Papers by Keyword: Thermal Explosion

Abstract: The results of investigation of the time and power parameters influence of high-temperature synthesis under pressure on the grain structure formation and strength properties of the Ni₃Al intermetallic compound are presented and discussed. Dependences of the grain size in the intermetallic compound synthesized under pressure and its strength properties on the value of the preload on the initial powder mixture (3Ni + Al) and on the delay time of pressure application to the thermoreacting system were determined from the time of initiation of intermetallic compound formation volumetric exothermic reaction.

Abstract: The influence of basic high-temperature synthesis parameters on the process of structure formation in the mechanically activated powder mixture 3Ti+Al was investigated in the study. The synthesis was realized by the method of induction heating in the thermal explosion mode. The heating temperature of the mixture reached 1500°C during the solid state reaction. This temperature exceeded the adiabatic combustion temperature. The investigations of the phase structure formation processes were conducted by XRD methods. In order to obtain a Ti₃Al single-phase compound, the optimal time-temperature parameters of the synthesis were determined.

Abstract: The intermetallic compounds (IMC) of Ni-Al system exhibit interest both by theoretical and practical point of view: theoretically, due to particular aspects in relation to their synthesis and practically, due to their qualities that recommend them for the top industries such as, for example, the aerospace industry. In this paper are shown the results of researches on obtaining of high temperature compounds of Ni-Al system by self-propagating high temperature synthesis and thermal explosion, through the initiation of process at a temperature below the melting temperature of the easy fusible component.

Abstract: The experimental investigation of structure formation processes in preliminary mechanically activated powder mixture 3Ti + Al was carried out. The synthesis was realized in the thermal explosion mode with the use of high-frequency induction heating. The characteristic features of structure and phase formation in this system by quenching of the mixture at different annealing times were installed. It was shown, that the processes of structure-phase formation occur in the following sequence: chemical reaction - structural relaxation - thermal relaxation - thermal equilibrium. The time-temperature intervals of Ti₃Al strictly single-phase compound existence with various concentrationsof non-equilibrium defects of the structure were established.

Abstract: For the thermal safety evaluation of energetic materials, the experimental devices, test method, conditions of determination, numerical calculation and simulation are listed in this paper on thermal explosion experiment both at home and abroad. By listing typical examples and comparing the existing researches, current study and developing trend of thermal explosion experiment are summarized and prospected.

Abstract: The Fe-Al₂O₃ composite has been prepared by high-frequency induction heated combustion synthesis (HFIHCS) from Fe₂O₃ and Al powders. The standard Gibbs energy minimization method was used to calculate the equilibrium compositions of the reacting species. The composition and microstructure of HFIHCS products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX).

Abstract: A new approach to the consideration of the thermal explosion macrokinetic features for monomolecular reactions in homogeneous systems based on a strict accounting of burnout during the reaction process is proposed. It is established, that the qualitative changes of the phase trajectory structure (phase portrait) on the plane: heating rate-temperature determine the characteristic modes of reaction. This approach makes it possible to go beyond the Semenov theory and allows us to consider the variety of the reaction modes. From this point of view, the theory of Semenov is a special case which is valid only for reactions of zero order. The phase trajectories analyze on the parametrical plane Semenov criterion – Todes criterion gives an opportunity to define the regions of the thermal explosion degeneration, the transition regions and the region of the thermal explosion realization. With the use of such consideration, the necessary and sufficient conditions of the thermal explosion are found.

Abstract: The nanocrystalline MgAl₂O₄ powder was prepared by thermal explosion mode of low-temperature combustion synthesis (LCS) using urea as fuel and nitrates as oxidizers. The molar ratio of nitrates to urea and the adiabatic flame temperature was calculated according to the propellant chemistry and combustion thermodynamics theory respectively, and the effect of thermal explosion temperature on the properties of powder was investigated. The phase and morphology of the synthesized powder were investigated by X-ray diffraction and scanning electron microscopy. The results showed that the combustion process completed in very shortly time, and the cauliflower-like powder with porous structure was obtained. The crystalline size of MgAl₂O₄ increased with the increasing of thermal explosion temperature, and the powder had good crystalline shape and purity. The average crystalline size of MgAl₂O₄ prepared at 400 was approximately 40nm.

Abstract: This paper introduces the methods and results of the overpressure in the thermal explosion, and analyzes the results according to the structure of the explosion cave. The experimental results show that the overpressure is close to that in detonation. It will generate electromagnetic radiation when the shell charge explodes, for the reason of electrokinetic’s effect and the friction of explosion product with the shell, and the electromagnetic radiation signal of shell charge and bare detonator are different from each other, including the duration and the complexity of signal.

Abstract: Porous NiTi shape memory alloys were fabricated by thermal explosion method using different Ti and Ni powder as initial materials. The effect of process parameters including heating rate, and particle size of Ti on pore characteristic and phase composition was analyzed. Microstructure, phase composition, and mechanical properties were studied by SEM, XRD, and compression test, respectively. The mechanism of thermal explosion reaction was studied. The results show higher heating rate and smaller Ti particle size result in higher porosity and bigger pores. The thermal explosion reaction starts with the melting of a eutectic between β-Ti(Ni) and Ti2Ni and the main phases of as-reacted products are TiNi phase which are the desired phases. NiTi2 and TiNi3 phases are also present in small amounts. The content of TiNi phase increases with increasing heating rate or decreasing Ti particle size. The compressive strength and Young’s modulus of compacts decrease with the increase of the porosity.