Aluminum diboride was chosen as an initial reagent to obtain BN/AlN composites with high homogene... more Aluminum diboride was chosen as an initial reagent to obtain BN/AlN composites with high homogeneity. By comparing the specific surface area of products, it was established that this parameter can be increased (up to 10-24 m 2 /g) by increasing the amount of boron nitride. The gasifying compounds have essential influence on the formation of submicron particles in products. Even at their negligible amounts the specific surface area can increase by a factor of 2, and at higher amounts (close to the combustion limit) by 4 times. The maximum value for specific surface area (86 m 2 /g) was obtained for the 80%BN+20%AlN composite. It was established that it is impossible to obtain BN-B4C composite by direct interaction between elements (B, C and N2). Therefore another way was developed aimed at synthesizing BN-B4C composite under the activated combustion mode. Organic nitrogen containing compounds (ONCC) were used as sources for both the carbon and nitrogen.
ABSTRACT Differential scanning calorimetry and a high-speed temperature scanner were used to char... more ABSTRACT Differential scanning calorimetry and a high-speed temperature scanner were used to characterize dynamic features of the reaction between polytetrafluoro-ethylene (PTFE) and Al 2 O 3 under heating rates ranging between 20 and 780 °C min -1 . Exothermic reaction behavior between PTFE and Al 2 O 3 was observed at heating rates of 150 °C min -1 and higher. Thermodynamic calcu-lations predicted an adiabatic temperature of 1,425 K for the PTFE/Al 2 O 3 stoichiometric ratio. At lower heating rates, endothermic decomposition of PTFE dominated the interaction, where PTFE decomposes into gaseous products that escape the system without interacting with alumina. The enthalpy of the PTFE–Al 2 O 3 exothermic reaction was estimated to be -103 kJ mol -1 with activation energy of 21 kJ mol -1 . This study shows that, for energetic formu-lation of Al–PTFE, the Al 2 O 3 layer on the aluminum par-ticles can exothermically react with PTFE, producing AlF 3 and carbon monoxide.
The kinetic regularities were studied of the carbidization of zirconium in a methane medium and d... more The kinetic regularities were studied of the carbidization of zirconium in a methane medium and during contact with pyrographite over a wide range of gas pressures P CH4 =10-600 mm Hg and temperatures 1000-1800 o C. The formation of two types of carbide layers has been established: finely crystalline-porous and macrocrystalline-compact. The conditions of their formation and the kinetic parameters of growth have been determined.
This work studies how to obtain Ti-Al-based porous material by self-propagating hightemperature s... more This work studies how to obtain Ti-Al-based porous material by self-propagating hightemperature synthesis (SHS). Due to the low exothermicity of this system and the passive nature of the starting powders (mainly owed to surface oxidation), there exist great difficulties to realise the synthesis reaction in a wave propagation mode. This problem has been tackled and successfully solved by the use of chemically activated process. It has been found that the same product used as chemical activator also plays the role of foaming agent. Consequently, intermetallic foams have been successfully synthesized by this method. The investigation has been divided in two main parts: First, the phase formation of the product was studied. It was shown that besides the dominant TiAl phase, a ternary phase (Ti4Al2C2) was also obtained, coming from the decomposition of the carbon-containing activator. Second, porosity formation was investigated and optimized. The role of the foaming agent (FA) in the pha...
The mechanism and kinetics of nickel oxide reduction by Mg + C combined reducer at non-isothermal... more The mechanism and kinetics of nickel oxide reduction by Mg + C combined reducer at non-isothermal conditions in a wide range of high heating rates (100–1200 °C min−1) were studied by high-speed temperature scanner technique. It was shown that both the magnesiothermal and magnesiocarbothermal reduction processes, unlike low heating rates (5–20 °C min−1, DTA/DTG method), start beyond the melting point of magnesium and proceed via solid + liquid scheme. It was found out that the utilization of Mg + C combined reducer allows to significantly lower the reduction temperature (by about 200–400 °C) of nickel oxide as compared with exclusively magnesium or carbon reducers evidencing on the synergetic effect of combined reducers in the ternary mixture. The effective values of activation energy (Ea) for the NiO + Mg and 2NiO + Mg + C reactions were determined to be 185 ± 15 kJ mol−1 and 195 ± 15 kJ mol−1, respectively.
Aluminum diboride was chosen as an initial reagent to obtain BN/AlN composites with high homogene... more Aluminum diboride was chosen as an initial reagent to obtain BN/AlN composites with high homogeneity. By comparing the specific surface area of products, it was established that this parameter can be increased (up to 10-24 m 2 /g) by increasing the amount of boron nitride. The gasifying compounds have essential influence on the formation of submicron particles in products. Even at their negligible amounts the specific surface area can increase by a factor of 2, and at higher amounts (close to the combustion limit) by 4 times. The maximum value for specific surface area (86 m 2 /g) was obtained for the 80%BN+20%AlN composite. It was established that it is impossible to obtain BN-B4C composite by direct interaction between elements (B, C and N2). Therefore another way was developed aimed at synthesizing BN-B4C composite under the activated combustion mode. Organic nitrogen containing compounds (ONCC) were used as sources for both the carbon and nitrogen.
ABSTRACT Differential scanning calorimetry and a high-speed temperature scanner were used to char... more ABSTRACT Differential scanning calorimetry and a high-speed temperature scanner were used to characterize dynamic features of the reaction between polytetrafluoro-ethylene (PTFE) and Al 2 O 3 under heating rates ranging between 20 and 780 °C min -1 . Exothermic reaction behavior between PTFE and Al 2 O 3 was observed at heating rates of 150 °C min -1 and higher. Thermodynamic calcu-lations predicted an adiabatic temperature of 1,425 K for the PTFE/Al 2 O 3 stoichiometric ratio. At lower heating rates, endothermic decomposition of PTFE dominated the interaction, where PTFE decomposes into gaseous products that escape the system without interacting with alumina. The enthalpy of the PTFE–Al 2 O 3 exothermic reaction was estimated to be -103 kJ mol -1 with activation energy of 21 kJ mol -1 . This study shows that, for energetic formu-lation of Al–PTFE, the Al 2 O 3 layer on the aluminum par-ticles can exothermically react with PTFE, producing AlF 3 and carbon monoxide.
The kinetic regularities were studied of the carbidization of zirconium in a methane medium and d... more The kinetic regularities were studied of the carbidization of zirconium in a methane medium and during contact with pyrographite over a wide range of gas pressures P CH4 =10-600 mm Hg and temperatures 1000-1800 o C. The formation of two types of carbide layers has been established: finely crystalline-porous and macrocrystalline-compact. The conditions of their formation and the kinetic parameters of growth have been determined.
This work studies how to obtain Ti-Al-based porous material by self-propagating hightemperature s... more This work studies how to obtain Ti-Al-based porous material by self-propagating hightemperature synthesis (SHS). Due to the low exothermicity of this system and the passive nature of the starting powders (mainly owed to surface oxidation), there exist great difficulties to realise the synthesis reaction in a wave propagation mode. This problem has been tackled and successfully solved by the use of chemically activated process. It has been found that the same product used as chemical activator also plays the role of foaming agent. Consequently, intermetallic foams have been successfully synthesized by this method. The investigation has been divided in two main parts: First, the phase formation of the product was studied. It was shown that besides the dominant TiAl phase, a ternary phase (Ti4Al2C2) was also obtained, coming from the decomposition of the carbon-containing activator. Second, porosity formation was investigated and optimized. The role of the foaming agent (FA) in the pha...
The mechanism and kinetics of nickel oxide reduction by Mg + C combined reducer at non-isothermal... more The mechanism and kinetics of nickel oxide reduction by Mg + C combined reducer at non-isothermal conditions in a wide range of high heating rates (100–1200 °C min−1) were studied by high-speed temperature scanner technique. It was shown that both the magnesiothermal and magnesiocarbothermal reduction processes, unlike low heating rates (5–20 °C min−1, DTA/DTG method), start beyond the melting point of magnesium and proceed via solid + liquid scheme. It was found out that the utilization of Mg + C combined reducer allows to significantly lower the reduction temperature (by about 200–400 °C) of nickel oxide as compared with exclusively magnesium or carbon reducers evidencing on the synergetic effect of combined reducers in the ternary mixture. The effective values of activation energy (Ea) for the NiO + Mg and 2NiO + Mg + C reactions were determined to be 185 ± 15 kJ mol−1 and 195 ± 15 kJ mol−1, respectively.
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Papers by S. Kharatyan