Alloying chromium with small amounts of platinum, palladium, iridium, rhodium, ruthenium, or osmium markedly improves its corrosion resistance to nonoxidizing acids such as sulfuric or hydrochloric acid. The presence of rhodium, palladium, or osmium has little influence on the resistance of chromium to an oxidizing acid such as nitric acid, while platinum, iridium, or ruthenium greatly increases corrosion rates in this medium. These phenomena can be explained in terms of the electrochemical and corrosion behavior of the metals involved and are related to the passive and transpassive behavior exhibited by chromium.

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Tantalum alloys containing up to about 50. percent titanium retain much of the superlative corrosion resistance of tantalum. For some environments, columbium may be substituted for a portion of the tantalum. Under more severe conditions, titanium content below 30 percent appears advisable, from the standpoint of both corrosion resistance and hydrogen embrittlement. Contacting or alloying the tantalum-titanium materials with noble metals greatly decreases the latter type of attack. Tantalum-titanium alloys cost less than tantalum because titanium is cheaper than tantalum and because the alloys are appreciably lower in density. These alloys are amenable to hot and cold work, and appear to have sufficient ductility to allow fabrication. In general, maximum ductility is obtained after heat treatment at 900 to 1000 C. 6.3.13, 6.3.15, 3.7.2

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