Surface Technology最新文献

The porous structure and surface area of alumina-supported cobalt molybdena catalysts were examined as functions of their activation conditions. It was revealed that the process of reduction by hydrogen as well as simultaneous reduction — sulphiding by a hydrogen and hydrogen sulphide mixture — results in the disappearance of pores of larger diameters. This is caused by the formation of monomeric, dimeric and/or polymeric species on pore surfaces as a result of thermal activation in hydrogen and H₂-H₂S atmospheres.

On the basis of the shapes of the hysteresis loops of nitrogen adsorption-desorption isotherms and on t plots of the samples investigated it was found that the dominant pores are those with diameters in the mesopore range.

The shapes of the mesopores resemble tubular capillaries with diameters o of various size and/or tubular capillaries with short necks and wide sloping bodies. Some of the mesopores can be closed at one end.

The uniformity of pore sizes appearing after the H₂-H₂S treatment provides good conditions for the diffusion of reactant molecules of large diameter. This is especially important for such catalytic reactions as depolymerization of asphaltenes, hydrodemetallization of metal porphyrins and other hydrotreatment processes.

The kinetics and the mechanism of organic film growth during the cathodic electrodeposition process are investigated by galvanostatic and constant voltage methods. Constant voltage experiments carried out at lower voltages enabled the more accurate observation of current density changes and enabled the proposal of a mathematical model which gives a consistent picture of film growth kinetics. It was shown that the film thickness increases with time but a limiting value was not achieved.

The flocculation of pure cellulose, of mercerized cellulose and of cellulose treated with dilute nitric acid has been studied. The adsorption of polymer flocculants on the cellulose is described and results interpreted. Acid pretreatment caused maximum adsorption and flocculation.

The sedimentation behaviour of concentrated cellulose suspensions has been investigated for the determination of the “nominal radius” of cellulose particles and of related parameters.

Brockmann alumina was subjected to chemical pretreatment with HNO₃, H₂SO₄ and H₃PO₄ of various concentrations, and samples of surface phase pH 3.5 − 8.5 (HNO₃Al₂O₃(n), H₂SO₄-treated Al₂O₃(s)) and pH 4.0 − 8.0 (H₃PO₄-treated Al₂O₃(p)) were prepared. Sorption-desorption behaviour of the anionic dye Orange II (C.I.15510) with change in pH on these substrates was studied. Quantitative sorption is shown at pH ⩽ 4.0 (Al₂O₃(n)), and a maximum is observed at pH 5.0 (Al₂O₃(s)) and pH 3.0 (Al₂O₃(p)). Variation in the amount of sorption with time (10 min – 72 h), temperature (30 – 60 °C) and regeneration of the substrates with aqueous inorganic electrolytes is also reported. Desorption efficacy of the anions is in the order PO₄³⁻ >SO₄²⁻ >NO₃⁻. The acid treatment, and hence the specifically adsorbed anions (NO₃⁻, SO₄²⁻, PO₄³⁻), appears to lower the isoelectric pH of alumina (pH 8.0). The results show the involvement of anion-exchange properties of the alumina.

Electrochemical determinations of the corrosion parameters of construction steel DIN St 12 and an experimental alloy (2.8 wt.% Cr) were made in synthetic sea water under defined hydrodynamic conditions. The direct method of measuring polarization resistance was used as well as voltammetric and comparative analytical methods.

Experimental results clearly indicated an influence of oxygen on the kinetics of the corrosion process, which could be seen as a change of the control mechanism as the oxygen concentration was varied.

It was shown that the alloying element chromium has a beneficial influence on the corrosion characteristics of the reference steel.

Sorption-desorption behaviour of three oxyanions (MnO₄⁻, CrO₄^2- and VO₃⁻) on chromatographic alumina pretreated with HNO₃ is described. The sorption is found to be pH dependent, and has maxima at surface pH values of 3.5 (MnO₄⁻), 2.5 (VO₃⁻) and 2.0 (CrO₄²⁻). The affinity of MnO₄^- and CrO₄^2- is almost negligible at surface pH values of 5.5 or more. However, VO₃^- shows affinity for the substrate in the pH range 5.0 - 8.8. The monovalent anion appears to be sorbed, primarily via electrostatic interaction with the surface sites created by the acid treatment. The CrO₄^2- appears to involve ion exchange and weak chemical interactions. Mixtures of the oxyanions have been separated (binary and ternary) by column chromatography using inorganic electrolytes as eluents.

The porous cadmium electrode in alkali has been studied using the impedance technique applied to minielectrodes (area, 1 cm²) of conventional sintered structure. It is shown that in a wide frequency domain the electrode behaviour confirms to that of a filmed porous electrode under charge-transfer and diffusion control. In the lower frequency domain the electrode behaviour is more complicated and it is concluded that the frequency response was modified by intruding phase formation effects which were relaxed out at the higher frequencies.

Fine-grained nickel powder has been successfully electrodeposited from a very dilute all-sulphate bath of the composition 0.0125 moll⁻¹ NiSO₄ · 7H₂O, 0.23 moll⁻¹ (NH₄)₂SO₄, 0.1 moll⁻¹ H₃BO₃ and 0.07moll⁻¹ Na₂SO₄ · 10H₂O. The current efficiency of the deposition process and the surface morphology, as well as the catalytic activity of the electrodeposited nickel powder towards the decomposition of 0.4% H₂O₂ solution, were found to be fundamentally influenced by the operating variables pH, current density and duration of the electrolysis. X-ray diffraction studies revealed that the nickel powder is free from oxide and hydroxide contaminations. Under the optimum operating conditions (pH = 7.7 j = 13.3 A dm⁻² and t = 10 min) the selected bath produced a nickel deposit characterized by catalytic activity approaching 100% with a deposition efficiency around 18%.

The corrosion (oxidation) of nickel in molten (Na, K)NO₃ eutectic has been investigated at temperatures ranging from 250 °C to 450 °C, for exposure periods of up to 12 h. The results of both weight-gain and potential measurements under open-circuit conditions reveal the formation of a passivating film consisting mainly of NiO. The thickening of the oxide film proceeds according to a parabolic law, at a rate depending on the temperature of the melt. The activation energy of the process was estimated to be 14.95 kcal mol⁻¹, indicating that the oxidation process of nickel is determined by diffusion of nickel in the form of ions and electrons via vacancies and holes. A break was observed in the parabolic plots at higher temperatures; this may indicate a change in the mechanism of film growth. The results are discussed in terms of oxidation kinetics data for nickel in both molten nitrates and air at high temperatures.

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.