I want to use silicon nitride ball bearings with a reciprocating piston that will be powered by $\ce{CO2}$ liquid heated to $\mathrm{288^oC}$ becoming super critical. That temperature is the maximum and the cylinder will not exceed that staying well below the $\mathrm{768^oC}$ rating of the bearings.
I can not use lubrication and the 1/4 bearings will be stacked 3 high with 4 of them surrounding the rod for a total of 12 bearings in direct contact with the rod that could have traces of supercritical $\ce{CO2}$ upon it. The bearings will be in contact with each other to provide both a seal and to align the piston and if there is any contamination it will spread.
Can I expect any type of reaction between the supercritical $\ce{CO2}$ and silicon nitride bearings?