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I am considering labware options to handle NaOH solutions at ~150°C. One appealing idea would be to coat my current glassware with gold. I've read different sources mentioning the possibility without further detail.

The most detailed description of a process for this is INSTRUCTIONS FOR GOLD PLATING ON GLASS by Peacock Laboratories, Inc who sells (or used to sell) products for doing so. Unfortunately, this says little as to the chemical mechanisms involved.

Would anyone guess what chemicals are being used in this process and know how to explain the mechanisms at hand, and perhaps describe properties to expect from the result?

Can I expect impermeability from the coating or at least a significantly reduced glass surface exposure to hydroxides? What is the best resistance to expect vs routine cleaning of glassware that would be coated with such a method? Can I expect it to not dissociate upon heat shocks that borosilicate glass can handle? Would there be any chemicals to avoid with such a coating, other than the few that would be expected to react with / dissolve gold metal?

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    $\begingroup$ I checked that well known auction site and found lots of titanium cups and such available. Apparently, campers buy titanium bowls, cups, etc. and the cost is lower than I expected. Maybe worthwhile to buy a titanium cup and check it out. $\endgroup$ – Ed V Aug 6 at 16:24
  • $\begingroup$ @EdV Thanks for the tip! Using titanium recipients is a possibility I didn't think about. I may have read somewhere that some titanium compounds are amphoteric though. Do you know if NaOH could dissolve traces of it from the cups? The prospect of being able to use my current glassware is appealing because the only work would be the coating part. But if titanium doesn't react I could try to recreate that equipment out of it (I really only need a cup to bring NaOH to high temperature and then a filtration apparatus). Another advantage of titanium would be not having to worry about thermal shocks $\endgroup$ – Hans Aug 7 at 6:08
  • $\begingroup$ @EdV I'm not sure what this translates into in the context of high temperature NaOH for a few dozen minutes, but I found the following statement in a paper: $\endgroup$ – Hans Aug 7 at 6:26
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    $\begingroup$ I would try a titanium cup, in any event. Also, I just checked and that same auction site lists lots of graphite and SiC crucibles, for not much money. No problem with the temperature, but only you can decide about your NaOH purity requirements. $\endgroup$ – Ed V Aug 7 at 19:02
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    $\begingroup$ How about Sterling silver (92.5% Ag, 7.5% Cu) cups? Lots available fairly inexpensive at that auction site. You could buy a small cup (“child’s cup”) and test it very easily. As well, pure silver is very easily purchased, thanks to all the silver bullion collectors, and could be tested with the NaOH. $\endgroup$ – Ed V Aug 8 at 12:49
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Gold plating glass could probably be 99.99% complete. It would make a nice mirror and would probably stay unoxidized for a long time.

However, if I wanted to remove the gold, I think I would rinse the glass with HF solution, or perhaps NaOH solution, either of which would find those teeny tiny gaps and undercut the whole gold plate.

I don't think there would be any strong chemical bonding, and no mechanical strength to a gold film. Glass is just a reactive substrate, and protecting it would require a finite thickness, with mechanical strength.

An example of plating not working well is chromium plating (although it can be done very well, it requires much attention to detail). Automobile bumpers used to be chrome plated, but developed rust spots after a few years because of porosity in the chromium film. I believe nickel plating to reduce corrosion tendency (but Ni is not shiny enough) followed by chrome plating works reasonably well. But then there is hexavalent chromium toxicity... So now we just paint the bumpers or make them out of plastic.

Perhaps you could coat the glass with teflon or polypropylene.

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    $\begingroup$ I see that polypropylene melts at 160C, and Teflon is only good up to 260C, so I don't think either of those would work for the application described...? $\endgroup$ – jeffB Aug 6 at 15:08
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    $\begingroup$ Your second sentence pretty much says it all. And stirring anything in a gold-plated beaker or flask, especially something moderately viscous, would be problem. $\endgroup$ – Ed V Aug 6 at 17:50
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    $\begingroup$ Pure gold is very soft and it is the most malleable metal, so it would be very easy to scratch, which would then expose the glass substrate. Therefore, stirring becomes a bit problematic: no stir bars, no boiling chips, no glass rod and so on. I think the gold layer would have to be unreasonably thick in order to be effective. But a rest piece, e.g., a gold coated microscope slide, or test tube, could be tried. $\endgroup$ – Ed V Aug 7 at 11:48
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    $\begingroup$ Two things: 1) "rest" was actually a typo for "test". Sorry! 2) If a PTFE stirring bar is OK at the specified temperature and putative NaOH concentration, why not use PTFE beakers? I currently have 8 brand new Teflon® beakers left from the dozen I purchased in 1987. Send me an e-mail (you can find my e-mail address pretty easily) and I will send you a beaker, gratis. Then test it! Like Yogi Berra might have said: "In theory, theory and practice are the same. In practice, they aren't." $\endgroup$ – Ed V Aug 8 at 2:22
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    $\begingroup$ One more thing: I have some titanium disks, about 2 inch diameter, so I will be happy to send along a few, if you want to test how they hold up to the NaOH. Just let me know. $\endgroup$ – Ed V Aug 8 at 2:41

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