Process for manufacturing boron nitride fiber mats

A process for producing a non-woven, boron nitride fiber mat, comprising the steps of:

• centrifugally spinning molten boron oxide into strands;
• attenuating said strands with a gas stream into fibers;
• collecting said fibers into a bundle;
• heating said fiber bundle in an anhydrous ammonia atmosphere at a sufficient temperature and for a sufficient time to convert boron oxide in the fibers to boron nitride;
• blending said boron nitride fibers with boron oxide fibers and a nonaqueous liquid medium to form a slurry;
• processing said slurry through a Fourdrinier machine to form a felt;
• passing said felt through the nip of a pair of cooperating calender rolls, at least one of which is heated to a temperature sufficient to soften said boron oxide fibers to bond the boron nitride fibers together;
• and
• heating said bonded felt in an anhydrous ammonia atmosphere at a sufficient temperature and for a sufficient time to convert boron oxide in the felt to boron nitride.