The effect of calcium fluoride on extracting magnesium from magnesite and calcium carbonate by silicothermal reduction in flowing argon

At present, the production of magnesium is mainly carried out semi-continuously with ferrosilicon as reducing agent under high temperature and high vacuum. In order to continuously produce magnesium, anew method of extracting magnesium from low-grade magnesite and calcium carbonate by silicothermal method in flowing inert gas was proposed. The effects of calcium fluoride(CaF2)on decomposition rate, decomposition kinetics, reduction rate of magnesia and crystal type of dicalcium silicate in reduction slag were investigated in the paper. The experimental results showed that calcium fluoride could accelerate the decomposition of carbonate, and had no side effect on the calcined products. In addition, the analysis results of DTA curves showed that calcium fluoridecould reduce the decomposition reaction activation energy and the reaction temperature of carbonatein the prefabricated pellets. The results of reduction experiments showed that proper calcium fluoridecould promote the reduction rate of magnesia, and in the temperature range of 1250? ~ 1350?, with same timeframe, the corresponding calcium fluoride contents were5%, 3% and 1% respectively when the reduction rate reached the maximum. Excessive calcium fluoride could reduce the reduction rate of magnesia, but it couldpromote the transformation of dicalcium silicate to ? phase in the reduction slag.

Thermodynamic modelling of the binary indium-lithium system, a promising li-ion battery material

The binary In - Li system is a promising Li-ion battery anode material as well as a part of the important ternary Ge - In - Li system. The thermodynamic descriptions of metallic systems are widely used to retrieve information necessary for alloy applications. In this work, a thermodynamic model of a binary indium - lithium system prepared by the Calphad approach is proposed. The liquid phase was described by an associate model, and the solid phases determined by the ab-initio calculation were included in thermodynamic modeling. The obtained set of self-consistent thermodynamic parameters well reproduces the available experimental data and enables further calculations of multi-component systems. A good agreement between the calculations and the available experimental data was found. The proposed model can be used for further descriptions of ternary systems.

Primary microstructure characterization of Co-20Ni-9Al-7W-3Re-2ti superalloy

The characterization of the primary microstructure of the new Co-based superalloy of Co-20Ni-9Al-7W-3Re-2Ti type was shown in this article. The investigated alloy was manufactured by induction melting process from pure feedstock materials. The fundamental technological problem related to Co-Al-W-X multicomponent alloys' casting process is a strong susceptibility to interdendritic segregation of alloying elements, especially tungsten and rhenium. The performed analysis revealed that the observed effect of alloying elements segregation is detectable and much stronger than for Co-9Al-9W and Co-20Ni-7Al-7W alloys, related to titanium, nickel and aluminium migration to inter-dendritic spaces. Consequently, the tungsten concentration gradient between dendritic and interdendritic zones is higher than for Co-9Al-9W and Co-20Ni-7Al-7W alloys. The same situation is in the case of rhenium and cobalt, but Co's concentration in the interdendritic zone is only slightly lower.

Application of two-step diffusion couple technique in high-throughput screening of optimal composition and aging temperatures for alloys design: A demonstration in binary Ni-Al system

In this paper, four binary Ni-13.4at.% Al/Ni-17.7at.% Al diffusion couples were first prepared and subjected to homogenization at 1573 K for 10800s, from which a continuous concentration profile forms. The three diffusion couples were then cooled down for aging at respective temperatures, i.e., 1173, 1123 and 1073 K, for 14400s. The effect of composition and aging temperature on the aging microstructure was studied in detail by means of different experimental techniques and statistical analysis. The volume fraction, grain size and shape factor of ?? precipitates in the three diffusion couples were plotted as a function of alloy composition and annealing temperatures. Together with the previously proposed evaluation function in which the phase fraction, grain size and shape factor of ?? precipitates were chosen as the evaluation indicators, the optimal alloy composition and aging temperature for binary Ni-Al alloys with the best mechanical properties were evaluated, and finaly validated by the measured hardness values. The successful demonstration of alloy design in the present binary Ni-Al alloys indicates that the two-step diffusion couple together with the evaluation function for mechanic properties should be of generality for high-throughput screening of optimal alloy composition and heat treatment process in different alloys.

Insight on the reduction of copper content in slags produced from the Ausmelt Converting Process

The reduction of copper content in converting slag using process control is significant to copper smelter. In this study, the slags produced from the Ausmelt Converting Process for copper matte have been analyzed using X-ray diffraction and chemical analysis. Thermodynamic calculation and effects of various conditions including the lance submerging depth in molten bath, the molten bath temperature, the addition of copper matte, and airflow rate were carried out to lower the content in the slag. Thermodynamic analysis indicates that the decrease of copper content was achieved by reducing Fe3O4, CuFe2O4and Cu2O in the slag, decreasing the magnetism of slag and lowering the viscosity of slag, which is feasible at the operating temperature of the molten bath. Experiments show that the optimal combination of operating conditions were found to be the addition of copper matte between 5000 -7000 kg/h, a lance airflow rate of 13000-14000 Nm3/h and a lance submergence depth into the molten bath of 700-900 mm, in which the copper content in the slag can be effectively reduced from 22.74 wt. % to 7.70 wt. %.This study provides a theoretical support and technical guidance for promoting the utilization of slags from the Ausmelt Converting Process.

A new method for determination of the theoretical reduction amount for wide-thick slab during the mechanical reduction process

Mechanical soft reduction (MSR) is an effective method for elimination of the centerline segregation and porosity of the continuous casting steel slab, and the reduction amount is a key parameter that determines whether the MSR could be applied successfully. In the present work, a 2D heat transfer model was developed for predicting the non-uniform solidification of the wide-thick slab. The measured shell thickness by nail shooting experiment and the measured slab surface temperature by infrared camera were applied to validate the 2D heat transfer model. A new calculation method of theoretical reduction amount that could consider the influence of non-uniform solidification of the wide-thick slab was then derived. Based on the predicted temperature field by the 2D heat transfer model and the newly-proposed calculation method, the required theoretical reduction amount and reduction gradient/rate for the wide-thick slab were calculated and discussed. The difference between the newly-proposed method and the previous method, the influence of the casting speed and slab thickness on the required theoretical reduction amount and reduction gradient/rate were also investigated.

Creep rupture properties of bare and coated polycrystalline nickel-based superalloy Rene®80

Creep deformation is one of the life time limiting reasons for gas turbine parts that are subjected to stresses at elevated temperatures. In this study, creep rupture behavior of uncoated and platinum-aluminide coated Rene?80 has been determined at 760?C/657 MPa, 871?C/343 MPa and 982?C/190 Mpa in air. For this purpose, an initial layer of platinum with a thickness of 6?m was applied on the creep specimens. Subsequently, the aluminizing were formed in the conventional pack cementation method via the Low Temperature-High Activity (LTHA) and High Temperature-Low Activity (HTLA) processes. Results of creep-rupture tests showed a decrease in resistance to creep rupture of coated specimen, compared to the uncoated ones. The reductions in rupture lives in LTHA and HTLA methods at 760?C/657 MPa, 871?C/343 MPa and 982?C/190 MPa were almost (26% and 41.8%), (27.6% and 38.5%) and (22.4% and 40.3%), respectively as compared to the uncoated ones. However, the HTLA aluminizing method showed an intense reduction in creep life. Results of fractographic studies on coated and uncoated specimens indicated a combination of ductile and brittle failure mechanisms for all samples. Although, the base failure mode in substrate was grain boundary voids, cracks initiated from coating at 760?C/657MPa and 871?C/343. No cracking in the coating was observed at 982?C/190MPa.

Removal of arsenic from liquid blister copper during remelting in an induction vacuum furnace

Using a reduced pressure during the smelting and refining of alloys removes dissolved gasses, as well as impurities with a high vapor pressure. When smelting is carried out in vacuum induction furnaces, the intensification of the discussed processes is achieved by intensive mixing of the bath, as well as an enhanced mass exchange surface (liquid metal surface) due to the formation of a meniscus. This is due to the electromagnetic field applied to the liquid metal. This study reports the removal of arsenic from blister copper via refining in an induction vacuum furnace in the temperature range of 1423-1523 K, at operating pressures from 8 to 1333 Pa. The overall mass transfer coefficient kAs determined from the experimental data ranged from 9.99?10-7 to 1.65?10-5 ms-1. Arsenic elimination was largely controlled by mass transfer in the gas phase. The kinetic analysis indicated that the arsenic evaporation rate was controlled by the combination of both liquid and gas-phase mass transfer only at a pressure of 8 Pa.

Simulation and analysis of the solidification characteristics of a Si-Mo ductile iron

High silicon and molybdenum ductile cast irons (Si-Mo alloys) are commonly used as exhaust manifold materials suffering from high temperature-oxidation and thermal-mechanical fatigue. The structural integrity of cast Si-Mo alloys under these service conditions is attributed to their microstructure consisting of spheroidal graphite and Mo-rich carbide embedded in a ferritic matrix. However, the cast structure includes also pearlite structure having a detrimental effect on the mechanical properties, therefore the cast matrix needs to be heat treated. In this study, the solidification of a Si-Mo ductile iron was investigated using (i) thermodynamic and kinetic calculations by Thermo-Calc and DICTRA software and (ii) thermal analysis in order to reveal out the sequence of phase formation and the phase transformations during solidification and (iii) microanalysis by energy dispersive spectrometer in order to determine elemental segregation and compare with the calculated values. The solidified structure was also characterized and all microstructural features were specified.

Nodule count effect on microstructure and mechanical properties of hypo-eutectic ADI alloyed with nickel

Samples of ductile iron alloyed with 0.88 % Ni with a nodule count of 606, 523, and 290 nod/mm2 were obtained from sand cast plates of different thickness in the range from 8.46 to 25.4 mm. The effect of the nodule count was evaluated during the austempering process held at 285?C and austempering times of 15, 30, 45, 60, 70, and 90 min. The volume fraction of high carbon austenite increased when the nodule count increased, however, the carbon content of the high carbon austenite kept almost constant. The process window was narrow, requiring a lower austempering time when the nodule count increased. The combination of a higher nodule count and low austempering temperature allowed obtaining a fine ausferritic microstructure which led to higher Brinell hardness and tensile strength. The process window was determined by XRD measurements and it was in good agreement with the microstructural and hardness evolution as the austempering time increased.