning, forming, and then firing clay or mixtures
substantial amounts of clay to form sintered or fused bodies of varying
porosity. Often the finished article is covered by a glaze or enamel.
clay products are clay refractories, china, pottery, sewer pipe, brick,
earthenware, stoneware, and chemical ware.
termed porcelain enamels, are defined as vitreous or glassy inorganic
bonded to metal by fusion at a temperature above 425oC.
Glazes, on the other hand, are
ceramic coatings, often low-melting silicate glasses, which are fusd to
bodies. Thus, enamels and glazes are rather low-melting ceramic
are distinguished primarily by the substrate on which they are applied.
glazes are usually premelted, quenched, ball-milled into a frit, and
a slurry for application and firing to the metal or ceramic body.
alloys which are commonly used as substates are iron, steel, and
various commercial applications and copper, gold, silver, and platinum
jewelry. Typical glazed ceramic ware includes china, pottery,
chemical and sanitary ware, and tile.
and Glass Ceramics
to ASTM, is “an inorganic product of fusion which has cooled to a rigid
condition without crystallizing”. It is not a supercooled liquid. Glass
capable of integrally accommodating many elements of widely differing
and physical properties. It is this property of glass which enables it
precisely “tailored” to a wide variety of applications. Strength,
modulus, acoustic attenuation, hardness, rheological properties,
expansion, electrical resistivity, dielectric constant, refractive
transmittance of electromagnetic radiation, photo-sensitivity,
photochromaticity, and chemical durability can all be adjusted to meet specific
represent a large family of economically important nonmetallic
can withstand high temperatures and corrosive environments. Physical
chamical stability at high temperature is the primary requirement for
acidic, basic ,and neutral refractories have had extensive and
Acidic refractories such as silica, fire clay, zircon, and zirconia are
characterized by a high-silica content; basic refractories such as
and dolomite contain substantial amounts of magnesia, lime, or alkaline
and neutral refractories such as high alumina, chrome, carbon, and
carbide consist of materials which are neither strongly acidic nor
twenty years a wide variety of nonmetallic inorganic substances have
developed with precisely controlled properties for applications in many
devices. These materials differ from traditional ceramics in that they
often nonsilicate synthetic compounds of moderate to very high purity.
control of the unique properties of these new ceramics is an important
growing branch of ceramic science. Examples of such materials include
aluminum, beryllium, magnesium, tin,uranium, and zirconium; magnetic
oxides and ferrites, ferroelectric niobates, tantalates, titanates, and
zirconates; and borides, carbides, nitrides, and silicides.
of the Chemical Composition
the chemical composition of ceramics is a fundamental guide for their
characterization. Although the actual analytical methods-gravimetric,
or instrumental—correspond to those discussed at the various elements
compounds, the sampling and sample dissolution of ceramics are unique
exception of glass, most ceramics are composed of one or more
phases and, accordingly, x-ray diffraction plays an important role even
cursory examination of these materials. Although some ceramics may
single crystals, most are made up of polycrystalline aggregates, and
x-ray techniques are usually employed for identification.
diffraction patterns of ceramics materials are readily obtained by
diffractometer, electronic detection techniques, or by x-ray
procedures such as the Debye-Scherrer powder camera. Specimen
preparation is an
extremely important consideration in phase identification in ceramics
very inhomogeneous ceramic bodies are often encountered and many of the
polycrystalline aggregates may be composed of grains of varying
density, size and orientation.
naturally occurring rock consisting chiefly of calcium carbonate. It is
principally the calcareous remains of organisms. When limestone is
decomposes into calcium oxide, commonly called quicklime, and carbon
The quicklime reacts with water to form calcium hydroxide. This process
usually referred to as slaking; the product is called hydrated lime or
lime. Lime is a general term applied to quicklime and hydrated lime.
limestone had been used by the Egyptians as early as 4000 BC
construction of the pyramids. Many of the other ancient civilizations
independently discovered the technique of burning limestone, and a
uses for the lime produced.
is a naturally occurring material, the chemical composition and
characteristics of limestone and its products vary considerably. The
discussion is presented to show some of the more common properties.
Color. The purer forms are white. The lime usually
has considerably less
gray or tan color then its parent limestone. Impurities in the
produce colors ranging through red (from iron) to black (from
material), including the variegated colors of marble and travertine.
usually has a uniform, fine-grained, crystal structure. However, stone
different deposits varies greatly in crystallite size and porosity.
often appear similar to their parent limestones. Hydrated lime are
massive limestone varies from 0.3 to 12%.
Porosity is the percentage of voids in the bulk volume of
Quicklime is usually considerably more porous than its parent
is either or rhombohedral or rhombohedral in crystal structure.
Quicklime is in
the cubic system and the hydrated lime are in the hexagonal
of limestone ranges from 2.0 to 2.8 g /cm3,
quicklime from 0.77 to
1.1 g /cm3,
lime from 0.40 to 0.64 g /cm3.
Mohs’ scale, for limestone and quicklime is from 2-4 and for hydrated
index is refraction, n is 1.48-1.69 for limestone,
quicklime, and 1.54-1.58 for hydrated lime.
heat of formation, at 25°C, is -151.9 kcal/ mole for calcium oxide, -
kcal/mole for calcium hydroxide, and-288.5
kcal/mole for calcium
limestone varies with temperature and carbon dioxide constant of the
25°C in water free of carbon dioxide, the solubility of calcite is
g/liter. Quicklime hydrates in water and then has the same solubility
hydrated lime, which decreases with increasing temperature. The
calcium hydroxide in water at 25°C is 1.6 g /liter.
and limestone are inexpensive neutralizing agents. Limes are more
then limestones on a mass basis because 44% of the limestone is carbon
which is not utilized in the neutralization process. The rate of
depends on the reaction products. For example, in neutralization oxalic
the reaction product is calcium oxalate, a relatively insoluble salt,
forms on the surface of the lime or limestone particles and retards
with silica and alumina.
limestone are used in many
to react with silica. When the reaction is carried
out at high temperatures,
produces fused calcium silicates.
the case of limestone,
carbon dioxide evolved serves to mix the molten mass,
in the manufacture of
and the refining of metals. When lime is mixed with a
pozzolan and water,
reaction can occur at room temperatures.
stabilization is an example of lime reacting with silica in clay minerals
water at a rate which depends on the calcination process:
lime reacts extremely
lime can react violently. When calcined properly,
is an effective desiccant.
can remove about one-third
its weight of water from air or organic liquids such
reacts with slightly
is the process which hardens lime mortars used in buildings.
As the carbonation proceeds,
reaction product forms a barrier which greatly
uses of lime
and limestone are widespread. For example, limestone is used for
ballast and poultry grit; quicklime is used in the production of steel
the production of glass; and hydrated lime is used in mortars for the
construction of buildings,-and the manufacture of grease.
applications have different purity requirements. In metallurgical
the limestone or quicklime is used as a fluxing agent for the silica
the ore. If, eg, the limestone contains 2.5% silica, that silica will
with about 7% of the remaining limestone. Therefore, about 10% more
by weight would be required in the furnace charge then for a stone free
silica. On the other hand, limestone for the manufacturing of portland
can have 20% silica and be very desirable of the magnesium constant is
Material to be used in food or food processing has to meet very low
certain impurities such as arsenic, lead, and fluorine.
In many samples
of lime and limestone, the value obtained for the percent acid
extremely close to the value obtained for silicon dioxide when a very
analysis is carried out i.e., recovering the silica lost even after two
dehydrations, and correcting the acid -insoluble residue for impurities
compensate each other. The total silicon dioxide in the acid -insoluble
can be determined by removing the silicon as the tetrafluoride.
5 ml of water to the weighed residue in the platinum crucible from
determination of acid-insoluble matter. Add 2-3 drops of concentrated
acid, and at least 5 ml of concentrated hydrofluoric acid; the crucible
be about one-third full. Evaporate to dryness in a fume hood. Ignite
residue at 1200°C in a muffle furnace for 5 min, cool, and weigh with
lid. The loss in weight represents the silicon dioxide content. Save
ignited residue for the ammonium hydroxide group oxides determination.
In the gravimetric
method below, the magnesium is precipitated as ammonium magnesium
Orthophosphate. If the oxidation of manganese and precipitation of the
group oxides were not carried out carefully enough, the ignited
pyrophosphate will contain manganous pyrophosphate. It is advisable,
to dissolve the residue in concentrated nitric acid and to check for
with sodium bismuthate.
Add 150 ml of concentrated nitric acid
to the combined filtrates and washing from the calcium oxalate
precipitation and evaporate to dryness on a steam bath. Add about 5 ml
concentrated hydrochloric acid and 50 ml water; and if a slight residue
silica remains, filter through a Whatman No. 40 or equivalent paper.
the filter paper to a platinum crucible weighed with the lid, char,
burn of the
carbon, cover the crucible, and ignite in a muffle furnace at 1200°C to
constant weight. Calculate the silicon dioxide content from the loss in
and correct the previously obtained silicon dioxide value accordingly.
the filtrate and washing (or the unfiltered solution) to about I50 ml
Add 20 ml of a saturated solution of sodium ammonium hydrogen phosphate
continue to boil for several minutes. Cool to room temperature. Add
concentrated ammonium hydroxide dropwise, with stirring but without
the sides of the beaker, until ammonium magnesium orthophosphate begins
form; then add about 10ml in excess. Continue stirring for 5 min, cover
watch glass, and let stand for 12-48 hr (longer when the sample
magnesium oxide). Filter through a retentive paper such as Whatman No.
wash moderately with cold 1 :20 ammonium hydroxide. Dissolve the
with about 50 ml of hot 1: 10 hydrochloric acid, wash the filter paper
ml of hot 1: 100 hydrochloric acid, and collect the solution in a 250
beaker. Boil the solution and reprecipitate the ammonium magnesium
orthophosphate in the same manner as before, except use only 3 ml of
saturated ammonium hydrogen phosphate solution and add only 5 ml excess
concentrated ammonium hydroxide. Let stand for 12-24 hr. Filter through
Whatman No.42 or equivalent paper and wash with cold 1:20 ammonium
until the washings, acidified with nitric acid, give no test for
with a dilute silver nitrate solution. Transfer the filter paper and
precipitate to a platinum crucible weighed with the lid, char, and bum
carbon at as low a
possible with free access of air. Cover the crucible and ignite at
1100°C in a
muffle furnace to constant weight. One gram of the resulting magnesium
pyrophosphate residue is equivalent to 0.3623 g of magnesium oxide.
Exact or even
approximate determinations of ferrous oxide are
often impossible in
samples which contain carbonaceous matter or manganese dioxide.
However, if the
amounts are small, acceptable re-sults are obtainable. In limestone
the ferrous iron usually is in the from of a carbonate.
The sample is
decomposed in hydrochloric acid. The liberated carbon dioxide is swept
the gas conditioning train, is absorbed in Ascarite, and is weighed.
The usual and
adequate method of determining the sulfur trioxide content of limes and
limestones is to precipitate the sulfate in the acid-soluble fraction
a 2-g sample in a 150-ml beaker, add 10 ml of cold water, and stir
the lumps are broken. Slowly add 15 ml of 1: 1 hydrochloric acid, heat
solution is complete, filter through a Whatman No. 40 or equivalent
thoroughly wash the residue with hot water. Collect the filtrate and
in a 400-ml beaker. Dilute the filtrate and washings to 250 ml with
to boiling, and add dropwise, with vigorous stirring, 10 ml of hot 10%
chloride solution. Stir for an additional 2 min, cover with a watch
let stand overnight. Filter through a retentive paper such as Whatman
and wash thoroughly with cold water. Transfer the moist filter paper
precipitate to a platinum crucible weighed with the lid, char, and burn
carbon. Cover the crucible and ignite in a muffle furnace at about
constant weight. One gram of the resulting barium sulfate residue is
to 0.343 g of sulfur trioxide.
the sample contains a considerable amount of silica, it is advisable to
the ignited barium sulfate residue with sulfuric acid and hydrofluoric
(see section on silicon dioxide, to remove any silica contamination in
barium sulfate before obtaining the final weight.
The arsenic is
distilled from the sample as arsine in a conventional arsine generator.
arsine is collected in diethyldithiocarbamate reagent after removing
hydrogen sulfide with lead acetate and is determined colorimetrically.
amounts of heavy metals tend to slow down the evolution of arsine, but
not a problem with most limes and limestones.
concentrated by separation of the Group II sulfides. After dissolving
sulfides, the lead cyanide complex is extracted into
diphenylthiocarbazone-chloroform, and its concentration is determined
colorimetrically. Ferric ion can interfere; therefore, as a precaution,
ferric ion present is reduced with hydroxylamine prior to the
greatest source of error is contamination from lead carying dust and
adhering to the glassware.
The large quantities of calcium present in lime and limestone samples
determination of sodium and potassium difficult. Acceptable results can
obtained by flame emission spectroscopy if aluminum is added to reduce
interference of the calcium and the standard solutions are prepared to
the same calcium content as the sample. Greater accuracy can be
obtained if the
standard solutions also contain the same proportions of sodium and
content is determined by steam distilling silicon tetrafluoride from
and measuring colorimetrically its bleaching action on alizarin red S
are determined by titration with mercuric nitrate solution using
diphenylcarbazone as the indicator and calculated on the basis of
This test measures the reactivity of the material: high reactivity lime
completely hydrated within 10 min; medium reactivity lime is completely
hydrated in 10-20 min; and low reactivity lime is completely hydrated
noncrystalline solid; it is characterized by an absence of long-range
its atomic structure. Although a definition on the basis of this
thus include organic as well as inorganic glasses and the metastable
state of a
variety of normally crystalline elements and compounds, consideration
given here only to those glasses of major commercial importance,
glasses.Consequently, the definition of the American Society for
Materials that describes glass as “an inorganic product of fusion which
cooled to a rigid condition without crystallizing” is appropriate.
applicable, but more descriptive is an alternate definition which
glass is an inorganic substance in a condition which is continuous
analogous to, the liquid state of that substance, but which, as the
having cooled from a fused condition, has attained so high a degree of
viscosity as to be, for all practical purposes, rigid.”
the diversity and range of properties and adaptability of glasses and
glass-ceramics makeup. Few materials are so diversely constituted.
every elements in the Periodic Table can be incorporated into a glass.
majority of the elements actively participate in the structure of glass
as network former, intermediate or modifier. The latter class of
ionic and interstitial in the structure, whereas the former
characteristically covalent in nature and combine to form the random
“backbone” structure of glass.
imparted, sometimes unintentionally from batch contaminants, through
dissolution of such transition elements as iron, chromium, nickel,
manganese, vanadium, copper, cerium, and uranium. Oxidation state,
number, and the presence of auxiliary elements such as titanium will
the color of a particular ion. Black glass is obtained with high
of a combination of manganese and chromium, or relatively high
of lead sulfide, iron sulfide, or cobalt polyselenide. Color is also
through controlled nucleation and growth of such species as cadmium
sulfoselenide, cadmium selenide, selenium, or metallic crystals,
copper, and silver, to colloidal particle size dimension.
industry-wide standardized compositions; glass compositions are usually
proprietary and traditionally they are specified by properties rather
composition. Neverthelss, it may be useful to classify the commercially
important products into the following nine categories: soda-lime,
aluminosilicate, opal, colored, optical, lead/barium, and special
glass-ceramics.Table 2 shows the approximate composition ranges in
percent for some of the leading members of each category, except
glasses. The range of optical glass compositions is a field in itself
indicated in Table 3.Table 4 gives typical compositions of some
important glasses and glasses-ceramics.Additional glass compositions
tabulated in the CERAMICS article.
glasses are decomposed by either acid attack with a mixture of
acid and another mineral acid, or by fusion with sodium carbonate
digestion with a mineral acid. The choice of approach is dependent on
elements to be determined and the method. Flame spectroscopy, for
cannot tolerate alkalies such as are introduced by introduced by
perchlorate is the preferred anion. Table 6 summarizes the common
be determined in glasses and glass-ceramics and the corresponding usual
sample decomposition. Obviously a compromise must be made when
sample for the determination of titanium in a
since perchloric acid is optimal for barium glasses and sulfuric acid
for glasses containing titanium.
Methods for Individual Constiluents
considering the great diversity of elemental combinations which may
glass materials, that no simple all -embracing classical chemical
scheme can be
given. However, the procedures given here are applicable to most of the
commercial glasses and glass-ceramics, such as might be typified by the
compositions shown in Table 2.
spectroscopy in its general sense embraces all those optical processes
occur in a flame, including emission from excited atoms, resonance
of monochromatic light by ground -state atoms, and fluorescent emission
suitably irradiated groud-state atoms. The last named phenomenon,
atomic fluorescent spectroscopy, has not yet found practical
glass analysis and hence will not be considered further. On the other
techniques have had the impact on the analytical technology of a class
materials as have flame emission and atomic absorption spectrometry on
analytical chemistry of glasses and glassceramics.
flame methods enable the glass analyst, without complex manipulations,
accomplish in a matter of hours what formerly required up to two or
Since the usual precision of both methods is of the order of 1 to 2% of
amount present, appliction of flame spectroscopy to glasses and
is usually limited to the minor (1-20 wt % ) and trace (less than 0.1
constituents. Improvements in the techniques are continuing ,
the area of precision, such that even now, taking special care, a
low as = 0.5 relative % can be achieved in special instances.
spectroscopy has been employed for many years for both qualitative and
quantitative chemical analysis of glass and similar silicate–base
such as slags, ores, rocks, soils, and ceramics. Early work on the
glass has been documented by Cooper, by Hegemann and Zoellner, by Waed
Hartley and by Lieberman. One of the principal applications of optical
spectroscopy to glass and glass–ceramic materials is to provide a
compositional survey prior to more extensive chemical analysis by other
spectrochemical pellet–spark technique for nonmetallic specimens,
Tingle and Matocha, and employing a multichannel photoelctric
be adapted for the quantitative analysis of glasses. Two hundred mg of
sample (–200 mesh) is with 1.8 g of anhydrous lithium tetraborate ( )
containing cobalt for an internal standard in a plastic vial for 60 sec
suitable mixer–mill. The sample-flux mixture is transferred to a
crucible and placed in a preheated furnace at 950 for 20 min.
methodology, and scope of applicability of this technique are discussed
and voltammetry. For
versatility, selectivity, and speed of analysis, polarography is
the other major electroanalytical techniques. Even in its conventional dc form,
this approach enabled Williams
et al. to develop selective method for the determination of zinc,
lead present in the same sample, and a specific method for antimony
has also determined lead and zinc in glass, and Marachevskii have
polarographic measurement of microgram amounts of arsenic and antimony
silicate materials after a distillation separation of the halides.
polarography was applied by Noshiro and Sugisaki, who reported the
determination of antimony and also the simultaneous determination of
useful spectral transmittance range of
most glasses is from near 300 nm in the ultraviolet to about 5.0mm
infrared. This is illustrated in Figure 7. The curve labeled “Plate” is
glass, and is typical
for alkali–lime–silica glass types. Code 1723 is an aluminosilicate
curve for this glass is similar to that for Code 7740 borosilicate
in laboratory glassware.
diffraction patterns of crystalline phases in glasses and
glass-ceramics can be
readily obtained by standard diffractometer-electron detection
techniques or by
photographic procedures, for example, with the Debye-Scherrer powder
Although x-ray diffraction is commonly thought to apply only to
materials, useful structural information may also be gathered from
noncrystalline bodies such as glass. The major distinction between the
types of material is that in crystalline matter long order gives rise
x-ray scattering, while
in glass short
range order produces rather diffuse patterns. A comparison of x-ray
patterns from a crystalline glass-ceramic and non-crystalline glass is
in. The discussion of x-ray diffraction in the ceramics articles
glass and glass-ceramics. In addition to the topics covered there, the
following information is pertinent.
resolution diffraction, a Guinier camera is very useful. A
in conjunction with this device will eliminate all undesirable x-ray
wavelengths except Ka1.
diffraction lines often found in glass-ceramics can be readily resolved
Guinier camera mounted on a fine focus of microfocus x-ray generator.
quality and optical constants of glass, surface topography, fracture
morphology, and break sources in glass and glass–ceramics, nucleation
separation in glass and glass–ceramics, and the variable
in glass–ceramics, all can be investigated advantageously by various
techniques. Electron microscopy is discussed and optical microscopy.
application of microscopy to glass and glass–ceramics is covered in the ceramics
article, Additional methods
and techniques are discussed below.
Preparation for Microscopic Examination.
The scope of microscopic examination
of glass and glass–ceramics is extremely broad, ranging from the
gross surface and optical defects at magnifications of 3 to 100 by
microscopy to transmission electron microscope of nucleation, phase
and crystal growth of particles 15–1000 A in size. Universal methods
preparation such as outlined by Insley and Frechette and Chamot and
Thornton and Kay are employed for optical, scanning and transmission
microscopy observations, respectively.
the application of the electron microprobe for glass analysis has been
increasingly exploited. Electron microprobe techniques are described in
A review of the application of these techniques to glass and ceramic
has been reported by Kane.
microprobe has been utilized to chemically analyze defects, stones,
and cord in glass, to study ion diffraction in simple glass systems to
investigate metal and refactory corrosion by molten glass, to scan
metal seals to determine structural correlations in silicates with
wavelength shifts and to
archaeological glass specimens.
glass–ceramics are nonporous and reasonably uniform in chemical
specimen preparation is often routine. However, complications may arise
exposure of glass effects is required, in which case, cutting and
operations can prove to be a major task. Some criteria for satisfactory
specimen preparation have been given by Yakowitz.
glass–ceramics are poor conductors of heat and electrons and a
coating should be applied to the polished specimen to prevent surface
build–up and consequent distortion and deflection of the electron beam.
evaporated copper, aluminum, or carbon films are usually employed to
of gases in glass
Blisters. Gaseous inclusions or
bubbles in glass,
usually called blisters, seriously affect the optical characteristics
and, therefore, are of importance in glass quality considerations. The
components present can often serve as a means of diagnosing the
governing the formation of the blisters, and the value of knowing the
composition of the gases present is self-evident. The mass spectrometer
analysis of the gases in blisters in glass was pioneered by Todd and an
improved sampling technique for the analysis has been reported by
chromatography has also been employed for the analysis of the gases in
bubbles. Work reported by Bryan indicate that reliable gas analyses can
obtained by gas chromatography, but larger sample volumes are required
compared to the mass spectrometer method.
gas evolved from glass at temperatures below the softening point is an
important characteristic when glass is used as an envelope in vacuum or
gas–filled devices. Outgassing of the glass envelope can lead to
of the vacuum, contamination of the gas fill, and possibly harmful
the components in the device. The energy required for the outgassing
may be furnished in different ways, depending on the conditions under
device is used. The principal gases evolved depend on the form of
supplied; heat produces water; electron bombardment, oxygen;
radiation, hydrogen, and thermal neutron bombardment of
glasses, helium. In addition to the major gases, all these processes
some carbon oxides and water.
Gases in Glass.
The use of glass in ultra high vacuum systems where pressures in the
-12 torr are required, in
closed systems which
contain radioactive or other dangerous gases, and in storage devices
might be utilized in outer space, has made the accurate determination
permeation of gases through glass necessary. Early gas flow
made by monitoring the low–pressure side of pressure gages, such as
Pirani gages, Mc Cleod gages, or ionization gages. More recently, mass
spectrometers have been employed to measuer the flow of gases for gases
diffusion studies. The advantage of the mass spectrometer is that the
gas to be
studied can be monitored independently of any other gas in the system.
particularly useful when, as in the case of diffusion in glasses, the
rates to be measured are of the same order of magnitude as the
rates, especially at high temperatures.