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Vol 27, No 4 (2018)
- Year: 2018
- Articles: 7
- URL: https://journals.rcsi.science/1061-3862/issue/view/12291
Article
To the Theory of Macrostructural Transformations during Gasless Combustion
Abstract
Macrostructural transformations taking place during gasless combustion of powder mixtures in a non-encapsulated sample were analyzed theoretically. Analytical expressions for estimating physicochemical and structural parameters of combustion wave have been derived.
201-206
Influence of Preheating Temperature on Solution Combustion Synthesis of Ni–NiO Nanocomposites: Mathematical Model and Experiment
Abstract
Solution combustion synthesis (SCS) is a widely recognized method to synthesize nanoscale materials. In this work, an attempt was made to analytically simulate (using the Semenov method) and evaluate the influence of preheating temperature on flame temperature as well as on physicochemical characteristics of SCS products. Preheating was found to affect combustion temperature only slightly. An increase in preheating temperature led to a decrease in the induction period due to enhanced heating rate and an increase in cooling time as a result of additional exothermic reactions taking place at higher temperatures. Variation in cooling time caused changes in composition and microstructure of product. For the first time, a mathematical model of SCS was suggested.
207-215
Thermal Explosion in Mechanochemically Treated Mixtures of Natural Sand with Aluminum Powder
Abstract
The influence of mechanochemical treatment (MCT) on thermal explosion in compacted blends of natural sand with Al powder subjected to MCT under varied conditions in the presence/absence of modifying agents—graphite and polyvinyl alcohol—was explored. MCT in the presence of modifiers was found to markedly increase a maximum temperature of thermal explosion, to shorten the induction period, and to stabilize the combustion process. Under optimized conditions, the extent of Al consumption attained a value of 96.9%.
216-220
Mesoporous Silica by Solution-Combustion Synthesis Followed by Etching
Abstract
Mesoporous silica was synthesized through the solution-combustion process followed by etching with aqueous solution of sodium dodecyl sulfate (SDS). Combustion products were characterized by XRD, FTIR, SEM, TEM, HRTEM, and BET analysis. After etching, the specific surface, mean pore size, and volume of porous space in silica increased up to 390 m2/g, 15 nm, and 1.6 cm3/g, respectively. The synthesized mesoporous silica exhibited good performance in the tests on elimination of methylene blue from aqueous solution.
221-227
Thermite-Related Technologies for Use in Extreme Geothermal Environments
Abstract
Thermite and related processes have attracted considerable attentions as highly useful technologies for material and energy supplies in extreme environments such as geothermal and disaster-stricken areas as well as in space exploration. As part of the development of casing pipes used in geothermal power plants started from the 1970s, long ceramic-lined pipes have been obtained via thermite reaction under effective centrifugal force without any additional heat treatment [Centrifugal-Thermite (C-T) process]. The potentials of the ceramic-lined pipes in deeper geothermal utilizations are revalidated in details by reviewing the results obtained through the erosion-corrosion tests carried out under the conditions of high velocities (up to 100 m/s) and various acidities (from pH 2.0 to pH 4.0) of two-phase flows provided by the geothermal field test apparatus at the Onikobe geothermal power plant in Japan. By reducing the FeO content of the ceramic layer processed under proper additives and reactant amounts, the tested ceramic-lined pipes were significantly improved compared to highly corrosion-resistant stainless steels. The technological advantages obtained through the development of the C-T process can show a useful model to promote thermite-related technologies onward.
228-235
Fabrication of Narrow-Fraction Micropowders of NiAl-Based Refractory Alloy CompoNiAl-M5-3
Abstract
Powders of new CompoNiAl M5-3 heat-resistant alloy were prepared by mechanoactivated SHS from (Ni–Al–Cr–Co–Hf)–NaCl mixtures. Ni dissolution in Al melt was found to be the motive force of combustion. Unlike the binary Ni–Al system, NiAl is formed not in the melt but in the post-combustion zone as a result of diffusion-controlled processes. Conditions for MASHS were optimized toward fabrication of a superalloy with homogeneous composition/structure and low content of gas impurities. As-prepared combustion product was disintegrated into a powder and the latter was subjected to plasma spheroidization, keeping in mind the needs of additive manufacturing. The attained degree of spheroidization was 98%. The structure and phase/chemical compositions of spherical powders did not differ from those of the synthesized powders. After plasma treatment, the content of gas impurities (О2 and N2) decreased.
236-244
SHS-Produced Al–Ti–B Master Alloys: Performance in Commercial Al Alloy
Abstract
Al–Ti–B master alloys (MAs) were SHS-produced from the elements taken in the amounts that would ensure the preparation of final combustion products (MAs) containing about 20, 25, and 30 mol % TiB2. Combustion products and the samples of commercial Al alloy doped with 0.2 wt % combustion-synthesized MAs were characterized by optical microscopy, XRD, SEM, and EDS. The effect of added MAs was explored by optical microscopy using Clemex Vision software to determine the ASTM grain size number (G) and percentage of intermetallic compounds in doped Al alloys. A higher microhardness (97.64 HV 0.05) was observed for the Al specimens doped with MA nominally containing 25 mol % TiB2.
245-254