Exploration of Heat-Induced Color Formation on Nickel

Abstract

In this research, various pure nickel and electroless nickel-plated samples were heat treated in a regular air atmosphere at different temperatures and times to explore their heat-induced color formation effects for decorative applications. This color formation is an effect of thin-film interference between the nickel and its resulting oxide layer after heat treatment causing various colors from straw, brown, reddish-brown, purple, and blue. Control of the color formation has the potential for commercialization as a decorative method for electroless nickel-plated material. Initial experiments attempted duplicating the color formation shown on heat-treated electroless nickel-plated diamond particles. Later experiments explored the effect of how different substrates of electroless nickel-plated samples led to different color formation kinetics with Energy Dispersive X-Ray analysis. Thin film interference calculations were also compared to oxidized pure nickel samples whose oxide layer was measured by Ellipsometry and Focused Ion Beam-Scanning Electron Microscopy. Lastly, the phosphorous content produced by five different electroless nickel plating recipes on pure nickel samples was measured with an Energy Dispersive X-Ray showing a correlation related to their color formation kinetics. The same samples were also analyzed with a NIX Color Sensor, which measured their red, green, and blue color values.