Effect of sandblasting and heat treatment on degradation of zirconia

Keywords: zirconia, sandblasting, biaxial flexure strength, low temperature degradation

Introduction:

In the present study, effect of sandblasting on the low temperature degradation (LTD) was evaluated through the measurement of biaxial flexure strength change of Y-TZP and Ce-TZP/Al₂O₃ nanocomposite.

Method:

Y-TZP powders (TZ-3YB-E, Tosoh, Tokyo, Japan) and the nanocomposite powders (NANOZR MACZ-100, Matsushita Electric Works, Osaka, Japan) were pressed to a cylindrical rod using CIP , and fired at 1450˚C for 2 hr and at 1350˚C for 6 hr, respectively. Two thirds specimens were sandblasted with 70µm alumina powder for 10 sec at air-pressure of 0.4MPa. Furthermore, half of them were heated at 1000˚C for 5 min. Biaxial flexure strength of these three kinds specimen of each zirconia were determined using piston-on-three ball in accordance to ISO-6872 before and after storage in physiological saline solution at 80˚C for 30 days, 4% acetic acid at 80˚C for 30 days, and autoclave at 121˚C for 10 days. The measurements were repeated 15 times for each condition. The content of monoclinic zirconia was derived from the peak intensity ratio of monoclinic to tetragonal zirconia in X-ray diffraction patterns after Toraya's equation.

Results:

The average biaxial flexure strength of the Ce-TZP/Al₂O₃ nanocomposite (180 disks) was 1273 MPa (s.d. 137 MPa) which is 28% higher than that of the Y-TZP, 991 MPa (s.d. 148 MPa) (p<0.01). Storage in saline and acetic acid solution and autoclaving after sandblasting in both zirconia increased the monoclinic zirconia content. In particular with Y-TZP, the autoclaving dramatically increased the monoclinic zirconia content and decreased the biaxial flexure strength. These results indicated that the residual stress induced by sandblasting possibly accelerated LTD and Ce-TZP/Al₂O₃nanocomposite had a better reliability against it.

Conclusion:

It is concluded that the Ce-TZP/Al₂O₃ nanocomposite has a superior resistance against the low temperature degradation than Y-TZP.