Method for producing transparent alumina sintered body

• US 10,717,677 B2
• Filed: 02/23/2018
• Issued: 07/21/2020
• Est. Priority Date: 09/30/2015
• Status: Active Grant

• Current Assignee: NGK Insulators Limited
• Original Assignee: NGK Insulators Limited
• Inventors: Watanabe, Morimichi, Matsushima, Kiyoshi, Sato, Kei, Nanataki, Tsutomu
• Primary Examiner(s): Snelting, Erin
• Application Number:
  US15/903,146
• Publication Number:
  US 20180244579A1
• Time in Patent Office: 879 Days
• CPC Class Codes: B32B 18/00 Layered products essentially comprising ceramics, e.g. refractory products
• CPC Class Codes: C04B 2235/3206 Magnesium oxides or oxide-forming salts thereof
• CPC Class Codes: C04B 2235/3217 Aluminum oxide or oxide forming salts thereof, e.g. bauxite, alpha-alumina
• CPC Class Codes: C04B 2235/322 Transition aluminas, e.g. delta or gamma aluminas
• CPC Class Codes: C04B 2235/40 Metallic constituents or additives not added as binding phase
• CPC Class Codes: C04B 2235/445 Fluoride containing anions, e.g. fluosilicate
• CPC Class Codes: C04B 2235/5292 Flakes, platelets or plates
• CPC Class Codes: C04B 2235/5296 with a defined aspect ratio, e.g. indicating sphericity
• CPC Class Codes: C04B 2235/5436 micrometer sized, i.e. from 1 to 100 micron
• CPC Class Codes: C04B 2235/5445 submicron sized, i.e. from 0,1 to 1 micron
• CPC Class Codes: C04B 2235/5472 Bimodal, multi-modal or multi-fraction
• CPC Class Codes: C04B 2235/6025 Tape casting, e.g. with a doctor blade
• CPC Class Codes: C04B 2235/604 Pressing at temperatures other than sintering temperatures
• CPC Class Codes: C04B 2235/656 characterised by specific heating conditions during heat treatment
• CPC Class Codes: C04B 2235/6581 Total pressure below 1 atmosphere, e.g. vacuum
• CPC Class Codes: C04B 2235/72 Products characterised by the absence or the low content of specific components, e.g. alkali metal free alumina ceramics
• CPC Class Codes: C04B 2235/727 Phosphorus or phosphorus compound content
• CPC Class Codes: C04B 2235/76 Crystal structural characteristics, e.g. symmetry
• CPC Class Codes: C04B 2235/77 Density
• CPC Class Codes: C04B 2235/787 Oriented grains
• CPC Class Codes: C04B 2235/96 : Properties of ceramic products, e.g. mechanical properties such as strength, toughness, wear resistance
• CPC Class Codes: C04B 2235/9623 : Ceramic setters properties
• CPC Class Codes: C04B 2237/343 : Alumina or aluminates
• CPC Class Codes: C04B 2237/704 : of one or more of the ceramic layers or articles
• CPC Class Codes: C04B 35/115 : Translucent or transparent products
• CPC Class Codes: C04B 35/6262 : of calcined, sintered clinker or ceramics
• CPC Class Codes: C04B 35/645 : Pressure sintering
• CPC Class Codes: C04B 35/6455 : Hot isostatic pressing
• CPC Class Codes: G02B 1/02 : made of crystals, e.g. rock-salt, semi-conductors G02B1/08 takes precedence

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 Al 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.

Claims

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, at a mixing ratio T;

(100−

T) of the plate-like alumina powder to the fine alumina powder in terms of mass ratio, T is 0.001 or more and less than 1, and a mass ratio R1 of F relative to Al 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;

R1=100×

[x1×

T+x2×

(100−

T)+x3×

Z]/[y1×

T+y2×

(100−

T)+y3×

z] 

 

(1)

where the unit is mass ppm;

Z is a ratio of an additive externally added to the alumina raw material powder relative to the alumina raw material powder (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 Al content (mass %) in the plate-like alumina powder, and y2 is an Al content (mass %) in the fine alumina powder;

the Al 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 Al and O), and multiplying the obtained result by 0.529;

the mass % of the impurity elements is determined as follows;

that is, 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 Al 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) while decreasing a temperature from a highest attained temperature during sintering, continuously applying a pressure of 50 kgf/cm² or more until a particular temperature set within a range of 1000 to 1400°

C. is reached, and decreasing the pressure to less than 50 kgf/cm² at a temperature equal to or lower than the particular temperature.