TiN粉末的制备方法

简要介绍了TiN的性能及主要用途,分析和阐述了TiN粉末制备的研究现状及发展趋势,重点讨论了碳热还原氮化合成TiN粉末存在的问题和前景。     

γ-AlON陶瓷粉体合成的研究进展

γ-AlON透明陶瓷具有硬度大、化学稳定性好以及光学透过率高等优点,在国防与商业领域具有广阔的应用前景。高纯超细、粒径分布均匀、几乎无团聚的单相γ-AlON粉体是制备高透明γ-AlON陶瓷的关键。本文首先对Al₂O₃-AlN相图及γ-AlON的热力学计算结果进行了简要介绍,然后综述了高温固相反应、铝热还原氮化、碳热还原氮化三种方法合成γ-AlON粉体的研究进展,最后对粒径小于100 nm的γ-AlON粉体合成方向进行了展望。     

TiAl基合金高温气体渗氮

研究了TiAl基合金在氨气中进行的高温渗氮行为,采用XRD和EPMA对渗氮层进行的测试分析显示,渗层由TiN和Ti2AlN组成。其中TiN分布于外层而TiAlN分布于内层。通过对渗氮前后的合金表面硬度和耐磨性的对比结果表明：经过不同工艺渗氮的试样其表面硬度及其耐磨性都有不同程度的提高,当渗氮温度提高到940℃,渗氮时间延长到50h,试样的表面努氏硬度可达1286kg/mm^2。     

热解前驱体制备AlN粉末

以硝酸铝、尿素、蔗糖为原料低分解得到均匀分散的前驱身粉末,对前驱体粉末的碳热的过程研究表明：不存在γ－ＡＩ２Ｏ３→α－ＡＩ２Ｏ３晶型转变,因而ＡＩＮ粉末的合成温度降低合成的ＡＩＮ粉末粒径约８０～１２０ｎｍ,比表面积１９．２ｍ＾２／ｇ,脱碳后的ＡＩＮ粉末氮的质量分数为３２．３％,氧的质量分数为２．１％,碳的质量分数为０．２％。     

电子从不同晶向Si隧穿快速热氮化SiO_2膜的电流增强及模型解释

用卤素钨灯作辐射热源快速热氮化 (RTN) 10 nm Si O2 膜 ,制备了〈10 0〉和〈111〉晶向 Si衬底上的 Si- Si Ox Ny-Al电容结构 .研究了电子从〈10 0〉和〈111〉不同晶向 N型硅积累层到 RTN后 Si O2 膜 (或原始 Si O2 膜 )的漏电流和高场 F- N隧穿电流 .研究结果表明 :经 RTN Si O2 膜比原始 Si O2 膜从低场到隧穿电场范围都明显地看到电导增强现象 .比较 RTN后两种不同晶向样品 ,低场漏电流没有多大的差别而在高场从〈10 0〉晶向比从〈111〉晶向 Si隧穿Si Ox Ny 膜的 F- N电流却明显增加 ,借用一种基于横向晶格动量守恒的理论模型解释了这种现象     

Optimization of time-temperature schedule for nitridation of silicon compact on the basis of silicon and nitrogen reaction kinetics

A time-temperature schedule for formation of silicon-nitride by direct nitridation of silicon compact was optimized by kinetic study of the reaction, 3Si + 2N₂ = Si₃N₄ at four different temperatures (1250°C, 1300°C, 1350°C and 1400°C). From kinetic study, three different temperature schedules were selected each of duration 20 h in the temperature range 1250°-1450°C, for complete nitridation. Theoretically full nitridation (100% i.e. 66.7% weight gain) was not achieved in the product having no unreacted silicon in the matrix, because impurities in Si powder and loss of material during nitridation would result in 5–10% reduction of weight gain. Green compact of density < 66% was fully nitrided by any one of the three schedules. For compact of density > 66%, the nitridation schedule was maneuvered for complete nitridation. Iron promotes nitridation reaction. Higher weight loss during nitridation of iron doped compact is the main cause of lower nitridation gain compared to undoped compact in the same firing schedule. Iron also enhances the amount of Β-Si₃N₄ phase by formation of low melting FeSi_x phase.     

The impact of nitridation and nucleation layer process conditions on morphology and electron transport in GaN epitaxial films

A systematic study has been performed to determine the characteristics of an optimized nucleation layer for GaN growth on sapphire. The films were grown during GaN process development in a vertical close-spaced showerhead metalorganic chemical vapor deposition reactor. The relationship between growth process parameters and the resultant properties of low temperature GaN nucleation layers and high temperature epitaxial GaN films is detailed. In particular, we discuss the combined influence of nitridation conditions, V/III ratio, temperature and pressure on optimized nucleation layer formation required to achieve reproducible high mobility GaN epitaxy in this reactor geometry. Atomic force microscopy and transmission electron microscopy have been used to study improvements in grain size and orientation of initial epitaxial film growth as a function of varied nitridation and nucleation layer process parameters. Improvements in film morphology and structure are directly related to Hall transport measurements of silicon-doped GaN films. Reproducible growth of silicon-doped GaN films having mobilities of 550 cm²/Vs with electron concentrations of 3 × 10¹⁷ cm⁻³, and defect densities less than 10⁸ cm⁻² is reported. These represent the best reported results to date for GaN growth using a standard two-step process in this reactor geometry.     

碳热还原法制备氮化铝反应机制的研究进展

本文综述了碳热还原反应制备AlN的各种反应机制,并进行了评述,详述了气-固反应机制和固-固反应机制的特点、实验证据及存在的不足.认为Al2O3蒸发分解零级反应与固相扩散反应共存的机理能较好地解释目前的实验现象,但仍需进行完善.     

Effects of nitridation temperature on properties of sintered reaction-bonded silicon nitride

We prepared sintered reaction-bonded silicon nitride ceramics by using yttria and magnesia as sintering additives and evaluated effects of the nitridation temperature on their microstructure, bending strength, fracture toughness, and thermal conductivity. The effects of the nitridation temperature were large, but different depending on the property. The ratio of β-phase in the nitrided compacts significantly increased with increasing the nitridation temperature, whereas their microstructures had no clear difference. Although the bending strength varied, it maintains a high value of 800 MPa. Fracture toughness was almost constant regardless the temperature. The thermal conductivity improved as the β-phase in the nitrided compact increases. This resulted in a decrease of the lattice oxygen content and increase of the thermal conductivity. Therefore, elevating the nitridation temperature and consequently the β-phase ratio should be a promising strategy for achieving compatibly high strength and high thermal conductivity, which are generally known to be in a trade-off relationship.     

Effects of nitrogen pressure on properties of sintered reaction-bonded silicon nitride

We prepared sintered reaction-bonded silicon nitride ceramics by using yttria and magnesia as sintering additives and evaluated the effects of nitrogen pressure (0.1–1.0 MPa) on their microstructure, bending strength, fracture toughness, and thermal conductivity. The ratio of β phase in the nitrided compacts varied with the pressure and increased with increasing it. Since many β grains in the nitrided compacts were formed and interlocked each other with a stable three-dimensional structure which restricted the shrinkage during the sintering procedure, many pores remained in the sintered body. Under the middle pressure (0.3–0.5 MPa), the grains grew large because the number of formed nuclei was small. On the other hand, under the high pressures (0.8–1.0 MPa), the grains were relatively fine and uniform because of a large number of nuclei. Since the porosity and grain length depended on the nitridation mechanism, which was affected by the nitrogen pressure, the properties largely varied accordingly. The nitridation at 0.1 MPa gave the best properties in this study.