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碳化硼，硼化钛
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| 各位强人，不知有哪位大虾对碳化硼及硼化钛有所了解，听说那些材料在航空航天方面有很大的应用！！请各位给点意见！！ |
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B4C
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(B4C), crystalline compound of boron and carbon. It is an extremely hard, synthetically produced material that is used in abrasive and wear-resistant products, in lightweight composite materials, and in control rods for nuclear power generation. With a Mohs hardness between 9 and 10, boron carbide is one of the hardest synthetic substances known, being exceeded only by cubic boron nitride and diamond. As an abrasive, it is used in powdered form in the lapping (fine abrading) of metal and ceramic products, though its low oxidation temperature of 400–500° C (750–930° F) makes it unable to withstand the heat of grinding hardened tool steels. Because of its hardness, together with its very low density, it has found application as a reinforcing agent for aluminum in military armour and high-performance bicycles, and its wear resistance has caused it to be employed in sandblasting nozzles and pump seals. A neutron absorber, boron carbide is used in powdered or solidified form to control the rate of fission in nuclear reactors. Boron carbide is produced by reducing boron oxide with carbon at high temperatures in an electric furnace. After grinding, the black powder is solidified by pressing at temperatures exceeding 2,000° C (3,630° F). Its melting point is approximately 2,350° C (4,260° F). |
9楼2007-01-24 08:30:02
2楼2006-10-31 10:58:50
woodworm
铁杆木虫 (小有名气)
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terry-adam(金币+2):3x，互学互助，材料板因你而精彩
terry-adam(金币+2):3x，互学互助，材料板因你而精彩
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Background TiB2 is the most stable of several titanium-boron compounds. The material does not occur in nature but may be synthesised by carbothermal reduction of TiO2 and B2O3. As with other largely covalent bonded materials, TiB2 is resistant to sintering and is usually densified by hot pressing or hot isostatic pressing. Pressureless sintering of TiB2 can achieve high densities but liquid forming sintering aids such as iron, chromium and carbon, are required. Key Properties Table 1. Typical Physical and mechanical properties of titanium diboride. Property Density (g.cm-3) 4.52 Melting Point (°C) 2970 Modulus of Rupture (MPa) 410-448 Hardness (Knoop) 1800 Elastic modulus (GPa) 510 -575 Poisson's Ratio 0.1 - 0.15 Volume resistivity (ohm.cm) at 20°C 15x10-6 Thermal conductivity (W/m.K) 25 TiB2 is resistant to oxidation in air up to 1000°C. It is also resistant to HCl and HF but reacts with H2SO4 and HNO3. It is readily attacked by alkalis. Hot pressing of TiB2 (with small additions of metallic or carbide sintering aids) is carried out at 1800 - 1900°C and achieves close to theoretical density. Pressureless sintering requires higher levels of sintering aids and sintering temperatures in excess of 2000°C. Applications Due to its high hardness, extreme melting point and chemical inertness, TiB2 is a candidate for a number of applications. Ballistic Armour The combination of high hardness and moderate strength make it attractive for ballistic armour, but its relatively high density and difficulty in forming shaped components make it less attractive for this purpose than some other ceramics. Aluminium Smelting The chemical inertness and good electrical conductivity of TiB2 have led to its use as cathodes in Hall-Heroult cells for primary aluminium smelting. It also finds use as crucibles for handling molten metals and as metal evaporation boats. Other Applications High hardness, moderate strength and good wear resistance make titanium diboride a candidate for use in seals, wear parts and, in composites with other materials and cutting tools. In combination with other primarily oxide ceramics, TiB2 is used to constitute composite materials in which the presence of the material serves to increase strength and fracture toughness of the matrix. |
3楼2006-11-01 22:34:12
davidzhh
木虫 (正式写手)
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- 专业: 其他无机非金属材料
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碳化硼 boron carbide 用于硬质合金、宝石等硬质材料的磨削、研磨、钻孔及抛光，金属硼化物的制造以及冶炼硼钠、硼合金和特殊焊接等。 灰黑色粉末。相对密度2.52。熔点2350℃。沸点＞3500℃。与酸、碱溶液不起反应，具有高化学位、中子吸收、耐磨及半导体导电性。是对酸最稳定的物质之一，在所有浓或稀的酸或碱水溶液中都稳定。用硫酸、氢氟酸的混合酸处理后，在空气中800℃煅烧21h，可完全分解并形成三氧化碳和三氧化二硼。当有一些过渡金属及其碳化物共存时，有特殊的稳定性。在1000～1100℃条件下元素周期表中第Ⅳ、Ⅴ和Ⅵ族过渡金属与碳化硼粉末强烈反应形成金属硼化物。在硝酸存在下用氢氧化钠、氢氧化钾、碳酸钠、碳酸钾熔融时，碳化硼容易分解和制成溶液。 |
5楼2006-11-03 11:19:51
