Norman E. Weston

Melt spun calcium aluminate fibers: infrared transmission

Abstract Inviscid melt spinning made it possible for the first time to obtain glassy calcium aluminate fibers. The fibers had tensile strengths of up to 1.06 GPa (151 kpsi), and their optical transmission properties between 0.4 and 6.0 μm were comparable to those of similar bulk glasses used in military and commercial applications (e.g., missile domes, thermal imaging). These experimental fibers were spun from melts having viscosities ranging from 8.7 to 0.5 Poise into propane as a reactive medium to stabilize the molten jet.

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

Abstract 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.

Inviscid melt spinning (IMS); as spun amorphous alumina fibers

Abstract Inviscid melt spinning (IMS) was developed nearly two decades ago to spin metal (primarily, stainless steel) fibers from low viscosity melts in a chemically reactive environment (O 2 , H 2 S, NH 3 ). This paper evaluates 17 IMS alumina-calcia fibers (50–80% Al 2 O 3 ) which were melt spun into propane gas. They were X-ray amorphous, had tensile strengths of 21–151 kpsi, diameters of 141–450 μm, and melt and crystallization temperatures ranging from 1341 to 1842°C and from 969 to 1021°C, respectively. The chemical reaction produced a carbonaceous fiber skin or sheath with a thickness of up to 6000 A.

Infrared optical tellurite glass fibers

The liquid viscosities of glass-forming telluria-alumina (6–11 wt% alumina) were found to be high relative to those of 100% telluria, but not high enough to permit processing of glass fibers by conventional methods, i.e., down-drawing from a preform or extrusion (spinning) through an orifice. The viscosities were, however, sufficiently high that the first tellurite fibers on record could be up-drawn from the surface of supercooled melts below the liquidus. A high speed, low cost process is feasible if development of infrared tellurite fibers is warranted.

Melt-processed calcium aluminate fibers: structural and optical properties

This paper compares melt processed calcium aluminate fibers from two technologies in terms of their optical and structural properties. Strong amorphous fibers with a modulus 15-16 Mpsi (vs. 9-12 Mpsi for silica fibers) can be drawn from quaternary, low-silica calcium aluminate melts with 42-44%/wt. Al2O3, <6% SiO2, and <5% MgO, and from quaternary, non-silica Ca aluminate melts with 46% Al2O3, 4% MgO, and 14% BaO. These fibers have excellent structural properties. Amorphous Ca aluminate melts with 51.5-80.2% Al2O3 (both with and without silica) have much lower viscosities. They cannot be drawn from supercooled melts, but can be spun, by inviscid melt spinning, whereby a low viscosity jet is ejected into propane, affording chemically induced jet stabilization. These fibers were weaker, but were found to have sapphire-like infrared transmission spectra. A carbon sheath from the pyrolytic decomposition of propane was formed on the surface of most spun fibers. It acted like a hermetic coating and was found to significantly enhance the hydrolytic stability of the fibers.

Glass Fibers from High and Low Viscosity Melts

Typical commercial and experimental oxide glass fibers are made from silicate melts, which have viscosities of log 2.5 to log 3.0 poise at the forming temperatures. But, strong fibers were recently also made from melts having viscosities of 0.5 to 2.0 poise, and a sharp melting point rather than a viscosity that gradually changes with temperature. This paper analyzes the various mechanisms of fiber formation, and proposes an answer to the apparent inconsistencies. In this context, the present paper bridges recent advances in the disciplines of advanced inorganic fibers [1], composite reinforcing fibers [2, 3, 4], and fiber glass reinforcements [5].

Science And Technology

Commercial products, which are derived from natural fibers, plastics or composites are being offered by entrepreneurial ventures (Nexia Biotechnologies), mid-size companies (e.g., Cargill-Dow) and large corporations (Daimler-Chrysler). In addition, new developments (hybrid natural/glass fiber reinforced composites, soy and corn oil derived plastics), and promising research results (nanoparticle reinforced natural plastics), continue to find their way into the scientific, trade and patent literature.