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KIRK- OTHMER
ENCYCLOPEDIA OF CHEMICAL TECHNOLOGY
THIRD EDITION
VOLUME 3
ANTIBIOTICS (PHENAZINES)
TO BLEACHING AGENTS
A WILEY- INTERSCIENCE PUBLICATION
John Wiley & Sons NEW YORK CHICHESTER BRISBANE TORONTO
The New Ybrk mec Library rte w ruas mural en
Copyright © 1978 by John Wiley & Sons, Inc.
All rights reserved. Published simultaneously in Canada.
Reproduction or translation of any part of this work beyond that permitted by Sections 107 or 108 of the 1976 United States Copyright Act without the permission of the copyright owner is unlawful. Requests for
permission or further information should be addressed to the Permissions Department, John Wiley & Sons, Inc.
Library of Congress Cataloging in Publication Data:
Main entry under title: Encyclopedia of chemical technology.
At head of title: Kirk -Othmer. "A Wiley -Interscience publication." Includes bibliographies. 1. Chemistry, Technical -Dictionaries. I. Kirk,
Raymond Eller, 1890 -1957. II. Othmer, Donald Frederick, 1904- III. Grayson, Martin. IV. Eckroth, David. V. Title: Kirk -Othmer encyclopedia of chemical tech- nology.
TP9.E685 1978 660'.03 77- 15820 ISBN 0- 471- 02039 -7
Printed in the United States of America
CONTENTS
--- Antibiotics (continued), 1
Antifreezes and deicing fluids, 79 - -- Antimony and antimony alloys, 96
Antimony compounds, 105 Antioxidants and antiozonants, 128 Antistatic agents, 149
1-- Appetite- suppressing agents, 184 Aquaculture, 194
Aramid fibers, 213 Arsenic and arsenic alloys, 243 Arsenic compounds, 251
Asbestos, 267 Asphalt, 284 Aviation and other gas turbine
fuels, 328 Azeotropic and extractive
distillation, 352
Azine dyes, 378 Azo dyes, 387 Bagasse, 434 Bakery processes and leavening
agents, 438 Barium, 457 Barium compounds, 463
- Barrier polymers, 480
Batteries and electric cells, primary, 503
Batteries and electric cells,
secondary, 569
- Bearing materials, 670 Beer, 692 Benzaldehyde, 736 Benzene, 744 Benzidine and related
biphenyldiamines, 772 - Benzoic acid, 778
Benzyl alcohol and ß- phenethyl alcohol, 793
- Beryllium and beryllium alloys, 803 Beryllium compounds, 824 Beverage spirits, distilled, 830 Biomedical automated
instrumentation, 863 Biopolymers, 884 Bismuth and bismuth alloys, 912 Bismuth compounds, 921 Bleaching agents, 938
EDITORIAL STAFF FOR VOLUME 3
Executive Editor: Martin Grayson Associate Editor: David Eckroth Production Supervisor: Michalina Bickford Editors: Galen J. Bushey Loretta Campbell
Lorraine van Nes Anna Klingsberg
CONTRIBUTORS TO VOLUME 3
John Ballance, l3rush Wellman Inc., Cleveland, Ohio, Beryllium and beryllium alloys Burton M. Baum, FMC Corporation, Princeton, New Jersey, Bleaching agents Douglas N. Bennion, University of California, Los Angeles, California, Introduction; Primary
cells (both under Batteries and electric cells, primary) Julius Berger, Hoffmann-La Roche Inc., Nutley, New Jersey, Phenazines (under Antibiot-
ics)
John H. Blumbergs, FMC Corporation, Princeton, New Jersey, Bleaching agents E. R. Booser, General Electric Company, Schenectady, New York, Bearing materials James H. Boothe, Lederle Laboratories Division, American Cyanamid Company, Pearl River,
New York, Tetracyclines (under Antibiotics) Lester A. Brooks, R. T. Vanderbilt Co., Norwalk, Connecticut, Antioxidants and antizo-
nants Elton J. Cairns, General Motors Research Laboratories, Warren, Missouri, Fuels cells (under
Batteries and electric cells, primary)
vii
viii CONTRIBUTORS TO VOLUME 3
*S. C. Carapella, Jr., ASARCO Inc., South Plainfield, New Jersey, Arsenic and arsenic alloys;
Bismuth and bismuth alloys
Sigmund C. Catino, GAF Corp., Rensselaer, New York, Azo dyes
William B. Chess, Stauffer Chemical Co., Dobbs Ferry, New York, Chemical leavening agents
(under Bakery processes and leavening agents)
Margaret A. Clarke, Cane Sugar Refining Research Project, Inc., New Orleans, Louisiana,
Bagasse
Howard P. Clemens, University of Oklahoma, Norman, Oklahoma, Aquaculture
J. Clyde Conger, Sr., American Cyanamid Company, Bound Brook, New Jersey, Azine
dyes Michael Conway, University of Oklahoma, Norman, Oklahoma, Aquaculture
G. O. Doak, North Carolina State University, Raleigh, North Carolina, Antimony compounds;
Arsenic compounds; Bismuth compounds
James B. Doe, ESB Technology Co., Yardley, Pennsylvania, Introduction; Secondary cells,
lead -acid; Other cells (all under Batteries and electric cells, secondary)
W. G. Dukek, Exxon Research and Engineering Company, Linden, New Jersey, Aviation and
other gas turbine fuels
Edward J. Elliott, FMC Corporation, Princeton, New Jersey, Bleaching agents
James V. Evans, Amoco Oil Company, Chicago, Illinois, Asphalt
Russell E. Farris, GAF Corp., Rensselaer, New York, Azo dyes
R. H. Fay, Dow Chemical, U.S.A., Freeport, Texas, Antifreezes and deicing fluids
Kelvin H. Ferber, Allied Chemical Corp., Buffalo, New York, Benzidine and related bi-
phenyldiamines Joseph H. Finley, FMC Corporation, Princeton, New Jersey, Bleaching agents
Leon D. Freedman, North Carolina State University, Raleigh, North Carolina, Antimony
compounds; Arsenic compounds; Bismuth compounds
Hiram Gu, University of California, Los Angeles, California, Primary cells (under Batteries
and electric cells, primary)
Zeev Gur- Arieh, Monsanto Textiles Company, Decatur, Alabama, Antistatic agents
Paul A. Hammes, Merck and Co., Rahway, New Jersey, Antioxidants and antiozonants
Frank N. Hepburn, U.S. Department of Agriculture, Hyattsville, Maryland, Yeast -raised
products (under Bakery processes and leavening agents)
Joseph J. Hlavka, Lederle Laboratories Division, American Cyanamid Company, Pearl River,
New York, Tetracyclines (under Antibiotics)
H. E. Howe, ASARCO Inc., South Plainfield, New Jersey, Bismuth and bismuth alloys
H. E. Hoyrup, Bryggeriforeningen, Copenhagen, Denmark, Beer
Truman Kirkpatrick, The Sherwin - Williams Company, Chicago, Illinois, Barium com-
pounds Karel Kulp, American institute of Baking, Chicago, Illinois, Yeast -raised products (under Bakery
processes and leavening agents) Charles J. Kunesh, Pfizer Inc., Easton, Pennsylvania, Barium G. Gilbert Long, North Carolina State University, Raleigh, North Carolina, Antimony com-
pounds; Arsenic compounds; Bismuth compounds Anthony M. Luxeder, The B. F. Goodrich Co., Chemical Division, Cleveland, Ohio, Antiox-
idants and antiozonants Alan K. Mallams, Schering- Plough Corporation, Bloomfield, New Jersey, Polyenes (under
Antibiotics)
Vol. 3 C Uti f Rlfill rt)it5 Tt) VOLUME 3 ix
Herman F. tiiark. j °t , 1't is 1, )rk t11, $1, A. 11 "it %.% 1 rte Hi( )1)01),(114:4's S. P. Nempho., ( orlt!.'sr, !,)I Pr f 11 hit to. ( t, Nh it 1rr1111)1, ( ()mu., trout Barrier
Paul P. Nicfx ic.. `'t ±; t i .414*A h t. r.! (.0(7x rtctf. RPNe.irrh ,.t ,li, r Ih1o. Artrrr,xirí.tnt ,
Donald F. t?thmer. fk)4.tek:lu is Iti tïtt,te of New York. Brooklyn, Nrw York AtPrtroptr f Ki tAtratilVe itit 4l t)n
Coe(r. e /tk Packow:ski, kAeph F Seagram & Sons, Inc ., New York, New York, BPvfir.fge o r (*st il ed
ugerpe Pearlman. [NB Te(hnok.)gy Co . }''ardlev. Pennsylvania, Secondary cells. alkaline under Batter. s and electrn Cells. secondary)
. Preston, N ortsanto T rangk' Park Development Center, Inc:., Research Triangle Park.. North Carolina .Aramid fibers
Waliarri P. Purcell, Union Oil Company of California, Brea, California, Benzene Glenn H. Rees, Brush Wellman Inc., Cleveland, Ohio, Beryllium compounds Sertie J. Reuben, A4onsanto Textiles Company, Decatur, Alabama, Antistatic agents 11Víiiam RingIc, Chemical Consultant, Westfield, New Jersey, Benzyl alcohol and 0- phenethyl
alcohol Stephen T. Ross, Smith Kline & French Laboratories, Philadelphiá, Pennsylvania, Appetite -
suppressing agents Salame, »onsanto Commercial Products Co., Bloomfield, Connecticut, Barrier poly-
mers Alvin 1. Salkind, ES8 Technology Co., Yardley, Pennsylvania, Secondary cells, alkaline (under
Batteries and electric cells, secondary) Fred Schuler. FMC Corporation, Princeton, New Jersey, Bleaching agents Morris H. Shamos, Technicon Instruments Corporation, Tarrytown, New York, Biomedical
automated instrumentation Lloyd R. Snyder, Technicon instruments Corporation, Tarrytown, New York, Biomedical
automated instrumentation S. Steiger, Monsanto Commercial Products Co., Bloomfield, Connecticut, Barrier poly -
mers A. tames Stonehouse, Brush Wellman Inc., Cleveland, Ohio, Beryllium and beryllium al-
rvv5
Wpm C. Streib, Johns - Manville Corporation, Denver, Colorado, Asbestos Ray Sweeney, Brush Wellman Inc.. Cleveland, Ohio, Beryllium and berllium alloys Ernst T Theifner, Consultant, Rumson, New Jersey, Benzyl alcohol arid ß- phenethyl alco-
kenneth Wes, Brush WeMnan inc... Cleveland, Ohio, Beryllium and beryllium alloys. Be- ryllium compounds
John W. WesUey, HOffrr;ar.vf -L a Roche /nc.-., Nutley, New Jersey, Polyethers (under Ant)br ois)
Arnold F. Wtlttarns, (ihr- rrik.a/ inr k'alarrra, Washington, Benzakicshyde Benzoic acid
Romeo R. Witherspoon, Genera/ Motorcc Research Laboratories. Warren, Missouri, Fuel cells (under Batteries and +.tri,. c, prunary)
Henry L. Wooten, f mK;; Corporation, Princeton, New Jersey, Bleaching agents
Vol. 3 ASBESTOS 267
ASBESTOS
Asbestos is a generic term describing a variety of naturally formed hydrated sil- icates that, upon mechanical processing, separate into mineral fibers. There are two fundamental varieties of asbestos: serpentine and the amphiboles. Serpentine asbestos is known as chrysotile and the amphiboles include five species identified as antho- phyllite, amosite, crocidolite, actinolite, and tremolite. Each of these varieties of as- bestos differ from each other chemically as illustrated in Table 1.
Asbestos fibers are unique minerals combining unusual physical and chemical properties which make them useful in the manufacture of a wide variety of residential and industrial products. Of mineral origin, asbestos does not burn, does not rot, and, dependent on variety, possesses extremely high tensile strength as well as resistance to acids, bases, and heat. Similarly, when processed into long, thin fibers, asbestos is sufficiently soft and flexible to be woven into fire- resistant fabrics.
Historical records show that asbestos has been known fór more than 2000 years. Applications of this noncombustible fiber are mentioned by Plutarch and Pliny, particularly with reference to asbestos textiles used for cremation cloths, oil lamp wicks, etc.
The asbestos industry per se had its inception in the 18th century in the Russian Ural mountains and by the mid -19th century both Italian chrysotile and tremolite varieties were mined and processed into commercial products. At the same time as- bestos was discovered and mined on a commercial scale at Thetford Asbestos in Quebec, Canada. To this day, these Canadian and Russian locations are the major producers of chrysotile asbestos.
The amphibole asbestos industry is of more recent origin. Blue asbestos, crocid- olite, was discovered in South Africa about 1803 to 1806, but it was not until 1893 that this variety was commercially exploited. Production, sale, and use of the amosite species from the Transvaal followed in the early 20th century (1).
Origin and Occurrence
Through the years, the origin of asbestos has been the subject of extensive geo- logical research. Serpentine asbestos occurs under widely differing geological conditions from the amphiboles. Similarly, the modes of occurrence or the manner in which the fibers are physically imbedded in the host rock also differ widely. The current opinion is that chrysotile fiber resulted from two separate metamorphic'reactions in ultrabasic
Table 1. Asbestos
CAS Species Registry Number Variety Chemical composition
chrysotilea [12007 -29 -5] serpentine 3Mg0.2Si02.2H20 anthophyllite [17068 -78 -9] amphibole 7Mg0.8Si02.H20 amositea [12172 -73 -5] amphibole 11Fe0.3Mg0.16Si02.2H20 actinolite [13768 -00 -8] amphibole 2Ca0.4MgO.Fe0.8SiO2.H20 tremolite 114567 -73 -81 amphibole 2Ca0.5Mg0.8Si02.H20 crocidolitea [12001 -28 -4] amphibole Na20.Fe203.3Fe0.8 Si02.H20
a Asbestos species of major commercial significance.
268 ASBESTOS
rocks of igneous origin. The initial hydrothermal reaction altered the olivines and pyroxenes to serpentine. At a subsequent point the serpentine was redissolved and the mineral -rich solutions flowed into cracks and crevices in the host rock where chrysotile fiber was reprecipitated.
In this reprecipitation process, asbestos fiber was usually deposited in a cross -vein mode of occurrence; ie, the fiber is arranged perpendicular to the wall rock as illustrated in Figure 1.
In some cases, chrysotile was either deposited or affected by earth movements such that the fibers lie principally parallel to the wall rock as illustrated in Figure 2. This mode of occurrence is referred to as slip fiber.
The third and unusual mode of occurrence of chrysotile is referred to as a massive or agglomerated form wherein the fibers have been deposited as platelets having no specific fiber orientation. This unique formation has been found and commercially mined in the New Idria serpentine deposits of California (2) and at Stragari, Yugo- slavia. In these cases the asbestos content of the ore is abnormally high, but the fiber length is very short as compared to commercially useful cross -vein or slip fiber deposits. This mode of occurrence is illustrated in Figure 3.
The origin of the amphibole varieties of asbestos are not as clearly defined as those of chrysotile. The two commercially significant amphibole fibers, crocidolite and amosite, occur in metamorphosed sedimentary strata known as banded ironstones. These sedimentary formations vary considerably in composition which accounts for the compositional variations of the associated amphibole fibers (1).
.... ,. .......r... ....._. .y. wr.........._...
Figure 1. Cross -vein chrysotile (Courtesy of Johns -Manville Research Center).
Vol. 3
a
ASBESTOS 269
.( Y
)
y
. '`. nd` , <{AF ' ',.kl _ 1 Z n s 72. .,;7í
1 .? t. YI ÿ . r N M
r.
.P.,owr.-di+-u+1.:rE:4.»uaw.u-.._ ..-... -.. _...r:yauve.ww:,;a..,a.._.__.-.. . :._ . ., y; .,. .......n+rovs.swvnrass.wrw... .
Figure 2. Slip fiber chrysotile (Courtesy of Johns -Manville Research Center).
Crocidolite and amosite species of asbestos occur in cross -vein modes and the an-
thophyllite and tremolite species often occur in slip modes although both of the latter can also occur in a massive mode wherein the fibers are nonoriented. Actinolite, a
noncommercial species of amphibole asbestos, is most often found as brittle, acicular,
or bladed forms in a massive mode. In its generic connotation, asbestos is a mineral found all over the world. In most
cases, however, the asbestos species most easily located are those having limited or
no commercial utility such as actinolite, anthophyllite, or tremolite. In 1977, Canada and Russia are the major producers of chrysotile asbestos, and Africa, China, and the United States provide modest quantities. The major producing area of the important amphiboles, crocidolite, and amosite is Africa. In fact, the only deposits of amosite known to date are in the Eastern Transvaal.
Chrysotile Asbestos Crystal Structure. The mineral species associated with the serpentine group,
serpentine [12168- 92 -2], chrysotile, lizardite [12161-84-1], and antigorite [12135- 86 -3],
although differing structurally, are compositionally almost identical. All have the approximate chemical composition of Mg3(Si205) (OH)4. The crystal structure of
chrysotile is layered or sheeted similarly to the kaolinite group [1318 -74 -7] (3 -4). It is based on an infinite silica sheet (Si205)n in which all the silica tetrahedra point one
way (see Silica). On one side of the sheet structure, and joining the silica tetrahedra, is a layer of brucite, Mg(OH)2i in which two out of every three hydroxyls are replaced by oxygens at the apices of the tetrahedra. The result is a layered structure illustrated in Figure 4 (1,5).
270 ASBESTOS
SNFi.iiIP7IE
Y....Y.il 11 . .I.. _ --'rnv.wuwlaaw:.YwJ.ru4w ...Gti:taM..`1i+t<rK4rliia'N.wrlr 'Mrv.eAi: w+:!+i.'4.ii.+.aac.a
Figure 3. New Idria (Coalinga) chrysotile platelets (Courtesy of Johns -Manville Research Center).
Unit cell composition Mg6(OH)8Si4Oto
Build -up of sheets into fundamental fibrils
r...ii.
Figure 4. Fundamental sheet of a chrysotile structure.
Mismatches and strains between the layers cause the structure to curve and form cylinders or fibers (6 -7). Individual chrysotile fibers have ultimate diameters of 0.02 -0.03 Am. X -ray and electron microscope studies have confirmed this cylindrical form and diameter range. In fact, the first electron microphotographs indicated a tubular structure as illustrated in Figure 5 (8-10). This characteristic appearance has now become one of the more definitive identification techniques for chrysotile.
Vol. 3 ASBESTOS 271
Figure 5. Electron photomicrograph (80,000X) of chrysotile (Courtesy of Johns -Manville Research Center).
Electron microphotographs have shown most chrysotile fibers with a hollow cy- lindrical form and a single magnesia -silica sheet rather than the earlier double -layer concept (11_ -12). The lattice planes have a multispiral arrangement as suggested by earlier x -ray studies (13).
272 ASBESTOS
Chemical and Surface Properties. Chrysotile asbestos is a naturally formed mineral. The chemical compositions vary somewhat, depending on deposit location, from the idealized composition of Mg3(Si205)(OH)4. Chemical analyses of chrysotile range approximately as follows: Si02, 37-44%; MgO, 39 -44 %; FeO, 0 -6.0%; Fe203, 0.1 -5.0%; A1203, 0.2 -1.5 %; CaO, trace -5.0 %; H20, 12.0 -15.0%. Variations in chemical analyses may be due to either associated mineral impurities or to isomorphic substitutions in the crystal lattice. Common mineral impurities found in commercial grades of chry- sotile from various locations include magnetite, chromite, brucite, calcite, dolomite, and awaruite. Within the chrysotile lattice, nickel and iron can occur as minor iso- morphic substitutions for magnesium (14 -17). Chrysotile, a hydrated silicate, is subject to thermal decomposition at elevated temperatures. This thermal decomposition is a two -stage reaction consisting first of a dehydroxylation phase and then a structure phase change. Dehydroxylation or the loss of water occurs at 600 -780 °C. At 800 -850 °C the anhydride breaks down to forsterite and silica. These reactions are irreversible and are illustrated by the typical differential thermal analysis shown in Figure 6.
Structural changes in chrysotile can occur under conditions of intense grinding. As a result of these effects the structure can become amorphous and no longer iden- tifiable by either x -ray diffraction or electron microscopy. These structural changes apparently occur because of localized temperature surges in the fibrils with accom- panying dehydroxylation as they absorb the tremendous impact energies, eg, extensive dry ball milling results in an amorphous mass and wet ball milling results in short fibrils that retain their crystallinity (16).
Because of its hydroxyl outer layer, chrysotile is readily attacked by acid and will, ultimately, completely dissolve the magnesium component, leaving essentially a fi- brous, but fragile, silica structure. Similarly, because of its alkaline surface, chrysotile is not readily attacked by caustic solutions except under conditions of extreme alkali concentration and elevated temperatures (18 -19).
Dispersions of chrysotile fiber in carbon dioxide -free distilled water exhibit al-
DTA -Z
/ Thermobaiance run?
_-------r- +' 100 200 300 400 500 600 700 800
Temperature (C °)
Figure 6. Typical differential thermal analysis of chrysotile.
14
12
10
8
4
2
0
900 1000
i
Vol. 3 ASBESTOS 273
kaline properties. Such suspensions will reach a pH of 10.33 as with magnesium hy-
droxide suspensions tested under the same conditions. Solubility product constants for chrysotile fibers range from 1.0 X 10 -11 to 3 X 10 -12, indicative of the magnesium hydroxide outer layer (20 -22).
The electrokinetic behavior of chrysotile is also related to its surface character- istics. Normally, below its isoelectric point of approximately pH 11 -12, chrysotile exhibits a positive charge. Above this pH range, it demonstrates a negative charge. Exceptions to this general behavior have been noted with chrysotile fibers from certain locations (23).
Because of its very small fiber diameter, its high specific surface area and its relatively reactive surface, chrysotile is a selectively adsorptive material. Commercial grades of chrysotile adsorb as much as 2 -3 wt % moisture from saturated air. Ad-
sorption studies of a variety of organic compounds from both vapor and liquid media show that chrysotile has a greater affinity for polar molecules. Heats of adsorption have been measured ranging from 38 kJ /g (9 kcal /g) for hexane to 67 kJ /g (16 kcal /g)
for water (5,24 -27). Chrysotile also adsorbs iodine from solutions in a manner similar
to magnesium hydroxide or brucite. This adsorption characteristic is often used as
a staining technique for the detection of chrysotile asbestos (28). Physical Properties. The common physical properties of chrysotile asbestos are
given in Table 2. Asbestos fibers are used in composite materials (qv) to provide reinforcement.
Tensile strength of the fiber is, therefore, an important and highly significant physical
property. Unfortunately, because of their extremely fine diameter and the complicating
factor of the effect of sample length on strength determinations, it is extremely difficult
to measure the tensile strengths of asbestos with precision. Most recent information indicates typical chrysotiles have tensile strengths in the order of 3727 MPa (5.4 X
105 psi) which exceeds corresponding values for steel piano wire and fiber glass. A
comparison of typical strength values for the different asbestos varieties is given in
Table 3. Since all these measured values are far less than the theoretical value of over
10,000 MPa (1.45 X 106 psi) attributable to silicate chain structures, the values given
should be considered as relative for the different varieties rather than specific
(1,29 -31). Physical strengths of asbestos are adversely affected by elevated temperatures.
Table 4 shows decreasing tensile strength as dehydroxylation takes place (1).
What visually appears to be a single fiber in commercial grades of asbestos is in
actuality a bundle of a large number of individual fibrils. These bundles can be sub-
divided into a multitude of finer bundles, but only with special processing can a large
portion of fiber mass be divided to its ultimate fibril diameter. The specific surface
areas of commercial asbestos fibers vary with the extent of mechanical defibrillation.
Surface areas by nitrogen adsorption tests on samples teased by hand from chrysotile
crude are 4-12 m2 /g; however, when aggressively milled or fiberized, surface areas of
30 -50 m2 /g result (32). Chrysotile asbestos can be separated into smaller diameter fibrils (higher specific area) more readily under wet processing conditions than under dry mechanical milling. For this reason many asbestos product manufacturing pro- cesses utilize wet opening techniques to provide improved fiber reinforcing efficien-
cies. The term harshness in the asbestos industry refers to the fiber's brittleness,
flexibility, form, and modulus of elasticity. Commercial grades of chrysotile are usually
Tab
le 2
. Pr
oper
ties
of A
sbes
tos
Fibe
rs
Chr
ysot
ile
Ant
hoph
yllit
e A
nios
ite
(fer
roan
thop
hylli
te)
Cro
cido
lite
Tre
mol
ite
Act
inol
ite
stru
ctur
e
N :
min
eral
as
soci
atio
n
orig
in
vein
ing
esse
ntia
l co
mpo
sitio
n
crys
tal
stru
ctur
e
crys
tal
syst
em
in v
eins
of s
erpe
ntin
e, e
tc
in a
ltere
d pe
rido
tite
adja
cent
to
serp
entin
e, a
nd l
imes
tone
nea
r co
ntac
t with
bas
ic ig
neou
s ro
cks
alte
ratio
n an
d m
etam
orph
ism
of
basi
c ig
neou
s ro
cks
rich
in
mag
nesi
um s
ilica
tes
cros
s an
d sl
ip fi
bers
hydr
ous
silic
ates
of m
agne
sia
fibr
ous
and
asbe
stif
orm
mon
oclin
ic
(pse
udoo
rtho
rhom
bic?
)
lam
ella
r, f
ibro
us
asbe
stif
orm
in c
ryst
allin
e sc
hist
e an
d gn
eiss
es
met
amor
phic
, us
ually
from
ol
ivin
e
slip
, mas
s fi
ber
unor
ient
ed a
nd
inte
rlac
ing
Mg
silic
ate
with
ir
on
pris
mat
ic,
lam
ella
r to
fi
brou
s or
thor
hom
bic
lam
ella
r, c
oars
e to
fin
e fi
brou
s in
iro
n -s
tone
s fi
brou
s an
d as
best
ifor
m
in c
ryst
allin
e sc
hist
s,
etc
met
amor
phic
cros
s fi
ber
long
, pr
ism
atic
and
fib
rous
ag
greg
ates
in ir
on -r
ich
silic
ious
in
Mg
limes
tone
s as
alte
ra-
argi
llite
in q
uart
zose
tio
n pr
oduc
t of
high
ly
schi
ste
mag
nesi
an r
ocks
, m
etam
orph
ic a
nd i
gneo
us
rock
s re
gion
al
met
amor
phic
m
etam
orph
ism
cros
s fi
ber
silic
ate
of F
e an
d M
g,
silic
ate
of N
a an
d Fe
hi
gher
iron
than
w
ater
an
thop
hylli
te
pris
mat
ic,
to
fibr
ous
fibr
ous
mon
oclin
ic
mon
oclin
ic
slip
or
mas
s fi
ber
retic
ulat
ed l
ong
pris
mat
ic c
ryst
als
and
fibe
rs
in
limes
tone
and
in
crys
talli
ne s
chis
te
resu
lts o
f con
tact
m
etam
orph
ism
slip
or
mas
s fi
ber
Ca
and
Mg
silic
ate
with
som
e C
a, M
g, F
e,
wat
er
silic
ates
, wat
er
up t
o 5%
long
and
thi
n co
lum
nar t
o lo
ng a
nd th
in
fibr
ous
colu
mna
r to
fi
brou
s m
onoc
linic
m
onoc
linic
colo
r
lust
er
hard
ness
, Moh
s sp
ecif
ic g
ravi
ty
clea
vage
op
tical
pro
pert
ies
refr
activ
e in
dex
fusi
bilit
y, S
eger
co
nes
flex
ibili
ty
leng
th
J1
text
ure
acid
res
ista
nce
spin
nabi
lity
spec
ific
hea
t, J /
(kgK
) [o
r B
tu /(
lb °F
)]
whi
te, g
ray,
gre
en,
yello
w
silk
y
gray
-whi
te,
brow
n, g
ray,
or
gree
n vi
treo
us t
o pe
arly
ash
gray
, gr
een,
or
brow
n
vitr
eous
, som
ewha
t pe
arly
lave
nder
, blu
e
silk
y to
dul
l
2.5 -4
.0
5.5
-6.0
5.
5 -6
.0
4 2.
4 -2
.6
2.85
-3.1
3.
1 -3
.25
3.2 -3
.3
010
perf
ect
biax
ial
posi
tive
extin
ctio
n pa
ralle
l
1.50
-1.5
5
fusi
ble
at 6
, 11
90-1
230°
C
very
fle
xibl
e
shor
t to
long
so
ft to
har
sh, a
lso
silk
y
110
perf
ect
biax
ial p
ositi
ve
extin
ctio
n pa
ralle
l ca
1.6
1
infu
sibl
e or
di
ffic
ult
to f
use
. ve
ry b
rittl
e,
nonf
lexi
ble
shor
t ha
rsh
solu
ble
up t
o ap
prox
imat
ely
57%
best
1113
[0.
266]
fair
ly r
esis
tant
to
acid
s po
or
879
[0.2
10]
110
perf
ect
biax
ial
posi
tive
extin
ctio
n pa
ralle
l
110
perf
ect
biax
ial
extin
ctio
n in
clin
ed
ca 1
.64
1.7
pleo
chro
ic
fusi
ble
at 6
, lo
ses
wat
er fu
sibl
e at
3,1
145 -
at
mod
erat
e 11
70 °C
te
mpe
ratu
res
good
, les
s th
an
fair
to g
ood
chry
sotil
e 5 -
28 c
m
shor
t to
long
co
arse
but
som
ewha
t so
ft t
o ha
rsh
plia
ble
gray
-whi
te, g
reen
, ye
llow
, bl
ue
silk
y
5.5
2.9
-3.2
11
0 pe
rfec
t bi
axia
l neg
ativ
e ex
tinct
ion
incl
ined
1.61
fusi
ble
at 4
, 11
65-1
190°
C
gene
rally
bri
ttle,
som
etim
es
flex
ible
sh
ort
to l
ong
gene
rally
har
sh, s
omet
imes
so
ft
fair
ly re
sist
ant t
o ac
ids
fair
ly re
sist
ant
to a
cids
fai
rly
resi
stan
t to
acid
s
fair
908
[0.2
17]
fair
841
[0.2
01]
gene
rally
poo
r, so
me
are
spin
nabl
e 88
7 [0
.212
1
gree
n
silk
y
ca 6
3.0 -3
.2
110
perf
ect
biax
ial n
egat
ive
extin
ctio
n in
clin
ed
1.63
wea
kly
pleo
chro
ic
fusi
ble
at 4
,116
5 -
1190
°C
britt
le a
nd
nonf
lexi
ble
shor
t to
long
ha
rsh
rela
tivel
y in
solu
ble
in H
C1
poor
908
[0.2
17]
C
alu®
A
a. v
. 1
iea
+ Y
--.
276 ASBESTOS
Table 3. Tensile Strength of Asbestos a
chrysotile, Arizona, USA chrysotile, Thetford, Canada crocidolite, Koegas, Cape Province, Africa crocidolite, Koegas, Cape Province, Africa crocidolite, Pomfret, Cape Province, Africa crocidolite, Pomfret, Cape Province, Africa crocidolite, Cochabambo, Bolivia amosite, Penge; Transvaal, Africa amosite, Penge, Transvaal, Africa anthophyllite, Paakilla, Finland
a See ref. 1.
Tensile strength, MPa (psi X 103)
Young's modulus, GPa (psi X 106)
3780 (548) 145 (21.1) 3640 (528) 146 (21.2) 2840 (413) 147 (21.3) 3090 (448) 151 (21.9) 4660 (675) 169 (24.5) 3550 (515) 175 (25.3) 1440 (209) 170 (24.6) 2580 (374) 143 (20.8) 1980 (287) 143 (20.8) 2450 (356) 156 (22.6)
Table 4. Effect of Temperature on Tensile Strength of Asbestosa
Percentage of original tensile strength Temperature, °C Chrysotile Crocidolite Amosite
200 100 100 320 91.6 70 58 430 73.3 32 32 550 59.5 20 15 670 32.0 period of heat soak 3 min 4 h 4 h
a See ref. 1.
classed as soft or nonharsh. Commonly, they are silky, of fine diameter, and extremely flexible. Contrary to chrysotile, the commercial amphiboles are harsh fibers. They are relatively stiff, brittle, coarser in diameter, and rodlike in appearance under the microscope. These differing physical characteristics account for the different operating characteristics exhibited in the manufacture of various asbestos -containing products. For example, soft chrysotiles can be more readily spun into textiles than the amphi- boles but they have poorer drainage properties when used in wet manufacturing processes. However, several fiber treatments have been developed to improve the filtration or drainage properties of chrysotile and thereby increase the production rate of wet machines manufacturing asbestos -cement products (33 -37).
Amphibole Asbestos
Crystal Structure. The structure of all the amphiboles consists of two chains or ribbons based on Si4011units separated by a band of cations. Seven cations form the basal unit. Two hydroxyl groups are attached to the central cation in each unit cell. These hydroxyls, unlike the chrysotile structure, are contained entirely within the amphibole structure. The final structure is composed of stacks of these sandwich ribbons as illustrated in Figure 7 (1,5). The bonding between these ribbons is rather weak and the crystals are easily cleaved parallel to the ribbons along cleavage line A -A. If the cleavage is very facile, the result is an asbestiform mineral (1,5). Amphiboles
Vol. 3 ASBESTOS 277
8 Oxygens 4 Silicons 3 Ox 'ens + 1 hydroxyl
Cation layer O O O
Silica ribbon
Figure 7. Amphibole structure.
can also occur in nonfibrous forms (38) which may result because of structural disorder (39). The dominant cations are Mg2+, Fe2 +, Fe3 +, Na +, and Ca2+ (see Table 1). Minor isomorphic substitutions of Ala +, Ti4 +, K +, and Li+ also occur. Because of the wide compositional range, the amphiboles are often assigned to three generic series; le, the anthophyllite-cummingtonite [17499 -08 -0] series, the calcic amphiboles and the soda amphiboles.
Chemical and Surface Properties. The chemical compositions of the amphibole fibers are more complex and variable than chrysotile. Typical compositions are shown in Table 5.
Like chrysotile, the amphibole asbestos fibers dehydroxylate and decompose at elevated temperatures. The presence of large quantities of iron (particularly ferrous iron) makes the decomposition or thermal analysis determinations particularly complex and very dependent on the composition of the atmosphere. Table 6 is an
Table 5. Typical Chemical Compositions of Amphibole Asbestos
Crocidolite, Amosite, Anthophyllite, Actinolite, Tremolite, 96 96 96 96 96
Si02 49 -53 49 -53 56-58 51 -52 55 -60 Mg0 0-3 1 -7 28-34 15-20 21 -26 Fe0 13 -20 34-44 3 -12 5-15 0-4 Fe203 17 -20 0-3 0-0.5 A1203 0-0.2 0.5 -1.5 1.5-3 0 -2.5 Ca0 0.3 -2.7 10 -12 11 -13 K20 0-0.4 0-0.4 0-0.5 0-0.6 Na20 4-8.5 trace 0.5 -1.5 0 -1.5 H20 2.5 -4.5 2.5 -4.5 1-6 1.5 -2.5 0.5 -2.5
278 ASBESTOS
Table 6. Decomposition Reactions of Amphiboles Under Neutral Conditionsa
Amphibole Dehydroxylation Structural Decomposition variety DTA peak, °C breakdown, °C products
crocidolite 610 800 Na -Fe pyroxene, magnetite, silica
amosite 780 600 -900 Fe-Mg pyroxene, silica
anthophyllite 950 950 Mg -Fe pyroxene, magnetite, silica
actinolite 1040 1040 CaMgFe pyroxene, silica
a See ref. 1.
oversimplification of the thermal decomposition reactions of the amphibole fibers (1,40).
Compared to chrysotile, the amphibole fibers are relatively acid resistant. How- ever, under boiling conditions and high acid concentrations the amphiboles can exhibit weight losses of approximately 2 -20%. Relative order of acid resistance is:
tremolite > anthophyllite > crocidolite > actinolite >
amosite >» chrÿsotile
Amphibole fibers have a negative charge as contrasted to chrysotile's usual positive charge. The magnitude of the charge exhibited by the amphiboles is substantially lower than chrysotile's.
Physical Properties. See Table 2 for the more common physical properties and characteristics of the various amphibole fibers. In general, amphibole fibers are harsh, springy, and brittle as compared to the chrysotile variety. These physical properties make the amphiboles fast draining and bulky when used in manufacturing pro- cesses.
As illustrated in Table 3, the tensile strengths of amphibole asbestos fibers differ widely. The typical tensile strengths of asbestos fibers have the order:
crocidolite > chrysotile > amosite > anthophyllite >
tremolite > actinolite
As shown in Table 4, the amphiboles also lose their strength with increasing temper- ature.
Amphibole fibers do not divide into fibrils as fine in diameter or as symmetrical as the chrysotile variety. Ultimate diameters of amphiboles have been reported to be about 0.1 pm (1) and the surface areas of amphibole asbestos are considerably smaller than chrysotile. Fully fiberized commercial grades of crocidolite, for example, have surface areas by gas adsorption of 3 -15 m2 /g compared to the 30 -50 m2 /g values of chrysotile (2,41).
Vol. 3
Milling
ASBESTOS 279
Imbedded asbestos fibers are removed from the ore by a repeated series of crushing, fiberizing, screening, aspirating, and grading operations (milling). A typical, greatly simplified asbestos mill is shown in Figure 8. The ore is crushed, dried, and fiberized in a variety of impact mills. The short fiber and granular material is removed by screening the fiberized mass. The oversized fractions are stratified on a screen where the spherical, granular material of high density seeks the screen's surface and the fluffy, low- density fiber rises to the top of the bed. At the end of the screen, the fiber is sep- arated from the rock by an aspirating hood. The coarse granular fractions that still contain veins of chrysotile fiber, are refiberized and rescreened to recover shorter fibers. Fibers recovered from these primary screening operations are rescreened to remove entrapped granular material and classified into grades by fiber length.
The recovery of milled asbestos fiber from ore is fairly low. In general, a 5% re- covery is typical. The chrysotile mines in California are notable exceptions where 50% recoveries are common from agglomerated ores (Fig. 3). The fibers, however, are very short and are normally sold as reinforcing fillers (qv).
Conventional asbestos milling uses large quantities of air both for separating the fibers as they are freed from the ore and for dust control. Approximately 130 m3 /s (275,000 cfm) are used to process one metric ton of ore (42). Preconcentration of ore includes selective grinding, screening, and magnetic techniques (43 -45).
Travelling conveyor,..-
Fiberizer
Vibrating screen
Gyrating crusher
Long fiber
collector
To Shaking graders screen and
packers
Dry rock storage
I INi I M..
!11114 , r- Sly dust filter I'ilt'I l n IIIi t, 45P;tn
Hot gases to collecter and stack
Shaking screens
Gyrating crusher
Vertical dryer and
furnace
Sly dust Exhaust air ducts -1
Medium fiber
\ / collector
Fiberizer
To graders
and packers
Short fiber collector
Shaking screens
Fiberizer
Shaking r- screen I l
To tailings
Figure 8. Schematic of a typical asbestos milling flowline.
To graders
and packers
280 ASBESTOS
Production and Usage
In 1977, 80% of the world's chrysotile was produced by Canada and Russia. Most of the Canadian production is from Quebec and the balance from Newfoundland, British Columbia, and the Yukon Territory. Russian production is predominantly in the Bazhenovo District in the Central Urals, the Dzhetygara area northwest of Kazakhstan, and the Aktourak deposits near the Yenisei River.
Crocidolite and Amosite are produced in significant quantities only in South Africa. Main producing areas are at Bosrand, Cornheim, Ouplaas, Owendale, the Kuruman area in the Cape Province, and the Lydenburg District in the Transvaal (46).
Production statistics vary widely with the source of information. Table 7 sum- marizes ranges given by various authorities (47 -53).
The largest use of asbestos is in asbestos- cement for products such as pipes, ducts, and flat and corrugated sheets. Pipe products find use in water supply, sewage disposal, and irrigation systems. Asbestos -cement sheets are used in a wide variety of con- struction applications. Othér uses of asbestos include fire -resistant textiles, friction materials (see Brake linings), underlayment and roofing papers, and floor tiles. Table 8 shows the uses of asbestos in the United States (the largest consumer) and the world. The United States usage patterns differ considerably from the rest of the world (54 -56).
Standards and Test Methods
Classification. Canadian chrysotile crudes are classified as follows:
crude # 1:
crude # 2: crude run of mine:
Table 7. 1976 Asbestos Production
1.9 cm staple and longer 0.95 cm to 1.9 cm staple unsorted crudes
Type and location Thousands of
metric tons
Chrysotile Canada 1537 USSR. 2285 South Africa 111 Rhodesia (estimate) 239 China (estimate) 150 Europe 321 USA 104 South America 69 Australia 66 others 45 Total chrysotile 4927
Amphiboles (South Africa) crocidolite 178 amosite 79 anthophyllite 2 Total amphiboles 259 Total asbestos 5186
Vol. 3
Table 8. Asbestos Usage by Product line Estimated Percent of Production
ASBESTOS 281
Product line United States
consumption, %
World consumption, %
asbestos -cement 23 -30 65-70 asbestos papers 26-38 7 -8
floor tile 13 -21 4-7 friction materials 6-8 2 -3 roof coatings 4 -7 2 -3 textiles 1 -2 1-4
plastics 1 -2 trace -1 miscellaneous 12 -20 13 -15
Milled Canadian fibers sold from Quebec are classified by a dry screen technique known as the Quebec Standard Asbestos Test. This test method grades fibers roughly by fiber or staple length. Minimum test values are guaranteed for each grade and a numerical classification system has been established for fibers ranging from Group 3, the longest grade, to Group 7, the shortest grade.
Chrysotile fibers produced outside Quebec are graded or controlled by screening test methods differing from the Quebec Screen Test; however, these basically identify grade by staple length.
Test Methods. The major properties of concern are length, granular content, degree of openness or effective surface area, drainage or filtration rate, color, ab- sorption, electrical resistivity, bulk density, and strength -giving properties (57).
Fiber length is most reliably measured by wet screening techniques. Fiber openness is commonly measured by air permeability surface area methods. A variety of filtration tests are used to estimate a fiber's operating performance in asbestos - cement wet machines or paper machines. Granular content is often determined by a dry screening test where the fibrous material is aspirated from the granular impurity remaining on the various screen meshes.
The most complex measurement is the determination of the strength -giving property of a fiber for use in asbestos- cement products. In this case, small pressed sheets are made from a slurry of fiber and cement. After curing, the sheet strength is determined and the reinforcing effectiveness or value of the fiber is calculated.
Health and Safety Factors
The inhalation of excessive quantities of free asbestos fibers over prolonged pe- riods of time can increase the risk of developing certain diseases of the lung within 20 or 30 years. The three diseases associated with the inhalation of asbestos are: as- bestosis, a nonmalignant fibrotic lung condition; bronchogenic (lung) carcinoma; and mesothelioma, a rare cancer of the lining of the chest or abdominal cavities (58) .
Reduction of asbestos dust exposure is at present the only known method of preventing disease among asbestos industry workmen. When dust levels are low, risk to employees and the incidence of asbestos -related disease drop sharply. Cigarette smoking greatly increases the risk of developing bronchogenic cancer among persons encountering heavy asbestos exposure. Nonsmoking asbestos workers show no greater incidence of bronchogenic cancer than the average nonsmoker.
282 ASBESTOS
There are governmental regulations (OSHA) that describe the allowable airborne fiber levels in work areas. Extensive dust control together with corrective work prac- tices are used to implement these regulations and medical examinations are regularly provided to assure worker protection (see Air pollution control methods; Industrial hygiene and toxicology).
BIBLIOGRAPHY
"Asbestos" in ECT 1st ed., Vol. 2, pp. 134 -142, by M. S. Badollet, Johns -Manville Research Center; "As- bestos" in ECT 2nd ed., Vol. 2, pp. 734 -747 by M. S. Badollet, Consultant.
1. A. A. Hodgson, "Fibrous Silicates," The Royal Institute of Chemistry, London, Lecture, Series No. 41965.
2. F. A. Mumpton, H. W. Jaffe, and C. S. Thompson, Am. Mineral. 50,1893 (1965). 3. B. E. Warren and W. L. Bragg, Krist. 76, 201 (1930). 4. B. E. Warren and K. W. Hearing, Phys. Rev. 59, 925 (1941). 5. S. Speil and J. P. Leineweber, Environ. Res. 2(3), (1969). 6. F. J. Wicks and E. J. W. Whittaker, Can. Mineral. 13, 227 (1975). 7. F. J. Wicks and J. Zussman, Can. Mineral. 13, 244 (1975). 8. T. F. Bates, L. P. Sand, and J. F. Mink, Science 111, 512 (1950). 9. W. Noll and H. Kercher, Naturwissenschaften 37, 540 (1950).
10. J. Turkevich and J. Hillier, Anal. Chem. 21, 475 (1949). 11. M. Maser, R. V. Rice, and H. P. Klug, Am. Mineral. 45, 680 (1960). 12. K. Yada, Acta Crystallogr. 23, 704 (1967). 13. E. J. W. Whittaker, Acta Crystallogr. 6, 747 (1953); 8, 571 (1955); 9, 855 (1956); 10, 149 (1957). 14. H. Berman, Am. Mineral. 17, 313 (1932). 15. E. H. Nickel, Can. Mineral. 6, 307 (1959). 16. G. P. Reimschussel, unpublished information, Johns -Manville Research Center, Denver, Colo. 17. P. Hahn -Weinheimer and A. Hirner, 3rd International Conference on the Physics and Chemistry
of Asbestos Minerals, Quebec, Canada, 1975. 18. M. S. Badollet, Can. Min. Metall. Bull. I (1951). 19. D. G. Hiscock, unpublished information, Cape Asbestos Ltd., 1964. 20. F. L. Pundsack, J. Phys. Chem. 59, 892 (1955). 21. F. L. Pundsack and G. P. Reimschussel, J. Phys. Chem. 60,1218 (1956). 22. J. W. Ryznar, J. Greon, and M. G. Winterstein, Ind. Eng. Chem. 38,1057 (1946). 23. E. Martinez and G. L. Zucker, J. Phys. Chem. 64, 924 (1960). 24. L. M. Pidgeon and A. van Wissen, Can. J. Res. 9,153 (1933). 25. G. J. Young and F. H. Healy, J. Phys. Chem. 58, 881 (1954). 26. A. C. Zettlemoyer, G. J. Young, and F. H. Healey, J. Phys. Chem. 57, 649 (1953). 27. C. H. Gorski and L. E. Stettler, Amer. Ind. Hyg. Assoc. J. 36, (1975). 28. M. Morton and W. G. Baker, Can. Inst. Min. Metall. Trans. XLIV, (1941). 29. M. S. Badollet, Can. Min. Metall. Bull. 1 (1951). 30. R. Zukowski and R. Gaze, Nature (London) 183, 35 (1959). 31. D. R. Burman, Paper No. 2-8, 1st International Conference on the Physics and Chemistry of Asbestos
Minerals, Oxford, Eng., 1967. 32. F. L. Pundsack, J. Phys. Chem. 65, 30 (1961). 33. M. S. Badollet and W. C. Streib, Can. Min. Metall. Bull. 48, (1955). 34. U.S. Pat. 2,616,801 (Nov. 1952), M. S. Badollet and W. C. Streib (to Johns -Manville). 35. U.S. Pat. 3,173,831 (Mar. 1965), F. L. Pundsack and G. P. Reimschussel (to Johns -Manville). 36. U.S. Pat. 3,891,498 (June 24, 1975), T. H. Sadler (to Johns -Manville). 37. U.S. Pat. 3,715,230 (Feb. 6, 1973), T. H. Sadler (to Johns- Manville). 38. J. E. Chisholm, J. Mater. Sci. 8, 475 (1973). 39. D. R. Veblen, R. R. Buseck, and C. W. Burnhem, Science 198, 359 (1977). 40. J. J. Cilliers and co- workers, Econ. Geol. 56, (1961). 41. J. H. Patterson and R. L. Thompson, Paper No. 2 -5, 1st International Conference on the Physics and
Chemistry of Asbestos Minerals, Oxford, Eng., 1967. 42. J. Goldfield, Min. Eng. 7, (Nov. 1955).
Vol. 3 ASPARTIC ACID 283
43. H. Berger, CIM Bull. 68, (Feb. 1975). 44. R. G. Evans, CIM Bull. 68, (July 1975). 45. E. Martinez, Trans. Soc. Min. Eng. 255, (1974). 46. H. H. Gossling, 2nd Industrial Minerals International Conference, Munich, Ger., 1976. 47. Asbestos 58, (Dec. 1976). 48. Asbestos 58, (Mar. 1977). 49. Asbestos 59, (Nov. 1977). 50. Mineral Industries of the USSR, U.S. Bureau of Mines, MP2, July 1977. 51. Asbestos -197, U.S. Bureau of Mines, MCP6, Sept. 1977. 52. Mineral Trade Notes, 74(6), (June 1977). 53. World Mining Magazine 30, June 25, 1977. 54. Ind. Min. (June 1975). 55. B. Lincoln, Ind. Min., (Oct. 1975). 56. N. W. Hendry, unpublished information, Johns -Manville Corporation, Denver, Colo. 57. Chrysotile Asbestos Test Manual, 3rd ed., Asbestos Textile Institute and the Quebec Asbestos Mining
Association, 1974. 58. Chem. Week,, 16 (May 3, 1978).
WILLIAM C. STREIB Johns - Manville Corporation
ASBESTOS- CEMENT PRODUCTS. See Cement.
ASBESTOSIS. See Industrial hygiene and toxicology.
ASCORBIC ACID. See Vitamins.
ASPARAGINE. See Amino acids.
ASPARTIC ACID. See Amino acids.
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