Papers by Keyword: Gibbs Free Energy

Abstract: The utilization of the Miedema semi-empirical model has proven to be an effective approach for the estimation of Gibbs free energy in solid solutions within binary and ternary systems. Research findings indicate that in systems such as FeAl, FeMn, FeB, FeV, FeGa, AlMn, AlGa, and AlV, the Gibbs free energy exhibits highly negative values. Conversely, systems FeSn, AlB, and AlSn demonstrate positive Gibbs free energy values, with the most negative observing at a molar fraction of 50% for Fe. These results have been corroborated through studies involving the mechanosynthesis of binary and ternary FeAl based alloys. It is thus inferred that the Miedema model can be reliably employed for predictive purposes, facilitating the estimation of Gibbs free energy and the exploration of potential multicomponent system formations.

Abstract: This study investigates the thermodynamics of manganese ion adsorption on nanozeolite to assess the nanomaterial’s heavy metal removal efficiency from surface water, industrial water, and groundwater. Using Isothermal Titration Calorimetry (ITC), the thermodynamic profile of nanozeolite is obtained, demonstrating a low equilibrium binding affinity. The thermodynamic signature showed favorable binding mechanisms, primarily from the change of entropy, suggesting spontaneous reactions. Meanwhile, the enthalpy change of adsorption increases as temperature rises, while ∆G and T∆S decrease. Using proper thermodynamic conditions, nanozeolite may efficiently remove manganese from different water sources.

Abstract: The thermodynamic, structural, surface and transport properties of PbSn eutectic alloys at 1050 K have been analyzed employing self association model. The model parameters have been evaluated on utilizing the experimental data of free energy of mixing of PbSn liquid alloys at 1050 K. For the validation of the model parameters, the calculated values of the excess free energy of mixing and activity of the components of PbSn liquid alloys have been compared with the experimentally measured data. Further, the estimated model parameters have been used to determine the thermodynamic functions i.e. the free energy of mixing, thermodynamic activity, entropy of mixing and heat (or enthalpy) of mixing, and the structural properties such as the concentration fluctuations and shortrange order parameter. The theoretical and experimental values are compared. A good agreement is observed. Again, the surface properties of PbSn liquid alloys at 1050 K have been investigated using the Butler model in the framework of self association model. The calculated values of surface tension of PbSn liquid alloys at 1050 K are in reasonable agreement with the data available in the literature. The transport properties like the diffusivity and viscosity of PbSn liquid alloys at 1050 K have been theoretically analyzed. For the computation of viscosity, the simple formula developed by Moelwin- Hughes has been used in conjunction with self association model. The present study reveals that PbSn eutectic liquid alloys at 1050 K are segregating in nature. Further, the model parameters are found to depend on temperature.Keywords: Gibbsfree energy; concentration fluctuations; short-range order parameter; surface tension; diffusivity; viscosity

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: Thickness dependent structural phase transformation in thin polycrystalline metal films has been reviewed. Various effects of film thickness reduction on film microstructure have been identified. Film thickness dependent structural phase transformation has been treated thermodynamically taking polycrystalline titanium (Ti) thin film as model example.

Abstract: Dried pulp waste, a manufactured solid waste by product was used as a biosorbent for the removal zinc (II) from aqueous solution. A series of experiments were conducted in a batch system to evaluate the thermodynamic parameters of the pulp waste for zinc (II) removal at an initial pH value of 6.0, ZnCl₂ concentration of 50-200 ppm and temperature 30-50 °C. Thermodynamic parameters, such as Gibbs free energy change (ΔG°), enthalpy (ΔH°) and entropy (ΔS°), evaluation of zinc (II) adsorption on pulp waste showed that the adsorption process under the selected conditions was spontaneous and endothermic nature for all concentration and temperature studied. The activation energy of zinc (II) adsorption (E_a) was determined using modified Arrhenius equation as 1.89, 3.76, 4.73 and 6.46 kJ/mol at different concentration 50, 100, 150 and 200 ppm, respectively. The sticking probability (SP*) was also evaluated.

Abstract: Cement hydration products carbonation is not only blamed for the carbonation-induced hardened cement paste or concrete cracking, also attributed to the pore water PH-value decrease, which causes the reinforcement corrosion under the existence of water and oxygen due to removal of oxide film passivating rebar surface, in hardened cement paste and concrete. Based on chemical thermodynamics, this paper presents the susceptibility of different cement hydration products to carbonation through calculating their Standard Gibbs Free Energy respectively, Gibbs free energy under temperature variation and the minimum equilibrium pressure of carbon dioxide triggering the carbonation process. The calculated results show that, under standard state (25°C, 100kpa), the minimum equilibrium pressure of carbon dioxide triggering carbonation process is significantly variable for different types of cement hydration products. For example, mono-sulfate sulfoferrite hydrates (3CaOFe₂O₃CaSO₄12H₂O) is the most susceptible to carbonation, followed by mono-sulfate aluminate hydrates (3CaOAl₂O₃CaSO₄12H₂O), while multi-sulfate sulfoaluminate hydrates (3CaOAl₂O₃3CaSO₄32H₂O) is the least vulnerable to carbonation, followed by silicate hydrates (5CaO6SiO₂5.5H₂O). The findings in this paper are significant in understanding thermodynamic mechanism of cement hydrates carbonation and seeking the solution to prevent cement hydrates from carbonation-induced deterioration.

Abstract: As for the existing surface energy adhesion theories which are used to evaluate asphalt and stone's adhesive performance quantitatively, they are either dealing with the interface between solid asphalt and solid stone which can not adhere according to the formulas and definitions in process of adhesion or else roughly characterizing the solid asphalt and stone's adhesion properties with the adhesion index of heated asphalt and solid stone. So according to the forming process of asphalt mixture , this paper puts forward the method and principle to evaluate asphalt and stone's adhesion based on the surface energy theory. It evaluates the adhesion properties of asphalt and stone under hydrous and anhydrous conditions respectively. In the anhydrous condition, we choose contact angle and the Gibbs free energy of failure stage as the indexes of evaluating asphalt - stone interface's adhesion properties, while the materials under the hydrous condition, we select cohesional work, contact angle, Gibbs free energy as the indexes of evaluating asphalt-stone system's resistance of moisture.

Abstract: Pyrotechnic mixtures commonly present fast combustible and even detonable reaction. The process of the reaction produces huge heat and gases, featuring the origin of explosion. Therefore, in the practical situations, some catastrophic disasters usually occur in the storage houses and production factories related to those materials. For the safety consideration, the assessment on the explosive performance of pyrotechnic mixtures becomes necessary. In the paper, the pressure, temperature, and amount of gases from reaction of pyrotechnic compositions are obtained by establishing an analytic procedure based on the minimum Gibbs free energy principle. The results provide an initial condition for the hydrodynamic computation on the blast effects coming from explosion of some specific accidents.

Abstract: This paper focuses on the zeolite-granule-adsorbent(ZGA)’s efficiency of removing ammonium ion. The ZGA shows good performance with up to 73.41% for ammonium removal on the condition of ZGA loading 6g, contact time 6h, initial ammonium concentration 50 mg/L and pH=6. The adsorption kinetics is best approximated by the pseudo-second-order model, whereas the adsorption isotherm results indicated that Langmuir model provides the best fit for the equilibrium data. Furthermore, with regard to thermodynamic parameters, it was found that Gibbs free energy change (ΔG°) −19.31kJ/mol at T=298K, The negative data indicates the spontaneous nature of the adsorption process.