碳热还原法合成ALON粉体的研究

本文以γ-Al_2O_3和活性碳为原料,采用碳热还原法合成高纯超细γ-ALON粉.并以γ-Al_2O_3和碳粉的配比、合成温度、保温时间以及除碳等方面分别探讨了碳热还原法合成γ-ALON粉的适宜工艺条件;通过对合成粉料的XRD、SEM分析,表明该方法合成的ALON粉晶形发育完善、粒度均匀、纯度高.     

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.     

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。     

Preparation of Spherical AlN Granules Directly by Carbothermal Reduction–Nitridation Method

In this work, an efficient carbothermal reduction–nitridation strategy was rationally designed and delicately tailored to directly synthesize spherical granules of aluminum nitride. Effects of processing parameters, such as N₂ pressure, additives and temperature on the nitridation ratio, especially on the morphologies of the AlN granules were elaborately investigated. The experimental results showed that the elevated N₂ pressure of 0.9 MPa and additives of CaF₂ and Y₂O₃ greatly favored for forming micrometer‐sized AlN granules with smooth spherical appearance. More significantly, the underlying formation mechanism of spherical morphology and large particle size was also attentively put forward.     

Preparation of Aluminum Oxynitride by Nitridation of a Precursor Derived from Aluminum–Glycine Gel and the Effects of the Presence of Europium

Spinel-type AlON, Al_2.75□_0.25O_3.74N_0.26, was obtained by ammonia nitridation of an oxide precursor prepared by peptizing a glycine gel with aluminum nitrate. To achieve crystallization, the nitrided product had to be annealed at 1500°C for 10 min in flowing nitrogen. The use of glycine instead of citric acid was important for obtaining a white product without residual carbon. A similar preparation method was used for adding small amounts of europium below 10 mol%. A strong blue emission was observed for products ranging from 0.5 to 3.0 mol% Eu doping. The product with 0.5 mol% doping had a maximum emission intensity at 400 nm for an excitation of 254 nm. The products with 1 and 3 mol% doping showed double maxima at 475 and 520 nm. These three emissions were due to the presence of divalent europium in the EuAl₁₂O₁₉ magnetoplumbite-like aluminum oxynitride impurity mixed with the AlON spinel major phase. The 1 mol% Eu-doped product exhibited expanded hexagonal lattice parameters ( a =0.5591 and c =2.236 nm) compared with the values for EuAl₁₂O₁₉ magnetoplumbite itself, observed in the 7.7 mol%-doped product without any strong emission. The above spectrum change was discussed in relation to the coordination around Eu²⁺.     

Silicon-Free Oxynitride Glasses Via Nitridation of Aluminate Glassmelts

Aluminate-oxynitride glasses were synthesized by melting calcium-aluminate-based compositions with various amounts of AlN in a nitrogen atmosphere. X-ray amorphous Ca-Al-Mg-Ba-O-N oxynitride glasses free of metallic inclusions containing up to ∼1 at. % N were obtained. Nitride additions increased the glass transition temperatures while decreasing thermal expansion, as in other Sicontaining oxynitride systems.     

Preparation of Aluminum Nitride–Silicon Carbide Nanocomposite Powder by the Nitridation of Aluminum Silicon Carbide

Aluminum nitride (AlN)–silicon carbide (SiC) nanocomposite powders were prepared by the nitridation of aluminum-silicon carbide (Al₄SiC₄) with the specific surface area of 15.5 m²·g⁻¹. The powders nitrided at and above 1400°C for 3 h contained the 2H-phases which consisted of AlN-rich and SiC-rich phases. The formation of homogeneous solid solution proceeded with increasing nitridation temperature from 1400° up to 1500°C. The specific surface area of the AlN–SiC powder nitrided at 1500°C for 3 h was 19.5 m²·g⁻¹, whereas the primary particle size (assuming spherical particles) was estimated to be ∼100 nm.     

Phase Relations and Reaction Sintering of Transparent Cubic Aluminum Oxynitride Spinel (ALON)

A new isobaric, condensed phase diagram in the region of stability of cubic aluminum oxynitride spinel (ALON) along the pseudobinary AI₂O₃-AIN composition join is presented, deduced primarily from various analytical measurements and microstructural observations. It is shown that cubic aluminum oxynitride spinel melts incongruently at ≊2050°C and is compositionally centered at ≊35.7 mol% AIN, which is equivalent to the following stoichiometric composition: AI₂₃O₂₇N₅ or 5AIN·9AI₂O₃. Single-phase ALON material sintered to nearly full density exhibits transparency in visible light.     

真空下碳热还原法制备碳氧化铝及其形成机制

研究了真空下在1300～1500℃通过氧化铝碳热还原法制备碳氧化铝.结果表明:真空下氧化铝碳热还原法制备碳氧化铝所需的温度明显低于氩气下,1300℃即开始大量生成Al4O4C.形成的冷凝产物均以Al4O4C为主,与原料的反应完全程度无关.最佳制备条件为:n(α-Al2O3):n(C)=2:3,1400℃、20 min时...     

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.     

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.     

Rapid Synthesis of Finely Dispersed Sialon Powder by Carbothermal Nitridation of Kaolin

A powder based on -sialon is prepared by carbothermal nitridation. A scheme for rapid synthesis of -sialon with controlled dispersity at high temperature is developed. The critical size range of -sialon particles is determined. Experimental data on phase composition and particle size of the synthetic sialon powders are in agreement with theory.     

碳热还原法合成AIN粉末的径向反应器设计

本文将传质原理与化学反应动力学相结合,导出了氮气流量与碳热还原法合成AIN反应速率之间的关系。基于动量守恒定律分析了径向反应器内部气体压力及其分布的规律,提出了气体在反应器内均匀分布的条件和反应器选型准则。根据这些条件和准则设计了合成AIN粉末的径向反应器。实验结果显示AIN的转化率及颗粒度在径向反应器内均匀分布,且产率高于平底状反应器。这一结果证明反应器设计合理,径向反应器比平底状反应器有更好的传质效果。     

碳热还原氮化法合成氮化钒/氮化铬复合粉末

以纳米V_2O_5、纳米Cr_2O_3和纳米碳黑为原料,经过干燥、球磨混料后,在流动氮气中焙烧,得到了氮化钒/氮化铬(VN/CrN)复合粉末。利用XRD、TG-DSC、SEM、BET和TEM对合成产物进行了表征和测试,考察了反应温度和保温时间对VN/CrN复合粉末的微观结构和性能的影响。结果表明:在1 200℃、保温2 h条件下,可制备出平均晶粒直径为40 nm的VN/CrN复合粉末。该复合粉末主要由VN、CrN和VCrN_2组成,这3种物质均为面心立方结构,空间群均属于Fm3m。复合粉末的比表面积为21.09 m~2/g。将复合粉末作为添加剂加入到陶瓷磨具结合剂中进行性能测试,结果显示:当w(复合粉末)=0.2%时,陶瓷磨具结合剂抗折强度和流动性分别提高约20%和50%;当w(复合粉末)=1.0%时,其抗折强度和流动性均达到最大值115.6 MPa和207.2%。     

Thermodynamic Analysis for Carbothermal Reduction and Nitridation of TiO2

The diagrams of stability relations(namely,Predominance area phase diagram,PAPD)of nitride,carbide and oxides in Ti-C-N-O system were plotted by thermodynamic calculation.The optimum conditions and main influence factors for the synthesis of titanium nitride and titanium carbide by carbothermal reduction in nitrogen atmosphere were discussed.     

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...     

水热法制备超细球形氧化铝粉体

以较为经济的水合硫酸铝为铝源,尿素为沉淀剂,利用水热法在内胆为聚四氟乙烯的水热釜中制备氧化铝前驱体,然后将烘干后的前驱体进行高温煅烧,制得超细球形氧化铝粉体.重点探究了水热反应温度、反应时间对产物微观形貌及粒度的影响,并对氧化铝粉体煅烧前后的微观形貌进行了对比.实验结果表明:前驱体的形貌具有遗传性;在水热反应温度120...     

Characterization of Sinterable Oxide Powders: I, BeO

The discovery of readily sinterable BeO powder facilitated the production of dense, high-strength BeO ceramics and created interest in the properties and preparation of sinterable BeO. BeO powders prepared by the thermal decomposition of Be(OH)₂ were studied in an effort to relate sinterability with other more basic characteristics of the oxide powder. Different BeO powders made from analyzed hydroxides showed a wide range of sinterability. The temperatures required for sintering the powder compacts to theoretical density ranged from 2300° to above 3200°F. Lattice parameters, thermal decomposition, surface areas, and refractive indices were determined on these powders after calcination in air at 750°, 1470°, 1830°, and 2190°F. Although unexpected variations in these properties were observed, no simple relation with sinterability was found. Occluded and surface impurities appeared to have a critical effect on sintering behavior.