KR100874578B1 - How to join the ceramic and metal parts - Google Patents

Abstract

In the method of joining a metal part and a ceramic part, an alumina forming metal part and a ceramic part are provided. After placing the brazing material between the alumina forming metal part and the ceramic part, the combination is heated in air at an oxidizing atmosphere, preferably at a temperature of 500-1300 ° C. Alumina forming metal parts include high temperature stainless steels such as Durafoil (alpha-4), Fecralloy, alumina-coated 430 stainless steel and Crofer-22APU, and Haynes 214 , High temperature superalloys such as Nicrofer 6025, and Ducraloy. The brazing material is selected from a metal oxide-noble metal mixture, preferably 30.65-100 mol% Ag in Ag-CuO, Ag-V ₂ O ₅ , and Pt-Nb ₂ O ₅ , more preferably CuO.

Description

Joining the ceramic part and the metal part {METHOD OF JOINING CERAMIC AND METAL PARTS}

(Government rights)

The invention was made with fiscal assistance under contract DE-AC0676RLO 1830 granted by the US Department of Energy. The government has certain rights in the invention.

(Cross reference to related application)

Priority is issued to provisional U.S. Patent Application No. 60 / 348,688 (named Oxidation Ceramic-to-Metal Braze, filed by Weil et al. On 1/11/02), all of which is hereby incorporated by reference. do.

In order to function properly, many high temperature electrochemical devices, such as ceramic fuel cells, oxygen generators, and chemical sensors, often require metal and ceramic components that are hermetically sealed to one another. Unfortunately, the chemical and physical properties of many ceramic and metal parts used in these devices present various challenges to the development of effective seals. For example, one standard electrolyte material currently employed in almost all of these devices is yttria stabilized zirconia (YSZ), which has excellent oxygen ion transport properties, insulating electronic properties, and excellent chemical stability under various operating conditions and environments. Because. However, in order to produce sufficiently high ion transport rates, the device should be operated at high temperatures, generally on the order of 650-900 ° C., and the thickness of the electrolyte membrane should be minimized, but to mitigate the formation of through-thickness pinhole defects in manufacturing. Generally not thinner than 5-10 μm. Solid state electrochemical devices, such as fuel cells, function by gradients of oxygen ions that grow across the electrolyte membrane, so that not only hermiticity across the membrane, but also the herme across the seal that bonds the electrolyte to the body of the device. It's also important. That is, the YSZ layer must be dense, contain no vents, and be connected to the remainder of the device with a high temperature, airtight seal. As defined by the particular application, these devices are expected to operate, and representative conditions under which the incidental YSZ-to-metal junction is exposed include: 1) an average operating temperature of 750 ° C .; 2) continuous exposure to an oxidizing atmosphere on the cathode side; And 3) an expected device life of 3000-30,000 + hours. For example, depending on the function of the device, such as energy generation, the seal may be exposed to a reducing atmosphere on the anode side.

One approach to the bonding of metals and YSZ to work in this environment, active metal soldering, utilizes a braze alloy containing one or more reactive elements, often titanium, which chemically reduces the ceramic adhesion surface and wets it. It greatly improves the behavior and adhesion with soldering. However, there are two or more problems when using this type of binder in the manufacture of solid-state electrochemical devices: 1) junctions at the ceramic / solder metal interface, often due to the complete oxidation of active species during soldering at high temperature operation of the device. Exposure to the entire device in an oxidizing atmosphere at temperatures higher than -800 ° C., which is a common processing condition for active metal soldering, often leads to rapid deterioration of the metal and final loss of hermeticity. There is a great demand for a lot of materials. When employed as electrochemically active electrodes, these mixed ion / electron conductive oxides are liable to decrease in the bonding operation and irreversibly deteriorate through phase separation, which ultimately leads to severe deterioration of device performance. Thus, there is a need for a new method of overcoming these problems and forming a seal that makes a metal to ceramic seal that functions satisfactorily in these stringent environments.

Accordingly, it is an object of the present invention to provide an improved seal between a metal part and a ceramic part that are oxidation resistant at high temperatures.

It is a further object of the present invention first to add a brazing material to the alumina forming metal part, to contact the ceramic part with the brazing material, and to heat the alumina forming metal part, the brazing material, and the ceramic part in an oxidizing atmosphere, between the metal part and the ceramic part. Provides improved sealing.

A further object of the present invention is to use a brazing material selected from metal oxide-noble metal mixtures including but not limited to Ag-CuO, Ag-V ₂ O ₅ , and Pt-Nb ₂ O ₅ .

A further object of the present invention is to use a brazing material selected from a mixture of 30.65-100 mole% Ag in CuO to form an improved seal between the metal and ceramic parts.

A further object of the present invention is to form an improved seal between the metal part and the ceramic part by heating the alumina forming metal part, the brazing material, and the ceramic part in air at a temperature of 500-1300 ° C.

A further object of the present invention is to first form the alumina forming metal part at a time and temperature sufficient to form an aluminized surface of the alumina forming metal part, and then in the air at a temperature of 500-1300 ° C. And by heating the sandwich of the ceramic portion to form an improved seal between the metal portion and the ceramic portion.

These and other objects of the present invention are accomplished by providing a solder that forms a seal between the ceramic portion and the oxide scale growing on the metal portion upon bonding under an oxidizing atmosphere. Therefore, it is an object of the present invention to reactively modify one or both oxide-adhesive surfaces of a metal part and an alumina forming part by soldering an oxide compound dissolved in a molten noble metal alloy, whereby a newly formed surface of the metal part is applied to the remaining solder material. It is easily wetted by. Preferably, the solder is selected from metal oxide-noble metal mixtures including but not limited to Ag-CuO, Ag-V ₂ O ₅ , and Pt-Nb ₂ O ₅ . The method of the present invention is expanded to solder with the addition of a soldering temperature riser selected from the group consisting of Pd, Pt, and combinations thereof, and a soldering temperature lowering agent selected from the group consisting of V ₂ O ₅ , MoO ₃ . A wider range of soldering temperatures for the ash can be provided. The brazing temperature increasing agent is preferably selected from 10-70 mol% of the brazing material. The brazing temperature lowering agent is preferably selected to 1-6 mol% of the brazing material.

The selection of the metal part requires that the metal part be oxidized to the junction temperature. Preferred metal parts include, but are not limited to, metal parts that form alumina on the surface when heated, such as high temperature stainless steel and high temperature superalloys, for example, US Pat. No. 10 / 260,630 (Title: GAS-TIGHT METAL / CERAMIC OR METAL / METAL SEALS FOR APPLICATIONS IN HIGH TEMPERATURE ELECTROCHEMICAL DEVICES AND METHOD OF MAKING, filed 09/27/02), the entire contents of which are incorporated herein by reference. Preferred high temperature stainless steels include, but are not limited to, durafoil (alpha-4), pectalloy, alumina-coated 430 stainless steel and Croper-22APU. Preferred high temperature superalloys include, but are not limited to, highness 214, Nikrofer 6025, and Dukralloy.

1 is a graph showing the contact angle of Ag—CuO solder on 5YSZ in air as a function of temperature in experiments conducted to demonstrate the present invention. The contact angle as a function of CuO content at 1100 ° C. is indicated in the insertion box.

FIG. 2 is a series of SEM micrographs showing the cross-sections of the solder / 5YSZ interfaces formed in the experiments conducted to demonstrate the invention: (a) Ag-1Cu, (b) Ag-2Cu, (c) Ag-4Cu , And (d) Ag-8Cu. Each wet sample is heated in air at a final soak temperature of 1100 ° C.

3 is a graph showing the contact angle of Ag—CuO solder on the scale surface of the pre-oxidized pelarloy in air as a function of temperature in the experiments conducted to demonstrate the invention. The contact angle as a function of CuO content at 1100 ° C. is indicated in the insertion box.

4 is a series of SEM micrographs showing the cross-sections of the solder / pre-oxidized pelarloy formed in the experiments conducted to demonstrate the present invention: (a) Ag-1Cu, (b) Ag-2Cu, (c) Ag-4Cu, and (d) Ag-8Cu. Each wet sample is heated in air at a final dipping temperature of 1100 ° C.

5 is a graph showing the contact angle of Ag—CuO solder on (La _0.6 Sr _0.4 ) (Co _0.2 Fe _0.8 ) O ₃ phase in air as a function of temperature. The holding time at each immersion temperature is 15 minutes.

6 is a series of SEM micrographs showing the cross section of the solder / LSCoF interface: (a) Ag-1Cu, (b) Ag-2Cu, (c) Ag-4Cu, and (d) Ag-8Cu. Each wet sample is heated in air at a final dipping temperature of 1100 ° C.

FIG. 7 is a graph showing the area resistivity of the junction between LSCoF and Ag-CuO solder containing 4% CuO as a function of time in air at 750 ° C. and under a DC current of 1.5 A. FIG.

8 is a series of SEM micrographs showing cross sections of the Ag-4Cu / LSCoF interface tested in air at 750 ° C. for 100 hours under (a) 1.5 A of continuous direct current and (b) no current.

9 is a balanced phase diagram in PbO-Ag and CuO-Ag systems (Shao, ZB; Liu, KR; Liu, LQ; Liu, HK; and Dou, S. 1993. Journal of the American Ceramic Society 76 (10). ): Ag-CuO phase diagram reproduced from 2663-2664).

A series of experiments were conducted according to the method of the present invention to form the junction, or seal, of the present invention. These experiments are useful for illustrating certain features and aspects of the present invention, but they should not be understood as comprehensive examples of all of the various aspects of the present invention. As will be appreciated by one of ordinary skill in the art, without limitation, many of the advantages of the present invention, including but not limited to the choice of materials and the methods and operating parameters used to combine these materials, are readily achieved from the experiments described herein with significant variations. Can be. Accordingly, the invention is to be broadly understood as including all such modifications and equivalents covered by the appended claims.

A first set of experiments was conducted to illustrate the operation and advantages of the present invention. 5% yttria stabilized zirconia (5YSZ) and thin gauge FeCrAlY (Fe, 22% Cr, 5% Al, 0.2% Y) were employed as the model ceramic electrolyte membrane / structural metal system in the soldering experiment. Although 5YSZ was chosen as a representative ceramic providing evidence of the utility of the present invention, one of ordinary skill in the art would expect that the methods and materials of the present invention would be carried out in a similar manner to other ceramics, and the choice of 5YSZ for these experiments is an application of the present invention. It should be understood that it should not be understood as limiting this to this specific example of ceramic. Rather, it includes, but is not limited to, yttria stabilized zirconia, alumina, silicon carbide, and mixed ion / electronic conductivity (MIEC) oxides described in the second set of experiments, described below, over the entire range of 3-8%. Contains all ceramics.

A high density, 10 μm thick 5YSZ coupon, measured nominally 2 cm on one side, was prepared using conventional tape casting and sintering techniques. Prior to these uses in soldering experiments, the samples were washed with acetone and ethanol at 300 ° C. for 1 hour. The 12 mm thick FeCrAlY sheet as received was cut into 2 cm 2 pieces, lightly polished on both sides with 1200 grit SiC paper, and ultrasonically washed in acetone for 10 minutes. To form a stable aluminum oxide scale layer on each metal coupon surface, they were pre-oxidized at 1100 ° C. for 2 hours in static outside air before use. The average thickness of the scale grown in this manner was ˜0.6 μm.

Solder pellets were prepared by mixing copper (10 μm average particle diameter; Alfa Aesar) and silver (5.5 μm average particle diameter; Alfa Aesar) powder in an appropriate proportion to produce the target composition shown in Table 1. The copper powder was oxidized as it is when heated in air to form CuO. Wetting experiments were conducted in a static air box furnace with a quartz door to observe the sample being heated. A high speed video camera equipped with a zoom lens was used to record the melting and wetting behavior of the solder pellets on a given substrate. The experiment was carried out by heating the sample at 30 ° C./min to 900 ° C., after which the temperature was maintained for 15 minutes, then heated to 10 ° C./min until a series of set values and held for 15 minutes. In this way, the contact angle between the solder and the substrate was stabilized at several different immersion temperatures: 900 ° C., 950 ° C., 1000 ° C., 1050 ° C., and 1100 ° C. during one heating cycle for measurement. The selection frame from the videotape was converted to a computer image from which the wetting angle between the solder and the substrate was measured and correlated with the temperature log for the heating run. Microstructural analysis of the wet sample was performed using a JEOL JSM-5900LV Scanning Electron Microscope (SEM) equipped with an Oxford Windowless Energy Dispersive X-ray Analysis (EDX) system for the polished cross-section sample.                 

Table 1

Contact angle measurements of molten Ag-CuO solder on 5YSZ films are shown as a function of temperature in FIG. 1. Balanced phase diagrams in the PbO-Ag and CuO-Ag systems, the entire contents of which are incorporated herein by reference (Shao, ZB; Liu, KR; Liu, LQ; Liu, HK; and Dou, S. 1993. As predicted by the Ag-CuO phase diagram shown in FIG. 9 reproduced from the American Ceramic Society 76 (10): 2663-2664, all solders melted above 900 ° C. The 15 minute holding time used to take the sessile drop measurement appears to be long enough for the interface to be balanced, and in each case a stable contact angle was reached within 5 minutes. Except pure silver, all solders show 5YSZ and some wetting. From any of the predetermined solders from FIG. 1, it is clear that the contact angle with the 5YSZ surface remains essentially unchanged for temperatures above 1000 ° C. However, as shown in the insert of FIG. 1, the degree of wetting increases dramatically with the ceramic content of the solder. As shown in Figures 2 (a) -2 (d), backscattered electron images of the four Ag-CuO braze compositions suggest possible reasons for this trend.

Each sample shown in FIG. 2 was heat treated to a final temperature of 1100 ° C. for 15 minutes under the conditions described for the field wetting experiment, ie through a series of intermediate immersion temperatures, and then the furnace was cooled to room temperature. It was. As expected, most phases in each solder are pure silver because CuO is not available for silver at room temperature. Fine precipitates of CuO on the order of 1-5 μm are commonly found in silver matrices spaced from the interface with 5YSZ. For two solders containing the lowest copper oxide content, discrete micron-sized CuO particles are found along the solder / 5YSZ interface. It is pure silver that is found in large areas between these particles and near perfect contact with the 5YSZ interface. In the case of high CuO content soldering, the interfacial layer of CuO almost completely covers the 5YSZ substrate, which is sometimes ruptured by thin lenticular islands of silver.

The contact angle results from FIG. 1 suggest that the formation of a continuous layer of CuO at the interface improves the wetting of Ag—CuO solder with 5YSZ. It is possible that the two different CuO morphologies observed in FIG. 2 are a direct result of the miscibility gap found in the Ag-CuO phase diagram. At 1100 ° C. all four braze compositions will form a single phase liquid. However, in the Ag-CuO phase diagram, as Ag-4Cu and Ag-8Cu solder cools, both systems will enter the miscibility gap where two liquids are formed, with a few phases rich in CuO and a large number of The phase is poor in CuO. Because the phases are immiscible, they will separate, and because of their higher oxide content and consequently lower expected interfacial energy in the oxide substrate, it is expected that the CuO rich liquid preferentially migrates to 5YSZ and wets. Upon further cooling to the monotectic temperature of 964 ° C., solid CuO will begin to precipitate out of this liquid, producing nuclei at the interface with 5YSZ. In doing so, the concentration of silver in the silver rich liquid increases. At 932 ° C., the eutectic temperature, solid CuO and Ag will nucleate simultaneously from the remaining liquid, possibly unevenly on the surface of the CuO layer at the preformed interface. On the other hand, hot Ag-1Cu and Ag-2Cu braze liquids do not exhibit immiscibility and liquid phase separation upon cooling. When the temperature of these solders decreases below their respective liquidus, a small amount of proeutectic silver or CuO precipitates out of solution and nucleates unevenly at the interface with 5YSZ. Upon further cooling to the process temperature, solid Ag and CuO are simultaneously formed from the process liquid.

The effect of the solder composition and the junction temperature on the contact angle between the Ag-CuO solder and the oxide scale surface of the pre-oxidized pelarloy is shown in FIG. 3. The solder appeared to melt in the same way as observed in the 5YSZ experiment, and in each case, a stable wetting angle was quickly obtained. In addition, like the 5YSZ experiment, it was found that the wetting behavior of the solder on the oxide scale of the pelarloy is essentially independent of temperature, but shows a dramatic improvement with increasing CuO content.

Backscattered electron images of four Ag-CuO braze compositions on pre-oxidized pelarloy are shown in FIGS. 4 (a) -4 (d). In each sample, a continuous 1 / 2-1 μm thick alumina scale was observed, which contained small amounts of ˜5 mol% and 3 mol% of iron and chromium, respectively. As found in the 5YSZ wet sample, bulk solder away from the solder / scale interface contains essentially micron sized CuO particles in a matrix of pure silver. However, along the soldering / scale interface, an apparent alloying reaction between CuO in the solder and Al ₂ O _{3 in the} scale occurs to form a region of CuO—Al ₂ O ₃ , which is a mixed oxide solid solution phase adjacent to the metal scale. For solders with a low CuO content, this reaction zone is thin and uneven and is hindered by discrete islands of silver and CuO and sometimes CuAlO ₂ crystals, roughly 1-3 μm in diameter, between the solder and the scale. It is seen as the second product from the reaction. For solders with higher CuO content, the silver and CuO particles and much larger microcrystals of CuAlO ₂ are still very inhabited, but the oxide alloyed regions are thicker, about 7 μm thick, and more continuous. The EDX results show that, regardless of the braze composition, each of 5-8 mol% of iron and chromium is dissolved in the CuO-Al ₂ O ₃ phase along the interface with the metal scale.

The second significant difference between solders in FIGS. 4 (A) -4 (d) is the size and morphology of the CuO layer in contact with the alloying regions of the interface and extending to the bulk of the solder. In Ag-1Cu and Ag-2Cu soldering, this oxide layer is thin and discrete and penetrated at many points by silver regions in direct contact with the alloying regions. In the case of Ag-4Cu and Ag-8Cu soldering, CuO is much thicker and specifies an intermediate layer that completely covers the reaction region and essentially closes the contact between the bulk silver and the interface region. The contact angle data for these solders in FIG. 3 again demonstrates the wetting advantage that a continuous layer of CuO is provided in proportion to the more discontinuous microstructure. As with the wetting of the 5YSZ phase, the morphological differences between the four two-component solders are partly consequent due to the miscibility gaps present in the Ag-CuO phase diagram that affect the microstructural development of high CuO content solders. It is assumed that it is not low.

A second set of experiments were conducted to provide the invention with mixed ion / electron conducting (MIEC) oxides including but not limited to SrFeCo _0.5 O _x , BaCeO ₃ , and (La _0.6 Sr _0.4 ) (Co _0.2 Fe _0.8 ) O ₃ Prove its benefits and actions. MIEC oxides are a class of ceramics that have a particular interest in the present invention, as they contain ionic and electron carriers in high enough concentrations where both forms of charge conduction appear at high levels. Lanthanum strontium cobalt ferrite (La _0.6 Sr _0.4 ) (Co _0.2 Fe _0.8 ) O ₃ (LSCoF) is selected as a representative MIEC oxide providing evidence of the utility of the present invention, but as will be apparent to those skilled in the art, The material is expected to be implemented in a similar manner to other MIEC oxides, and the selection of lanthanum strontium cobalt ferrite for these experiments should not be understood as limiting the application of the invention to this example of MIEC oxide.

LSCoF pellets were uniaxially compressed into oxide powder (99.9% purity; Praxair Specialty Ceramics, Inc.) in a carbon steel mold under a pressure of 7 ksi, followed by cold isostatic pressing at 20 ksi for 1 hour It was prepared by sintering in air at. The final pellet has measurements of 1 "diameter, 1/8" thickness, and has an average density of 96% in theory. The pellet is then ground on one side using a continuous fine grit diamond paste to a 10 μm finish, washed with acetone and propanol, air dried and static at 600 ° C. for 4 hours to burn off any residual organic contaminants. Heat in air

Solder pellets were prepared by mixing copper (10 μm average particle diameter; Alfa Aesar) and silver (5.5 μm average particle diameter; Alfa Aesar) powder in an appropriate proportion to produce the target composition shown in Table 1. The copper powder was oxidized as it is when heated in air to form CuO. Wetting experiments were conducted in a static air box furnace with a quartz door to observe the sample being heated. Using a high speed video camera equipped with a zoom lens, the melting and wetting behavior of the solder pellets on the LSCoF substrate was recorded. The experiment was carried out by heating the sample at 30 ° C./min to 900 ° C., after which the temperature was maintained for 15 minutes, then heated to 10 ° C./min until a series of set values and held for 15 minutes. In this way, the contact angle between the solder and the substrate was stabilized at several different immersion temperatures: 900 ° C., 950 ° C., 1000 ° C., 1050 ° C., and 1100 ° C. during one heating cycle for measurement. The selection frame from the videotape was converted to a computer image from which the wetting angle between the solder and the substrate was measured and correlated with the temperature log for the heating run.

Conductive samples were prepared by bonding two LSCoF pellets to each other using Ag-Cu braze foil pre-made in air at 1050 ° C. for 0.5 h. In addition, copper oxidizes in situ to form CuO. A 10 ° C./min heating and cooling rate was employed at the time of soldering. Solder foils were synthesized by diffusion bonding copper and silver foils having the same area dimensions but with the appropriate thickness required to obtain the target braze composition. After diffusion bonding was carried out in Ar / 4% H ₂ carver gas at 720 ° C. for 10 hours under a static load of ˜1 / 2 psi, the foil was wound to a thickness of 0.07 mm. The high temperature conductivity measurement of the contacts was performed using a modified four point probe technique. Two contactors were prepared by spot welding a pair of platinum conductors to a piece of Pt foil having the same area dimensions as LSCoF. The contactor was then bonded up and down the LSCoF / Solder / LSCoF sandwich using a platinum paste. One lead from the top and bottom contactors was connected to the HP 3263A DC power supply and the other two leads were connected to the HP 34401A multimeter and the device that continuously recorded the data history. Samples were heated at 5 ° C./min to 750 ° C. in an air muffle furnace and maintained for the duration of the test. 1.5 A of continuous direct current was added to the sample during the test, and the voltage measurements were recorded every two minutes. Microstructural analysis of wet and conductive samples was performed using a JEOL JSM-5900LV Scanning Electron Microscope (SEM) equipped with an Oxford Windowless Energy Dispersive X-ray Analysis (EDX) system for polished cross-section samples.

Contact angle measurements of molten Ag—CuO solder on polished LSCoF are shown as a function of temperature in FIG. 5. As expected by the Ag-CuO phase diagram, all solders melted above 900 ° C. The 15 minute holding time used to take the sessile drop measurement seems to be long enough for the interface to be balanced, and in all cases a stable contact angle was obtained within this period. In addition to pure silver, all solders exhibited wetting with LSCoF. As shown in the figure, the wet behavior of this series of solders on LSCoF appears to be invariant of temperature, but is quite sensitive to CuO content and improves dramatically with increasing amounts of oxide.                 

Backscattered electron images of the four Ag—CuO wet samples shown in FIGS. 6 (a) -6 (d) suggest that the dependence of this composition is related to the concentration and morphology of CuO along the solder / LSCoF interface. The bulk area of the solder in each sample consists of small ~ 1-5 μm diameter particles of CuO surrounded by a matrix of pure silver, taking into account the high silver content of the solder and the fact that CuO is not available to silver at room temperature. Not surprising. Along the soldering / LSCoF interface in each sample, CuO appears to wet the substrate preferentially and forms a thin but clear area in the solder that represents one of the two microstructured patterns. In the case of two solders containing 2% or less CuO, the interface is adorned with a discrete ˜1 μm half lens-like precipitate of CuO. The distance separating these precipitates appears to be greater in Ag-1Cu than in Ag-2Cu. For higher CuO content samples, a nearly continuous band of CuO is found in contact with the previous LSCoF surface and is sometimes burst by small islands of pure silver. The oxide band is the thickest in the Ag-8Cu sample, which contains the highest CuO concentration of the five solders investigated in this review. For all samples in FIG. 6, evidence of Ag and CuO infiltration into the substrate is observed, possibly occurring through interconnected surface pores.

Relevant to the results of the wetting experiments, these micrographs show that the higher coverage of CuO on the LSCoF surface improves the wetting of Ag—CuO solders. The two different CuO morphologies observed in Figures 6 (a) -6 (d) are direct results of miscibility gaps in the Ag-CuO phase diagram. At 1100 ° C. all four braze compositions will form a single phase liquid. However, upon cooling, both Ag-4Cu and Ag-8Cu systems enter the miscibility gap, forming a silver rich and CuO rich liquid phase, while the liquid in Ag-1Cu and Ag-2Cu solders reaches process temperature. Keep single phase until Since the two liquid phases in Ag-4Cu and Ag-8Cu solders are immiscible, they will probably be separated and because of their higher oxide content and consequently lower expected interfacial energy in the MIEC oxide substrate, the CuO rich liquid is preferred. Move to LSCoF and wet. Upon further cooling down to the excitation temperature of 964 ° C, CuO will begin to precipitate out of this liquid, resulting in nucleation at the interface with LSCoF. In doing so, the concentration of silver in the silver rich liquid increases. At process temperatures, solid CuO and Ag will nucleate simultaneously from the remaining liquid. On the other hand, Ag-1Cu and Ag-2Cu solders do not contain enough CuO to cause the braking reaction, and when cooled to just above the process temperature, a small amount of proeutectic silver or CuO precipitates out of solution. , It is assumed that nuclei are generated unevenly and decorate the interface with LSCoF. Upon cooling to the process temperature, solid Ag and CuO are simultaneously formed from the process liquid and nuclei regenerate non-uniformly on proeutectic silver and undecorated LSCoF surfaces, respectively.

Ag-4Cu solder was chosen as a convenient starting point for electrical testing because it shows a reasonable balance between wettability with LSCoF and silver contact at the solder / LSCoF interface, and as a result the expected conductivity. 7 shows the area resistivity (ASR) measurements of Ag-4Cu / LSCoF contacts as a function of time at 1.5 A of continuous direct current and at 750 ° C. under static ambient air. The junction was tested at these conditions for 100 hours. The value of ASR was determined by subtracting the temperature adjustment resistance of the LSCoF pellet from the raw data and dividing these correction values by two to account for the presence of two solder / LSCoF interfaces in the sample. The sample shows an almost steady ASR of 3.3 mPa · cm 2 for the duration of the test. It is generally agreed that the tolerance of ASR for SOFC interconnection applications is ˜40 mPa · cm 2, which is greater than the magnitude of the larger than observed at the LSCoF contacts of the solder. As shown in FIG. 8, the metallographic examination of the electrically tested junction did not show any significant microstructural change for the sample heat treated at 750 ° C. for 100 hours under no current application.

While the preferred embodiments of the invention have been shown and described, it will be apparent to those skilled in the art that many changes and modifications may be made in their broad aspects without departing from the invention. For example, a wide range of metals, glasses, solders, and ceramics may be employed, and various methods for forming such materials in layers on the same and others may also be employed. Therefore, the appended claims are intended to cover all such variations and modifications as fall within the true intent and scope of the present invention.

Claims (27)

a) providing an alumina forming metal part, b) providing a ceramic portion, c) providing a brazing material between the alumina forming metal portion and the ceramic portion, and d) heating the alumina forming metal part, the brazing material, and the ceramic part in an oxidizing atmosphere. Method for producing a metal-to-ceramic seal comprising a. The method of claim 1, wherein the alumina forming metal portion is selected from the group consisting of high temperature stainless steel and high temperature superalloy. The method of claim 2, wherein the high temperature stainless steel is selected from the group consisting of Durafoil (alpha-4), Fecralloy, alumina-coated 430 stainless steel and Crofer-22APU. Which is a metal-to-ceramic seal. The method of claim 2, wherein the high temperature superalloy is selected from the group consisting of Haynes 214, Nicrofer 6025, and Ducraloy. . The method of claim 1, wherein the braze material is selected from a metal oxide-noble metal mixture. The method of claim 5, wherein the braze material is selected from the group consisting of Ag—CuO, Ag—V ₂ O ₅ , and Pt—Nb ₂ O ₅ . The method of claim 6, wherein the braze material further contains a brazing temperature increasing agent selected from the group consisting of Pd, Pt, and combinations thereof. 8. The method of claim 7, wherein the brazing temperature increasing agent is selected from 10-70 mole percent of the brazing material. The method of claim 6, wherein the braze material further contains a brazing temperature lowering agent selected from the group consisting of V ₂ O ₅ , MoO ₃ , and combinations thereof. The method of claim 7, wherein the brazing temperature lowering agent is selected from 1-6 mole percent of the brazing material. The method of claim 6, wherein the brazing material is 30.65-100 mole% Ag in CuO. The method of claim 1, wherein the heating of the alumina forming metal portion, the brazing material, and the ceramic portion in an oxidizing atmosphere is performed in air at a temperature of 500-1300 ° C. 3. A metal-to-ceramic seal formed by the method of claim 1. a) providing an alumina forming metal part, b) heating the alumina forming metal portion at a time and at a temperature sufficient to form an aluminized surface of the alumina forming metal portion, c) providing a ceramic portion, d) providing a brazing material between the alumina forming metal portion and the ceramic portion, and e) heating the alumina forming metal part, the brazing material, and the ceramic part in an oxidizing atmosphere. Method for producing a metal-to-ceramic seal comprising a. The method of claim 14, wherein the alumina forming metal portion is selected from the group consisting of high temperature stainless steel and high temperature superalloy. The metal-to-ceramic seal of claim 15, wherein the high temperature stainless steel is selected from the group consisting of durafoil (alpha-4), pectalloy, alumina-coated 430 stainless steel, and cropper-22APU. How to prepare. 16. The method of claim 15, wherein the high temperature superalloy is selected from the group consisting of highness 214, nicroper 6025, and ducralloy. The method of claim 14, wherein the braze material is selected from a metal oxide-noble metal mixture. 19. The method of claim 18, wherein the braze is selected from the group consisting of Ag-CuO, Ag-V ₂ O ₅ , and Pt-Nb ₂ O ₅ . 20. The method of claim 19, wherein the braze is 30.65-100 mole% Ag in CuO. 15. The method of claim 14, wherein the braze further contains a braze temperature increasing agent selected from the group consisting of Pd, Pt, and combinations thereof. 22. The method of claim 21, wherein the brazing temperature raising agent is selected from 10-70 mole percent of the brazing material. The method of claim 14, wherein the braze material further contains a brazing temperature lowering agent selected from the group consisting of V ₂ O ₅ , MoO ₃ , and combinations thereof. 24. The method of claim 23, wherein the soldering temperature lowering agent is selected from 1-6 mole percent of the brazing material. The method of claim 14, wherein the braze is 30.65-100 mol% Ag in CuO. The method of claim 14, wherein heating the alumina forming metal portion, the brazing material, and the ceramic portion in an oxidizing atmosphere is carried out in air at a temperature of 500-1300 ° C. 16. A metal-to-ceramic seal formed by the method of claim 14.

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