Document Lo1g1YjVMzjzOZay2JjEQNDg

U 90 0409 58 Asbestos Fundamentals white and silky; they are characterized by a low content of accom panying minerals, which furthermore almost always consist of talc. In pnrt the length of the fibers is great, the fibers spin well, and the material has other desirable fibrous characteristics. An outstanding feature is the uniformity of composition in these chrysolites: SiO, AlxOa FeO NotO,CoO MgO HtO 41 to 42% 0 to 2% 0 to 1 % (no FejOafejO, 0 to 3% 36 to 42% 14 to 18% Tsana 5 MAGNETITE CONTENTS OF ASBESTOS Variety Chrysolites . Quebec 'Shabani, 8outbcm Rhodesia 'Asbeat, Ural McDame, British Columbia . Barbertoo, Transvaal Lobatsi, Bechosnaland QoridoCtes Cape blue , Transvaal blue `Australian blue FnOi content (%> 0.8 to 5.9 0.5 to 2.0* 0 to 9.7 How iron ehrysotflee") S.O to 5.9 * -- -- -- AatbopbylCte asbestoses Georgia, USA Motambique ArooaUe Tremolita asbestos doos -- -- Done none SXK nlvn sftr B*4oGt U|1m t plintl to riooft BvebftkaQf W--rfilr tomond wrhinloWy Magnetic noting (MR) 0.8 to 6.7 -- -- 0.7 to U 0.1 to 0.3 03 0.4 to 2.0 2.1 5.4 -- 0.1 0.6 0.2 to 0.3 -- -- Chiysotiles of the composition shown above, free of FejOe are formed' from serpentines in accord with the principle outlined schematically in part A of 2.1 whereas chrysotiles coming from serpentines through the processes described in a and 5 contain huger or smaller amounts of Fe,0 (e.g., up to 4% in Quebec; see Table' 5). The high content of magnetite is not the sole dctcr- Propekties or Asbestos 59 mining factor, however, but in the case of chrysotiles containing relatively much FeiO -- in contrast to low-iron chrysotiles -- the extent to which this compound adheres to the fillers and the ease with which it can be removed by mechanical disintegration are also decisive. Examples of chrysotiles with weakly-adhering magnetite include the fibers from Shabana (Southern Rhodesia) and from Asbest (Urals). See Tabic 5. On the other hand, as it is very difficult to remove the magnetite from Quebec chrysolite mechanically other methods (discussed in detail in Part H) must be employed in the processing of this type of asbestos rock. In general, the content of magnetite falls as it is more widely distributed, as the degree of disintegration rises, or `as the fibers become shorter. The chrysotiles intended for the fabrication of electrical insulants are divided by the US Military Specification MIL-3053 A (August 3, 1951) into the following classes, without regard to their origin or pretreatment of the fibers: Class a 4 6 Total iron content mac. % 2.5 4.9 S.O Ft,Ot content max. % 0.75 2.0 4.0 When conducted by the procedures given in DIN 51070-72,* the chemical determination of the content of FeiO in asbestoses is so complicated by the simultaneous presence of Fe(II) and Fe(III) that at present the magnetite content is ascertained elec tronically (oscillograph in combination with visual and recording equipment). When samples of asbestos containing much magnetite are being studied, the signal effect may be distinctly above the signal level of the measuring devices. The best procedure has been found to be the methods prescribed in ASTM D 1118-57, which employs the Mapes analyzer. The found MR-vatues (mag netic ratings, Mapes ratings) are comparative values based on a standard substance with a known content of FeiO; they may not be equated directly with the magnetite content. Among the most important general findings obtained with the Mapes device is the observation that the some quantities of a sample with known magnetite content give decreosing'MR-vnlucs Method* of Reinhanit-Zimmermano, Yiiimnthsn-Suryaraman, StachigolBurtschfoskaja: lead platinum apparatus, hydrofluoric acid decomposition In atream of GO* eto.