Sulfuric acid titanium corroded

R 16a] [R 17] [R 19] [P 36] High sulfuric acid contents can lead to steel corrosion [37, 38,97]. This may even lead to blockage by accumulation of corroded material in the tube. It is also claimed [38] that steels are not suited for nitration however, since the grade of the steel employed is not given, it cannot be excluded that high-aUoy steels may behave better. Silicon, glass and titanium are recommended materials [38]. 

Titanium, like zirconium, relies on a protective passive film for corrosion protection. It has excellent resistance to corrosion in nitric acid, chromic acid, wet chlorine, and hypochlorites. It corrodes quickly in hydrofluoric acid and in hot sulfuric and hydrochloric acids. Titanium is used extensively in sea water applications, primarily as heat-exchanger tubing. 

The purposes of the grid are to hold the active material mechanically and conduct electricity between the active material and the ceU terminals. The mechanical support can be provided by nonmetallic materials (polymer, ceramic, rabber, etc.) inside the plate, but these are not electrically conductive. Additional mechanical support is sometimes gained by the construction method or by various wrappings on the outside of the plate. Metals other than lead alloys have been investigated to provide electrieal conductivity, and some (copper, aluminum, silver) are more conductive than lead. These alternate conductors are not corrosion-resistant in the sulfuric acid electrolyte and are often more expensive than lead alloys. Titanium has been evaluated as a grid material it is not corroded after special surface treatments but is very expensive. Copper grids are used in the negatives of some submarine batteries. 

General corrosion is characterized by a uniform attack over the entire exposed surface of the metal. The severity of this kind of attack can be expressed by a corrosion rate. With titanium, this type of corrosion is most frequently encoimtered in hot, reducing acid solutions. In environments where titanium would be subject to this type of corrosion, oxidizing agents and certain multivalent metal ions have the ability to passivate the titanium. Many process streams, particularly sulfuric and hydrochloric acid solutions, contain enough impurities in the form of ferric ions, cupric ions, etc., to passivate titanium and give trouble-free service. Refer to Table 20.6 for compatibility of titanium with selected corrodents. 

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