Anthony Manerbino

Effects of the fabrication process on the grain-boundary resistance in BaZr0.9Y0.1O3−δ

This paper reports on the effect of the fabrication process on the conductivity of BZY10 (BaZr0.9Y0.1O3−δ). The dense specimens were prepared by four methods: (1) solid-state reactive sintering (SSRS), (2) conventional sintering using powder prepared by solid-state reaction and NiO as sintering aid, (3) conventional sintering using powder prepared by solid-state reaction followed by high-temperature annealing (HT), and (4) spark plasma sintering (SPS). The four specimens crystallize in a cubic structure, without any observable secondary phases. The AC conductivities of these four specimens were measured by impedance spectroscopy in moist reducing atmosphere from 600 to 200 °C; the grain boundary and bulk contributions were distinguished by the analysis of the low-temperature spectra. The grain-boundaries of the sample prepared by solid-state reactive sintering exhibited a resistance typical of the bulk material, while the three other specimens had more resistive grain boundaries. Similar activation energies for proton transport were obtained for the bulk resistance of the four specimens (0.39–0.42 eV). The activation energy for the grain boundaries increased from 0.45 eV for the solid-state reactive sintered BZY10 to 0.84 eV for the conventional solid-state reaction using NiO as sintering aid. This study highlights the potential of the solid-state reactive sintering process as a time and cost-effective method for producing dense ceramic with lower resistance BZY10 grain boundaries.

Preparation of calcium aluminate matrix composites by combustion synthesis

CaO–Al2O3–TiB2 composites have been produced by the Combustion Synthesis technique. These materials have matrices based on binary calcium-aluminate compounds, i.e., Ca3Al2O6 (C3A), Ca12Al14O33 (C12A7), CaAl2O4 (CA), CaAl4O7 (CA2) and CaAl12O19 (CA6). Except for samples with the matrix composition of C3A, the combustion synthesis reactions can be characterized as stable self-propagating waves with combustion temperatures ranging from 2125 K to 2717 K and combustion wave velocity from 4.0 mm/s to 10.6 mm/s. For samples with a matrix composition of C12A7, CA, and CA2, predominantly equilibrium compound phase was formed, while for samples with a matrix composition of C3A, non-equilibrium phases were also present. There was no evidence of CA6 formation for samples with a matrix composition corresponding to CA6.

Preparation of dense mixed electron- and proton-conducting ceramic composite materials using solid-state reactive sintering: BaCe0.8Y0.1M0.1O3−δ–Ce0.8Y0.1M0.1O2−δ (M=Y, Yb, Er, Eu)

Mixed electronic and protonic conductor materials were prepared using BaCe0.8Y0.1M0.1O3−δ (BCYM) as the protonic conductive phase and Ce0.8Y0.1M0.1O2−δ (MYDC) as the electronic conductive phase (in reducing atmosphere), with M=Y, Yb, Er, Eu. Dense specimens of these ceramic/ceramic composite materials (cercers) were prepared by solid-state reactive sintering: all the precursors for BCYM and MYDC were mixed, pelletized, and fired without any pre-calcination step of the individual ceramic phases. The X-ray diffraction patterns revealed the presence of the two desired phases. The study of the lattice parameters showed that the Y and M co-dopants were fairly well distributed between the perovskite phase BCYM and the fluorite phase MYDC. This interesting discovery is of importance for the preparation of two-phase ceramic materials. In addition to the structural study, the samples were analyzed by scanning electron microscopy and were found to be free of any undesirable phases. The two ceramic phases could easily be distinguished using the back-scattered electron mode, with grains between 10 and 30 microns. Energy dispersive X-ray spectroscopy confirmed the distribution of the co-dopant between the two phases.

Fabrication of Yttrium-Doped Barium Zirconate for High Performance Protonic Ceramic Membranes

Barium zirconate has emerged as the leading candidate material for fabricating dense ce‐ ramic membranes for hydrogen separation. B-sites in the ABO3 perovskite are acceptordoped with a +3 cation – most commonly yttrium – charge-compensated by the formation of oxygen ion vacancies in the lattice. A minor fraction of B-sites can be filled with cerium to give BaZr0.9-xCexY0.1O3-d, x ≤ 0.2. Upon hydration at elevated temperatures, weaklybound protons are formed in the lattice. This produces a cubic perovskite ceramic proton conductor useful in diverse applications, such as protonic ceramic fuel cells, electrolysers, and catalytic membrane reactors operating at temperatures between 600 and 800 °C. A necessary requirement for fabricating thin ceramic membranes for proton diffusion is to maximize grain size while eliminating percolating porosity. However, high-density, large-grained barium zirconate is a very difficult material to prepare by traditional pow‐ der sintering methods. This chapter describes a new methodology for making protonic ceramic membranes with large grains and virtually no residual porosity. This discovery has the potential to have a profound impact on energy conversion efficiency of the vari‐ ous membrane devices envisioned for the coming hydrogen energy economy.

Evolution of Copper Electrodes Fabricated by Electroless Plating on BaZr0.7Ce0.2Y0.1O3-δ Proton-Conducting Ceramic Membrane: From Deposition to Testing in Methane

We investigated copper electrodes deposited onto a BaZr0.7Ce0.2Y0.1O3-δ (BZCY72) proton-conducting membrane via a novel electroless plating method, which resulted in significantly improved performance when compared to a traditional painted copper electrode. The increased performance was examined with a multiscale multitechnique characterization method including time-of-flight secondary-ion mass spectroscopy (TOF-SIMS), transmission electron microscopy (TEM), scanning spreading-resistance microscopy (SSRM), and atom-probe tomography (APT). Through this method, we observed that a palladium catalyst layer alloys with the copper electrode. We also explored the nature of a non-coking-induced carbon-rich phase that may be involved with the improved performance of the electrode.