Surface Technology最新文献

Solution-sprayed cured layers of Michlers ketone were overcoated with various polymers to enhance their charge acceptance. It is found that an overlayer of poly(vinyl butyral) gives the best electrophotographic characteristics, showing a maximum charge acceptance of 825 V and a contrast potential of 540 V.

The influence of the continuous mechanical renewal of the electrode surface on the effective activation energy of copper deposition on a copper cathode in the Tafel potential region was studied using a self-cleaning rotating electrode. The effective activation energy decreased by about 5 kcal mol^-1 when the cathode was continuously mechanically renewed.

Mass transport during the electrodeposition of copper from acidified sulphate solution using single and multiple pulses was studied. Experimental results obtained in a diffusion cell and with a rotating hemispherical electrode are compared with published theoretical calculations of various degrees of mathematical sophistication and complexity. The simple duplex diffusion-layer model proposed by Ibl gives adequate values of the pulse limiting current density for many practical purposes. The agreement with experiment can be further improved by using a semi-empirical modification of the model.

Extensive investigations of the aluminium electrolyte interface were undertaken in order to check the pH dependence of the corrosion rate aluminium, i.e. the pH value at which the rate of aluminium corrosion is lowest. Part of this research which deals with measurements of the loss of mass and polarization resistance as functions of pH is presented in this paper. The measurements were performed over a broad range of pH in the presence and absence of ethylenediamine inhibitor. The results are shown as plots of log(1/R_p) and log Δm against the pH. Two straight lines of opposite slope were obtained for each method of investigation and each system investigated. The intercepts obtained by extrapolating the straight lines, which represent minima of 1/R_p and mass loss, indicate the corresponding pH values. The results obtained are discussed in terms of the interaction of water dipoles with the oxide film during the corrosion process. The change in the surface charge of the corroding aluminium as the pH is altered plays an important role in the corrosion process.

A detailed study of the variation in the nucleation density and growth of ammonium hydrogen tartrate (AHT) single crystals as a function of the concentration of the feed solution, the gel density, the gel pH, the gel aging time and the temperature is presented. Whereas opaque crystals were produced from high density high pH gels, good quality transparent single crystals were obtained in low density low pH gels. The use of intermediate neutral gel column and gel aging times considerably reduces the number of nucleation sites. The nucleation density decreases as the temperature increases. A simple procedure to control nucleation sites in gels was adopted and resulted in a dramatic increase in the size of the crystals. Kinetics studies of the nucleation and growth of AHT needle crystals showed that these crystals grow by a one-dimensional diffusion-controlled reaction between ammonium chloride and tartaric acid. The implications of this behaviour are discussed.

An Nb-Nb₂O₅ electrode was prepared by the electrolytic oxidation of niobium in molten KNO₃. This electrode can be used as an indicator electrode in potentiometric acid-base titrations. It behaves reversibly and responds theoretically to the oxide ion concentration in molten KNO₃. Its potential varies linearly with ln[O^2-] and the line has a slope of 68 mV at 350 °C. The standard potential of the Nb-Nb₂O₅, O^2- electrode, i.e. the potential at [O^2-] = 1, is computed as -810 mV with respect to the Ag-Ag⁺ reference electrode.

The beginnings of dendrite formation in electrodeposited zinc were investigated by electron microscopy. Numerous dendritically shaped crystallites were already present in the very early stages of deposition. They had definite crystallographic characteristics. Only a few of these crystallites developed into optically visible dendrites. High local current densities favored the development of fewer, but larger, dendrites.

Bi-In alloys containing up to 90% In were electrodeposited from aqueous solutions containing the diethylenetriaminepentaacetate ion as the complexing agent. An increase in the current density and the indium content of the bath decreased the percentage of bismuth in the deposit. The current efficiency decreased with increasing current density but was not significantly affected by a change in the indium content of the bath. Deposits containing 63%–89% In were of good visual quality and offer promise as a decorative finish. The X-ray phase structure of the deposited alloys is reported.

Thermal etch pits with rhombic outlines on the cleavage surfaces of natural calcite crystals are observed in a narrow range of etching temperature between 540 and 625 °C in air. The thermal etch rates V_t and V_s of the tangential dissolution of ledges and the surface dissolution respectively were determined in the above temperature range. The activation energies E_{t th} and E_{s th} of tangential thermal dissolution and surface thermal dissolution respectively are calculated and are compared with those of controlled chemical dissolution initiated to produce dislocation etch pits on calcite cleavages. A quantitative study of the activation energies suggests that the thermal etch pits on calcite cleavage faces originate at dislocation-free sites such as kinks, steps and/or impurity centres.

The effect of benzotriazole (BTA) on the corrosion of brass in 0.1 N HCl, 0.1 N H₂SO₄ and 0.1 N NH₄Cl was studied by means of immersion tests and galvanostatic measurements. BTA showed a good inhibition effect in some corrosive media. The percentage inhibition in 0.1 N HCl solution was found to increase with increasing BTA concentration. In contrast, the percentage inhibition in 0.1 N H₂SO₄ was inversely proportional to the BTA concentration. The highest inhibition efficiency was obtained in 0.1 N NH₄Cl. The role of BTA as an inhibitor for brass was explained in terms of the chemisorption of BTA molecules at some active sites on brass surfaces.