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$\ce{K2CO3}$ 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?

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    $\begingroup$ 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. $\endgroup$ – Mithoron Sep 20 '19 at 22:49
  • $\begingroup$ 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? $\endgroup$ – R Dev Sep 21 '19 at 0:00
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This question serves as a prime example of how much fake and scientifically incorrect information, or more famously, fake news is there on the web. This is why ordinary web should not be anyone's first priority to search about scientific topics. There is a famous saying that "paper never refused an ink" which applies to the web as well in the sense that anyone can write anything. Use Google Scholar, which only searches research level articles (relatively more authentic).

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.

References

  1. A. Reisman, Reactions of the Group VB pentoxides with alkali oxides and carbonates. IX. A DTA study of alkali metal carbonates, J. Am. Chem. Soc. 80 (1958) 3558-3561.
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