High hydrogen pressure could be a necessity for the dogbone, and controlling that pressure could be a looming issue.
For those who do not think that metal to ceramic hermetic bonding is feasible, in the design of an advanced version of the dogbone, here is a counter-argument in the form of a common RF amplifier tube, which can have 6 or more metal to ceramic joints and operates at 20,000 watts output and higher – and it gets rather hot (even with water cooling). http://www.cpii.com/docs/datasheets/76/3CW20-000H7.pdf Not only that, many of these tubes can be opened and resealed. I have an Eimac beauty which is a holdover from what was to be an attempt to replicate Naudin’s MAHG years ago, but never got off the ground. Actually, one wonders about the feasibility of adding LiAlH4 directly to this type of tube, if it were not for the resultant high pressure. The problem is that any kind of metal to ceramic seal works only in a narrow range of temps, and an RF tube needs to hold a vacuum, not pressure. In retrospect, it is possible the MAHG was producing SPP but was being operated at too low hydrogen pressure. However, if by using a well-engineered metal to ceramic seal - one can provide a controlled entry port for hydrogen, then high pressure is not needed (presumably), and the main additional requirement is to have a ceramic tube offset connector, separating the dogbone from the stainless plumbing via temperature gradient, which can drop the temperature in a controlled fashion from perhaps 1400C down to 300C. That should require no more than a 20 cm long extension. One can use the clamp and hub connector method if a flange is provided on the extension tube.
