Fabrication of Low-Porosity Indium Tin Oxide Ceramics in Air from Hydrothermally Prepared Powder

Compositionally homogeneous indium tin oxide (ITO) ceramics with low porosity were obtained successfully by sintering hydrothermally prepared powders. The fabrication technique began with the preparation of microcrystalline, homogeneously tin-doped (5 wt%) indium oxyhydroxide powder, under hydrothermal conditions. Low-temperature (∼500°C) calcination of the hydrothermally derived powder led to the formation of a substitutional-vacancy-type solid solution of In₂Sn_{1− x} O_{5− y} , and further heating of this phase at temperatures of >1000°C resulted in the formation of the tin-doped indium oxide phase, which had the C -type rare-earth-oxide structure. The sintering of uniformly packed, calcined powder compacts at 1450°C for 3 h in air resulted in low-porosity (∼0.7%) ITO ceramics.     

An oscillatory pressure sintering of zirconia powder: Rapid densification with limited grain growth

A novel oscillatory pressure sintering (OPS) process is reported to prepare high‐quality ceramics. The oscillatory pressure was applied at three stages (initial, intermediate, and final) during sintering process of zirconia ceramics for the first time. The microstructure of the samples prepared by OPS develops in a more homogeneous manner, leading to a higher final density, a smaller average grain size, and a narrower distribution of grain sizes compared with the samples prepared by conventional pressureless sintering (PS) and hot‐pressing (HP) processes. Remarkably, the OPS samples was obtained at relatively lower heating temperature and less soaking time for 1300°C and 0.5 hours than the samples prepared by other two techniques at 1450°C and 1 hour. The current results suggest that OPS is an effective technique for preparing high‐quality zirconia ceramics with low heating temperature and short sintering time, thus, it obviously reduces cost.     

Effects of particle size and dispersion methods of In2O3‐SnO2 mixed powders on the sintering properties of indium tin oxide ceramics

Three group samples were used to investigate the effects of particle size and dispersion methods of In₂O₃‐SnO₂ mixed powders on the sintering properties of ITO ceramics by BET, SEM, XRD, and EPMA, etc. High‐density (99.8% of TD) ITO ceramics, with dimensions of 350 × 250 × 8 mm³ for the industrial application, were obtained by the mixed powders of In₂O₃ calcined at 1000°C and SnO₂ with BET 6.0 ± 0.5 m²/g and collocation use of ball mill for 300 minutes, stirred mill for 60 minutes, and sand mill for 3 minutes. The results indicate that: (i) the larger the SnO₂/In₂O₃ particle size ratio, the higher the density of ITO ceramics, (ii) the dispersion of mechanical ball‐mill methods for nanosized In₂O₃ and SnO₂ powders is beneficial to the densification and structural homogeneity, and (iii) the smaller the relative grain size, the more uniform the distribution of grain size.     

Liquid‐phase sintering,microstructural evolution,and microwave dielectric properties of Li2Mg3SnO6–LiF ceramics

The liquid‐phase sintering behavior and microstructural evolution of x wt% LiF aided Li₂Mg₃SnO₆ ceramics (x = 1‐7) were investigated for the purpose to prepare dense phase‐pure ceramic samples. The grain and pore morphology, density variation, and phase structures were especially correlated with the subsequent microwave dielectric properties. The experimental results demonstrate a typical liquid‐phase sintering in LiF–Li₂Mg₃SnO₆ ceramics, in which LiF proves to be an effective sintering aid for the Li₂Mg₃SnO₆ ceramic and obviously reduces its optimum sintering temperature from ~1200°C to ~850°C. The actual sample density and microstructure (grain and pores) strongly depended on both the amount of LiF additive and the sintering temperature. Higher sintering temperature tended to cause the formation of closed pores in Li₂Mg₃SnO₆‐x wt% LiF ceramics owing to the increase in the migration ability of grain boundary. An obvious transition of fracture modes from transgranular to intergranular ones was observed approximately at x = 4. A single‐phase dense Li₂Mg₃SnO₆ ceramic could be obtained in the temperature range of 875°C‐1100°C, beyond which the secondary phase Li₄MgSn₂O₇ (<850°C) and Mg₂SnO₄ (>1100°C) appeared. Excellent microwave dielectric properties of Q × f = 230 000‐330 000 GHz, ε_r = ~10.5 and τ_f = ~?40 ppm/°C were obtained for Li₂Mg₃SnO₆ ceramics with x = 2‐5 as sintered at ~1150°C. For LTCC applications, a desirable Q × f value of ~133 000 GHz could be achieved in samples with x = 3‐4 as sintered at 875°C.     

低温无压烧结氮化硅陶瓷的相变及致密化研究

采用氧化铝（Al2 O3）和氧化钇（Y2 O3）为烧结助剂,利用无压烧结工艺在低温下制备氮化硅陶瓷材料。利用XRD和SEM等着重研究了无压烧结氮化硅陶瓷低温阶段时的物相组成及其致密化。结果表明：当添加剂含量为10％,烧结温度高于1430℃时,α→β相转变较快;当烧结温度达到1510℃时,α相全部转变为β相。     

热压烧结制备粉煤灰建筑陶瓷的工艺研究

以固体废弃物粉煤灰为主要原料,通过对原料进行预烧处理工艺得到活化粉煤灰粉体,分别在850 ℃、875℃、900 ℃、925 ℃、950 ℃度进行真空热压烧结,制备粉煤灰建筑陶瓷复合材料.利用XRD对复合材料的物相组成进行分析、采用SEM分析样品的微观结构,结合烧成样品的吸水率、体积密度、硬度等,分析不同的烧结温度对陶瓷性能的影响.结果表明:真空热压烧结过程中,随着温度升高,样品低共熔相增多,致密化程度增加.当烧结温度达到925℃时,所得复合陶瓷材料晶粒分布均匀、细小,晶粒尺寸为0.4~0.5 μm;陶瓷样品的体积密度、吸水率、硬度分别为2.62 g/cm3、0.05%、6.5 GPa.     

Effect of magnetic CoFe2O4 component on sintering densification process of Bi3.15Nd0.85Ti3O12 ceramics

Sintering densification processes of the composite ceramics (Bi_3.15Nd_0.85Ti₃O₁₂ (BNdT)/CoFe₂O₄ (CFO)) have been investigated using dilatometric experiments combining with the TG-DTA, density measurements and microstructure studies. Microstructures analyses and quantitative calculations show that the composite ceramics achieve densification at low temperatures (<1150 °C). The formation of coherent-lattice interfaces between (200)/(020)_BNdT and (310)_CFO are considered to play an important role on such densification. The intrinsic preferred orientation of BNdT grains is suppressed by CFO phase because of this coherent relationship. Although the sintering activation energies of 0.8BNdT-0.2CFO are about 2.7 times larger than those of pure BNdT due to the pinning effect, the composite ceramic could still be densified, indicating the formation energy of coherent-lattices provided the extra sintering force. The even coercive electric fields of the resulting pure BNdT and 0.8BNdT-0.2CFO ceramic are approximately 89 and 97 kV/cm, respectively, at 250 kV/cm. The polarization of 0.8BNdT-0.2CFO reaches saturation around 430 kV/cm.     

Densification characteristics of chromia/alumina castables by particle size distribution

The quality of the refractories applied on integrated gasification combined cycle should be a key factor that affects both the reliability and the economics of gasifier operation. To enhance the workability of chromia/alumina castables, three types of ultrafine alumina powder were added to improve the workability. Densification behavior of such castables in the presence of ultrafine alumina was assessed through the measurement of parameters like flow value, viscosity, bulk density, apparent porosity, and microstructure evaluation by an SEM study. It's proved that the specific surface area and particle size distribution of ultrafine powders in matrix parts greatly influence the densification behavior of these castables.