1998 MRS Spring Meeting & Exhibit

Chairs 

Gary Burns
Dow Corning Corp
MS C043C1
Midland, MI 48686-0994
517-496-6090

Hua Duen-Wu 
Res & Tech Americas Tech Ctr 
Millennium Inorganic Chemicals 
Baltimore, MD 21226-1899 
410-354-7823

James E. Mark
Dept of Chemistry
Univ of Cincinnati
Crosley Tower, Mail location 0172
Cincinnati, Ohio 45221-0172
513-556-9292

* Invited paper

SESSION P1: OVERVIEW OF NANOPARTICLE TECHNOLOGY 
Chair: Gregory Beaucage 
Monday Morning, April 13, 1998 
Salon 15

8:30 AM *P1.1 NANOPARTICLE TECHNOLOGY - AN EMERGING MATERIALS RESEARCH FRONTIER. D.T. Shaw, State University of New York at Buffalo, Amherst, NY; M.C. Raoco, National Science Foundation, Washington, DC. 

The paper will summarize the findings of a technology evaluation study organized by the World Technology Evaluation Center (WTEC) under the sponsorship of the National Science Foundation. Nanometer-size particles are the building blocks in an emerging field generally referred to as nanoparticle technology. R&D in the field is driven by the realization that when the particle size is reduced to the point where critical length scales of physical phenomena become comparable to or larger than the particle size, the fundamental characteristics of these particles are very different from those of bulk materials. Applications take advantage of high surface area and quantum confinement effects, which lead to devices with innovative performance properties tha are not possible with conventional materials. Synthesis and processing of nanoparticles with controlled monodispersity and phase purity will require new aerosol, colloidal, thermal, chemical and physical vapor deposition approaches. These particles are assembled into useful functional and structural materials for opto-electronic and manufacturing applications, as well as used as coatings, catalysts and sensors. The paper will review recent progress on nanoparticle processing and on manufacturing into new devices and applications. Issues related to characterization techniques, scale-up production and device miniaturization will also be discussed 

9:00 AM *P1.2 
FLAME AEROSOL SYNTHESIS OF NANOPARTICLES. Sotiris E. Pratsinis, University of Cincinnati, Dept. of Chemical Engineering, Cincinnati, OH. 

Flame aerosol technology is used for large scale manufacture of ceramic commodities such as pigmentary titania, fumed silica and alumina. In addition, the introduction of this technology to manufacture of optical fibers and its potential for cheap synthesis of ultrafine particles (e.g. nanoparticles) has renewed the research interest for better understanding of flame aerosol reactors. Here, after an overview of this technology, the current state of knowledge on the role of flame process variables (additives, mixing etc.) on the characteristics of product powders is summarized in a tutorial fashion. The fundamentals of particle formation and growth are highlighted. The latest advances on the theory of aggregate particle dynamics that are typically encountered in flame synthesis of powders are presented. Specific applications in manufacture of fumed silica, pigmentary titania, alumina, and other oxide and non-oxide ceramic powders are reviewed. Finally research needs are highlighted by pointing out the most promising areas for advancing the field with emphasis on instrumentation and need for detailed simulators of the process accounting for the concurrent chemistry, transport and aggregate particle dynamics. With major recent advances in diagnostics and understanding in both combustion and aerosol science and engineering, this field is ready for a new leap forward. 

9:30 AM *P1.3 
PRECIPITATED SILICAS FOR INDUSTRIAL APPLICATIONS. underlineR.W. Pekala, T.G. Krivak, and H.E. Swift, PPG Industries Inc., Monroeville, PA. 

Precipitated silica is derived from the reaction of sodium silicate, an alkaline liquid silicate known as waterglass, with an acid to form porous silica aggregates that are usually washed, dried, and milled to a final product. The precipitation process can impart a broad range of product properties. Typical particle diameters range from 1-200 micrometers with oil absorption values of 70-300 cc/100 g silica, and BET surface areas of 60-250 m2/g. Precipitated silica finds applications in consumer products ranging from tires to toothpaste. This paper provides a general overview of the synthesis, properties, and applications of precipitated silica. 

10:30 AM *P1.4 
DRYING OF NANO-SCALE MATERIALS. D.M. Smith, S. Wallace, A. Maskara, NanoPore Incorporated, Albuquerque, NM. 

Drying is a critical step in processing of almost all nanosize materials such as powders, gels, and films. Even materials produced in a dry process must often be incorporated in a fluid during subsequent processing. How drying is performed affects the properties of the material and can contribute dramatically to the final product cost. This is especially true for length scales less than 10 nm since this dramatically increases capillary stress and slows drying. For powders produced in solution, the problem is how to maintain uniform nanostucture during fluid removal. The literature is saturated with papers describing the synthesis of nanometer-scale powders but when these powders are processed into a finished part, the potential advantages (mechanical, electrical, optical, etc.) are lost because of larger-scale defects introduced during the drying step. For low density compliant, nanosize materials such as gels, the problem is how to avoid excessive shrinkage during drying. In this talk, the use of both physical (i.e., suface tension, drying rate and temperature, etc.) as well as chemical (i.e., contact angle, surface chemistry passivation, pH, ionic strength, etc.) will be discussed. Specific examples will be used such as drying of colloidal meal oxide particles, supercritical drying of powders, and ambient pressure routes to aerogels will be used to illustrate these concepts. 

11:00 AM *P1.5 
FABRICATION OF AGGLOMERATE-FREE NANOPOWDERS BY HYDROTHERMAL CHEMICAL PROCESSING. H. Schmidt, Institut fuer Neue Materialien GmbH, Saarbruecken, GERMANY. 

For the fabrication of nanopowders, a chemical processing route has been developed. The route is based on precipitation processes in solutions, either within aqueous droplets in microemulsions in the presence of surface modifiers like surfactants or by direct precipitation in solutions in the presence of these surface modifiers or small organic molecules directly bonded to the particle surface. In order to obtain well crystallized or densified particles, a continuous flow hydrothermal process has been developed which allows the fabrication of agglomerate-free surface modified nanopowders. The surface modification provides a full redispersibility after drying and permits the fabrication of high density green bodies with volume fractions beween 45 and 60 % by wet processing. These gel-like of green bodies, in general, do not show a gelation point like usual, but an increase in viscosity with increasing solid content. Nanoparticulate systems have been produced meanwhile from Al₂O₃, ZrO₂, ITO, ATO, TiO₂, SnO₂ doped rutile and anatase, talkum and others. Various types of surface modifiers were used to the particle-to-particle interaction for obtaining high green densities or to reduce the interfacial free energy and to obtain a good dispersion of the particles in polymer matrices, for example to improve UV stability or abrasion resistance. 

11:30 AM *P1.6 
COMPACTION STRESS IN FINE POWDERS. Alan J. Hurd, Sandia National Laboratories, Albuquerque, NM; V.M. Kenkre, J.E. Scott, and E.A. Pease, Department of Physics and Astronomy, University of New Mexico, Albuquerque, NM. 

A vexing feature in granular materials compaction is density extrema interior to a compacted shape. Such inhomogeneities can lead to weaknesses and loss of dimensional control in ceramic parts, unpredictable dissolution of pharmaceuticals, and undesirable stress concentration in load-bearing soil. As an example, the centerline density in a cylindrical compact often does not decrease monotonically from the pressure source but exhibits local maxima and minima. Two lines of thought in the literature follow, respectively, diffusive and wavelike propagation of stress. Here, a general memory function approach has been formulated that unifies these previous treatments as special cases; by analyzing a convenient intermediate case, the telegrapher1s equation, one sees that local density maxima arise via semidiffusive stress 3waves2 reflecting from the die walls and adding constructively at the centerline.This work was supported in part by Sandia National Laboratories, a Lockheed Martin Company, under Department of Energy contract DE-AC04-94AL85000. 

SESSION P2: PHYSICAL ASPECTS OF NANOSTRUCTURED POWDERS 
Chair: Sotiris E. Pratsinis 
Monday Afternoon, April 13, 1998 
Salon 15

1:30 PM *P2.1 
ELASTIC BEHAVIOR OF NANOPARTICLE CHAIN AGGREGATES. Sheldon K. Friedlander, Department of Chemical Engineering, UCLA, Los Angeles, CA; Hee Dong Jang, Korea Institute of Geology, Mining and Materials, Taejeon, KOREA; Kevin H. Ryu, Department of Materials Science and Engineering, UCLA, Los Angeles, CA. 

Nanoparticle chain aggregates (NCA) possess elastomeric properties including stretch under tension, and contraction when the tension is relaxed. Titania NCA were generated by thermal decomposition of titanium tetraisopropoxide vapor in a nitrogen stream at 800 C. The chain aggregate fractal dimension was about 2.3 and the individual (primary) particle size about 7 nm. Chain aggregates a few hundred nm long were deposited on an electron micrograph grid and observed in the electron microscope. By focusing on an individual NCA, a hole was produced in the carbon film on the grid due to localized evaporation. The NCA stretched across the expanding hole in the film. After stretching up to 90%, the NCA broke loose at one end and contracted to a tightly folded chain on the other side of the film. This pattern was observed in repeated tests. Strain measurements were made from a videotape of the event. Mechanisms for this behavior and reasons for its generality are proposed. Implications are discussed for the ductility and elasticity of nanoparticle compacts and the increased tensile strength and elastic modulus of rubber due to nanoparticle additives. 

2:00 PM *P2.2 
RHEOLOGY OF COLLOIDAL AGGREGATES. Kimberly M. Hill, James E. Martin, Douglas A. Adolf, Sandia National Laboratories, Albuquerque, NM. 

The aggregation of colloids can greatly affect the rheology of dispersions and can be a serious impediment to the processing of nanosized powders. For example, at the Hanford site the radioactive tank wastes are very concentrated and have aggregated to form sludge that is too viscous to process without sluicing. We are interested in understanding the rheology of colloidal aggregates and have completed extensive studies on a model silica system whose particles can interact through chemical bonding, Keesom interactions, and Coulombic interactions. Through systematic variation of the solvent and the particle concentration, we can control the surface chemistry and solution thermodynamics, thus changing the rheology from Newtonian, to shear thinning or shear thickening. We will describe the results of these measurements and present a model of aggregate rheology. 

2:30 PM P2.3 
FABRICATION OF NANOSTRACTURED MONOCLINIC ZIRCONIA CERAMICS BY COLLOIDAL PROCESSING. Tetsuo Uchikoshi, Yoshio Sakka, Kiyoshi Ozawa, Keijiro Hiraga, National Research Institute for Metals, Ibaraki, JAPAN. 

Pure zirconia transforms from monoclinic to tetragonal and cubic at high temperatures. Large volume change and crack making during cooling accompany the transformation between monoclinic and tetragonal. This fatal problem makes it very difficult to sinter monoclinic zirconia powder to a dense body, since the temperatures necessary for sintering of zirconia have always been well above the monoclinic-tetragonal transformation temperature. To fabricate dense monoclinic zirconia ceramics at lower temperatures than the monoclinic-tetragonal transformation temperature, high-purity, finer-sized and non-flocculated powder is required. Dense particle packing is also very important to reduce the densifying temperature. This study is an approach to process the fine-grained monoclinic zirconia polycrystal using monoclinic zirconia powder by colloidal processing. In this study, two kinds of zirconia sols prepared by different methods, which were acid and neutral sols, were used as starting materials. Complete re-dispersion of flocculated particles for the neutral sol was impossible even by changing the pH while no flocculation was observed for the acid sol. In case of the acid sol, chloride ions inevitably included were removed by using anion exchange resin. Consolidation of the sols was performed by pressure filtration at 10 MPa. The relative green density of the compact was improved by the following CIP treatment at 400 MPa. In case of the compact from the acid sol, it was possible to densify the compact by pressureless sintering to >98% of theoretical density in air at 1373 K, which temperature is lower than that of monoclinic to tetragonal transformation of pure zirconia. The average green size of the sintered monoclinic zirconia ceramics was 92 nm. 

2:45 PM P2.4 
PREPARATION OF NANOCRYSTALLINE TITANIA POWDER BY AEROSOL PYROLYSIS OF TITANIUM ALKOXIDE. P.P. Ahonen, E.I. Kauppinen, VTT Chemical Technology, Aerosol Technology Group, Espoo, FINLAND; J.L. Deschanvres, J.C. Joubert, LMGP-ENSPG, Grenoble, FRANCE; G. Van Tendeloo, EMAT-University of Antwerpen, Antwerpen, BELGIUM. 

Titanium (IV) oxide, titania, is a widely used ceramic material. The applications of titania include pigment manufacturing, waste water purification, catalyst materials, and gas sensor materials. We have prepared nanocrystalline titania powder via aerosol droplet pyrolysis of titanium tetrabutoxide precursor dissolved in butanol solvent. The precursor solution was atomized with an ultrasonic nebulizer. The droplets were carried through a hot wall flow reactor in the temperature range of 150-580ºC with average residence time of 2-4 seconds. Air and nitrogen were used as the carrier gases. Gas-phase particle mass size distributions were determined with a Berner-type low pressure impactor. The powder was collected with an electrostatic precipitator. Afterwards, powders were taken to thermal annealing to study the crystallinity and morphology evolution. Powder crystallinity was characterized with XRD. Particle morphology and crystallinity were studied with the field-emission-SEM (Leo DSM982 Gemini) and with the field-emission-TEM (Philips CM200 FEG). In addition, powders were analyzed by thermogravimetry, specific surface area measurements, and by Raman and IR-spectroscopy. The results show that as-received powder particles were mostly micrometer sized droplet residues containing some organic species. In lower preparation temperatures powders were amorphous by XRD but with highest temperatures traces of anatase structure were obtained. Using air as the carries gas always led to powder consisting of smooth, round particles. In nitrogen a part of precursor droplets evaporated leading to a large number of 10-50 nm particles in the gas phase in addition to the larger droplet residues. Powders annealed at 500ºC were transformed to nanocrystalline titania particles with anatase structure. Powders annealed at 900ºC were converted to rutile structure, but with certain preparation conditions it was possible to achieve phase pure anatase by XRD even at this temperature. Mechanism for this unusual crystallinity evolution is proposed on the basis of the high resolution TEM results. 

3:30 PM *P2.5 
SYNTHESIS OF NANOSTRUCTURED SILICA POWDERS BY A ROOM TEMPERATURE AEROSOL PROCESS . Jingyu Hyeon-Lee, Gregory Beaucage, Univ of Cincinnati, Dept of Materials Science and Engineering, Cincinnati, OH; Sotiris E. Pratsinis, Univ of Cincinnati, Dept of Chemical Engineering, Cincinnati, OH. 

A room temperature aerosol process can be used to produce silica powders which show high specific surface areas. This process combines features of sol-gel and flame aerosol processes. Silica powders are formed by the hydrolysis and condensation of metal organic precursors such as TEOS (Si(OC₂H₅)₄). These powders show high specific surface areas around 500 m²/g, far in excess of the 300 m²/g limit of pyrolytic methods. The specific surface area shows a dependence on the reaction parameters such as temperature, or type of precursors. The structure of these powders is a mass-fractal in the nano-scale by small angle x-ray scattering (In press, Chem. Mater. 1997). 

4:00 PM P2.6 
MORPHOLOGICAL AND PHASE EVOLUTION CHARACTERISTICS OF IRON OXIDE ULTRAFINE PARTICLES AS A FUNCTION OF BURNER CONDITIONS DURING COUNTERFLOW DIFFUSION FLAME SYNTHESIS. Mukul Kumar and Kevin J. Hemker, Department of Mechanical Engineering, Johns Hopkins University, Baltimore, MD. 

Magnetic recording media with ultrafine ferromagnetic particles have potential advantages over thin film media. As the particle size shrinks, a threshold should be reached where single-domain particles dominate. In principle, this makes the characteristics of granular magnetic solids comparable to, or better than, those of existing media. In addition are the added benefits of enhanced hardness, wear and corrosion resistance. Processing of iron oxide powder at such length scales is being attempted by flame synthesis techniques under different burner feed conditions with overall reducing or oxidizing environments. The attendant morphological and phase changes in the particles are subsequently analyzed by transmission electron microscopy using conventional and high resolution imaging, and electron and x-ray diffraction. These results will be presented and discussed in light of the far from equilibrium conditions that prevail during the processing of these powders. 

4:15 PM P2.7 
PHYSICAL CHARACTERIZATION OF ZIRCONIUM-DOPED ZINC OXIDE THIN FILMS DEPOSITED BY SPRAY PYROLYSIS. A. Maldonado*, D.R. Acosta**, M. de la Olvera*, R. Castanedo***, G. Torres-Delgado***, J. Canetas-Ortega**, R. Asomoza*, *Departamento de Ingenieria Eléctria, Centro de Investigación y de Estudios Avanzados, Instituto Politécnico Nacional, Mexico, MEXICO; **Instituto de Fisica, Universidad Nacional Autónoma de Mexico, Mexico, MEXICO; ***Laboratorio de Investigaciión en Materiales, CINVESTAV-IPN, Centro Universitario, Querétaro, MEXICO. 

Zirconium-doped zinc oxide thin films were obtained by chemical spray. Doping concentration and substrate temperature effect on structure, morphology and optical properties were anayzed. Preferential growth of (002) planes are obtained in all cases. As substrate temperature and doping concentration are increased the grain size decreases, with a well defined hexagonal geometry. TEM measurements show that grain size is between 5.4 to 15 nm. Resistivity was of the order of 794 -cm. The effect of the dopant on the physical properties is discussed too. 

4:30 PM P2.8 
CRYSTAL GROWTH STUDIES DURING AEROSOL SYNTHESIS OF NANOSTRUCTURED FULLERENE PARTICLES. Jorma Joutsensaari, Esko I. Kauppinen, VTT Chemical Technology, Aerosol Technology Group, Espoo, FINLAND; Dirk Bernaerts, Gustaaf Van Tendeloo, EMAT, University of Antwerp (RUCA), Antwerp, BELGIUM. 

We have studied crystal growth of nanostructured fullerene particles during aerosol synthesis. C₆₀, C₇₀ and mixed fullerene (C₆₀/C₇₀) particles (10-300 nm in diameter) were produced via aerosol droplet drying and crystallization as well as via vapor condensation starting from solutions of fullerenes in toluene at temperatures of 400-700ºC. Particle morphology, crystallite size and crystal structure were studied by field-emission scanning electron microscopy (SEM) and high resolution transmission electron microscopy (TEM). Particle number size distributions in gas-phase were determined with a differential mobility analyzer (DMA). 
Two types of the particles in the different size ranges were observed by DMA. Particles with a size of 100 nm are formed via aerosol droplet drying. Additionally, ultrafine particles (30 nm) are formed via vapor condensation at higher temperatures. TEM results show that crystalline C₆₀ particles are formed already at 400ºC. At 500ºC both highly disordered and single crystal particles with a size of 100 nm are found. Some particles are faceted. The ultrafine particles are mostly polycrystalline. At 600ºC the larger particles are mostly single crystals and some of them are perfectly faceted. The ultrafine particles are polycrystalline or (defected) single crystals. Also, SEM results show that many clearly faceted particles are formed at 500ºC and above. Different shapes of the faceted particles are observed, e.g. hexagonal platelike, decahedral and icosahedral (i.e. multiply twinned) particles. Similar results are observed for C₇₀ and C₆₀/C₇₀, but the particles show less crystallinity. Electron diffraction results show that the structure of well crystallized C₆₀, C₆₀/C₇₀ and C₇₀ particles is fcc with lattice constant of 1.41, 1.43 and 1.47 nm, respectively. The results indicate that defects, i.e. stacking faults and twins, play an important role during the crystal growth of the fullerene particles. The results illustrate that C₆₀ can be considered as a model system for fcc crystal growth. 

SESSION P3: INDUSTRIAL AEROGEL SYNTHESIS 
Chair: James E. Mark 
Tuesday Morning, April 14, 1998 
Salon 15

8:30 AM *P3.1 
NEW COST-EFFECTIVE PROCESS TO COMMERCIALIZE HYDROPHOBIC SILICA AEROGELS. Fritz Schwertfeger, Marc Schmidt, Hoechst AG, CR&T/TP Aerogels, Frankfurt, GERMANY. 

Silica aerogels are in principle well known since the work of Kistler in 1932. The usual production process including supercritical drying and expensive raw materials like Tetraethoxysilane prohibited a commercialization on an industrial scale. 
To avoid the costs of supercritical drying one can modify the internal surface with a silation agent. The resulting hydrophobization of the lyogel makes it possible to dry at ambient pressure. 
The next step to reduce the costs of the aerogel production significantly is the use of waterglass as the cheapest silica source. This system requires at least one solvent exchange from water for the surface modification. The necessary time for the diffusion during the solvent exchange, the recycling of the water/solvent solutions by distillation still cause considerable costs. 
In the last year, Corporate Research & Technology of the Hoechst group developed a new cost-effective process which avoid these disadvantages. 
Now silation is carried out directly in the water phase of the hydrogel. This results in a solvent exchange by chemical reaction as well as a phase separation of the gelwater and the solvent. This opens the door for a commercial production on a larger scale. 

9:00 AM *P3.2 
SCHNELL GEL. RAPID ROUTE TO ULTRALOW DENSITY GELS WITH NO CATALYST REQUIRED. Kenneth G. Sharp, Central Research, DuPont Co., Wilmington, DE. 

A new family of simple precursors to silica gel has been developed. The gel precursors are tetra(polyfluoroalkoxy)silanes, the prototype being Si(OCH₂CF₃)₄. Rapid formation of transparent monolithic gels is possible even at very low concentrations in water/alcohol solvents with no added catalyst. Pore sizes in the wet gels were estimated from hydrodynamic relaxation in a beam-bending experiment on cylindrical logs. In a gel at 1% solids, the pore size was approximately 100 nm. At this concentration gels can easily be generated in seconds; gelation rates can be six orders of magnitude higher than that for TEOS at the same solids content and pH*. Monolithic-and very fragile-gels can be created at concentrations at least as low as 0.1% solids. Syneresis occurs rapidly in the sparse gels although the corresponding TEOS-derived gels show no syneresis below 4% solids. Mechanistic evidence from NMR, GC/IR and mass spectrometry indicates very low concentrations of both silanols and cyclic spacies in the sol. 

9:30 AM *P3.3 
SILICA AEROGEL PRODUCTS FOR INSULATION, REINFORCEMENT AND RHEOLOGY CONTROL. Douglas M. Smith, Alok Maskara, Nanopore Inc, Albuquerque, NM; Ulrich Boes, Cabot Corp, Cab-O-Sil Div, Hanau, GERMANY; Rex Field, David J. Kaul, Kenneth C. Koehlert, Cabot Corp, Cab-O-Sil Div, Tuscola, IL. 

The successful commercialization of aerogels for advanced thermal insulation,reinforcement, rheology control and other applications depends upon both maximizing performance and minimizing cost. Although the performance of aerogels may be extremely attractive (thermal conductivity in the range of 0.002 to 0.03 W/mK and efficient polymer reinforcment & rheology control), their commercial application has been limited by cost/performance reasons. For most commercial applications, aerogel products will be based on the use of aerogel granules or powders as a result of the much shorter processing times relative to monoliths. 
For each application, different aerogel properties are required to achieve maximum performance per cost. Aerogel properties which affect both cost and performance include density, pore size and distribution, type and concentration of opacifier (if any), type and degree of surface modification (if any), granule size & size distribution and strength. For a given application, an optimum co 

10:30 AM *P3.4 
PREPARATION OF HIGHLY POROUS SILICA GEL FROM POLY(TETRAMETHYLENE OXIDE) (PTMO)/SILICA HYBRIDS. J. Wen, B. Dhandapani, S.T. Oyama, G.L. Wilkes, Dept. of Chemical Engineering, Virginia Tech, Blacksburg, VA. 

Porous silica gels with high surface area were prepared by calcination of silica/poly(tetramethylene oxide) (PTMO) hybrid network materials. The variation of the surface area of these silica gels with PTMO/silica composition and molecular weight of PTMO was investigated. Surface area analysis showed that for all oligomeric molecular weights of PTMO, high values in the range of 700-1000 m²g^-1 could be obtained. The optimum PTMO/TEOS weight ratio was 30-50. Pore size analysis indicated that samples with high surfaces areas were mesoporous, while samples with low or medium surface areas were microporous. This unusual result was obtained as a consequence of the particle size of the materials, small for the high surface area materials and large for the low surface area materials. The hysteresis in the adsorption-desorption isotherms suggested that the pores were cylindrical in shape. 

11:00 AM *P3.5 
ROLES OF POLYMERIZATION, PRECIPITATION, AND AGGREGATION IN THE SYNTHESIS OF MONODISPERSE NONPOROUS OR CONTROLLED PORE CERAMIC MICROSPHERES. Alon McCormick, Kangtaek Lee, Arun Sathyagal, David Reeder, Sabir Majumder, and Peter Carr, University of Minnesota, Chemical Engineering and Materials Science and Chemistry Departments, Minneapolis, MN. 

Using experimentally measured transients of monomer concentration, intermediate concentration, ionic strength, and particle size distribution, we test the success of the population balance model in predicting the performance of sol/gel batch reactors giving monodisperse colloids ca. tens to hundreds nanometer diameter. We note characteristic dynamics in the particle size distribution for those reactors yielding the largest particles. We propose and test methods to grow larger particles. Finally, we present a hybrid sol/gel-oil emulsion route to synthesize micrometer scale, spherical, monodisperse colloidal aggregates, the pore space of which is unusually open and useful for applications such as protein chromatography. 

11:30 AM P3.6 
EFFECT OF PH AND CONCENTRATION ON THE SYNTHESIS OF MONODISPERSED SPHERICAL FINE ZIRCONIA POWDERS USING GAS-LIQUID PHASE REACTION. Chang-Hyun Kim, Kaya Univ, Dept of Engineering, Kyungpook, SOUTH KOREA; Chang-Seop Ri, Keimyung Univ, Dept of Chemistry, Taegu, SOUTH KOREA; Dae-Hee Lee, Byung-Kyo Lee, Kyungpook National Univ, Dept of Inorganic Material Engineering, Taegu, SOUTH KOREA; Jong-Jae Chung, Kyungpook National Univ, Dept of Chemistry, Taegu, SOUTH KOREA. 

Ammonia gas was blown into the solution of zirconium ion to induce precipitation of supersaturated zirconium ion at gas-liquid interface with increase in pH and concentration. The influence of pH and concentration on the shape and particle size of precipitate and calcined powders has been investigated. The precipitates formed using interface of gas-liquid phase were decomposed into fine spherical zirconia powder of high purity. As concentration of zirconium solution increase, particle size increased. At pH 4.5 of zirconium solution, maximum yield of 98.7 percent was obtained. Above pH 5.5, large aggregates of precipitates consisting of primary particles were formed and this may have been caused due to the existence of isoelectric point.