Basic surface quantities, material

B. Material Displacement Derivative of Basic Surface Quantities. 245... 

With respect to the first requirement, a polycrystalline metal as ordinarily used exposes at die surface many different types of crystal structure (different crystal faces, edges, corners, and boundaries between crystals). Each type of structure has its special chemical properties. Measurements made on ordinary polycrystalline material are a composite quantity which may be useful for technological purposes but which give little information for an understanding of the basic process of oxidation. It is not yet generally appreciated that for thin oxide films die differences in rates and structures on the different crystal faces are under many conditions quite large, as indicated below. 

The sorption and desorption of aqueous plutonium in the range of 10 7 to 10 8M was studied on quartz and other silica surfaces. Sorption continued typically for 12 to 15 days before apparent equilibrium was reached, and the distribution of plutonium particle sizes sorbed on the silica was different from that in solution. At pH 7, sorption increased with increasing ionic strength, but decreased when bicarbonate was added. The amount of sorption varied at pH 5 and 7, but differently at high and low ionic strengths, as well as with the age of the solution. Plutonium desorption indicated that there were two basically different sorbed species, and the rate and quantity of desorbed material increased at pH 5 compared with 7 and 9. 

Just as there should be careful analysis in the selection of the ideal basic or primary process, so must there be sound planning in the specification of the secondary processes. The parameters associated with aU process planning include the size of the part, the geometric configuration or shape required, the material, the tolerance and surface finished needed, the quantity to be produced, tmd of course the cost. Just as there are several alternatives in the selection of a basic process, so there are several alternatives in determining how a final configuration can be achieved. 

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