Thermodynamic database for multicomponent oxide systems

Received: 21.02.2018. Accepted: 22.03.2018. Published: 10.05.2018.A state-of-the-art thermodynamic database has been developed for multicomponent oxide systems. It can be used in combination with FactSage software to calculate the properties of metallurgical slags, glasses, ceramics, refractories, minerals, cements, etc. The database has been developed by collecting all available structural, thermodynamic, and phase equilibria data for a particular chemical system, critical evaluation of this information, developing a thermodynamic model for each solution phase and optimization of model parameters to reproduce the experimental data. Then the models are used to estimate the thermodynamic properties of multicomponent solutions from the properties of lower-order subsystems. Oxide phases often exhibit complex structures and strong interactions between components, which require more sophisticated models than are normally used, for example, for metal alloys. Short-range ordering is rather common and random mixing is often not a good approximation. The models for multicomponent liquid and solid solutions have been developed within the Modified Quasichemical Formalism and Compound Energy Formalism. Optimized model equations are consistent with thermodynamic principles and fully characterize a chemical system, requiring much less experimental work to achieve this goal since only a few measurements are needed in higher-order systems to validate the model estimates. The database can be readily used in conjunction with the FactSage Gibbs energy minimization software to calculate any stable or metastable phase equilibria and phase diagrams. The present article outlines the major components and phases that are currently available in the oxide database, as well as the most important features of the models that have been developed. The model and database have also been developed for the viscosity of oxide melts and glasses. The model links the viscosity to the structure of the liquid phase, which is estimated using the thermodynamic database

Morphology and Orientation Selection of Non-Metallic Inclusions in Electrified Molten Metal

The effect of electric current on morphology and orientation selection of non-metallic inclusions in molten metal has been investigated using theoretical modelling and numerical calculation. Two geometric factors, namely the circularity (fc) and alignment ratio (fe) were introduced to describe the inclusions shape and configuration. Electric current free energy was calculated and the values were used to determine the thermodynamic preference between different microstructures. Electric current promotes the development of inclusion along the current direction by either expatiating directional growth or enhancing directional agglomeration. Reconfiguration of the inclusions to reduce the system electric resistance drives the phenomena. The morphology and orientation selection follows the routine to reduce electric free energy. The numerical results are in agreement with our experimental observations

Thermodynamic assessment of the Ge-Si-O-Cl-H system

An assessed thermodynamic dataset for the Ge-Si-O-Cl- H system useful for application in the glass fiber industry is presented. The focus of the work is on the germanium-bearing species. Taking into account the available vapor pressure measurements on the Ge-O , Ge-Cl, Ge-Cl-H , and Ge-O-Cl Systems, modifications have been made to the recommended data for the important oxide and halide species. The GeO2-SiO2 and GeCl4-SiCl4 binary systems have been thermodynamically optimized using simple models. The current dataset, when combined with the data from the FactSage™ database for the other required species/phases, can be used to make useful calculations of glass vapor equilibria pertinent to the manufacture of germanium-doped silica glass fibers using vapor deposition methods

Zirconia Transport by Liquid Convection during Oxidation of Zirconium Diboride–Silicon Carbide

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/65610/1/j.1551-2916.2007.02142.x.pd

High-temperature experimental and thermodynamic modelling research on the pyrometallurgical processing of copper

Uncertainty in the metal price and competition between producers mean that the daily operation of a smelter needs to target high recovery of valuable elements at low operating cost. Options for the improvement of the plant operation can be examined and decision making can be informed based on accurate information from laboratory experimentation coupled with predictions using advanced thermodynamic models. Integrated high-temperature experimental and thermodynamic modelling research on phase equilibria and thermodynamics of copper-containing systems have been undertaken at the Pyrometallurgy Innovation Centre (PYROSEARCH). The experimental phase equilibria studies involve high-temperature equilibration, rapid quenching and direct measurement of phase compositions using electron probe X-ray microanalysis (EPMA). The thermodynamic modelling deals with the development of accurate thermodynamic database built through critical evaluation of experimental data, selection of solution models, and optimization of models parameters. The database covers the Al-Ca-Cu-Fe-Mg-O-S-Si chemical system. The gas, slag, matte, liquid and solid metal phases, spinel solid solution as well as numerous solid oxide and sulphide phases are included. The database works within the FactSage software environment. Examples of phase equilibria data and thermodynamic models of selected systems, as well as possible implementation of the research outcomes to selected copper making processes are presented

Modeling the viscosity of silicate melts containing manganese oxide

Our recently developed model for the viscosity of silicate melts is applied to describe and predict the viscosities of oxide melts containing manganese oxide. The model requires three pairs of adjustable parameters that describe the viscosities in three systems: pure MnO, MnO–SiO2 and MnO–Al2O3–iO2. The viscosity of other ternary and multicomponent silicate melts containing MnO is then predicted by the model without any additional adjustable model parameters. Experimental viscosity data are reviewed for melts formed by MnO with SiO2, Al2O3, CaO, MgO, PbO, Na2O and K2O. The deviation of the available experimental data from the viscosities predicted by the model is shown to be within experimental error limit

The impact of aluminosilicate-based additives upon the sintering and melting behaviour of biomass ash

The composition of ash arising from biomass combustion can cause significant slagging and fouling issues in pulverised-fuel boilers, particularly if high concentrations of alkalis are present. Al–Si additives have shown promise in improving the ash deposition characteristics of troublesome biomass, converting volatile potassium to potassium aluminosilicates. This article presents results of lab-scale testing for two high-potassium biomass ashes, olive-cake (OCA) and white-wood (WWA), combined with two promising additives, coal pulverised fuel ash (PFA) and kaolin powder, at 5% mass fraction. Ash fusion testing results show that the use of these additives consistently increases flow temperatures. For WWA, kaolin was observed to reduce deformation temperatures and increase flow temperatures to far above combustion temperatures. Sinter strength testing showed that additive use significantly improves the deposition properties of OCA, preventing the precipitation of KCl and formation of deposits that are highly undesirable for removal via sootblower. Sintering was eliminated at all temperatures measured with the use of kaolin. Both additives had negative effects upon the sintering of WWA, indicating that Al–Si additive use should be restricted to high K, high Cl biomass. High temperature viscometry of OCA, combined with thermodynamic modelling, showed that viscosities at combustion temperatures were far below ideal values due high Mg concentration and silicate formation. Kaolin at 5% mass fraction was predicted to significantly improve this behaviour, with aluminosilicate formation producing favourable viscosities. Results indicate that kaolin addition to high K, high Cl biomass such as OCA shows promise in making the ash compositions viable for pulverised-fuel combustion

Molecular Analyses of the Mouse Anorexia Mutation

The mouse anorexia (anx) mutant displays food restriction leading to emaciation and may represent an animal model of anorexia nervosa. To date, the causative anorexia gene(s) remain to be identified. Our lab’s previous analyses found early deficits in glutamatergic and GABAergic synapses in the cerebella of anx/anx mice at postnatal day 10 (P10). Gene expression analyses of P10 anx/anx cerebella identified two genes within the anx critical interval with notable expression differences: Pla2g4d was ~7-fold downregulated, while Pla2g4e was ~10-fold upregulated. These phospholipases are involved in the synthesis of arachidonic acid, a key endocannabinoid precursor. Endocannabinoids have widespread roles in synaptic plasticity and in the reward mechanisms of feeding and activity and may influence risk of developing Anorexia Nervosa. We anticipate that further research into the roles of these phospholipases will contribute to better understanding of the endocannabinoid system and its roles in anorexia nervosa.M.Sc.2021-11-19 00:00:0