MgF2 SYSTEM FLUORIDE SINTERED BODY FOR RADIATION MODERATOR AND METHOD FOR PRODUCING THE SAME

Patent metadata

Field	Value
Publication number	US-2016351282-A1
Application number	US-201514911748-A
Country	US
Kind code	A1
Filing date	Dec 18, 2015
Priority date	Dec 26, 2014
Publication date	Dec 1, 2016
Grant date	—

Abstract

A MgF 2 system fluoride sintered body for a radiation moderator having a compact polycrystalline structure excellent in radiation moderation performance, especially neutron moderation performance, contains CaF 2 of 90% by weight at the maximum and has a relative density of 95.2% or more.

First claim

1 . A MgF 2 system fluoride sintered body for a radiation moderator, comprising MgF 2 having a compact polycrystalline structure with a bulk density of 3.07 g/cm 3 (a relative density of 97.5%) or more.

2 . The MgF 2 system fluoride sintered body for a radiation moderator according to claim 1 , which has a bending strength of 12 MPa or more and a Vickers hardness of 100 or more as regards mechanical strengths.

3 . A method for producing the MgF 2 system fluoride sintered body for a radiation moderator according to claim 1 , comprising the steps of:
pulverizing a high-purity MgF 2 raw material to control the particle size, so as to allow the maximum particle diameter in a particle size distribution to be 50 μm or less, the shape of the particle size distribution curve to be of sub-1-peak type or 1-peak type, and the median diameter to be 6 μm or less; adding 0.02-1% by weight of a sintering aid to the particle-size-controlled raw material to mix; molding the compound at a molding pressure of 5 MPa or more using a press molding device; molding the press molded article at a molding pressure of 5 MPa or more using a cold isostatic pressing (CIP) device; conducting preliminary sintering by heating the CIP molded article in a temperature range of 600° C.-700° C. in an air atmosphere (preliminary sintering step); conducting atmospheric sintering or pressure sintering by heating in a temperature range from (Tn−100)° C. to (Tn)° C. when the starting temperature of foaming of the preliminary sintered body is (Tn)° C., in an air atmosphere or in an inert gas atmosphere or in a vacuum atmosphere (primary sintering step); and forming a sintered body having a compact structure by heating in a temperature range of 900° C.-1150° C. under atmospheric pressure or under pressure in the same atmosphere as the preceding step.

4 . The method for producing the MgF 2 system fluoride sintered body for a radiation moderator according to claim 3 , further comprising the step of:
conducting tertiary sintering by reheating in a temperature range of 900° C.-1150° C. under pressure in an inert gas atmosphere or in a vacuum atmosphere.

5 . A MgF 2 system fluoride sintered body for a radiation moderator, which is a MgF 2 —CaF 2 binary system fluoride sintered body having a compact polycrystalline structure, containing CaF 2 of 90% by weight at the maximum with a relative density of 95.2% or more.

6 . The MgF 2 system fluoride sintered body for a radiation moderator according to claim 5 , which has a bending strength of 13 MPa or more and a Vickers hardness of 100 or more as regards mechanical strengths.

7 . A method for producing the MgF 2 system fluoride sintered body for a radiation moderator according to claim 5 , comprising the steps of:
mixing a high-purity MgF 2 powder with a high-purity CaF 2 powder in such a manner that the content of CaF 2 is 90% by weight at the maximum, and then pulverizing the same to control the particle size, so as to allow the maximum particle diameter in a particle size distribution to be 50 μm or less, the shape of the particle size distribution curve to be of sub-1-peak type or 1-peak type, and the median diameter to be 6 μm or less; adding 0.02-1% by weight of a sintering aid to the particle-size-controlled raw material to mix; molding the compound at a molding pressure of 5 MPa or more using a press molding device; molding the press molded article at a molding pressure of 5 MPa or more using a cold isostatic pressing (CIP) device; conducting preliminary sintering by heating the CIP molded article in a temperature range of 600° C.-700° C. in an air atmosphere (preliminary sintering step); conducting atmospheric sintering or pressure sintering by heating in a temperature range from (Tn−100)° C. to (Tn)° C. when the starting temperature of foaming of the preliminary sintered body is (Tn)° C., in an air atmosphere or in an inert gas atmosphere or in a vacuum atmosphere (primary sintering step); and forming a sintered body having a compact structure by heating in a temperature range of 900° C.-1150° C. under atmospheric pressure or under pressure in the same atmosphere as the preceding step.

8 . The method for producing the MgF 2 system fluoride sintered body for a radiation moderator according to claim 7 , further comprising the step of:
conducting tertiary sintering by reheating in a temperature range of 900° C.-1150° C. under pressure in an inert gas atmosphere or in a vacuum atmosphere.

9 . The method for producing the MgF 2 system fluoride sintered body for a radiation moderator according to claim 3 , wherein the inert gas atmosphere in the two sintering steps (primary and secondary sintering steps) comprises one kind of gas or a mixture of plural kinds of gases, selected from among nitrogen, helium and argon, and hot molding work is conducted in the heating process using a hot press furnace or a hot isostatic pressing furnace.

10 . The method for producing the MgF 2 system fluoride sintered body for a radiation moderator according to claim 4 , wherein the inert gas atmosphere in the three sintering steps (primary, secondary and tertiary sintering steps) comprises one kind of gas or a mixture of plural kinds of gases, selected from among nitrogen, helium and argon, and hot molding work is conducted in the heating process using a hot press furnace or a hot isostatic pressing furnace.

11 . The method for producing the MgF 2 system fluoride sintered body for a radiation moderator according to claim 3 , wherein in the two sintering steps (primary and secondary sintering steps), in a vacuum atmosphere of less than 100 Pa, using a hot press furnace, hot molding work is conducted in the heating process.

12 . The method for producing the MgF 2 system fluoride sintered body for a radiation moderator according to claim 4 , wherein in the three sintering steps (primary, secondary and tertiary sintering steps), in a vacuum atmosphere of less than 100 Pa, using a hot press furnace, hot molding work is conducted in the heating process.

Assignees

• Univ Tsukuba
• Techno Eye Corp
• Daico Mfg Co Ltd
• Univ Tsukuba

Inventors

• Kumada Hiroaki
• Nakamura Tetsuyuki
• Ikeda Takeshi
• Shigeoka Takuji

Classifications

• C04B35/6365

  Cellulose or derivatives thereof · CPC title

• C04B35/553

  based on fluorides · CPC title

• C04B2235/5436

  micrometer sized, i.e. from 1 to 100 micron · CPC title

• C04B2235/449

  Organic acids, e.g. EDTA, citrate, acetate, oxalate · CPC title

• C04B2235/95

  Products characterised by their size, e.g. microceramics · CPC title