Nanostructured materials have distinctly different properties than the bulk because the number of atoms or molecules on their surface is comparable to that inside the particles creating a number of new materials and applications. Despite this potential for nanoparticles, very few practical applications have been developed because of the current high cost of these materials ($100/lb). On the other hand, flame aerosol reactors are routinely used for inexpensive production (∼$1/lb) of submicron sized commodities such as carbon blacks, pigmentary titania, fumed silica and preforms for optical fibers in telecommunications. Flame technology can be used also for synthesis of nanoparticles with precisely controlled characteristics. In these reactors, gas mixing is used to widely control the primary particle size and crystallinity of product powders while electric fields can be used to narrowly control the primary, and aggregate particle size and crystallinity. Here the application of axial electrical fields on a silica producing flame using hexamethyldisiloxane (HMDS) as precursor is presented. Experiments varying the precursor delivery rate corresponding to total production rates of 10, 20 and 30 g/h are presented. Electric fields decreased the particle size by electrostatic dispersion and repulsion of charged particles and by the reduced particle residence time inside the flame.

The physics and chemistry of drying of nano-size materials (porous solids or particles with characteristic dimensions less than 100 nm) is considered. Approaches for reducing capillary pressure and surface passivation in an effort to avoid shrinkage are presented. In addition, the effect of key variables on drying costs (both capital and operating/energy) is presented.

A chemical processing technique for the fabrication of nanopowders has been developed. The route is based on precipitation processes in solutions, either within aqueous droplets in micro-emulsions 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 a water-based processing. Nanoparticles preparation for ZrO2, ITO and ATO by this route are described.

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 predict, 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 telegrapher's equation, one sees that local density maxima arise via semidiffusive stress “waves” reflecting from the die walls and adding constructively at the centerline.

Nanoparticle chain aggregates (NCA) of 7 nm titania particles stretch under tension, and contract when the tension is relaxed. The NCA were stretched across expanding holes produced in the carbon film on an electron micrograph grid. After stretching up to 90%, the NCA broke loose at one end and contracted to a tightly folded chain. This pattern was observed in repeated tests. Mechanisms for this behavior and reasons for its generality are proposed. Implications are discussed for the ductility of nanoparticle ceramics, and the improved properties of rubber due to nanoparticle additives.

The rheology of colloidal suspensions can vary enormously depending on the contents of the suspensions and the details of how they were produced. Certain interactions between particles within colloidal suspensions can greatly affect their rheology which can be a serious impediment to their processing. For example, at DOE's Hanford site, the radioactive tank wastes are very concentrated and have formed a sludge that is too viscous to process. We are interested in understanding the rheology of this system in order to develop an efficient method for processing the waste. Towards this end we have developed a model silica system for the tank wastes whose particles can interact through chemical bonding, Keesom interactions, and Coulombic interactions. Through systematic variation of the solvent and the particle concentration we can alter the rheological behavior from shear thickening to shear thinning to Newtonian. We present preliminary results for this system as it applies to the processing of the tank waste at Hanford.

Zinc oxide thin films doped with zirconium were prepared from solutions with doping material dispersed at several concentrations and using the spray pyrolysis technique.The films were deposited over sodocalcic glasses at different substrate temperatures. Effects of doping material concentration and substrate temperatures on electrical, optical, structural and morphological film properties are presented. Results show an evolution in morphology and grains size as the doping concentration is increased. Preferential growth in the (002) orientation was detected for each thin film from X ray diffractograms.

We have studied crystal growth during aerosol synthesis of nanostructured C60, C70 and mixed fullerene particles. Fullerene particles have been produced by aerosol droplet drying and crystallization as well as via vapor condensation starting from solutions of fullerenes in toluene. Morphology, crystallinity and crystal structure of fullerene particles produced in various processing temperatures were studied by scanning and transmission electron microscopy. The results show that both highly disordered and single crystal particles with a size of about 100 nm are formed at reactor operating temperatures of 500 °C and above. The ultrafine particles formed via vapor condensation are mostly polycrystalline. Many of crystalline particles have perfectly faceted morphology, i.e., hexagonal plate-like, decahedral and icosahedral shapes. The plate-like particles are lamellar-twinned and the decahedral and icosahedral particles are multiply twinned. Crystallite formation and growth mechanisms of the particles are discussed. In addition, electron diffraction results show that fullerene alloys with fcc structure can be produced via aerosol synthesis methods.

Monodispersely-sized spherical metal oxide particles have recently attracted growing attention for many industrial applications. In particulate coating applications, controlling the size and distribution of the starting colloid plays a crucial role in the final coating properties (1,2). In chromatography, both porous and nonporous monodispersely sized colloidal particles have been used as a column-packing material (3,4). Monodisperse particles can also be used as a startingn material in a ceramic processing to make ceramic materials with uniform properties for mechanical, refractory, and catalysis applications.

Even though various monodisperse metal oxide colloids are already widely used in industry, predicting and controlling the particle size distribution is frequently more dependent on experience and ingenuity rather than on modeling. There is nothing wrong with empiricism, but models can help to achieve process control, optimization, and flexibility. We have sought to assess what combination of processes in solution (both reactive and aggregative) need to be modeled, and in doing so we have found a number of very useful references that give insight into 1) the mechanism of the particle formation and growth, and 2) the effect of reaction parameters on the final size distribution by using both experimental and numerical techniques. Understanding these should allow us to intelligently design a new process in order to make particles with the desired size and distribution. In this short contribution we hope that it will be of service to provide a brief overview of some key work that may yield itself to modeling. This review is not intended to be comprehensive; instead, we have selected work that shows features that one hopes should be captured by meaningful models.

The conditions of in ultrasound (US) transmission through a nanodispersed powder (NP) and possible effects of US-action at compacting of NP ZrO2 − Y2O3 are analyzed. These effLcts include agglomerate crushing, NP particle activation under the conditions of acoustic flows; dense NP compacting with the preservation of a compact nanostructure in the absence of acoustic flows. It was shown that the result of 13S action was dcfined by the compacting pressure P and ItS intensity level I, the values of which were divided into the ranges by the critical parameters PC and IC NP transfers from the state of gas-dispersed medium to the state of a solid porous body at P = PC, and IC characterizes the threshold of acoustic flows appearance in the powder body.

The influence of Pb/Ti ratio on the particle size of hydrothermally derived lead titanate (PbTiO3) powders was investigated. Phase pure PbTiO3 powder was synthesized by reacting nanocrystalline TiC2 powder in a 1 m KOH solution for 15 h at 200°C with Pb/Ti ratios of 1 and 5. Faceted platelet particles with a low aspect ratio were formed in solutions with Pb/Ti ratios of 1 and 5. The observed particle size of PbTiO3 was 200 nm and larger when Pb/Ti = 1, while 50 - 100 nm sized particles formed when Pb/Ti = 5. In support of TEM observations, the BET specific surface area data increased from 4.4 m2/g to 7.3 m2/g as the Pb/Ti ratio was increased from I to 5. PbTiO3 particle size was controlled by either inhibiting or promoting dissolution-precipitation. Dissolution-precipitation in a high pH solution was inhibited by maintaining an excess of Pb ions in solution and it was promoted when input concentrations of Pb and Ti were equivalent.

The mechanisms of radiation-induced desorption (RID) from the nanodispersed powder (NDP) surface under the impulse excitation of heavy-current electron beam (HCEB) were studied. Electron-induced desorption (EID); temperature-induced desorption (TID) as a result of radiation heating of the adsorbent; radiation-induced diffusion of the adsorbed atoms; re-adsorption were considered.

It was shown that radiation-induced desorption was observed during the first two pulses. The main mechanism of this process was electron-induced desorption (EID).

The structure of a surfactant-templated silica aerogel is studied by small-angle x-ray and light scattering. By combining the two techniques, we obtain structural information on length scales from Ångstroms to 0.1 millimeters. For this sample, we find five structural features, including the morphology of large scale aggregates.

Fabrication of fine-grained monoclinic zirconia ceramics has been attempted from acid and neutral zirconia sols, which have been prepared by different methods. Complete re-dispersion of flocculated particles for the neutral sol is impossible even by changing its pH, while no flocculation is observed for the acid sol. Chloride ions, which are inevitably present in the acid sol, are removed effectively by using anion exchange resin. Consolidation of the sols is performed by the pressure filtration method at 10 MPa, followed by CIP treatment at 400 MPa. It is possible to densify the compacts from both sols to >98% of theoretical density by pressureless sintering in air at 1100 °C. This temperature is lower than that for the monoclinic to tetragonal transformation of pure zirconia. Fine and homogenous-grained microstructures, which have an average grain size of 92 nm, are observed for monoclinic zirconia fabricated from the acid sol. However, more coarse and heterogeneous microstructures are observed for the compact fabricated from the neutral sol.

Nanocrystalline titania powders were prepared via aerosol pyrolysis of titanium tetrabutoxide precursor. As-received and annealed powders were characterized by XRD, SEM and TEM (+EDS), thermogravimetry, Raman- and IR-spectrometry, surface area analysis and XRF. In addition, gas-phase mass size distributions were obtained by low-pressure impactor aerosol measurements. Powders consisted of micrometer sized spherical particles. Amorphous titanium oxide powders were obtained at lower pyrolysis temperatures and only after subsequent thermal annealings crystallized titania was formed. Not until at 500°C in nitrogen and 580°C in air did pyrolysis synthesis form nanocrystalline anatase phase in-situ. During the annealing at 900°C for one hour rutile phase was usually approached, but phase pure anatase was obtained when powder had been synthesized in nitrogen atmosphere at 500°C. The proposed reason for the thermally stable anatase formation is the formation of oxygen deficient anatase phase which has a high thermal barrier to convert to rutile. Titanium tetrabutoxide evaporation and subsequent gas-to-particle formation of additional 30-80 nm particles was observed in nitrogen atmosphere at temperatures higher than precursor boiling point.

Nano-sized porous silica powders are synthesized by a room temperature aerosol process. Reactant mixing configuration, reactant temperature, and drying temperature effects on the physical and morphological features of these powders are studied by nitrogen adsorption and small angle xray scattering techniques. These silica powders have high specific surface areas up to 600 m2/g, and show narrowly confined mesoporous characteristics. The powders display some structural change with temperature. The morphological features are modeled as mass fractals by small angle x-ray scattering. Measured fractal dimensions are around 2.8, indicating diffusion limited growth processes.

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. Formation of transparent monolithic gels with no added catalyst can be six orders of magnitude faster than comparable reactions of Si(OCH2CH3)4[TEOS]. Extremely low density gels can be generated in minutes at concentrations at which TEOS does not gel at all. 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. Monolithic gels can be created at concentrations at least as low as 0.1% solids and have higher moduli than predicted. NMR and GC/IR evidence indicates extremely facile hydrolysis and condensation pathways and very few silanol or cyclic intermediates in the sol. The chemistry can also be conducted in perfluorinated solvents, enabling synthesis of silica/fluoropolymer nanocomposites.

Ammonia gas was blown into the solution of zirconium ion to induce homogeneous precipitation of supersaturated zirconium ion at gas-liquid interface with increase in pH. The precipitates formed using interface of gas-liquid phase were decomposed into fine spherical zirconia powder of high purity. As Concentration increase, mean diameter of particles increases to 140, 180, 240, 290 and 630nm. At pH of 4.5, maximum yield of 98.7% was obtained. From the above pH of 4.5, yield has been kept constant. Above pH of 5.0, large aggregates of precipitate consisting of primary particles were formed, and this may have been caused due to the existence of isoelectric point. Below pH of 4.5, almost aggregate-free fine spherical powders with particle size of below 100nm were produced.

The microwave plasma process is capable to produce larger quantities of nanoparticulate powders with mean particle sizes in the range from 5 to 20 nm. The products may be oxides, nitrides, sulphides, selenides, or even metals. Additional, it is possible to coat these particles with a layer of a second ceramic, a polymer or carbon. Sintered ZrO2-Al2O3 nanocomposites and super-paramagnetic cores of γ-Fe2O3-polymer composites are given as examples.

The fine ceramic particles of zirconia toughened alumina (ZTA), titania toughened alumina (TTA), and zirconia-titania toughened alumina(ZTTA) were synthesized through ultrasonic spray pyrolysis at various temperatures and compositions. The starting solution was prepared to have the concentration of 0.05 ∼ 0.1 M adjusting with water as a solvent. The temperature regulated for particle synthesis was 400 ∼ 550 °C as a drying zone, 850 ∼ 1400 °C as a pyrolysis zone. The produced particles were collected by a wet process and were analyzed to give characteristic properties after being dried. Various properties such as thermal behavior, phase, particle size and size distribution, shape, diffraction pattern, content of elements, etc, of particles synthesized with different experimental conditions were determined and studied by XRD, TG/DTA, PSA, ICP, and SEM, and the optimum experimental conditions for the particle synthesis were proposed.