Celsian formation in fiber-reinforced barium aluminosilicate glass–ceramic matrix composites

Hot pressing of barium aluminosilcate (BAS) glass or its composites reinforced with large diameter Textron chemical vapor deposited (CVD) silicon carbide SCS-6 monofilaments or small diameter multifilament Nicalon or Hi-Nicalon fibers resulted in the crystallization of both hexacelsian and monoclinic celsian phases. Effects of additions of monoclinic celsian seeds and strontium aluminosilicate (SAS) glass on crystal phase formation during hot pressing has been investigated. On doping BAS with 5 wt.% monoclinic celsian seeds or 10 wt.% SAS, only the celsian phase was formed in hot pressed monolithic specimens. However, in fiber-reinforced composites hot pressed under similar conditions, a small concentration of hexacelsian was still present as hexacelsian nucleates preferentially on surfaces and the presence of fibers provides a large surface area. When the additive concentration was increased to 10 wt.% celsian seeds or 20 wt.% SAS, celsian was the only phase detected from X-ray diffraction, with complete elimination of hexacelsian, in the hot pressed composites reinforced with large or small diameter SiC fibers.