非水滴定法测定SiC超细粉末中的碳

本以Na2O2作为且助熔剂和氧化剂,在空气流中于1250℃下使SiC超细粉末氧化生成CO2然后用非水滴定法测定其总碳量。同时在不加任何其它助溶剂和氧化剂的条件下,在空气流中于850℃下,使SiC超细粉末中的游离碳氧化生成CO2,再用非水滴定法测定其游离碳。结果表明,用该方法测定SiC超细粉末中的碳含量时,其置信度在95%以上。     

碳化硅超细粉末形核生长过程的研究

用热化学气相合成法制备的超细SiC粉末的组织结构,保留了许多与形核生长过程直接有关的许多特点,为用高分辨电子显微术研究其形核生长过程提供了有利条件。据此,本文讨论了SiC超细粉末形成的主要机制——均相形核生长过程。它可分为5个主要方面:非晶相核的形成;SiC旋涡状生长及受阻;亚稳的SiC旋涡的析晶;聚结;表面非晶SiC的形成。另外,也分析了固态Si上的SiC的异相成核、外延以及固态Si的碳化过程。     

SiC超细粉的化学分析（I）——示差分光光度法测定SiC超细粉末中的总硅量

在碳化硅的总硅量测定中，样品的分解是关键之一。本采用NaOH和Na2O2（2：1）的混合溶剂，在银坩埚中于700℃下熔融20分钟来分解Si C超细粉末。由于SiC中的总硅量高达70％左右，所以用500μg/100ml的标准SiO2溶液作为参比溶液，以硅钼示差分光光度法测定SiC超细粉末中的总硅量。本方法的最大吸收波长λ＝800nm，在该波长的表观摩尔吸光系数ε＝2．51×10^4。     

等离子体法制备碳化硅超细粉末研究

本文采用直流电弧等离子体法合成β－SiC超细粉末．产品纯度大于97％，平均粒径范围0．05～0．5μm，产率1km／h．此外，对其工业开发前景作了展望．     

SiC／B复合超细粉末的溶胶—凝胶法合成

以硅溶胶、炭黑和硼酸或硼粉为原料,用溶胶-凝胶法合成了SiC/B复合超细粉末。粉末中硼的含量取决于硼源的种类和用量。硼的引入促进了粉末的昌粒长大并抑制了α-SiC相的生成。     

溶胶—凝胶法全成SiC—AlN复合超细粉末的机理研究

本文通过对热力学过程动力学过程的研究，探讨了ＳｉＣ－ＡｌＮ复合细粉末的合成机理，由于Ａｌ４ＳｉＣ４产物的出现，反映了合成的非单一化。通过ＸＲＤ分析，研究了ＳｉＣ－ＡｌＮ粉末合成反应历程，并指出ＡｌＮ的生成比ＳｉＣ生成滞后５０－１００℃，从自由能和反应常数作了理论上的分析。通过对合成过程中转化率的测定和颗粒形貌的观察，探讨反应动力学过程，说明了系统中晶核和晶体大长机制。最后，本文分析了粉末中晶须产生     

红外碳硫分析仪分析铸造碳化钨粉中总碳含量的方法之一

通常铸造碳化钨粉 (以下简称钨粉 )中总碳含量采用GB/T 5 1 2 4·1— 85硬质合金化学分析方法重量法测定总碳量。这种方法不仅周期长而且步骤烦琐 ,是将试料与助熔剂在高温管式炉内通氧燃烧 ,碳被完全氧化成二氧化碳 ,除去二氧化硫后将混合气体收集于量气管中 ,测量其体积 ,然后以氢氧化钾溶液吸收二氧化碳 ,再测量剩余气体的体积 ,吸收前后气体体积之差即为二氧化碳之体积 ,以其计算碳含量 ,而应用红外碳硫分析仪则能简便、准确、快速的分析钨粉中总碳的含量。HCS——— 1 40A型高频红外碳硫分析仪是以热释电能传感器为核心 ,由高频感应…     

碳热还原法制备重结晶SiC粉末的研究

研究了碳热还原制备重结晶α-SiC粉末的工艺过程，重点讨论了重结晶α-SiC的生长机理，同时，还探讨了SiC各相的稳定范围及工艺参数对产物形貌及产率的影响。     

铁合金中总碳量准确测定的分析探讨

对气体容量法中影响铁合金总碳量准确测定的一些因素，如助熔剂、燃烧炉温度、氧气流量、样品预热时间等，进行了分析探讨，提出了准确测定的最佳条件。     

碳热还原粘土合成Al2O3/SiC复相陶瓷粉末

本文以苏州土与碳黑为原料,研究了其在高温下的反应过程及一些工艺参数对反应产物的意识,结果表明：１）反应过程包括高岭石矿物的分解及还原过程,两个过程反应程度不同,可获得不同相组成的陶瓷粉末。２）在一定温度下,粘土中引入合适的碳含量能制备出高Ａｌ２Ｏ３与ＳｉＣ含量的复相粉末（Ａｌ２Ｏ３≥５０％）,ＳｉＣ≥４０％）。３）碳热还原法是合成粒径细小、相成分分布均匀且杂质有所杂质有所降低陶瓷复合粉末的一种途径     

用SiO2微粉制备碳化硅粉体的研究

为回收利用SiO2微粉,探究了以SiO2微粉为原料通过碳热还原法制备碳化硅粉体的最佳工艺条件;研究了分别以石油焦、活性炭和石墨粉为还原剂对冶炼效果的影响。在最佳碳质还原剂的基础上,研究了不同配碳比(还原剂与SiO2微粉的质量比为1∶3.5、1∶3、1∶2.5、1∶2、1∶1.5)和不同冶炼时间(15、30、45、60 min)对冶炼效果的影响。结果表明:石油焦、活性炭、石墨粉3种碳质还原剂中,石油焦的冶炼效果最佳;将石油焦与原料SiO2微粉以质量比1∶2进行混合,在中频感应炉中以1650℃冶炼45 min为最佳冶炼工艺条件;以此能够得到晶粒生长较好、品质较高的碳化硅粉体,碳化硅含量高达93.50%(w)。     

碳化硅冶炼炉逸出气体的组成及理化性质研究

利用自行发明的多热源碳化硅冶炼炉，以煤（或焦炭）和石英砂为原料合成SiC，同时伴生大量副产品可燃性气体，研究了煤种和冶炼工艺对燃气的组成及酸碱性的影响，并对经济效益进行分析。结果表明，燃气中以CO气体为主，平均含量可达70％，CO＋H2平均含量达85％，CO＋H2＋CH4平均含量达90％，使用无烟煤、烟煤焦炭或焙烧料法可提高合成气中CO含量，若燃气用于火力发电可节约25．8％的电费成本。     

碳化硅晶片的制备技术

碳化硅晶须和晶片都是陶瓷基、金属基、树脂基复合材料的理想增强体，与碳化硅晶须相比，有关碳化硅晶片制备与应用的报道相对较少。论述了碳化硅晶片在复合材料中的应用，比较了国内外碳化硅晶片的各种制备技术。阐明了加热方式对碳化硅晶片制备的影响。指出低成本、新型热源的开发与推广应用有利于实现碳化硅晶片的规模化生产。     

Synthesis of ultrafine silicon carbide nanoparticles using nonthermal arc plasma at atmospheric pressure

It remains a significant challenge for the scalable production of ultrafine silicon carbide (SiC) nanoparticles with sizes smaller than 10 nm. In this work, a novel process based on atmospheric nonthermal arc plasma was proposed for the continuous synthesis of ultrafine SiC nanoparticles. This low-cost and scalable technique allows preparation of SiC nanoparticles with small size (5–9 nm) and narrow size distribution via hexamethyldisilane (HMDS) decomposition in an argon/hydrogen plasma environment. The as-synthesized products were carbon-rich β-SiC nanoparticles with plentiful functional groups on the surface. The addition of hydrogen in plasma gas can tune the product characteristics, such as decreasing particle size, improving crystallinity, and reducing carbon and oxygen contents. Moreover, the as-prepared β-SiC nanoparticles had a high band gap (around 2.5 eV), and their photoluminescence peak showed an obvious blueshift relative to that of bulk β-SiC, which was mainly attributed to the quantum confinement effect induced by their ultrafine size. According to the spectral information of arc plasma, the formation of SiC nanoparticles in the plasma was discussed.     

Determination of silicon carbide fiber electrical resistivity at elevated temperature

The resistance of Sylramic‐iBN and Hi‐Nicalon SiC fiber tows was measured at elevated temperature in air. Resistivity could not be directly measured, since the fibers passed through a furnace with varying temperature along the length. The resistivity of the isothermal section of the fiber tow was modeled by a series circuit of finite elements. Existing data for Hi‐Nicalon resistivity vs temperature was used to verify the model and then extend it to Sylramic‐iBN, for which there is no literature data readily available. The model matched experimental values with low overall error (<±14%). Fiber resistivity decreased by more than two orders of magnitude when heating from 25°C to 1400°C. Sylramic‐iBN tow resistance was also measured during a 500 hour hold at 1315°C. The resistance increased by more than 140% during heat treatment. The resistance change correlated well with the decrease in SiC fiber diameter that resulted from oxidation.     

碳纤维增强碳化硅基复合材料的研究

碳纤维增强碳化硅基复合材料(Cf/SiC)具有良好的力学性能,作为特殊结构的功能材料,是航空航天领域和新能源领域的研究热点之一。本文主要阐述了增强相碳纤维的发展,复合材料的基体复合技术,以及复合材料界面相的研究,并展望了碳纤维复合材料在高新技术领域中的应用与发展前景。     

Joining of silicon carbide ceramics using a silicon carbide tape

This paper reports the joining of liquid-phase sintered SiC ceramics using a thin SiC tape with the same composition as base SiC material. The base SiC ceramics were fabricated by hot pressing of submicron SiC powders with 4 wt% Al₂O₃–Y₂O₃–MgO additives. The base SiC ceramics were joined by hot-pressing at 1800-1900°C under a pressure of 10 or 20 MPa in an argon atmosphere. The effects of sintering temperature and pressure were examined carefully in terms of microstructure and strength of the joined samples. The flexural strength of the SiC ceramic which was joined at 1850°C under 20 MPa, was 343 ± 53 MPa, higher than the SiC material (289 ± 53 MPa). The joined SiC ceramics showed no residual stress built up near the joining layer, which was evidenced by indentation cracks with almost the same lengths in four directions.     

Preparation of reaction bonded silicon carbide (RBSC) using boron carbide as an alternative source of carbon

RBSC composites are fully dense materials fabricated by infiltration of compacted mixtures of silicon carbide and carbon by molten silicon. Free carbon is usually added in the form of an organic resin that undergoes subsequent pyrolysis. The environmentally unfriendly pyrolysis process and the presence of residual silicon are serious drawbacks of this process. The study describes an alternative approach that minimizes the residual silicon fraction by making use of a multimodal particle size distribution, in order to increase the green density of the preforms prior infiltration. The addition of boron carbide provides an alternative source of carbon, thereby eliminating the need for pyrolized organic compounds. The residual silicon fraction in the RBSC composites, prepared according to the novel processing route, is significantly reduced. Their mechanical properties, in particular the specific flexural strength is by 15% higher than the value reported for RBSC composites prepared by the conventional approach.     

Evaluation of tribological behavior of silicon carbide and silicon nitride ceramics under different conditions

A comparative analysis of the tribological behavior of commercially available sintered silicon carbide (SiC) and three different types of silicon nitride (Si₃N₄) ceramics have been carried out using the ball-on-disk method in dry and lubrication (deionized [DI] water and ethanol) environment. Scanning electron microscopy (SEM) was used to understand the morphology and chemical composition of the tribo-surfaces. Sintered SiC (Hexoloy-SA) had the highest friction coefficient during dry sliding with an average of ∼0.34. Deionized water showed a minor improvement in friction (∼0.27) while ethanol reduced the friction greatly to ∼0.18 compared to dry sliding. During dry sliding, the presence of an abrasive third body was responsible for the high wear rates (WRs) in these compositions. Hexoloy-SA showed a lower WR during ethanol and DI water lubrication due to the formation of stable tribofilms as well as higher hardness which resisted the formation of third bodies. In comparison, Si₃N₄ samples showed a lower WR in DI water and ethanol. The samples also showed composition-dependent behavior which indicates that grain structure and grain boundary chemistry are playing a vital role in the tribological process.