Titanium sulfuric acid corrosion

Materials that are corrosion resistant to the expected cathodic polarization qualify as impressed current cathodes. Austenitic CrNi steels are used with strong acids. The oleum (i.e., fuming sulfuric acid) and concentrated sulfuric acid tanks used in sulfonating alkanes and in the neutralization of sulfonic acids are anodi-cally protected using platinized brass as cathodes [15]. Lead cathodes are used to protect titanium heat exchangers in rayon spinning baths [16]. 

The corrosion resistance of unalloyed titanium in hydrochloric or sulfuric acids can be increased significantly by anodic protection, which maintains the oxide film so that the corrosion will be negligible even in severely reducing conditions. 

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 dioxide (Ti02) is one of the most widely used semiconductors for heterogeneous photocatalysis. This is mainly due to its activity, photostabihty, non-toxicity and commercial availability. It is found in nature and can exist in three crystal modifications rutile, anatase and brookite (Kirk-Othmer, 1996). Its composition is temperature dependent at calcination temperatures above 900 K, the anatase modification is transformed into rutile. Ti02 is insoluble in water and in diluted acids, but it dissolves slowly in hot sulfuric acid (Remy, 1973). It has a high surface activity and corrosion stabihty. The commercial production of this white pigment has been known since the early 1900s. 

SAFETY PROFILE A highly corrosive irritant to the eyes, skin, and mucous membranes. Mildly toxic by inhalation, Explosive reaction with alcohols + hydrogen cyanide, potassium permanganate, sodium (with aqueous HCl), tetraselenium tetranitride. Ignition on contact with aluminum-titanium alloys (with HCl vapor), fluorine, hexa-lithium disilicide, metal acetylides or carbides (e.g., cesium acetylide, rubidium ace-tylide). Violent reaction with 1,1-difluoro-ethylene. Vigorous reaction with aluminum, chlorine + dinitroanilines (evolves gas). Potentially dangerous reaction with sulfuric acid releases HCl gas. Adsorption of the acid onto silicon dioxide is exothermic. See also HYDROGEN CHLORIDE (AEROSOL) and HYDROCHLORIC ACID. 

Materials classes that were tested included ceramics, nickel-based and cobalt-based alloys, refractory metals and alloys, reactive metals and alloys, noble metals and alloys, and high-temperature polymers, a total of 26 materials. Test periods varied between 37.5 and 47.5 hours. None of the materials was found to be suitable for all test conditions, and most exhibited moderate (equivalent to between 10 and 200 mil per year) to severe (>2()0 mil per year) corrosion. Titanium and titanium alloys (Nb/Ti and Ti-21S) exhibited the best performance, showing only slight corrosion in the presence of excess sodium hydroxide. Under acidic conditions, titanium showed increased rates of corrosion, apparently from attack by sulfuric acid and hydrochloric acid. Both localized pitting and wall thinning were observed. 

Valve Metals Titanium is extensively used in the chemical process industry owing to its excellent corrosion resistance. However, anodic protection of titanium is required for certain environments. For example, anodic protection has been recommended widely for application of titanium in sulfuric acid applications. Experiments indicated that anodic protection considerably increased the corrosion resistance of titanium. In sulfuric acid up to 65% concentration at 65 C, the corrosion rate of anodically protected titanium was found to be 0.025 mmyr . Even at a higher temperature of 90 °C, for sulfuric acid concentration of 57%, the corrosion rate under anodic protection was found to be only 0.13 mm yr [18,19]. A... 

The primary advantage of anodic protection is its applicability for extremely corrosive environments. It is most extensively applied to protect equipment used to produce, store, and handle sulfuric acid. It is also used in chemical and nuclear industries, during the production of fertilizers, and for the protection of heat exchangers and tankers with hot concentrated adds sulfuric, nitric, phosphoric, ammonium nitrate, and so on, involving components usually made of carbon steels, alloy steels, stainless steels, titanium, nickel and its alloys, and so on. 

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