Hydrotermální koroze nano a mikrostrukturní zirkoničité keramiky

Hydrothermal corrosion of nano- and microstructured tetragonal zirconia

conference paper

en

Due to their mechanical properties, materials based on yttria stabilized tetragonal zirconia (t-ZrO2) stand out among ceramic materials. However, they are known to be sensitive to their surrounding environment, whose action can lead to changes in these properties. It is in particular the aqueous medium, the water vapour medium or the medium of other liquids that cause (at relatively low starting temperatures from 65C) a degradation of material. The reason is the transformation of t-ZrO2 into the monoclinic phase (mZrO2). The phase transformation is affected both by material properties (grain size, stabilizer content, composition ) and surrounding conditions (enviroment type, temperature, time). Previous research showed that intensity of transformation has increased with increasing temeperature and time. The grain size is another parameter influencing the intensity of transformation. There exists so-called critical grain size (which is Y2O3 content dependent) under which no phase transformation is induced. The aim of the present work is the study of grain size effect on phase transformation of micro- and nanostructured tetragonal ZrO2 stabilized by 3 mol% of Y2O3 under hydrothermal conditions and the determination of the critical grain size of this material. There tZrO2 ceramics stabilized by 3 mol% of Y2O3 with different grain size (ca 60 nm 500 nm) was prepared. The ceramics was aged in high pressure reactor at 240C for 10 hours in distilled water. Aged samples were analysed by means of scanning electron microscopy to detect a thickness of transformated layer on sample crossection and by means of X-ray diffraction to detect a content of monoclinic phase on sample surface. It was found that the phase transformation under hydrothermal conditions has proceeded in t-ZrO2 ceramics stabilized by 3 mol% of Y2O3 with grain size greater than 300 nm. Above this critical size the extent of transformation, it means amount of monoclinic phase and the thickness of transformed layer, was not affected by grain size.

Materiály na bázi stabilizovaného tetragonálního Byla studována hydrotermální koroze (hydrothermal ageing) (240C/10h) tetragonálního ZrO2 (t-ZrO2) stabilizovaného 3 mol% Y2O3 v závislosti na velikosti zrna materiálu. Bylo zjištěno, že u materiálu s velikosti, zrna do 220 nm k fázové transformaci t-ZrO2 nedošlo. U materiálu s velikostí zrna větší než 370 nm k fázové transformaci došlo, a to tak, že se vytvořila povrchová vrstva transformovaného materiálu, jejíž tloušťka rostla s rostoucí velikostí zrna. Kritická velikost zrna t-ZrO2, stabilizovaného 3 mol% Y2O3, pod kterou nedochází za hydrotermální podmínek k fázové transformaci a změně mechanických vlastností, tedy ležela v rozmezí 220 a 370 nm.

Due to their mechanical properties, materials based on yttria stabilized tetragonal zirconia (t-ZrO2) stand out among ceramic materials. However, they are known to be sensitive to their surrounding environment, whose action can lead to changes in these properties. It is in particular the aqueous medium, the water vapour medium or the medium of other liquids that cause (at relatively low starting temperatures from 65C) a degradation of material. The reason is the transformation of t-ZrO2 into the monoclinic phase (mZrO2). The phase transformation is affected both by material properties (grain size, stabilizer content, composition ) and surrounding conditions (enviroment type, temperature, time). Previous research showed that intensity of transformation has increased with increasing temeperature and time. The grain size is another parameter influencing the intensity of transformation. There exists so-called critical grain size (which is Y2O3 content dependent) under which no phase transformation is induced. The aim of the present work is the study of grain size effect on phase transformation of micro- and nanostructured tetragonal ZrO2 stabilized by 3 mol% of Y2O3 under hydrothermal conditions and the determination of the critical grain size of this material. There tZrO2 ceramics stabilized by 3 mol% of Y2O3 with different grain size (ca 60 nm 500 nm) was prepared. The ceramics was aged in high pressure reactor at 240C for 10 hours in distilled water. Aged samples were analysed by means of scanning electron microscopy to detect a thickness of transformated layer on sample crossection and by means of X-ray diffraction to detect a content of monoclinic phase on sample surface. It was found that the phase transformation under hydrothermal conditions has proceeded in t-ZrO2 ceramics stabilized by 3 mol% of Y2O3 with grain size greater than 300 nm. Above this critical size the extent of transformation, it means amount of monoclinic phase and the thickness of transformed layer, was not affected by grain size.

zirconia, nanoceramics, phase transformation

2004

01.01.2004

VUT v Brně

Brno

80-214-2793-0

Proceedings of International Conference NANO 04

4