ACIDS
OXIDIZING ACIDS
Titanium is highly resistant to oxidizing acids over a wide range of concentrations and temperatures.
Common acids in this category include nitric, chromic, perchloric, and hypochlorous (wet Cl2)
acids. These oxidizing compounds assure oxide film stability. Low, but finite, corrosion rates from
continued surface oxidation may be observed under high temperature, highly oxidizing conditions.
Titanium has been extensively utilized for handling and producing nitric acid^(4,21) in applications
where stainless steels have exhibited significant uniform or intergranular attack
(Table 10). Titanium
offers excellent resistance over the full concentration range at sub-boiling temperatures. At higher
temperatures, however, titanium's corrosion resistance is highly dependent on nitric acid purity. In
hot, very pure solutions or vapor condensates of nitric acid, significant general corrosion (and
trickling acid condensate attack) may occur in the 20 to 70 wt.% range as seen in
Figure 5. Under
marginal high temperature conditions, higher purity unalloyed grades of titanium (i.e., TIMETAL
35A) are preferred for curtailing accelerated corrosion of weldments.
On the other hand, various metallic species such as Si, Cr, Fe, Ti or various precious metal ions
(i.e., Pt, Ru) in very minute amounts tend to inhibit high temperature corrosion of titanium in nitric
acid solutions (Table 11). Titanium often exhibits superior performance to stainless steel alloys in
high temperature metal-contaminated nitric acid media, such as those associated with the Purex
Process for U3O8 recovery. Titanium's own corrosion product Ti^+4, is a very potent inhibitor as
shown in Table 12. This is particularly useful in recirculating nitric acid process streams, such as
stripper reboiler loops (Table 10), where effective inhibition results from achievement of steady-
state levels of dissolved Ti^+4.
NITRIC ACID
The data in Table 13 shows that titanium also offers good resistance to nitric acid vapors.
CAUTION: Titanium is not recommended for use in red fuming nitric acid because of the danger of
pyrophoric reactions.