Answer to Question #210208 in General Chemistry for eddie

Question

I would like to know what gases are produced from electrolytic etching of galvanized steel using lemon juice and water as the electrolyte.

Answer 1

Electrochemical etching of silicon was discovered already several decades ago [1]. The process is discussed in detail in Chapter 23, Silicon direct bonding, and only briefly introduced here. In electrochemical etching a silicon wafer is connected to an anode and immersed into a solution, which consists of hydrofluoric acid (HF), water, and ethanol [2,3]. The etching reaction is maintained by applying a bias voltage or current, and all chemicals have their own role in the process: HF removes silicon oxide, which is produced during the etching process, H2O participates in the oxidation and is used to dilute the HF concentration, and ethanol reduces surface tension and improves wettability of the wafer surface. The process is controlled by adjusting the bias current: low current density results in an oxidation-limited process and forms porous silicon (PS), whereas a high current density polishes the surface via an oxide etching–limited process. Current densities between the PS formation and electrochemical polishing conditions form randomly distributed nanopillars on the surface [4]. Electrochemical etching can produce a large variety of PS morphologies with pore diameter ranging from nanometer to micrometer scale and up to 100 µm porous layer thickness. The porosity and the morphology of the nanopillars can be adjusted by controlling the current density and etching time. However, the exact morphology depends on various factors, such as doping type and concentration of the wafer, HF concentration of the solution, and illumination conditions [3,4].