Investigation of Cobalt (II)-Tungsten (Vl)-Oxide Reduction in Hydrogen: Part II

CoWO₄ monocrystals were prepared by the flux growth method and their reduction in pure hydrogen was investigated for comparison with that of powdery specimen S1 (Part I). Here again phaseϕ is observed, besideβ-W, as a low temperature reaction product (from which cph-Co₃W alloy crystallizes at higher temperatures). Present results tend to show that ϕ can most logically be regarded as a noncrystalline alloy with defined composition Co 25 at. pct W(i.e. Co₃W), similar to that whose characteristics and electrodeposition conditions are reported in the literature.     

由氢还原草酸钴和氧化钴制取金属钴粉的物理性能

在400—580℃温度范围内用氢气将草酸钴和氧化钴还原为金属钴粉,研究了原料粒度和还原温度对钴粉粒度、比表面、松装密度和摇实密度的影响,讨论了还原期间在不同原料表面上发生的局部化学反应机理。结果表明,用草酸钴可制得具有费氏粒度0.5μm、BET 比表面400000cm~2/cm~3的极细钴粉,得自草酸钴的钴粉还具有易于研磨的脆性多孔结构。对于形成多孔产物相的固体物质的分解和还原反应,作者推出了产物核心粒度的计算式。D=1.96(V′/V~p)~(1/2)(G/N)~(1/3)=1.96(V′/V~p)~(1/2)·A·e~(-(E_g-E_(?))/(3RT))     

Cr(VI) Reduction in Continuous-Flow Coculture Bioreactor

A continuous-flow coculture bioreactor with a phenol-degrading organism, Pseudomonas putida DMP-1, and a Cr(VI)-reducing species, Escherichia coli ATCC 33456, was developed for simultaneous removal of phenol and Cr(VI). Phenol was the sole energy and carbon source added to the coculture along with a basal medium and hexavalent chromium. The coculture bioreactor was operated under three liquid detention times (0.20, 0.31, and 0.52 days) with phenol and Cr(VI) loadings ranging from 2,500 to 8,200 mg∕L∕day and 4.5–33.2 mg∕L∕day, respectively. After 279 days of continuous operation, eight quasi-steady-state operation conditions were obtained with near complete removal of phenol and Cr(VI). Elevated levels of Cr(VI) and phenol were observed in the effluent under a high influent Cr(VI) concentration (16 mg∕L) or a short liquid detention time (0.20 days). The system recovered from Cr(VI) toxicity after influent Cr(VI) level was reduced. Chromium mass balance analysis revealed that nearly all of the influent Cr(VI) was reduced to Cr(III) in the coculture bioreactor through biological activity. Spectra of UV-Vis and mass spectrometers suggested that phenol metabolites produced by P. putida were utilized by E. coli.     

Hydrogen transport during deformation in nickel: Part I. Polycrystalline nickel

The electrochemical permeation technique was used to study the effects of deformation on the steady state flux of hydrogen in polycrystalline nickel 270. The hydrogen flux change was found to depend strongly on strain rate. At fast strain rates, the hydrogen flux decreased due to dynamic trapping by newly created dislocations. At slow strain rates, new traps were created more slowly with time and the lattice had a chance to be refilled with hydrogen from the charging surface. Lattice refilling masks the trapping effect so that less of a decrease in hydrogen flux was observed. Under the conditions of total lattice refilling, a decrease in specimen thickness and an increase in input concentration resulted in an increase in the permeation flux. No evidence of dislocation transport was observed in polycrystalline nickel. Formerly Graduate Student, The H.H. Uhlig Corrosion Laboratory, Massachusetts Institute of Technology, Cambridge, MA 02139.     

Hydrogen transport during deformation in nickel: Part II. Single crystal nickel

Direct evidence for dislocation transport of hydrogen was observed in nickel single crystal slices using the electrochemical permeation technique modified to allow for simultaneous deformation. The hydrogen flux increased in the easy glide region of deformation even after accounting for the effects of a decrease in specimen thickness. At a fast strain rate the only explanation for this increase is dislocation transport. Formerly Graduate Student, The H. H. Uhlig Corrosion Laboratory, Massachusetts Institute of Technology, Cambridge, MA 02139.     

高压氢还原制备钴包球形碳化钨的工艺研究

钴包碳化钨粉是一种用于等离子、爆炸喷涂工艺的复合型粉末材料,广泛应用于航天、航空和冶金等部门的特殊环境下。本文采用高压氢还原的湿法冶金工艺制备了高质量钴包碳化钨粉末。讨论了不同工艺参数如催化剂、试验温度、硫酸铵、氨水及氧分压等,对碳化钨粉末的钴包覆质量的影响。探究发现,最初的敏化和活化处理非常重要。通过大量实验结果得到制备包覆完整的球形碳化钨/钴颗粒合适的工艺参数。     

Gaseous reduction of iron oxides: Part I. Reduction of hematite in hydrogen

The reduction of high-grade hematite ore in hydrogen has been investigated. There is an unusual temperature effect for small granules with a dip in the rate at about 700°C, similar to those reported by previous investigators for different types of iron oxides. The particlesize effect on the time of reduction suggests that there are three major limiting rate-controlling processes: i) uniform internal reduction, ii) limiting mixed control and iii) gas diffusion in porous iron layer. Processes (ii) and (iii) are special cases of a so-called topochemical mode of reduction associated with the formation of product layers. Unidirectional reduction experiments revealed the significant role played by gas diffusion in porous iron layer as a rate-controlling process. The effective H₂-H₂O diffusivity in porous iron derived from, the reduction data is found to decrease markedly with decreasing reduction temperature. This is consistent with the fracture surfaces of porous iron as viewed by scanning electron microscopy. The present interpretation of the rate of reduction of hematite ore is found to apply equally well to previously published data on the hydrogen-reduction of natural and synthetic hematite pellets.     

Cyclooxygenase-2 inhibitors in tumorigenesis (Part II)

The rate-limiting step in arachidonate metabolism is mediated by enzymes known as cyclooxygenases (COXs). These enzymes catalyze the biosynthesis of prostaglandin H2, the precursor of molecules such as prostaglandins, prostacyclin, and thromboxanes. The COX enzyme family consists of the classical COX-1 enzyme, which is constitutively expressed in many tissues, and a second isozyme, i.e., COX-2, which is induced by various stimuli, such as mitogens and cytokines, and is involved in many inflammatory reactions. Because nonsteroidal anti-inflammatory drugs (NSAIDs) inhibit both COX-1 and COX-2, these drugs also cause unwanted side effects, exemplified by gastrointestinal bleeding. Accumulating evidence indicates that NSAIDs can reduce the incidence of colorectal cancers in human and experimental animals and can reduce the number and size of polyps in patients with familial adenomatous polyposis. This Part II (of a two-part review) focuses on the growing clinical and experimental evidence that NSAIDS and COX-2 inhibitors can influence the risk of colon (and possibly of other) cancers.     

Modeling Cr(VI) Reduction and Phenol Degradation in a Coculture Biofilm Reactor

A transient-state model was developed to simulate simultaneous Cr(VI) reduction and phenol degradation by a coculture of Cr(VI)-reducing/phenol-degrading bacteria growing on glass bead surfaces in a fixed-film bioreactor. The coculture consisted of the Cr(VI) reducers, Escherichia coli ATCC 33456, and the phenol degraders, Pseudomonas putida DMP-1. Phenol was supplied as the sole added carbon source and electron donor. The model simulated cell growth kinetics with E. coli utilizing metabolites formed from phenol degradation in P. putida as carbon sources. Substrate utilization and Cr(VI) reduction in the fixed-film bioreactor was represented by a system of (second-order) partial differential equations (PDEs). The PDE system was solved by the fourth-order Runge–Kutta method adjusted for mass transport resistance by the second-order Crank–Nicholson and backward Euler methods. A heuristic procedure, genetic search algorithm, was used to optimize the model against experimental data. The model predicted effluent concentration with 98.6% confidence for Cr(VI), 93.4% confidence for phenol, and 88.3% confidence for metabolites. Parameters determined showed higher Cr(VI) and phenol removal kinetics in the biofilm system than previously observed in batch systems.     

Reduction of phosphate ore by carbon: Part II. Rate limiting steps

Considerations of intraparticle mass transport processes are presented for the reduction of phosphate ore by carbon in the presence of silica. Under conditions of temperature and composition which produce reaction rates of commercial interest, the conversion is limited by product mass transport away from the reaction sites. This results in a pseudo-first order dependence of conversion on reaction time which is explained by our model. Thermochemical data derived from conversion is consistent with published data on heat of formation. At lower temperatures, where the reaction is limited by reactant diffusion in a silicate melt, contained within the overall matrix, diffusivities and activation energy were measured. Detailed diffusion studies were conducted in a graphite crucible where the interfacial reaction between the apatite-silica mixture and the graphite boundary could be detected. A mathematical model based on diffusion theory was developed, and it was found to be consistent with the diffusion data and the overall conversion at lower temperature.     

Investigation of Freeze-Linings in Copper-Containing Slag Systems: Part I. Preliminary Experiments

Slag freeze-linings are increasingly used in industrial pyrometallurgical processes to insure that furnace integrity is maintained in aggressive high-temperature environments. Most previous studies of freeze-linings have analyzed the formation of slag deposits based solely on heat-transfer models. The focus of the present research is to determine the impact of slag chemistry and local process conditions on the microstructures, thickness, stability, and heat-transfer characteristics of the frozen deposit at steady-state conditions. The formation of the freeze-linings is studied under controlled laboratory conditions using an air-cooled “cold-finger” technique for Cu-Fe-Si-Al-O slag at equilibrium with metallic copper relevant to the industrial copper smelting processes. The phase assemblages and microstructures of the deposits formed in the cold-finger experiments differ significantly from those expected from phase equilibrium considerations. The freeze-lining deposits have been found, in general, to consist of several layers. Starting from the cold finger, these layers consist of glass; glass with microcrystalline precipitates; closed crystalline layer; and open crystalline layer. Even at steady-state conditions, there was no primary phase sealing layer of delafossite [Cu₂O · (Al, Fe)₂O₃] present at the deposit/liquid interface—these observations differ markedly from those expected from phase equilibrium considerations. The findings have significant practical implications, and potential for the improved design and operation of industrial metallurgical furnaces.     

Gas Atomization of Amorphous Aluminum Powder: Part II. Experimental Investigation

The optimal processing parameters that are required to atomize amorphous Al were established on the basis of numerical simulations in part I of this study. In this part II, the characterization of cooling rate experienced by gas-atomized, Al-based amorphous powders was studied via experiments. An experimental investigation was implemented to validate the numerical predictions reported in part I of this study. The cooling rate experienced by the powders, for example, was experimentally determined on the basis of dendrite arm spacing correlations, and the results were compared with the numerical predictions. The experimental studies were completed using commercial Al 2024 as a baseline material and Al₉₀Gd₇Ni₂Fe₁ metallic glass (MG). The results showed that the cooling rate of droplets increases with decreasing particle size, with an increasing proportion of helium in the atomization gas and with increasing melt superheat. The experimental results reported in this article suggest good agreement between experiments and numerical simulations.     

Trace Elements in the Si Furnace. Part I: Behavior of Impurities in Quartz During Reduction

Quartz and carbonaceous materials, which are used in the production of silicon as well as electrodes and refractories in the silicon furnace, contain trace elements mostly in the form of oxides. These oxides can be reduced to gaseous compounds and leave the furnace or stay in the reaction products—metal and slag. This article examines the behavior of trace elements in hydrothermal quartz and quartzite in the reaction of SiO₂ with Si or SiC. Mixtures of SiO₂ (quartz or quartzite), SiC, and Si in forms of lumps or pellets were heated to 1923 K and 2123 K (1650°C and 1850°C) in high purity graphite crucibles under Argon gas flow. The gaseous compounds condensed in the inner lining of the tube attached to the crucible. The phases present in the reacted charge and the collected condensates were studied quantitatively by X-ray diffraction (XRD) and qualitatively by Electron Probe Micro Analyzer (EPMA). Contaminants in the charge materials, reacted charge and condensate were analyzed by Inductively Coupled Plasma-Mass Spectroscopy (ICP-MS). Muscovite in the mineral phase of quartz melted and formed two immiscible liquid phases: an Al-rich melt at the core of the mineral, and a SiO₂-rich melt at the mineral boundaries. B, Mn, and Pb in quartz were removed during heating in reducing atmosphere at temperature above 1923 K (1650°C). Mn, Fe, Al and B diffused from quartz into silicon. P concentration was under the detection limit. Quartzite and hydrothermal quartz had different initial impurity levels: quartzite remained more impure after reduction experiment but approached purity of hydrothermal quartz upon silica reduction.     

Precipitation of K-V(V)-Oxide from V(IV) Sulfate Solution by Ozonation

Abstract

The oxidative precipitation of vanadium(IV) from its sulfate solutions with ozone has been investigated. During the ozonation, the solution pH was maintained constant by consuming the liberated hydrogen ion with drops of KOH solution. Chemical analysis of the precipitates showed that the values of x and y for the final solid product, K_xV₂O_y are from 0.30-0.47 (depending on pH) and 5.0, respectively. X-ray diffraction revealed that these potassium-incorporating vanadium(V) oxides have the basic structure of V₂O₅. The progress of oxidation of vanadium(IV) and precipitation of vanadium(V) were monitored by determining the concentrations of vanadium(IV) and vanadium(V) remaining in the solution and by ORP measurement. The rate of ozonation of vanadium(IV) increases with increasing pH, while the precipitation of vanadium(V) proceeds favourably at pH 1.5 at 25 °C and at pH 2.0 at 70 °C. A rise in temperature accelerates the oxidative precipitation of vanadium(IV) to make recovery of vanadium ion effective.