Σldritch - 21-1-2020 at 10:57
Does a combination of materials exist with the following properties?
Material 1: Dissolves carbon
Material 2: Does not dissolve in material 1 and does not dissolve nor degrade in molten Sodium Fluoride.
A mix of transition metals is an obvious choice for M1 but M2 seems harder. Alumina will probably dissolve, especially at the temperatures needed for
M1 to work. Looking at softer acidic oxides such as zirconia and molybdenia the problem becomes that they have volatile fluorides that will probably
boil off leaving Sodium Oxide. So there is two solutions as i see it:
1. Find miracle solvent for carbon that can do its thing at around 800 C .
2. Find a better ceramic.
I realize i am letting my curiosity run a bit wild here but maybe some intersting discussion can result from the oft asked question of a solvent for
carbon.
Paper on alumina solubiliy in various molten salts: https://www.pyrometallurgy.co.za/MoltenSlags2009/1393-Xiao.p...
Atomistry on Nickel Carbide: http://nickel.atomistry.com
/nickel_carbide.html
Carbon solubility in various transition metals:
https://dspace.mit.edu/bitstream/handle/1721.1/82742/2700202...
[Edited on 21-1-2020 by Σldritch]
unionised - 21-1-2020 at 11:06
I suspect that a solution of carbon in molten- let's say, iron- will convert zirconia into CO2 and ZrC
karlos³ - 21-1-2020 at 12:35
Miracle solvent? Thats a case for alkahest! 
https://en.wikipedia.org/wiki/Alkahest
clearly_not_atara - 21-1-2020 at 12:41
1: Some kind of molten metal
2: http://en.wikipedia.org/wiki/Titanium_diboride ?
Σldritch - 21-1-2020 at 22:48
Titanium Diboride sounds interesting sadly it seems very hard to get. Thinking of similar ceramics, Titanium Nitride may be just what i am looking
for:
It is readily available, inert and under these conditions maybe more so than Titanium Boride since carbon is a stronger oxidizer than boron but not
stronger than Nitrogen. Wikipedia also mentions that a compound known as Titanium Carbon Nitride exist with even better properties. So some reaction
may actually be beneficial assuming the coating does not crack (considering the temperatures and the low thickness it should not be a problem even for
a ceramic). This line is very interesting too:
From Wikipedia:
"Titanium nitride is also produced intentionally within some steels by judicious addition of titanium to the alloy. TiN forms at very high
temperatures because of its very low enthalpy of formation, and even nucleates directly from the melt in secondary steelmaking. It forms discrete,
micrometre-sized cubic particles at grain boundaries and triple points, and prevents grain growth by Ostwald ripening up to very high homologous
temperatures. Titanium nitride has the lowest solubility product of any metal nitride or carbide in austenite, a useful attribute in microalloyed
steel formulas."
I also thought of a solvent: Perhaps alkali carbides or some mixture thereof can absorb excess carbon. I have a really hard time finding information
on these though, seems most of them are unstable releasing carbon at high temperature.
[Edited on 22-1-2020 by Σldritch]