| Though having disadvantage such as low current efficiency and toxicity, the electrodeposition of traditional chromium or chromium alloy had been employed from heaxvalent chromium electrolyte since the first use of the process. With the more and more attention having been paid to the pollution control and economical efficiency at the present time, it has been hoped to substitute by nontoxicity trivalent chromium electrolyte little by little. While high quality deposition from trivalent chromium electrolyte could only be sustained for short periods and thin deposits obtained of decorative value only, it is difficult to substitute heaxvalent chromium plating in engineering electrodeposits by trivalent chromium plating at all. In order to resolve the problem of substitution for heaxvalent chromium electrodeposits, the technology and mechanism of pulse plating nanocrystalline chromium, chromium-nickel-iron alloys from trivalent chromium electrolyte have been investigated based on the electroplating nanocrystalline iron-nickel alloy foil.In this dissertation, methods of plating nanocrystalline iron-nickel alloy foil and iron-nickel-chromium alloy foil, which are used in electromagnet fields, have been studied for the first time based on the electroplating nanocrystalline iron-nickel alloy. The technological parameters, which affect the alloy composition and current efficiency, have also been studied systemically. The optimum technology of iron-nickel alloy foil plating is followed as that: 52g l-11 FeSO4 7H2O,about 3.5 of the concentration ratio of Fe2+ and Ni2+ , 29~34g l-1 stabilizer I , 10g l-1 stabilizer II. with 5 A dm-2 current density ,at 48-52C temperature in the solution of pH restricted between 1.75 and 2.25. The optimum technology of iron-nickel-chromium alloy foil plating is followed as that: 20 g l-1 CrCl3 6H2O,65~70 g l-1 FeSO4 7H2O,180 g l-1 NiSO4 6H2O,45 g l-1 NiCl2 6H2O,45 g l-1 H3BO3, 25~30 g l-1 stabilizer I , and 10g l-1 stabilizer II, 1-5 g l-1brighteners ,0.2-0.5 g l-1 addictives with 10-12 A çŽ m" current density ,at 58~65C temperature in the solution of pH from2.0 to 2.50. The thickness of alloy foils are up to 50 u m with a mirror-like appearance , uniform composition and delicate grain. The iron-nickel alloy foil contains 46%~48%Ni, 50%~52%%Fe, and a little other elements such as Cr, S, B, C and P, while the iron-nickel-chromium alloy foil contains 65%~70%Fe, 30%~35%Ni, l%~2%Cr% and a little other elements such as S, B, C, O and P. The experiment proved that it is difficult to obtain thick deposits with >2% Cr from aqueous solution by direct current plating.For the first time, some new methods of pulse plating nanocrystalline chromium, and chromium-nickel-iron alloy deposits from trivalent chromium chloride -N, N-dimethylformamide (DMF) solution have been studied systemically. The effects on electrodeposit rate, current efficiency, alloy composition, surface appearance and grainsize by pulse plating periods, duty cycle, concentration of different metal ions, cathodic average current density, pH of electrolyte, operation temperature, stirring velocity and plating time from chloride-N, N-dimethylformamide solution have been studied systemically for the first time. All the nanocrystalline deposits have beenobtained at room temperature with a mirror like appearance. The thickness of nanocrystalline chromium-nickel-iron alloy deposit was up to 80 um. Nanocrystalline chromium-nickel-iron alloy deposits contain 40%~60%Cr, 10%~40%Ni, 10%~30%Fe and a little other elements such as S, B, C, O and H. The optimum technology of bright nanocrystalline chromium plating is followed as that:0.8~l ,2mol l-1 CrCl3 6H2O ,period is 100ms,duty cycle is from 0.3-0.5,average current density is from 18-20A ?dm'2 ,at temperature about 30C in the solution of pH restricted at 0.9. The optimum technology of bright nanocrystalline chromium-nickel-iron alloy plating is followed as that: period is 100ms,duty cycle is from 0.3-0.5,average current density is from 18-20A dm-2 ,at temperature about of 30C in the...
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