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This question regarding appropriate handling of hot concentrated aqueous $\ce{NaOH}$ - with particular concern for avoiding dissolution of borosilicate glassware and contamination of the $\ce{NaOH}$ solution and other reagents - led me to think of two possible solutions:

  1. Coat the glassware with a silane, providing say a polyfluorinated or other inert protective coat

  2. Avoid using glass, choose instead metal or plastic, if possible

Is either of these choices reasonable or common, or is there a better alternative? If so, which is best (considering chemical inertness, safety, complexity (including potentially cost), in that order of priority)?

In the case of choice 2, what commercial sources are there for such labware (for handling hot caustic solution for extended period). A cursory search - eg google and Merck website - did not turn up such products.

Note this question is about relatively small-scale labware (benchtop), not for reactors and the like. Volume max $\pu{5 L}$, $\pu{1 M}$ $\ce{NaOH}$, $\pu{>100^oC}$, exposure time >1 h.

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    $\begingroup$ Even a weak alkali solution should not be stored in glass or quartz vessels for an extended time as it will inevitably react with any glass ("hard" borosilicate glass reacts slower, but still). For a hot alkaline solution exposure should be limited to minutes, maybe an hour if the glass is thick enough. Old lab textbooks suggested to coat glassware used for storing alkali solutions from the inside with paraffin; these days teflon seems to be better alternative, as you suggested. $\endgroup$ – andselisk Aug 3 at 5:22
  • $\begingroup$ @andselisk Thanks. Thermo-fisher offers plastic-coated glassware ("kimcote") but that's not ptfe and not sure it would hold up. I find it strange ptfe coated products are not more prominent in product catalogues. A websearch shows me hits that cater mostly to manufacturing, not labs. $\endgroup$ – Buck Thorn Aug 3 at 5:38
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    $\begingroup$ TBH, I think we never bought teflon labware as it was always ridiculously overpriced. It was always cheaper and faster to craft own reactors with a lathe from a raw piece of teflon which is quite cheap (speaking of central Russia). $\endgroup$ – andselisk Aug 3 at 5:45
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Instead of glassware, you might have to think about metallic containers. A 1 M NaOH solution should not be that harsh for stainless steel for a short period of time. Imagine, in the chlor-alkali industry, nothing is made of glass. The electrodes are made of titanium as far as I remember. If we were rich, a platinum lined crucible would have worked! Titanium might work too, very resistant to bases.

Here is a useful link: Selecting Stainless Steel for Caustic Soda

Regarding silanes, the Achilles heel is not the perfluoro functional group on the silane but the siloxane bond itself- i.e., the Si-O-Si ---- (functional group). Base will chew this bond apart into pieces even at pH 8-9. This is the biggest drawback of HPLC silica columns. We have not been able to synthesize any base stable silica bonding.

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    $\begingroup$ No, I haven't yet, but eventually I found 1940 ed. of Hildebrand's Reference book of inorganic chemistry which also says the same, quoting from p. 415: "Platinum … is almost indispensable in the manu­facture of chemical utensils for high temperature ignitions. Such ware, however, must be handled with some care since it is attacked by a number of reagents, e.g. aqua regia, chlorine solution, ferric chloride, and fused alkalies. It alloys with many metals, especially lead, tin, bismuth, and mercury; and unites with carbon, phosphorus, sulfur, and silicon, becoming brittle." $\endgroup$ – andselisk Aug 3 at 19:38
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    $\begingroup$ Found a soft copy from the great Internet Archive. My original copy of Applied Inorganic Analysis is sitting in another country. Cannot find it anywhere now. Pretty rare book of the 1940s. $\endgroup$ – M. Farooq Aug 3 at 23:32
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    $\begingroup$ Thanks for your answer. I chose the term "aqueous NaOH" to avoid ambiguity, although the original post that inspired my question is ambiguous about concentrations and temperature. Seems my question ended up being ambiguous too. $\endgroup$ – Buck Thorn Aug 4 at 11:26
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    $\begingroup$ @andselisk they are in geochemistry. Interesting how the usage of terms differs between various fields. $\endgroup$ – Gimelist Aug 24 at 10:52
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    $\begingroup$ I don't think there is any authoritative source. You guys have IUPAC, we don't. Sometimes nomenclature differs between subfields in geochemistry, or even labs doing the same thing! There are geological dictionaries, but they don't often contain all terms used in geochemistry. That said, I think any undergraduate-level modern geochemistry book would cover most of it. $\endgroup$ – Gimelist Aug 24 at 11:07

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