Yttria-doped Zirconia Powders Research Articles

Textural characterization of zirconia and yttria-doped zirconia powders

Abstract Pure zirconia and yttria-doped zirconia powders were obtained by precipitation from zirconium and yttrium salt solutions and then treated at 723 K in air. The evolution of the texture and structure has been studied as a function of the treatment time of the powders. After 2 h of treatment, doped samples correspond to the cubic form and pure zirconia to the tetragonal form. With increase in the time of treatment, the transformation to phases with lower symmetry (cubic→tetragonal→monoclinic) occurs but it is delayed as the yttria content in the sample is increased. However, a degradation of the porous texture promoted by thermal treatment is observed in both pure and doped samples, and the textural stability is not improved by addition of yttria. The elimination of volatile species from the starting gels must be responsible for the differences observed in the textural evolution.

Preparation of weakly agglomerate nanometer ZrO2(3 mol% Y2O3) ceramic powder

Yttria-doped zirconia powders (3 mol%) with an extremely small crystallite size (10–15 nm) and a narrow size distribution had been prepared by gel precipitation. Hydrothermal technique was used to suppress agglomerate formation, which occurs during the synthesis and processing of wet-chemical prepared powder. Precipitates aging under hydrothermal condition resulted in weaker agglomerates which were fractured during isostatic compaction. The homogeneous pore structure of compact provided a better indicator for densification during sintering. Agglomerate-free powders were sintered to 98·5% of theoretical density in constant heating rate sintering to 1220°C which was 300°C lower than necessary for a normal route prepared powders. Zirkoniumdioxidpulver mit 3 mol% Yttriumdioxid-Dotierung und einer extrem geringen Kristallitgröße (10–15 nm) mit einer engen Größenverteilung wurden mittels Ausscheidung aus einem Gel hergestellt. Eine hydrothermische Methode wurde angewendet, um die Agglomeratbildung, die bei der Synthese und der Verarbeitung naßchemisch hergesteller Pulver auftritt, zu unterdrücken. Bei hydrothermischen Bedingungen führt das Wachsen der Ausscheidungen zu schwächeren Agglomeraten, die bei isostatischer Verdichtung des Pulvers zerfallen. Die homogene Porenstruktur kompaktierter Teile zeigt ein besseres Verdichtungsverhalten beim Sintern. Agglomeratfreie Pulver wurden bis zu 98·5% theoretischer Dichte durch CHR Sintern bis zu 1220°C, also 300°C niedriger als bei der konventionellen Pulverherstellung, gesintert. Des poudres de zircone dopées avec 3% en mole d'yttrium de taille très fine (10–15 mm) et de distribution granulométrique étroite, ont été préparées par précipitation de gel. Une technique hydrothermale a été utilisée pour éviter la formation d'agglomérats qui apparaissent pendant la synthèse et le traitement par voie humide. Les précipités qui se forment dans les conditions du traitement hydrothermal sont en fait des agglomérats faiblement liés qui sont facilement fracturés lors du pressage isostatique. L'homogénéité de la structure des pores dans des échantillons compactés nous indique une bonne aptitude au frittage. Les poudres sans agglomérat ont été frittées à 98·5% de la densité théorique par frittage CHR à 1220°C, c'est-à-dire 300°C en dessous de la température nécessaire pour les voies mêmes poudres préparées par la voie chimique.

Powder preparation and compaction behaviour of fine-grained Y-TZP

Two wet chemical preparation methods are described for yttria-doped tetragonal zirconia powders. Both methods yield powders with an extremely small crystallite size (8 nm) and a narrow size distribution. The agglomerate and aggregate structure of these powders have been investigated by several techniques. Gel precipitation from an alkoxide solution in water (ldquoalkoxiderdquo synthesis) results in a ceramic powder with irregular-shaped weak and porous agglomerates, which are built up from dense aggregates with a size of 18 nm. Gel precipitates formed from a metal-chloride solution in ammonia (ldquochloriderdquo synthesis) do not contain aggregates. Both types of agglomerate are fractured during isostatic compaction. Hydrolysis and washing under (strong) basic conditions probably decrease the degree of aggregation. The aggregate morphology and structure are key parameters in the microstructure development during sintering of a ceramic. Several characteristics of these powders are compared with those of a commerical one (Toyo Soda TZ3Y).

Microstructure characteristics of ultra-fine ZrO 2Y 2O 3 ceramic powders

Yttria-doped zirconia powders with an extremely small crystallite size (8 nm) and a narrow size distribution have been prepared by gel precipitation methods. Precipitation of an alkoxide solution in water (“alkoxide” synthesis) results in weaker agglomerates when compared with a precipitation of a metal chloride solution in ammonia (“chloride” synthesis). Both types of agglomerate are fractured during isostatic compaction. The “alkoxide” agglomerates consist of strong small aggregates (15–20 nm) while within the “chloride” agglomerates no, or only a few, aggregates are present.