In my bachelor thesis, I have researched the zirconia solid solution (ZrO₂)0.92(Y₂O₃)0.08
with additions of yttria or (YSZ) which is a key component of solid oxide cells (SOC).
SOC have recently emerged as an effective interface between renewable energy
sources and consumers for stabilizing electrical power grid. During periods of energy
surplus, they produce hydrogen, and during energy shortages, they convert it back
into electrical energy. SOC consist of a fuel electrode, an oxygen electrode, and a
solid oxide electrolyte. Since SOC operate at high temperatures, typically between
700 °C and 1000 °C, controlled manufacturing and a deep understanding of materials
are of key importance.
YSZ ceramic electrolyte was prepared and studied in detail. The literature review
describes the structural properties of the electrolyte, manufacturing technologies, and
the measurement of electrical properties.
The experimental procedure involved preparing a ceramic suspension containing YSZ
powder, solvents, binders, and plastifiers. Ceramic tapes were produced using the
tape casting technique and then joined into a multilayer structure through lamination.
Disc-shaped samples were cut from this structure using a laser cutter. The sintering
range of the YSZ ceramics was determined with a heating microscope. The samples
were sintered in a chamber furnace at temperatures from 1300 °C to 1500 °C for 3
hours. The microstructure of the sintered samples was analysed by scanning electron
microscopy. The electrical properties were evaluated using electrochemical
impedance spectroscopy, which enabled the separation of grain, grain boundary, and
electrode contributions to the total resistance of the material via Nyquist plots.
The results showed that increasing the sintering temperature increases the grain size,
while simultaneously leading to a lower relative density. Ion conductivity was found to
increase with larger grain size. However, at temperatures of 1450 °C and above, the
porosity of the material becomes so significant that the pores begin to affect and
slightly reduce the ionic conductivity, offsetting the effect of increased grain size.
The properties of YSZ ceramics depend on the several processing parameters, which
include the preparation of a stable suspension, casting conditions, precise component
shaping, and the selection of appropriate sintering conditions. By controlling these
parameters, we can produce ceramics with a dense and uniform microstructure, which
is crucial for tailoring the properties of YSZ, especially for use in SOC.
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