Document 3N46kQZkmrJv1kv69O4X9Vv9J

Properties o Asbestos Fibres Imported into the United States By M. S. BADOLLET* and N. W. EDGERTON {Annual General Meeting, Montreal, April, 1959) (Transactions, Volume LX1II, I960, pp. 10-15) ABSTRACT A 3tudy of the physical properties of long grades of asbestos fibres im ported into the United States dur ing the past eight years has dis closed information that will con tribute materially to effective selec tion and use of fibres for electrical products. The study embraced fibre lengths, volume resistivity under three different conditions, total iron by chemical analysis, magnetic rat ing, conductivity of an aqueous ex tract and its sodium chloride equiv alent. The fibres examined included chrysotiles from Rhodesia, British Columbia, and Barberton area; mariime from Bechuanaland and Province of Quebec; amosite and crocidolites from Africa and Aus tralia ; and anthophyllites from Mozambique and from Georgia in the United States. Volume resistivity values provide a relative basis for estimating the electrical performance of end prod ucts; magnetic rating -- an estimate of the quantity of iron compounds present in excess of those in the as bestos structure; conductivity of an aqueous extract; and an estimate of the ionizable impurities in fibres. Tests of these factors yield in formation, not heretofore generally known, which may serve as a guide in the evaluation of asbestos fibres for electrical products. * Section Chief of Asbestos Fibre, Johns-Manville Research Center, Manvilte, N.J. fPhysicist, Physic* Section, JohnsManville Research Center, Manville, N.J. ST'.. , . ,' ShfSifiSfcj'-k'';lv. - - Introduction sbestos fibres imported Ainto the United States include chrysotiles from Canada and Rho desia; crocidolites from Africa and Australia; amosite from Africa; and miscellaneous small quantities of anthophyllite, tremolite, and chrysotile from other countries. For the year of 1958, the United States imparts of long fibres amounted to approximately 20,000 tons of chrysotile from Canada, 7,800 tons of chrysptile from Rho desia, 18,000 tons of crocidolite from Africa, 5,700 tons of crocidolite from Australia, and 13,000 tons of amosite from Africa. Since all asbestos fibres are graded and sold according to length for use in a wide variety of indus trial products, this discussion has been limited to the longer fibres and to some of the physical and chemical properties that make them attractive in textiles, plastics, and other products that require long fibres. . Tests Applied to Fibres Fibre lengths are normally de termined by the standard Quebec Screen test. Such large percentages of the fibres are retained on the top screen, however, that this test does not necessarily indicate the true length distribution. For this com parison, a 20-gram sample of the fibre was spread out upon a sheet of paper and lines representing the different lengths were placed at various intervals so that fibres of these lengths could be placed in piles above the mark of th$ ap proximate length. The fibres *were then weighed and the result! ex pressed in percentages per given length range. To define a limit for the fibre bundles that were picked out by tweezers, it was arbitrarily decided that any fibre with a cross section less than 0.01 in. would be set aside and classed as "open fibre of miscellaneous lengths". All crudy fibres were graded between 0 to 14 in., % to y2 in., l/3 to % in., % . to I in., 1 to 1^4 in., over in-, open fibre, and rock not selected for size. Crocidolite fibres are in most cases shorter than the chrysotile spinning fibres. They were classed in lengths of 0 to % in., % to 1 in., 1 in. and longer, open fibre, and rock. atfikJtMtm Haa.'Atrr/ty. VX 1 -- 50 -- Figure 3.--Aqueous extract conductivity apparatus. UCC 004626 Volume RlsrsTrviTV " {Figure 1) / 7i* Pbwa/ fiubtoft Ovibuf AOV, tttc Volume resistivity provides a relative basis for estimating the electrical performance of products to be made from fibre. Expressed in megohm-inches megohm-cen- timetrs), it is the resistance be tween opposite faces of a unit cube of material. Jnd<j&+n-*ec Zait vvi I rw'*JTkSTJFlf*F*-- f\--I ' ! n aP fimjth tttf War Filter O*c.///o3<-oje In4t0J0u0ctTay/rrcrr2e *C?oC>/ (*{J.FmtM Sufficient fibre is packed into a plastic cylinder on a brass base to reach a height of about 1 in. when compressed under a load of 260 p.s.i. The load is applied by a brass piston 1 sq. in. in area. A megohm bridge is used to measure the resistance between the piston and the base of the cylinder with 500 volts d.c. applied for one min ute. The volume resistivity is cal culated from the resistance and the measured height of the fibre by th formula: V. R. Area X Resistance Height Resistance Height for these electrodes csjak CSC? The volume resistivity is meas ured after exposure to three con ditions. The fibre is first dried for 16 hr. at 105C.; exposed to laboratory standard conditions of 75F., 50% RH for three days; and finally to humid conditions, 75F., 91% RH for 16 hours. The meas urement is made as soon as prac ticable after removal of the fibre from the oven or humidity chamber. C&Gl C&G2 C&G3 csg4 C&G5 Total Iron as a Percentage of Fe The total quantity of iron ex pressed as a percentage of Fe is determined by the regular wet chemical analysis. This test re ports all the iron regardless of its form, e.g., magnetite, ferric oxide, or any complex ;ariltcate that may be a part of tRt&molecule. CEG1 CSC2 C&03 CSC4 CM? --\ Indut+Qr Cotibrafeci fg_f Moontfic 3a /on ct Figure 2.--Magnetic rating apparatus Table I.--Rhodesian Fibre ApproxlBiRta Lengths 1/4-1/2", 1/2-3/r, 3/4-1", 1-li", __ i_________U______ _i__ _i__ Ovtr li" 90-98 96 - 98 0 0 0-0.6 0 - 0.4 00 0 0 00 0 0 Open Bock, iL_ 39 - 53 Tr - 0.2 20-53 T* - 1 10- 15 Tr 4-6 Tr - 1.5 Tr- 2 1-3 Dry 16 ur 8105c Volume Resistivity, megohm-:in. Standard 3 days 975F, 5056 RH After Drying Humid 16 hr S75F, 91# HE After Standard 6.2 0.26 0.063 5.7 0,22 0.075 16 - 530 0.27 - 0.96 0.05 * 0.13 760 - 1500 0.75 - 1-2 0.12 - 0.39 2100 0.48 0.07 Total Iron a* Fie, 4 Magnetic Batina Aaueoua Extract Conductivity, Equiv. NACl, nricronhos/cEi _ ... .. 1.0 * 2.6 0.3 - 0.7 182 0.087 1.5 - 2.7 0.27- 2-9 0.2 - 0.9 1.1 - 1.5 117 ^ 180-290 0.056 0.08 - 0.13 ' 2-5 - 3.2 2.9 - 3.1 1.2 - 1.9 2.0 - 2.4 190 - 280 200 - 240 0.09 - 0.13 0.09 - 0.11 Table 11.--Cassiar 3K Fibre Magnetic Rating {Figure 2) The magnetic rating test provides an estimate of the quantity of iron compounds present in excess of those in the asbestos structure it self. These are important because they are conductors and as such are undesirable in fibre for electrical applications. Ten grams of fibre are placed in a test tube and inserted in a coil which forms one arm of an indus- 0-1/4", * 18 - 19 l/U-1/2", ... * 10-28 Aivroximate Length. % 1/2-3A", 3/4-1", *i 1-lf", # 3-10 1-4 O-l Over l", Qpm i Flbar i 0 45-57 Rock, i 0-1 Dry 16 hr J05C . Volxm Raalativity. wumtai-fii. Standard, 3 day. 75f, 50# HE After Drying Humid 16 hr 975F, 91# RE After Standard 21-27 0.2 - 0.39 0.05 - 0.06 Total X*qb *__ 1.6 - 2.3 jhguatle Rating 0.7 - 1.3 alcTQmfaoi/c 322 i Extract Squlv. Sad, i 0.154 -- 51 -- UCC 004627 brated WtblU.Si Bureau of Stand ard* standard magnetic, sample 29a, and herns* yields a direct read ing in magxetm.rating, , Unit magnedensting corresponds to 1,8 grains otjrtandard magnetite. However, all nhigPetite is not of the same composition or permeabil ity. Sample 29a was selected for uniformity and most be considered an arbitrary standard. Magnetic ratings based on it are, of course, also arbitrary. Aqueous Extract Conductivity (Figure 3) The aqueous extract conductivity test provides an estimate of the ionizable impurities in the fibre. These impurities contribute to elec trical conduction through fibre and may be important in other respects -- for example, in corrosive ten dency. The impurities content is ex pressed in micromhos per centi meter. It depends directly on the proportion of water and fibre used in making the extract, and values should be compared only when these are the same. As an aid in visualiz ing the quantity of impurity, the equivalent NaCl content of the fibre is calculated. This is the quantity of NaCl which would yield the ob served conductivity, but it is not meant to imply that NaCl is actu ally present. In making this teat, 30 grams of fibre is added to 500 e.c. of dis tilled water. The mixture is. shaken vigorously for one hour and al lowed to stand overnight at 75F., after which the liquid is separated by. vacuum filtering! The resistance of the filtrate is measured, by means of a conductivity dip ceH with platinized electrodes and: ad impedence bridge operated at one kilo cycle per second^!*: conductivity, k, is calculated fiSwr the resistance and cell constant and is corrected for the conductivity of` the distilled water by the following formula: (i ~ x)TMk = 10*>C micromhos/cm. where C = Cell constant, reciprocal, cm. R,, = Resistance of cell filled with sample, ohms . R,, = Resistance of cell filled with distilled water, ohms Table IV.--Quebec Group 3 Fibres Approxlwrta Length, * 1/4-1/2", 1/M/V, 3/4*1" l-lf. 0vwr li**t Open Rock, * * % . i Fiber.* -I.. 3D 13-20- 7 - SO 12-30 2-9 0-4 4-6 30-53 rpj. 3K 15-24 3R 20-25 5 - 18 5- 8 5-15 10-15 1-6 1-3 0-4 4-12 4-7 0 32-64 Tr 47 - 50 Tr Dry 16 hr more YolunM gflJtlrlty, aaeotoM.-.l.a. 3 dor* orrsr, ref hh After Drying_______ . Hmli 16 hr 0T3C ni RH After atjoAorA 3D 3.5 - 46 0.31 - 0.76 0.05 - 0.17 3t 0.04- 3.5. <1 0.009 - 0.36 <0.009 - o.n 3R 0.24 0.04 0.023 Total Iron Ifcowtle Bating Agaaon* Extract _______________ Conductivity,. Equiv. Haci, alerOBho/ae * 3D 2.2 - 3-6 0.8 - 1.9 3S 3.0 - 4.3 2.3 - 6.7 3R 4.0 3-6 0.069 -0.160 0.140 - 0.266 0.144 All of these tests were applied to a series of fibres that have been1 imported into the United States during the past eight years. Discussion of Properties the form of soluble salts which are frequently associated with asbestos. Chrysotile, in addition, has a type of surface which has little resistance when even a small quantity of mois ture is present. ' The electrical resistance of as bestos depends primarily on its very fine fibrous structure. It has such large surface area that the flow through the volume of the fibrils is negligible as compared with the flow over their surface. This would be true even if the surface resist ance were as good as that of a good, electrical insulator. It is further re duced by conducting imparities in The volume resistivity test meas ures the resultant of all these fac tors. An increase in the moisture condensed on a good insulating sur face would decrease its resistance considerably; the other factors mul tiply this effect. Thus a large drop in volume resistivity is observed in going from the dry to the standard condition, or from the standard to the humid. -- 52 -- UCC 004628 " : V: - *" - 'v1 In this test the electric current flows along the surface of a fibre, through the junction where two fi bres make contact, and along the next fibre as it pursues a some what tortuous path through the mass. The surface resistance to cur rent along the fibre may be low as compared with the resistance of the junction between fibres. When this is so, the resistivity decreases with fibre length because, with long fi bres, there are fewer junctions to be traversed and it is the junctions which provide most of the resist ance. At high humidity, the mois ture at the junctions enlarges their effective cross-section more than that of the film on the fibre. The junction resistance is then reduced more than the fibre surface resist ance, and the correlation with length tends to disappear. The magnetic rating test suffers from several defects and even more from frequent misinterpretation. In addition to the mass of conduct ing particles, the test result is in fluenced by their permeability, size, shape, and orientation. Because of these influences, attempts to use it as an adjunct to the total iron test to separate structural iron from that in the form of inclusions are not usually very successful. The real purpose of the test is to estimate the danger of electrical failure from conducting particles bridging, or partially bridging, the insulation. The fact that the test yields an un duly high result when the particles are large or elongated is actually an advantage, because these are the particles which are most likely to bridge a gap. The principal defect of the test is that it does not go far enough in the direction of pick ing out large particles. The fibres which are associated with magnetite will usually, after the milling pro cess, contain so many small particles of magnetite that these completely determine the result of the test, and a few of the large dangerous ones may pass undetected. The milling process tends to con centrate magnetite with the shorter fibre lengths, so that magnetic rat ings are higher in lower-grade fibres. There is a great tendency to at tribute any poor electrical property of asbestos to its magnetic content. Although it is conceivable that the magnetite particles might bridge a gap and reduce its resistance to zero, this is relatively unlikely. If the particles are uniformly dis- Table V.--Amosite Fibre from Africa Airjnroattinate Length, $ 0 .1 t-* 1 - 1-3/Vj 1-3/4 - 2-3/4", 2-3/4 - 3-1/2", Over 3i' Open Hock i .i . * FiberAt % Bl 2-15 0.2-18 0.3 - 16 1-34 15-85 0-3 - 12 o-2 -1 D3 1-7 1 - 12 4 - 54 1-34 6-63 1 - 12 0 -4 ML 22-54 14 - 22 3 - 14 0.1-6 0-2 9 - 41 3 -10 DLL 49-58 13 - 25 1.5 - 6 0-5: 0-1 2 - 22 1 -24 HD 39-49 15 - 20 9 - 15 0-4 0 15 - 29 1 - 4 0 - 3/8", 3/8 - 1", 1" and Over, 1> i Open Fiber, Hock * W3 27-30 36 - 39 17 - 18 14 - 15 1-3 K3 21-30 41-50 7-11 15-22 1-2 Dry 16 hr S105C Volume Hesiativitr. megohms-in* Standard 3 days S75F, 5* RS After Drying ffumld 16 hr 9T5F, 91* RH After Standard W3 30,000 Ik 0.78 VD 8,000 1400 1360 K3 20,1HOO 34 1.32 Total Iron as Pe 4 Magnetic Rating 3 28.5 0*2 HD 30.8 0,2 K3 27-9 0.3 Aoueous Extract Conductivity, Equiv. NaCl, micronhos/cm * 156 0.076 73-9 0.035 160 0.076 tributed and not too large as com pared with the gap, they will affect such properties as volume resistiv ity and power factor only in pro portion to the volume of magnetite present, i.e., a few percentage points lower than in asbestos with no mag netite, They have their greatest ef fect on properties like dielectric strength and burnout rating, which are sensitive to local defects. The aqueous extract test provides an estimate of the contribution that ionizable salts make to the reduction of volume resistivity. This is im portant because it is usually the only factor over which we have any con trol, The type of fibre to be used is apt to be determined by economic or workability considerations, and the volume resistivity enters only as a secondary consideration. The fi bre may be improved by finding a new source with a low ionizable salt content; in a dry process not much more can be done. In a wet process the test indicates how much washing may be required to raise a particular fibre to a satisfactory level. There are some indications that asbestos fibres tend to contain more ionizable salts than the parent rock with which they are associated. The conductivity is therefore greater with long fibres than with short. Fibre length measurement is a problem that has always confronted the asbestos industry. The normal Quebec Screen test for classifying asbestos, for example, does not dis tinguish 1/g*in. fibre length from 14-in. or any other length. A RoTap analysis likewise does not make a distinction between fibres of dif ferent lengths. In these cases fibres intertwine and prevent a true length classification, and these `balling up' effects are greatly increased as the fibres are shaken or rotated on a screen surface. The Sutter-Webb combining ap paratus has been suggested and tried by many; some believe that it is a good way of determining length of fibres. The most frequent objection is that the small sample used in the test is not a good rep resentation of the fibre product. In the fibre length measurements made in this presentation, a large -- 63 -- UCC 004629 Vt.--CrocidoliW -rati fibre bundles' ldSgefthaif OiOl-in. irt cross-sectfSii were measured. Fines AtFnroalnta Lenfftbs* i i which in^KWicanjr adhered to the bMcUeff-We^^w^laecoanted for, so 0 - 3/8", 4 3/6 - 1", 4 1" and Over, 4 Open Fiber, *; Rock, 4 liljii K>fiI'n>lil|TftH|l iTiffi ii ill lengths represent* eruStekiObre bundles that will' prbdfife:y^^Tohime in wil- SMipt* 1 Capo Province 39 - 46 12-17 2-8 30-40 2-4 lowing or eardhfcjpeqiiipinent. Sample s Ca$e Province 46 - 59 14-22 1-5 17 - 30 , Tr- k Rhodesian Fibres gaitipl* 3 Transvaal 54-58 27-31 0-2 9 - 16 ` ' 1 - 2 . A series of C. & G. fibres which had been gathered over a period of eight years were examined. Deter mination of the various properties discussed in the foregoing pages were made on these with the re sults shown in Table I. Whenever possible, the data show the varia tions with a minimum and maxi mum range.* Hand-picked fibre lengths show that they have a fairly good dis tribution over the ranges for each length increment. The data show the usual trends of resistance and magnetic iron with fibre length. The soluble salt contents seemed to in crease with shorter fibre, which is contrary to the previously men tioned indication. Cassiar 3K Fibre Castiar 3K fibre has been of con siderable interest in textiles and is used in plastics and other electrical products. This grade of fibre is con sidered equal to some grades of. Rhodesian and better than many Canadian equivalent grades (see Table II). 4 Australia #3 41-58 17 - 37 o - 15 Tr - 20 2 - 10 Saapla 1 Capo Province Sample 2 capo Province P*irp1* 3 Transvaal Prov . H*wp1* 4 Australian ^3 Voluna HBeietivity. megobms-in. Standard Dry 3 daye S75T, 50* RH 16 hr L05C After Drylna 46.000 3k 64.000 34 109,000 95 68.000 51 Humic 16 hr B75R, 91# SB After Standard 1.42 0.56 2-3 1.15 Total Iron as 9b. i EUunpl* 1 Capo Previnc* 26.2 2 Cape Province 26.8 Sample 3 Transvaal Prov. 25.3 SugCte 4 Australian #3 26.0 Aouaoua Extract tfcgnetlc - Conductivity Equiv. Sod, Hatlnfl nslcroahos/esi . i 2.0 1240.4 114 o.$9" -SST - 0.0^ 2.1 7k 5.4 H4 0.0035 , 0.05k TaiIle VII.--Anthofhylltte Fibre Voluna Resistivity, aenotas-la..______ Standard Ruai4 Dry 3 dayb 07*50* ID 16 hr r$r, <&$ SB 16 hr mosc After Drying After Standard Miscellaneous Chrysotile Fibres from Africa .. An interesting sample of chryso tile from the Barberton District and one from the Marlime deposit'; in Bechuanaland, Africa, were exam ined for lengt&J||^lectrical prop erties (see . - U. S. Georgia MDnufel<ie 0* 3. Georgia 900,000 190,000 Total Iron as Fa . # ttegnetle Ratine Aausooa Extract doaduettvity altaroBiioe/ca Equlv. Wail, 4 The iron, mag netic rating, orfptM^Vity, and NaCl equivalent values are similar to those of Arizona fibres' and are better than Canadian chrysotile fibres. These fibres should be valuable for use in electrical products and plastics. Quebec Group 3 Fibreb The tests on Quebec Group 3 fi bres (Table IV) show that, even Variations in test data could also be due to fibre from different mine areas during this eight-year period. Moaafea from neighbouring locations, the fibres may differ considerably in soluble salt content, and hence in volume resistivity. The 3K and 3B fibres with the exceptionally' high magnetic ratings were ground and re-mcasured, with no significant change. This elimin ates the. possibility of orientation and shape effects. Since there was not sufficient total iron to account for it, the high rating value is at tributed to high permeability of the; magnetite. Amobitk Fibre from Africa- The grading of African amosite fibres by, *, Canadian classification method is difficult owing to the long fibre lengths' and high perventage of crudy fibre bundles that remain- on the top screen by the' Quebec Screen test. -- 54 -- UCC - 004630 Seven different grades of amosite were examined for length and three samples were studied for their elec trical properties (Table V). The length measurements were made on a large number of samples received during the past ten years. The total percentage of iron is normally high since iron is part of the structure. However, this is not detrimental because the magnetic iron is low. These fibres, when dry, show the high resistance that the non-chrysotile fibres may attain. The W3 and KZ fibres suffer from soluble salts which lower the re sistance when moisture is present. Crocidolite Asbestos Several grades of crocidolite as bestos fibres were examined for length and electrical properties (see Table VI). The data are based upon miscellaneous samples exam ined over the past ten years. Sample 3, which represents a Blue fibre from the Transvaal, has the highest volume resistivity, low est conductivity, and lowest NaCl equivalent. Although the magnetic rating of this sample is equal to that of the Cape sample 1 and high er than that of the Cape sample 2, it is much lower than that of the Australian sample 4. The Cape sample 2 magnetic rating of 0.4 is unusually low, values normally be ing within the range of 3 to 5. Anthophyllite Deposits of anthophyllite appear in many parts of the world and in Table VII a comparison is made of fibres from two of these deposits. In most cases the fibre lengths, that may appear long before milling, are greatly reduced after processing -- as a result of poor flexibility and brittleness; therefore, fibre length measurements are of little value. In these two particular cases, however, the sample from Mozambique varied in length from ys to iy2 in.; the Georgia sample, from l/l(J to y2 in. Both fibres have good electrical properties. Conclusions (1) A series of long chrysotile fibres representing deposits in Rhodesia, British Columbia, the Province of Quebec, and Africa have been tested, with measurement of length and determination of other physical properties such as volume resistivity, total iron content, mag netic rating, conductivity, and NaCl equivalent. (2) The same types of tests were applied to a series of amosites, erocidolites, and two anthophyllites. (3) Length measurements were indicative of the quantities of crudy fibre bundles larger in cross-section than 0.01 in. that would increase in bulk during any willowing or card ing action. (4) The physical properties as shown by volume resistivity, iron content, magnetic rating, and con ductivity are new data that can be applied to fibres that are to be used in electrical products. -- 55 -- UCC 004631