Thermochemical synthesis of tribotechnical coatings based on molybdenum diselenide MoSe2 on structural steels

The study results of the influence of parameters of the process of chemical-thermal treatment in selenium vapor during the preparation of solid lubricating coatings from molybdenum diselenide on specimens of structural steels with a plasma Mo-coating are presented. An empirical mathematical model of the temperature-time parameters of the Mo selenization process is proposed, which makes possible to control the quality of the obtained coatings depending on requirements for their tribotechnical properties. An assessment of their tribotechnical characteristics in air and in vacuum in the temperature range 20—600 °С has been carried out.

Advances in Thermochemical Synthesis and Characterization of the Prepared Copper/Alumina Nanocomposites

This paper presents thermochemical synthesis of copper/alumina nanocomposites in a Cu-Al2O3 system with 1–2.5 wt.% of alumina and their characterization, which included: transmission electron microscopy: focused ion beam (FIB), analytical electron microscopy (AEM) and high resolution transmission electron microscopy (HRTEM). Thermodynamic analysis was used to study the formation mechanism of desirable products during drying, thermal decomposition and reduction processes. Upon synthesis of powders, samples were cold pressed (2 GPa) in tools dimension 8 × 32 × 2 mm and sintered at temperatures within the range 800–1000 °C for 15 to 120 min in a hydrogen atmosphere. Results of characterization showed that dispersion-strengthened compacts could be produced by sintering of thermo-chemically prepared Cu-Al2O3 powders with properties suitable for material application, such as a contact material exhibiting high strength and high electrical conductivity at the same time. Additional research was carried out in order to analyze the application of the obtained nanocomposite powders for the synthesis of copper/alumina nanocomposites by a new method, which is a combination of a thermochemical procedure and mechanical alloying. The measured values of an electric conductivity and hardness were compared with ones in literature, confirming an advantage of the proposed combined strategy.

Study of Crystallization Kinetics of Amorphous Zirconia in Fe2O3 Matrix by Kissinger Method

The composite materials Fe2O3-ZrO2 with different content of zirconium oxide have been obtained by thermochemical synthesis. The process of crystallization of zirconium dioxide and the effect of the amount of zirconium dioxide on the phase transformation have been studied by DTA and microscopy. The activation energy of the crystallization process was calculated by the Kissinger method to be in average 170 KJ/mol. It is shown that an increase of the ZrO2 content leads to an increase of temperature of crystallization.

THERMOCHEMICAL SYNTHESIS OF NANOSTRUCTURED Y2O3: Eu3+ AND Y2O3:Bi3+,Eu3+ POWDERS AND THEIR LUMINESCENT PROPERTIES

This article describes a new method of thermochemical synthesis of luminescent nanostructured powders of Y2O3:Eu3+ and Y2O3:Bi3+, Eu3+ based on the burning of nitrate salts in the presence of a complex organic fuel consisting of a mixture of carbamide and hexamethylenetetramine (HMTA). It is established that using a combined fuel - a mixture of carbamide and HMTA - in a thermochemical reaction followed by calcination of the precursor at 650ºC gives more friable powders than the reaction with pure carbamide as a fuel, with a large amount of cavities. It is shown that when preparing Y2O3:Eu3+powders, complex compounds of anhydrous nitrates Y(NО3)3∙3СO(NH2)2 and Eu(NO3)3∙6CO(NH2)2 with urea are formed at the gel stage. They are decomposed at a higher temperature (about 1200ºС) resulting from the combustion process. As a result, corresponding crystalline oxides are formed. The europium ions replace a part of the yttrium ions in the structure of Y2O3 favouring the formation of a luminescent powder. X-ray diffraction, scanning electron microscopy, and photoluminescence spectroscopy have been used to characterize these powders. The powders synthesized in this manner (calcination at 650ºC) show a sharp peak in the X-ray diffraction picture at 2θ = 28.94° corresponding to crystalline Y2O3 particles with average particle size 62.3 nm. However, when treatment temperature is increased to 1200ºC, and the process duration is 1 h, the average particle size increases to 0.25 microns. Measurement of photoluminescence spectra of the samples revealed a maximum in the red region (λ=612 nm) when exciting at a wavelength of 395 nm (violet radiation). Luminescence intensity increases by 15% when introducing bismuth ions into the Y2O3 matrix and decreases by 30% when calcinating the Y2O3:Eu3+ powders at 1100ºС. The nanostructured Y2O3:Bi3+, Eu3+ powders obtained by the burning method can be applied in systems for protecting valuable security and industrial products, because these powders have special luminescent characteristics allowing to make visual observation of texts and tags under the radiation of LED sources without application of UV-lamps.