Simulation of the heteroagglomeration between highly size-asymmetric ceramic particles.

Aggregation phenomena of dilute suspensions composed of two kinds of oxide particles (alumina d(1)=400 nm and silica d(2)=25 nm) have been studied by computer simulations. These particles are oppositely charged and so are prone to heteroagglomerate. The interaction between particles has been modeled by the DLVO potential. Two kinds of simulations have been performed: Brownian dynamics simulations to study the aggregation kinetics and global minimization searches that permit the examination of the most stable configurations of agglomerates. We demonstrate that aggregation should occur also for quite large fractions of added silica (even when 200 silica particles are adsorbed on each alumina particle) and that aggregates are likely to present chainlike shapes. Both findings are in agreement with experiments.

Heteroaggregation between Al2O3 submicrometer particles and SiO2 nanoparticles: experiment and simulation.

The aggregation process of a two-component dilute system (3 vol %), made of alumina submicrometer particles and silica nanoparticles, is studied by Brownian dynamics simulations. Alumina and silica particles have very different sizes (diameters of 400 and 25 nm, respectively). The particle-particle interaction potential is of the DLVO form. The parameters of the potential are extracted from the experiments. The simulations show that the experimentally observed aggregation phenomena between alumina particles are due to the silica-alumina attraction that induces an effective driving force for alumina-alumina aggregation. The experimental data for silica adsorption on alumina are very well reproduced.

Isolation of a chromosomally engineered durum wheat line carrying the Aegilops ventricosa pchl gene for resistance to eyespot.

The chromosome 7Dv of Aegilops ventricosa (syn. Triticum ventricosum, 2n = 4x = 28, genome DvDvMvMv) carries the gene Pch1 for resistance to eyespot. This gene has previously been transferred to chromosome 7D of bread wheat, T. aestivum (2n = 6x = 42, genome AABBDD). To (1) enhance the level of resistance of bread wheat by increasing the copy number of Pch1, and (2) create eyespot-resistant triticales, meiotically stable Pch1-carrying durum lines were selected from the backcross progenies of a cross between Ae. ventricosa and T. durum cv. Creso ph1c (2n = 4x = 28, genome AABB). The Pch1 transfer, likely resulting from homoeologous recombination, was located at the distal position on the long arm of chromosome 7A. The 7A microsatellite marker Xgwm 698 was found closely linked in repulsion to the introgression in the resistant recombination lines, and the endopeptidase allele located on chromosome 7A of cv. Creso ph1c was lost.

Electrical Conductivity and Dielectric Dispersion Phenomena of Concentrated TiO(2) Suspensions.

The complex conductivity of concentrated TiO(2) suspensions (up to 50 vol%) was measured over a large frequency range (1 MHz-1.8 GHz), as a function of grain volume content. These measurements highlight relaxation phenomena in the intermediate frequency range, which are associated with the dispersed powder. These phenomena were previously noted in O'Brien's theoretical developments. A quantitative data analysis was made, in terms of time constant distribution, using the CONTIN software, from Provencher. As a result, a complex process is highlighted, including two main mechanisms in different ranges of time constants. Particularly, we showed good agreement between the higher frequency mechanism and the O'Brien theory. From Dukhin's lambda ratios, which are ratios of grain surface to bulk electrolyte conductances, we calculated the electrolyte conductivity as a function of powder concentrations. At higher powder concentrations, these values are different from those measured with centrifuged liquids. Copyright 2000 Academic Press.