Conduction-controlled limiting case

Just as in the limiting case of ohmic control, the depth of the corrosion pit increases with the square root of the time. However, the proportionality constant here differs, it includes the saturation concentration rather than the potential and the diffusion coefficient rather than the electrolyte conductivity. Figure 7.64 shows experimental results for potentiostatic anodic dissolution of nickel in chloride solution. The geometry of the electrochemical cell corresponds to the one-dimensional pit model represented in Figure 7.62. The results show that, after a certain time, the current density decreases according to the square root of the polarization time, independent of potential. Mass-transport controlled growth of corrosion pits is favored by a highly electrolyte conductivity and weakly soluble dissolution products. 

Maximumtotal alkalinity consistentwith acceptable steam purity. If necessary, the limitation on total alkalinity should override conductance as the control parameter. If make-up is demineralized waterat 600-1000 Ib/in g, boiler wateralkalinity and conductance should be shown in the table for the 1001 -1500 Ib/in g range. NS (not specified) in these cases refers to free sodium- or potassium-hydroxide alkalinity. Some small variable amount of total alkalinity will be present, and measurable with the assumed congruent control or volatile treatment employed at these high-pressure ranges. 

A similar experiment was conducted using N-299 carbon black. In this case the premastication was limited to 3 min of mixing time. The average batch temperature measured after this mixing operation was 309°F. Each experiment was performed in duplicate the average of two mixes is shown in Figure 16.6. The viscosity of the final control compound was similar to that of the premasticated mbber. 

Tubal ligation is another procedure that has shown potential for risk reduction. However, it is not recommended as a sole procedure in prophylaxis. Protective effect may be due to limiting exposure of the ovary to environmental carcinogens. A case-control study conducted by Narod and colleagues found that a history of tubal ligation in /f RCA-positive women was associated with a statistically significant 63% reduction in risk.22... 

---