Paola Pinasco

Tribological behaviour of Al2O3/ZrO2-ZrO2 laminated composites

Abstract Laminated composites were prepared in the system Al 2 O 3 -ZrO 2 . Starting from sheets produced by tape casting a symmetric structure was obtained by superimposing alternated layers of Al 2 O 3 /ZrO 2 composite and ZrO 2 . Due to the different thermal expansion coefficients and shrinkage of the two materials the alumina/zirconia external layers of the samples exhibit a compressive residual stress which leads to an improved apparent surface toughness. The value of this stress was determined by indentation technique. The tribological behaviour of the laminated composites and of a stress free material, with the same composition of the external layers, was assessed by Pin-on-Disc method at different loads and sliding speeds. The effect of differences in properties and microstructural features among the different materials on wear and friction were determined and discussed. Possible wear mechanisms are proposed. In spite of the increased surface toughness in the range of the experimental conditions considered, the presence of compressive residual stresses at the surface does not lead to an improvement of wear resistance in the laminated structure.

PZT-based suspensions for tape casting

Abstract A PZT powder of composition Pb 0.988 (Zr 0.52 Ti 0.48 ) 0.976 Nb 0.024 O 3 was prepared by conventional mechanical mixing of the raw materials in water, freeze-drying and calcination. Sedimentation tests of four deflocculants in an azeotropic mixture of methyl ethyl ketone/ethanol were carried out to check the dispersing effect. Attention was focused on a phosphate ester based deflocculant. Electrical conductivity and electrophoretic mobility were investigated. Slurries for tape casting were prepared with commercial binder and plasticizer and different volumes of solid. The rheological behaviour was recorded as yield stress values and flow curves. The slurries were tape-cast and technological results compared with previous characterization results.

Stainless steel porous substrates produced by tape casting

In this work the technological issues related to the production of tape cast large-area porous stainless steel supports for Solid Oxide Fuel Cells (SOFC) applications were carefully investigated. The slurry formulation was optimized in terms of amount and nature of the organic components needed: rice starch and polymethyl metacrylate were found to be, respectively, the most suitable pore former and binder because easily eliminated during the thermal treatment in reducing atmosphere. The compatibility of the binder system chosen with the most widely used solvents for screen printing inks was also evaluated. Finally the influence of the sintering temperature and of the refractory supports to be used during the thermal treatments onto the production of porous stainless steel supports was discussed. The whole process optimization allows to produce flat, crack-free metallic substrate 900-1000 μm thick, dimensions up to 5×5 cm and with a tailored porosity of 40% suitable for SOFCs application.

High Temperature Deformation of Laminated Ceramic Composites Obtained from the Al2O3-ZrO2 System

Symmetric structures of laminated ceramic composites were produced by super imposing alternating layers of Al2O3 and Al2O3/ZrO2 (60/40 vol%) composite prepared by tape casting. The laminated structure was designed in order to have alumina layers at the surface. The high temperature plastic deformation of the layered composites was examined in uniaxial compression testing. Compressive tests at constant strain rate and constant load were carried out in air at temperature between 1350 °C and 1500°C with the stress axis parallel to the layer interfaces. The stress exponent n and the activation energy Q were obtained. Damage was observed during creep, however more than 50% of deformation can be achieved in this configuration without macroscopic failure of these layered composites.