A highly porous object can be made directly from the powder, without a need to vapor deposit it on a substrate. Porous Metal Design Guidebook Section 1 (about 700 kb pdf file)
I would be worried about the control rate and having a runaway reaction. The cereamic could act a a “Buffer” but not sure how “Hot” the reaction would be...
My impresion is that the reaction isn't that fast (and therefore hot). Does regulating the H2 introduction rate modulate the rate of reaction? Maybe there is a gas mixture that quenches the reaction.
Doesn't vapor deposition tend to work just the visible/exposed parts of the object(s) in the chamber?
I'm sure people smarter than I am have looked into fabrication and control options - I was just offering my knee jerk reaction.
a runaway reaction.
***A legitimate concern. Pons & Fleischmann saw at least one meltdown; Rossi had one in a demonstration; there are several other references in LENR history.