湿化学过程中锆英石生成机制的探讨

利用Ｘ射线衍射（ＸＲＤ）、透射电镜（ＴＥＭ）等手段研究了湿化学法合成锆英石粉末过程中锆英石相的生成机制。对于该过程中影响锆英石合成的几个因素，如反应温度、晶种含量等进行了分析讨论，并在此基础上提出了锆英石相的生成机制。结果表明：晶种引入对于锆英石的生成是至关重要的，其反应机理是晶种存在条件下的非均相成核反应，固相反应中的扩散速率决定了整个反应的速率。     

烧结合成镁锆熟料的研究

采用轻烧氧化镁和锆英石粉为原料,研究了锆英石配合量、粉料细度及烧成温度对合成料的烧结及显微结构的影响。结果表明：在氧化镁与锆英石反应烧结过程中,锆英石分解后在初始锆英石颗粒内形成的气孔是阻碍合成料烧结致密化的不良因素;粉料细度,特别是锆英石的细度,对合成料的致密化有决定性的影响     

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。     

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。     

MgO-ZrO2-C材料的性能和显微结构

研究了在MgO-C耐火材料中添加单斜氧化锆或锆英石所形成的MgO-ZrO2-C材料的性能和显微结构.结果表明(1)加入单斜氧化锆和锆英石导致材料的高温抗折强度降低.(2)热震温度低于1000 ℃时,加入不同量的单斜氧化锆或锆英石对材料抗折强度损失率的影响较小;而热震温度为1200 ℃时,不同的添加量有较大的差别,当单斜氧化锆的添加量为5%～7%,锆英石的添加量为1.54%时,MgO-ZrO2-C材料的抗折强度损失率最小.(3)添加的单斜氧化锆在1200 ℃的热震温度下有部分ZrO2固溶到了镁砂颗粒的内部;而添加的锆英石在1200 ℃下变化轻微,但在1400 ℃下,材料中仅存在少量未分解或分解不完全的锆英石,MgO由基质向锆英石颗粒内部扩散,导致分解完全的锆英石颗粒转变为ZrO2、CMS和c- ZrO2小颗粒.     

锆莫来石材料的反应烧结机制和显微结构特征

研究了用锆英石和工业氧化铝合成锆莫来石材料的反应烧结过程和显微结构。结果表明，添加适量ＭｇＣｌ２·６Ｈ２Ｏ可以促进反应烧结进程。锆英石大颗粒完全分解以后形成ＺｒＯ２聚集体，结构中出现封闭气孔可能与ＺｒＯ２聚集体有密切关系。加入ＭｇＣｌ２·６Ｈ２Ｏ后锆莫来石材料显微结构的主要特征：ＺｒＯ２有聚集体和均匀分布两种赋存形式；封闭气孔一般与ＺｒＯ２聚集体相邻。     

等离子分解锆英石合成锆镨黄

利用等离子分解锆英石原料成功地合成出了锆谱黄陶瓷颜料，讨论了各工艺参数对颜料合成的影响，优化出了以等离子分解锆英石为原料合成镨黄颜料的最佳工艺制度。     

用锆英石和粉煤灰原位合成ZrO_2/(β+O')-Sialon复合材料的物相和过程分析

以锆英石和粉煤灰为原料,活性炭为还原剂,采用碳热还原氮化法在1 450℃保温6h条件下合成Zr O2/(β+O)-Sialon复合材料。研究了配炭量对制备试样物相组成的影响,并分析了其合成过程。研究结果表明,按锆英石:粉煤灰:活性炭的质量比为49:100:80进行配料,可以合成主晶相为m-ZrO_2、β-Sialon(z=2)和O-Sialon(x=0.17)的复合材料;增加试样中的配炭量,有利于锆英石和粉煤灰中莫来石的分解及复合材料的生成;ZrO_2/(β+O)-Sialon复合材料的合成过程包括锆英石和莫来石的分解,以及m-Zr O_2、β-Sialon和O-Sialon的生成过程。     

优质机压锆英石砖的研制

研究了钛白粉、轻烧镁粉、α Al2 O3微粉的添加量及不同的烧成制度对合成锆英石骨料性能的影响 ,确定了最佳的复合添加剂加入量和适宜的烧成温度 ,并运用普通制砖生产线生产了优质机压锆英石制品。该制品的理化性能指标达到了国外同类产品水平。     

PDZ合成锆铁红陶瓷颜料的试验研究

以ＰＤＺ（等离子分解锆英石）为原料进行了锆铁红颜料的合成试验，讨论了各工艺参数对颜料合成的影响，对利用ＰＤＺ合成锆英石颜料的工艺制度进行了优化。     

Porous stabilized zirconia coatings on zircon using volatility diagrams

A process for obtaining porous coatings of yttria stabilized zirconia on zircon substrates is described. The calcination in reducing atmospheres (oxygen partial pressures below 2 × 10^?9 atm and at temperatures over 1300 °C) of test samples containing zircon and small amounts of yttria led to the formation of porous stabilized zirconia coatings (up to 240 μm thick) on the samples. The process led to the decomposition of the silica contained in the zircon, volatilized in the form of SiO_(gas), originating pores in its place. The conditions required for the process were inferred from the volatility diagrams of the involved chemical species, which were likewise used to analyze the experimental results.     

ZrSiO4-ZrO2质中间包上水口的研究

以锆英石、电熔PSZ-Mg,电熔PSZ-Ca为原料,Y2O3为添加剂,试制出高致密体的ZrSiO4-ZrO2质中间包上水口,研究了颗粒级配、成型压力和Y2O3添加剂对ZrSiO4-ZrO2质中间包上水口性能的影响,并利用XRD进行物相分析,利用SEM和EDS进行显微结构分析.实验结果表明:选用合理的级配和成型压力能够获得高性能的材料,Y2O3对锆质材料具有烧结剂的作用,同时也能促进ZrSiO4的分解.     

Influence of Impurities of Zircon Sand on the Microstructure of Fused Zirconia Grains for Continuous Casting of Steel Refractories

Certain impurities of zircon sands,especially alumina,titania,calcia and yttria cannot be completely removed in the production of fused zirconia and may have an influence on the corrosion resistance and other product properties of refractories for continuous casting of steel.In this paper,we present our findings on how impurities in raw materials end up in different stabilised zirconia refractory grains,in particular calcia-,magnesia-and yttria-stabilised zirconia. The microstructure(and phase composition) is affected by both the raw materials and the fusion conditions(furnace type and cooling technology).     

Emulsion Precipitation of Yttria-Stabilized Zirconia for Plasma Spray Coatings

Chemically uniform, high-purity, yttria-stabilized zirconia (YSZ) powders were prepared by emulsion hydrolysis of the metal alkoxides, acetates, and mixtures of alkoxides and acetates. Both the morphology and particle size of the powders can be controlled by varying the hydrolysis conditions. Spherical or granular powders with particle sizes ranging from submicrometer to a few hundred micrometers were obtained. X-ray diffraction and EDX results showed that yttria was evenly distributed throughout the zirconia particles. The crystalline phase of the powders after calcination at 800°C was 100% nontransformable tetragonal. The powders were successfully sprayed by a plasma coating technique on stainless steel coupons, and the coatings were evaluated.     

Mechanical Properties of Submicrometer‐Grained Transparent Yttria Ceramics by Hot Pressing with Hot‐Isostatic Pressing

Here, we report the fabrication and mechanical properties of submicrometer‐grained (0.29–0.58 μm) transparent yttria ceramics by hot pressing combined with hot‐isostatic pressing. The effects of the grain size on the microhardness and the fracture toughness were studied. An unusual decrease of the fracture toughness with an increase in the grain size was revealed, which may be attributed to the different grain size dependence of the fracture behavior of the ZrO₂‐doped yttria ceramics compared to that of other yttria ceramics. The microhardness and fracture toughness of the transparent yttria ceramics were found to be better than those of the large‐grained yttria ceramics.     

Synthesis of yttria precursor nano-powders using a symmetrical alternating current assisted precipitation method

Symmetrical alternating current (SAC) was applied during yttria precursor nano-powder precipitation. The effects of SAC on the morphology and grain size of the yttria precursor were investigated via scanning electron microscopy (SEM) and X-ray diffraction (XRD). It was found the precursor to be transformed from irregular platelets/spheres to uniform spheres due to the SAC vibration effect. High frequency and density of SAC exerted greater influence on the morphology and grain size of the yttria precursor than weaker one.     

Improved Low-Temperature Environmental Degradation of Yttria-Stabilized Tetragonal Zirconia Polycrystals by Surface Encapsulation

An encapsulating layer was deposited on the surface of tetragonal zirconia polycrystals doped with 3 mol% of yttria (3Y-TZP), to prevent low-temperature environmental degradation (aging) of the material. The layer, which was composed of silica and zircon, was formed on the surface by exposing the specimens next to a bed of silicon carbide powder in a flowing hydrogen atmosphere that contained ∼0.1% water vapor at 1450°C. The layer was ∼0.5 µm thick and is expected to be under strong residual compressive stress. This encapsulation process remarkably improved the low-temperature degradation of the material. The strength of the specimens also was improved by this process.     

Improvement on sintering property of the face coat of yttria mould shells for investment casting

In order to explore methods for improving the sintering property of yttria face coat to prevent the thermal spalling phenomenon during investment casting, without significantly increasing the cost，the effects of electrode types in the vacuum furnace and the doping of oxides on the sintering character of yttria face coat at high temperature have been investigated. By contrast with the results of traditionally sintered pure yttria face coat at 1700?℃, the promotion in densification of the yttria face coat of the mould shells by doping La₂O₃ +?ZrO₂ is the most efficacious, whereas doping CeO₂ +?ZrO₂ can impede the densification of the yttria face coat. After sintering at 2000?℃ in a vacuum furnace with graphite electrodes, the yttria face coat can get complete densification, while the yttria face coat shows incomplete densification in a furnace with tungsten electrodes, whatever doped or undoped. But yttria grains in the face coats doped with oxides are larger than those in the un-doped one. Both CaO?+?ZrO₂ doping and MgO + ZrO₂ doping can make greater acceleration of the yttria grain growth than La₂O₃ +?ZrO₂ doping and CeO₂ +?ZrO₂ doping.     

Colloidal Stability of Zirconia-Doped Yttria–Silica Binary Aqueous Suspensions

Minor amounts of zirconia (up to 5 wt%) were fused with yttria and their effect on water solubility of yttria, and colloidal stability of yttria–silica aqueous binary suspensions, was examined. It is shown that incorporated zirconia reduces the water sensitivity of yttria while maintaining the hydrophilic nature of the surface. This fusion procedure makes yttria particles suitable for production of longlasting yttria–silica aqueous suspensions.     

Effects of Yttrium on the Sintering and Microstructure of Alumina–Silicon Carbide "Nanocomposites"

Alumina and alumina-based "nanocomposites" with 2 and 5 vol% silicon carbide and varying amounts of yttria (0–1.5 wt%) have been prepared by pressureless sintering in the temperature range 1450°–1650°C. The effects of composition and sintering temperature on density and microstructure are reported. Yttria inhibited sintering in alumina, but enhanced the sinterability of the nanocomposites. It also induced abnormal grain growth in both alumina and nanocomposites, but strongly bimodal grain size distributions could be prevented by careful choice of the composition and the sintering temperature. Fully dense (>99%), fine-grained alumina–5 vol% SiC–1.5 wt% yttria nanocomposites were produced from uniaxially pressed powders with a yttria content of 1.5 wt% and a sintering temperature of 1600°C. Reasons for this behavior are discussed, and it is suggested that the enhancement of sintering in the alumina–SiC materials is because of the reaction of silica on the surface of the silicon carbide particles with alumina, yttria, and possibly magnesia, modifying the grain boundary composition, resulting in enhanced grain boundary diffusion. scanning transmission electron microscopy/energy-dispersive X-ray data show that such co-segregation does occur in the yttria-containing nanocomposites.