Synthesis of Aluminum Nitride Nanopowder by Gas-Reduction–Nitridation Method

Aluminum nitride (AlN) nanopowder was successfully synthesized from transition alumina nanopowder using an NH₃–C₃H₈ gas mixture as a reduction–nitridation agent. Phase-pure, nanocrystalline AlN powder with a specific surface area of 36.4 m²/g and a mean particle size of 51 nm was prepared under typical reaction conditions. The resulting AlN nanopowders possessed excellent sinterability, allowing full densification in conventional processing, even without the addition of sintering aids.     

Effects of Technological Parameters on Carbothermal Reduction and Nitridation of Zircon

Carbothermal reduction and nitridation(CRN)of zircon(ZrSiO4)permits obtaining different composites of oxides and nitrides such as ZrO2-Si2N2O and ZrN-Si3N4.The effects of technological parameters(carbon source,reaction temperature,and carbon content)on the reaction rate and product phase composition of CRN of zircon were investigated by TGA and XRD.The results show that:(1)carbon source is an important factor for a rapid reaction,and activated carbon is chosen as the carbon source considering the expect pro...     

Aluminum Nitride Prepared by Nitridation of Aluminum Oxide Precursors

Aluminum nitride (AlN) powders were prepared from the oxide precursors aluminum nitrate, aluminum hydroxide, aluminum 2-ethyl-hexanoate, and aluminum isopropoxide (i.e., Al(NO₃)₃, Al(OH)₃, Al(OH)(O₂CCH(C₂H₅)(C₄H₉))₂, and Al(OCH(CH₃)₂)₃). Pyrolyses were performed in flowing dry NH₃ and N₂ at 1000°–1500°C. For comparison, the nitride precursors aluminum dimethylamide (Al(N(CH₃)₂)₃) and aluminum trimethylamino alane (AlH₃·N(CH₃)₃) were exposed to the same nitridation conditions. Products were investigated using XRD, TEM, EDX, SEM, and elemental analysis. The results showed that nitridation was primarily controlled by the water:ammonia ratio in the atmosphere. Single-phase AlN powders were obtained from all oxide precursors. Complete nitridation was not obtained using pure N₂, even for the non-oxide precursors.     

Carbothermal/aluminothermic reduction nitridation synthesis of ZrN–SiAlON refractory composites from zircon and bauxite: a comparative study of the reduction effect of reducers

The ZrN–SiAlON composite refractory powder was successfully synthesised from zircon and bauxite minerals by the carbothermal reduction nitridation or the aluminothermic reduction nitridation method with three typical reducers, including carbon coke, carbon black and aluminium powder. The effect of reaction temperatures on phase composition and microstructure was investigated using X-ray diffraction and a scanning electron microscopy (SEM), respectively. The thermodynamics equilibrium relationships of the condensed phases were analysed as well. The results showed that carbon coke was the most optimum reducer and when it was used as the reducer, the main final products were granular ZrN with a little β-SiAlON. Nevertheless, ZrO₂ was produced during reduction at 1600°C when the reducer was carbon black, because the activity of carbon black was the poorest. Additionally, more byproducts were produced in the case of Al powder used as reducer at 1600°C, such as AlN polytype and Al₂O₃.     

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.     

Fabrication of ThN Using a Carbothermic Reduction to Nitridation Process

A carbothermic reduction to nitridation process was developed which is capable of producing high‐purity thorium mononitride (ThN) in bulk quantities. This was accomplished through study of three distinct processing routes using thermogravimetric analysis. The information gathered was then used to guide development of a draft process, which was tested within a tungsten production furnace. Scaling issues were identified and corrected following the draft process. Finally, a partitioned process was developed in response to the draft process which separates the reduction from the nitridation and carbon cleanup steps. This partitioned process was demonstrated to be capable of producing phase‐pure ThN, with oxygen and carbon impurities of 990 ± 130 wppm and 240 ± 30 wppm, respectively.     

碳热还原氮化法制备SiAlON陶瓷材料

碳热还原氮化工艺是近年来制备低成本高性能SiAION陶瓷材料的一种实用方法．具有产业化生产潜力。本文对碳热还原氮化法制备SiAION的进展进行了综述,归纳分析了不同条件对生成物性能的影响,对今后的研究进行了展望。     

非水解溶胶-凝胶碳热还原氮化法制备TiN粉体研究

首先,以四氯化钛为原料,异丙醚为氧供体,二氯甲烷为溶剂,采用非水解溶胶凝胶法合成高活性的TiO2凝胶;其次以其为钛源,选用分子量为1300000的聚乙烯吡咯烷酮为碳源,采用碳热还原氮化法合成TiN粉体。X射线衍射仪、场发射扫描电镜和激光粒度仪测试结果表明,与水解法相比,采用非水解法合成的TiO2凝胶经800℃煅烧0．5h仍为活性较高的锐钛矿相,以该凝胶为钛源,经1200℃碳热还原氮化2h可合成纯度相对较高的TiN粉体,将合成温度升至1300℃还原氮化5h可合成更高纯度的TiN粉体。TiN粉体颗粒呈近似球形,发育较好,粒径在1μm以下,激光粒度测定粒径主要集中在10μm左右,d50为8μm。     

Preparation and Microstructure of Bauxite-Based Sialon by Reduction Nitridation

The phase composition and microstructure of Sialon prepared from Chinese bauxite have been studied. The use of Si powder is more effective than that of activated carbon for reduction-nitridation. For bauxite specimens with 40～50% Si addition, more than 90% of Sialon may be obtained when nitrided at 1450～1500℃ ; the main crystalline phase is O‘-Sialon ( Z =0.2).     

Al粉氮化制备超细AlN粉

以Al粉和C粉为原料,经球磨、干燥后在1400℃氮气气氛中氮化.氮化产物于650℃煅烧脱碳,制备出粒度为50nm左右的超细AlN粉.用SEM、TEM观察AlN粉的形貌.碳黑的高活性是形成无团聚纳米AlN粉的原因.     

Reaction Synthesis of Aluminum Nitride–Boron Nitride Composites Based on the Nitridation of Aluminum Boride

Aluminum nitride–boron nitride (AlN–BN) composites were prepared based on the nitridation of aluminum boride (AlB₂). AlN powder was added to change the BN volume fraction in the obtained composites. Thermogravimetry–differential thermal analysis (TG-DTA), X-ray diffractometry, and the nitridation ratio were used to investigate the nitridation process of AlB₂. At ∼1000°C, a sharp exothermic peak occurred in the DTA curve, corresponding to the rapid nitridation of aluminum in AlB₂. On the other hand, the nitridation of the transient phase, Al_1.67B₂₂, was very slow when the temperature was <1400°C. However, the nitridation speed obviously accelerated at temperatures >1600°C. The pressure of the nitrogen atmosphere was also an important factor; high nitrogen pressure remarkably promoted nitridation. Treatment at 2000°C was disadvantageous for nitridation, because of the rapid formation of a dense surface layer that inhibited nitrogen diffusion into the specimen interior. Three specimens, with 5 wt% Y₂O₃ additive and different BN contents, were prepared by pressureless reactive sintering, according to the determined sintering schedule. Electron microscopy (scanning and transmission) observations revealed that the in-situ -formed BN flakes were homogeneously and isotropically distributed in the AlN matrix. A schematic mechanism for microstructural formation was developed, based on the results of nitridation and the microstructural features of the obtained composites. The obtained composites, with a low BN content, exhibited a high bending strength, comparable to that of reported hot-pressed AlN–BN composites.     

天然原料碳热还原氮化合成β''''-SiAlON的研究进展

本文介绍β'-SiAlON的结构、基本性能及应用领域,阐述了合成β'-SiAlON的原材料和各种合成方法,重点介绍了利用天然原料合成β'-SiAlON的还原剂外加法和还原剂内加法即有机插层法.详细阐述了各工艺条件(反应原料的组成、反应温度、反应时间、反应气氛、流速及反应物颗粒尺寸、添加剂等)对合成β'-SiAlON反应结果的影响.同时本文指出目前该研究可能存在的问题及解决的途径.     

Aluminum Nitride Fibers Synthesized from Alumina Fibers Using Gas-Reduction–Nitridation Method

Aluminum nitride fibers were successfully synthesized from alumina fibers using an NH₃–C₃H₈gas mixture as a reduction–nitridation agent. Observation using SEM clearly demonstrated that the morphology of the nitrided fibers was exactly the same as that of the raw alumina fibers, retaining the original regular shape and smooth surface. Up to 95% of the starting alumina was converted to aluminum nitride at 1400°C within 0.5 h via a single-step synthesis process.     

Thermodynamics of Vapor Synthesis of AlN by Nitridation of Aluminum and Its Halides

A thermodynamic analysis for the vapor synthesis of AlN is presented. A thermodynamic equilibrium computer code and recent thermochemical tables are used to evaluate various reactant gases for their potential to produce high-purity AlN at high yields. The Al/N/H/X/Y systems are examined, where X is any halide atom and Y is an inert gas. The effects of reactant ratio, temperature, and pressure on reactant conversion and product purity are estimated. Results from two systems are presented in the form of design diagrams, which represent the phases formed and the conversion achieved at various process conditions.     

叶蜡石在碳热还原氮化过程中的相变

研究了叶蜡石在不同温度下碳热还原氮化合成SiAlON过程中的相变。SEM、XRD以及EDS分析结果表明 :130 0℃开始氮化形成O’ SiAlON ,14 0 0℃时O’ SiAlON的XRD峰已经很明显 ,14 5 0℃时O’ SiAlON大量生成并在 15 0 0℃时达到最大值 ;14 5 0℃时开始形成β SiAlON(z=2 )和少量SiC ;15 5 0℃时 ,β SiAlON成为主要的氮化产物 ,与少量的O’ SiAlON并存 ;莫来石和方石英直到 15 0 0℃仍然存在 ,15 5 0℃消失。     

铝源对碳热还原氮化法制备AIN粉末的影响

本文用无机铝盐借助溶胶-凝胶工艺和表面活性剂的作用制得了一种铝碳良好结合、均匀、无(或弱)团聚的混合凝胶细粉(文中简称“均质混料”),以此为原料氮化合成了纯度达98%的超细AIN粉末,文中着重分析了使用这种均质混料能降低合成条件、提高粉末性能的热力学机制,探讨了影响合成过程的诸因素,最后得出结论认为:铝凝胶均质混料的制备和使用是改进成热还原氮化工艺的最有效途径。     

Hollow Beads Composed of Nanosize Ca α-SiAlON Grains

Carbothermal reduction—nitridation (CRN) of SiO₂ is an attractive method to manufacture Si₃N₄ powders with controlled grain morphology. Moreover, β-SiAlON powders could also be synthesized from either pure powder mixture or some inexpensive raw minerals by CRN and the resulting powders favored the sintering of SiAlON product. However, there have been few works on preparing α-SiAlON powders so far. In this work, Ca α-SiAlON powder was synthesized by CRN of a SiO₂—Al₂O₃—CaCO₃ mixture. An unusual morphology of hollow beads 200 to 500 nm in diameter with a great deal of nanosize α-SiAlON particles around 10 to 30 nm in diameter was observed from the resultant Ca α-SiAlON powders, which has not been reported for SiAlON ceramics before.     

低品位铝土矿合成β-SiAlON的相变过程研究

采用XRD、SEM和EDS等手段 ,研究了低品位铝土矿碳热还原氮化合成SiAlON过程的相变。结果表明 :130 0℃开始氮化 ,形成Si2 N2 O和X SiAlON ;14 0 0℃开始形成 β SiAlON (z =3) ,X相明显增加 ;14 5 0℃时 ,β SiAlON (z =3)成为主要的氮化产物 ,并与少量的Si3 N4和刚玉并存 ;15 0 0℃开始形成 15R ,同时 ,β SiAlON的z值开始由 3变为 4 ;15 5 0℃时 ,15R和 β SiAlON成为主要物相 ,同时含有部分刚玉相和Si3 N4相。 14 5 0℃时 ,由低品位铝土矿合成纯净的 β SiAlON复合少量刚玉相粉体材料的最佳保温时间是 6～ 9h ,时间过短则含有较多的X相 ;时间过长则发生过量氮化 ,形成部分 15R和少量Si3 N4。