The corrosion of 18-8 steel by the aqueous solution of ammonium sulphate (NH
4)
2SO
4, which often happens in industrial operation, and its protection are studied under various conditions. Results obtained are as follows:
1. Temperature effects on the corrosion
The corrosion of 18-8 steel progresses slowly at below 80°C, but very rapidly when the temperature is raised above 90°C.
2. Effects of (NH
4)
2SO
4 concentration on the corrosion.
When H
2SO
4 concentration is constant, the corrosion rate is lowered in proportion to the increase of (NH
4)
2SO
4 content, and is minimized when it gets saturated.
3. The corrosion of 18-8 modifications.
Most of 18-8 modifications are more corrodible than ordinary 18-3 steel, except for 18-8 Mo., etc.
4. The corrosion of higher stainless alloys to which Mo or Mo+Cu is added.
18-12 Mo-Cu stainless alloy was found best against corrosion in the plant test.
5. The corrosion of 18-8 steel in galvanizing operation.
When 18-8 steel is in contact with lead (or bronze) in the liquor, corrosion of 18-8 steel (active) is accelerated. But when is in passive state, the rate of its corrosion is lowered, and the corrosion of lead (or bronze) is greatly accelerated in turn.
6. Effects of Cu-ion on 18-8 corrosion:
18-8 corrosion comes to a stop when more than 0.26% CuSO
4 is added.
7. Effect of As-ion on corrosion (carbon steel):
Corrosion loss in weight is lowered to about 4.5% by addition of more than 0.3% Na
3AsO
4.
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