Papers by Keyword: Gibbs Free Energy

Paper TitlePage

Authors: Dong Lei, Ge Li, Bin Kai Shi, Jian Hua Zhao
Abstract: An improved model has been developed to predict fatigue crack initiation life using the criterion of minimizing the Gibbs free energy change considering plastic energy. The prediction process was described in this paper and used to predict the fatigue crack initiation life of notched GH4169 superalloy rolled bar at room temperature and 450°C. The results are acceptable for fatigue crack initiation life prediction in engineering experience and show that the improved model for predicting fatigue crack initiation life as an extension of the concept of minimizing the Gibbs free energy change considering plastic energy is adoptable to some superplastic materials such as GH4169.
Authors: Ovidiu Dumitrescu, Dorel Radu
Abstract: In present paper there are presented such correlations for the silica-alkali systems (M2O – SiO2) where reliable thermodynamic data exists from the thermal equilibrium diagrams. It was observed that with the saturation of SiO2 tetrahedron with metal ions, the difference in basicity between the reactants is diminished, in the order SiO2 → disilicate → metasilicate → orthosilicate, and that confirms the role of driving force for these reactions of the acid-base interaction between oxides and the intermediate silicates formed. Also, there were proposed some correlations between the standard formation Gibbs free energy, (Gº298), and basicity percentage, pB, for the binary compounds from the same oxide systems. Considering the fact that for a system at equilibrium, reaction constant Kp depends on the reaction free Gibbs energy (rG0 298) and temperature, a correlation between basicity difference through basicity percentage, pB, and rG0 298 is proposed.
Authors: Zhi Yue Liu, Ru Yan Xu, Li Qiong Wang
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.
Authors: A.K. Gupta, P.H. Marois, David J. Lloyd
Abstract: AA6111 sheet alloy has been used in automotive panel applications in North America and Europe for several years. This alloy exhibits an excellent combination of strength, formability, ageing response and surface appearance following forming and painting operations. Such a combination of properties is obtained by carefully tailoring the processing route to obtain the desired microstructure of the alloy. In recent years, the ability to predict the phase stability in different alloys has improved significantly, and it is now relatively easy to predict the particles that could form in complex multi component alloys during different processing steps. The accuracy of the predictions is dependent on whether or not the free energy expressions used in the calculations are correct. In this study, the AA6111 alloy was subjected to various annealing treatments that are reflective of different phase fields computed by the Thermo-Calc software. The particles were extracted using the phenol extraction technique and were identified using energy dispersive analysis. The interrelation of the particle analyses with the computed phase stability in AA6111 is presented.
Authors: Panida Sampranpiboon, Pisit Charnkeitkong, Xian She Feng
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 (Ea) 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.
Authors: Yuan Ming Huang, Qing Lan Ma, Bao Gai Zhai
Abstract: The effects of cyclic heating and cooling on the banana-phase growth behaviors of the prototype banana-shaped liquid crystal 1,3-phenylene-bis[4-(4-octylphenylimino)methyl]benzoate were investigated with differential scanning calorimetry and polarized optical microscopy, respectively. Cyclic heating and cooling can reduce the phase transition temperatures and increase the domain sizes of the banana phases of the banana-shaped liquid crystal. These results can be interpreted in terms of the nucleation and growth of the banana phases out of its isotropic phase of the banana-shaped liquid crystal.
Authors: Bao Gai Zhai, Qing Lan Ma, Ming Meng, Yuan Ming Huang
Abstract: In this article, we report on the observations that in the aqueous electrolyte of aluminum nitrate, the thin metallic conducting films on both internal and external surface of porous silicon (PS) thin films that emit visible photoluminescence at room temperature prior to electrochemical deposition have been obtained under electrochemical deposition condition. Add to this high surface-to-volume ratio and these make it a good candidate for the catalyst supporter. We have investigated the surface morphology of PS after the interval of about 30 hours of electrochemically deposited aluminum by means of scanning electron microscopy (SEM). It has been shown from SEM images that not only micrometer-sized pores are smoothed by deposition of aluminum microcrystal, but also the presences of semi-sphere aluminum microcrystal which rooted in the tip of micrometer-sized pores are observed. On the one hand, this extremely interesting phenomenon which the micrometer-sized pores are smoothed may be explained in terms of principle of electrochemical deposition; on the other hand, we have laid the formation mechanism of semi-spherical aluminum microcrystal at the door of Gibbs free energy.
Authors: Heena Dhurandhar, Kirit N. Lad, Arun Pratap, G.K. Dey
Abstract: The Gibbs Free Energy Difference between the solid and liquid phases (DG) is related to nucleation frequency and has played an important role in predicting the glass forming ability (GFA) of multicomponent metallic alloys. This is due to the fact that the maximum energy for nucleus formation i.e. the activation barrier for nucleation has an inverse square relation with DG. The Gibbs Free Energy Difference of three multi-component bulk metallic glasses namely Mg65Cu25Y10, Zr57Cu15.4Ni12.6Al10Nb5 and Zr52.5Cu17.9Ni14.6Al10Ti5 have been evaluated using two new expressions. The results show that the DG values calculated assuming DCp to be constant lie closer to the experimental values for the Mg based system while in the case of two Zr based systems, DG computed using the hyperbolic variation of DCp show improved agreement with the experimental data.
Authors: Ashmi T. Patel, Kirit N. Lad, Arun Pratap
Abstract: Knowledge of glass forming ability (GFA) of amorphous metallic alloys is very important from both theoretical and practical point of view. Thermodynamically, the Gibbs free energy difference, ΔG between the undercooled liquid and the corresponding crystalline state is driving force for crystallization. As a consequence, it is a good indicator for glass forming ability of metallic glasses. A novel expression for ΔG has been used to estimate the GFA of recently developed Ca-based bulk metallic glasses viz. Ca53Mg23Cu24,Ca65Mg15Cu20,Ca40Mg25Cu35, Ca50Mg22.5Cu27.5 and Ca55Mg15Cu30. Different GFA criteria are also evaluated for systems taken up in the study and effect of addition of variation in composition of Ca-Mg-Cu system is also investigated. Present work suggests that among different GFA criteria, ΔG is the best criterion for the prediction of GFA for Ca-based bulk metallic glasses.
Authors: R.A. Andrievski, R.A. Lutikov, Ju.F. Khromov
Showing 1 to 10 of 21 Paper Titles