用于低损耗特种玻璃熔炼的高纯致密锆英石的研制

以纯度大于99.9%(质量分数)的高纯ZrO₂和SiO₂为原料,少量TiO₂为添加剂,采用高温固相法合成高纯锆英石(ZrSiO₄)粉料。研究温度和反应时间对高纯锆英石合成效率的影响,发现粒度小于50 μm的原料粉末经1 500 ℃反应48 h后,ZrSiO₄相的含量可以达到95.77%(质量分数)。将合成的高纯锆英石粉料球磨并冷等静压成型后,在1 550 ℃高温烧结成高纯致密锆英石砖。高纯致密锆英石中杂质Fe的含量仅为29 μg/g,Cu的含量小于1 μg/g,是普通商用致密锆英石的1/10;对磷酸盐玻璃静态光吸收损耗的影响仅为普通致密锆英石材料的1/3。将这种高纯致密锆英石材料用于激光玻璃窑炉,有助于降低玻璃对1 053 nm激光的损耗,提升激光玻璃的激光性能。     

MgO与ZrSiO_4反应烧结过程的研究

本工作以镁砂和锆英石为原料，研究了二者的反应烧结过程的热力学和动力学条件，结果表明：镁砂和锆英石反应的热力学条件具备，动力学因素受镁砂活性的影响；二者的烧结过程是固相反应和致密化过程同时进行，反应先于致密化结束；以酒精力混合介质，烧结镁砂为原料获得致密的陶瓷烧结制品是可行的。     

氧化铝和锆英石合成锆刚玉莫来石材料的烧结机理

氧化铝和锆英石混合物加热过程变化可分三个阶段：①初期致密化阶段，②分解反应阶段，③重结晶烧结阶段。莫来石化反应和伴随ZrO2聚集体的封闭气孔形成是影响烧结过程的主要因素。加入Mg2＋对锆刚玉莫来石材料的烧结起着促进作用，烧结的关键阶段在1370～1420℃之间。     

锆英石对镁砂烧结性及其制品性能的影响

探讨了锆英石对镁砂烧结性能的影响 ,并研究了由这种合成镁锆砂制成的镁砖的性能。结果表明 :锆英石能显著提高镁砂的烧结性能 ;利用合成镁锆砂制成的镁砖以高熔点的第二固相为结合相 ,性能明显优于普通镁砖     

锆英石的合成

概述了近年来化学法合成锆英石（ＺｒＳｉＯ４）的典型工艺及合成温度,并对合成过程中的晶相变化,影响锆英石合成的因素及锆英石合成机理进行了综述。     

锆莫来石-碳化硅材料反应烧结过程的研究

研究了用锆英石、氧化铝和炭黑的混合物制备原位SiC颗料复合锆莫来石材料的反应烧结进程和显微结构特征。结果表明：反应烧过程中,SiC、莫来石的生成反应滞后于锆莫来石的分解反应;反应前期,SiC的生成占主导作用。反应后期,莫来石的形成及致密化进程占主导作用;材料中存在大量气孔,ZrO3以均匀分布和聚集体两种形式分布于莫来石、SiC及玻璃相构成的基质中。     

湿法合成锆刚玉莫来石熟料

本文对ＺｒＳｉＯ４－Ａｌ２Ｏ３反应烧结过程进行了系统地研究。结果表明，化学反应于１３８０℃开始。首先锆英石分解，到１４３０～１４５０℃反应迅速，并生成莫来石，同时产生一定的体积膨胀，对致密化产生不利的影响。化学反应与致密化过程同时进行。影响反应烧结过程的因素包括原料特性（原料种类、粒径）、外加剂、坯体均匀性及升温制度等。     

锆英石对固相反应制备钛酸铝材料性能的影响

以铁合金厂铝钛渣为主要原料,通过固相反应烧结法制备钛酸铝材料,研究了锆英石对不同温度煅烧所得钛酸铝材料的分解率及烧结性能的影响。利用X射线衍射（XRD）、扫描电镜（SEM）及相关分析软件对煅烧后试样的相组成、晶胞参数、相对结晶度及微观结构进行分析。结果表明,锆英石中Zr⁴⁺和Si⁴⁺对钛酸铝中Ti⁴⁺的置换行为加速了钛酸铝材料的固相反应,加入氧化锆有利于降低钛酸铝材料的分解率,提高钛酸铝材料的致密度。升高煅烧温度可以增强锆英石对钛酸铝材料性能的影响,抑制钛酸铝材料的分解。     

电熔镁锆合成料的抗渣性研究

采用坩埚法研究了不同组成的电熔镁锆合成料的抗渣性。结果表明镁锆合成料比镁质材料具有更好的抗渣渗透性。随着原始配料中锆英石的增加,合成料抗渣渗透性增强。当配料中锆英石配入量超过8％后,合成料的抗渣渗透性改善已不明显。文中还探讨了镁锆合成科抗渣渗透性机理。     

利用等离子分解锆英石合成锆钒蓝

利用等离子分解锆英石为原料成功地合成出了锆钒蓝陶瓷颜料，讨论了各工艺参数对颜料合成的影响，优化出了等离子分解锆英石合成锆钒蓝颜料的最佳工艺制度。     

Effect of MgO Solute on Microstructure Development in Al2O3

The effect of MgO as a solid-solution additive in the sintering of Al₂O₃ was studied. The separate effects of the additive on densification and grain growth were assessed. Magnesia was found to increase the densification rate during sintering by a factor of 3 through a raising of the diffusion rate. The grain-size dependence of the densification rate indicated control primarily by grain-boundary diffusion. Magnesia also increased the grain growth rate during sintering by a factor of 2.5. The dependence of the grain growth rate on density and grain size suggested a mechanism of surface-diffusion-controlled pore drag. It was argued, therefore, that MgO enhanced grain growth by raising the surface diffusion coefficient. The effect of MgO on the densification rate/grain growth rate ratio was, therefore, found to be minimal and, consequently, MgO did not have a significant effect on the grain size/density trajectory during sintering. The role of MgO in the sintering of alumina was attributed mainly to its ability to lower the grain-boundary mobility.     

Comparison of the Microwave and Conventional Sintering of Alumina: Effect of MgO Doping and Particle Size

The effects of MgO doping and specific surface area of powder on microwave sintering behavior of α‐Al₂O₃ were investigated. A comparative study was simultaneously achieved in conventional and microwave heating with an identical thermal process. The experimental results show that both MgO and particle size have significant influence on microwave enhancement in the densification of the alumina samples. It is found that an amount of MgO surrounding the solubility limit in Al₂O₃ or leading to second phase precipitation of MgAl₂O₄ spinel induces more significant microwave enhancement. A significant microwave gain in densification is also observed while powder has a high specific surface area. These results indicate that the enhancements during microwave sintering processes are associated with the formation of lattice defect and with the increase in concentration of grain‐boundary region.     

Enhanced Densification of Liquid-Phase-Sintered WC–Co by Use of Coarse WC Powder: Experimental Support for the Pore-Filling Theory

Densification during liquid-phase sintering of WC–Co with various WC powder sizes has been measured in order to identify the densification mechanism. During heating of powder compacts in the solid state, densification was enhanced with a reduction of WC powder size. However, the behavior was reversed when the densification occurred in the presence of a liquid: enhanced densification with increasing WC powder size. This result is in contradiction to a prediction of the conventional theory of liquid-phase sintering, the contact flattening theory, but in good agreement with a prediction of the pore-filling theory. Microstructural analysis further confirmed that the densification at the liquid-phase sintering temperature occurred by pore filling. The calculated densification kinetics based on the pore-filling theory also fitted well with the measured data. The observed densification behavior thus demonstrates experimentally the prediction of the pore-filling theory that the densification is enhanced with increasing average grain size for the same pore size distribution.     

Synthesis and sintering of YAG:Eu nanopowder

YAG:Eu nanopowder was synthesized through a sol–gel method. A master sintering curve was used as a practical approach to analyze the sintering behavior of the synthesized powder. The effect of MgO doping on sintering of the synthesized nanopowders was evaluated. An amorphous nanopowder was synthesized and crystallized to YAG after heat-treatment via a solid-state reaction. MgO improved the sintering rate of the YAG nanopowders and suppressed grain boundary mobility. The activation energy for sintering decreased from 917 to 837 kJ/mol by adding MgO to the nanopowders. The results of this study can be used to predict the densification of YAG:Eu nanopowder.     

Powder chemistry effects on the sintering of MgO‐doped specialty Al2O3

In this work, we investigate the effects of powder chemistry on the sintering of MgO‐doped specialty alumina. The stages at which MgO influences densification of Al₂O₃ were identified by comparing dilatometry measurements and the sintering kinetics of MgO‐free and MgO‐doped specialty alumina powders. MgO is observed to reduce the grain boundary thickness during densification using TEM. We show that MgO increases the solubility of SiO₂ in alumina grains near the boundaries using EDS. First‐principles DFT calculations demonstrate that the co‐dissolution of MgO and SiO₂ in alumina is thermodynamically favored over the dissolution of MgO or SiO₂ individually in alumina. This study experimentally demonstrates for the first time that removal of SiO₂ from the grain boundaries is a key process by which MgO enhances the sintering of alumina.     

Controlled Gelation and Sintering of Monolithic Gels Prepared from γ-Alumina Fume Powder

The gelation, phase transformation, and densification of a colloidal monolithic gel made from γ-Al₂O₃ fume powder are investigated. Among the six gelation agents that we use, formamide and urea are quick in causing gelation and easy to burn off. The densification rate of this gel decreases rapidly after the γ-to-α phase transformation. TiO₂ is an effective sintering aid to overcome this bottleneck of densification because (1) it enhances the phase transformation rate so that the sintering of α-alumina occurs at a lower temperature, and (2) it promotes sintering rates at the initial and intermediate stages after phase transformation. On the other hand, MgO has an inappreciable effect on gel sintering. The effect of MgO at the final sintering stage is obstructed by this densification barrier after transformation. The titania-doped gel monoliths can be sintered to high density and fine microstructure at 1400°C.     

Sintering of Ultra-High-Purity Alumina Doped Simultaneously with MgO and FeO

The use of ultra-high-purity powder processing and multiple solid-solution additive doping has been evaluated as an effective approach for the fabrication of alumina ceramics. MgO was found to inhibit grain growth more strongly in very pure powders because of its stronger solute drag effect. The degree of inhibition was severe enough to render grain growth insensitive to porosity. By diminishing the dragging influence of pores on grain-boundary motion, MgO guards against abnormal grain growth due to inhomogeneous densification. FeO acted singly in alumina to promote grain growth more than densification. FeO was not, therefore, an effective sintering additive for undoped alumina. FeO did, however, Ceramic benefit the sintering of MgO-doped alumina.     

Al2O3的加入对合成莫来石粉烧结性能的影响

采用玻璃相的后消除法以除去合成莫来石粉中的玻璃相,提高莫来石的高温烧结性能。结果表明：地可有效地除去合成莫来石粉中的玻璃相;烧结体的线收缩率与其体积密度、吸水率、显气孔率及抗弯强同步的;较粗大的Ａｌ２Ｏ３的加入,虽避免了贯穿大孔洞的出现,但却影响了烧结体的致密效果,综合分析,认为延长保温时间和加入微细的Ａｌ２Ｏ３,粉可提高其和密结果。     

Ultra low-density mullite foams by reaction sintering of thermo-foamed alumina-silica powder dispersions in molten sucrose

Ultra low-density mullite foams are prepared by thermo-foaming followed by reaction sintering of alumina-silica powder dispersions in molten sucrose. The foaming & setting time, foam rise, sintering shrinkage, porosity, cell size and compressive strength are studied as a function of ceramic powder loading, foaming temperature and magnesium nitrate (blowing agent and setting agent) concentration. Phase pure mullite is produced by reaction sintering at 1600 °C. The mullite foams produced without magnesium nitrate have porous struts and cell walls due to improper densification. The magnesium nitrate drastically decreases the foaming & setting time and increases the foam rise and cell interconnectivity. The MgO produced from the magnesium nitrate assists the densification of the mullite as evidenced from the non-porous struts and cell walls at higher magnesium nitrate concentrations. The maximum porosity of 94.92 and 96.28 vol.% achieved without and with magnesium nitrate, respectively, is the highest reported for mullite foams.     

Precoarsening to Improve Microstructure and Sintering of Powder Compacts

MgO and Al₂O₃ were sintered by two types of processes: a conventional isothermal sintering and a two-step sintering consisting of an initial low-temperature precoarsening treatment before conventional isothermal sintering. The final microstructure from two-step sintering can be more uniform and finer than that of compacts sintered conventionally. A narrow-size-distribution alumina powder was sintered under constant-heating-rate conditions, with and without a precoarsening treatment, and the results were compared. The differences between two-step and conventional processing were clarified by experiments on precoarsened and as-received ZnO powders. These compacts were precoarsened at 450°C for 90 h with virtually no increase in the overall density. The resulting grain size was 1.7 times the starting one, but the standard deviation of the precoarsened powder size distribution was smaller than that of the asreceived powder. Precoarsened compacts sintered to nearly full density showed improved homogeneity. The sintering stress of the precoarsened ZnO was approximately 0.8 that of the as-received one. A computational model has been used with two components of coarsening to describe the differences in pore spacing evolution between the precoarsened and the as-received system. The benefit of two-step sintering is attributed to the increase in uniformity resulting from precoarsening. The increased uniformity decreases sintering damage and allows the system to stay in the open porosity state longer, delaying or inhibiting additional coarsening (grain growth) during the final stage of densification. Two-step sintering is especially useful for nonuniform powder systems with a wide size distribution and is a simple and convenient method of making more uniform ceramic bodies without resorting to specialized powders or complicated heat schedules.