Method for producing transparent alumina sintered body

Patent metadata

Field	Value
Publication number	US-2018244579-A1
Application number	US-201815903146-A
Country	US
Kind code	A1
Filing date	Feb 23, 2018
Priority date	Sep 30, 2015
Publication date	Aug 30, 2018
Grant date	—

Abstract

A method for producing a transparent alumina sintered body according to the present invention includes (a) a step of preparing an alumina raw material powder containing a plate-like alumina powder having an aspect ratio of 3 or more and a fine alumina powder having an average particle diameter smaller than that of the plate-like alumina powder so that, when a mixing ratio of the plate-like alumina powder to the fine alumina powder in terms of mass ratio is assumed to be T:(100−T), T is 0.001 or more and less than 1, and so that a mass ratio R1 of F relative to A1 in the alumina raw material powder is less than 15 ppm; (b) a step of forming a raw material for forming containing the alumina raw material powder into a compact; and (c) a step of sintering the compact so as to obtain 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) a step of preparing an alumina raw material powder containing a plate-like alumina powder having an aspect ratio of 3 or more and a fine alumina powder having an average particle diameter smaller than that of the plate-like alumina powder so that, when a mixing ratio of the plate-like alumina powder to the fine alumina powder in terms of mass ratio is assumed to be T:(100−T), T is 0.001 or more and less than 1, and so that a mass ratio R1 of F relative to A1 in the alumina raw material powder is less than 15 ppm; (b) a step of forming a raw material for forming containing the alumina raw material powder into a compact; and (c) a step of sintering the compact so as to obtain a transparent alumina sintered body, where the mass ratio R1 is a value calculated from formula (1) below:
R 1=100 ×[x 1 ×T+x 2×(100 −T )+ x 3 ×Z]/[y 1 ×T+y 2×(100 −T )+ y 3 ×Z}   (1)

where the unit is mass ppm; when an additive is externally added to the alumina raw material powder, a ratio of the additive relative to the alumina raw material powder is Z (mass %); x1 is an F content (mass ppm) in the plate-like alumina powder, x2 is an F content (mass ppm) in the fine alumina powder, and x3 is an F content (mass ppm) in the additive; the F contents are determined by alkali fusion-ion chromatography; y1 is an A1 content (mass %) in the plate-like alumina powder, and y2 is an A1 content (mass %) in the fine alumina powder; the A1 contents are values (mass %) each obtained by determining an alumina purity of each alumina powder as 100—(sum in terms of mass % of impurity elements other than A1 and 0), and multiplying the obtained result by 0.529; the mass % of the impurity elements is determined as follows: that is, firing (high-frequency heating)-infrared absorption spectroscopy is used to determine an S content, an inert gas fusion-thermal conductivity method is used to determine an N content, inert gas fusion-nondispersive infrared absorption spectroscopy is used to determine an H content, alkali fusion-ion chromatography is used to determine an F content, and inductively coupled plasma (ICP) emission spectroscopy is used to determine contents of other elements; and y3 is an A1 content (mass %) in the additive and is determined by inductively coupled plasma (ICP) emission spectrometry.

2 . The method for producing a transparent alumina sintered body according to claim 1 ,
wherein, in step (b), a mixture prepared by adding 0.005 to 0.5 parts by mass of MgO to 100 parts by mass of the alumina raw material powder is used as the raw material for forming.

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

4 . The method for producing a transparent alumina sintered body according to claim 1 ,
wherein, in step (c), the compact is sintered at 1850° C. or higher.

5 . The method for producing a transparent alumina sintered body according to claim 1 ,
wherein, in step (c), the compact is subjected to pressure-sintering.

6 . The method for producing a transparent alumina sintered body according to claim 5 ,
wherein, in step (c), when the temperature is being decreased from a highest attained temperature during sintering, a pressure of 50 kgf/cm 2 or more is continuously applied until a particular temperature set within a range of 1000 to 1400° C. is reached, and depressurizing is performed to less than 50 kgf/cm 2 in a temperature range equal to or lower than the particular temperature.

Assignees

• Ngk Insulators Ltd

Inventors

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

Classifications

• C04B2237/343

  Alumina or aluminates · CPC title

• C04B2235/3217

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

• C04B2235/3206

  Magnesium oxides or oxide-forming salts thereof · CPC title

• C04B2235/9623

  Ceramic setters properties · CPC title

• C04B2235/727

  Phosphorus or phosphorus compound content · CPC title