刚玉和β-SiAlON对MgO基浇注料流变性的影响

采用65%(质量分数,下同)电熔镁砂作骨料(8~5mm,5~3mm,3~1mm,≤1mm),27%电熔镁砂粉(≤0.044mm和≤0.074mm)、4%Al2O3微粉和4%SiO2微粉作基质料,以此为基础配方,首先分别用5%、10%、15%、20%的电熔白刚玉粉(≤0.044mm)等量取代同粒度的镁砂粉,然后在加入10%刚玉粉的基础上,分别用2.5%、5%、7.5%和10%的矾土基β-SiAlON(≤0.088mm)取代等量的刚玉粉,分别加水制成两组MgO基浇注料,并采用浇注料流变仪研究了刚玉粉和β-SiAlON粉的加入量对浇注料流变性(扭矩、流动阻力和粘度)的影响。研究结果表明在MgO基浇注料中加入≤10%的刚玉粉时,浇注料的扭矩、粘度和流动阻力较低,流变性较好;加入低于7.5%的β-SiAlON时,对MgO基浇注料的流变性影响不大,但超过7.5%后,浇注料的流变性趋于变差。     

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.     

Synthesis and luminescent properties of low oxygen contained Eu^2＋-doped Ca-α-SiAION phosphor from calcium cyanamide reduction

A new convenient calcium cyanamide （CaCN2） reduction route was developed to synthesize the Eu^2＋ activated Ca-α-SiAION phosphors containing low oxygen content. The luminescence properties of the obtained products were investigated for white LEDs application. The critical Eu^2＋ concentration in various hosts and its effect on the photoluminescence properties were studied. The optimized sample （10at.% Eu^2＋ vs. Ca^2＋） could be efficiently excited by the current GaN/InGaN blue LED chips and provided emission intensity competitive with that of YAG：Ce^3＋ （P46-Y3） standard, revealing that this phosphor was a potential candidate for phosphor-converted white LEDs.     

影响凝胶注模成型SiAlON-SiC复相材料坯体性能的因素

选用Al粉、Si粉、SiO2 等活性原料与较大颗粒的SiC ,采用凝胶注模成型工艺制备了SiAlON-SiC复相耐火材料的坯体 ,并研究了有机单体、分散剂和引发剂的加入量以及催化剂、胶凝温度等因素对坯体性能的影响。最终 ,在有机单体AM加入量为 1.8% (质量分数 ,下同 ) ,交联剂MBAM加入量为 0 .6‰ ,引发剂过硫酸铵溶液的最佳加入量为 0 .9% (体积分数 ) ,胶凝温度在 6 0℃左右 ,不加催化剂的条件下 ,制备出了抗折强度达到 32MPa ,密度为 2 .5g·cm- 3的均匀致密的SiAlON -SiC复相材料坯体。     

Microstructural Tailoring and Characterization of a Calcium α-SiAlON Composition

Three calcium α-SiAlON microstructures—namely, fine-grained, bimodal, and large elongated—were developed using powders of the same composition and then characterized. The evolution of grain size and morphology was determined to be a process of nucleation and growth that could be controlled with a two-step sintering technique. The extent of texture was identified in the as-hot-pressed materials as a function of sintering conditions. Samples with different microstructures exhibited different hardness and fracture toughness. The true hardness was derived from the intrinsic relation between applied loads and indent sizes. The effect of microstructure on hardness and fracture toughness was analyzed.     

多型体SiAlON(12H,21R)结合刚玉耐火材料的制备及力学性能

以电熔白刚玉、矾土细粉、铝(Al)粉和硅(Si)粉为原料,通过原位氮化反应烧结工艺在较低温度(1 500 ℃)下制备了多型体SiAlON[12H(SiAl5O2N5),21R(SiAl6O2N6)]结合刚玉耐火材料.研究了多型体SiAlON含量对材料的体积密度、显气孔率、常温及高温抗折强度的影响.用X射线衍射和扫描电镜分析材料的物相组成及显微结构.结果表明:随多型体SiAlON含量的增加,材料的常温及高温抗折强度显著提高,多型体SiAlON的质量分数为15%时,1 400 ℃材料的抗折强度可达29MPa.显微结构的研究表明:多型体SiAlON(12H,21R结合刚玉耐火材料的高温断裂方式以穿晶断裂为主.     

Liquid-Phase Growth of Small Crystals for Seeding α-SiAlON Ceramics

Single-phase small crystals of Li-, Mg-, Ca-, Y-, Nd-, and Yb-α-SiAlONs have been obtained by liquid-phase sintering for various compositions and processing conditions. These crystals are suitable for seeding grain growth in α-SiAlON ceramics. The influence of chemical and processing parameters (starting composition and powders, green density, liquid content, heating schedule, nitrogen pressure, and temperature) on the size and morphology of seed crystals has been investigated. The results are compared with those for β-Si₃N₄ crystal formation, and the differences are discussed in terms of nucleation and growth kinetics during liquid-phase sintering.     

Subsurface Indentation Damage and Mechanical Characterization of α-Sialon Ceramics

Two hot-pressed sintered α-sialon samples of differing microstructures, but identical chemical composition, were evaluated first, in terms of indentation hardness and modulus, by depth-sensing indentation (DSI) tests on planes parallel and normal to the hot-pressed surface. The surface and subsurface cracks created under the DSI tests have also been investigated in relation to the effect of microstructure. Subsequently, Vickers indentation tests were conducted to explore the deformation and fracture characteristics in the two samples. The effect of microstructure and grain orientation on the development of different types of cracks, in particular subsurface cracks, was revealed and analyzed. Additionally, it suggested that the focused ion beam (FIB) miller is a preferred tool, in comparison to the conventional cross-sectioning techniques, for examining subsurface crack formation and structural characteristics.     

Spark plasma sintering behavior of combustion-synthesized (Y,Ca)-α-SiAlON

This paper describes the sintering behavior of combustion-synthesized (Y, Ca)-α-SiAlON powders when using spark plasma sintering (SPS) technology. The effects of sintering temperature, heating rate, and holding time on the densification behavior, α→β phase transformation, and Vickers hardness were investigated in detail. Fully dense Y-α-Si_12−(m+n)Al_m+nO_nN_16−n (m=1.2, n=0.6, Y-α-SiAlON) and Ca-α-Si_12−(m+n)Al_m+nO_nN_16−n (m=1.0, n=0.5, Ca-α-SiAlON) were obtained during sintering for 10 min at final temperatures as low as 1400 °C and 1500 °C, respectively. X-ray diffraction results showed that more than 50 mass% of α-phase transformed to the β-phase for Y-α-SiAlON after SPS, whereas no obvious α→β phase transformation was observed for Ca-α-SiAlON, even after sintering at a high temperature of 1600 °C. A maximum Vickers hardness of 18.56 GPa and 19.95 GPa was reached for Y-α-SiAlON and Ca-α-SiAlON, respectively.