Method of Forming Corrosion Resistant Coating and Related Apparatus

Abstract

A method of forming a corrosion-resistant ceramic coating on a metallic substrate, the method comprising providing a passivation layer on a surface of the metallic substrate by electrochemical passivation of the metallic substrate under a first electrical current and using a first electrically conducting solution; and providing the corrosion-resistant ceramic coating on an outermost surface of the metallic substrate, the outermost surface in use adapted to be exposed to a corrosive environment, by plasma electrolytic oxidation of the metallic substrate with the passivation layer, in a second electrically conducting solution and under a second electrical current having a discharge voltage. The first and the second electrically conducting solutions comprise a tetrafluoroborate compound.

1 .- 12 . (canceled) 
     
     
         13 . An apparatus for forming a corrosion-resistant ceramic-oxide coating on a metallic substrate, the apparatus comprising:
 an electrolytic cell including a housing containing an electrically conducting solution and adapted to receive the metallic substrate therein; and   an anode and a cathode that are spaced apart and operable to supply current though the electrically conducting solution between the anode and the cathode;   wherein the electrically conducting solution comprises at least one tetrafluoroborate compound.   
     
     
         14 . The apparatus as defined in  claim 13 , wherein the tetrafluoroborate compound is selected from the group comprising potassium tetrafluoroborate, sodium tetrafluoroborate, lithium tetrafluoroborate and ammonium tetrafluoroborate. 
     
     
         15 . The apparatus as defined in  claim 13 , wherein the electrically conducting solution has a tetrafluoroborate concentration of 0.1-50 g/L. 
     
     
         16 . The apparatus as defined in  claim 13 , further comprising a mounting assembly comprising:
 an upper arm connected in electrical contact to the anode; and   a lower arm having a first end connected in electrical contact to the upper arm and a second end adapted to be connected in electrical contact to the substrate to be coated, the lower arm being movable relative to the upper arm to allow movement of the substrate within the electrically conducting solution.   
     
     
         17 . The apparatus as defined in  claim 16 , wherein the lower arm is pivotably connected to the upper arm as to be movable in an upright direction between at a first position and at least one second position, the first and second positions being angularly separated by an angle of from 90 to 135°. 
     
     
         18 . The apparatus as defined in  claim 13 , further comprising a cathode frame having a plurality cathode frame portions, each cathode frame portion being disposed along a wall of the housing and being removably connected to at least another of the cathodes frame portions, the cathodes frame portions having reversible connecting features as to be movable relative to each other, the cathode comprising a plurality of cathode plates connected to the cathode frame portions and disposed around the housing. 
     
     
         19 . The apparatus as defined in  claim 13 , further comprising:
 a filter connected to the electrolytic cell and adapted to filter a stream of the electrically conducting solution received from the electrolytic cell;   a heat exchanger connected downstream the filter and upstream the electrolytic cell, the heat exchanger being adapted to remove heat from the stream of the electrically conducting solution exiting the filter before the stream is circulated back to the electrolytic cell; and   a flow generating device operably connected to the electrolytic cell as to circulate the electrically conducting solution around the substrate, from the electrolytic cell to the filter and the heat exchanger, and from the filter and heat exchanger back to the electrolytic cell.   
     
     
         20 . The apparatus as defined in  claim 19 , wherein the flow generating device is a pump, the pump including a compressor operable to supply a gas and circulate the electrically conducting solution.