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ASBESTOS
A number of different minerals containing varying
amounts of silicon, oxygen, calcium and magnesium
qualify as form asbestos but all have one feature in
common, a structure based on long-chain molecules
containing the repeating unit (Si4!!" -#
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AS$%S&S AS A
'%A&' 'A)A*+ung cancerAsbestosis (a chronic
inflammation of the lungs"
$S%&% *+./&S /0&A10102 AS$%S&S
1. Raw asbestos fibres 3ere used as insulation %xample ac5ing for 3alls
and floors 1nsulation of batteries
2. Asbestos textiles 3ere used in belting for conveying hot materials, friction
materials, and as electrical and thermal insulation
3. Asbestos paper 3as used as electrical and thermal insulation and for fire
protection in military helmets, armored car roofs
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4. Asbestos-cement products contained up to 678 ortland cement 'ere the
strong asbestos fibres 3ere used to strengthen the product as 3ell as to
improve thermal insulation properties
5. Asbestos reinforced and filled plastics included both thermoplastic andthermosetting types to 3hich asbestos 3as added as loose fibre, 3oven
textile or paper
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*%/A.&10S 0 %0/.0&%*102
AS$%S&S
1f dealing 3ith the ra3 fibre and 3oven forms of it, protective clothing
should be 3orn, including a respirator, rubber gloves and gumboots
+rilling and cutting of asbestos-cement and other composites should only
be underta5en if the surface can be 5ept 3et and continual damping do3n
is possible to prevent the formation of air-borne dust 9achining processes should only be permitted if adequate exhaust systems
are available to ta5e off the dust-laden air
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CLAY PRODUCTS
&he mineral kaolinite, from 3hich high-quality porcelain is
manufactured ure 5aolinite is an alumino-silicate of the
formula Al:;:Si::':, but natural clays vary 3idely in
composition
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?/ Since ra3
fireclay is relatively expensive, crushed used firebric5 (5no3n as @grog@" isadded to ne3 clay, partly for reasons of economy but also to reduce shrin5age
of the product during firing
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S'A102 /A= *+./&S (i) The plaster mould is flled with slip
(ii) a layer o clay particles collects on the mould surace aswater is absorbed by the mould
(iii) when the shell is thick enough, excess slip is pouredaway
(iv) the resultant 'casting' is removed rom the dry mould
beore being urther dried and fred'.
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'=+*AS&1/
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&'% '%A&-&*%A&9%0& < /A= *+./&S
1. Drin! in 3hich the 3or5 is loaded on to rac5s in large ovens and thetemperature then raised to about !:>?/ in an atmospheresaturated wit"
water #apour. &he humidity is then very gradually reduced so that 3ater
evaporates slo3ly and evenly from the 3or5
2. $irin! is usually carried out in long gas- or electrically-heated tunnel
5ilns through 3hich the 3or5 moves very slo3ly to3ards the hottest one(about !7>>?/", then into the cooling one through 3hich the 3or5 again
moves very slo3ly before being discharged
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