Electrode-embedded ceramic structure

Abstract

Provided is an electrode-embedded ceramic structure comprising: a ceramic shaft having an electrode provided on an outer peripheral section thereof; and a ceramic cylinder that houses the ceramic shaft and that is joined with the ceramic shaft. In the electrode-embedded ceramic structure, the relative density of a first ceramic constituting the ceramic shaft and the relative density of a second ceramic constituting the ceramic cylinder are different.

Description

Ceramic structure with embedded electrodes

[0001] This specification discloses a technique relating to a ceramic structure with embedded electrodes.

[0002] Japanese Patent Laid-Open Publication No. 2006-228713 (hereinafter referred to as Patent Document 1) discloses a ceramic structure (a columnar ceramic heater) with electrodes embedded therein. In Patent Document 1, electrodes are first printed on the surface of a ceramic sheet. Then, a new ceramic sheet is laminated on the ceramic sheet with the printed electrodes, and the laminated ceramic sheet is wrapped around it to produce a ceramic structure with embedded electrodes.

[0003] As described above, electrodes are embedded inside the ceramic structure by printing the electrodes on the ceramic sheets during the lamination of the ceramic sheets. In such an electrode-embedded ceramic structure, the heating efficiency of the object to be heated (i.e., the heating efficiency of the surface of the ceramic structure) depends on the thickness, material, etc. of the ceramic sheet. In the field of electrode-embedded ceramic structures, there is a demand for further improvement in the heating efficiency of the object to be heated without degrading properties such as durability. The purpose of this specification is to realize an electrode-embedded ceramic structure with improved heating efficiency of the object to be heated.

[0004] A first technique disclosed in this specification may be an electrode-embedded ceramic structure including a ceramic shaft having an electrode provided on its outer periphery and a ceramic cylinder that houses the ceramic shaft and is connected to the ceramic shaft. In this electrode-embedded ceramic structure, the relative density of the first ceramic constituting the ceramic shaft may be different from the relative density of the second ceramic constituting the ceramic cylinder.

[0005] A second technique disclosed in this specification is the electrode-embedded ceramic structure of the first technique, wherein the relative density ratio of the second ceramic to the first ceramic may be 0.3 or more and 1.0 or less.

[0006] A third technique disclosed in this specification is the electrode-embedded ceramic structure of the first technique, wherein the relative density ratio of the first ceramic to the second ceramic may be 0.3 or more and 1.0 or less.

[0007] A fourth technology disclosed in this specification is the electrode-embedded ceramic structure of any one of the first to third technologies, in which the relative density of the first ceramic may be 0.30 or more and 1.0 or less.

[0008] A fifth technology disclosed in this specification is the electrode-embedded ceramic structure of any one of the first to fourth technologies, wherein the second ceramic may have a relative density of 0.30 or more and 1.0 or less.

[0009] A sixth technology disclosed in this specification is an electrode-embedded ceramic structure according to any one of the first to fifth technologies, wherein the ratio of the outer diameter of the ceramic cylinder to the outer diameter of the ceramic shaft may be 1.1 or more and 4.0 or less.

[0010] A seventh technique disclosed in this specification is the electrode-embedded ceramic structure of any one of the first to sixth techniques, wherein the outer diameter of the ceramic shaft may be 0.5 mm or more and 20 mm or less.

[0011] An eighth technique disclosed in this specification is the electrode-embedded ceramic structure of any one of the first to seventh techniques, wherein the outer diameter of the ceramic cylinder may be 1 mm or more and 25 mm or less.

[0012] A ninth technology disclosed in this specification is an electrode-embedded ceramic structure according to any one of the first to eighth technologies, wherein the ceramic shaft has a first hole extending from one end to the other end in the axial direction, and the first hole may be open to at least one end in the axial direction.

[0013] The tenth technology disclosed in this specification is an electrode-embedded ceramic structure of any one of the first to ninth technologies, wherein the ceramic cylinder has a second hole extending from one end in the axial direction to the other end, and the second hole may be open to at least one end in the axial direction.

[0014] An eleventh technology disclosed in this specification is an electrode-embedded ceramic structure according to any one of the first to tenth technologies, in which a tapered portion is provided at the end of the ceramic tube, the outer diameter of which decreases toward the tip, and the relative density of the tapered portion may be smaller than the relative density of the portion other than the tapered portion.

[0015] A twelfth technique disclosed in this specification is the electrode-embedded ceramic structure of any one of the first to eleventh techniques, in which the cross-sectional shape of the ceramic cylinder may be circular, elliptical, or polygonal.

[0016] A thirteenth technology disclosed in this specification is the electrode-embedded ceramic structure of any one of the first to twelfth technologies, wherein the ceramic shaft may be made of a material mainly made of alumina, zirconia, aluminum nitride, silicon nitride, or silica, and the ceramic cylinder may be made of a material mainly made of alumina, zirconia, aluminum nitride, silicon nitride, or silica.

[0017] A fourteenth technology disclosed in this specification is an electrode-embedded ceramic structure according to any one of the first to thirteenth technologies, in which the material of the electrode may be a metal mainly containing platinum, tungsten, or molybdenum.

[0018] 1 shows a schematic diagram (perspective view) of an electrode-embedded ceramic structure of a first embodiment; a cross-sectional view taken along line II-II in FIG. 1; a manufacturing process for a ceramic structure; a cross-sectional view taken along line IV-IV in FIG. 2; a cross-sectional view of an electrode-embedded ceramic structure of a second embodiment; a cross-sectional view taken along line VI-VI in FIG. 5; a cross-sectional view of an electrode-embedded ceramic structure of a third embodiment; a cross-sectional view of an electrode-embedded ceramic structure of a fourth embodiment; a cross-sectional view of an electrode-embedded ceramic structure of a fifth embodiment; a modified example of the electrode-embedded ceramic structure of the first ... 10 shows a modified example of the electrode-embedded ceramic structure of the second embodiment.

[0019] The electrode-embedded ceramic structure disclosed herein may include a ceramic shaft having an electrode provided on its outer periphery and a ceramic cylinder housing the ceramic shaft. The ceramic shaft and the ceramic cylinder may be bonded. Furthermore, the relative density of the first ceramic constituting the ceramic shaft may differ from the relative density of the second ceramic constituting the ceramic cylinder. Specifically, the relative density of the first ceramic may be lower than the relative density of the second ceramic. Alternatively, the relative density of the second ceramic may be lower than the relative density of the first ceramic. Note that "relative density" refers to the actual density of a ceramic relative to its theoretical density (actual density / theoretical density). Specifically, the relative density can be calculated by calculating (1 - porosity).

[0020] An electrode-embedded ceramic structure in which the ceramic shaft and the ceramic cylinder have different relative densities can be manufactured by separately preparing a ceramic shaft with an electrode (wiring pattern) formed on its outer periphery and a ceramic cylinder, inserting the ceramic shaft into the ceramic cylinder, firing the ceramic shaft, and integrating (sintering) the two. In this case, the ceramic shaft and the ceramic cylinder having different relative densities may be separately prepared in advance and then integrated (sintered). Alternatively, a pore-forming material may be added to the ceramic shaft or ceramic cylinder whose relative density is to be lowered, and the pore-forming material may be removed when the two are integrated (fired, sintered), resulting in the relative density of one being lower than the relative density of the other.

[0021] As the relative density decreases, the heat capacity decreases, making the ceramics more susceptible to temperature changes (heating up or down). That is, reducing the relative density of the ceramics constituting the electrode-embedded ceramic structure improves the heating efficiency (speeding up and down the temperature) of the contact surface with the heated object (surface of the electrode-embedded ceramic structure). For example, when heating the external space of the electrode-embedded ceramic structure, the relative density of the second ceramic is made smaller than the relative density of the first ceramic. Also, when heating the internal space (inner space) of the electrode-embedded ceramic structure, the relative density of the first ceramic is made smaller than the relative density of the second ceramic.

[0022] When the relative density of the second ceramic is lower than the relative density of the first ceramic, the relative density ratio of the second ceramic to the first ceramic may be 0.3 or more and 1.0 or less. When the relative density of the first ceramic is lower than the relative density of the second ceramic, the relative density ratio of the first ceramic to the second ceramic may be 0.3 or more and 1.0 or less. By making the relative density ratio of the two ceramics 0.3 or more, it is possible to prevent cracks, chips, etc. from occurring in the electrode-embedded ceramic structure. The relative density ratio of the two ceramics may be 0.4 or more, 0.5 or more, 0.6 or more, 0.7 or more, 0.8 or more, or 0.9 or more. The relative density ratio of the two ceramics may be 0.9 or less, 0.8 or less, 0.7 or less, 0.6 or less, 0.5 or less, or 0.4 or less.

[0023] The relative density of the first ceramic may be 0.30 or more and 1.0 or less. By making the relative density of the first ceramic 0.3 or more, it is possible to suppress the occurrence of cracks, chips, etc. when manufacturing the electrode-embedded ceramic structure (when forming an electrode on the surface of the ceramic shaft, when inserting the ceramic shaft into the ceramic cylinder). The relative density of the first ceramic may be 0.4 or more, 0.5 or more, 0.6 or more, 0.7 or more, 0.8 or more, or 0.9 or more. Alternatively, the relative density of the first ceramic may be 0.9 or less, 0.8 or less, 0.7 or less, 0.6 or less, 0.5 or less, or 0.4 or less.

[0024] The relative density of the second ceramic may be 0.30 or more and 1.0 or less. By making the relative density of the second ceramic 0.3 or more, it is possible to suppress the occurrence of cracks, chips, etc. when manufacturing the electrode-embedded ceramic structure (when inserting the ceramic shaft into the ceramic cylinder). The relative density of the second ceramic may be 0.4 or more, 0.5 or more, 0.6 or more, 0.7 or more, 0.8 or more, or 0.9 or more. Furthermore, the relative density of the second ceramic may be 0.9 or less, 0.8 or less, 0.7 or less, 0.6 or less, 0.5 or less, or 0.4 or less.

[0025] The ratio of the outer diameter of the ceramic cylinder to the outer diameter of the ceramic shaft may be 1.1 or more and 4.0 or less. By setting the outer diameter ratio to 1.1 or more, the strength of the ceramic cylinder can be ensured. For example, damage to the ceramic cylinder when inserting the ceramic shaft into the ceramic cylinder can be suppressed. Furthermore, by setting the outer diameter ratio to 4.0 or less, the electrode-embedded ceramic structure can be reduced in size and the heating efficiency of the electrode-embedded ceramic structure can be improved. For example, when heating the external space of the electrode-embedded ceramic structure, setting the outer diameter ratio to 4.0 or less reduces the heat capacity of the ceramic cylinder and improves the heating efficiency of the electrode-embedded ceramic structure. Furthermore, when heating the external space of the electrode-embedded ceramic structure, setting the outer diameter ratio to 4.0 or less reduces the size of the portion (ceramic cylinder) that does not contribute to heating efficiency, allowing the electrode-embedded ceramic structure to be reduced in size. The ratio of the outer diameter of the ceramic cylinder to the outer diameter of the ceramic shaft may be 1.2 or more, 1.3 or more, 1.4 or more, 1.5 or more, 2.0 or more, 2.5 or more, 3.0 or more, 3.5 or more, 3.6 or more, 3.7 or more, 3.8 or more, or 3.9 or more. The ratio of the outer diameter of the ceramic cylinder to the outer diameter of the ceramic shaft may be 3.9 or less, 3.8 or less, 3.7 or less, 3.6 or less, 3.5 or less, 3.0 or less, 2.5 or less, 2.0 or less, 1.5 or less, 1.4 or less, 1.3 or less, or 1.2 or less.

[0026] The outer diameters of the ceramic shaft and the ceramic cylinder can be set as desired. In order to ensure ease of handling during production of the electrode-embedded ceramic structure, strength of the electrode-embedded ceramic structure, and heater performance when the electrode-embedded ceramic structure is used as a ceramic heater, the outer diameter of the ceramic shaft may be 0.5 mm or more and 20 mm or less, and the outer diameter of the ceramic cylinder may be 1 mm or more and 25 mm or less.

[0027] The ceramic shaft may be columnar or cylindrical. That is, the ceramic shaft may be solid or hollow. In the case of a cylindrical ceramic shaft, the ceramic shaft may have a first hole extending from one end to the other end in the axial direction. Furthermore, when the ceramic shaft has a first hole, one end may be closed (cylindrical with a bottom) or both ends may be open. That is, the first hole may be open at least at one end in the axial direction. By providing a first hole in the ceramic shaft, an object (a liquid such as water, or a solid such as a metal wire) can be placed inside the ceramic shaft. When the ceramic shaft has a first hole, the relative density of the first ceramic may be lower than the relative density of the second ceramic.

[0028] The ceramic cylinder may have a second hole extending from one axial end to the other end to accommodate the ceramic shaft. Specifically, the ceramic cylinder may be a bottomed cylinder having a bottom surface facing the longitudinal end face of the ceramic shaft and an inner circumferential surface in contact with the outer circumferential surface of the ceramic shaft. The bottom surface may also have a through-hole communicating with the outside of the ceramic cylinder. That is, the second hole may close one end of the ceramic cylinder or may extend from one end to the other end of the ceramic cylinder.

[0029] The end of the ceramic tube may also be provided with a tapered portion in which the outer diameter decreases toward the tip. The relative density of the tapered portion may be smaller than the relative density of the rest of the tapered portion. Since the tapered portion has a reduced outer diameter, the electrode (ceramic shaft) is often not located inside. Therefore, the heating efficiency of the tapered portion is lower than that of the rest of the tapered portion. By making the relative density of the tapered portion smaller than that of the rest of the tapered portion, the heating efficiency of the tapered portion can be improved. The outer shape of the ceramic tube (cross-sectional shape perpendicular to the axial direction) is optional and can be selected depending on the application. The outer shape of the ceramic tube may be, for example, circular, elliptical, or polygonal.

[0030] The ceramic shaft (first ceramic) and the ceramic cylinder (second ceramic) may be made of a material mainly made of alumina, zirconia, aluminum nitride, silicon nitride, or silica. The term "mainly made of" means that the main material accounts for 50% by mass or more of the material constituting the first ceramic or the second ceramic. An example of an alumina material is alumina (Al ２ O ３ ), mullite (Al ６ O １３ Si ２ ), spinel (MgAl ３ O ４ An example of a zirconia material is zirconia (ZrO ２ ), yttria (Y) as a stabilizer ２ O ３ Examples of suitable zirconia include partially stabilized zirconia and stabilized zirconia containing added calcia (CaO). In order to ensure good sintering between the ceramic shaft and the ceramic cylinder, it is preferable that the first ceramic and the second ceramic are made of the same material.

[0031] The electrode material may be, for example, a metal or metal alloy mainly composed of platinum (Pt), tungsten (W), or molybdenum (Mo). "A metal mainly composed of platinum, tungsten, or molybdenum" means that the main metal accounts for 50 mass% of the constituent metals of the electrode. The electrode may be formed on the outer peripheral surface of the ceramic shaft by screen printing, vapor deposition, or the like. After the electrode is formed on the outer peripheral surface of the ceramic shaft, the surface of the electrode may be covered with a protective layer. There are no particular restrictions on the material of the protective layer, and resin, ceramics, etc. may be used.

[0032] First Embodiment A ceramic structure 50 will be described with reference to the drawings. The ceramic structure 50 is an example of a ceramic structure with an embedded electrode. The ceramic structure 50 is used as a ceramic heater. As shown in FIGS. 1 and 2 , the ceramic structure 50 includes a cylindrical ceramic shaft 20 having an electrode 22 disposed on its outer periphery (outer peripheral surface) and a cylindrical ceramic tube 10 with a bottom. The ceramic tube 10 has a substantially cylindrical outer shape, but one end (tip) is generally conical, with the diameter decreasing toward the end. That is, the end of the ceramic tube 10 has a tapered portion whose outer diameter decreases toward the tip. The ceramic shaft 20 is housed in the ceramic tube 10. The ceramic shaft 20 and the ceramic tube 10 are sintered and integrated. Therefore, the electrode 22 is embedded in the ceramic.

[0033] A method for manufacturing a ceramic structure 50 will be described with reference to FIG. 3 . First, an electrode (Pt electrode) 22 was vapor-deposited on the surface, followed by firing at 1500°C in an air atmosphere to prepare a ceramic shaft 20 made of alumina with a diameter of 2 mm. The alumina constituting the ceramic shaft 20 (portions other than the electrode 22) is an example of a first ceramic. A ceramic cylinder 10 made of alumina with a hole (bottomed hole) 12 with a diameter of 2 mm in its center was also prepared separately from the ceramic shaft 20. The alumina constituting the ceramic cylinder 10 is an example of a second ceramic. The hole 12 is an example of a second hole. The ceramic shaft 20 was then inserted into the hole 12 and fired at 1500°C in an air atmosphere to obtain a ceramic structure 50. The ceramic shaft 20 was inserted until its end face contacted the bottom of the hole 12.

[0034] The features of the ceramic structure 50 will be described with reference to FIG. 4 . As shown in FIG. 5 , the front and back surfaces of the electrode 22 are in contact with the ceramic (the ceramic shaft 20 and the ceramic cylinder 10). That is, the electrode 22 is embedded in the ceramic that constitutes the ceramic structure 50. In the ceramic structure 50, the electrode 22 does not extend in the circumferential direction, and a portion where the ceramic shaft 20 and the ceramic cylinder 10 are sintered exists between the electrodes 22. The relative density of the alumina (second ceramic) that constitutes the ceramic cylinder 10 is lower than the relative density of the alumina (first ceramic) that constitutes the ceramic shaft 20. Specifically, the relative density ratio of the alumina that constitutes the ceramic cylinder 10 to the alumina that constitutes the ceramic cylinder 20 is adjusted to be 0.3 or more and 1.0 or less. The relative densities of the ceramic cylinder 10 and the ceramic shaft 20 can be adjusted by adjusting the raw material filling amounts, raw material particle sizes, etc. of the ceramic cylinder 10 and the ceramic shaft 20 when manufacturing the ceramic cylinder 10 and the ceramic shaft 20. Alternatively, the relative density of the ceramic tube 10 and the ceramic shaft 20 can be adjusted (the relative density of the ceramic tube 10 can be made smaller than the relative density of the ceramic shaft 20) by adding a pore-forming material to the raw material of the ceramic tube 10 (second ceramic).

[0035] As described above, in the ceramic structure 50, the relative density of the second ceramic is lower than the relative density of the first ceramic. Therefore, the heat capacity of the ceramic cylinder 10 is lower than the heat capacity of the ceramic shaft 20. As a result, heat generated when current is applied to the electrode 22 is easily transferred (heat transferred) to the ceramic cylinder 10, thereby increasing the temperature rise rate of the outer surface of the ceramic structure 50 (ceramic cylinder 10). As a result, an object to be heated in the space outside the ceramic structure 50 can be quickly heated. Furthermore, because there are many voids in the ceramic cylinder 10, even if force is applied to the ceramic cylinder 10 due to the difference in thermal expansion between the electrode 22 and the ceramic cylinder 10, the force is absorbed by the voids, thereby preventing damage to the ceramic cylinder 10.

[0036] The relative densities of the ceramic shaft 20 (first ceramic) and the ceramic cylinder 10 (second ceramic) can be measured using cross-sectional images (e.g., the cross-sections shown in FIG. 4 ). Specifically, the relative densities can be calculated by taking SEM images of the cross sections of the ceramic shaft 20 and the ceramic cylinder 10 and measuring the area of ​​voids. The void area can be calculated by, for example, processing the captured SEM images using iTEM analysis software (manufactured by Seika Sangyo Co., Ltd.).

[0037] Second Example A ceramic structure 150 will be described with reference to Fig. 5 and Fig. 6. The ceramic structure 150 is a modified example of the ceramic structure 50, and the description of the structures that are substantially the same as those of the ceramic structure 50 may be omitted by assigning the same reference numbers as those assigned to the ceramic structure 50. Fig. 5 corresponds to the cross section of the ceramic structure 50 shown in Fig. 2, and Fig. 6 corresponds to the cross section of the ceramic structure 50 shown in Fig. 4.

[0038] In the ceramic structure 150, a hole 24 is provided in the ceramic shaft 120, and a hole 18 is provided at the tip (tapered portion) of the ceramic cylinder 110. The hole 24 is an example of a first hole. In the ceramic structure 150, the holes 12 and 18 are examples of second holes. The hole 24 is a through hole extending from one end of the ceramic shaft 120 to the other. That is, the hole 24 is open at both axial ends of the ceramic shaft 120. The ceramic shaft 120 has a hollow structure. The hole 18 extends from the bottom of the hole 12 to the outside of the ceramic cylinder 110. The holes 12 and 18 open both axial ends of the ceramic cylinder 110. The hole 24 in the ceramic shaft 120 and the hole 18 in the ceramic cylinder 110 are connected to each other. However, the size (diameter) of the hole 18 is smaller than the size (diameter) of the hole 24. The ceramic structure 150 can be considered to have through holes (holes 18 and 24) extending from one end to the other end in the axial direction.

[0039] In the ceramic structure 150, the relative density of the alumina (first ceramic) constituting the ceramic shaft 120 is lower than the relative density of the alumina (second ceramic) constituting the ceramic cylinder 110. Specifically, the relative density ratio of the alumina constituting the ceramic cylinder 110 to the alumina constituting the ceramic shaft 120 is adjusted to be 0.3 or more and 1.0 or less. The relative densities of the ceramic cylinder 110 and the ceramic shaft 120 can be adjusted by adjusting the raw material filling amounts, raw material particle sizes, etc. of the ceramic cylinder 110 and the ceramic shaft 120, as with the ceramic cylinder 10 and the ceramic shaft 20. Alternatively, the relative density can be adjusted by adding a pore-forming material to the raw material of the ceramic shaft 120 (first ceramic).

[0040] The ceramic structure 150 can be used as a heater for placing an object (liquid or solid) in the holes 24 and heating the object. The ceramic structure 150 can also be used as a vacuum suction device for degassing the gas in the holes 24 through the holes 18 to reduce the pressure in the holes 24 and adsorbing other substances onto the object placed in the holes 24. In this case, by turning on the heater, the object in the holes 24 can be heated while the other substance is adsorbed onto the object. Typically, the higher the temperature of the object, the faster the adsorption rate. The ceramic structure 150 can also be used as a vacuum suction device with a heater.

[0041] As described above, in the ceramic structure 150, the relative density of the first ceramic is lower than the relative density of the second ceramic. Therefore, heat generated when a current is applied to the electrode 22 is easily transferred (heat transferred) to the ceramic shaft 120, and the temperature rise rate of the inner circumferential surface of the ceramic shaft 120 (the space inside the hole 24) can be increased. As a result, the object inside the hole 24 can be heated quickly.

[0042] Third Example A ceramic structure 250 will be described with reference to Fig. 7. The ceramic structure 250 is a modified example of the ceramic structure 150, and the same reference numbers as those used for the ceramic structure 150 will be used to denote structures that are substantially the same as those used for the ceramic structure 150, and descriptions thereof may be omitted.

[0043] The ceramic structure 250 is formed by a ceramic shaft 220 and a ceramic cylinder 110. The ceramic shaft 220 is provided with a hole 24 (through hole) extending from one end to the other end of the ceramic shaft 220. However, one end of the hole 24 of the ceramic shaft 220 is tapered toward the end. Specifically, the diameter of the opening at one end of the hole 24 is tapered so that it becomes the same as the diameter of the hole 18. The ceramic structure 250 can reduce the fluid movement resistance (enable smooth movement of the fluid) when a fluid moves into the hole 24 through the hole 18 (when a fluid moves from the outside of the ceramic structure 250 into the hole 24, or when a fluid moves from the hole 24 to the outside of the ceramic structure 250).

[0044] Fourth Example A ceramic structure 350 will be described with reference to Fig. 8. The ceramic structure 350 is a modified example of the ceramic structure 150, and the same reference numbers as those assigned to the ceramic structure 150 will be used to denote structures that are substantially the same as those of the ceramic structure 150, and descriptions thereof may be omitted.

[0045] The ceramic structure 350 is formed by a ceramic shaft 320 and a ceramic cylinder 310. The ceramic shaft 320 is provided with a hole 24 extending from one end to the other end of the ceramic shaft 320. However, one end of the hole 24 in the ceramic shaft 320 is closed, and the end of the ceramic shaft 320 on the closed side is in contact with the bottom of the hole 12 provided in the ceramic cylinder 310.

[0046] The shape of the ceramic cylinder 310 is the same as that of the ceramic cylinder 10, but the relative density is different from that of the ceramic cylinder 10 (see also FIG. 2). Specifically, the relative density of the ceramic cylinder 310 (second ceramic) is greater than that of the ceramic cylinder 10, and the relative density of the alumina (first ceramic) constituting the ceramic shaft 320 is less than that of the alumina (second ceramic) constituting the ceramic cylinder 310. The ceramic structure 350 can also be used as a heater for heating an object (liquid or solid) placed in the hole 24.

[0047] As a modification of the ceramic structure 350, the relative density of the alumina (second ceramic) constituting the ceramic cylinder 310 may be made lower than the relative density of the alumina (first ceramic) constituting the ceramic shaft 320. In this case, the ceramic structure 350 can be used as a heater that heats an object to be heated that is present in the external space of the ceramic structure 350. In this case, the holes 24 contribute to reducing the weight of the ceramic structure 350.

[0048] Fifth Example A ceramic structure 450 will be described with reference to Fig. 9. The ceramic structure 450 is a modified example of the ceramic structure 350, and the same reference numbers as those assigned to the ceramic structure 350 will be used to denote structures that are substantially the same as those of the ceramic structure 350, and descriptions thereof may be omitted.

[0049] The ceramic structure 450 is formed by a ceramic shaft 320 and a ceramic cylinder 410. The ceramic cylinder 410 has a hole 12 extending from one end to the other end of the ceramic cylinder 410. One end of the hole 12 is closed in the ceramic cylinder 410, and the bottom of the hole 12 is located at the tip portion (tapered portion) of the ceramic cylinder 410. This allows the tip portion of the ceramic cylinder 410 to be heated well as well.

[0050] In the ceramic structure 450, the relative density of the alumina (first ceramic) constituting the ceramic shaft 320 is lower than the relative density of the alumina (second ceramic) constituting the ceramic cylinder 410. The ceramic structure 450 can be used as a heater for heating an object (liquid or solid) placed in the hole 24. Alternatively, as a modification of the ceramic structure 450, the relative density of the alumina (second ceramic) constituting the ceramic cylinder 410 may be lower than the relative density of the alumina (first ceramic) constituting the ceramic shaft 320, similar to the ceramic structure 350. This allows the ceramic structure 450 to be used as a heater for heating an object to be heated that is present in the external space of the ceramic structure 450.

[0051] (Modifications of the ceramic structure 50) Ceramic structures 50a to 50g will be described with reference to FIGS. 10 to 16. The ceramic structures 50a to 50g are modifications of the ceramic structure 50, and descriptions of structures that are substantially the same as those of the ceramic structure 50 may be omitted by assigning the same reference numbers as those assigned to the ceramic structure 50. Note that for the ceramic structures 50a to 50e, views corresponding to the cross section of the ceramic structure 50 shown in FIG. 4 are shown (FIGS. 10 to 14). Furthermore, for the ceramic structures 50f and 50g, views corresponding to the cross section of the ceramic structure 50 shown in FIG. 2 are shown (FIGS. 15 and 16).

[0052] As shown in Fig. 10, the ceramic structure 50a is formed by a ceramic shaft 20a and a ceramic cylinder 10. The ceramic shaft 20a has a plurality of through holes 26. The ceramic structure 50a has four through holes 26. The ceramic structure 50a achieves a lighter weight by providing the through holes 26 in the ceramic shaft 20a. Furthermore, the through holes 26 can also relieve internal stress that occurs when the ceramic structure 50a is fired (shrunk-fit).

[0053] As shown in FIG. 11 , the ceramic structure 50b is formed by a ceramic shaft 20b and a ceramic cylinder 10. A plurality of recesses 28 are formed on the outer peripheral surface of the ceramic shaft 20b. In the ceramic structure 50b, four recesses 28 are formed on the outer peripheral surface of the ceramic shaft 20b in a portion where the electrode 22 is not provided. The recesses 28 are provided at equal intervals in the circumferential direction of the ceramic shaft 20b. By providing the recesses 28 on the outer peripheral surface of the ceramic shaft 20b, it is possible to reduce the local concentration of internal stress in the circumferential direction when the ceramic structure 50b is fired (shrunk-fitted). Note that, as a modification of the ceramic structure 50b, a plurality of through holes 26 may be formed in the ceramic shaft 20b, similar to the ceramic shaft 20a (see also FIG. 10 ).

[0054] As shown in Fig. 12, a ceramic structure 50c is formed by a ceramic shaft 20 and a ceramic cylinder 10c. The ceramic cylinder 10c has an elliptical outer circumferential surface. As a modification of the ceramic structure 50c, a plurality of through holes 26 may be provided in the ceramic shaft 20 (see also Fig. 10), or a plurality of recesses 28 may be provided on the outer circumferential surface (see also Fig. 11). Furthermore, the outer circumferential surface of the ceramic cylinder 10c may be elliptical.

[0055] As shown in Fig. 13, a ceramic structure 50d is formed by a ceramic shaft 20 and a ceramic cylinder 10d. The ceramic cylinder 10d has an outer peripheral surface that is substantially square in shape. As a modification of the ceramic structure 50d, a plurality of through holes 26 may be provided in the ceramic shaft 20 (see also Fig. 10), or a plurality of recesses 28 may be provided on the outer peripheral surface (see also Fig. 11). Furthermore, the outer peripheral surface of the ceramic cylinder 10d may have a substantially rectangular shape.

[0056] As shown in Fig. 14, a ceramic structure 50e is formed by a ceramic shaft 20 and a ceramic cylinder 10e. The ceramic cylinder 10e has an outer peripheral surface that is a regular hexagon. As a modification of the ceramic structure 50e, a plurality of through holes 26 may be provided in the ceramic shaft 20 (see also Fig. 10), or a plurality of recesses 28 may be provided on the outer peripheral surface (see also Fig. 11). Furthermore, the outer peripheral surface of the ceramic cylinder 10e may have another polygonal shape.

[0057] As shown in Fig. 15, the ceramic structure 50f is formed by a ceramic shaft 20 and a ceramic cylinder 10f. An enlarged diameter portion 30 is provided on the outer peripheral surface of the end of the ceramic cylinder 10f (the end opposite the tapered portion). The enlarged diameter portion 30 can be used to fix the ceramic structure 50f to an object to be heated. The enlarged diameter portion 30 may be provided on the ceramic structures 50, 50a, 50b, 50c, 50d, and 50e.

[0058] As shown in Fig. 16, a ceramic structure 50g is formed by a ceramic shaft 20 and a ceramic cylinder 10g. An expanded diameter portion 30 is provided on the outer peripheral surface of the end portion (the end opposite the tapered portion) of the ceramic cylinder 10g. The outer diameter of the ceramic cylinder 10g decreases from the expanded diameter portion 30 toward the tapered portion. Note that the outer diameter of the ceramic structures 50, 50a, 50b, 50c, 50d, and 50e may also decrease from the end portion (the end opposite the tapered portion) of the ceramic cylinder (10, 10c, 10d, and 10e) toward the tapered portion.

[0059] (Modifications of ceramic structure 150) Ceramic structures 150a and 150b will be described with reference to Figures 17 and 18. The ceramic structures 150a and 150b are modifications of the ceramic structure 150, and the description of structures that are substantially the same as those of the ceramic structure 150 may be omitted by assigning the same reference numbers as those assigned to the ceramic structure 150. Note that the ceramic structures 150a and 150b will be shown in a view corresponding to the cross section of the ceramic structure 150 shown in Figure 6.

[0060] As shown in Fig. 17, the ceramic structure 150a is formed by a ceramic shaft 120a and a ceramic cylinder 110. The ceramic shaft 120a has a plurality of through holes 26. The ceramic structure 150a has four through holes 26. The ceramic structure 150a achieves a reduced weight by providing the through holes 26 in the ceramic shaft 120a. Furthermore, the through holes 26 can also relieve internal stress that occurs when the ceramic structure 150a is fired (shrunk-fit).

[0061] As shown in FIG. 18 , the ceramic structure 150b is formed by a ceramic shaft 120b and a ceramic cylinder 110. A plurality of recesses 28 are formed on the outer peripheral surface of the ceramic shaft 120b. In the ceramic structure 150b, four recesses 28 are formed on the outer peripheral surface of the ceramic shaft 120b in a portion where the electrodes 22 are not provided. The recesses 28 are provided at equal intervals around the circumference of the ceramic shaft 120b. By providing the recesses 28 on the outer peripheral surface of the ceramic shaft 120b, it is possible to reduce the local concentration of internal stress in the circumferential direction when the ceramic structure 150b is fired (shrunk-fitted). As a modification of the ceramic structure 150b, a plurality of through holes 26 may be formed in the ceramic shaft 120b, similar to the ceramic shaft 120a (see also FIG. 17 ).

[0062] As a modification of the ceramic structures 150, 150a, and 150b, the shape of the outer peripheral surface of the ceramic cylinder 110 may be an oval (see also FIG. 12), a substantially square (see also FIG. 13), a regular hexagon (see also FIG. 14), an ellipse, a substantially rectangular shape, or another polygonal shape. Furthermore, in the ceramic structures 150, 150a, and 150b, an expanded diameter portion 30 may be provided on the outer peripheral surface of the ceramic cylinder 110 (see FIG. 15), or the outer diameter may decrease from the end of the ceramic cylinder 110 (the end opposite the tapered portion) toward the tapered portion.

[0063] Although specific examples of the present invention have been described in detail above, these are merely examples and do not limit the scope of the claims. The claimed technology includes various modifications and variations of the specific examples exemplified above. Furthermore, the technical elements described in this specification or drawings exhibit technical utility alone or in various combinations, and are not limited to the combinations described in the claims at the time of filing. Furthermore, the technology exemplified in this specification or drawings can achieve multiple objectives simultaneously, and achieving one of these objectives alone is technically useful.

Claims

1. An electrode-embedded ceramic structure comprising a ceramic shaft with an electrode provided on its outer periphery, and a ceramic cylinder that houses the ceramic shaft and is connected to the ceramic shaft, wherein the relative density of the first ceramic constituting the ceramic shaft is different from the relative density of the second ceramic constituting the ceramic cylinder.

2. The ceramic structure with embedded electrodes according to claim 1, wherein the relative density ratio of the second ceramic to the first ceramic is 0.3 to 1.

0.

3. The ceramic structure with embedded electrodes according to claim 1, wherein the relative density ratio of the first ceramic to the second ceramic is 0.3 to 1.

0.

4. The electrode-embedded ceramic structure according to claim 1, wherein the relative density of the first ceramic is 0.30 or more and 1.0 or less.

5. The electrode-embedded ceramic structure according to claim 1, wherein the second ceramic has a relative density of 0.30 to 1.

0.

6. The ceramic structure with embedded electrodes according to claim 1, wherein the ratio of the outer diameter of the ceramic cylinder to the outer diameter of the ceramic shaft is 1.1 or more and 4.0 or less.

7. The electrode-embedded ceramic structure according to claim 6, wherein the outer diameter of the ceramic shaft is 0.5 mm or more and 20 mm or less.

8. The electrode-embedded ceramic structure according to claim 6, wherein the outer diameter of the ceramic cylinder is 1 mm or more and 25 mm or less.

9. The electrode-embedded ceramic structure according to claim 1, wherein the ceramic shaft has a first hole extending from one end to the other end in the axial direction, the first hole opening at least at one end in the axial direction.

10. The electrode-embedded ceramic structure according to claim 1, wherein the ceramic cylinder has a second hole extending from one end to the other end in the axial direction, the second hole opening at least at one end in the axial direction.

11. A ceramic structure with embedded electrodes according to any one of claims 1 to 10, wherein the end of the ceramic cylinder is provided with a tapered portion in which the outer diameter decreases toward the tip, and the relative density of the tapered portion is lower than the relative density of the portion other than the tapered portion.

12. The electrode-embedded ceramic structure according to any one of claims 1 to 10, wherein the cross-sectional shape of the ceramic cylinder is circular, elliptical or polygonal.

13. An electrode-embedded ceramic structure according to any one of claims 1 to 10, wherein the first ceramic is formed of a material mainly composed of alumina, zirconia, aluminum nitride, silicon nitride, or silica, and the second ceramic is formed of a material mainly composed of alumina, zirconia, aluminum nitride, silicon nitride, or silica.

14. The ceramic structure with embedded electrodes according to any one of claims 1 to 10, wherein the material of the electrodes is a metal mainly containing platinum, tungsten or molybdenum.

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