Patent Application
20070102672
The present invention relates to the field ceramics and particularly to a cold fired zeolite (alumino-silicate) containing ceramic having radiation shielding characteristics.
Radiation containment and shielding, including radiation shielding and electromagnetic shielding, is of increasing importance in a technologically advanced society. While nuclear power generation offers an alternative to fossil fuel energy sources, containment of waste materials currently raise the expense thereby decreasing the overall economic feasibility of generating power. Other low level radioactive materials such as medical wastes, industrial wastes, wastes from depleted uranium ordinance, and the like also experience the same storage, shielding, and containment issues. Additionally, the proliferation of electronic devices has increased the need to provide effective electromagnetic shielding. Electronic devices such as cellular telephones, microwave ovens, and the like may require electromagnetic energy shielding which blocks radiated energy from being directed towards the user. The medical diagnostic field also makes extensive use of radioactive materials to aid in detection of human maladies. The utilization of x-rays and other forms of radioactive material to detect these problems has provided doctors with valuable insight into the patient's medical condition. Drawbacks to these diagnostic methods include the shielding necessary to protect the patient and medical personnel from unwanted exposure from radiation and other forms of electromagnetic energy. Currently, radioactive medical diagnostics make extensive use of lead as a shielding material. For example, a patient may wear a lead lined vest to minimize exposure during an x-ray. The x-ray machine itself may require significant shielding, such as provided by lead sheeting, to prevent undue human exposure to radioactive materials. Metallic lead shielding is extensively utilized because it allows for efficient shielding without unduly consuming space. For example, a sheet of lead less than one inch thick may be implemented to shield an x-ray machine. Lead shielding drawbacks include the mass of lead, the difficulty in forming structures for holding the lead sheeting in place, the desire for aesthetically pleasing structures, and the like.
Utilization of cementitious materials to contain and shield radioactive materials is evidenced by U.S. Pat. No. 6,565,647, entitled: Cementitious Shotcrete Composition, which is hereby incorporated by reference in its entirety, may be problematic as concrete based systems implement weak hydrogen bonding (in comparison to ionic bonding and covalent bonding). Also these systems suffer from high levels of porosity (in comparison to other matrices such as a polymeric based material) and cracking issues. The exothermic hydrolysis reaction which occurs in a Portland cement curing may cause difficulties in waste containment situations. Portland cement structures also require quite massive wall structures to effectively shield radioactive radiation. For instance wall thicknesses of over one foot thick, which may be required for proper shielding in some medical environments, may hinder the utilization of cementitious based shielding and containment systems due to their size, mass and generally inferior ability to shield radioactive energy without additives included for this purpose. For example, in a medical diagnostic situation, cement based shielding may require additional building supports thereby preventing retrofitting without extensive reconstruction. Portland cement matrices also require extensive curing (twenty-one days) to ensure proper matrix formation. Other alternatives such as a polymeric based matrix may offer lower porosity but, may degrade when exposed to organic solvents and either high or low pH materials. Cement matrices also are susceptible to corrosive attack from a variety of materials typically found in radioactive wastes.
Fired or high temperature curing ceramic materials (such as over several hundred degrees Celsius) do not offer a viable alternative to cement structures. High curing temperatures may prevent the materials from being utilized in waste containment and shielding applications as high temperature firing (above several hundred degrees Celsius) requires the components be formed and fired in a remote location prior to transport and assembly in the desired location. High temperature cured ceramics may not be practical for forming large components due to the firing requirements. In-situ formation of fired ceramics for waste containment may be problematic because of the wastes being contained and the location of final storage. Ammonia may be liberated during the firing process. Inclusion of ammonia in the ceramic matrix may be detrimental to the resultant formation. While experiencing the foregoing drawbacks, ceramic structures may form low porosity structures in comparison to Portland cement structures.
Cold fired ceramic materials such as evidenced in U.S. Pat. No. 5,830,815, entitled: Method of Waste Stabilization via Chemically Bonded Phosphate ceramics, which is hereby incorporated by reference in its entirety, offer low porosity, low mass, and low wall thickness (all in comparison to cement materials). Phosphate bonded ceramics may be formed at or near ambient temperatures (under one hundred degrees Celsius) via an exothermic reaction. Phosphate bonded ceramics also may offer some radiation shielding due to the ceramic matrix itself. The foregoing patent discloses a method of utilizing a magnesium oxide in combination with a phosphoric or other acid phosphate to generate a resultant magnesium phosphate composition (in the present example a tri-hydrated form). In an exemplary embodiment, the following magnesium oxide/phosphoric acid reaction may be characteristic:
MgO+H3PO4+H2O→MgHPO4.3H2O
Other contemplated metal oxides included aluminum oxides, iron oxides, calcium oxides. Minimizing the pH of the reaction, in comparison to a phosphoric acid (i.e., a more basic reaction) may be achieved through utilization of a carbonate, bicarbonate, or hydroxide of a monovalent metal reacting with the phosphoric acid prior to reacting with the metal oxide or metal hydroxide. Other contemplated metals (M′) being potassium, sodium, and lithium. A partial exemplary reaction being:
H3PO4+M2CO3+M′Oxide→M′HPO4
Additionally the utilization of a dihydrogen phosphate utilizing to form the ceramic at higher pH (in comparison to the utilization of phosphoric acid) was also indicated:
MgO+LiH2PO4+nH2O→MgLiPO4.(n+1)H2O
Other suitable monvalent metal dihydrogen phosphates being sodium dihydrogen phosphate and potassium dihydrogen phosphate. Each being utilized in a hydrated form.
An additional reference evidenced in United States Patent Application Publication 2002/0165082, entitled: Radiation Shielding Phosphate Bonded Ceramics Using Enriched Isotopic Boron Compounds, which is hereby incorporated by reference in its entirety, discloses the utilization of boron compound additives for phosphate bonded ceramics for increased shielding of phosphate bonded ceramics.
Therefore, it would be desirable to provide a cold fired phosphate bonded zeolite ceramic having radiation shielding characteristics.
Accordingly, the present invention is directed to a phosphate bonded ceramic including a zeolite with radiation shielding characteristics for containment, electromagnetic shielding, attenuation of electromagnetic energy, and construction applications.
In an aspect of the present invention, a composition of matter and method of forming a radiation shielding member at ambient temperatures in which the composition of matter includes a phosphate bonded ceramic, a radiation shielding material dispersed in the phosphate bonded ceramic matrix is disclosed.
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 the specification, illustrate an embodiment of the invention and together with the general description, serve to explain the principles of the invention.
Reference will now be made in detail to the presently preferred embodiments of the invention. The present invention is directed to a composition of matter and method for forming a radiation shielding member at ambient conditions. Those of skill in the art will appreciate the composition of matter of the present invention may be utilized for shielding and attenuation of various forms of radiation included in the electromagnetic spectrum from alpha, beta, or gamma emissions; microwaves; energy from electron-beam welding (bremsstrahlung radiation or secondary radiation) and the like.
The composition of matter and method provides an efficient composition for utilization in constructing members which exhibit radiation shielding capability in a region of the electromagnetic spectrum. The resultant material may be formed at ambient conditions in a rapid time frame (two days curing to one-half hour of curing). This allows for formation of a phosphate bonded ceramic matrix with radiation shielding inclusion materials without the high temperature firing typically required. Typical high temperature firing may exceed several hundred degrees Celsius and usually may occur in the range about 1800° C. (one thousand eight hundred degrees Celsius). While the present method of cold firing (curing at ambient temperatures) may occur at or below 100° C. (one hundred degrees Celsius). The foregoing may allow for in-situ formation of a member such as a shielding structure or efficient transportation and installation of a preformed panel or structure formed of the composition of matter in comparison to other radiation shielding materials. For example, a structure formed in accordance with the present invention may allow for a fully cured wall partition to be formed in the time frame of several days. A wall partition formed in the foregoing manner may be less massive then a Portland concrete system. The utilization of a phosphate bonded ceramic material of the present invention may minimize the mass and size (i.e., thickness) required for a shielding component over a Portland concrete based matrix (for the same effective shielding) as disclosed in U.S. Pat. No. 6,565,647.
A composition of matter of the present invention implements a phosphate bonded ceramic material to form a matrix for including additional radiation shielding material therein. A phosphate bonded ceramic matrix may be formed by the incorporation of a metal oxide with a phosphates containing substance or material. Those of skill in the art will appreciate that the resultant phosphate ceramic may be a hydrated form based on the constituent metal phosphate. Suitable metal oxides may include metal oxides in which the cationic component is associated with radiation shielding such that the resultant metal phosphate ceramic may exhibit radiation shielding capability. Suitable phosphate containing substances or materials include phosphoric acid, an acid phosphate, monohydrogen phosphates, dihydrogen phosphates and the like. Suitable oxides include magnesium, iron(II or III), calcium, bismuth, cerium(III or IV), barium, depleted uranium(III) (substantially uranium 238), or aluminum.
The resultant phosphate ceramics may include MgHPO4.3H2O (magnesium hydrogen phosphate trihydrate), MgHPO4 magnesium hydrogen phosphate, Fe3(HPO4)2 (iron(II) phosphate), Fe3(HPO4)2.8H2O (iron(II) phosphate octahydrate), FeHPO4 (iron(III) phosphate), FeHPO4.2H2O (iron(III) phosphate dihydrate) AlPO4 aluminum phosphate, AlPO4.1.5H2O (aluminum phosphate hydrate), CaHPO4 (calcium hydrogen phosphate), CaHPO4.2H2O (calcium hydrogen phosphate dihydrate), BiPO4 (bismuth phosphate), CePO4 (cerium(III) phosphate), CePO4.2H2O (cerium(III) phosphate dihydrate), BaHPO4 (barium hydrogen phosphate), and UPO4 (depleted uranium (U-238) phosphate). In further instances, different metal phosphates/hydrogen phosphates may be implemented as well. Suitable multiple metal phosphates may include magnesium hydrogen phosphate, iron(III) phosphate, aluminum phosphate, calcium hydrogen phosphate, bismuth phosphate, cerium(III) phosphate, and barium hydrogen phosphate. In an embodiment the ceramic matrix is of the formula: ceramic matrix is of the formula: MHPO4.xH2O in which M is a divalent cation selected from the group consisting of: Mg (magnesium), Ca (calcium), Fe (iron(II)), and Ba (barium); wherein x is at least one of 0 (zero), 2 (two), 3 (three), or 8 (eight). In a further example, the phosphate based ceramic matrix is of the formula: MPO4.xH2O in which M is a trivalent cation selected from: Al (aluminum), Ce (cerium (III)), U238 (depleated uranium) ; and Fe (iron(III)); and x is at least one of 0 (zero), 1.5 (one point five), or 2 (two). In further embodiments, a multiple layer structure is formed to provide effective attenuation across a range of kilovolt-peak (kVp) ranges. For example, a multiple layer material is formed via a casting or spray application to form a mono structure exhibiting shielding and attenuation across a range. The layers may be formed of differing combinations of ceramics/shielding materials to achieve the desired shielding/attenuation. For example, a first layer is formed with a bismuth shielding material while a second layer is formed of a cerium based ceramic. A third layer of a ceramic including a barite shielding material may be included as well. In the present example, cerium oxide is included for its attenuation X-rays at 120 kVp at a material thickness of 0.5 inches. Greater material thickness may effectively attenuate x-radiation at higher levels of energy.
In embodiments, suitable radiation shielding materials may be dispersed in the matrix. Those of skill in the art will appreciate that combinations of shielding materials may be incorporated in a matrix to provide attenuation across a portion of the electromagnetic spectrum, such as X-rays, microwaves, and the like regions or portions of regions of the electromagnetic spectrum. Examples include powders, aggregates, fibers, woven fibers and the like. Exemplary materials include barite, barium sulfate, bismuth metal, tungsten metal, annealed leaded glass fibers and powders, cerium oxide, zeolite, clinoptilotite, plagioclase, pyroxene, olivine, and celestite. A zeolite may be approximately by weight percentage 52.4% (fifty two point four percent) SiO2 (silicon dioxide), 13.13% (thirteen point one three percent) Al2O3 (alumina oxide), 8.94% (eight point nine four percent) Fe2O3 (ferric oxide), 6.81% (six point eight one percent) CaO (calcium oxide), 2.64% (two point six four percent) Na2O (sodium oxide), 4.26% (four point two six percent) MgO (magnesium oxide). While barite may be approximately 89% (eighty nine percent) BaSO4 (barium sulfate) and 5.8% (five point eight percent) silicates with the remainder consisting of naturally varying percentages of titanium dioxide, calcium oxide, magnesium oxide, manganese oxide, and potassium oxide. The foregoing approximation being dependent on naturally occurring weight percentage variations.
In an exemplary embodiment, a method of constructing a shielding member includes mixing a metal oxide, such as a metal oxide including divalent metal cation with a phosphate containing material. Suitable phosphate containing materials include phosphoric acid, hydrogen phosphate substances (such as monohydrogen phosphates and dihydrogen phosphates) and the like. A radiation shielding material may be incorporated into the metal oxide and phosphate containing material mix. Incorporating may include dispersing aggregate, powder, fibers. Woven fibers may be incorporated as part of a casting process, a layering process, or the like. The incorporated radiation shielding material and metal phosphate ceramic may be cured to hardness (maximum compressive strength) at ambient conditions. For example, the member may be cast in place and the curing reaction being conducted at ambient conditions (i.e., ambient temperature). In an embodiment, the reaction and curing of the radiation shielding member occurs at or at less than 100° C. (one hundred degrees Celsius). Those of skill in the art will appreciate that the porosity of the resultant member may be varied based on the reagents selected.
In a specific embodiment, a radiation shielding member composed of a composition of matter of the present invention is constructed by mixing 1 lb. (one pound) of a metal oxide and monopotassium phosphate mixture with 1 lb. (one pound) of radiation shielding mater such as a aggregate, powder, fiber filler material, H2O (water) is added to approximately 20% (twenty percent) by weight and the resultant “cold-fired” material allowed to cure. In an embodiment, the metal oxide to monopotassium phosphate ratio, by weight, is ⅓ (one third) metal oxide, such as magnesium oxide, to two thirds monopotassium phosphate, or MKP(KH2PO4).
In further embodiments, various carbonates, bicabonate (such as sodium bicarbonate, potassium bicarbonate and the like) or metal hydroxides reagents may be reacted in a two step process with an acid phosphate to limit the maximum reaction temperature of the metal oxide and the result of the carbonate, bicabonate or hydroxide reaction with an acid phosphate.
In further embodiments, other acids may be implemented to form a resultant metal phosphate ceramic based material. The selection of the acid may be based on the metal oxide to be utilized, suitable metal oxides include divalent and trivalent metals (including transition metals and lanthanide series and actinide series metals). Other suitable acids include boric acid and hydrochloric acid.
In specific examples, exemplary compositions were formed by mixing the selected ceramic cement with the desired shielding material. The following specific examples being only exemplary and utilized to explain the principles of the present invention. The following procedures were conducted in ambient conditions (e.g., temperature, pressure). For instances, carried out at a room temperature of between 65° F. to 85° F. (sixty-five degrees Fahrenheit to eighty-five degrees Fahrenheit) under atmospheric pressure. No attempt was made to fully homogenize the material to obtain uniform particles, while substantially uniform distribution of shielding material within the ceramic cement was attempted. For samples in which woven fiber shielding material is utilized, the ceramic is hydrolized and cast in contact with the fabric. In instances in which powdered shielding materials are incorporated, the particle size varied depending on the material. Those of skill in the art will appreciate that a wide range of particle sizes may be utilized. Water is added to hydrolyze the dry mixture. The combination water/ceramic cement/shielding material is mixed for a sufficient duration and with sufficient force to cause the material to exhibit an exothermic rise of between 20%-40% (twenty percent. to forty percent) of the original temperature of the mixture. The hydrolyzed mix was compacted via vacuum or vibratory, or equivalent method to eliminate voids. Compaction being conducted in a container, such as a polymeric container formed from polypropylene or polyethylene, having a low coefficient of friction to facilitate removal. The samples were allowed to harden to the touch (at least twenty-four hours) at ambient conditions. The samples were submitted for testing. The samples submitted for testing were formed when a metal oxide such as MgO (Magnesium Oxide) and radiopaque additives as set forth in the present invention, are stirred in an acid-phosphate solution, (such as mono potassium phosphate and water). The dissolution of the metal oxide forms cations that react with the phosphate anions to form a phosphate gel. This gel subsequently crystallizes and hardens into a ceramic. Dissolution of the oxide also raises the pH of the solution, with the ceramic being formed at a near-neutral pH. The chemically bonded phosphate ceramic is produced by controlling the solubility of the oxide in the acid-phosphate solution. Oxides or oxide minerals of low solubility are good candidates to form chemically bonded phosphate ceramics because their solubility can be controlled. The metal oxide in the sample formulations is known “deadburn” Magnesium Oxide (MgO), calcinated at 1300° C. or above in order to lower the solubility in the acid-phosphate solution. Such “deadburn” magnesium oxide can then be reacted at room temperature with any acid-phosphate solution, such as potassium hydrogen phosphate, to form a ceramic of the magnesium potassium phosphate. In the case of magnesium potassium phosphate, a mixture of MgO (Magnesium Oxide) and KH2PO4 (Potassium Phosphate) can simply be added to water and mixed from 5 minutes to 25 minutes, depending on the batch size. Potassium Phosphate dissolves in the water first and forms the acid-phosphate solution in which the MgO dissolves. The chemically bonded phosphate ceramics are formed by stirring the powder mixture of oxides and additives such as retardants and radiopaque fillers as have been clearly defined by this invention, into an acid-phosphate solution in which the MgO dissolves and reacts with the phosphate and sets into a ceramic material.
*Due to the high attenuation of this sample, lead equivalency cannot be accurately reported for a tube potential of 60 kVp. The lead equivalency will be no less than that of the next higher kVp setting. (Wherein kVp—kilovolt-peak; mmA1 - )
It is understood that the specific order or hierarchy of steps in the processes disclosed is an example of exemplary approaches. Based upon design preferences, it is understood that the specific order or hierarchy of steps in the processes may be rearranged while remaining within the scope of the present invention. The accompanying method claims present elements of the various steps in a sample order, and are not meant to be limited to the specific order or hierarchy presented.
It is believed that the present invention and many of its attendant advantages will be understood by the foregoing description. It is also believed that it will be apparent that various changes may be made in the form, construction and arrangement of the components thereof without departing from the scope and spirit of the invention or without sacrificing all of its material advantages. The form herein before described being merely an explanatory embodiment thereof. It is the intention of the following claims to encompass and include such changes.
The present application claims priority as a Continuation-in-Part under 35 U.S.C. §120 to U.S. patent application Ser. No. 11/295,708, entitled Ceramic Radiation Shielding Material and Method of Preparation, filed Dec. 6, 2005 which in turn claims priority under 35 U.S.C. §119(e) to U.S. Provisional patent application Ser. No. 60/633,595, filed on Dec. 6, 2004, both of which are hereby incorporated by reference in their entirety.
| Number | Date | Country | |
|---|---|---|---|
| 60633595 | Dec 2004 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 11295708 | Dec 2005 | US |
| Child | 11441833 | May 2006 | US |
