Calcium aluminate glass fibers: drawing from supercooled melts versus inviscid melt spinning

Calcium aluminate melts with 35–50%/wt. alumina and some silica as a network former can have viscosities high enough to facilitate the drawing of fibers from supercooled melts. Strong fibers could also be drawn from the melt of a non-silica calcium aluminate glass with a quaternary composition; thus silica is not necessarily required as a viscosity builder. Calcium aluminate melts with 50–80% alumina have much lower viscosities. Fibers cannot be drawn from these melts, but they can be spun if a low-viscosity (inviscid) jet is ejected through an orifice into propane, a reactive medium that chemically stabilizes the jet. A carbon sheath (coating) is formed on the fiber surface under most, but not all, process conditions. This Letter shows for the first time that a carbon sheath significantly improves the hydrolytic stability of the resulting fibers.