Yes, it is possible to braze ceramics together with more ceramics. Typically called "fusing". Tends to work better (i.e. achieve closer to monolithic stress capabilities), if done on higher purity aluminas. It can be done on fired ceramics, or on green.
I would guess that there are glass frits available for joining the aluminas/aslumina.
If you can tolerate a thin interface of a few thousandts of an inch of metal, the Moly-Manganese metalllizing process will give you as much as 9,000 psi tensile strength. I can give most of the processing details if you are intereted.
I did a word search for glass frits on this forum and came up witht this thread so I did a Google search and seletcted a few links that might lead you to something:
You can try an active metal paste from Wesgo or Lucas Milhaupt. It will be a silver-based braze with titanium added (a few percent). You paint it on the mating faces. dry them, put them together in an graphite alignment fixture and heat the assembly in vacuum or argon to 900-950C. When the parts cool down, take them out. Your parts are brazed together.
JvdWal,
1) By monolithic, I assumed you wanted the same material throughout (Alumina in this case). But if you simply mean one contiguous piece then JimMetalsCeramics suggstion might simplest if it provides the properties you need.
2) The Mo-Mn process mentioned in my June 27 post, will give you leak tightness of 1 x 10^-8 cc/year leak rate of Helium. Also note the high tensile strength attained with the Mo-Mn process.
Thank you for your replies, Jimmetalsceramics and metman.
As said in your first point metman, I want the same material throughout for a semiconductor application. Metal may not be used in this application. What is possible
For an other application where leak tightness is important, sounds the Mo-Mn process interesting. I can tolerate a thin interface of a few thousandts of an inch of metal. Refering to your post June 27, wat are most of the processing details?