Catalytic coating and method of manufacturing thereof

Abstract

The invention relates to a catalytic coating of surfaces of valve metals, for example titanium, suitable for operation in highly aggressive electrolytic environments such as electrolysis cells of hydrochloric acid. The coating may be used as catalytic activation of electrodes, for example for anodic evolution of chlorine, or for protection from crevice corrosion of flanges and other elements of electrolysers subject to stagnation of liquid.

1 . A coated valve metal substrate having a coating comprising a titanium-free first catalytic layer consisting of an amorphous phase of Ta 2 O 5  in admixture with a tetragonal ditetragonal dipyramidal crystalline phase consisting of either RuO 2  or a solid solution of RuO 2  and SnO 2 , said first catalytic layer obtained from a solution of compounds of tantalum, ruthenium and optionally tin in one or more coats, with subsequent thermal decomposition after each coat. 
     
     
         2 . The coating according to  claim 1  wherein the weight ratio of said amorphous phase to said crystalline phase ranges from 0.25 to 4. 
     
     
         3 . The coating according to  claim 1  wherein the Ru to Sn weight ratio in said crystalline phase ranges from 0.5 to 2. 
     
     
         4 . The coating according to  claim 1  comprising a second catalytic layer applied externally to said first catalytic layer, wherein said first catalytic layer has a weight ratio of said amorphous phase to said crystalline phase ranging from 0.25 to 2.5 and said second catalytic layer consists of an amorphous phase of Ta 2 O 5  mixed with a tetragonal ditetragonal dipyramidal crystalline phase of RuO 2  with a Ru to Ta weight ratio ranging from 3 to 5. 
     
     
         5 . The coating according to  claim 1  comprising a protective pre-layer consisting of a mixture of oxides of titanium and tantalum interposed between the valve metal surface and said first catalytic layer. 
     
     
         6 . The coating according to  claim 1  applied to a substrate of titanium or titanium alloy. 
     
     
         7 . The coating according to  claim 6  wherein said substrate is an anode substrate or a flange of a chlorine-producing electrolyser. 
     
     
         8 . The coating according to  claim 7  wherein said electrolyser is a hydrochloric acid electrolyser. 
     
     
         9 . A method for manufacturing a coating according to  claim 1  comprising the following simultaneous or sequential steps:
 optionally applying a solution of compounds of titanium and tantalum to a valve metal substrate in one or more coats, with subsequent thermal decomposition after each coat; 
 applying of a solution of compounds of tantalum, ruthenium and optionally tin in one or more coats, with subsequent thermal decomposition after each coat, until obtaining a first catalytic layer; and 
 optionally applying of a solution of compounds of tantalum and ruthenium to said first catalytic layer in one or more coats, with subsequent thermal decomposition after each coat, until obtaining of a second catalytic layer. 
 
     
     
         10 . The method according to  claim 9 , wherein said compounds of ruthenium and tin are hydroxyacetochloride complexes.