Stanley A. Dunn

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.

Inviscid melt spinning: As-spun crystalline alumina fibers

Inviscid melt spinning yielded the first crystalline alumina fibers directly from the melts. In this experimental process, a liquid jet having a melt viscosity of 1 poise (vs>10 4 for fiberglass) is extruded into propane and is thus chemically stabilized (vs rapidly quenched) before it forms Rayleigh waves and breaks up into droplets. This letter describes a 65.5% alumina-zirconia fiber, an 81.5% and a 90.6% alumina-calcia fiber, a 98.6% alumina-magnesia fiber, and a 100% alumina fiber. The δ-allomorph was identified as the crystalline phase of the melt spun 100% alumina fibers, compared to the α-allomorph reported for FIBER FP, a slurry spun and sintered 100% alumina fiber.

Phase identification in calcia-alumina fibers crystallized from amorphous precursors

Amorphous fibers of a 46.5 wt% CaO-53.5 wt% Al2O3 eutectic compound were produced by inviscid melt-spinning. Fibers were subsequently heat treated at 900, 1000 and 1100°C for times ranging from 6 to 6000 s to elucidate crystallization processes. Fiber samples were ground for X-ray analysis. Equilibrium compounds Ca12Al14O33, Ca3Al10O18 and CaAl4O7 were present in varying amounts in all crystallized fibers. Liquid formation in fibers exposed to 1100°C for 6000 s was noted.

The effect of boria and titania addition on the crystallization and sintering behavior of Li2O-Al2O3-4SiO2 glass

Abstract Crystallization and sintering behaviors of four β-spodumene (Li 2 O-Al 2 O 3 -4SiO 2 ) glasses having different compositions were investigated and compared by differential thermal analysis (DTA), X-ray diffraction (XRD), and scanning electron microscopy (SEM). The Li 2 O-Al 2 O 3 -4SiO 2 glass containing both B 2 O 3 and TiO 2 showed the lowest activation energy value for crystallization (220 ± 8 kJ/mol), whereas the stoichiometric Li 2 O-Al 2 O 3 -4SiO 2 glass showed the highest value (322 ± 4 kJ/mol). The crystallization peak temperature (T p ) decreased from 918 to 819°C by the addition of both B 2 O 3 and TiO 2 to the stoichiometric Li 2 O-Al 2 O 3 -4SiO 2 glass. The Li 2 O-Al 2 O 3 -4SiO 2 glass containing both B 2 O 3 and TiO 2 showed approximately the same degree of sintering as the Li 2 O-Al 2 O 3 -4SiO 2 glass containing only B 2 O 3 .

Wetting behaviour and mullite formation at the interface of inviscid melt-spun CaO-Al2O3 fibre-reinforced Al-Si alloy (4032) composite

Inviscid melt-spun calcia-alumina fibre-reinforced aluminium-silicon alloy (4032) composites were produced using a melt-infiltration technique. Scanning electron microscopy, energy dispersive X-ray spectroscopy (EDS), and X-ray diffraction (XRD) were used to investigate interfacial wetting and interphase formation, and identify the crystalline phase of the interphase of these composites. The composites processed at 700°C showed a good interfacial wetting and silicon accumulation at the interface. The composites processed at 927°C showed formation of an interphase region of about 10–20 μm thick, as well as excellent interfacial wetting. EDS analysis gave averaged compositions of this interphase region at 74 wt % Al and 26 wt % Si, which corresponds to the composition of mullite (3Al2O3 · 2SiO2). The formation of mullite at the interface was confirmed by XRD analysis.

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.

Inviscid melt-spun high-temperature alumina-magnesia fibres

Al2O3-MgO (AM) fibres containing 98.16 wt% Al2O3 and 1.84 wt% MgO, were produced via inviscid melt spinning. By using scanning electron microscopy it was found that the as-spun AM fibres were hollow and their surfaces were very rough. The X-ray diffraction pattern of the as-spun AM fibre showed δ-Al2O3 as a major phase and α-Al2O3 as a minor phase. The DTA curve of the as-spun AM fibre showed a single endothermic peak representing the phase transformation of δ-Al2O3 to α-Al2O3. This phase transformation was readily confirmed by analysing the X-ray diffraction pattern of heat-treated AM fibres.

Attenuation effects in aluminum and lead fibers formed by inviscid melt-spinning (IMS)

Abstract Aluminum fibers 66 and 75 μm in diameter, and lead fibers from 19 to 313 μm in diameter have been produced by means of inviscid melt-spinning (IMS). The nascent streams were attenuated by aerodynamic acceleration. Attenuation factors ranging from D 0 D f = 1.3 to 3.8 have been achieved, representing some of the largest IMS attenuation effects yet reported.

Inviscid melt spinning (IMS) and phase identification of CaOAl2O3MgO fiber

Abstract CaOAl2O3MgO (CAM) fibers were produced using inviscid melt spinning (IMS). Scanning electron microscopy (SEM) and X-ray diffraction (XRD) were used to examine a fiber morphology and identify the non-equilibrium/equilibrium phases in CAM fibers. The SEM of as-spun CAM fibers showed a surface roughness indicating a crystallinity and some porosity due to a gas evolution during fiber processing. The as-spun CAM fibers showed a formation of the non-equilibrium crystalline phases of MgO·Al2O3, CaO·Al2O3 and α-Al2O3, whereas the CAM fibers heat treated at 1000°C for 24 h showed a formation of the equilibrium phases of 3CaO·5Al2O3 and α-Al2O3.

Crystallization of inviscid melt spun (IMS) calcia-alumina (CA) eutectic fibers

Abstract Crystallization behavior of vitreous calcia-alumina (CA) fibers of eutectic composition (46.5 wt% CaO–53.5 wt% Al2O3) was studied by differential thermal analysis (DTA), scanning electron microscopy (SEM) and X-ray diffraction (XRD). From DTA results, crystallization temperature of the CA fibers ranges from 948 to 1034 °C according to DTA heating rates. The activation energy value for crystallization of the CA fibers was determined as 490 kJ/mol and 477 kJ/mol via Kissinger and Augis-Bennett methods, respectively. SEM for crystallized CA fibers showed surface roughness, whereas that for vitreous CA fibers showed typical glassy fracture. Wide angle X-ray diffractometer analysis on CA fibers which were crystallized by the DTA scans showed Ca12Al14O33 formation as a major phase and CaAl2O4 formation as a minor phase.