ochoco

Not concerned about making caustic, but am concerned about decomposition of Na2CO3 to CO2(g) and Na2O(s) in a high temperature operation in our plant. I understand that decomposition can begin at 400 C. Fusion occurs at 854 C, with a corresponding increase in decomp pressure (CO2 gas). What I'm interested in is: What are the decomposition pressures within the range of 400 C to 880 C, before fusion occurs? thanks.