Be Thou Exalted, Volume 3: O Lord, By Thee Delivered: Vocal

Pages 1-4 in Be Thou Exalted, Volume 3: Vocal

Isothermal Hydrogen Reduction of a Lime-Added Bauxite Residue Agglomerate at Elevated Temperatures for Iron and Alumina Recovery

The hydrogen reduction of bauxite residue lime pellets at elevated temperatures was carried out to recover iron and alumina from the bauxite residue in a new process route. Prior to the H2 reduction, oxide pellets were initially prepared via the mixing of an industrial bauxite residue with fine calcite powder followed by calcination and high-temperature sintering. The chemical, compositional, and microstructural properties of both oxide and reduced pellets were studied by advanced characterization techniques. It was found that iron in the oxide pellets is mainly in the form of brownmillerite, and calcium–iron–titanate phases, while upon reduction they are converted to wüstite and shulamitite intermediate phases and further to metallic iron. Moreover, it was found that the reduction at lower temperature of 1000 °C is faster than that at higher temperatures of 1100 °C and 1200 °C. The slower rate and extent of reduction at the higher temperatures is attributed to the porosity loss and reduction mechanism change to a diffusion-controlled process step. In addition, it was found that Al-containing phases in the raw materials are converted mainly to gehlenite in sintered pellets and further to the leachable mayenite phase. The alkaline leaching of selected reduced pellets by a sodium carbonate solution yielded up to 87% Al recovery into the solution, while the metallic iron was not affected.publishedVersio

Vacuum refining of silicon at ultra-high temperatures

In the production of solar grade silicon (SoG-Si), Phosphorus (P) removal from Si is a challenge as it cannot be eliminated effectively by the final key directional solidification step in the value chain of the silicon solar cell technologies. The present research investigates the application of ultra-high temperatures (UHTs) up to 1900 °C for the P removal from Si in the vacuum-induction refining (VIR) process. Kinetic parameters such as mass transfer coefficient and activation energy for P removal from Si melt by vacuum evaporation are determined. It is shown that the P removal kinetics is significantly accelerated with increasing temperature, and about 1800 °C is a critical temperature in which the process rate is doubled. The silicon loss of the process to reach SoG-Si quality is formulated, and it is shown that it is lower at ultra-high temperatures, while it is insignificantly increased with the temperature rise in each temperature regime, and is independent of the melt geometry. The results from UHTs experiments showed complete phosphorus removal from silicon melts with even as high as P concentrations as 92.71 ppmw in short durations. It is shown that the application of UHTs in VIR process reduces the power consumption to reach SoG-Si

Mechanisms of graphite crucible degradation in contact with Si–Al melts at high temperatures and vacuum conditions

Graphite is a common refractory material for processing high purity silicon; however, it cannot be applied for holding Si–Al melts at high temperatures due to significant melt infiltration into the crucible. This research investigates the interaction mechanisms of graphite with Si at 1500 and 1800 °C and graphite with Si-20 wt%Al melt at 1500 °C and vacuum conditions. Scanning Electron Microscopy (SEM) and X-Ray powder Diffraction (XRD) methods are applied to investigate the morphology and chemistry of the phases formed at the interface of graphite with Si and graphite with Si–Al melts. Results showed that Al in Si–Al melt infiltrates into graphite leading to the formation of aluminum carbides, which accompanies with volume expansion and therefore the crucible destruction. The formation mechanisms of silicon carbide (SiC) from Si melt, and aluminum carbide from a Si-20 wt%Al melt in graphite crucibles are compared. It is shown that graphite crucible can be passivated by controlled formation of a dense SiC layer on the surface, and further can be used for different melts treatments with no melt infiltration and crucible destruction. The effect of temperature on the growth of the passive SiC layer was also investigated

Selective Vacuum Evaporation by the Control of the Chemistry of Gas Phase in Vacuum Refining of Si

( Engelsk ) The evaporation of P from liquid Si under vacuum and reduced pressures of H2, He, and Ar was studied to evaluate the feasibility of effective P removal with insignificant Si loss. It was found that the introduction of Ar and He inert gases at low pressures reduces the rate of P removal, and their pressure decrease will increase the process rate. Moreover, the kinetics of P removal was higher in He than in Ar, with simultaneous lower Si loss. Under reduced pressures of H2 gas, however, the P removal rate was higher than that under vacuum conditions with the lowest Si loss. Quantum chemistry and dynamics simulations were applied, and the results indicated that P can maintain its momentum for longer distances in H2 once it is evaporated from the melt surface and then can travel far away from the surface, while Si atoms lose their momentum in closer distances, yielding less net Si flux to the gas phase. Moreover, this distance is significantly increased with decreasing pressure for H2, He, and Ar gases; however, it is the largest for H2 and the lowest for Ar for a given pressure, while the temperature effect is insignificant. The rate of P evaporation was accelerated by applying an additional vacuum tube close to the melt surface for taking out the hot gas particles before they lose their temperature and velocity. It was shown that this technique contributes to the rate of process by preventing condensing gas stream back to the melt surface.publishedVersio

Kinetic study of vacuum evaporation of elements from ternary melts; case of dilute solution of P in Si-Al melts

This research is devoted to study phosphorus removal from Si-Al alloys by vacuum refining of the ternary system of dilute solutions of P in Si-20 wt%Al. The experiments were carried out in an induction furnace and after the refining process, the melt was characterized by ICP-MS technique to trace the concentration change of the volatile elements. The experimental results show that P removal from Si-Al-P melts takes place faster compared to Si-P melts and Al evaporates during the vacuum refining as well. The empirical kinetics of P and Al evaporation is discussed and the apparent activation energy for P and Al evaporation from Si-Al melts is obtained as and respectively. Results show that the composition of the melt changes continuously during the refining process due to rapid Al evaporation. In order to investigate the evaporation kinetics of the melt constituents, we developed a numerical approach by applying the Hertz-Knudsen-Langmuir equation for evaporation. This approach can be applied to model the evaporation of the melt constituents in a ternary system whose composition changes during the vacuum refining process. The model is validated with performed experimental results and it can be applied to discuss the effect of temperature, pressure, initial melt composition on the time of vacuum refining

Selective Vacuum Evaporation by the Control of the Chemistry of Gas Phase in Vacuum Refining of Si

( Engelsk ) The evaporation of P from liquid Si under vacuum and reduced pressures of H2, He, and Ar was studied to evaluate the feasibility of effective P removal with insignificant Si loss. It was found that the introduction of Ar and He inert gases at low pressures reduces the rate of P removal, and their pressure decrease will increase the process rate. Moreover, the kinetics of P removal was higher in He than in Ar, with simultaneous lower Si loss. Under reduced pressures of H2 gas, however, the P removal rate was higher than that under vacuum conditions with the lowest Si loss. Quantum chemistry and dynamics simulations were applied, and the results indicated that P can maintain its momentum for longer distances in H2 once it is evaporated from the melt surface and then can travel far away from the surface, while Si atoms lose their momentum in closer distances, yielding less net Si flux to the gas phase. Moreover, this distance is significantly increased with decreasing pressure for H2, He, and Ar gases; however, it is the largest for H2 and the lowest for Ar for a given pressure, while the temperature effect is insignificant. The rate of P evaporation was accelerated by applying an additional vacuum tube close to the melt surface for taking out the hot gas particles before they lose their temperature and velocity. It was shown that this technique contributes to the rate of process by preventing condensing gas stream back to the melt surface

As, Sb, and Fe removal from industrial copper electrolyte by solvent displacement crystallization technique

The presence of impurities in the copper electrolyte increases the energy consumption of an electrorefining process and contaminates the deposited copper on cathode. The concentration of impurities increases over time making it necessary to remove them from the solution. This research introduces a fast, effective, and simple method to refine the industrial electrolyte from arsenic, iron and antimony by solvent displacement crystallisation technique. In this method, when alcohol is added to the electrolyte, the impurities precipitate from the solution as amorphous arsenato antimonite phase. Results show that Fe, Sb, and As are removed from the copper electrolyte by 75.2, 96.9 and 99.8%, respectively. Electro winning experiments show that the electric energy consumption for electrodeposition of copper is 15.5% lower when the electrolyte is free of impurities

Selective Vacuum Evaporation by the Control of the Chemistry of Gas Phase in Vacuum Refining of Si

( Engelsk ) The evaporation of P from liquid Si under vacuum and reduced pressures of H2, He, and Ar was studied to evaluate the feasibility of effective P removal with insignificant Si loss. It was found that the introduction of Ar and He inert gases at low pressures reduces the rate of P removal, and their pressure decrease will increase the process rate. Moreover, the kinetics of P removal was higher in He than in Ar, with simultaneous lower Si loss. Under reduced pressures of H2 gas, however, the P removal rate was higher than that under vacuum conditions with the lowest Si loss. Quantum chemistry and dynamics simulations were applied, and the results indicated that P can maintain its momentum for longer distances in H2 once it is evaporated from the melt surface and then can travel far away from the surface, while Si atoms lose their momentum in closer distances, yielding less net Si flux to the gas phase. Moreover, this distance is significantly increased with decreasing pressure for H2, He, and Ar gases; however, it is the largest for H2 and the lowest for Ar for a given pressure, while the temperature effect is insignificant. The rate of P evaporation was accelerated by applying an additional vacuum tube close to the melt surface for taking out the hot gas particles before they lose their temperature and velocity. It was shown that this technique contributes to the rate of process by preventing condensing gas stream back to the melt surface

Selective Vacuum Evaporation by the Control of the Chemistry of Gas Phase in Vacuum Refining of Si

The evaporation of P from liquid Si under vacuum and reduced pressures of H2, He, and Ar was studied to evaluate the feasibility of effective P removal with insignificant Si loss. It was found that the introduction of Ar and He inert gases at low pressures reduces the rate of P removal, and their pressure decrease will increase the process rate. Moreover, the kinetics of P removal was higher in He than in Ar, with simultaneous lower Si loss. Under reduced pressures of H2 gas, however, the P removal rate was higher than that under vacuum conditions with the lowest Si loss. Quantum chemistry and dynamics simulations were applied, and the results indicated that P can maintain its momentum for longer distances in H2 once it is evaporated from the melt surface and then can travel far away from the surface, while Si atoms lose their momentum in closer distances, yielding less net Si flux to the gas phase. Moreover, this distance is significantly increased with decreasing pressure for H2, He, and Ar gases; however, it is the largest for H2 and the lowest for Ar for a given pressure, while the temperature effect is insignificant. The rate of P evaporation was accelerated by applying an additional vacuum tube close to the melt surface for taking out the hot gas particles before they lose their temperature and velocity. It was shown that this technique contributes to the rate of process by preventing condensing gas stream back to the melt surface