Titanium dioxide coating method

Abstract

A titanium dioxide coating method is disclosed. An electrolyte containing Ti 3+ , an oxidant, and at least one of NO 3 − and NO 2 − is provided for an electrodeposition device, wherein the oxidant is configured for essentially oxidizing Ti 3+ into Ti 4+ . A substrate is immersed into the electrolyte and electrically connected to the electrodeposition device. A cathodic current is applied to the substrate via the electrodeposition device for reduction of NO 2 − or NO 3 − . A titanium dioxide film is thus formed on the surface of the substrate. The thickness, porosity, and morphology of the titanium dioxide film can be controlled by varying the electroplating parameters, and relatively uniform deposits on various substrates of complex shapes can be obtained by use of low cost instruments. The resultant structure of Ti 4+ species oxidized from Ti 3+ by the oxidant can be used to control the deposition rate of TiO 2 .

1 . A titanium dioxide coating method comprising:
 providing an electrolyte with a pH value ≦2 and containing Ti 3+ , an oxidant, and at least one of NO 3   −  and NO 2   −  for an electrodeposition device, wherein the oxidant is configured for essentially oxidizing Ti 3+  into Ti 4+ ;   immersing a substrate into the electrolyte;   electrically connecting the substrate to the electrodeposition device; and   applying a cathodic current to the substrate via the electrodeposition device whereby NO 3   −  or NO 2   −  is reduced to generate extensive OH −  for forming a titanium dioxide film on the surface of the substrate.   
     
     
         2 . The method as claimed in  claim 1 , wherein the oxidant is a weak oxidant which is unable to further oxidize Ti 4+  to Ti 6+ . 
     
     
         3 . The method as claimed in  claim 2 , wherein the weak oxidant comprises NO 3   −  or NO 2   − . 
     
     
         4 . The method as claimed in  claim 2 , wherein the weak oxidant comprises S 2 O 8   2− , ClO 4   − , ClO − , BrO 4   − , BrO − , IO 4   −  or IO − . 
     
     
         5 . The method as claimed in  claim 2 , wherein a ratio of Ti 3+  to the weak oxidant is equal to/above the stoichiometric ratio. 
     
     
         6 . The method as claimed in  claim 1 , wherein the oxidant is a strong oxidant in a stoichiometric ratio to Ti 3+ . 
     
     
         7 . The method as claimed in  claim 6 , wherein the strong oxidant comprises H 2 O 2  or O 3 . 
     
     
         8 . The method as claimed in  claim 1 , wherein the pH value of the electrolyte is less than 1. 
     
     
         9 . The method as claimed in  claim 1  further comprising a post annealing step after forming the titanium dioxide film. 
     
     
         10 . The method as claimed in  claim 9 , wherein the post annealing step is carried out at about 100-800° C. 
     
     
         11 . The method as claimed in  claim 1 , wherein the cathodic current is applied by galvanostatic (constant dc current), potentiostatic (constant voltage), potentiodynamic, or galvanodynamic methods, or in the pulse voltage or pulse current modes. 
     
     
         12 . The method as claimed in  claim 1 , wherein OH −  is generated by reduction of NO 3   −  or NO 2   −  at the cathode. 
     
     
         13 . The method as claimed in  claim 12 , wherein TiO(OH) 2  is generated from a reaction between Ti 4+  and OH −  and then dehydrated to form TiO 2 . 
     
     
         14 . The method as claimed in  claim 13 , wherein the generation of OH −  by NO 3   −  or NO 2   −  reduction at the cathode is catalyzed by TiO(OH) 2  and TiO 2 . 
     
     
         15 . The method as claimed in  claim 1 , wherein the Ti 3+  is obtained from dissolution of titanium.