镁铝尖晶石烧结致密化用烧结助剂的研究进展

添加烧结助剂是镁铝尖晶石获得致密微观结构的重要途径.综述了不同的烧结助剂对镁铝尖晶石烧结致密化的影响,根据烧结助剂促进镁铝尖晶石致密化的烧结机理不同,将其主要分为三类.第一类是烧结助剂在一定温度下与镁铝尖晶石形成固溶体;第二类是在较低温度下产生液相以促进尖晶石的烧结;第三类烧结助剂在镁铝尖晶石基体中形成第二相促进其烧结致密化.明晰烧结助剂在镁铝尖晶石烧结过程中的作用机理,同时从环境友好、降低成本、改善材料性能等角度出发选择烧结助剂,以助于镁铝尖晶石在耐火材料、光学材料、透明陶瓷等领域得到更好的应用.     

乙二胺四乙酸配位螯合法制备钴铝尖晶石蓝色颜料

提出一种可以在较低温度下焙烧制备出钴铝尖晶石蓝色颜料的方法.以六水合硝酸钴、九水合硝酸铝为主要原料,乙二胺四乙酸(EDTA)为配位螯合剂,通过EDTA配位螯合钴、铝得到有机配合物前驱体,经过焙烧制备钴蓝颜料.通过X射线衍射和国际照明委员会的色度图谱分别对所制备样品的物相和呈色进行研究表征.主要考察了钴铝比、反应体系pH值、焙烧温度等工艺条件对铝酸钴尖晶石相的完整性和颜料呈色的影响.研究结果表明,焙烧温度对颜料的物相完整性和呈色的影响最大,钴铝比和反应过程中的pH值对颜料的物相完整性和呈色的影响其次;当钴铝比比值大于或等于1∶2.5时,前驱体经700℃和900℃热处理制备出的尖晶石相颜料分别呈灰蓝色和钴蓝色;钴铝比比值低于1∶2.5时,在上述同样温度下制备出的尖晶石相颜料呈灰蓝色;pH值低于9时,不能形成紫红色的透明前驱体溶液.制备钴铝尖晶石蓝色颜料的最佳工艺参数是钴铝比为1∶2.5,pH值为9～10,900℃温度下保温时间为2h.     

原位合成方镁石-铁铝尖晶石材料的烧结工艺及性能研究

以镁砂细粉、Fe粉、Fe2O3粉和α-Al2O3粉为原料,采用原位合成法制备方镁石-铁铝尖晶石材料。不同气氛下烧成试验显示N2气氛是合成铁铝尖晶石的最佳气氛。通过XRD和SEM分析在N2气氛中不同热处理温度制备铁铝尖晶石材料的相组成及其显微结构,研究了烧结温度和铁加入量对试样烧结性能的影响。结果表明,试样在N2气氛中于1450、1500、1550℃下保温3h处理后都能原位合成出方镁石-铁铝尖晶石材料;烧结温度的提高有利于铁铝尖晶石的发育和试样烧结性能的提高;铁加入量为10％时烧结性能最佳。     

水泥窑用碱性耐火材料的高温力学性能研究

采用扭转方法对水泥窑用直接结合镁铬砖、镁铝尖晶石砖和白云石砖的高温力学性能进行了研究,结果表明:3种砖的刚性模量-温度曲线和抗折强度-温度曲线均为Ⅰ型曲线,刚性模量和抗剪强度由大到小的顺序为:白云石砖＞镁铝尖晶石砖＞直接结合镁铬砖.白云石砖、镁铝尖晶石砖和镁铬砖的塑性变形开始温度分别为600,800和800 ℃;在发生快速流动的温度范围内(1 250～1 350 ℃),流动量的大小顺序为:白云石砖＞镁铝尖晶石砖＞直接结合镁铬砖.     

用富镁蒙脱石合成堇青石－莫来石复合材料

以天然富镁蒙脱石为原料，以碳酸镁和氢氧化铝为助剂合成了堇青石－莫来石复合材料，其主要物相有堇青石和莫来石，次要物相为刚玉、方石英和镁铝尖晶石等矿物．材料试块具霏细结构，由球粒和胶结物构成，它们反映了两种不同的形成机理．材料的气孔率随温度的升高而下降，随保温时间的延长而趋于达到一个最小值，热膨胀系数和耐火度则随堇青石含量的增加而下降。     

多孔有序阳极氧化铝膜的制备及其机理分析

以草酸为电解液,利用电化学阳极氧化法制备多孔有序阳极氧化铝阵列模板,用透射电镜对其形貌和结构进行表征在此基础上,对多孔有序阳极氧化铝阵列模板的生长过程和形成机理进行了分析.结果表明,经阳极氧化处理后的铝片明显分成了未反应的铝、阻挡层氧化铝和多孔氧化铝3层结构,且阻挡层位于未反应铝和多孔层之间.多孔有序阳极氧化铝膜的形成更符合"电场支持下的溶解"模型.     

用富镁蒙脱石合成堇青石—莫来石复合材料

以天然富镁蒙脱石为原料，以碳酸镁和氢氧化铝为助剂合成了堇青石－莫来石复合材料，其主要物相有堇青石和莫来石，次要物相为刚玉、方石英和镁铝尖晶石等矿物。材料试块具霏细结构，由球粒和胶结物构成，它们反映了两种不同的形成机理。材料的气孔率随温度的升高而下降，随保温时间的延长而趋于达到一个最小值，热膨胀系数和耐火度则随堇青石含量的增加而下降。     

以硝酸根型层状双氢氧化物为前驱体在温和条件下原位合成尖晶石

采用共沉淀法合成镁铝硝酸根型层状双氢氧化物前驱体（ＭｇＡｌ－ＮＯ₃^－ －ＬＤＨｓ）,通过低温焙烧 －重构、原位合成方法合成了镁铝尖晶石,研究了反应物中不同铝离子摩尔分数 ｘ值（Ａｌ^３＋ ／（Ｍｇ^２＋ ＋Ａｌ^３＋））、重构作用、原位合成温度等因素对合成产物相组成和结构特征的影响。结果表明：随着 ｘ值不断增大,镁铝尖晶石的结晶度和质量分数不断提高,晶体初始发育温度不断降低;重构作用使层状双氢氧化物在 ｃ轴上层状结构规整度降低,三价铝离子迁移,有助于镁铝尖晶石的合成;随着合成温度的升高,合成产物中镁铝尖晶石相含量和结晶度不断提高,在 １０００℃时可以合成结晶良好的镁铝尖晶石。当 ｘ＝０.６０时,其含量达 ８９.５１％。     

La-Sr掺杂和助成胶剂对氧化铝热稳定性的影响

通过水溶液成胶和聚乙二醇络合助成胶制备了不同结构的氧化铝,利用XRD、BET及SEM等表征测试手段研究了镧、锶物种双组分改性对氧化铝热稳定性的影响.结果表明,不同温度焙烧时,双组分掺杂改性能提高纯氧化铝的比表面积,改善其热稳定性,共同掺杂改性时,可与氧化铝作用形成复合氧化物占据其间隙,防止铝离子的迁移,从而提高氧化铝的热稳定性和比表面积;添加聚乙二醇助成胶时,低温提高氧化铝比表面积的机理是在氧化铝粒子中间形成许多孔道,高温时,则通过La、Sr物种补充到氧化铝表面的空位中阻止铝离子的迁移来提高氧化铝的热稳定性和比表面积.     

镁铝尖晶石的铝铬渣与用后镁碳砖低温合成

用铝铬渣和转炉用后镁碳砖细粉为主要原料,通过固相烧结反应合成MgAl_2O_4材料。用X射线衍射、扫描电镜及XPert plus软件对材料中主晶相进行表征。结果表明：当烧成温度为1 400℃,镁碳砖与铝铬渣摩尔比为5：1时,生成的镁铝尖晶石晶粒发育完整清晰,排列致密,外貌呈典型的八面体形貌。镁铝尖晶石质量百分数达到92%。     

Effect of sintering time on the electrochemical properties of spinel LiMn_2O_4 synthesized by solid-state reaction

LiMn_2O_4 powder as a cathode materials for rechargeable lithium-ion batteries was prepared by solid-state reaction from Li_2CO_3 and electrolytic MnO_2 at different sintering periods(2,6,18,and 32 h).X-ray diffraction(XRD)patterns of the prepared samples are identified as the spinel structure with a space group of Fd(?)m.The lattice parameters almost remain the same as the sin- tering periods increase.The sample with a sintering period of 32 h shows good cycling performance at both low and high current densities,and also elevated temperature.It is believed that the excellent electrochemical behavior of this sample results from its good crystallinity and large grain size compared with other samples.Different electrochemical measurements were conducted to investi- gate the electrochemical properties of spinel LiMn_2O_4.     

Effect of sintering time on the electrochemical properties of spinel LiMn2O4 synthesized by solid-state reaction

LiMn2O4 powder as a cathode materials for rechargeable lithium-ion batteries was prepared by solid-state reaction from LitCO3 and electrolytic MnOz at different sintering periods （2, 6, 18, and 32 h）. X-ray diffraction （XRD） patterns of the prepared samples are identified as the spinel structure with a space group of Fd3 m. The lattice parameters almost remain the same as the sintering periods increase. The sample with a sintering period of 32 h shows good cycling performance at both low and nigh current densities, and also elevated temperature. It is believed that the excellent electrochemical behavior of this sample results from its good crystallinity and large grain size compared with other samples. Different electrochemical measurements were conducted to investigate the electrochemical properties of spinel LiMn204. 2008 University of Science and Technology Beijing. All rights reserved.     

新型含镁铝尖晶石的铝酸盐水泥的研究

以白云石和工业三氧化二铝为原料，采用反应烧结技术制得了含镁铝尖晶石的铝酸盐水泥，探讨了原料及烧结温度和添加剂对含镁铝尖晶石的铝酸盐水泥性能的影响，XRD结果表明产物的物相组成为MA，CA，CA2；采用扫描电镜（SEM）及能谱（EDS）对产物的显微结构进行了观察与分析。结果表明：以轻烧白云石和工业Al2O3为原料制得的水泥具有较高的结合强度；所制得的含镁铝尖晶石的铝酸盐水泥的显微结构较为均匀，外加剂CaCl2具有明显的早强效果。     

Effect of spinel content on the properties of phosphoric acid bonded high alumina castables

In order to study the effect of fused spinel on the properties of phosphoric acid bonded high alumina castables, samples with different contents of fused spinel were prepared. The results show that when the contents of the fused spinel are between 8% and 16% (mass fraction), the castables have good properties. The castables overcome the shortages of the phosphoric acid bonded high alumina castables with bauxite cement as a hardening promoter. The experiments demonstrate that most of the service properties of the castables with fused spinel are better than those of the normal phosphoric acid bonded castables which use bauxite cement as a hardening promoter. The examination of the materials indicates that free MgO inclusions in the spinel powder can promote the hardening of the castables.     

In-situ formation of spinel fibers in MgO-C refractory matrixes

In-situ magnesia-rich spinel fiber was formed resulting from the addition of ferrocene into MgO-C refractory matrixes. The formation of in-situ spinel fiber was detected to start at 1300 °C. The amount, diameter and length of the fibers increased with rising temperature. Ferrocene may have catalytic effects on the growth of the fibers in two aspects. First, the reaction between MgO and C and the decomposition of Al₄C₃ may be catalyzed at high temperature. Suitable concentration gaseous phase is then created for vapor-vapor reaction which could result in the in-situ formation of fibers. Second, Fe nanoparticle produced from ferrocene can act as catalytic droplets and catalyze the growth of the fibers. The fibers are formed via the vapor-liquid-solid and vapor-solid mechanisms. In terms of chemical thermodynamics, the partial pressure of CO and Mg(g) are found to play an important role in the in-situ fibers formation. Different concentration of vapors affects the size, amount and composition of the fibers at different temperatures. The mechanical properties of MgO-C brick was found to be improved by ferrocene addition.     

镁橄榄石质隔热材料的制备及其性能研究

以天然镁橄榄石和NaCl为原料,采用熔盐法制备镁橄榄石质隔热材料。研究不同熔盐配比和烧结温度对材料显气孔率、体积密度和耐压强度的影响,并利用X射线衍射仪（XRD）和扫描电镜（SEM）对其相组成及微观形貌进行表征。结果表明,熔融的NaCl提供了液相环境,促进了镁橄榄石的烧结,经过水溶液处理后,NaCl溶于水中,其占据的空间形成了气孔;烧结温度为1 100℃,熔盐含量为50%时,制得的隔热材料有较低的体积密度、较高的显气孔率和耐压强度,气孔分布更均匀,材料的隔热性能较佳。     

Preparation of β-Sialon/ZrN bonded corundum composites from zircon by nitridation reaction sintering process

β-Sialon/ZrN bonded corundum composites were synthesized using fused white corundum, alumina micro powder, zircon and carbon black by nitridation reaction sintering process. Phase composition and microstructure of the synthesized composites were investigated by X-ray powder diffraction and scanning electronic microscope, and the formation process of the composites was discussed. The results show that the composites with different compositions can be obtained by controlling the heating temperature and contents of zircon and carbon black. The proper temperature to synthesize the composites is 1 773 K.     

中温烧结Mg_4Nb_2O_9-CaTiO_3陶瓷相结构的研究

采用传统固态反应方法制备了(1-x)Mg4Nb2O9+xCaTiO3[(1-x)MN-xCT]复合陶瓷。探讨了烧结温度、组分x对Mg4Nb2O9/CaTiO3复合材料相结构的影响。通过XRD和EDS进行物相分析。实验结果表明:V2O5添加能够有效降低Mg4Nb2O9/CaTiO3陶瓷的烧结温度;(1-x)MN-xCT复相的形成主要取决于烧结温度和x的含量。1150℃烧结、0.5≤x≤0.7范围内,形成了Mg4Nb2O9/CaTiO3复相,无新相生成,但元素在不同相之间发生了扩散。     

LOW TEMPERATURE SINTERING OF ALUMINA BIOCERAMIC UNDER NORMAL PRESSURE

Superfine alumina powder with high purity (mean particle size is less than 0.35μm) were used as main starting material for sintering alumina ceramic.A multiple additive MgO-ZrO_2 (Y_2O_3) was homogeneously added into the batch by the chemical coprecipitation method. Sintering of alumina bioceramic at low temperature (<1600C) was achieved resulting in a dense and high strength alumina ceramic with the bending strength up to 382 MPa and an improved fracture toughness.Mechanism that the multiple additives promote the sintering of alumina ceramic is discussed on the base of XRD and SEM analysis.     

Liquid Phase Sintering （LPS） and Dielectric Constant of α-Silicon Nitride Ceramic

The spark plasma sintering （SPS） was applied to prepare α-Si3 N4 ceramics of different densities with magnesia, silicon dioxide, alumina as the sintering aids. The mechanism of liquid phase sintering （LPS） wus discussed and the factors influencing the density of the prepared samples were analyzed. The dielectric constant of sintered samples was tested. The experimental results show that the density can be controlled from 2.48 g/ cm^3 to 3.09 g/ cm^3 while the content of the sintering aids and the sintering temperature alter and the dielectric constant is closely dependent on the density of obtained samples.