Patent Application
20200207669
The present invention claims the benefit of priority to Patent Application No. 107147555, filed in Taiwan on Dec. 28, 2018, which is hereby incorporated by reference in its entirety.
The present invention is related to a porous ceramic composite structure and a method of making the same and, more particularly, to a porous ceramic composite structure having high porosity and high mechanical strength and a method of making the same.
There is often a need for fluid dispersion, fluid flow regulation, filtration and the like in industries such as automobile, purification, filtration and semiconductor. In the current market, a monolithic porous ceramic (for example, high-purity alumina or cordierite) sintered body is mainly used as a carrier to achieve the aforementioned functions. When such a monolithic porous ceramic sintered body is used as a carrier, the larger the porosity, pore size or pore connectivity, the more fluid that can pass through it. As a result, more fluid can be processed per unit time. However, as the porosity and pore size increase, the carrier has lower mechanical strength. Due to the mechanical strength required, the porosity and/or pore size of the carrier cannot be arbitrarily increased in order to regulate the range of fluid flow. Especially in the case where large porosity and high flow rate are required, the mechanical strength of the carrier may be too low, leading to a great limitation on application in harsh circumstance where corrosion resistance is required.
It is in this context that various embodiments of the present invention arise.
The present invention solves the aforementioned problems by providing a porous ceramic composite structure. One or more inner porous ceramic bodies in the porous ceramic composite structure have high porosity, allowing more fluid to pass therethrough. Furthermore, the inner porous ceramic bodies are supported by a ceramic sheath with high density such that the porous ceramic composite structure of the present invention can maintain good mechanical properties.
The present invention provides a porous ceramic composite structure, comprising a ceramic sheath and one or more porous ceramic bodies. The ceramic sheath comprises a pillar and one or more through-holes. The pillar comprises a top surface, a bottom surface and a sidewall. The one or more through-holes extend between the top surface and the bottom surface. The one or more porous ceramic bodies are located in the one or more through-holes of the ceramic sheath, and have a plurality of pores, which are interconnected with one another to enable fluid to pass therethrough. The ceramic sheath comprises a ceramic material having a theoretical density, and the ceramic material has a high density of between about 70% and about 99.99% of the theoretical density.
In one embodiment, in a cross section of the pillar, the cross-sectional area of the ceramic sheath occupies about 10% to about 90% of the cross-sectional area of the porous ceramic composite structure. For example, the cross section is parallel to the top surface of the pillar. The total cross-sectional area of the porous ceramic composite structure includes the cross-sectional areas of the ceramic sheath and the one or more porous ceramic bodies.
In one embodiment, the one or more porous ceramic bodies have a porosity of between about 30% and about 90%. The one or more porous ceramic bodies have a pore diameter of between about 0.1 and about 500 μm.
In one embodiment, the one or more porous ceramic bodies comprise the same ceramic material as the ceramic sheath. The ceramic material is selected from the group consisting of oxide ceramic, silicon carbide, silicon nitride, aluminum nitride and a combination thereof. The oxide ceramic may be, for example, aluminum oxide, zirconium oxide, magnesium oxide, mullite, cordierite or a combination thereof.
In one embodiment, the one or more porous ceramic bodies partly fill the one or more through-holes of the ceramic sheath, thereby forming one or more blind holes in the pillar.
The present invention also provides a method of making porous ceramic composite structure, comprising: (a) forming a composite structure green body comprising a sheath green body and one or more pore-forming green bodies, the sheath green body comprising a pillar and one or more through-holes, the one or more pore-forming green bodies are located in the one or more through-holes of the sheath green body; (b) sintering the composite structure green body; and (c) cooling to form the porous ceramic composite structure.
In one embodiment, the step (a) comprises: pressing ceramic powder into the sheath green body by a mold; mixing an additional amount of the ceramic powder with a pore former to form pore-forming powder; pressing the pore-forming powder to form the pore-forming green body; and filling the one or more through-holes of the sheath green body with the pore-forming green body to form the composite structure green body.
In another embodiment, the step (a) comprises: mixing a ceramic powder, a dispersant, a binder and a liquid to form sheath slurry; mixing an additional amount of the ceramic powder, an additional amount of the dispersant, an additional amount of the binder, an additional amount of the liquid and a pore former to form pore-forming slurry; forming a composite structure by co-extrusion of the sheath slurry and the pore-forming slurry; and drying the composite structure to form the composite structure green body. The sheath green body is formed from the sheath slurry. The one or more pore-forming green bodies are formed from the pore-forming slurry.
In one example, the pore former may be carbon powder, graphite powder or carbon-containing compound. In another example, the pore former may be a mixture of starch and hydrogen peroxide.
These and other aspects are described further below with reference to the drawings.
In the drawings, similar or the same components are designated by the same numerals.
The objects, advantages and features of the present invention will become apparent from the following detailed descriptions in conjunction with the accompanying drawings.
In the following description, numerous specific details are set forth to provide a thorough understanding of the presented embodiments. The disclosed embodiments may be practiced without some or all of these specific details. In other instances, well-known structures and process operations have not been described in detail to not unnecessarily obscure the disclosed embodiments. While the present invention will be described in conjunction with the specific embodiments, it will be understood that the specific embodiments are not intended to limit the disclosed embodiments. Terms such as “above”, “below”, “top”, “bottom”, “inner”, “outer” and so forth will be used in the following description. However, these relative terms are used for ease of understanding and are not used in a limiting sense. Furthermore, the various embodiments shown in the drawings are illustrative, and are not necessarily drawn to scale.
As shown in
After the composite structure green body is formed, it is sintered in operation 104. For example, in an atmosphere containing 6 to 18% by volume of oxygen, the composite structure green body is heated at a temperature of about 500 to 900° C. to decompose pore former therein, thereby forming voids in the pore-forming green body. Next, the composite structure green body is heated, at a heating rate of 5 to 600° C. per hour, to a sintering temperature for a period of time, such as 180 minutes. The sintering temperature may be between about 1200 and 1800° C. This sintering treatment converts the sheath green body into a ceramic sheath having a high density, which serves as the main support structure of the entire porous ceramic composite structure. Further, after the sintering treatment, the pore former in the pore-forming green body is decomposed, so that a porous ceramic body can be formed. The porous ceramic body has many tiny pores that can be interconnected with one another to allow fluid to pass therethrough to achieve the functions of fluid filtration, flow regulation or the like.
Then, in operation 106, the temperature is lowered to obtain the porous ceramic composite structure of the present invention.
Referring to
The ceramic sheath 210 is substantially composed of ceramic material. The ceramic material may be selected from, for example, oxide ceramic, silicon carbide, silicon nitride, aluminum nitride and a combination thereof. The oxide ceramic may be selected from aluminum oxide, zirconium oxide, magnesium oxide, mullite, cordierite and a combination thereof, but is not limited thereto. In general, a ceramic material has a theoretical density. In order to provide good mechanical strength, the ceramic material in the ceramic sheath 210 has a high density of between about 70% and 99.99% of its theoretical density.
The porous ceramic body 220, having many tiny pores, is also substantially composed of ceramic material. In general, the ceramic materials of the porous ceramic body 220 and the ceramic sheath 210 have the same chemical composition but have different density. In another embodiment, the ceramic materials of the porous ceramic body and the ceramic sheath may be different. The ceramic material of the porous ceramic body 220 may be selected from, for example, oxide ceramic, silicon carbide, silicon nitride, aluminum nitride and a combination thereof. The oxide ceramic may be selected from aluminum oxide, zirconium oxide, magnesium oxide, mullite, cordierite and a combination thereof, but is not limited thereto. In one embodiment, the porous ceramic body 220 has a porosity of between about 10% and 90%. In one embodiment, the porous ceramic body 220 has a pore diameter of between about 0.1 and 1000 μm. Alternatively, the porous ceramic body has a pore diameter of between about 0.5 and 500 μm.
In a cross section of the pillar 212 of the porous ceramic composite structure 200 or 300, the cross-sectional area of the ceramic sheath occupies about 10% to about 90% of the entire cross-sectional area of the porous ceramic composite structure, which includes the cross-sectional areas of both of the ceramic sheath 210 and the one or more porous ceramic bodies 220.
In the porous ceramic composite structure 200 shown in
Returning to
In operation 504, ceramic powder is mixed with a pore former to form granular powder. The ceramic powder used to form the granular powder may be selected from oxides (for example, aluminum oxide, zirconium oxide and magnesium oxide), silicon nitride, aluminum nitride, silicon carbide and a combination thereof. In one embodiment, the ceramic powder used to form the sheath green body may be different from the ceramic powder used to form the granular powder. In another embodiment, the ceramic powder used to form the sheath green body is the same as the ceramic powder used to form the granular powder. The pore former may be selected from carbon powder, graphite powder and a carbon-containing compound. The carbon-containing compound may be a carbon-containing organic compound such as flour, petroleum coke, starch, carbon black, foamable resin, foam resin, poly(methyl methacrylate) (PMMA), polystyrene (PS), poly(ethylene terephthalate) and a combination thereof. Alternatively, the pore former can be a mixture of starch and hydrogen peroxide. In other embodiments, the ceramic powder used to form the sheath green body and the ceramic powder used to form the granular powder may be mixed with other chemical additives such as dispersant, release agent, binder or plasticizer.
In one embodiment, in operation 504, after the ceramic powder is mixed with the pore former, a liquid may be added and the mixture is stirred to form slurry. The slurry is dried to form the granular powder. Then, in operation 505, the granular powder is pressed to form a pore-forming green body.
In another embodiment, in operation 504, after the slurry is dried to form the granular powder, the granular powder is not pressed. Instead, in the next operation 506, the granular powder is filled into the sheath green body, and then the granular powder is pressed and shaped.
While operation 502 is described first and operations 504 and 505 are described next in the foregoing, it should be understood that the order of these operations is not limited thereto. Operations 504 and 505 may be performed first, followed by operation 502. Alternatively, operation 502 and operations 504 and 505 can be performed simultaneously.
Next, in operation 506, the pore-forming green body is filled into the one or more through-holes of the sheath green body, and then pressure is applied thereto so that the outer periphery of the pore-forming green body makes close contact with the inner periphery of the sheath green body, thereby obtaining a composite structure green body. After the pore-forming green body is filled and the pressure is applied, the pore-forming green body may fully fill the one or more through-holes of the sheath green body. Alternatively, the pore-forming green body may not fully fill the one or more through-holes of the sheath green body so as to form one or more blind holes (such as the blind hole 230 shown in
In one embodiment, the ceramic powder used to form the sheath slurry may be different from the ceramic powder used to form the pore-forming slurry. In another embodiment, the ceramic powder used to form the sheath slurry is the same as the ceramic powder used to form the pore-forming slurry. Any suitable ceramic powder and pore former can be used, such as the ceramic powder and pore former described above. The dispersant may be polyvinyl alcohol. The binder may be selected from sodium hydroxymethylcellulose, hydroxymethylcellulose, polyvinyl alcohol and a combination thereof. The liquid may be selected from various suitable solvents, such as water and ethanol.
Referring to
The porous ceramic composite structure of the present invention has a high-density ceramic sheath as a main support structure, making the whole porous ceramic composite structure have good mechanical properties. Since the ceramic sheath can support the inner porous ceramic body, the porosity, pore size, pore connectivity, etc. of the porous ceramic body can be adjusted as needed to regulate the range of fluid flow without being limited by the mechanical strength required.
Although the foregoing embodiments have been described in some detail for purposes of clarity of understanding, it will be apparent that certain changes and modifications may be practiced within the scope of the appended claims. It should be noted that there are many alternative ways of implementing the methods and structures of the present embodiments. Accordingly, the present embodiments are to be considered as illustrative and not restrictive, and the present invention is not to be limited to the details given herein.
It is to be understood that the configurations and/or approaches described herein are exemplary in nature, and that these specific embodiments or examples are not to be considered in a limiting sense, because numerous variations are possible. The specific routines or methods described herein may represent one or more of any number of processing strategies. As such, various acts illustrated may be performed in the sequence illustrated, in other sequences, in parallel, or in some cases omitted. Likewise, the order of the foregoing processes may be changed.
The subject matter of the present disclosure includes all novel and nonobvious combinations and sub-combinations of the various processes and configurations, and other features, functions, acts, and/or properties disclosed herein, as well as any and all equivalents thereof.
| Number | Date | Country | Kind |
|---|---|---|---|
| 107147555 | Dec 2018 | TW | national |
