Method for producing transparent alumina sintered body

Patent metadata

Field	Value
Publication number	US-10315957-B2
Application number	US-201715446416-A
Country	US
Kind code	B2
Filing date	Mar 1, 2017
Priority date	Nov 28, 2014
Publication date	Jun 11, 2019
Grant date	Jun 11, 2019

Abstract

A method for producing a transparent alumina sintered body includes (a) the step of preparing an alumina raw material powder containing a plate-like alumina powder having an aspect ratio of 3 or more so that the mass ratio R1 of F to Al in the alumina raw material powder is 5 ppm or more, and forming a compaction raw material containing the alumina raw material powder into a compact, and (b) the step of pressure-sintering the compact at a temperature at which F evaporate to yield a transparent alumina sintered body.

First claim

What is claimed is:

1. A method for producing a transparent alumina sintered body, the method comprising:
(a) the step of preparing an alumina raw material powder by mixing a plate-like alumina powder with a fine alumina powder having a smaller average particle diameter than the plate-like alumina powder so that the proportion of the plate-like alumina powder to the fine alumina powder is 0.1:99.9 to 15:85 on a mass basis, the plate-like alumina powder having an aspect ratio of 3 or more so that a mass ratio R1 of F to Al in the alumina raw material powder is 5 ppm or more, and forming a compaction raw material containing the alumina raw material powder into a compact; and
(b) the step of pressure-sintering the compact at 1700° C. or more to yield a transparent alumina sintered body,
wherein the mass ratio R1 is a ppm-by-mass value calculated using the following equation (1), and wherein in equation (1), X represents the mass ratio, in ppm-by-mass, of F to Al in the plate-like alumina powder, the F content in the plate-like alumina powder is obtained by pyrohydrolysis-ion chromatography, the Al content in the plate-like alumina powder is calculated by using a value obtained by multiplying by 0.529 the alumina purity of the plate-like alumina powder defined as 100−(total percentage by mass of impurity elements other than Al and O), and the percentage by mass of each impurity element is determined by performing high-frequency heating infrared absorption spectroscopy for S, inert gas fusion-thermal conductivity method for N, inert gas fusion-non-dispersive infrared absorption spectroscopy for H, pyrohydrolysis-ion chromatography for F, and inductively coupled plasma emission (ICP) spectroscopy for all other elements:
R 1= X ×(mass of plate-like alumina/mass of alumina raw material powder)  (1).

2. The method for producing a transparent alumina sintered body according to claim 1 , wherein a mixed raw material powder is prepared in the step of (a) by adding 100 ppm to 5000 ppm by mass of MgO to 100 parts by mass of the alumina raw material powder.

3. The method for producing a transparent alumina sintered body according to claim 1 , wherein the sintering in the step of (b) is performed so that each of the contents of impurity elements other than Mg and C becomes 10 ppm by mass or less.

4. The method for producing a transparent alumina sintered body according to claim 1 , wherein the step of (b) includes applying a pressure of 50 kgf/cm 2 or more during cooling of the compact from the pressure-sintering temperature to a predetermined temperature in the range of 1000° C. to 1400° C., and reducing the pressure to less than 50 kgf/cm 2 in the temperature range of the predetermined temperature or less.

5. A method for producing a transparent alumina sintered body, the method comprising:
(a) the step of preparing an alumina raw material powder by mixing a plate-like alumina powder with a fine alumina powder having a smaller average particle diameter than the plate-like alumina powder so that the proportion of the plate-like alumina powder to the fine alumina powder is 0.1:99.9 to 15:85 on a mass basis, the plate-like alumina powder having an aspect ratio of 3 or more so that a mass ratio R2 of F to Al in the alumina raw material powder is 15 ppm or more, and forming a compaction raw material containing the alumina raw material powder into a compact; and
(b) the step of pressure-sintering the compact at 1700° C. or more to yield a transparent alumina sintered body,
wherein the mass ratio R2 is a ppm-by-mass value calculated using the following equation (2), and wherein the proportion of the plate-like alumina powder to the fine alumina powder in the alumina raw material powder is T:(100−T), wherein T and (100−T) are on a mass % basis, and if an additive is externally added to the alumina raw material powder, the proportion of the additive to the alumina raw material powder is Z, in % by mass, wherein x1 represents the F content, in ppm-by-mass in the plate-like alumina powder, x2 represents the F content in ppm-by-mass, in the fine alumina powder, x3 represents the F content, in ppm-by-mass in the additive, and the F content is obtained by alkali fusion-ion chromatography, wherein y1 represents the Al content, in % by mass, in the plate-like alumina powder, y2 represents the Al content (% by mass) in the fine alumina powder, the Al content is defined as a value obtained by multiplying by 0.529 the alumina purity of the corresponding alumina powder defined as 100−(total percentage by mass of impurity elements other than Al and O), and the percentage by mass of each impurity element is determined by performing high-frequency heating infrared absorption spectroscopy for S, inert gas fusion-thermal conductivity method for N, inert gas fusion-non-dispersive infrared absorption spectroscopy for H, alkali fusion-ion chromatography for F, and ICP emission spectroscopy for all other elements, and wherein y3 represents the Al content, in % by mass, in the additive, determined by ICP emission spectroscopy:
R 2=100×[ x 1× T+x 2×(100− T )+ x 3× Z ]/[ y 1× T+y 2×(100− T )+ y 3× Z ]  (2).

6. The method for producing a transparent alumina sintered body according to claim 5 , wherein a mixed raw material powder is prepared in the step of (a) by adding 100 ppm to 5000 ppm by mass of MgO to 100 parts by mass of the alumina raw material powder.

7. The method for producing a transparent alumina sintered body according to claim 5 , wherein the sintering in the step of (b) is performed so that each of the contents of impurity elements other than Mg and C becomes 10 ppm by mass or less.

8. The method for producing a transparent alumina sintered body according to claim 5 , wherein the step of (b) includes applying a pressure of 50 kgf/cm 2 or more during cooling of the compact from the pressure-sintering temperature to a predetermined temperature in the range of 1000° C. to 1400° C., and reducing the pressure to less than 50 kgf/cm 2 in the temperature range of the predetermined temperature or less.

Assignees

• Ngk Insulators Ltd

Inventors

• Matsushima Kiyoshi
• Watanabe Morimichi
• Sato Kei
• Nanataki Tsutomu

Classifications

• C04B2235/602

  Making the green bodies or pre-forms by moulding · CPC title

• C04B35/115 Primary

  Translucent or transparent products · CPC title

• C04B2235/6586

  Processes characterised by the flow of gas · CPC title

• C01P2004/54

  Particles characterised by their aspect ratio, i.e. the ratio of sizes in the longest to the shortest dimension · CPC title

• C04B2235/3217

  Aluminum oxide or oxide forming salts thereof, e.g. bauxite, alpha-alumina · CPC title