CA1097906A - Neutron-absorber plates based on boron carbide and carbon and a process for their production - Google Patents
Neutron-absorber plates based on boron carbide and carbon and a process for their productionInfo
- Publication number
- CA1097906A CA1097906A CA316,397A CA316397A CA1097906A CA 1097906 A CA1097906 A CA 1097906A CA 316397 A CA316397 A CA 316397A CA 1097906 A CA1097906 A CA 1097906A
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- Canada
- Prior art keywords
- finer
- weight
- boron carbide
- plates
- room temperature
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Classifications
-
- G—PHYSICS
- G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
- G21F—PROTECTION AGAINST X-RADIATION, GAMMA RADIATION, CORPUSCULAR RADIATION OR PARTICLE BOMBARDMENT; TREATING RADIOACTIVELY CONTAMINATED MATERIAL; DECONTAMINATION ARRANGEMENTS THEREFOR
- G21F1/00—Shielding characterised by the composition of the materials
- G21F1/02—Selection of uniform shielding materials
- G21F1/06—Ceramics; Glasses; Refractories
Abstract
ABSTRACT OF THE DISCLOSURE
The subject of the invention is thin large-area neutron-absorber plates having a volume composition of from 40 to 60%
and preferably from 45 to 60% by volume of boron carbide, from 25 to 5% by volume and preferably 15 to 5% by volume of free carbon, the remainder being pores, a density of from 1.4 to 1.8 g/cm3, a flexural strength at room temperature of from 15 to 45 N/mm2, a compressive strength at room temperature of from 25 to 60 N/mm2, a modulus of elasticity at room temperature of from 10,000 to 20,000 N/mm2, and a resistance to ionizing radiation of at least 1011 rad, which plates may be produced by mixing boron carbide powder, containing at least 75% by weight of boron and a proportion of boron oxide of less than 0.5% by weight, and having a particle size distribution of at least 95% finer than 50 µm and, optionally, graphite powder with a pulverulent organic resin binder and a wetting agent, shaping the mixture under pressure at room tempera-ture, curing the resin binder at temperatures of up to 180°C, and then coking the shaped plates with the exclusion of air at temperatures of up to approximately 1000°C with a controlled temperature increase.
The subject of the invention is thin large-area neutron-absorber plates having a volume composition of from 40 to 60%
and preferably from 45 to 60% by volume of boron carbide, from 25 to 5% by volume and preferably 15 to 5% by volume of free carbon, the remainder being pores, a density of from 1.4 to 1.8 g/cm3, a flexural strength at room temperature of from 15 to 45 N/mm2, a compressive strength at room temperature of from 25 to 60 N/mm2, a modulus of elasticity at room temperature of from 10,000 to 20,000 N/mm2, and a resistance to ionizing radiation of at least 1011 rad, which plates may be produced by mixing boron carbide powder, containing at least 75% by weight of boron and a proportion of boron oxide of less than 0.5% by weight, and having a particle size distribution of at least 95% finer than 50 µm and, optionally, graphite powder with a pulverulent organic resin binder and a wetting agent, shaping the mixture under pressure at room tempera-ture, curing the resin binder at temperatures of up to 180°C, and then coking the shaped plates with the exclusion of air at temperatures of up to approximately 1000°C with a controlled temperature increase.
Description
U~Wp- 1,803 (ES7701 "
~7~
NEUTRO~ ABSORBER MATE:RIAL
The present invention relates to a neutron absor~er material comprising boron carbide, sui~able for use as a neut.ron .shield in nuclear reactors, and to a process for its manufacture.
Boron is known to be a good absorber of neutrons and various boron-containing neutron-absorber materials have prevlously been described~
Neutron-shiPld blocks prepared by intimate~y incorporating a ~ine~y divid~d boron compound ~prefexably horax~ in a graphite mix which preferably contains a carbonizable binder (preferably tax or pitch~, and subsequently heating the mixture to a temperature (prefexab~y about 1000C) high enough to carbonize the binder and melt the boron compound but not so high as to decompose or volatil-ize the boron compound, are described in British Patent Specification 797,692. The boron content of these blocks is said to be preferab~y from 0.25 to l~/o ~y weight. These neutron-shield blocks do not have a high fire-resistance, nor do they have a high resistance to oxidationO Moreover, they have only a l~w ~lexural strength.
The manufacture of a heat-resistant ~oron-containing material by heating a boron containing component (for example boron carbide3, a carbon-containing component (~or example graphite or coXe powder) and, optionally~ a carbon-containing binder, to a temperature of at least 1800C under a pressure of at least 1.758 kg/mm2 (about 175 MPa), provided that the substances added to the carbon-containing matexial melt under the conditions used~ is described in DE-PS 1,302~877~ It is apparent rom this speciication that the manu~acture of high-strength and high-density materials containing bor~n and carbon has generally requir~d the use of high temperatures and high pressures. The material descri.bed i.n British Patent Specification 797,692 is manufactured by pressureless heat treat-ment at a temperature of on~y about 1000C and does not have a high strength.
This view is confirmed by U.SO Patent 3,153,636, which des-cribes the manufacture of various porous materials, including a neu-tron-shield matexial having a minimum horon content of 0.54 g/cm3, an average density of from 0.71 to 0.85 g/cm3, and an average compressivestrength (or pressure resistance) of 5,62 N/mm2 (800 pos.i.~. This material is manufactured by mixing a pulverulent epo~y-modiried phenolic resin and a phenol/formaldehyde resin in the form of hollow thin-walled spheres with pulverulent boron carbide, curing the mixture after having been transferred to a mould with vibration at a temperature of from 140 to 160C, and subse~uently firing it in an inert atmosphere at a temperature of about 950C. Higher-density materials (from 1.5 to 2 g/cm3) can be o~tained only if graphite is used in such large amounts (from 80 to 9~/O by weight) that the product is a borated graphite (cf.
UOS~ Patent 3,231,521), and it is then necessary to use pressures of about 70 MPa (about 10,000 pn S~ i~ ) when moulding the material, and temperatures of about 600C when baking it.
It is thus apparent from the prior art that only porous ceramic materials could be obtained from mixtures of pulverulent boron carbide, phenolic resin binders and graphite (if the graphite was not present in large quantities) when curing the mixture after moulding~ and suhsequently firing it in an inert atmosphere at a temperature of not more than 1000C. An approximately uniform distribution of the pores could be achieved by using part of the binder in the form of hollow thin-wallea spheres. Such materials have a low density combined with mediocre strength properties.
Although a process for the manu~acture of a high-density material comprising boron carbide and a phenolic resin binder is described in French Patent 1,568,883, this process requires the application of pressure of from l to 4 t/cm2 (about lO0 to 400 MPa) during moulding and prior to curing and coking~ The appli-cation of a pressure of this magnitude is not practicable when manu-facturing thin large-area plates.
Highly densified materials containing a relative~y large proportion of boron carbide (from 50 to 6~/~ by volume) can be manufactured by a hot-pressing process, but such processes are limited as regards the shape in which the material may be formed and the production of thin large-area plates ~y this method is very difficult.
Thin large-area plates of neutron-absorber material have sometimes to be manufactured ~y sawing blocks of such material.
The present invention provides a neutron-absorber material having a composition of from 40 to 60%~ preferably 45 to 6~/o,by volume of boron carbide and from 5 to 25%, preferably 5 to 15% by volume of free carbon, the remainder being pores;
a density within the range of from 1.4 to 108 g/cm3;
a flexural strength at room temperature within the range of from 15 to 45 N/mm2;
a compressive stre.ngth at room temperature within the range of from 25 to 60 N/mm2;
a modulus of elasticity at room temperature within the range of from lO,000 to 20,000 N/mm2; and a resistance to ionizing radiation of at least lO
rad.
The present invention also provides a process for th~ manu-facture of a neutron-absorber material which comprises:
(i) formin~ ~ mixture of boron carbide containing at least 75% ~y weight of boron and not more than 0.5% ~y weight of boron oxide and having a particle size distribution (by weight of~
at least 95% finer than 50~um, at least 9~/O finer than 30 ~m, at least 700/O iner than 20 ~m, at least 500/O finer than lO ~m, at least 3~/0 finer than 5Jum, and at least 10% finer than 2~wm, with an organic resin binder, a wetting agent and9 option-al~y, pulverulent graphite (ii~ shaping the mixture under pressure within the range of from 25 to 30 MPa at room temperature;
~iii) curing the mixture at a temperature of not more than 180C; and subsequently, (iv) coking ~he mixture in the absence of air at a temperature , . of up to 1000C with a controlled temperature increase ~ not more than 120~C/hour.
The neutron-absor~er material of the invention and manufactured according to the process of the invention ~s the advantage that it can be manufactured in the form of thin large-area plates.
~7~
NEUTRO~ ABSORBER MATE:RIAL
The present invention relates to a neutron absor~er material comprising boron carbide, sui~able for use as a neut.ron .shield in nuclear reactors, and to a process for its manufacture.
Boron is known to be a good absorber of neutrons and various boron-containing neutron-absorber materials have prevlously been described~
Neutron-shiPld blocks prepared by intimate~y incorporating a ~ine~y divid~d boron compound ~prefexably horax~ in a graphite mix which preferably contains a carbonizable binder (preferably tax or pitch~, and subsequently heating the mixture to a temperature (prefexab~y about 1000C) high enough to carbonize the binder and melt the boron compound but not so high as to decompose or volatil-ize the boron compound, are described in British Patent Specification 797,692. The boron content of these blocks is said to be preferab~y from 0.25 to l~/o ~y weight. These neutron-shield blocks do not have a high fire-resistance, nor do they have a high resistance to oxidationO Moreover, they have only a l~w ~lexural strength.
The manufacture of a heat-resistant ~oron-containing material by heating a boron containing component (for example boron carbide3, a carbon-containing component (~or example graphite or coXe powder) and, optionally~ a carbon-containing binder, to a temperature of at least 1800C under a pressure of at least 1.758 kg/mm2 (about 175 MPa), provided that the substances added to the carbon-containing matexial melt under the conditions used~ is described in DE-PS 1,302~877~ It is apparent rom this speciication that the manu~acture of high-strength and high-density materials containing bor~n and carbon has generally requir~d the use of high temperatures and high pressures. The material descri.bed i.n British Patent Specification 797,692 is manufactured by pressureless heat treat-ment at a temperature of on~y about 1000C and does not have a high strength.
This view is confirmed by U.SO Patent 3,153,636, which des-cribes the manufacture of various porous materials, including a neu-tron-shield matexial having a minimum horon content of 0.54 g/cm3, an average density of from 0.71 to 0.85 g/cm3, and an average compressivestrength (or pressure resistance) of 5,62 N/mm2 (800 pos.i.~. This material is manufactured by mixing a pulverulent epo~y-modiried phenolic resin and a phenol/formaldehyde resin in the form of hollow thin-walled spheres with pulverulent boron carbide, curing the mixture after having been transferred to a mould with vibration at a temperature of from 140 to 160C, and subse~uently firing it in an inert atmosphere at a temperature of about 950C. Higher-density materials (from 1.5 to 2 g/cm3) can be o~tained only if graphite is used in such large amounts (from 80 to 9~/O by weight) that the product is a borated graphite (cf.
UOS~ Patent 3,231,521), and it is then necessary to use pressures of about 70 MPa (about 10,000 pn S~ i~ ) when moulding the material, and temperatures of about 600C when baking it.
It is thus apparent from the prior art that only porous ceramic materials could be obtained from mixtures of pulverulent boron carbide, phenolic resin binders and graphite (if the graphite was not present in large quantities) when curing the mixture after moulding~ and suhsequently firing it in an inert atmosphere at a temperature of not more than 1000C. An approximately uniform distribution of the pores could be achieved by using part of the binder in the form of hollow thin-wallea spheres. Such materials have a low density combined with mediocre strength properties.
Although a process for the manu~acture of a high-density material comprising boron carbide and a phenolic resin binder is described in French Patent 1,568,883, this process requires the application of pressure of from l to 4 t/cm2 (about lO0 to 400 MPa) during moulding and prior to curing and coking~ The appli-cation of a pressure of this magnitude is not practicable when manu-facturing thin large-area plates.
Highly densified materials containing a relative~y large proportion of boron carbide (from 50 to 6~/~ by volume) can be manufactured by a hot-pressing process, but such processes are limited as regards the shape in which the material may be formed and the production of thin large-area plates ~y this method is very difficult.
Thin large-area plates of neutron-absorber material have sometimes to be manufactured ~y sawing blocks of such material.
The present invention provides a neutron-absorber material having a composition of from 40 to 60%~ preferably 45 to 6~/o,by volume of boron carbide and from 5 to 25%, preferably 5 to 15% by volume of free carbon, the remainder being pores;
a density within the range of from 1.4 to 108 g/cm3;
a flexural strength at room temperature within the range of from 15 to 45 N/mm2;
a compressive stre.ngth at room temperature within the range of from 25 to 60 N/mm2;
a modulus of elasticity at room temperature within the range of from lO,000 to 20,000 N/mm2; and a resistance to ionizing radiation of at least lO
rad.
The present invention also provides a process for th~ manu-facture of a neutron-absorber material which comprises:
(i) formin~ ~ mixture of boron carbide containing at least 75% ~y weight of boron and not more than 0.5% ~y weight of boron oxide and having a particle size distribution (by weight of~
at least 95% finer than 50~um, at least 9~/O finer than 30 ~m, at least 700/O iner than 20 ~m, at least 500/O finer than lO ~m, at least 3~/0 finer than 5Jum, and at least 10% finer than 2~wm, with an organic resin binder, a wetting agent and9 option-al~y, pulverulent graphite (ii~ shaping the mixture under pressure within the range of from 25 to 30 MPa at room temperature;
~iii) curing the mixture at a temperature of not more than 180C; and subsequently, (iv) coking ~he mixture in the absence of air at a temperature , . of up to 1000C with a controlled temperature increase ~ not more than 120~C/hour.
The neutron-absor~er material of the invention and manufactured according to the process of the invention ~s the advantage that it can be manufactured in the form of thin large-area plates.
2.5 The neutron~absorber material of the invention consists almost exclusively of boron and carbon, with a volume density of from 40 to 6~/o and preferably from 45 to 60~/o ~y volume of boron carbide and from 5 to 25% and preferab~y from 5 to 15% by volume of free carbon, the remainder being pores. This compositîon corresponds to about 60 to 93% by weight, preferably about 70 to 93% by weight boron carbide, and about 40 to 7% by weight, preferably about 30 to 7% ~y weight free carbon~
The boron carbide portion of the material results from ~he pulverulent boron carbide used .in the manufacture ~f the material9 the purity and particle size distribution of the boron carbide being important in order $o prcduce material having the desired S properties. The term !'free car~on" means carbon that is not chem-ically bonded in the boron car~ide, and this carbon results from the organic resin binder, which decomposes to form amorphous carhon duxing coking, and from the graphite,if any is used, The pulverulent boron carbide used in the manufacture o~ the neutron-absorber material according to the invention advantageously has a purity of at least 98% by weight (by which is meant that ~he sum of the boron content and the carbon content should total at least 9~/O by weight). This corresponds to a boron content of from 75 to 7~/O by weight. Boxon carbide generally contains boron oxide as an impurity resulting from its manufacture, but the boron car-bide used according to the invention must not contain more than 0.5%
by weight of boron oxide. Metallic impurities~ especially iron and calcium, may also be present in minor amounts, but the amount of such impurities should advantayeous~y not exceed 0~5% by weight eachO Fluorine and chlorine should advantageously not be present in amounts exceeding lO0 ppm by weight each.
The boron car~ide should advantageously have at least 9~%, preferab~y at least 9~/O~ and especially 10~/o~ ~y ~eight of particles finer than 50Jlm. A preferred particle size distribution is 100% finer than 50 ~m, at least 99~/O finer than 30 ~m, at least 97% finer than 20 ~m, at least 90/~ finer than lO ~m, at least 75% finer than 5 ~m, and at least 5~/O finer than 2 ~m, The organlc resin binder used is advantageously one that is pulverulent and especially, pulverulent at room temperature. It is preferably a phenolic resin, especially a phenol/formalae~yde condensation product of the no~olak or resole type, which will S decompose at a temperature of not more ~han 1000C to form amorphous carbon in a yield of from 35 to 5~/~. The resin should advantageously be substantially free of impurities, that is to say, that calcium, iron, sodium and potassium should ~e present in amounts not exceeding 20 ppm by weight each, magnesium in an amount not exceeding 5 ppm by weight, and copper in an amount not exceeding 1 ppm ~y weight~
~he pulverulent graphite optionally used in the preparation of the mixture i5 advantageously natural graphite and advantageously has a particle size distribution of finer than 40_~m.
The boron carbide, organic resin and, optionally, graphite are mixed together in the proportions necessary to give the desired final composition, together with a wetting agent (for example furfural) to form a homogeneous ~lowable powder.
In order to o~tain the desired end composition in the fini~hed materials, the starting materials are used preferably in the follow-~0 ing guantities:
50 to 85% by weight, preferab~y 60 to ~5% ~y weight boron carbide powder, 25 to ~/O ~y weight, preferably 15 to ~/O by weight graphite powder9 20 to 12% by weight resin powder and 5 to 3% by weight wetting agent.
The powder thus o~tained is then poured into a press mould and molded at room temperature, under a pressure within the range of ~rom 25 to 30 MPa. When the neutron-absorber material according to the invention is to be manufactured in the shape of plates, a plate 7~
press mould is used, for example a hydraulic press with a press mould in the Eorm of a steel box. The mixture is advantageously moulded into the shape of plates having a thickness w~thin the range of from 5 to 10 mm.
The soft shaped mixture is then removed from the mould and cured at a temperatuxe of not more than 180C. If the mixture is in the shape of plates, the soft plates may be stacked between glass carrier plates for the curing.
Finally, the shaped cured mixture is coked in the absence of air at a temperature of up to lOOO~C in order to decompose the organic resin binder. If the mixture is in the shape of plates, these may be stac]ced between graphite carrier plates of approximately the same thickness for the coking operation. Coking has to be carried out with a controlled temperature increase~ that means not more than 120c/hour~ although the actual temperature program (consisting o~ heating, dwelling and cooling) depends on the shape and size of the mixture. For example, when the mixture is in the shape of plates measuring abou-t Z30 mm x 300 mm, a temperature difference within each plate of about 150C should advantageous~y not be exceeded; this can be ensuredt for example, by heating a stack of such plates to 200C over 4.5 hours to 400C over 7 hours, to 600C over 9 hours, to 800C over 12 hours, to 900C over 15 hours and to 1000C over 19 hours (all periods being measuxed from the commencement of heating), then maintaining this temperature for 3 hoursJ and cooling the stack over a ~urt~r 24 hours.
Stacking of the plates between carrier plates during curing and coking assists in preventing them from becoming warped. The linear shrinkage of the plates during coking is general~y only ~ about 1%.
When it has been cooled su~sequent to the coking operationy the neutron-absorber material according to the invention is ready for use and does not need to be machined further, except, for example, in the case of plates, to remove the edges and trim them to size. The neutron-absorber material according to the in~ention S can be manufactured in the desired shape, espe~ially in the form of thin large-area plates, and therefore such plates do not have to be prepared by sawing blocks of material.
The material according to the invention has good neutron-absorbing properties and is suitable, inter alia, for use in the manufacture of storage tanks for burnt-out fuel elements from nuclear reactors in instances where the radiation resistance of the plates is of paramount importance~ Thus, there is practically no change in the mechanical properties and particular~y no change in the dimensions when there is exposure to the action of an ionizing radiation of at least lOll rad that is, the outgassing ra~e or the quantity of gaseous material produced is extremely low and negligible in practice.
The following examples illustrate the manufacture and proper-ties of neutron-absorber material according to the invention. A11 parts and percentages are calculated ~y weight, unless oth~rwise stated.
Example l lO0 parts by weight boron carbide powder, 18 parts by weight phenolac resin powder, and 4O2 parts by weight furfural were processed into a molding compound. The boron carbide powder contained 76.5%
by weight boron and 0~5% by weight B203, with a particle size distribution of 10~/o finer than 50Jum, 99% finer than 30 ~m, 97%
finer than ~OJum, 90o/0 finer than lO~m, 75% finer than 5~lm, 5~/~
~iner than 2JumO The mixture was molded into plates of 5 mm ~hick-ness under a pressure of 30 MPa, after which the plates were curedat 180C ~or 15 hours. The plates were then coked under a protec-tive nitrogen atmosphere with a linear heating rate of up to 1000C, where the temperature was attained in 18 hours and was kept constant for 4 hours~
Properties of the plates thus o~taLned:
density: 1.71 g/cm3 boron content: 6403% by weight, corresponding to 56% by vol. boron carbide ~otal carbon content, 31.5% by weight, corresponding to 10% by vol. free carbon flexural strength: 21 ~/mm2 compression strength: 55 N/mm2 modulus of elasticity: 12000 N/mm2 lS Radiation resistance 1011 rad (no measurable change in the flexural streng~h and the dimensions)~
Exam~le 2 Mixing, pressing, curing and coking were carried out as described in Example 1.
Composition of the moulding compound~ 95 parts by weight o:E
boron carb.ide, 5 parts by weight of graphit~, 18 parts ~y weight of phenolic resin, 4.5 parts ~y weight of furfural. The boron carbide used contained 75. 6% of boron and 0~2% of B2O3O Particle si~e distribution:
96% finer -than 50 ~m, 92% finer than 30 ~m, 80% finer than 20 ~m, 60% finer than 10 ~m,
The boron carbide portion of the material results from ~he pulverulent boron carbide used .in the manufacture ~f the material9 the purity and particle size distribution of the boron carbide being important in order $o prcduce material having the desired S properties. The term !'free car~on" means carbon that is not chem-ically bonded in the boron car~ide, and this carbon results from the organic resin binder, which decomposes to form amorphous carhon duxing coking, and from the graphite,if any is used, The pulverulent boron carbide used in the manufacture o~ the neutron-absorber material according to the invention advantageously has a purity of at least 98% by weight (by which is meant that ~he sum of the boron content and the carbon content should total at least 9~/O by weight). This corresponds to a boron content of from 75 to 7~/O by weight. Boxon carbide generally contains boron oxide as an impurity resulting from its manufacture, but the boron car-bide used according to the invention must not contain more than 0.5%
by weight of boron oxide. Metallic impurities~ especially iron and calcium, may also be present in minor amounts, but the amount of such impurities should advantayeous~y not exceed 0~5% by weight eachO Fluorine and chlorine should advantageously not be present in amounts exceeding lO0 ppm by weight each.
The boron car~ide should advantageously have at least 9~%, preferab~y at least 9~/O~ and especially 10~/o~ ~y ~eight of particles finer than 50Jlm. A preferred particle size distribution is 100% finer than 50 ~m, at least 99~/O finer than 30 ~m, at least 97% finer than 20 ~m, at least 90/~ finer than lO ~m, at least 75% finer than 5 ~m, and at least 5~/O finer than 2 ~m, The organlc resin binder used is advantageously one that is pulverulent and especially, pulverulent at room temperature. It is preferably a phenolic resin, especially a phenol/formalae~yde condensation product of the no~olak or resole type, which will S decompose at a temperature of not more ~han 1000C to form amorphous carbon in a yield of from 35 to 5~/~. The resin should advantageously be substantially free of impurities, that is to say, that calcium, iron, sodium and potassium should ~e present in amounts not exceeding 20 ppm by weight each, magnesium in an amount not exceeding 5 ppm by weight, and copper in an amount not exceeding 1 ppm ~y weight~
~he pulverulent graphite optionally used in the preparation of the mixture i5 advantageously natural graphite and advantageously has a particle size distribution of finer than 40_~m.
The boron carbide, organic resin and, optionally, graphite are mixed together in the proportions necessary to give the desired final composition, together with a wetting agent (for example furfural) to form a homogeneous ~lowable powder.
In order to o~tain the desired end composition in the fini~hed materials, the starting materials are used preferably in the follow-~0 ing guantities:
50 to 85% by weight, preferab~y 60 to ~5% ~y weight boron carbide powder, 25 to ~/O ~y weight, preferably 15 to ~/O by weight graphite powder9 20 to 12% by weight resin powder and 5 to 3% by weight wetting agent.
The powder thus o~tained is then poured into a press mould and molded at room temperature, under a pressure within the range of ~rom 25 to 30 MPa. When the neutron-absorber material according to the invention is to be manufactured in the shape of plates, a plate 7~
press mould is used, for example a hydraulic press with a press mould in the Eorm of a steel box. The mixture is advantageously moulded into the shape of plates having a thickness w~thin the range of from 5 to 10 mm.
The soft shaped mixture is then removed from the mould and cured at a temperatuxe of not more than 180C. If the mixture is in the shape of plates, the soft plates may be stacked between glass carrier plates for the curing.
Finally, the shaped cured mixture is coked in the absence of air at a temperature of up to lOOO~C in order to decompose the organic resin binder. If the mixture is in the shape of plates, these may be stac]ced between graphite carrier plates of approximately the same thickness for the coking operation. Coking has to be carried out with a controlled temperature increase~ that means not more than 120c/hour~ although the actual temperature program (consisting o~ heating, dwelling and cooling) depends on the shape and size of the mixture. For example, when the mixture is in the shape of plates measuring abou-t Z30 mm x 300 mm, a temperature difference within each plate of about 150C should advantageous~y not be exceeded; this can be ensuredt for example, by heating a stack of such plates to 200C over 4.5 hours to 400C over 7 hours, to 600C over 9 hours, to 800C over 12 hours, to 900C over 15 hours and to 1000C over 19 hours (all periods being measuxed from the commencement of heating), then maintaining this temperature for 3 hoursJ and cooling the stack over a ~urt~r 24 hours.
Stacking of the plates between carrier plates during curing and coking assists in preventing them from becoming warped. The linear shrinkage of the plates during coking is general~y only ~ about 1%.
When it has been cooled su~sequent to the coking operationy the neutron-absorber material according to the invention is ready for use and does not need to be machined further, except, for example, in the case of plates, to remove the edges and trim them to size. The neutron-absorber material according to the in~ention S can be manufactured in the desired shape, espe~ially in the form of thin large-area plates, and therefore such plates do not have to be prepared by sawing blocks of material.
The material according to the invention has good neutron-absorbing properties and is suitable, inter alia, for use in the manufacture of storage tanks for burnt-out fuel elements from nuclear reactors in instances where the radiation resistance of the plates is of paramount importance~ Thus, there is practically no change in the mechanical properties and particular~y no change in the dimensions when there is exposure to the action of an ionizing radiation of at least lOll rad that is, the outgassing ra~e or the quantity of gaseous material produced is extremely low and negligible in practice.
The following examples illustrate the manufacture and proper-ties of neutron-absorber material according to the invention. A11 parts and percentages are calculated ~y weight, unless oth~rwise stated.
Example l lO0 parts by weight boron carbide powder, 18 parts by weight phenolac resin powder, and 4O2 parts by weight furfural were processed into a molding compound. The boron carbide powder contained 76.5%
by weight boron and 0~5% by weight B203, with a particle size distribution of 10~/o finer than 50Jum, 99% finer than 30 ~m, 97%
finer than ~OJum, 90o/0 finer than lO~m, 75% finer than 5~lm, 5~/~
~iner than 2JumO The mixture was molded into plates of 5 mm ~hick-ness under a pressure of 30 MPa, after which the plates were curedat 180C ~or 15 hours. The plates were then coked under a protec-tive nitrogen atmosphere with a linear heating rate of up to 1000C, where the temperature was attained in 18 hours and was kept constant for 4 hours~
Properties of the plates thus o~taLned:
density: 1.71 g/cm3 boron content: 6403% by weight, corresponding to 56% by vol. boron carbide ~otal carbon content, 31.5% by weight, corresponding to 10% by vol. free carbon flexural strength: 21 ~/mm2 compression strength: 55 N/mm2 modulus of elasticity: 12000 N/mm2 lS Radiation resistance 1011 rad (no measurable change in the flexural streng~h and the dimensions)~
Exam~le 2 Mixing, pressing, curing and coking were carried out as described in Example 1.
Composition of the moulding compound~ 95 parts by weight o:E
boron carb.ide, 5 parts by weight of graphit~, 18 parts ~y weight of phenolic resin, 4.5 parts ~y weight of furfural. The boron carbide used contained 75. 6% of boron and 0~2% of B2O3O Particle si~e distribution:
96% finer -than 50 ~m, 92% finer than 30 ~m, 80% finer than 20 ~m, 60% finer than 10 ~m,
3~/O finer than 5 um, and 10% finer than 2 ~m.
As graphite, there was used a screened natural graphite f~ac-tion fir.er than 40 microns Properties of the boron carbide plates produced therefrom:
density: 1.44 g/cm3 boron content: 62D3% by weight, corresponding to 46% by volume of boron carbide;
total carbon content: 33.3% ~y weight, corresponding to l~/o by volume of free carbon;
flexural strength: 16 N/mm2;
compressive strength 36 N/mm2;
modulus of elastici~y 13,000 N/mm2;
resistance to irradiation lOll rad (no measurable changes in the di.mensions and strength).
As graphite, there was used a screened natural graphite f~ac-tion fir.er than 40 microns Properties of the boron carbide plates produced therefrom:
density: 1.44 g/cm3 boron content: 62D3% by weight, corresponding to 46% by volume of boron carbide;
total carbon content: 33.3% ~y weight, corresponding to l~/o by volume of free carbon;
flexural strength: 16 N/mm2;
compressive strength 36 N/mm2;
modulus of elastici~y 13,000 N/mm2;
resistance to irradiation lOll rad (no measurable changes in the di.mensions and strength).
Claims (11)
1. A neutron-absorber material having a volume composition of from 40 to 60% by volume of boron carbide and from 5 to 25% by volume of free carbon, the remainder being pores, said neutron-absorber material having the following properties:
a density of from 1.4 to 1.8 g/cm3, a flexural strength at room temperature of from 15 to 45 N/mm2, a compressive strength at room temperature of from 25 to 60 N/mm2, a modulus of elasticity at room temperature of from 10,000 to 20,000 N/mm2, and a resistance to ionising radiation of at least 1011 rad.
a density of from 1.4 to 1.8 g/cm3, a flexural strength at room temperature of from 15 to 45 N/mm2, a compressive strength at room temperature of from 25 to 60 N/mm2, a modulus of elasticity at room temperature of from 10,000 to 20,000 N/mm2, and a resistance to ionising radiation of at least 1011 rad.
2. A neutron-absorber material according to claim l in the form of thin large plates.
3. A process for the production of a neutron-absorber material of claim 1, which comprises forming a mixture containing from about 50 to 85% by weight of boron carbide powder containing at least 75% by weight of boron and a proportion of B2O3 of less than 0.5% by weight, and having a particle size distribution of at least 95% finer than 50 µm at least 90% finer than 30 µm at least 70% finer than 20 µm at least 50% finer than 10 µm at least 30% finer than 5 µm at least 10% finer than 2 µm, up to about 25% by weight graphite powder, from about 12 to 20%
by weight of an organic resin binder and about 3 to 5% by weight of a wetting agent; shaping the mixture under pressure at room temperature curing the resin binder at temperatures of up to 180°C; and then coking the shaped mixture with the exclusion of air at temperatures of up to approximately 1000°C, with a controlled temperature increase not exceeding 120°C/hour.
by weight of an organic resin binder and about 3 to 5% by weight of a wetting agent; shaping the mixture under pressure at room temperature curing the resin binder at temperatures of up to 180°C; and then coking the shaped mixture with the exclusion of air at temperatures of up to approximately 1000°C, with a controlled temperature increase not exceeding 120°C/hour.
4. A process according to claim 3, wherein 50 to 85% by weight of boron carbide powder 25 to 0% by weight graphite with a particle size finer than 40 µm 20 to 12% by weight of a powdered phenol-formaldehyde condensation product as a resin binder and 5 to 3% by weight of furfural as a wetting agent, are mixed homogeneously, the powder mixture thus obtained is then molded into plates of about 5 to 10 µm thickness at room tempera-ture and a pressure of 25 to 30 MPa, the plates thus formed are stacked between carrier plates of an inert material, heated to temperatures of up to 180°C to harden the resin binder, then further heated up to about 1000°C to cure the resin binder, with a temperature rise of not more than 120°C/hour and subsequently cooled over a period of about 24 hours.
5. A process according to claim 3, wherein graphite powder with a pulverulent organic resin and a wetting agent are included in the starting mixture.
6. A process according to claim 3, wherein the boron carbide has a particle size distribution in which 100% by weight of the particles are finer than 50 µm.
7. A process according to claim 3, wherein the organic resin is pulverulent at room temperature.
8. A process according to claim 7, wherein the resin is a phenolic resin.
9. A process according to claim 8, wherein the phenolic resin is a phenol formaldehyde resin selected from the group consisting of novalak resins, resole resins and mixtures thereof.
10. A process according to claim 5, wherein the graphite powder is natural graphite having a particle size distribution finer than 40 µm.
11. A process according to claim 6, wherein the boron carbide has a particle size distribution (by weight) of 100% finer than 50 µm, at least 99% finer than 30 µm, at least 97% finer than 20 µm, at least 90% finer than 10 µm, at least 75% finer than 5 µm, and at least 50% finer than 2 µm.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DE2752040A DE2752040C3 (en) | 1977-11-22 | 1977-11-22 | Neutron absorber plates based on boron carbide and carbon and process for their manufacture |
| DEP2752040.7 | 1977-11-22 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1097906A true CA1097906A (en) | 1981-03-24 |
Family
ID=6024301
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA316,397A Expired CA1097906A (en) | 1977-11-22 | 1978-11-17 | Neutron-absorber plates based on boron carbide and carbon and a process for their production |
Country Status (12)
| Country | Link |
|---|---|
| US (1) | US4252691A (en) |
| JP (1) | JPS5481315A (en) |
| BE (1) | BE872204A (en) |
| CA (1) | CA1097906A (en) |
| CH (1) | CH636470A5 (en) |
| DE (1) | DE2752040C3 (en) |
| FR (1) | FR2409582A1 (en) |
| GB (1) | GB2012096B (en) |
| IT (1) | IT1111369B (en) |
| NL (1) | NL7810877A (en) |
| NO (1) | NO144923C (en) |
| SE (1) | SE7812042L (en) |
Families Citing this family (16)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR2503695A1 (en) * | 1981-04-13 | 1982-10-15 | Commissariat Energie Atomique | Porous boron carbide pellets prodn. - by mixing carbide powder with resin binder, compressing and heating to carbonise the resin, used in nuclear reactors |
| US4635675A (en) * | 1981-10-15 | 1987-01-13 | Crosby Valve & Gage Company | Flat sided ball valve |
| US4522744A (en) * | 1982-09-10 | 1985-06-11 | Westinghouse Electric Corp. | Burnable neutron absorbers |
| US4541984A (en) * | 1982-09-29 | 1985-09-17 | Combustion Engineering, Inc. | Getter-lubricant coating for nuclear fuel elements |
| DE3403257A1 (en) * | 1984-01-31 | 1985-08-01 | Elektroschmelzwerk Kempten GmbH, 8000 München | NEUTRON ABSORBER PLATES WITH CERAMIC BINDING BASED ON BORCARBIDE AND FREE CARBON |
| US4818477A (en) * | 1984-07-10 | 1989-04-04 | Westinghouse Electric Corp. | PCI resistant fuel and method and apparatus for controlling reactivity in a reactor core |
| US4695476A (en) * | 1985-06-06 | 1987-09-22 | Westinghouse Electric Corp. | Process for coating the internal surface of zirconium tubes with neutron absorbers |
| US4744922A (en) * | 1986-07-10 | 1988-05-17 | Advanced Refractory Technologies, Inc. | Neutron-absorbing material and method of making same |
| FR2713818B1 (en) * | 1993-12-10 | 1996-01-12 | Commissariat Energie Atomique | Neutron absorbing composite material and its manufacturing process. |
| WO2001072659A1 (en) * | 2000-03-31 | 2001-10-04 | Toto Ltd. | Method for wet forming of powder, method for producing powder sintered compact, powdery sintered compact, and apparatus using powdery sintered compact |
| UA74603C2 (en) * | 2003-06-18 | 2006-01-16 | Yurii Serhiiovych Aleksieiev | Method for producing articles for protection against radiation |
| JP4812462B2 (en) * | 2006-02-27 | 2011-11-09 | 京セラ株式会社 | Boron carbide sintered body and protective member using the same |
| CN101746756B (en) * | 2009-12-15 | 2011-11-30 | 山东大学 | Boron carbide powder rich in 10B and preparation method thereof |
| US20140225039A1 (en) * | 2013-02-11 | 2014-08-14 | Industrial Technology Research Institute | Radiation shielding composite material including radiation absorbing material and method for preparing the same |
| CN103524138A (en) * | 2013-11-01 | 2014-01-22 | 张婷 | Heat radiation coating for steel heating furnace |
| CN108840681B (en) * | 2018-08-16 | 2022-01-14 | 景德镇陶瓷大学 | Nano boron carbide and preparation method thereof |
Family Cites Families (11)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CA625555A (en) * | 1961-08-15 | Duchene Jean | Flexible neutron shield | |
| LU34572A1 (en) * | 1955-08-12 | |||
| US3133887A (en) * | 1958-10-06 | 1964-05-19 | Norton Co | Neutron shields and methods of manufacturing them |
| US3153636A (en) * | 1958-10-31 | 1964-10-20 | Carborundum Co | Porous bodies of controlled densities and methods of making them |
| US3231521A (en) * | 1961-05-24 | 1966-01-25 | Carborundum Co | Neutron shielding using a composition comprising graphite, boron carbide and carbonized residue |
| GB986179A (en) * | 1962-06-18 | 1965-03-17 | Union Carbide Corp | Improvements in and relating to composites |
| FR1568883A (en) * | 1968-02-09 | 1969-05-30 | ||
| DE1901624A1 (en) * | 1969-01-14 | 1970-08-13 | Sigri Elektrographit Gmbh | Foam charcoal, process for making and using the same |
| US3810963A (en) * | 1971-10-29 | 1974-05-14 | Atomic Energy Commission | Method of preparing a syntactic carbon foam |
| US3969124A (en) * | 1974-02-11 | 1976-07-13 | Exxon Research And Engineering Company | Carbon articles |
| US4156147A (en) * | 1977-12-30 | 1979-05-22 | The Carborundum Company | Neutron absorbing article |
-
1977
- 1977-11-22 DE DE2752040A patent/DE2752040C3/en not_active Expired
-
1978
- 1978-10-18 JP JP12744678A patent/JPS5481315A/en active Granted
- 1978-11-01 NL NL7810877A patent/NL7810877A/en not_active Application Discontinuation
- 1978-11-15 US US05/960,777 patent/US4252691A/en not_active Expired - Lifetime
- 1978-11-17 GB GB7845087A patent/GB2012096B/en not_active Expired
- 1978-11-17 CA CA316,397A patent/CA1097906A/en not_active Expired
- 1978-11-20 IT IT51963/78A patent/IT1111369B/en active
- 1978-11-21 CH CH1194678A patent/CH636470A5/en not_active IP Right Cessation
- 1978-11-21 NO NO783916A patent/NO144923C/en unknown
- 1978-11-22 FR FR7832935A patent/FR2409582A1/en active Granted
- 1978-11-22 BE BE191876A patent/BE872204A/en not_active IP Right Cessation
- 1978-11-22 SE SE7812042A patent/SE7812042L/en unknown
Also Published As
| Publication number | Publication date |
|---|---|
| DE2752040A1 (en) | 1979-05-23 |
| FR2409582A1 (en) | 1979-06-15 |
| NO144923B (en) | 1981-08-31 |
| DE2752040C3 (en) | 1981-10-08 |
| JPS5481315A (en) | 1979-06-28 |
| FR2409582B1 (en) | 1982-01-22 |
| DE2752040B2 (en) | 1981-01-29 |
| GB2012096B (en) | 1982-05-06 |
| IT7851963A0 (en) | 1978-11-20 |
| SE7812042L (en) | 1979-05-23 |
| CH636470A5 (en) | 1983-05-31 |
| JPS6111399B2 (en) | 1986-04-02 |
| NO144923C (en) | 1981-12-09 |
| NL7810877A (en) | 1979-05-25 |
| BE872204A (en) | 1979-05-22 |
| US4252691A (en) | 1981-02-24 |
| NO783916L (en) | 1979-05-23 |
| GB2012096A (en) | 1979-07-18 |
| IT1111369B (en) | 1986-01-13 |
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