ORGANIC ACIDS
Titanium is generally quite resistant to organic acids.^(33) Its behavior is dependent on whether the environment is reducing or oxidizing. Only a few organic acids are known to attack titanium. Among these are hot non-aerated formic acid, hot oxalic acid, concentrated trichloroacetic acid and solutions of sulfamic acid. Aeration improves the resistance of titanium in most of these nonoxidizing acid solutions. In the case of formic acid, it reduces the corrosion rates to very low values (Table 20).

Unalloyed titanium corrodes at a very low rate in boiling 0.3 percent sulfamic acid and at a rate of over 100 mpy (2.54 mm/y) in 0.7 percent boiling sulfamic acid. Addition of ferric chloride (0.375 g/l) to the 0.7 percent solution reduces the corrosion rate to 1.2 mpy (0.031 mm/y).

Boiling solutions containing more than 3.5 g/l of sulfamic acid can rapidly attack unalloyed titanium. For this reason, extreme care should be exercised when titanium heat exchangers are descaled with sulfamic acid. The pH of the acid should not be allowed to go below 1.0 to avoid corrosion of titanium. Consideration should also be given to inhibiting the acid with ferric chloride.

Titanium is resistant to acetic acid^(4) over a wide range of concentrations and temperatures well beyond the boiling point. It is being used in terephthalic acid and adipic acid up to 400 degrees F (204 degrees C) and at 67% concentration. Good resistance is observed in citric, tartaric, stearic, lactic and tannic acids (see Table 20).

TIMETAL Code-12 and 50A Pd may offer considerably improved corrosion resistance to organic acids which attack unalloyed titanium (Table 21). Similarly, the presence of multivalent metal ions in solution may result in substantially reduced corrosion rates.