Microstructures

The fabrication of composites formed by alumina grains (95 vol%) in the micrometer size range and aluminium titanate nanoparticles (5 vol%) by reaction sintering of alumina (Al 2 O 3 ) and titania (TiO 2 ) is investigated. The green bodies were constituted by mixtures of sub-micrometric alumina and nano-titania obtained from freeze-drying homogeneous water based suspensions, and pressing the powders. The optimization of the colloidal processing variables was performed using the viscosity of the suspensions as control parameter. Different one step and two step sintering schedules using as maximum dwell temperatures 1300 and 1400 8C were established from dynamic sintering experiments. Specimens cooled at 5 8C/min as well as quenched specimens were prepared and characterized in terms of crystalline phases, by X-ray diffraction, and microstructure by scanning electron microscopy of fracture surfaces.

Proteinepolysaccharide interactions are of great importance in the design of dairy formulations, as they play a key role in the formation of structure and texture in dairy products. With a detailed understanding of the factors affecting the interactions, the ability of charged polysaccharides to associate with the milk proteins is continuously exploited to create functional complexes, novel ingredients and delivery systems. In addition, formulations containing non-interacting polysaccharides also need to be carefully controlled, as these biopolymers may give rise to segregative phase separation, with important consequences to the stability and quality of the final matrix. As casein micelles play a major role in imparting structure to dairy products, emphasis in this review will be given to the molecular details of the interactions between polysaccharides with these protein particles. Some of the most researched polysaccharides will be highlighted in this context, and the progress made in understanding their role during structure formation of dairy matrices will be discussed. The opportunity of creating novel microstructures provided by association or/and incompatibility of milk proteins and different polysaccharides will be assessed.

In orogenic systems, thrust faults play a major role in stacking different tectonic units and may act as conduits for the expulsion of large amounts of fluid of different origins (metamorphic, diagenetic, meteoric). This study focuses on the Monte Perdido thrust unit emplaced in the Paleogene Jaca thrustsheet-top basin, in the SW-central Pyrenees. We aim to decipher the mechanisms and P-T conditions of deformation in fault zones and characterize the related fluid involvement, through combined microstructural, geochemical and microthermometry analyses. Two thrust faults cutting platform limestones, marls and siliciclastic turbidites of the lower part of the basin-fill (Paleoceneelower Eocene) have been studied. The fault zones are characterized by metre-thick shear zones with highly deformed, foliated clay-rich sediments. Foliation is underlined by preferentially oriented phyllosilicates. Several generations of shear and extension calcite, quartz and chlorite-bearing veins attest to fluid-rock interactions during a multi-stage deformation. Microstructural observations and stable isotope analyses on calcite from veins and host sediments suggest that deformation was aseismic and dominated by diffusive mass transfer from pressure solution sites along cleavage and stylolites to the precipitation sites in veins, with mineralizing fluids in equilibrium with the host sediments. Our results suggest an essentially closed hydrologic system, and imply the absence of significant fluid flow along the studied fault zones. Microthermometric study on fluid inclusions present in calcite and quartz veins, and calcite-quartz oxygen isotopic fractionation determined for the first generation shear veins, allow a geothermal gradient of 34 C/km to be estimated. Analytical results demonstrate an evolution of the fault zones in three stages. The first stage was related to the emplacement of the Monte Perdido thrust unit during the middle Eocene at a temperature of w208 C and a burial depth of w5.7 km. The second stage corresponds to a fault reactivation at a temperature of w240 C and a burial depth of w6.5 km. The latter deformation may have been related to folding of the Monte Perdido thrust unit during the emplacement of the underlying Gavarnie thrust unit during the late Eoceneeearly Oligocene, with deeper burial resulting from aggradation of the thrust-sheet-top basin-fill. The last event corresponds to the formation of a dilatant vein system likely related to the exhumation of the massif.

We w ould like to thank Sheldon Natenberg for suggesting this topic and providing the rationale for the volume induc ed strate gies inv estigate d in this pa per. W e also tha nk Terranc e Skantz for valuable comm ents on an earlier ve rsion of this pape r. Errors remai n ours alone . A previ ous version of this paper was presented at the Financial Management Meetings 1998.

The mechanical properties of reinforced thermoplastics depend on such characteristics of the filler as granulometry, orientation and dispersion. These d@erent microtextural parameters were determined by using a single tool: image analysis, which was coupled with optical and electron microscopies. The dtflerent materials tested were based on polypropylene obtained by extrusion and injection steps. For the deferent samples analysed, the processing conditions and the filler concentration were constant, and variability was due to the dtflerent average lengths of the$ller incorporated in the matrix. The dtrerent filler parameters were determined with particular emphasis on the techniques of dispersion characterisation. The techniques developed in this study were based on image analysis. They enabled us to estimate filler-size distribution and development of the three-dimensional orientation inside the material and between direrent samples. The development of the filler dispersion was also made apparent. In addition, the relationships obtained between the direrent microtextural parameters were investigated. The general conclusion is that image analysis is very suitable for characterisation of this kind of material. 0 1998 Elsevier Science Ltd. All rights reserved

Crystalline Cd(OH) 2 /CdCO 3 nanowires, having lengths in the range from 0.3 up to several microns and 5-30 nm in diameter, were synthesized by a microwave-assisted wet chemical route and used as a precursor to obtain CdO nanostructures after a suitable thermal treatment in air. The morphology and microstructure of the as-synthesized and annealed materials have been investigated by scanning electron microscopy, transmission electron microscopy, x-ray diffraction and thermogravimetry-differential scanning calorimetry. The change in morphology and electrical properties with temperature has revealed a wire-to-rod transformation along with a decreases of electrical resistance.

Summary: Several actual developments in medical therapy are focussing on the potential of a surface-dependent selection and proliferation of special cell types. For an improvement of biocompatibility it is interesting to understand the interactions between cells and material ...