Transparent zirconia sintered body

Abstract

A primary sintered body having a density of 95% or more obtained by sintering a zirconia powder comprising an yttria main component as a stabilizer under ordinary pressure is set in a vessel of a semi-sealed state and subjected to HIP treatment (secondary sintering) at a temperature of from 1,600 to 1,900° C. under a pressure of 50 MPa or higher, and according to need, heated treated in an oxidizing atmosphere, thereby producing a polycrystalline sintered body of zirconia having high transparency of an in-line transmission of 50% or higher.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph showing in-line transmission to a visible light of 1) a polycrystalline sintered body of the present invention (Table 1, Sample No. 2) and 2) a commercially available YSZ single crystal (sample thickness 1 mm).

FIG. 2 is a graph showing in-line transmission to a infrared light of a sintered body of the present invention (Table 1, Sample No. 2, thickness 1 mm).

FIG. 3 is an SEM image of a tissue of a polycrystalline sintered body of the present invention (Table 1, Sample No. 2).

FIGS. 4A to 4C each is a cross-sectional view showing a setting method of a primary sintered body in a HIP apparatus. FIG. 4A is a cross-sectional view showing the case where the primary sintered body is placed in an alumina vessel with a lid (present invention), FIG. 4B is a cross-sectional view showing the case where the primary sintered body is embedded in a zirconia powder, and placed in an alumina vessel with a lid (present invention), and FIG. 4C is a cross-sectional view showing the case where the primary sintered body is placed in an alumina vessel without a lid (Comparative Example).

Claims

1. A transparent polycrystalline sintered body comprising zirconia containing from 6 to 15 mol % of yttria as a stabilizer.

2. The transparent polycrystalline sintered body as claimed in claim 1, further comprising at least one of the following stabilizers in the total amount of 2 mol % or less. Stabilizer: each oxide of alkaline earth metal, lanthanum rare earth metal, scandium, titanium, niobium, tantalum, indium and germanium.

3. The transparent polycrystalline sintered body as claimed in claim 1, wherein in-line transmission to visible light having a wavelength of 550 nm is 50% or more in a sample having a thickness of 1 mm.

4. The transparent polycrystalline sintered body as claimed in claim 1, wherein a crystal phase is a cubic fluorite structure.

5. A method of producing a transparent polycrystalline sintered body comprising zirconia containing from 6 to 15 mol % of yttria as a stabilizer, which is characterized by high temperature and high pressure treating a primary sintered body obtained by molding a zirconia powder containing a stabilizer and pressureless sintering until a relative density of 95% or more, by hot isostatic press (HIP).

6. The production method as claimed in claim 5, characterized in that the pressureless sintering is conducted at a temperature of from 1,300 to 1,500° C. in an air atmosphere.

7. The production method as claimed in claim 5, characterized in that the high temperature and high pressure treatment by hot isostatic press (HIP) is conducted at a temperature of from 1,600 to 1,900° C. under a pressure of 50 MPa or more.

8. The production method as claimed in claim 5, characterized in that the HIP treatment of the primary sintered body having a relative density of 95% or more is conducted by providing a vessel of a semi-sealed state in a HIP treatment apparatus, and providing the primary sintered body in the vessel.

9. The production method as claimed in claim 5, characterized in that the HIP treatment of the primary sintered body having a relative density of 95% or more is conducted by providing a vessel of a semi-sealed state formed by placing a ceramic flat plate on an opening of a ceramic vessel having the opening in a HIP treatment apparatus, and providing the primary sintered body in the vessel.

10. The production method as claimed in claim 5, characterized in that the HIP treatment of the primary sintered body having a relative density of 95% or more is conducted by providing a vessel of a semi-sealed state formed by placing a ceramic flat plate on an opening of a ceramic vessel having the opening in a HIP treatment apparatus and providing the primary sintered body in the vessel, and further embedding the primary sintered body in the vessel in a ceramic powder.

11. The production method as claimed in claim 5, characterized in that the HIP treatment of the primary sintered body having a relative density of 95% or more is conducted by providing a vessel of a semi-sealed state formed by placing a ceramic flat plate on an opening of a ceramic vessel having the opening in a HIP treatment apparatus and providing the primary sintered body in the vessel, and optionally further embedding the primary sintered body in the vessel in a ceramic powder, and wherein a surface carbon concentration of the sintered body after the HIP treatment is less than 1%.

12. The production method as claimed in claim 5, characterized in that the HIP treatment of the primary sintered body having a relative density of 95% or more is conducted by providing a vessel of a semi-sealed state formed by placing a ceramic flat plate on an opening of a ceramic vessel having the opening in a HIP treatment apparatus and providing the primary sintered body in the vessel, optionally further embedding the primary sintered body in the vessel in a ceramic powder, and characterized by comprising after the high temperature and high pressure treatment, further heat-treating at 1,000 to 1,200° C. in an oxidizing atmosphere.

13. The production method as claimed in claim 5, characterized in that the zirconia powder containing a stabilizer has a purity of 99% or more, a specific surface area of from 5 to 20 m2/g and a crystallite diameter of from 10 to 70 nm.

14. An orthodontic bracket comprising using the transparent polycrystalline sintered body as claimed in claim 1.

15. An orthodontic bracket comprising using the transparent polycrystalline sintered body as claimed in claim 2.

16. An orthodontic bracket comprising using the transparent polycrystalline sintered body as claimed in claim 3.

17. An orthodontic bracket comprising using the transparent polycrystalline sintered body as claimed in claim 4.