Production and use of ferrosilicotitanium produced by self-propagating high-temperature synthesis

The production of silicotitanium alloys by self-propagating high-temperature synthesis in the titanium-ferrosilicon and ferrotitanium-silicon systems is investigated. On the basis of the results, a production technology is developed for a new material: ferrosilicotitanium (titanium ferrosilicide) produced by self-propagating high-temperature synthesis, for use in economical titanium alloying of steel. Industrial tests at OAO MMK show that the assimilation of titanium from titanium ferrosilicide is greater (by a factor of 1.5) and more stable than from ferrotitanium.     

Features of the growth of nitride layers in the self-propagating high-temperature synthesis of chromium nitrides

The formation of product layers during combustion of a chromium powder in nitrogen under a pressure of 1–10 MPa is studied. It is shown that nitride Cr₂N forms continuous protective layers, whereas during the formation of CrN, the product layer is partially destroyed. Strength properties of chromium nitrides were determined by the indentation method with a diamond indenter. CrN has a lower strength and higher brittleness compared with Cr₂N, which can explain the above phenomenon.     

Application of titanium to self-propagating high-temperature synthesis

An overview of the application of various kinds of titanium to self-propagating high-temperature synthesis (SHS) is presented. Kinds of Ti include powders of various origins, sponge, dioxide (rutile concentrate and pigment powder), and scrap (namely, chips and scale). Using the combustion of solid-solid and solid-gas systems (titanium-carbon and titanium-nitrogen) as an example, the influence of general titanium characteristics on the properties of the final SHS product is shown. The principles are substantiated for selecting titanium for SHS which are defined by the following factors: chemical and granulometric compositions, the morphology of the particle surface, fire-and-explosion safety, and the cost and availability of one or another kind of titanium. SHS-based methods for the production of Ti powder, namely, the magnesiothermic reduction of dioxide with the subsequent acid enrichment and SHS hydrogenation of the sponge with the following dehydrogenation, are briefly considered. A short list of areas for the use of some titanium-based SHS products is given.     

Thermodynamic analysis of the reaction of titanium with boron carbide in a self-propagating high-temperature synthesis regime

Adiabatic temperatures, thermal characteristics, and the concentration of reaction products in the system Ti−B₄C containing 1–99 mass % B₄C are determined by thermodynamic analysis using the ASTRA package of programs. In order to prepare alloys of titanium with titanium boride and titanium carbide in a self-propagating high-temperature synthesis regime a mixture with 10–13 mass % B₄C is recommended, and for alloys of boron carbide with titanium carbide a mixture containing 53–70 mass % B₄C is recommended. Institute for Problems of Materials Science, Ukraine National Academy of Sciences, Kiev. Translated from Poroshkovaya Metallurgiya, Nos. 3–4(406), pp. 72–76, March–April, 1999.     

Finite-difference modelling of self-propagating high-temperature synthesis of materials

The modelling of self-propagating high-temperature reactions is attempted using a finite difference model. The model is described and model results are compared with experimentally observed combustion wave velocities for the reaction 3TiO₂ + 4Al + 3C → 3tiC + 2Al₂O₃ using various processing parameters (diluents, preheating etc.). The model is extended to derive a parameter which determines under what conditions a reaction will become self-propagating.     

Reactive properties exhibited by various types of carbon during the preparation of titanium carbide by self-propagating high-temperature synthesis

Conclusions As a result of an investigation into the behavior of various types of carbon during the self-propagating high-temperature synthesis of titanium carbide it has been established how the nature of the carbon material employed affects its rate of combustion and extent of transformation. It is shown that, with the types of carbon investigated, their specific surface has no effect on their reactivity. Differences in reactivity between different types of carbon are linked with their structure and the energetic and chemical state of their surface. The highest activity is exhibited by the readily graphitizing PM-15 and TG-10 carbon blacks.The authors wish to thank L. P. Savenkova and M. P. Izotova for the chemical analyses.Translated from Poroshkovaya Metallurgiya, No. 10(202), pp. 6–10, October, 1979.     

Magnesium-thermic reduction of tantalum oxide by self-propagating high-temperature synthesis

The magnesium-thermic reduction of tantalum pentoxide is studied during self-propagating high-temperature synthesis, i.e., under the conditions of manufacturing solid products in an autowave combustion mode. The effects of the charge density, the charge temperature, the particle size of reagents, and thermal ballast on the combustion rate and the maximum process temperature are investigated. Depending on the charge parameters, the combustion rate changes from 1.6 to 13 mm/s and the measured combustion temperatures varies in the range 1100–1885°C.     

Granulation in the powder technology of self-propagating high-temperature synthesis

Granulation, which is a very simple procedure for the formation of an artificial structure of a powder medium, is widespread in conventional powder metallurgy. However, it is very rarely used to implement self-propagating high-temperature synthesis (SHS). It is shown by the examples of various SHS processes (with directed gas filtration, with a reduction stage, in an aluminum melt, and the combustion of a thermite mixture) that charge granulation can substantially affect both the parameters of the SHS process and the properties of its product.     

Optimization of self-propagating high-temperature synthesis using a halogen fluoride as an igniter for reagents

The minimum quantity of the high-activity chemical reagent (HACR) that is required for the initiation of self-propagating high-temperature synthesis (SHS) is determined. The experimental results show that 1–1.3 mg ClF₃ (gravity flow from a dosing device), BrF₃ on the end of a filling knife, or a few ClF₂ ⁺ SbF₆ ^- crystals are sufficient for the initiation of titanium–boron or titanium–carbon high-energy powder charge compositions. Since the quantity of HACR required for SHS initiation is very small, the chemical method of initiation can be used for the development of a mobile ignition device for estimating the ignition of various SHS charge compositions under laboratory conditions and for application in standard reactors.     

Effect of the oxygen content of titanium powder on the synthesis of titanium carbide by the self-propagating high-temperature method

Conclusions An investigation was carried out into the possibility of employing various grades of titanium powder for the production of titanium carbide by the SHS process. The relationship between the chemical composition of the end product and synthesis parameters has been established. The completeness of chemical transformation, degree of purification of the titanium carbide from oxygen, and velocity of propagation of the synthesis wave depend on the oxygen content and particle size of the titanium powder as well as on the synthesis (combustion) temperature and time of residence of the reaction mass in the inert atmosphere at high temperature. Raising the CO concentration in synthesis increases the contamination of the titanium carbide with oxygen and the amount of free carbon in the synthesis product. The authors wish to thank Professor A. G. Merzhanov for helpful advice and discussion.The authors wish to thank Professor A. G. Merzhanov for helpful advice and discussion.Translated from Poroshkovaya Metallurgiya, No. 12(228), pp. 49–54, December, 1981.     

Deoxidation of the tantalum powder produced by self-propagating high-temperature synthesis

The possibility of removal of oxygen and magnesium from the products of the magnesium reduction of tantalum pentoxide under self-propagating high-temperature synthesis conditions that contain 30 wt % Mg₄Ta₂O₉ is studied. Additional reduction of this material can decrease the magnesium content to <0.01%. The oxygen content in the fabricated tantalum powder does not exceed its amount in the surface oxide (3 × 10^?3 g/m²). The specific surface area of the powder is an order of magnitude higher than that of the initial material, which can result from the formation of a tantalum powder with a specific surface area >30 m²/g during the reduction of Mg₄Ta₂O₉.     

Reaction of boron-containing materials with titanium during self-propagating high-temperature synthesis

We have studied the contact reaction of titanium, chromium, and tungsten borides with titanium. We have established that the materials react according to an exothermic solid-phase reaction mechanism with formation of titanium monoboride and diboride. The reaction is limited by diffusion of boron atoms through the layer of titanium monoboride formed. This makes it possible to successfully use reaction to effectively control the process for obtaining composite materials in the Ti-B₄C system under selfpropagating high-temperature synthesis conditions. __________ Translated from Poroshkovaya Metallurgiya, Nos. 3–4(448), pp. 67–72, March–April, 2006.