Papers by Keyword: Thermodynamics

Abstract: Based on the analysis of the defect formation in silicon carbide polytypes in different semiconductor manufacturing processing steps, device operation and environmental-device interaction it is concluded that external material and energy fluxes are generally able to destabilize the polytype structure. The governing reason is the formation of stacking faults and instabilities of the partial dislocation associated with them. A new ansatz is proposed to describe the structural instabilities using none-equilibrium thermodynamics and the entropy production. A criterial form for polyype transitions is proposed. The developed criterial form is applied to describe observed structural instabilities occur­ring under different external actions.

Abstract: In this paper, the temperature dependence of charge carrier lifetimes in n-type 4H-SiC epitaxial layers is studied in a temperature range of 300-500 K. It is assumed that shallow (B) and deep (D) boron-related defects are the dominating lifetime killers in as-grown epitaxial layers. The thermodynamic behavior of these two types of defects is obtained from DLTS measurements, and implemented in the Shockley-Read-Hall (SRH) model to calculate lifetimes, using Gibbs free energies to describe the accurate temperature dependence for capture and emission processes of the defects. Calculation results show that the lifetimes controlled by shallow boron defects increase with increasing temperature, while D-defects give the opposite temperature dependence. The theoretical results are also compared to measured data from 10 kV 4H-SiC PiN-structures, showing that the temperature dependence of the effective lifetime can be changed by proton implantations, which gives rise to additional Z_1/2 defects that have similar temperature effects on lifetimes as D-related defects.

Abstract: Refined Coconut oil (RCNO) is the most used feedstock for biodiesel production, which undergoes alkali-catalyzed transesterification to produce fatty acid alkyl esters due to its low free-fatty acids (FFA) content. This study utilized coconut oil fatty acid distillate (COFAD) as an alternative feedstock to RCNO. As it contains high amounts of FFA, it is pretreated through acid-catalyzed esterification to derive fatty acid methyl esters. The kinetics of the hydrochloric acid catalyzed esterification was investigated with the conditions of 10:1 methanol-to-COFAD molar ratio, 5wt% acid catalyst loading (0.4729N with respect to reaction mixture), reaction temperatures at 45°C, 55°C and 65°C, and 2 hours reaction time. It was found that temperature had a positive effect on the reaction. The highest FFA conversion was observed when the reaction temperature was set to 65°C, where it reached 87%, and the activation energy of the reaction was 29690.96 J^.mol^-1. The highest conversion predicted by the kinetic model is approximately equal to 89%. A good fit of the experimental and calculated data was observed with r² > 0.96. Moreover, the spontaneity of the reaction, as well as the effect of water on the reaction, were identified through the determination of thermodynamic parameters. The esterification reaction was found to be spontaneous only at high temperatures.

Abstract: In this study, we focus on studying the application of methyl blue pigment treatment by Fe/M-MOF (Ni, Co) metal ion modified materials. The factors affecting the adsorption process such as time, initial concentration, pH, and adsorbent content were evaluated. The results showed that the adsorption capacity was highest in the following conditions: pH6, initial concentration 50 ppm, adsorbent content 0.1 g/L and time was 60 minutes. The kinetic data are suitable for Langmuir and Pseudo-second-order models.

Abstract: Rutin flavonoid compounds have been isolated from cassava leaves and tested for their corrosion resistance against mild steel. Inhibition efficiency and adsorption properties were studied using the weight loss method at temperature variations of 303K, 313K, 323K and 333K and concentration variations of 0.1; 0.5; 1.0; 5.0; and 10 g/L. Potentiodynamic polarization was used to determine the inhibitor type of Cassava Leaf Routine (RCL). The results showed that RCL can reduce the corrosion rate and increase the corrosion inhibition efficiency of mild steel. The thermodynamic parameters have been calculated and the result is that the adsorption corrosion mechanism by physisorption takes place spontaneously with increasing temperature. Based on potentiodynamic polarization, the efficiency of corrosion inhibition by RCL with a concentration of 10 g//L on mild steel was 81.58%. RCL as a mixed corrosion inhibitor.

Abstract: The practice of benefication of copper-zinc ores has established that the production of high-quality zinc concentrates is impossible without the addition of sphalerite and pyrite modifiers to various flotation operations. This article present the result of study of the effect of copper (II), zinc and iron (II) sulfate on the froth flotation of sphalerite by sulfhdryl collectors. Typically, it is achieved through optimisation of flotation circuits, installation of modern equipment and changing the flotation reagents modes. Therefore, the floatability of sphalerite in an alkaline lime medium was studied with the addition of one of these metal sulphates to the mineral flotation operation. The effect of each of copper (II), zinc and iron (II) sulphates on the floatability of sphalerite was studied by flotation of the mineral and by potassium butyl xanthate and sodium dibutyl dithiophosphate at pH = 8, 10 and 12.

Abstract: Metallurgical processes in Me-O-C systems cannot be studied and controlled using conventional analytical and physicochemical techniques. This is due to the complex physical and chemical interactions occurring in high-temperature metallurgical systems with the formation of various compounds. To study such processes, mathematical (thermodynamic) simulation and other techniques are widely used, among which graphical diagrams illustrating the equilibrium between individual phases or their systems occupy a special place. Diagrams have been proposed that are more common, informative, and herewith universal to study pyrometallurgical processes. The main research objective was to determine the equilibrium composition of the Me-O-C system, i.e., the amount or ratio of its various compounds such as carbides, oxides, pure substances, and, possibly, ternary compounds. The equilibrium compositions of the system were obtained to plot diagrams from not only experimental studies but also the chemical equilibria mathematical simulation results using the Selector software package. The diagrams proposed herein allow establishing a quantitative relationship between the temperature, the ratio of independent components (metal, oxygen, and carbon), on the one hand, and the complete equilibrium composition of the system, which implies data on the amount and type of condensed and gas phases in the system and their ratios, on the other hand. This mechanism is a new tool to study chemical conversions in complex metallurgical processes, which will be very useful for metallurgists, chemists, and technologists.

Abstract: The innovative G-H graphical technique, a plot of Enthalpy vs Gibbs free energy was utilized to obtain a thermodynamically attainable region (AR) for the gasification of waste tyres. The AR is used to examine the interaction between the competing reactions in a gasifier and used to identify optimal targets for the conversion of waste tyres. The objective is to investigate the effect of temperature on the product selectivity. a temperature range of 25-1500°C at 1 bar was used for the analysis. The results show that at temperatures from 200°C to 600°C methane and carbon dioxide are dominant products at minimum Gibbs free energy. However, as the temperature increases, methane production decreases and hydrogen production become more favourable. Between 600°C and 700°C, carbon dioxide and hydrogen are dominant products. The AR results show that the products of gasification (CO and H₂) are preferred products at minimum Gibbs free energy only at temperatures from 800°C to 1500°C, when both water and oxygen are used as oxidants. Therefore, syngas production from tyres is only feasible at high temperatures. Temperatures above 1000°C are recommended to prevent the formation of intermediate radicals.

Abstract: Slag is widely used as mineral admixtures in cement-based materials by its potential hydration activity. It has the advantage of saving resources and energy, reducing carbon emission, improving the performance of concrete, and plays an increasingly important role in the building materials industry. But the early strength of slag is low, and the industrialization of useful hydration products also need to be activated, so the utilization rate of slag in high grade cement is restricted. The hydration activity of slag depends not only on the content of vitreous in slag, but also on the structure of vitreous slag. To explore slag glass micro composition and structure of its active role, The slag micro-structure was analyzed from the structure levels, and then the factors affecting the activity of slag was evaluated. The potential advantages and disadvantages of some different methods to active slag were discussed such as physical ways, chemical activation method and compound activation way. The existing problems and development direction of improving the activity of slag were summarized , which could provide a valuable reference for the efficient use of slag.

Abstract: This study is to explore the changes in the performance of sports equipment under the action of carbon fiber reinforced epoxy composites. This paper studies the effects of carbon fiber reinforced epoxy composites in pole vault, bicycle, and tennis. The research results show that the performance of sports equipment based on carbon fiber reinforced epoxy composite materials has been greatly improved, with outstanding effects in terms of thermal properties, interface properties, mechanical properties, and fatigue resistance. Carbon fiber reinforced epoxy composite material damage expansion is divided into five stages: matrix cracking, interfacial degumming, delamination, fiber fracture, fracture. Therefore, carbon fiber reinforced epoxy composite materials are comprehensive for the improvement of sports equipment, which has greatly promoted the further development of sports. Carbon fiber reinforced epoxy composite materials can be promoted in other fields, thereby obtaining greater progress with help of high technology. The study of carbon fiber reinforced epoxy composites in this paper has a positive effect on subsequent research.