Corrosion resistance of porous titanium in some aggressive media

Conclusions

• 1. Titanium specimens, of 30% porosity, prepared from an electrolytic powder of the −1 +0.25 mm fraction exhibit low corrosion resistance in 40%H₂SO₄ and 20%HCl solutions at room temperature. Specimens nitrided at 850°C for 30 min differ only little in this respect from specimens which have not been nitrided.

• 2. The nitriding of such specimens for 8 h at 850°C substantially increases their resistance to corrosion by 20% HCl. After 600 h of testing, the electrical resistivity of the specimens rises only negligibly and their surface remains bright. The corrosion resistance of such specimens in 40% H₂SO₄ is essentially no different from that of specimens from pure titanium.

• 3. The surface alloying of titanium powder with 2, 0.2, and 0.1% palladium, performed from a PdCl₂ solution, passivates specimens prepared from such powder in 20% HCl, as a result of which they resist corrosion in this acid at room temperature and holding periods of up to 600 h. Specimens containing 0.05% palladium begin to corrode after 400 h of holding in this acid. In 40% H₂SO₄, passivity of specimens is attained by introducing 2 or 0.2 wt.% palladium into titanium powder. Decreasing the palladium addition to 0.1 or or 0.05 wt.% lowers the corrosion resistance of titanium specimens.

• 4. Specimens of all the porous titanium materials investigated are totally immune to corrosion in 30% caustic soda solutions.