Searching for fully sintered boron nitride ceramic

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Fully sintered boron nitride ceramics are challenging to obtain due to their high sintering temperatures, making them expensive and difficult to produce. The discussion highlights a specific need for large crucible parts, measuring 200mm in diameter and 400mm in length, with currently available materials being semi-sintered and not meeting the desired specifications. A previously encountered sample of light yellow boron nitride was noted for its smooth, semi-transparent quality, contrasting with the white, powdery material recently acquired. The conversation also references research indicating that achieving a relative density above 96% in hBN powder sintering is currently impossible, even at high temperatures. The thread concludes with a call for information on suppliers of fully sintered boron nitride and their maximum size offerings.
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Anyone can supply slightly yellow, fully sintered boron nitride ceramic?
I understand that boron nitride has quite high sintering temperature so it is not easy and could be quite expensive to get fully sintered material. But there are something available, right? I think I saw a small smaple of lilght yellow boron nitride ceramic years ago, but I don't remember the manufacturers name. It was quite smooth and semi-transparent, like alumina(I'm quite sure it's not PBN, because it's a block of about 1" cube). I believe it should be a fully sintered one. However, the BN I recently obtained are quite white, not transparent, and can be scraped off into powder. I guess it should be semi-sintered material, not fully sintered.

My job is now working on a quite big crucible like parts, that requires about 200mm Dia. x 400mm L in size. We puchased some [Link redacted by the Mentors], as they are the only one we found that could make such big parts. The parts are acceptable but, like what I said, they are more like a semi-sintered material. I was wondering is there anyone knows who can supply the fully sintered material? And, the maximum size available?
 
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