Transparent polycrystalline aluminium oxide

• US 20050248277A1
• Filed: 07/02/2003
• Published: 11/10/2005
• Est. Priority Date: 07/10/2002
• Status: Active Grant

• Current Assignee: Fraunhofer Gesellschaft Zur Foerderung Der Angewandten Forsching E.V.
• Original Assignee: Koninklijke Philips Electronics N.V. (Koninklijke Philips N.V.)
• Inventors: Kop, Theo Arnold, Van Bruggen, Michel Paul Barbara, Apetz, Rolf Theo Anton
• Granted Patent: US 7,396,792 B2
• Time in Patent Office: Days
• US Class Current: 313/636
• CPC Class Codes: C04B 35/115 Translucent or transparent products
• CPC Class Codes: C04B 35/6455 Hot isostatic pressing
• CPC Class Codes: H01J 61/302 characterised by the material of the vessel

Abstract

The present invention relates to highly dense translucent and transparent aluminium oxide components for applications, e.g. in the lighting industry, where a fine crystal size has to be obtained and stabilized for use at temperatures of 800° C. or more. Disclosed are high-strength polycrystalline alumina products which include 0.001-0.5 weight-% ZrO₂ stabilizing a fine crystal size <2 μm or, preferably, <1 μm if used at temperatures of 800° C. or more. The microstructure exhibits an extremely high relative density enabling a high real in-line transmission >30% measured over an angular aperture of at most 0.5° at a sample thickness of 0.8 mm and with a monochromatic wavelength of lightλ, preferably, of 645 run.

Claims

1. Polycrystalline alumina components with an additive of at least 0.001 wt-% ZrO₂ and optionally containing MgO in a concentration of at most 0.3 wt-% characterized in that the alumina contains at most 0.5 wt-% ZrO₂ as an additive and has an average crystal size ≦

2 μ

m, and a relative density higher than 99.95% with a real in-line transmission RIT≧

30% measured over an angular aperture of at most 0.5°

at a sample thickness of 0.8 mm and with a monochromatic wavelength of light λ

.

2. Polycrystalline alumina components according to claim 1, characterized in that the average crystal size is ≦

1 μ

m and the real in-line transmission RIT is at least 40%.

3. Polycrystalline alumina components according to claim 1, characterized in that the ZrO₂ additive is in a concentration from 0.1 wt-% to 0.3 wt-%, inclusive.

4. Discharge lamp characterized in that the lamp is provided with a discharge tube having a wall of a ceramic as claimed in claim 1.

5. Lamp according to claim 4 characterized in that the discharge tube has an ionisable filling containing a metal halide.

6. Method for forming a polycrystalline alumina component as claimed in claim 1 characterized in that the process includes the steps of

preparing a slurry of corundum power with a mean grain size ≦

0.2 μ

m,

adding a dopant, selected from zirconia and a zirconium containing precursor,

casting the slurry in a mould,

drying and sintering of the moulded body thus formed, and

performing a HIP treatment at a temperature of at least 1150°

C. for at least 2 hours.

7. Method according to claim 6, wherein the dopant is added as finely grained ZrO₂.

8. Method according to claim 6, wherein the finely grained ZrO₂ dopant has an average particle size of at most 100 nm.

9. Method according to claim 6, wherein after the addition of the zirconia dopant the prepared slurry is slip cast in a mould.

10. Method according to claim 6, wherein after the addition of the zirconia dopant the prepared slurry is gel cast in a mould.