Aluminum nitride by microwave-assisted synthesis: Effect of added ammonium chloride

Hexagonal aluminum nitride (AlN) crystals were synthesized by microwave method with ammonium chloride used as an additive. Starting mixtures consisted of Al powder, NH₄Cl, and urea as a fuel taken in a 1: 3: 1 ratio. The microwave oven operated at 630 W, the synthesis time was 10, 30, 60, and 120 min. The results showed that the pure AlN powder with regular and fine grains could be obtained in 30 min. The synthesized powders were characterized by TGA/DTA, XRD, FT-IR, UV-VIS, SEM, and TEM.     

氮化铝粉末的制备及扩大实验研究

主要进行了碳热还原法制备氮化铝粉末扩大实验研究。研究了不同的铝源、碳源、氮化温度、保温时间、添加剂对合成氮化铝粉末的影响,并采用XRD、SEM、化学物理分析等手段对中试实验制备的氮化铝粉末进行分析。研究结果表明,采用经砂磨处理的铝源B（α-Al₂O₃）和3^#碳源（乙炔黑）为原料,有助于碳热还原反应;采用添加剂C可以降低反应活化能,提高氮化率;造粒工艺有助于扩大实验的碳热还原反应。     

含添加剂沸石分子筛混合吸附剂物理特性及其制冷应用性能

为改善吸附剂用于吸附制冷的传热传质性能,以微米级铁粉、铝粉和非金属膨胀石墨为添加剂,制备了8 种不同烧结型13X 沸石分子筛(包括粉末型和颗粒型)混合吸附剂,对其进行了SEM 观察以及热导率、吸附等 温线、孔径分布等物性的测量与表征分析。结果显示,添加剂为膨胀石墨的粉末型分子筛微粒之间的紧密型最 好,接触面积最大;添加剂为铝粉的粉末型分子筛热导率和热扩散系数最高,相比纯组分颗粒型分子筛的分别 提高了100.9%和315.6%,添加剂为铁粉的粉末型分子筛比热容最低,相比纯组分颗粒型分子筛的降低了33.9%; 加入添加剂的粉末型和颗粒型分子筛的比表面积和孔隙率都有不同程度的降低,其顺序由高到低均为膨胀石墨、铝粉、铁粉。将制备的各种混合吸附剂应用于吸附制冷单元管进行实验测试,讨论分析了其循环周期、制冷量、COP 和SCP 等性能指标的改进与吸附剂物性改变之间的内在联系。     

A review: 3D printing of microwave absorption ceramics

Along with extensive research on the 3D printing and microwave absorption ceramics, 3D printing technology provides a great possibility for microwave absorption ceramics with arbitrary shapes in a faster, cheaper and more flexible way. This review focuses on the latest evolution in the raw materials, the structure design and the advanced additive manufacturing technologies of 3D printing microwave absorption ceramics. Firstly, the representative raw materials are divided into three categories, including ceramic powder, cermet powder and precursor resin. In addition, additives give rise to improvement of microwave absorption properties of ceramics. Secondly, based on two attenuation theories, structure design makes further efforts to enhance the microwave absorption performance of ceramics. Finally, comparisons are made between diversified manufacturing technologies to facilitate the selection of the best ones for different application in practical use. This study presents a summary of research that has been conducted to produce microwave absorption ceramics by additive manufacturing.     

Smoothing the electromagnetic heating pattern in polymers

In the production of polymers, particles and fibers are often added for coloring and/or improvement of mechanical, electrical, and thermal properties. Carefully choosing the electrical properties and size of these additives can allow manipulation of the electrical properties of the composite so that the material can then be heated in both the electric and magnetic fields. Heating can be induced by fields at microwave frequences, where the electric and magnetic fields tend to be concentrated in different regions, or by fields that are quasistatic. These features add a degree of freedom in smoothing the total heating pattern. Models for predicting the electrical properties with the addition of particles or fibers are developed and verified experimentally. Engineering guidelines are established in choosing the electrical properties and size of the additives. Experimentally, a rectangular cavity at 2.45 GHz is used to heat a casting resin with a 5.7 micrometer aluminum powder additive, demonstrating the dramatic smoothing in the heating, pattern made possible by using these additives. Some examples are also suggested to indicate the use of this technique in quasistatic heating configurations.     

Influence of Additives on Suppression of Racemization in Peptide Synthesis. V. Additives Based on Liquid Crystal Forming Structure Elements for Suppressing Racemization in Reptide Synthesis by the DCC- and Mixed Anhydrides Methods

A new type of additives suppressing racemization during peptide synthesis by the DCC- and mixed anhydrides methods are liquid crystal forming organic molecules or similar compounds with a specific long chain structure. The suppressing effect of the new additives was followed by the Anderson test, the modified Young and n.m.r. tests. There was no racemization in a new Leu-enkephalin synthesis by the mixed anhydrides method with azoxybenzene as additive.     

Microwave Synthesis of Corundum Materials with Various Densities

Materials with various densities obtained by high-temperature microwave synthesis from aluminum oxide powders with various grain sizes and prehistories, which are modified by additives of radio-transparent and radio-absorbing substances, are described. The process of high-temperature consolidation of the initial particles by a welding mechanism provides a high level of strength in the materials.     

Novel Way to Synthesize Nanocrystalline Aluminum Nitride from Coarse Aluminum Powder

A new process has been developed for the synthesis of nanocrystalline AlN powder by the nitridation of coarse aluminum powder in flowing NH₃ gas, using NH₄Cl and KCl as additives. The resulting powders have been characterized using XRD, TEM, and XRF techniques. XRD-pure AlN nanoparticles with a diameter of 10–20 nm can be obtained by nitridation at 1273 K for 5 h. NH₃ is proved to eliminate the effect of water impurity. The effects of the additives on the conversion of aluminum are also discussed.     

Sintering Behavior of Fine Aluminum Nitride Powder Synthesized from Aluminum Polynuclear Complexes

The sintering behavior of fine AIN powder synthesized from an aluminum polynuclear complex was investigated. The focus of this work was to investigate the densification behavior of the AIN powder with different particle sizes (specific surface area: 3.2–22.8 m²/g). The AIN powder was synthesized from basic aluminum chloride and glucose mixed in a water solution. This powder was divided into two groups: one with 2 wt% Y₂O₃ added as the sintering aid and the other without such an additive. The AIN powder investigated possessed favorable densification potential. The density of the AIN powder with a surface area of 16.6 m²/g and without additives attained theoretical density at 1700°C. Adding Y₂O₃ further decreased the sintering temperature required for full densification to 1600°C. It is speculated that low-temperature sintering of our fine AIN powder with Y₂O₃ proceeds in two steps: in the initial stage, sintering proceeds predominantly through interdiffusion between yttrium aluminates formed on the AIN powder surface; in the second stage, the densification may occur by the interdiffusion between solid phases formed by a reaction between the yttrium aluminates and AIN. To investigate the effect of oxygen on sintering, the content of oxygen in AIN powder was varied while the particle size was kept constant. In this study, the difference in surface oxygen content scarcely affected the sintering behavior of fine AIN powder.     

Mechanochemical sulfidization of a mixed oxide-sulphide copper ore by co-grinding with sulfur and its effect on the flotation efficiency

Mechanochemical sulfidization of a mixed sulfide/oxide copper ore by co-grinding with sulfur and additives including Mg(NO₃)₂ and Fe(NO₃)₃ salts and iron, aluminum and magnesium powders was investigated for the first time. Also, the influence of sulfidization during the wet-milling process was examined on the separation efficiency and recovery of copper in detail. The results demonstrated that co-grinding with sulfur solely had the best flotation performance at the value of 0.5 wt.% and it was attributed to the possible existence of S-O bonding on copper oxides surfaces. In addition, adding magnesium nitrate salt, magnesium powder, iron nitrate salt and aluminum powder as additive associated with 0.5 wt% sulfur into ball milling caused the flotation improvement at the amounts of 0.2 wt%, 0.2 wt%, 0.5 wt% and 0.5 wt%, respectively. Also, the effect of grinding time and sulfidization pH with 0.5 wt% sulfur solely was determined and pHs of 7.5 to 8.5 gave the best results. The highest recovery (75.76%) and separation efficiency (63.44%) were achieved at pH of 7.5 and 8.5, respectively.     

Self-Propagating High-Temperature Synthesis of Aluminum Nitride under Lower Nitrogen Pressures

The synthesis of aluminum nitride (AlN) via self-propagating high-temperature synthesis (SHS) was attempted, using aluminum powder that was mixed with AlN powder as a diluent. The AlN content in the reactant was varied over a range of 30%–70%, and the nitrogen pressure was varied over a range of 0.1–1.0 MPa. The SHS reaction that was performed using a reactant that contained 50% AlN diluent, under a nitrogen-gas pressure of 0.8 MPa, yielded the highest conversion ratio of aluminum powder to AlN powder. A mechanism for the reaction of aluminum with nitrogen gas during the SHS process was discussed, based on observations of the microstructures of the reaction zone and products.     

Influence of additives on combustion of ultradisperse aluminum powder and chemical binding of air nitrogen

Experimental results are presented on combustion in air of ultradisperse aluminum powder with additives of ultradisperse powders of copper, nickel, iron, tin, silicon, graphite, boron, tungsten, and molybdenum.X-Ray diffraction and chemical analyses were used to study the composition of the end products. A tin additive has an inhibiting action on the chemical combining of air nitrogen as aluminum nitride and oxynitride, whereas iron, tungsten, and molybdenum additives favor an increase in nitrogen content. As is established, the influence of additives on the processes determining the duration of two combustion stages is greater than on the content of bound nitrogen in the products.Translated from Fizika Goreniya i Vzryva, Vol. 32, No. 2, pp. 108–110, March–April, 1996.     

Synthesis of aluminomagnesian spinel with excess magnesium oxide under varying flow rates of cation mass transfer

The synthesis of MgAl₂O₄ with 10 mol. % excess of MgO by heating a mixture of highly dispersed magnesium and aluminum oxide powders to 800 and 1100°C is investigated. The diffusion mass transfer rate of aluminum cations in the synthesis of spinel was accelerated by introducing a TiO₂ additive into Al₂O₃, whereas the mass transfer rate of magnesium cations was delayed by introducing a Na₂O additive into MgO. Simultaneously, spinel was synthesized without additives. The products of synthesis were investigated using petrography, x-ray phase analysis, and dissolution in HCl. The use of the additives and increasing the temperature of synthesis decrease the solubility of powders in HCl, which facilitates bringing initially formed solid solutions of Al₂O₃ in MgAl₂O₄ closer to the composition of stoichiometric spinel. __________ Translated from Steklo i Keramika, No. 2, pp. 14–19, February, 2006.     

影响新拌高铝浇注料浆体触变性的因素

以特级高铝矾土细粉为原料 ,纯铝酸钙水泥为结合剂 ,三聚磷酸钠或六偏磷酸钠为添加剂 ,配制了高铝浇注料浆体 ,并采用旋转粘度计测量了新拌浆体的剪切应力 ,定量地计算了其触变性的大小。结果表明 :水泥品种、添加剂的种类及其加入量对浆体的流变性均有较大影响 ,添加剂加入量过多或过少 ,浆体的触变性均较大 ,流变性较差。     

水性汽车金属闪光底色漆的制备及性能

采用核壳结构的丙烯酸乳液作为成膜树脂,与非浮型水性铝粉颜料、各种涂料助剂等制备出一种汽车涂料用的水性金属闪光底色漆,介绍了水性金属闪光漆的配方及各项技术指标,讨论了成膜树脂、铝粉、助剂、成膜助剂及施工工艺的选择。结果表明,将核壳结构的丙烯酸乳液引入金属闪光体系,可以有效地减少金属漆中粒子的沉降,提高了体系的稳定性和各项涂膜性能。本项目研制的水性汽车金属闪光漆能满足合同规定的指标要求,而且具有良好的施工性能。     

Effect of catalytic additives and aluminum particle size on the combustion of mixed compositions with a chlorine-free oxidizer

Experimental results on the stationary burning rate and solid content in the combustion products of mixed compositions with a chlorine-free oxidizer and an active fuel binder in the pressure range 0.025–6.0 MPa are presented. The effect of catalytic additives (silica and carbon black), the particle size of aluminum powder, and the method of preparing samples for combustion of the mixed compositions under consideration are analyzed.     

Combustion synthesis of β-SiAlON from a mixture of aluminum ferrosilicon and kaolin with nitrogen-containing additives using acid enrichment

In the work, single-phase β-SiAlON was prepared from a powder mixture based on aluminum ferrosilicon and aluminosilicate (kaolin) with nitrogen-containing additives (product of nitriding of the starting mixture and NH₄F) by combustion synthesis followed by acid enrichment of the synthesized product. Self-propagating combustion synthesis was conducted under natural nitrogen filtration. The synthesis parameters (nitrogen pressure, sample diameter, density of the starting mixture) and the conditions of acid enrichment of the synthesized products (acid concentration, temperature of acid enrichment and dispersion of the starting powder) were determined. After acid enrichment of the synthesized product, which contained β-SiAlON and α-Fe phases, the phase content of β-SiAlON was 99.5 wt%.     

磷酸盐陶瓷添加剂的生产工艺开发

介绍磷酸盐乳浊剂和骨粉两种磷酸盐陶瓷添加剂的生产技术。两种添加剂的组成为磷酸根和钙离子,采用湿法合成代替热法解决了生产中钙、磷反应不完全,产品质量不稳定的问题,降低了成本,并用于陶瓷生产。     

AIN陶瓷烧结技术研究进展

氮化铝（AIN）因其具有高热导率，作为基片材料在电子元器件中得到日益重视。本文主要论述了氮化铝陶瓷制备过程中各种烧结参数，包括烧结助剂、烧结气氛、保温时间、常压烧结、热压烧结、微波烧结和等离子烧结等对氮化铝陶瓷性能的影响。并指出可通过合适的AIN粉体制备技术，结合快速烧结方法可得到具有晶粒细小、结构均匀、高致密度和高导热率的AIN陶瓷。     

Laser initiation of low-density mixtures of PETN with metal additives

This paper presents data on laser initiation of low-density mixtures of PETN with metal additives with varying dispersity of PETN and particle size of the additive. A laser with a wavelength of 1.06 μm and a pulse length of 40 and 30 ns was used. Curves of the threshold initiation parameters on the additive content are shown to have minima. For coarse additives, no significant dependence of the initiation threshold of the mixtures on the nature of the metal at its optimal content (except for aluminum) was observed. For PETN mixtures with an optimal amount of fine aluminum, a significantly greater (a factor of 6.2) decrease in the threshold initiation parameters compared to direct initiation of PETN was found. It is shown that the initiation thresholds of the mixtures do not depend on the dispersity of PETN with the optimal additive content. Increasing the dispersity of PETN extends the dependences of the threshold parameters on the additive content while the optimal additive content is shifted to higher values. The initiation thresholds are found to strongly depend on the density of the mixture charge. The key points of the mechanism of laser initiation of PETN mixtures with additives are formulated.