Pierre Cenedese

Structure and surface reactivity of novel nanoporous alumina fillers

Recent studies have shown that the particle size of fillers used for the reinforcement of dental resin composites should be multimodally distributed, in which micron-sized fillers are mixed with nanoparticles so as to achieve a higher filler level in the resin, and should be kept well dispersed so as to be functionalized by a silane. In this study, porous alumina monoliths with high specific surface area, measured by the Brunauer-Emmett-Teller (BET) method, were obtained using a novel preparation method. Structure and surface reactivity have been investigated as functions of temperature and chemical treatments. The impregnation of the as-prepared material by triméthyletoxysilane (TMES) stabilized alumina with high specific surface area at higher temperature. FTIR study has described the effect of TMES treatment and temperature on the structure of the material. The use of allyldimethoxysilane (ADMS), as a probe molecule for measuring the surface reactivity, has allowed us to show that the treatment of samples with TMES and their reheating at 1300 degrees C results in adsorption sites which give stronger chemical bonds. This preliminary study has, therefore, allowed us to optimize the structural and surface treatment of experimental fillers before their use in the reinforcement of resin composites or resin-modified glass ionomer cements.

Numerical limit of the spinodal point

The relation is studied between the phase boundary Cpb and the spinodal point Cs of the ferromagnetic Ising model, in the two dimensional triangular lattice, using a series of approximations in the CVM (cluster variation method) hierarchy. We keep the magnetization M fixed, and extrapolate the temperature difference Tpb(M, n) − Ts(M, n) for n = 1, 3, 5, 7 and 9 triangle approximations of the CVM. It is found that the limiting value of the difference is practically zero. Our analysis indicates: (i) The spinodal decomposition is to be treated as a system changing from the quenched initial state, and the “free energy” curve used in the spinodal analysis is not a fixed curve but is changing in time, and (ii) cases can occur in which a quenched system is initially decomposing in the nucleation mode, but switches to the spinodal decomposition mode in time.

Investigation of the fivefold icosahedral AlPdMn surface by photoemission and Auger electron spectroscopy

Surface composition and electronic structure of AlPdMn quasicrystalline alloy have been studied for temperature ranging from 300 K to 873 K. The quasicrystalline nature of the in-situ prepared surface was identified by the unusual behaviour of the core level photoemission peaks of Mn as already demonstrated by Thiel et al. Quantitative estimation of surface concentration by measuring the peak on background ratio in Auger electron spectroscopy (AES) do not allow to concluded to surface segregation of one element whatever the substrate temperature. Auger transitions implying valence band electrons in the Auger relaxation reveal interesting shapes and energies modifications that can be correlated with the typical electronic structure of this alloy. The appearance of strong satellite structure in the Auger and photoemission spectrum can be attributed to bulk plasmon of the quasicrystalline phase.

Efficient CVM Methods to Study Interphase Boundary Properties

The surface tension σ due to an interphase boundary (IPB) in the 2D square lattice and in the 3D cubic lattice is computed using the scalar product (SP) and the sum (S) CVM methods. It is shown that the resulting values of σ bracket the exact solution and extrapolation methods to the rigorous limit are outlined.