【作者】 刘军芳；

【导师】 傅正义；

【作者基本信息】 武汉理工大学 ， 材料学， 2002， 硕士

【摘要】 AlN陶瓷具有优异的综合性能，如高热导率、低介电常数、高绝缘性、低介电损耗等，透明AlN陶瓷不仅继承了氮化铝陶瓷自身的优点，而且还具有透明性，使其在红外导流罩以及窗体材料等领域有着广泛的应用前景。然而，AlN是强共价键化合物，烧结活性低，而且AlN很容易水解引入氧杂质。因此，纯的AlN因其很难烧结达到完全致密而限制了它的实际应用。而透明AlN陶瓷的烧结就更加困难。目前国内外成功烧结AlN透明陶瓷的报导极少。 本论文采用放电等离子烧结法（Spark Plasma Sintering，简称SPS）制备AlN透明陶瓷的研究。SPS技术是90年代发展起来的一种技术，它具有升温、降温速度快、能在较低的温度下烧结以及烧结时间短的特点。放电等离子烧结法已成功应用于梯度功能材料、金属基复合材料、纤维增强复合材料、纳米材料、多孔材料等多种材料的制备。目前，尚未见用放电等离子烧结法制备透明陶瓷的相关报导。 在其它条件相同时，将试样分别在1700℃、1730℃、1800℃、1850℃的烧结温度下进行烧结，试样的相对密度为95.9～99.3％，在烧结温度为1730℃时就获得了高致密的氮化铝陶瓷。SEM分析表明随着烧结温度的升高，烧结体晶粒发育更趋于完善。 在其它条件相同时，将试样分别以100℃／min、150℃／min、200℃／min、300℃／min、550℃／min的升温速率升温，试样的相对密度为97.6～99.1％，说明在任何升温速率下烧结体均能达到高的致密度，表明SPS可实现快速烧结。SEM分析表明随着升温速率的减慢，晶粒生长的更为均匀，晶界更为平滑，晶粒稍有长大，但并不明显。 在其它条件相同时，将试样分别保温4min、10min、15min、20min，试样的相对密度为97.5～99.1％，表明，在SPS烧结中，仅保温4min就能得到高的致密度，烧结主要发生在烧结升温阶段，随烧结时间的延长，对烧结体致密度影响不大。SEM分析表明随保温时间的增加，晶粒的形状更趋于同一化，同时晶粒稍有长大。 在其它条件相同时，在N₂气氛和真空条件下的烧结表明，N₂气氛对晶粒的生长更为有利。 X-Ray、XPS、EMPA表明试样纯净，为纯净的氮化铝，没有第二相物质； 戎江理工上到页士q位伦支金相分析表明烧结体结构分布均匀；综合排水法测定的试样高的致密度以及SEM观察到的致密的结构，证明使用SPS技术制备的氮化铝陶瓷基本上满足陶瓷透明的几个必要条件。 将试样粗磨、细磨＼抛光至0．50mm左右后，用肉眼观察是透明的。 在红外光谱仪上的光透过率分析表明：试样在中红外波段（2．5～25 u m）是透明的，但最大透过率随升温速率、保温时间以及烧结温度的变化而变化。研究表明减慢升温速率、延长烧结时间、提高烧结温度可增加光透过率。 透射电镜分析表明：烧结的氮化铝透明陶瓷整体结构致密，分布均匀，颗粒排列有致，为材料透明提供了良好的基础，但材料中存在一些缺陷，尤其是大量的位错、层错缺陷以及少量的气孔、第二相包裹体等，这些缺陷都将损害氮化铝透明陶瓷的透光性能。 对透明陶瓷的透光机理及透光回素的研究表明影响透明陶瓷透光的因素主要有吸收系数、反射系数以及散射系数，其中散射系数是最主要的影响因素，它从几个方面对材料的透光性能造成影响；气孔、晶界组织结构、第二相以及晶粒排列取向。更多还原

【Abstract】 Because aluminum nitride (A1N) demonstrates high thermal -conductivity (theory thermal conductivity is 320W/(m.k)), dielectric constant (about 8.8), thermal expansion match to silicon(293-773K, 4.8 X 10-6K-1), good electrical insulation properties and other potential properties, it is expected to be a high-performance ceramic substrate and packaging material for high-power, high-speed microelectronics. A1N will replace other substrate materials such as SiC, BeO, Al2O3, which are now used because of their high thermal conductivity. However, as a covalent chemical compound with the wurtzite crystal structure, A1N is not easy to sinter. Densification of A1N is typically achieved by the addition of alkaline earth oxides, rare earth oxides or mixtures of oxides, fluorides or carbides. There are little reports about sintering of transparent A1N ceramics at home and abroad.Plasma spark sintering (SPS), developed by Sodick, Ltd., of Japan, is a recently developed densification method which consists of a pulsed electrical discharge step when plasma is generated between powder particles, followed by resistance heating while a uniaxial pressure is applied. The following are expected merits of SPS: rapid heating and cooling; short sintering time; lowering sintering temperature. This process has been successfully used to sinter FGM, MMC, FRC and so on. In this paper, SPS was selected to reduce the need for additives and to rapidly and successfully sinter transparent A1N ceramics.Experiment condition: without any sintering aids, at a pressure of 25MPa, sintered at 1700-1850, with heat rate of 100-550/min for 4-20min, in vacuum of 6Pa or in nitrogen of 0.56 X 105Pa.The samples were sintered at 1700, 1730, 1800 and 1850. The measured relative density ranged between 95.9 and 99.3%, demonstrating that high density could achieve just at 1730. The fracture SEM micrographs of A1N ceramics shown that grains became more uniform along with the increase of sintering temperature.The samples were sintered with heat rate of 100/min, 150/min, 200 /min, 300/min, 550/min. The measured relative density ranged between 97.6 and 99.1%, and shown that high density could achieve with any heat rate,demonstrating that SPS technique could short consolidation process and could achieve quick sintering.The samples were sintered for 4min, lOmin, ISmin and 20min. The measured relative density ranged between 97.5 and 99.1%, demonstrating that high density could achieve just for 4min. Density became a little higher and a little grain growth was found with the prolong of soaking time.The samples were sintered in Na of 0.56 X 105Pa. The fracture SEM micrographs of A1N ceramics shown that grains grow better in nitrogen.The test results of X-ray, XPS and EPMA indicated that the ceramics prepared by this technique had high purity. Optical micrographs of A1N ceramics displayed uniform microstructure and fine grains. Together with high density measured by the Archimedes method and consolidated structure viewed by SEM, demonstrated that the sintered samples basically met with transparent ceramics sintering conditions.The samples were transparent observed by naked eyes after coarse-grinded, fine-grinded and polished to about O.5Omm-thickness.The samples were transparent in infrared wavelength(2.5-25 u m). The maximum transmittance was changed with heat rate, soaking time and sintering temperature. With the slow of heat rate, prolong of soaking time and enhanced sintered temperature, the maximum transmittance was increased.TEM observation displayed consolidated and uniform structure, which contributed to transmittance of A1N transparent ceramics. From TEM micrographs, dislocation, intergranular pores, pores in crystals and secondary grain boundary phase were also observed, which were adverse to transmittance of A1N transparent ceramics.The study on the transparent mechanism and transmissivity factors of transparent ceramics indicates that the absorption coefficient, reflectivity and scattering coefficient all have effect on the tran更多还原