Self-propagating high temperature synthesis of MoSi_2 matrix composites

MoSi2 is presently regarded as the most important material for electrical heating and as one with huge potential for high temperature structural uses. MoSi2 and MoSi2 matrix composites were prepared by self-propagating high temperature synthesis （SHS）. Pure MoSi2 was obtained and a compound of MoSi2 and WSi2was synthesized in the form of predominant solid solution （Mo,W）Si2. By adding aluminum of 5.5 at.% to Mo-Si, the crystal structure of MoSi2 changed into a mixture of tetragonal Cllb MoSi2and hexagonal C40 Mo（Si,Al）2. The （Mo,W）Si2-Mo（Si,Al）2-W（Si,Al）2 composite materials were synthesized by adding aluminum of 5.5 at.% to Mo-W-Si. However, if the amount of the added aluminum was not larger than 2.5 at.%, it did not have any significant effect. SHS is an effective technology for synthesis of MoSi2 and MoSi2 matrix composites.

A Self-propagating high-temperature synthesis process for the fabrication of Fe（Cr）–Al2O3 nanocomposite

Self-propagating high-temperature synthesis(SHS)was used to fabricate a Fe(Cr)–Al2O3 nanocomposite.The composite was fabricated by the reactions between the powders of Fe,Fe2O3,Cr2O3,and Al.The effect of blending ratio and mechanical activation of the initial powders and the precursor compressing pressure on the microstructure of the final product was studied by optical microscopy,scanning electron microscopy,transmission electron microscopy,and X-ray diffraction.The significance of the effect of each of the aforementioned parameters on the quality of the composite(assessed by measuring the compressive strength and wear resistance)was determined using a full-factorial design of experiments method.The results showed that the best molar powder ratio that produced the most homogeneous product through a sustainable SHS reaction was Fe:Fe2O3:Cr2O3:Al=10:1:1:4.A lower Fe content caused the Fe(Cr)phase to melt and separate from the rest of the materials.

Preparation of low-oxygen Ti powder from TiO_(2) through combining self-propagating high temperature synthesis and electrodeoxidation

An effective method was reported to prepare low-oxygen Ti powder,which included two experimental steps:the fast conversion of TiO_(2) to TiO_(x<1) powder by self-propagating high-temperature synthesis(SHS)process and the generation of low-oxygen Ti powder by electrodeoxidizing TiO_(x<1) powder at the cathode in molten CaCl_(2).The key intermediate steps were analyzed by XRD,SEM and electrochemical testing techniques.The results demonstrated that TiO_(x<1) powder(TiO_(0.325) and TiO_(0.97))was generated after acid leaching MgO in SHS products with TiO_(2)/Mg molar ratio of 1:2,and the TiO_(x<1) powder with 16.3 wt.%oxygen could be transformed into pure titanium powder with 0.121 wt.%oxygen by electrodeoxidation at a constant potential of−3.3 V for 10 h.The electrodeoxidation of TiO_(x<1) powder in CaCl_(2) molten salt follows the step-by-step deoxidation mode,and the lattice of TiO_(x<1) powder after electrodeoxidation shrinks.

Optimal design of self-propagating high temperature one-dimensional nano-SnO_2 synthesis

The success in synthesizing high purity SnO2 nanobelts via self-propagating high tem- perature synthesis was achieved. According to the experimental results, a relationship between the residual heat of the reaction system at 2848 K and SnO2 nanobelts yield was identified. The most appropriate formula for this self-propagating high tempera- ture synthesis method is turned out to be composed of Sn powder and thermite with weight ratio of 1：1.

Synthesis gas production on glass cloth catalysts modified by Ni and Co oxides

The catalytic activity of nanostructured low percent (1%) Co-Ni catalysts on the basis of glass fiber (GF) prepared by a"solution combustion" (SC) method was studied.The catalytic activity of the prepared samples was studied in the reaction of dry reforming of methane (DRM) with CO2.The obtained samples were characterized by a number of physico-chemical methods,including XRD,SEM,TEM,TGA and AFM.The active component was shown to be dispersed in the near-surface layer of the support as nanoparticles of 10—20 nm in size.The active component showed a Co3O4 or(Co,Ni)Co2O4 spinel structure,depending on the catalyst composition.The spinel structure of the active component interacted strongly with the carrier,providing resistance to carbonization,high catalytic activity toward DRM,and high activity and stability in oxidation reactions.

陶瓷内衬钢管的研究

采用ＳＨＳ－离心法制备陶瓷内衬钢管时，离心力对Ｆｅ＿２Ｏ＿３和Ａｌ的燃烧过程及其产物的相分离和组织有重要影响，陶瓷内衬钢管具有良好的机械性能和耐蚀性，计算表明，复合钢管中，陶瓷层受压应力，金属管受张应力，这种残余应力分布使复合管具有良好的抗机械冲击和抗热冲击性。

SHS铝热-离心技术的研究进展

介绍了SHS铝热 -离心技术的基本原理和铝热反应机制 ,综述了铝热 -离心技术制备陶瓷内衬复合钢管的研究成果和该技术在其它方面的应用情况 。

离心SHS陶瓷内衬复合管的微观结构和性能研究

采用离心自蔓延高温合成法，在普通碳素钢管内壁涂覆上一层较为均匀致密的厚陶瓷层。对复合管的微观结构进行的详细研究发现：过渡层与基体为冶金结合，与陶瓷层为机械结合；陶瓷层呈枝晶结构特征，为复相结构，主要相为α－Ａｌ＿２Ｏ＿３，还有ＦｅＡｌ＿２Ｏ＿３和Ｆｅ＿２ＳｉＯ＿４等相；添加ＳｉＯ＿２生成了低熔点硅化合物，延长了凝固和排气时间，提高了陶瓷层的致密度；过渡层中存在大量未分离的陶瓷粒子和高密度的位错，致使其硬度高于基体。

SHS-离心法陶瓷衬管致密性的提高

采用自蔓延高温合成技术 (SHS法 )与离心技术相结合 ,在普通碳素钢管的内壁复合上一层均匀的陶瓷层 ,制成金属 -陶瓷复合管。利用X射线衍射和扫描电镜进行陶瓷层的组织结构、相组成和成分分析 ,并测定了陶瓷层的密度、硬度和耐磨性能。结果表明 ,适量添加SiO2 ,在陶瓷的凝固和致密化过程中 ,降低了反应凝固终了温度 ,延长了陶瓷的熔融时间 ,提高了陶瓷层液相的流动性 ,加速了气体排除 ,陶瓷层的致密性得到提高。

离心SHS陶瓷复合钢管裂纹的控制

总结了近年来在离心SHS陶瓷复合钢管陶瓷层上形成的裂纹类型及其形成机理、陶瓷层裂纹控制方面取得的进展。热应力和钢管的压迫力是离心SHS陶瓷复合钢管陶瓷层产生裂纹的两个主要原因 ,欲减少陶瓷层裂纹的形成 ,除了选用合适的工艺配方 。

特种管件陶瓷内衬涂层静态自蔓延熔涂工艺

通过对静态自蔓延法制备弯管、三通管、细管、厚壁管及双层涂层管工艺的研究,提出了静态-离心法复合工艺,并探讨了作为隔热层应用于发动机气缸套、排气管、排气道领域的可能性。采用静态自蔓延法研制了半固态金属加工用陶瓷涂层模具,并进行了涂层熔涂工艺参数优化设计、X射线无损探伤、热震性测试和铝合金及高温钢质液态模锻应用试验。试验表明,在半固态金属加工模具内表面用静态法制备陶瓷涂层,将显著提高模具的使用寿命。

添加剂对离心自蔓延高温合成陶瓷层组织结构与性能的影响

为了改善钢管内衬陶瓷层的韧性,在铝热剂中分别添加ZrO2,Al2O3,SiO2进行改性,采用离心自蔓延高温合成工艺制备了钢管内衬陶瓷层,研究了添加剂对陶瓷层形貌、结构和性能的影响。结果表明:加入ZrO2或Al2O3可以改变陶瓷层的组织结构,使Al2O3由树枝状晶变为等轴晶;加入SiO2可在Al2O3枝晶间隙形成网状Ca2Si化合物,提高陶瓷层的硬度;加入ZrO2可以显著改善陶瓷层的断裂韧性,加入SiO2次之,而加入Al2O3则降低了陶瓷层的断裂韧性。

自蔓延高温合成离心涂敷陶瓷衬里钢管

综述了国内外自蔓延高温合成离心涂敷陶瓷衬里钢管的发展概况，包括生产原理、生产装置和产品性能等。

SHS-离心法制备陶瓷内衬复合钢管的组织结构

采用SHS-离心法在薄壁钢管内壁复合了一层厚度为2～3mm的陶瓷层。通过XRD、SEM、EDS手段分析了陶瓷层及其与钢管结合界面的组织结构。结果发现,陶瓷层由Al2O3、复合化合物和少量的残余Fe组成;陶瓷层与钢管之间存在着界面过渡层,过渡层的存在,有利于改善陶瓷与钢管之间的界面结合。

SHS离心复合钢管陶瓷内衬的组织结构

采用自蔓延高温合成技术离心法制备Al2 O3陶瓷内衬复合钢管。利用扫描电镜及X射线衍射方法对陶瓷内衬的显微组织及物相构成进行了分析。结果表明 ,陶瓷内衬复合钢管由钢管层、金属铁和陶瓷组成的过渡层以及陶瓷层共三层构成 ,其中钢管与铁过渡层之间为机械结合 ,铁过渡层与陶瓷层之间形成冶金结合。陶瓷层组织由垂直管壁生长的α Al2 O3柱状晶和沿其晶间分布的FeO·Al2 O3铁铝尖晶石相以及少量FeO·Al2 O3·SiO2 玻璃相构成 ,玻璃相分布于铁铝尖晶石的晶界并将其包围起来 ,这种结构有利于减轻铁铝尖晶石对复合管内衬抗腐蚀性的不良影响。

离心SHS陶瓷衬管裂纹类型的研究

研究了生产工艺因素对离心ＳＨＳ陶瓷衬管裂纹的影响；提出了准压裂纹的概念，归纳出陶瓷层裂纹类型随工艺因素变化的转变规律，即随冷却速率的提高，裂纹类型依次发生压裂纹→无裂纹→准压裂纹→张裂纹的转化；料管比（铝热剂量与母管重量之比）和涂料厚度对陶瓷层裂纹的影响最为显著。

提高SHS复合管陶瓷层性能的工艺方法研究

自蔓延高温合成(Self-propagating High-Temperature Synthesis,SHS)是材料合成新技术,具有工艺简便,能耗低,无污染,效率高等特点,应用该技术制造的陶瓷内衬复合钢管具有耐磨、耐蚀、隔热等优点,SHS复合管的性能决定于内衬陶瓷层性能。论述了离心法和重力分析法2种复合管制造方法,并从提高陶瓷层致密度、韧性、表面质量及降低裂纹率等方面,综述了提高SHS复合管内衬陶瓷层性能的措施。

自蔓延高温合成陶瓷内衬复合钢管的研究与展望

耐腐蚀、耐磨损、耐高温是管道选材的难点 ,尤其在其中两项或诸因素共存时。介绍了自蔓延高温合成技术的原理与特点 ,着重讨论了离心分离法和重力分离法制造陶瓷内衬复合钢管的原理及其性能 。

金属-陶瓷复合管的制造

将自蔓延高温合成法与离心技术相结合，在普通碳素钢管的内表面复合上一层陶瓷衬里，制成复合管，并对控制复合管质量的制造工艺参数进行了分析，测定了复合管的综合性能。结果表明，用此方法制造的金属陶瓷复合管，在具有一般碳钢管优点的基础上，还具备了较高的耐磨性、耐热性等，从而扩大了碳钢管的使用范围。

Influences of NiCO_3 content on the microstructure and magnetic properties of Ni_(0.5)Zn_(0.5)Fe_2O_4 powders prepared by SHS

Stoichiometric Ni0.5Zn0.5Fe2O4 powders were produced by self-propagating high temperature synthesis （SHS）. The effects of NiCO3 content in the raw materials on the microstructure and magnetic properties of Ni-Zn ferrite powders were systematically studied. The Ni0.5Zn0.5Fe2O4 powders were characterized by X-ray diffraction （XRD） and scanning electron microscopy （SEM）. The magnetic properties of the powders were evaluated by vibrating sample magnetometry （VSM）. The results show that the introduction of NiCO3 into reactants improves the con- version percentage and refines the Ni0.5Zn0.5Fe2O4 particles. The increase of NiCO3 content enhances the magnetic properties of Ni0.5Zn0.5Fe2O4. Particularly, the saturation magnetization reaches the maximum when the NiCO3 content is 3 at.%.