Proposal of a New Stability Index Taking Account of Corrosion Inhibiting Action of Silica and Derivation of Empirical Equations Containing the New Index for Corrosiveness and Scale Formation of Water

摘要

A new stability index [an improved stability index (SI')] has been proposed that introduces corrosion inhibiting ability of silica in a broad range of temperature and pH into the conventional index of the corrosive action and scale formation of water, and new empirical equations [Eqs. 1 - 3] that characterize water were derived using the new index. The derived SI' was effective in the range of SI> 6. The SI' was balanced at 0, and then SI'=0 differed from SI = 6. In addition, a possibility was found for prediction and inhibition of corrosion of ferrous metals based on the equations by controlling the concentration of silica ([SiO_2]). y=K_0{1-exp(-3.06 X 10~(-1)SI')} (1) K_0 = (2.09T+ 1.872 X 10~2) exp {-(-1.08 X 10~(-4)T+ 7.62 X 10~(-3)) [SiO_2]} (2) SI'=x-7.21 {1- 1.71 X 10~(-1)exp(-8.59 X 10~(-3)[SiO_2])} (3) [y: corrosion rate (V) (mdd), K0: constant affecting saturation value of corrosion rate (y) (mdd), T: temperature (deg C), [SiO_2]: silica concentration (mg SiO2/dm3), x: stability index(SI) (-)].