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.

     

The reduction of iron oxides by volatiles in a rotary hearth furnace process: Part II. The reduction of iron oxide/carbon composites

The reduction of iron oxide/carbon composite pellets with hydrogen at 900 °C to 1000 °C was studied. Compared to hydrogen, the reduction by carbon was negligible at 900 °C and below. However, significant carbon oxidation of the iron oxide/graphite pellets by H₂O generated from the reduction of Fe₂O₃ by H₂ was observed. At higher temperatures, reduction by carbon complicates the overall reduction mechanism, with the iron oxide/graphite composite pellet found to be more reactive than the iron oxide/char composite pellet. From the scanning electron micrographs, partially reduced composite pellets showed a typical topochemical interface with an intermediate region between an oxygen-rich unreacted core and an iron-rich outer shell. To determine the possibility of reduction by volatiles, a layer of iron oxide powders was spread on top of a high volatile containing bituminous coal and heated inside a reactor using infra-red radiation. By separating the individual reactions involved for an iron oxide/coal mixture where a complex set of reactions occur simultaneously, it was possible to determine the sole effect of volatile reduction. It was found that the light reducing gases evolve initially and react with the iron oxide, with complex hydrocarbons evolving at the later stages. The volatiles caused about 20 to 50 pct reduction of the iron oxide.     

Optical properties of Si–O–N–F films as a phase shift mask material for 157 nm optical lithography

Si–O–N–F has been studied as a new candidate material for a high transmittance attenuated phase shift mask (HT-Att-PSM). The requirements of HT-Att-PSM are 20 ± 5% transmittance and 180° phase shift at the exposure wavelength (157 nm) and less than 40% transmittance at the inspection wavelength (193 nm). Si–O–N–F films were deposited with varying process parameters, such as gas flow rate and deposition time, to find optimum conditions to meet the above requirements. In this study, the effects of process parameters on the optical properties and the degradation of Si–O–N–F films were examined. To satisfy the requirements of HT-Att-PSM, a new mask structure was suggested and analyzed.     

Fabrication and MFM study of 60 nm track-pitch discrete track media

Discrete track magnetic recording media with a 60 nm track pitch and prewritten servo patterns were fabricated and tested for read/write performance, and a feasibility analysis of the embedded servo was performed. The fabrication process consisted of ultraviolet nanoimprint lithography (UV-NIL) and sequential ion beam etching on a conventional perpendicular magnetic recording medium. Magnetic patterns were written to the fabricated tracks at 700 kilo flux changes per inch (kFCI) using a spin stand and were read using magnetic force microscopy (MFM), with a resulting signal-to-noise ratio (SNR) of 12.15 dB. The servo pattern was also visualized with MFM. These results demonstrated the feasibility of writing to a 30 nm wide discrete data track and the workability of the embedded servo pattern.     

Differential effects of rANF and chronic guanabenz to presynaptic and postsynaptic alpha 2-adrenoceptor-mediated cardiovascular response in pithed rats

1. In normal rats, intracerebroventricular (i.c.v.) guanabenz induced a decrease in blood pressure (BP) and heart rate (HR), and this hypotension or bradycardia was not changed by rANF pretreatment (3 micrograms i.c.v.). 2. In pithed rats, intravenous (i.v.) guanabenz, an alpha 2-adrenoceptor agonist, produced an increase in mean blood pressure (MBP) in a dose-dependent manner. The pressor response by guanabenz was attenuated by infusion of rANF. This attenuation was additive when incubated in combination with yohimbine. 3. In pithed rats, the pressor response due to the increase of sympathetic outflow with electrical stimulation was partially blocked by rANF infusion or chronic guanabenz treatment. This reduction was not augmented by chronic guanabenz plus rANF treatment. 4. The inhibitory action of guanabenz in tachycardia evoked by electrical stimulation at the C7-T1 site was attenuated by rANF, but not by chronic treatment with guanabenz.     

Thermophysical Properties of Continuous Casting Mold Flux for Advanced Steel Developments

The effect of Al₂O₃ on the crystallization and viscosity of calcium-silicate based fluxes with Na₂O and Li₂O additions used for continuous casting mold fluxes have been studied using the confocal laser scanning microscope and the rotating spindle rheometer. Al₂O₃ additions lowered the crystallization temperature of the flux and several crystalline phases for fluxes with high concentrations of SiO₂ forms depending on the cooling rate. High Al₂O₃ containing fluxes formed relatively few crystalline phases and were not highly dependent on the cooling rate. At slow cooling rates of 25 K/min for 10 and 20 wt% Al₂O₃ containing samples, SEM images revealed dendrites formed within the crystalline phases. At faster cooling rates the dendrite formation is inhibited and a spherical morphology could be observed. The substitution of SiO₂ with Al₂O₃ content modified the dominant silicate network into complex alumino-silicates. This increased the viscosity of the melt. FTIR and Raman analysis showed increased amounts of symmetric Al–O⁰ stretching with higher Al₂O₃. With higher CaO/(SiO₂ + Al₂O₃), the symmetric Al–O⁰ stretching and the Si–O–Al seems to decrease.     

Reduction of molybdenite with carbon in the presence of lime

The thermodynamics of the MoS₂-C-CaO system has been studied in order to understand the carbothermic reduction of molybdenite in the presence of CaO. Kinetic studies were also conducted with mixtures of MoS₂+C+CaO in the temperature range of 900 °C 1200 °C. The reduction of MoS₂ with carbon in the presence of lime proceeds through the direct oxidation of MoS₂ by CaO to form intermediate molybdenum oxidized species, MoO₂ and CaMoO₄, which subsequently undergo reduction by CO to yield mixtures of Mo, Mo₂C, and CaS. Complete conversion of MoS₂ can be obtained at 1200 °C in less than 20 minutes for molar concentrations of MoS₂:C:CaO=1:2:2. The kinetic model ln (1−X)=kt was used to determine the rate constants. The activation energy found for the temperature range studied was 218.8 kJ/mol.     

The selective oxidation of mixed metal sulfides with lime in the presence of steam without emitting sulfur-containing pollutants

The selective oxidation of mixed metal sulfides with lime in the presence of steam was studied as a function of the mixing ratio of the constituents, temperature, and steam concentration. Two combinations of samples were used in this study: ZnS/PbS/CaO and ZnS/FeS/CaO. The steam oxidizes one or both of the metal sulfides, and the hydrogen sulfide produced reacts with lime to form calcium sulfide and regenerate steam. There is no net consumption or generation of gaseous species; therefore, this process can be carried out in a closed system. The free energy of the reaction is negative only for certain metal sulfides, and thus selective oxidation for mixed sulfides can be achieved. An overall rate equation developed in this work satisfactorily predicted the experimental data obtained in the temperature range 823 to 1113 K. The potential implications of the results of this work in the treatment of complex sulfide ores are discussed. This paper is based on a presentation made in the T.B. King Memorial Symposium on “Physical Chemistry in Metals Processing” presented at the Annual Meeting of The Metallurgical Society, Denver, CO, February, 1987, under the auspices of the Physical Chemistry Committee and the PTD/ISS.     

Interdiffusion, Intrinsic Diffusion, Atomic Mobility, and Vacancy Wind Effect in γ(bcc) Uranium-Molybdenum Alloy

U-Mo alloys are being developed as low enrichment uranium fuels under the Reduced Enrichment for Research and Test Reactor (RERTR) Program. In order to understand the fundamental diffusion behavior of this system, solid-to-solid pure U vs Mo diffusion couples were assembled and annealed at 923 K, 973 K, 1073 K, 1173 K, and 1273 K (650 °C, 700 °C, 800 °C, 900 °C, and 1000 °C) for various times. The interdiffusion microstructures and concentration profiles were examined via scanning electron microscopy and electron probe microanalysis, respectively. As the Mo concentration increased from 2 to 26 at. pct, the interdiffusion coefficient decreased, while the activation energy increased. A Kirkendall marker plane was clearly identified in each diffusion couple and utilized to determine intrinsic diffusion coefficients. Uranium intrinsically diffused 5-10 times faster than Mo. Molar excess Gibbs free energy of U-Mo alloy was applied to calculate the thermodynamic factor using ideal, regular, and subregular solution models. Based on the intrinsic diffusion coefficients and thermodynamic factors, Manning’s formalism was used to calculate the tracer diffusion coefficients, atomic mobilities, and vacancy wind parameters of U and Mo at the marker composition. The tracer diffusion coefficients and atomic mobilities of U were about five times larger than those of Mo, and the vacancy wind effect increased the intrinsic flux of U by approximately 30 pct.     

The Effects of CaF2, Basicity, and Atmospheric Conditions on the Solubility of Carbon and Nitrogen in the CaO-SiO2-Al2O3-Based Slag System

The solubility of carbon and nitrogen in the CaF₂-CaO-SiO₂-Al₂O₃ slag system was studied. The effects of the CaF₂, extended basicity (CaO/(SiO₂ + Al₂O₃)), and atmospheric conditions on the dissolution behavior of the carbon and nitrogen, as well as the correlations of the behaviors with the slag structure observed at 1773 K (1500 °C), are presented. Increases in the extended basicity and the CaF₂ increased the solubility of carbon in the slag. In the case of nitrogen dissolution, a characteristic parabolic curve with an identifiable minimum was observed for the slag. This curve shape correlated with a change in the dominant mechanism of dissolution from an incorporated to a free nitride. The solubility of carbon in the mixture of CO with N₂ was significantly higher than that of carbon in the mixture of CO with Ar and is likely due to the formation of cyanide. Thus, when carbon is present in significant quantities in the slag, the solubility of nitrogen in the slag increases. The degree of depolymerization of the slag with increased content of CaO/(SiO₂ + Al₂O₃) and CaF₂ was verified using Fourier transform infrared and Raman spectroscopy.