# Moving phase boundary electrochemical etching **URL:** \ **Category:** General Discussion\ **Created:** [April 23, 2023, 12:31am UTC](https://community.freefem.org/t/moving-phase-boundary-electrochemical-etching/2414 "2023-04-23T00:31:19Z")\ **Posts on this page:** 1\ **Page:** 1
**Author:** ![marchywka](https://avatars.discourse-cdn.com/v4/letter/m/ee59a6/32.png) [@marchywka](https://community.freefem.org/u/marchywka)\ **Post date:** [April 23, 2023, 12:31am UTC](https://community.freefem.org/t/moving-phase-boundary-electrochemical-etching/2414/1 "2023-04-23T00:31:19Z")
I was just curious if anyone had any particular thoughts on FF features related to this exercise. It is nominally anodic etching of a metal with a normalized/fictional Butler-Volmer equation for now. The initial equillibrium ( zero transport ) ion densities are found with the SNES non[linear solver and written to a file to be used in a seprate run. The initial and time stepping runs may need different number of cores etc. The etching was solved with the sparsesolver and time stepped. The etch progress is encoded in a phase variable, 1 in the solid and 0 in the liqud. In the images below, the top is the liquid and the bottom red is the metal being etched. At the interface, the diffusivity changes drastically and the amount of reactive ion that diffuses into the metal determines the etch amount 🙂 The one bump becomes a point before finally polishing out a bit. " any similiaritties between these simulations and real physical systems is purely coincidental " for now… ![etch0](https://canada1.discourse-cdn.com/flex030/uploads/freefem/original/2X/0/0b44b791deae9287e5d40d63a31202df9fa75d24.jpeg) ![etch43](https://canada1.discourse-cdn.com/flex030/uploads/freefem/original/2X/7/75160ea8086c280374b4d90b67602b839bf26e8b.jpeg) ![etch52](https://canada1.discourse-cdn.com/flex030/uploads/freefem/original/2X/c/c7ef32d76a34afb7ae58796922abf9ecc549a64b.jpeg)