Hong Yong Sohn

Hydrogen Storage Properties of Nanosized MgH2−0.1TiH2 Prepared by Ultrahigh-Energy−High-Pressure Milling

Magnesium hydride (MgH(2)) is an attractive candidate for solid-state hydrogen storage applications. To improve the kinetics and thermodynamic properties of MgH(2) during dehydrogenation-rehydrogenation cycles, a nanostructured MgH(2)-0.1TiH(2) material system prepared by ultrahigh-energy-high-pressure mechanical milling was investigated. High-resolution transmission electron microscope (TEM) and scanning TEM analysis showed that the grain size of the milled MgH(2)-0.1TiH(2) powder is approximately 5-10 nm with uniform distributions of TiH(2) among MgH(2) particles. Pressure-composition-temperature (PCT) analysis demonstrated that both the nanosize and the addition of TiH(2) contributed to the significant improvement of the kinetics of dehydrogenation and hydrogenation compared to commercial MgH(2). More importantly, PCT cycle analysis demonstrated that the MgH(2)-0.1TiH(2) material system showed excellent cycle stability. The results also showed that the DeltaH value for the dehydrogenation of nanostructured MgH(2)-0.1TiH(2) is significantly lower than that of commercial MgH(2). However, the DeltaS value of the reaction was also lower, which results in minimum net effects of the nanosize and the addition of TiH(2) on the equilibrium pressure of dehydrogenation reaction of MgH(2).

Hydrogenation of Nanocrystalline Mg at Room Temperature in the Presence of TiH2

Magnesium and magnesium-based alloys are considered attractive candidates as rechargeable hydrogen storage materials because of their high hydrogen storage capacities (theoretically up to 7.6 wt %), reversibility, and low cost. In this work, the hydrogenation of nanocrystalline magnesium at room temperature in the presence of TiH(2) was studied. The magnesium was derived by dehydrogenation of nanostructured MgH(2)-0.1TiH(2) prepared by using an ultra-high-energy and high-pressure planetary milling technique. Significant uptake of hydrogen by magnesium at room temperature was observed. The results demonstrate that the nanostructured MgH(2)-0.1TiH(2) system is superior to undoped nano- or micrometer-scaled MgH(2) with respect to the hydrogenation properties of magnesium at room temperature. This finding is potentially useful for a range of energy applications including mobile or stationary hydrogen fuel cells, cooling medium in electricity generation, and differential pressure compressors.

The reduction of stannic oxide with carbon

The rate of reduction of stannic oxide (cassiterite) with carbonaceous materials was investigated in the temperature range 1073 to 1273 K, using thermogravimetic analysis. The effects of the type, the particle size, and the relative amount of carbon were studied. The results indicate that cassiterite is reduced directly to Sn proceeding through the gaseous intermediates of CO and CO2. The overall rate of reduction is controlled by the oxidation of carbon by CO2 ·An energy of activation of 220.9 kj/mole (52.8 kcal/mole) was calculated for the reduction of SnO2 with coconut charcoal within the temperature range 1073 to 1173 K and 323.8 kjJ.mole (77.4 kcalJ.mole) with graphite within the temperature range 1198 to 1273 K.A direct comparison was made between the rate of oxidation of coconut charcoal in CO2- CO mixtures and the rate of reduction of SnO2 with coconut charcoal, which are not in agreement. The reason for this disagreement was found to be the catalytic action of the tin formed during the reduction.

Development of green suspension ironmaking technology based on hydrogen reduction of iron oxide concentrate: rate measurements

Abstract A novel ironmaking technology is under development at the University of Utah. This technology produces iron directly from fine iron oxide concentrate by a gas–solid suspension reduction, utilising hydrogen as the main reducing agent for high reactivity, for the elimination of carbon dioxide release during ironmaking operations and also pursuing the direct use of concentrates to bypass the problematic pelletisation/sintering and cokemaking steps in the steel industry. This paper is mainly focused on the kinetic feasibility tests of the proposed process showing that the reduction rate was fast enough to obtain 90–99% reduction within 1–7 s at 1200–1500°C, depending on the amount of excess hydrogen supplied with the iron oxide. This indicates that the reduction rate of concentrate particles by hydrogen containing gases is sufficiently fast for a suspension reduction process and forms the most important basis for the new technology.

Mathematical modeling of sulfide flash smelting process: Part I. Model development and verification with laboratory and pilot plant measurements for chalcopyrite concentrate smelting

A mathematical model has been developed to describe the various processes occurring in a flash furnace shaft. The model incorporates turbulent fluid dynamics, chemical reaction kinetics, and heat and mass transfer. The key features include the use of thek-ε turbulence model, incorporating the effect of particles on the turbulence, and the four-flux model for radiative heat transfer. The model predictions were compared with measurements obtained in a laboratory flash furnace and a pilot plant flash furnace. Good agreement was obtained between the predicted and measured data in terms of the SO2 and O2 concentrations, the amount of sulfur remaining in the particles, and the gas temperature. Model predictions show that the reactions of sulfide particles are mostly completed within about 1 m of the burner, and the double-entry burner system with radial feeding of the concentrate particles gives better performance than the singleentry burner system. The model thus verified was used to further predict various aspects of industrial flash furnace operation. The results indicate that from the viewpoint of sulfide oxidation, smelting rate can be substantially increased in most existing industrial flash furnaces.

The selective chlorination of iron from llmenite ore by CO-Cl2 mixtures: Part I. intrinsic kinetics

The intrinsic kinetics of the selective chlorination of iron from ilmenite ore using carbon monoxide as the reducing agent were studied in a shallow fluidized bed. Experiments on the effects of chlorination temperature, carbon monoxide and chlorine gas partial pressures, and particle size were conducted in the absence of mass- and heat-transfer influences. Results indicate that the kinetics in the temperature range 923 to 1123 K are represented by the following pore-blocking rate law: λ[ exp (XFe/λ) − 1 ] = 33.7 exp (− E/RT)pco0.5220.32t where E is 37.2 kJ/mol and p and t are in atm (=101.3 kPa) and minutes, respectively. The partial pressure of carbon monoxide was found to affect the chlorination rate more strongly than that of chlorine. A reaction mechanism in which iron in ilmenite reacts with chlorine before the liberated oxygen is removed by carbon monoxide is proposed.

Sodium aluminate leaching and desilication in lime-soda sinter process for alumina from coal wastes

Sodium aluminate in the sinter produced from coal wastes using the lime-soda sinter process can be leached with dilute alkaline solutions. The extraction of alumina by leaching with water and sodium hydroxide solutions was comparable to extraction by leaching with Na2CO3 solutions. However, leaching with water dissolved the least amount of silica. The optimal conditions for water leaching were determined to be temperatures of 60 to 70 °C and times of 30 to 40 minutes. The sodium aluminate solution obtained under these conditions readily responded to desilication with Ca(OH)2 suspensions at atmospheric pressure, reducing the silica-to-alumina ratio to less than 10-3, which is lower than the specification for reduction-grade alumina.

Mathematical modeling of minor-element behavior in flash smelting of copper concentrates and flash converting of copper mattes

A mathematical model has been developed to describe the behavior of minor elements during flash smelting and flash converting. The model incorporates equations describing volatilization of minor elements from the molten particles and distribution of these elements between the molten phases in the settler. The basic premise of the volatilization model is that at the surface of the molten particle, the partial pressures of the minor-element species are those at equilibrium. Transport of the minor-element species to the gas then is described by external mass transfer. Good agreement has been obtained between observed and predicted behaviors. The effects of oxygen enrichment, matte grade, and wall temperature, as well as the bath temperature, on minor-element behavior have been elucidated.

Intrinsic kinetics of the oxidation of chalcopyrite particles under isothermal and nonisothermal conditions

The overall kinetics of oxidation of chalcopyrite in the absence of heat- and mass-transfer effects were studied for temperatures up to 1150 K. Experiments were conducted using a nonisothermal technique. Below 873 K, the pore-blocking model was applicable with an activation energy of 71 kJ/mol in the temperature range 754 to 873 K and 215 kJ/mol below 754 K. Above 873 K, the rate of sulfur vaporization dominates the kinetics of oxidation in the initial stage. The oxidation of the decomposition product above 873 K is described by power-law kinetics. The kinetics of sulfur vaporization were found to follow the power-law kinetics with an activation energy of 208 kJ/mol. The results indicate that the oxidation rate is first order with respect to oxygen concentration and inversely proportional to the square of the particle size over the entire range of temperatures studied. Predominance area diagrams were constructed at various temperatures and used in conjunction with X-ray analyses of partially oxidized samples to determine the intermediate phases formed during the reaction. This analysis also provides a justification for the kinetic models used.

Sintering kinetics and alumina yield in lime-soda sinter process for alumina from coal wastes

An investigation of the application of the lime-soda sinter process to alumina extraction from coal wastes has been carried out. In the sintering stage, the optimal operating conditions have been obtained for the highest yield of alumina. The kinetics of sodium aluminate formation have also been studied in the sintering stage. The sinter mixes have been fired isothermally in air in the temperature range 1100 to 1350 °C. Alumina recovery of about 80 pct has been obtained by sintering coal-waste mixes having molar ratios of Na2O/Al2O3 = 1.3 and CaO/SiO2 = 1.8 at 1200 to 1250 °C for 20 to 30 minutes. Insoluble alumina compounds are responsible for the incomplete recovery. The major sinter components are identified as sodium aluminate and β-dicalcium silicate. The nucleation and growth kinetics equation is used to correlate the experimental data of sodium aluminate formation obtained under atmospheric pressure in the temperature range 1000 to 1200 °C. An activation energy of 286 kJ/mol has been calculated for fine coal-waste powder mixtures.