Solubilities of Chlorine in CaO-SiO<Subscript>2</Subscript>-Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-MgO Slags: Correlation Between Sulfide and Chloride Capacities

To derive a correlation between sulfide and chloride capacities through our own systematic experimental studies by using a gas equilibrium technique involving Ar-H₂-H₂O-HCl gas mixtures, the solubilities of chlorine were determined for CaO-SiO₂-MgO-Al₂O₃ slags at temperatures between 1673 K and 1823 K (1400 °C and 1550 °C). As a formula to correlate sulfide and chloride capacities, the following equation that is the function of temperature only was obtainable;

Effect of Firing Temperature and Reducing Gas Composition during Low-Temperature Reduction of Nanocrystalline Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>

Pure nanocrystalline hematite (40 to 100 nm) compacts were prepared and sintered at various temperatures (300 °C to 600 °C) and then reduced with 100 pct H₂ at 500 °C. On the other hand, fired compacts at 500 °C were reduced with a H₂-Ar gas mixture containing different concentration of hydrogen (100, 75, 50, and 25 pct) at 500 °C using thermogravimetric techniques. Nanocrystalline Fe₂O₃ compacts were characterized before and after reduction with X-ray diffraction, scanning electron microscopy (SEM), vibrating sample magnetometer (VSM), and reflected light microscope. It was found that the fired compacts at 400 °C to 600 °C have relatively faster reaction behaviors compared to that at lower firing temperature 300 °C. By decreasing the firing temperature to 300 °C, partial sintering with grain growth was observed clearly during reduction. Also, it was found that the reduction rate increased with increasing hydrogen content in the reducing gas. Comparatively, grain growth and partial coalescence took place during reduction with 25 pct H₂ due to long reaction time.

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Thermodynamic behavior of nickel in CaO-SiO<Subscript>2</Subscript>-Fe<Subscript>t</Subscript>O slag

The distribution ratio of nickel between Ag-Ni alloy and CaO-SiO₂-Fe _t O slag at high temperatures was measured to clarify the dissolution mechanism of nickel in this melt. Also, the nickel oxide capacity was suggested and was compared to phosphate and sulfide capacities. The dissolution mechanism of nickel into the CaO-SiO₂-Fe _t O slags could be described by the following equation from the effect of oxygen potential and slag basicity on nickel dissolution behavior:

The Thermodynamic Behavior of Copper in the CaO-B<Subscript>2</Subscript>O<Subscript>3</Subscript> and BaO-B<Subscript>2</Subscript>O<Subscript>3</Subscript> Slag System

The Cu solubility was measured in the CaO-B₂O₃ and BaO-B₂O₃ slag systems to understand the dissolution mechanism of Cu in the slags. The Cu solubility had a linear relationship with oxygen partial pressure in the CaO-B₂O₃ slag system, which corresponds with previous studies. Also, the Cu solubilities in slag decreased with increasing the slag basicity, which value of slope was close to –0.5 in logarithmic form. From the results of experiment, the Cu dissolution mechanism established as follows:

Effects of Annealing and Pressure on Devitrification and Mechanical Properties of Amorphous Al<Subscript>87</Subscript>Ni<Subscript>7</Subscript>Gd<Subscript>6</Subscript>

Annealing studies at different temperatures, as well as those conducted with 940 MPa hydrostatic pressure, were conducted on amorphous ribbons of Al₈₇Ni₇Gd₆. The studies were performed to investigate the evolution of structure under different conditions and to particularly examine the effects of superimposed hydrostatic pressure during annealing. This amorphous alloy devitrifies at low temperatures via the precipitation of nano-crystalline α-Al particles. The effects of these various exposures on the amount of devitrification have been quantified using a variety of analytical techniques (i.e., X-ray diffraction (XRD), differential scanning calorimetry (DSC), and transmission electron microscopy (TEM)). In addition, the effects of devitrification on the mechanical properties have been quantified using microhardness indentation and uniaxial tension tests. This article is based on a presentation given in the symposium entitled “Bulk Metallic Glasses IV,” which occurred February 25–March 1, 2007 during the TMS Annual Meeting in Orlando, Florida under the auspices of the TMS/ASM Mechanical Behavior of Materials Committee.

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Experimental Studies on the Sulfide Capacities of CaO-SiO<Subscript>2</Subscript>-CrO<Subscript>x</Subscript> Slags

To understand the desulfurization process during the refining of Cr-containing steel grades, this work was initiated to study the reactions between Cr-sulfur and chromium-containing slags. The sulfide capacities of CaO-SiO₂-CrO_x pseudo-ternary slags were measured using the traditional gas-slag equilibration technique between 1823 K and 1923 K. Sixteen different slag compositions were examined, and two different equilibrium oxygen partial pressures were used to understand the impact of the varying valence of Cr on the sulfide capacities. The results showed that log₁₀ Cs varied linearly with the reciprocal T, and the slope was higher than the corresponding value reported for the binary CaO-SiO₂ of corresponding composition. It was difficult to isolate the relative effects of the bi- and trivalent Cr in the slags because the Cr²⁺/Cr³⁺ ratio was influenced by the basicity of the slag. By using the equation developed by these authors earlier that related Cr²⁺/Cr³⁺ with basicity, oxygen partial pressure, and temperature, it was possible to obtain an approximate trend of the CrO effect on the sulfide capacities; viz. the sulfide shows a decreasing trend as Cr²⁺ replaces Ca²⁺ in the slag. With a continued increase of Cr²⁺ content, indications of the occurrence of a minimum point were observed; beyond which the sulfide capacities showed a slight increasing trend. The latter was attributed, based on slag-structure analysis by Gaskell et al., to the increasing extent of the polymerization reaction releasing oxygen ions for sulfide reactions.     

Effect of Slag Composition on the Crystallization Kinetics of Synthetic CaO-SiO<Subscript>2</Subscript>-Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-MgO Slags

The crystallization kinetics of CaO-SiO₂-Al₂O₃-MgO (CSAM) slags was studied with the aid of single hot thermocouple technique (SHTT). Kinetic parameters such as the Avrami exponent (n), rate coefficient (K), and effective activation energy of crystallization (E _A ) were obtained by kinetic analysis of data obtained from in situ observation of glassy to crystalline transformation and image analysis. Also, the dependence of nucleation and growth rates of crystalline phases were quantified as a function of time, temperature, and slag basicity. Together with the observations of crystallization front, they facilitated establishing the dominant mechanisms of crystallization. In an attempt to predict crystallization rate under non-isothermal conditions, a mathematical model was developed that employs the rate data of isothermal transformation. The model was validated by reproducing an experimental continuous cooling transformation diagram purely from isothermal data.