Self-propagating High Temperature Research Articles

Investigation of kinetic mechanisms of photocatalytic hydrogen generation from formic aside using metal-ceramic composites under visible-light irradiation

Processes of photocatalytic hydrogen generation from the formic acid water solution under vis-light irradiation with tantalum contained metal-ceramic silicon nitride-based composites were investigated depending on pH of the solution and hydrogen peroxide adding. These compounds were obtained by self-propagated high temperature (SHS) synthesis in the way of the ferrosilicoaluminum (FSA) and silicon-aluminum powders ignition in a nitrogen atmosphere with the tantalum addition. During the investigation it was found out that the reaction rate of the hydrogen production without hydrogen peroxide can be described within the Langmuir–Hinshelwood mechanism. There is the reaction mechanism changing simultaneously with a formic acid concentration increasing in the presence of H2O2. The most significant reaction rate of hydrogen production from HCOOH is observed with the Fe-contained composite synthesized from FSA in the solution system without H2O2 addition, the reaction turns of frequency (TOF) is 4.55 µmol/min.

Effect of sintering temperature on the synthesis of LiZnMnFe microwave ceramics with controllable electro/magnetic properties

Self-propagating high-temperature (SPHT) assisted method was successfully used to obtain soft magnetic ceramics based on the nanostructured powder of multicomponent lithium ferrite Li0·45Zn0·08Mn0·06Fe2·41O4. The influence of various temperature modes of sintering (900–1075 °C) on the microstructure, morphology, phase composition, and magnetic and electromagnetic properties of the initial powder and final ceramic products was analyzed in detail by methods of scanning electron microscopy, transmission electron microscopy, energy-dispersive and atomic absorption spectroscopy, thermogravimetry, calorimetry, X-ray diffractometry, induction magnetometry and measurement of electromagnetic parameters. It was shown that the particle size of the initial powder is 40 nm and depending on the sintering modes, it is possible to obtain lithium-zinc-manganese ferrite ceramics with an average grain size from 0.35 to 2.96 μm and porosity varying from 3.8 to 23.3%. The coercive force, residual induction, and saturation induction of the obtained samples were 51.3–816.6 A/m, 761.40–2131.30 G, and 1234.28–3431.71 G, respectively. It was found that the sample sintered at a temperature of 1075 °C for 8 h demonstrated the most pronounced soft magnetic behavior. The electromagnetic characteristics of the obtained samples also depended on the selected sintering mode and reached their maximum for ceramics sintered at a temperature of 1075 °C (ϵ’ = 11.52; ϵ” = 6.32⸱10−3; tan δϵ = 5.49⸱10−4; ΔH = 280 Oe; ΔHk = 1.87 Oe).

Structural-phase and morphological characteristics of silver catalysts on modified ceramic supports for selective oxidation of alcohols

New ceramic materials based on silicon nitride and obtained by self-propagating high-temperature (SPHT) synthesis were investigated. The Si3N4 materials modified with Zr and Al compounds were used as supports for silver-containing catalysts of selective oxidation of ethyleneglycol into glyoxal. The procedure for the synthesis of supported silver-containing catalysts affected the structural and morphological states of the active component before and after the catalytic reaction.

Geochemical conditions for the isolation of the long-lived radioisotope technetium-99

Conditions required for the isolation of Tcbearing wastes include their incorporating into metal� lic alloys and placement in underground waste repositories under reduced conditions. The paper reports means of synthesizing these matrices and distinctive structural features of samples produced by selfpropa� gating hightemperature synthesis (SHS).

Evaluation of fuels for the synthesis of Li2CoMn3O8

Li2CoMn3O8, a 5 V cathode material used in rechargeable lithium batteries, has been synthesized by adopting a novel technique of using fuels along with the nitrate reactants. The effect of the fuel on the synthesis of Li2CoMn3O8 has been analyzed in terms of the physical and electrochemical properties of the final product formed by various methods such as solid-state carbonate fusion and the solution route using acetate and nitrate precursors. Powder X-ray diffraction FT IR spectrum, particle size, surface area and SEM analysis were carried out. The combustion method, also known as selfpropagating high temperature (SPHT) method, has been employed in the present study by using nitrate mixtures of the respective salts and a nitrogeneous fuel (urea or glycine) at a temperature of 300 °C for 3 hrs. The nitrate reactants without the addition of fuel gave only a deliquescent product even at elevated temperature (600 °C) thus indicating the necessity of fuels. Similar attempts using acetate reactants with and without the addition of nitrogeneous fuels were made separately in order to find out the necessity of fuel also in this case. The characterization of the product in terms of purity, single-phase formation and surface morphology suggested that the fuel played no role in the case of the acetate precursors. A comparative study was made on the products obtained by the acetate precursor, combustion method and the conventional carbonate method. Among the three methods, the combustion method with glycine as fuel yielded the spinel phase with high purity Li2CoMn3O8 with superior electrochemical behavior both in terms of high cell voltage and good cycle life behavior.

Yttrium oxide:Eu 3+ red phosphor by self-propagating high temperature synthesis

Yttrium oxide doped with trivalent europium has been prepared by self-propagating high temperature (SPHT) synthesis, also known as combustion synthesis, with nitrogen-based fuels. The materials synthesized have been characterized by X-ray diffraction, scanning electron microscopy, and luminescent emission spectroscopy. Crystallite size, powder density, and photoluminescent-emission intensity/efficiency are found to depend on the fuels used. The phosphor products were sintered with and without sintering aids. The results obtained are discussed with respect to the processing method employed.