Nanocrystalline Ni–C Electrodeposits Prepared in Electrolytes Containing Supercritical Carbon Dioxide

Abstract

Electrodeposition of Ni in a Watt's bath at different applied pressures and in the presence of supercritical CO 2 ͑sc-CO 2 ͒, either with or without surfactant addition, was investigated. The current efficiency was evaluated under constantly applied current density conditions. The crystal structure of the resulting Ni film was characterized by performing X-ray diffraction. The composition of the deposit was analyzed using X-ray photoelectron spectroscopy. Transmission electron microscopy was employed for microstructure analysis. Microhardness of the deposited film was measured to distinguish the role of bath composition. The experimental results showed that carbon-containing nanocrystalline Ni films could be obtained in the bath with the presence of sc-CO 2 . A significant increase in microhardness was found for the film electrodeposited in sc-CO 2 fluid, as compared with that formed in plain aqueous electrolyte. The fine grain size and solid solution strengthening caused by carbon were responsible for the increased hardness.Electroplating of nickel incorporating supercritical carbon dioxide ͑sc-CO 2 ͒ has been successfully developed. 1-4 Because sc-CO 2 has a low conductivity, electroplating in such a medium always involves an aqueous electrolyte. However, highly polar substances ͑such as water͒ and high molecular weight substances are less soluble in sc-CO 2 , and thus a surfactant is needed. When an effective surfactant is added to the sc-CO 2 /aqueous electrolyte, thermodynamically stable carbon dioxide-in-water ͑CO 2 /W͒ microemulsions that contain polar microaqueous domains can be produced. Superior properties of a Ni film electroplated in such an emulsified fluid, compared with that electrodeposited at atmospheric pressure, have been reported. 5 However, the same study has also shown that electroplating efficiency in this environmentally friendly sc-CO 2 fluid was less than that of the conventional process.In the absence of any surfactant, the coexistence of sc-CO 2 and the aqueous electrolyte gives rise to a system with two separate phases. Without any surfactant, the roles of pressure and the presence of sc-CO 2 on the plating efficiency are of interest and are explored. Furthermore, CO 2 can be dissolved in water to form carbonic acid at ambient pressure. Under high pressure conditions, such as in a supercritical state, whether CO 2 participates in the film formation and modifies the composition of the deposited layer is also of interest. The incorporation of C into the Ni deposit is thus focused upon and highlighted in this investigation. ExperimentalFor the electrodeposition, brass sheets of 1 ϫ 2.4 cm were used as substrates. The brass substrates were successively ground with SiC paper to a grit of #2000, followed by polishing with Al 2 O 3 slurry to 0.3 m, degreased in 0.1 M NaOH solution followed by water rinsing, etched in 0.1 M H 2 SO 4 solution, rinsed with deionized water, and finally dried using a stream of hot air.A high pressure cell made of stainless steel was fabricated for the electrodepo...

Nanoscale Cu Wiring by Electrodeposition in Supercritical Carbon Dioxide Emulsified Electrolyte

“…Ni films obtained by the ED-SCE were found to contain carbon content higher than the Ni films obtained by the conventional electrodeposition methods [38,39]. Carbon impurities would cause the high electric resistance problem in electrodeposited Cu [40].…”

Evaluations of Mechanical Properties of Electrodeposited Nickel Film by Using Micro-Testing Method

“…Chung and W.T. Tsai 18) reported in electrodeposition with supercritical CO 2 . Smaller grain size observed from the lm with a high carbon content indicates the co-deposited carbon would contributed to the grain re nement.…”

Crystal Growth by Electrodeposition with Supercritical Carbon Dioxide Emulsion

“…Because of the nano-grains, wear properties of the Ni films could be improved significantly [18]. Chung and Tsai proposed the grain refinement and improvement in mechanical strength are also caused by C impurity in the Ni film from decomposition of CO 2 in the electrolyte; evidence of the C impurity is detected from Xray photoelectron spectra [19].…”