| 摘要 |
<PICT:0995263/C6-C7/1> Metal surfaces, especially nickel-iron alloys and stainless steel, are freed from scale by treating in an electrolytic bath consisting of a fused mixture at 600-1000 DEG F. of sodium sulphate and sodium hydroxide, preferably containing 6-18% Na2SO4. Voltage applied is 1-7.5 V., at a C.D. of -5 to 3 A.S.Z. The electrolysis effects reduction of sodium sulphate to sulphite, pyrosulphite, dithionate, thiosulphate, sulphide and like compounds which are effective in removing the oxide scale. These compounds may be used to replace part of the Na2SO4 in the initial bath mixture. A protective layer of carbon may be floated on the surface of the bath. The metal to be treated is immersed in the catholyte which is of larger volume than the anode space, the latter preferably being in the form of a separate insertable unit. For example a tank 9 containing the fused electrolyte 15, is provided with a steel housing 10 with an anode 12 having an ion permeable diaphragm 11 in the wall facing the cathode 13. A number of such anode units (called "cyclotrons") may be used. Preferably the frame and diaphragm are connected to a low potential positive terminal to passivate these metal structures in the electrolyte. The main power is 4 volts at 40 amps, and the passivating source is less, e.g. 2 volts at 2 amps. The submerged cathode lead is protected by a zirconium metal sheath. The cathode may be of Cu, Ni, Ag, Zr, or Mo, and the anode of Fe, Ni, or Co, the diaphragm is a perforated sheet of Fe, Ni or Zr. In examples corroded sheets of stainless steel, titanium, copper or silicon steels, are treated and then washed, first in water then in acid, e.g. H2SO4 or HNO3 and HF, and finally washed with water. |
