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1994

Ren, T. et al. “Biogenic Hydroxylated Carboxylate Monomers Serve As Dispersants for Ceramic Particles.” Biomolecular Materials by Design. Vol. 330. Pittsburgh: Materials Research Soc, 1994. 113–118. Print.
Keimer, B. et al. “Vortex Structures in YBa2Cu3O7.” Journal of Applied Physics 76 (1994): 6778–6783. Print.
Son, Y. B. et al. “Crystallization Behavior of Cordierite-Based Glass With Excess SiO2 and Al2O3 at Initial-Stage.” Japanese Journal of Applied Physics Part 1-Regular Papers Short Notes & Review Papers 33 (1994): 1101–1108. Print.
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.
Shih, W. H. et al. “Equilibrium-State Density Profiles of Centrifuged Cakes.” Journal of the American Ceramic Society 77 (1994): 540–546. Print.
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.
Reznik, D. et al. “High-Resolution Inelastic Neutron-Scattering Study of Phonon Self-Energy Effects in YBCO.” Physica C 235 (1994): 1733–1734. Print.
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. et al. “Hydrothermal Processing of BaTiO3 Polymer-Films.” Better Ceramics through Chemistry Vi. Vol. 346. Pittsburgh: Materials Research Soc, 1994. 63–68. Print.
Humbert, R. et al. “Preliminary Characterization of Organic Nucleator and Framework Macromolecules in Mollusk Shells.” Biomolecular Materials by Design. Vol. 330. Pittsburgh: Materials Research Soc, 1994. 89–94. Print.
Aksay, I.A. “Processing of Complex Ceramics With the Aid of Biopolymers and Biomonomers.” Abstracts of Papers of the American Chemical Society 207 (1994): 11-ANYL. Print.
Aksay, I.A. “Processing of Complex Ceramics With the Aid of Biopolymers and Biomonomers.” Abstracts of Papers of the American Chemical Society 207 (1994): 207-IEC. Print.
Jun, Y. N. et al. “Processing of Monolithic Magnetic Gels for Magnetophoresis.” Langmuir 10 (1994): 3377–3379. Print.
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.
Abel, J. S. et al. “Sedimentation in Flocculating Colloidal Suspensions.” Journal of Materials Research 9 (1994): 451–461. Print.
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. et al. “Silification of Wood-Cell Walls.” Fifty-Second Annual Meeting - Microscopy Society of America Twenty-Ninth Annual Meeting - Microbeam Analysis Society, Proceedings. San Francisco: San Francisco Press Inc, 1994. 428–429. Print.
Shih, W. Y., W. H. Shih, and I.A. Aksay. “Size Dependence of the Ferroelectric Transition of Small BaTiO3 Particles - Effect of Depolarization.” Physical Review B 50 (1994): 15575–15585. Print.
Dabbs, D. M. et al. “Surfactant Mediated Deformation of Gold Particles.” Fifty-Second Annual Meeting - Microscopy Society of America Twenty-Ninth Annual Meeting - Microbeam Analysis Society, Proceedings. San Francisco: San Francisco Press Inc, 1994. 446–447. Print.
McGehee, M. D. et al. “Synthesis of Mesoscopic Structures by Co-Assembly.” Fifty-Second Annual Meeting - Microscopy Society of America Twenty-Ninth Annual Meeting - Microbeam Analysis Society, Proceedings. San Francisco: San Francisco Press Inc, 1994. 448–449. Print.
Yogo, T., and I.A. Aksay. “Synthesis of Mullite Fiber from an Aluminosiloxane Precursor.” Journal of Materials Chemistry 4 (1994): 353–359. Print.
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.

1993

Blohowiak, K. Y. et al. “Evaluation of YBa2Cu3O7-X Bulk Superconductors for High Field Magnet Applications.” IEEE Transactions on Applied Superconductivity 3 (1993): 1049–1052. Print.
Processing of YBCO single crystals was carried out by solidification of semi-liquid YBCO composition using a seeding technique. Microstructural characterization of the pinning centers was investigated by TEM. Characterization of single crystals was carried out, relating grain size and shape to the corresponding flux profiles. Current densities were calculated based on measured trapped fields. Once circulating currents were established, flux pumping and quenching experiments were conducted. These large single crystals will be incorporated into electromagnetic forming devices for use in the military and commercial aircraft manufacturing and service industries.
A detailed small-angle neutron scattering study of the vortex lattice in a single crystal of YBa2Cu3O7 was made for a field of 0.5 tesla inclined at angles between 0 and 80 degrees to the crystalline c axis. The vortex lattice is triangular for all angles, and for angles less than or equal to 70 degrees its orientation adjusts itself to maximize the pinning energy to densely and highly regularly spaced twin planes. These observations have important implications for the microscopic flux-pinning mechanism, and hence for the critical current achievable in YBaCu3O7. For large angles (about 80 degrees) the vortex lattice consists of independent chains in the orientation predicted by anisotropic London theory.
Sarikaya, M., I.A. Aksay, and K. M. Krishnan. “An Introduction to Biomimetics - a Structural Viewpoint.” Microstructure of Materials. San Francisco: San Francisco Press Inc, 1993. 141–148. Print.

1992

Hama, Masaaki, Daniel M. Dabbs, and Ilhan A. Aksay. “Manufacture of Ultrasmooth Ceramics by Low-Temperature Sintering.” 1992: 9 pp. Print.
The process comprises forming a consolidated ceramic, e.g., green compact of Al2O3 powder, impregnating the greenware with an inorg. polymer, e.g., polyaluminoxane having general formula [-M(R)n-X(R1)p-]m, (M = trivalent or tetravalent inorg. ion; when M = trivalent, n = 1, when M = tetravalent, n = 2; X is O-2, S-2, or N-3; when X = O-2 or S-2, p = 0; when X is N-3, p = 1; R, R1 = alkyl, alkoxy, acyloxy, Ph, or phenoxy group contg. a chain of ≥3 C atoms; and m = 5-1000) and sintering the greenware, preferably at 1000-1400°. The ceramics are useful for the electronics industry. [on SciFinder(R)]
Bergstrom, L. et al. “Compressive Yield Stresses of Flocculated Particle Suspensions.” Theoretical and Applied Rheology, Vols 1 and 2. Amsterdam: Elsevier Science Bv, 1992. 579–581. Print.
Bergstrom, L., C. H. Schilling, and I.A. Aksay. “Consolidation Behavior of Flocculated Alumina Suspensions.” Journal of the American Ceramic Society 75 (1992): 3305–3314. Print.
The consolidation behavior of flocculated alumina suspensions has been analyzed as a function of the interparticle energy. Consolidation was performed by a centrifugal force field or by gravity, and both the time-dependent and equilibrium density profiles were measured by a gamma-ray absorption technique. The interparticle energy at contact was controlled by adsorbing fatty acids of varying molecular weight at the alumina/decalin interface. We found that strongly attractive interactions result in a particle network which resists consolidation and shows compressible behavior over a large stress range. The most weakly flocculated suspension showed an essentially incompressible, homogeneous density profile after consolidation at different centrifugal speeds. We also found a significant variation in the maximum volume fraction, phi(m), obtained, with phi(m) almost-equal-to 0.54 for the most strongly flocculated suspension to phi(m) almost-equal-to 0.63 for the most weakly flocculated suspension. The compressive yield stresses show a behavior which can be fitted to a modified power law. In this paper, we discuss possible correlations between the fitting parameters and physical properties of the flocculated suspensions.
Ren, T. et al. “Dispersion of Small Ceramic Particles (Al2O3) With Azotobacter-Vinelandii.” Applied and Environmental Microbiology 58 (1992): 3130–3135. Print.
The high surface charge of small ceramic particles such as alumina particles prevents them from dispersing evenly in aqueous suspensions and forming high-density compacts. However, suspensions of 400-nm-diameter alumina particles treated with alginate from the bacterium Azotobacter vinelandii were well dispersed. The alginate bound firmly to the particle surface and could not be removed by repeated washing with distilled water (2.82 mg of the bacterial alginate adsorbed to 1 g of the alumina particles). Furthermore, A. vinelandii grew and produced alginate in the presence of up to 15% (vol/vol) alumina particles. These results suggest that an in situ process using this bacterium to coat ceramic particles with alginate might be developed. In in situ processing experiments, the particle-packing densities were significantly increased and the viscosities of 5 and 10% (vol/vol) suspensions were reduced 4- and 60-fold, respectively, over those of controls. The bacteria were readily removed from the alumina particles by washing.

1991

Sundaresan, S., and I.A. Aksay. “Mullitization of Diphasic Aluminosilicate Gels.” Journal of the American Ceramic Society 74 (1991): 2388–2392. Print.
Recent studies have shown that the mullitization of diphasic aluminosilicate matrices comprising transitional alumina and amorphous silica occurs via a nucleation and growth process. Nucleation is preceded by a temperature-dependent incubation period. Following this incubation period, rapid nucleation of mullite occurs, producing about 1.8 x 10(11) nuclei/cm3, which remains constant throughout the rest of the transformation. Both incubation and mullite growth are thermally activated processes with apparent activation energies of 987 +/- 63 and 1070 +/- 200 kJ/mol, respectively. The growth rate of mullite grains under isothermal conditions is time dependent. An interpretation of these results is proposed on the basis of the nucleation and growth concepts of LaMer and Dinegar which supports the concept that the growth rate of mullite grains is controlled by the dissolution of transitional alumina into the amorphous matrix.
Aksay, I.A., and S. M. Wiederhorn. “Symposium for Mullite Processing, Structure, and Properties.” Journal of the American Ceramic Society 74 (1991): 2341–2341. Print.
Staley, J. T. et al. “Use of Acidic Biopolymers As Dispersants for Processing of Ceramics.” Abstracts of Papers of the American Chemical Society 201 (1991): 146-IEC. Print.
Ceramic precursor mixt. comprising a metal cation capable of being converted to a metal oxide by thermal energy, a carbohydrate, and an anion capable of participating in an anionic oxidn.-redn. reaction with the carbohydrate is converted to ceramic powder by forming droplets of the precursor mixt., removing all the solvent from the droplets, thermally initiating an anionic oxidn.-redn. reaction between the anion and carbohydrate to form a multiphase ceramic material consisting of carbonates, hydroxides, and oxides of metal cation, and heating the particles to convert the multiphase ceramic into a single-phase ceramic. This process is used for the manuf. of superconductive and nonsuperconductive ceramic powders.
Shih, W. Y. et al. “Aggregation of Colloidal Particles With a Finite Interparticle Attraction Energy.” Journal of Statistical Physics 62 (1991): 961–984. Print.
Aggregation of colloidal particles with a finite attraction energy was investigated with computer simulations and with gold particles coated with a surfactant. Computer simulations were carried out with the Shih-Aksay-Kikuchi (SAK) model, which incorporates a finite nearest-neighbor attraction energy - E into the diffusion-limited-cluster-aggregation (DLCA) model. Both the computer simulations and the experiments showed that (i) with a finite interparticle attraction energy, aggregates can still remain fractal, and (ii) the fractal dimension remains unchanged at large interparticle attraction energies and increases when the interparticle attraction energy is smaller than 4k(B)T, where T is the temperature and k(B) is the Boltzmann constant. The agreement between the simulations and the experimental results suggests that the reversible aggregation process in a colloidal system can be represented by the SAK model.
Yasrebi, M., W. Y. Shih, and I.A. Aksay. “Clustering of Binary Colloidal Suspensions - Experiment.” Journal of Colloid and Interface Science 142 (1991): 357–368. Print.
Liu, J. et al. “Clustering of Binary Colloidal Suspensions - Theory.” Journal of Colloid and Interface Science 142 (1991): 369–377. Print.
Aksay, I.A. “Molecular and Colloidal Engineering of Ceramics.” Ceramics International 17 (1991): 267–274. Print.
During the last decade, significant advances have been made in the processing of ceramics by a combination of techniques utilizing molecular precursors and colloids for powder consolidation. Powder consolidation methods have mainly dealt with the formation of unagglomerated powders in the size range of 0.1-1-mu-m, the preparation of colloidal suspensions that are suitable for the formation of high density compacts by filtration and/or plastic forming techniques, the removal of the processing aids, and the role of consolidation methods on microstructural evolution. In contrast, the molecular and/or sol-gel techniques dealt with processing at a finer dimensional scale of 10-1000 angstrom with either molecularly homogeneous precursors or nanometer-sized particulates that are used in the preparation of gels that display linear viscoelastic behavior. Similar to green compacts of micron-sized powders, these gels are then converted to dense ceramics by heat treatment. This review summarizes the concepts that are common to both of these regimes and points to the synergistic benefits of coupling molecular precursors with colloids in a process path. The emphasis is on the control of the structure of a final product at scale lengths ranging from molecular to micro- and macroscopic dimensions.
Aksay, I.A., D. M. Dabbs, and M. Sarikaya. “Mullite for Structural, Electronic, and Optical Applications.” Journal of the American Ceramic Society 74 (1991): 2343–2358. Print.
Mullite (3Al2O3.2SiO2) is becoming increasingly important in electronic, optical, and high-temperature structural applications. This paper reviews the current state of mullite-related research at a fundamental level, within the framework of phase equilibria, crystal structure, synthesis, processing, and properties. Phase equilibria are discussed in terms of the problems associated with the nucleation kinetics of mullite and the large variations observed in the solid-solution range. The incongruent melting behavior of mullite is now widely accepted. Large variations in the solid solubility from 58 to 76 mol% alumina are related to the ordering/disordering of oxygen vacancies and are strongly coupled with the method of synthesis used to form mullite. Similarly, reaction sequences which lead to the formation of mullite upon heating depend on the spatial scale at which the components are mixed. Mixing at the atomic level is useful for low-temperature (< 1000-degrees-C) synthesis of mullite but not for low-temperature sintering. In contrast, precursors that are segregated are better suited for low-temperature (1250-degrees to 1500-degrees-C) densification through viscous deformation. Flexural strength and creep resistance at elevated temperatures are significantly affected by the presence of glassy boundary inclusions; in the absence of glassy inclusions, polycrystalline mullite retains > 90% of its room-temperature strength to 1500-degrees-C and displays very high creep resistance. Because of its low dielectric constant, mullite has now emerged as a substrate material in high-performance packaging applications. Interest in optical applications mainly centers on its applicability as a window material within the mid-infrared range.

1990

Shih, W. H. et al. “Scaling Behavior of the Elastic Properties of Colloidal Gels.” Physical Review A 42 (1990): 4772–4779. Print.
Shih, W. Y., W. H. Shih, and I.A. Aksay. “Semidilute Athermal Polymer-Solutions Near a Hard-Wall.” Macromolecules 23 (1990): 3291–3296. Print.
Sundaresan, S., and I.A. Aksay. “Sintering With Rigid Inclusions - Pair Interactions.” Journal of the American Ceramic Society 73 (1990): 54–60. Print.
Choi, J. S. et al. “Theory of Oxygen Diffusion in the YBa2Cu3O7-X Superconducting Compound.” Physical Review B 42 (1990): 4244–4254. Print.

1989

Shih, W. H. et al. MECHANICAL-PROPERTIES OF COLLOIDAL GELS. Vol. 155. Pittsburgh: Materials Research Soc, 1989. Print.
Shih, W. Y., W. H. Shih, and I.A. Aksay. “THE STABILITY OF BINARY CHARGED COLLOIDAL CRYSTALS.” Journal of Chemical PhysicsJournal of Chemical Physics 90 (1989): 4506–4512. Print.
Shih, W. Y. et al. SINTERING BEHAVIOR OF AN ISOLATED PORE - MONTE-CARLO SIMULATION. Vol. 138. Pittsburgh: Materials Research Soc, 1989. Print.
Shih, W. Y. et al. DENSITY PROFILES OF SEMI-DILUTE POLYMER-SOLUTIONS NEAR A HARD-WALL - MONTE-CARLO SIMULATION. Vol. 153. Pittsburgh: Materials Research Soc, 1989. Print.
Shih, W. Y. et al. STABILITY OF A BINARY COLLOIDAL SUSPENSION AND ITS EFFECT ON COLLOIDAL PROCESSING. Vol. 155. Pittsburgh: Materials Research Soc, 1989. Print.
Stangle, G. C. et al. REMOVAL OF PROCESSING AIDS FROM CERAMIC POLYMER COMPOSITES. Vol. 155. Pittsburgh: Materials Research Soc, 1989. Print.
Thomson, W. J. et al. “REACTION SEQUENCING DURING PROCESSING OF THE 123-SUPERCONDUCTOR.” Journal of the American Ceramic SocietyJournal of the American Ceramic Society 72 (1989): 1977–1979. Print.
Aksay, I.A., M. Sarikaya, and B. Sonupariak. “SPINEL PHASE FORMATION DURING 980-DEGREES-C EXOTHERMIC REACTION IN THE KAOLINITE-TO-MULLITE-REACTION SERIES - REPLY.” Journal of the American Ceramic SocietyJournal of the American Ceramic Society 72 (1989): 1571–1571. Print.
Chick, L. A. et al. PACKING AND STRUCTURE IN SYSTEMS CONTAINING ROD-LIKE PARTICLES. Vol. 155. Pittsburgh: Materials Research Soc, 1989. Print.
Halverson, D. C. et al. “PROCESSING OF BORON CARBIDE-ALUMINUM COMPOSITES.” Journal of the American Ceramic SocietyJournal of the American Ceramic Society 72 (1989): 775–780. Print.
Lannutti, J.J. et al. CERAMIC PROCESSING USING INORGANIC POLYMERS. Vol. 155. Pittsburgh: Materials Research Soc, 1989. Print.