Fragility melts

Forming glass fibers from fragile melts... 

Thus, fibers are best formed from strong silica and silicate melts by down-drawing them from preforms or from conventional bushings. Glass fibers can be formed from fragile melts, but they must be super-cooled to a viscosity in the log 2.5 and log 3.0 poise range. 

Quaternary calcium aluminate glass fibers were also downdrawn from preforms on a laboratory [9] and a development unit [41], Downdrawing is a valid, but costly, method for fiberizing fragile melts. In addition, only one of >500 compositions could be fiberized on a conventional melt fiberizing unit [17], This process is not suitable for fragile melts. 

Figure 7. Calcia-alumina-silica system. This illustration compares the melt viscosity of the inviscid binary aluminate melts from 60% CaO to 75% alumina. Addition of MgO and CaO produces quaternary aluminate melts, raises the viscosity significantly and produces a fragile melt with high viscosities below the liquidus temperature and low viscosities above the liquidus temperature. Redrawn from F. T. Wallenberger and S. D. Brown, High modulus glass fibers for new transportation and infrastructure composites and for new infrared uses, Composites Science and Technology, 51.243-263 (1994).

Quaternary calcium aluminate glass fibers made by updrawing from a supercooled fragile melt offer superior mechanical properties and sapphire-like infrared transmission spectra. 

Fragile melt Molten material which is difficult to process into fibers. 

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