Patent Application
20140225039
This disclosure relates to a radiation shielding composite material, and more particularly, to a radiation shielding composite material including a radiation absorbing material.
Radiation is a process in which electromagnetic waves of the whole electromagnetic spectrum as well as energetic particles including atomic and subatomic particles travel through a medium. Radiation is largely classified into ionizing radiation and non-ionizing radiation. Neutron radiation is a type of ionizing radiation which consists of free neutrons. Compared to other types of ionizing radiation such as X-rays or gamma rays with a strong destructive force, neutron radiation may cause greater biological harm to the human body. Therefore, it is desirable to provide a neutron shielding material to shield against neutron radiation, in order to protect the safety of employees and the general public at sites where neutron radiation exists. In addition, neutron radiation may interfere with or damage electronic devices onboard aircraft when they are airborne and in contact with cosmic rays containing cosmogenic neutrons, resulting in the potential for a disastrous accident. Therefore, it is important to provide proper neutron shielding for electronics used in aviation applications.
Traditional means of shielding neutrons includes decelerating fast neutrons into slow thermal neutrons by using hydrogen atoms, and then absorbing the slow thermal neutrons by using neutron absorbing elements with relatively large neutron absorption cross sections. In order to effectively shield neutrons, it is desirable for a neutron shielding material to contain at least one material with a large quantity of hydrogen and at least one neutron absorbing element with a large neutron absorption cross section. The more hydrogen there is in the neutron shielding material, the stronger the deceleration effect is. Polyethylene (PE) is generally used in a neutron shielding member because it contains a relatively large amount of hydrogen. Examples of neutron absorbing elements include boron (B), lithium (Li), cadmium (Cd), iron (Fe), lead (Pd), and gadolinium (Ga). Boron (B) is a popular neutron absorbing element because it is easy to obtain.
A conventional method of forming a neutron shielding material includes blending a compound containing boron, such as boron oxide (B2O3) or boron carbide (B4C), into a matrix with a high hydrogen density, to form a composite material with a high neutron shielding capability. However, in such neutron shielding material, the majority of boron atoms aggregate to form clusters having a size measured in microns. There is no individual boron atom distributed between the clusters of the boron atoms, making the neutron shielding material difficult to trap incident neutrons. Therefore, the incident neutrons may penetrate through the neutron shielding material, resulting in unsatisfactory shielding performance. Improving the performance of such a neutron shielding member may require addition of a large amount of boron compound into the matrix or increasing the thickness of the composite material. However, adding a large amount of the boron compound increases costs, and thicker shielding members may not be suitable for use in certain applications such as protective clothing or protective masks.
Recent reports show that radiation shielding members including atomic scale radiation absorbing materials in the range of nanometers may improve radiation absorption performance.
According to an embodiment of the disclosure, a radiation absorbing material is provided. The radiation absorbing material includes a carrier, and a heterogeneous element attached to the carrier. A content of the heterogeneous element in the carrier is higher than 15 atomic percent (at %).
According to another embodiment of the disclosure, a radiation shielding composite material is provided. The radiation shielding composite material includes a matrix material, and a radiation absorbing material dispersed in the matrix material.
According to still another embodiment of the disclosure, a method of preparing a radiation absorbing material is provided. The method includes adding a carrier and a heterogeneous element precursor for a heterogeneous element into a solvent, and mixing the carrier and the heterogeneous element precursor in the solvent to prepare a solution; and inducing a thermal reaction between the carrier and the heterogeneous element precursor to form the radiation absorbing material in which the carrier is doped with the heterogeneous element. The thermal reaction is carried out with a reactant gas.
According to a further embodiment of the disclosure, a method of preparing a radiation shielding composite material is provided. The method includes adding a carrier and a heterogeneous element precursor for a heterogeneous element into a solvent, and mixing the carrier and the heterogeneous element precursor in the solvent to prepare a solution; heating the solution to remove the solvent, and drying the carrier and the heterogeneous element precursor to prepare a mixed powder; inducing a thermal reaction between the carrier and the heterogeneous element precursor to form a radiation absorbing material in which the carrier is doped with the heterogeneous element, wherein the thermal reaction is carried out with a reactant gas containing an inert gas and an etching gas; mixing the radiation absorbing material with a matrix material to prepare a mixture; and processing the mixture to form the radiation shielding composite material.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.
The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description, serve to explain principles of the invention.
Reference will now be made in detail to the present embodiments, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts.
The disclosed embodiments provide a radiation shielding composite material.
Matrix material 120 includes polymer, ceramic material, metal, alloy, fiber, cellulose, silicon oxide (SiO2), and silicon. The polymer matrix material includes at least one of polyvinylalcohol (PVA), polyethylene (PE), high density polyethylene (HDPE), low density polyethylene (LDPE), polymethyl methacrylate (PMMA), ethylene-vinyl acetate (EVA), epoxy, and rubber. The metal matrix material includes at least one of stainless steel, aluminum (Al), titanium (Ti), zirconium (Zr), Scandium (Sc), yttrium (Y), cobalt (Co), chromium (Cr), nickel (Ni), tantalum (Ta), molybdenum (Mo), and tungsten (W).
Radiation absorbing material 110 is dispersed in matrix material 120 by homogenization methods including at least one of blending, mixing, compounding, ultrasonucation-assisted homogenization, ball milling, milling, and jet milling.
Radiation Absorbing Material
As described above, radiation absorbing material 110 includes a carrier 130 and a heterogeneous element 140 doped in carrier 130. Carrier 130 may include at least one of zero dimensional (0D), one dimensional (1D), two dimensional (2D), and three dimensional (3D) materials. Examples of 0D nano materials include carbon black and quantum dots. A 1D nano material may have a structure of nanowire, nanorod, nanotube, or nanofiber. Examples of 1D nano materials include carbon nanowire, single-walled carbon nanotube (SWCNT), double-walled carbon nanotubes (DWCNT), multi-walled carbon nanotube (MWCNT), carbon nanofiber, and any other inorganic nanowire such as silicon nanowire. The average length of the 1D nano material may be about 0.01 μm to 100 μm, and the average diameter of the 1D nano material may be about 1 nm to 100 nm. A 2D nanomaterial may have a structure of sheet, film, or plate. Examples of 2D nano materials include graphene, graphene oxide, reduced graphene oxide, diamond film, and silicon dioxide (SiO2) film. Examples of 3D nano materials (i.e., bulk materials) include graphite, diamond, and silicon wafer. Carrier 130 may be made from at least one material of carbon (C), silicon (Si), mesoporous material, polymer, ceramics, metal, ionic salts, or any other materials. In an embodiment, heterogeneous elements can be doped in a carrier with a doping rate higher than 15 atomic percent (at %). In another embodiment, heterogeneous elements can be doped in a carrier with a doping rate higher than 25 atomic percent (at %). In still another embodiment, heterogeneous elements can be doped in a carrier with a doping rate higher than 32.15 atomic percent (at %). Heterogeneous elements can be doped in a Si system, such as SiO2 film or Si wafer, with a doping rate higher than 10 atomic percent (at %).
Heterogeneous element 140 is a radiation absorbing element having a relatively large radiation absorption cross section. Heterogeneous element 140 may include a metal selected from a group of boron (B), lithium (Li), gadolinium (Gd), samarium (Sm), europium (Eu), cadmium (Cd), dysprosium (Dy), lead (Pb), iron (Fe), nickel (Ni), and silver (Ag). Heterogeneous element 140 may have a size in a range of about 0.05 nm to several tenths of nanometers.
In some embodiments, carrier 130 is made from carbon, and heterogeneous element 140 is boron. The molar ratio of boron to carbon in radiation absorbing material 110 may be in the range of about 0.1 to about 100. In addition, radiation absorbing material 110 may have a boron content of about 0.01 at % to about 50 at %.
Heterogeneous element 140 may be doped in carrier 130 in two types: intercalation and substitution. Intercalation occurs when clusters of atoms of heterogeneous element 140 are trapped or inserted between layers of two-dimensional carrier 130.
Substitution occurs when at least one atom of carrier 130 is replaced by an atom of heterogeneous element 140, thus forming a chemical bond between other atoms of carrier 130 and the atom of heterogeneous element 140.
Besides doping, heterogeneous element 140 may be attached to carrier 130 by functionalization in which an atom of heterogeneous element 140 can be attached to the atoms of carrier 130. Functionalization methods include covalent bonding, non-covalent functionalization, and absorption.
In a method of covalent bonding, chemical covalent bonds are formed between an atom of heterogeneous element 140 and the atoms of carrier 130. Normally, a carrier oxidation and a subsequent redox reaction can be used for this purpose. First, a treatment of carrier 130, such as carbon nanotubes, with strong oxidizing agents such as nitric acid, KMnO4/H2SO4, and oxygen gas, tends to oxidize carrier 130 and subsequently generate oxygenated functional groups on the surface of carrier 130. These oxygenated functional groups are chemically active moieties and can be used as further chemical activation sites to bond atoms of heterogeneous element 140 via a redox reaction. Hence the second step is to induce the redox reaction between reactive chemical compounds composed with atoms of heterogeneous element 140 such as salts with the oxidized carrier.
In a method of non-covalent functionalization by π-interactions, functional groups are attached to carrier 130 without disturbing an electronic network of carrier 130. When the countermolecule in heterogeneous element 140 is a metal cation in the π-interactions, a combination of electrostatic and induction energies dominate the cation-π interaction. Various kinds of receptors such as Na+, Ag+, Li+, and Fe2+ with strong binding energies and high selectivities for metal cations utilizing the cation-π interactions have been designed.
In a method of absorption, metal nanoparticles of heterogeneous element 140 are attached to carbon-based carrier 130 by direct reduction of melt precursors such as metal salts with or without reducing agents.
Method of Preparing Radiation Absorbing Material
When heterogeneous element 140 is boron, the boron may be made from at least one of a solid boron precursor, a liquid boron precursor, and a gaseous boron precursor. Examples of the solid boron precursor include boron oxide (B2O3), boron carbide (B4C), boron nitride (BN), boric acid (H3BO3), and any other compound containing boron. Examples of the liquid boron precursor include aqueous solution of boric acid (H3BO3 (aq)), triethyl borate (C6H15BO3), and the like. Examples of the gaseous boron precursor include triethylborane ((C2H5)3B), boron trichloride (BCl3), diborane (B2H6), and the like.
When the solid boron precursor is boron oxide (B2O3), the reaction between the boron oxide (B2O3) and the carbon nanotube is represented by the following equation:
xB2O3+(2+3x)CCNT→2BxCCNT+3xCO
where CCNT represents the carbon nanotube, and x is an integer larger than or equal to 0.
The process of preparing radiation absorbing material 110 begins with a pretreatment process 510 for pretreating raw materials including the solid boron precursors and pristine carbon nanotubes. The molar ratio of boron and carbon in the raw materials can be between 1 and 10. The pristine carbon nanotubes are hydrophobic and tend to bundle together due to a strong Van der Waal force. The bundling of the pristine carbon nanotubes may reduce a contact area between the carbon nanotube and the boron precursor, thus reducing a doping rate of boron in the carbon nanotubes. The purpose of pretreatment process 510 is to increase the contact area between the carbon nanotube and the boron precursor.
During pretreatment process 510, the solid boron precursors are first dissolved into a solvent. The solvent includes at least one of water, an organic solvent, and an ionic liquid. The solvent may be heated or unheated. Next, the pristine carbon nanotubes are added into the solvent. In some embodiments, before adding the carbon nanotubes into the solvent, the carbon nanotubes may be modified to become hydrophilic, increasing the contact area between the carbon nanotubes and the boron precursors. In some other embodiments, a dispersant may be added into the solvent. After the pristine carbon nanotubes are added into the solvent, the pristine carbon nanotubes and the boron precursors are mixed evenly in the solvent. The pristine carbon nanotubes and the boron precursors are mixed in the solvent by at least one mixing method of co-sonication, impregnation, and co-precipitation. Then, the solution containing the pristine carbon nanotubes and the boron precursors is heated to remove excess solvent. Last, the carbon nanotubes and the boron precursors are filtered and dried into a mixed powder.
Referring back to
In some embodiments, the mixed powder of the carbon nanotubes and the boron precursors is placed in a reactor 700 as shown in
Chamber 710 may be made of alumina, and may have a diameter of about 50 mm. The mixed powder is placed in a boat 760, which is then placed inside chamber 710. Gas supply port 720 supplies a reactant gas including an inert gas and about 0 to 20% of an etching gas into chamber 710. Examples of the inert gas include argon (Ar), hydrogen (H2), or nitrogen (N2). Examples of the etching gas include ammonia (NH3), or any other gas that can etch carbon nanotube. The etching gas creates vacancy defects on the crystalline lattice of the carbon nanotube, and these vacancies may be later doped with boron atoms. The element of the etching gas such as nitrogen may be doped in the carbon nanotube. Typically nitrogen and boron are both doped in the carbon nanotube with a molar ratio close to 1:1. When the carbon nanotube is doped with both boron and nitrogen, the BxCyNz structure allows higher boron doping. Gas discharge port 730 discharges a reaction by-product gas generated by the carbon thermal reaction.
Upper heater 740 and lower heater 750 are configured to preheat chamber 710 from room temperature to a reaction temperature. The preheating rate may be 5° C./min. Upper heater 740 and lower heater 750 are also configured to heat chamber 710 to a reaction temperature of at least 900° C. for a predetermined period of time to allow for sufficient reaction between the carbon nanotubes and the boron precursors. In addition, the reaction is conducted at atmospheric pressure.
Referring back to
After cooling process 530, a cleaning process 540 is performed. During cleaning process 540, the product generated in reaction process 520 is cleaned to remove unreacted raw materials. In some embodiment, the cleaning process may be omitted, because the unreacted raw materials contain boron, which still has neutron absorption properties, and thus the unreacted raw materials may be included in the radiation shielding composite material together with the radiation absorbing material. As a final product of the reaction, the radiation absorbing material in which boron is doped in the carbon nanotubes, is generated.
Radiation Shielding Composite Material
Referring back to
In some embodiments, radiation shielding composite material 100 may also include one or more of dispersants, surfactants, rheological agents, and anti-settling agents. The content of radiation absorbing material 110 in radiation shielding composite material 100 is in the range of about 0.01 wt % to about 50 wt %. Radiation absorbing material 110 is dispersed homogeneously throughout matrix material 120 to form a network structure, increasing the performance of radiation absorption by radiation shielding composite material 100. In another embodiments, the content of radiation absorbing material 110 in radiation shielding composite material 100 is less than 20 wt %.
Radiation shielding composite material 100 may be applied as construction material for operating rooms in hospitals. In such case, radiation shielding composite material 100 may be formed in a plate shape having a thickness in the range of about 3 cm to about 5 cm. Alternatively, radiation shielding composite material 100 may be applied as a coating layer on a substance to be protected by radiation shielding composite material 100. In such case, radiation shielding composite material 100 may have a thickness in the range of about 0.01 μm to about 100 μm. Still alternatively, radiation shielding composite material 100 may be applied as a soft composite material in the form of a thin film. In such case, the thin film material made of radiation shielding composite material 100 may have a thickness in the range of about 0.01 cm to 0.1 cm.
Method of Preparing Radiation Shielding Composite Material
In one embodiment, radiation shielding composite material 100 may be prepared by mixing matrix material 120 with radiation absorbing material 110, and then thermally compressing the mixture to form radiation shielding composite material 100. The parameters of the mixing process, such as the temperature, rotational speed, and duration, can be modified to adjust the dispersion and compatibility of radiation absorbing material 110 in matrix material 120. Besides thermal compression, the mixture may be subjected to injection molding, blow molding, compression molding, extrusion, extrusion casting, laminating, foaming, coating, paste formulating, casting, fiber spinning/drawing, spraying, cell casting, and alloying to form radiation shielding composite material 100.
In another embodiment, matrix material 120 may be thermally compressed, and then radiation absorbing material 110 may be formed as a layer on at least one side of the compressed matrix material 120 by using coating, injecting, laminating, dipping, scrape-coating, or spraying.
In still another embodiment, when matrix material 120 is a metal or an alloy, radiation shielding composite material 100 may be prepared by mixing matrix material 120 with radiation absorbing material 110, and then smelting or thermally compressing the mixture to form radiation shielding composite material 100.
In some embodiments, the mixture is thermally compressed to form radiation shielding composite material 100. In addition, before processing the mixture to form the radiation shielding composite material, certain additives may be added into the mixture. The additives may include at least one of dispersants, surfactant, rheological agents, and anti-settling agents.
A further understanding of the disclosure may be obtained through the following examples, which are set forth to illustrate, but are not to be construed to limit the present invention.
Preparation of Boron Doped Carbon Nanotubes
For a sample preparation without a pretreatment process, boron oxide (B2O3) powder and pristine multi-walled carbon nanotubes (MWCNT) are mixed together evenly to prepare a reactant. The molar ratio of boron and carbon in the reactant can be between 1 and 10. If the molar ratio of boron and carbon is less than 1, boron cannot be effectively doped in the MWCNTs. If the molar ratio is higher than 10, most boron are wasted due to insufficient MWCNTs.
For a sample preparation with a pretreatment process, the pretreatment process is conducted firstly by dissolving B2O3 in de-ionized water at 80° C. Then, pristine MWCNTs are slowly added into the de-ionized water to form a slurry-like solution. The molar ratio of boron and carbon in the slurry-like solution can be between 1 and 10. The solution is continuously mixed evenly using magnetic stirring at 450 rpm. Then, the solution containing the pristine MWCNT and B2O3 is heated to remove excess water. Last, the mixture is filtered and dried at 60° C. to prepare a reactant in the form of a mixed powder.
In both cases of preparing boron doped carbon nanotubes with and without the pretreatment process, the molar ratio of boron to carbon in the reactant is within a range from 3 to 7. The mixed reactant is then transferred to an alumina boat and a reaction takes place in a reaction chamber at a high temperature. The reaction temperature is controlled in a range from 900° C. to 1200° C. Argon or an ammonia/argon mixture is used as a reactant gas. The duration of the reaction is controlled to be 4 hours. Following the reaction, the un-reacted boron oxide is washed from the product by using hot water, and then the product is filtered and transferred to a dryer and dried at 60° C. Table 1 summarizes samples 1 through 29 prepared via different reactions having different reaction conditions.
X-ray photoelectron spectroscopy (XPS) is utilized to determine the atomic concentration of boron in samples 1-29, and the results are summarized in Table 1, and shown in
X-ray photoelectron spectroscopy (XPS) is also utilized to determine the doping type of boron in the carbon nanotubes in the samples.
Generally, the location of the peaks in XPS spectra may determine the doping type of boron in the carbon nanotube. Peaks exhibited in the binding energy range of 190 eV and 194 eV indicates that boron is doped in the carbon nanotube by substitution doping. Peaks exhibited in the binding energy range of 186 eV and 190 eV indicates that boron is doped in carbon by intercalation doping. As shown in
Electron energy loss spectroscopy (EELS) is further utilized to determine the presence of boron substitution.
As explained previously, intercalation occurs when clusters of boron atoms in the order of about 0.1 nm to 1 nm are inserted between layers of the carbon nanotube, and substitution occurs when at least one carbon atom of the carbon nanotube is replaced by a boron atom. Therefore, boron is dispersed more homogeneously in the carbon nanotube by substitution than by intercalation, and thus the radiation absorbing material formed by boron substitution has better radiation absorbing efficiency.
Preparation of Boron Doped Nanomaterials
The preparation method is the same as Example 1, except that various carriers are used, instead of the MWCNT. Table 2 summarizes samples 30 through 35 prepared with different nanomaterials as the carriers.
Sample 30, 33, 34 and 35 show very high B content above 30 at %, which should be useful for neutron absorbing and shielding applications.
Preparation of Radiation Shielding Composite Material Including Boron Doped Carbon Nanotube
A twin screw compounder is used to mix a polymer matrix and samples 16 and 28 prepared in Example 1, respectively, to prepare a first mixture and a second mixture. The polymer matrix is high density polyethylene (HDPE). The mixing duration is 5 minutes. The screw of the twin screw compounder rotates at 75 rpm. The mixing temperature is 180° C. The estimated weight percentage of boron in the first mixture is about 0.25%. The estimated weight percentage of boron in the second mixture is 1.44%. Each one of the first and second mixtures is then thermally compressed to form a radiation shielding composite material in the form of a plate with a thickness of 3 mm. The results are sample 36 made from sample 16, and sample 37 made from sample 28.
Preparation of Boric Acid Absorbed Carbon Nanotube
A commercially available boron oxide (B2O3) powder is dissolved in hot water at 80° C. to form a boric acid aqueous solution. Multi-walled carbon nanotubes (MWCNT) are then mixed into the solution and the mixture is stirred continuously for 30 minutes. The molar ratio of boron oxide to carbon nanotube is 5. The heating at 80° C. is continued until the water evaporates and the mixture becomes a slurry. The slurry is then placed into a dryer and dried at 80° C. to form a dry powder. The dry powder is examined by scanning electron microscope (SEM) to ensure that there are no boron oxide particles and that only carbon tubes in a tubular structure are present. X-ray diffraction results show that boric acid (H3BO3) is present, and that the graphite sp2 (002) peak, the (002) peak of the product, and the pristine carbon tube (002) peak position are the same. This result confirms that there is no lattice structure of boron doped carbon tube, and thus in the product, boric acid has been absorbed to the carbon tubes.
Preparation of Radiation Shielding Composite Material Including Boric Acid Absorbed Carbon Nanotube
The preparation method is the same as Example 3, except that the boric acid absorbed carbon nanotubes prepared in Example 4 is used, instead of the boron doped carbon nanotubes. The result is sample 38.
Preparation of Radiation Shielding Composite Material Including Boron Oxide Particles
The preparation method is the same as Example 3, except that various amounts of boron oxide particles are used, instead of the boron doped carbon nanotubes. The boron oxide particles are 200 to 500 microns in size. The results are samples 39 and 40.
Preparation of Radiation Shielding Composite Material Including Carbon Nanotubes
The preparation method is the same as Example 3, except that pure carbon nanotubes are used, instead of the boron doped carbon nanotubes. The result is sample 41.
Preparation of Radiation Shielding Composite Material Including Only Matrix Material
The preparation method is the same as Example 3, except that no boron doped carbon nanotube is added. The resultant is sample 42.
Table 2 summarizes the preparation conditions for the radiation shielding composite materials (samples 36-39) prepared in Examples 2 and 5 and Comparative Example 1.
The neutron attenuation rate may be represented by the following equation:
wherein t is the thickness of the plate made from the composite material, and Σth is the macroscopic neutron absorption cross section. For each sample, Σth may be calculated based on the slopes of the corresponding line.
Based on macroscopic neutron absorption cross section Σth, a specific macroscopic neutron absorption cross section, specific Σth, for the composite material may be calculated according to the following equation:
The specific macroscopic neutron absorption cross section is a characteristic parameter for a specific neutron shielding material, and indicates how well the neutron shielding material can absorb neutrons. Generally, the higher the specific neutron absorption cross section of a specific neutron shielding material, the better the neutron shielding performance.
Table 3 summarizes the macroscopic neutron absorption cross sections and the specific neutron absorption cross sections of samples 36-40. According to Table 3, the radiation shielding performance of samples 36 and 37 prepared according to the embodiments of the disclosure is superior to that of samples 38, 39 and 40.
Brunauer-Emmett-Teller (BET) method is used to measure surface area of a boron doped carbon nanotube prepared according to an embodiment of the disclosure, carbon nanotube, and boron oxide. Table 4 summarizes the results of the different materials.
Generally, when the surface area of a neutron absorbing material is larger, there is an increased chance of collision between the boron atoms and the neutrons, which is favorable for capturing and absorbing the neutrons. According to Table 4, the boron doped carbon nanotube prepared according to the embodiment has a larger BET surface area than other material, and thus would have superior neutron absorbing performance.
American Society for Testing and Materials (ASTM) D638 method is used to measure mechanical properties of radiation shielding composite materials. The results are summarized in Table 5.
Generally, the presence of carbon nanotubes improves the mechanical properties of the radiation shielding material, making it suitable as building material for operating rooms in hospitals. However, the presence of boron oxide lowers the tensile strength of the radiation shielding material. According to Table 5, the radiation shielding material includes the boron doped carbon nanotubes as the radiation absorption material, which has mechanical properties superior to those of other radiation shielding materials.
The above-described embodiments provide a radiation shielding composite material including a radiation absorbing material, and a method of preparing the radiation shielding composite material. The method allows the atoms of the radiation absorbing element (e.g., boron) to replace the carbon atoms in the surface lattice of the carbon material, and to form a stable bond with the adjacent non-substituted carbon atoms, resulting in an atomic scale radiation absorbing material.
The radiation shielding composite material prepared according to the embodiments of the present disclosure has the following advantages. First, the radiation absorbing element (e.g., boron) is distributed in its atomic state throughout the radiation shielding composite material, thus reducing the chance of radiation leakage. Second, the substitution reaction produces a stable covalent bond which increases the durability of the radiation shielding composite material. Third, the carbon carrier material features a high specific surface area which increases the chances of contact with the radiation particle (e.g., neutron), thus increasing the chance of radiation absorption by the radiation absorbing element (e.g., boron). Fourth, carbon material is pliable, and features light mass and low density, making it suitable for use in pliable radiation shielding members light in mass, thus increasing its range of applications. Fifth, the mechanical properties of carbon material are excellent, in that they enhance the mechanical properties of the radiation shielding composite material and improve durability. Sixth, carbon atoms have a light mass, and graphite is a good neutron moderating material, thus increasing the overall neutron shielding action in shielding members. Last, the surface of carbon carrier material is non-polar, and the HDPE matrix material is also non-polar, making for excellent compatibility between the two so that the dispersion of the carbon carrier material in the HDPE matrix material can be uniform.
Other embodiments of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the invention being indicated by the following claims.
The radiation absorbing materials described herein can also be utilized in applications in addition to the radiation shielding applications, such as hydrogen storage applications, electrochemical sensor applications, neutron detector applications, electro materials for Li-ion battery applications, fuel cell oxygen reduction reaction applications, electro materials for supercapacitor applications, organic/oil clean up process, water purification process, catalyst support applications, scaffold support for tissue engineering and cell growth, mechanical sensor applications, materials of transparent conduction film applications, radiation hardening packaging for electronics, energy harvesting applications, building materials of nuclear medicine operation room, coatings or films for nuclear medicine therapy, and flexible/pliable/bendable materials. The radiation absorbing material may have a thickness in a range of 1 cm to 5 cm for the application of building materials of nuclear medicine operation room. The radiation absorbing material may have a thickness in a range of 0.01 μm to 10 μm for the application of coatings or films for nuclear medicine therapy. The radiation absorbing material may have a thickness in a range of 0.01 cm to 0.5 cm for the application of flexible/pliable/bendable materials.
In addition, the mechanical robustness of the radiation absorbing materials constructed according to the disclosed embodiments may be changed or altered in view of the desired application. For instance, a matrix such as polymers or metals may be used to form a composite as discussed above. In some embodiments, the radiation absorbing material may be self-sufficient for the desired application.
The examples provided herein are to more fully illustrate some of the embodiments of the present invention. It should be appreciated by those of skill in the art that the techniques disclosed in the examples above represent techniques discovered by the inventors to function well in the practice of the invention, and thus can be considered to constitute exemplary modes for its practice. However, those of skill in the art should, in light of the present disclosure, appreciate that many changes can be made in the specific embodiments that are disclosed and still obtain a like or similar result without departing from the spirit and scope of the invention.
This application claims benefit of U.S. Provisional Application No. 61/763,178, filed on Feb. 11, 2013, the disclosure of which is incorporated herein by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 61763178 | Feb 2013 | US |
