Improvement of Grain-Boundary Conductivity of 8 mol % Yttria-Stabilized Zirconia by Precursor Scavenging of Siliceous Phase

Abstract

A new method of scavenging highly resistive siliceous phase using two-stage sintering, named as "precursor scavenging," is suggested for improving the grain-boundary conductivity of 8 mol % yttria-stabilized zirconia (YSZ). The scavenging efficiency and mechanism were studied and compared with those of 8YSZ-Al 2 O 3 composites prepared by various methods using impedance spectroscopy and imaging secondary-ion mass spectroscopy. A heat-treatment at 1200ЊC for longer than 20 h before sintering increased grain-boundary conductivity remarkably. The forming of inclusions containing Si was considered to be the origin of scavenging. The grain-interior resistivity was not changed by precursor scavenging, while it increased more than 15% by adding 1 mol % Al 2 O 3 when sintered at 1600ЊC. Precursor scavenging, therefore, is a potential and promising way for improving the grain boundary conductivity without deteriorating the grain-interior one.

Oxygen Ion‐Conducting Materials

“…Figure 9.4a displays typical values of the total conductivity (predominantly ionic) for selected ZrO 2 -based phases and one YSZAl 2 O 3 composite. Small additions of highly dispersed alumina make it possible to improve the mechanical strength and to reduce the grain-boundary resistance due to the scavenging of silica-rich phases [45][46][47]; this approach has been used successfully to prepare a variety of solid electrolyte ceramics (e.g., [48][49][50]). …”

Oxygen transport in ferrite-based ceramic membranes: Effects of alumina sintering aid

“…The microstructural modification via incorporation of small amounts of highly dispersed Al 2 O 3 is a well-established approach in the engineering of oxygen ion-conducting solid electrolyte materials. [15][16][17][18][19] While significant volume fractions of insulating aluminum oxide lead to decreasing ionic conductivity, moderate additions have no significant blocking effect, but decrease grainboundary resistance due to "scavenging" of silica-rich impurity phases. Alumina additions to solid oxide electrolyte ceramics make it possible also to improve the mechanical strength, to suppress grain growth in the course of sintering and, often, to increase sinterability.…”

“…Alumina additions to solid oxide electrolyte ceramics make it possible also to improve the mechanical strength, to suppress grain growth in the course of sintering and, often, to increase sinterability. [15][16][17][18][19] All these effects may be of great interest for the developments of mixed-conducting membrane materials, taking into account the stability and low costs of alumina.…”

Comparison between barium and strontium-glass composites for sealing SOFCs

“…5 The borate glasses contain 40% B 2 O 3 , 10% Al 2 O 3 , 20% MgO, 20% CaO and 10% BaO-SrO for the Ba and Sr-compositions, respectively. The glasses were synthesized by calcining and melting their respective carbonates and oxides in a platinum crucible at 1500 • C for 2 h, then casting and annealing at 615 • C for 4 h. The cast ingots were ground in a vibratory mill to obtain a particle size distribution of −270 mesh.…”