Preparation of rhodium nano-particles using microwaves

A new process for synthesizing rhodium (Rh) nano-particles by sol–gel processing using acrylamide and microwaves is reported and discussed. Three heat treatments were applied: the first required the use of microwaves, with an inert gas (Ar) flux, to decompose the organic material; the second and third treatments, respectively, were carried out into a furnace in air at temperatures of 600 and 1,000 °C. This procedure ensured the removal of by-products produced during the sol–gel reaction. The synthesis of a pure nano-Rh was confirmed by X-ray diffraction (XRD), where the presence of a cubic structure was observed (PDF file 089-7383), and EDX. Thermogravimetric analysis (TGA), in addition to determining the decomposition temperatures, enabled the heat treatment conditions needed to obtain pure nano- Rh to be elucidated. Furthermore, the morphology was observed with a scanning electron microscope (SEM). After the heat treatment at 1,000 °C, SEM images showed grain sizes between 3 and 200 nm. High-resolution transmission electron microscopy (HR-TEM) confirmed the production of those nano- particles, and the beginning of the formation of clusters as a consequence of the high temperature applied to the system.     

Identification of a novel series of alkylitaconic acids in wood cultures of Ceriporiopsis subvermispora by gas chromatography/mass spectrometry.

A novel series of long-chain unsaturated dicarboxylic acids consisting of a long aliphatic chain attached to the C-3 position of itaconic acid has been identified by gas chromatography/mass spectrometry during in vitro decay of eucalypt wood by the white-rot basidiomycete Ceriporiopsis subvermispora. The major compounds were identified as tetradecyl-, 7-hexadecenyl- and hexadecylitaconic acids by their mass fragmentation patterns. Other members of the same compound series, identified as dodecanyl-, tridecanyl-, tetradecenyl-, pentadecanyl-, octadecenyl- and octadecanylitaconic acids, were present in very minor amounts or traces. Whereas hexadecenylitaconic acid has already been reported in cultures of C. subvermispora, to our knowledge this is the first report of the presence of the other alkylitaconic acids in fungal cultures. These new alkylitaconic-type metabolites may constitute a source for peroxidizable lipids involved in lignin degradation during wood decay by C. subvermispora and other white-rot basidiomycetes.     

Method for combinatorial screening of moisture vapor transmission rate

A high-throughput method for screening the moisture vapor transmission rate of barrier films was developed. This moisture high-throughput screening (MHTS) technique is based upon a Nafion-crystal violet (CVN) sensor that changes color from yellow to green upon absorption of water. Using an appropriate set of known standards, the slope of absorbance (at 630 nm) as a function of time can be converted into moisture vapor transmission rate (MVTR) values that agree with those obtained using ASTM F1290. High-throughput screening was demonstrated by depositing 20 emulsion-based poly(vinylidene chloride) films, using a 48-well template, of varying thicknesses onto the CVN sensor film and aging at 40 degrees C and 90% relative humidity for 72 h. MVTR values were accurately determined to a level of 0.9 g/m(2).day, at which point side-diffusion of moisture between the barrier and sensor films prevented observation of lower values. Larger sample size and edge-sealing are two proposed methods for improving the sensitivity of MHTS.     

Synthesis and structural characterization of YVO3 prepared by sol–gel acrylamide polymerization and solid state reaction methods

The formation of the YVO₃ compound obtained by sol–gel acrylamide polymerization is reported. This synthesis method is contrasted with solid state reaction. Differential thermal analysis (DTA) results show the formation of YVO₃ at 805 °C compared with 1312 °C for solid state reaction. Thermogravimetric analysis (TG) results show that between 400 and 600 °C the denaturalization of the organic part, ethylenediamine, and the decomposition of nitrates occur. The evolution of YVO₄ into YVO₃ was also studied by X-ray powder diffraction (XRD). The refinement results obtained for both YVO₃ samples show an orthorhombic phase with Pbnm (62) space group and lattice parameters: a = 5.283 Å, b = 5.605 Å and c = 7.580 Å. Grain size and morphology evolution for different heat treatments were studied with scanning electron microscopy (SEM). The use of sol–gel acrylamide synthesis allows us to start with a homogeneous grain distribution with a mean size of 5.03 ± 0.65 nm growing up to 4.11 ± 0.87 μm in YVO_4. After reduction to YVO₃ the final grain size was 2.87 ± 0.10 μm also with grain size homogeneity. This is in contrast with samples prepared by solid state reaction for which the grain size starts (YVO₄) between 1 and 7.0 μm and ends (YVO₃) with a size distribution centered at 90.32 ± 74.46 μm. Transmission electron microscopy (TEM) results corroborate XRD results. Energy dispersive X-ray (EDX) results are in agreement with theoretical values.     

Quenching of giant hysteresis effects in La(1-z)Y(z)Hx switchable mirrors

Hydrogen atoms adsorbed on TiO2(110)-(1x1) surfaces have been characterized by scanning tunneling microscopy (STM) combined with electron stimulated desorption (ESD) technique. Certain amounts of H atoms are unexpectedly found on the TiO2 surfaces annealed at 900 K. Two forms of adsorption were discriminated in STM images from the different sensitivity to ESD and tentatively assigned to hydroxyl-type (O-H) and hydride-type (Ti-H) species.     

Comparative study of the synthesis of KReO<Subscript>4</Subscript> using acrylamide sol–gel and solid-state reaction methods

KReO₄ was synthesized by solid-state reaction and for the first time by sol–gel method via acrylamide polymerization. X-ray diffraction analysis showed that a single phase of KReO₄ was obtained by both methods at 500–505 °C having a tetragonal unit cell. The solid-state reaction samples had a grain size of 5 μm and the sol–gel samples had fibrous aspect, agglomerated between 10 and 100 μm. By TEM it was observed nanocrystals of 100 nm, it is suggested that the xerogel fibers are formed by nanocrystals. From the results obtained, we concluded that the morphology is strongly influenced by the method of synthesis used.