Papers by Keyword: Thermodynamic Calculations

Abstract: The aim of the article is to determine the dependencies of the combustion product temperatures of four-component mixtures, the content of high-temperature condensate, and unoxidized metal on the excess oxidizer coefficient, the number of additives, and external pressure using thermodynamic calculations. Modern methods of physicochemical analysis (such as cinephotography and microcinephotography methods, X-ray analysis methods, non-contact and contact temperature measurement methods), nonlinear thermal conductivity and thermal stability methods, as well as mathematical and experimental-statistical modeling, were employed to investigate the influence of elevated heating temperatures (up to 800 K) and external pressures (up to 10⁷ Pa) on the ignition and combustion processes of pyrotechnic products. Standard pyrotechnic equipment was used to test pyrotechnic product samples under specified conditions. Calculations based on models were conducted in real-time and dialog mode on computer devices that meet modern requirements for the use of specialized software. The results of thermodynamic calculations are presented for the dependencies of combustion product temperatures of multicomponent pyrotechnic mixtures based on powders of metal fuels (magnesium, aluminium), nitrate oxidizer (sodium nitrate), additives of organic and inorganic substances (paraffin, sodium fluoride), and the content of high-temperature condensate and unoxidized metal depending on the excess oxidizer coefficient α = 0.1…4.0, the amount of paraffin additive ε_p = 0…0.2, sodium fluoride additive ε_f = 0…0.06, and external pressure P = 10⁵…10⁷ Pa. Based on the obtained results of thermodynamic calculations, statistical models in the form of regression dependencies of the specified combustion characteristics on their technological parameters and external conditions have been developed. These models enable the determination of fire hazardous properties of mixtures in real-time dialog and PC-based scenarios, considering premature initiation of products based on them under external thermal actions.

Abstract: The results of thermodynamic calculations of temperature dependences of combustion products of pyrotechnic mixtures based on magnesium, aluminum and metal oxides and their content of high-temperature condensate on the relevant technological parameters and relevant external conditions are presented. The ratio of the components of the mixture, the type of metal fuel, the type of oxidant are considered as technological parameters of pyrotechnic mixtures. The influence of temperature and external pressure is determined as external conditions. It is determined that high values of combustion products and high content of condensed combustion products of pyrotechnic oxide-containing mixtures pose a fire hazard to the surrounding objects when the products are forced to operate under external thermal conditions. As a result of the calculations, it was found that the value of the combustion temperature of oxide-containing mixtures has a maximum value of 3870 K at a maximum value of the relative fuel content of 0.35 and the corresponding external pressures of 10⁵...310⁷ Pa. It is determined that with increasing external pressure in the ranges from 10⁵ tо 310⁷ Pa there is a significant increase in the temperature of combustion products: for oxide-containing mixtures based on metallic fuel magnesium - up to 3650 K; for oxide-containing mixtures based on metallic aluminum fuel - up to 3870 K. It is determined that in oxide-containing mixtures with metallic fuel content from 0.06 to 0.49, regardless of the type of metallic fuel and oxidant with increasing external pressure increases the temperature to 1.8 times.

Abstract: The authors studied the possibility of modifying aluminum-silicon alloys using titanium dioxide at standard melting temperatures up to 800 °C. The result is achieved due to the combined use of titanium dioxide and alkali and alkaline-earth metal fluorides. Calculations of the change in the Gibbs energy of chemical reactions of interaction of titanium dioxide with aluminum, cryolite, barium fluoride were carried out. The thermodynamic possibility of modifying silumin by the reduction of titanium from dioxide in the presence of additives selected was shown. Experimental melting was carried out and the results of mechanical tests of experimental alloys depending on the additives used were obtained. After melt treatment using the study combinations, the alloy structure becomes partially modified, which increases the mechanical properties of silumin.

Abstract: This paper presents a methodology in order to predict A1, solidus and liquidus temperatures using a relatively simple approach. The proposed approach is based on the combined use of the thermodynamic software Thermo-Calc and the composite centered design of experiments (DOE) method. Four important alloying elements (C, Ni, Mn and Cr) were considered in the DOE. The impact of each alloying element on the transformation temperatures was determined and discussed. It was found that carbon has the most important impact on solidus and liquidus whereas Ni, Mn, and Cr have a significant impact on A1. The proposed models were generated using Analysis of Variance (ANOVA) method. A good agreement between experimental and predicted results was found with a maximum error of 1.1 % for transformation temperatures. Furthermore, the proposed models were validated using a large amount of experimental data published in the literature with a maximum error equal to 7.8 %.

Abstract: Steelmaking is accompanied with releasing a large quantity of solid particle in the form of dust. Electric arc furnace dust (EAFD) is known to have high pH number and traces of heavy metals. The objective of this work was to find a suitable procedure for converting the dust waste into inert and useful byproducts using thermodynamic calculations and experimental investigation. The physical, chemical and mineralogical characteristics of initial EAFD were analyzed using different techniques, such as: X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), grain size analysis and metallography. The pH measurement procedure was carried out in accordance with the standard test method for pH of soils “ASTM 4972-95a”. The results of XRD, SEM and EDS analysis were consistent and showed that Fe₂O₃, CaO, Al₂O₃, SiO₂, MgO, ZnO and traces of other oxides are in the main composition of the EAFD batches with different relative amounts. Furthermore, the particle size measurements revealed that the EAFD particles are in the 0.1 to 394 μm size range. The pH number was ranging between 11.15 and 12.21 for all measurements. The experimental results were used as input data for thermodynamic calculations and accordingly SiO₂ and Al₂O₃ were among the candidates for making ceramic materials through forming glass regions that surround and encapsulate the iron oxide particles. SiO₂ modified samples exhibited better apparent structural properties than other compositions. Whereas Al₂O₃-modified samples showed variation in the product color. Thus, it is concluded from this work that a mixture of EAFD can be modified by 5-20 wt.% of SiO₂ and then fired at 1100°C to make inert ceramic materials with reasonable mechanical properties.

Abstract: In this paper the method of experimental estimation of the temperature in a penetration channel in laser welding is described on the basis of chemical elements concentration in the vapors above welding zone. The temperature of a vapor-gas phase in the penetration channel is determined when equating calculated and experimental concentrations of the elements.

Abstract: The investigated Mongolian lakes are marked by a large range of trace element concentrations even in very small geographical areas. This work includes the data on major and trace element concentrations along of a series of samples collected in 2009 and 2012. Three geochemical types of lakes have been distinguished within the study area: (1) alkaline soda lakes, (2) chloride lakes with pH < 9.0 and Na-Cl-dominated composition, and (3) sulfate ones with pH < 8. The soda lakes show high concentrations of As, U, F and relatively low salinity. The chloride lakes have higher salinities and one of them was the most saline of all the lakes (Davsan Nuur). These lakes have higher concentrations of Li (up to 82.1 mg/L), Rb (up to 1350 mg/L), Br and Sr. Sulfate rich lakes are far less common in the area. Characteristic trace elements are Mo, Al and Sr. Thermodynamic modeling at 25°C and 1 bar total pressure was performed with the “HCh” code. We considered mineral and solution equilibria in soda lake waters and calculated the main uranium and arsenic species in solutions and bottom sediments of Shaazgay-Nuur lake to offer a possible way of As removal as an undesirable impurity in commercial products.

Abstract: In this paper, thermodynamic calculations and reaction process for the production of metal Sm by metal thermal reduction method were analyzed. Two main factors effecting reducing yield were determined, namely: heating system and briquetting. By changing the conditions of heating system and briquetting, the direct yield of metal Sm increased to over 95%.

Abstract: In the present paper, the influences of rolling temperatures on microstructure and precipitate in high purified Fe- 17 wt% Cr alloy steels were investigated by conventional process and low temperature rolling process. The hot rolled bands were annealed, cold rolled and annealed in the same processes. By means of optical microscopy observations, transmission electron microscopy analyses and thermodynamic calculations, the microstructural evolutions were studied and compared. It was shown that low temperature rolling process resulted in the refined rolling and annealing microstructure; Low temperature rolling process could form more fine TiC precipitates than in the conventional process due to the occurrence of strain-induced precipitation. These results have been confirmed by the thermodynamic calculations.

Abstract: The achievement of lighter automotive components is an important driving force in the development and optimization of casting techniques. In this sense, semisolid forming is an emerging technology that has allowed the production of security components using aluminum alloys. The foundry alloys A356 and A357 remain, up to the present, the most used alloys for the semisolid processing of components. Nevertheless, several authors have pointed out the gain in properties that other alloy families could provide. In the present work, thixoformability of 7000 series aluminum alloys is studied. Thermodynamic calculations (CALPHAD method) and calorimetric experiments have been performed to determine the composition of alloys with an optimum process window. A modification of the 7075 alloy is proposed in order to improve its thixoformability parameters and optimize the process control. A simple component has been produced by semisolid forging and mechanical properties have been measured from tensile samples.