Diffusion of Au in the Intermetallic Compound Ti<Subscript>3</Subscript>Al

The Au diffusion in the Ti₃Al compound was investigated at six compositions from 25 to 35 at. pct Al by using the diffusion couples (Ti-X at. pct Al/Ti-X at. pct Al-2 at. pct Au; X = 25, 27, 29, 31, 32, and 35) at 1273 to 1423 K. The diffusion coefficients of Au in Ti₃Al ( D_\textAu^{\textTi₃ \textAl} ) \left( {D_{\text{Au}}^{{{\text{Ti}}_{3} {\text{Al}}}} } \right) are relatively close to those of Ti. The D_\textAu^{\textTi₃ \textAl} \texts {D}_{\text{Au}}^{{{\text{Ti}}_{3} {\text{Al}}}} {\text{s}} slightly increase with Al concentration within the same order of magnitude. The activation energies of Au diffusion, Q_\textAu^{\textTi₃ \textAl} \texts, Q_{\text{Au}}^{{{\text{Ti}}_{3} {\text{Al}}}} {\text{s}}, evaluated from the Arrhenius plots were relatively close to those of Ti diffusion, Q_\textTi^{\textTi₃ \textAl} \texts, Q_{\text{Ti}}^{{{\text{Ti}}_{3} {\text{Al}}}} {\text{s}}, rather than those of Al diffusion, Q_\textAl^{\textTi₃ \textAl} \texts; {Q}_{\text{Al}}^{{{\text{Ti}}_{3} {\text{Al}}}} {\text{s}}; therefore, it was suggested that Au atoms diffuse by the sublattice diffusion mechanism in which Au atoms substitute for Ti sites preferentially in Ti₃Al and diffuse by vacancy mechanism on Ti sublattice. The influence of the D0₁₉ ordered structure (hcp base) of Ti₃Al on diffusion of Au and other elements is discussed by comparing the diffusivities in Ti₃Al and α-Ti.     

Separation of Antimony from a Stibnite Concentrate Through a Low-Temperature Smelting Process to Eliminate SO<Subscript>2</Subscript> Emission

The main purpose of this study is to characterize and separate antimony from a stibnite concentrate through a low-temperature sulfur-fixing smelting process. This article reports on a study conducted on the optimization of process parameters, such as flux and zinc oxide weight percentage, in charging, smelting temperature, smelting duration on the antimony yield, resultant crude antimony grade, and sulfur-fixing rate. A maximum antimony recovery of 97.07 pct, crude antimony grade of 96.45 pct, and 98.61 pct sulfur-fixing rate are obtained when a charge (containing 63.20 wt pct of flux and 21.30 wt pct of stibnite, a flux composition of W_\textNaOH /W_{\textNa 2 \textCO3} W_{\text{NaOH}} /W_{{{\text{Na}}_{ 2} {\text{CO}}_{3} }} = 10/147, where W represents weight, and more than 10 pct of the stoichiometric requirement of zinc oxide dosage) is smelted at 1153 K (880 °C) for 120 minutes. This smelting operation is free from atmospheric pollution because zinc oxide is used as the sulfur-fixing agent. The solid residue is subjected to mineral dressing operation to obtain suspension, which is filtered ultimately to produce a cake, representing the solid particles of zinc sulfide. Based on the results of the chemical content analysis of as-resultant zinc sulfide, more than 90 pct zinc sulfide can be recovered, and the recovered zinc sulfide grade can reach 66.70 pct. This material can be sold as zinc sulfide concentrate or roasted to regenerate into zinc oxide.     

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;

Density Measurements of Low Silica CaO-SiO<Subscript>2</Subscript>-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> Slags

Density measurements of a low-silica CaO-SiO₂-Al₂O₃ system were carried out using the Archimedes principle. A Pt 30 pct Rh bob and wire arrangement was used for this purpose. The results obtained were in good agreement with those obtained from the model developed in the current group as well as with other results reported earlier. The density for the CaO-SiO₂ and the CaO-Al₂O₃ binary slag systems also was estimated from the ternary values. The extrapolation of density values for high-silica systems also showed good agreement with previous works. An estimation for the density value of CaO was made from the current experimental data. The density decrease at high temperatures was interpreted based on the silicate structure. As the mole percent of SiO₂ was below the 33 pct required for the orthosilicate composition, discrete \textSiO₄^{4 -} {\text{SiO}}_{4}^{4 - } tetrahedral units in the silicate melt would exist along with O^2– ions. The change in melt expansivity may be attributed to the ionic expansions in the order of

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:

Distribution Ratios of Phosphorus Between CaO-FeO-SiO<Subscript>2</Subscript>-Al<Subscript>2</Subscript>O<Subscript>3</Subscript>/Na<Subscript>2</Subscript>O/TiO<Subscript>2</Subscript> Slags and Carbon-Saturated Iron

In order to effectively enhance the efficiency of dephosphorization, the distribution ratios of phosphorus between CaO-FeO-SiO₂-Al₂O₃/Na₂O/TiO₂ slags and carbon-saturated iron (\( L_{\text{P}}^{\text{Fe-C}} \)) were examined through laboratory experiments in this study, along with the effects of different influencing factors such as the temperature and concentrations of the various slag components. Thermodynamic simulations showed that, with the addition of Na₂O and Al₂O₃, the liquid areas of the CaO-FeO-SiO₂ slag are enlarged significantly, with Al₂O₃ and Na₂O acting as fluxes when added to the slag in the appropriate concentrations. The experimental data suggested that \( L_{\text{P}}^{\text{Fe-C}} \) increases with an increase in the binary basicity of the slag, with the basicity having a greater effect than the temperature and FeO content; \( L_{\text{P}}^{\text{Fe-C}} \) increases with an increase in the Na₂O content and decrease in the Al₂O₃ content. In contrast to the case for the dephosphorization of molten steel, for the hot-metal dephosphorization process investigated in this study, the FeO content of the slag had a smaller effect on \( L_{\text{P}}^{\text{Fe-C}} \) than did the other factors such as the temperature and slag basicity. Based on the experimental data, by using regression analysis, \( \log L_{\text{P}}^{\text{Fe-C}} \) could be expressed as a function of the temperature and the slag component concentrations as follows:

$$ \begin{aligned} \log L_{\text{P}}^{\text{Fe-C}} & = 0.059({\text{pct}}\;{\text{CaO}}) + 1.583\log ({\text{TFe}}) - 0.052\left( {{\text{pct}}\;{\text{SiO}}_{2} } \right) - 0.014\left( {{\text{pct}}\;{\text{Al}}_{2} {\text{O}}_{3} } \right) \\ \, & \quad + 0.142\left( {{\text{pct}}\;{\text{Na}}_{2} {\text{O}}} \right) - 0.003\left( {{\text{pct}}\;{\text{TiO}}_{2} } \right) + 0.049\left( {{\text{pct}}\;{\text{P}}_{2} {\text{O}}_{5} } \right) + \frac{13{,}527}{T} - 9.87. \\ \end{aligned} $$

     

Redox Equilibrium of Niobium in Calcium Silicate Base Melts

The oxidation state of niobium has been determined at 1873 K (1600 °C) in CaO-SiO₂-NbO _x melts with CaO/SiO₂ ratios (mass pct) of 0.66, 0.93 and 1.10, and 5.72 to 11.44 pct Nb₂O₅ (initial). The slag samples were equilibrated with gas phases of controlled oxygen pressure, then quenched to room temperature and analyzed chemically. The niobium is mainly pentavalent with small amounts in the tetravalent state. It was found that the Nb⁵⁺/Nb⁴⁺ ratio increases with oxygen pressure at a constant CaO/SiO₂ ratio and constant content of total niobium, closely according to the ideal law of mass action, which is proportional to \textp_\textO2 ^1/4 . {\text{p}}_{{{\text{O}}_{2} }}^{1/4} . The ratio also increases with total niobium content, and it seems to have a maximum at a basicity of about 0.93. The color of the solidified slag samples is described and is explained with the help of transmission spectra.     

Precious Metal Distributions in Direct Nickel Matte Smelting with Low-Cu Mattes

Base metal (Cu, Fe, and Ni) and trace element (Ag, Au, Co, Pd, and Pt) distributions between low-iron nickel mattes with [Ni]:[Cu] = 4 (w/w) have been studied at 1623 K to 1723 K (1350 °C to 1450 °C). We equilibrated small slag–matte samples with CO–CO₂–SO₂–Ar atmospheres in pre-selected \( P_{{{\text{S}}_{2} }} \)–\( P_{{{\text{O}}_{2} }} \) points, maintaining silica saturation by fused silica crucibles. The slags studied contained about 0 to 8.5 wt pct MgO. The matte–slag distribution coefficients L ^m/s[Me] were obtained from assays by electron probe X-ray microanalysis for the matte and by laser ablation-ICP-mass spectrometry for the slag. The measured L ^m/s[Me] values were clearly dependent on iron concentration of the matte and on MgO concentration of the slag, with values on the order of 10⁴, 10⁵, and 10⁴ for gold, platinum, and palladium, respectively, in the 5 wt pct iron in matte experiments. The obtained data for silver were scattered, due to volatilization, resulting in depletion of most silver and its escape from matte to gas phase during the 3-hour equilibration period. The matte-to-slag distribution coefficient for silver was estimated to be L ^m/s[Ag] = 100 to 400. We also measured the distributions of the base metals Cu and Ni in the same conditions as the trace elements.     

Oxidation and Condensation of Zinc Fume From Zn-CO<Subscript>2</Subscript>-CO-H<Subscript>2</Subscript>O Streams Relevant to Steelmaking Off-Gas Systems

The objective of this research was to study the condensation of zinc vapor to metallic zinc and zinc oxide solid under varying environments to investigate the feasibility of in-process separation of zinc from steelmaking off-gas dusts. Water vapor content, temperature, degree of cooling, gas composition, and initial zinc partial pressure were varied to simulate the possible conditions that can occur within steelmaking off-gas systems, limited to Zn-CO₂-CO-H₂O gas compositions. The temperature of deposition and the effect of rapidly quenching the gas were specifically studied. A homogeneous nucleation model for applicable experiments was applied to the analysis of the experimental data. It was determined that under the experimental conditions, oxidation of zinc vapor by H₂O or CO₂ does not occur above 1108 K (835 °C) even for highly oxidizing streams (CO₂/CO = 40/7). Rate expressions that correlate CO₂ and H₂O oxidation rates to gas composition, partial pressure of water vapor, temperature, and zinc partial pressure were determined to be as follows:

$$ {\text{Rate}}\left( {\frac{\text{mol}}{{{\text{m}}^{2} {\text{s}}}}} \right) = 406 \exp \left( {\frac{{ - 50.2 \,{\text{kJ}}/{\text{mol}}}}{RT}} \right)\left( {p_{\text{Zn}} p_{{{\text{CO}}_{2} }} - p_{\text{CO}} /K_{{{\text{eq}},{\text{CO}}_{2} }} } \right)\,\frac{\text{mol}}{{{\text{m}}^{2} \times {\text{s}}}} $$

$$ {\text{Rate}}\left( {\frac{\text{mol}}{{{\text{m}}^{2} {\text{s}}}}} \right) = 32.9 \exp \left( {\frac{{ - 13.7\, {\text{kJ}}/{\text{mol}}}}{RT}} \right)\left( {p_{\text{Zn}} p_{{{\text{H}}_{2} {\text{O}}}} - p_{{{\text{H}}_{2} }} /K_{{{\text{eq}},{\text{H}}_{2} {\text{O}}}} } \right)\,\frac{\text{mol}}{{{\text{m}}^{2} \times {\text{s}}}} $$

It was proven that a rapid cooling rate (500 K/s) significantly increases the ratio of metallic zinc to zinc oxide as opposed to a slow cooling rate (250 K/s). SEM analysis found evidence of heterogeneous growth of ZnO as well as of homogeneous formation of metallic zinc. The homogeneous nucleation model fit well with experiments where only metallic zinc deposited. An expanded model with rates of oxidation by CO₂ and H₂O as shown was combined with the homogenous nucleation model and then compared with experimental data. The calculated results based on the model gave a reasonable fit to the measured data. For the conditions used in this study, the rate equations for the oxidation of zinc by carbon dioxide and water vapor as well as the homogeneous nucleation model of metallic zinc were applicable for various temperatures, zinc partial pressures, CO₂:CO ratios, and H₂O partial pressures.

     

Thermodynamics of Arsenic in FeOx-CaO-SiO<Subscript>2</Subscript> Slags

The distribution of arsenic between calcium ferrite slag and liquid silver (wt pct As in slag/ wt pct As in liquid silver) with 22 wt pct CaO and between iron silicate slag with 24 wt pct SiO₂ and calcium iron silicate slags was measured at 1573 K (1300 °C) under a controlled CO-CO₂-Ar atmosphere. For the calcium ferrite slags, a broad range of oxygen partial pressure (10^–11 to 0.21 atm) was covered, whereas for the silicate slags, the oxygen partial pressure was varied from 10^–9 to 3.1 × 10^–7 atm. The measured relations between the distribution ratio of As and the oxygen partial pressure indicates that the oxidation state of arsenic in these slags is predominantly As³⁺ or AsO_1.5. The measured distribution ratio of arsenic between the calcium ferrite slag and the liquid silver was about an order of magnitude higher than that of the iron silicate slag. In addition, an increasing concentration of SiO₂ in the calcium-ferrite-based melts resulted in decreases in the distribution of arsenic into the slag. Through the use of measured equilibrium data on the arsenic content of the metal and slag in conjunction with the composition dependent on the activity of arsenic in the metal, the activity of AsO_1.5 in the slags was deduced. These activity data on AsO_1.5 show a negative deviation from the ideal behavior in these slags.     

Effect of Al<Subscript>2</Subscript>O<Subscript>3</Subscript> Concentration on Density and Structure of (CaO-SiO<Subscript>2</Subscript>)-xAl<Subscript>2</Subscript>O<Subscript>3</Subscript> Slag

The effect of Al₂O₃ concentration on the density and structure of CaO-SiO₂-Al₂O₃ slag was investigated at multiple Al₂O₃ mole percentages and at a fixed CaO/SiO₂ ratio of 1. The experiments were conducted in the temperature range of 2154 K to 2423 K (1881 °C to 2150 °C) using the aerodynamic levitation technique. In order to understand the relationship between density and structure, structural analysis of the silicate melts was carried out using Raman spectroscopy. The density of each slag sample investigated in this study decreased linearly with increasing temperature. When the Al₂O₃ content was less than 15 mole pct, density decreased with increasing Al₂O₃ content due to the coupling of Si (Al), whereas above 20 mole pct density of the slag increased due to the role of Al³⁺ ion as a network modifier.     

Confocal Scanning Laser Microscopy Studies of Crystal Growth During Oxidation of a Liquid FeO-CaO-SiO<Subscript>2</Subscript> Slag

The oxidation of FeO in 30 wt pct FeO-35 wt pct CaO-35 wt pct SiO₂ slag was investigated as part of a wider study on the recovery of Fe units through magnetic separation. A confocal scanning laser microscopy (CSLM) technique was used to visualize the oxidation of FeO in the liquid slag. The formation event was observed in situ under the CSLM and the onset of precipitation on a surface of the slag liquid was recorded at various temperatures in an oxidizing atmosphere. A Time-Temperature-Transformation (TTT) diagram was constructed based on the CSLM results. Samples obtained from the CSLM heating chamber were analyzed by a scanning electron microscope (SEM) equipped with an energy-dispersive spectrometer (EDS).     

Oxidation Behavior of a Pd<Subscript>43</Subscript>Cu<Subscript>27</Subscript>Ni<Subscript>10</Subscript>P<Subscript>20</Subscript> Bulk Metallic Glass and Foam in Dry Air

The oxidation behavior of both Pd₄₃Cu₂₇Ni₁₀P₂₀ bulk metallic glass (Pd4-BMG) and its amorphous foam containing 45 pct porosity (Pd4-AF) was investigated over the temperature range of 343 K (70 °C) to 623 K (350 °C) in dry air. The results showed that virtually no oxidation occurred in the Pd4-BMG at T < 523 K (250 °C), revealing the alloy’s favorable oxidation resistance in this temperature range. In addition, the oxidation kinetics at T ≥ 523 K (250 °C) followed a parabolic-rate law, and the parabolic-rate constants (k _p values) generally increased with temperature. It was found that the oxidation k _p values of the Pd4-AF are slightly lower than those of the Pd4-BMG, indicating that the porous structure contributes to improving the overall oxidation resistance. The scale formed on the alloys was composed exclusively of CuO at T ≥ 548 K (275 °C), whose thickness gradually increased with increasing temperature. In addition, the amorphous structure remained unchanged at T ≤ 548 K (275 °C), while a triplex-phase structure developed after the oxidation at higher temperatures, consisting of Pd₂Ni₂P, Cu₃P, and Pd₃P.     

A Eutectoid Reaction for the Decomposition of Austenite into Pearlitic Lamellae of Ferrite and M<Subscript>23</Subscript>C<Subscript>6</Subscript> Carbide in a Mn-Al Steel

We discovered a eutectoid reaction in an Fe-13.4Mn-3.0Al-0.63C (wt pct) steel after solution heat treatment at 1373 K (1100 °C) and holding at temperatures below 923 K (650 °C). The steel is single austenite at temperatures from 1373 K to 923 K (1100 °C to 650 °C). A eutectoid reaction involves the replacement of the metastable austenite by a more stable mixture of ferrite and M₂₃C₆ phases at temperatures below 923 K (650 °C). The mixture of ferrite and M₂₃C₆ is in the form of pearlitic lamellae. The morphology of the lamellae of the product phases is similar to that of pearlite in steels. Thus, we found a new pearlite from the eutectoid reaction of the Mn-Al steel featuring γ  → α + M₂₃C₆. A Kurdjumov–Sachs (K-S) orientation relationship exists between the pearlitic ferrite (α) and M₂₃C₆ (C6) grains, i.e., (110)_α // (111)_C6 and [[`1] \overline{1} 11]<sub>α</sub> // [0[`1] \overline{1} 1]_C6. The upper temperature limit for the eutectoid reaction is between 923 K and 898 K (650 °C and 625 °C).