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Chemically Polishing Fused Silica
Q. Hi Everyone,
This is my first post here. This actually has to do with glass finishing but when I use Google this site shows up a bunch (especially when it comes to the use of Ammonium Bi-fluoride). Hopefully this question is appropriate for the forum.
I am trying to not only etch but chemically polish fused silica with an ABF solution. The solution is saturated at 95 deg c and also has a small amount of surfactant added (FC-99). So far I can target my removal just fine but my results in terms of wanting a smooth finish are lacking. The surface is still fairly rough in the range of 30µ inch rms, where I want to be <5.
Here is the curious thing, If I let the solution evaporate a little I start to get a very strange effect. the edges of the part start to clear up dramatically (and measure ~3µ inch rms) but you get more than ~1.5 mm from any edge and there is a very cloudy surface left that is ~35µinch rms. The parts look horrible when this happens but there seems to be a glimmer of hope if I could just get the whole part to look like the edges!
Has anyone out there seen this before? Any suggestions would be greatly appreciated!
Manufacturing engineer - Boulder, Colorado, USA
2007
2007
A. Chemical polishing solutions form a somewhat viscous surface layer that acts as a diffusion barrier between the substrate and the reactant. This limits the reaction more in low spots than in high. Add something to thicken the solution. Or perhaps add ABF to a pickling gel for stainless steel welds.
Ken Vlach [deceased]- Goleta, California
Finishing.com honored Ken for his countless carefully researched responses. He passed away May 14, 2015.Rest in peace, Ken. Thank you for your hard work which the finishing world, and we at finishing.com, continue to benefit from.
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