A comparative study of cellulose crystallinity based on the sample crystallinity and the cellulose content in plant fibres was performed for samples of different origin. Strong acid hydrolysis was found superior to agricultural fibre analysis and comprehensive plant fibre analysis for a consistent determination of the cellulose content. Crystallinity determinations were based on X-ray powder diffraction methods using sideloaded samples in reflection (Bragg-Brentano) mode. Rietveld refinements based on the recently published crystal structure of cellulose Ib followed by integration of the crystalline and amorphous (background) parts were performed. This was shown to be straightforward to use and in many ways advantageous to traditional crystallinity determinations using the Segal or the Ruland -Vonk methods. The determined cellulose crystallinities were 90 -100 g/100 g cellulose in plant-based fibres and 60 -70 g/100 g cellulose in wood based fibres. These findings are significant in relation to strong fibre composites and bio-ethanol production.

Carbon nanotubes are shown to be useful materials for introduction of nanopores with a controlled diameter into zeolite single crystals. The intracrystalline nanopores are created by crystallization of the zeolite around the carbon nanotubes that are subsequently removed by combustion.

We successfully synthesized large-scale and highly pure ultrathin SnO2 nanosheets (NSs), with a minimum thickness in the regime of ca. 2.1 nm as determined by HRTEM and in good agreement with XRD refinements and AFM height profiles. Through TEM and HRTEM observations on time-dependent samples, we found that the as-prepared SnO2 NSs were assembled by “oriented attachment” of preformed SnO2 nanoparticles (NPs). Systematic trials showed that well-defined ultrathin SnO2 NSs could only be obtained under appropriate reaction time, solvent, additive, precursor concentration, and cooling rate. A certain degree of nonstoichiometry appears inevitable in the well-defined SnO2 NSs sample. However, deviations from the optimal synthetic parameters give rise to severe nonstoichiometry in the products, resulting in the formation of Sn3O4 or SnO. This finding may open new accesses to the fundamental investigations of tin oxides as well as their intertransition processes. Finally, we investigated the lithium-ion storage of the SnO2 NSs as compared to SnO2 hollow spheres and NPs. The results showed superior performance of SnO2 NSs sample over its two counterparts. This greatly enhanced Li-ion storage capability of SnO2 NSs is probably resulting from the ultrathin thicknesses and the unique porous structures: the nanometer-sized networks provide negligible diffusion times of ions thus faster phase transitions, while the “breathable” interior porous structure can effectively buffer the drastic volume changes during lithiation and delithiation reactions.

No abstract

A new X-ray crystallographic beamline is operational at the MAX II synchrotron in Lund. The beamline has been in regular use since August 1998 and is used both for macro-and small molecule diffraction as well as powder diffraction experiments. The radiation source is a 1.8 T multipole wiggler. The beam is focused vertically by a bendable mirror and horizontally by an asymmetrically cut Si(111) monochromator. The wavelength range is 0.8±1.55 A Ê with a measured¯ux at 1 A Ê of more than 10 11 photons s À1 in 0.3 mm  0.3 mm at the sample position. The station is currently equipped with a Mar345 imaging plate, a Bruker Smart 1000 area CCD detector and a Huber imaging-plate Guinier camera. An ADSC 210 area CCD detector is planned to be installed during 2000.

Barium-promoted cobalt catalysts supported on carbon exhibit higher ammonia activities at synthesis temperatures than the commercial, multipromoted iron catalyst and also a lower ammonia inhibition.

No abstract

The hardness and thermal stability of cubic spinel silicon nitride (c-Si3N4), synthesized under high-pressure and high-temperature conditions, have been studied by microindentation measurements, and x-ray powder diffraction and scanning electron microscopy, respectively. The phase at ambient temperature has an average hardness of 35.31 GPa, slightly larger than SiO2 stishovite, which is often referred to as the third hardest material after diamond and cubic boron nitride. The cubic phase is stable up to 1673 K in air. At 1873 K, α- and β-Si3N4 phases are observed, indicating a phase transformation sequence of c-to-α-to-β-Si3N4 phases.