We have investigated on a rapid method of estimating the life of anode graphite at the amalgam process chlorine-caustic cell, by electrolysis of sodium sulphate solution and by electrolysis of sodium chloride solution containing sulphate.
This method is based on our researches about the mechanism of corrosion of anode graphite described in the previous papers.
That is to say, the corrosion in electrolysis of sodium sulphate solution under conditions of above 40°C, acidity of below 1N, and anode current density of above 5amp/dm
2, and that at the amalgam process chlorine-caustic cell were of just the same mechanism, namely, the pure chemical oxidation consumption from surface of graphite crystal.
The following methods were found preferable:
(1) The sodium sulphate solution electrolysis method for the domestic anode graphite:
The corrosion rates in mg/Ah unit of anode graphites treated for 3 hours under electrolytic conditions of sulphate concentration of Na
2SO
4·10H
2O 100g/
l, 60°C, anode current density of 10amp/dm
2 are compared with each other.
This method was found to be better than the other method for the domestic anode graphite.
(2) The rapid method, combining electrolysis of sodium sulphate solution with electrolysis of sodium chloride solution containing sulphate, for domestic and A cheson's anode graphites:
The anode graphites were treated preliminarily by the above-mentioned sulphate solution electrolysis, and then treated intermediately for 2 hours under conditions of 60°C, acidity of pH 2 to 3, and anodic current density of 50amp/dm
2 with sodium chloride solution of concentration of NaCl 260g/
l contained sulphate of Na
2SO
4 25g is one liter of brine.
In the last formal electrolysis, the samples are treated for 4 hours under the same condition as intermediate treatment, and the corrosion rates which were measured as difference of weight in this formal electrolysis are compared with each other.
This method resulted in the best coincidence with the order obtained in long time test by amalgam process chlorine-caustic cell as for the domestic and Acheson's anode graphites.
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