Aluminum Reduction and Nitridation of Bauxite

The application of bauxite with low Al2O3 content has been studied in this paper and β-SiAlON has been obtained from two kinds of bauxites (Al2O3 content 68.08 mass% and 46.30 mass% respectively) by aluminum reduction and nitridation method. The sequence of reactions has been studied using thermal analysis (TG-DTA), X-ray diffraction (XRD) analysis and scanning electron microscopy (SEM) with EDS. Compared with carbon thermal reduction and nitridation of aluminosilicates employed presently, the reaction in the system of bauxite-Al-N2 occurs at lower temperature. β-SiAlON appears as one of the main products from 1573K and exists stably in the range of the present experimental temperature. The microstructure of β-SiAlON obtained at 1773 K is short column with 5-10μm observed by SEM.     

SiAlON对MgO基浇注料高温性能的影响

以电熔镁砂为骨料,以电熔镁砂细粉、电熔白刚玉、矾土基β-SiAlON、α-Al2O3微粉和SiO2微粉为基质,固定电熔镁砂骨料与基质的质量比,并固定基质中各成分的质量分数,基质中用SiAlON逐步取代刚玉细粉,试样经 1600℃ 3h烧成后,考察SiAlON加入量(0、2. 5%、5%、7. 5%、10% )对浇注料热震稳定性、高温抗折强度(1400℃)等性能的影响,并对试样进行扫描电镜和能谱分析。结果表明:由于SiAlON的引入,在MgO基浇注料基质中起到了强化增韧作用,提高了浇注料的抗热震性能和高温抗折强度。     

Self-Reinforced α-SiAlON Ceramics with Improved Damage Tolerance Developed by a New Processing Strategy

Alpha-SiAlON ceramics with a refined self-reinforced microstructure, i.e., containing acicular grains with dimensions much smaller than those obtained in previous studies, embedded in a matrix consisting of submicrometer-sized isotropic grains, were prepared by applying a rapid one-step sintering procedure. To suppress the overabundant formation of α-SiAlON nuclei, a combination of stabilizing cations, Y + Yb, was used; to encourage formation of acicular α-SiAlON grains, a small amount of an extra liquid (∼3 vol%) was introduced; to avoid abnormal grain coarsening resulting from dynamic ripening, the final sintering temperature was set to just slightly above the minimum temperature threshold for activating grain growth (1700°C). The fully dense compacts obtained exhibited excellent thermal-shock resistance, and hardness and fracture toughness values of 20 GPa and 5.1 MPa·m^1/2, respectively.     

用于白光LED稀土Eu掺杂SiAlON基荧光粉的发光性能

SiAlON基荧光粉因其优异的化学和物理稳定性,成为近年来发光领域的一个研究热点,尤其在LED等领域,受到研究者的热切关注。稀土掺杂SiAlON基荧光粉体有望成为新一代照明光源。由于缺乏青色光发射,往往会造成显色性能不足。本研究通过传统高温固相法合成了β-Si₅AlON₇:Eu荧光粉,采用X射线衍射仪(XRD)、扫描电镜(SEM)、X射线光电子能谱(XPS)等研究了其结构、形貌、元素和价态。通过光谱仪表征了样品的激发光谱以及发射光谱的波长范围并测试了热猝灭性能,发现激发波长覆盖紫外至蓝色光区域,并且发射光谱显示出典型的Eu²⁺跃迁的宽谱。在300℃下,样品的发射光强度依然可达到室温强度的40%左右,热激活活化能(E_a)达到了3.7 eV,相比较商用YAG:Ce³⁺(YAG)荧光粉,热稳定性有一定的提升。在与蓝色芯片复合后成功制备了高显色(显色指数R_a=87)的白色发光LED,对应的色温也达到了暖白光范围(CCT=4501K)。本研究实现了SiAlON基青色...     

一维SiAlON的合成及其生长机理

SiAlON具有优异的常温、高温力学性能和良好的化学稳定性,是一种重要的高温结构材料。一维SiAlON(纳米线、纳米棒、纳米带等)特有的单晶结构更是赋予了其优异的力学性能以及独特的光学和电学性能,使其在高温陶瓷、光学及电学等领域具有广阔的应用前景。综述了近年来一维SiAlON的研究现状,总结了一维SiAlON的合成及其生长机理,并展望了其应用前景及发展方向。     

Carbothermal/aluminothermic reduction nitridation synthesis of ZrN–SiAlON refractory composites from zircon and bauxite: a comparative study of the reduction effect of reducers

The ZrN–SiAlON composite refractory powder was successfully synthesised from zircon and bauxite minerals by the carbothermal reduction nitridation or the aluminothermic reduction nitridation method with three typical reducers, including carbon coke, carbon black and aluminium powder. The effect of reaction temperatures on phase composition and microstructure was investigated using X-ray diffraction and a scanning electron microscopy (SEM), respectively. The thermodynamics equilibrium relationships of the condensed phases were analysed as well. The results showed that carbon coke was the most optimum reducer and when it was used as the reducer, the main final products were granular ZrN with a little β-SiAlON. Nevertheless, ZrO₂ was produced during reduction at 1600°C when the reducer was carbon black, because the activity of carbon black was the poorest. Additionally, more byproducts were produced in the case of Al powder used as reducer at 1600°C, such as AlN polytype and Al₂O₃.     

Effect of Y2O3 on the physical properties and biocompatibility of β–SiAlON ceramics

To investigate the effects of Y₂O₃ on the physical properties and biocompatibility of β–SiAlON ceramics, β–SiAlON ceramics were prepared with Al, Si, and α–Al₂O₃ powders using a direct nitriding technique. As a sintering additive, Y₂O₃ helps lower the sintering temperature and forms β–SiAlON ceramics. In this study, the physical and biological properties of the prepared ceramics were investigated to evaluate their use as bone-repairing material. Experiments revealed that the main crystal composition of the sample was Si₄Al₂O₂N₆, containing small amount of additional phases Y₃Al₅O₁₂ with increasing content of Y₂O₃. The porosity and compressive strength initially decrease and then increase to their initial values, whereas the bulk density exhibits the opposite trend with an increased proportion of Y₂O₃. The proliferation of osteoblastic and angiogenic cells demonstrates that β–SiAlON and Y₃Al₅O₁₂ have good biocompatibility; however, the sample porosity has a slight effect on the cell proliferation rate. This implies that in human tissues, bone-repairing speed can be adjusted by modifying the sample porosity or material surface roughness. Therefore, Y₂O₃ can be added to β–SiAlON ceramics to regulate their microstructure, physical properties, and biological properties for tissue engineering applications.     

Improvement of Mechanical Properties and Corrosion Resistance of Porous β-SiAlON Ceramics by Low Y2O3 Additions

Addition of Y₂O₃ as a sintering additive to porous β-SiAlON (Si_{6− z} Al _z O _z N_{8− z} , z = 0.5) ceramics has been investigated for improved mechanical properties. Porous SiAlON ceramics with 0.05–0.15 wt% (500–1500 wppm) Y₂O₃ were fabricated by pressureless sintering at temperatures of 1700°, 1800°, and 1850°C. The densification, microstructure, and mechanical properties were compared with those of Y₂O₃-free ceramics of the same chemical composition. Although this level of Y₂O₃ addition did not change the phase formation and grain size, the grain bonding appeared to be promoted, and the densification to be enhanced. There was a significant increase in the flexural strength of the SiAlON ceramics relative to the Y₂O₃-free counterpart. After exposure in 1 M hydrochloric acid solution at 70°C for 120 h, no remarkable weight loss and degradation of the mechanical properties (flexural and compression strength) was observed, which was attributed to the limited grain boundary phase, and with the minor Y₂O₃ addition the supposed formation of Y-α-SiAlON.     

Combustion synthesis of high‐purity β‐SiAlON fine powders using natural kaolin

Single‐phase β‐SiAlON particles with submicron size were prepared via combustion synthesis (CS) using natural kaolin, Si, and Al as raw materials under a nitrogen atmosphere of 1 MPa. Kaolin could not only act as the raw material to provide the source of oxygen, but also act as the diluent to reduce the reaction temperature by eliminating the structural water during reaction process.