Ceramic component having a superhydrophilic surface region, method for production, and use of such a ceramic component

Abstract

The invention relates to a ceramic component having a superhydrophilic surface region, to a method for production, and to a use of such a ceramic component, in which, inside a vacuum chamber (11), a main body (12) consisting of sinter ceramics is heated to a temperature of at least 400°C and subsequently a tungsten oxide layer (21; 31) is deposited on the heated main body (12), at least within the superhydrophilic surface region, by means of a pulsed magnetron sputtering process, wherein a pulse frequency in the range from 0.5 kHz to 100 kHz is used.

Description

[0001] Ceramic component with a superhydrophilic surface area, method for producing and use of such a ceramic component

[0002] Description

[0003] The invention relates to a ceramic component that has superhydrophilic properties in at least one surface region and is thus highly wettable with water in this surface region. Furthermore, a method for producing and a use of such a ceramic component with a superhydrophilic surface region are specified.

[0004] It is known to modify the surface properties of components by depositing at least one layer on a surface region of the component. For example, JP 2013-222 662 A describes dye-sensitized solar cells in which a porous layer comprising tungsten trioxide particles is deposited on a ceramic substrate. Tungsten trioxide layers deposited on glass substrates are known from "BALAJI et al.: Porous orthorhombic tungsten oxide thin films: synthesis, characterization, and application in electrochromic and photochromic devices. In: Journal of Materials Chemistry, 21 , 2011 , 3940." The tungsten trioxide is at least partially formed as an orthorhombic phase and can be used in electrochromic and photochromic applications. JP 2015-199 065 A discloses tungsten trioxide layers that can be deposited on a substrate and used as photocatalyst layers.Tungsten trioxide layers are also known from US 2009 / 0268371 A1, which can be used as capacitor electrodes. US 2017 / 0284999 A1 also describes tungsten trioxide layers as a component of gas sensors.

[0005] Coatings are also known which influence the wettability of component surfaces with water. In some applications the aim is for components to have a water-repellent surface. Such surface areas with water-repellent properties are also referred to as hydrophobic. In contrast, there are also applications in which the surface of a component should be as wettable as possible with water. If a surface is easily wettable with water, this surface is also referred to as hydrophilic. The angle which a water droplet on the component forms with the component surface is often used as a measure of the wettability of a component surface with water. This angle is also referred to as the contact angle. While the contact angle is as large as possible for hydrophobic surfaces, the aim is to have the smallest possible contact angle for hydrophilic surfaces.

[0006] Hydrophilic properties are advantageous, for example, in glass substrates with an optical function, such as mirrors, where fogging with small liquid droplets must be prevented. Hydrophilic properties are also advantageous in modern heat pumps based on the electrocaloric effect. Electrocaloric heat pumps exploit the fact that certain materials change their temperature (e.g., they heat up) when an electric field is applied to them. When the electric field is removed, the material cools below its initial temperature. The material can then absorb thermal energy from a heat source. Electrocaloric materials can thus be used to establish an efficient heat cycle. Since this effect is reversible, it can be used for both heating and cooling.In electrocaloric heat pumps, as described above, an electric field is applied to a material several times per second and then switched off again. As a result, the material's surface is coated with a liquid film several times per second as the temperature changes occur several times per second, which then also has to be removed several times per second. This requires material surfaces with very good hydrophilic properties.

[0007] Coatings have been developed that enable a contact angle of almost 0° to be achieved on component surfaces. Such surfaces are also referred to as superhydrophilic. Since there is still no precise definition for the term "superhydrophilic" in the professional world, and contact angles of less than 5° can only be determined with insufficient accuracy using known measurement methods, for the purposes of the invention, surface areas are considered superhydrophilic if a contact angle of less than 5° can be achieved when wetted with a water droplet.

[0008] EP 1 304 366 B2 proposes first depositing a photocatalytically active layer comprising at least one of the elements titanium, tungsten, tin, zinc, iron, or silicon on the surface of a substrate and then exposing this layer to sunlight to obtain a surface with hydrophilic properties. The photocatalytically active layer can be deposited, for example, by magnetron sputtering.

[0009] A photocatalytically active layer also serves as the basis for the formation of a hydrophilic surface in Masahiro Miyauchi et al., "Hydrophilic Layered SiO2 / TiO2 / WO3 Thin Film for Indoor Anti-Fogging Coatings." Here, a photocatalytic layer of SiO2, TiO2, WO3, or a mixture of at least two of the aforementioned oxides is first deposited on a substrate and then exposed to light irradiation. Using this procedure, the hydrophilic properties could be maintained for a period of up to 65 days.

[0010] WO 2009 / 092664 discloses methods in which a component made of glass or ceramic is provided with a superhydrophilic surface by wet-chemically depositing an oxide layer of at least one of the elements silicon, titanium and zinc on the surface of the component and then crosslinking it by adding a substance.

[0011] What all of the previously described processes have in common is that the resulting hydrophilic properties are only maintained for a relatively short period of time. Furthermore, the components produced with them are not particularly well suited for use in electrocaloric heat pumps, because they do not sufficiently enable the surface to be wetted with a liquid film several times per second.

[0012] The invention is therefore based on the technical problem of creating a component with a superhydrophilic surface region with which the disadvantages of the prior art can be overcome. In particular, the superhydrophilic properties of a component according to the invention should be maintained for longer than is known from the prior art. Furthermore, the component should be able to wet the superhydrophilic surface region with a liquid film several times per second and then break this film down again. Furthermore, a method for producing and using such a component with a superhydrophilic surface region should be specified. The solution to the technical problem results from subject matter having the features of patent claims 1, 7 and 10. Further advantageous embodiments of the invention arise from the dependent patent claims.

[0013] A component according to the invention initially comprises a base body consisting of a sintered ceramic. The starting material for a sintered ceramic is, as is known, a ceramic powder, which can be mixed with water, binder, liquefier, and other additives. Ceramic powders are essentially divided into the groups of silicates, oxides, and non-oxides. All of these groups of ceramic powders can be used as starting materials for the base body of a component according to the invention. The ceramic powder mixed with additives is pressed and then subjected to a sintering process, during which most of the additive components, which are volatile at high temperatures, escape from the pressed molded part. What remains is a ceramic molded part in which the grain boundaries of the pressed ceramic powder particles can be detected using suitable means.Such a sintered ceramic is used as a base body in an inventive component.

[0014] According to the invention, an inventive component also comprises a tungsten trioxide layer deposited on the base body at least within the surface region of the component in which superhydrophilic properties are to be developed. The layer material of the tungsten trioxide layer is formed to more than 50% as an orthorhombic phase and has a porous nanostructure comprising gaps that arise from the grain boundaries of the sintered ceramic and extend along the thickness of the tungsten trioxide layer through the entire tungsten trioxide layer. These previously described material properties of the tungsten trioxide layer result in superhydrophilic properties on the component surface in the surface region in which the tungsten trioxide layer is deposited.

[0015] Such a ceramic component with superhydrophilic properties within a surface region can be produced according to the invention by heating a base body consisting of a sintered ceramic to a temperature of at least 400 °C within a vacuum chamber and then depositing a tungsten trioxide layer on the heated base body at least within the surface region in which superhydrophilic properties are to be formed by means of a pulsed magnetron sputtering process, wherein a pulse frequency in the range of 0.5 kHz to 100 kHz is used.

[0016] The invention is described in more detail below using exemplary embodiments. The figures show:

[0017] Fig. 1 is a schematic representation of an apparatus suitable for carrying out the method according to the invention;

[0018] Fig. 2 is a schematic representation of a section through a component according to the invention; Fig. 3 is a schematic representation of a section through an alternative component according to the invention.

[0019] Fig. 1 schematically shows a device 10 with which the method according to the invention can be carried out and a ceramic component according to the invention with a superhydrophilic surface region can be produced. Fig. 2 shows a section of a component according to the invention produced by means of device 10, schematically in section. The device 10 comprises a vacuum chamber 11, within which a tungsten trioxide layer 21 is to be deposited on one side of a plate-shaped base body 12. According to the invention, the base body 12 consists of a sintered ceramic. The tungsten trioxide layer 21 is to be deposited on the base body 12 by means of a reactive magnetron sputtering process. For this purpose, a magnetron 13, which is equipped with a tungsten target 14, is arranged within the vacuum chamber 11 opposite the side of the base body 12 to be coated.To carry out the reactive magnetron sputtering process, the reactive gas oxygen is introduced into the vacuum chamber 11 through a first inlet 15 and the working gas argon through a second inlet 16. As an alternative to the working gas argon, any other inert gas known in magnetron sputtering processes can also be used as the working gas.

[0020] According to the invention, the base body 12 consisting of a sintered ceramic is heated to a temperature of at least 400°C prior to layer deposition. In a preferred embodiment of the invention, the base body 12 is heated to a temperature of at least 500°C prior to layer deposition. A heating device 17 is used to heat the base body 12, which in the exemplary embodiment is designed as a radiant heater. Alternatively, other means can also be used to heat the base body 12. For example, the base body 12 can be heated by bombardment with electrically charged particles, such as accelerated electrons or ions. Alternatively, the base body 12 can also be heated with a laser beam.

[0021] After heating the base body 12, the tungsten trioxide layer 21 is deposited by sputtering tungsten particles from the tungsten target 14 using the magnetron 13. These particles combine with the reactive gas oxygen in a reactive process and are deposited as tungsten trioxide on the side of the base body 12 to be coated. Alternatively, a non-reactive sputtering process can be selected for the deposition of the tungsten trioxide layer, in which a target consisting of tungsten trioxide is sputtered using the magnetron 13. In such an alternative procedure, no reactive gas is admitted into the vacuum chamber 11 through the first inlet 15.

[0022] According to the invention, the tungsten trioxide layer 21 is deposited on the heated base body 12 using a pulsed magnetron sputtering process, using a pulse frequency in the range of 0.5 kHz to 100 kHz. It is particularly advantageous for forming a desired layer structure if a pulse frequency in the range of 2 kHz to 10 kHz is used.

[0023] In the procedure described above, a tungsten trioxide layer 21 is deposited on the base body 12 designed as a sintered ceramic, wherein the layer material of the tungsten trioxide layer 21 is formed to more than 50% as an orthorhombic phase and has a porous nanostructure comprising gaps 22 that arise from the grain boundaries of the sintered ceramic and that extend through the tungsten trioxide layer 21 along the layer thickness of the tungsten trioxide layer. The tungsten trioxide layer 21 of a component according to the invention is further characterized in that it has crystallites with a size of 2 nm to 200 nm and a porosity of 5% to 50%. In a preferred embodiment, the tungsten trioxide layer 21 has crystallites with a size of 5 nm to 50 nm and a porosity of 10% to 30%. The size of the crystallites of the tungsten trioxide layer 21 can be adjusted using known means.In this case, two parameters or two tendencies essentially need to be coordinated. First, the higher the base body 12 is heated by the heating device 17, the larger the crystallites are formed. Second, the more strongly the growing tungsten trioxide layer is exposed to ions resulting from the sputtering process, the smaller the crystallites are formed. Therefore, it is possible, for example, to determine in laboratory tests to which temperature above 400°C a base body should be heated and which magnetron parameters should be set to achieve a desired crystallite size during the deposition of the tungsten trioxide layer 21.

[0024] It has been shown that a tungsten trioxide layer 21 with the previously described layer structure parameters exhibits superhydrophilic properties, with contact angles of approximately 0° being demonstrated. In contrast, with ceramic substrates not formed as sintered ceramics, such a previously described layer structure could not be formed, and consequently, superhydrophilic properties could not be achieved. A sintered ceramic as the base body 12, on the other hand, causes pores and even entire gaps 22 to form during the growth of the tungsten trioxide layer 21, starting from the grain boundaries of the sintered ceramic, which have a positive effect on the hydrophilic surface properties.

[0025] According to the invention, the tungsten trioxide layer 21 can be formed with a layer thickness of 0.1 μm to 5 μm. In a preferred embodiment, in a ceramic component according to the invention, the tungsten trioxide layer 21 deposited on the base body 12 at least within a surface region is formed with a layer thickness of 0.5 μm to 2 μm.

[0026] In one embodiment of the method according to the invention, the inlet of the reactive gas oxygen into the vacuum chamber 11 is regulated during a reactive deposition process of the tungsten trioxide layer 21. For this purpose, an actual value for the intensity of at least one spectral line of at least one chemical element involved in the magnetron sputtering process is recorded by means of at least one sensor 18, compared with a target value, and the inlet of the reactive gas oxygen into the vacuum chamber 11 is regulated depending on the comparison result. It has been shown that by means of such a control, the layer structure can be kept constant during layer growth. The sensor 18 can be designed, for example, as a spectrometer. In the exemplary embodiment described with reference to Fig. 1, the actual values ​​for the intensity of the spectral lines of two chemical elements involved in the sputtering process are recorded by means of the sensor 18.First, a first actual value for the intensity of a spectral line of the reactive gas oxygen is recorded, and second, a second actual value for the intensity of a spectral line of the working gas argon is recorded. A quotient is then calculated from the first actual value and the second actual value in an evaluation device (not shown in Fig. 1). The quotient is compared with a target value. Depending on the comparison result, the amount of the reactive gas oxygen flowing through the first inlet 15 into the vacuum chamber 11 is regulated.

[0027] As previously explained, an inventive ceramic component exhibits superhydrophilic properties in the surface region in which a tungsten trioxide layer 21 has been deposited according to the invention. A ceramic component according to the invention can therefore be used, for example, as a component of a heat transfer device operating according to the heat pipe principle. A ceramic component according to the invention is further characterized in that the superhydrophilic surface region coated with a tungsten trioxide layer 21 can be wetted with a liquid several times per second, and the liquid film can also be removed again. Such a component can therefore also be used in a heat transfer device configured as a component of an electrocaloric heat pump.

[0028] In a further embodiment of the invention, a tungsten layer 33 is deposited between the base body 12 and a tungsten trioxide layer 31 according to the invention, which tungsten layer 33 consists of more than 50% crystalline u-tungsten and has crystallites with a size of 50 nm to 1000 nm, preferably 100 nm to 500 nm. Such a tungsten layer 33 can be deposited, for example, using the device 10 shown in Fig. 1 as follows. First, the base body 12 is heated to a temperature of at least 400 °C by means of the heating device 17. After the base body 12 has been heated, the tungsten target 14 is sputtered through the first inlet 15 by means of the magnetron 13 without the supply of oxygen, so that tungsten particles are deposited on the base body 12.After the tungsten layer 33 has been completely deposited, the oxygen supply through the first inlet 15 is additionally switched on, and a tungsten trioxide layer 31 is deposited on the base body 12, which has been heated to at least 400°C, and the tungsten layer 33 located thereon using the previously described reactive deposition process. It has been shown that a tungsten layer 33 deposited in this way on the base body 12 also forms pores and gaps, which can then continue as gaps 32 in the overlying tungsten trioxide layer 31. If a component according to the invention is used as part of an electrocaloric heat pump, the tungsten layer 33 can be used, for example, as an electrode layer for applying an electric field. Such a tungsten layer 33 is to be deposited with a layer thickness of 0.1 pm to 10 pm, and preferably with a layer thickness of 1 pm to 5 pm.

[0029] In a next embodiment, a mixed layer is deposited on the tungsten trioxide layer 21 or the tungsten trioxide layer 31, which comprises titanium oxide and silicon oxide with a mixing ratio of 10:1 to 1:10 and preferably a mixing ratio of 3:1 to 1:3. Surprisingly, it has been found that with such a mixed layer on the tungsten trioxide layer 21 or 31, the superhydrophilic

[0030] Properties can be maintained in a long-term stable manner. It has been demonstrated that in a component according to the invention designed in this way, the superhydrophilic

[0031] Properties can be maintained over a period of 12 months. A previously described mixed layer can be deposited, for example, reactively or non-reactively in the vacuum chamber 10 or, alternatively, in another vacuum chamber using known magnetron sputtering processes.

Claims

Patent claims 1. Ceramic component with a superhydrophilic surface region, comprising a base body (12) consisting of a sintered ceramic, on the surface of which a tungsten trioxide layer (21; 31) is deposited at least within the superhydrophilic surface region, wherein the layer material of the tungsten trioxide layer (21; 31) a) is formed to more than 50% as an orthorhombic phase and b) has a porous nanostructure which comprises gaps (22; 32) which arise from the grain boundaries of the sintered ceramic and which extend through the tungsten trioxide layer (21; 31) along the layer thickness extent of the tungsten trioxide layer (21; 31).

2. Component according to claim 1, characterized in that the tungsten trioxide layer (21; 31) is formed with a layer thickness of 0.1 pm to 5 pm.

3. Component according to claim 1 or 2, characterized in that the tungsten trioxide layer (21; 31) has crystallites with a size of 2 nm to 200 nm and a porosity of 5% to 50%.

4. Component according to one of the preceding claims, characterized in that a tungsten layer (33) with a layer thickness of 0.1 pm to 10 pm is deposited between the base body (12) and the tungsten trioxide layer (31).

5. Component according to claim 4, characterized in that the tungsten layer (33) consists of more than 50% crystalline a-tungsten and has crystallites with a size of 50 nm to 1000 nm.

6. Component according to one of the preceding claims, characterized in that a mixed layer of titanium oxide and silicon oxide with a layer thickness of 0.05 pm to 2 pm is deposited on the tungsten trioxide layer (21; 31).

7. A method for producing a ceramic component with a superhydrophilic surface region according to claim 1, wherein within a vacuum chamber (11) a) a base body (12) consisting of a sintered ceramic is heated to a temperature of at least 400 °C and b) a worm gear trioxide layer (21; 31) is then deposited on the heated base body (12), at least within the superhydrophilic surface area, by means of a pulsed magnetron sputtering process, wherein a pulse frequency in the range of 0.5 kHz to 100 kHz is used.

8. The method according to claim 7, characterized in that a reactive magnetron sputtering process is used, in which at least one tungsten target (14) is sputtered by means of at least one magnetron (13) with simultaneous admission of the reactive gas oxygen into the vacuum chamber (11).

9. Method according to claim 8, characterized in that by means of at least one sensor (18) an actual value for the intensity of at least one spectral line of at least one chemical element involved in the magnetron sputtering process is detected, compared with a desired value and the inlet of the reactive gas oxygen into the vacuum chamber (11) is regulated depending on the comparison result.

10. Use of a component according to one of claims 1 to 6 as a component of a heat transfer device operating according to the heat pipe principle.

11. Use according to claim 10, characterized in that the heat transfer device is designed as a component of an electrocaloric heat pump.

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