Influence of the zirconia transformation on the thermal behavior of zircon–zirconia composites

N. RENDTORFF; G. SUAREZ; YOSHIO SAKKA; E. AGLIETTI

JOURNAL OF THERMAL ANALYSIS AND CALORIMETRY

SPRINGER

Año: 2011 p. 1 - 8

1388-6150

Abstract During a heating–cooling cycle, zirconia ZrO2) undergoes a martensitic transformation from monoclinic to tetragonal structure hases, which presents special hysteresis loop in the dilatometry curve at temperatures between 800 and 1100 C. Monoclinic zirconia (m-ZrO2) particles reinforced ceramic matrix composites not always present this behavior. In order to elucidate this fact a series of zircon–zirconia (ZrSiO4–ZrO2) ceramic composites have been obtained by slip casting and char- acterized. The final properties were also correlated with the zirconia content (0–30 vol.%). The influence of the mar- tensitic transformation (m–t) in well-dispersed zirconia grains ceramic composite on the thermal behavior was analyzed. Thermal behavior evaluation was carried out; the correlation between the thermal expansion coefficients, with the zirconia content showed a deviation from the mixing rule applied. A hysteresis loop was observed in the reversible dilatometric curve of composites with enough zirconia grains (C10 vol.%). Over this threshold the zir- conia content is correlated with the loop area. The trans formation temperatures were evaluated and correlated with the zirconia addition. When detected the m–t temperature transformation is slightly influenced by the zirconia content (due to the previously evaluated decrease in the material stiffness) and similar to the temperature reported in liter ature. The reverse (cooling) transformation temperature is strongly decreased by the ceramic matrix. The DTA results are consistent with the dilatometric analysis, but this technique showed more reliable results. Particularly the endothermic m–t transformation temperature showed to be easily detected even when the only m-ZrO2 present was the product of the slight thermal dissociation of the zircon during the processing of the pure zircon material.