“Molecular Clusters” on the Surface of an Oxidizing Metal
FIELD ion microscopy, which holds the possibility of resolving the individual atoms in a metallic surface, should in principle be a powerful tool for the study of reactions on surfaces. As part of an extensive study of the mechanism of oxidation of several metals, we have recently observed the formation of characteristic, reproducible, small clusters of atoms of regular shape when a perfect iridium surface is exposed to oxygen.
The nature of adsorbed oxygen on rhodium, palladium and gold electrodes
Summary Oxygen coverage has been determined on rhodium, palladium and gold anodes as a function of potential and time. The oxygen-containing film consists of chemisorbed oxygen atoms, but phase oxide can nucleate and grow under severe conditions of anodization. A basis for distinguishing between chemisorption and phase formation is presented. Comparison with previous work on platinum allows the stoichiometry of chemisorbed oxygen at coverage steps and limiting coverage regions to be determined. This stoichiometry can be utilized for accurate measurement of real surface area of rhodium and palladium electrodes.
Control of reflective cracking
The first is 'fatigue' cracking of the layer. This type of cracking is the result of the application of loads on the pavement and is controlled by appropriate thickness design which 'ill not be discussed in detail here. Thickness design includes not only the design strength and thickness of the stabilised, but other design elements such as delaying reflection cracking, or limiting stresses in the stabilised layer, by adopting a minimum thickness of overlying material. This may include an unbound layer utilising the 'upside down' pavement approach. The actual thickness required of the overlying material varies but for example PIARC (Ref.1) recently reported when the thickness of coated materials exceeds 20 cm the emergence of shrinkage cracks at the surface is generally uncommon; when it is 15 cm thick, the cracks emerge at the surface, but do not shorten the life of the surface course, especially if they are sealed. This experience has been gained 'with legal axle loads of 130 kN, considerably greater than the Australian legal axle load.