Suren Levoni Kharatyan

Institute of chemical physics National Academy of Sciences of Armenia · Laboratory of Macrokinetiks of Solid State Reactions

This work reports the combustion synthesis mechanism in a system with hexamethylenetetramine (C 6 H 12 N 4) as the fuel and nickel nitrate (Ni(NO 3) 2) as the oxidizer. Detailed investigations using combustion diagnostic methods, thermal analysis, and mass spectroscopy measurements allow us to propose that the process includes the multistage decomp...

The present work reports the direct production of a high-entropy (HE) intermetallic CoNi0.3Fe0.3Cr0.15Al material with a B2 structure from mechanically activated elemental powder mixtures. Fast and efficient combustion synthesis (CS), spark plasma sintering (SPS), and reactive SPS (RSPS) methods were used to synthesize the HE powders and bulks. The...

Novel AlCo-rich AlCoNiFe and AlCoNiFeCr high entropy alloys (HEAs) were prepared from the non-activated and mechanically activated (MA) quaternary Al40Co40Ni10Fe10at% and quinary Al35Co35Ni10Fe10Cr10at% mixtures. The wide temperature range of the formation of a single high entropy alloy of BCC structure in quaternary system and the formation of pur...

Hexagonal close-packed (hcp) Ni exists only on a nanometric scale and readily converts into the stable face-centered cubic (fcc) polymorph. This work reports a spontaneous crystallization (SC) process in amorphous nanoparticles to tailor polymorphism in nanoscale Ni. The heat generated during the amorphous–crystalline transition enables SC to self-...

The programmed reduction of tungstates and molybdates may yield the production of an intimate mixture of metals, pseudo-alloys or composite powders. As an extension of the study of obtaining powders of tungsten-copper, molybdenum-copper and tungsten-nickel from their respective salts, in the present study the reduction of silver tungstate was perfo...

Single-phase, fine-grained high entropy MnFeCoNiCu alloy and (MnFeCoNiCu)3O4 oxide powders have been pioneered by in-situ solution combustion synthesis without post-treatment, utilizing alanine and glycine as organic reducers and ammonium nitrate as an auxiliary oxidizing agent. In order to regulate the porosity, homogeneity, phase composition and...

Modeling the self-sustained high-temperature synthesis (SHS) reaction via thermal dilution and transformation of the reaction heterogeneous media into a moderate exothermic one has unlimited potential for designing inorganic powders of a certain morphology beneficial for advanced consolidation. Thermal/inert dilution of the high-exothermic mixtures...

Understanding of the decisive role of non-isothermal treatment on the interaction mechanism and kinetics of the MoO3-CuO-Mg-C system is highly relevant for the elaboration of optimal conditions at obtaining Mo-Cu composite powder in the combustion processes. The reduction pathway of copper and molybdenum oxides with combined Mg + C reducing agents...

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 mi...

The exothermic reactions in the ZrF4−Mg-Si and ZrF4-Al-Si systems are investigated by a fast temperature recording (thermocouple) technique, differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). A quenching method is used to arrest the combustion process and conduct a layer-by-layer analysis of the products by x-ray diffrac...

The capability of self-propagating high-temperature synthesis (SHS) to produce powders that are characterized by a high sintering ability, owing to high heating and cooling rates inherent to the exothermic reaction, is of a special interest for the industry. In particular, SHS-derived powders comprise a significant defect concentration in order to...

Functional features of Ni-W composite materials combined with successful performance enabled a breakthrough in their broad application. To disclose the formation pathway of Ni-W composite materials at extreme conditions of combustion synthesis in the NiO-WO3-Mg-C and NiWO4-Mg-C systems for the optimization of the synthesis procedure, the process wa...

Understanding of the decisive role of the interaction mechanism and kinetics in the combustion processes is highly relevant for the elaboration of optimal conditions for obtaining Mo-Cu composite powders. From this perspective, the efficient delivery of the reduction mechanism of copper and molybdenum oxides with combined Mg + C reducing agents at...

In the paper the mechanism of reduction of silver tungstate with combined (Mg + C) reducer under the conditions of linear heating with the rates of 5-30 °C min-1 was studied. It was shown that for both the cases of using separate reducing agents and a combined reducer, the interaction begins before reaching the melting point of magnesium, and incre...

Solution combustion synthesis (SCS) utilizes exothermic self-propagating reactions to prepare nanoscale materials that can be used widely in energy, electronics, and biomedical technologies and other applications. SCS is a specific variety of a more general combustion synthesis (CS) method. Investigations of the thermodynamics, kinetics, and the me...

The reaction pathway for the joint reduction of nickel and tungsten oxides with the use of Mg/C combined reducer was studied by DTA/TG technique. It was revealed that reduction of the metal oxides is initiated with double-stage magnesiothermal reduction (reducing the nickel oxide, firstly, and tungsten oxide, secondly) at temperatures near the melt...

Here we report on a single-step, eco-friendly, and facile approach to combustion-assisted reprocessing of oily copper waste into copper powder without preliminary cleaning. Complete reduction of copper from oily copper waste in the combustion wave was reached in the presence of ammonium nitrate and without introducing any reducing agent. The optima...

Nickel oxide reduction by methane is of particular importance in catalysis, extractive metallurgy, and clean power generation technologies. Despite extensive investigations of the NiO+CH4 reaction, many questions remain about its kinetics, molecular and structural transformation mechanisms. This work reports the reduction kinetics of bulk polycryst...

Methods for the preparation of raw materials to produce leucosapphire are considered. It is shown that the main directions in the production of high-purity aluminum oxide raw materials are: electrochemical oxidation of aluminum, decomposition of alkoxides, high-temperature treatment of aluminum oxide in a halogen-containing atmosphere, and prelimin...

Ni-W nanocomposite material was synthesized by self propagating high temperature synthesis method from the NiO-WO3 oxides mixture using Mg+C combined reducers via thermo-kinetic coupling approach. Thermodynamic modeling was performed to design combustion synthesis in the NiO-WO3-yMg-xC system to find out optimum values for x and y in a moderate tem...

The in situ preparation of Mo–Cu from copper molybdate in the combustion mode with the help of thermo-kinetic coupling approach using the combined magnesium/carbon reducer to provide controllable thermal conditions is reported. To determine the optimum processing parameters, the stepwise nature of reaction mechanism in the CuMoO4–Mg–C system was co...

Kinetic parameters and reaction pathway for the reduction of nickel oxide with simultaneous utilization of magnesium and carbon were established to assess the feasibility of using combined reducers to produce powdered nickel from the NiO-Mg-C system. It was revealed that in this system the reduction of the metal oxide is initiated by Mg, followed b...

Introduction The Transcaucasia region is constantly exposed to the risk of incursion of new FMD strains which can represent a high risk of epizootic development with significant economic impact. The veterinary services of Armenia, Azerbaijan, Georgia, Iran, Turkey and the Russian Federation agreed on a common vision for the intensified collaboratio...

A high-speed electrothermography approach is applied to investigate the mechanism and kinetics for nanostructured Al/Ni foils. Application of the Kolmogorov-Johnson-Mehl-Avrami and adiabatic thermal explosion models reveal that the activation energy for nucleation appears to be much higher than that for reaction. It is shown that formation of inter...

Manufacturing W-Cu composite nanopowders was performed via joint reduction of CuO and WO3 oxides with various ratios (W:Cu = 2:1, 1:1, 1:3, 1:13.5) using combined Mg+C reducer. Combustion synthesis was used to synthesize homogeneous composite powders of W-Cu and hot explosive consolidation (HEC) technique was utilized to fabricate dense compacts fr...

A simple and efficient microwave-assisted preparation of ReB2-based material is reported utilizing ammonium perrhenate (NH4ReO4), magnesium boride (MgB12) reactants and carbon as an absorber of microwave irradiation. The investigation of microwave irradiated NH4ReO4 +MgB12 +C mixtures, thermal analysis results and electron microscopy examination re...

A novel approach for the preparation of molybdenum carbide by solution combustion synthesis (SCS) combined with subsequent programmed heating of SCS products was proposed using ammonium heptamolybdate (AHM) and organic reducers (glycine, alanine, glucose, etc.) as precursors. It has been shown that SCS temperature and composition of the products ar...

Mesoporous networks with a special distribution of functional centers are an important class of high performance materials for catalysts, bioscaffolds, energy conversion and storage systems. Methods of fabrication allowing to control over special distribution of the functional sites of required phases and designed morphology are still of a great ch...

The mechanism and kinetics of tungsten and copper oxides joint reduction by Mg + C combined reducer was studied at high heating rates by thermal analysis method utilizing high-speed temperature scanner. The effective values of activation energy for magnesiothermic reduction stage for the binary (WO3–Mg, CuO–Mg), ternary (WO3–Mg–C, CuO–Mg–C, WO3–CuO...

Electrothermography is a method for studying the kinetics of high-temperature solid-phase reactions at isothermal and non-isothermal conditions, including those taking place at SHS of a variety of inorganic materials. One of advantages of the electrothermography method is the possibility of measuring in situ the rate of the chemical heat release (d...

The article covers the organisation and development of SHS research in Armenia from its initiation in 1969 to the present. It includes the establishment of an SHS sector in the Laboratory of Chemical Physics of Armenian Academy of Sciences, and in 1980 the organization of a new engineering division at the Institute of Chemical Physics, which was so...

The primary condition for the implementation of an SHS process is the ability to generate a sufficient amount of energy that makes the progression of reactions in combustion mode possible. But often it is difficult to initiate the reactions in combustion mode because of kinetic/diffusion barriers. To overcome these limitations, that is, to activate...

Fabrication of copper, nickel, and cobalt powders by reduction of metal oxygenous compounds (MOC) by organic reducers (e.g., polystyrene) is reported. It is shown that new reaction schemes, which include metal oxide reduction by decomposition products of organic reducer, allow to obtain such powder in combustion regime at relatively low temperature...

In the present work for the fabrication of W/Cu nanopowders (with 15 and 51 wt.% Cu) an energy-saving combustion synthesis method was used, with carefully selected precursors and Mg/C reducing mixture. Combustion synthesis was performed from fine CuWO4/WО3 and CuWO4/CuО precursors obtained via solution combustion synthesis (SCS) or sol-gel combusti...

In the work, the preparation of fine-grained silicon was performed in combustion mode by magnesiothermic reduction of silica, obtained from serpentine mineral, which is characterized by a high specific surface area (about 560 m²/g) and high reaction activity. It is manifested by the fact that the measured combustion temperature exceeded the adiabat...

W-Cu composite materials with various molar ratio of constituent metals (W:Cu = 2:1 and 1:3) were synthesized via co-reduction of WO3 and CuO oxides precursors with Mg + C combined reducer in the combustion mode by applying reaction's thermo-kinetic coupling approach. The interaction mechanism and phase and microstructure formation laws in the 2WO3...

Composite powders W–Cu were prepared via joint reduction of WO3 and CuO oxides with Mg‒C combined reducer in a combustion mode by using the method of coupled reactions. Combustion phenomenology and the processes of phase and microstructure formation were investigated by thermocouple and copper- wedge techniques combined with XRD, SEM, and EDS analy...

Copper-molybdenum composite powders with various molar ratios of metals (Cu-2Mo and 3Cu-Mo) were synthesized in combustion mode. For this purpose co-reduction of copper and molybdenum oxides by Mg+C combined reducers was carried out by applying reactions' coupling approach. Estimation of products composition, adiabatic temperature and optimum areas...

We studied the reduction kinetics of bulk NiO crystals by hydrogen and the corresponding structural transformations in the temperature range of 543−1593 K. A new experimental approach allows us to arrest and quench the reaction at different stages with millisecond time resolution. Two distinctive temperature intervals are found where the reaction k...

The mechanism of copper (II) oxide and molybdenum (VI) oxide co-reduction by Mg + C mixture was investigated at non-isothermal conditions by carrying out simultaneous differential thermal (DTA) and thermogravimetric (TG) analyses combined with X-ray diffraction (XRD) analysis of intermediate and final products. The whole process was found to involv...

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 hi...

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 highe...

A new electrothermographic method, viz. high-speed temperature scanning, was applied to kinetic studies of reactions taking place in the Ni-Al system, including those after mechanical activation in a planetary ball mill. Treatment of the temperature profiles taken at different heating rates in terms of the Kissinger-Akahira-Sunose (KAS) approximati...

The mechanism of copper molybdate carbothermal reduction was investigated at non-isothermal conditions by carrying out simultaneous differential thermal (DTA) and thermal-gravimetric (TGA) analyses combined with X-ray diffraction (XRD) analysis of intermediate and final products. In order to understand the influence of copper molybdate preparation...

В настоящей работе электротермографическим методом изучены кинетические закономерности восстановления трехокиси вольфрама водородом в температурном интервале 750-1150oC и при давлении водорода P=10-300 Торр. Рентгенофазовым анализом установлено, что восстановление вольфрама из ангидрида протекает через образование промежуточной оксидной фазы WO2, а...

Non�isothermal siliconizing in Si�-clad Mo wires has been studied over a wide range of heating rates Vh and silicon layer thicknesses δSi. At T = 1000–1600°C, the reaction was found to proceed in two stages: by Mo(s) + Si(s) mechanism (stage I) and by Mo(s) + Si(l) mechanism (stage II). For sufficiently thin silicon layers, non�isothermal Mo–Si rea...

Non�isothermal siliconizing in Si clad Mo wires has been studied over a wide range of heating rates Vh and silicon layer thicknesses δSi. At T = 1000–1600°C, the reaction was found to proceed in two stages: by Mo(s) + Si(s) mechanism (stage I) and by Mo(s) + Si(l) mechanism (stage II). For sufficiently thin silicon layers, non-isothermal Mo–Si reac...

In this work the reaction mechanism in the WO3–Mg/C systems and ammonium paratungstate (APT)–Mg/C systems are studied. As reducer magnesium, carbon or combinations of both are explored. It is shown that in the WO3–Mg system the reduction undergoes by solid–solid mechanism before melting Mg, where metallic tungsten and MgO are formed. Unlike this sy...

1100-1500 о C. Установлено образование однофазной диффузионной зоны NiO, рост которой описы-вается известным из реакционной диффузии кинетическим уравнением параболического типа. Определены значения параболических констант привеса и роста оксидного слоя и их темпера-турные зависимости. Для энергии активации процесса окисления никеля получено значен...

The influence of calcium fluoride (CaF2) on combustion characteristics of Na2WO4 + 3 Mg system and microstructure of the produced W and WO3/W crystals is investigated. The results of thermodynamic analysis and experimental investigations show that CaF2 simultaneously enhances the conversion of Na2WO4 toward tungsten and binds sodium through the for...

Macrokinetic features and mechanism of Mo-Si reaction in conditions of rapid heating on a single particle level (Mo/Si diffusion couple) were studied by high-speed scanning electrothermography. The experiments were conducted in the temperature-time conditions (T = 1000–1600°C, t = 0.01–3.0 s) comparable to those of combustion synthesis of molybdenu...

The dynamic features of Al2O3 - polytetrafluoroethylene (PTFE) and Al - PTFE reactions in non-isothermal conditions are presented. The Differential Scanning Calorimetry (DSC) and High-Speed Temperature Scanner (HSTS) were used to characterize the Al2O3/Al – PTFE reactions at different heating rates. The study shows that the HSTS instrument can give...

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...

Considered were the thermodynamic and kinetic aspects for different kinds of coupled SHS reactions: thermally coupled, chemically coupled, and thermochemically coupled ones. Thermodynamic calculations confirmed the applicability of coupling as a useful route to materials synthesis in a one-step combustion process.

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-chro...

abStract The objective of this work was in vitro testing on biocompatibility of a new NiZr alloy as po-tential biomaterial for reconstructive medicine. Flat tablets of porous NiZr alloy and non-porous zirconium were prepared by combustion synthesis technique. the cytotoxicity of materials was evaluated in KCL-22 (human chronic myeloid leukemia) sus...

The objective of this work was in vitro testing on biocompatibility of a new NiZr alloy as potential biomaterial for reconstructive medicine. Flat tablets of porous NiZr alloy and non-porous zirconium were prepared by combustion synthesis technique. The cytotoxicity of materials was evaluated in KCL-22 (human chronic myeloid leukemia) suspension ce...