Tailoring the morphology of WO₃films with substitutional cation doping: Effect on the photoelectrochemical properties

With the aim of improving the performance and extending the range of applications of mesoporous WO₃films, which were initially developed for the photoelectrochemical oxidation of water, we investigated the effect of a number of dopants (lithium, silicon, ruthenium, molybdenum and tin) upon the transparency, crystallinity, porosity and conductivity of the modified films. Tin, molybdenum and silicon were shown to improve the electrochromic behaviour of the layers whereas ruthenium enhanced considerably the electronic conductivity of the WO₃films. Interestingly, most of the dopants also affected the film morphology and the size of WO₃nanocrystals. X-ray photoelectron spectra revealed absence of significant segregation of doping elements within the film. Raman analyses confirmed that the monoclinic structure of WO₃films does not change upon substitutional cation doping; thus, the crystallinity of WO₃films is maintained.

Mathematical modelling of the solidification of liquid tin with electromagnetic stirring

It is well known that during alloy solidification, convection currents close to the so-lidification front have an influence on the structure of dendrites, the local solute concentration, the pattern of solid segregation, and eventually the microstructure of the casting and hence its mechanical properties. Controlled stirring of the melt in continuous casting or in ingot solidification is thought to have a beneficial effect. Free convection currents occur naturally due to temperature differences in the melt and for any given configuration, their strength is a function of the degree of superheat present. A more controlled forced convection current can be induced using electro-magnetic stirring. The authors have applied their Control-Volume based MHD method [1, 2] to the problem of tin solidification in an annular crucible with a water-cooled inner wall and a resistance heated outer one, for both free and forced convection situations and for various degrees of superheat. This problem was studied experimentally by Vives and Perry [3] who obtained temperature measurements, front positions and maps of electro-magnetic body force for a range of superheat values. The results of the mathematical model are compared critically against the experimental ones, in order to validate the model and also to demonstrate the usefulness of the coupled solution technique followed, as a predictive tool and a design aid. Figs 6, refs 19.