634-ZO !! .... >95% zirconium oxide? Dewey, I do recall you mentioning Pyro Paint, but just not the specific version.
Not 634-AL ? (Alumina based)
You can see perhaps why I like clarification.
(The spectral emissivity of zirconia is pretty close to that of alumina, and within the Optris camera spectral sensitivity band, the two oxides are nearly the same. They sure would look different by any chemical analysis, though.)
What can be the advantage of coating the dogbone with zirconium oxide paint ?
It beats me ! But I am open to any suggestion.
Could it be that the construction of the dogone started with a tube where the heating coils where wound on ?
And that this then was coated with the zirconium oxide paint to settle the heating coils and preventing possible shorts due to movement of the heating element due to temperature changes.
And that as a final step the rest of the dogbone was casted on this with an alumina casting ?
Remember that the Lugano testers took a sample of the outside of the dogbone and analyzed it and reported that it was more then 99 % alumina.
So where was the zirconium oxide ?
The above possible construction also explains the possible extension of the heater coil under the end-caps (And thereby the flatter temperature profile compared to the MFMP dogbone)
Maybe Dewey has some more details to share ?