Considerable efforts have been made to obtain clinically durable adhesive bonding of tooth tissues to composite resins and/or dental alloys. Approaches to the goal included etching with acid, surface treatments before the application of resins, and the use of special monomers which advantageously interact with tooth and/or metal. Based on results from extensive testing of dental adhesives, it is concluded that performance is highly dependent on pre-treatment prior to resin applications. History and current status of dental adhesives are described and bonding systems with adhesives are discussed.
Recent studies of the photocatalysis on metal oxides have been reviewed. The excited charge transfer complex, [Me(n-1)+—0-]* plays a significant role in the primary processes of photocatalysis on both unsupported and supported metal oxides. All the photocatalytic systems composed of metal oxides and reactants have been classified into four groups according to the presence or absence of both water and oxygen as reactant. As the initial electron or hole trapping processes associated with the formation of reaction products, the following four processes have been proposed; H++e-→H, O2+e-→O2-, OH-+h+→OH, O2-(l)+h+→O-(l). The relative importance of the four processes varies with the group of photocatalytic systems. The significance of the studies of excited states of metal oxides as well as the reaction intermediates has been emphasized. Finally, the correlation of photocatalysis on metal oxides for utilization of solar energy has been mentioned.
Ni (5)-Zn alloy has been etched by energetic Ar+ ions. White matrix (A), black (B) and gray particle (C) were observed by SEM. These correspond to the η, γ and δ phases, respectively although they could not be found on the surface before etching. Corns were formed on the phase by etching it and increased in size and sharpness with increasing etching time. Ni content analyzed by Auger electron spectroscopy is 1, 50 and 44 at. % for (A), (B) and (C), respectively. The results for (B) and (C) were not in agreement with those by EPMA. The disagreement is discussed in terms of differential sputtering and the relative sensitivity factor for Auger peaks.
Kinetics for the oxidation reaction of hydrogen on Pd-Al2O3 catalyst has been studied at 297K, 50-300 Torr hydrogen pressure and 30-150 Torr oxygen pressure. The reaction is first order with respecpect to hydrogen. In the Low pressure range (30-70 Torr), the kinetic order with respect to oxygen is 1, regardless of the hydrogen pressure. In the high pressure range (70-150 Torr), the kinetic order is -1. The reaction is not retarded by the product during the reaction. The kinetic results fit the equation: ν=(KSKH2KO2L2[H2][O2])/(1+KH2[H2]+KO2[O2]+KH2O[H2O])2, where v is reaction rate, Ks is a proportionality constant, KH2, KO2 and KH2O are adsorption coefficients, [H2], [O2] and [H2O] are partial pressures for hydrogen, oxygen and water, respectively, and L is the number of adsorptionsites. The experimental results can be explained on the basis of the mechanism resulting from surface reaction between competively adsorbed molecular hydrogen and oxygen.
The nature of surface tension of liquid and crystal, the tension appearance in thin film, and their diffusional creep were discussed theoretically. The creep rate controlled by diffusion process for thin liquid film is shown as follows under the condition, σa being sufficiently large in (dε/dt)D1(4/δ2)(σaV/RT) comparison with the contribution of surface energy or tension, where ε is a strain observed on the film at time t, D1 effective diffusion coefficient of liquid molecules, δ thickness of the film, σa applied external stress, and V molar volume of the liquid. Similarly the creep rate of the thin film of single crystal is shown for the condition where the (dε/dt)=Ds(4/δ2)(σa2V/2ERT) value, (σa2V/2E), is sufficiently large in contrast with the molar surface energy of the film, where Ds is effective diffusion coefficient of solid atoms and E Young's modulus of the crystal.
Initial processes of taste and olfactory reception are reviewed from the aspect of surface science. Salts and acids are adsorbed on negative sites on the surface of the receptor membranes. This leads to changes in the surface potential of the cells. Bitter substances and odorants are adsorbed on hydrophobic sites within the receptor membranes and induce changes in conformation of the boundary region of the membranes leading to changes in boundary potential of the cells (potential within the membranes near the surface of the cells). Sweet substances and amino acids are adsorbed on specific receptor proteins in the receptor membranes and induce changes in the conformation of the receptor domains resulting in changes in the surface potential and/or the boundary potential. Changes in the phase boundary potential (surface potential and boundary potential) directly affect the membrane potentials of the cells and induce electric impulses in the sensory nerves.