Heidi Van Den Rul

Sulphur group analysis in solid matrices by atmospheric pressure-temperature programmed reduction

The atmospheric pressure-temperature programmed reduction (AP-TPR) has become an established and reliable method amongst the different sulphur characterisation techniques for solid materials, like coal and coal derived products, rubber and clay. The analytical method is based upon the fact that specific sulphur functional groups are hydrogenated at specific temperatures. During the last few years, several adjustments have been made to the hard- and software as well as to the experimental parameters. The changes and the reliability of the method are extensively discussed in this paper.

Hydrothermal synthesis of ZnO nanorods: a statistical determination of the significant parameters in view of reducing the diameter

In this paper a 2(8-4) fractional factorial design of experiments is applied to identify the important parameters that affect the average diameter of ZnO rods, synthesized by means of a hydrothermal procedure. A water-based Zn(2+) precursor is used for the formation of one-dimensional ZnO particles, without the presence of an organic additive. Results indicate that, at the investigated levels, four of the parameters have a significant effect on the mean diameter. These are the temperature, the heating rate, stirring and an ultrasonic pre-treatment of the precursor solution. Experiments carried out with zinc acetate and zinc chloride do not show a significant difference in rod diameter. Other parameters that do not show a significant effect are the concentration of Zn(2+), the molar ratio between the hydroxyl and the zinc ions, and the reaction time. Interactions are observed between stirring and an ultrasonic pre-treatment and between the zinc concentration and the OH:Zn ratio. By fixing the significant factors at their optimal value it is possible to decrease the mean diameter. The particles are characterized by means of x-ray diffraction (XRD) and transmission electron microscopy (TEM).

Crystallization resistance of barium titanate zirconate ultrathin films from aqueous CSD: a study of cause and effect

Ultrathin BaZr0.8Ti0.2O3 films (t < 30 nm) on SiOx/Si substrates were obtained by means of aqueous chemical solution deposition (CSD). Though the precursor crystallized into cubic perovskite powder at 600 °C, ultrathin films only crystallized at 950 to 1000 °C, even after addition of excess Ba to compensate for loss of Ba. Films with thickness above 100 nm, on the other hand, crystallized readily around 650 °C. The crystallization is related to film thickness, affecting the crystallization activation energy, and to silicate formation by reaction with the substrate, exerting its largest influence in ultrathin films. Barium deficiency, silicate formation, carbonate secondary phase and the high activation energy for crystallization resulted in the amorphous nature of the ultrathin films, which strongly affects the observed k value (∼ 15). The paper contributes insights with implications for the application of BaZr0.8Ti0.2O3 as an alternative high-k gate dielectric.

Influence of Heat Treatment on Sr0.9Bi2.2Ta2O9 Thin Films Prepared by Aqueous CSD

Sr0.9Bi2.2Ta2O9 thin films were prepared on a Pt-substrate by aqueous chemical solution deposition. The applied heat treatment seems to have a significant influence on the ferroelectric response, crystallinity and surface morphology. For two-layer thin films annealed at 700°C in oxygen, the Pr-value increased from 3.6 until 5.5 μ C/cm2, c-axis preferred orientation was considerably lowered and rod-like instead of spherical grains were grown when the second pyrolysis step at 520°C was omitted.