Aim of the study was the investigation of the influence of sintering temperatures and specimen volumes on the grain sizes of a presintered zirconia ceramic and the effect on material parameters.
Methods:
54 specimen bars of the tested ceramic, DCShrink (Bien Air, Switzerland) were cut in three different strengthes (1,5 mm; 2 mm and 2,5 mm). The resulting 18 bars of each strength were sintered at six different temperatures (1350°C, 1400°C, 1480°C, 1500°C, 1530°C and 1580°C), three bars a temperature.
Afterwards elastic modulus and fracture toughness were determined respectively calculated.
The specimens were prepared with thermal etching to examine the surfaces with scanning electron micrograph (SEM). The grains per area were calculated.
Results:
Reguarding the sintering temperature the smallest grains were measured at 1350°C (0,12 µm2), the biggest at 1580°C (0,24 µm2. The ascend of grain sizes was not linear.
It could be seen that a rising specimen volume led to a smaller grain size (1,5 mm : 0,19 µm2; 2 mm : 0,18 µm2; 2,5 mm : 0,16 µm2).
A comparison of the graphs for grain size with the graphs for elastic modulus and fracture toughness showed a correlation. An ascend of grain size led to a descend of the parameters and vice versa. These results revealed for specimen volume as well.
Conclusion:
The received results reflect the low heat conductivity of zirconia. As lower sintering temperatures and a higher volume come along with smaller grain sizes.
Through the results it also appears that material parameters of presintered zirconia ceramics mustn't be presumed as fix figures. It rather has to be assumed that sintering temperature and specimen volume have an influence on them.
This leaves room for further investigation on the topic, especially concentrating on a combination of fractographic and non- destructive testing to analyze grains and structure of a ceramic.