Gelcasting and Pressureless Sintering of Translucent Alumina Ceramics

Gelcasting is a very useful technique for producing ceramic parts with complex shapes. In this work, gelcasting in air and pressureless sintering in hydrogen were applied to manufacture translucent alumina ceramics. A stable suspension with 75 wt% solids was prepared by ball milling. Trapped bubbles were removed completely before casting to obtain homogeneous green bodies. Final sintering was carried out in a hydrogen furnace at 1850°C for 3 h. Homogeneous microstructures of both calcined and sintered bodies were obtained. The in-line transmission of the sample with a thickness of 0.5 mm increased gently from 9% to 10% in the wavelength range of 190–1100 nm.     

Translucent Mg-α-Sialon Ceramics Prepared by Spark Plasma Sintering

The translucent Mg-α-sialon ceramics have been prepared by spark plasma sintering (SPS) α-Si₃N₄ powder with AlN and MgO as the additives at 1850°C for 5 min. The sample possesses a uniform, dense microstructure under the rapid densification of SPS process. The translucent Mg-α-sialon ceramics achieve the maximum transmittance of 66.4% for the sample of 0.5 mm in thickness in the medium infrared region, which could be attributed to the equiaxed microstructure and few glassy phase confirmed by the observation of transmission electron microscopy. The material also exhibits good mechanical properties of high hardness (21.4±0.3 GPa) and fracture toughness (6.1±0.1 MPa·m^1/2).     

α-SiAlON Ceramics Obtained by Slip Casting and Pressureless Sintering

Dense α-SiAlON ceramics were obtained by pressureless sintering of green compacts prepared using slip casting. The rheological properties of the reaction SiAlON suspension were optimized to achieve a high degree of dispersion with a high solids volume fraction, which resulted in homogeneous and relatively dense green bodies with high sintering ability, which could be densified by pressureless sintering at 1750°C for 2 h. The sintered samples revealed a high degree of uniformity and almost fully dense microstructures that consisted of many small, elongated grains homogeneously dispersed in the fracture surfaces, which had properties comparable with those of other SiAlONs obtained using hot pressing.     

Optically Translucent Mullite Ceramics

The optical transmittance of pressureless sintered and of hot isostatically pressed (HIPed) mullite ceramics was studied in the near infrared (NIR), visible light (VIS), and the ultraviolet (UV) spectrum ranges. Both processing methods provided fine-grained microstructures (mean grain size of 5–10 μm) with equiaxed grains and a narrow grain-size distribution. In pressureless sintered mullite, the porosity was 5.5% and transmittance was 20% in the VIS and NIR ranges. In the HIPed mullite, with porosity <1%, a transmittance of 40% was measured in the VIS range and up to 80% in NIR. UV transmittance of both pressureless sintered and HIPed mullite samples was low. The optically translucent mullite was found suitable for optical windows in the VIS and NIR ranges, particularly at elevated temperatures.     

掺杂Sb2O3的SnO2基陶瓷的SPS制备及性能研究

采用放电等离子烧结技术(SPS)制备了掺Sb2O3的SnO2基陶瓷.研究了烧结温度及Sb2O3的含量对SnO2基陶瓷的密度、物相、结构和电学性能的影响.研究袭明:随着烧结温度的提高,SnO2基陶瓷的相对密度逐渐增大,室温电阻率璧先减小后增大的趋势;随着Sb2O3掺杂量的增加,样品的相对密度呈先增加后减小的趋势,室温电阻...     

Spark Plasma Sintering of High-Density Antimony-Doped Tin Oxide Ceramics from Nanoparticles

The spark plasma sintering (SPS) technique was used for the first time to fabricate antimony-doped tin oxide (ATO) ceramics from monodispersed ATO nanoparticles synthesized by the hydrothermal method. The ceramics' relative density increased from 83.7% when sintered at 750°C to the highest value of 97.4% at 850°C, and a corresponding highest conductivity of 2.2 × 10⁻⁴Ω·cm was also obtained at this temperature.     

Sintering Kinetics of Porous Ceramics from Natural Diatomite

The sintering kinetics of the porous ceramics from natural diatomite is investigated by means of stepwise isothermal dilatometry (SID) accompanied with XRD, scanning electron microscope (SEM), and porosity measurement. We find that the isothermal shrinkage data from SID could be well analyzed to get kinetic parameters according to the empirical rate equation developed by Makipirtti–Meng , where Y is the fractional volume shrinkage during sintering process and n a dimensionless exponent. The apparent activation energy Δ E values obtained for 850°–1000°C and 1050°–1150°C are 911.8 and 610.5 kJ/mol, respectively. Correspondingly, the exponent n values for the two temperature ranges are also much different and can be served to reveal the morphology changing during the sintering process, which is well consistent with the SEM observation.     

Translucent Yttria‐ and Silica‐Doped Mullite Ceramics with Anisotropic Grains Produced by Spark Plasma Sintering

Translucent, high‐performance, mullite ceramics with anisotropic grains were prepared by the spark plasma sintering (SPS) of a powder mixture consisting of commercial mullite powder, which already contained small amounts of alumina (θ and α) and silica (cristobalite) (≤3 wt% in total), to which 2 and 1 wt% of yttria and amorphous silica was admixed, respectively. The combination of low‐viscosity Y₂O₃–Al₂O₃–SiO₂ transient liquid formation and SPS sintering provided enhanced densification, also provoking anisotropic grain growth (which became exaggerated after 20 min of SPS dwell time), at a relatively low sintering temperature of 1370°C. In this way, it was possible to meet the conflicting demands for obtaining a dense mullite ceramic with anisotropic grains, ensuring good mechanical properties, while preserving a noticeable light transmittance. In terms of mechanical and optical properties, the best results were obtained when SPS dwell times of 5 and 10 min were employed. The as‐sintered samples possessed densities in the range 3.16–3.18 g/cm³, anisotropic grains with an aspect ratio (AR) of 7 and a grain thickness of approximately 0.45 μm, a flexural strength between 350 and 420 MPa, a Vickers indentation toughness and a hardness of approximately 2.45 MPa·m^1/2 and 15 GPa, respectively, and an optical transmittance of between 30% and almost 50% in the IR range.     

Translucent α-Sialon Ceramics by Hot Pressing

The single-phase α-sialon ceramics with high optical transmittance have been prepared by hot pressing. The maximum transmittance reached 65.2% and 52.2% in the infrared wavelength region, 58.5% and 40% in the visible region for the samples 1.0 and 1.5 mm thickness, respectively. The material also exhibited good mechanical properties of high hardness (20 GPa) and better fracture toughness (5.1 MPa·m^1/2). Both high optical transmittance and improved toughness of α-sialon ceramics were attributed to the less-grain-boundary glassy phase and the homogeneous microstructure, which was obtained by a proper process and confirmed by SEM and TEM observation, compared to that prepared by ordinary sintering. It is, therefore, expected that the translucent α-sialon ceramics could be a promising optical window material.     

Fabrication of Translucent Magnesium Aluminum Spinel Ceramics

A precursor for magnesium aluminum spinel powder, composed of crystalline ammonium dawsonite hydrate (NH₄Al(OH)₂CO₃·H₂O) and hydrotalcite (Mg₆Al₂(CO₃)(OH)₁₆·4H₂O) phases, was synthesized via precipitation, using ammonium bicarbonate as the precipitant. The precursor was characterized by differential thermal analysis/thermogravimetry, X-ray diffractometry, and scanning electron microscopy. Reactive spinel powder, which could be densified to translucency under vacuum at 1750°C in 2 h without additives, was obtained by calcining the precursor at 1100°C for 2 h.     

溶胶—凝胶法制备莫来石先驱粉末的烧结特性及材料的显微结构变化

对用溶胶－凝胶法制备的莫来石先驱粉末的晶化及烧结行为为进行了研究，先驱粉末在１０００℃煅烧１ｈ形成少量尖晶石，在更高的高度由这种尖晶石相及无定形ＳｉＯ２相形成莫来石，煅烧后的粉末具有很高的活性，在１５５０℃烧成０．５ｈ，烧结体相对密度达到９８．７％，陶瓷显微结构由细小等轴莫来石晶粒构成，随着烧成时间的延长或烧成温度的升高，烧结体中柱状莫来石晶粒变得越来越多。     

氧化亚锡废渣制备二氧化锡的方法研究

探索了利用氧化亚锡废渣制备二氧化锡的工艺条件。利用回转窑煅烧氧化亚锡制备二氧化锡,优化的工艺条件为:煅烧温度为650℃、煅烧时间为30 min,回转窑回转速率为2 r/min,产品的质量指标符合《GB/T26013-2010二氧化锡》的要求。     

微波烧结AlN陶瓷的初步研究

采用微波高温烧结工艺,制备了致密的AlN陶瓷,并初步探讨了微波烧成环境对烧结体性能的影响.结果表明:利用微波烧结AlN陶瓷,虽然在节能省时方面效果显著,但是微波烧成环境对AlN陶瓷的烧成影响比较复杂,本文着重指出烧成环境中的碳热还原气氛能极大地加快AlN陶瓷的致密化速率,但容易在AlN陶瓷晶界相内部产生气孔,使AlN陶瓷的热导率降低.     

Translucent Cerium Fluoride Ceramics Fabricated by Hot‐Pressing for Scintillation Application

In this study, translucent CeF₃ ceramics was firstly fabricated by hot‐pressing, aiming to develop an economical, radiation hard scintillation material. After sintering at 950°C and pressure exertion of 300MPa for 2 h, a transmittance of 10–25% was achieved in the visible region, through a thickness of 0.75 mm. Microstructure investigations indicated the average grain size was around 42.7 μm, with no obvious pores observed on the fracture surface. The X‐ray luminescence spectra, decay time, and thermoluminescence spectra were measured, and the results of the ceramics were similar to its corresponding single crystals, which proved it to be a promising scintillation material.     

Liquid-Phase Sintering of Ceramics

Expressions for the sintering rate in liquid-phase sintering are derived for coupled-interface dissolution and liquid-phase diffusion. The analysis reveals the important role of stress gradients in the grain boundary phase and also shows that such gradients cannot be supplied by liquid-phase flow. Stress-supporting structure in the grain boundary phase is thus implied. The probable existence of such structure is revealed by diffuse dark-field scattering studies, using transmission electron microscopy, on partially sintered alumina/anorthite bodies.     

低温放电等离子烧结法制备氮化硅陶瓷

分别以MgO-Al2O3或MgO-AlPO4作为烧结助剂,采用放电等离子体低温快速烧结方法制备了主相为α相的Si3N4陶瓷材料.采用X射线衍射和扫描电子显微镜分析了样品的物相组成和显微结构;研究了烧结助剂及其含量、烧结温度对陶瓷样品的相对密度与力学性能的影响.结果表明:当采用4%质量分数,下同)MgO-4%Al2O3烧...     

放电等离子烧结制备AlON陶瓷

以A1N粉和A12O3为原料，用放电等离子烧结(SPS)技术制备单相A1ON陶瓷。研究表明：用SPS技术在1700℃仅保温3min就可得到99TD％的A1ON陶瓷，该技术是实现A1ON陶瓷低温快速烧结的有效途径。