高温反应合成TiAl金属间化合物的研究

研究了以自蔓延高温合成(SHS)技术合成TiAl金属间化合物的燃烧反应过程及有关工艺参数(受热温度、压坯密度、加热速率和原始粉末粒度)对反应合成TiAl金属间化合物的影响。研究结果表明,Ti与Al之间的剧烈放热反应是在Al熔化之后产生的。当加热速率快时,压坯密度高较有利于燃烧反应的进行及TiAl金属间化合物的合成。加热速率和Al粉粒度对燃烧反应过程的影响与预燃烧相的形成有关。     

自蔓延高温合成（SHS）及其应用（一）

本文简要介绍了SHS法的优点、适用范围、研制发展过程及工艺现状。系统地阐述了燃烧理论和过程、燃烧模式及点火技术等,并以氮化物陶瓷、金属间化合物和金属氢化物为例,概述了合成的具体工艺过程。此外还讨论了合成材料的致密方法及SHS过程在焊接和涂层等方面的用途,及现阶段SHS技术所面临的主要问题。     

乙二醇溶液燃烧法一步合成纳米CoO

以硝酸钴为氧化剂,乙二醇为燃料,采用溶液燃烧法在200～400℃合成了纳米CoO晶体。采用X射线衍射仪(XRD)、扫描电子显微镜(SEM)、低温N2吸附等手段对产物的晶相结构、形貌和比表面积进行了表征,系统地研究了不同燃料比和燃烧温度对合成产物的影响。结果发现:乙二醇燃料缺50%时制备得到纳米Co3O4,化学计量比量燃料时得到CoO,而燃料过量50%时则得到CoO和金属Co的混晶。通过选取化学计量比量的乙二醇,燃烧温度300～400℃的反应条件,可以控制合成出多孔网状结构的纯相纳米CoO晶体,晶粒大小约为17 nm,BET比表面积7.7 m2·g-1。     

Ti—Si—C三元体系自蔓延高温合成的反应热力学研究

根据热力学原理对Ti-Si-C三元体系进行了热力学计算分析,计算了Ti3SiC2自蔓延高温合成的绝热温度,绘出了体系各反应产物的反应自由焓ΔG与反应温度T的关系曲线,并测量了Ti3SiC2自蔓延高温合成的实际燃烧温度.研究结果表明:Ti-Si-C三元体系在SHS反应过程中其燃烧波能够自发进行;在SHS反应的高温区域,反应产物的热力学稳定性从高到低依次为Ti3SiC2、SiC、TiC,TiC和SiC有向Ti3SiC2反应转化的趋势;Ti3SiC2的SHS反应实际燃烧温度低于其理论绝热温度,主要原因是实际进行的SHS反应存在热量损失所致.     

用燃烧合成法制备纳米氧化锌

以尿素或三（羟甲基）氨基甲烷（THAM）为燃料，以硝酸锌为锌源和氧化剂，采用燃烧合成的方法制备了纳米氧化锌。由于反应物吸水，直接将它们混合就可以得到均匀的浆状先驱物；这种先驱物可以在电炉上加热点燃，得到蓬松的泡沫状纳米氧化锌。探讨了燃料和氧化剂配比对反应的影响，发现燃料过剩是自蔓延高温合成的必备条件。采用X-射线衍射、透射电镜以及比表面分析等方法对所制得的粉末进行表征。结果表明：燃烧法可以制备纳米氧化锌，具有简单，快速，便宜的优点。     

Ti-W-C体系的自蔓延高温合成与反应机理

研究了Ti-W-C体系自蔓延高温合成(SHS)的燃烧温度和燃烧速度与W含量、Ti粉粒度及预热温度的关系。分析了不同W含量和预热温度时SHS产物的相组成,并对体系的SHS反应机理进行了研究。结果表明:W/(Ti+W)≤ 0.3时,基本能合成单相(W/Ti)C;而预热可促进(W,Ti) C的SHS合成;体系的SHS反应过程中存在两种反应机制,即溶解-析出机制和扩散-固溶机制     

燃烧合成焊接

燃烧合成(CS，也称自蔓延高温合成，SHS)焊接是利用CS反应的放热及其产物来焊接受焊母材的技术。作为一种新型的焊接技术，引起了众多研究者的兴趣。本文概述了燃烧合成焊接的概念、分类、特点、过程以及研究进程，分析了其影响因素，并指出了燃烧合成焊接几个值得注意的研究方向。     

自蔓延高温合成含钛材料

事实证明,自蔓延高温合成(SHS)是生产含钛材料的有效途径之一。燃烧固结:它利用了在SHS反应过程中或者结束时的放热。与一般烧结材料产生的收缩不同,在SHS时产品出现膨胀,导致孔隙度提高。在(Ti+C)的SHS中,将钼电极接到坯料上,通电使其引燃;SHS之     

燃烧合成/准热等静压TiC-Fe基复合材料耐磨损性能的研究

利用燃烧合成结合准热等静压技术(SHS/PHIP)原位合成了TiC颗粒增强铁基复合材料。利用SEM,XRD研究了复合材料的相组成和显微组织。结果表明:该复合材料由TiC增强颗粒和金属Fe粘结相组成,组织较为致密,球形的TiC颗粒相被包围在近于立体网状结构的Fe粘结相中。TiC颗粒相和金属Fe粘结相的界面结合良好。在橡胶轮式磨损试验条件下,TiC颗粒增强铁基复合材料表现出良好的耐磨性能。其磨损机制主要是磨粒磨损和少量硬质相脱落。     

基于自蔓延高温合成(SHS)的涂层技术

综述了几种利用自蔓延高温合成(SHS)反应制备涂层的技术,包括反应热喷涂、SHS离心铸造涂层、SHS熔铸涂层以及反应铸渗涂层.介绍了它们的工艺过程、工艺特点、适应的反应体系以及涂层性能.这些基于SHS反应,用于制备耐磨耐蚀陶瓷或金属陶瓷涂层的涂层技术,充分利用SHS技术本身具有的节能、工艺简单、产物纯度高等优点,显示出了很强的竞争优势.     

The self-propagating high-temperature synthesis of a nanostructured titanium nitride powder with the use of sodium azide and haloid titanium-containing salt

The use of the “ammonium hexafluorotitanate (NH₄)₂TiF₆-sodium azide NaN₃” system during self-propagating high-temperature synthesis (SHS) allows researchers to obtain nanostructured titanium nitride powder. Nanopowders of silicon, boron, and aluminum nitrides are formed from similar “halogenide of nitrided element-sodium azide” systems by SHS. It is confirmed that the use of compounds rather than pure elements in the starting powder mixtures for SHS makes it possible to substantially decrease the dimensionality of the combustion products and obtain them in the form of nanostructured particles, nanofibers, and nanopowders.     

SHS Technology for Composite Ferroalloys. 1. Metallurgical SHS: Nitrides of Ferrovanadium and Ferrochromium

The development of specialized self-propagating high-temperature synthesis (SHS) for complex ferroalloys used in steel smelting and in blast-furnace technology is discussed. To that end, a new approach to the SHS process has been conceived: the metallurgical SHS process, in which the basic raw material consists of various metallurgical alloys including dusty waste from ferroalloy production. In that case, synthesis involves exchange exothermal reactions. The product is a composite based on the initial inorganic compounds; the binder is iron or an iron alloy. Depending on the state of the initial reagents, the metallurgical SHS processes may be gas-free, gas-absorbing, or gas-liberating. For each case, the combustion conditions will be very different. Thermal matching may be used in organizing the metallurgical SHS process in systems that are not strongly exothermal. The self-propagating high-temperature synthesis of nitrided ferrovanadium and ferrochrome is investigated. It is shown that the phase composition of the initial alloy strongly affects the combustion of ferrovanadium in nitrogen. In the nitriding of σ ferrovanadium, transformation of the intermetallide to an α solid solution is activated on reaching the phase-transition temperature (~1200°C). The composite structure of the nitriding products of ferrovanadium is formed under the influence of solid–liquid droplets consisting of molten iron and solid vanadium nitride. Solid-phase reaction of ferrochrome with nitrogen facilitates high degrees of nitriding. The combustion rate of ferrochrome on nitriding during coflow filtration, as in chromium, increases with increase in the nitrogen flow rate. The degree of nitriding of the ferrochrome in forced filtration (4.7–7.5% N) is much less than that in natural filtration (8.8–14.2% N).     

The Synthesis of Cast Materials Based on the MAX Phases in a Cr–Ti–Al–C System

Russian Journal of Non-Ferrous Metals - Two variants of the self-propagating high-temperature synthesis (SHS) process, namely, SHS from elements and SHS metallurgy, are combined to obtain cast...     

自蔓燃高温合成碳化物陶瓷

介绍了自蔓延高温合成（SHS）制备碳化物粉体。单晶、多孔材料和致密材料。重点讨论了通过控制反应参数,控制合成材料的组织结构和性能的一些措施。以催化剂载体、泡沫陶瓷过滤器、粗TiC磨料以及Si-SiC复合材料为例,介绍了SHS在材料合成中的应用和控制方法。参考Ti3SiC2陶瓷的合成,讨论了多元SHS体系中产物相的控制问题。另外,文中还介绍了提高烧结助剂BxC在SiC中的分散性,从而提高SHSSiC烧结性的实例。     

Preparation of CeB6 nano-powders by self-propagating high-temperature synthesis （SHS）

CeB6 powders were prepared by high-temperature self-propagating synthesis(SHS) in which CeO2,B2O3 and Mg were taken asreactants.The adiabatic temperature and dynamics of SHS reactions were investigated.The SHS reaction products and leached products werecharacterized by X-ray diffraction(XRD) and scanning electron microscopy(SEM).The results indicated that the adiabatic temperature ofMg-B2O3-CeO2 reaction system was rather higher than 1800 K to make the reaction propagate by itself,and the apparent activation energy(Ea)and reaction order(n) of exothermic peak on Mg-B2O3-CeO2 differential scanning calorimetry(DSC) curve were 23.03 kJ/mol and 1.31,respectively.The apparent activation energy was lower,so the reaction occurred easily.The SHS products consisted of MgO,CeB6 and littleMg3B2O6.The leached products consisted of single CeB6 phase and its purity was higher than 99.0%,and the average particle sizes of CeB6were smaller than 150 nm.     

Composition,structure, and properties of SHS-compacted cathodes of the Ti-C-Al-Si system and vacuum-arc coatings obtained from them

The phase composition, structure, and properties of self-propagating high-temperature synthesis (SHS)-compacted materials of the Ti-C-Al-Si system are investigated. It is shown that metal-like titanium compounds can be used as cathodes for vacuum-arc evaporators. The coatings fabricated from SHS cathodes are single-phase and represent cubic titanium nitride of the (Ti, Al, Si)N composition. The volume of a microdrop phase in them is smaller by a factor of 2.5–3.0 as compared with TiN, while their microstructure is not fragmented into low-strength columnar elements; the CSR size is twice smaller than that of titanium nitride. Being approximately identically hard, the (Ti, Al, Si)N coatings substantially surpass TiN coatings in elastic and plastic failure resistance due to the lower elasticity modulus. When milling the tungsten-copper alloy, the hardness of hard-alloy milling cutters with the (Ti, Al, Si)N coating is higher by a factor of 2.4 than with the TiN coating fabricated from the titanium cathode with the magnetic plasma flow separation.     

Thermal analysis of self-propagating high-temperature reactions in titanium, boron, and aluminum powder compacts

This article focuses on the characterization of self-propagating high-temperature synthesis (SHS) reactions that occur in powder compacts containing titanium, boron, and aluminum. Interest in this powder system is based on the critical need to develop new joining techniques for bonding ceramics to metals. The exothermic reactions of particular interest in this study include those that generate TiB₂, TiB, Ti₃Al, and TiAl from their elemental powders. Data from differential thermal analysis (DTA), thermogravimetric analysis (TGA), and X-ray diffractometry are presented. These results demonstrate that the gas phase surrounding the SHS powders plays an important role in initiating the SHS reaction and in determining which reaction products will form in the final bond.     

固体氧化物燃料电池阴极材料La1-xSrxMnO3的制备方法

固体氧化物燃料电池是目前最成熟、最有发展潜力的燃料电池,具有广泛的应用前景。文章综述了该电池阴极材料La1-xSrxMnO3的制备方法,比较了各种制备方法的优缺点,介绍了一种新型的制备方法—自蔓延高温合成法的研究进展。指出:自蔓延高温合成法能显著缩短阴极材料的制备周期和减少能耗,从而能降低其制造成本、促进其实用化和产业化。     

Optimization of the Technological Synthesis of Refractory Compounds

The results of experimental studies, which are related to the regulation of the fractional composition of refractory compounds by roll milling in using controlled roll opening and unbalanced peripheral speeds of rollers, are reported. The content of prepared fine, middle, and coarse fractions is within 50–80%; in this case, the milling time of synthesis products is less than the time of ball milling by an order of magnitude. The application of roll milling for refining the products of self-propagating high-temperature synthesis can be most efficient in using together with heat-generating reactor to solve the main problem of self-propagating synthesis (SHS), which is a problem for recent several decades (the problem is the creation of intense automated production of refractory compounds in using continuous manufacturing cycle within a energotechnological system with the recovery of a great quantity of heat released during SHS).