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.

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.

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.

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.

Surface area measurements were carried out by nitrogen adsorption at —196 °C on cobalt oxide and on lithium- and ferric-doped cobalt oxides. Thermal products were obtained by calcination in the temperature range 250–1000 °C. Structural and phase changes were studied by differential thermal analysis (DTA) and X-ray techniques.

DTA of samples showed that heating of the pure and doped cobalt hydroxide in air in the temperature range 250–700 °C yields Co₃O₄. On increasing the heating temperature to 800 °C CoO is formed. The dehydration products obtained at temperature less than 500 °C were amorphous to X-rays. Doping with foreign ions causes textural changes in the parent solid.

The settling behaviour of concentrated suspensions of glass ballotini in water and in glycerine-water mixtures is determined. A nominal diameter could be assigned to the various grades of glass ballotini, so the calculation of the diameter from the settling mass of suspended material and the clear supernatant could be checked. The nominal diameters were based on optical microscopy experiments. The value of the diameter can be calculated either by extrapolation of data to infinite dilution conditions or by the use of various formulae which can be represented as modifications of Stokes' Law. It is shown that reasonable results can be obtained in a number of cases. The behaviour of some of the algebraic functions in these calculations is a subject of a detailed analysis. In one set of experiments the data are collected on a monosized dispersion of ballotini but the work is extended to cover suspensions of different sizes.