No abstract

Crystallite size distributions and particle size distributions were determined by transmissions electron microscopy (TEM), X-ray powder diffraction (XRD), and small-angle X-ray scattering (SAXS) for three commercially available TiO 2 powders (P25, UV100, and TiO2_5 nm) and one SSEC produced powder (SSEC78). The theoretical Guinier model was fitted to the experimental obtained XRD data and compared to analytical expressions. Modeling of the XRD spectra showed a difference between the analytical size dependent expressions and the theoretical Guinier model. Primary particle size distributions were extracted from SAXS measurements by the hard sphere model including an interparticle interference factor. The sizes obtained from SAXS were smaller than the sizes obtained from the XRD experiments; however, a good agreement was obtained between the two techniques. Electron microscopy confirmed the primary particle sizes and the shapes obtained by XRD and SAXS. The SSEC78 powder and the commercially available powders showed different morphologies, but SSEC78, UV100, and TiO2_5 nm all consisted of both primary particles as well as a secondary structure comprised of nanosized primary particles agglomeration into larger clusters. P25 showed the largest primary particle size, but did not show a secondary structure.

Extremely broadband grazing-incidence multilayers for hard-x-ray reflection can be obtained by a gradual change of the layer thicknesses down through the structure. Existing approaches for designing similar neutron optics, called supermirrors, are shown to provide respectable performance when applied to x-ray multilayers. However, none of these approaches consider the effects of imperfect layer interfaces and absorption in the overlying layers. Adaptations of neutron designs that take these effects into account are presented, and a thorough analysis of two specific applications (a single hard-x-ray reflector and a hard-x-ray telescope) shows that an improved performance can be obtained. A multilayer whose bilayer thicknesses are given by a power law expression is found to provide the best solution; however, it is only slightly better than some of the adapted neutron designs.

Nanostructured materials have drawn much attention because of the dramatically different properties observed on going from bulk material to nanosized particles. Nanoparticles have properties that lie between the quantum effects of atoms and molecules and the bulk properties of materials. In the nanometer range (1-100 nm) the particle size affects structural characteristics (e.g., lattice symmetry, unit-cell dimension), electronic properties (e.g., band gap), and therefore also the physical (e.g., wetting, melting point) and chemical properties (e.g., catalytic effects) of a material. The applications of nanomaterials include lithium-based batteries, fuel cells, [1, 2] thin films, inorganic-organic hybrid materials, [3] sensors, piezoelectric devices, and catalysts. [4,5] In all production methods for nanomaterials, a key requirement is the ability to control nanoparticle size, shape, and crystallinity. Special attention has been devoted to metal oxides. These can adopt many different crystal structures and have metallic, semiconducting, or insulating properties.[5] Their chemical properties range from strong catalytic reactivity to chemical inertness and high-temperature stability, and the application of metal oxides is a multibillion-dollar industry.Several wet-chemistry synthesis routes are capable of producing nanomaterials, [6] but the sol-gel technique has become the standard method for fabricating metal oxides because of the possibility of obtaining high chemical homogeneity at low temperature and under mild chemical conditions. [5,7] The downside is the relatively long process time and the need for posttreatment (e.g., calcination), which make the process less attractive for industry. The solution appears to be synthesis in supercritical fluids, which provides unique control of chemistry and nanocrystal properties. [8][9][10][11][12][13][14][15][16][17] Use of supercritical fluids as solvents in sol-gel processes enhances the kinetics by more than an order of magnitude. Furthermore, supercritical fluids exhibit particularly attractive properties such as gaslike mass-transfer behavior, liquidlike densities, and changed dielectric properties. These properties can be fine-tuned by simple changes in pressure and temperature; for example, the solubility of a compound can be dramatically changed to cause very fast precipitation.To manipulate the properties of nanomaterials and synthesize new materials with unprecedented properties, the main challenge is to understand the nucleation, crystallization, and growth processes.[5] This requires development of analytical tools capable of following nanoparticle formation in real time. In situ measurements by dynamic light scattering (DLS) have been used to study particle growth and stabilization of primary particles by surfactants. [18] In situ synchrotron powder diffraction has become a widely used tool for following solid-state reactions and crystallization processes. [19][20][21] The crux of this technique is the high intensity of the synchrotron beam, which allow...

Nanostructured materials have drawn much attention because of the dramatically different properties observed on going from bulk material to nanosized particles. Nanoparticles have properties that lie between the quantum effects of atoms and molecules and the bulk properties of materials. In the nanometer range (1-100 nm) the particle size affects structural characteristics (e.g., lattice symmetry, unit-cell dimension), electronic properties (e.g., band gap), and therefore also the physical (e.g., wetting, melting point) and chemical properties (e.g., catalytic effects) of a material. The applications of nanomaterials include lithium-based batteries, fuel cells, [1, 2] thin films, inorganic-organic hybrid materials, [3] sensors, piezoelectric devices, and catalysts. [4,5] In all production methods for nanomaterials, a key requirement is the ability to control nanoparticle size, shape, and crystallinity. Special attention has been devoted to metal oxides. These can adopt many different crystal structures and have metallic, semiconducting, or insulating properties.[5] Their chemical properties range from strong catalytic reactivity to chemical inertness and high-temperature stability, and the application of metal oxides is a multibillion-dollar industry.Several wet-chemistry synthesis routes are capable of producing nanomaterials, [6] but the sol-gel technique has become the standard method for fabricating metal oxides because of the possibility of obtaining high chemical homogeneity at low temperature and under mild chemical conditions. [5,7] The downside is the relatively long process time and the need for posttreatment (e.g., calcination), which make the process less attractive for industry. The solution appears to be synthesis in supercritical fluids, which provides unique control of chemistry and nanocrystal properties. [8][9][10][11][12][13][14][15][16][17] Use of supercritical fluids as solvents in sol-gel processes enhances the kinetics by more than an order of magnitude. Furthermore, supercritical fluids exhibit particularly attractive properties such as gaslike mass-transfer behavior, liquidlike densities, and changed dielectric properties. These properties can be fine-tuned by simple changes in pressure and temperature; for example, the solubility of a compound can be dramatically changed to cause very fast precipitation.To manipulate the properties of nanomaterials and synthesize new materials with unprecedented properties, the main challenge is to understand the nucleation, crystallization, and growth processes.[5] This requires development of analytical tools capable of following nanoparticle formation in real time. In situ measurements by dynamic light scattering (DLS) have been used to study particle growth and stabilization of primary particles by surfactants. [18] In situ synchrotron powder diffraction has become a widely used tool for following solid-state reactions and crystallization processes. [19][20][21] The crux of this technique is the high intensity of the synchrotron beam, which allow...