自蔓延高温合成耐火材料

介绍了自蔓延法 (SHS)制备耐火材料的原理 ,并对SHS制备耐火材料的影响因素、应用现状和发展前景以及存在的问题进行了系统的论述     

Self-propagating high-temperature synthesis of strontium hexaferrite

We study the relations governing combustion front propagation and the influence of certain factors (relationship of the starting components, relative density of the specimens being synthesized, oxygen gage pressure, and iron powder particle size) on the temperature and velocity of combustion in the systems Fe−Fe₂O₃−SrO₂−O₂ and Fe−Fe₂O₃−SrCO₃−O₂. We show that by varying these factors we can realize various synthesis conditions, and we establish that the technology of SHS of strontium hexaferrite powders makes it possible to obtain articles with high electrophysical characteristics. Chernogolovka. Translated from Fizika Goreniya i Vzryva, Vol. 29, No. 5, pp. 51–56, September–October, 1993.     

Self-propagating high-temperature synthesis of ultradisperse molybdenum disulfide

The synthesis of molybdenum disulfide in a combustion wave, from mixtures of sulfur with ultradisperse molybdenum powder obtained by electrical explosion of wires, is investigated. Experimental data are give on the combustion rate and temperature and the degree of conversion to the final product as a function of the pressure and component ratio. It is shown that the process corresponds to a parabolic law with an activation energy of 80 J/mole and be described by an elementary model of combustion of the second kind. Optimal conditions of synthesis with a yield of up to 99% are determined. Institute of Petroleum Chemistry, Siberian Branch, Russian Academy of Sciences, Tomsk 634055. Translated from Fizika Goreniya i Vzryva, Vol. 30, No. 5, pp. 54–58, September–October, 1994.     

Self-propagating high-temperature synthesis of porous Ti-Si-Al-C based materials

The pore formation process and the phase composition of the products of combustion of the Ti—Si—Al—C system were studied. The structure of Ti₅(Si,Al)₃C_0.6 single crystals formed in small amounts was determined. The dependences of the burning rate and elongation of the samples on their density and the gas pressure were determined. __________ Translated from Fizika Goreniya i Vzryva, Vol. 42, No. 2, pp. 53–60, March–April, 2006.     

Self-propagating high-temperature synthesis of ceramic composites based on sialons

Factors affecting the density of composite sialon ceramics synthesized in a regime of filtration combustion are established, namely, the composition of the initial reaction mixture and the nitrogen pressure in the reactor. The electrical resistance, strength, resistance to the action of aggressive media (melts of steel and slags), and thermal-shock strength are presented.     

Self-propagating high-temperature synthesis technology for preparation of porous permeable materials

The principles for development of porous permeable materials based on the self-propagating high-temperature synthesis are discussed. A technology based on the use of industrial oxide wastes from the mechanical engineering industry is proposed. __________ Translated from Novye Ogneupory, No. 12, pp. 40–43, December, 2005.     

Features of self-propagating high-temperature synthesis of spinel pigments

The method of self-propagating high-temperature synthesis (SHS) was used to synthesize spinel ceramic pigments. Producing aluminum-nickel and aluminum-cobalt pigments in a finely dispersed state is a complex stepwise (combined) process involving a reduction stage and simultaneous natural air filtration. In the case of small-diameter samples, a flat combustion front is observed and in large samples, the front is formed of many hot spots. The dependence of combustion rate on porosity is presented. The maximum combustion rate of these systems are recorded for porosity of 50–60%. Powdered SHS pigments were obtained for the first time.     

Self-propagating high-temperature synthesis of intermetallide/oxide nanocomposite powders using mechanocomposite precursors

It was found that mechanical activation of a mixture containing iron, aluminum, and oxide iron resulted in mechanochemical reduction of iron oxide and formation of a Fe/Al/Al₂O₃ nanostructural mechanocomposite. High-temperature self-propagating synthesis (SHS) using this composite as a precursor yielded a FeAl/Al₂O₃ composite, which retained the morphology and dimensional characteristics of the precursor. During mechanical activation of a mixture of iron, aluminum, and chromium oxide, complete reduction of the latter did not occur but SHS also led to the formation of an intermetallide/oxide nanocomposite, in which chromium atoms were incorporated in the structure of iron aluminide.     

Self-propagating high-temperature synthesis of cubic niobium nitride under high pressures of nitrogen

Cubic niobium nitrides δ-NbN_x with different x = 0.87–1.015 were prepared by the self-propagating high-temperature synthesis (SHS) under nitrogen pressures of P(N₂) = 48–230 MPa.Nitrogen composition x as a function of P(N₂) was determined in weight gain experiments and compared with that determined by chemical (Kjeldahl) analysis. For powders with different x, the superconducting transition temperature T_c was measured as a function of lattice parameter a. The T_c values were found to grow linearly with increasing a. A maximum value of T_c = 15.0 K for cubic niobium nitride corresponded to a maximum value of a = 4.3901 Å.     

Self-propagating high-temperature synthesis in mechanically activated mixtures of boron carbide and titanium

Self-propagating high-temperature synthesis in both the modes of both layer-by-layer combustion and dynamic thermal explosion was carried out using preliminary mechanical activation of B₄C–Ti powder mixtures in a planetary ball mill. Preliminary mechanical activation conditions of reaction mixtures that provide a reduction in the reaction initiation temperature to 600 ± 20?C were determined. The reaction products consist of mixtures of TiC and TiB₂ with submicron grain size. The results of x-ray diffraction and electron microscopy studies of activated samples and reaction products are presented.     

Self-propagating high-temperature synthesis of nitride-and carbide-containing composite materials based on mechanically activated quartz

The possibility of preparing multicomponent refractory composites based on quartz-containing raw materials by self-propagating high-temperature synthesis is investigated. It is demonstrated that the combined use of preliminary mechanochemical treatment, thermal carbonization, and modification of batch mixtures with nitrogen-containing additives favors the formation of carbide and nitride phases in the synthesis products.     

Effect of chromium-containing additives on the structure of spinel-type pigments

Self-propagating high-temperature synthesis was used to synthesize rose-colored corundum and spinels with chromium-containing additives. The synthesized pigments can be used to decorate porcelains and other ceramic articles. __________ Translated from Steklo i Keramika, No. 3, pp. 19–20, March, 2007.     

Self-propagating high-temperature synthesis of nanocomposite ceramics TaSi2-SiC with hierarchical structure and superior properties

This study focuses on the investigation of the combustion kinetics and mechanisms, as well as the phase and structure formation processes, during elemental self-propagating high temperature synthesis of ceramics in Ta-Si-C system.Thermodynamic and kinetic features of SHS are discussed. Thermodynamic calculations, time-resolved XRD and investigation of stopped combustion front suggest the following chemical reactions sequence in combustion wave for the Ta-Si-C system: Ta + Si_solid + C → TaC + Si_solid + C → TaC + SiC + Si_liquid + C → TaC + TaSi₂ + Ta₅Si₃ + SiC + Si_solid + C → TaSi₂ + SiC.Significant microstructure refinement occurs due to the formation of SiC within the TaC, Ta₅Si₃ and TaSi₂ particles during the SHS. Combustion products consist of agglomerated SiC and TaSi₂ particles with the size of individual grains equal to 15–50 nm. Hot pressing of TaSi₂-SiC powders at 1600 °C produces the bulk nanocomposites with a relative density of 97%. In comparison to similar materials reported in the literature, bulk SHS composite TaSi₂-30%SiC exhibits superior hardness (19.1 GPa) as well as fracture toughness (6.7 MPa m^1/2) and shows a great potential for application as a structural material and as a precursor for ion-plasma deposition of high-temperature tribological coatings.     

Self-propagating high-temperature synthesis of nano-TiCx particles with different shapes by using carbon nano-tube as C source

With using the carbon nano-tube (CNT) of high chemical activity, nano-TiC_x particles with different growth shapes were synthesized through the self-propagating high temperature in the 80 wt.% metal (Cu, Al, and Fe)-Ti-CNT systems. The growth shapes of the TiC_x particles are mainly octahedron in the Cu- and Al-Ti-CNT systems, while mainly cube- and sphere-like in the Fe-Ti-CNT system.     

Self-propagating high-temperature synthesis of barium titanate and subsequent densification by spark plasma sintering (SPS)

This paper describes the self-propagating high-temperature synthesis (SHS) of perovskitic oxides, specifically BaTiO₃, and their subsequent densification by spark plasma sintering. With the final goal of obtaining dense nanostructured materials, SHS products were mechanically treated at different milling time conditions, before densification. It was found that the grain size of ball milled powders decreases with increasing milling time, this effect being more evident at early stages of milling. Depending upon the ball milling (BM) conditions adopted, crystallite size in the range 15–70 nm was obtained. After milling for 5 h, the resulting powders (20–30 nm) were sintered by SPS, at 700 A, for different periods of time. By properly varying sintering time in the interval 70–140 s, it is possible to obtain products with relative density in the range 66–99%, respectively. In particular, grain growth during sintering was found to be limited (below 50 nm) if the electric current is applied for time intervals equal to or less than 100 s. The observed dielectric properties are typical of a nanocrystalline BaTiO₃ ceramic.