Michael T. Harris

Effect of solvent on the homogeneous precipitation of titania by titanium ethoxide hydrolysis

Abstract A method has been developed for studying and controlling the growth of colloidal titania by titanium ethoxide hydrolysis in ethanol, 1-butanol, and tert-butyl alcohol. Particle growth was followed from approximately 0.02 to 1.0 μm by dynamic laser-light scattering. Evaluation of the particle growth kinetics indicated that growth was controlled by surface phenomena and that the type of precipitate formed was affected by the solvent. Electron microscopy showed that monodisperse spherical particles were formed in the solvents ethanol and 1-butanol. The precipitate that was formed in tert-butyl alcohol had no regular shape and was characteristic of uncontrolled homogeneous precipitation.

Investigation of electrokinetic decontamination of concrete

Abstract Experiments have been conducted to investigate the capabilities of electrokinetic decontamination of conceret. Batch equilibration studies have determined that the loading of cesium and strontium on concrete may be decreased using electrolyte solutions containing competing cations, while solubilization of uranium and cobalt, that precipitate at high pH, will require lixiviants containing complexing agents. Dynamic electrokinetic experiments showed greater mobility of cesium than strontium, while some positive results were obtained for the transport of cobalt through concrete using EDTA and for uranium using carbonate. *Managed by Lockheed Martin Energy Research Corp. for the U. S. Department of Energy under contract DE-AC05-96OR22464.

FTIR Spectroscopy, SAXS and Electrical Conductivity Studies of the Hydrolysis and Condensation of Zirconium and Titanium Alkoxides

A continuous flowing-rapid mixing technique was combined with FTIR, SAXS and electrical conductivity to study the early stages of polymer formation and growth during the acid-catalyzed hydrolysis and condensation of titanium and zirconium alkoxides. Reaction times as short as 80 milliseconds were investigated. FTIR spectroscopy was used to monitor the water and M−OR concentrations during the reaction. Hydrolysis of ∼25–50% of the alkoxy groups was facile. The FTIR and SAXS data showed that condensation was also very rapid. The activity and mobility of the ions in the solution were monitored by electrical conductivity measurements. The decrease in the normalized solution conductivity during the reaction correlated with the loss of [M−OR]. Furthermore, the radius of gyration of the growing polymers increased rapidly in regimes where the conductivity and [M−OR] decreased fastest. This finding suggests that the mobility of some of the charge carrying species decreases because of the growth in size of the polymers.

The synthesis of metal hydrous oxide particles by multiphase electrodispersion

Abstract A multiphase electrodispersion precipitation reactor called the electric dispersion reactor (EDR) was developed to synthesize ultrafine particles for the production of precursor powders of advanced ceramic materials. A pulsed electric field is employed to create dispersions of micrometer- and submicrometer-scale conducting (aqueous-based) drops in non-conducting (organic) liquids. Species initially dissolved in the organic phase diffuse into the aqueous droplets containing the other reagents. Reaction ensues, leading immediately to precipitation and gelation in the aqueous droplets. The EDR has produced 0.1–5 μm particles of silica, alumina, zirconia, yttria, and composite hydrous oxide particles from metal alkoxide and metal salt precursors. Also considered is the application of the EDR to the control and modification of the morphological characteristics of these particles, with illustrative examples.

Modeling the Electrokinetic Decontamination of Concrete

Abstract The decontamination of concrete is a major concern in many Department of Energy (DOE) facilities. Numerous techniques (abrasive methods, manual methods, ultrasonics, concrete surface layer removal, chemical extraction methods, etc.) have been used to remove radioactive contamination from the surface of concrete. Recently, processes that are based on electrokinetic phenomena have been developed to decontaminate concrete. Electrokinetic decontamination has been shown to remove from 70 to over 90% of the surface radioactivity. To evaluate and improve the electrokinetic processes, a model has been developed to simulate the transport of ionic radionuclei constituents through the pores of concrete and into the anolyte and catholyte. The model takes into account the adsorption and desorption kinetics of the radionuclei from the pore walls, and ion transport by electro-osmosis, electromigration, and diffusion. A numerical technique, orthogonal collocation, is used to simultaneously solve the governing co...

Para- and Dia-Magnetic Particle Flocculation in a Magnetic Field

Abstract An experimental apparatus has been assembled for the study of high-gradient magnetic separations of para- and dia-magnetic particles suspended in a liquid. The components of this system include a cryogenic magnet, equipment for light-intensity measurements, and a dynamic light-scattering technique for transient particle-size measurements. The flocculation of paramagnetic hematite particles of approximately 200-nm diameter under the influence of a uniform magnetic field is experimentally investigated. The effect of solution pH on particle growth as a result of flocculation is examined with and without the presence of the magnetic field. Results show that the flocculation rate of hematite particles increases with the intensity of the magnetic field.

A study of solvent effects on the synthesis of pure component and composite ceramic powders by metal alkoxide hydrolysis

The production of ceramics having high density, low porosity, and fine grains requires the use of high-purity metal oxide powders that consist of particles of uniform shape, size, and composition. Metal Alkoxide hydrolysis is an attractive method for the synthesis of high-purity metal oxide particles. The nature of the precipitate formed is affected by the solvent. This present study investigates the growth kinetics and characteristics of metal oxide particles (i.e., ZrO/sub 2/ and TiO/sub 2/) that are produced in various alcohol solvents (ethanol, 1-butanol, 2-butanol, and tert-butyl alcohol). Results are also presented for the synthesis of uniform homogeneous composite metal oxide particles (i.e., Y/sub 2/O/sub 3/-ZrO/sub 2/ and ZrO/sub 2/-TiO/sub 2/) by low-temperature metal alkoxide hydrolysis. 3 figs., 7 refs.

Structure and growth kinetics of zirconium hydrous polymers in organic solutions

Abstract The objective of this study was to understand the kinetics of hydrolysis and condensation reactions and structures of zirconium hydrous polymers formed by these reactions. Small angle X-ray scattering (SAXS) measurements were made on solutions for an aging period ranging from 109 ms to few days. Results prove that condensation reactions start before completion of hydrolysis and as a result polymers formed at the earlier stages ( t xa0≈xa0100 ms) are weakly cross-linked (linear). On further aging, due to the internal condensation process these weakly cross-linked polymers convert to highly branched polymers with a structure identical to an ideal Gaussian randomly branched polymer with a persistent length (building block) of 8.3xa0±xa00.5 A.

Removal of submicron silica particles from tert-amyl alcohol by dielectric/electric packed bed filtration

Abstract A packed bed with an applied electric field is used to remove submicron and nanometer particles from a nonconducting or slightly conducting solution. Several studies have shown that the application of an electric field to a packed bed significantly increases the performance of the filtration. To enhance the electric-field filtration efficiency, it is desired that the packing materials have a higher dielectric constant than the solution so that the electric-field lines will be diverted into the packing materials. In the present studies, a dc voltage of 0 to 8 kV/cm is applied to a packed bed (2.5-cm diameter and 3.0-cm length) filled with 1-mm-diameter glass beads. The filtration medium contains submicrometer or nanometer SiO2 particles dispersed in tert-amyl alcohol. Two particle sizes are investigated: the average particle sizes are about 300 nm and 50 nm, respectively. Visible light spectrophotometry is used to estimate the amount of SiO2 particles in the effluent. The experimental results are ...

Porous spherical shells and microspheres by electrodispersion precipitation

The ability to reproduce the synthesis of dense- and porous-microspheres and micron-sized spherical shells is very important in (a) the development of ceramics for structural, electronic, catalyst and thermal applications; and (b) the encapsulation of products for controlled-release of drugs, flavors and perfumes, and inks and dyes, and the protection of light-sensitive components and mechanical support of fragile materials. Larger metallic- and ceramic-spherical shells have been used in inertial confinement fusion (ICF) experiments and as catalyst supports. The current paper will focus on a recent technique that has been developed for synthesizing ceramic microspheres and micro-shells. Pulsed electric fields have been used to enhance the dispersion of aqueous metal (Zr and Al) salt solutions from a nozzle and into a nonconducting liquid continuous phase that is immiscible with the aqueous phase. The diameter of the resulting microdroplets ranged in size from approximately 0.1 to 10 {mu}m. Precipitation of hydrous metal oxides occurred as ammonia, which was dissolved in varying amounts in the continuous phase, diffused into the aqueous microdroplets. Spherical shells were formed at higher ammonia concentrations and microspheres were produced at lower ammonia concentrations. Upon drying, dimples appeared in the particles that were synthesized at higher ammonia concentrations. The latter result accords with the well known fact that under certain conditions spherical shells collapse when a fluid is extracted from the core of the particle. No dimples were observed in the microspheres that were produced at lower ammonia concentrations. Analog X-ray dot maps for aluminum and zirconium were done to determine the spatial distribution of each metal in the particles.