先驱体转化法制备SiCO陶瓷粉体的氧化性能

以先驱体转化法制备的SiCO陶瓷粉体为原材料,采用热重法研究了粉体在干燥空气中的氧化性能。采用液态聚碳硅烷裂解制备的SiCO 陶瓷粉体平均粒径为7μm,氧化处理温度分别为：900℃、950℃、1000℃、1050℃,氧化时间均为4 h。结果表明：液态聚碳硅烷裂解制备的SiC_{1. 12}O_{0. 12}陶瓷粉体在1173～1373 K、干燥空气中,氧化增重表现为典型的2阶段变化规律：900℃ 下的前80 min至1050℃下的前20 min时间内,材料氧化表现为快速增重趋势;随后较长的氧化时间里,材料内部气孔的氧化由于封孔而停止,氧化反应主要由扩散控制,样品增重不太明显。经计算SiCO陶瓷粉体的氧化活化能为121 kJ/mol,并在此基础上推导了热重法与厚度测量法获得的2种氧化速率常数的转变公式。     

Rheology of silicone-coated ceramic powders

Abstracts are not published in this journal This revised version was published online in November 2006 with corrections to the Cover Date.     

Tensile strength of ceramic powders

The tensile strength of granular materials has been extensively studied and is of great technological importance. Several theoretical or experimental relationships between density and strength have been proposed. This paper compares these models with experimental data from zirconia powders. It is shown that the most important parameter determining the strength of a green compact is not density but compaction pressure. A micromechanical model, which gives a qualitative understanding of ceramic powder behaviour under tensile stress, is also presented.     

BaTiO3陶瓷粉体凝胶注模成型的研究

为了研究BaTiO3粉体的凝胶注模成型，以聚甲基丙稀酰胺(PMAA—NH4)为分散剂，通过球磨制备稳定分散的BaTiO3浆料．采用正交实验设计原则，讨论了有机单体、交联剂和引发剂的用量对浆料的固化时间、坯体强度和密度的影响，确定最佳加入量(质量分数)分别为4％，1．5％和0．02％．在1340℃下烧结得到的BaTiO3陶瓷的晶粒尺寸均匀，气孔较少，致密度高，具有良好的PTC特性。     

水热法制备ZST微波陶瓷粉体

采用水热法制备了(Zr0.8Sn0.2)TiO4粉体,并借助于XRD、SEM、热分析等手段对反应后的结晶粉末进行了表征.实验结果表明,粉末性能受反应溶液pH值的影响显著.随着pH值的增大,晶粒的生长更加充分,完整.反应后的晶粒粒度为纳米尺度,表面活性大,有利于烧结.烧结温度在1260-1320℃之间,比传统固相法制备的ZST陶瓷烧结温度降低了300多度.     

Selective laser sintering of PZT ceramic powders

Conditions for the selective laser-induced layer sintering of a stoichiometric mixture of PbO, ZrO₂, and TiO₂ powders with the formation of bulk PZT ceramic articles were studied. The laser processing allows articles of the PZT ceramics to be obtained immediately in the course of sintering or upon additional annealing. Data on the microstructure and phase composition of the synthesized PZT ceramics are presented.     

Air-plasma spraying colloidal solutions of nanosized ceramic powders

Coatings prepared from nanosized powders were obtained by spraying ethanol-based colloidal solutions into a plasma plume. The powders investigated included 40 nm -Al₂O₃, 75 nm 8 wt% Y₂O₃-ZrO₂, and 750 nm 25 wt% CeO₂-ZrO₂. Spray distances from approximately 50 to 63 mm were required to achieve significant coating deposition. As observed in the TEM, the typical lamella morphology of air plasma sprayed oxide coatings was not observed in coatings fabricated from 40 nm -Al₂O₃, which was comprised of spherical powders that had partially sintered. However, lamellae were observed in the coatings prepared with both nanosized zirconia powders. The characteristic size of the lamella and the grains that comprised the zirconia coatings were nominally a few nanometers.     

氧化锌压敏陶瓷粉体的研究进展

综述了氧化锌压敏陶瓷粉体的研究进展,分析了粉体特性对压敏电阻微观结构和电性能的影响以及粉体制备中存在的问题.对粉体的制备方法和应用前景进行了展望,指出化学法合成复合粉体和高能球磨法制备纳米粉体是氧化锌压敏陶瓷粉体的两个主要发展趋势.     

Dynamic consolidation of metal powders

A brief review and assessment of the dynamic consolidation of metal powders is presented. Primary emphasis is placed on demonstrating the relationship between the shock-wave physics during consolidation and the initial and final metallurgical states of the compact. Some of the technological aspects of the process are also discussed.     

Metallic and ceramic powders for vacuum plasma spraying

All product families, including hard materials, hard metals, hard alloys, cermets, intermetallics and refractories, are usable for vacuum plasma spraying. Fine powders (less than 45 μm) that are narrowly classified within well-defined limits for oversize and undersize are used. The determination of the size distribution is of particular importance.The morphology of powders for vacuum plasma spraying has to be stressed in particular, e.g. the particle shape, the surface area, the density and the composition (agglomerate, primary grain, crystal formation).In addition, the chemical composition, i.e. the main, secondary and trace elements and the gas contents (O₂, N₂, H₂, noble gases), is specified and the lowest specification values have to be met for vacuum plasma spray powders such as M-Cr-Al-Y.Single-phase and refractory compounds with uniformity of structure as well as solid solutions can be vacuum plasma sprayed without any changes and with strict maintenance of phase uniformity and stoichiometry.     

Processing defects in ceramic powders and powder compacts

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Synthesis of ceramic oxide powders by microwave plasma pyrolysis

Ceramic powders prepared pyrolytically exhibit homogeneity and, in most cases, small grain sizes. The energy efficiency of electrically heated systems performing the pyrolysis in a stream of carrier gas is poor. Similar considerations concerning energy demand are valid for spray drying of suspensions. This situation can be improved using a microwave plasma as a source for thermal energy. The process described in this paper works with any aqueous solution of salts used as starting material in ceramics. The process was demonstrated by the synthesis of alumina, zirconia, and zirconia-based ceramic powders; where an energy efficiency of more than 80% was found. For the powder synthesis, aqueous solutions of the nitrates were used as starting materials. Through proper selection of conditions for synthesis, it is possible to obtain nanocrystalline powders, as demonstrated by electron microscopy. Because of the extreme conditions associated with plasma during synthesis, it is possible to prepare nonequilibrium structures and solid solutions in systems in which nearly no equilibrium solubility exists.     

Sintering of glass bonded ceramic barium hexaferrite magnetic powders

Mixtures of low-melting glasses (glazes) and barium hexaferrite magnetic powders sinter at relatively low temperatures (800° C) and produce dense items in which excessive grain growth has been inhibited.     

Preparation and characterization of perovskite ceramic powders by gelcasting

Perovskite La0.6Sr0.4Co0.8Fe0.2O3– (LSCF) powders have been successfully synthesized from oxide and carbonates based on the principle of gelcasting. Phase-forming temperature is very dependent on the ball-milling process during the suspension preparation. As the ball-milling time is increased, the temperature of phase formation decreases, therefore the perovskite powder obtained has a larger Brunaver–Emmett–Teller (BET) specific surface area. The grain sizes were around 1 m at 1000°C and 2 m at 1100°C from scanning electron microscopy (SEM) photographs. The perovskite powders have good sinterability: the sintering densities of ceramic bodies shaped with as-prepared powders were investigated. SEM photos show that sintered ceramics exhibit a well defined morphology in the packing and sintering of particles. The oxygen permeance of disc shaped samples, with a thickness ranging from 1.02 to 1.98 mm was 6.39 × 10–8–1.99 × 10–8 mol cm–2 s–1 at 900°C indicating that LSCF ceramics have high oxygen permeation. It can be concluded that gelcasting is a simple and effective method for preparing practical multicomponent perovskite powders.     

Preparation of ceramic composite powders from waste colliery minestones

An investigation was carried out to examine the potential for producing ceramic composites from waste colliery minestones. The nature of the raw materials had a marked influence on the kinetics and the product morphology. The product phases and product composition were dependent on the reaction temperature. Mullite-SiC composite powders could be formed at temperatures below 1300C while Al₂O₂-SiC was the final product of reduction at higher temperatures.Visiting scientist from Changsha Research Institute of Mining and Metallurgy, China.     

Dispersion of ceramic powders into particulate superplastic Al-Li alloy

A new method for dispersing homogeneously fine ceramic powders into a particulate alloy matrix has been developed. The Al-Li matrix alloy, with controlled crystal grain size and shape, shows superplastic behaviour under certain conditions. The homogeneous dispersion of SiC in the matrix alloy was achieved by introducing the fine particles of filler along the grain boundaries within the alloy particles. This new compounding method yields a composite powder (i.e. each particle itself is a composite) rather than a mixture of different components.     

纳米3Y-TZP陶瓷粉体形貌的分形分析

为了应用分形理论确定纳米3Y－TZP粉体制备方法的优劣，采用共沸蒸馏法和醇水溶液加热法制备了纳米3Y－TZP粉体，利用TEM观察确定了粉体粒径尺寸和团聚体形貌，并运用分形理论分析了分形维数和粉体烧结性能的关系。结果表明：纳米粉体在颗粒尺寸相同的情况下，粉体分形维数越低，团聚体半径越小，烧结性能越好；对粉体TEM图像进行分形维数计算并与粉体红外光谱分析和烧结结果进行了比较，确定醇水溶液加热法制备纳米3Y－TZP粉体效果较好。