【作者】 任克刚；

【导师】 周和平； 陈克新；

【作者基本信息】 清华大学 ， 材料科学与工程， 2009， 博士

【摘要】 由于具有优异的导热性,良好的绝缘性,氮化铝、氮化硅作为导热材料有着广阔的应用前景,其作为导热填料应用于导热复合材料也很有吸引力。除了具有高的本征热导率之外,导热填料的晶体形态对复合材料的导热性能有重要的影响。本文主要研究具有不同的结晶形态的氮化铝、氮化硅粉体的制备,并研究利用所制备的陶瓷粉体制备高热导硅脂复合热界面材料。利用机械力活化辅助燃烧合成技术制备了高纯度的单相氮化铝、β-氮化硅粉体,研究了机械力活化处理时间、氮气压力和稀释剂含量对燃烧合成结果的影响。研究表明:通过选择适当的稀释剂含量、氮气压力以及机械力活化时间可以有效的控制燃烧合成过程的氮气供应状况以及燃烧温度而获得单相产物;机械力活化可以有效降低体系的激活能。利用高温液相辅助修饰的方法处理燃烧合成氮化铝粉体,通过筛选合适的添加剂,控制温度等工艺条件,得到了低氧含量的球形氮化铝粉体。探讨了处理温度、保温时间等参数对氮化铝球形化的影响规律。分析表明:添加剂与表面氧化层反应形成液相,这种液相在表面产生的张力是使AlN球形化的驱动力,表面反应同时消耗了表面氧化层的氧杂质,降低了AlN的氧含量。利用悬浮燃烧合成的流态化工艺,合成了AlN晶须。研究表明:该方法合成晶须主要沿<0001>方向生长。“淬火法”研究证实,氮化铝晶须的生长机制主要为VLS机制。采用泡沫法成型工艺,燃烧合成了单相氮化硅粉体。研究发现:泡沫法可以有效的降低“微烧结”现象,得到易于粉碎的产物;原料中含有的C元素可以减少合成过程生成的液相量,促使氮化硅晶粒的长度减小,直径增大,端部呈现锥形,添加Ca元素的作用则相反。以合成的多形态氮化铝、氮化硅粉体为填料,与二甲基硅油复合制备了导热硅脂。结果表明:通过降低粉体填料本身热阻可以提高导热硅脂的传热性能;通过粒子级配和添加偶联剂可以降低硅脂的粘度进而提高导热硅脂的传热能力。更多还原

【Abstract】 Because of excellent properties of thermal conductivity and electrical resistance, AlN and Si3N4 ceramics have shown great application potentials as thermal conductive substrate. Besides, the usage as thermal fillers in high thermal conductive composite materials is attractive as well. In addition to the high thermal conductivity, grain morphology of the thermal fillers is of great importance, too. This dissertation deals with the synthesis of AlN and Si3N4 ceramics powders with different grain morphologies by using various improved combustion synthesis methods and the preparation of thermal grease with high thermal conductivity by using the synthesized AlN and Si3N4 ceramics powders as thermal fillers.By using mechanical-activation-assistant combustion synthesis method, single phase AlN andβ-Si3N4 ceramics powders with high purity were synthesized. Influence of nitrogen pressure, mechanical dealing time and content of diluents on the results was invetigated. The experiment results showed that, single-phase AlN orβ-Si3N4 ceramics powders could be achieved by chosing appropriate diluents content, nitrogen pressure and mechanical dealing time and effective decrease of the activation energy of Al or Si could be achieved after treating by mechanical-activation process.With high-temperature-liquid-assisted sphericizing method, Spherical AlN powders with low oxygen content could be acquired by choosing proper additive, the temperature and the dwell time at chosen temperature. It is revealed that the surface tention, which was causing by eutectic liquid around the AlN particles formed at high temperature, is the driven force to realize the formation of spherical AlN. Oxygen could be removed from the AlN surface because of the reaction between CaO and the oxide surface layer.AlN whiskers were prepared with fluidized combustion synthesis method. SEM and TEM analysis results showed that majority of the AlN whiskers grew along <0001> direction. By using quenching method, VLS mechanism was confirmed to be the main growth mechanism of the AlN whiskers.Assisted by foaming process, single phaseβ-Si3N4 ceramics powders were synthesized. Results showed that“micro-sinter”phenomenon in the product was alleviated effectively and thus the synthesized product could be easily smashed. The presence of C made the oxygen consumed and, as a result, made theβ-Si3N4 crystal shorter and thicker. However, the presence of Ca madeβ-Si3N4 crystal longer and thiner.Thermal grease is prepared by using the synthesized AlN andβ-Si3N4 powders as thermal fillers and combining with silicone oil (polydimethyl siloxane fluid). Results showed that higher thermal conductivity of filler are employed, higher thermal conductive property could be achieved. With addition of proper and appropriate amount of coupling agent and fine particle size fillers, higher thermal conductive properties of thermal grease could be obtained.更多还原