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learner5310木虫 (正式写手)
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【求助】二氧化锆形态描述求助
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【请教】二氧化锆形态描述求助 哪位高人，能用英文帮我描述一下二氧化锆的形貌，或者团聚状态下的二氧化锆。有没有参考文献，鄙人将会有5~10个金币的奖励！ the average diameter is 20 nm. [ Last edited by learner5310 on 2009-10-16 at 14:18 ] |
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小木虫(金币+0.5):给个红包，谢谢回帖交流
薰衣草儿(金币+2,VIP+0):欢迎应助~ 10-16 13:38
小木虫(金币+0.5):给个红包，谢谢回帖交流
薰衣草儿(金币+2,VIP+0):欢迎应助~ 10-16 13:38
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Zirconium dioxide (ZrO2), sometimes known as zirconia, is a white crystalline oxide of zirconium. Its most naturally occurring form, with a monoclinic crystalline structure, is the rare mineral, baddeleyite. The high temperature cubic crystalline form, called 'cubic zirconia', is rarely found in nature as mineral tazheranite (Zr,Ti,Ca)O2 (and a doubtful mineral arkelite), but is synthesized in various colours for use as a gemstone. The cubic crystal structured variety cubic zirconia is the best-known diamond simulant. Zirconium dioxide is one of the most studied ceramic materials. Pure ZrO2 has a monoclinic crystal structure at room temperature and transitions to tetragonal and cubic at increasing temperatures. The volume expansion caused by the cubic to tetragonal to monoclinic transformation induces very large stresses, and will cause pure ZrO2 to crack upon cooling from high temperatures. Several different oxides are added to zirconia to stabilize the tetragonal and/or cubic phases: magnesium oxide (MgO), yttrium oxide, (Y2O3), calcium oxide (CaO), and cerium(III) oxide (Ce2O3), amongst others.[1] Zirconia is very useful in its 'stabilized' state. In some cases, the tetragonal phase can be metastable. If sufficient quantities of the metastable tetragonal phase is present, then an applied stress, magnified by the stress concentration at a crack tip, can cause the tetragonal phase to convert to monoclinic, with the associated volume expansion. This phase transformation can then put the crack into compression, retarding its growth, and enhancing the fracture toughness. This mechanism is known as transformation toughening, and significantly extends the reliability and lifetime of products made with stabilized zirconia. [2][1] A special case of zirconia is that of tetragonal zirconia polycrystaline or TZP, which is indicative of polycrystalline zirconia composed of only the metastable tetragonal phase. The cubic phase of zirconia also has a very low thermal conductivity, which has led to its use as a thermal barrier coating or TBC in jet and diesel engines to allow operation at higher temperatures. Thermodynamically the higher the operation temperature of an engine, the greater the possible efficiency (see Carnot heat engine). As of 2004, a great deal of research is ongoing to improve the quality and durability of these coatings. It is used as a refractory material, in insulation, abrasives, enamels and ceramic glazes. Stabilized zirconia is used in oxygen sensors and fuel cell membranes because it has the ability to allow oxygen ions to move freely through the crystal structure at high temperatures. This high ionic conductivity (and a low electronic conductivity) makes it one of the most useful electroceramics. The ZrO2 band gap is dependent on the phase (cubic, tetragonal, monoclinic, or amorphous) and preparation methods, with typical estimates from 5-7 eV.[3] This material is also used in the manufacture of subframes for the construction of dental restorations such as crowns and bridges, which are then veneered with a conventional feldspathic porcelain.[4] Zirconium dioxide can occur as a white powder which possesses both acidic and basic properties. On account of its infusibility and brilliant luminosity when incandescent, it was used as an ingredient of sticks for limelight. Zirconia is also an important high-k dielectric material that is being investigated for potential applications as an insulator in transistors in futur |
2楼2009-10-16 12:41:51
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薰衣草儿(金币+1,VIP+0):欢迎应助~ 10-16 13:38
薰衣草儿(金币+1,VIP+0):欢迎应助~ 10-16 13:38
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Other names Zirconia CAS number 1314-23-4 Y Molecular formula ZrO2 Molar mass 123.218 g/mol Appearance white powder Density 5.68 g/cm3 Melting point 2715 °C Boiling point 4300 °C Solubility in water negligible Solubility soluble in HF, and hot HSO4, HNO3, HCl Refractive index (nD) 2.13 Std enthalpy of formation ΔfHo298 −1080 kJ/mol Standard molar entropy So298 50.3 J K−1 mol−1 MSDS MSDS EU Index Not listed Flash point Non-flammable LD50 > 8800 mg/kg (oral, rat) Other anions Zirconium disulfide |
3楼2009-10-16 12:46:23
learner5310
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4楼2009-10-16 14:24:29
