WO1996003355A1

WO1996003355A1 - Process for producing ceramic microstructures

Info

Publication number: WO1996003355A1
Application number: PCT/EP1995/002242
Authority: WO
Inventors: Hans-Joachim Ritzhaupt-Kleissl; Jürgen Laubersheimer
Original assignee: Forschungszentrum Karlsruhe Gmbh
Priority date: 1994-07-22
Filing date: 1995-06-10
Publication date: 1996-02-08
Also published as: DE4425978C1

Abstract

The purpose of the invention is to propose a process for producing ceramic microstructures. According to the invention, the process comprises the following steps: a) a gelling sol is made from several organo-metallic liquid components; b) a mould is prepared which bears complementary structures to the microstructures having an electrically conductive surface; c) the complementary structures of the mould are electrophoretically and uniformly filled with the sol, in which the electrically conductive surface is used as an electrode and the sol is turned into a gel; d) the gel is dried; e) the mould is removed and f) the gel is made into a ceramic by burning off the organic components.

Description

Process for the production of ceramic microstructures

The invention relates to a method for producing ceramic microstructures according to claim 1.

DE 43 10 068 C1 discloses a process for producing a plate-shaped microstructure body made of ceramic, in which a film produced according to the "Doctor-Blade ^M process is provided with a microstructured embossing tool with the complementary structures of the embossing tool The embossed film is sintered and transferred into a ceramic microstructure body.

An overview of the processes for producing a ceramic body by molding is contained in the publication E. Briscoe, CB Ponton: "ceramics - the fabrication challenge", Materials Science and Technology, September 1986, Vol. 2, 910-912 in particular various pressing processes, casting processes, extrusion processes and the coating of metals by gas phase deposition (CVD). The manufacture of various machine parts is described.

Electrophoresis and its use in shaping ceramics are described in the "Handbook of Ceramics", edited by Dr.-Ing. Wilhelm Büke, Verlag Schmid GmbH, Freiburg i. Brg. , treated. Electrophoresis using "lyophobic" brine (eg iron (II hydroxide, clay, quartz, sulfur in water) is explained on page 16. On page 20, the use of electrophoresis for the production of articles of daily use is reported Manufacture is based, inter alia, on a slip of 50% quartz and 59% clay, and the electrophoretic deposition is carried out on a porous sintered bronze or a porous graphite or graphite cement.

The basics of electrophoresis and its application for the production of ceramic bodies are described in detail in "Advanced Ceramic Processing and Technology", edited by John GP Bin ner, Nayes Publications (1990). The theoretical basics of electrophoresis of ceramic base materials suspended in a solvent are discussed in the chapter "Fundamentals of Electrodeposition" on page 257 ff. The chapter "Applications Developed to Pilot Plant Scale" on page 268 ff. Describes the production of a film made of clay and a tube made of β-aluminate which is closed on one side. It is stated that it is almost impossible to predict whether a suspension will precipitate electrophoretically (page 263 below).

The object of the invention is, in addition to the above-mentioned impression of a film produced by the "doctor blade" process, to provide a further process by means of which ceramic microstructures can be produced.

The object is achieved according to the invention by the method described in claim 1. The further claims indicate preferred embodiments of the method.

The starting point of the process are liquid organometallic compounds from which a gellable sol is formed. Mostly alcoholates are used for the production of sol. As a sol, for example, the precursor for a ceramic made of lead zirconium titanium oxide [PZT ceramic, Pb (Zrn 52 ^τi _{0 48} ) ° ₃ 3 can be used. To avoid drying cracks in a later process step, organic auxiliaries, for example formamide, can be added to the sol. The microstructure in the finished ceramic microstructures can be adjusted by adding binders and plasticizers.

Furthermore, to carry out the method, a "lost" shape is required, which can either consist of a metal that can be selectively dissolved with respect to the ceramic, or of a plastic that can be burned or that can be selectively dissolved by chemical means. A suitable material for the shape is poly methyl methacrylate (PMMA), which can be burned without residue. The form contains the complementary structures of the microstructures to be produced from ceramic. The complementary structures can in turn be obtained by deep X-ray lithography, mechanical microfabrication or by molding an embossing tool. A metal mold can be produced by galvanic molding of a plastic mold.

The complementary structures must be provided with an electrically conductive surface, provided that the material of the mold is not electrically conductive per se. In a form made of electrically non-conductive plastic such as. B. PMMA, the conductive surface is preferably by dusting a metal (sputtering), e.g. B. made of gold.

The electrically conductive surface of the complementary structures is switched as an electrode during the subsequent electrophoresis step. Any inert electrode, e.g. B. a platinum sheet can be used. The gel particles are preferably deposited on the electrically conductive surface at constant current, preferably at 30 to 100 mA, with voltages of up to 250 V being established. Typical and particularly preferred values for current and voltage in the PZT deposition are 30 mA and 80 V. The deposition rate of the PZT sol in this case is approximately 20 μm / min. The distance between the two electrodes should be at least 3 cm. Electrophoretic deposition can continue until the complementary structures of the form are filled and covered.

Surprisingly, in electrophoresis, the components of the sol are deposited homogeneously in accordance with the stoichiometric composition of the sol. In the electrophoresis step, the auxiliaries, binders and plasticizers are deposited in the mold together with the components. The sol gels during the electrophoretic deposition. After the electrophoretic gel separation, the gel filling the mold is dried. Drying is preferably carried out in several steps, each lasting a few hours: B. Luft¬ drying, drying at 50 to 100 ° C in air and finally at 50 to 100 ° C in a vacuum. If drying cracks cannot be completely ruled out, in this case again gel of the same composition can be deposited electrophoretically. Since the deposition preferably begins at the points closest to the electrode, drying cracks are filled in from the bottom of the crack.

Alternatively, the complementary structure of the mold can first be filled in only partially, after which it is dried and then a further electrophoresis step takes place. These steps can be repeated several times. In the subsequent electrophoresis step, the cracks which have arisen in the layer produced by the previous electrophoresis step during drying are automatically filled in, so that finally a gel is obtained which at most shows surface cracks.

Then the shape is removed. In the case of plastic molds, this can be done without residue by thermal pyrolysis. Alternatively, the plastic form can be selectively removed using chemical solvents. A form made of PMMA can be detached, for example, by acetonitrile or hot ethyl acetate. Metal molds with a low melting point can be removed by selective melting. Since shrinkage occurs during drying, the dried gel can in many cases be easily removed from the metal mold anyway without destroying the mold.

The gel is then ceramized and densely sintered in a known manner by using high temperatures. The ceramization is preferably carried out at temperatures of 500 to 800 ° C. The sealing sintering takes place by increasing the temperature, for example to temperatures between 1000 and 1500 ° C. at PZT ceramics, the optimal temperature is 1150 ^β C with a holding time of 90 to 150 min.

The invention is explained in more detail below on the basis of an implementation example.

Production of a sol for a PZT ceramic

In a thermostatically controlled glass vessel atmosphere substance 77.4 ml of Zr (n-Propylalkoholat) ^β 4 to 95 C er¬ were Stick¬ warmed, then 51.2 ml of Ti (n-Propylalkoholat) _4, 14.7 ml Acetylace- ton and 99.2 g of basic lead acetate were added and the mixture was stirred until a clear, brown, slightly opalescent, viscous solution had formed. Then 239.5 ml of ethylene glycol were added, whereupon the solution gelled immediately. The mixture was stirred vigorously overnight, after which the reaction mixture appeared liquid and clear. Then 10 ml of formamide as drying aid, 6.6 ml of polyethylene glycol (MW = 300) as plasticizer, 2 g of polyethylene glycol (MW = 10,000) were dissolved in a few ml of Et (OH) 2 as a binder to avoid cracks in the ceramic surface and 1.3 ml of tetraethylene glycol added. Then 17.2 ml of water were added. After stirring for about an hour at 95 ° C. and a full oil pump vacuum, the solvent was condensed into a receiver cooled with liquid nitrogen, whereupon a dark brown, viscous liquid remained. The batch gave 500.2 g of precursor.

Making the mold

A plate of PMMA provided with microstructures and produced by X-ray lithography (irradiation through a mask and dissolution of the irradiated areas) was sputtered with gold. The gold layer was about 30 n thick. The microstructures formed a pattern of free-standing hexagonal columns with a height of 250 μm and a thickness of 50 μm, the distances between which corresponded to the column thickness. Each column was surrounded by six neighboring columns. Electrophoresis

The gelled sol produced was placed in a thermostated electrophoresis cell. The electrically conductive surface of the mold (2 x 2 cm) was switched as an anode. A platinum sheet (2 x 2 cm) was used as the cathode, and its distance from the mold was at least 3 cm. The electrophoresis was carried out at a constant current of 30 mA and approx. 80 V. After a deposition time of approx. 2 hours, a layer thickness of 2 mm was obtained, so that the microstructures were completely covered by the gel.

Drying the electrophoretically deposited gel

Drying was carried out in three steps: one day in air, then several hours at 80 ° C and finally at 80 ° C in a vacuum. Drying cracks were filled in by repeating the electrophoresis step.

Ceramicizing and removing the form

In the next process step, both the organic constituents in the dried gel and the PMMA-For were burned off in a suitable oven, with continuous heating from 200 ° C. to 500 ° C. slowly (1.5 ° C./min). After that there was a ceramic microstructure. The ceramic structure was densely sintered by sintering at a temperature of 1150 ° C. for 90 minutes. A ceramic microstructure was obtained in the form of a plate which had a hexagonal pattern of hexagonal openings. The diameter of the openings was approximately 40 μm because of the shrinkage.

Claims

Claims:

1. A method for producing ceramic microstructures, in which a) a gellable sol is produced from a plurality of organometallic liquid components, b) a mold is provided which

- Complementary structures of the microstructures, which carries

- are provided with an electrically conductive surface, c) the complementary structures of the form are electrophoretically filled homogeneously with the sol, the electrically conductive surface being switched as an electrode and the sol being converted into a gel, d) the gel dried, e ) the mold is removed and f) the gel is ceramized by burning the organic constituents.

2. The method according to claim 1, wherein the mold consists of a plastic and the electrically conductive surface is produced by dusting (sputtering) a metal.

3. The method according to claim 1 or 2, in which the cracks formed in the dried gel are electrophoretically filled with the sol.