Production of a high-temperature superconducting ceramic

Translated from Steklo i Keramika, No. 12, pp. 6–8, December, 1990.     

Preparation of ZrC by self-propagating high-temperature synthesis

ZrC fine powder has been prepared by self-propagating high-temperature synthesis (SHS) based on exothermic reduction reaction of ZrO₂–C–Mg. The combustion temperature observed was 1979 K. The effects of Mg content and particle size on the combustion temperature and chemical composition of the product were investigated. The reducing agent Mg plays an important role on the purity of ZrC powder obtained by SHS process. Post-heat treatment was applied to decrease the oxygen content of the final product further.     

Obtaining aluminomagnesia spinel by self-propagating high-temperature synthesis

The conditions for forming a solid solution of aluminomagnesia spinel with magnesium oxide in the regime of self-propagating high-temperature synthesis and the properties of the resultant refractory are investigated. The main parameters of the synthesis are determined. Test batches of specimens are used to study the main physicomechanical properties.Translated from Ogneupory, No. 12, pp. 10 – 12, December, 1994.     

Acoustic emission during self-propagating high-temperature synthesis

It was established experimentally that during SHS, reaction systems (Ni-Al, Ti-B, Mo-B, etc.) generated acoustic oscillations in the frequency range from 5 Hz to 1.1 MHz with a pulse power of up to 17 W. It was found that the combustion of different systems is characterized by an individual set of dynamic parameters of acoustic emission in the modes of low ordered discrete pulses and highly ordered self-oscillations. It is shown that the spatial zone of acoustic emission is localized near the combustion wave. Analysis of the acoustic emission mechanisms of SHS is performed.     

Features of self-propagating high-temperature synthesis in a titanium-based system

The combustion temperature and rate have been measured and the product structure has been examined to define the interactions in a system designed to produce a porous permeable material having a heterogeneous framework.Barnaul. Translated from Fizika Goreniya i Vzryva, Vol. 29, No. 4, pp. 37–42, July–August, 1993.     

自蔓延高温合成镧掺杂钡铁氧体改性研究

采用白蔓延高温合成法制备了La掺杂的M型钡铁氧体BaLaxFe12-xO19（x=0,0．3,0.4,0．6）。用X射线衍射仪、振动样品磁强计和扫描电镜对粉末产品的结构与磁学性能进行了观测。系统地研究了La掺杂对M型钡铁氧体结构和磁性能的影响。实验结果表明,随着掺杂量（x）的增大,矫顽力He增大,而饱和磁化强度M6和剩余磁化强度Mr均减小。当掺杂量x=0．3时,钡铁氧体具有最佳的综合磁性能。     

Preparation of a charge for firing high-temperature superconducting ceramic

Results are presented for a study of the effect of charge material on the sintering capacity and structure of high-temperature superconducting (HTSC) ceramic. Compositions are developed and proved for charge preparation. Use of the material compositions proposed for preparing refractory crucibles and supports provides relatively low refractory cost, and the purity of the HTSC-ceramic obtained has a favorable effect on its superconducting properties.     

Preparation of nano-size ZrB2 powder by self-propagating high-temperature synthesis

Preparation of nano-size ZrB₂ powder by SHS has been investigated. Zr and B elemental powders were mixed with 10–50 wt.% NaCl, and prepared pellets were reacted under argon. Adiabatic temperatures were calculated by HSC software. Increasing NaCl content led to a continuous decrease in adiabatic temperatures and reaction wave velocity. Products were subjected to XRD, SEM and FESEM analyses. Average crystallite size of ZrB₂, which was 303 nm without NaCl, decreased to 32 nm with 40% NaCl addition. Distinct decrease in ZrB₂ particle size was also observed from SEM analyses. 30% NaCl addition was found to be optimum for ensuring a stable SHS reaction and providing the formation of nano-size ZrB₂ particles. It was revealed from particle size distribution measurements that ZrB₂ powder obtained by 30 wt.% NaCl addition contained particles mostly finer than 200 nm. A mechanism, similar to solution-precipitation was proposed for the particle size refining effect of NaCl.     

X-ray radiation in self-propagating high-temperature synthesis processes

Emission effects of heterogeneous combustion in the region of ionization radiation are studied. By an example of a Ti-B powder system, it is demonstrated that the processes of self-propagating high-temperature synthesis in the thermal explosion regime is accompanied by “soft” X-ray radiation with the quantum energy estimated as ≈5 keV. Key words: heterogeneous combustion, X-ray radiation. __________ Translated from Fizika Goreniya i Vzryva, Vol. 44, No. 6, pp. 127–129, November–December, 2008.     

Formation of self-propagating high-temperature synthesis products in a magnetic field

The combustion of compressed Ni+16% Al, Ni+50% Al, Co+30% S, Ti+58% FeB, Ti+20% C, and FeO+10% Fe+18% Al mixtures in a constant magnetic field is studied. The depth of conversion is found to increase and the geometric dimensions of the phase components of the reaction end products to coarsen under the influence of the field in the systems containing a ferromagnetic metal. The changes in the reaction product are related to additional mass transport behind the self-propagating high-temperature synthesis wave. Translated fromFizika Goreniya i Vzryva, Vol. 35, No. 3, pp. 63–66, May–June 1999.     

Degeneration of a steady combustion wave in self-propagating high-temperature synthesis

Degeneration of a steady wave in self-propagating high-temperature synthesis (SHS) is considered in the paper. An analytical expression for the derivative of the squared combustion rate with respect to the cutoff temperature of a thermal source is obtained. It is shown that there is a domain of combustion parameters for which the combustion wave can be roughly considered steady.Translated from Fizika Goreniya i Vzryva, Vol. 32, No. 3, pp. 65–67, May–June, 1996.     

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.     

Directed self-propagating high-temperature synthesis of a series of explosion-emissive metalloceramic materials

The problem of production of materials for electron emitters with specified characteristics using the method of self-propagating high-temperature synthesis has been examined. The conditions under which this process occurs in a reagent mixture containing components that interact by two scheme have been analyzed by thermodynamic calculations of adiabatic temperature. Some laws of combustion have been studied experimentally. A satisfactory agreement has been reached between the experimental and calculated data. The possibility of producing materials with a reinforcing frame has been considered.Translated from Fizika Goreniya i Vzryva, Vol. 32, No. 1, pp. 58–65, January–February, 1996.     

Electroimpulsive activation of self-propagating high-temperature synthesis in powder mixtures

The effect of frequency electroimpulsive treatment on the self-propagating high-temperature synthesis reaction in a powder mixture is studied with the use of the Ni-Al system as an example. The longitudinal direction of the electric field applied to the sample and of the electric current relative to the direction of combustion-wave propagation was used. It is established that under the action of electrotreatment, the linear combustion rate increases by a factor of 1.3-1.6, the structure is transformed, and the completeness of chemical transformation increases. It is shown that the effects observed are of a nonthermal nature. Translated fromFizika Goreniya i Vzryva, Vol. 36, No. 4, pp. 133–136, July–August, 2000. This work was supported by the Russian Foundation for Fundamental Research (Grant No. 99-03-32465).     

Structure and phase composition of zinc sulfide produced by self-propagating high-temperature synthesis

The structure of polycrystalline ZnS produced by self-propagating high-temperature synthesis is investigated. The monolithic specimens produced are a mixture of wurtzite and sphalerite. In the cross section of the specimens there are three distinct zones: an outer zone of fine crystals and zones of acicular and equiaxial crystals. Changing heat-exchange conditions, one can affect the dimensions of the second and third zones. Introduction of the disperser NH₄Cl into the starting mixture changes the crystallization mechanism and produces powder ZnS of a hexagonal modification with a varying grain size. Experimental results are explained within the framework of a two-phase model of crystallization and Ostwald’s phase rule. Translated fromFizika Goreniya i Vzryva, Vol. 34, No. 1, pp. 39–44, January–February, 1998.     

Study of self-propagating high-temperature synthesis of aluminium nitride using a laser monitor

This study focused on the synthesis of aluminium nitride (AlN) by combusting aluminium nanopowder in air. To investigate the combustion of aluminium nanopowder, a copper bromide laser monitor was used. The optical system equipped with brightness amplification allowed the elimination of the background lighting effect and enabled the high time-resolved recording of the process. In particular, the laser monitor enabled us to detect changes in the morphology and optical properties of the surface of the aluminium nanopowder sample as well as to observe the propagation of the combustion waves in spite of the intense background lighting during combustion. The main time parameters of the combustion of aluminium nanopowder in air were determined. To improve and facilitate the processing of laser monitored high-speed video recordings, we proposed to analyse the time dependence of the intensity of the output signal of the laser monitor. The dependence was used to successfully detect the occurrences of all combustion waves and describe their dynamics. The time dependence also favourably represented the evolution of the reflection coefficient of the combustion products of aluminium nanopowder. This is the first time that this property of aluminium nanopowder has been investigated. The reflection coefficient evolution coupled with video recordings of the sample surface development during the combustion of nanopowder could be used to control the combustion process.     

Shape-formation in the processes of self-propagating high-temperature synthesis of foams

Self-propagating high-temperature synthesis of cylindrical specimens of foam cermet with a relatively large length (l/D≫1) is performed. A Ti+0.6C mixture containing foaming agent Na₂B₂O₇·10H₂O was used. The initial compacts were enclosed in burning paper shells, which during self-propagating high-temperature synthesis made it possible to produce straight rods of foam ceramics, distinguished by an even surface. The dependence of the relative elongation of the specimens on the shell thickness was established. The possibility of controlling the shape of the foam SHS product by varying the slope of the combustion-front plane to the specimen axis was considered. Translated fromFizika Goreniya i Vzryva, Vol. 34, No. 3, pp. 121–122, May–June 1998.