ELECTRICALLY CONDUCTIVE, POROUS SINTERING BODY

Abstract

An evaporator is provided that includes a porous sintered body. The porous sintered body is formed by a composite of at least one electrically conductive material and at least one dielectric material. The sintered body has an open porosity in a range from 10 to 90% and an electrical conductivity in a range from 0.1 to 105 S/m. The fraction of electrically conductive material in the sintered body is a maximum of 90 wt. %.

Claims

1. An evaporator comprising: a porous sintered body formed by a composite of an electrically conductive material and a dielectric material, wherein the porous sintered body has an open porosity in a range from 10 to 90% and an electrical conductivity in the range from 0.1 to 105 S/m, wherein the dielectric material is selected from a group consisting of glass, glass-ceramic, ceramic, plastic, and combinations thereof, and wherein the composite has a faction of the dielectric material of 10 to 95 vol % and a fraction of the electrically conductive material of not more than 90 vol %.

2. The evaporator of claim 1, wherein the electrical conductivity is in the range from 10 to 10000 S/m.

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

4. The evaporator of claim 3, wherein the electrical resistance is from 0.1 to 5 ohms.

5. The evaporator of claim 3, wherein the porous sintered body comprises the electrical resistance.

6. The evaporator 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.

7. The evaporator of claim 1, wherein the electrically conductive material is selected from a group consisting of: tungsten, molybdenum, iron, titanium, aluminum, copper, chromium, nickel, precious metal, platinum, gold, silver, stainless steel, silicon, titanium nitride, graphite, and any mixture or alloys thereof.

8. The evaporator of claim 1, wherein the electrically conducting material has a feature selected from a group consisting of: a resistance with positive temperature coefficient, a temperature coefficient of resistance of at least −0.0001 l/K, a temperature coefficient of resistance of less than 0.008 l/K, and a temperature coefficient of resistance of at least −0.0001 l/K and less than 0.008 l/K.

9. The evaporator of claim 1, wherein the faction of the electrically conductive material is in a range from 15 to 40 vol %.

10. The evaporator of claim 1, wherein the faction of the electrically conductive material is in a range from 5 to 70 vol % and the sintered body further comprises an electrically conductive coating.

11. The evaporator of claim 10, wherein the electrically conductive coating is on internal surface of pores of the open porosity.

12. The evaporator of claim 1, wherein the electrically conductive material comprises 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 200 μm, a particle size d.sub.50 in a range from 1 to 50 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.

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

14. The evaporator of claim 1, wherein the electrical conductivity is in a range from >30 to 70 S/μm and the fraction of the electrically conductive material in the sintered body is 5 to 40 vol %.

15. The evaporator of claim 1, wherein the electrical conductivity in the range from 10 to 30 S/μm and the fraction of the electrically conductive material in the sintered body is 10 to 60 vol %.

16. The evaporator of claim 1, wherein the electrical conductivity in the range from 1 to <10 S/μm and the fraction of the electrically conductive material is 15 to 90 vol %.

17. The evaporator 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.

18. The evaporator 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.

19. The evaporator of claim 1, wherein the porous sintered body 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.

20. A method for producing an evaporator, comprising: a) providing an electrically conducting material and a dielectric material in powder form; b) mixing the electrically conducting material and the dielectric material provided in step a) with at least one pore former to produce a powder mixture; c) generating a green body from the powder mixture provided in step b) by pressing, casting or extruding; and d) sintering the green body generated in step c), wherein the dielectric material comprises a material selected from a group consisting of glass, glass-ceramic, ceramic, and plastics, and wherein the providing in step a) further comprises providing a fraction of the dielectric material from 5% to 70% by volume.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0103] The invention is described in more detail below with reference to exemplary embodiments and figures, in which:

[0104] FIG. 1 shows a schematic representation of a conventional evaporator,

[0105] FIG. 2 shows a schematic representation of a sintered body with electrical contacting on the lateral faces of the sintered body,

[0106] FIG. 3 shows a schematic representation of one embodiment of an evaporator of the invention,

[0107] FIG. 4 shows a schematic representation of one embodiment of a sintered body of the invention in cross section,

[0108] FIG. 5 shows an enlarged detail of the cross section shown in FIG. 4, and

[0109] FIG. 6 shows an SEM micrograph of an exemplary embodiment, and

[0110] FIG. 7 shows a schematic representation of a further exemplary embodiment with an additional electrically conductive coating on the sintered body.

DETAILED DESCRIPTION

[0111] FIG. 1 shows an example of a conventional evaporator with a porous sintered body 2 as liquid reservoir. As a result of the capillary forces of the porous sintered body 2, the liquid 1 for evaporation is taken up by the porous sintered body 2 and transported further in all directions of the sintered body 2. The capillary forces here are symbolized by the arrows 4. In the upper portion of the sintered body 2, a heating coil 3 is positioned such that the corresponding portion 2a of the sintered body 2 is heated by thermal radiation. The heating coil 3 is therefore brought very close to the lateral faces of the sintered body 2 and is intended as far as possible not to contact the lateral faces. In practice, however, direct contact between heating wire and lateral face is often unavoidable.

[0112] In the heating region 2a, the liquid 1 is evaporated. This is represented by the arrows 5. The rate of evaporation here is dependent on the temperature and on the ambient pressure. The higher the temperature and the lower the pressure, the quicker the liquid evaporates in the heating region 2a.

[0113] Since the evaporation of the liquid 1 takes place only locally on the lateral faces of the heating region 2a of the sintered body, this local region must be heated with relatively high heating powers in order to achieve rapid evaporation within from 1 to 2 seconds. It is therefore necessary to apply high temperatures of more than 200° C. High heating powers, particularly in a narrowly locally confined region, however, may lead to local overheating and may therefore lead possibly to a decomposition of the liquid 1 for evaporation and of the material of the liquid reservoir and/or wick.

[0114] Furthermore, high heating powers may also lead to excessively rapid evaporation, so that the capillary forces are unable to provide further liquid 1 for evaporation quickly enough. This likewise leads to an overheating of the lateral surfaces of the sintered body in the heating region 2a. It is therefore possible to install a unit, as for example a voltage, power and/or temperature adjusting, controlling or regulating unit (not represented here), although this is at the expense of the battery life and limits the maximum evaporation quantity.

[0115] Disadvantages of the evaporator represented in FIG. 1 and known from the prior art are therefore the local heating method and the associated ineffective heat transport, the complex and expensive control unit, and the risk of overheating and decomposition of the liquid for evaporation and of the reservoir/wick material.

[0116] FIG. 2 shows an evaporator 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. A connection of this kind may be achieved in particular by designing the heating element 30 as a film resistor. For this purpose, an electrically conducting coating with a ladder-like structuring is applied in the manner of a film resistor to the sintered body 20. One of the advantages of a heating element 30 in the form of a coating applied directly on the sintered body 20 is that of achieving effective heat contact, which enables rapid heating. However, the evaporator unit shown in FIG. 2 also has only a locally limited evaporation surface, and so here as well there is a risk of overheating of the surface.

[0117] FIG. 3 shows schematically the construction of an evaporator with a sintered body 6 of the invention. As for the porous sintered body 2 in FIG. 1 and FIG. 2, this sintered body 6 is immersed in the liquid 1 for evaporation. Capillary forces (represented by the arrows 4) bring about transport of the liquid for evaporation into the entire volume of the sintered body 6. Therefore, 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 of high surface area. In contradistinction to the evaporator shown in FIG. 2, therefore, the liquid 1 is formed not only on the lateral faces of the sintered body, but rather in the entire volume region between the electrical contacts of the sintered body 6. There is therefore no need for capillary transport to the lateral faces or heated faces or elements of the sintered body 6. Moreover, there is less risk of a local overheating. Since the evaporation in the volume operates with substantially greater efficiency than by means of a heating coil in a locally limited heating region, the evaporation can take place at substantially lower temperatures and with a lower heating power. A lower electrical power requirement is advantageous in that it thus increases the usage time per secondary cell charge and/or allows smaller secondary cells or batteries to be installed.

[0118] FIG. 4 shows a schematic representation of a cross section through a sintered body 10 as an exemplary embodiment of the invention. This sintered body 10 comprises a composite material 11 and pores 12a and 12b distributed therein. The composite material 11 has an electrical conductivity in the range from 0.1 to 105 S/m. Where a voltage is applied to the sintered body 10, current flows through the entire volume of the sintered body 10, which is heated accordingly.

[0119] FIG. 5 represents a detail of the sintered body 10, in enlarged form. The composite material 11 is formed by a dielectric matrix 13a and also by electrically conductive particles 13b distributed homogeneously in the matrix 13a. In the embodiment shown in FIG. 5, the electrically conductive particles 13b have a platelet-shaped geometry. A corresponding sintered body 6 as example 1 with an electrical conductivity in the range from 1 to 5 S/m and a porosity of around 30 vol % can be obtained here according to operating steps a to d, by first providing a mixture of 50 vol % each of a glass and titanium, with a particle size d.sub.50 selected from the range from 20 to 50 μm and an elongate particle morphology, producing a green body from this mixture, and subsequently sintering this green body by thermal treatment in a regular kiln atmosphere at a temperature which corresponds approximately to the softening temperature of the glass employed, in this case around 700° C., for 20 min-120 min to form the sintered body 6.

[0120] When using a further glass with a softening temperature about 200° C. higher on the part of the glass employed, accordingly, it is possible to obtain, on sintering at around 920 to 940° C. for 20 min to 120 min, a sintered body 6 as example 2 with an electrical conductivity in the range from 1 to 10 S/m.

[0121] Here and in examples below, unless noted otherwise, the electrical conductivity is ascertained by resistance measurement on, for example, specimens of around 5 to 10 mm in diameter and 5 to 10 mm in height and by conversion of the resistance value into electrical conductivity, with the measurement tips being mounted or arranged mechanically, manually at the opposite diameters, without further auxiliaries (for example, conductive paste or soldering-on of contacts). From these examples 1 and 2 it is clear here that the dielectric material, in this case the type of glass used, exerts only a moderate influence over the electrical conductivity of the sintered body. Instead, the electrical conductivity is critically determined by the nature of the electrically conductive material and the amount thereof in the sintered body.

[0122] In another refinement, the dielectric material, in accordance for instance with examples 1 and 2, is modified such that the dielectric fraction of the sintered body contains not only glass but also ceramic. Hence the ceramic fraction in the dielectric material may be for example up to 97 vol %. Hence in the case of sintered bodies with a ceramic fraction of 97 vol % (based on the dielectric fraction), for example, it is likewise possible to obtain electrical conductivities in the range from 1 to 10 S/m. Sintered bodies which, conversely, have only a low ceramic fraction in the dielectric material likewise exhibit comparable electrical conductivities. The inventors therefore suppose that the nature of the dielectric material used, while influencing the mechanical properties, has only a very low influence on the electrical conductivity of the sintered body. The same is true of sintered bodies whose dielectric fraction contains a mixture of glass-ceramic with one or both of the glass and ceramic constituents. A glass-ceramic fraction may be formed here also by the inclusion in the green body of a crystallizable glass which on sintering at a corresponding temperature for ceramization of this glass undergoes ceramization and is then present as a glass-ceramic. Below such a temperature, a crystallizable glass remains in the glassy state.

[0123] Moreover, sintered bodies 6 as example 3 with an electrical conductivity in the range from 100 to 1000 S/m for a porosity of around 55 vol %, may be obtained according to operating steps a to d by the provision first of a mixture of 85 vol % each of a glass and 15 vol % of silver, with a particle size d.sub.50 of 15 to 20 μm and an elongate particle morphology, the production therefrom of a green body, and the subsequent sintering of this green body by thermal treatment in a regular kiln atmosphere at a temperature which corresponds approximately to the softening temperature of the glass employed, here around 930 to 950° C., for 20 min-120 min to form the sintered body 6. When using a different particle morphology on the part of the silver employed, in the present case round particle morphology with d.sub.50 of likewise 15 to 20 μm, accordingly, sintered bodies 6 as example 4 are obtained with an electrical conductivity in the range from 0.5 to 1 S/m. This highlights the influence of the particle shape of the electrically conducting material on the electrical conductivity.

[0124] Sintered bodies 6 as example 5 or 6 with a porosity of around 55 vol % and a conductivity of around 1500 S/m may be obtained by means of mixtures of 70 vol % of glass with 30 vol % of molybdenum (d.sub.50 of 1 to 3 μm) or of a mixture of 70 vol % of glass with 30 vol % of tungsten (d.sub.50 of 1 to 2 μm), by thermal treatment in regular kiln atmosphere at a temperature which corresponds approximately to the softening temperature of the glass employed, here around 900 to 950° C., for 20 min-120 min. In this case the resistance of the specimens was measured on their two opposite diameters with the aid of conductive paste applied there.

[0125] FIG. 6 shows an SEM micrograph of a cross section through a sintered body of the invention, as a further exemplary embodiment. Here the electrically conductive particles 13b appear as light-colored structures in the dielectric material 13a. The pores 12a have a primarily round cross section. The cross-sectional geometry of the pores 12a is determined by the particle geometry of the pore former used in the production method.

[0126] FIG. 7 shows the construction of a coated sintered body 6 with open porosity by means of a schematic cross section through a further exemplary embodiment. The coated sintered body 1 comprises a porous matrix of composite material 11 with open pores 12a, 12b. Some of the open pores 12b with their pore surface form the lateral faces of the sintered body, while another set of the pores 12a form the interior of the sintered body. All of the surfaces of the sintered body have an electrically conductive coating 9a, in the form of an ITO coating, for example. When a voltage is applied on the sintered body, the current flows through the entire volume of the sintered body.

[0127] A correspondingly coated sintered body 6 as example 8 may be obtained in this context by first producing a glass-metal composite having a relatively low electrical conductivity in the range from 0.1 to 100 S/m, according to one of examples 1 or 4, for example. For this purpose it is also possible further, for example, to produce a sintered body from 95 to 86 vol % of borosilicate glass and 5-15 vol % of silver with elongate silver particles having a particle size in the range from 1 to 60 μm by sintering in air at a temperature in the sintering range of 900-950° C. for 20 min to 120 min. To obtain a desired electrical conductivity in the range from 100 to 600 S/m, the sintered body is provided subsequently with an electrically conductive coating, for example an ITO-containing or AZO-containing coating. As a result of the basic electrical conductivity of the sintered body, in this case (compared with a sintered body without electrically conductive material) less than 50% of the coating material is needed. Furthermore, the coating operation is also less time-intensive. Hence the operating time needed for the coating process can be reduced by up to 70%.

LIST OF REFERENCE SIGNS

[0128] 1 carrier liquid [0129] 2 sintered body [0130] 2a heating zone [0131] 3, 30 heating element [0132] 3a, 3b contacts [0133] 4 capillary forces [0134] 5 vapor [0135] 6 sintered body [0136] 8a, 8b pores [0137] 9, 9a electrically conductive coating [0138] 10 electrically conductive sintered body [0139] 11 composite material [0140] 12a, 12b pore [0141] 13a dielectric material [0142] 13b electrically conductive particles [0143] 14 distance between adjacent electrically conductive particles [0144] sintered body [0145] 22 evaporator [0146] 31, 32 contacting