Synthesis and characterization of molybdenum disulphide formed from ammonium tetrathiomolybdate

An investigation has been carried out into the possibility of in situ formation of MoS2 within porous anodic films on aluminium, to improve subsequent tribological behaviour, by re-anodizing in thiomolybdate electrolyte. Acidification of thiomolybdate was employed to simulate the conditions for formation of the sulphide at the anodic film/electrolyte interface, followed by appropriate vacuum heat treatments to study possible temperature effects on the sulphide due to either friction or Joule heating during anodizing. The products of both acidification and heat treatment, characterized by X-ray powder diffraction and scanning electron microscopy, were compared with those formed by direct thermal decomposition of ammonium tetrathiomolybdate crystals. The precipitate formed by acidification was mainly amorphous molybdenum trisulphide (MoS3), which on heat treatment at 450 and 850°C yielded 3R-MoS2. 3R-MoS2 also formed by the thermal decomposition of thiomolybdate crystals. Thermogravimetric and differential thermal analyses showed that the decomposition of MoS3 to MoS2 occurred in the range 220–370°C and revealed the sequence of reaction steps. The findings suggest that mainly amorphous MoS3 is formed as a consequence of changes in the pH of the film/electrolyte interface during re-anodizing but the product is relatively easily transformed to crystalline MoS2 on moderate heating which may occur during wear processes.     

CHARACTERISATION OF PATTERNS OF CHEWING BEHAVIOUR IN HUMAN SUBJECTS AND THEIR INFLUENCE ON TEXTURE PERCEPTION

Electromyography was used as a noninvasive and unobtrusive technique to characterise chewing patterns for a range of foods. Differences between subjects for a variety of aspects of chewing sequence are recorded for a range of foods (carrot, apple, roast pork, salami, biscuit and toast). Identifiable subgroups of subjects differing in chewing behaviour existed within the random sample of 52 dentate subjects. The five subgroups accounted for 52%, 21%, 11%, 10% and 6% of the sample population. Major discriminating factors between the behavioural groups lie in their chewing time and the muscle work rate during chewing. Sensory ratings for firmness and rubberiness of model foods differed significantly between the subjects exhibiting different chewing behaviours. Chewing behaviour may influence consumers' perceptions about the texture of a food.     

High-pressure-induced changes in bovine milk: a review

High-pressure (HP) treatment of food products is a novel processing technique during which the product is treated in a vessel of suitable strength at a high pressure, generally in the range 100–1000 MPa. As a result, several constituents and properties of the treated product are altered. HP-induced changes in the constituents and properties of milk are arguably among the most extensive of the range of food products studied to date. HP treatment of milk induces solubilization of minerals associated with the casein micelles, denatures whey proteins and, depending on pressure, can either induce aggregation or disruption of the casein micelles. These HP-induced changes in milk constituents affect the properties of the milk; cheesemaking properties of milk can be enhanced considerably, indicating potential application of HP treatment in this area; furthermore, encouraging results have also been reported for HP treatment of milk prior to yogurt manufacture. HP treatment of milk also affects its microflora; however, considerable variation in baroresistance between bacterial species and strains exists. Further applied research appears warranted to establish the full commercial potential of HP treatment of milk.     

Stability of Aqueous α-Al2O3 Suspensions with Poly(methacrylic acid) Polyelectrolyte

Stability of aqueous α-Al₂O₃ suspensions with Na⁺ salt of poly(methacrylic acid) (PMAA-Na) polyelectrolyte was studied as a function of pH. At a given pH, the transition from the flocculated to the dispersed state corresponded to the adsorption saturation limit of the powders by the PMAA. As the pH was decreased, the adsorption saturation limit increased until insolubility and charge neutralization of the PMAA was approached. The critical amount of PMAA required to achieve stability is outlined in a stability map.     

Pressure Acid Leaching of Nickel Laterites: A Review

Abstract

A review of the literature over the past 30 years on the processing of nickel laterites by high temperature acid leaching has been carried out to provide a better understanding of the mineralogy, leaching process chemistry and effect of operating conditions on nickel recovery, residue properties and scaling. Particular attention is paid to the leaching experience of the commercial Moa Bay plant and to the recently reported testwork and flowsheets associated with the three Western Australia lalerite plants that will be operating in 1999.

It is shown that laterites can vary significantly in their mineralogy according to location, climate and depth, and that the main host minerals for nickel and cobalt can be either goethite (iron oxide) or nontronite (clay) or manganese oxides. The mechanism of leaching involves acid dissolution of the host mineral lattice followed by hydrolysis and precipitation (transformation) of a variety of insoluble oxides and sulphates of iron, aluminium and silica under the high temperature conditions. Optimum leaching conditions and final liquor composition varies according to the ore mineralogy. More fundamental studies have demonstrated that the rate of leaching and character of the residue is dependent upon the level of Mg, Mn and Cr in the ore, the Eh of the slurry and salinity of the process water.

A number of studies are reviewed on the chemistry and precipitation of iron, aluminium, magnesium and silica to understand how the process conditions affect the solubility of the species and the nature of the scale which they form. Early work at Moa Bay indicates that the incorporation of chromium into alunite scale also affects the incorporation of silica and nickel and the settling of the residues. Various types of scale have been identified during different stages of leaching and possible means of minimising scale are discussed.

The clay-rich nickel laterites in Western Australia differ from Moa Bay laterite in mineralogy and have comparatively high silica and low chromium content. Since no commercial plant has previously processed such ores or used saline process water, there is little published in this area. It is therefore recommended that further research be carried out on understanding the process chemistry and species equilibrium from various ore types under autoclave conditions.     

Corrosion of Lead Glasses in Acid Media: I, Leaching Kinetics

The leaching kinetics of lead glasses (25 to 35 mol% PbO-75 to 65 mol% SiO₂; some with K₂O and A1₂O₃, additions) were determined in 10% acetic acid. Except for a ternary glass (SiO₂-PbO-K₂O) which had a linear dependence on time, all compositions exhibited a linear dependence on the square root of time for the amount of Pb and K removed. Increasing the SiO₂: PbO ratio or the Al₂O₃ content improved the durability whereas adding K₂O to a binary PbO-Si0₂ glass greatly increased the corrosion rate. Activation energies for the rates of Pb and K removal were determined for three compositions and it was deduced that the diffusion of H⁺ controlled the leaching for binary and 4-component glasses whereas dissolution of the silica network was rate-controlling for the ternary.     

Soil moisture estimation over grass-covered areas using AIRSAR

An empirical study of the relation between the AIRSAR's signals and land surface parameters is conducted using data collected during MACEUROPE' 91. General additive regression models are fitted to the data simulated from a calibrated microwave backscattering model. A comparison between the model predictions and field observations indicates that the regression models are good predictors to the AIRSAR's signals over the grass-covered areas. Based on the regression relationships, a soil moisture retrieval algorithm combining the Lvband multi-polarization AIRSAR data is proposed and used to create spatial soil moisture maps of the Slapton Wood catchment.     

CASTLES IN TORONTO'S SKY: CONDO‐ISM AS URBAN TRANSFORMATION

This article analyzes the evolution and spatial dynamics of condominium development in Toronto, the largest housing market in Canada and the site of a rapid take‐up of condominium tenure and construction over the last 40 years. The article probes the most influential policies that fostered and regulated condominium growth, and explores the implications for the continued restructuring of the city. A host of factors, including neoliberal state policies, have played a decisive role in fostering what we term condo‐ism, referring to an emerging nexus of economic development, finance, and consumption sector interests that have coalesced around condominium construction and culture. Policies have redirected growth to the urban core, channeled capital investments and young residents, and promoted gentrification, ultimately transforming the character of Toronto's central business district. The article explores these changes, and discusses their implications for contemporary emerging forms of capitalist urbanization and restructuring of the city.