Surface Technology最新文献

The textural and structural characteristics of NiO obtained by the thermal decomposition of Ni(OH)₂ in vacuum up to 500 °C are studied by the analysis of nitrogen adsorption measurements and X-ray line profile analysis. The decomposition occurs via the formation of a network of cracks and a slit-shaped porous system that changes to cylindrical on increasing the temperature. The particles are composed of small crystallites with most of their surface exposed to gas adsorption. A significant microstrain content is observed in all samples.

A series of Ni-Al mixed oxides having different compositions was prepared by coprecipitation and by impregnation. The solids obtained were heated in air at 450–1000 °C. The surface properties, namely, S_BET, S_t, V_p and $\text{r}$, of each adsorbent were determined from nitrogen adsorption isotherms. The change in S_BET as a function of calcination temperature permitted the calculation of the apparent energy of activation of sintering.

The results obtained revealed that the catalysts prepared by coprecipitation had higher surface areas than those obtained by impregnation. The mixed oxide solids seemed to be composed of wide pores. However, the pores of the adsorbents prepared by impregnation were narrower than those measured for the adsorbents prepared by coprecipitation. Also, the specific surface area depended on the NiO/Al₂O₃ ratio. The presence of Al₂O₃ increased the degree of dispersion of NiO grains leading to a significant increase in its surface area, with effective retardation of sintering of the NiO phase. The apparent energy E_s of activation of sintering indicated that the increase in alumina content was followed by a corresponding increase in the magnitude of E_s.

This review is concerned with the photoluminescent and electroluminescent properties of semiconductor electrodes used in photoelectrochemicall cells for optical-to-electrical energy conversion. Luminescence not only provides insight into the excited-state deactivation routes which are crucial to efficient energy conversion, but also allows one to obtain in a relatively simple manner valuable information about bulk and surface imperfections that negatively influence photoelectrochemical performance of the semiconductor.

The catalytic activity of pure NiO and Ni-Al mixed oxides subjected to various doses of γ irradiation was investigated using the oxidation of CO with O₂ at various temperatures. The effect of lithium doping on the catalytic activity of Ni-Al was also investigated. The results obtained revealed that γ irradiation of pure NiO using doses up to 10 Mrad effected a decrease of 45% in its catalytic activity which suffered a further slight change when the dose was increased to 20 Mrad. The activity of Ni-Al mixed oxide was modified in a somewhat complicated manner by γ irradiation. Doses of 5 – 10 Mrad produced an increase of 34% in its catalytic activity and a dose of 15 Mrad caused a drastic decrease in its activity of 57%. Increasing the dose of 20 Mrad produced a slight increase in the catalytic activity of the mixed oxide solid.

The modifications in the catalytic activity of pure NiO and mixed oxide solids arising from γ irradiation were attributed to an induced removal of chemisorbed O₂ in the case of pure NiO and to a possible increase in the [Ni]/[Al] ratio, especially in the outermost surface layers, of the mixed oxide catalyst.

Lithium doping was found to cause a significant increase in the catalytic activity of Ni-Al mixed oxide which was attributed to the increase in the amount of chemisorbed O₂ and to an increase in the [Ni]/[Al] ratio.

Differential scanning calorimetry and Fourier transform IR reflectance spectroscopy have been used to study the interactions of oleic acid with the surfaces of aluminum, magnesium and Al-Mg alloys. Measurements were made in both air and argon from 150 to 575 °C. The magnesium content of the alloys ranged from 2.6 to 10.7 wt.% and samples were examined in the form of fine powders or smooth plates. A few experiments were also conducted using granular magnesium and aluminium oxides to assist in evaluating the role of surface oxides in the reactions. The IR reflectance signals at about 1590 and 1450 cm^-1 showed the formation of magnesium oleate in the various magnesium samples at 175 to 300 °C. With the alloy series there was a marked trend towards greater absorbance of these bands with increase in the magnesium content. Little or no evidence was obtained for the formation of aluminum oleate from IR spectra while thermal measurements showed enthalpy changes of -1050 and -650 cal g^-1 respectively for magnesium and aluminium grains in reactions with the acid in air over the range from 150 to 575 °C. Supplementary details of the surface properties of samples were obtained from profilometric, nitrogen adsorption and electron spectroscopy for chemical analysis measurements. Some preliminary work is described in which alloys were laminated to high density polyethylene in an attempt to assess the influence of surface composition on joint strengths.

The mechanism of dendritic growth initiation for metals whose deposition is characterized by high exchange current densities is discussed. It is shown that in this case dendritic growth is possible at very low overpotentials in potentiostatic deposition. Dendritic growth is also possible in galvanostatic deposition. It is also shown that instantaneous dendritic growth is not possible at low overpotentials. The discussion is exemplified by an experimental study of the electrocrystallization of lead from lead nitrate solution.

It is shown that dendritic growth of silver at low overpotentials is not possible, because two-dimensional nucleation becomes the rate determining step in prolonged deposition.

The optical sensitivity of the excess impurity lone-pair electrons is discussed on the basis of the values of the IR reflection integral which were derived from the plasma edge profile of the (001) face of GaAs(Te) for eight levels of dopant concentration. From the analysis of the variation in the reflectivity including annihilation and creation of some fine step bands induced by applying an alternating electromagnetic field with frequency f = A × 10^m−1 (m = 1, 2, …, 7) parallel to the <100 > direction, we estimate that this sensitive effect may be induced primarily by the dynamical variation of the matrix elements of these oscillators, the values of which are determined by the dipole moments and oscillator concentrations. By using the Nf-R relations of the fine step bands measurable at 274 cm^-1, 290 cm^-1 and 315 cm^-1, the degree of variation in the effective oscillator concentration and the effective charge are estimated and reasonable values are obtained, by comparison with the Born effective charge the dipole-moments were determined. The step property of the nine fine step bands superimposed on the fundmental lattice band and the plasma edge is analysed for the two types of sample.