Document babyaR08pwO0xdVLy38p6jz33

.r. .*'W Asbestos, A Mineral of Unparalleled Properties By M. S. BADOLLET* {Annual General Meeting, Quebec City, Que., April, 1951) (Transactions, Volume LIV, 1951, pp. 151-160) Introduction This information was obtained over a period of years by search of the THE DEMAND for general literature and by experimental in knowledge oil asbestos fibres vestigations. has increased considerably in recent years. A few publications have printed data showing some of the Properties of Asbestos Fibres physical and chemical properties of asbestos, but in many cases this information is difficult to find and is seldom available when needed. Table I (1, 2) presents, in con venient form for easy comparison, data on the principal properties of the several varieties of commercial During the past ten years, Johns- `asbestos' -- actinolite, amosite, an- Manville have received many inquir thophyllite, chrysotile, crocidolite, ies on the physical and chemical and tremolite. Under each variety properties of asbestos fibres. For of fibre is a brief statement describ tunately, we have had some of the ing the properties in terms of struc information in our files, and we wil ture, mineral association, origin, lingly supplied the data. etc. Some of the more important To help relieve this need, we have data in Table I are expanded and tried to present briefly in this paper presented in Table II (3). some of the interesting and out standing properties of asbestos. Solubility of Asbestos *Research Center, Johns-Manville Corporation, Manville, N.J. (1) For references see end of pa per. A report (4, 5) discussing the effects of acids and caustic on as bestos fibres was published in Ger many in 1927. Re-published several times, it appears to be the only in formation available on the subject. When, several years ago, it be came necessary to obtain technical data, not available in the literature, on the solubility of commercial grades of asbestos, tests were ar ranged following the plan adopted bv the author of the original article (4). Samples were obtained of actino lite from Canada amosite from Af rica, anthophyllite from Georgia, chrysotile from Canada, crocidolite from Africa, and tremolite from California. These samples repre sented fibres obtainable in commer cial quantities. They contained some mineral impurities and thus their degree of solubility was not identical with that of hand-pickled, highgrade crudes from these localities. The acids used in these tests were hydrochloric, acetic, phosphoric, and sulphuric. All were diluted to a 25 per cent acid solution, by weight. Table II.--Physical Properties of Asbestos Chrysotile Specific heat B.t.u./lb./F......... Tensile strength, lb./sq. in........ Temp, at max. ignition loss, F........................................ Filtration properties.................... Electric charge....................... .. Fusion point, F......... .................. Spinnability.................................. Resistance to acids & alkalies Magnetite content....................... Mineral impurities present... . Flexibility...................................... Resistance to heat....................... Ionizable salts, micro-mhos... (Relative elec, conductance) Colour......................... .................. 0.266 80,000 100,000 1.800 Slow Pos. 2,770 Very good Poor 0-5.2 Iron, chrome, nickel, lime High Good. Brittle at high temp. 1.82 Green, grey to white Amosite 0.193 16,000 90,000 1,600 to 1,800 Fast Neg. 2,550 Fair Good 0 Iron Good Good, Brittle at high temp. 1.34 Yeilowishbrown Anthophyllite Crocidolite 0.210 4,000 & less 0.201 100,000 300,000 1,800 Medium Neg. 2,675 Poor Very good 0 Iron 1,200 Fast Neg. 2,180 Fair Good 3.0-5.9 Iron Poor Very good Good Poor, fuses 0.58 0.84 Yellowishbrown, Some times almost white Blue Tremolite 0.212 1,000 8,000 1,800 Medium Neg. 2,400 Poor Good 0 Lime Poor Fair to good -- White Actinolite 0.217 1,000 & less -- Medium Neg. 2,540 Poor Fair -- Lime, iron Poor -- -- Greenish -- 15 -- UCC 004659 PROPERTIES OF ASBESTOS FIBRES --- 7. .- 'Recent studies dim that tkc cfysIcI structure is monotlimc For the caustic solubility tests, Table III.--Solubility of Asbestos solid pellets of sodium hydroxide i were dissolved in distilled water to j obtain a 25 per cent solution, by Per Cent Loss in Weight, Re-fluxing Two Hours 25% Acid or Caustic weight. HCI CH;iCOOH H3PO1 HiSOi NaOH i Each fibre sample, consisting of I 10 grams, was accurately weighed Actinolite..................... 20.31 12.28 20.19 20.38 9.25 and placed in a flask containing 300 Amosite......................... 12.84 2.63 11.67 11.35 6.97 c.e. of the 25 per cent acid or caus tic solution. Two sets of tests were conducted, Anthophyllite.............. Chrysotile..................... Crocidolite................... Tremolite...................... 2.66 55.69 4.38 4.77 0.60 23.42 0.91 1.99 3.16 S5.18 4.37 4.99 2.73 55.75 3.69 4.58 1.22 0.99 1.35 1.80 one at room temperature (26C.) for indefinite periods, the other at boiling temperature in a reflux con denser for two hours. At the end of Per Cent Loss in Weight, Room Temperature 26C. for 528 Hours 25% Acid or Caustic each test, the fibres were removed from the solutions, washed free from acids or caustic, dried, and weighed. HCI CH3COOH H.,PO, H.^SO* NaOH Table III shows the solubilities of these particular asbestos fibres in the four acids used and in caus tic soda. The action of boiling acids on asbestos fibres is severe, with chry- Actinolite..................... Amosite......................... Anthophylite............... Chrysotile..................... Crocidolite................... Tremolite..................... 22.55 12.00 2.13 56.00 3.14 4.22 12.14 3.08 1.04 24.04 1.02 1.41 20.10 11.83 3.29 56.45 3.91 4.89 20.60 11.71 2.90 56.00 3.48 4.74 9.43 6.82 1.77 1.03 1.20 1.65 sotile the most soluble. Acetic acid was not so effective as the mineral acids in dissolving chrysotile, and caustic had even less action on this mineral. After chrysotile fibres had lost 55 per cent of their weight, exam ination showed the fibre structure to be almost all silica, brittle, and very fragile. The high solubility values for actinolite are, it is believed, due to the presence of soluble minerals as impurities in the commercial product used by industry. Anthophyllite seemed to resist acid action better than any other variety with crocidolite second at room temperature is slower than at boiling temperatures but if the fibres are kept immersed in the solv ent for a sufficient length of time, the solubilities finally reach the values obtained at boiling tempera tures. The tests at room temperature were conducted for periods of 24 hours, 192 hours, 360 hours, and 528 hours. After each time period, the fibres were removed, washed, and weighed, and the solubility cal culated. The fibres were then re placed in fresh solutions of acid or caustic to begin the next cycle. Such information is invaluable to a manufacturer desiring to produce an asbestos product which will be exposed to conditions similar to those in the tests. The most resist ant fibre, if available in commercial quantities, naturally will be select ed for the product. Effect of Heat on Asbestos Since asbestos fibres frequently are exposed to elevated tempera tures, it is necessary to determine which fibre most satisfactorily meets the demands. best, tremolite third, and amosite For convenience, only the solubil With this in mind, the same fibres fourth. ity data for 528 hours are given in as used in the solubility tests were All these solubilities would vary Table III since at this point most subjected to two hours' exposure at depending upon the source of the of the fibres apparently reached temperatures varying from 400F. fibre and whether the samples rep their maximum solubility, and this to 1,800 F., and the weight loss resented pieces of `crudes', or milled was approximately equal to the sol measured. The samples, after dry fibres as purchased on the market. ubility after a two-hour treatment ing to eliminate surface moisture, The action of acids and caustic in boiling acids or caustic. were weighed, placed in a muffle Table IV.-- Effect of Temperature on Loss in Weight of Asbestos Fibres Temp. F. 400 600 700 800 900 1.000 1,100 1,200 1,400 1,500 1,600 1.700 1,800 Time 2 hr. Amosite % 0.23 0.57 0.80 0.98 1.07 1.16 1.36 1.39 1.43 1.52 --- 1.53 Iron changing in weight due to oxidation. Loss in Weight Anthophyllite % 0.05 0.24 0.30 0.38 0.41 0.44 0.52 0.54 0.54 0.64 1.12 1.73 2.39 Chrysotile % 0.30 0.85 1.78 2.17 2.83 3.99 10.38 12.75 13.43 13.62 13.77 Crocidolite % 0.08 0.25 0.49 0.73 0.83 0.86 1.00 1.04 1.03 0.93* 0.77* Tremolite % 0.04 0.08 0.13 0.22 0.26 0.29 0.37 0.37 0.47 0.56 0.67 1.40 2.18 . - ... ........... :. '.'C' *' . ,, where temperature WM. maintained: automaticafiy, removed after a two- hour exposure,, cooled to room tem perature in a desiccator, and re weighed. The pewaartages of loss in weight are prestaghdiid Table IV. Generally gpckfch^t. ..the amphi- bole fibres sb<!&' J&- ainthophyHite and tremolite resisted'the heat fair ly well at temperatures below 700 F. The chrysotile fibre, on the other hand, began to show a sudden ly increased weight loss at 700F., and a rapid increase above 1,000F. At higher temperatures, all fibres began to change in physical charac teristics, but the amphiboles did not disintegrate so rapidly as the chry sotile fibres. The croeidolite fibre at 1,600F. and higher showed a de finite oxidation of iron and became brittle. Chemical analysis of chrysotile fi bres showed that the ignition loss values varied with the mineral im purity present. Therefore, it was decided to determine the nature of these impurities and their effect on ignition loss values. . A series of chrysotile asbestos fi bres from Arizona, Australia, Rho desia, Russia, and Canada were se lected. These fibres were individual ly tested by placing a sample in an ultimate analysis train, with heat ing units electrically controlled. The air taken into the combustion chamber was dried by passing it through sulphuric acid and absorb ing the water and carbon dioxide with magnesium perchlorate, Mg(CIO,).,, and ascarite. The temperature of the combus tion unit was accurately determined by a chromelalumel thermocouple ... ........... "w ' --.I. - --, . connected on one end to a potentio a temperature of approximate^ meter, and on the other to the side I,68QF.; a temperature of 1,800F.' of the asbestos sample in the com for one hoar, therefore, should be bustion tube. sufficient to drive off all the CO*. Any gases, such as water and car The Australian fibre contained- bon dioxide, driven off the asbestos 12.48 per cent H20 and 0.96 sample were weighed after being re cent C02; loss in weight on covered in a second absorbing train tion was 18.33 per cent:- Be containing Mg(C10,)2 and ascarite tion of the carbon dioxide as car in two different U tubes. bonates indicated that this fibre cbtte| Prior to the test, the combustion tained 1.26 per cent MgCO* train was purged for half an hour 0.68 per cent CaCOs as impurities*- at 220F. with dry air. Then the The Canadian fibre identified temperature was raised by 1,000 F. "A" shows a water content of 14.2 and the absorbed gases weighed. per cent, which is higher than Later, the test was repeated by rais theoretical amount of water in ing the temperature to 1,800 F. asbestos molecule. X-ray diffractional and weighing the absorbed gases. patterns of this fibre show the pres-1 The data shown in Table V give ence of brucite, Mg(OH)2, which | the percentages of water and car would break down and produce bon dioxide driven off each fibre at ter during the heating period, ac-: the two temperatures. counting for the high water content^! The Arizona fibre had a high ig of the fibre. The magnesium car-1, nition loss at 1,800F. This loss bonate is calculated at 1.62 per cent ` consisted of 12.89 per cent water and calcium carbonate at 0.27 per and 1.91 per cent carbon dioxide. cent. At 1,000F., 0.54 per cent carbon The Rhodesian fibre contained dioxide was expelled from the sam much higher percentage of magne-'j ple. Calculated as MgCOa, this in sium carbonate than any of the^pthe dicates the presence of 1.03 per fibres tested -- 4.85 per cen^.Th cent MgCOs. As the temperature calculated amount of calcium^ car was raised to I,80OF., additional bonate is 0.79 per cent. i: quantities of carbon dioxide were The Canadian fibre identified driven off, which, assumed as hav "B" resembles the "A" sample ing been combined with CaO, would having a water content higher ' represent 8.11 per cent CaCOa, in that of pure serpentine, and her dicating that the Arizona fibre test again the X-ray diffraction patter ed. contained a high' percentage of showed the presence of calcium carbonate. brucite. The magnesium earn These calculations of C02 as rep content was calculated to be Oil resenting- MgCOs and CaCOs, re per cent, and calcium carbon spectively, are based upon the dis 0.07 per. cent. sociation temperatures of these com The Rnssian fibre is a hki pounds. Magnesium carbonate dis chrysotile having a low water sociates at temperatures below tent (11.74 per cent at 1,800 1,000F.,: and calcium carbonate at The presence of 1.47 per cent" : V,--Table -Combustion Analysis of Chrysotile Asbestos: ' .t Source of c-' Temperature iffil I*- F. K ' Arizoi*na............ r 1,800 1,800 1,000 1,800 Per Cent HjO 3.37 12.89 1.50 12.48 . Per Cent CO* 0.54 1.91 0.66 0.96 Total Per Cent H*0+COa 3.91 14.80 2.16 13.44 Per Cent Ignition Loss OF Fibre 3.87 14.80 2.06 13.33 III ------ --- Dioxide , rf ed in Terms STAGE Oft'-'J MgCOj CaCGr'-.jl 1.03 1.03 1.26 1.26 , '-V 3-H 1 ' & 0.66 Canadian (A) .............. 1,000 1,800 5.47 14.28 0.85 0.97 6.32 15.25 6.23 15.17 1.62 1.62 0.27 ^ Rhodesian .................. 1,000 1,800 1.82 2.54' 4.36 4.28 4.86 4 12.00 2.89 14.89 14.84 4.85 0.79 . Canadian (B) .............. Russian........................ 1,000 1,800 1,000 1,800 3.75 13.31 1.98 11.74 0.45 4.20 4.14 0.86 0.48 13.79 13,75 . 0.86 0.77 2.75 2.64 1.06 12.80 12.72 1.47 1.47 90T 3 0.66 v Canadian (C) .............. 1,000 1,800 2.25 11.93 0.47 2.72 2.66 0.51 12.44 12.40 0.90 0.90 0.09 UCC 004662 -18- f I 1 t t r ii r et i ii s1 ii ' a e ii ' d e (> h L ). nesium carbonate and 0.66 per cent calcium carbonate was indicated. Canadian fibre identified as "C" is a semi-harsh fibre with a low wa ter content (11.93 per cent). The total amount of COj driven off is small and is calculated as represent ing 0.90 per cent MgC03 and 0.09 per cent CaC03. From these data it can be seen bow readily ordinary ignition-loss figures can be misunderstood if the presence of mineral impurity is not taken into account. For example, most ignition-loss tests on chryso tile asbestos are made to determine molecular water content. If the fibre contains impurities such as brucite, magnesium carbonate, or calcium carbonate, an error is introduced in to the calculations and the fibre is shown to have an ignition loss great er than the theoretical quantity of molecular water. This could be a serious error in determining the as bestos content of an asbestos tex tile, from which the organic fibre is burned purposely and a correction factor is applied for the molecular water content of the asbestos. Effect of Heat on Tensile Strength A piece of Canadian crude was set aside and a number of small fibre bundles, approximating 20 to 30 microns in cross-section, were se lected and heat-treated at different temperatures in an automatic con trolled muffle. The original fibre bundles had a tensile strength of 131,000 lb./sq. in. Four sets of fibre bundles were heated for 3-minute periods at tem peratures of 600F., 800F., 1,000F., and 1,200F. The effects on the tensile strengths of the fi bres are shown in Table VI. At temperatures higher than l,20OF., the fibre bundles were too brittle to handle and were con sidered rather weak. The same fibre, when heated for one hour at the temperature stated, had a tensile strength as follows: -K)0JF., 129.000 lb./sq. in.; 60OF., 100,000 lb./sq. in.; 1,200F., less than 2,000 lb./sq. in. These data show that tempera tures and times of exposure affect the tensile strength of chrysotile fibres, especially at 1,000F. and higher, where the strength begins to decrease rapidly. Tensile Strength of Various Materials Reference has been made on sev eral occasions to the fact that as Table VI.--Effect of Heat on Tensile Strength of Canadian Chrysotile Crude Original crude--No heat.............. Heated 3 mm. at 600F............... .......................SOOT................ ...................... 1,000F........... " " " " 1,20QF........... Tensile Strength (lb./sq. in.) 131,000 120,000 96,000 78,000 42,000 Per Cent of Original Tensile Strength 91.6 73,3 59.5 32.0 bestos fibres are strong. As an in teresting comparison, data have been selected showing the approximate tensile strengths of such materials as iron, steel, cotton, rock wool, glass, and several varieties of as bestos. Table VII. -- Comparison of Tensile Strengths of Various Materials Type of Material Tensile Strength (Lb./Sq. In.) Ingot iron.................. 45,000 Wrought iron............ 48,000 Carbon steel.............. 155,000 Ni-Cr steel................ 243,000 Piano steel wire........ 300,000 Cotton fibre.............. 73,000 to 89,000 Rockwool................. 60,000 Glass fibre................. 100,000 to200,000 Chrysotile asbestos . SO.OOOto 100,000 Crocidolite asbestos. 100,000 to 300,000 Amosite asbestos ... 16,000 to 90,000 Tremoliteasbestos.. 1,000 to 8,000 The values given in Table VII are approximate and are cited sole ly for the purpose of illustrating the comparative strengths of some materials used in industry. It will be noted that chrysotile and crocidolite asbestos fibres are exception ally strong and are comparable in that respect to glass and to some grades of steel. The tensile strength values for the asbestos fibres are based upon breaking loads applied to fibre bun dles measuring approximately 20 microns in cross-section. Comparison of Surface Area of Fibres It is a recognized fact that as bestos fibres appear as bundles con sisting of many thousands of in dividual fibrils not visible to the eye. This would indicate that asbestos should have a great surface area when folly opened. Table VIII.--Comparison of the Surface Area of Various] Fibres Type of Fibre Surface Area by Na Adsorption (Sq. Cm,/Gram) Nylon........................... 3,100 Acetate rayon............. 3,800 Cotton......................... 7,200 Silk............................... 7,600 Wool............................. 9,600 Viscose rayon............. 9,800 Asbestos (Chrysotile) 130,000 to 220,000 The data in Table VIII show the surface areas of nylon, rayon, cot ton, silk, wool, and chrysotile asbes tos. The values for asbestos are so large in comparison with the other fibres tested that it seems hardly possible that they could have such great surface area. The large surface area value of asbestos is a very important factor. It gives wide coverage and at the same time furnishes strength to as bestos products. Comparison of Fibre Diameters The approximate diameter of fi bres of various types has been measured and* recalculated in terms of the number of fibres or fibrils required to equal one linear inch. The results are interesting and they show that a very large number of as bestos fibrils is required to make a linear inch. Table IX gives approxi mate data for. fibres of hair, ramie, wool, cotton, rayon, nylon, glass, rock wool and asbestos. The ex tremely small cross-section of asbes tos fibres as compared with others will be noted. 19 -- UCC 004663 T; li * 1 ......, TAblk TX.--Comparison op Approximate Fibre Diameters > Type of Fibre* ' . ' Fibre Diameter in Inches Human hair...... . T'.V Ramie..................... . ........ Wool....................... Cotton..................... Rayons.................... Nylon.................... Glass....................... Rock wool............... Asbestos (Chrysotile) 0.00158 0.000985 0.0008 to 0.0011 0.0004 0.0003 0.0003 0.00026 0.000142 to 0.000284 0.000000706 to 0.00000118 Fibrils in One Linear Inch 630 1,015 900 to 1,250 2,500 3,300 3,300 3,840 3,520 to 7,040 850,000 to 1,400,000 method of investigation is of con siderable interest. On a number of occasions we have had the opportunity of examining asbestos fibre under the electron microscope through the courtesy and-. '; co-operation of Dr. James Hillier*: ' The several varieties of fibres sttjfe|^ ied and discussed in this paper were^, -^ submitted to the RCA Laboratory, to be photographed at two differenfc"* magnifications to show the strne- ture of the fibrils. Chrysolite The soft Arizona chrysotile at a 4,000 magnification shows fibre bundles which appear wavy with frayed ends (see Figure 2)|. The same fibre at a magnification of 35,000 shows bundles in which Li's? Harsh type Semi-harsh type. Figure l-1 -Photomicrograph* of chrywtile asbestos. x 100. Soft type Photomicrographs of Chrysotile Three samples of chrysotile-were, selected, representing three differ ent degrees of texture. Each of these three fibres, mounted on a cover glass, was placed under a microscope and photographed at 100 magnifica tions. They are shown in Figure 1, The harsh chryy^l^ fibre at this magnification resClmSs^ the Struc ture of splinters a needle like structure. TEe- fibres are springy, bulky, fast-filtering, and usually not so high in tensile strength as soft, silky fibres." This type of fibre will break quickly un der flexing action. The semi-harsh fibre appears par tially as a harsh, and partially as a soft, fibre. The fibres have lost most of the needle-like structure and ap pear as thick, wavy bundles. It is difficult to show in a picture that they are different from soft fibres. Chemically, they are the same as the latter, but the measurements show quite different' physical properties. Such physical tests as filtration, willowing, surface; *rea, bulk, and, strength will- bring, out the true properties of this fibre and show how it differs from the soft, silky chrysotile,, , . The soft- fibres appear as thin , threads which are very soft,, not bulky, slow-filtering, and extremely strong. As noted above, they have the 1 same chemical composition as the semi-harsh fibres, bnt quite dif ferent physical characters. The soft, silky chrysotile, fibres make up the bulk of asbestos used in industry. They are available in large quantity and usually are cheaper than the semi-harsh or harsh fibres. the fibres appear as hollow tubes (Figure 3). This feature was first reported, by Dr. Hillier in April-, , 1949 (6), using a magnification of- 94,000, and it has since been -; re ported by Bates, Sand, and Mink (7), of Pennsylvania State College.' Onr measurement of the thin fibrils 1 indicated; a cross-section in- the range of 214 and 284 At units, while Dr. Hillier reported fibril diameters of' 186s A units. This would account for the fact - that soft chrysotile i fibres hare large snrface areas and' show a preference to open length wise if properly fiberized. Amosite The amositd. from South Africa, at a magnification of 4,000, shows Electron Micrographs of Asbestos The electron microscope is a. val-' uable tool for examining materials: which are difficult to see by ordin ary microscopic means. Since asbes tos exists in thin cross-sections, this *RCA Laboratories, Princeton, N.J. tin this and all succeeding Fig ures showing electron micrographs, the magnification has been reduced from that stated in the text. The cap tion below each Figure gives the magnification as thus reduced. tAngstrom. .t -20- UCC 004664: Figure 2.--Electro micrograph, chrysotile asbestos, x 1,733. Figure 3.--Electron micrograph, chrysotile asbestos, x 15,200. straight bundles criss-crossing the field (Figure 4). The same fibre at 35,000 magni fication shows rather thick bundles that still remain straight and indi cate a plane of cleavage that is clean-cut and abrupt (Figure 5}. Whenever a small fibril is split from a small bundle, its cross-sec tion appears to be approximately 300 A units. However, only a few small bundles appear in this pic ture, while chrysotile fibre, on the. other hand, apparently breaks down lengthwise easily and shows numer ous small fibrils within the range of 300 A units and less. The fact that amosite fibre tends to remain as large, thick bundles may well account for its freeness in filtration, small surface area, and bulky appearance. inthophyllite noted that no hollow-tube structure appears .within these thin fibrils. This particular sample of ant$lophyllite is soft, not strong, and breaks easily during processing. Y At a 4,000 magnification, anthophyllite fibre* appear,as a mixture of thick and thin bundles which The ' mineral impurities in the fibre are visible as plates in the electron micrographs. show clean, even breaks at the ends This fibre is found in Georgia (Figure 6). ' ;: as a mass fibre, and considerable At a 35,000 magnification, some non-fibrous material Is associated fibrils appear thin and flexible while * with the recovered fibre. others are stubby, thick bnndles (Figure 7). The cross-section of the thin flexible fibrils is equal to, and- Crocidolite possibly smaller than, that of chry The crocidolite used in this in sotile fibrils, placing them at apr vestigation was the . typical' bine fi proximately 200 A units. Tt is to be : bre' from. Soutk. Africa. Figure 4.--Electron micrograph, amosite asbestos, x 1,733. Figure 5.--Electron micrograph, amosite asbestos, x 13,200. UCC 004665 -- 21 -- :r' J. V., CEEj.^ fl8* is. Figure 6.- -Blectroo micrograph, anthophylltte asbeatoa.. * 1,733. . , . - . Figure 7.--Ebctroa micrograph, anthophyllite asbestos. v: . x 15,200. r'- - .. - At a 4,000 magnification, the fi of croeidolite^ fibre which differs \ " . , Treatolitc bre appears as straight, stiff, brii- . somewhat front, normal African cw tie bundles, and in most case* the cidoBte in chemical composition!. A' -The ticmoHte under invest ends show clean breaks (Figure 8). is a soft, iiliy flhres'nqt,very strong 1 ha from California and is cons At a 3fi,000 magnification, the and casily pnlveriaed," ` 1 of- good quality. *' .bundles appear fairly thick, but there is evidence that slender fibrils of approximately 300 A units exist'. (Figure 9), though* they- are.. W; and far apart. The brittle nature of- the fibre probably prevents inditid- ual fibrils from splitting off length-., wise, and consequently all that iy seen is the large bundles. . ... - . . - if' At i ijOOO nsi^f^ificatidn tbc jfl- bre hpsit;-5?*(i' efcin, tlgtely bound, and'shOwr evidence of tadtr tlcnesa ' ry * '** -- ? AH' a -magnification, croas-seetioB' of-the bundles rar fromthick-tothlft(F^ I2J. bandit# dfeniafe, appear to be '__ . At *r3|^i-m%ificdtiou,' the (rghtjfy togedfifeir'tad they sbow. bundles atfitb%fanea Clean and tfghfa''- texj&ney' ii};- Aen1.; -'.4/,'... 1.>-.r:-v atn -'i;' V ." U. . * thcjitf^m^ates^tilaitj; if the bnm ExaminatSwf 'of the bundles 30,p!OO nmgnifictttldn shows evid Bolivian Blue " > dles sre tnojferIy'opened:; tfiey win show fibrihr efiapproximately 306 A of individual fibrifir existing at proximately 300 A units (Fi| mr v: *>'-' f--.Bolivian blue asbestos is a, type unit, . v.f, . e- vv.v-i v**: - Figure 8.--Electron micrograph, crocidollte abafea x 1,733. ' . ... ... P**Br? UCC 004666'' ,"Sv'? '*43'. '"`HaptsSr'i.aa micrograph, crocidoKta aabertoa. .. a 15,200s, . mm ' yJsi 3Pii m WifiS asss iiis mmm lK: MS 1 TMsi t !:%*i Figure 10.---Electron micrograph, Bolivian blue asbetto*. * 1,733. Kf`ek '-V, H- i I ... -S >:e* ... ___. Figure 11.--Electron micrograph, Bolivan blue aabestoa. x 15,200. Actinolite The sample of actinolite was ob tained from Canada. Previous tests showed high solubility, indicating the presence of impurities. The electron micrograph at 4,000 magnification verifies this fact as it shows only a few fibre bundles, with a high percentage of plate-like minerals present (Figure 14). Sampling this grade of actinolite for electron microscope studies is a considerable problem and many ex aminations would be required to ob tain a satisfactory field. However, it was recognized that this sample was a milled commercial product and the pictures do show the true nature of the material. At a 35,000 magnification, only one large, thick bundle appears in the picture. There is a suggestion of breaks along the end, but there is no indication as to the size of the individual fibril (Figure IS), Conclusion' The various properties of the six varieties of asbestos investigated are given in convenient table form to serve as a quick reference. . Solubility data of the six varie ties of asbestos show that chryso- tile asbestos is readily attacked! by acids and that the amphibole fibres are fairly acid-resistant. ? The effect of heat on the differ-' ent varieties of asbestos varies. Chrysotile shows small ignition losses at temperatures below 700F. and a rapid increase in loss at 1,000 F> . and above. The arnphiboles show small ignition losses since they contain only small percentages of water of crystallization. Ignition losses also indicate the presence of water and carbon di oxide. Some chrysotile fibres - show the presence of brucite, magnesium SA' - 1j 1 s- .w: 3 > > .. S ml Figure 12.--Electron micrograph, tremolite asbestos. x 1,733. Figure 13.--Electron micrograph, tremolite asbesto*, x 15,200. 23 -- UCC 004667 , ' < 4 ... ^m:. Figure 14.--Electron micrograph, actinolite aabettoa, x 1,733. Figure 13.--Electron micrograph, actinolite asbestos, z 13,200. carbonate, and calcium carbonate;1 therefore, great care should be taken in interpreting ignition-loss data. High temperatures and lengths of exposure decrease the tensile strength of chrysotile fibres. At temperatures above 1,0000F., the strength decreases rapidly. and 33,000 magnifications show the fibre bundles, individual fibrils, and their approximate cross-sec tions, and majr help to explain some of the physical properties of asbes tos fibres used in commercial prod ucts.. . .V ' , . Acknowledgments Charts are presented to show that The author wishes to thank Dr. asbestos fibres have great tensile' dames Hilliet and tKeltCA Labor strength and large surface areas. ' atory ?or their help' ' is 1 producing Photomicrographs at 100 magniflcation show that the soft, silky, chrysotile fibre is wavy, whereas the electron micrographs of the six varieties of 'spsht^tdif described in this paper. 1 ^ *. the harsh fibre has a straight: 9r needle-like structure. i .. . , , ' 7r References _ The electron micrographs, of the. six varieties of asbestos at 4,000' 1. Cummins, AL* Bv unpublished pa- per. . ^c % v' 2. Rogers, A. F., and Kerr, P. F,, Optical Mineralogy, 1942, pp. 277, 282, 289, and 363. J' 3. Casey, R. S., Material* o/aCon- . ttruchon; Indust. and Eng. Chem., ? Sf Vol. 40, Oct., 1948, p. 1793; also pp. 1837-1860. J 4. NO AUTHOR, Add Resistance of Asbestos; Gummi Zeitung, May, 1927, p. 1861, . .. . ' t . - ,'t; 6. No Author, Acid Resistance o/.Vj , Spirmable Types of Asbestos; As-, ',s bestos, 1931, pp. 22-24. > 6. Turkevich, J., and Electron Microscopy of Coll Systems; Anal. Chem., VoL 21, April, 1949; pp. 480-481. - 7. Bates, T. F., Sand; L. B., and Mink, J. F., Tubular Crystals of Chrysotile Asbestos; Science, May. 12, 1950, p. 512. -> ^ x . , 1 f- -f*` -- 24 -- UCC 004668 .