US007700202B2
(12) United States Patent (10) Patent No.: US 7,700,202 B2 Easler et al. (45) Date of Patent: Apr. 20, 2010
(54) PRECURSOR FORMULATION OF A SILICON 6,261,509 B1 7/2001 Barnard et al. CARBDE MATERAL 2005/0205798 A1* 9/2005 Downing et al...... 250,390.11 (75) Inventors: Timothy E. Easler, San Diego, CA (US); Andrew Szweda, San Deigo, CA FOREIGN PATENT DOCUMENTS (US); Eric Stein, Poway, CA (US) JP 2000-1551.89 * 11/1999 (73) Assignee: Alliant Techsystems Inc., Minneapolis, MN (US) (*) Notice: Subject to any disclaimer, the term of this OTHER PUBLICATIONS patent is extended or adjusted under 35 Pramono et al. (“Helium Release and Physical property Change of U.S.C. 154(b) by 259 days. Neutron Irradiated alpha-SiC Containing B4C of Different 10B con centrations'), Journal of Nuclear Science and Technology, vol. 40, (21) Appl. No.: 11/357,716 No. 7, p. 531-536 (Jul 2003).* Phelps et al. (“Step Bunching Fabrication Constraints in Silicon (22) Filed: Feb. 16, 2006 Carbide'). Semiconductor Science and Technology, vol. 17, No. 5, (May 2002) pp. L17-L21.* (65) Prior Publication Data “New High-Performance SiC Fiber Developed for Ceramic Compos ites.”
US 7,700,202 B2 Page 2
OTHER PUBLICATIONS com/news/newsreleasedetails.aspx?id=154, printed Jun. 3, 2009, 2 Certificate of Analysis and Conformance, Enriched Boron Oxide pageS. (11B2O3), EaglePicher Technologies, LLC., Quapaw, OK, Mar. 17. (11)B Enriched Boron Oxide Product Specification, Ceradyne, Inc., 2005, 2 pages. Document No. BP-SSSm-11B03, Feb. 21, 2008, 1 page. Ceradyne, Inc. Completes EaglePicher Boron LLC Acquisition, Ceradyne, Inc. New Release, Sep. 4, 2007. http://www.ceradyne. * cited by examiner U.S. Patent Apr. 20, 2010 Sheet 1 of 3 US 7,700,202 B2
U.S. Patent Apr. 20, 2010 Sheet 2 of 3 US 7,700,202 B2
FIG. 2 U.S. Patent Apr. 20, 2010 Sheet 3 of 3 US 7,700,202 B2
FIG. 3
?i??i???????????????????????????????????à US 7,700,202 B2 1. 2 PRECURSORFORMULATION OF A SILICON instruments for detecting neutrons. However, 'B is unstable CARBIDE MATERAL and undergoes fission when irradiated, producing a gamma ray, an alpha particle, and a lithium ion. Therefore, when a FIELD OF THE INVENTION component formed from conventional SiC fibers is irradiated, the boron compound undergoes fission, which is accompa The present invention relates to a stable silicon carbide nied by outgassing and degradation of the SiC fibers or the (“SiC) material for use in the nuclear industry, such as in SiC bodies. As such, conventional SiC fibers are not suitable components of a nuclear reactor, as well as to Such compo for use in a component to be used in the nuclear industry, Such nents. More specifically, the present invention relates to a SiC as in a nuclear reactor. material that includes aboron-11 ("B") isotope, as well as to 10 It would be desirable to produce SiC fibers or SiC bodies a precursor and method for forming the SiC material, and that are more stable to irradiation for use in components to be components including the SiC material. used in the nuclear industry. For instance, it would be desir able to produce SiC fibers or SiC bodies that are useful in BACKGROUND OF THE INVENTION nuclear applications without outgassing or degradation. 15 SiC fibers are known in the art for providing mechanical BRIEF SUMMARY OF THE INVENTION strength at high temperatures to fibrous products, such as high temperature insulation, belting, gaskets, or curtains, or as The present invention relates to a precursor formulation of reinforcements in plastic, ceramic, or metal matrices of high a SiC material that includes a ceramic material and aboron-11 performance composite materials. To provide good mechani compound. As used herein, the term “SiC material refers to cal strength to these products or materials, the SiC fibers have SiC fibers, SiC bodies, or other forms of SiC ceramics, such a relatively high density (i.e., low residual porosity) and fine as monolithic SiC. SiC coatings, SiC thin substrates, or grain sizes. However, producing SiC fibers with these prop porous SiC ceramics. The ceramic material may include sili erties is difficult because the SiC fibers typically undergo con and carbon and, optionally, oxygen, nitrogen, titanium, coarsening or growth of crystallites and pores during a high 25 aluminum, Zirconium, or mixtures thereof. For the sake of temperature heat treatment. example only, the ceramic material may include SiC fibers, Sintering aids have been used to improve densification of silicon oxycarbide fibers, silicon carbon nitride fibers, silicon the SiC fibers and to prevent coarsening, allowing the SiC oxycarbonitride fibers, polytitanocarbosilane fibers, or mix fibers to be fabricated with high density and fine grain sizes. tures thereof. The boron-11 compound may be a boron-11 These sintering aids are typically compounds of boron. As 30 isotope of boron oxide, boron hydride, boron hydroxide, disclosed in U.S. Pat. No. 5,366,943 to Lipowitz et al., which boron carbide, boron nitride, borontrichloride, borontrifluo is incorporated by reference in its entirety herein, the SiC ride, boron metal, or mixtures thereof. The boron-11 com fibers are formed by converting amorphous ceramic fibers to pound may account for less than or equal to approximately polycrystalline SiC fibers. The ceramic fibers are heated in 2% by weight (“wt %) of a total weight of the precursor the presence of a sintering aid to produce the polycrystalline 35 formulation. Thus, while the present invention is referred to SiC fibers. The sintering aid is boron or a boron-containing for the sake of convenience in the singular as 'a' precursor compound, such as a boron oxide (“BO). An example of and “a” SiC material, it will be appreciated that a number of SiC fibers prepared by this process is SYLRAMICR), which is different SiC materials and precursors that may be used to available from COI Ceramics, Inc. (San Diego, Calif., an form a variety of materials are encompassed by the present affiliate of ATK Space Systems). 40 invention. Another method of forming SiC fibers is by spinning a The present invention also relates to a material for use in a polycarbosilane resin into green fibers, treating the green nuclear reactor component. The material includes a SiC mate fibers with boron, and curing and pyrolyzing the green fibers, rial and a boron-11 compound. The SiC material may be SiC as disclosed in U.S. Pat. No. 5,071,600 to Deleeuw et al. fibers, a SiC body, a SiC ceramic, a SiC coating, a SiC thin Other methods of forming SiC fibers are known, such as 45 Substrate, or a porous SiC ceramic. The boron-11 compound spinning organosilicon polymers into fibers, curing the fibers, may be one of the compounds previously described. The and ceramifying the fibers at elevated temperatures. However, boron-11 compound may account for from approximately 0.1 many of these methods undesirably introduce oxygen or wt % of a total weight of the material to approximately 4 wt % nitrogen into the SiC fibers. When these SiC fibers are heated of the total weight of the material. A layer of boron nitride that to temperatures above 1400° C., the oxygen or nitrogen is 50 includes the 'Bisotope (''BN”) may, optionally, be present Volatilized, causing weight loss, porosity, and decreased ten on a Surface of the material. sile strength in the SiC fibers. In addition to SiC fibers, SiC The present invention also relates to a method of producing bodies are known to be formed by molding SiC powder and a SiC material by converting a ceramic material to a SiC elemental carbon into a desired shape and heating the molded material in the presence of a boron-11 compound. The structure in a boron-containing environment. 55 ceramic material may be converted by heating the ceramic While many methods of producing SiC fibers (or SiC bod material in an environment that includes the boron-11 com ies) are known, components or products formed from con pound. The ceramic material and the boron-11 compound ventional SiC fibers, such as those described above, are not may include one of the compounds previously described. Suitable for use in nuclear applications due to the boron com Alternatively, the boron-11 compound may be formed by pound used as the sintering aid. The boron compound typi 60 reacting a boron-11 containing material with an oxidizing cally includes boron-10 ('B'). Boron has thirteen isotopes, agent in situ. The boron-11 containing material may be two of which, 'B and 'B, are naturally occurring. The selected from the group consisting of boron carbide, boron, natural abundance of 'B and ''B is 19.9% and 80.1%, boron Suboxide, and mixtures thereof and the oxidizing agent respectively. However, 'B is the most commercially avail may be selected from the group consisting of carbon dioxide, able isotope because 'B is more easily extracted from ore 65 carbon monoxide, oxygen, and mixtures thereof. As with the than B. 'Babsorbs neutrons and is used in control rods of precursor and material of the present invention, the method nuclear reactors, as a shield against nuclear radiation, and in may be varied within the scope of the invention. US 7,700,202 B2 3 4 The ceramic material and the boron-11 compound may be or moderately carbon-rich amounts. As used herein, the heated to a temperature that is greater than approximately phrase “moderately carbon-rich refers to a carbon content of 1200° C., such as from approximately 1200° C. to approxi less than or equal to approximately 2%. In one embodiment, mately 1400° C., for an amount of time sufficient for the the silicon and carbon are present in near Stoichiometric boron-11 compound to vaporize and diffuse into the ceramic amounts. The ceramic material may be amorphous or micro material and for volatile by-products to be released. The crystalline ceramic fibers that include sufficient silicon and silicon carbide material may, optionally, be exposed to a carbon to form a 'B SiC material that includes stoichio nitrogen atmosphere to form a layer of ''BN on a surface of metric amounts of silicon and carbon or is carbon-rich. As the silicon carbide material. used herein, the phrase “carbon-rich refers to a carbon con The present invention also encompasses structures formed 10 tent of greater than approximately 2%. The ceramic fibers at least in part of a material including an SiC material and a may also include oxygen (“O), nitrogen (“N), titanium boron-11 compound, which structures may be exposed to (“Ti”), aluminum (Al), Zirconium (“Zr'), or mixtures nuclear radiation without outgassing or degradation and, so, thereof. If present, these elements may volatilize out of the. are suitable for use in nuclear applications. By way of 'B-SiC material during Subsequent processing or remainin example only, such structures include components for nuclear 15 the 'B SiC material without affecting its integrity or prop reactors, such as control rods, control rod guides, fuel clad erties. Other elements may also be present in the ceramic ding, core Support pedestals, reactor core blocks, upper core fibers as long as the elements are volatilized or remain in the gas plenum, interior insulation covers, hot ducts, heat 'B SiC material without affecting its integrity and proper exchangers, and combinations thereof. ties. As described in more detail below, oxygen present in the ceramic material may, optionally, be removed (deoxygen BRIEF DESCRIPTION OF THE SEVERAL ated) before converting the ceramic material into the 'B- VIEWS OF THE DRAWINGS SiC material. Methods of manufacturing the ceramic material used in the While the specification concludes with claims particularly precursor formulation are known in the art and, therefore, are pointing out and distinctly claiming that which is regarded as 25 not discussed in detail herein. For instance, organosilicon the present invention, the advantages of this invention may be polymers (with or without ceramic powder additives) may be more readily ascertained from the following description of spun into fibers, and the fibers cured (infusibilized) and pyro the invention when read in conjunction with the accompany lyzed to form the ceramic material. In addition, Sol-gel pro ing drawings in which: cessing techniques or chemical vapor deposition techniques FIG. 1 is a schematic illustration of a very high temperature 30 may be used to produce the ceramic material. The ceramic nuclear reactor, material used in the precursor formulation may have any FIG. 2 is a schematic illustration of a control rod; length or any form desired. For instance, if fibers are used, the FIG. 3 illustrates an embodiment of a heat exchanger ceramic fibers may be substantially continuous and may be formed from the 'B SiC material of the present invention; used as either single strands (or 1 or many filaments (tows)) or and 35 are aligned unidirectionally (e.g., tapes), wovenas a 2-dimen FIG. 4 illustrates an embodiment of fuel cladding formed sional fabric or shaped as a 3-dimensional perform. from the 'B SiC material of the present invention. Examples of ceramic fibers that may be used include, but are not limited to, SiC fibers, silicon oxycarbide (“SiOC) DETAILED DESCRIPTION OF THE INVENTION fibers, silicon carbon nitride (“SiCN) fibers, silicon oxycar 40 bonitride (“SiCON”) fibers, or polytitanocarbosilane fibers A SiC material that is stable to irradiation is disclosed. A (“SiCOTi”). In addition, mixtures of these ceramic fibers may precursor formulation of the SiC material includes a ceramic be used. Such ceramic fibers are known in the art and are material and at least one-boron compound having a 'B iso commercially available from various sources. For instance, tope (referred to herein as the''B compound”). Since 'B is SiOC fibers having a diameter in the range of from approxi a stable isotope, the SiC material having the 'B compound 45 mately 10 um to approximately 20 Lum are manufactured by (referred to herein as the "B SiC material”) may be used Nippon Carbon Co. (Tokyo, Japan) and are sold under the to produce components stable to irradiation. These compo NICALONR tradename (e.g., Ceramic Grade (CG), High nents may be used in the nuclear industry, Such as in nuclear Volume Resistivity (HVR)). SiCOTi fibers having a diameter fission reactors and fusion reactors. An example of a fission in the range of from approximately 8 um to approximately 12 reactor includes, but is not limited to, a GEN IV Very High 50 um are manufactured by Ube Industries, Ltd. (Yamaguchi, Temperature Reactor. An example of a fusion reactor Japan) and are sold under the TYRANNOR tradename. includes, but is not limited to, a Tokamak reactor. By using Experimental ceramic fibers may also be used. Such as 'B in the boron compound, the 'B SiC material does not SiCON fibers having a diameter in the range of from approxi undergo fission when irradiated. In addition, no outgassing or mately 6 Lum to approximately 10 Lum and SiCON fibers hav degradation occurs when the component is irradiated. 55 ing a diameter in the range of from approximately 10 um to The precursor formulation of the 'B SiC material approximately 15 um (produced by Dow Coming (Midland, includes the ceramic material and the 'B compound. Minor Mich.) and designated as “MPDZ). In one embodiment, the amounts of additional ingredients or additives may also be ceramic material includes SiOC fibers. In another embodi present in the precursor formulation, such as to improve pro ment, the ceramic material includes SiCOTi fibers, such as cessability of the precursor formulation or performance of the 60 TYRANNOR LOX M fibers. 'B SiC material. However, these ingredients or additives The 'B compound in the precursor formulation may func are not needed to provide the desired stability of the 'B SiC tion as a volatile, sintering aid. The B compound in the pre material to nuclear environments. The ceramic material in the cursor formulation may initially melt and then volatilize to precursor formulation may be converted to the 'B SiC form a vapor. To achieve the desired properties in the 'B- material by heating at a sufficient temperature in the presence 65 SiC material, an excess amount of the ''B compound may be of the 'B compound. The ceramic material may include used relative to the amount of the ceramic material. As silicon and carbon, which are present in near Stoichiometric explained below, a smallamount of the 'B compound may be US 7,700,202 B2 5 6 present in the 'B SiC material after processing of the pre in a furnace or other heat source with the ceramic material. cursor formulation to form the 'B SiC material. The 'B The ceramic material and the 'B compound may be mixed compound may have a significant vapor pressure at and above together or placed separately in the furnace and Volatilized a temperature at which the ceramic material begins to decom under the heat of the furnace so that the ceramic material is pose or density. For the sake of example only, for SiCO doped with the 11B compound. Alternatively, the 'B com ceramic fibers, the decomposition temperature may be as low pound in a solid or liquid state may be volatilized outside the as approximately 1200° C. for slow temperature heating furnace and introduced to the furnace in the vaporous or (ramp) rates (e.g., <1° C./min) or may range from approxi gaseous form. If the 'B compound is in a gaseous state at mately 1400° C. to approximately 1500° C. for heating rates room temperature, the 'B compound may be flowed over the of several degrees per minute or more. The 'B compound 10 may be a Solid, a liquid, or a gas at room temperature. ceramic material in the furnace. The 'B compound may be The boron-11 compound may be a 'B isotope of boron used in the furnace neat, diluted in a carrier gas (e.g. an inert oxide (“'BO), boron hydride (“'BH'), boron hydrox gas, such as argon, helium, etc.), or added under a vacuum. ide (“B(OH)), boron carbide (''BC), boron nitride The ceramic material may be heated in the presence of the (“BN), boron chloride (“BC1), boron fluoride(“BF), 15 'B compound at a temperature sufficient to convert the boron metal, or mixtures thereof. In one embodiment, the 'B ceramic material to the 'B SiC material. During the heat compound is 'BOs. Compounds that include the 'B iso ing, the 'B compound may diffuse into the ceramic material. tope are commercially available from various sources. For The temperature needed to densify the ceramic material may instance, 'BO is available from Sigma-Aldrich Co. (St. be greater than approximately 1400° C., such as from Louis, Mo.) or EaglePicher Inc. (Phoenix, Ariz.). In addition, approximately 1600° C. to approximately 2200° C. In one a mixture of two or more 'B compounds may be used in the embodiment, the temperature ranges from approximately precursor formulation. 1700° C. to approximately 2000° C. The temperature used to The 'B compound may be present at less than or equal to convert the ceramic material to the 'B SiC material should approximately 2 wt % of a total weight of the precursor be at least equivalent to the temperature expected in any formulation, Such as from approximately 0.5 wt % to approxi 25 subsequent processing and/or the final utility of the 'B SiC mately 1.5 wt % of the total weight of the precursor formu material. As the ceramic material is heated, Volatile by-prod lation. The amount of 'B compound used in the precursor ucts may form and should be released from the ceramic mate formulation may be adjusted as long as crystallite growth and rial. A rate at which the ceramic material and the 'B com porosity are minimized such that the strength of the 'B-SIC pound are heated and a hold time (hold) at a maximum material remains in an acceptable range. The remainder of the 30 temperature during the heating may be adjusted as long as the precursor formulation may include the ceramic material and heating rate and the hold time enable the 'B compound to any optional ingredients. As such, the ceramic material may diffuse into the ceramic material and the volatile by-products account for greater than or equal to approximately 98 wt % of to evolve. For the sake of example only, the heating rate may the total weight of the precursor formulation. range from approximately 1° C./minute to approximately 50° Alternatively, the 'B compound may be formed in situ by 35 C./minute, with either no hold or a hold time of up to approxi reacting a 'B-containing material with an oxidizing agent, as mately several hours. However, a total thermal exposure of described in U.S. Pat. No. 6,261,509 to Barnard et al., which the ceramic material, which depends on the heating rate, is incorporated by reference in its entirety herein. For maximum temperature, and the time at the maximum tem instance, the 'B-containing containing material and the oxi perature, may affect characteristics and properties of the dizing agent may be reacted at a temperature that ranges from 40 'B SiC material, such as modulus and grain growth. For approximately 1300° C. to approximately 1600° C., produc example, the properties of the 'B SiC material may be ing 'BO, vapor. The 'B-containing material may include, optimized after exposure that ranges from approximately 5 but is not limited to, boron carbide (“BC), boron, or boron minutes to approximately 10 minutes in the case of 10 um suboxide (“BO'). The oxidizing agent may include, but is diameter fibers, which may equilibrate quickly. However, not limited to, carbon dioxide (“CO), carbon monoxide 45 longer exposure times, on the order of many hours, may be (“CO), oxygen (“O), or mixtures thereof. When the 'B- used for a 'B SiC material having a more substantial diam containing material and oxidizing agent react, the oxidizing eter. agent is the rate-limiting reagent. Therefore, the concentra The ceramic material may be heated with the 'B com tion of the oxidizing agent may be adjusted to control the pound for an amount of time sufficient to achieve the desired concentration of vaporous 'BO produced. In addition, the 50 densification of the ceramic material. For instance, the rate of addition of the oxidizing agent may be adjusted to ceramic material may be exposed to the 'B compound during control the production of vaporous 'BO. The amount of the entire heat treatment (to convert the ceramic material to oxidizing agent reacted with the 'B-containing material may the 'B SiC material) after the ceramic material begins to be sufficient to provide a 'BO concentration sufficient to decompose or densify. Alternatively, the ceramic material produce a minimum of 0.1 wt % of the 'B compound in the 55 may be maintained at a temperature at or above its decompo resulting 'B SiC material. sition or densification temperature in an atmosphere that To produce the precursor formulation of the 'B SiC includes the 'B compound for an amount of time sufficient to material, the ceramic material may be doped with the 'B enable the 'B compound to incorporate into the ceramic compound and densified, such as by heating the ceramic material. The ceramic material may then be further heated in material in an environment or atmosphere that includes the 60 the absence of the 'B compound to complete the densifica 'B compound. The ceramic material and the 'B compound tion process. Without being bound to a theory, the 'B in the may be heated at a temperature sufficient to convert the 'B compound may limit grain growth of the ceramic material ceramic material to a polycrystalline SiC material. While the and aid in densifying the ceramic material, which is believed 'B compound is in a volatile state during the doping and to decrease porosity of the 'B SiC material. The ''B com densification, the 'B compound may be a solid, a liquid, or a 65 pound may be incorporated into a conventional fiber manu gas at room temperature. If the 'B compound is a solid or a facturing approach and the production of the 'B SiC mate liquid at room temperature, the 'B compound may be placed rial may be run in batches or on a continuous production line. US 7,700,202 B2 7 8 If the ceramic material to be used in the precursor formu insulation covers, hot ducts, heat exchangers, or combina lation includes oxygen, the ceramic material may, optionally, tions thereof. A nuclear reactor 2 is schematically illustrated be deoxygenated before doping and densification. For in FIG. 1. The nuclear reactor 2 includes control rods 4, a instance, the ceramic material may be heated to a temperature reactor core 6, a reflector 8, a coolant 10, a pump 12, a heat greater than or equal to approximately 1300° C. to remove the exchanger 14, and a heat sink 16. The control rods 4 or the oxygen, Such as a temperature that ranges from approxi heat exchanger 14 may be formed from the 'B SiC mate mately 1300° C. to approximately 1600°C. The oxygen may rial. As known in the art, the nuclear reactor 2 may be con volatilize out of the ceramic material as silicon oxide (“SiO') nected to a hydrogen production plant 18. A close-up view of or carbon monoxide (“CO). By removing the oxygen, the a control rod 4 is shown in FIG. 2. The control rod 4 includes ceramic material used in the precursor formulation may not 10 an upper tie plate 20, a uranium dioxide pellet 22, a water rod be limited to a ceramic material having a low oxygen content, 24, and a lower tie plate 26. FIG.3 illustrates aheat exchanger which expands the types of ceramic materials that may be 14 formed from the 'B SiC material. FIG. 4 shows fuel used. After deoxygenating the ceramic material, the precursor cladding 28 formed from the 'B SiC material. formulation may be doped and densified as described above. The component formed from the 'B SiC material may After doping and densifying the precursor formulation, the 15 be heat resistant (able to withstand temperatures of greater resulting 'B SiC material may have at least approximately than or equal to approximately 1400° C.) and have a high 0.1 wt % of the ''B compound incorporated therein. For resistance to nuclear irradiation. When irradiated, the com instance, the 'B SiC material may include from at least ponent may not undergo outgassing or degradation since 'B approximately 0.1 wt % of the 'B compound to approxi is more stable to irradiation than 'B and does not undergo mately 4 wt % of the 'B compound, such as from approxi fission. As such, the component formed from the 'B SiC mately 0.3 wt % of the 'B compound to approximately 2.5 wt material may be used in a high temperature, corrosive, irra % of the 'B compound. diative environment. Using 'B instead of "B also does not The 'B SiC material may have substantially similar significantly increase the expense of the 'B SiC material properties to SiC fibers produced from a formulation that because the cost of ''B is only slightly greater than that of includes a 'B compound as the sintering aid. For instance, 25 'B. Additionally, since 'B is chemically identical to 'B, the 'B SiC material may have properties that are substan special equipment or additional processing steps are not tially similar to those of SYLRAMICR fibers. The 'B SiC needed. material may be high-strength, beat resistant, and corrosion Before shaping or producing the 'B SiC material into resistant. In addition, the 'B SiC material may have at least the product or component, the 'B SiC material may, 75% crystallinity and a density of at least approximately 2.9 30 optionally, be subject to an in situ boron nitride (“i'BN) g/cm. Any oxygen or nitrogen that was initially present in the treatment. The 'B SiC material may beheated in a nitrogen ceramic material may be absent in the 'B SiC material, atmosphere, enabling an excess of the 'B compound that producing a 'B SiC material having a low residual oxygen remains at a surface of the 'B SiC material to react with the content or a low residual nitrogen content. The 'B SiC nitrogen. The 'B SiC material may be heated at a tempera material may also have an average grain size of less than 35 ture that ranges from approximately 1750° C. to approxi approximately 1 um, Such as less than approximately 0.5um mately 1950° C., such as at a temperature of approximately or less than approximately 0.2um. The diameter of the 'B- 1800° C. The 'B compound may react with the nitrogen to SiC material may range from approximately 5um to approxi form a 'BN layer on the surface of the 'B SiC material. mately 20 Lim, depending on the diameter of the ceramic The 'BN layer is oxidation resistant and provides an envi fibers initially used in the precursor formulation. In addition, 40 ronmentally durable surface and a physical barrier to the the 'B SiC material may have a tensile strength of at least 'B SiC material. The remainder of the 'B compound in approximately 2,070 MPa, such as at least approximately the 'B SiC material may form grainboundary precipitates, 2,760 MPa. The 'B SiC material may also have an elastic specifically as titanium diboride (“TiB). Removing the modulus that is greater than or equal to approximately 275 excess 'B compound may maintain the high tensile strength GPa, Such as an elastic modulus that ranges from approxi 45 of the 'B SiC material and improves its creep resistance, mately 323 GPa to approximately 483 GPa. electrical conductivity, and thermal conductivity. The treated, After densifying, a sizing may, optionally, be applied to the 'B SiC material may also have improved rupture strength 'B SiC material, as known in the art. The 'B SiC mate at high temperatures in air. rial may then be wound onto spools or otherwise stored until The following examples serve to explain embodiments of the 'B SiC material is to be shaped or produced into a 50 the 'B SiC material in more detail. These examples are not product or component. For the sake of example only, the to be construed as being exhaustive or exclusive as to the 'B SiC material may be formed into tows (yams) that Scope of the invention. include approximately 800 filaments. The tows may be con tinuous filaments of the 'B SiC material and may have a EXAMPLES diameter of approximately 10 um and a length of approxi 55 mately 1000 m. The tows may be woven into fabrics and Example 1 formed into components, such as nuclear reactor compo nents. The 'B SiC material may beformed into the nuclear Formation of ''B-Doped SiC Fibers reactor component in the same manner as conventional SiC fibers. Since methods of forming nuclear reactor components 60 TYRANNOR LOX M fibers were obtained from Ube from conventional SiC materials are known in the art, these Industries, Ltd. and solid ''BO, was obtained from EaglePi methods are not discussed in detail herein. cher, Inc. The TYRANNOR Lox M fibers are polymer-de The 'B SiC material may be formed into a component rived, Si Ti-C-O fibers having reduced oxygen content. for use in a nuclear reactor or in other nuclear application. To deoxygenate the TYRANNOR Lox M fibers in a batch Examples of components include, but are not limited to, 65 operation, 800 g of TYRANNOR Lox M fibers were placed control rods, control rod guides, fuel cladding, core Support onto four Grafoil spool packages and placed in a furnace with pedestals, reactor core blocks, upper core gasplenum, interior 108 g of 'BO, powder in several Grafoil boats in flowing US 7,700,202 B2 9 argon at approximately 1600° C. for approximately 5 hours. The TYRANNOR Lox M fibers and the 'BO, powder were -continued then heated at approximately 1650° C. for approximately 1.5 B-Doped SiC B-Doped hours to enable doping of the TYRANNOR LOX M fibers B-Doped Fibers Exposed to SC with boron. The TYRANNOR LOX M fibers lost approxi 5 mately 20% of their weight during the doping operation. The Property SiC Fibers iBN treatment Fibers fiber spool was then removed from the furnace. Oxygen (wt %) O.O2 O.O1 O.O2 In a second, separate, operation, the doped fibers described Tensile Strength (MPa) 2700 2600 >2O67 above were densified in a continuous spool-to-spool opera Tensile Modulus (GPa.) 310 290 >276 tion by exposing the doped TYRANNOR LOX M fibers to a 10 temperature of approximately 1650° C. in flowing argon for While the invention may be susceptible to various modifi approximately 15 seconds. Upon densification, the doped cations and alternative forms, specific embodiments have TYRANNOR LOX M fibers were converted to 'B SiC been shown by way of example in the drawings and have been fibers. The 'B SiC fibers lost no weight during this second described in detail herein. However, it should be understood operation. At this stage, the fibers had a typical filament 15 that the invention is not intended to be limited to the particular diameter of 8.5um, a density of 3.14 g/cm, a tensile strength forms disclosed. Rather, the invention is to cover all modifi of 2714 MPa and an elastic modulus of 289 GPa. cations, equivalents, and alternatives falling within the spirit In a third, separate operation, a sizing was placed on the and scope of the invention as defined by the following 'B SiC fibers by applying a 0.5 wt % aqueous solution of appended claims. polyvinylalcohol at a level of 0.1 wt %. The 'B SiC fibers What is claimed is: were then cured at 300° C., producing continuous 'B SiC 1. A precursor formulation of a silicon carbide material, fibers approximately 10 Lum in diameter and approximately comprising: 1000 meters in length. The 'B SiC fibers were wound onto a ceramic material comprising silicon and carbon; and spools for storage as tows (yarn) of 800 filaments. a sintering aid consisting of a boron-11 isotope of boron 25 oxide. Example 2 2. The precursor formulation of claim 1, wherein the ceramic material comprises silicon and carbon in Stoichio ''B-Doped SiC Fibers Exposed to iBN Treatment metric amounts or in carbon-rich amounts. 3. The precursor formulation of claim 1, wherein the Approximately 800g of 'B SiC fibers from Example 1 30 ceramic material further comprises oxygen, nitrogen, tita were wound onto a Grafoil spool and placed into a furnace. nium, Zirconium, aluminum, or mixtures thereof. The furnace was heated to approximately 1850° C. for 4. The precursor formulation of claim 1, wherein the approximately 1.5 hours in a controlled flowing nitrogen gas. ceramic material comprises silicon carbide fibers, silicon During this process, the nitrogen gas diffused into the SiC oxycarbide fibers, silicon carbon nitride fibers, silicon oxy fiber surface and reacted with the 'B that was present, form 35 carbonitride fibers, polytitanocarbosilane fibers, or mixtures ing a thin, 'BN-rich, in-situ layer at the near fiber surface. thereof. Auger analysis showed that the 11 BN-rich, in-situ layer was 5. The precursor formulation of claim 1, wherein the approximately 200 nm in thickness. The resulting i'BNSiC boron-11 isotope of boron oxide is a Solid, a liquid, or a gas at fibers had a density of 3.14g/cm, a tensile strength of 2411 room temperature. MPa and an elastic modulus of 324 GPa. 40 6. The precursor formulation of claim 1, wherein the Properties of the 'B SiC fibers described in Example 1 boron-11 isotope of boron oxide comprises less than or equal and the i'N SiC fibers described in Example 2 are shown in to approximately 2% by weight of a total weight of the pre Table 1. For comparison, the properties of "B-doped SiC cursor formulation. fibers (SYLRAMICR) fibers, commercially available from 7. The precursor formulation of claim 1, wherein the COI Ceramics, Inc.) are also provided. These properties were 45 boron-11 isotope of boron oxide comprises from approxi determined by conventional techniques. mately 0.5% by weight of a total weight of the precursor formulation to approximately 1.5% by weight of the total weight of the precursor formulation. B-Doped SiC B-Doped 8. A precursor formulation of a silicon carbide material, 'B-Doped Fibers Exposed to SC 50 comprising: Property SiC Fibers iBN treatment Fibers a sintering aid incorporated in a silicon and carbon mate Denier (g/9000 m) 1605 1605 1475-1750 rial, the sintering aid consisting of a boron-11 isotope of Density (g/cm) 3.14 3.14 3.12 boron oxide. Diameter (Lm) 8-10 8-10 8-10 UNITED STATES PATENT AND TRADEMARK OFFICE CERTIFICATE OF CORRECTION PATENT NO. : 7,700,202 B2 Page 1 of 1 APPLICATIONNO. : 1 1/357716 DATED : April 20, 2010 INVENTOR(S) : Timothy E. Easler, Andrew Szweda and Eric Stein It is certified that error appears in the above-identified patent and that said Letters Patent is hereby corrected as shown below:
On the title page: In ITEM (73) Assignee: Delete “Alliant Techsystems Inc., Minneapolis, MN (US)' and replace with --COI Ceramics, Inc., San Diego, CA (US)--
Signed and Sealed this Eighteenth Day of January, 2011
David J. Kappos Director of the United States Patent and Trademark Office