【作者】 李凯；

【导师】 崔得良；

【作者基本信息】 山东大学 ， 材料学， 2007， 博士

【摘要】 立方氮化硼（cubic boron nitride，cBN）具有高硬度、宽带隙、高热稳定性和化学稳定性，而且在应用于精密机械加工时与铁系金属之间呈现高惰性，因此，在精密机械加工、电子和光学器件的研制等领域具有广阔的应用前景。多年来，人们发展了各种各样的合成方法，试图有效地制备立方氮化硼。这些方法包括高温高压法、化学气相沉积法、溶剂热法和水热法等。在已有的水热合成氮化硼工作基础上，本文作者又系统地研究了各个关键因素对合成氮化硼结果的影响，并在此基础上优化了合成立方氮化硼的工艺参数，成功地在水热条件下制备了纯相的立方氮化硼。此外，作者又探索了通过籽晶诱导作用生长立方氮化硼体块晶体的新方法，得到了一些具有较高参考价值的研究结果，具体如下：（1）作为优化实验条件的第一步，作者系统研究了氮源种类、加入方式以及它们的用量对实验结果的影响。结果表明：当反应温度为300℃、压力为10MPa时，随着R_N值（一次氮源中NaN₃的摩尔数同二次氮源中NaN₃摩尔数的比值）的增加，样品中cBN含量逐渐增加，在R_N=3∶1时可以合成出纯相的cBN。另一方面，随着三甲胺和氨水用量的增加，氮化硼样品的产率有所提高，但这时样品中六方氮化硼（hexagonal boron nitride，hBN）的含量相应地增加。（2）另外，反应温度和二次氮源的加入速度也对氮化硼样品的物相和产率有较大影响。当反应温度为300℃时，可以制备出纯相的cBN样品，但当反应温度继续升高时，样品中出现了较多杂相；此外，在高温高压条件下原位加入二次氮源时，如果分多次加入，则会引起反应体系温度和压力的频繁波动，使样品中同时存在cBN和hBN。（3）除了上述影响因素外，反应原料的种类以及添加剂同样影响着样品的物相和产率。如果用硼酸铵和三聚氰胺作原料，样品的产率有所提高，但hBN成了样品中的主要物相；再有，如果在反应溶液中加入适量的盐酸作为添加剂，则在优化的实验条件下不但可以合成出纯相cBN样品，而且样品的产率也得到明显提高。除此之外，样品的结晶质量和实验结果的重现性也都得到了明显改善。（4）系统研究的结果表明：在水热合成氮化硼时，如果使用两种以上的原料作为氮源，则不仅易于获得纯相cBN，而且样品的产率和结晶质量也大幅度提高。我们把这种现象称为“混合氮源效应”。（5）在系统优化了制备cBN的实验条件的基础上，作者探索了利用cBN籽晶诱导作用生长cBN体块晶体的新方法。实验结果显示，在大多数情况下，cBN籽晶与后来生成的氮化硼混杂在一起，籽晶本身并没有明显长大。但是，在优化的生长条件下，在较大的cBN籽晶表面上出现了二维层状生长模式。这说明了在水热条件下籽晶生长的可能性。更多还原

【Abstract】 Because of the excellent merits, such as supreme hardness, wide band gap, high thermal stability, excellent chemical stability and inertness against ferrous metals etc, cBN is of high value in fabricating machining tools, electronic and optical devices etc. For preparing cBN, many methods have been developed, for example, high temperature & high pressure （HTHP） method, chemical vapor deposition （CVD） method, solvothermal method and hydrothermal method. In this thesis, results from systematical investigations on some key factors influencing the production of boron nitride by hydrothermal method will be reported. Furthermore, optimized parameters for synthesizing pure cBN samples will be given. Based on the above mentioned work, a new route to grow cBN bulk crystals by using cBN seed-crystals will be presented. The major results are as follows:（1） It was shown that the sort of nitrogen sources, their quantity and the ways to introduce them into the reaction autoclave could effect the phases and yields of BN samples.At 300℃and 10 MPa, the content of cBN increased with the increase of R_N value （R_N is defined as the molar ratio of NaN₃ in primary nitrogen source to it in the secondary one）, and pure cBN could be obtained at Rn=3:1. The yield of BN samples would be increased slightly, mainly of hBN, if the quantity of N（CH₃）₃ or NH₃H₂O increased.（2） The temperature of the reaction solution and the rate of introducing secondary nitrogen source were found to have important effects on the phases and yields of BN samples. Pure cBN sample was prepared at 300℃. However, if the temperature was further elevated, the phase purity would be deteriorated. Introducing the secondary nitrogen source into the autoclave by multi-steps would cause both the temperature and pressure undulating frequently, resulting in to favorite the formation of hBN and, thus, the coexistence of hBN and cBN.（3） The reactants and additives played an important role during the synthesis of BN by hydrothermal method. The yield of BN sample could be improved by using NH₄HB₄O₇·3H₂O and C₃N₆H₆ as the reactants. In this case, hBN became the dominant phase. By adding some HC1 into reaction systems for preparing BN, pure cBN could be synthesized. Its crystalinity and reproducibility of the experiment could be improved significantly.（4） Pure cBN could be prepared by using more than two reactants as the nitrogen source simultaneously, and its crystalline perfection and yield could be improved very much. We call this phenomenon as "mixed nitrogen sources effect".（5） To mention at last, lamellar growth process was observed on the surface of some larger cBN seed-crystals introduced into the reaction system for preparing cBN under optimized conditions. This indicates the possibility to grow large single crystals of cBN under hydrothermal conditions.更多还原