tailieunhanh - Materials Handbook 15th ed - G. Brady_ H. Clauser_ J. Vaccari (McGraw-Hill_ 2002) WW Part 12

Tham khảo tài liệu 'materials handbook 15th ed - g. brady_ h. clauser_ j. vaccari (mcgraw-hill_ 2002) ww part 12', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 770 QUARTZ Barium titanate crystals are used to replace quartz for electronic use. Ethylenediamine tartrate crystals may be used to replace quartz for telephone and sonar work. Quartz is harder than most minerals being Mohs 7 and the crushed material is much used for abrasive purposes. Finely ground quartz is also used as a filler and powdered quartz is employed as a flux in melting metals. When quartz is fused it loses its crystalline structure and becomes a silica glass with a specific gravity of compressive strength 210 000 lb in2 1 448 MPa tensile strength 4 000 lb in2 28 MPa Mohs hardness 5 and dielectric strength 410 V mil 16 X 106 V m . The chemical formula of this material is sometimes given as SiO3 but is really SiO2 repeated in a lattice structure but different from that of quartz crystal. Fused quartz or quartz glass is used for bulbs optical glass crucibles and tubes and rods in furnaces. Its softening and working temperature is about 3040 F 1671 C and it fuses at 3193 F 1755 C . The translucent material made from sand has a specific gravity of with much lower strength. It withstands rapid changes of temperature without breaking. Fused quartz made from rock crystal is transparent to visible light while fused silica is normally translucent or opaque. Vitreosil is fused quartz containing silica. It comes opaque translucent and transparent. It transmits ultraviolet and short wavelengths has high electrical resistance and has a coefficient of expansion about one-seventeenth that of ordinary glass. Quartz tubing for electronic use comes in round square hexagonal and other shapes. The softening point is 3033 F 1667 C . Tubing as small as in cm produced by Monsanto Co. is flexible and as strong as steel. Quartz fiber originally was made by extruding the molten quartz through a stream of high-pressure hot air which produced a fluffy mass of fine fibers of random lengths. Quartz fibers are now made with many differing compositions and .

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