LIQUID METALS
Titanium has good resistance to many liquid metals at moderate temperatures. In some cases at higher temperatures it dissolves rapidly. It is used successfully in some applications up to 1,650 degrees F (899 degrees C). Kane cites the use of titanium in molten aluminum for pouring nozzles, skimmer rakes and casting ladles.^(4) Rapidly flowing molten aluminum, however, can erode titanium; and some metals such as cadmium can cause stress corrosion cracking. Some data for titanium in liquid metals is reported in Table 26.

ANODIZING AND OXIDATION TREATMENTS
Anodizing has been recommended for many years as a method of improving the corrosion resistance of titanium and removing surface impurities such as embedded iron particles.^(44) It was reasoned that since titanium's corrosion resistance is due to the oxide film that forms on its surface, any treatment, such as anodizing, which thickens this film will serve to increase the corrosion resistance of titanium.

Careful laboratory tests have shown this may not be true. The films formed on titanium at elevated temperatures in air have been found to have a rutile structure which is quite resistant to acids and can, therefore, improve the corrosion resistance. Anodizing, on the other hand, forms a hydrated structure which is much less resistant to acids.^(45,46) Tests in boiling HCl solution (Table 27) have shown no significant difference in corrosion resistance between anodized and freshly pickled specimens. Anodizing has been shown to give a marginal improvement in resistance to hydrogen absorption (Table 28) but not nearly as much as thermal oxidation.^(45)

It is true that anodizing helps to remove surface impurities such as embedded iron particles. However, excessively long anodizng times may be required to completely remove these particles. Examination with a scanning electron microscope has proven that surface iron contamination still persists, although diminished, even after 20 minutes anodizing. A more effective method is to pickle in 12% HNO3/1% HF at ambient temperature for 5 minutes followed by a water rinse. Specimens known to have embedded iron particles were found to be completely free of any surface iron contamination by the scanning electron microscope following this procedure.