Ceramic radiation shielding material and method of preparation

Abstract

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.

Description

CROSS REFERENCE [0001] 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.FIELD OF THE INVENTION [0002] The present invention relates to the field ceramics and particularly to a cold fired zeolite (alumino-silicate) containing ceramic having radiation shielding characteristics. BACKGROUND OF THE INVENTION [0003] 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 e...

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Benefits of technology

[0021] 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. TABLE 1Ceramic Sample FormulationSampleH20 (g)ceramic (g)shielding material (g)particle sizedensity lbs / ft2160.0-120.0100.0-300.0200.0-600.0  10 μm (microns)152.0barium sulphate(90% to 99.9%chemical grade)260.0-120.0100.0-300.0200.0-600.0325 mesh (bismuth)197.0barium sulphate(90% to 99.9%chemical grade)200.0-600.0bismuth360.0-120.0100.0-300.0200.0-600.0325 mesh225.0bismuth460.0-120.0100.0-300.0200.0-600.05.24 μm (microns)175.0cerium IIIoxide560.0-120.0100.0-300.0200.0-600.0  10 μm (microns)74.0barium sulphate325 mesh (bismuth)(90% to 99.9%5.24 μm (microns)chemical grade)200.0-600.0bismuth200.0-600.0cerium IIIoxide660.0-120.0100.0-300.0basalt powder130.0200.0-600.0

Problems solved by technology

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.

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.

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.

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 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.

Inclusion of ammonia in the ceramic matrix may be detrimental to the resultant formation.