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.

Dissolution-precipitation mechanism of self-propagating high-temperature synthesis of TiC-Cu cermets

The mechanism of self-propagating high-temperature synthesis （SHS） of TiC-Cu cermets was studied using a combustion front quenching method. Microstructural evolution in the quenched sample was observed using scanning electron microscope （SEM） with energy dispersive X-ray （EDX） spectrometry, and the combustion temperature was measured. The results showed that the combustion reaction started with local formation of Ti-Cu melt and could be described with the dissolution-precipitation mechanism, namely, Ti, Cu, and C particles dissolved into the Ti-Cu solution and TiC particles precipitated in the saturated Ti-Cu-C liquid solution. The local formation of Ti-Cu melt resulted from the solid diffusion between Ti and Cu particles.

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.

High-temperature synthesis of SAPO-34 molecular sieve using a dry gel method

SAPO-34 is one of the main catalysts used in the petrochemical industry. Various effective methods have been developed to synthesize SAPO-34 with optimal size and characteristics for such application, In the present study, SAPO-34 was synthesized using a dry gel method at high temperatures. Morpholine was used as an organic template. The products were characterized by X-ray diffraction, field-emission scan- ning electron microscopy, energy-dispersive X-ray spectroscopy, and gas sorption analysis, The results showed that application of the dry gel method at high temperatures successfully afforded a pure catalyst with high crystallinity, Small particles of less than 500 nm could be obtained within a short reaction time of 30 min.

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.

新型红外非线性硒镓钡多晶的合成与提纯研究

硒镓钡晶体(BaGa_(4)Se_(7),BGSe)是目前广受关注的一种新型红外非线性晶体。本文分别采用双温区法和高压辅助法合成硒镓钡多晶原料,并设计大温度梯度快速提纯方法对合成后的多晶料进行提纯。通过粉末X射线衍射仪(XRD)、电感耦合等离子体质谱仪(ICP-MS)和X射线能谱仪(EDS)对提纯前后的BGSe多晶的物相组成和杂质浓度进行了表征。X射线衍射谱与理论模拟图谱结果一致,无杂峰;ICP-MS等测试结果表明,提纯后晶锭中的Fe、Al等金属杂质以及O杂质含量均得到明显降低。本工作可为高品质单晶生长提供原料基础。

氧化镧掺杂锰酸锂材料的制备及其电化学性能

采用高温固相合成法制备氧化镧掺杂的锰酸锂材料,研究了氧化镧不同掺杂比例(与二氧化锰的质量比分别为0%、0.5%、1.0%和1.5%)对样品性能的影响。实验结果表明:当氧化镧掺杂量为1%时,所制的锰酸锂材料在1 C下比容量最大,达到120.42 mAh/g;首次充放电效率最高,达96.76%;100次循环的1 C容量保持率最大,为90.28%。

基于炭/炭复合材料加工余料制备碳化硅粉末的组织及性能

以炭/炭复合材料加工余料为碳源,与硅粉充分混合,通过高温合成法制备单晶生长用碳化硅粉末,并对其显微组织和表面性能进行研究。结果表明:制备出的碳化硅粉末晶型为β-SiC,部分继承了炭/炭复合材料加工余料的管槽状、脊状结构。在拉曼光谱中,该粉末的折叠横光与折叠纵光的半峰全宽之比为0.709,其相对纯度高于以石墨粉为碳源同工艺制备的碳化硅粉末。该碳化硅粉末具有多孔特征,比表面积为25.7426 m^(2)/g,可用于物理气相传输单晶生长工艺,且已初步验证其可行性。

碳/氮化物陶瓷粉体的熔盐法合成研究进展

熔盐法利用了液态中物质混合更均匀、扩散更快这一特点,显著降低了陶瓷粉体的合成温度、缩短合成时间。该方法制备的产物粉体粒度均匀、表面洁净、形态可控,在各类无机粉体特别是纳米粉体制备中获得广泛应用,是制备高质量粉体材料的绿色、可靠途径。本文介绍了熔盐的选择原则和常用的熔盐体系,论述了近几年熔盐法在合成碳化物、氮化物的研究进展,对熔盐法制备陶瓷粉体的优势和不足进行了说明,提出了未来需重点研究的方向。

金刚石粒度和含量对自蔓延高温合成NiAl结合金刚石复合材料性能的影响

以Ni粉、Al粉、金刚石为原料,采用自蔓延高温合成法制备了NiAl结合金刚石复合材料,研究了金刚石的粒度和含量对Ni-Al体系燃烧温度和燃烧波蔓延速度的影响以及对复合材料性能的影响。结果表明:金刚石降低了Ni-Al体系的燃烧温度和燃烧波蔓延速度,并提高NiAl基体的抗压强度和维氏硬度。但随着金刚石含量的增加,复合材料的力学性能有所下降,NiAl峰升高,Ni_(3)Al峰下降。随着金刚石的粒度降低,Ni-Al体系的燃烧温度先降低后升高,燃烧波蔓延速度则是先增大后减小,复合材料的抗压强度先升高后降低,维氏硬度降低,Ni_(3)Al峰先升高后降低,NiAl和Ni峰则是先降低后升高。当金刚石含量为10 mass%、粒度为150~180μm时,复合材料的综合性能最佳,体积密度为3.28 g/cm^(3),抗压强度为92.0 MPa,维氏硬度为122.06 HV,Ni3Al峰达到最高。

Al@Co微米核壳含能粒子的可控制备与性能

为提高铝粉能量释放速率,分别通过置换和先置换后化学镀的方法将微米铝表面的惰性氧化铝层替换为导热系数更高的钴壳层,得到钴壳层厚度分别为90,150,200,250 nm的Al@Co核壳含能粒子,并对其进行扫描电镜、透射电镜、能量色散谱、振动样品磁强计,以及热性能测试。结果表明,钴壳层致密均匀、厚度可控,且随着钴壳层厚度增加,粒子的自然抗氧化能力逐渐增强;各粒子表现出典型的铁磁滞回线,进一步证实了铁磁性物质钴的存在;包覆有200 nm钴壳层的Al@Co核壳含能粒子完全克服铝粉吸热,对外表现为剧烈放热,放热量为521.40 J·g^(-1),是一种有潜力的新型绿色起爆药燃料组分。

金刚石-碳纤维复合材料的高温高压合成及组织结构分析

以正硅酸乙酯(TEOS)为反应前驱体,采用溶胶-凝胶方法在金刚石微粉及碳纤维表面包覆一层非晶氧化硅凝胶膜,将二者以不同比例混合后在1350℃、5 GPa条件下进行高温高压(HTHP)处理,合成出了以氧化硅为界面结合相的金刚石-碳纤维复合块体材料,并发现组织中出现了原位生成的纳米针。利用扫描电镜(SEM)、扫描电镜能谱分析(EDS)、X-射线衍射(XRD)等手段研究分析了复合材料中金刚石/碳纤维间的界面组织结构特性。对HTHP合成样品进行了热重分析,结果表明,复合材料在580℃后失重明显,其抗氧化能力较金刚石原料微粉提高了80℃。

自蔓延高温合成/快速加压法制备(TiB_2+Fe)/Fe梯度材料

通过对不同Fe含量的Ti+B +Fe体系绝热温度计算和试样温度有限元计算 ,确定了 (TiB2 +Fe) /Fe梯度材料各层合理的厚度 ,并采用SHS/QP技术制备了 (TiB2 +Fe) /Fe梯度材料。电子探针分析表明 (TiB2 +Fe) /Fe梯度试样中各层间没有了明显的界面 ,沿厚度方向由富陶瓷相向富金属相连续转变。背散射电子像分析表明从富陶瓷侧到富金属侧 ,材料的显微结构也是梯度变化的。SEM分析表明 ,从富陶瓷层到富金属层 ,TiB2 晶粒减小。

高纯氮化硅粉合成研究进展

氮化硅陶瓷是综合性能最好的结构陶瓷材料。纯度高、性能稳定且成本低廉的氮化硅粉体是影响氮化硅陶瓷性能和应用的关键。本文总结了目前常用的几种氮化硅粉体制备方法:硅粉氮化法、碳热还原法、自蔓延高温合成等,分析比较了几种方法的原理及特点,并对氮化硅粉体的未来发展进行了展望。

TiC-Cu复合材料自蔓延高温合成中的显微结构演变

用燃烧波前沿淬熄法研究了自蔓延高温合成(SHS)TiC-Cu复合材料的显微结构演变,用扫描电子显微镜(SEM)观察了燃烧反应中原始粉、反应区和产物区的显微结构,用能谱仪(EDX)分析了各微区的成分变化,测量了燃烧温度T_c,并用XRD分析了反应产物的相组成。结果表明,自蔓延高温合成(SHS)TiC-Cu复合材料的机理为溶解析出机制。铜粉与钛粉的固态扩散导致低熔点Ti-Cu熔液形成,Ti、Cu、C粉粒逐渐向Ti-Cu熔液中溶解,当Ti-Cu-C熔液中的Ti和C浓度饱和时,从中析出TiC颗粒,同时形成粘结TiC颗粒的Cu基体。

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％。

自蔓延高温合成/快速加压法制备二硼化钛陶瓷的致密化机理

用自蔓延高温合成/快速加压(self-propagating high temperature synthesis/quick pressing,SHS/QP)法制备了TiB2陶瓷。用扫描电镜及透射电镜观察陶瓷产品的微观形貌。对TiB2陶瓷致密化的动力学过程及结构形成过程进行了分析,并提出SHS/QP陶瓷烧结的致密化机理。结果表明:在SHS/QP过程中TiB2陶瓷的致密化是晶粒的重排及高温塑性变形共同作用的结果。

用钙钛矿固化核素废物锶

采用自蔓延高温合成技术制备核废物固化体,并实验研究钙钛矿固化体对锶核素(Sr2+)的最大包容量。通过X射线衍射、扫描电镜和浸出法分析了该固化体的物相组成、微观结构和化学稳定性。结果表明:钙钛矿固化体对SrO的包容量可达到36%(质量分数),且产物成分均匀,浸出率低,化学稳定性好,是固化锶核素废物的理想固化体。