Some Characteristic Features of Formation of Ceramics Based on Composite Powders SiC ― Si3N4 ― Si2N2O

We have studied the characteristic features of synthesis of composite powders SiC Si₃N₄ Si₂N₂O. We have investigated processes involving hot pressing of these powders without activating additives and a protective atmosphere. We consider the mechanical properties of ceramics obtained on the basis of these composite powders.     

Sialon／SiC和Si3N4／SiC材料的性能及氧化研究

通过研究Sialon/SiC和Si3N4/SiC制品长时间处于800～950 ℃(铝电解槽工作温度)空气中的动态质量变化以及氧化前后气孔率、体积密度和孔径分布的改变来反映制品的抗氧化性能.结果表明,浇注成型Sialon/SiC试样抗氧化性能最好,压力成型Sialon/SiC试样次之,压力成型Si3N4/SiC最差,并得到其氧化动力学方程.     

SiC/Si3N4复合纳米粉的微观结构与形态

用X-射线衍射（XRD）、扫描电镜（SEM）、透射电镜（TEM）和图像分析等分析手段，对激光诱导六甲基乙硅胺烷加氨气气相合成纳米陶瓷粉进行了结构分析及表征．结果表明：利用激光诱导六甲基乙硅胺烷合成出了理想的纳米陶瓷粉，实验制备的粉体由非晶态相和少量晶态相组成，颗粒形状规则呈球形；其微粒粒径多为10—20nm范围，大部分分散性较好，粉中无游离的硅生成；主要相为非晶态结构的SiC和Si3N4组成，少量晶态相为α-SiC、β-SIC和Si3N4．在可控制备工艺条件下能够合成理想的非晶纳米SiC粉体．     

我国纳米级超细粉Si3N4,SiC产业化基地建成投产

一项具有国内领先、世界先进水平的纳米级超细粉生产线已建成投产,它的投产意味着我国纳米级碳化物、氮化物的超细粉材料已经进入产业化、商品化。该项目是由石家庄依斯特专利技术发展公司开发研制的,采用等离子体法气相合成工艺,该工艺具有反应气氛可调,生成物纯度高、颗...     

氮化硅新型耐火材料中游离Si,Si3N4,SiO2,SiC的测定

测定Si_3N_4时,用NaOH熔融试样,硼酸吸收,硫酸标准溶液滴定。游离硅的测定用氟硅酸钾法。采用HF(HNO_3存在下)冷溶的方法测定(Si SiO_2)。碳化硅的含量用100%—(Si游% Si_3N_4% SiO_2)而得。     

RS—Si3N4／SiC复相耐火材料的组织与性能

利用三点弯曲试验,ＲＸＤ,ＳＥＭ等手段了原料组成对ＲＳ－Ｓｉ３Ｎ４／ＳｉＣ复相耐火材料的密度、抗折强度、抗热震能力以及相组成、显微组织和断口形貌的影响,结果表明,当原料中硅质量分数为２５％时,Ｓｉ３Ｎ４／ＳｉＣ复相耐火材料具有最高的抗折强度和抗震稳定性产生,论文对此种材料的相结合,显微组织和断口形貌进行了分析。     

硅锭线切割回收料制备高性能Si3N4结合SiC耐火材料的研究

以硅锭线切割回收料为主要原料,采用氮气气氛中反应烧结制备Si3N4结合SiC耐火材料,研究了烧成制度、原料配比、颗粒级配等对制品的气孔率、抗弯强度的影响.结果表明:原料Si含量为25％为最优配方;1300 ℃、1400℃分别保温2.5 h是合适烧成制度;合适颗粒级配的骨料添加可以降低气孔率.硅锭线切割回收料制备的Si3...     

氮化硅结合碳化硅（Si3N4.SiC）耐火制品及应用

文章介绍了氮化硅结合碳化硅耐火制品的基本特性和生产原理，并就其发展前景和应用范围进行了分析与探讨。     

New functionally gradient materials in the Ti−Si−C system

A new ceramic functionally gradient material (FGM) with controlled hardness and fracture toughness is presented. Very hard SiC and soft, fracture resistant Ti₃SiC₂ ceramics were manufactured as one multilayered composite. This composite was prepared by hot-pressing from SHS-derived powders. Microstructure and indentation tests proved the FGM structure. Mining and Metallurgy University, Krakow, Poland. Published in Poroshkovaya Metallurgiya, Nos. 3–4(406), pp. 42–45, March–April, 1999.     

Study of Phase Formation Processes in the Systems Li ― N,Si3N4 ― Li3N,Si3N4 ― Li3N ― Y2O3

We have studied phase formation processes in the systems Li N and Si₃N₄ Li₃N. By nitriding lithium powder at temperatures of 400-600°C, we obtained lithium nitride Li₃N with a composition approaching stoichiometric. In the system Si₃N₄ Li₃N in the temperature range 300-1300°C, the ternary compounds Li₈SiN₄ (500°C), Li₅SiN₃, Li₂SiN₂ (900°C), and LiSi₂N₃ (1300°C) are formed. The studied properties of the hot-pressed composite material of the system Si₃N₄ Li₃N Y₂O₃ allow us to provisionally assign it to the class of solid electrolytes.     

SiC纳米及晶须增强Si3N4基复相陶瓷断裂行为的研究

用扫描电镜、透射电镜及努氏压痕法研究了添加ＳｉＣ晶须、纳米颗粒及晶须和纳米颗粒的三种Ｓｉ３Ｎ４基复相陶瓷在外力作用下的断裂行为。这三种材料断裂的主要方式是沿晶断裂,偶尔可见穿晶断裂。在裂纹发展的路径上当裂纹尖端遇到了晶须、集聚的纳米颗粒及类晶须时,会产生扭转、偏转、断裂、拔出和终止,从而使裂纹能量消耗,抑制和阻碍了裂纹的扩展和传播,起到了增韧补强的作用。     

Effect of heat treatment on the dispersity of Sn(IV)—Sb—O powders and the porosity of thick-film gas sensors based on them

A study is made of how the granulometric composition and porosity of powders of solid solutions in the system Sn(IV)−Sb−O is affected by the conditions of precipitation of mixtures of tin hydroxide and antimony hydroxide and the heat-treatment temperature. Powders of tin and antimony hydroxides have a microporous structure and a high (≥200 m ²/g) specific surface. Heat treatment above 870 K forms Sn_1−xSb_xO₂ solid solutions, this being accompanied by an increase in the size of the particles and transformation of the microporous structure to a mesoporous structure. An increase in the antimony content of the solid solutions helps form finer powders. A examination is made of the parameters of the pore structure of bulk specimens of semiconductor gas sensors obtained by heat-treating mixtures of powders of solid solutions and ultrafine clay. Institute for Problems of Materials Science, Ukraine National Academy of Sciences, Kiev. Translated from Poroshkovaya Metallurgiya, Nos. 5–6(407), pp. 111–116, May–June, 1999.     

Fabrication of micro-fine spherical Ti–6Al–4V alloy powders based on hydrogen decrepitation and plasma spheroidisation

A novel process was developed for scalable fabrication of micro-fine spherical Ti–6Al–4V alloy powders. The hydrogenation-treated Ti–6Al–4V alloy ingot was mechanically crushed into particles and then sieved into three size grades. The powders were separately sent through the radio frequency (RF) argon plasma system for spheroidisation. The fabrication process and powder characteristics were investigated. The results indicate the alloy ingot upon hydrogenation treatment can be efficiently crushed into fine particles with size of 5–76?μm. During RF plasma processing, the powders are found to be greatly refined due to hydrogen decrepitation with subsequent transformation into spherical morphology. The effect of hydrogen decrepitation on particle refinement is impaired with decreasing particle size of feed powders. The spherical powders exhibit a narrow particle size distribution and the average size is in the range of 8.2–27.9?μm. The spheroidised powders mainly consist of β-Ti and TiH_1.5.     

Effect of Y2O3, CeO2 on Sintering Properties of Si3N4 Ceramics

The effect of rare earth oxides Y203 or Ce02 on sintering properties of Si3N4 ceramics was studied and the mechanism of assisting action during sintering was analyzed. The results in dicate that the best sintering properties appear in Si3N4 ceramics with 5% Y203 or 8% CeO2. Secondary crystallites are formed at grain boundaries after heat treatment,which decreases the amount of glass phase and contributes to the improvement of high-temperature mechanical properties of silicon nitride.     

Fe-Si3N4结合SiC特种陶瓷的烧成过程

利用TG－DSC法对Fe-Si3N4结合SiC陶瓷在氮化炉内烧成时发生的化学过程进行了研究，并分析了当硅铁的加入量大于15％时,成形试样在反应合成过程中开裂的原因及防止措施。认为反应合成过程中主要发生了碳的氧化、硅铁的溶解和氮化3个化学反应；为防止试样损坏可采取控制氮化炉内氮平衡分压和减缓升温速率等措施。