Glass joint body

Abstract: In order to improve a reliability of a glass joint body, first ceramic member (1) and second ceramic member (6) are connected by using (a) glass (9) consisting of 10-65% weight SiO₂, 30 wt% or less of Na₂O, and the balance of B₂O₃ and Al₂O₃, (b) glass including less than 10 wt% of SiO₂, and 30-80 wt% of B₂O₃, (c) glass including substantially none of SiO₂, and 30-80 wt% of B₂O₃, or (d) glass consisting of 10-65 wt% of SiO₂, 20 wt% or less of Na₂O, 30 wt% or less of Al₂O₃, 20 wt% or less of MgO, and the balance of B₂O₃. The glass has good resistance to sodium corrosion.

Description: The present invention relates to glass joint bodies which are exposed in corrosive substances, and especially relates to the glass joint bodies to be used for a conjunction between β alumina and insulation ceramics in Alkali Metal Thermo-Electric Converter (AMTEC) or a secondary cell to be used in high temperatures such as a sodium-sulfur cell. Usually, as for one example of glass joint bodies which are exposed in corrosive substances, there is known a sodium-sulfur cell or Alkali Metal Thermo-Electric Converter. The sodium-sulfur cells are high temperature type secondary cells which operate at 300°C ∼ 350°C and composed of metallic sodium as a cathode active material, sulfur and/or sodium polysulfide as an anode active material, a sodium ion conductive ceramic as a solid electrolyte, and a metal container. The structure of a typical sodium sulfur cell is shown in Fig. 1. In Fig. 1, the numeral 1 is a beta alumina tube, 2 metal container functioning as an anode, 3 sulfur or sodium polysulfide, 4 metal container functioning as a cathode, 5 sodium, 6 insulator such as α-alumina, 7 metal lid, 8 welded portion, and a numeral 9 is a joint glass for connecting the beta alumina tube 1 and the insulator 6. As for beta alumina material forming the beta alumina tube 1, use is made of β"-alumina, β-alumina, and mixture of the both, or the like. Processes for manufacturing the above-described sodium-sulfur cells generally comprise the steps of: bonding the open end periphery of the beta alumina tube 1 with the ring insulator 6'made of α-alumina by means of glass or the like; bonding the ring insulator 6 supporting the beta alumina tube 1 with the metal containers 2 and 4 by a solid phase reaction or the like at a high temperature under pressure; supplying the sodium 5 and the sulfur or sodium polysulfide 3 into the metal containers 4 and 2 respectively; and hermetically closing the metal container 4 with the lid 7 by means of the welding to provide a cell. In the sodium-sulfur cells mentioned above, since the joint glass 9 arranged-between the beta alumina tube 1 and the insulator 6 made of α-alumina and the like is to be corroded by the sodium, a life of the sodium-sulfur cell is decreased. To eliminate the drawback mentioned above, a joint glass having a good durability against sodium corrosion consisting of 1 wt% of alkali earth metal oxides or less, SiO 2 : 65∼75 wt%, B 2 O 3 : 10∼25 wt%, and the balance of Aℓ 2 O 3 and alkali metal oxides is disclosed in Japanese Patent Laid-Open Publication No. 1-54672. The joint glass having the composition mentioned above shows a good durability against sodium corrosion as compared with the known silicate glass and boron silicate glass, but does not show a sufficient durability against sodium corrosion as yet. Therefore, the joint glass mentioned above is also corroded by the sodium and thus there is a drawback such that a life of the sodium-sulfur cell is also decreased. An object of the invention is to eliminate the drawbacks mentioned above and to provide a glass joint body having a reliable glass joint portion. The present invention provides a glass joint body as described in claim 1. In the structures of the present invention, since the joint glass including less than 10 wt% or substantially none of SiO 2 and 30∼80 wt% of B 2 O 3 is used for a connection between ceramic member and ceramic member, the corrosion rate due to sodium can be controlled to be slow, and thus reliability of the glass joint portion can be improved. Therefore, life of the sodium-sulfur cell or the Alkali Metal Thermo-Electric Converter can be increased. In the glass composition of the present invention, the reason for limiting the amount of SiO 2 as less than 10 wt% is as follows. If the amount of SiO 2 is 10 wt% or more, durability against sodium corrosion of the glass is decreased, and thus cracks are generated in the glass portion due to corrosion. Moreover if the amount of SiO 2 is substantially none a glass is obtained which is not corroded at all by sodium. The reason for limiting the amount of B 2 O 3 as 30∼80 wt% is as follows. If the amount of B 2 O 3 is less than 30 wt%, it is not possible to generate glass states. Moreover, if the amount of B 2 O 3 is more than 80 wt%, the glass is easily deteriorated due to water absorption. Further, it is preferred to limit the amount of Na 2 O as 30 wt% or less, because the thermal expansion coefficient becomes larger and cracks are easily generated in the case of connection operations if the amount of Na 2 O is more than 30 wt%. It is preferred to include an amount of Aℓ 2 O 3 of 13∼28 wt% and an amount of MgO of 12∼25 wt%, because the cantilever flextural strength of the glass joint body is increased. Further, preferable methods of connecting ceramic member to ceramic member are (1) method comprising the steps of arranging a glass frit between an alpha alumina and a beta alumina, and melting the glass by heat to connect the alpha alumina and the beta alumina by reacting glass and alpha alumina and also by reacting glass and beta alumina, or (2) method comprising the steps of arranging a glass block on a space between alpha alumina and beta alumina, melting the glass block by heat to be flowed into the space, and connecting the alpha alumina and the beta alumina by reacting glass and alpha alumina and also by reacting glass and beta alumina. Fig. 1 is a schematic view showing a sodium sulfur cell, as one embodiment of a glass joint body according to the invention; Fig. 2 is a schematic-view illustrating an Alkali Metal Thermo-Electric Converter, as another embodiment of a glass joint body according to the invention; Fig. 3 3 is a cross sectional view depicting one embodiment of a specimen to which an anti-sodium test is performed; Fig. 4 is a cross sectional view showing another embodiment of a specimen to which an anti-sodium test is performed; and Fig. 5 is a cross sectional view for explaining a cantilever bending test. Fig. 1 is a schematic view showing one embodiment of a glass joint body according to the invention. In Fig. 1, the present invention is applied to a sodium-sulfur cell, and a construction of the sodium-sulfur cell is explained before, so that the explanation thereof is not repeated here. In this embodiment, as for the joint glass 9, use is made of glass as described in claim 1. Fig. 2 is a schematic view showing another embodiment of a glass joint body according to the invention. In Fig. 2, the present invention is applied to a thermoelectric converting apparatus. In the Alkali Metal Thermo-Electric Converter shown in Fig. 2, a heat energy is directly converted into an electric energy to generate electricity by utilizing a beta alumina solid electrolyte through which a sodium ion is easily moved. In this embodiment, a numeral 11 is a stainless container, 12 an insulator made of α-alumina and arranged to the stainless container 11, 13 a beta alumina tube, 14 a joint glass for connecting the insulator 12 made of α-alumina and the beta alumina tube 13, 15 a heater for heating a sodium supplied into the beta alumina tube 13, 16 an Mo porous electrode formed on an outer surface of the beta alumina tube 13, 17 a pipe for supplying a sodium in the stainless container 11 into the beta alumina tube 13, 18 an electromagnetic pump for moving a sodium in the pipe 17, and numerals 19-1 and 19-2 are electrodes for output terminals. Also in this embodiment, it is necessary to use the joint glass 14 having a composition as mentioned above. In the thermoelectric converting apparatus mentioned above, sodium supplied in the beta alumina tube 13 is heated by the heater 15 and is moved to the Mo porous electrode 16 by means of ion conductivity, so that an output current flows between the electrodes 19-1 and 19-2. Moreover, sodium moved to the Mo porous electrode 16 by means of an ion conductivity is vaporised from the Mo porous electrode 16, and is liquefied on an inner surface of the stainless container 17 maintained in low temperatures. In this- manner, sodium is circulated in the thermoelectric converting apparatus. Hereinafter, actual embodiments will be explained. Example 1 In order to examine a connection state of a glass joint specimen and a durability against sodium corrosion of a glass of the present invention, the following tests were performed. At first, glass frits having various chemical compositions as shown in Table 1 were prepared by measuring respective raw materials by means of an electric balance, mixing and crushing the raw materials in a mortar made of alumina by using an alumina pestle, melting the mixed and crushed raw materials at 1200∼1600°C in a platinum crucible, and dropping the melted raw materials into water. In order to make properties of the glass uniform, the thus prepared glass frits were further crushed in a mortar made of alumina by using an alumina pestle, and were re-melted at the same temperature as that of the above melting operation in a crucible made of platinum. After that, the thus re-melted glass was dropped into water, and the cooled glass was further crushed in a mortar made of alumina by using an alumina pestle to obtain glass frits for a connection. By using the thus obtained glass frits, an α alumina ring 42 having a diameter of 32 mm and a beta alumina circular plate 43 having a diameter of 25 mm and a thickness of 3 mm were connected with each other at 800∼1000°C to obtain a glass joint specimen as shown in Fig. 4. Then, the glass joint specimen was gradually cooled from 800°C to 300°C at a cooling rate of 0.5°C/min to eliminate stresses. After that, the thus formed glass joint specimen was immersed in sodium at 450°C under N 2 atmosphere for 100 hours, and sodium was eliminated by using methanol. Then, crack generation was examined by using fluorescent penetrant inspection every 100 hours. Moreover, generation of a colored layer was also examined by observing a cross section of the glass joint specimen by means of an optical microscope. The results and the chemical compositions of the conjunction glasses used in this example 1 were shown in Table 1. It should be noted that, in Table 1, SiO 2 <1.0 wt% means the joint glass included substantially no SiO 2 . From the results shown in Table 1, it is understood that the specimen Nos. 1∼32 of the invention show good durability against sodium corrosion since cracks are not generated at least for 1000 hours, but the specimen Nos. 33∼35 of the comparative example can not endure for 1000 hours and do not show sufficient durability against sodium corrosion since cracks are generated. Moreover, among the specimens according to the invention, the specimen Nos. 1 and 2, to which less than 10 wt% of SiO 2 is added positively, generate no cracks for 1000 hours but contain colored layers due to corrosion. Contrary to this, the specimen Nos. 3∼32, in which substantially no SiO 2 is included, generate no cracks and no colored layers, and show better durability against sodium corrosion than those of the specimen Nos. 1 and 2. Example 2 A charge-discharge test was performed with respect to NaS cell using the glass joint body of the invention. That is to say, with respect to the sodium-sulfur cells wherein the beta alumina and the alpha alumina are connected as shown in Fig. 2 by using glasses of the specimen Nos. 1∼32 in the example 1, the charge-discharge test was performed under a temperature of 350°C and a current density of 150 mA/cm 2 . As a result, all the sodium-sulfur cells can endure until 1000 cycles. Example 3 A cantilever bending test was performed with respect to a glass joint specimen using the glasses of the specimen Nos. 1∼21 shown in Table 2. That is to say, with respect to the glass joint specimen shown in Fig. 5 wherein a beta alumina tube 52 having an inner diameter of 20 mm and a thickness of 2 mm and an α-alumina ring 53 having an outer diameter of 35 mm are connected by using the glass mentioned above, a load P is applied at a position 200 mm apart from a connection portion of the beta alumina tube 52. Then, a load when the beta alumina tube 52 is broken is measured as a break load. The results are shown in Table 2. Specimen No. Chemical composition (wt%) Break load P (Kgf) SiO 2 B 2 O 3 Na 2 O Aℓ 2 O 3 MgO TiO 2 1 <1.0 43.0 32.0 25.0 31.0 2 <1.0 50.0 17.0 33.0 32.5 3 <1.0 68.0 9.0 23.0 30.0 4 <1.0 58.0 23.0 19.0 36.5 5 <1.0 65.0 3.0 15.0 17.0 30.0 6 <1.0 65.0 16.0 19.0 38.0 7 <1.0 61.2 22.8 15.0 39.5 8 <1.0 62.2 10.3 22.5 37.0 9 <1.0 57.0 17.0 26.0 29.5 10 <1.0 67.8 32.2 28.0 11 <1.0 66.6 27.9 5.5 31.0 12 <1.0 40.7 22.6 33.7 31.0 13 <1.0 45.4 25.0 29.6 29.5 14 <1.0 62.2 22.8 15.0 30.0 15 <1.0 46.0 12.0 42.0 23.0 16 <1.0 50.0 36.0 14.0 18.5 17 <1.0 59.0 38.0 12.0 20.0 18 <1.0 68.0 18.0 14.0 28.0 19 <1.0 62.0 16.0 13.0 9.0 30.5 20 <1.0 61.0 27.0 12.0 29.0 21 <1.0 65.0 17.0 14.0 4.0 29.5 From the results shown in Table 2, among the glasses according to the present invention, the specimen Nos. 16 and 17 in which 30 wt% or more of Aℓ 2 O 3 is included and the specimen No. 15 in which 40 wt% or more of MgO is included show small break load P as compared with the other specimens. Moreover, the specimen Nos. 4, 6, 7, 8 in which 13∼28 wt% of Aℓ 2 O 3 and 12∼25 wt% of MgO are included show large break load P as compared with the other specimens. It should be noted that, among the specimens including substantially no SiO 2 , no differences in the durability against sodium corrosion were found. As mentioned above, According to the invention, since ceramics and ceramics are connected with each other by using a glass having a predetermined chemical composition, the durability against sodium corrosion of the glass joint body can be improved. Therefore, if the present invention is applied to the glass joint body used in the secondary cell of high temperature type such as the sodium-sulfur cell or the Alkali Metal Thermo-Electric Converter, the life of the apparatus can be increased.

Claims: A glass joint body comprising a first ceramic member and a second ceramic member which are connected by a glass consisting of i) B 2 O 3 in an amount of 30 to 80 wt%, ii) optionally, SiO 2 in an amount of not more than 10 wt%, iii) optionally, Na 2 O in an amount of not more than 30 wt%, iv) balance at least one of Al 2 O 3 , MgO, TiO 2 , ZrO 2 , Ta 2 O 5 and rare earth oxides. A glass joint body according to claim 1, wherein said glass contains substantially no SiO 2 . A glass joint body according to claim 2, wherein in said glass Al 2 O 3 is present in an amount of not less than 9 wt% and MgO is present in an amount of not less than 5.5 wt% and Na 2 O is present in an amount of not more than 16.0%. A glass joint body according to claim 3, wherein Na 2 O is substantially absent from said glass. A glass joint body according to claim 3 or 4, wherein in said glass the amount of Al 2 O 3 is in the range 9 to 38 wt% and the amount of MgO is in the range 5.5 to 42 wt%. A glass joint body according to claim 5 , wherein in said glass the amount of Al 2 O 3 is in the range 9 to 32% and the amount of MgO is in the range 5.5 to 33.7 wt%. A glass joint body according to claim 5 or 6, wherein in said glass the total amount of Al 2 O 3 and MgO is at least 22 wt%. A glass joint body according to any one of claims 2 to 7, wherein in said glass said balance consists of Al 2 O 3 and MgO. A glass joint body according to claim 1 or 2, wherein said balance consists of Al 2 O 3 in an amount not exceeding 35 wt% and MgO in an amount not exceeding 40 wt%. A glass joint body according to any one of claims 1 to 9, wherein in said glass the amount of Al 2 O 3 is in the range 13-28 wt% and the amount of MgO is in the range 12-25 wt%. A sodium-sulphur cell having a glass joint body according to any one of claims 1 to 10, in which said first and second ceramic members of said body joined by said glass of said body are made of alpha alumina and beta alumina respectively.

Inventors: MURAI MAKOTO, TAKAHASHI TOMONORI, YOSHIDA AKIHIKO, MURAI, MAKOTO, TAKAHASHI, TOMONORI, YOSHIDA, AKIHIKO
Applicants: NGK INSULATORS LTD, NGK INSULATORS, LTD.
Application year: 1991
Main classification: C03C3
IPC codes: C04B37, C03C8, H01M10, H01M2