Surface Technology最新文献

Charcoal prepared by heating walnut shells at 500 °C in a nitrogen atmosphere was activated by CO₂ at various temperatures. The adsorption equilibrium and mass transfer characteristics of the activated carbon were studied. The structural properties were determined by means of additional measurements. A pore model is proposed to explain the variation of the pore structure with the activation process. The micropore sizes predicted by the model agree with the adsorption data.

Hot-pressed silicon nitride specimens containing magnesia additives were prepared and oxidized in air at high temperatures. The oxidized specimens were examined using a scanning electron microscope. The electronic and IR absorption spectra were measured. The scanning electron microscopy results indicated a decrease in the grain size with increasing intergranular area. The grain boundaries become sharper with increasing oxidation temperature and magnesia content. The sharpness of the grain boundaries is due to high temperature thermal etching effects. Electronic and IR absorption spectra revealed band broadening, a slight shift towards longer wavelength and the appearance of new bands as a function of MgO content and firing temperature. In conformity with all the present data, this could also be correlated with the decreased degree of crystallinity, the enlargement of the intergranular areas and the formation and propagation of oxidation products. In the oxidation mechanism additive and impurity cations diffuse outwards from the glassy phase in the bulk Si₃N₄ through the oxide film. The driving force is the formation of a reaction couple between the surface silica and the phase containing bulk magnesia and impurities.

The effect of temperature on the etch pit morphology of the (111) cleavage planes of bismuth single crystals are described. A chemical etchant which revealed the emergent ends of dislocations was used. The shape of the dislocation etch pits changes from the characteristic triangular shape at room temperature to a hexagonal shape as the etching temperature is increased to 60 °C. This change in etch pit morphology is explained in terms of the removal of atoms from steps.

The banded structure observed in metallographically polished and etched cross sections of Ni-P electrodeposits consisting of alternate dark and light layers parallel to the surface was investigated. The dark bands were attributed to a galvanic attack by the etchant at locations where the phosphorus content of the deposit changed relatively abruptly with thickness. A mechanism for the development of the compositional changes is proposed. Pulsed plating was found to eliminate the banded structure, but had little effect on the fracture strength and ductility.

A review of the literature on the electrodeposition of antimony and antimony alloys is presented. Literature up to the end of 1983 has been surveyed. The compositions of electrolytic baths and plating conditions are reported in some detail.

The effects of various plant extracts on the dissolution of mild steel in HCl solutions were studied. The additives investigated were Papaia, Poinciana pulcherrima, Cassia occidentalis and Datura stramonium seeds and Papaia, Calotropis procera B, Azydracta indica and Auforpio turkiale sap. Weight-loss determinations and electrochemical measurements were performed. It was found that all extracts except those of Auforpio turkiale and Azydracta indica reduced the corrosion of steel with an efficiency of 88%–96% in 1 N HCl and with a slightly lower efficiency in 2 N HCl. Both the cathodic evolution of hydrogen and the anodic dissolution of steel are inhibited. We believe that the inhibition action is mostly due to the products of the hydrolysis of the protein content of these plants.

Studies at 25 °C of changes of the electrode potential of palladium electrodes coated with palladium black during hydrogen absorption at low rates have revealed a feature which appears to be related to other evidence of subsurface absorption of hydrogen by palladium at much lower hydrogen potentials than the main region of α→β phase transition in the Pd-H system. Implications of these findings are discussed.

Diffusion coatings of aluminium on iron and steels were obtained by an aluminization pack-cementation process, principally at 900 °C. A mathematical analysis of diffusion during aluminization allows the calculation of the concentration profiles in the coatings and of the incorporation rates of aluminium to be made. Analytical solutions are employed for the one-, two- and three-phase, semi-infinite planar diffusion problem. The theoretical and experimental results on pure iron are in good agreement; the theoretical predictions can be extended to 13% and 17% Cr steels, to a first approximation. On 24% Cr steel the diffusion rate is very low and the coatings obtained on austenitic stainless steel exhibit a diffusion barrier of nickel.

The aluminium surface concentration, the incorporation rate and concentration profiles can be controlled by changing the aluminium activity in the pack.

Electrochemical measurements and corrosion tests were performed at room temperature using mild steel specimens immersed in 1 N H₂SO₄ solution in the presence and absence of cysteine, cystine and methionine. Inhibition by the three amino acids increased with increasing additive concentration. More than 60% inhibition was achieved with an amino acid concentration as low as 10^-3 M. Polarization curves indicated that these amino acids act as mixed-type inhibitors, i.e. both the cathodic and anodic curves were affected. Adsorption of the amino acids on the steel occurs in two steps: a monolayer of the adsorbate is formed on the metal surface, and this is followed by the deposition of a second adsorbate layer.

The anodic dissolution of hot-rolled Delta-52 steel (an Egyptian product) was studied potentiodynamically in H₂SO₄ solutions of various concentrations. The rate of dissolution increases with increasing acid concentration. The effects of the addition of Cl^-, Br^- and I^- anions on the dissolution kinetics of the electrode in 0.1 M H₂SO₄ were investigated. The data reveal that the Cl^- ion participates in the anodic dissolution while both the Br^- and I^- ions decrease the steel dissolution reaction.

The addition of NO₂^-, CrO₄^3- anions to the H₂SO₄ solution inhibits the anodic reaction of steel dissolution. The dissolution current density j in the Tafel region varied with the concentration C_inh of the added anions according to the relation. log j=a−blogC_inh where a and b are constants.