Francesca Teocoli

Preparation and Characterization of Nanocomposite Polymer Membranes Containing Functionalized SnO2 Additives

In the research of new nanocomposite proton-conducting membranes, SnO2 ceramic powders with surface functionalization have been synthesized and adopted as additives in Nafion-based polymer systems. Different synthetic routes have been explored to obtain suitable, nanometer-sized sulphated tin oxide particles. Structural and morphological characteristics, as well as surface and bulk properties of the obtained oxide powders, have been determined by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier Transform Infrared (FTIR) and Raman spectroscopies, N2 adsorption, and thermal gravimetric analysis (TGA). In addition, dynamic mechanical analysis (DMA), atomic force microscopy (AFM), thermal investigations, water uptake (WU) measurements, and ionic exchange capacity (IEC) tests have been used as characterization tools for the nanocomposite membranes. The nature of the tin oxide precursor, as well as the synthesis procedure, were found to play an important role in determining the morphology and the particle size distribution of the ceramic powder, this affecting the effective functionalization of the oxides. The incorporation of such particles, having sulphate groups on their surface, altered some peculiar properties of the resulting composite membrane, such as water content, thermo-mechanical, and morphological characteristics.

Fast mass interdiffusion in ceria/alumina composite

Gadolinium-doped ceria (CGO) presents unique processes at low oxygen partial pressure (pO2 800 °C) such as faster mass diffusion, which are not observed in conventional sintering under ambient air conditions. In CGO/Al2O3 composites the resulting effects driven by such mass diffusion are low viscosity flows and high reactivity between phases, indicated by the formation of CeAlO3. This reaction is promoted by the high content of oxygen defects and the chemical reduction of Ce4+ cations to Ce3+ in CGO/Al2O3 composites under low temperature and low pO2. In this work, a comparison is made between sintering CGO/Al2O3 under ambient air conditions and under low pO2, focusing on densification, viscosity and the evolution of the microstructure.

Accelerated ceria–zirconia solubilization by cationic diffusion inversion at low oxygen activity

Fast elemental diffusion at the Gd-doped ceria/Y-stabilized zirconia interface occurs under reducing conditions at low oxygen activity (pO2 < 10−12 atm) and high temperature (1400 °C). This effect leads to formation of thick ceria–zirconia solid solution reaction layers in the micro-range vs. thin layers of few tens of nanometers under oxidative conditions (i.e. in synthetic air at pO2 = 0.21 atm). The fast dissolution occurs by an inversion of the dominating limiting mechanism from the expected Zr4+ diffusion into the CGO lattice at high pO2 to an unexpected Ce3+ diffusion into the YSZ component under reducing conditions. The diffusion coefficient of 8-fold coordinated Ce3+ in YSZ at 1400 °C and pO2 = 10−13 atm is estimated to be around 10−11 cm2 s−1. This value is around 3 orders of magnitude higher than Zr4+ interdiffusion in CGO under oxidative conditions and about 8 orders of magnitude higher than Ce4+ self-diffusion in CGO in air at the same temperature.