Characterization of tin selenides synthesized by high-energy milling
Tin selenides SnSeX (x=1,2) were synthesized from tin and selenium powder precursors by high-energy milling in the planetary ball mill Pulverisette 6 (Fritsch, Germany). The orthorhombic tin selenide SnSe and the hexagonal tin diselenide SnSe2 phases were formed after 4 min and 5 min of milling, respectively. Specific surface area of both selenides increased with increasing time of mechanochemical synthesis. The particle size distribution analysis demonstrated that the synthesized products contain agglomerated selenide particles consisting of numerous idiomorphic tin selenide crystals, measuring from 2 to more than 100 nm in diameter, which were also documented by TEM. UV-Vis spectrophotometry confirmed that tin selenide particles do not behave as quantum dots.
Semiconducting tin selenide thin films prepared by heating Se–Sn layers
Deposition of Se thin films of 80–350 nm in thickness from a chemical bath at a deposition yield of more than 95% is reported. These films are utilized to prepare SnSe and SnSe2 thin films either by heating a vacuum deposited Sn thin film in close contact with the Se thin film at 200 °C in a nitrogen atmosphere for 1 h or by heating a Se–Sn stack in air at 400 °C for about 5 min. By controlling individual film thicknesses and the conditions of heating, SnSe2 or composite films of SnSe2 and SnSe are formed. An optical band gap of 1–1.27 eV, electrical conductivity of 0.01–0.2 Ω−1 cm−1 and the photoconductivity of these materials fulfil the basic requirements for their integration into photovoltaic structures.
Computer-Aided System of Virtual Testing of Gas Turbine Engines
The article describes the concept of a virtual lab that includes subsystem of gas turbine engine simulation, subsystem of experiment planning, subsystem of measurement errors simulation, subsystem of simulator identification and others. The basis for virtual lab development is the computer-aided system of thermogasdynamic research and analysis “ASTRA”. The features of gas turbine engine transient modes simulator are described. The principal difference between the simulators of transient and stationary modes of gas turbine engines is that the energy balance of the compressor and turbine becomes not applicable. The computer-aided system of virtual gas turbine engine testing was created using the developed transient modes simulator. This system solves the tasks of operational (throttling, speed, climatic, altitude) characteristics calculation, analysis of transient dynamics and selection of optimal control laws. Besides, the system of virtual gas turbine engine testing is a clear demonstration of gas turbine engine working process and the regularities of engine elements collaboration. The interface of the system of virtual gas turbine engine testing is described in the article and some screenshots of the interface elements are provided. The developed system of virtual gas turbine engine testing provides means for reducing the laboriousness of gas turbine engines testing. Besides, the implementation of this system in the learning process allows the diversification of lab works and therefore improve the quality of training.