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Can I electrically insulate stainless steel by painting Sodium Silicate solution on it and heating it to 200C for 30min or so?

  1. The solution should be conductive, and I've been told (to be verified) sodium silicate itself is non-conductive. Will it work from an electrical standpoint?

  2. Will it work chemically in the long term, or will it corrode the stainless steel or something?

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    $\begingroup$ I don't think it would actually work in practice. Even if you somehow manage to make a layer good enough for insulation, it would probably easily wear off. $\endgroup$
    – Mithoron
    Commented Jul 15, 2021 at 8:32
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    $\begingroup$ The issue at hand has little to do with the properties of sodium silicate or a baked coating of it. The question is whether any such coating would either form or be robust once formed when applied as described on untreated stainless steel. this seems very unlikely. And unnecessary as there are plenty of paints and varnishes that are already known to work. $\endgroup$
    – matt_black
    Commented Jul 16, 2021 at 13:30
  • $\begingroup$ Do you know of one that works well above 450C and conducts heat acceptably well? $\endgroup$
    – Hans
    Commented Jul 17, 2021 at 12:07

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The short answer is yes since1:

Amorphous silica is, in general, a good electric insulator but exhibits a finite dc electrical conductivity, especially when impurity alkali ions are contained

You will also find more info and specific references on that paper(ref. 1). For sure tests will be needed depending on the service conditions (it seems that porosity is also a critical aspect of the insulation properties).

It will also work well for improving the corrosion resistance of an existing coating. From the abstract of this paper2:

To improve the corrosion resistance of phosphate coatings, the phosphated hot-dip galvanized (HDG) sheets were post-sealed with sodium silicate (water glass) solutions. The results show that after the silicate post-treatment the pores among zinc phosphate crystals are sealed with the films containing Si, P, O and Zn, leading to the formation of the continuous composite coatings on the surface of HDG steel. The corrosion resistance of the composite coatings depending on concentration of sodium silicate and post-sealing time is greatly improved by the silicate post-treatment.

References

  1. Minoru Tomozawa, Chapter 3 - Amorphous silica, Editor(s): Hari Singh Nalwa, Silicon-Based Material and Devices, Academic Press, 2001, Pages 127-154, ISBN 9780125139090, DOI: 10.1016/B978-012513909-0/50005-2
  2. Bi-lan Lin, Jin-tang Lu, Gang Kong, Synergistic corrosion protection for galvanized steel by phosphating and sodium silicate post-sealing, Surface and Coatings Technology, Volume 202, Issue 9, 2008, Pages 1831-1838, ISSN 0257-8972, DOI: 10.1016/j.surfcoat.2007.08.001.
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  • $\begingroup$ Thank you Jojostack! Will this electrically insulate the stainless steel? $\endgroup$
    – Hans
    Commented Jul 14, 2021 at 19:57
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    $\begingroup$ yes, when all water is boiled out you're left with non conductive glass. it shouldnt be redissolved by atmospheric moisture $\endgroup$
    – Francis L.
    Commented Jul 14, 2021 at 22:24
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    $\begingroup$ The paper does not show that a simple sodium silicate solution does a good job of insulating steel. It only shows that a steel already heavily treated and coated with other substances can be further protected with sodium silicate (if fact the silicate closes pores in the phosphate coating on galvanised steel). So irrelevant to the question as asked. $\endgroup$
    – matt_black
    Commented Jul 16, 2021 at 13:26
  • $\begingroup$ added It will also work well for improving the corrosion resistance of an existing coating as it was reported in the abstract $\endgroup$
    – Jojostack
    Commented Jul 18, 2021 at 9:02
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The water glass will have no affect on the stainless (304 ?). But insulation will depend on thickness of glass and the voltage, so specifics would need to be researched. I understand water glass redissolves if exposed to water.

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