Oxide films discontinuous

Discontinuities in conducting oxide film or scale or discontinuities in applied metallic or non-metallic coatings. Exposed substrate (provided that this is more electrochemically active than the coating). 

Figure 53.3 illustrates a pit in a stainless steel such as type 534 or 316 austenitic alloy. Pitting starts at heterogeneity in the steel surface, such as an outcropping sulfide inclusion, the shielded region beneath a deposit or even a discontinuity in the naturally present oxide film caused by a scratch or embedded particle of abrasive grit. This initiation phase of pitting corrosion may take seconds... 

Platinised Ti, Ta or Nb < 1000 Am/m (consumption) Discontinuities in Pt coat protected by oxide film on subtrate sensitive (< lOOHz) a.c. ripple in d.c. or negative current spikes causing electrode consumption maximum operating potential with Ti substrate 9 V... 

It is a valve metal and when made anodic in a chloride-containing solution it forms an anodic oxide film of TiOj (rutile form), that thickens with an increase in voltage up to 8-12 V, when localised film breakdown occurs with subsequent pitting. The TiOj film has a high electrical resistivity, and this coupled with the fact that breakdown can occur at the e.m.f. s produced by the transformer rectifiers used in cathodic protection makes it unsuitable for use as an anode material. Nevertheless, it forms a most valuable substrate for platinum, which may be applied to titanium in the form of a thin coating. The composite anode is characterised by the fact that the titanium exposed at discontinuities is protected by the anodically formed dielectric Ti02 film. Platinised titanium therefore provides an economical method of utilising the inertness and electronic conductivity of platinum on a relatively inexpensive, yet inert substrate. 

Thus films can be divided into two groups according to their morphology. Discontinuous films are porous, have a low resistance and are formed at potentials close to the equilibrium potential of the corresponding electrode of the second kind. They often have substantial thickness (up to 1 mm). Films of this kind include halide films on copper, silver, lead and mercury, sulphate films on lead, iron and nickel oxide films on cadmium, zinc and magnesium, etc. Because of their low resistance and the reversible electrode reactions of their formation and dissolution, these films are often very important for electrode systems in storage batteries. 

Lead-based inhibitors and zinc phosphate inhibitors are thought to plug up the discontinuities in the natural oxide layer and hence offer protection. This is akin to the repair of an imperfect oxide film of iron by chromates, molybdates or tungstates. 

Using 10/ii films, Beck and his collaborators (21t 22) studied the continuous and discontinuous recrystallizarion strain-induced growth and polygonization of AL It should be pointed out that these oxide films have the same properties with regard to metallographic applications as the anodic films formed in... 

Next, the pattern is developed by dissolving the exposed parts of the pattern in the correct solvent. The quality of the pattern (contrast) depends on both the exposure and the development time, both of which must be experimentally determined for different resist systems and substrates. Once the pattern has been exposed and developed, the actual catalytically active metal(s) or oxide(s) is vapor deposited both within the holes in the pol3mier and on top of the polymer (step 5). This metal (or oxide) film should be discontinuous at the pattern boundaries in order to make possible the liftoff the remaining resist. This requires that the resist layer is thicker than the deposited film, and that the developed resist features have an undercut or negative profile... 

Demonstration of the creation of multilayer line structures in the seal will result in the collection of physical measurement data on the change in seal features during heat up, steady state operation, transients, or on cool down. A radar type image of the signal characteristics will show build up or relaxation of stresses, discontinuities in seal structure including porosity, delamination of the seal from either the cell or interconnect, and ultimately the catastrophic failure of the seal. Additionally with the ability to use a metal interconnect as one of the plane references coupled with a trace on the oxide coating on the interconnect, electrical conductivity and structural integrity of the thin oxide film on the metal interconnect can be determined within the vicinity of the trace. 

If a discontinuity in the passive oxide film occurs for one reason or another, and the metal corrodes rapidly at this point, the oxide film may be undermined by corrosion. An extreme example is the behaviour of aluminium in the presence of mercury [5.5],... 

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