S. D. Brown

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.

Hydrogenation of SiC: Theory and experiments☆

Abstract The effects of hydrogen on the microstructure of a pressureless-sintered α-SiC is currently under study. Thermodynamic calculations have been made and compared with results from various microstructural and microchemical methods. A full thermodynamic evaluation was performed, showing that hydrogen will tend to cause a silicon-rich solid. Microstructural results confirm that an α-SiC material that is high in carbon will tend to decarburize when annealed in hydrogen at 1400°C. High voltage electron microscope in situ studies at lower temperatures show that the graphite in the system disintegrates when in contact with hydrogen while a reaction involving both SiC and carbon also seems to be taking place.

Adherence* failure and measurement: some troubling questions

It is pointed out that many methods used to determine the adherence of films and coatings to their substrates are inadequate. Sometimes, they are misleading. Key test conditions must appropriately simulate the conditions of service under which adherence failure may be brought about. It is indicated that the test environment and the rate and mode of stress application are among the important factors to consider. The nature of adherence failure is discussed against a background of multibarrier fracture kinetics. A brief review of multibarrier fracture kinetics as it applies to adherence failure and testing is given. Some evidence is cited to show that competitive failure mechanisms operate in many cases of adherence failure, and that which mechanism dominates depends on the conditions of failure.

ZnO-modified high modulus glass fibers

Abstract It was found that zinc oxide is a modifier that effectively increases the modulus of aluminate and silicate glass fibers. Glass fibers having a higher fiber modulus than that of S-Glass were prepared by modifying aluminate and silicate composition with 5–25 mol% ZnO under conventional glass-forming conditions by melting the mixed oxide powders above the liquidus. The highest fiber modulus obtained in the ZnO-modified aluminate system (44CaO30Al2O310ZnO5MgO 5Li2O4SiO2) was 1.44 × that of S-Glass, but a new drawing process would be required. The highest modulus obtained in the silicate system (46.8SiO216.9ZnO12.1CaO11.8MgO5.3TiO25.3Li2O0.9ZrO20.9CeO 0.01Fe2O3) was 1.20 × that of S-Glass and no new process is required.

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.

Aluminum Ion Deposition in Rat Tissues Following Implantation of a Ceramic-Metal Disc

Plasma-sprayed alumina on 316L stainless steel discs was implanted in Sprague-Dawley rats for six months; at which time the animals were sacrificed, and selected tissues analyzed for aluminum concentration using atomic absorption spectrophotometry. The liver, testes, and kidneys exhibited significant increases in aluminum ion concentration.

Melt processing of calcium aluminate fibers with sapphirelike infrared transmission

X-ray amorphous, calcium aluminate glass fibers can be made by one of three melt processing methods. This review compares products and processes, and points to a potentially promising future. Selected amorphous fibers with 23-47% A1203 have high melt viscosities (>100 Pa-s) and can either be drawn from supercooled melts or spun above the liquidus through an orifice. The vast majority of fibers, especially those with 50-100% A1203 have low viscosities (<1 Pa-s) and can only be made by inviscid melt spinning, a process whereby the molten low viscosity jet is ejected through an orifice above the liquidus, and chemically stabilized in a reactive environment. As-spun fibers with 50-81% A1203 were x-ray amorphous and strong, but polycrystalline and weak with 82-100% A1203. Fibers by either process were aimed at structural uses (fiber reinforced composites). Recent work shows that x-ray amorphous fibers have sapphire-like infrared transmission spectra and have greater potential in optical than in structural applications. Thus new non-silica optical fibers can now be explored by any of the three processes; all promise to afford lower cost fibers at higher production rates than possible with slow processes (e.g., single crystal fiber growth) yielding costly specialty non-silica optical fibers (e.g., sapphire).