稀土添加剂在硬质合金中的应用研究

对国内含稀土元素的硬质合金10多年来的研制情况及稀土元素对硬质合金组织和性能的影响进行了概述。     

Characterization of Gold—Aluminum Nitride and Gold—Silicon Carbide Interfaces

Aluminum nitride and silicon carbide substrates were screen-printed with fritless gold and fired at 850°C in air. Interfacial diffusion zones up to 7 αm thick were observed, in which the concentrations of Au, Na impurities, and combined O varied together. Secondary ion mass and photoelectron spectroscopy revealed oxidized Al in the gold conductor supported by AIN. It is suggested that enhanced oxidation accompanies the diffusion of Au into the ceramics.     

硬质合金刀具在刀具总值中的变化

分析了21世纪初日本及西方其它国家的硬质合金刀具销售值(或产值)占刀具总销售的比例,及几种发展迅速的新兴硬质合金刀具品种。     

Microstructural Studies in Alkoxide-Derived Mullite/Zirconia/Silicon Carbide-Whisker Composites

Mullite composites toughened with ZrO₂ (with or without a MgO or Y₂O₃ stabilizer) and/or SiC whiskers (SiC( w )) were fabricated by hot-pressing powders prepared from Al, Si, Zr, and Mg(Y) alkoxide precursors by a sol–gel process. Micro-structures were studied by using XRD. SEM, and analytical STEM. Pure mullite samples contained prismatic, preferentially oriented mullite grains. However, the addition of ZrO₂, as well as the hot-pressing temperature, affected the morphology and grain size in the composites; a fine, uniform, equiaxed microstructure was obtained. The effect of SiC( W ) was less pronounced than that of ZrO₂. Glassy phases were present in mullite and mullite/SiC( W ) composites, but were rarely observed in Al₂O₃-rich or ZrO₂-containing samples. The formation of zircon due to the reaction between ZrO₂ and SiO₂ and the considerable solid solution of SiO₂ in ZrO₂ prevented the formation of the glassy phase, whereas the reaction between Al₂O₃ and MgO in MgO-containing samples formed a spinel phase and also deprived the ZrO₂ phase of the stabilizer. Intergranular ZrO₂ particles were either monoclinic or tetragonal, depending on size and stabilizer content; small intragranular ZrO₂ inclusions were usually tetragonal in structure.     

长诏混凝土浆砌块石重力坝渗流观测成果分析

根据长诏大坝的渗流实测资料，分析了坝体、坝基面和坝基有关部位的渗流变化规律及变化趋势，建立了各个渗流观测量的统计模型，探讨了各种环境物理量对大坝渗流的影响；对大坝的渗流状态进行了综合评价，并针对存在问题提出具体建议。     

用电石废渣制备纳米碳酸钙的研究

利用电石废渣制备得到了不同形貌的纳米级碳酸钙晶体。实验过程包括:电石废渣经过提纯后制成CaCl2溶液,然后在一定条件下和(NH4)2CO3溶液反应。在添加剂存在的情况下,制备出了纳米级碳酸钙晶体。并对反应条件如物料的浓度、反应温度、添加剂种类及作用机理进行探讨,确定了用电石废渣生产纳米碳酸钙的最佳方法,即控制温度为25℃,物料浓度为1.5mol/L,使用自制水溶性高分子添加剂,得到立方形碳酸钙,使用硼砂等可得到链状碳酸钙,添加醇类有机物可得到针状碳酸钙。     

Selectivity of Silicon Carbide/Stainless Steel Solid-State Reactions and Discontinuous Decomposition of Silicon Carbide

Solid-state reactions of SiC with a multicomponent system, stainless steel, have been studied at 1125°C. Four-layered reaction products consisting of modulated carbon precipitation zone, random carbon precipitation zone, four-phase mixture zone, and grain-boundary precipitation zone were formed in the reaction zone. The carbon precipitates were embedded in a matrix of complex metal silicides. In addition, extensive interfacial melting was noted. Carbon atom was found to diffuse faster than Si and selectively reacted with Cr to form Cr carbide(s) along the grain boundaries of stainless steel. No Fe carbides or Ni carbides were ever detected. Among the consituents existing in stainless steel, Ni atoms have the highest affinity for Si. An uphill diffusion of Ni toward the SiC reaction front was observed. While the diffusion of Cr and Fe toward SiC followed a downhill concentration gradient, very small amounts of Cr reached the SiC interface. The selective reactions of Si and C with Ni, Fe, and Cr are discussed on the basis of Gibbs free energy of formation of various compounds. The diffusion kinetics of C and Si atoms in selected metal/SiC reactions are discussed on the basis of their chemical affinities for respective metals. The modulation of carbon precipitation is correlated with previous results from Ni/SiC, Ni₃Al/SiC, Fe/SiC, Co/SiC, and Pt/SiC, reactions. A general model describing discontinuous decomposition of SiC is proposed to explain the origin of carbon modulation.     

Single-Step Synthesis of Chemically Cross-Linked Polysilastyrene and Its Conversion to β-Silicon Carbide

A new method for chemically cross-linking polysilastyrene using divinylbenzene as the cross-linking agent is reported. The procedure involves a single-step synthesis using the alkali-metal sodium to promote the polymerization of dimethyldichlorsilane in the presence of the comonomers phenylmethyldichlorosilane and divinylbenzene. The cross-linked polymer can be readily converted to β-SiC on pyrolysis at 1500°C. The β-SiC obtained by this procedure is nanocrystalline and has a grain-size distribution of 8–20 nm.     

碳化硼合成及其烧结体密度

直接合成了碳化硼粉，测定了其化学成分、点阵常数、平均粒径，确定了合成反应的最佳工艺参数。研究了热压烧结碳化硼体积密度的控制方法，测试了烧结体微观组织和性能。采用炉内限位法控制试样密度精度，最大偏差为理论密度（Ｔ．Ｄ．）的±２％。富碳或富硼相阻碍晶粒长大。碳化硼体积密度为９２％Ｔ．Ｄ．时，其各项性能达到或超过反应堆工作性能要求指标。从室温升到６００°Ｃ，其抗弯强度约下降１０％。