ELECTRICALLY CONDUCTIVE POROUS SINTERING BODY HAVING ELECTRICALLY CONDUCTIVE MATERIALS METHOD FOR PRODUCING

Abstract

An evaporator that includes a porous sintering body is provided. The sintering body is made of a composite consisting of at least one first electrically conductive material and at least one second electrically conductive material as well as at least one dielectric material. The sintering body has an open porosity ranging from 10 to 90%, and the dielectric material is selected from the group consisting of crystallizable glass and/or glass ceramic, wherein the first electrically conductive material has a lower electric conductivity than the second electrically conductive material; the content of dielectric material in the composite equals 5 to 70 vol. %; the content of the first electrically conductive material in the composite equals 10 to 90 vol. %; the content of the second electrically conductive material equals 5 to 50 vol. %; and the sintering body has an electrical conductivity ranging from 0.1 to 105 S/m.

Claims

1. A vaporizer comprising: a porous sintered body formed by a composite of a first electrically conductive material, a second electrically conductive material, and a dielectric material, wherein the porous sintered body has an open porosity in the range from 10% to 90% and an electrical conductivity in a range from 0.1 to 10.sup.5 S/m, wherein the dielectric material is selected from a group consisting of glass, crystallizable glass, glass-ceramic, ceramic, plastic and combinations thereof, wherein the first electrically conductive material has a lower electrical conductivity than the second electrically conductive material, and wherein the composite has a proportion of the dielectric material from 5% to 70% by volume, the first electrically conductive material from 10% to 90% by volume, and the second electrically conductive material from 5% to 50% by volume.

2. The vaporizer of claim 1, wherein the proportion is selected from a group consisting of: the first electrically conductive material from 40% to 90% by volume, the first electrically conductive material from 55% to 75% by volume, the second electrically conductive material from 5% to 50% by volume, the second electrically conductive material from 15% to 30% by volume, a total of the first and second electrically conductive materials from 30% to 95% by volume, and a total of the first and second electrically conductive materials from 40% to 90% by volume.

3. The vaporizer of claim 1, wherein the composite comprises a feature selected from a group consisting of: the first electrically conductive material having an electrical conductivity of up to 30 S/μm, the first electrically conductive material having an electrical conductivity of up to 20 S/μm, the first electrically conductive material having an electrical conductivity from 0.001 to 10 S/μm, the second electrically conductive material having an electrical conductivity of greater than 10 S/μm, the second electrically conductive material having an electrical conductivity of greater than 20 S/μm, the second electrically conductive material having an electrical conductivity of greater than 30 S/μm, the second electrically conductive material having an electrical conductivity of up to 70 S/μm, the first electrically conductive material having a resistance with a positive temperature coefficient, the second electrically conductive material having a resistance with a positive temperature coefficient, the first and second electrically conductive materials having a resistance with a positive temperature coefficient, the first electrically conductive material having a temperature coefficient of resistance of at least −0.0001 l/K, the second electrically conductive material having a temperature coefficient of resistance of at least −0.0001 l/K, the first electrically conductive material having a temperature coefficient of resistance of less than 0.008 l/K, the second electrically conductive material having a temperature coefficient of resistance of less than 0.008 l/K, the first electrically conductive material having a temperature coefficient of resistance of at least −0.0001 l/K and less than 0.008 l/K, and the second electrically conductive material having a temperature coefficient of resistance of at least −0.0001 l/K and less than 0.008 l/K.

4. The vaporizer of claim 1, further comprising an electrical resistance in a range from 0.05 to 5 ohms.

5. The vaporizer of claim 4, wherein the electrical resistance is from 0.1 to 5 ohms.

6. The vaporizer of claim 4, wherein the porous sintered body comprises the electrical resistance.

7. The vaporizer of claim 1, further comprising a voltage in the range from 1 to 12 V and/or a heating output of from 1 to 500 W.

8. The vaporizer of claim 1, wherein the first and/or second electrically conductive material comprise a material selected from a group consisting of: titanium, chromium, steel, iron, molybdenum, tungsten, manganese, nickel, copper, silicon, stainless steel, aluminium, platinum, gold, silver, and any mixture or alloys thereof.

9. The vaporizer of claim 1, wherein the porous sintered body further comprises an electrically conductive coating.

10. The vaporizer of claim 1, wherein the first and/or the second electrically conductive materials comprise particles having a feature selected from a group consisting of: a particle size d.sub.50 in a range from 0.1 μm to 1000 μm, a particle size d.sub.50 in a range from 1 to 300 μm, a particle size d.sub.50 in a range from 0 1 to 150 μm, a shape that is platelet-shape, a maximum length that is larger than a maximum thickness, a maximum length that is larger than twice a maximum thickness, and a maximum length that is larger than seven times a maximum thickness.

11. The vaporizer of claim 1, wherein the open porosity comprises pores having a mean pore size in a range from 1 μm to 5000 μm.

12. The vaporizer of claim 1, wherein the dielectric material comprises glass having a feature selected from a group consisting of: an alkali metal content≤15% by weight, having an alkali metal content≤6% by weight, a proportion of network formers of at least 50% by weight, a proportion of network formers of at least 70% by weight, a transformation temperature in a range from 300° C. to 900° C., a transformation temperature in a range from 500° C. to 800° C., a class 3 hydrolytic resistance measured in accordance with ISO 719, a class 2 hydrolytic resistance measured in accordance with ISO 719, and a class 1 hydrolytic resistance measured in accordance with ISO 719.

13. The vaporizer of claim 1, wherein the dielectric material comprises glass comprising: TABLE-US-00003 SiO.sub.2 50% to 85% by weight, B.sub.2O.sub.3  1% to 30% by weight, Al.sub.2O.sub.3  1% to 30% by weight, ΣNa.sub.2O + K.sub.2O  1% to 30% by weight, and ΣMgO + CaO + BaO + SrO  1% to 40% by weight.

14. The vaporizer of claim 1, wherein the vaporizer is configured as a component for a use selected from a group consisting of an electronic cigarette, a medical inhaler, a fragrance dispenser, a room humidifier, a disinfection device, and a gas heating device.

15. A porous sintered body, comprising a porous sintered body formed by a composite of a first electrically conductive material, a second electrically conductive material, and a dielectric material, wherein the porous sintered body has an open porosity in the range from 10% to 90% and an electrical conductivity in a range from 0.1 to 10.sup.5 S/m, wherein the dielectric material is selected from a group consisting of glass, crystallizable glass, glass-ceramic, ceramic, and combinations thereof, wherein the first electrically conductive material has a lower electrical conductivity than the second electrically conductive material, and wherein the composite has a proportion of the dielectric material from 5% to 70% by volume, the first electrically conductive material from 10% to 90% by volume, and the second electrically conductive material from 5% to 50% by volume.

16. A method for producing a vaporizer, comprising: a) providing a first electrically conductive material, a second electrically conductive material, and a dielectric material in powder form; b) mixing the first electrically conductive material, the second electrically conductive material, and the dielectric material in powder form provided in step a) with at least one pore former to produce a powder mixture; c) producing a green body from the powder mixture provided in step b) by pressing, casting or extrusion; and d) sintering the green body produced in step c) at a sintering temperature.

17. The method of claim 16, wherein the providing in step a) further comprises: providing a proportion of the dielectric material from 5% to 70% by volume; providing a proportion of the first electrically conductive material from 10% to 90% by volume; and providing a proportion of the second electrically conductive material from 5% to 50% by volume.

18. The method of claim 16, wherein the pore former has a decomposition and/or vaporization temperature that is below the sintering temperature and the first electrically conductive material has a first melting temperature, wherein the first melting temperature is greater than the sintering temperature, the method further comprising: heating the green body, prior to step d), to a temperature that is above the decomposition and/or the vaporization temperature of the pore former but lower than the sintering temperature.

19. The method of claim 16, further comprising reworking the sintered body, wherein the reworking is a process selected from a group consisting of grinding, drilling, polishing, milling, turning, applying an electrically conductive paste, and applying electrically conductive solder lines.

20. The method of claim 16, further comprising coating, using a sol-gel method or CVD method, the sintered body with an electrically conductive coating after step d).

Description

DETAILED DESCRIPTION

[0108] The invention will be described in greater detail below on the basis of exemplary embodiments and figures, where:

[0109] FIG. 1 shows a schematic representation of a conventional vaporizer,

[0110] FIG. 2 shows a schematic representation of a sintered body having electrical contacting on the lateral surfaces of the sintered body,

[0111] FIG. 3 shows a schematic representation of one embodiment of a vaporizer according to the invention,

[0112] FIG. 4 shows a schematic representation of one embodiment of a sintered body according to the invention in cross section,

[0113] FIG. 5 shows an enlarged detail of the cross section shown in FIG. 4 and

[0114] FIG. 6 shows an SEM image of one exemplary embodiment and

[0115] FIG. 7 shows a schematic representation of a further exemplary embodiment with an additional electrically conductive coating on the sintered body.

DETAILED DESCRIPTION

[0116] FIG. 1 shows an example of a conventional vaporizer comprising a porous sintered body 2 as a liquid store. Owing to the capillary forces of the porous sintered body 2, the liquid 1 to be vaporized is absorbed by the porous sintered body 2 and further transported in all directions of the sintered body 2. The capillary forces are symbolized by the arrows 4. In the upper section of the sintered body 2, a heating coil 3 is positioned in such a way that the corresponding section 2a of the sintered body 2 is heated by thermal radiation. The heating coil 3 is therefore brought very close to the lateral surfaces of the sintered body 2 and should not touch the lateral surfaces if possible. However, in practice, direct contact between heating wire and lateral surface is often unavoidable.

[0117] What takes place in the heating region 2a is the vaporization of the liquid 1. This is represented by the 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 vaporization of the liquid in the heating region 2a.

[0118] Since the vaporization of the liquid 1 takes place only locally on the lateral surfaces of the heating region 2a of the sintered body, the heating of this local region must be done with relatively high heating outputs in order to achieve rapid vaporization within 1 to 2 seconds. Therefore, high temperatures of greater than 200° C. must be applied. However, high heating outputs, especially in a localized region, can lead to local overheating and thus possibly to decomposition of the liquid 1 to be vaporized and of the material of the liquid store or wick.

[0119] Furthermore, high heating outputs can also lead to excessively rapid vaporization, with the result that further liquid 1 for vaporization cannot be provided quickly enough by the capillary forces. This likewise leads to overheating of the lateral surfaces of the sintered body in the heating region 2a. Therefore, what can be installed is a unit, for example a voltage, power and/or temperature-adjustment control unit (not depicted here), which, however, is at the expense of battery life and limits the maximum vaporization rate.

[0120] Therefore, the disadvantages of the vaporizer depicted in FIG. 1 and known from the prior art are the local heating method 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 and of the store/wick material.

[0121] FIG. 2 shows a vaporizer unit known from the prior art, in which the heating element 30 is arranged directly on the sintered body 20. In particular, the heating element 30 is fixedly connected to the sintered body 20. Such a connection can be achieved in particular by the heating element 30 being in the form of a film resistor. To this end, what is applied to the sintered body 20 is a ladder-structured electrically conductive coating in the manner of a film resistor. A coating applied directly to the sintered body 20 as a heating element 30 is, inter alia, advantageous for achieving good thermal contact, which allows rapid heating. However, the vaporizer unit shown in FIG. 2 also has only a localized vaporization surface, and so there is also the risk here of overheating of the surface.

[0122] FIG. 3 schematically shows the structure of a vaporizer comprising a sintered body 6 according to the invention. Like the porous sintered body 2 in FIG. 1 and FIG. 2, it is dipped into the liquid 1 to be vaporized. As a result of capillary forces (represented by the arrows 4), the liquid to be vaporized is transported into the entire volume of the sintered body 6. Thus, when an electrical voltage is applied between the contacts 3a and 3b, the sintered body 6 is heated in the entire volume region between the contacts 3a and 3b with a large surface area. Thus, in contrast to the vaporizer shown in FIG. 2, the liquid 1 is formed not just on the lateral surfaces of the sintered body, but in the entire volume region between the electrical contacts 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 less risk of local overheating. Since volume vaporization proceeds substantially more efficiently than vaporization by means of a heating coil in a localized heating region, vaporization can occur at substantially lower temperatures and at a lower heating output. A lower electrical power requirement is advantageous in that it is thus possible to increase the usage time per battery charge or to install smaller rechargeable batteries or smaller batteries.

[0123] FIG. 4 shows a schematic representation of a cross section through a sintered body 10 as one exemplary embodiment of the invention. Here, the sintered body 10 comprises a composite material 11 and, distributed therein, pores 12a, 12b. The composite material 11 has an electrical conductivity in the range from 0.1 to 10.sup.5 S/m. If a voltage is applied to the sintered body 10, current flows through the entire volume of the sintered body 10 and said volume is thus heated. FIG. 5 depicts an enlarged detail of the sintered body 10. The composite material 11 contains the first electrically conductive material 13a as a main constituent and contains electrically conductive particles of the second electrically conductive material 13b that are distributed, preferably homogeneously, between or on the first electrically conductive material 13a. Here, the electrically conductive particles 13a and 13b are held together by the dielectric material 13c. In the embodiment shown in FIG. 5, the electrically conductive particles 13a and 13b have a platelet-shaped geometry.

[0124] As described above, the heating of the sintered body 10 can be achieved by a current flow. Accordingly, a heating device in the form of a power source can be provided for this purpose. However, in general, without restriction to specific exemplary embodiments, induction heating is also possible. Accordingly, what is provided for this purpose in one embodiment is an induction heater configured to generate an induction field. For induction heating, the sintered body 10 is designed to absorb energy from the induction field and to heat up as a result. In general, induction heating is particularly easily realizable if the sintered body comprises an electrically conductive material that is ferromagnetic. Preferably, a ferromagnetic special steel as a first conductive material is provided for this purpose. Electrically conductive materials selected in this way thus also open up the possibility of carrying out the sintering process by means of induction heating. Also conceivable is heating in the sintering process by means of microwaves or capacitive technology.

[0125] Here, a corresponding sintered body 6 as Example 1 having an electrical conductivity of approx. 1 S/m and a porosity of approx. 55% by volume can be obtained in step a) by providing a mixture of 25% by volume of glass with 65% by volume of special steel 1.4404 (d50 of 50-150 μm) and 10% by volume of silver (d50 of 1-10 μm). In step b), a pore former, preferably an organic pore former, is added, followed by the production of a green body. It is subsequently heated by thermal treatment in a regular furnace atmosphere to a temperature approximately corresponding to the softening temperature of the glass used, and sintered to form the sintered body 6.

[0126] In a second exemplary embodiment, the sintered body has a porosity of 55% by volume. Here, the composite material contains 23% by volume of borosilicate glass (FIOLAX®) as dielectric material, 60% by volume of special steel 1.4404 as first electrically conductive material and 17% by volume of silver as second electrically conductive material. Here, the particles of the electrically conductive materials have a mean grain size d50 in the range from 20 to 60 μm. The electrical conductivity of the sintered body is 2000 S/m.

[0127] The electrical conductivity is determined by resistance measurement on, for example, test specimens of approx. 5 to 10 mm in diameter and 5 to 10 mm in height and conversion of the resistance value into electrical conductivity, with manual or mechanical arrangement or attachment of the measurement tips on/to the opposing diameters without further aids (e.g., conductive paste or soldering of contacts).

[0128] According to another development, the dielectric material, for instance according to Examples 1 and 2, is modified such that the dielectric component of the sintered body contains both glass and ceramic. According to one exemplary embodiment, the proportion of ceramic in the dielectric material is 85% by volume and the proportion of glass in the dielectric material is 15% by volume. Here, electrical conductivities in the range from 1 to 10 S/m can likewise be obtained. The inventors suspect that, although the nature of the dielectric material used influences the mechanical properties, it has only a very slight influence on the electrical conductivity of the sintered body. This also applies to sintered bodies, the dielectric component of which contains a mixture of glass-ceramic with one of the constituents glass and ceramic or both of said constituents. A glass-ceramic component can also be formed by initially introducing a crystallizable glass in the green body, which glass ceramizes during sintering at an appropriate temperature for ceramization of said glass and is then present as a glass-ceramic. Below such a temperature, a crystallizable glass remains in the vitreous state.

[0129] FIG. 6 shows an SEM image of a cross section through a sintered body according to the invention as a further exemplary embodiment. The scaffold-forming metal used in this example was special steel. The special steel particles are substantially round, in particular oval to spherical. Some of these round particles 23 can be seen as round, light-gray elements in the SEM image. In the SEM image, the glass exhibits a similar contrast to the special steel, and so differentiation thereof in the image is hardly possible. Appearing as very light regions are the sintered particles 24 of the second electrically conductive material, which are silver particles here. The pores can be seen in the image as black regions. In general, the mean grain sizes of the first and the second conductive material can differ. As can also be seen in the example in FIG. 6, the mean grain size of the second electrically conductive material (silver particles in the example) is preferably smaller than the mean grain size of the first electrically conductive material (special steel particles in the example).

[0130] FIG. 7 shows the structure of a coated sintered body 6 having open porosity on the basis of a schematic cross section through a further exemplary embodiment. The coated sintered body 1 comprises a porous composite material 11 composed of dielectric material, first electrically conductive material and second electrically conductive material having open pores 12a, 12b. By means of their pore surface, one portion of the open pores 12b forms the lateral surfaces of the sintered body, whereas another portion of the pores 12a forms the interior of the sintered body. All surfaces of the sintered body comprise an electrically conductive coating 9a, for example in the form of an ITO coating. If a voltage is applied to the sintered body, the current flows through the entire volume of the sintered body.

[0131] Here, a correspondingly coated sintered body 6 as Example 8 can be obtained by first producing a sintered body having a relatively low electrical conductivity in the range from 0.1 to 100 S/m. In order to obtain the desired, relatively high electrical conductivity, for example in the range from 100 to 600 S/m, the sintered body is subsequently provided with an electrically conductive coating, for example an ITO-containing or AZO-containing coating. Here, the basic electrical conductivity of the sintered body means that 50% less coating material is required (compared to a sintered body without electrically conductive material). Furthermore, the coating process is also less time-consuming. Thus, the process time required for the coating process can be reduced by up to 70%.

LIST OF REFERENCE SIGNS

[0132] 1 Carrier liquid [0133] 2 Sintered body [0134] 2a Heating zone [0135] 3, 30 Heating element [0136] 3a, 3b Contacts [0137] 4 Capillary forces [0138] 5 Vapor [0139] 6 Sintered body [0140] 8a, 8b Pores [0141] 9, 9a Electrically conductive coating [0142] 10 Electrically conductive sintered body [0143] 11 Composite material [0144] 12a, 12b Pore [0145] 13a First electrically conductive material [0146] 13b Electrically conductive particles of the second electrically conductive material [0147] 13c Dielectric material [0148] 14 Distance between adjacent electrically conductive particles [0149] 20 Sintered body [0150] 22 Vaporizer [0151] 23 Round particle [0152] 24 Particle of the second electrically conductive material [0153] 31, 32 Contacting