SINTERED BODY WITH ELECTRICALLY CONDUCTIVE COATING

Abstract

A porous sintered body with an electrically conductive coating is provided. The sintered body has an open porosity in a range from 10 to 90%. The electrically conductive coating is bonded to the surface of the pores and is part of a heating device in a vaporizer. The electrically conductive coating lines the pores located in the interior of the sintered body so that when the sintered body is electrically connected and a current is applied, the current flows at least partially through the interior of the sintered body so that the interior of the sintered body is heated. A method for producing a porous sintered body with an electrically conductive coating is also provided.

Claims

1. A vaporizer comprising a sintered body made of glass or glass ceramic and having open pores defining an open porosity in a range from 10 to 90%; and an electrically conductive coating that form part of a heating device of the vaporizer, wherein the electrically conductive coating is deposited on a surface of the sintered body and is bonded to the surface of the sintered body so that the electrically conductive coating lines the open pores located in an interior of the sintered body so that when the sintered body is connected electrically and an electrical current is applied the current flows at least partially through the interior of the sintered body heating the interior of the sintered body.

2. The vaporizer as in claim 1, wherein the open porosity is in a range from 50 to 80%.

3. The vaporizer as in claim 1, wherein the open pores have a pore size in a range from 1 m to 5000 m.

4. The vaporizer as in claim 1, wherein the sintered body further comprises closed pores, the sintered body having a proportion the closed pores in the total volume of the open pores of not more than 10%.

5. The vaporizer as in claim 1, wherein the open pores exhibit an at least bimodal pore size distribution.

6. The vaporizer as in claim 5, wherein the sintered body has large open pores with a pore size in a range from 500 to 700 m and small open pores with a pore size in a range from 100 to 300 m.

7. The vaporizer as in claim 6, further comprising a proportion of the large pores of 5 to 95%.

8. The vaporizer as in claim 1, wherein the sintered body is made of glass.

9. The vaporizer as in claim 8, wherein the glass has an alkali content of not more than 11 wt %.

10. The vaporizer as in claim 8, wherein the glass has a transition temperature T.sub.g in a range from 300 to 900 C.

11. The vaporizer as in claim 8, wherein the glass is an aluminoborosilicate glass containing the following constituents: SiO.sub.2 50 to 85 wt % B.sub.2O.sub.3 1 to 20 wt % Al.sub.2O.sub.3 1 to 17 wt % Na.sub.2O+K.sub.2O 1 to 11 wt % MgO+CaO+BaO+SrO 1 to 13 wt %.

12. The vaporizer as in claim 8, wherein the sintered body has a coefficient of linear thermal expansion .sub.20-300 C..sub._.sub.sintered body of not more than 20*10.sup.6 K.sup.1 and wherein the electrically conductive coating has a coefficient of linear thermal expansion .sub.20-300 C..sub._.sub.coating in a range from 1*10.sup.6 K.sup.1 to 20*10.sup.6 K.sup.1.

13. The vaporizer as in claim 8, wherein the sintered body and the electrically conductive coating have a difference of coefficients of thermal expansion of .sub.20-300 C.=.sub.20-300 C..sub._.sub.coating.sub.20-300 C..sub._.sub.sintered body from 0 to 20*10.sup.6 K.sup.1.

14. The vaporizer as in claim 1, wherein the sintered body provided with the electrically conductive coating exhibits an electrical conductivity in a range from 0.001 to 10.sup.6 S/m.

15. The vaporizer as in claim 1, wherein the electrically conductive coating comprises a metal oxide selected from the group consisting of indium tin oxide (ITO), aluminum-doped zinc oxide (AZO), fluorine tin oxide (FTO), antimony tin oxide (ATO), and combinations thereof.

16. The vaporizer as in claim 1, wherein the electrically conductive coating is made of a metal selected from the group consisting of silver, gold, platinum, chromium, and combinations thereof.

17. The vaporizer as in claim 1, wherein the electrically conductive coating has a thickness from 1 nm to 1000 m.

18. The vaporizer as in claim 1, wherein the vaporizer configured for use as a component of an electronic cigarette or a medical inhaler or a fragrance dispenser or a room humidifier.

19. The vaporizer as in claim 1, wherein the sintered body with the electrically conductive coating applied thereon exhibits an electrical resistance in a range from 0.2 to 5 ohms, and wherein the vaporizer is operated at a voltage in a range from 1 to 12 V and/or at a heating power from 1 to 80 W.

20. The vaporizer as in claim 1, wherein the sintered body with the electrically conductive coating applied thereon exhibits an electrical resistance in a range from 0.2 ohms to 3000 ohms, and wherein the vaporizer is operated at a voltage in a range from 110 to 380 V and/or at a heating power from 10 to 1000 W.

21. The vaporizer as in claim 1, wherein the vaporizer is electrically connected through a mechanical connection or is electrically connected through an electrically conductive connector, or is electrically connected through an electrically conductive material bond.

22. The vaporizer as in claim 1, wherein the electrically conductive coating comprises at least one further component selected from the group consisting of an antimicrobial component, antibacterial component, silver, ZnO, TiO.sub.2, and combinations thereof.

23. A vaporizer head, comprising: a housing; the vaporizer as in claim 1 in the housing, and electrical contacts for connection of the sintered body.

24. A method for producing a vaporizer, comprising the steps of: providing a sintered body made of glass, glass ceramics, or ceramics and having open pores with an open porosity in a range from 10 to 90%; and coating a surface of the sintered body as defined by the open pores, including the surface of pores in an interior of the sintered body, with an electrically conductive coating.

25. The method as in claim 24, wherein the step of providing the sintered body comprises providing a sintered glass body made of glass with an alkali content of less than 11 wt %.

26. The method as in claim 24, wherein the step of providing the sintered body comprises providing a sintered glass body made of aluminoborosilicate glass.

27. The method as in claim 24, wherein the coating step comprises depositing the electrically conductive coating on an entire surface of the sintered body as defined by the surface area of the open pores, by condensation or precipitation of solids from a dispersion, condensation or precipitation of solids from a solution, condensation or precipitation of solids from a gas phase, or by a galvanic process.

28. The method as in claim 24, wherein the electrically conductive coating comprises a metal oxide selected from the group consisting of indium tin oxide (ITO), aluminum-doped zinc oxide (AZO), fluorine tin oxide (FTO), antimony tin oxide (ATO), and combinations thereof.

29. The method as claimed in claim 28, wherein the coating step comprises depositing the metal oxide by a dipping process comprising at least the steps of: providing a dispersion or solution of the metal oxide; immersing the sintered body into the dispersion or solution for a predefined dipping time t.sub.dip; and firing the coating obtained by the immersing step for a firing time t.sub.fire at a firing temperature T.sub.fire.

30. The method as in claim 29, wherein the firing temperature T.sub.fire is in a range from 60 to 1000 C.

31. The method as in claim 29, wherein the firing step further comprises firing under an atmosphere selected from the group consisting of an inert gas, a vacuum, and a reducing atmosphere.

32. The method as in claim 29, wherein the dispersion or solution has a solids content from 1 to 50 wt %.

33. The method as in claim 29, further comprising repeating the immersing and firing steps.

Description

DETAILED DESCRIPTION

[0094] The patent or application file contains at least one drawing executed in color. Copies of this patent or patent application publication with color drawing(s) will be provided by the Office upon request and payment of the necessary fee.

[0095] The invention will now be described in more detail with reference to exemplary embodiments and the figures, wherein:

[0096] FIG. 1 is a schematic view of a conventional vaporizer,

[0097] FIG. 2 is a schematic view of a sintered body with electrical contacts on the lateral surfaces of the sintered body;

[0098] FIG. 3 is a schematic view of a vaporizer comprising a sintered body coated according to the invention, as a heating element;

[0099] FIG. 4 is a schematic cross-sectional view of a sintered body coated according to the invention;

[0100] FIG. 5 shows an SEM image of a first exemplary embodiment;

[0101] FIG. 6 is a photomicrograph of a second exemplary embodiment;

[0102] FIG. 7 is a schematic view of a refinement of the invention with a bimodal pore size distribution;

[0103] FIG. 8 illustrates the pore size distribution of a third exemplary embodiment;

[0104] FIGS. 9a and 9b are schematic views of a sintered body coated according to the invention, as a component in a vaporizer,

[0105] FIG. 10a shows a thermal image of a vaporizer with a sintered body coated according to the invention as a heating element; and

[0106] FIG. 10b shows a thermal image of a conventional vaporizer.

DETAILED DESCRIPTION

[0107] Tables 1 and 2 show the compositions of the porous sintered body according to various exemplary embodiments. Due to their different composition, the individual exemplary embodiments have different thermal expansion coefficients. For example, exemplary embodiments 8 to 10 have expansion coefficients in a range from 3.2*10.sup.6 K.sup.1 to 3.8*10.sup.6 K.sup.1 and are particularly suitable for porous sintered bodies with an electrically conductive coating based on a metal oxide, e.g. ITO. Moreover, glasses 8 to 10 are free or at least substantially free of sodium, which has an effect not only on the thermal expansion coefficient but also on the glass transition temperatures T.sub.g, which are above 700 C. and therefore allow for high firing temperatures during the coating process with ITO, so that it is possible to obtain crack-free or at least largely crack-free electrically conductive coatings of particularly high mechanical stability.

[0108] Glasses 2 to 7, by contrast, have a relatively high content of sodium and, accordingly, higher coefficients of thermal expansion. They are therefore particularly suitable for producing porous sintered bodies to be coated with a metallic coating. Furthermore, due to their high content of sodium, the glasses of exemplary embodiments 2 to 7 lend themselves for being chemically toughened. For example, the sintered body may be chemically toughened prior to being coated. This increases the mechanical stability of the porous sintered body.

TABLE-US-00018 TABLE 1 EXEMPLARY EMBODIMENTS 1 TO 7 1 2 3 4 5 6 7 SiO.sub.2 64.0 62.3 62.2 52 60.7 62 61.1 B.sub.2O.sub.3 8.3 0.2 4.5 Al.sub.2O.sub.3 4.0 16.7 18.1 17 16.9 17 19.6 Li.sub.2O 5.2 Na.sub.2O 6.5 11.8 9.7 12 12.2 13 12.1 K.sub.2O 7.0 3.8 0.1 4 4.1 3.5 0.9 SrO 0.1 CaO 0.6 6 0.3 0.1 SnO.sub.2 0.4 0.1 0.2 TiO.sub.2 4.0 0.8 0.6 Sb.sub.2O.sub.3 0.6 As.sub.2O.sub.3 0.7 Cl.sup. 0.1 P.sub.2O.sub.5 0.1 MgO 3.7 4 1.2 ZrO.sub.2 0.1 3.6 1.5 1.5 CeO.sub.2 0.1 0.3 0.3 ZnO 5.5 0.1 3.5 T.sub.g [ C.] 607 505 556 623 600 .sub.(20-300 C.) 8.6 * 10.sup.6 8.5 * 10.sup.6 9.7 * 10.sup.6 8.3 * 10.sup.6 8.9 * 10.sup.6 [K.sup.1] Density 2.4 2.5 2.6 2.4 2.4 [g/cm.sup.3]

TABLE-US-00019 TABLE 2 EXEMPLARY EMBODIMENTS 8 TO 12 8 9 10 11 12 SiO.sub.2 59.7 58.8 62.5 74.3 72.8 B.sub.2O.sub.3 7.8 10.3 10.3 Al.sub.2O.sub.3 17.1 14.6 17.5 1.3 0.2 Li.sub.2O Na.sub.2O 13.2 13.9 K.sub.2O 0.3 0.1 SrO 7.7 3.8 0.7 BaO 0.1 5.7 CaO 4.2 4.7 7.6 10.7 9.0 SnO.sub.2 TiO.sub.2 Sb.sub.2O.sub.3 0.2 As.sub.2O.sub.3 0.7 Cl.sup. P.sub.2O.sub.5 MgO 1.2 1.4 0.2 4.0 ZrO.sub.2 CeO.sub.2 ZnO T.sub.g [ C.] 719 705 573 564 .sub.(20-300 C.) 3.8 * 10.sup.6 3.73 * 10.sup.6 3.2 * 10.sup.6 9 * 10.sup.6 9.5 * 10.sup.6 [K.sup.1] Density 2.51 2.49 2.38 [g/cm.sup.3]

[0109] FIG. 1 shows an example of a conventional vaporizer comprising a porous sintered body 2 as a liquid reservoir. Due to the capillary forces of the porous sintered body 2, the liquid 1 to be vaporized is taken up by the porous sintered body 2 and is further conveyed in all directions of the sintered body 2. The capillary forces are symbolized by arrows 4. In the upper portion of sintered body 2, a heating coil 3 is positioned such that the corresponding area 2a of the sintered body 2 is heated by heat radiation. The heating coil 3 is therefore brought very close to the lateral surfaces of the sintered body 2 and should preferably not touch the lateral surfaces. In practice, however, a direct contact between heating wire and lateral surface is often unavoidable.

[0110] Vaporization of the liquid 1 occurs in the heated area 2a. This is illustrated by arrows 5. The vaporization rate depends on the temperature and the ambient pressure. The higher the temperature and the lower the pressure, the faster the liquid will be vaporized in heated area 2a.

[0111] Since vaporization of the liquid 1 occurs only locally, on the lateral surfaces of the heated area 2a of the sintered body, this local area has to be heated with relatively high heating powers in order to achieve rapid vaporization within 1 to 2 seconds. Therefore, high temperatures of more than 200 C. must be employed. However, high heating output power, especially in a localized area, can lead to local overheating and thus possibly to a decomposition of the liquid 1 to be vaporized and of the material of the liquid reservoir or of the wick.

[0112] Furthermore, high heating output power can also lead to vaporization at an excessive rate, so that more liquid 1 for vaporization cannot be supplied quickly enough by the capillary forces. This also results in overheating of the lateral surfaces of the sintered body in the heated area 2a. Therefore, a unit such as a control or regulation unit (not shown) for voltage, power and/or temperature adjustment may be incorporated, but at the expense of battery life and limiting the maximum amount of vaporization.

[0113] Drawbacks of the vaporizer illustrated in FIG. 1 and known from the prior art, therefore, include the technique of localized heating and the associated ineffective heat transfer, the complex and expensive control unit, and the risk of overheating and decomposition of the liquid to be vaporized.

[0114] FIG. 2 shows a vaporizer unit known from the prior art, in which the heating element 30 is disposed directly on the sintered body 20. More particularly, the heating element 30 is firmly connected to the sintered body 20. Such a connection can in particular be achieved if the heating element 30 is provided in the form of a sheet resistor. For this purpose, an electrically conductive sheet resistor type coating patterned in the form of a conductive path is applied onto the sintered body 20. A coating that is directly applied to the sintered body 20 as a heating element 30 is advantageous in order to achieve good thermal contact which provides for fast heating, inter alia. However, the vaporizer unit shown in FIG. 2 also presents only a locally limited vaporization surface, so that there is again a risk of overheating of the surface here.

[0115] FIG. 3 schematically shows the configuration of a vaporizer that comprises a sintered body 6 according to the invention. Like the porous sintered body 2 of FIG. 1 and FIG. 2, it is immersed in the liquid 1 to be vaporized. Due to capillary forces (represented by arrows 4), the liquid to be vaporized is conveyed into the entire volume of the sintered body 6. Sintered body 6 has an electrically conductive coating, the electrically conductive coating being provided on the surface defined by the open pores. Therefore, when a voltage is applied, the sintered body 6 is heated in the entire volume which has a large surface area. So, unlike in the vaporizer shown in FIG. 2, the liquid 1 is not only vaporized at the lateral surfaces of the sintered body, i.e. in a localized portion of the sintered body 6, but in the entire volume of the sintered body 6. Capillary transport to the lateral surfaces or heated surfaces or elements of the sintered body 6 is therefore not necessary. Moreover, there is no risk of local overheating. Since vaporization throughout the volume is much more efficient than when using a heating coil in a localized heated area, vaporization can occur at much lower temperatures and at lower heating power. Lower electrical power requirement is advantageous as it increases the lifecycle per battery charge or allows to install smaller rechargeable or disposable batteries.

[0116] FIG. 4 shows the structure of a coated sintered body 6 with open porosity by way of a schematic cross-sectional view through one exemplary embodiment. The coated sintered body 6 comprises a porous sintered glass matrix 7 with open pores 8a, 8b. Part of the open pores 8b define, with their pore surface area, the lateral surfaces of the sintered body, while another part of the pores 8a define the interior of the sintered body. All of the pores of the sintered body are provided with an electrically conductive coating 9.

[0117] FIG. 5 is an SEM micrograph of a sintered body with an electrically conductive coating. The surface of pores 8 is coated with an ITO layer 9 as an electrically conductive coating. The sintered glass matrix 7 is an aluminoborosilicate glass of the following composition: [0118] Alkali oxides 1 to 11 wt % [0119] Alkaline earth oxides 1 to 13 wt % [0120] B.sub.2O.sub.3 1 to 20 wt % [0121] Al.sub.2O.sub.3 1 to 17 wt % [0122] SiO.sub.2 50 to 96 wt %.

[0123] A glass with the above composition melts very slowly and in a wide temperature range. Therefore, it is particularly suitable for producing porous materials by melting and sintering processes. Glasses of this composition range may have melting temperatures of more than 1000 C., which allows firing of the electrically conductive coating at temperatures of up to 900 C. and which has a positive effect on coating properties such as density and prevents cracks in the coating. The low coefficient of linear thermal expansion (.sub.20-300 C.) of glass reduces thermally induced stresses and therefore increases the mechanical resilience of the material to temperature differences that occur in the vaporizer when being turned on and off. Furthermore, the glass with the electrically conductive coating as a heating element permanently resists temperatures of up to 600 C.

[0124] FIG. 6 shows a photomicrograph of a sintered body coated with an ITO layer.

[0125] Optical and electron microscopic measurements on the illustrated sintered body showed that the ITO layer has a thickness between 200 nm and 2000 nm and, surprisingly, does not exhibit any cracks. This is surprising, since the glass (3.3*10.sup.6 K.sup.1) and ITO (7.2*10.sup.6 K.sup.1) have different coefficients of linear thermal expansion.

[0126] FIG. 7 is a schematic cross-sectional view illustrating the structure of a coated sintered body 60 according to one refinement of the invention. The coated sintered body 60 comprises a porous sintered glass matrix 70 with open pores 80, 81, the pores exhibiting a bimodal pore size distribution including large pores 80 and small pores 81. Part of the open pores define, with their pore surface area, the lateral surfaces of the sintered body, while another part of the pores define the interior of the sintered body. All of the pores of the sintered body are provided with an electrically conductive coating 90. The small pores 81 provide for good and rapid uptake of the liquid to be vaporized in the sintered body, while the large pores 80 provide for quick release of the vapor. Depending on the application, the uptake behavior and desorption properties during operation of the vaporizer can be adjusted through the ratio of large to small pores and the pore size.

[0127] FIG. 8 shows the pore size distribution of an exemplary embodiment of the refinement schematically illustrated in FIG. 7. Here, the pore size distribution of the porous sintered body has a maximum at about 200 m and a maximum at about 600 m, and the proportion of small pores (200 m) corresponds to the proportion of large pores (600 m) in this exemplary embodiment. The pore size can be adjusted during the manufacturing process through the grain size of the salt that is used as a pore former, and the ratio of large to small pores accordingly through the ratio of the grain sizes that are used and the grain size distributions thereof.

[0128] FIGS. 9a and 9b schematically show a sintered body 3 coated according to the invention as a component in a possible vaporizer. The vaporizer has a reservoir including the liquid 1 to be vaporized. The vaporization chamber 11 is separated from the liquid 1 to be vaporized by a steel wall 12. Through openings (12a, 12b) in the steel wall, the liquid 1 to be vaporized is in communication with the coated sintered body 3 which sucks in the liquid 1 to be vaporized by virtue of capillary forces. When a voltage 10 is applied to the sintered body 3 with the electrically conductive coating, the sintered body is heated throughout its volume, so that the liquid 1 is vaporized in the entire volume of the sintered body 3. Vaporization continues until the pores of the sintered body 3 and/or the reservoir no longer contain liquid 1 or the current flow is switched off. When the vaporizer is switched off, the pores will again suck in liquid, due to the capillary force, so that when the user turns on the vaporizer again, enough liquid 1 will again be available for vaporization.

[0129] The maximum possible amount of vapor that can be produced is equal to the amount of liquid that is or can be stored in the porous sintered body 3. The producible amount of vapor may therefore be controlled, for example, via the dimensions of the sintered body 3 and its porosity. Small sintered bodies with high porosity have proved to be particularly advantageous here in terms of efficiency of the vaporization process and of energy consumption and resupply of liquid or filling rate.

[0130] FIG. 10a shows a vaporizer comprising a sintered body coated according to the invention as a heating element and FIG. 10b shows thermal images of a conventional vaporizer and. While in the vaporizer with a sintered body coated according to the invention as a heating element of FIG. 10a, vaporization temperatures range from 127 to 135 C. only, a conventional vaporizer with a heating element in the form of a spiral heating wire of FIG. 10b requires vaporization temperatures in a range from 252 to 274 C. to produce the same or at least similar amount of vapor.

[0131] Table 3 shows vaporization parameters of a conventional vaporizer and of a vaporizer comprising a sintered body coated according to the invention as an exemplary embodiment. The respective vaporizers were operated in a configuration similar to an electronic cigarette. The output power was determined by measurement of the applied voltage and current flow using electrical measuring devices, the amount of generated vapor was determined through the weight loss of the liquid.

TABLE-US-00020 TABLE 3 COMPARISON OF VAPORIZERS Conventional vaporizer Exemplary embodiment Dimensions OD = 5 mm, ID = 3 mm, Hollow cylinder with length 12 mm OD = 6 mm, ID = 2 mm, length of cylinder 5 mm Applied voltage 4 V 4 V Heating power 16 W 2 W required Operation 252-274 C. 127-135 C. temperature Amount of vapor max. 72 min. 72 [milligram/min]

[0132] As can be seen from Table 3, both vaporizers have a comparable size. In order to produce the same amount of vapor as a conventional vaporizer, a vaporizer with a sintered body coated according to the invention requires much lower heating power and lower vaporization temperatures.

[0133] For the exemplary embodiment, the vaporization temperature is significantly below the decomposition temperatures of the vaporizable substances that are typically used, so that so-called coking of the vaporizer by decomposition products will not occur and, therefore, a release of corresponding decomposition products is not to be expected. This increases the service life of the vaporizer.

[0134] Because of the lower heating power that is required, the vaporizer comprising a sintered body coated according to the invention is moreover far superior to a conventional vaporizer in terms of energy efficiency and the service life of the electrical power source.