Rapid quenching during flame spray synthesis of Pt/TiO 2 (0-10 wt% Pt) is demonstrated as a versatile method for independent control of support (TiO 2 ) and noble metal (Pt) cluster characteristics. Titania grain size, morphology, crystal phase structure, and crystal size were analyzed by nitrogen adsorption, electron microscopy and x-ray diffraction, respectively, while Pt-dispersion and size were determined by CO-pulse chemisorption. The influence of quench cooling on the flame temperature was analyzed by Fourier transform infrared spectroscopy. Increasing the quench flow rate reduced the Pt diameter asymptotically. Optimal quenching with respect to maximum Pt-dispersion (∼60%) resulted in average Pt diameters of 1.7 to 2.3 nm for Pt-contents of 1-10 wt%, respectively.

Flame-made airborne V 2 O 5 /TiO 2 nanoparticles were deposited directly onto mullite foam supports to create ready-to-use catalysts for the o-xylene conversion to phthalic anhydride. These particles containing 10% (w/w) V 2 O 5 were created by combustion of liquid precursor sprays and characterized by transmission electron microscopy, nitrogen adsorption, X-ray diffraction (XRD), temperature-programmed reduction (TPR), and Raman spectroscopy. The specific surface area, anatase content, and dominantly monomeric vanadia species on titania were thermally stable up to 450 • C. Catalyst structure was controlled in situ during deposition by the particle-laden gas flow rate through the foam, resulting in homogeneous to patchy V 2 O 5 /TiO 2 coatings. The catalytic activity and selectivity were affected by both coating texture and particle morphology. These flamecoated foams showed superior catalytic activity and selectivity at high conversions than classic, wet-made V 2 O 5 /TiO 2 catalysts.

Mixed Ta2O5‐containing SiO2 particles, 6–14 nm in diameter, with closely controlled refractive index, transparency, and crystallinity are prepared via flame spray pyrolysis (FSP) at production rates of 6.7–100 g h–1. The effect of precursor solution composition on product filler (particle) size, crystallinity, Ta dispersity, and transparency is studied using nitrogen adsorption, X‐ray diffraction, optical microscopy, high‐resolution transmission electron microscopy (HRTEM), and diffuse‐reflectance infrared Fourier‐transform spectroscopy (DRIFTS). Emphasis is placed on the transparency of the composite that is made with Ta2O5/SiO2 filler and dimethylacrylate. Increasing Ta2O5 crystallinity and decreasing Ta dispersity on SiO2 decreases both filler and composite transparencies. Powders with identical specific surface area (SSA), refractive index (RI), and Ta2O5 content (24 wt.‐%) show a wide range of composite transparencies, 33–78 %, depending on filler crystallinity and Ta dispersity. Amorphous fillers with a high Ta dispersity and an RI matching that of the polymer matrix lead to the highest composite transparency, 86 %. The composite containing 16.5 wt.‐% filler that itself contains 35 wt.‐% Ta2O5 has the optimal radiopacity for dental fillings.

The microwave properties of single crystalline TiO2 (rutile) were investigated. At a frequency of 7.5 GHz the loss tangent tan δ was found to increase from 1.4×10−7 at 4 K to 4×10−6 at 70 K for electric fields parallel to the crystallographic a,b plane. The high permittivity of 105 and the small tanδ in combination with the low microwave losses of high temperature superconductors (HTS) were utilized to construct a miniaturized X-band resonator with a high quality factor Q. An assembly of two YBa2Cu3O7 films of 8 mm in diameter separated by a rutile cylinder of 2 mm height provides a TE011 resonance at 9.7 GHz with Qs ranging from 6×105 at 10 K to 105 at 70 K. Frequency scaling of the losses in rutile and in the HTS films indicates Qs in excess of 106 at 1.8 GHz using YBa2Cu3O7 films of two inches in diameter. Such resonators are considered to be key elements for high-power filters in mobile communications.

Silica-and alumina-doped nanocrystalline ceria/zirconia (Ce 0.5 Zr 0.5 O 2 ) were prepared in one step by flamespray pyrolysis. Structural and textural properties were characterized using high-resolution electron microscopy, nitrogen adsorption and X-ray diffraction. Oxygen exchange capacity was studied by pulse thermal analysis using H 2 as reducing agent. Adding silica (up to 20 wt%) or alumina (up to 16 wt%) altered the particle morphology from polyhedral to spherical particles. In doped ceria/zirconia, the oxygen exchange capacity (OEC) was affected by the silica content but very little by the alumina content. The highest OEC (450 mmol O 2 kg 21 ) was measured for ceria/zirconia doped with 3 wt% silica, whereas for flame-made ceria/zirconia (360 mmol O 2 kg 21 ) and corresponding precipitated silica-or alumina-doped materials the OEC was considerably lower. For high dopant contents (20 wt% silica) an amorphous layer was formed on top of a crystalline core. This layer acted as a diffusion barrier, so that the OEC dropped to about 76 mmol O 2 kg 21 .

No abstract

The formation of nanostructured silica particles by oxidation of hexamethyldisiloxane (HMDSO) in co-annular diffusion flames is investigated by in-situ small-angle X-ray scattering (SAXS). This enabled the nonintrusive monitoring of the mass fractal dimension, the aggregate size, and the number of primary particles per aggregate, along with the silica volume fraction, the primary particle diameter, the geometric standard deviation, and the number density along the flame axis. Parallel to this, thermophoretic sampling (TS) of the particles and analysis by transmission electron microscopy (TEM) allowed for direct comparison of particle morphology to that obtained from the above SAXS analysis, which were compared also to the ultra-small-angle X-ray scattering (US-

No abstract