The combustion process in the Ni + Zr + Polytetrafluoroethylene (PTFE) system is investigated. Ef... more The combustion process in the Ni + Zr + Polytetrafluoroethylene (PTFE) system is investigated. Effect of PTFE addition on the process parameters and characteristics of products are studied. The reacting mixtures and product obtained are studied by differential thermal analysis (DTA) and thermogravimetric (TG) techniques, mass-spectroscopy, ion-chromatography, and XRD analysis. Results are discussed in terms of literature data. The mechanism of combustion process is proposed according to which at initial stages monomer formed at PTFE decomposition reacts with metals to form ZrC, ZrF2, and NiF2. At elevated temperatures, ZrF2 disproportionate to form gaseous ZrF4. Heat generated at early stages of the process stimulates the formation of Ni–Zr intermetallic phases.
The combustion process in the Ni + Zr + Polytetrafluoroethylene (PTFE) system is investigated. Ef... more The combustion process in the Ni + Zr + Polytetrafluoroethylene (PTFE) system is investigated. Effect of PTFE addition on the process parameters and characteristics of products are studied. The reacting mixtures and product obtained are studied by differential thermal analysis (DTA) and thermogravimetric (TG) techniques, mass-spectroscopy, ion-chromatography, and XRD analysis. Results are discussed in terms of literature data. The mechanism of combustion process is proposed according to which at initial stages monomer formed at PTFE decomposition reacts with metals to form ZrC, ZrF2, and NiF2. At elevated temperatures, ZrF2 disproportionate to form gaseous ZrF4. Heat generated at early stages of the process stimulates the formation of Ni–Zr intermetallic phases.
The present work was undertaken to study the chemistry and phase formation mechanism in the salt-... more The present work was undertaken to study the chemistry and phase formation mechanism in the salt-controlled MoO3 + Mg + NaCl thermite reaction. It was found that the structure and phase formation mechanism in the studied system primarily depend on the salt content in the initial mixtures. In salt-poor mixtures, nucleation of product particles takes place in the molten magnesium, whereas under salt-rich conditions, products are mainly formed in molten sodium chloride. Analyses of combustion temperature profiles and product microstructures and thermal analysis of reacting mixtures suggested that the molybdenum oxide reacts with the salt at early stages of the process. The formed intermediate molybdenum oxychloride and sodium molybdate then react with magnesium, yielding Mo, MgO, and NaCl phases. The low value of the activation energy (50 kJ/mol) of the combustion process also suggests that gaseous (liquid) intermediates play an important role in the phase formation mechanism.
Fundamental aspects of a novel combinational approach to reduce molybdenum trioxide by magnesium ... more Fundamental aspects of a novel combinational approach to reduce molybdenum trioxide by magnesium and carbon were studied. Temperature profile analysis, DTA/TG, XRD, SEM/EDS methods were applied to investigate the mechanism of the reduction reaction. It was shown that in the early stages of process carbon reduces the MoO 3 to MoO 2. Highly exothermic magnesium reduction of MoO 2 starts at 700°C and nucleation of Mo particles took place in liquid magnesium. It was shown that the last transformation in this reacting system, MoO 2 + C, starts at 800-900°C. Depending on the reaction conditions, e.g. temperature, reduction of MoO 2 may yield either molybdenum or molybdenum carbide, with enhanced microstructure.
In this work we first time investigate the reaction mechanism and possibility of synthesizing NiA... more In this work we first time investigate the reaction mechanism and possibility of synthesizing NiAl intermetallic compound under the activated combustion mode. A halogen containing organic polymer, namely, polytetrafluoroethylene-PTFE is used as promoter. It is shown that the single-phase target product is obtained when amount of the promoter is 0.1%. Differential thermal (DTA), thermogravimetric (TG) and XRD analyses testify that reaction proceeds stepwise. It is shown that in first stage decomposition products of PTFE remove the oxide film from Al particles; then follows reaction between Ni and pure Al. This reaction undergoes two different modes. First the solid-state reaction takes place, then Al melts and reaction continues between solid Ni and molten Al. It is established that the increase in the promoter amount higher than 1% shifts kinetic activation mode to thermal-kinetic mode. The latter leads to misbalance of green mixture and formation of undesired by-products. The optimal conditions of chemically activated synthesis for NiAl intermetallic are established.
The combustion process in the Ni + Zr + Polytetrafluoroethylene (PTFE) system is investigated. Ef... more The combustion process in the Ni + Zr + Polytetrafluoroethylene (PTFE) system is investigated. Effect of PTFE addition on the process parameters and characteristics of products are studied. The reacting mixtures and product obtained are studied by differential thermal analysis (DTA) and thermogravimetric (TG) techniques, mass-spectroscopy, ion-chromatography, and XRD analysis. Results are discussed in terms of literature data. The mechanism of combustion process is proposed according to which at initial stages monomer formed at PTFE decomposition reacts with metals to form ZrC, ZrF2, and NiF2. At elevated temperatures, ZrF2 disproportionate to form gaseous ZrF4. Heat generated at early stages of the process stimulates the formation of Ni–Zr intermetallic phases.
The combustion process in the Ni + Zr + Polytetrafluoroethylene (PTFE) system is investigated. Ef... more The combustion process in the Ni + Zr + Polytetrafluoroethylene (PTFE) system is investigated. Effect of PTFE addition on the process parameters and characteristics of products are studied. The reacting mixtures and product obtained are studied by differential thermal analysis (DTA) and thermogravimetric (TG) techniques, mass-spectroscopy, ion-chromatography, and XRD analysis. Results are discussed in terms of literature data. The mechanism of combustion process is proposed according to which at initial stages monomer formed at PTFE decomposition reacts with metals to form ZrC, ZrF2, and NiF2. At elevated temperatures, ZrF2 disproportionate to form gaseous ZrF4. Heat generated at early stages of the process stimulates the formation of Ni–Zr intermetallic phases.
The present work was undertaken to study the chemistry and phase formation mechanism in the salt-... more The present work was undertaken to study the chemistry and phase formation mechanism in the salt-controlled MoO3 + Mg + NaCl thermite reaction. It was found that the structure and phase formation mechanism in the studied system primarily depend on the salt content in the initial mixtures. In salt-poor mixtures, nucleation of product particles takes place in the molten magnesium, whereas under salt-rich conditions, products are mainly formed in molten sodium chloride. Analyses of combustion temperature profiles and product microstructures and thermal analysis of reacting mixtures suggested that the molybdenum oxide reacts with the salt at early stages of the process. The formed intermediate molybdenum oxychloride and sodium molybdate then react with magnesium, yielding Mo, MgO, and NaCl phases. The low value of the activation energy (50 kJ/mol) of the combustion process also suggests that gaseous (liquid) intermediates play an important role in the phase formation mechanism.
Fundamental aspects of a novel combinational approach to reduce molybdenum trioxide by magnesium ... more Fundamental aspects of a novel combinational approach to reduce molybdenum trioxide by magnesium and carbon were studied. Temperature profile analysis, DTA/TG, XRD, SEM/EDS methods were applied to investigate the mechanism of the reduction reaction. It was shown that in the early stages of process carbon reduces the MoO 3 to MoO 2. Highly exothermic magnesium reduction of MoO 2 starts at 700°C and nucleation of Mo particles took place in liquid magnesium. It was shown that the last transformation in this reacting system, MoO 2 + C, starts at 800-900°C. Depending on the reaction conditions, e.g. temperature, reduction of MoO 2 may yield either molybdenum or molybdenum carbide, with enhanced microstructure.
In this work we first time investigate the reaction mechanism and possibility of synthesizing NiA... more In this work we first time investigate the reaction mechanism and possibility of synthesizing NiAl intermetallic compound under the activated combustion mode. A halogen containing organic polymer, namely, polytetrafluoroethylene-PTFE is used as promoter. It is shown that the single-phase target product is obtained when amount of the promoter is 0.1%. Differential thermal (DTA), thermogravimetric (TG) and XRD analyses testify that reaction proceeds stepwise. It is shown that in first stage decomposition products of PTFE remove the oxide film from Al particles; then follows reaction between Ni and pure Al. This reaction undergoes two different modes. First the solid-state reaction takes place, then Al melts and reaction continues between solid Ni and molten Al. It is established that the increase in the promoter amount higher than 1% shifts kinetic activation mode to thermal-kinetic mode. The latter leads to misbalance of green mixture and formation of undesired by-products. The optimal conditions of chemically activated synthesis for NiAl intermetallic are established.
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Papers by Yeva Grigoryan