Phase Composition Of Combustion Products Research Articles

Combustion Synthesis of Magnesium-Aluminum Oxynitride MgAlON with Tunable Composition.

Magnesium-aluminum oxynitride MgAlON has garnered significant attention in recent years due to its unique properties and potential applications. Herein, we report a systematic study on the synthesis of MgAlON with tunable composition by employing the combustion method. The Al/Al2O3/MgO mixture was combusted in nitrogen gas, and the effects of Al nitriding and oxidation by Mg(ClO4)2 on the exothermicity of the mixture, combustion kinetics, and phase composition of combustion products were investigated. Our results demonstrate that the MgAlON lattice parameter can be controlled by varying the AlON/MgAl2O4 ratio in the mixture, which corresponds to the MgO content in the combustion products. This work provides a new pathway for tailoring the properties of MgAlON, which may have significant implications in various technological applications. In particular, we reveal the dependence of the MgAlON lattice parameter on the AlON/MgAl2O4 ratio. The limitation of the combustion temperature by 1650 °C resulted in obtaining submicron powders with a specific surface area of about 3.8 m/g2.

Chemically activated combustion synthesis of AlON under high nitrogen pressure

This work explores the synthesis of aluminum oxynitride (AlON) by combustion of Al/Al2O3 mixtures under a high-pressure nitrogen atmosphere. The effect of nitrogen pressure and addition of Mg(ClO4)2 and excess Al on the exothermicity of the mixture, kinetics of the combustion process, and phase composition of combustion products is studied. In particular, we reveal the dependence of the AlON lattice parameter on nitrogen pressure (and, correspondingly, nitrogen content in the combustion products). Finally, we demonstrate the possibility of the fabrication of transparent Y2O3-doped AlON ceramics from the combustion products.

Effect of Iron Oxalate Additions on the Phase Composition of Combustion Products of Silicon–Carbon Mixtures in Nitrogen

We have examined the effect of iron oxalate (Fe2(C2O4)3 · 5H2O) additions on the phase composition of combustion products of silicon–carbon mixtures in nitrogen. The phase composition of the combustion products has been determined as a function of starting-mixture composition and nitrogen pressure. We have investigated the microstructure of the synthesized powders. The addition of SiO2 to the starting mixture has been shown to increase the percentage of Si2N2O in the combustion products.

High-temperature synthesis of cast materials based on Nb2AlC MAX phase

Cast materials based on Nb2AlC MAX phase were prepared by metallothermic self-propagating high-temperature synthesis (SHS) under 5 MPa of Ar pressure from green mixtures containing Nb2O5, Al, and C powders, and additive of CaO2 + Al blend as a heat-generating agent. Variation in the amount (α) of the additive markedly affected the process parameters and phase composition of combustion products. An increase in α led to an increase in the combustion temperature. A key factor responsible for successful phase separation in the melt is the lifetime of the liquid phase. A maximum content of Nb2AlC MAX phase in the ingot (67 wt%) was reached under optimized conditions (α = 15%).

Structure and phase formation of combustion products during the synthesis of γ-AlON in self-propagating high-temperature synthesis

Synthesis of aluminum oxynitride (γ-AlON) in conditions of self-propagating high-temperature synthesis (SHS) gas-statting under high pressures (10–100 MPa) of gaseous nitrogen, including the mode of so-called coupled combustion reactions (chemical furnaces) is investigated. It is shown that chemical and phase compositions of combustion products, as well as their structure and morphology of powder particles, depend on the reagent ratio in Al–Al2O3 initial mixture, as well as on nitrogen pressure, combustion temperature of highly exothermic components of chemical furnaces, and grade of initial reagents. The structure of γ-AlON powder particles are determind and its relation with operation conditions of SHS. Optimal SHS parameters for Al5O6N (γ-AlON) formation are established.

Nitride nanopowders by azide SHS technology

Azide SHS technology with NaN3 powder as a nitriding agent was used to fabricate TiN–BN, AlN–BN, and Si3N4–TiN nanopowders using Nа2TiF6, (NH4)2TiF6, KBF4, NH4BF4, Nа3AlF6, AlF3, Na2SiF6, and (NH4)2SiF6 as precursors. Mixtures of the above salts with sodium azide NaN3 readily burned in an SHS reactor to yield agglomerated nanosized or fine target powders. Phase composition of combustion products not always corresponded to expectations and often contained insoluble byproducts. Reported are optimal green compositions and procedures that afford the preparation of target TiN–BN, AlN–BN, and Si3N4–TiN nanopowders free of byproducts.

Cast ceramics by metallothermic SHS under elevated argon pressure

Cast ceramic composites were prepared by metallothermic SHS under elevated Ar pressure (5 MPa). Variation in green composition was used to affect the phase composition of combustion products. Under some optimized conditions, resultant ceramics can be obtained in the form of Al2O3–Cr2O3 solid solutions, Al2O3–Cr2O3 ∙ хZrO2 composites or single-phase Al2MgO4. Such materials seem promising for use in jewelry, process engineering (casting molds, cutting tools), and aerospace industry.

STRUCTURE AND PHASE FORMATION OF COMBUSTION PRODUCTS DURING Γ-ALON SYNTHESIS IN SHS GAS-STATTING MODE

The paper studies synthesis of aluminum oxynitride (γ-AlON) under the conditions of SHS gas-statting at high pressures (10–100 MPa) of gaseous nitrogen including the mode of so-called conjoint combustion reactions (chemical furnaces). It was shown that chemical and phase compositions of combustion products, their structure and morphology of powder particles depend on the reagent ratio in the initial Al–Al 2 O 3 mixture, as well as nitrogen pressure, combustion temperature of high-exothermic components of chemical furnaces, and type of initial reagents. The structure of γ-AlON powder particles was studied and its relation to self-propagating high-temperature synthesis conditions was found. It determines the optimum SHS parameters for Al 5 O 6 N (γ-AlON) synthesis.

Thermal explosion in Ti–Ni blends: Influence of mechanocomposite size

Influence of the size of the layered mechanocomposites formed during mechanical activation of Ti–Ni blends on the parameters of thermal explosion in Ti–Ni blends was studied experimentally. Periodic variation in the size of mechanocomposites was found responsible for the observed changes in the main parameters of thermal explosion—ignition temperature and maximum combustion temperature—as well as in the phase composition of combustion products.

Effects of reaction medium on combustion of the Zr-Nb-C system

Self-propagating high-temperature synthesis was used to study combustion of theZr-Nb-C system in argon, nitrogen, and a nitrogen-hydrogen mixture. In combustion in argon a deviation from the carbon stoichiometry facilitates the mutual dissolution of the formed phases and leads to the formation of single-phase complex carbides. The homogenizing role of hydrogen in the formation of the complex combustion products of theZr-Nb-C-N-H system was shown. It was found that there is competition among the effects of nitrogen, hydrogen, and carbon in this system. Concentration triangles of theZr-Nb-C system were constructed which show the evolution of the phase composition of combustion products depending on the reaction medium.

Nonuniqueness of stationary states in combustion of mixtures of zirconium and soot powders in hydrogen

This article attempts to clarify the question of the existence of the nonuniqueness of regimes accompanying the combustion of a three-component system of zirconium-carbon-hydrogen. Values of the rates and temperatures of combustion, as well as the phase composition of combustion products of mixtures of zirconium with soot for three different cases of ignition, are presented. The results indicate that all the compositions investigated burn in the low-temperature regime with the formation of zirconium hydrides. It is concluded that the theoretically predicted nonuniqueness of stationary regimes of combustion and the critical transition from the high-temperature regime to the low-temperature regime using ignition sources with different temperature can be observed experimentally in the combustion of zirconium-carbon-hydrogen systems.