Crystallization behavior of cordierite-based glass with excess SiO2 and Al2O3 (CM glass) was studied at the initial crystallization stage. Two kinds of glass-in-glass phase separation occurred during the heat treatment of glass powder. The secondary glass-in-glass phase separation, which consists of an SiO2-rich phase and an Al2O3-rich phase significantly affects the crystallization of the glass and the resultant microstructures of the crystallized glass. Mullite nucleated first in the Al2O3-rich amorphous phase which is no longer a stable glass-forming region. Metastable mu-cordierite crystallized in the SiO2-rich amorphous phase and grew rapidly. A fine-grained cordierite-mullite composite with mullite as the grain boundary phase was produced.
We have examined the equilibrium-state density profiles of centrifuged cakes both theoretically and experimentally. The theoretical density profiles were obtained by implementing the experimental pressure-density relationship into the general differential equation for centrifugation with appropriate boundary conditions. With a power-law pressure-density relationship, P = beta phi(n), we show that phi(Z)/phi(max) = (1 - Z/Z(m))(1/(n - 1)) where phi(max) is the density at the bottom of the cake, Z the distance measured from the bottom of the cake, and Z(m) the distance at which the cake density vanishes. Experimentally, the density profiles were examined with gamma-ray densitometry. The predicted density profiles are in good agreement with the experimental ones. We also show that form phi(Z)/phi(max) = (1 - Z/Z(m))(1/(n - 1)) applies to sedimentation cakes as well, provided the pressure-density relationship of sedimentation cakes is also a power-law one.
We report preliminary results of the high resolution inelastic neutron scattering measurements of the 42.5 meV optical phonon branch in YBCO, whose behavior at momentum transfer q=0 has been extensively studied by Raman scattering. The experiment was done on a large (75g) single crystal of YBa2Cu3O7-x (T-c approximate to 90K) with the resolution of 2 meV (full width at half maximum). In cooling from 100K to 50K we observe a small softening of the phonon energy at q=0.25,0.25,0, but no significant linewidth change.
Slamovich, E. B. ; Aksay, I. A.Hydrothermal processing of BaTiO3 polymer-films. In Better Ceramics through Chemistry Vi; Cheetham, A. K. ; Brinker, C. J. ; Mecartney, M. L. ; Sanchez, C., Ed. Materials Research Soc: Pittsburgh, 1994; Vol. 346, pp. 63-68.
Magnetite particles and monosized polystyrene beads were trapped in a silica-gel, which was then dried by using supercritical fluid extraction. When the monolithic dried gel is sintered, the polystyrene beads are pyrolyzed, leaving a porous magnetized piece of ceramic with controlled pore sizes. These ''magnetic gel'' ceramics provide a novel class of materials for use in gel magnetophoresis and other biophysical applications.
A combined experimental and theoretical investigation of the sedimentation of unstable colloidal ceramic suspensions has been performed. Suspensions containing submicron-sized alpha - Al2O3 particles were prepared at various pH values in order to modify suspension stability. Particle volume fraction during sedimentation was determined as a function of position and time by gamma-ray densitometry. A population balance model was developed to account for various coagulation and decoagulation mechanisms that affect sedimentation behavior in flocculating suspensions. Model predictions were then compared with experimental measurements, in order to establish the validity of the theoretical model.
Keckler, S. E. ; Dabbs, D. M. ; Yao, N. ; Aksay, I. A.Silification of wood-cell walls. In Fifty-Second Annual Meeting - Microscopy Society of America/Twenty-Ninth Annual Meeting - Microbeam Analysis Society, Proceedings; Bailey, G. W. ; GarrattReed, A. J., Ed. San Francisco Press Inc: San Francisco, 1994; pp. 428-429.
Dabbs, D. M. ; Yao, N. ; Aksay, I. A.Surfactant Mediated Deformation of Gold Particles. In Fifty-Second Annual Meeting - Microscopy Society of America/Twenty-Ninth Annual Meeting - Microbeam Analysis Society, Proceedings; Bailey, G. W. ; GarrattReed, A. J., Ed. San Francisco Press Inc: San Francisco, 1994; pp. 446-447.
McGehee, M. D. ; Gruner, S. M. ; Yao, N. ; Chun, C. M. ; Navrotsky, A. ; Aksay, I. A.Synthesis of Mesoscopic Structures by Co-assembly. In Fifty-Second Annual Meeting - Microscopy Society of America/Twenty-Ninth Annual Meeting - Microbeam Analysis Society, Proceedings; Bailey, G. W. ; GarrattReed, A. J., Ed. San Francisco Press Inc: San Francisco, 1994; pp. 448-449.
Mullite fibre was successfully synthesized by pyrolysis of aluminosiloxane formed from ethyl 3-oxobutanoatodiisopropoxyaluminium and di-(sec-butoxy)aluminoxytriethoxysilane. Aluminosiloxane increased in viscosity with increasing coordination number of aluminium, which was analysed by Al-27 NMR spectroscopy. The viscosity of aluminosiloxane was controlled by the amount of added glacial acetic acid as well as the working temperature for the spinning of precursor fibre. Aluminosiloxane gave amorphoUS SiO2-Al2O3 at 500-degrees-C, which began to crystallize to mullite at 930-degrees-C. Single-phase mullite was produced on heating to 1000-degrees-C for 1 h. The polymer fibre spun from aluminosiloxane was pyrolysed yielding crack-free mullite fibre at 1000-degrees-C for 1 h.