Ceramic compositions and methods for making ceramic compositions

Abstract

To provide a ceramic composite, a method of producing the same and a method of enhancing the same.SOLUTION: A method of producing a ceramic composite that comprises the step of forming a wet ceramic composition containing a plurality of individual ceramic components and a flux agent dissolved in solvent. In order to form a dry ceramic composition that contains the plurality of ceramic components each coated with the flux agent, at least a portion of the solvent is taken out from the wet ceramic composition. In order to obtain a ceramic composite, dried ceramic compositions are sintered. The sintering step is carried out at a sinter temperature sufficient to fuse the individual ceramic components at bridging sites formed where two or more of the individual ceramic components coated with the flux agent are in physical contact.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a method of making a ceramic composite and the ceramic composite produced from the method. [Background technology]

[0002] Ceramic composites, such as ceramic oxide composites, are well known for their use in a variety of applications, including thermal insulation and protection systems for aerospace vehicles. For example, composites made from ceramic oxide fibers, such as alumina ceramics and / or silica fiber-based ceramics, are well known for their use in lightweight thermal insulation tiles that can be used as heat shields for spaceflight vehicles, as well as in other applications where rapid heat dissipation, thermal insulation, and the ability to maintain structural integrity at very high temperatures are useful.

[0003] It is known to use a solid particulate boron source to bond ceramic oxide fibers together. The solid particulate boron source allows high melting point ceramic fibers to melt and bond together in the vicinity of the solid particulate. The solid particulate boron source remains solid throughout the ceramic composite manufacturing process until the sintering stage, where it decomposes and reacts with the nearby oxide fibers.

[0004] Lithium metaborate is a fluxing agent known to lower the melting point of ceramic compositions, such as ceramic oxides, allowing the ceramic to dissolve into solution for chemical analysis. Fluxing agents, such as lithium metaborate, used in such chemical analysis processes are generally used to completely melt the ceramic oxide or to destroy the mechanical structure of the ceramic oxide.

[0005] Generally, ceramic materials are brittle and can lack strength. New materials and techniques for increasing the strength of ceramic materials would be a valuable step forward in the art. Summary of the Invention [Means for solving the problem]

[0006] The present disclosure relates to a method for making a ceramic composite, the method including forming a wet ceramic composition including a plurality of individual ceramic components and a fluxing agent dissolved in a solvent. At least a portion of the solvent is removed from the wet ceramic composition to form a dry ceramic composition including the plurality of individual ceramic components coated with the fluxing agent. The dry ceramic composition is sintered to form the ceramic composite, the sintering being carried out at a sintering temperature sufficient to fuse the individual ceramic components at crosslink sites formed where two or more individual ceramic components coated with the fluxing agent physically contact each other.

[0007] The present disclosure also relates to ceramic composites that include a plurality of individual ceramic components that include (i) one or more ceramic compounds and (ii) one or more soluble fluxing agent atoms incorporated into the surfaces of the ceramic components, and that fuse together at bridge sites located where two or more individual ceramic components physically contact each other.

[0008] The present disclosure also relates to a method for strengthening a ceramic composite, the method including forming a wet ceramic composition including a plurality of individual ceramic components and a fluxing agent dissolved in a solvent. At least a portion of the solvent is removed from the wet ceramic composition to form a dry ceramic composition including the plurality of individual ceramic components coated with the fluxing agent. The dry ceramic composition is sintered to form the ceramic composite, the sintering being carried out at a sintering temperature sufficient to fuse the individual ceramic components at crosslink sites formed where two or more individual ceramic components coated with the fluxing agent physically contact each other. The ceramic composite has a first tensile strength greater than a second tensile strength of a second ceramic composite, except that the only fluxing agent in the second ceramic composite is insoluble and remains solid until the sintering step during the production of the second ceramic composite. It is manufactured using the same process, ingredients, and weight as the ceramic composite with the first tensile strength.

[0009] 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 present teachings, as claimed.

[0010] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate aspects of the present teachings and, together with the description, serve to explain the principles of the present teachings. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a flowchart of a method for manufacturing a ceramic composite according to one aspect of the present disclosure. [Figure 2] 1 is an SEM micrograph of a sintered ceramic composite according to an example of the present disclosure. [Figure 3] FIG. 1 is a cross-sectional view of a fiber modified to include a fluxing agent according to an example of the present disclosure. [Figure 4]1 is an SEM micrograph of a sintered ceramic composite having an overly molten region according to an example of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0012] It should be noted that the details of the figures have been somewhat simplified and are drawn for ease of understanding rather than to maintain strict structural accuracy, detail, and scale.

[0013] Reference will now be made in detail to the present teachings, examples of which are illustrated in the accompanying drawings, in which like reference numerals are used throughout to refer to identical elements. In the following description, reference is made to the accompanying drawings, which form a part hereof, and in which are shown by way of illustration specific examples embodying the present teachings. Accordingly, the following description is by way of example only.

[0014] The inventors of the present disclosure have discovered that insoluble solid particulate boron sources traditionally used to fuse ceramics do not produce sufficient nodal sites to bond networks of ceramic fibers or other ceramic particulates, resulting in ceramic composites with low tensile strength. In the present disclosure, a soluble fluxing agent is used to increase the bonding sites in the microstructure of the resulting ceramic composite after sintering. This new technology is shown to provide composites with improved tensile strength compared to composites produced using processes that use only insoluble solid fluxing agents, while maintaining the composite's thermal performance characteristics.

[0015] The present disclosure relates to a method for manufacturing a ceramic composite. As shown in step 2 of Figure 1, the method includes forming a wet ceramic composition including a plurality of individual ceramic components and a soluble fluxing agent dissolved in a solvent. As described herein, the soluble fluxing agent can be used with or without an insoluble fluxing agent. The term "individual ceramic component" refers to ceramic fibers or other ceramic particles, for example, as described herein below. Referring to step 4, at least a portion of the solvent is removed from the wet ceramic composition to form a dry ceramic composition. The dry ceramic composition includes a plurality of individual ceramic components coated with a fluxing agent. As shown in step 6, the dry ceramic composition is sintered at a sintering temperature sufficient to fuse the individual ceramic components to form crosslink sites without causing excessive melting, which could compromise tensile strength. At the crosslink sites, two or more individual ceramic components coated with the fluxing agent are in physical contact with each other.

[0016] Soluble fluxing agents, when incorporated therein, have the ability to lower the melting temperature of the ceramic material at the surface of the ceramic component. Additionally, the soluble fluxing agent may soften or partially melt the material at the surface of the ceramic component. Soluble fluxing agents are soluble in solvents, such as any aqueous or non-aqueous solvent compatible with the method of FIG. 1. Aqueous and non-aqueous solvents are described in more detail below. The particular soluble fluxing agent employed will depend, among other things, on the materials used for the individual ceramic components. For example, suitable fluxing agents can be selected from borates, carbonates, phosphates, silicates, and combinations thereof. Specific examples include borates such as lithium metaborate, lithium tetraborate, and other alkali or alkaline earth metal borates; carbonates such as alkali or alkaline earth metal carbonates (e.g., sodium carbonate, potassium carbonate, and other alkali or alkaline earth metal carbonates); phosphates such as alkali or alkaline earth metal phosphates; silicates such as alkali or alkaline earth metal silicates; and combinations of any of the above borates, carbonates, phosphates, and silicates.

[0017] By controlling the concentration of the soluble fluxing agent, the total amount of fluxing agent coated on the individual ceramic components can be adjusted to sufficiently lower the melting temperature at the surface of the individual ceramic components. The amount of fluxing agent used is sufficient to lower the melting temperature at the surface of the individual ceramic components without destroying the structure of the individual ceramic components. Using too much soluble or insoluble fluxing agent or both can result in knots or nodules at the fiber joints where excessive melting occurs. Excessive melting at the fiber joints does not increase the tensile strength of the composite and can lead to undesirable effects such as embrittlement or reduced mechanical or thermal performance. An example of such a sintered composite is shown in Figure 4, where the over-melted area is circled. The composite in Figure 4 was fabricated using two fluxing agents (lithium metaborate and boron carbide). Undesirable excessive melting can occur as a result of too much fluxing agent (either soluble or insoluble), too high a sintering temperature, or a combination of both. Using too little soluble fluxing agent can result in insufficient fusion of the individual ceramic components, preventing the desired increase in tensile strength. In one example, the amount of soluble fluxing agent (e.g., lithium metaborate or any other soluble fluxing agent described herein) ranges from about 0.5 to about 2 weight percent, such as about 0.6 to about 1.2 weight percent or about 0.9 to about 1.0 weight percent, based on the total weight of the individual ceramic components in the wet composition. In one example, the amount of insoluble fluxing agent (e.g., boron carbide or any other insoluble fluxing agent described herein) can range from about 0.3 to 2 weight percent, based on the total weight of the individual ceramic components in the wet composition. If all of the fluxing agent is consumed in the reaction, very little or no fluxing agent may remain in the final product after the ceramic is formed and dried; however, it is estimated that about 0.01 to about 0.5 weight percent of the total fluxing agent will remain in the final product after the ceramic is formed and dried. Amounts of fluxing agent outside these ranges may also be used.

[0018] The soluble fluxing agent can be dissolved in a solvent before or during the process of FIG. 1. In one example, the soluble fluxing agent is added directly to the slurry in powder form and partially or completely dissolved in the slurry solvent. In one example, 80% to 100% by weight of the soluble fluxing agent can be dissolved in the solvent, such as 90% to 100% by weight or 95% to 100% by weight. The solvent used in the process of FIG. 1 has the ability to dissolve the fluxing agent without dissolving the individual ceramic components. The solvent can be aqueous, non-aqueous, or a combination thereof. Examples of aqueous solvents include water or any solvent composed primarily of water. Examples of non-aqueous solvents include polar solvents such as alcohol.

[0019] The individual ceramic components from which the ceramic oxide is made may be in particulate or fibrous form, or any other suitable form. Examples of suitable particles include spherical or non-spherical granules, such as flakes, tubes, whiskers, or other particles. Any suitable ceramic fiber may be used. When the ceramic component is fibrous, the aspect ratio of the fiber may be as small as about 1:10 or as large as 10,000 or more, such as from about 2 to 10,000 or from about 5 to about 1000. The fiber may include solid fibers, tubular fibers such as nanotubes, or a mixture thereof. Any combination of the particles and fibers listed herein may be used.

[0020] The plurality of individual ceramic components can comprise any suitable ceramic material. Examples of suitable materials include ceramic oxides such as materials selected from titania, silica, alumina, zirconia, and combinations thereof. An example of a combination of these oxides is silica-alumina with zeolite. Other types of ceramics, such as clays and non-oxide ceramics, can also be used.

[0021] During the practice of the method of Figure 1, the solubilized fluxing agent coats the individual ceramic components as the solvent is removed during a drying step. The drying step can be accomplished by any suitable technique, such as air drying, heat, and / or vacuum to evaporate the solvent. The drying step can be performed separately or simultaneously with the heating step used in the sintering step of the method of Figure 1.

[0022] Contacting the individual ceramic components with a fluxing agent during steps 2 and 4 of FIG. 1 reduces the melting temperature of at least the surface portions of the individual ceramic components compared to the melting temperature of the untreated individual ceramic components. During subsequent sintering, the ceramic surface portions of the individual ceramic components with lower melting temperatures may fuse or "sinter" together, forming cross-link sites. Cross-link sites bond two or more individual ceramic components together where they physically contact each other. This promotes the formation of sufficient cross-link sites to bond a network of ceramic fibers or other individual ceramic components together, increasing the tensile strength of the sintered composite. An example of a sintered ceramic composite 8 including cross-link sites 10 bonding individual ceramic components 12 together is shown in FIG. 2.

[0023] The sintering temperature and sintering time used in the method of FIG. 1 depend on the materials used for the individual ceramic components and the type of fluxing agent used. The sintering temperature and sintering time can be selected to provide a desired degree of fusion or melting at the points where the individual ceramic components contact each other. Over-sintering can cause problems, such as leading to a composite that is too hard or too brittle. For example, a suitable sintering temperature is in the range of about 2000°F to about 2700°F, such as about 2200°F to about 2600°F or about 2300°F to about 2500°F. The peak firing temperature can be maintained for a suitable time to fuse the desired amount of ceramic components, such as about 1 hour to about 5 hours or about 2 hours to about 3 hours.

[0024] In addition to the soluble fluxing agents, solvents, and individual ceramic components already described, optional ingredients can be added during step 2 of the method of Figure 1. Examples of optional ingredients include colorants or emissive agents to modify the optical properties of the ceramic composite, surfactants, and particulate fluxing agents. Any other desired optional ingredients can also be used.

[0025] In one example, the disclosed method does not use an insoluble fluxing agent (e.g., a granular fluxing agent, which does not appreciably dissolve in the solvent at the process temperature, so that 80% to 100% by weight of the insoluble fluxing agent remains solid before sintering) to form the ceramic composition. In another example, the composition includes an insoluble fluxing agent in addition to a soluble fluxing agent. The insoluble fluxing agent may be, for example, a granular fluxing agent. The granular fluxing agent does not appreciably dissolve in the solvent, so that 80% to 100% by weight of the insoluble fluxing agent remains solid before sintering. Examples of suitable insoluble fluxing agents include boron carbide (B4C), boron nitride powder, and aluminoborosilicate fibers, among others. In one example, both one or more of the disclosed soluble fluxing agents and one or more of the disclosed insoluble fluxing agents are used. The "crosslink sites" described herein can be formed using soluble fluxing agents with or without the use of insoluble (eg, particulate) fluxing agents.

[0026] The present disclosure also relates to a ceramic composite. The ceramic composite includes a plurality of individual ceramic components. The individual ceramic components include (i) one or more ceramic compounds and (ii) one or more soluble fluxing agent atoms. The soluble fluxing agent atoms are incorporated into the surface of the ceramic components, thereby effectively lowering the melting temperature of the surface of the individual ceramic components. The term "incorporated," as used in the phrase "soluble fluxing agent atoms are incorporated into the surface of the ceramic components," means that atoms from the soluble fluxing agent coating are infused into, intermingled with, or bonded to the surface of the individual ceramic composite. For example, the fluxing agent atoms can be incorporated into 40% to 100% of the total surface of the individual ceramic components, such as 50% to 100%, 70% to 100%, or 90% to 100% of the total surface. Because the fluxing agent is incorporated into the surface of the individual ceramic components, the individual ceramic components can fuse together and form bridge sites where two or more individual ceramic components physically contact each other. For example, bridge sites may be formed at 30% to 100% of the contact points where two or more individual ceramic components physically contact each other.

[0027] The fluxing agent atoms incorporated into the individual ceramic components can be any atom or combination of atoms from the fluxing agent compound. For example, if the fluxing agent is lithium metaborate, the atoms incorporated into the individual ceramic components can include lithium, boron, and / or oxygen atoms. The atoms can be bonded in any manner, such as ionically or covalently, to the materials that make up the individual ceramic components to form a modified ceramic compound that has a melting point lower than the melting point of the individual ceramic components prior to the incorporation of the fluxing agent.

[0028] Any of the individual ceramic component materials described herein can be used. For example, if the individual ceramic component includes a ceramic oxide selected from titania, silica, alumina, zirconia, or a combination thereof, the modified ceramic after the introduction of the fluxing agent and sintering can be a titania ceramic, silica ceramic, alumina ceramic, and / or zirconia ceramic having lithium incorporated therein. FIG. 3 shows an example of a fiber modified to include a fluxing agent. The fiber 100 includes a ceramic oxide inner core 102. The fiber was fabricated from a ceramic oxide prior to the introduction of the fluxing agent (e.g., titania ceramic, silica ceramic, alumina ceramic, and / or zirconia ceramic). A coating 104 surrounds the inner core. The coating 104 includes a modified fiber material incorporating fluxing agent atoms mixed with the original ceramic fiber material, as described above. An example of a modifying material for the coating 104 includes lithium aluminosilicate, where lithium metaborate is used as the fluxing agent, and the individual ceramic component is an aluminosilicate fiber. The modified individual ceramic components are not limited to fibers, but may be in any desired form, such as particles, as described herein. The individual ceramic components are bonded to one another at one or more crosslink sites, as shown in Figure 2 and described above. In one example, the sintered ceramic composition includes at least one nodule formed from an insoluble fluxing agent, as described herein above.

[0029] The resulting composite may contain any optional components described herein or any resulting compounds that are the product of any reaction between these components and other components during the preparation of the composite. Exemplary optional components, including colorants, emissive agents, surfactants, and insoluble fluxing agents, may be used in any effective amount as can be determined by one skilled in the art.

[0030] The composites of the present disclosure have increased tensile strength compared to composites made using only granular fluxing agents. For example, the tensile strength of a ceramic composite can be increased by, for example, 10% to 40% or more compared to the tensile strength of a second ceramic composite made using a granular fluxing agent that is not dissolved in a solvent prior to sintering. Tensile strength as described herein is measured by ASTM D-1623-type B test procedure (tensile test) using test specimens oriented through the thickness ("TTT") or in the in-plane (IP) direction. In one example, the number of crosslink sites per unit volume of a ceramic composite of the present disclosure is greater than that of a second ceramic composite made using a similar process, with the same ingredients, and by weight, as a first ceramic composite, except that the only fluxing agent used in the second ceramic composite is an insoluble fluxing agent.

[0031] Example Test specimens were machined from selected areas representative of the entire fired and trimmed ceramic foam. Specimens were oriented along the through-thickness (TTT) and in-plane (IP) directions of the ceramic foam. A band saw was used to perform the initial rough cuts. A diamond-tipped radial arm saw and / or a disk sander were used for all final machining to minimize surface scratches. Each test specimen was bonded to a tensile load block using epoxy adhesive. After the adhesive cured overnight under ambient conditions, each specimen was placed in an Instron machine with a moving crosshead, as required by ASTM E-4. Room-temperature tensile testing was performed per ASTM D 1623, Type B.

[0032] [Table 1]

[0033] The % strength of the Example 1 ceramic relative to the baseline showed an improvement of approximately 29% for the through thickness (TTT) oriented specimens and 37% for the in-plane (IP) oriented specimens.

[0034] Additionally, the present disclosure includes examples described in the following sections. Item 1. A method for producing a ceramic composite, the method comprising: forming a wet ceramic composition comprising a plurality of individual ceramic components and a fluxing agent dissolved in a solvent; removing at least a portion of the solvent from the wet ceramic composition to form a dry ceramic composition comprising a plurality of individual ceramic components coated with the fluxing agent; and sintering the dry ceramic composition to form a ceramic composite, the sintering being carried out at a sintering temperature sufficient to fuse the individual ceramic components at crosslink sites formed where two or more individual ceramic components coated with the fluxing agent physically contact each other. Item 2. The method of item 1, wherein the fluxing agent is selected from lithium metaborate, carbonates, borates, phosphates, silicates, and combinations thereof. Item 3. The method of items 1 or 2, wherein the fluxing agent is lithium metaborate. Item 4. The method of any one of items 1 to 3, wherein the amount of soluble fluxing agent in the wet ceramic composition is in the range of about 0.5 to about 2 weight percent, based on the total weight of the individual ceramic components. Item 5. The method according to any one of items 1 to 4, wherein the solvent comprises a compound selected from water, a non-aqueous solvent, and a mixture thereof. Item 6. The method of any one of items 1 to 5, wherein the plurality of individual ceramic components comprises a ceramic oxide. Item 7. The method of item 6, wherein the ceramic oxide comprises a material selected from titania, silica, alumina, zirconia, and combinations thereof. Item 8. The method of any one of items 1 to 7, wherein the plurality of individual ceramic components are in particulate or fibrous form. Item 9. The method of any one of items 1 to 8, wherein the sintering temperature is in the range of about 2200°F to about 2700°F. Item 10. The method of any one of items 1 to 9, wherein the wet ceramic composition does not contain an insoluble fluxing agent. Item 11. The method of any one of items 1 to 10, wherein the wet ceramic composition further comprises at least one insoluble fluxing agent. Item 12. The method of item 11, wherein the amount of insoluble fluxing agent in the wet ceramic composition is in the range of about 0.3 to about 2 weight percent, based on the total weight of the individual ceramic components. Section 13. A ceramic composite comprising a plurality of individual ceramic components comprising (i) one or more ceramic compounds and (ii) one or more soluble fluxing agent atoms incorporated into at least the surface of the individual ceramic components, wherein the individual ceramic components are fused together at bridge sites located where two or more individual ceramic components physically contact one another. Item 14. The ceramic composite of item 13, wherein the fluxing agent atoms include lithium. Item 15. The ceramic composite of items 13 or 14, wherein the plurality of individual ceramic components comprises a ceramic oxide. Item 16. The ceramic composite of item 15, wherein the ceramic oxide comprises a material selected from titania, silica, alumina, zirconia, and combinations thereof. Item 17. The ceramic composite of items 15 or 16, wherein the fluxing agent atoms comprise lithium atoms bonded to the ceramic oxide. Item 18. The ceramic composite according to any one of items 15 to 17, wherein the plurality of individual ceramic components are in particulate or fibrous form. Item 19. The ceramic composite according to any one of Items 13 to 18, wherein the crosslinked sites are formed without using an insoluble fluxing agent. Item 20. The ceramic composite of any one of items 13 to 19, wherein the wet ceramic composition further comprises at least one insoluble fluxing agent. Item 21. The ceramic composite of any one of items 13 to 20, wherein the number of crosslinking sites per unit volume of the first ceramic composite is greater than that of the second ceramic composite, and the second ceramic composite is manufactured using the same process, ingredients, and weight as the first ceramic composite, except that the only fluxing agent used in the second ceramic composite is an insoluble fluxing agent. Item 22. A method for strengthening a ceramic composite, the method comprising: forming a wet ceramic composition comprising a plurality of individual ceramic components and a fluxing agent dissolved in a solvent; removing at least a portion of the solvent from the wet ceramic composition to form a dry ceramic composition comprising the plurality of individual ceramic components coated with the fluxing agent; and sintering the dry ceramic composition to form a ceramic composite, the sintering being carried out at a sintering temperature sufficient to fuse the individual ceramic components at crosslink sites formed where two or more of the individual ceramic components coated with the fluxing agent physically contact one another; wherein the ceramic composite has a first tensile strength greater than a second tensile strength of a second ceramic composite, the second ceramic composite being made with the same steps, ingredients, and weight as the ceramic composite having the first tensile strength, except that the fluxing agent of the second ceramic composite is insoluble and remains solid without dissolving in the solvent during the production of the second ceramic composite. Item 23. The method of item 22, wherein the first tensile strength is increased in the range of 10% to 40% compared to the second tensile strength, and both the first tensile strength and the second tensile strength are measured by ASTM D-1623-type B test procedure using a test specimen oriented in the through-the-thickness ("TTT") direction.

[0035] Notwithstanding that the numerical ranges and parameters setting forth the broad scope of the present disclosure are approximations, the numerical values set forth in the specific examples are reported as precisely as possible. However, any numerical value inherently contains certain errors necessarily resulting from the standard deviation found in their respective testing measurements. Moreover, all ranges disclosed herein should be understood to encompass any and all subranges encompassed within that range.

[0036] While the present teachings have been described with respect to one or more implementations, changes and / or modifications can be made to the described examples without departing from the spirit and scope of the appended claims. Furthermore, while a particular form of the present teachings may have been disclosed with respect to only one of several implementations, such form can be combined with one or more other forms of other implementations as desired and advantageous for any given or particular function. Furthermore, to the extent the terms "comprises," "includes," "has," "having," "with," or variations of these terms are used in either the detailed description or the claims, such terms are intended to be as inclusive as the term "comprises." Furthermore, in the description and claims herein, the term "about" indicates that a stated value may be slightly modified unless such modification results in non-suitability of the process or structure for the intended purpose described herein. Finally, the term "exemplary" indicates that the description is used as an example, rather than being ideal.

[0037] It will be understood that these and other form and function variations, or alternatives thereof, may be combined into many other different systems or applications. Various presently unforeseen or unexpected alternatives, modifications, variations, or improvements therein may subsequently occur to those skilled in the art, and are also intended to be within the scope of the following claims. [Explanation of symbols]

[0038] 8. Ceramic Composites 10 Crosslinking site 12 Ceramic components 100 Fiber 102 Inner Core 104 Coating

Claims

1. A method for manufacturing a ceramic composite (8), said method comprising: forming a wet ceramic composition comprising a plurality of individual ceramic components (12) and a soluble fluxing agent dissolved in a solvent, wherein 80% to 100% by weight of the soluble fluxing agent is dissolved in the solvent; removing at least a portion of the solvent from the wet ceramic composition to form a dry ceramic composition comprising the plurality of individual ceramic components (12) coated with the soluble fluxing agent; sintering the dried ceramic composition to form the ceramic composite (8), wherein the sintering is carried out at a sintering temperature sufficient to fuse the individual ceramic components (12) at crosslink sites (10) formed where two or more of the individual ceramic components (12) coated with the soluble fluxing agent physically contact one another; Including, The method wherein the amount of soluble fluxing agent in the wet ceramic composition is in the range of 0.5 to 2 weight percent, based on the total weight of the individual ceramic components (12).

2. The method of claim 1 , wherein the soluble fluxing agent is selected from lithium metaborate, carbonates, borates, phosphates, silicates, and combinations thereof.

3. The method of claim 1, wherein the plurality of individual ceramic components (12) comprises a ceramic oxide, and the plurality of individual ceramic components (12) are in particulate or fibrous form.

4. 10. The method of claim 1, wherein the sintering temperature is in the range of 2200°F (1204.4°C) to 2700°F (1482.2°C).

5. The method of claim 1 , wherein the wet ceramic composition is free of insoluble fluxing agents.

6. 10. The method of claim 1, wherein the wet ceramic composition further comprises at least one insoluble fluxing agent, and the amount of insoluble fluxing agent in the wet ceramic composition ranges from 0.3 to 2 weight percent, based on the total weight of the individual ceramic components (12).

7. A ceramic composite (8) comprising a plurality of individual ceramic components (12) including one or more soluble fluxing agent atoms incorporated into at least the surface of said individual ceramic components (12), A ceramic composite (8) in which a plurality of the individual ceramic components (12) are bonded to one another at one or more cross-linking sites, and cross-linking sites (10) are formed at 30% to 100% of the contact points where two or more of the individual ceramic components (12) physically contact one another.

8. The ceramic composite (8) of claim 7, wherein the fluxing agent atoms include lithium.

9. The ceramic composite (8) of claim 7, wherein the plurality of individual ceramic components (12) comprises a ceramic oxide, and the plurality of individual ceramic components (12) are in particulate or fibrous (100) form.

10. 10. The ceramic composite (8) of claim 9, wherein the ceramic oxide comprises a material selected from titania, silica, alumina, zirconia, and combinations thereof.

11. A method for strengthening a ceramic composite (8), said method comprising: forming a wet ceramic composition comprising a plurality of individual ceramic components (12) and a soluble fluxing agent dissolved in a solvent, wherein 80% to 100% by weight of the soluble fluxing agent is dissolved in the solvent; removing at least a portion of the solvent from the wet ceramic composition to form a dry ceramic composition comprising the plurality of individual ceramic components (12) coated with the soluble fluxing agent; sintering the dried ceramic composition to form the ceramic composite (8), wherein the sintering is carried out at a sintering temperature sufficient to fuse the individual ceramic components (12) at crosslink sites (10) formed where two or more of the individual ceramic components (12) coated with the soluble fluxing agent physically contact one another; Including, the amount of soluble fluxing agent in the wet ceramic composition is in the range of 0.5 to 2 weight percent, based on the total weight of the individual ceramic components (12); The method includes: the ceramic composite (8) having a first tensile strength greater than a second tensile strength of a second ceramic composite; the second ceramic composite is manufactured using the same process, ingredients, and weight as the ceramic composite (8) having the first tensile strength, except that the fluxing agent of the second ceramic composite is insoluble and remains solid without dissolving in a solvent during the manufacture of the second ceramic composite; the first tensile strength increases in the range of 10% to 40% compared to the second tensile strength; and both the first tensile strength and the second tensile strength are measured by ASTM D-1623-type B test procedure using test specimens oriented in the through-the-thickness ("TTT") direction.

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