# Is there a Material that is High Heat Resistent and soluble?

What i‘m looking for is any sort of material that dissolves, while being able to resist temperatures of up to 1000°C. And it doesn‘t have to resist during dissolution, only while it‘s solid. And the solvent should not be corrosive, or at least only be corrosive for the soluble Material, but not for other (or most) materials (mainly metals).

Also it would be good if said material can be reused afterwards. (Like you can reuse salt if you dissolved it in water and then dried it again.) And the solvent should be environmentaly friendly.

Now, the first Part is basically what i‘m looking for and the Second is just some bonus, so it‘s good even if it‘s not consistent with the 2nd Part.

If anyone knows such a Material, it‘d be nice if you could tell me.

• Good quality quartzware does fine at 1000C (but don’t go above 1100C), and dissolves in HF, but that probably isn’t quite what you are looking for... – Jon Custer Jan 7 at 2:01
• @JonCuster Thanks for your answer, but sadly no, i forgot to mention that the solvent shouldn‘t be corrosive (or at least not corrosive for metals(or some metals)). – Lexyth Jan 7 at 2:13
• Such high temperatures pretty much rule out any organic material. A very brief search suggests maybe sodium aluminate meets your requirements. It is cheap and easy to make or buy, doesn't decompose, melts at >1600 °C, is apparently highly soluble in water and could easily be recovered by drying the aqueous solution. It's likely possible to also tune the composition somewhat by adding other inorganic salts/oxides, so you can optimise for your applications. I myself have no experience with sodium aluminate, however. – Nicolau Saker Neto Jan 7 at 2:55
• @NicolauSakerNeto Thanks, that is exactly what i was looking for. Though i don‘t know how you found it with a brief search 😅 All I could find the past 2 weeks had at most a resistance to 300°C... also, i had this Same question on Quora for 2 weeks and got 0 answers 😅 glad i joined StackExchange 😊 Thanks again. – Lexyth Jan 7 at 3:15

I cannot guarantee the materials in this answer will meet all your requirements, so it would still be very helpful if anyone else could pitch in (especially an inorganic chemist or someone with hands-on knowledge of refractory materials). I will describe my thought process, which may ultimately be more useful than the suggestions themselves.

Immediately, the requirement to resist temperatures up to 1000 °C implies organic materials are very unlikely to be suitable. Almost all reasonable organic compounds would boil, decompose or burn (in air) well before then.

So now we focus on inorganic materials. Simple examples of very heat-resistant compounds are quartz ($$\ce{SiO2}$$) and alumina ($$\ce{Al2O3}$$), both melting only past 1500 °C and with no decomposition. However, these materials also resist dissolution; quartz dissolves only in concentrated hot aqueous base, whereas alumina dissolves in both of concentrated hot aqueous base or aqueous acid.

That said, it is possible to add other compounds to these materials and change their properties. For example, mixing $$\ce{SiO2}$$ with a number of other inorganic substances causes its melting point to lower to more manageable temperatures. This is how we make most kinds of glass. Particularly interesting is that the addition of sufficient alkali metal ions can turn the glass water-soluble. For example, there are a variety of sodium silicates, whose exact composition and properties will vary with the sodium content, and at high sodium content they become very water-soluble. However, it appears these silicates melt close to 1000 °C, which may preclude their use.

Fortunately the same approach works with alumina; increasing its alkali metal ion content eventually renders the material highly water-soluble. Sodium aluminate with a 1:1 mol ratio of sodium to aluminium forms $$\ce{NaAlO2}$$, which appears to be very water soluble and still melts at >1600 °C. In principle, this material could be made into a concentrated, thick aqueous solution or slurry, poured into a mould, dried at low heat to solidify then calcined to obtain a sodium aluminate object of the desired shape. This could then be used for your applications, and redissolved in water when necessary.

In both of the previous examples, it's certainly possible to add further inorganic compounds (e.g. borax, lime, etc.) to tweak properties further. However, much of this kind of research has already been performed, so I would recommend digging into glass fabrication/cement research rather than rediscovering the wheel.

I should also mention there are ways in which my above suggestions may be inadequate. Alkali aluminates/silicates appear to be strongly hygroscopic, which may make their use more cumbersome. More worryingly, at high alkali metal content they become strongly basic, which could corrode some of the metals you plan to use, both during dissolution in water, or by direct reaction with the aluminate/silicate surface at high temperatures. You'll have to see whether this is a potential deal-breaker.

• Thanks again, and i‘m not trying to rediscover the wheel, but i need such material for an application i‘m working on, but since i‘m not too versed in chemistry it might just end as a failure 😅 Also, i‘m a bit worried about whether there will be a significant chemical reaction if it were to come into contact with molten aluminum, since that would be one of the materials i‘d like it to have contact with... but that‘s something i should worry about when it happens(or best some Time before it happens, not that it blows up or so...) 😅 Also, did you mention the low-heat drying to avoid cracks? – Lexyth Jan 7 at 10:32
• I had a feeling you wanted to use molten aluminium, which is a somewhat harder case, as it's comparatively quite reactive. Molten aluminium will rip oxygen out of most compounds (I presume you've heard of thermite?), but it might not rip oxygen out of sodium aluminate (which is kind of like ripping oxygen "from itself"), so things may work out. There might be some corrosion of the aluminium metal, especially when water is added to dissolve the sodium aluminate, but I don't know to what extent. I suggested drying in steps to reduce issues with poor setting, yes. – Nicolau Saker Neto Jan 7 at 10:49
• I also want to share another source of information: Lesker. This table shows a number of substances which are heated to high temperatures so they can be evaporated in a vacuum. Look at the "thermal evaporation" columns; they suggest what kind of materials are best able to withstand the hot substance. For example, hot aluminium is best handled by a boron nitride/titanium diboride crucible, or tungsten. However, neither of these are soluble. It also doesn't necessarily mean other crucibles are incompatible. – Nicolau Saker Neto Jan 7 at 10:56
• One more thing: you can look into methods for making aluminium casts. Most people will pour aluminium into clay, but perhaps someone out there has found a casting substrate which is soluble in water. – Nicolau Saker Neto Jan 7 at 11:01
• Well, it will still be good even if i can't use it with aluminium, but i'll work that out when the time comes. But one thing might prove to be problematic, and that is the drying speed... i would need it to go from the dissolved state (with a relatively high viscosity, to maintain it's shape, without a particular strain applied to it) to become completely solid within around 1 minute at most, the faster the better, since it should be a relatively fast process, but without loosing any structural integrity of the resulting shape. – Lexyth Jan 7 at 11:01