Surface Technology最新文献

The precipitation of goethite particles by a hydrothermal procedure is described. The reaction involves the oxidation of ferrous ion solutions with hydroxylamine salts at 85 °C.

The phase purity of the oxide is discussed as a function of the solution composition, and in particular of the pH and of the different anions. Scanning electron microscope examinations show that goethite particles are acicular crystals with a rather narrow size distribution. The crystals show prismatic shape and appear to be elongated in the [001] crystallographic direction. The attribution of {110} form to the side faces of the prisms is proposed.

The influence of Cl⁻, F⁻, S²⁻, SO²⁻₄, SiO²⁻₃, Fe³⁺, Al³⁺, Ca²⁺ and Mg²⁺ ions, in phosphoric acid, on the corrosion behaviour of stainless steels 304 and 316, alloys 825, 625, 230 and Hastelloys C and G was investigated. The alloys were tested in 75% H₃PO₄ in the absence and presence of various concentrations of each of the impurities at 85 °C under reflux and stirring conditions. Chloride ion was the most aggressive of the impurities because of its physicochemical properties. The best corrosion resistance in chloride contaminated H₃PO₄ was shown by the alloy containing the highest molybdenum and tungsten contents as an insoluble protective basic molybdenum and tungsten chloride film is formed. The presence of sulphide ion in H₃PO₄ considerably affected the corrosion rate as a result of the increased electrocatalytic activity of the passive film for oxygen reduction as a result of film contamination. Corrosion resistance was improved in such a sulphide environment by increasing the chromium content of the alloys.

The work reported in this paper concerns a study of the anodizing of aluminium in alkaline electrolyte based on borax (sodium tetraborate) using alternating current. Coating thicknesses of 11 μm were produced from 50 g l⁻¹ borax solution the pH of which is adjusted with sodium hydroxide to a value of 10.5 at 65 °C, using a current density of 1.5 A dm⁻². The effect of bath composition, temperature, current density, anodizing time and pH on the rate of build up of oxide coating and their relation to anodizing voltage and coating ratio were studied.

Various AT-cut quartz plates, mechanically lapped or polished prior to etching are etched at a constant temperature. The variations in the dissolution rate with the time of etching are found to depend on the surface damage in the initial stages of the chemical attack, but with prolonged etching all the dissolution rates tend to a common limiting value. Lapped and polished quartz plates exhibit opposite changes in roughness parameters with the depth of etch for short etching times. Subsequent dissolution leads, whatever the original surface preparation of the quartz plate, to equilibrium values of the roughness parameters characterized by the direction of the profilometry traces. Scanning electron micrographs are in agreement with these observations and reveal that pits of the same shape develop on polished and lapped quartz plates. Thus the initial surface damage has no influence on the final surface texture of deeply etched quartz plates which is determined primarily by the crystal orientation.

Electrochemical properties of immobilized ferrocene compounds on high-order pyrolytic graphite (HOPG), and first- and second-order ferricinium decay kinetics for a series of ferrocylidene cyclohexanones and acetophenones and diferrocenylphenylphosphine immobilized on HOPG are described.

The degradation behaviour of a titanium supported RuO₂TiO₂ electrode in HClH₂SO₄ solutions is investigated. In the early stage of electrolysis cracks on the electrode surface grow by dissolution of oxide in the strongly acidified medium, the proton concentration of which is controlled by the main electrolytic reactions. It is concluded that the titanium component in the oxide is responsible for the dissolution of the oxides in the cracks.

Standard nitrogen adsorption isotherms were determined on largely dehydroxylated silica and alumina references, prepared by calcination at 1200 °C for 72 h. The reliability of the reduced adsorption data α_s derived was checked for use in the analysis of experimental isotherms determined on a series of porous silicas and aluminas, prepared by calcination of Davison silica gel and Degussa aluminium oxide C in the range 400–800 °C for 5 h, by comparison with existing standard adsorption data of hydroxylated silica and alumina references. The results obtained demonstrate the importance of having accurate standard data derived from an isotherm determined on a reference solid virtually identical in surface structure with the solid being tested.