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- Type of Document: M.Sc. Thesis
- Language: Farsi
- Document No: 41351 (07)
- University: Sharif University of Technology
- Department: Materials Science and Engineering
- Advisor(s): Dolati, Abolghasem; Ghorbani, Mohammad
- Abstract:
- In recent years use of expensive metals plating has taken much interest from decorative state to industry trends. In this research the effect of pulse plating on the structure and properties of pure gold and gold-nickel has been studied.In case of pure gold pulse plating from cyanide bath, it was shown that current efficiency increased by increasing duty cycle up to 30% and decreased, afterwards. By increasing frequency from 1 to 150 Hz current efficiency decreased. By reducing the level of frequency, average grain size was increased, owing to the occurrence of recrystallization. An increase in the value of current density was also shown to be responsible for a reduction in current efficiency, as well as it caused the surface overpotential and grain size to increase in some level. In pure gold pulse plating from the cyanide-citrate bath it was indicated that, by increasing duty cycle from 25% to 55%, current efficiency takes higher values and then is declined. By increasing current density, grain size is increased due to blocking active surface sites for nucleation. By increasing temperature, the dendritic structure was transformed to a spherical structure. In order to achieve hard pure gold pulse plated from cyanide and cyanide-citrate baths, 55% duty cycle, 150 Hz frequency, 6 mA/cm2 average current density and 59?C temperature, as the optimum conditions were determined. In gold-nickel pulse plating from cyanide-citrate bath it was found that increasing the duty cycle up to 55% may cause an increase in the Ni content in deposits on the basis of Cheh diffusion layer model. Also influences of pulse parameters were in good agreement with Roy model. By increasing duty cycle from 25% to 55% current efficiency slightly increased. Decreasing the level of frequency to 50 Hz resulted in an increase in Ni content of the deposits up to 1.5 %. By increasing frequency up to 150 Hz, current efficiency increased to 60%. By decreasing frequency, grain size decreased. By increasing average current density to 15 mA/cm2, Ni content in deposits decreased to 0.7 % and current efficiency decreased from 63% to 50%. In order to achieve hard gold-nickel pulse plated from cyanide-citrate baths, 55% duty cycle, 150 Hz frequency, 7 mA/cm2 average current density and 59 ?C temperature, as the optimum conditions were selected
- Keywords:
- Cyanide-Citrate Bath ; Gold-Nickel Alloy Coating ; Pulse Plating ; Pure Gold ; Cyanide Bath
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