The fracture of brittle coatings on a strained substrate is examined from two points of view. In the first case, the substrate deforms continuously and regularly spaced fractures occur in the coating. The spacing d at any strain ε is given by In ε/ε0 = (4g/d) (1−d/d0), where d0, ε0 are any convenient set of data points, and g is a parameter having the units of length. In the second case, the substrate deforms by crystallographic slip and fracture of the oxide may or may not occur at the slip step. The criteria for fracture are that the interface adhesive stresses be too large for the coating to sustain the necessary peel stress. Quantitative relations are given in terms of the coating thickness, fracture strain, and the orientation of the slip step with respect to the surface. The results for both cases are compared with experiment and found to be in essential agreement.

Mackinawite, a tetragonal iron sulfide mineral, is generally a major corrosion product when iron alloys are corroded by sulfatereducing bacterie (SRB). The experimental database for the mineraf indicates that on nongeologic time scales, mackinawite, if it forms at all in nonbiological corrosion, does so only under very reducing conditions and in the presence of sulfide activities notnormally found in the biosphere or in ordinary corrosion testing.

No abstract

No abstract

(Maximum 200 words).Mineralogical data, thermodynamic stability (Pourbaix) diagrams, and the siinplexity principle for precipitation reactions were used to evaluate corrosion product mineralogy on copper alloys exposed to sulf ate-reducing bacteria. The formation of copper sulfides as corrosion products in natural surface environments is suggestive of microbiologically influenced corrosion. Sulfide corrosion products other than chalcocite (Cu 2 S) indicate that reactions within a biofilm induced corrosion. /Y