DE19643148C2 - Manufacturing process for ceramic bodies with microstructure and uses - Google Patents

Description

Structured, functional ceramic layers made of piezoceramic, Ferroelectrics or ceramic phosphors are used for use spatially resolved applications as sensor or actuator arrays Untitled. Continuous layers in la terally disassembled individual elements. at Ceramic thin films can be used in microelectronics known lithographic processes are used. At ke Ramische thick layers with a thickness of more than 100 microns can usually only be structured after layer generation by mechanical separation, such as sawing, successfully gene.

Furthermore, ceramic processes are known in which the Ceramic raw mass in structured plastic matrices is poured. This plastic burns during sintering matrix or volatilize otherwise, the matrix Zen shape largely in the cast ceramic as a negative shape preserved. However, this technique is limited to relatively large structures with low aspect ratios.

From US 5 137 776 a ceramic body with a ge ordered patterns of cavities known by single laminate a burnable pattern between ceramic green foils lien and subsequent sintering are generated.

WO 88/08360 describes a method for producing a ceramic body with cavities arranged therein knows the green foils with the help of a liquid jet eroded and then sintered together.

Another problem with known structured, ceramic Layers consists in the fact that the kera mix individual elements have no cohesion, so that  the structure has to be fixed in some way for example by mounting on a substrate or by Filling the spaces with an auxiliary.

There are also structured ceramic layers Integrated processes are also known. By directed, anisotropic evaporation of alkali halide phosphors pre-structured substrates will receive phosphor layers ten that have structural dislocations. Will also be a Substrate selected with a low coefficient of thermal expansion;  so the structural dislocations in the phosphor layer form cracks when cooling, so that with a grid structure the fluorescent layer completely from each other separate individual elements disintegrate. That kind of structure However, it is not suitable for most ceramics and also leads to individual elements that are insufficient only small distances apart.

The object of the present invention is a Manufacturing process for a monolithic, structured Specify ceramics.

According to the invention, this object is achieved by a method Claim 1 solved. Advantageous embodiments of the invention can be found in the other claims.

The ceramic body produced in this way is characterized by a microstructure made up of areas with a is formed higher density than the other areas. For example, the microstructure represents a two-dimensional one Pattern that is approximately vertical to the pattern plane congruent over the entire thickness of the ceramic body extends. Each section plane of the body parallel to that Pattern plane of the one- or two-dimensional pattern points therefore approximately the same pattern.

The ceramic body can be flat as a layer or foil be formed in which the two-dimensional pattern in the Foil level is arranged. The ceramic body can also be a solid body with spatial shape. The two dim Sional patterns or their pattern plane can be parallel to a main surface or parallel to one of the smaller surfaces of the solid body can be arranged.

The advantage of the ceramic body produced according to the invention is its monolithic structure, the good mechanical properties of the  Body guaranteed. The microstructure is integrated into the body and is essentially differentiated by areas density. In addition to the difference in density different areas of the microstructure can Areas also in others, directly or indirectly by density differentiate dependent properties. Take it with you the density reduces the porosity of a ceramic. This in turn is direct for translucent translucency responsible ceramics.

A lower density also has a lower heat capacity and lower heat conduction. A low gere density affects the impedance and thus also the piezo electrical properties of a piezoelectric ceramic, such as coupling factor, quality factor and piezoelectric trical coefficient. The polarizability of a ferro electrical ceramics can depend on the density. just so is the conductivity to heat or sound as well with conductive ceramics also against current of density dependent. The permeability to gases and liquids varies with density. In general, with the Erfin anisotropic with regard to the properties mentioned Achieve behavior.

With the invention it is thus possible to relate one under various properties integrated structured, kera to get mix body. In an embodiment of the body the pattern of the microstructure has an aspect ratio from more than 5. That is, the depth of the two-dimensional len pattern is high compared to the lateral structural dimensions solutions in the pattern plane. The lateral structure dimensions, with a rastered structure, for example the rasterab stood, can be varied in wide widths, at for example between 5 and 1000 microns. Preferably, the ceramic body has a regular microstructure. at for example, discrete areas are of relatively high density laterally distributed next to each other so that a regular,  two-dimensional pattern is created in which the area higher density completely from areas lower Density are surrounded. In this way, the areas ho dense discrete individual elements of a ceramic component represent those where the density improved Property of the functional ceramic is used.

According to the areas of higher density in the Her setting process through specific and targeted addition of Sin auxiliary materials to ceramic raw mass or to ceramic Green foils reached, which are then sintered. The Areas of ceramics provided with sintering aids are accelerated or improved sintering, so that these areas have a higher density after sintering exhibit.

According to the invention, for example, a green sheet is produced in conventionally drawn or poured. The addition of the Sin The auxiliary agent is made by applying the sintering agent on the green sheet, for example by printing, spraying hen or other processes that are used to produce a Mu are suitable. With this version it is from before part of applying the sintering aid in liquid form for example as a liquid or as a solution. Also a pa The consistency of the sintering aid is structural suitable application. The amount of liquid or the sintering aid is dimensioned so that a sufficient but minimum amount of sinter tool is applied to the ceramic. In this way sharp structures can be created. The sintering aid medium can be superficially applied to the green sheet or due to its preferably liquid nature also penetrate the green sheet. With superficial opening The sinter is diffused onto the green sheet tools through the entire film, so that the areas defined by the addition of sintering aids  higher density through the entire thickness of the green sheet by extending.

From green foils, onto the sintering aids according to the Patterns for the microstructure can be applied by stacking, laminating and sintering together also massi ve manufacture ceramic bodies with a microstructure. meh rere foils are with sintering aids in the same Mu ster and stacked flush so that the Patterns lie congruently on top of each other. In this way it is ensured that the sintering aid is not by Dif fusion must penetrate the entire thickness of the body. because through particularly sharp structures in solid bodies pern get the high aspect ratios of up to 100 can have. The lamination takes place in a manner known per se Way, where appropriate with the help of bindemite the stack under pressure and possibly under increased pressure Temperature is compressed. Because during the sintering all of the binder burns or volatilizes a monolithic, ceramic body in this way too obtained, which has a high mechanical stability.

In a further embodiment of the invention Next, ceramic green sheets are produced in which the sinter auxiliary is already part of the ceramic raw material and therefore homogeneous in mass and therefore in every green sheet is distributed. Such ceramic green foils with sinter tools alternately stacked with green foils that are not Contain sintering aids, is by lamination and ge joint sintering of such a stack is a monolithic, ceramic body with microstructure obtained, the Mi krostructure a layer structure with alternating layers is higher and lower density. By varying the thickness of the green foils or by appropriate stacking order can use different layer structures with the same or different layer thicknesses are generated. Since the The thickness of a green sheet, for example, is between 10 and 1000 µm  Ceramic can be selected in this way Microstructured bodies are obtained in which the mini male lateral dimension (layer thickness of the individual layers) is 10 µm minus the sintering shrinkage.

In a further embodiment of the invention, a sol Stack of green foils with a layered structure after laminating vertical to the film levels in plates or layers divided. These plates now point in the plate plane stripe pattern. By laminating several sol cher plates, possibly in alternation with homogeneous Green sheets, second batches can be obtained through Sintering in a ceramic body with a more complex mi Crostruct can be transferred. Will the plates at for example alternating with homogeneous green foils without Sin aids are stacked after laminating and sintering preserved a ceramic body, the narrow channels with rela tiv long length and high aspect ratio contains. A sol cher body is particularly for anisotropic conduction of ins special light, electricity or heat, provided a prin partially conductive ceramic is used. It is possible also, this body again vertically to the channels in small nere body to divide, then the identical Mi have crostructure. For anisotropic conduction of liquids Gases or gases are the discrete channels in the body as loading rich lower density and thus higher porosity trained over the remaining areas.

The invention is suitable for any type of ceramic, since sintering aids are known in principle for each type of ceramic. These are often specific to individual types of ceramics. Since a large number of ceramic types and sintering aids are known, only an exemplary list should suffice here. A compilation of common sintering aids for certain types of ceramics including the proposed concentration is given, for example, in the following table:

Regarding the mode of action of sintering aids, ver different mechanisms known. In principle, the accelerates Adding sintering aids to compact the powder bodies Ceramics, for example by suppressing grain growth in the compression phase, increasing the vacancy diffusion rate or by forming liquid or secondary phases.

In the following the invention is based on exemplary embodiments play and the associated, not to scale seven Figures explained in more detail.

Figs. 1 to 4 show cross-sections with reference to schematic various process steps in the manufacture ke ramischer body with microstructure.

Fig. 5 shows another ceramic body in perspective view, while

FIGS. 6 and 7 in a perspective view the herstel development of a solid ceramic body having aufwendi ger microstructure show.

embodiments

In the first exemplary embodiment, a body is to be produced from a phosphor ceramic which has defined areas of high transparency. For this purpose, polymer-bound foils 1 are drawn, for example, from the oxide powder (y _x Gd _1-x ) ₂ O ₃ : Eu without the addition of sintering aids. The thickness of the individual foils is between 10 and 1000 µm and in particular between 30 and 500 µm. The area of the green foils can be chosen between 0.1 cm ² and 1 m ² , in particular between 1 cm ² and 0.1 m ² . The green density is between 10 and 60 percent, especially between 30 and 50 percent. The binder consists, for example, of PMMA ester (polymethyl methacrylate). Sintering aids 2 are now applied to the foils 1 in a structured manner. Magnesium oxide MgO or titanium dioxide TiO ₂ is particularly suitable as a sintering aid for the selected phosphor ceramic. The sintering aid is preferably not applied via the (solid) oxides, but in particular via organometallic precursor compounds. These are brought up in the form of their solutions in suitable solvents in liquid form on the green sheets 1 . Printing processes are suitable as application processes, in particular those which are known from ink-jet printing processes. Suitable precursor compounds are, for example, tetrabutyl orthotitanate, magnesium ethylate or magnesium acetate.

The sintering aid is applied in a structured manner in the form of a pattern, the structure width of which is chosen between 10 and 500 μm and in particular between 50 and 200 μm. The structure distance is between 15 µm and 1 mm and in particular between 50 and 500 µm. In FIG. 1, such printed with sintering aids 2 green sheet 1 is illustrated in schematic cross section in which the printed sintering aid in the form of raised structures is shown. On the other hand, a liquid sintering aid can completely penetrate the green sheet.

Then the green sheet is at temperatures between 1400 and 2000 ° C in air, in an oxygen-containing atmosphere  or sintered in a vacuum. Preferred sintering temperatures lie between 1500 and 1700 ° C.

Fig. 2 shows the ceramic body 5 , which is obtained after sintering. In the areas where structured sintering aid 2 has been printed on, the ceramic body 5 has areas 4 of relatively high density and areas 3 relatively lower density. The regions 3 with a relatively lower density can thus have 5 percent porosity and thus have an approximately 4 × higher porosity than the regions 4 with a higher density and a porosity of, for example, 1.2 percent.

The sharpness of the structures or the delimitation of the areas different density from each other depends on the ge chose sintering aids. With titanium-containing sintering aid tel are particularly strong changes in the field of printed sintering aid achieved as it is opposite magne sium-containing sintering aids have better sintering activity shows. In addition, since the diffusion of titanium oxide during the Sintering is less, so they are particularly sharp get limited areas of different densities.

For the ceramic body 5 made of fluorescent ceramic produced in the first exemplary embodiment, it is primarily not a microstructuring by regions of different density but rather the associated different pore quantity that is interesting for certain applications. The transparency of the fluorescent ceramic 5 is closely linked to the pore quantity, which depends not only on the number of pores but also on the size of the pores. Since the light in the phosphor ceramic 5 is scattered at each pore, the transparency of the ceramic decreases with an increasing number of pores. With the same porosity, which is determined as the volume fraction of the pores in the ceramic, a ceramic that has more small pores has a lower transparency than a ceramic with fewer but larger pores. Since the microstructuring of the ceramic body 5 made of fluorescent ceramic is preferably a differentiation with regard to the transparency, the sintering aid and the sintering process are preferably designed so that fewer and larger po ren arise in the areas printed with sintering aid 2 . This can be achieved with higher sintering times, for example. Magnesium oxide as a sintering aid also produces larger pores than titanium oxide.

Fig. 3 shows a modification of the method with the aid of which thicker ceramic bodies can be produced. For this purpose, a number of green foils 1 are printed in a structured manner with sintering aids 2 , as has already been illustrated with reference to FIG. 1. Subsequently, several of the printed foils are stacked flush on top of one another, so that the structures 2 of the printed sintering aid come to lie on top of one another in an identical manner. The number of film layers is chosen between 2 and 50 and in particular between 5 and 25. The lamination can be supported with the help of additional binders. However, it is sufficient to simply stack the printed foils and press them together under pressure and at a slightly elevated temperature. The sintering of the laminated stack can take place under the same conditions as the sintering of the individual foils.

Fig. 4: After sintering, a monolithic, ceramic body 5 is obtained from the film stack, which has areas 4 with a relatively high density compared to the other areas 3 . In contrast to ceramic bodies, which are obtained from an individual printed green film, the structures produced in this way have a higher aspect ratio, which can be up to approximately 50, depending on the number of individual films laminated.

In a further process which is fundamentally different from the first two exemplary embodiments, green foils 6 are again drawn, for example, from the oxide powder (Y _x Gd _1-x ) ₂ O ₃ : Eu ge. In addition, green foils 7 are produced in the same way, in which a sintering aid is already homogeneously distributed in the ceramic slip. For example, about 1000 ppm magnesium acetate Mg (OC ₂ H ₅ ) _{2 are} added to the ceramic slip. The thickness of the green sheets 6 and 7 be between 10 and 1000 microns and is chosen in particular between 30 and 500 microns. The area of the individual foils is between 0.1 cm ² and 1 m ² and is chosen in particular between 1 cm ² and 0.1 m ² . The green density is between 60 percent and 10 percent and in particular between 30 and 60 percent. Polyvinyl alcohol is preferably used as the binder. Different green foils 6 and 7 are now layered and laminated together. The number of green foils in the stack is between 3 and 10,000 and in particular between 50 and 1000. The stack is then sintered between 1400 and 2000 ° C. in air, in an oxygen-containing atmosphere or in a vacuum. Preferred sintering temperatures are between 1500 and 1700 ° C.

A ceramic body with a layer structure is obtained, of alternating layers with higher and lower density having. This ceramic body is characterized by a particularly high property gradients at the borders of the un different layers, so it has a sharp structured microstructure. Since the individual layers or the different areas of different density of the monolithic ceramic body due to its transparency compared to visible light, the ceramic Body for the production of a one-dimensional radiation detection torarrays (detector line) for high-energy radiation be set. By absorbing high-energy radiation luminescence generated within the ceramic body light can be due to the different transparency of the layers predominantly within the more transparent Layers through the ceramic body (fluorescent body) conduct. So the one-dimensional location information remains  get the place of absorption of the high-energy radiation The luminescent light can on the transparent layer of the ceramic body can be detected within the the absorption of the high-energy radiation has taken place. For use as a radiation converter array, the mono lithic, ceramic bodies by sawing vertically to the Layer levels in smaller bodies with identical microstructure be divided. A surface coating and coating device with reflective layers can follow.

Fig. 6: In a further embodiment of the invention, the laminated film stack shown in Fig. 5 is divided vertically to the layer planes into several similar plates with an identical layer structure (stripe pattern) prior to sintering (see, for example, the cutting line indicated in Fig. 5 SL). Several such plates 8 with stripe pattern can now be alternately stacked with complete green foils 6 or 7 (with or without) sintering aids to form a further foil stack 9 . This is sintered in an analogous manner to form a monolithic, ceramic body which has a microstructure in the form of a now two-dimensional pattern. The ceramic body, which is designed similarly to the stack 9 shown in FIG. 7, now has fine channels 10 which have a higher density than the other regions of the stack and thus have higher transparency. These channels 10 run through the entire ceramic body and are completely separated from each other, that is, each channel is ben on the whole from ceramic with a relatively lower density ben. This ceramic body can be used to produce a two-dimensional resolving radiation converter array. Luminescent light generated in the ceramic body 9 is now passed through the body 9 not only parallel to the layers but parallel to the channels 10 , the two-dimensional location information, that is to say the location of the absorption of the higher energy radiation, being retained.

Although the invention is only based on the exemplary embodiments fluorescent ceramic was explained, it can be in principle with any type of ceramic for which Sintering aids are known. Ceramic bodies are obtained by, whose microstructuring not only be regarding different density but also regarding white other, typical ceramic properties.

Claims (10)

1. A method for producing a ceramic body ( 5 ) with a microstructure,
in which first regions ( 4 ) of higher density are defined by adding a sintering aid ( 2 ) to an unsintered ceramic ( 1 ),
in which second areas of low density are provided by not adding sintering aids,
in which the green ceramic ( 1 , 2 ), in which the named first and second regions are defined, is sintered to the ceramic body ( 5 ), and
in which after sintering in the ceramic body, where sintering aid has been added, regions ( 4 ) with a higher density than the other regions ( 3 ), which represent the microstructure, form. 2. The method according to claim 1, wherein the addition of the sintering aid is carried out by printing ( 2 ) on ceramic green sheets ( 1 ). 3. The method according to claim 1 or 2, in which a plurality of ceramic green sheets ( 1 ) are printed in the same way with sintering aids ( 2 ) and are transferred into a monolithic, thicker body ( 5 ) by flush stacking, laminating and sintering together. 4. The method according to claim 1, in which homogeneous, ceramic green sheets ( 6 , 7 ) are produced without and with homogeneously distributed sintering aid, stacked on top of one another in the desired manner and order, and transferred and sintered together into a monolithic, thicker body and where the microstructure is one-dimensional due to the order of layers with higher and lower density. 5. The method according to claim 4, wherein the stacked green sheets ( 6 , 7 ) after lamination vertically to the film planes into a strip pattern having de plates ( 8 ) are divided, in which several such plates ten ( 8 ) with the same or different strip pattern alternating with homogeneous green foils ( 6 ) to a second stack ( 9 ) and laminated, and in which this second stack by sintering in the ceramic body is performed. 6. The method according to claim 5, where the body vertically to the foil planes into smaller ones Body with identical microstructure is divided. 7. Use of one of claims 1 to 6 herge posed bodies with microstructure for spatially resolving Radiation detectors. 8. Use of a herge according to one of claims 1 to 6 provided body with microstructure for anisotropic conduction of light, electricity or heat. 9. Use of one of claims 1 to 6 herge made bodies with microstructure as ultrasound transmitters or receiver. 10. Use of one according to one of claims 1 to 6 Herge provided body with microstructure for anisotropic conduction of finely dosed gases and liquids.