The liquidus surface and tie-lines in the iron-cobalt-sulfur system between 1473 and 1623 K

The liquidus surface and tie-lines in the iron-cobalt-sulfur ternary system have been determined between 1473 and 1623 K. The experiments were conducted by equilibrating the liquid sulfide phase with the metallic alloy phase. The liquid sulfide phase was sampled and chemically analyzed. The alloy phase was analyzed by electron microprobe. Combining the present results with the available literature data, the thermodynamic properties of this system were calculated.     

Chloride metallurgy: PGM recovery and titanium dioxide production

This paper examines in detail the thermodynamics and application of chloride metallurgy for the extraction of precious metals, such as gold and silver, and platinum-group metals. The advantages with regard to the solubilities of metal ion species and their reduction potentials in chloride media are discussed with examples. The use of chloride media for the extraction of platinum-group metals from spent autocatalysts and for the production of high-purity pigment-grade TiO₂ and titanium metal from ilmenite feed stocks is discussed in the case studies provided. For more information, contact V.I. Lakshmanan, Process Research Ortech, 2395 Speakman Dr., Mississauga, ON, L5K 1B3 Canada; (905) 822-4941; fax (905) 822-9537.     

Morphological Forms of α-Alumina Particles Synthesized in 1,4-Butanediol Solution

Phase-pure, monodispersed, hexagonal plates of single-crystal α-alumina (∼ 2 μm wide and ∼0.5 μm thick) have been prepared via precipitation by treating an aluminum hydrous oxide precursor in 1,4-butanediol at 300°C under autogenous vapor pressure. Present work shows that KOH is the only reagent that precipitates an aluminum hydrous oxide precursor suitable to synthesize α-alumina in 1,4-butanediol solution. In contrast, the use of NaOH or NH₄OH as the precipitating reagent for the precursor material does not yield the alpha phase. The solution pH at which the precursor materials are precipitated is also a critical factor for the formation of α-Al₂O₃. Phase-pure α-alumina powders were also only synthesized from the aluminum hydrous oxide precursors precipitated in the pH range from 10 to 10.5. The results of X-ray diffraction and scanning electron microscopy indicate that longer reaction times promote the phase transformation from the intermediate boehmite phase to α-alumina. The complete transformation from boehmite to α-alumina requires reaction times of about 12 h.     

Anionic Clays as Potential Slow-Release Fertilizers: Nitrate Ion Exchange

Several nitrate containing anionic clays were synthesized at different temperatures and the kinetics of NO₃ ^– release were determined to test their suitability as slow-release N fertilizers. A sample (Mg:Al = 2:1) synthesized at 60°C with smaller particle size released 75, 86 and 100% of its NO₃ ^– in 1, 3 and 7 days, respectively when equilibrated with a simulated soil solution. On the other hand, the 175°C/2 hrs sample with larger particle size released 65, 77 and 84% of its nitrate in 1, 3 and 7 days, respectively. Another anionic clay (synthesized at 175°C/24 hrs) of higher charge density (Mg:Al = 2:1) containing NO₃ ^– was equilibrated with a 0.012 N NaCl or Na₂CO₃ to test the role of different anions in releasing the NO₃ ^– anion from the interlayers. The results showed that Cl^– released more NO₃ ^– than did CO₃ ^2– from this anionic clay after all the treatment times probably as a result of the CO₃ ^2– anion blocking the release of NO₃ ^– from the interior of the crystals. When a lower charge density (Mg:Al = 3:1) sample (synthesized at 175°C/48 hrs) was equilibrated with 0.02N solution of anions the release of nitrate was as follows: Cl^– < F^– < SO₄ ⁼ CO₃ ^2–. These results suggest that the divalent SO₄ ⁼ and CO₃ ^2– anions are more effective in the release of NO₃ ^– from this lower charge density anionic clay. Time-resolved structural analysis of NO₃ ^– exchange with CO₃ ^2– in the above anionic clay using synchrotron x-ray diffraction showed that ion exchange is rapid because of small crystal size and lower charge density. Thus the release of NO₃ ^– from anionic clays is an interplay among the type of anions present in soil solution, their concentration, pH of soil solution, the charge density and crystal size of anionic clay etc.     

Porous mullite ceramics through diphasic gels of large boehmite and small silica particles

Mullite formation process has been studied in stoichiometric mullite (3Al₂O₃·2SiO₂) diphasic gel containing large boehmite (1 m) and small silica (10 nm) particles. It has been found that initial mullitization did not take place inside the silica phase (cristobalite), but took place in the defect -alumina phase. -alumina was stabilized by silica when the temperature was below 1350°C. At temperatures above 1350°C, mullite crystallized directly. It was suggested that silica diffused into the pores (<1.8 nm) of -alumina and prevented the collapse of -alumina pore structure. On the other hand, when silica was not present, the pore structure of -alumina collapsed and -alumina crystallized at 1100°C. Porous mullite ceramics were obtained by using special diphasic gels containing large boehmite and small silica particles.     

Dehydration of tetrahydrofuran by pervaporation using crosslinked PVA/PEI blend membranes

Dense blend membranes were prepared by blending hydrophilic polymers poly(vinyl alcohol) (PVA) and poly(ethyleneimine) (PEI), which were then crosslinked by glutaraldehyde (GA) in a mixture of solvents under the catalysis of hydrochloric acid (HCl) for the dehydration of tetrahydrofuran (THF) by pervaporation. The effect of experimental parameters such as feed water concentration, permeate pressure, and membrane thicknesses on permeate parameters, i.e., flux and selectivity were determined with feed water concentration less than 40 wt %. The membranes were found to have good potential for breaking the azeotrope of 94 wt % THF with a flux of 1.072 and 0.376 kg/m² h for plane PVA/PEI and crosslinked PVA/PEI blend membrane, which exhibited high selectivity of 156 and 579 respectively. Selectivity was found to improve with decreasing feed water concentration and increasing membrane thickness, whereas flux decreased correspondingly. High permeate pressure causes a reduction in both flux and selectivity. These effects were clearly elucidated with the aid of the known relationship among plasticization effect, degree of swelling, permeate pressure, and feed water concentration. These blend membranes were also subjected to sorption studies to evaluate the extent of interaction and degree of swelling in pure as well as binary feed mixtures. Further ion exchange capacity studies were carried out for all the crosslinked and uncrosslinked membranes to determine the total number of interacting groups present in the membranes. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 1152–1161, 2006     

Sequestration of Cesium and Strontium by Tobermorite Synthesized from Fly Ashes

Tobermorites were synthesized from oxides and from fly ashes under mild hydrothermal conditions. The bulk compositions of the ash-based formulations were adjusted to give the same [Ca]/[Si + Al] ratio as for the oxides. Selective Cs and Sr exchange with these tobermorites was measured. Compared to those prepared from the oxides and from class C fly ash, the tobermorites obtained from class F fly ash exhibited superior Cs and Sr selective properties. This is apparently a result of more extensive Al incorporation with class F fly ash. For example, tobermorite synthesized from class F fly ash exhibited a cesium K _d (mL/g) of 3826 while those prepared from oxides and from class C fly ash showed K _d values of 1112 and 796, respectively, under the same conditions. These results suggest that fly ash waste materials can be converted into tobermorite, which can serve as a resource in the separation, immobilization, and disposal of radioactive species such as Cs and Sr.     

Nanocomposite route to the stabilization of porous ϑ-alumina

Stabilization of -alumina phase by silica was studied in nanocomposite (diphasic) alumina-silica gels by XRD and BET surface areas measurements. Five wt.% of silica (22 nm particles) increased the crystallization temperature of to -alumina by about 100°C from boehmite (10 nm particles) derived alumina. Stabilization of -alumina was caused by the formation of intimate contact (Al-O-Si) between components by diffusion of silica into the defect alumina structure.Also with the Department of Agronomy.     

Microwave-Hydrothermal Processing of BiFeO3 and CsAl2PO6

Microwave-hydrothermal (M-H) processing was compared with conventional-hydrothermal (C-H) processing in the crystallization of BiFeO₃ and CsAl₂PO₆ phases. The presence of the microwave field led to accelerated kinetics of the crystallization of both these phases as detected by powder X-ray diffraction. The acceleration of reaction rates under microwave field is expected to lead to energy savings during ceramic processing.     

Ameliorating effect of silica addition in the anode-catalyst layer of the membrane electrode assemblies for polymer electrolyte fuel cells

Incorporation of silica particles through a sol-gel process into the anode-catalyst layer with a sol-gel modified Nafion-silica composite membrane renders easy retention of back-diffused water from the cathode to anode through the composite membrane electrolyte, increases the catalyst-layer wettability and improves the performance of the Polymer Electrolyte Fuel Cell (PEFC) while operating under relative humidity (RH) values ranging between 18% and 100% with gaseous hydrogen and oxygen reactants at atmospheric pressure. A peak power density of 300 mW cm⁻² is achieved at a load current-density value of 1200 mA cm⁻² for the PEFC employing a sol-gel modified Nafion-silica composite membrane and operating at 18% RH. Under similar operating conditions, the PEFC with a Membrane Electrode Assembly (MEA) comprising Nafion-silica composite membrane with silica in the anode-catalyst layer delivers a peak power density of 375 mW cm⁻². By comparison, the PEFC employing commercial Nafion membrane fails to deliver satisfactory performance at 18% RH due to the limited availability of water at its anode, acerbated electro-osmotic drag of water from anode to cathode and insufficient water back diffusion from cathode to anode causing the MEA to dehydrate.