Apparatus for coating metal with oxide

An electric circuit for implementing an electrolysis process that applies an oxide coating to the surface of a metal by immersing said metal in an electrolyte water solution, and applying an alternating voltage of more than 250 volts peak-to-peak between said metal and an inert electrode, wherein said electric circuit consists of the series connection of (a) an alternating voltage power source, (b) a capacitor, (c) a pair of back-to-back thyristors, called series thyristors, and (d) the tank electrolysis circuit, which is the electric conduction path between said metal sample and said inert electrode, and where there is additionally (e) a pair of back-to-back thyristors, called shunt thyristors, in parallel with said tank electrolysis circuit;

• wherein the improvement comprises the following:
• the control electrode of each thyristor of said electric circuit is excited by a long voltage pulse, of duration more that 5 percent of the period of said alternating voltage power source, where said long voltage pulse is applied to said control electrode when the anode voltage of said thyristor is less than the cathode voltage, and where said long voltage pulse is maintained until said anode voltage of said thyristor exceeds said cathode voltage by the excitation threshold of said thyristor, thereby allowing said thyristor to turn on.