Papers by Keyword: Thermodynamic

Abstract: Thermoplastic polymer matrix composites with continuous carbon fibre reinforcements are of crucial relevance in automotive industry. The mix of high performance and cost effective manufacturing makes them attractive for high volume production. However, it could be shown that production integrated end of line quality control is of strong importance to ensure continuous and traceable part quality. Besides, typical non destructive testing method specifications, higher production volumes additionally require short testing times. Herein, the application of active thermography as end of line quality control in composite production is evaluated and compared with results obtained by X-ray radiometry. It could be revealed that transient pulse phase thermography is a powerful tool to analyse part quality of continuous thermoplastic polymer matrix composites in short testing times.

Abstract: The paper presents the results of both ab initio and thermodynamic analysis of vacancy and divacancy formation and hydrogen interaction with them in alpha (bcc) iron. Ab initio calculations were performed by DFT method using LAPW in WIEN2k package. Monovacancy formation energy was found to be 2.15 eV and divacancy binding energy 0.22 ± 0.01 eV. Equlibrium fraction of vacancies bound into divacancies is of the order of 10^–5 even at the highest temperatures close to bcc → fcc transformation point. Hydrogen has a strong interaction with monovacancies (vacancy-hydrogen binding energy decreasing from 0.60 to 0.31 eV for the first–fifth H atom inside a single vacancy) but has only a small effect on divacancy formation energy that is equal to 0.28, 0.19 and 0.17 for the case of joining of VH + V, VH + VH and VH₂ + VH₂, respectively. This means that the presence of hydrogen cannot significantly increase the equilibrium concentration of divacancies.

Abstract: The specific features of atmospheric nitrogen surface nitriding of cold-rolled foils (the value of the coherent-scattering region is 10 nm) from stainless maraging steels after hardening in a confined space containing air are considered. Thermodynamic evaluation of the probability of influence caused by the confined space air on the phase transformations and solubility of the atmospheric nitrogen shows that the surface modification takes place in two stages: at the first stage, oxidation dominates; and at the second stage, predominantly the nitrogen absorption by the surface takes place. While changing, the nitrogen solubility reaches the maximum in the range of 10 – 22 % of Cr and has the largest values at the air pressure in the range of 0.001 – 0.04 MPa. Based on the nitrogen solubility diagrams, optimal conditions for the nitrogen austenite formation without the formation of nitrides are established. The developed method for nitriding allows the formation of nitrogen austenite layer of about 20 μm in thickness in the surface of nanostructured maraging steels without deteriorating the surface electrochemical properties.

Abstract: Due to their high melting temperatures, low densities and excellent high-temperature strengths, Nb-Si-Ti-based ultra high temperature alloys shows great potential for vane materials on the next generation of high thrust-weight ratio aero-engines. In the present paper, the Nb-Si-Ti ternary system was studied, the phase diagram of Nb-Si-Ti and the phase fraction calculated, and the curve of solidification process established. The calculated results provide primary guidance for developing Nb-Si-Ti-X ultrahigh temperature alloys. Moreover, it is very useful as a guide for alloy design and processing development.

Abstract: Thermodynamic analysis of the phase equilibria in the Fe–Mn–Cr–Si–Al–Ti– Ni–V–Mo–B–S–P–C–N–O system at fixed concentrations of boron, manganese, chromium, silicon, aluminum, titanium, nickel, vanadium, molybdenum, sulfur, phosphorus, carbon and nitrogen was performed. Formation of nonmetallic phases upon cooling and crystallization of liquid metal solutions of various compositions was studied. It was established how aluminum and nitrogen content in the liquid metal solution affects the composition and amount of separated excess phases. Calculations demonstrated that boron nitride was not formed in the liquid metal and during crystallization.

Abstract: The thermodynamically possible reactions in MnTe-H₂O system at room temperature have been studied. The potential–pH diagram has been plotted assuming quasi-equilibrium on interfacial boundary. The possible mechanism of formation and the composition of a surface in dependence on electrode potential and pH have been discussed and the stable conditions for manganese telluride, i.e. the specific area in the diagram (pH from −2 to 14 and potential from −1.5…− 1.1 to −0.9…−0.6 V) have been found. The obtained results may help optimize the conditions for electodeposition of manganese telluride thin films and for liquid chemical etching for the formation of interfacial boundaries.

Abstract: The study is concentrated on thermodynamic analyses of gas desulfurization process (deep removal of H₂S, COS, thiophene) by selected solid sorbents (ZnO, MnO, Ce_xO_y and La₂O₃) and on interferences caused by presence of hydrogen halides in a temperature range 500-1100 K. The results show that theoretically Ce₂O₃ and La₂O₃ are the best sorbents for sulfur compounds at temperatures over approx. 700 K. The Ce_xO_y, La₂O₃ and MnO based sorbents can suffer from significant interferences caused by higher concentrations of HCl and HF in gas phase. The thermodynamic equilibria suggest that removal of HCl (HF) by soda based sorbents at temperatures 650 – 850 K is practically without interferences from sulfur compounds. The common alkali carbonates are less suitable than the calcium based (Ca (OH)₂, CaCO₃) sorbents for deep removal of HF.

Abstract: Besides other possible applications, the thermitic compositions based on iron oxides are meant to the achieving of the permanent joints of the railroad tracks. In addition to the iron oxides, the thermitic kit include also the reducing agent – aluminum powder, a carbon source to adjust the percent of this element in the obtained steel and a flux with a view to allow the steel composition and temperature control. The metallothermic process efficiency is given by strictness in the selection of ratio of the thermitic components and mainly in that of the iron oxides types. Their correct dosage makes possible the estimation and rigorous control of the thermal effect of reactions. In this work, using thermodynamic calculations, is analyzed and quantified the development of the thermal effect of the metallothermic reduction reactions of iron oxides depending on the iron oxides proportions in the thermitic composition.

Abstract: Numerical simulation appeared till now as the only tool able to describe the SiC growth by PVT process, while the chemistry of the Si-C system and its coupling to mass transfer were not considered in a satisfactory way. To assess the chemistry of SiC crystal, the coupling of numerical and thermodynamic calculations computed by FEM, and by treating SiC as a solid solution, respectively, is presented. This enables the possibilities to control the activity of each component in SiC crystal during the growth. The link between growth conditions and SiC crystal chemistry could be one of the key issues to link the growth and the occurrence of cubic or hexagonal polytypes.

Abstract: In this paper, the calculation software HSC indium mine under vacuum carbothermal reduction reaction during the Gibbs free energy. The result show that when the pressure of 10-100Pa and temperature is 380-449K, In₂O₃ and C reaction to reaction thermodynamic conditions under pressure from the same system, material In₂O₃: C mole ratio is 1:3, needed to generate elemental In reaction temperature is the lowest. In₂O₃ generated In₂O thermal decomposition, with the loss of the system pressure, the initial reaction temperature from 1247K to 10Pa for 423K; Intermediate In2O pyrolysis generating elemental In, when the system pressure drop to 10 Pa, starting temperature dropped to 781K; InO reaction with products CO, as the system pressure is reduced, the gibbs free energy increase, therefore, step-down to InO reaction with CO. This study to provide experimental evidence for preparation of indium by carbothermic reaction of indium ore in vacuum. Keywords: Indium ore;Carbon thermal reduction;Vacuum; Thermodynamics;Introduction