Rupture/breakdown potential

As indicated above, when a positive direct current is impressed upon a piece of titanium immersed in an electrolyte, the consequent rise in potential induces the formation of a protective surface film, which is resistant to passage of any further appreciable quantity of current into the electrolyte. The upper potential limit that can be attained without breakdown of the surface film will depend upon the nature of the electrolyte. Thus, in strong sulphuric acid the metal/oxide system will sustain voltages of between 80 and 100 V before a spark-type dielectric rupture ensues, while in sodium chloride solutions or in sea water film rupture takes place when the voltage across the oxide film reaches a value of about 12 to 14 V. Above the critical voltage, anodic dissolution takes place at weak spots in the surface film and appreciable current passes into the electrolyte, presumably by an initial mechanism involving the formation of soluble titanium ions. 

The critical breakdown potential, which is the positive potential limit of stability of the oxide film. At this potential and more positive potentials, the oxide film is unstable with respect to the action of anions, especially halide ions, in causing localised rupture and initiating pitting corrosion. 

Calcareous (Ca + > breakdown of organic compounds 2. Lysis of microbial dead cells on death 1. Potential loss of FRP on CO2 TP or Preserve with HgCh Acidify with 1 mL cone. HCl with oligotrophic water) Avoid freezing unfiltered samples because of cell rupture Adjust HgCh quantity to sample organic content... 

The phenomena ofbreakdown ofpassive films at more noble values of potential leads to an accelerated rate of corrosion (transpassive corrosion). The potential at which the breakdown or rupture of protective film takes place and the current density rises sharply is called transpassive potential (Iitranspassive)- In Fig. 3.26, the effect of chromium... 

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