# Thermal decomposition of K2CO3

$$\ce{K2CO3}$$ doesn't boil. It thermally decomposes at $$\pu{1200 ^\circ C}$$. However, I find conflicting information online about this. Roughly what I have found say three inconsistent things:

1. It doesn't decompose
2. At $$\pu{1200 ^\circ C}$$, it decomposes into $$\ce{K + O + CO}$$ (Chemiday)
3. At $$\pu{1200 ^\circ C}$$ it decomposes into $$\ce{K2O + CO2}$$ (allreaction)

What actually happens when $$\ce{K2CO3}$$ thermally decomposes? Most sources agree with (3). But how can that be? Wouldn't it just decompose some more? $$\ce{K2O}$$ decomposes at $$\pu{300 ^\circ C}$$ into ($$\ce{K2O2 + K}$$) and $$\ce{K2O2}$$ decomposes back into ($$\ce{K2O + O2}$$) at $$\pu{500 ^\circ C}$$.

What is going on here? Is $$\ce{K2O2}$$ really decomposing back again to $$\ce{K2O}$$? If so, then at $$\pu{500 ^\circ C}$$ do both of these decompositions occur, cyclically pumping out $$\ce{O2}$$ and $$\ce{K}$$?

I read elsewhere that at temperatures over $$\pu{500 ^\circ C}$$, $$\ce{K2O2}$$ decomposes into ($$\ce{2K + O2}$$). This would resolve the conflict. But I find the source is unreliable. What is right?

• There's only mention "it starts decomposing" around 300 when heated, but that's probably just that it's not favourable in low temperatures, not high. – Mithoron Sep 20 '19 at 22:49
• I suppose it's possible. But I have doubts that it becomes stable again at higher temperatures. There's no mention of its boiling point anywhere. Do any other compounds begin thermally decomposing, then reach a plateau of stability at higher temperatures? – R Dev Sep 21 '19 at 0:00

With this type of search one can arrive at Thermal stability of potassium carbonate near its melting point. This paper rules out the possibilities of (1) and (2). The authors note that there is significant vapor pressure of carbon dioxide near the melting point, and suggest $$\ce{K2O}$$ formation. They also advise the readers to consult the following as the most comprehensive study on alkali carbonates. I will let you try Google Scholar for this one.