Volume 37, Issue 1 -

This paper is a contribution to the theoretical and quantitative understanding of the processes for the production of magnesium metal by metallothermic process in vacuum (Pidgeon Process). In the present study, effects of reductant type and amount were investigated. CaC 2 is a low-cost alternative to FeSi (ferrosilicon) which is the common reductant in the Pidgeon Process. CaC 2 slightly decreases the Mg recovery ratios but it remarkably decreases the process cost. The experimental study, conducted with the change of mass % FeSi–CaC 2 ratio at 1,250 °C for 360 min, the optimum Mg recovery was measured as 94.7 % at 20 % CaC 2 addition. Also aluminum, as a reductant, allows conducting the process at lower temperatures than that of FeSi. For the experiments conducted with Al addition, the highest Mg recovery ratio was measured as 88.0 % in the conditions for 300 min process duration and 100 % stoichiometric Al addition at 1,200 °C.

The tensile properties of the alloy 2618 and 2618-Ti were tested using a tensile testing machine. The morphologies of the fracture of tensile samples were observed using scanning electron microscopy. The strengthening and toughening mechanisms of alloy 2618-Ti at elevated temperature were systematically investigated based on the analyses of experimental results. The results showed that the tensile strength of alloy 2618-Ti is much higher than that of alloy 2618 at the temperature range of 250 and 300 °C. But the elongation of alloy 2618-Ti is much higher than that of alloy 2618 at the temperature range of 200 and 300 °C. The equal-strength temperature of intragranular and grain boundary of alloy 2618-Ti is about 235 °C. When the temperature is lower than 235 °C, the strengthening of alloy 2618-Ti is ascribed to the strengthening effect of fine grains and dispersed Al 3 Ti/Al 18 Mg 3 Ti 2 phase. When the temperature is higher than 235 °C, the strengthening effect of alloy 2618-Ti is mainly attributed to the load transfer of Al 3 Ti and Al 18 Mg 3 Ti 2 particles. The toughening of alloy 2618-Ti at elevated temperature is mainly ascribed to the fine grain microstructure, excellent combination between matrix and dispersed Al 3 Ti/Al 18 Mg 3 Ti 2 particles as well as the recrystallization of the alloy at elevated temperature.

In this paper the doping effect has been used to indirectly calculate point defect concentration in metal-deficient Zn 1-y O zinc oxide. The proposed method consists of determining the concentration of prevailing point defects in the studied oxide from the influence of chromium addition on the point defect situation in doped zinc oxide. It has been found that chromium addition into the crystal lattice of zinc oxide changes its ionic disorder, enabling calculation of predominant point defects in Zn 1-y O. The concentration of predominant point defects in Zn 1-y O is the following function of oxygen pressure and temperature: V′′Zn=12h∙=0.63⋅pO21/6⋅K1/3=5.6⋅10−3⋅pO21/6⋅exp−27kJ/molRT⋅$$\eqalign{\left[{\,{{\rm V''}_{\rm Zn}}\,} \right]\, &= \,{1 \over 2}\left[{\,{\rm h^ \bullet}\,} \right]\, = \,0.63 \cdot \,\rm p_{{O_2}}^{1/6}\, \cdot {K^{1/3}}\,_{}^{}\, \cr& = \,\,5.6 \cdot {10^{- 3}} \cdot \,\rm p_{{O_2}}^{1/6}\, \cdot \exp \left({- {{27\,kJ/mol} \over {RT}}} \right)\cdot}$$

The effect of a dissipative ladle shroud (DLS) on mixing in tundish was investigated, compared with that of a conventional ladle shroud (CLS) using mathematical and physical modelling. The tracer profiles of mathematical results, achieved using large eddy simulation, were validated by physical observations employing high-speed cinephotography. The design of a DLS dramatically changed the flow patterns and contributed the intermixing of fluid elements inside the ladle shroud. The vortex flow encouraged the turbulent mixing and was verified by tracking of physical tracer dispersion inside the DLS. Residence Time Distribution (RTD) curves were obtained in two different sized tundishes to examine the mixing behaviours. The findings indicated that the DLS benefited the tundish mixing in terms of increasing active volume. The effect seemed to be more remarkable in the smaller tundish. The DLS gave rise to a more plug-like flow pattern inside the tundish, showing potential to shorten the transition length during grade change.

The chemical structure of mineral wool fiber was investigated by using Fourier Transform Infrared Spectroscopy (FTIR). Next, the glass transition temperature and the crystallization temperature of the fibers were studied. Finally, the crystallization kinetics of fiber was studied. The results show that the chemical bond structure of fibers gets more random with the increase of acidity coefficient. The crystallization phases of the fibers are mainly melilites, and also a few anorthites and diopsides. The growth mechanism of the crystals is three dimensional. The fibers with acidity coefficient of 1.2 exhibit the best thermal stability and is hard to crystallize as it has the maximum aviation energy of crystallization kinetics.

Constitutive model of materials is one of the most requisite mathematical model in the finite element analysis, which describes the relationships of flow behaviors with strain, strain rate and temperature. In order to construct such constitutive relationships of ultra-high-strength BR1500HS steel at medium and low temperature regions, the true stress-strain data over a wide temperature range of 293–873 K and strain rate range of 0.01–10 s −1 were collected from a series of isothermal uniaxial tensile tests. The experimental results show that stress-strain relationships are highly non-linear and susceptible to three parameters involving temperature, strain and strain rate. By considering the impacts of strain rate and temperature on strain hardening, a modified constitutive model based on Johnson-Cook model was proposed to characterize flow behaviors in medium and low temperature ranges. The predictability of the improved model was also evaluated by the relative error (W(%)$W(\%)$), correlation coefficient ( R ) and average absolute relative error ( AARE ). The R -value and AARE -value for modified constitutive model at medium and low temperature regions are 0.9915 & 1.56 % and 0.9570 & 5.39 %, respectively, which indicates that the modified constitutive model can precisely estimate the flow behaviors for BR1500HS steel in the medium and low temperature regions.

The spent phenolic resin is as raw material for preparing high surface area activated carbon (HSAAC) by microwave-assisted KOH activation. The effects of microwave power, activation duration and impregnation ratio (IR) on the iodine adsorption capability and yield of HSAAC were investigated. The surface characteristics of HSAAC were characterized by nitrogen adsorption isotherms, FTIR, SEM and TEM. The operating variables were optimized utilizing the response surface methodology (RSM) and were identified to be microwave power of 700 W, activation duration of 15 min and IR of 4, corresponding to a yield of 51.25 % and an iodine number of 2,384 mg/g. The pore structure parameters of the HSAAC, i. e., Brunauer–Emmett–Teller (BET) surface area, total pore volume, and average pore diameter were estimated to be 4,269 m 2 /g, 2.396 ml/g and 2.25 nm, respectively, under optimum conditions. The findings strongly support the feasibility of microwave-assisted KOH activation for preparation of HSAAC from spent phenolic resin.

The Al-Si melts that contain different silicon contents were solidified with a series of cooling rates, and the boron contents in primary silicon phases and eutectic silicon phases were measured and discussed. The results indicate that the boron content in the eutectic silicon phases is higher than that in the primary silicon phases when the cooling rate is constant. When the cooling rate decreases, the boron content in the primary silicon phases decreases, but the boron content in the eutectic silicon phases increases. The microstructure observations of solidified ingots show that there is an interface transition layer beside the primary silicon phase, and the average width of the interface transition layer increases with decreasing cooling rate.

Constitutive analysis for hot working of BFe10-1-2 alloy was carried out by using experimental stress–strain data from isothermal hot compression tests, in a wide range of temperature of 1,023~1,273 K, and strain rate range of 0.001~10 s –1 . A constitutive equation based on modified double multiple nonlinear regression was proposed considering the independent effects of strain, strain rate, temperature and their interrelation. The predicted flow stress data calculated from the developed equation was compared with the experimental data. Correlation coefficient ( R ), average absolute relative error ( AARE ) and relative errors were introduced to verify the validity of the developed constitutive equation. Subsequently, a comparative study was made on the capability of strain-compensated Arrhenius-type constitutive model. The results showed that the developed constitutive equation based on modified double multiple nonlinear regression could predict flow stress of BFe10-1-2 alloy with good correlation and generalization.

This study investigated a series of single phase Mg x -Zn 1-x -Fe 2 O 4 spinel ferrites, prepared using co-precipitation technique and sintered at 600 °C. The X-ray diffraction (XRD) patterns of the ferrite samples revealed the formation of impurity free single phase spinel structures. The formation of ferrite phases and face centered cubic structures was confirmed at Bragg angles of 35.9°, 54.3° and 62.7°. The lattice parameter increased with an increase in ‘x’ content in the ferrite composition. The grain size, estimated from SEM micrographs, was found in the range of 0.5–2 mµ. The lattice parameter of the ferrite samples exhibited an initial increase upto a certain extent, thereafter suddenly dropped down due to fracturing and re-welding processes. Overall, the lattice parameter ‘a’ varied from 0.80 to 0.85 nm, crystallite size from 34 to 80 nm, unit cell volume from 0.528 × 10 −21 to 0.62 × 10 −21  cm 3 and X-ray density from 5.8 to 4.5 g/cm 3 .

The effects of Bi on the microstructure and mechanical properties of AZ80-2Sn alloy were investigated. The results show that the addition of Bi within the as-cast AZ80-2Sn alloy promotes the formation of Mg 3 Bi 2 phase, which can refine the grains and make the eutectic phases discontinuous. The addition of 0.5 % Bi within the as-extruded AZ80-2Sn alloy, the average grain size decreases to 12 μm and the fine granular Mg 17 Al 12 and Mg 3 Bi 2 phases are dispersed in the α-Mg matrix. With an increase in Bi content, the Mg 17 Al 12 and Mg 3 Bi 2 phases become coarsened and the grain size increases. The as-extruded AZ80-2Sn-0.5 %Bi alloy has the optimal properties, and the ultimate tensile strength, yield strength and elongation are 379.6 MPa, 247.1 MPa and 14.8 %, respectively.