Corrosion Resistance Of Titanium in Inorganic Acids

Generally speaking, titanium in oxidizing medium (such as nitric acid, chromic acid, hypochlorite and perchloric acid, etc.) corrosion resistance is better, and in reducing acid (such as dilute sulfuric acid solution, hydrochloric acid solution, etc.), due to the destruction of the passivity of the oxide film, corrosion rate is relatively fast, and with the increase in temperature and concentration. In reducing acid, the addition of heavy metal salts can play a significant role in corrosion inhibition, titanium-palladium alloy TA9 (Ti-0.2Pd) and titanium-nickel-molybdenum alloy TA10 (Ti-0.3Mo-0.8Ni) than the corrosion resistance of industrial titanium is much higher.

Titanium is the best metal material for nitric acid solution heating equipment. Titanium heat exchanger withstood 193 ℃ about 60% of nitric acid, the use of many years without corrosion. In the boiling 40% and 68% of nitric acid, the beginning of some corrosion, after a short period of time after the titanium passivity recovery, corrosion rate decreased significantly, may be related to the corrosion inhibition of titanium ions.

In high temperature nitric acid, titanium corrosion resistance depends on the purity of nitric acid. In high temperature pure nitric acid solution or nitric acid vapor, when the concentration of nitric acid in 20% ~ 60% when the corrosion is more obvious. Various metal ions even if the content is very low, such as Si, Cr, Fe, Ti, etc., also have to slow down the corrosion of titanium in high temperature nitric acid solution. In high temperature nitric acid solution, titanium than stainless steel shows stronger corrosion resistance. Titanium corrosion products (Tif+), is a very good corrosion inhibitor for nitric acid corrosion.

At room temperature in airborne sulfuric acid, industrially pure titanium is only resistant to sulfuric acid solutions of less than 5%; if the temperature drops to about 0°C, the sulfuric acid concentration can be increased to 20%. If the temperature is raised to boiling, the sulfuric acid concentration will still corrode even if it is reduced to 0.5%. At the same temperature, sulfuric acid solution into the nitrogen, titanium corrosion rate is significantly greater than the case of air. This corrosion law in other reducing inorganic acid is basically the same.

At room temperature, industrial pure titanium can withstand 7% of the following hydrochloric acid solution, the temperature increases the corrosion resistance decreased significantly. Titanium-nickel-molybdenum alloys can withstand 9% of hydrochloric acid solution, and titanium-palladium alloys can reach 27%. High-valent heavy metal ions, such as iron, nickel, copper, molybdenum, etc., can significantly improve the corrosion resistance of titanium, which is the reason why titanium has been successfully used in hydrochloric acid systems in the hydrometallurgical industry.

At room temperature, industrially pure titanium is resistant to phosphoric acid solutions of up to 30%. As the temperature rises to 60°C, the concentration drops to about 10 percent. At a temperature of 100°C, the concentration of phosphoric acid can only be maintained at about 2%, and when the temperature reaches boiling, the corrosion of titanium is not accelerated.