自蔓延燃烧法制备AlN陶瓷粉体的研究进展

概述了自蔓延燃烧法(Self-propagating high-temperature synthesis,简称SHS)制备氮化铝(A1N)粉体的原理及方法.重点综述了纳米A1N陶瓷粉体的最新制备工艺研究进展,并对SHS法制备A1N粉体的发展进行了展望.     

Microwave Synthesis of Yttrium Iron Garnet Powder

A 28 GHz microwave heating method was used to react an Fe₂O₃+ Y₂O₃ powder mixture to form yttrium iron garnet (YIG, Y₃Fe₅O₁₂) powder. The minimum temperature to form YIG was lower than the conventional (external) heating method. YIG began to form after only 70 s of irradiation, which means that the solid-state reaction proceeded very rapidly. The amounts of byproducts were controlled by the starting composition and by the Y₂O₃ particle size. The resultant YIG particle size also was controlled by the Y₂O₃ particle size.     

微波辅助Sol-Gel法合成Na-β″-Al2O3电解质粉末

传统制备Na-β″-Al2O3（SBA）固体电解质主要采用固相合成法，需要极高的烧结温度（1873K）和极长的反应时间（30h）。长时间的高温下有效成分Na2O很容易挥发掉，这对使用SBA作为固体电解质的钠硫电池是非常有害的。微波烧结具有升温速率快、反应时间短和体加热等显著特点，能解决传统烧结带来的问题。本实验采用微波辅助Sol—Gel法合成Na-β″-Al2O3电解质粉末，实验表明制备出的凝胶在一定温度下预烧成粉末后具有很好的微波吸收能力。粉末经1323K预烧1h，微波处理30min后几乎全部为Na-β″-Al2O3。     

Zn掺杂BaTiO3微粉的微波水热合成

以钛酸丁酯、硝酸钡和醋酸锌为原料,采用微波水热法制备了掺锌的BaTiO3微粉。利用XRD和SEM对产物进行了表征。研究表明,掺杂后锌固溶到了钛酸钡的晶格中并取代钡位或钛位。微波水热合成锌掺杂钛酸钡微粉温度更低,同时反应速率明显提高。     

pH值对AlN粉末水解产物的影响

通过测定500nm的氮化铝粉末在不同pH值下的水解行为,利用XRD、SEM和TEM分析研究了氮化铝粉末的水解产物。结果表明,在pH=12环境下水解产物为纳米纤维状,在Ph=7环境下水解产物为短棒状,在pH=5环境下水解受到抑制。XDR表明,在80℃下水解时,AlN粉末的水解产物为AlOOH。SEM和TEM表明,在pH=5环境AlN形成了一个保护层,在pH=12环境下时,氨水会使水解产物形成团聚。     

微波介质陶瓷的研究进展及其粉末合成方法

在现代通讯技术中,微波介质陶瓷是其微波通信电路中谐振器、滤波器、振荡器等重要元件的关键基础材料,它的研究越来越受到人们的重视.本文介绍了低介电常数、中介电常数、高介电常数三类微波介质陶瓷的研究现状,总结了其粉末制备的新方法.     

Using Nanoscaled Powder as an Additive in Coarse-Grained Powder

Nanoscaled Al₂O₃ powder is used as additive in coarse-grained Al₂O₃ green bodies. Its influence on the green density is investigated. The potential effect of powder mixing on the green density is described by a model for multimodal powder mixtures that predicts the powder composition for maximum green body density. The model is applied to bimodal and trimodal mixtures with one of the components being nano-powder. The calculated relative densities are compared with experimental results. Furthermore, sintering experiments are conducted to investigate the influence of the amount of nanoscaled powder on the sintered densities of bimodal bodies.     

微波法制备氧化镁粉体工艺研究

以草酸铵和氯化镁为主要原料,利用热分解和微波辅助煅烧草酸镁制备氧化镁粉体,研究了微波功率、微波辐射时间对草酸镁分解率的影响,并通过X射线衍射对制得的氧化镁粉体进行表征;结果表明微波辅助加热具有时间短,粉体结晶度好的优点.     

Effects of Transition-Metal Additions on the Properties of AlN

Transition-metal oxide additions to AlN ceramics produced no significant deterioration in thermal conductivity. In the present study, TiN, ZrN, TaC, NbC, W, and unidentified Hf phases, found as fine particles located inter- and intragranularly, were distributed randomly in the AlN. Phases containing Fe, Co, and Cr, on the contrary, always were located at the three grain points. Most of the added transition-metal compounds turned the ceramics black or gray. The shading mechanism was attributed to optical absorption by the surfaces of the electrically conductive fine particles and to multiple reflections among these particles.     

Synthesis of AlN Powder by Carbothermal Reduction-Nitridation of Various Al2O3 Powders with CaF2

We investigated the effect of characteristics of raw Al₂O₃ powder on the synthesis of AlN by the carbothermal reduction-nitridation method, in which CaF₂ was added as a catalytic material. Four types of Al₂O₃ powders were selected. An Al₂O₃/C molar ratio of 0.29 was fixed, and the amount of CaF₂ was varied from 3 to 30 wt%. The carbothermal reduction-nitridation was conducted from 1350° to 1450°C in N₂ flow. The nitridation rate tended to increase with decreasing particle size of raw Al₂O₃ and was found to depend on the Al₂O₃ synthesizing method. The particle sizes of the synthesized AlN increased somewhat with increasing reaction temperatures. However, even though different particle sizes of Al₂O₃ powders were used, AlN powders synthesized under the same conditions exhibited almost the same particle size, round shape, and narrow size distribution. From XRD analysis, CaO·6Al₂O₃ and CaO·2Al₂O₃ were identified as intermediate compounds during these reactions. The above phenomena suggest that the synthesis mechanism of AlN powder by carbothermal reduction-nitridation of Al₂O₃ with CaF₂ addition was the nitridation of the intermediate compounds through the liquid phase of the system CaF₂-CaO·6Al₂O₃-CaO·2Al₂O₃.     

微波辐射合成多功能腐植酸-马来酸酐共聚物陶瓷添加剂

采用微波辐射技术,以天然有机质钠盐腐植酸钠(NaHA)为原料,以马来酸酐(MA)为改性单体,通过自由基共聚合制备了新型腐植酸钠-马来酸酐共聚物(NaHA-co-MA)陶瓷添加剂。探讨了引发剂种类对陶瓷泥浆流动性的影响,确定硝酸铈铵为最有效引发剂。通过正交试验得到最佳合成条件为引发剂用量0.04%(质量分数)、NaHA与MA质量比1.2∶1.0、微波功率320W、间歇辐射时间15min、聚合后中和程度pH为7.5,此时陶瓷泥浆的相对黏度为1.34,流动性最好。采用红外光谱分析及坯体强度、可塑性测试等手段对NaHA-co-MA结构和性能进行分析:红外光谱显示NaHA结构中的-OH为与MA接枝共聚的活性点;坯体强度和可塑性试验表明,当NaHA-co-MA添加量为基体的0.08%(质量分数)时,坯体的干燥强度达4.16mPa,可塑性指标为5.49kg.cm,经与NaHA比较,综合性能有较大提高。     

Microwave Drying of Multi-component Powder Systems

Abstract

The rate of uptake of microwave technology within the pharmaceutical sector has been slow due to stringent regulatory procedures and unsuccessful microwave trials. However, microwave systems offer significant energy and time savings compared with conventional dryers. Common pharmaceutical excipients, lactose, stearic acid, and active ingredients, Aspirin, Paracetamol, were wetted with water and dried within an experimental atmospheric microwave drying system (2.45 GHz, 90 W). The drying curves obtained showed a constant drying rate, followed by two falling rate periods. Two- and three-component mixtures were dried under the same conditions. The drying characteristics were found to lie between those of the pure components. Drying kinetics of samples wetted with a range of solvents (methanol, ethanol, acetone), and two-component solvent mixtures, were examined. The relative evaporation rates of the solvents showed some dependence on their dielectric properties; latent heat of vaporisation and boiling point having greater influence on drying characteristics. Clearly this research provides information vital to achieve increased acceptance of this technology within the pharmaceutical industry.     

Microwave Drying of Multi-component Powder Systems

The rate of uptake of microwave technology within the pharmaceutical sector has been slow due to stringent regulatory procedures and unsuccessful microwave trials. However, microwave systems offer significant energy and time savings compared with conventional dryers. Common pharmaceutical excipients, lactose, stearic acid, and active ingredients, Aspirin, Paracetamol, were wetted with water and dried within an experimental atmospheric microwave drying system (2.45 GHz, 90 W). The drying curves obtained showed a constant drying rate, followed by two falling rate periods. Two- and three-component mixtures were dried under the same conditions. The drying characteristics were found to lie between those of the pure components. Drying kinetics of samples wetted with a range of solvents (methanol, ethanol, acetone), and two-component solvent mixtures, were examined. The relative evaporation rates of the solvents showed some dependence on their dielectric properties; latent heat of vaporisation and boiling point having greater influence on drying characteristics. Clearly this research provides information vital to achieve increased acceptance of this technology within the pharmaceutical industry.     

Microwave sintering of AlN powder synthesized by a SHS method

Sintering of the AlN powder synthesized by a combustion synthesis method, which was developed recently by the present authors, was studied by using a microwave sintering technique. A single mode microwave cavity was used and an insulation package with a simple configuration was developed. A high sintering temperature (1900 °C or higher) and a stable and uniform heating were readily achieved. A temperature measurement technique using a thermocouple with extrapolation was established to obtain the sintering temperature. A percent theoretical density of 99.5% and a thermal conductivity of 186 W/m K were obtained for a specimen which was sintered at 1900 °C with a soaking time of 30 min and 3 wt.% of Y₂O₃ added. The effects of sintering aid (i.e., Y₂O₃) and sintering temperature on densification, microstructure and thermal conductivity of the sintered specimens were investigated.     

微波介电热效应在化学合成中的应用

介绍微波介电热效应原理及其在化学合成中的应用.利用微波介电热效应不仅能加快化学反应速度,缩短反应时间,而且还能合成出一些新的化合物.     

凹凸棒石粉体作为润滑油添加剂的摩擦学性能

采用摩擦磨损试验机研究了凹凸棒石粉体作为润滑油添加剂对钢-钢摩擦副的减摩抗磨性能,采用扫描电子显微镜和能量色散谱仪分析了磨损表面的微观形貌及元素组成,采用三维轮廓测量仪测量了磨痕宽度和体积,探讨了凹凸棒石粉体的减摩抗磨机理.结果表明:在润滑油中添加0.5％(质量分数)以上的凹凸棒石粉体时,能显著降低钢-钢摩擦副的摩擦系数.添加量为1.0％时具有最佳的减摩抗磨性.通过摩擦物理和摩擦化学作用,凹凸棒石粉体在磨损表面形成光滑平整的修复层,从而提高摩擦副的摩擦学性能.     

微波辐射合成水煤浆添加剂的研究

研究在微波辐射条件下,利用木质素磺酸钠和丙烯酸在硝酸铈铵引发下进行非均相接枝共聚反应,合成接枝共聚物作为水煤浆添加剂。经过正交实验得出最佳合成工艺条件:单体体积与木质素磺酸钠用量比为5:1,引发剂硝酸铈铵的用量为0.12mL,中和度为75%。在微波炉内反应3min,用所得的接枝共聚物配制的水煤浆质量分数可达65%以上。     

微波等离子体技术在纳米粉体中的应用

介绍了微波等离子体技术制备纳米粉体的原理和特点,综述了微波等离子体在纳米粉体中的应用情况。