Surface Technology最新文献

The effect of the calcination and/or the incorporation of Cr, Al or Fe ions in NiO catalysts on the excess oxygen on the surface and the structural and textural properties was investigated using a number of physico-chemical techniques. The results indicated that homogeneous solid solutions were obtained only when the doping level was less than 3 at.% M³⁺. NiOOH species formed topochemically during the hydrothermal decomposition of the parent Ni(OH)₂ at 300 – 400 °C were found to be associated with the maximum surface content of excess oxygen. The excess oxygen species were identified from IR and X-ray photoelectron spectra.

Fracture faces and polished surfaces of Synroc C specimens with 10% and 20% simulated high-level nuclear waste (HLW) have been studied with X-ray photoelectron spectroscopy. Elemental abundances and chemical environments for all matrix and most HLW atomic species have been investigated in the surface and near-surface layers before and after chemical attack. These observations suggest that the fracture mechanism is mainly intergranular, that particular phases are not preferentially exposed in the fracture faces, that some HLW species (caesium and molybdenum) are found in the grain boundaries, that intergranular regions are thin amorphous films or larger “glassy” triple points and that the intergranular films exhibit low chemical durability in an aqueous environment. These effects are independent of waste loading up to 20% and are consistent with the very good chemical durability reported for large monoliths.

CoCl₂- and NiCl₂- loaded aluminas were thermally dehrdrated in vacuo at various temperatures ranging from 20 to 500 °C. The water loss, nitrogen surface area and integral heat of water immersion were determined for the thermally treated samples. The samples inder investigation were analysed using several methods. Changes in porosity were detected by means of the V_a-t method. The corrected modelless method was used to determine the surface locations, and the area fraction located in the mesopores was also calculated. This fraction denotes the surface accessibility of various samples for nitrogen adsorbate molecules as well as for the smaller water molecules.

Both the integral heat of immersion and the water loss were normalized to the unit nitrogen Brunauer-Emmett-Teller surface area. The correspondence between the changes in the heat of immersion per unit area and the water loss per unit area when they are plotted as functions of the heat treatment temperature indicated that a reversible dehydration-hydration phenomenon occured at high treatment temperatures.

Since samples which have the highest surface accessibility for water molecules and are characterized by a relatively high heat of immersion can be assumed to be effective dehydrating materials, it can be concluded from our results that CoCl₂-loaded alumina should be heat treated at 400 °C to obtain optimum dessicant properties. However, the NiCl₂-loaded alumina requires heat treatment at 200 °C. Further details are presented and discussed.

Reduction by hydrogen of the residual oxide and carbon present on the inner wall of the tokamak type of nuclear fusion test reactor is found to be an efficient method of ensuring test conditions relatively free from such impurities. The inner wall, which is usually made of stainless steel or Inconel, is exposed to a low pressure electrical discharge through molecular hydrogen within the tokamak vessel which provides the atomic hydrogen necessary for the reduction process. As this discharge cleaning proceeds, the surface oxide and carbon are reduced, with the consequent emission of H₂O, CH₄ and CO as “impurities” from the walls into the chamber.

The analysis of these “impurity” gases during discharge cleaning indicates emission of wall impurity reduction products to be driven by a diffusion-controlled physical process. Evidence for this comes in part from the time-variation characteristics of emission products where a classical t^{-$\text{1}\text{2}$} dependence is found. Comparatively low values of the activation energy for oxide reduction (5.8 kcal mol^-1 or less) confirm this mechanism as the rate-determining step and can be shown to support the same mechanism even in situations where the impurity-time characteristics differ from the classical case. An oxide reduction sequence is presented which is consistent with the kinetic parameters derived from data on discharge cleaning. Kinetic similarities are also shown between the discharge cleaning process in tokamaks and the reduction of iron oxides by hydrogen at high temperature.

Interesting surface problems in this field are focused on by a brief review of representative discharge cleaning data, followed by an analysis and interpretation that approaches the problem from a kinetic-mechanistic viewpoint.

The distribution coefficients K_d of three cationic dyes (methyl violet 6B, phenosafranine and Janus Red) on hydrated stannic oxide with a surface phase pH of 6.0–11.0 were determined at dye concentrations of 20 x 10⁵, 100 x 10⁵ and 180 x 10⁵ mol 1^-1 at 30 ± 1 °C for a contact period of 24 h. Elution studies of the dyes on some of the substrates (pH 7.0–8.5) were conducted using inorganic electrolytes (barium nitrate and aluminum nitrate (0.1 M–1.0 M) and ethanol. On the basis of the K_d values and the elution behaviour, some binary separations of the dyes on a column were achieved. The study shows the usefulness of chemical pretreatment of hydrated oxides, such as stannic oxide, in chromatography.

The copper deposition overvoltage in the Tafel potential region on both non-renewed and continuously mechanically renewed working electrode surfaces in H₂SO₄-CuSO₄ solutions of various compositions (0.06 - 0.75 M CuSO₄ + 2 M H₂SO₄) was studied using a copper self-cleaning rotating electrode. A decrease in the overvoltage on the continuously mechanically renewed electrode surface was observed in the Tafel region for all solution compositions investigated.

The electrodeposition of silver from four selected baths with almost the same composition except for the anion was examined electrochemically and electron microscopically. The baths were prepared mainly from aqueous cyanide solutions containing silver cyanide, silver chloride, silver bromide and silver iodide. The results reveal that the electrodeposited silver grains become finer in the order Cl^- < Br^- < I^-, in good agreement with measurements of the electrochemical properties such as cathodic polarization, cathodic current efficiency and throwing power. This can be attributed to the adsorption sensitivity of the anions on the silver surface owing to their increasing polarizabilities and ionic radii.

SrCl₂- and BaCl₂-loaded aluminas were thermally dehydrated in vacuo at various temperatures in the range 20–500 °C. The water loss, specific surface area for nitrogen adsorption and the integral heat of water immersion were determined for thermally treated samples. Possible changes in the porosity of the samples investigated were studied using the V₁-t method. The model-less method was used to determine the surface locations and the area fraction located in the mesopores was calculated. This fraction indicates the surface accessibility of various samples to nitrogen adsorbate molecules and to the smaller water molecules. The integral heats of water immersion normalized to nitrogen Brunauer-Emmett-Teller surface areas were studied over the entire temperature range. The samples with the highest surface accessibility to water molecules together with relatively high heats of immersion in water were assumed to be effective dehydrating materials. It was found that SrCl₂- and BaCl₂-loaded aluminas required heat treatment at 400 °C and 300 °C respectively to optimize their use as desiccant materials. Further detailed discussion is presented.

The electrodeposition of iron-rich Ni-Fe alloy deposits from both sulphate and chloride baths and their mechanical properties (hardness, ductility and internal stress) are discussed in detail as a function of bath composition and current density. The current efficiencies of Ni-Fe alloy deposition in the sulphate and chloride baths were found to be 85%–95% and 46%–65% respectively. The composition of the Ni-Fe alloy deposits changed markedly with increasing current density. The hardness of the Ni-Fe alloy deposits with nickel contents above 20 wt.% was 400–500 HV. Large internal stresses were observed in the pure iron and Ni-Fe alloy deposits obtained from both sulphate and chloride baths. However, the Ni-Fe alloy deposits have no cracks. The ductility of the Ni-Fe alloy deposits obtained from the sulphate bath ([Fe]/[Ni] = 1) increased with increasing current density. The electroplated iron had a textured structure. However, addition of Ni²⁺ ions to the iron plating bath led to a fine-grained lamellar structure.

The coefficient of static friction for bone-to-bone contacting surfaces has been measured. Unembalmed human cadaveric tibial and femoral bones were cut with three types of surgical saw, two power driven and one hand held, and the bone-to-bone static friction was determined using an in vitro shear method. It was found that both the type of saw and the type of bone affected the coefficient of friction. Greater coefficients of static friction were found with a coarse cutting saw (the hand-held Gigli saw) and tibial bone which is harder than femoral bone. The findings suggest that a rough surface finish to cut bone, in a well-reduced fracture, should promote healing by stabilizing the fracture interface.