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

Abstract

During a heating-cooling cycle, zirconia (ZrO 2 ) undergoes a martensitic transformation from monoclinic to tetragonal structure phases, which presents special hysteresis loop in the dilatometry curve at temperatures between 800 and 1100 °C. Monoclinic zirconia (m-ZrO 2 ) particles reinforced ceramic matrix composites not always present this behavior. In order to elucidate this fact a series of zircon-zirconia (ZrSiO 4 -ZrO 2 ) ceramic composites have been obtained by slip casting and characterized. The final properties were also correlated with the zirconia content (0-30 vol.%). The influence of the martensitic 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 zirconia content is correlated with the loop area. The transformation 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 literature. 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-ZrO 2 present was the product of the slight thermal dissociation of the zircon during the processing of the pure zircon material.

Colloidal processing, sintering and mechanical properties of zircon (ZrSiO4)

“…This dissociation is known to be responsible for fracture toughness reinforcement by transformation toughening mechanism and micro cracks formation among other mechanisms [16,17]. Fig.…”

“…10 is well documented in literature. Zircon dissociated in silica and Zirconia producing the transformation toughening mechanism in Zirconia grains [16,17]. Fig.…”

Ultra-dense (Bi, V, B)-oxide-added zircon ceramics fabricated by liquid-phase assisted spark plasma sintering (SPS)

“…240 − 288 GPa. Previous investigators have reported the Young's modulus (E) of zircon ceramics as 210 [38], 275 [39] and 288 GPa [26]. The zircon ceramics in this work are multiphase, i.e., crystalline oxides of zircon and monoclinic zirconia as well as non-crystalline phases of amorphous silica and additive glass.…”

Ductilization of Nanoporous Ceramics by Crystallinity Control

“…As the samples are annealed to a temperature of 500 °C, tetragonal ZrO 2 peaks begin to appear in both air and vacuum environments. Zirconia has a unique feature of the temperature-dependent reversibility of crystal phases thus the tetragonal ZrO 2 formed after annealing converts back to monoclinic ZrO 2 upon cooling the samples down to room temperature (Figure a). In the air, this phenomenon of phase transitions typically results in severe cracking because of 4–5% volume difference between two phases (Figure c).…”