JPS60235096A - Manufacturing method for neutron shielding and absorption materials - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION OBJECTS OF THE INVENTION It is an object of the present invention to provide for the production of neutron shielding and absorbing materials in which boron carbide is uniformly dispersed.

Conventional technology Although boron carbide is an excellent thermal neutron absorbing material.

It is usually supplied as a powder, and there are some restrictions on its use. In addition, in order to obtain a high-density product, manufacturing conditions are severe, such as requiring hot pressing or high-temperature sintering, and the product is expensive, so it is not used in large quantities. As a way to solve this problem, research is being conducted to manufacture products in which boron carbide is dispersed in plastics and metals.
The aim is to find out how uniformly a given amount of boron carbide can be dispersed and to make the product as strong as possible.

In order to increase the strength, it is important to select the material that will serve as the matrix, and plastic has the disadvantage that it has low strength, and furthermore, the strength decreases more significantly as the temperature increases. Furthermore, plastics have low thermal conductivity, making it difficult to achieve satisfactory results when used as this type of neutron shielding material. Metals such as lead or aluminum may be used as an alternative to plastic, and these materials may have improved strength or thermal conductivity over plastic. However, these materials commonly have a low melting point, and cannot be sufficiently reliable under the conditions in which they are used. This is thought to cause many problems, especially in the event of an accident such as a fire. It is important to select materials such as plastic, lead, and aluminum that have high strength, a high melting point, and at the same time excellent thermal conductivity.

In the present invention, as a matrix material.

By selecting nickel or an alloy thereof, the above drawbacks could be eliminated. In other words, one key point of the present invention is that one or both of copper and nickel are used as the matrix material.

The present invention shows a method for producing products in which boron carbide is uniformly dispersed in a matrix of copper and/or nickel at an industrially reasonable price.

Conventional methods for dispersing boron carbide in a gold-copper and/or nickel matrix include a method in which boron carbide powder is completely mixed with copper powder or nickel powder, and the mixed powder is molded and sintered. Conventional powder metallurgy methods such as hot pressing of mixed powders are conceivable. However, when we investigated the uniformity of dispersion of boron carbide in composites produced by this method.

It was confirmed that sufficient uniformity could not be obtained. The reason for this is that the density of boron carbide is 2.5117/ct/l, the density of copper is 8.6&/cr/l, and the density of nickel is 8.9. !
if/cIIt, and the difference in density between boron carbide and the matrix material is large, so even if these powders are mixed, it is difficult to disperse them uniformly. When used as a neutron shielding material, uniform dispersion of boron carbide in the matrix is an important factor, so such a conventional powder metallurgy manufacturing method is not suitable.

As a method other than the usual powder metallurgy, it is conceivable to melt copper and nickel in a crucible, put boron carbide powder into the crucible, and solidify while stirring the molten liquid.

This method can be said to be an interesting technology when assuming future mass production, but eq.

Since the melting point of nickel is as high as 1000 degrees or more, it is not technically well established at this stage to disperse boron carbide powder in such a high-temperature water bath. moreover,
As with the powder metallurgy method, there is a large difference in density between boron carbide and copper or boron carbide and nickel, so it is considered difficult to obtain a product in which boron carbide is sufficiently uniformly dispersed even by this method.

Structure of the Invention The present invention provides a method for producing a neutron shielding and absorbing material in which boron carbide is uniformly dispersed, which comprises coating boron carbide particles with gold copper or nickel or an alloy thereof, and compressing and sintering or hot pressing the coated particles. provide.

According to the invention, copper is produced in the manner described in detail below.

It is possible to manufacture products in which boron carbide is uniformly dispersed using nickel or an alloy thereof as an entire matrix.

Vapor phase growth or liquid phase growth can be used as a method for coating boron carbide powder with copper, nickel, or their alloys, and the present invention can be achieved by either method, but from the viewpoint of productivity and cost. Therefore, it is preferable to adopt electroless plating or electrolytic plating after electroless plating.

In the present invention.

Among the vapor phase growth methods, vacuum evaporation is particularly preferred, and among the liquid phase growth methods, electroless plating is particularly preferred.

When coating copper, nickel, or their alloys on the back side of boron carbide powder by vapor phase growth or liquid phase growth, if the particle size of the powder is too coarse, it may be difficult to coat the specified amount of metal due to the small surface area of the powder. It takes a long time to complete the process, which is unfavorable from a manufacturing standpoint.

Furthermore, the particle size of the boron carbide powder is extremely coarse.

If a product has a structure in which this coarse boron carbide is distributed in islands, this is disadvantageous from the viewpoint of distributing boron carbide as uniformly as possible over the entire surface, which is required as a neutron shield. As a result of conducting tests, it was found that the average particle size of the boron carbide powder is preferably 500 microns or more.

Although it is considered that the sharper the particle size distribution with respect to the average particle diameter is, the better it is, but it is not necessary to specify the particle size distribution at 1%.

As described above, by molding and sintering boron carbide powder whose surface was coated with a predetermined amount of copper or nickel, a product in which boron carbide was uniformly dispersed could be obtained. however.

It was found that it was difficult to obtain a composite with sufficiently high sintered density using this tube sintering method. A low sintered density generally results in a decrease in strength and a decrease in thermal conductivity, which is undesirable under the conditions in which this type of material is used. Furthermore, a decrease in sintered density leads to a decrease in boron carbide content per product volume, which results in a decrease in boron content concentration and a decrease in neutron shielding and absorption ability. It is desirable that the carbon content is high, and it is necessary that the boron carbide content be high. In the present invention, copper is added to the boron carbide powder.
By coating with nickel or an alloy thereof and hot pressing, it is possible to produce a composite with high density and uniform dispersion of boron carbide in the matrix.

In the present invention, boron carbide powder is coated with j(nl, nickel or an alloy thereof).

As a result of the L test, it becomes difficult to obtain a sufficiently dense sintered body when the volume occupied by the metal becomes low. Even if hot pressing is performed, the composite is difficult to obtain when the volume ratio of the metal is less than 25 cm of the theoretical volume of the composite. It became difficult to reach a body density of 95%, and it was not possible to obtain a sufficiently high strength.On the other hand, there is no particular limit to the amount of boron carbide, but
If it is too small, the amount of the composite must be increased to enhance the shielding/absorbing effect, so for industrial use, it is desirable that this amount be 40 volumes or more.

In the present invention, a satisfactory product can be obtained not only by the hot press method but also by the hot insta-take press method. Furthermore, in the present invention, as a method for manufacturing in large quantities and at low cost, 1. rolling a composite obtained by a normal sintering method results in a high density, and a rolling temperature of 300°C or higher yields good results. is obtained.

Effects of the Invention According to the method of the present invention, a boron carbide neutron shielding/absorbing material having a density of 98% or more of the theoretical density can be easily produced.

Implementation mode Next, the present invention will be explained in detail using examples.

Example 1 100 g of B, C powder with an average particle size of 50 μm was heated to Pd at 60°C.
Activated with Cl, (0,005fj,/1.pH4, () ) solution for 5 minutes, washed with water, and plated with Cu at 50°C.
(OPC copper manufactured by Okuno Riyaku Kogyo, pi-110,5)
Soak for 6 hours in H2SO41rd, wash with water, and neutralize.
/ l) Washed with water and dried. In addition, the total Cu in the Cu plating solution
The ion concentration was 360y, and after 6 hours of plating, 995% of the ions precipitated on the surface of the B and C powders. The thickness of the coating layer was such that the volume of boron carbide and the volume of copper were the same (the volume of copper was 50 cm in the volume of the void portion of the composite). This copper-coated powder was placed in a graphite mold under a pressure of 150 kg/Cd.

Hot pressing was carried out at a temperature of 800°C. The density of this composite was 98% of the theoretical density. As a result of microscopic observation, it was confirmed that boron carbide in the matrix was uniformly distributed. Thermal conductivity and bending strength were measured as characteristics of this boron carbide/copper composite. Thermal conductivity is 90
kcal/CwL-h-.

The bending strength was 15#/-, which was sufficient to be used as a neutron shield.

Example 2 100 g of B and C powders with an average particle size of 120 μm were heated at 60° C.
dcl, (0,003 g/C pH 4,0) solution for 5 minutes, washed with water, and immersed in Ni plating solution (Nippon Kanigen Sakai, 5B-55, pH 6,9) at 60°C for 5 hours.
Washed with water and dried. 370g Ni is B4
It precipitated on the surface of C powder. As in Example 1, the thickness of the coating layer was 50 inches of the product volume after coating. Using this nickel powder in a graphite mold, the pressure was 150 k.
g/Cr/1. Hot pressing was carried out at a temperature of 950°C. The density of this product was 98 cm compared to the theoretical density.

Example 6 Boron carbide powder electrolessly plated with copper or nickel obtained by the same method as Example 1 and Example 2 was mixed to have an equal weight percentage, and the mixed powder was heated using a graphite mold under a pressure of 150 kg. /cI/l and hot-pressed at a temperature of 900°C. As a result of observing the structure of this product, it was confirmed that the powder coated with copper and nickel was uniformly dispersed, and the sintered density was 99% or more of the theoretical density. The reason for the high density is thought to be the effect of mixing different types of powder, that is, the different particle sizes of the powder coated with copper and nickel lead to densification, and the solid solution of copper and nickel promotes sintering. .

Example 4 B4C powder 10, 9.35 g of C with an average particle size of 20 ttm
u was vacuum evaporated. Vacuum deposition conditions are 2 x 10-'
Torr, graphite Ruho was used as the evaporation source, and heating was performed by high frequency induction heating. The deposition time was 2.5 hours. At this time, the amount of Cu precipitated on the B and C powders was 3
It was 5.5g. As in Example 1, the thickness of the coating layer was 50 inches of the product volume after coating. This copper-coated powder was heated using a graphite mold at a pressure of 1501c9.
/Cr/l and hot pressed at a temperature of 800°C. The density of this product was 9 days higher than the theoretical density.

Example 5 A stainless copper container was filled with boron carbide/copper powder coated in the same manner as in Example 1, and the temperature was 900°C.

Hot isostatic pressing was carried out at an ultimate pressure of 1000 atm. The density of this product was 98% of the theoretical density.

Example 6 Boron carbide/copper powder coated in the same manner as Example 1 was
After molding at a pressure of t/m, it was sintered at 960° C. for 6 hours in a vacuum atmosphere. The density of this sintered body is 7 compared to the theoretical density.
It was 5chi. In order to further obtain a high-density product, this sintered body was vacuum sealed in a stainless steel can and rolled at a temperature of 800°C. The density of the product after rolling was 96%.

In all of the products shown in the examples above, boron carbide was uniformly dispersed and had a high density, so they were found to be useful as neutron shielding materials.

Example 7 After activating 100 boron carbide powder with an average particle size of 50 μm by the method of Example 1.

Electroless plating of Ni--Cu alloy was performed using a plating solution to obtain a metal coating covering 55% of the product volume after coating. This boron carbide/Ni-Cu powder was filled into a stainless steel container and hot isostatically pressed at a temperature of 1000°C and an ultimate pressure of 1000 atm. The density of this product was 99% of the theoretical density.

Example 8 Example 2 was added to 10 il of boron carbide powder with an average particle size of 120μ.
After coating with 5μ of Ni in the same manner as above.

Ni 10w%Co alloy' plating using plating solution
Ni-Co alloy electroplating on coated B and C powders is as follows:
By dispersing the coating B and C powders in the plating solution and creating a periodic magnetic field on the cathode,! 7 * By adsorbing the N+ coated B4C powder onto the cathode and performing electrolysis during the adsorption, Ni-C is formed on the Ni coated B and C powders.

An alloy coating was obtained.

The thus prepared metal coated & B4C powder was subjected to hot isostatic pressing in the same manner as in Example 7, and a product with a theoretical density of 98 cm was obtained.

Masahiro I

Claims (1)

[Claims] 1. A neutron shielding and absorbing material in which boron carbide is uniformly dispersed, which is obtained by coating boron carbide particles with copper or nickel or an alloy thereof, and compressing and sintering or hot pressing the coated particles. manufacturing method. 2. The manufacturing method according to claim 1. A method in which coating is performed by electroless plating or electrolytic plating after Fi electroless plating. 6. The method according to claim 1. A method in which coating is performed by vacuum evaporation. 4. The method according to claim 1. A method in which compression is performed using an inostatic press method. 5. The manufacturing method according to any one of claims 1 to 4, wherein the boron carbide particles have a particle size of 500 μm (32 mesh) or less. 6. A manufacturing method according to any one of claims 1 to 5, in which copper-coated boron carbide particles and nickel-coated boron carbide particles are compression-molded. Z Boron carbide particles coated with copper or nickel. A method for producing a neutron shielding and absorbing material in which boron carbide is uniformly dispersed, which comprises compressing and sintering coated particles and rolling the resulting sintered body.