JP7232106B2 - Glass bonding material and its use - Google Patents

Description

The present invention relates to a glass bonding material. More specifically, it relates to a glass bonding material for sealing and bonding inorganic members by low-temperature firing.

Inorganic members such as ceramic members mainly composed of ceramic materials such as alumina and zirconia and metal members mainly composed of metal materials such as stainless steel are widely used in various fields. Various bonding materials are used for bonding such inorganic members depending on the application, bonding conditions, and the like. For example, in a solid oxide fuel cell (SOFC), a sealed joint is formed to seal and join a fuel electrode (anode), which is a ceramic member, and a gas supply pipe, which is a metal member. A glass bonding material is used to form the bonding portion. Such a glass bonding material contains a glass composition as a main component, and forms a dense sealed joint by fusion-bonding and solidifying the glass composition by firing treatment at a predetermined temperature. The firing temperature at this time is usually set to a temperature corresponding to the operating temperature of the SOFC. For example, since the operating temperature of a general SOFC is about 700.degree. C. to 900.degree.

Examples of glass bonding materials include the glass bonding materials described in Patent Documents 1 to 3. Patent _{Document 1 discloses a} glass matrix (glass _composition A glass encapsulating material having a material) is disclosed. The glass sealing material described in Patent Document 1 is fired at 600° C. or higher (for example, 700° C. to 900° C.) and exhibits suitable viscosity, heat resistance, and durability in an environment of 800° C. to 850° C. be. Further, Patent Document 2 describes a heat-resistant glass containing BaO, MgO, CaO, SiO ₂ , Al ₂ O ₃ and Bi ₂ O ₃ in a predetermined ratio and substantially free of boron components and alkaline components. A bonding material is disclosed. The heat-resistant glass bonding material described in Patent Document 2 exhibits suitable heat resistance and durability in a high-temperature environment of 1000° C. or higher. Patent Document 3 discloses a glass matrix containing SiO ₂ , Al ₂ O ₃ , Na ₂ O, K ₂ O, MgO, CaO, and B ₂ O ₃ in a predetermined ratio, and leucite crystals in the glass matrix. A deposited bonding material is disclosed. The bonding material described in Patent Document 3 is also assumed to be used in a high temperature range of 800°C to 1200°C.

On the other hand, in the recent field of electrochemical systems (for example, solid oxide fuel cells (SOFC)), lower operating temperatures are required. For example, in SOFCs, it is expected that by lowering the operating temperature to 650° C. or less, material costs, operating costs, etc. can be reduced and versatility can be improved (see Patent Document 4). As described above, the firing temperature for forming the sealed joint from the glass bonding material is set to a temperature corresponding to the operating temperature of the SOFC. There is a demand for a glass bonding material that can suitably form a sealed joint by firing. As an example of such a glass composition that can be fused and solidified by low-temperature firing, non-patent document 1 describes low-melting glass (lead-based glass, phosphate-based glass, telluride-based glass, vanadate-based glass, fluoride-based glass, chalcogenide glass, etc.).

Patent No. 6305315 Patent No. 5947758 Patent No. 4619417 Patent No. 5750764

Institute of Industrial Science, The University of Tokyo Production Research Vol.13 No.11, P441-445

However, the low-melting-point glass described above has various problems, and it has been difficult to use it as a bonding material for electrochemical systems such as SOFC. Specifically, since lead-based glass and fluoride-based glass contain a lead component (Pb), there is concern about adverse effects on the environment and the human body. Furthermore, the phosphorus component (P) contained in the phosphate glass can cause chemical deterioration (phosphorus poisoning) of the SOFC. Furthermore, telluride-based glasses containing a tellurium component (Te), vanadate-based glasses containing a vanadium component (V), high bismuth-lead-based glasses containing bismuth (Bi), and the like are reduced during the firing process and become conductive. This makes it difficult to use as a bonding material in electrochemical systems. Chalcogenide glass also contains an arsenic component (As), which may adversely affect the human body and the environment.

On the other hand, when ordinary glass bonding materials such as those described in Patent Documents 1 to 3 are used for low-temperature firing, the glass composition is not melted appropriately, resulting in insufficient fluidity during firing. The bondability of the sealing joint tends to deteriorate. Also, if the melting temperature of the glass composition is lowered, a glass bonding material that melts at low temperature firing can be produced, but such a glass bonding material that melts at a low temperature tends to have low heat resistance. As described above, in the field of glass bonding materials for low-temperature firing, it is difficult to achieve both bondability and heat resistance at high levels.

The present invention has been made in view of such circumstances, and its object is to be able to suitably join objects to be joined by firing at a low temperature of 650° C. or less without causing various problems such as adverse effects on the environment. Furthermore, it is another object of the present invention to provide a glass bonding material capable of exhibiting suitable heat resistance after firing.

In order to solve the above problems, a glass bonding material disclosed herein is provided.

The glass bonding material disclosed herein is a bonding material that sealingly bonds inorganic members by low-temperature firing at 650° C. or less. Such a glass bonding material contains a glass composition as a main component. This glass composition substantially does not contain alkali metal elements, P, Pb, Bi, Te, V, and As, and when the entire glass composition is 100 mol %, 95 mol % or more is oxide conversion MO: 30 to 75 mol%, Al ₂ O ₃ : 0.7 to 12 mol%, Si ₂ O: 5 to 30 mol%, B ₂ O ₃ : 15 to 45 mol%, ZnO: 1 to 10 mol% composed of ingredients. Here, the MO contains at least one group 2 element oxide and contains at least 3 mol % of MgO.

As described above, a glass bonding material containing, as a main component, a glass composition containing 30 mol% or more of an oxide (MO) of a Group 2 element and containing at least 3 mol% of MgO in the oxide of a Group 2 element It has been confirmed by experiments by the present inventors that the material exhibits sufficient bondability in low-temperature firing of 650° C. or less and exhibits good heat resistance after firing. In addition, the glass bonding material disclosed herein does not substantially contain alkali metal elements, P, Pb, Bi, Te, V, and As. Various problems such as chemical deterioration of the electrochemical system can be prevented from occurring.

In one preferred aspect of the glass bonding material disclosed herein, the glass composition contains 1 mol % or less of at least one selected from the group consisting of Cu ₂ O, Fe ₂ O ₃ , NiO, and ZrO ₂ . By adding these optional components to construct a multi-component glass composition, the physical stability of the sealed joint after firing can be improved.

In one preferred aspect of the glass bonding material disclosed herein, the viscosity at 650° C. is 5 Pa·s to 8 Pa·s. As a result, the glass bonding material being fired at a low temperature can be appropriately fluidized and can be appropriately fixed to the surface of the inorganic member, so that a sealed joint that is difficult to come off even when fired at a low temperature can be formed. In addition, since the shape of the joint can be stably maintained at the operating temperature, better heat resistance and durability can be achieved. As used herein, the term "viscosity" refers to a viscosity calculated based on the Gent's equation from a deformation rate measured using a glass parallel plate viscometer.

In a preferred aspect of the glass bonding material disclosed herein, the thermal expansion coefficient from 30°C to 500°C is 6×10 ^-6 K ^-1 to 13×10 ^-6 K ^-1 . From the viewpoint of suppressing breakage of the sealed joint, it is generally considered preferable that the coefficient of thermal expansion of the glass bonding material approximates the coefficient of thermal expansion of the inorganic member to be bonded. According to this aspect, since the thermal expansion coefficient can be approximated with an inorganic member (for example, a metal member) having a relatively high thermal expansion coefficient, it is possible to suitably prevent damage to the sealed joint after firing. .
As used herein, the term “thermal expansion coefficient” refers to an average expansion coefficient (average linear expansion coefficient) measured using a thermomechanical analysis (TMA) in a temperature range from 30° C. to 500° C. , is the value obtained by dividing the amount of change in sample length from the initial length of the sample by the temperature difference. The thermal expansion coefficient can be measured according to JIS R 3102 (1995).

In a preferred embodiment of the glass bonding material disclosed herein, the rate of change in thermal expansion before and after heat exposure is 10% or less when subjected to heat exposure at 650° C. or higher for 100 hours or longer in an air atmosphere. As a result, it is possible to form a sealed joint that can maintain high airtightness over a long period of time and is excellent in high-temperature durability.

Another aspect of the present invention provides an inorganic member joined body. Such an inorganic member joined body includes two or more inorganic members, and a sealed joint that seals and joins the two or more inorganic members. Then, the sealed joint portion of the inorganic member joint body does not substantially contain alkali metal elements, P, Pb, Bi, Te, V, and As, and when the entire glass composition is 100 mol %, , Mo: 30 to 75 mol%, Al ₂ O ₃ : 0.7 to 12 mol%, Si ₂ O: 5 to 30 mol%, B ₂ O ₃ : 15 to 45 mol%, at a molar ratio of 95 mol% or more in terms of oxides. , ZnO: 1 to 10 mol %. The above MO contains at least one group 2 element oxide and contains at least 3 mol % of MgO.
In such an inorganic member joined body, since the sealed joint portion is formed from a glass jointing material that exhibits suitable bondability in low-temperature firing, it is possible to suitably prevent the sealed joint portion from falling off. Moreover, it has a suitable heat resistance that can maintain the coefficient of thermal expansion even when exposed to an environment of about 650° C. for a long period of time. Furthermore, since such a sealed joint substantially does not contain alkali metal elements, P, Pb, Bi, Te, V, and As, it has an adverse effect on the environment and the human body, a decrease in insulation, and an electrochemical system. Various problems such as chemical deterioration are obviated.

In a preferred aspect _{of the inorganic member joined body disclosed herein, the sealed joint is a crystal selected from the group consisting of BaMgSiO4, BaAl2O4 , BaZnSiO4 , BaAl2Si2O8 , and MgSiO3} . is generated at least one. By adjusting the components of the glass composition and the firing conditions so that such crystals are generated, the heat resistance of the sealed joint can be further improved.

1 is a cross-sectional view schematically showing an SOFC system according to an embodiment of the invention; FIG.

Preferred embodiments of the present invention are described below. Matters other than those specifically mentioned in this specification, which are necessary for implementing the present invention (for example, a general SOFC manufacturing process, etc.), can be understood by those skilled in the art based on the prior art in the relevant field. It can be grasped as a design matter. The present invention can be implemented based on the contents disclosed in this specification and common general technical knowledge in the field. In the following description, "A to B (where A and B are arbitrary values)" includes the values of A and B (upper limit and lower limit). In addition, in the drawings described in this specification, members and parts having the same function are denoted by the same reference numerals, and redundant description may be omitted or simplified. Also, the dimensional relationships (length, width, thickness, etc.) in each drawing do not necessarily reflect the actual dimensional relationships.

≪Glass bonding material≫
The glass bonding material disclosed herein is a glass bonding material for low-temperature firing used for bonding inorganic members by low-temperature firing at 650° C. or less. Although the details will be described later, the term “inorganic member” in the present specification is a concept that includes a ceramic member mainly composed of a ceramic material and a metallic member mainly composed of a metallic material.

1. Glass Composition The glass bonding material disclosed herein contains a glass composition as a main component. Typically, the content of the glass composition when the entire glass bonding material is 100% by mass is preferably 50% by mass or more, more preferably 70% by mass or more, further preferably 80% by mass or more, and 90% by mass. % or more is particularly preferred. The upper limit of the content of the glass composition is not particularly limited, and may be 100% by mass, 99% by mass or less, or 95% by mass or less. 95 mol % or more of the glass composition disclosed herein is composed of group 2 element oxide (MO), aluminum component (Al ₂ O ₃ ), silicon component (Si ₂ O), and boron component (B ₂ O ₃ ) and a zinc component (ZnO). Each component will be described below.

(1) Group 2 Element Oxide The glass composition of the glass bonding material disclosed herein contains a Group 2 element oxide (MO). Examples of oxides of Group 2 elements include MgO, CaO, BaO, SrO, and RaO. These group 2 element oxides contribute to adjustment of the thermal expansion coefficient and improvement of heat resistance after firing, and contribute to improvement of fluidity (jointability) in low-temperature firing. The glass composition disclosed herein contains magnesium oxide (MgO) among the group 2 element oxides as an essential component. According to the studies of the present inventors, among oxides of Group 2 elements, MgO is particularly excellent in the function of improving bondability in low temperature firing of 650 ° C. or less and the function of improving heat resistance at operating temperatures of about 650 ° C. . From these points of view, the glass composition of the glass bonding material disclosed herein contains 30 mol % or more of the group 2 element oxide (MO) and 3 mol % or more of MgO. This makes it possible to achieve both bondability in low-temperature firing and heat resistance after firing at a high level. The ratio of the group 2 element oxide (MO) in the entire glass composition is preferably 32 mol % or more, more preferably 35 mol % or more, and even more preferably 45 mol % or more in terms of oxide. In addition, from the viewpoint of improving physical stability by containing other components, the upper limit of the MO ratio is set to 75 mol% or less, preferably 72 mol% or less, more preferably 70 mol% or less, and 65 mol% or less. is more preferred. The proportion of MgO in the entire glass composition is preferably 6 mol % or more, more preferably 7 mol % or more, and even more preferably 9 mol % or more in terms of oxide. As a result, it is possible to favorably achieve both bondability in low-temperature firing and durability after firing. Moreover, the upper limit of the proportion of MgO can be arbitrarily set within a range not exceeding the upper limit of the proportion of oxides (MO) of Group 2 elements, and is not particularly limited. As an example, the upper limit of the proportion of MgO may be 75 mol % or less, 50 mol % or less, 25 mol % or less, or 20 mol % or less. In addition, the glass composition disclosed herein may contain only MgO as a group 2 element oxide, but from the viewpoint of improving the physical stability of the sealed joint after firing, other It is preferable to form a multi-component glass composition by mixing with an oxide of a Group 2 element.

(2) Aluminum Component The aluminum component (Al ₂ O ₃ ) has the function of controlling the fluidity of the glass bonding material during low-temperature firing. It is also a component that stabilizes the glass bonding material and improves chemical durability. Heat resistance tends to improve as the proportion of the aluminum component increases. From this point of view, in the glass bonding material disclosed herein, the proportion of Al ₂ O ₃ in the entire glass composition is set to 0.7 mol% or more (preferably 1 mol% or more, more preferably 2 mol% or more). there is On the other hand, if the _{aluminum component} is excessively increased, the bondability in low-temperature firing tends to decrease. more preferably 5 mol % or less).

(3) Silicon Component The glass bonding material disclosed herein contains silicon oxide (Si ₂ O) in addition to the aluminum oxide (Al ₂ O ₃ ) described above. That is, the glass compositions disclosed herein are based on aluminosilicate glasses. Such a silicon component (silicon oxide) is a component that constitutes the skeleton of the glass after firing, and also has the function of reducing the viscosity during firing. Also, the heat resistance tends to improve as the proportion of Si ₂ O increases. Therefore, the ratio of Si ₂ O in the entire glass composition is set to 5 mol % or more in terms of oxide, preferably 8 mol % or more, more preferably 10 mol % or more, and even more preferably 14 mol % or more. In addition, from the viewpoint of ensuring a constant viscosity during firing, the upper limit of the Si ₂ O ratio is set to 30 mol% or less, preferably 27 mol% or less, more preferably 25 mol% or less, and even more preferably 23 mol% or less. .

(4) Boron component The boron component (boron oxide (B ₂ O ₃ )) contributes to increasing the fluidity in the firing process, so increasing the content tends to improve the bondability in low-temperature firing. . Therefore, the proportion of B ₂ O ₃ in the entire glass composition is set to 15 mol % or more, preferably 16 mol % or more, more preferably 17 mol % or more, and even more preferably 18 mol % or more. On the other hand, when B ₂ O ₃ is too much, the heat resistance and thermal expansion coefficient tend to decrease. Therefore, the upper limit of the proportion of B ₂ O ₃ in the entire glass composition is set to 45 mol % or less, preferably 43 mol % or less, more preferably 40 mol % or less, and even more preferably 38 mol % or less.

(5) Zinc component The zinc component (zinc oxide (ZnO)) has the function of adjusting the viscosity of the glass bonding material during firing and improving the airtightness and stability of the sealed joint after firing. there is Furthermore, it is possible to suppress the formation of SiO ₂ crystals (cristobalite crystals) in the sealed joint after firing, which would otherwise lower the heat resistance. From this point of view, the ratio of ZnO in the entire glass composition is set to 1 mol% or more, preferably 3 mol% or more, more preferably 3.5 mol% or more, and further 4 mol% or more, in terms of oxide. preferable. On the other hand, if the amount of ZnO is excessively increased, Zn-based crystals are extremely likely to precipitate, which may increase the viscosity of the glass and impede low-temperature bondability. From this point of view, the upper limit of the ZnO ratio is set to 10 mol % or less, preferably 8 mol % or less, more preferably 7 mol % or less, and even more preferably 6 mol % or less. In addition, by including ZnO in the above ratio, at least one of water resistance, thermal shock resistance, and durability of the sealed joint can be improved.

(6) Other Components The glass composition disclosed herein may contain optional components other than the above five main components as long as they do not significantly impair the effects of the present invention. Examples _{of such optional components include Cu2O, Fe2O3, NiO, ZrO2, TiO2, Nb2O5, FeO, Fe3O4 , CuO , SnO , SnO2 , La2O3 , CeO2 .} etc. By adding these optional components to form a multi-component glass composition, the physical stability of the sealed joint after firing can be improved. For example, the glass composition is preferably composed of a multi-component system of six or more components. This can improve the physical stability of the sealing joint. Moreover, from the viewpoint of workability and cost, it is preferable that the glass matrix is composed of 10 or less components. When these optional components are added, the ratio of the above optional components to the entire glass composition is preferably 0.01 mol % to 1 mol % or less, and more preferably 0.05 mol % to 0.75 mol %. is more preferable, and 0.1 mol % to 0.5 mol % or less is even more preferable.

(7) Prohibited Ingredients In order to prevent the above-described various problems from occurring, the glass bonding material disclosed herein specifies ingredients that it does not substantially contain (prohibited ingredients). First, the glass composition of the glass bonding material disclosed herein does not substantially contain an alkali metal element. Such alkali metal elements include Li, Na, K, Rb, Cs, Fr and the like. A glass bonding material containing these alkali metal components (particularly Na and K) may generate substances that adversely affect the environment during firing. For example, when a glass bonding material containing an alkali metal element is used for bonding ferritic stainless steel, hexavalent chromium, which is an environmentally regulated substance, may be generated. On the other hand, the glass bonding material disclosed herein does not substantially contain an alkali metal element, so it is possible to prevent the generation of environmentally controlled substances during firing.
Next, the glass composition of the glass bonding material disclosed herein does not substantially contain a lead component (Pb) and arsenic (As). This makes it possible to prevent Pb and As from adversely affecting the human body and the environment. Furthermore, the glass bonding material disclosed herein does not substantially contain a phosphorus component (P). Therefore, it is possible to prevent chemical deterioration of the electrochemical system (such as SOFC) due to phosphorus poisoning. The glass composition of the glass bonding material disclosed herein does not substantially contain a bismuth component (Bi), a tellurium component (Te), or a vanadium component (V). Therefore, it is possible to prevent the glass (sealed joint portion) from being conductive after the firing process.
In this specification, "substantially does not contain" means that the above-mentioned prohibited ingredients are not intentionally added. Therefore, in the present specification, the concept of "substantially free" includes the case where a trace amount of a component that can be interpreted as a prohibited component is contained due to raw materials, manufacturing processes, or the like. For example, the content of the prohibited component in the entire glass composition is 0.01 mol% or less (preferably 0.005 wt% or less, more preferably 0.001 wt% or less, still more preferably 0.0005 wt% or less, particularly preferably is 0.0001 wt% or less), it can be said to be "substantially free".

The glass bonding material disclosed herein preferably has a viscosity of 5 Pa·s to 8 Pa·s at 650°C. As a result, the glass bonding material being fired at a low temperature can be appropriately fluidized and can be suitably fixed to the surface of the inorganic member, so that a sealed joint that is difficult to fall off even when fired at a low temperature can be formed. In addition, since the shape of the joint can be stably maintained at the operating temperature, better heat resistance and durability can be achieved. Considering fixability to inorganic members, the lower limit of the viscosity in low-temperature firing is more preferably 5.5 Pa·s or more, and further preferably 6 Pa·s or more. On the other hand, considering the stability of the sealed joint after firing, it is preferably 7.5 Pa·s or less, more preferably 7 Pa·s or less.

Further, it is more preferable that the components of the glass composition described above are appropriately adjusted from the viewpoint of approximating the coefficient of thermal expansion between the glass composition and the inorganic member to be joined. For example, the thermal expansion coefficient of the glass bonding material is 6×10 ⁻⁶ K ⁻¹ to 13×10 ⁻⁶ K ⁻¹ (preferably 6.4×10 ⁻⁶ K ⁻¹ to 12.2×10 ⁻⁶ K ^-1 ). As a result, it is possible to suppress damage to the sealing joint due to a difference in expansion amount between the joint and the object to be joined. In addition, the "thermal expansion coefficient" in this specification refers to the average linear thermal expansion coefficient at 30°C to 500°C.

Further, the glass bonding material disclosed herein exhibits a difference of 10% or less in thermal expansion coefficient before and after the heat exposure at 650° C. or higher for 100 hours in an air atmosphere. Thus, the glass bonding material in which the decrease in thermal expansion coefficient due to heat exposure is suppressed can form a sealed joint having suitable heat resistance.

2. Materials Other than Glass Composition In addition to the glass composition described above, conventionally known materials that can be added to this type of glass bonding material can be appropriately added to the glass bonding material disclosed herein. Examples of such additive components include organic materials such as organic binders and organic solvents. As organic binders, various binders commonly used in glass pastes of this type can be considered. For example, cellulose-based polymers such as methyl cellulose, ethyl cellulose and nitrocellulose, acrylic resins, epoxy-based resins, amine-based resins, and the like can be exemplified. The same applies to organic solvents, and various organic solvents that are commonly used for this type of glass paste can be considered. For example, terpineol, ether-based solvents, ester-based solvents, various glycols, and the like can be exemplified.

The form of the glass bonding material disclosed herein is not particularly limited, and any form can be adopted according to the application. For example, it can be in the form of cullet, powder, frit, pellet, sheet, paste, and the like. For example, in the case of a paste-like glass bonding material, by appropriately adjusting the viscosity, it can be easily applied to the bonding target (inorganic member) by a technique such as coating or printing. From the viewpoint of work convenience, it is also possible to employ a mode in which a sheet-like bonding material is formed in advance and the sheet-like bonding material is attached to the object to be bonded.

<<Method for manufacturing glass bonding material>>
Next, an example of a method for manufacturing the glass bonding material disclosed herein will be described. It should be noted that the description of such a manufacturing method is not intended to limit the glass bonding material disclosed herein.

When manufacturing the glass bonding material disclosed herein, first, the group 2 element oxides, Al ₂ O ₃ , Si ₂ O, B ₂ O ₃ and ZnO mentioned above are used as main constituents (five types occupies 95 mol % or more in a molar ratio of oxide conversion) raw material powder is prepared. For example, industrial products, reagents, or various mineral raw materials containing oxides, carbonates, nitrates, composite oxides, etc. containing the various constituents described above are prepared and mixed so that they have a desired composition ratio. . Mixing and preparation of the raw material powder can be performed by, for example, putting the raw material into a mixer such as a ball mill and mixing for several hours to several tens of hours.

Next, after drying the obtained frit powder, it is heated under a predetermined temperature condition (typically 900° C. to 1200° C.) to melt the frit powder. Then, by cooling (preferably quenching) the molten glass, the glass composition having the above structure can be obtained. After that, the obtained glass composition is pulverized and classified (sieved) until it reaches a desired size (particle size) to obtain cullet-like or powder-like glass powder. The average particle size of such glass powder is preferably 0.5 μm to 50 μm (typically 1 μm to 10 μm), for example.

Then, the glass bonding material is obtained by appropriately processing the obtained glass powder into a desired shape. As means for processing the glass bonding material into a desired shape, conventionally known methods can be employed without particular limitation as long as the effects of the present invention are not hindered. For example, a glass bonding material in the form of pellets can be obtained by compressing and molding glass powder into an arbitrary shape, followed by calcining. A paste-like glass bonding material can also be obtained by mixing an organic material such as a binder or an organic solvent with glass powder.

≪Joining method≫
As described above, the glass bonding material disclosed herein can be easily fixed by firing at a low temperature of 650° C. or less, and can exhibit suitable heat resistance after firing. For this reason, it is preferably applied to the formation of a sealed joint of an inorganic member joint (for example, a low-temperature SOFC) used in a temperature environment of 650° C. or lower, which is lower than the conventional temperature.

As described above, the inorganic member to be joined in the technology disclosed herein is a concept that includes metal materials and ceramic members. Examples of metal materials to be joined include stainless steel, aluminum, chromium, iron, nickel, copper, silver, manganese, and alloys thereof. Examples of ceramic members include zirconia, alumina, forsterite, titania, and yttria. Among these, the glass bonding material disclosed herein can be particularly suitably used when ferritic stainless steel, which is a metal member, is to be bonded. Since the strength of such ferritic stainless steel is greatly reduced when heated to a temperature exceeding 650° C., it is required to set the firing temperature to 650° C. or lower when forming the sealed joint. As described above, the glass bonding material disclosed herein can ensure suitable bondability even when fired at a low temperature of 650° C. or less, and thus can suitably prevent deterioration of the ferritic stainless steel. In addition, when a glass bonding material containing an alkali metal element is used for bonding ferritic stainless steel, hexavalent chromium is generated during firing, which may adversely affect the environment and the human body. In contrast, the glass bonding material disclosed herein does not contain an alkali metal element, and thus can prevent the generation of hexavalent chromium.

Further, when forming a sealed joint using the glass bonding material disclosed herein, low-temperature firing is performed after the glass bonding material is applied to the bonding object (inorganic member). As described above, the temperature in the low-temperature firing is appropriately changed according to the temperature of the environment used after firing (for example, the operating temperature of the SOFC in the case of the sealing joint of the SOFC). Specifically, the temperature of the low-temperature firing may be 500°C to 650°C, 550°C to 650°C, or 600°C to 650°C. Also, the firing atmosphere is set to, for example, a reducing atmosphere. The baking time is set to 0.5 hours to 10 hours (for example, 2 hours). As a result, the glass composition in the glass bonding material is welded and solidified to form a dense sealed joint containing glass as a main component.

Crystals selected from the group consisting of BaMgSiO ₄ , BaAl ₂ O ₄ , BaZnSiO ₄ , BaAl ₂ Si ₂ O ₈ , and MgSiO ₃ may be generated in the sealed joint after firing. When these crystals are produced, the thermal stability of the sealing joint is further improved, and better heat resistance and durability can be obtained. Therefore, it is more preferable to appropriately adjust the components of the glass composition and the conditions of low-temperature firing so that the crystals as described above are generated. However, the sealed joint formed using the glass bonding material disclosed herein has a certain level of heat resistance and durability even if the above-described crystal is not formed. This is confirmed by the experiments of the authors. Therefore, the presence or absence of crystal formation does not limit the present invention, and the sealed joint may be formed under conditions that do not produce crystals in consideration of the production cost and bondability during firing.

≪Solid oxide fuel cell (SOFC) system≫
As a preferred example of the inorganic member assembly described above, a low-temperature operating solid oxide fuel cell (SOFC) system will be described. FIG. 1 is a cross-sectional view schematically showing a solid oxide fuel cell system.

The SOFC system 100 shown in FIG. 1 comprises a single anode-supported cylindrical SOFC cell 10 . In this unit cell 10, a dense layered solid electrolyte 14 made of an oxide ion conductor and a porous air electrode (cathode) are disposed on the outer surface of a cylindrical fuel electrode (anode) 12 having a porous structure. ) 16 are formed in sequence. In the SOFC system with such a structure, a fuel gas (typically hydrogen (H ₂ ) gas) is supplied to the inner space 11 of the cylindrical fuel electrode 12, and the air electrode 16 exposed to the outside of the single cell 10 An oxygen ( _O2 ) containing gas (typically air) is supplied.

The fuel electrode 12 is a so-called ceramic member exemplified by a cermet made of nickel (Ni) and YSZ. The solid electrolyte 14 is a ceramic member exemplified by yttria-stabilized zirconia (YSZ), gadolinia-doped ceria (GDC), and lanthanum gallate (LaGaO ₃ ). As the air electrode 16, lanthanum manganate ( _LaMnO3 ) systems represented by (LaSr) _MnO3 and (LaCa)MnO3, _LaCoO3 , (LaSr) _CoO3 , (LaSr)(CoFe) _O3 , and the like are used _. Examples include lanthanum cobaltate-based perovskite-type oxides typified by (LaSr)(TiFe)O ₃ and lanthanum titanate-based perovskite oxides.

This SOFC system has at least one pair of gas supply pipes 20 having substantially the same diameter as the fuel electrode 12 . The end face 21 of one gas supply pipe 20 and one end face 13 of the fuel electrode 12 are in contact, and the end face 23 of the other gas supply pipe 20 and the other end face 15 of the fuel electrode 12 are in contact. . These gas supply pipes 20 are metal members mainly composed of various metal materials. The material of the gas supply pipe 20 is not particularly limited, but stainless steel, aluminum, chromium, iron, nickel, copper, silver, manganese, alloys thereof, and the like are used. In particular, in the case of a low-temperature SOFC system, an inexpensive metal member with relatively low heat resistance (for example, ferritic stainless steel, etc.) can be preferably used as the material for the gas supply pipe 20 .

A junction 1 is formed at each boundary between the fuel electrode 12 and the gas supply pipe 20 . In this SOFC system 100, the joint 1 is formed using the glass jointing material disclosed herein. Specifically, the above-described glass bonding material is adhered so as to cover the boundary between the fuel electrode 12 and the gas supply pipe 20 and the end of the solid electrolyte 14 . Then, after degreasing treatment is performed to remove organic substances, a baking treatment is performed to fuse and solidify the glass powder, thereby forming the joint 1 .

As noted above, the SOFC system shown in FIG. 1 uses a cold-operating SOFC as the single cell 10 . At this time, in the case of a normal SOFC with an operating temperature of 800 ° C. or higher, a relatively high temperature (750 ° C. to 800 ° C.) firing treatment can be performed according to the operating temperature, so the joints with excellent heat resistance can be formed. On the other hand, in the case of a low-temperature operating SOFC with an operating temperature of 650° C. or less, it is required to perform low-temperature sintering at 650° C. or less due to restrictions on the operating temperature (limitations on the heat resistance of constituent materials). On the other hand, the glass bonding material disclosed herein can form the bonding portion 1 between the fuel electrode 12 and the gas supply pipe 20 with suitable bondability even when firing at a low temperature of 650° C. or less. . Furthermore, the joint 1 formed of the glass jointing material disclosed herein has suitable heat resistance even though it is formed by low-temperature firing.

[Test example]
Several test examples relating to the present invention will be described below, but the present invention is not intended to be limited to those shown in such test examples.

1. Preparation of Samples In this test, a total of 23 kinds of glass powders (Samples 1 to 23) were prepared with different components of the glass composition. Specifically, first, raw material powder having a predetermined composition was melted at 900° C. to 1200° C. and then rapidly cooled to obtain a glass body. Next, this glass body was pulverized and classified to obtain glass powder. Table 1 shows the components of the glass composition in each sample. The unit of numerical values in Table 1 is "mol%".

2. Evaluation test (1) Evaluation of high-temperature viscosity The viscosity of the glass powder of each sample was measured at 650°C. With such a viscosity, the glass powder of each sample was press-molded into a cylinder having a diameter of 7 to 10 mm and a height of 5 to 7 mm, and was calcined at 650° C. for 10 minutes. Then, the calcined test piece was heated again, and the amount of deformation in the height direction from room temperature (25°C) to 650°C was detected using a glass parallel plate viscosity measuring device. Then, the viscosity η at 650° C. was calculated based on the Gent's formula from the deformation rate of the measurement sample.
Gent formula: η = 2πMgH ⁵ /3V (-dH/dt) (2πH ³ +V)
(However, η: viscosity (Poise), M: load (g), H: sample height (cm), g: gravitational acceleration (cm/s ² ), V: sample volume (cm ³ ), dH/dt : Sample deformation speed (cm/s).)

(2) Evaluation of bondability Glass powder of each sample was mixed with a solvent (terpineol) to prepare a paste-like glass bonding material. This glass bonding material was placed on the surface of a plate-like inorganic member and baked in an air atmosphere for 2 hours. Then, the baked inorganic member was reversed, and the case where the bonding material (sealed joint) fell was evaluated as "x", and the case where the bonding material did not fall was evaluated as "good". In this test, three types of inorganic members, ferritic stainless steel (SUS430), zirconia, and alumina, were used as objects to be joined, and the bondability to each inorganic member was evaluated. In addition, the firing temperature was changed within the range of 600° C. to 700° C. for the above three inorganic members, and the lowest temperature (bonding temperature) at which the sealed joint did not drop was also measured.

(3) Evaluation of Thermal Expansion Coefficient The glass powder prepared above was press-molded into a disc having a diameter of 20 mm and a thickness of 7 mm, and heated at a temperature in the range of 600° C. or higher and 700° C. or lower for 2 hours. Then, using a diamond cutter, a cylinder having a diameter of about 5 mm×15 mm was cut out, and the thermal expansion coefficient was measured using a thermomechanical analyzer (manufactured by Rigaku Corporation, TMA8310). Specifically, the coefficient of thermal expansion was calculated from the average linear expansion amount between 30° C. and 500° C. when the temperature was raised from room temperature (25° C.) to 1000° C. at a constant rate of 10° C./min. Note that the coefficient of thermal expansion of Sample 22 was calculated from the average amount of linear expansion between 30°C and 300°C, unlike the other samples.

(4) Evaluation of heat resistance The coefficient of thermal expansion of the glass powder of each sample was obtained in the same manner as in the "Evaluation of coefficient of thermal expansion" described above. Next, each sample was subjected to thermal exposure (heating time: 100 hours) with different heating temperatures in increments of 50°C within the range of 300°C to 1000°C, and the coefficient of thermal expansion after the thermal exposure was measured. . The temperature at which the coefficient of thermal expansion decreased by 10% or more before and after the heat exposure was defined as the "durability temperature".

(5) Evaluation of crystal phase After heat treatment was performed in the same procedure as the above-mentioned "Evaluation of thermal expansion coefficient", the obtained glass was pulverized to obtain a powdery sample. Then, powder X-ray crystal diffraction (XRD) was performed on the powdery sample to confirm the presence or absence of crystal precipitation, and the precipitated crystal was identified.

(6) Evaluation of element evaporativity A powdery sample was obtained in the same procedure as the above-mentioned "Evaluation of crystal phase". Then, about 1 g of a powdery sample is placed in an alumina boat, the alumina boat is placed in a quartz tube in a tubular furnace, and the tubular furnace is heated to 700 ° C. while air is circulated in the quartz tube at a flow rate of 100 ml / min. warmed up. After that, a collection container filled with a collection solution (nitric acid aqueous solution) was attached to the quartz tube and held for 3 hours. The glass-containing elements contained in the collection solution were quantified based on ICP emission spectrometry, and were regarded as the elements evaporated from the glass. The lower limit of analysis for 1 g of powdery sample was set at 5 μg, and elements below this lower limit of analysis were judged to be “undetected”.

3. Evaluation Results Table 2 shows the results of each evaluation test described above.

From the above results, MO: 30 to 75 mol%, Al ₂ O ₃ : 0.7 to 12 mol%, Si ₂ O: 5 to 30 mol%, B ₂ O ₃ : 15 to 45 mol%, ZnO: 1 to 10 mol% It was confirmed that the glass bonding materials (Samples 1 to 19) containing the glass composition composed of the above components develop suitable viscosity and exhibit good bondability when fired at a low temperature of 650° C. or less. Furthermore, it was found that the glass bonding materials of Samples 1 to 19 exhibit good heat resistance after firing. On the other hand, it was confirmed that Samples 20 and 21 containing less than 15 mol % of B ₂ O ₃ exhibited good heat resistance after firing, but their bondability was greatly reduced. In addition, it was found that Sample 22, which does not contain oxides of group 2 elements (MO), exhibits relatively good bondability, but the heat resistance temperature is lowered to 400°C. It was confirmed that sample 23, which contained less than 0.7 mol% of Al ₂ O ₃ , exhibits relatively good heat resistance, but the bondability is greatly reduced, as with samples 20 and 21. . Also, from the results of samples 16 to 18, it was found that the group 2 element oxide (MO) should contain at least 3.0 mol % or more of MgO.

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 technology described in the claims includes various modifications and changes of the specific examples illustrated above.

1 Gas Seal Portion 10 Single Cell 12 Fuel Electrode (Anode)
Reference Signs List 13, 15 end of fuel electrode 14 solid electrolyte layer 16 air electrode (cathode)
20 gas pipe 100 SOFC system

Claims (7)

A glass bonding material for sealing and bonding inorganic members by firing at a low temperature of 650 ° C. or less,
containing a glass composition as a main component,
The glass composition substantially does not contain alkali metal elements, P, Pb, Bi, Te, V, and As, and when the entire glass composition is 100 mol %, 95 mol % or more is oxide conversion in the molar ratio of
MO: 30 to 75 mol%,
Al ₂ O ₃ : 0.7 to 12 mol%,
SiO ₂ : 5 to 30 mol%,
B ₂ O ₃ : 15 to 45 mol%,
ZnO: 1 to 10 mol%,
(Here, the above MO is an oxide of a Group 2 element and contains 3 mol % or more and 25 mol % or less of MgO.). The glass bonding material according to claim 1, wherein the glass composition contains 1 mol% or less of at least one selected from _the group consisting of _Cu2O , _Fe2O3 , NiO, and _ZrO2 . The glass bonding material according to claim 1 or 2, which has a viscosity of 5 Pa·s to 8 Pa·s at 650°C. The glass bonding material according to any one of claims 1 to 3, having a thermal expansion coefficient of 6 x 10 ^-6 K ^-1 to 13 x 10 ^-6 K ^-1 from 30°C to 500°C. The glass bonding material according to any one of claims 1 to 4, wherein the rate of change in thermal expansion before and after the heat exposure is 10% or less when subjected to heat exposure at 650°C or more for 100 hours or more in an air atmosphere. An inorganic member joined body comprising two or more inorganic members and a sealing joint for sealing and joining the two or more inorganic members,
The sealing joint substantially does not contain alkali metal elements, P, Pb, Bi, Te, V, and As, and is 95 mol% or more oxidized when the entire sealing joint is 100 mol%. In terms of molar ratio,
MO: 30 to 75 mol%,
Al ₂ O ₃ : 0.7 to 12 mol%,
SiO ₂ : 5 to 30 mol%,
B ₂ O ₃ : 15 to 45 mol%,
ZnO: 1 to 10 mol%,
(Here, the above MO is an oxide of a Group 2 element and contains MgO in an amount of 3 mol % to 25 mol % .). 7. The sealing joint according to claim 6, _wherein at least one crystal selected from _the group consisting of _BaMgSiO4 , _BaAl2O4 , _BaZnSiO4 , _BaAl2Si2O8 , and _MgSiO3 is produced _. Inorganic member joined body.

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