MgF2 system fluoride sintered body for radiation moderator and method for producing the same

Patent metadata

Field	Value
Publication number	US-10777330-B2
Application number	US-201514911748-A
Country	US
Kind code	B2
Filing date	Dec 18, 2015
Priority date	Dec 26, 2014
Publication date	Sep 15, 2020
Grant date	Sep 15, 2020

Abstract

A MgF2 system fluoride sintered body for a radiation moderator having a compact polycrystalline structure excellent in radiation moderation performance, especially neutron moderation performance, contains CaF2 of 90% by weight at the maximum and has a relative density of 95.2% or more.

First claim

The invention claimed is:

1. A MgF 2 system fluoride sintered body for a radiation moderator, consisting of MgF 2 having a compact polycrystalline structure with a bulk density of more than 3.07 g/cm 3 and a relative density of more than 97.5%, which has a bending strength of 12 MPa or more and 59 MPa or less and a Vickers hardness of 100 or more and 242 or less as regards mechanical strengths.

2. A method for producing a MgF 2 system fluoride sintered body for a radiation moderator, 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 (secondary sintering step), and
wherein the sintered body consisting of MgF 2 having a compact polycrystalline structure with a bulk density of more than 3.07 g/cm 3 and a relative density of more than 97.5%, which has a bending strength of 12 MPa or more and a Vickers hardness of 100 or more as regards mechanical strengths.

3. The method for producing the MgF 2 system fluoride sintered body for a radiation moderator according to claim 2 , further comprising the steps of:
cooling the sintered body after the secondary sintering step; and
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.

4. The method for producing the MgF 2 system fluoride sintered body for a radiation moderator according to claim 2 , 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.

5. 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 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.

6. The method for producing the MgF 2 system fluoride sintered body for a radiation moderator according to claim 2 , 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.

7. The method for producing the MgF 2 system fluoride sintered body for a radiation moderator according to claim 3 , 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

Inventors

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

Classifications

• G21K1/00

  Arrangements for handling particles or ionising radiation, e.g. focusing or moderating · CPC title

• C04B35/62685

  characterised by the order of addition of constituents or additives · CPC title

• C04B2235/95

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

• C04B2235/5481

  Monomodal · CPC title

• C04B2235/658

  Atmosphere during thermal treatment · CPC title