Hayk H. Nersisyan

Self-propagating high-temperature synthesis of nano-sized titanium carbide powder

The combustion process of a titanium–carbon system with sodium chloride as an inert diluent was investigated. The combustion laws and microstructure of final products according to diluent content were obtained. It was shown that sodium chloride not only decreases combustion temperature but also makes effective protective shells around primary carbide crystals and keeps this ultrafine structure up to the end of combustion. As a result, nano-sized titanium carbide powders were successfully obtained.

Highly effective synthesis and photoluminescence of Sr2Si5N8:Eu2+ red-emitting phosphor for LEDs.

We developed a highly effective and self-sustaining route for synthesizing Sr(2)Si(5)N(8):Eu(2+) red-emitting phosphor particles for use in light emitting diodes (LEDs). The phosphors thus synthesized showed excellent emission characteristics under a blue excitation wavelength of 450 nm, had a uniform particle size distribution, and showed high performance in LED packages.

Few-atomic-layer boron nitride nanosheets synthesized in solid thermal waves

In this study, we demonstrate the synthesis of few-atomic-layer hexagonal boron nitride (h-BN) sheets in a solid thermal wave implemented in a B2O3 + (3 + 0.5k)Mg + kNH4Cl exothermic mixture (here, k is the mole number of NH4Cl). The maximum synthesis temperature, developed using a thermal wave, was between 1030 and 1250 °C as k was changed from 5 to 7 moles. The phase content, morphology, and optical properties of the products were characterized. It is shown that BN sheets synthesized at the given k were 1.5–3 nm thick and had a hexagonal structure. The number of atomic layers in one sheet ranged from 5 to 10; the lateral dimension of individual sheets ranged from 50 to 1000 nm. The developed method allowed the synthesis of a large amount of uniform and high quality BN nanosheets (tens of grams in laboratory-scale experiments); this method will reduce the overall production cost.

Iron-assisted electroless deposition reaction for synthesizing copper and silver dendritic structures

Electroless deposition reaction (EDR) is a promising route for the synthesis of copper (Cu) and silver (Ag) dendritic structures with a controllable morphology. Here, we demonstrate the use of an electroless deposition reaction on the interface between an iron foil and aqueous solutions of either Cu or Ag salts to produce well-defined Cu and Ag dendritic nanostructures at room temperature. The dendritic structures and morphology were characterized based on the reaction time, Cu and Ag salt concentration, and diethylene glycol (DEG) content in the aqueous solution. We also demonstrate control over the dendrite sizes, morphologies and growth mechanisms. The electrical resistivity and improved sheet resistance were also evaluated in an anisotropic conductive film prepared from dendritic silver powder.

Aluminothermic Reduction of K2TiF6 to Prepare TiC, TiB2, and TiN Nanoparticles

Aluminothermic reduction of K2TiF6 in the presence of C, B, or N2 was investigated as a low exothermic combustion process for synthesizing nanoparticles of titanium ceramics such as TiC, TiB2, and TiN. Sample pellets were prepared by mixing powders of K2TiF6, Al, and non-metal (C, B) powders in stoichiometric ratios. Experiments were conducted at room temperature under either an Ar or N2 atmosphere. The combustion parameters were estimated from the temperature-time profiles, measured in the combustion wave using thermocouples. The reaction drastically proceeds within seconds, raising the temperature to 890–1170°C. The size of TiC, TiB2, and TiN nanoparticles prepared by the developed approach were, respectively, 5–30 nm, 10–60 nm, and 70–100 nm.

Size Tailored Nanoparticles of ZrN Prepared by Single-Step Exothermic Chemical Route

Abstract ZrN nanoparticles were prepared by an exothermic reduction of ZrCl 4 with NaN 3 in the presence of NaCl flux ina nitrogen atmosphere. Using a solid-state combustion approach, we have demonstrated that the zirconium nitride nanoparticlessynthesis process can be completed in only several minutes compared with a few hours for previous synthesis approaches. Thechemistry of the combustion process is not complex and is based on a metathesis reaction between ZrCl 4 and NaN 3 . Becauseof the low melting and boiling points of the raw materials it was possible to synthesize the ZrN phase at low combustiontemperatures. It was shown that the combustion temperature and the size of the particles can be readily controlled by tuningthe concentration of the NaCl flux. The results show that an increase in the NaCl concentration (from 2 to 13 M) results ina temperature decrease from 1280 to 750 o C. ZrN nanoparticles have a high surface area (50-70 m 2 /g), narrow pore sizedistribution, and nano-particle size between 10 and 30 nm. The activation energy, which can be extracted from the experimentalcombustion temperature data, is: E = 20 kcal/mol. The method reported here is self-sustaining, rapid, and can be scaled up fora large scale production of a transition metal nitride nanoparticle system (TiN, TaN, HfN, etc.) with suitable halide salts andalkali metal azide.Key wordszirconium nitride, nanoparticles, combustion synthesis, particle size, sodium chloride.

Mechanism of combustion and phase formation in the BaO2-TiO2-organic compound system

The high-temperature combustion mechanism of the BaO 2 -TiO 2 -organic compound system [urea, CO(NH 2 ) 2 ; hexamethylenetetramine, C 6 H 1 2 N 4 ] was investigated by the microthermocouple technique. The adiabatic combustion temperatures (T a d ) and equilibrium compositions of the final products were calculated by the computer program THERMO. The distribution of the temperature T(x), rate of heat generation Φ(x), and degree of conversion η(x) in the combustion wave were determined. The relative sizes of the combustion zones, the leading stage of the reaction, the kinetic law of components interaction, and parameters (activation energy, pre-exponential factor, braking parameter) were then calculated. Through this method, the optimal conditions for tetragonal BaTiO 3 powder synthesis with spherical form and particles size of 2-5 μm were found.

Synthesis of Tungsten Boride using SHS(Self-propagating High-temperature Synthesis) and Effect of Its Parameters

Due to their unique properties, tungsten borides are good candidates for the industrial applications where certain features such as high hardness, chemical inertness, resistance to high temperatures, thermal shock and corrosion. In this study, conditions were investigated for producing tungsten boride powder from tungsten oxide() by self-propagating high-temperature synthesis (SHS) followed by HCl leaching techniques. In the first stage of the study, the exothermicity of the -Mg reaction was investigated by computer simulation. Based on the simulation experimental study was conducted and the SHS products consisting of borides and other compounds were obtained starting with different initial molar ratios of , Mg and . It was found that , Mg and reaction system produced high combustion temperature and radical reaction so that diffusion between W and B was not properly occurred. Addition of NaCl and replacement of with B successfully solved the diffusion problem. From the optimum condition tungsten boride( and WB) powders which has 0.1~0.9 um particle size were synthesized.

Synthesis of Sr 3 Al 2 O 6 Phosphors by Solid State Reaction and Its Luminescent Properties

A red strontium aluminate phosphor (Sr₃Al₂O?:Eu³?, Eu²?) is synthesized using a solid state reaction method in air and reducing atmosphere. The investigation of firing temperature indicates that a single phase of Sr₃Al₂O? is formed when the firing temperature is higher than 1300℃. The effect of firing temperature and doping concentration on luminescent properties are investigated. Sr₃Al₂O? phosphor exhibits the typical red luminescent properties of Eu³? and Eu²?.

The laws of silicon ingot formation by combustion reaction

The formation of a phase pure silicon ingot from SiO2+Al+KClO3 and Na2SiO3+Al+KClO3 systems was investigated thermodynamically and experimentally under combustion mode, known also as self-propagating high-temperature synthesis (SHS). The regularities of combustion and phase formation versus KClO3 concentration by a thermocouple technique were obtained. The morphology, chemical and phase composition of the silicon ingot were analyzed by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), and ICP-analysis. The method reported here proved effective in producing silicon ingots with a purity of 98%.