Surface Technology最新文献

This paper presents a general analysis of chemical vapour deposition (CVD) of silicon dioxide by oxidizing silane with oxygen. The proposed model is based on the scheme of surface reactions described in Part I. The model considers all the important process steps, namely mass transport in the gas phase, adsorption and chemical reactions. The proposed approach makes it possible to analyse the kinetics of the process for a wide range of parameters. However, the resulting equation is complicated and includes some unknown coefficients. In a Part III these coefficients will be determined by fitting the model to the experimental data and the experimental verification of the model will be presented.

The surface properties of black acetylene which had undergone preliminary treatment were studied. The results seem to show a relation between the surface behaviour and the preliminary treatment of the sample.

Zinc trifluoromethanesulphonate (Zn(CF₃SO₃)₂) was prepared. Its purity was better than 98.7%. The zinc salt did not decompose below 600 °C. It was soluble in 100 g of methanol, ethanol, acetonitrile, N,N-dimethyl formamide and formamide at 25 °C in amounts of 117 g, 63.9 g, 71.8 g, 42.7 g and 29.8 g respectively. A maximum conductivity of 300 μS cm^-1 was observed in methanol solution. The molar conductivity at 45 °C at infinite dilution was 132 ω^-1 cm² mol^-1 for methanol solution, 147 ω^-1 cm² mol^-1 for N,N-dimethylformamide solution, 20.5 ω^-1 cm² mol^-1 for ethanol solution, 80 ω^-1 cm² mol^-1 formamide solution and 137 ω^-1 cm² mol^-1 for acetonitrile solution.

A dental amalgam made from a lathe-cut powder with a high copper content was characterized with respect to its microstructure by means of scanning electron microscopy techniques. A comparison was made between the in vitro corrosion resistance of this relatively new high copper amalgam, a dispersion-type amalgam and a ‘single composition alloy’ amalgam. The effect of toothbrushing was included to avoid the superficial accumulation of corrosion products. Electrochemical data on the behaviour of the three types of high copper amalgams examined were collected by tracing anodic polarization curves and by measuring the polarization resistance. After immersion in synthetic saliva for 30 days, the amalgam made from the lathe-cut powder with high copper content and the dispersion-type amalgam showed preferential attack on the copper-rich phases, while the γ₁ phase appeared only slightly altered; corrosion products rich in tin and chlorine were detected. The ‘single composition alloy’ corroded to a lesser extent.

This is a preliminary study on the behaviour in regenerative photoelectrochemical cells of large-grained polycrystalline n-CuInSe₂ films prepared by a new technique consisting in depositing the semiconducting material on thin metal layers kept at a temperature close to, but lower than, their melting point. After characterization of the surface morphology of the films by scanning electron microscopy and by systematic scanning laser spot analysis, their output power characteristics when in contact with different redox couples have been examined. The results are discussed and further developments of the research outlined.

It is shown that the improvement in the quality of electrodeposits obtained from CdSO₄ solution in the presence of strongly adsorbed species compared with that of deposits obtained in the absence of such species is due to a decrease in the exchange current density and an increase in the Tafel slope for the deposition process in the former case.

The effect of a sinusoidal alternating current (a.c.) on the corrosion of Delta-52 steel in K₂SO₄ solutions was investigated. The data reveal that on applying a.c. the corrosion rate increases. The corrosion rate also increases with increasing a.c. density. This behaviour can be interpreted in terms of the effect of a.c. on the anodic and cathodic polarization and consequently on the rate of the electrode processes. A potentiodynamic anodic potential scan of the steel electrode was performed under the influence of superimposed a.c. The results show that the dissolution current density is enhanced and the corrosion potential is shifted to more active values. This effect decreases at higher a.c. frequencies.

The recent literature on the application of digital techniques to electrochemical and electrode kinetic studies is reviewed. The principles of operation of a technical microcomputer are described, and are illustrated with examples from electrode kinetic studies in the field of electrochemical energy conversion.

Reversal in the zinc/iron galvanic cell occurs in aerated solutions of both sodium bicarbonate and sodium nitrate.

The sodium nitrate reversal occurs over the temperature range from 25 °C to 80 °C. The time to reversal and the stability of the reversed cell are concentration and temperature dependent. The most rapid and stable reversal at 80 °C occurs in 0.1 mM solution. At room temperature the role of the electrodes cycles, but the long-term tendency is for the zinc to become the cathode in the system.