Microgravity-induced wet chemical etching of borosilicate glass enhances the process rate

In the paper, microgravity simulators-Random Positioning Machine (RPM) and Rotary Wall Vessel (RWV) - were used to investigate the potential influence of quasi zero-gravity force onto the wet chemical etching of borosilicate glass substrates. For the first time, straight microchannels of different widths were etched utilizing RPM and RWV in a solution of hydrofluoric acid (HF) with additives (40% HF: 65% HNO3, 10:1, v/v). Substantial differences compared to the reference etching could be observed and the highest etching rate could be obtained for RPM (3.06 μm/min), next reference with a stirrer (2.01 μm/min) and RWV simulator (1.71 μm/min). For both RPM and RWV, also the potential aging of the solution, defined as the decrease of etching rates in a function of etched samples, was found to be the smallest (circa 10-11%). Apart from the kinetics of the etching process, the quality of the etched microchannels was also a subject of this research. As a result, good quality surfaces of the samples were observed for RPM, RWV and a reference with stirrer. When it comes to the RPM, the microfabricated structures were the deepest, but simultaneously, characterized by uniform edges and devoid of any accidental imperfections. Research on RWV, in turn, showed that the structures obtained utilizing this microgravity simulator have the smallest etching edge and have a potential to be reproduced the most precisely. Results presented in this paper can be a significant base for the further development in the field of microgravity-induced chemical research and reaction kinetics with microgravity simulators.