CROSS REFERENCE TO RELATED APPLICATIONS
This application relates to, and claims priority from, provisionally filed U.S.
patent application having docket number 256606-1 and serial number 61/651,817, entitled
"COMPOSITIONS FOR BRAZING, AND RELATED METHODS AND DEVICES", filed
on May 25"^, 2012, which application is hereby incorporated by reference.
TECHNICAL FIELD
This invention generally relates to a braze composition. In some specific
embodiments, the invention relates to a braze composition that provides corrosion-resistant
sealing and other benefits to high temperature rechargeable batteries.
BACKGROUND OF THE INVENTION
Many types of seal materials have been considered for use in high-temperature
rechargeable batteries/cells for joining different components. Sodium/sulfur or sodium/metal
halide cells generally include several ceramic and metal components. The ceramic
components include an electrically insulating alpha-alumina collar and an ion-conductive
electrolyte beta-alumina tube, and are generally joined or bonded via a sealing glass. The
metal components include a metallic casing, current collector components, and other metallic
components which are often joined by welding or thermal compression bonding (TCB).
However, metal-to-ceramic bonding can sometimes present some difficulty, mainly due to
thermal stress caused by a mismatch in the coefficient of thermal expansion for the ceramic
and metal components.
The metal-to ceramic bonding is most critical for the reliability and safety of
the cell. Many types of seal materials and sealing processes have been considered for joining
metal to ceramic components, including ceramic adhesives, brazing, and sintering. However,
most of the seals may not be able to withstand high temperatures and corrosive environments.
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A common bonding technique involves multiple steps of metalizing the
ceramic component, followed by bonding the metallized ceramic component to the metal
component using TCB. The bond strength of such metal-to-ceramic joints is controlled by a
wide range of variables, for example, the microstructure of the ceramic component, the
metallization of the ceramic component, and various TCB process parameters. In order to
ensure good bond strength, the process requires close control of several parameters involved
in various process steps. In short, the method is relatively expensive, and complicated, in
view of the multiple processing steps, and the difficulty in controlling the processing steps.
Brazing is another potential technique for making the ceramic-to-metal joints.
A braze material is heated above its melting point, and distributed between two or more
close-fitting parts by capillary action. However, most of the brazing materials (or braze
materials) have limitations that prevent them from fulfilling all of the necessary requirements
of high temperature batteries. Moreover, some of the commercial braze materials can be
quite expensive themselves; and using them efficiently in various processes can also be
costly.
It may be desirable to develop new braze alloy compositions that have
properties and characteristics that meet performance requirements for high temperature
rechargeable batteries, and are less complicated and less expensive to process, as compared to
the existing sealing methods.
BRIEF DESCRIPTION
Various embodiments of the present invention may provide braze alloy
compositions for sealing a ceramic to a metal, to form a seal that can withstand corrosive
environments.
In accordance with an embodiment of the invention, a braze alloy composition
is disclosed, comprising copper, nickel, and an active metal element. The braze alloy
includes nickel in an amount less than about 30 weight percent, and the active metal element
in an amount less than about 10 weight percent.
In one embodiment, an electrochemical cell incorporating the braze alloy
composition is disclosed. The braze alloy includes an active metal element that forms a
ceramic-to-metal joint, and has good sodium- and halide-resistance at operating temperatures,
3
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along with other complimentary mechanical properties; stability at high temperatures; and
good thermal expansion properties, and the like. In one embodiment, an energy storage
device is also disclosed.
BRIEF DESCRIPTION OF DRAWINGS
These and other features, aspects, and advantages of the present invention will
become better understood when the following detailed description is read with reference to
the accompanying drawings, wherein:
Fig. 1 is a schematic view showing a cross-section of an electrochemical cell,
according to an embodiment; and
Fig. 2 is a scanning electron micrograph showing an interface between a ceramic
and a braze alloy.
DETAILED DESCRIPTION
The invention includes embodiments that relate to a braze alloy composition for
sealing an electrochemical cell, for example a sodium/sulfur or a sodium metal halide battery.
The invention also includes embodiments that relate to an electrochemical cell made by using
the braze composition. As discussed in detail below, some of the embodiments of the present
invention provide a braze alloy for sealing a ceramic component to a metal component, and a
method for the same, e.g., for a metal halide battery. These embodiments advantageously
provide an improved seal and method for the sealing. Though the present discussion
provides examples in the context of a metal halide battery, these processes can be applied to
any other application, including ceramic-to-metal or ceramic-to-ceramic joining.
When introducing elements of various embodiments of the present invention, the
articles "a," "an," "the," and "said" are intended to mean that there are one or more of the
elements, unless otherwise indicated. The terms "comprising," "including," and "having" are
intended to be inclusive, and mean that there may be additional elements other than the listed
elements. As used herein, the term "and/or" includes any and all combinations of one or
more of the associated listed items. Unless otherwise indicated herein, the terms "disposed
on", "deposited on" or "disposed between" refer to both direct contact between layers,
objects, and the like, or indirect contact, e.g., having intervening layers therebetween.
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Approximating language, as used herein throughout the specification and claims,
may be applied to modify any quantitative representation that could permissibly vary without
resulting in a change in the basic fiinction to which it may be related. Accordingly, a value
modified by a term such as "about" is not limited to the precise value specified. In some
instances, the approximating language may correspond to the precision of an instrument for
measuring the value.
I As used herein, the term "liquidus temperature" generally refers to a temperature
at which an alloy is transformed from a solid into a molten or viscous state. The liquidus
temperature specifies the maximum temperature at which crystals can co-exist with the melt
in thermodynamic equilibrium. Above the liquidus temperature, the alloy is homogeneous,
and below the liquidus temperature, an increasing number of crystals begin to form in the
melt with time, depending on the particular alloy. Generally, an alloy, at its liquidus
temperature, melts and forms a seal between two components to be joined.
The liquidus temperature can be contrasted with a "solidus temperature". The
solidus temperature quantifies the point at which a material completely solidifies
(crystallizes). The liquidus and solidus temperatures do not necessarily align or overlap. If a
gap exists between the liquidus and solidus temperatures, then within that gap, the material
consists of solid and liquid phases simultaneously (like a "slurry").
"Sealing" is a function performed by a structure that joins other structures
together, to reduce or prevent leakage through the joint between the other structures. The
seal structure may also be referred to as a "seal" herein, for the sake of simplicity.
Typically, "brazing" uses a braze material (usually an alloy) having a lower
liquidus temperature than the melting points of the components (i.e. their materials) to be
joined. The braze material is brought slightly above its melting (or liquidus) temperature
while protected by a suitable atmosphere. The braze material then flows over the
components (known as wetting), and is then cooled to join the components together. As used
herein, "braze alloy composition" or "braze alloy", "braze material" or "brazing alloy", refers
to a composition that has the ability to wet the components to be joined, and to seal them. A
braze alloy, for a particular application, should withstand the service conditions required, and
melts at a lower temperature than the base materials; or melts at a very specific temperature.
Conventional braze alloys usually do not wet ceramic surfaces sufficiently to form a strong
bond at the interface of a joint. In addition, the alloys may be prone to sodium and halide
corrosion.
As used herein, the term "brazing temperature" refers to a temperature to which a
brazing structure is heated to enable a braze alloy to wet the components to be joined, and to
form a braze joint or seal. The brazing temperature is often higher than or equal to the
liquidus temperature of the braze alloy. In addition, the brazing temperature should be lower
than the temperature at which the components to be joined may become chemically,
compositionally, and mechanically unstable. There may be several other factors that
influence the brazing temperature selection, as those skilled in the art understand.
Embodiments of the present invention provide a braze alloy composition capable
of forming a joint by "active brazing" (described below). In some specific embodiments, the
composition also has high resistance to sodium and halide corrosion. The braze alloy
composition includes copper, nickel, and an active metal element, as described herein. Each
of the elements of the alloy usually contributes to at least one property of the overall braze
composition. These properties may include liquidus temperature, coefficient of thermal
expansion, flowability or wettability of the braze alloy with a ceramic; corrosion resistance,
and ease-of-processing. Some of the properties are described below.
According to most of the embodiments of the invention, the braze alloy
composition is a copper-based alloy, that is, the braze alloy contains a relatively high amount
of copper compared to the amount of other elements in the alloy. Usually, the level of copper
present is at least about 50 weight percent, based on the total weight of the braze alloy
composition. In some specific embodiments, e.g., some of those related to structures for
sodium metal halide batteries, the level of copper is at least about 70 weight percent. In other
preferred embodiments, the level of copper is at least about 90 weight percent. In addition to
being relatively inexpensive, copper is a highly ductile metal, and thus copper-based alloys
can be processed using a wide variety of cost-effective techniques, such as rolling, meltspinning,
and powder atomization. Generally, copper containing alloys have good corrosion
resistance in a sodium-containing environment, but may be susceptible to corrosion in a
halide-containing environment.
In order to address some of the problems associated with corrosion, the present
inventors discovered that nickel could be used along with the copper. Nickel provides a
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degree of chemical inertness in a corrosive environment. Additionally, nickel can also
increase the liquidus temperature of the alloy composition. However, a high amount of
nickel may undesirably raise the liquidus temperature of the alloy composition, i.e., above the
required brazing temperature.
Thus, the present inventors conceived of a balance of nickel and copper levels
that optimized the liquidus temperature requirements and the requirements for corrosion
resistance. It was also discovered that the presence of nickel in these specific types of braze
alloys may enhance other properties, such as the thermal expansion coefficient, and the phase
stability. In some embodiments of this invention, a suitable level for the amount of nickel is
less than about 30 weight percent, based on the total weight of the braze alloy. In some
embodiments, nickel is present from about 1 weight percent to about 25 weight percent,
based on the total weight of the braze alloy. In some specific embodiments, nickel is present
from about 3 weight percent to about 20 weight percent, based on the total weight of the
braze alloy.
As mentioned above, the concept of "active brazing" is important for
embodiments of this invention. Active brazing is a technique often used to join a ceramic to
a metal, or a ceramic to a ceramic. Active brazing uses an active metal element that promotes
wetting of a ceramic surface, enhancing the capability of providing a hermetic seal. An
"active metal elemenf, as used herein, refers to a reactive metal that has high affinity to the
oxygen within the ceramic, and thereby reacts with the ceramic. A braze alloy containing an
active metal element can also be referred to as an "active braze alloy." The active metal
element undergoes a decomposition reaction with the ceramic, when the braze alloy is in
molten state, and leads to the formation of a thin reaction layer on the interface of the ceramic
and the braze alloy. The thin reaction layer allows the braze alloy to wet the ceramic surface,
resulting in the formation of a ceramic-ceramic or a ceramic-metal joint/bond, which may
also be referred to as "active braze seal."
Thus, an active metal element is an essential constituent of a braze alloy for
employing active brazing. A variety of suitable active metal elements may be used to form
the active braze alloy. The selection of a suitable active metal element mainly depends on the
chemical reaction with the ceramic (e.g., alumina) to form a uniform and continuous reaction
layer, and the capability of the active metal element of forming an alloy with a base alloy
(e.g. Cu-Ni alloy). In some preferred embodiments for the present invention, the active metal
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element is titanium. Other suitable examples of the active metal element include, but are not
limited to, zirconium, hafnium, and vanadium. A combination of two or more active metal
elements may also be used.
The presence and the amount of the active metal may influence the thickness and
the quality of the thin reactive layer, which contributes to the wettability or flowability of the
braze alloy, and therefore, the bond strength of the resulting joint. In some embodiments, the
active metal is present in an amount less than about 10 weight percent, based on the total
weight of the braze alloy. A suitable range is often from about 0.5 weight percent to about 5
weight percent. In some specific embodiments, the active metal is present in an amount
ranging from about 1 weight percent to about 3 weight percent, based on the total weight of
the braze alloy. The active metal element is generally present in small amounts suitable for
improving the wetting of the ceramic surface, and forming the thin reaction layer, for
example, less than about 10 microns. A high amount of the active metal layer may cause or
accelerate halide corrosion.
The braze alloy composition may further include at least one alloying element.
The alloying element may provide further adjustments in several required properties of the
braze alloy, for example, the coefficient of thermal expansion, liquidus temperature, brazing
temperature, corrosion resistance, and the strength of the braze alloy. In one embodiment, the
alloying element can include, but is not limited to, cobalt, iron, chromium, niobium,
molybdenum, tungsten, palladium, or a combination thereof In some embodiments, the
braze alloy includes up to about 30 weight percent (e.g., about l%-30%) of the alloying
element, based on the total weight of the braze alloy. In some embodiments, the braze alloy
includes up to about 10 weight percent chromium, and in some specific embodiments, up to
about 5 weight percent chromium, based on the total weight of the braze alloy. In other
specific embodiments, the braze alloy includes up to about 2 weight percent niobium, based
on the total weight of the braze alloy. In some embodiments, the braze alloy includes up to
about 1 weight percent of molybdenum, based on the total weight of the braze alloy.
In some embodiments, any of the braze alloys described herein may also include
palladium. The addition of palladium may improve the corrosion resistance of the overall
composition. The braze alloy may include up to about 40 weight percent palladium, based on
the total weight of the braze alloy. In some specific embodiments, the braze alloy includes up
to about 10 weight percent of palladium, based on the total weight of the braze alloy.
As discussed above, the braze alloy has a liquidus temperature lower than the
melting temperatures of the components to be joined. In one embodiment, the braze alloy has
a liquidus temperature of at least about 850 degrees Celsius. In one embodiment, the braze
alloy has a liquidus temperature from about 850 degrees Celsius to about 1300 degrees
Celsius, and in some specific embodiments, from about 950 degrees Celsius to about 1250
degrees Celsius.
Some embodiments provide an electrochemical cell that comprises a first
component and a second component joined to each other by a braze alloy composition. The
cell may be a sodium-sulfur cell or a sodium-metal halide cell, for example. As described
previously, the braze alloy composition includes copper, nickel, and an active metal element.
At least one additional alloying element, such as chromium, palladium, niobium,
molybdenum, and/or tungsten may further be added. The constituents of the alloy and their
respective amounts are described above.
As discussed above, the braze alloy composition may provide an active braze seal
to join components in the cell. In one embodiment, the first component of the cell comprises
a metal, and the second component comprises a ceramic. The metal component can be a ring
that includes nickel. The ceramic component can be a collar that includes an electrically
insulating material, such as alpha-alumina.
For example, sodium-sulfur or sodium-metal halide cells may contain the braze
alloy composition that forms an active braze seal to form metal-to-ceramic joints. The active
braze seal secures an alpha-alumina collar and a nickel ring. Fig. 1 is a schematic diagram
depicting an exemplary embodiment of a sodium-metal halide battery cell 10. The cell 10
has an ion-conductive separator tube 20 disposed in a cell case 30. The separator tube 20 is
usually made of P-alumina or P"-alumina. The tube 20 defines an anodic chamber 40
between the cell case 30 and the tube 20, and a cathodic chamber 50, inside the tube 30. The
anodic chamber 40 is usually filled with an anodic material 45, e.g. sodium. The cathodic
chamber 50 contains a cathode material 55 (e.g. nickel and sodium chloride), and a molten
electrolyte, usually sodium chloroaluminate (NaAlCU).
An electrically insulating ceramic collar 60, which may be made of alphaalumina,
is situated at a top end 70 of the tube 20. A cathode current collector assembly 80 is
disposed in the cathode chamber 50, with a cap structure 90, in the top region of the cell. The
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ceramic collar 60 is fitted onto the top end 70 of the separator tube 20, and is sealed by a
glass seal 100. In one embodiment, the collar 60 includes an upper portion 62, and a lower
inner portion 64 that abuts against an inner wall of the tube 20, as illustrated in Fig. 1.
In order to seal the cell 10 at the top end (i.e., its upper region), and protect the
alumina collar 60 in the corrosive environment, a metal ring 110 is sometimes disposed,
covering the alpha alumina collar 60, and joining the collar with the current collector
assembly 80, underneath the cap structure 90. The metal ring 110 has two portions; an outer
metal ring 120 and an inner metal ring 130, which are joined, respectively, with the upper
portion 62 and the lower portion 64 of the ceramic collar 60, by means of the active braze
seals 140 and 150. The active braze seal 140, the seal 150, or both, may be formed by using
one of the suitable braze alloy compositions described above. The collar 60 and the metal
ring 110 may be temporarily held together with an assembly (e.g., a clamp), or by other
techniques, until sealing is complete.
The outer metal ring 120 and the inner metal ring 130 are usually welded shut to
seal the cell, after joining with the ceramic collar 60 is completed. The outer metal ring 120
can be welded to the cell case 30; and the inner metal ring 130 can be welded to the current
collector assembly 80.
The shape and size of the several components discussed above with reference to
FIG. 1 are only illustrative for the understanding of the cell structure; and are not meant to
limit the scope of the invention. The exact position of the seals and the joined components
can vary to some degree. Moreover, each of the terms "collar" and "ring" is meant to
comprise metal or ceramic parts of circular or polygonal shape, and in general, all shapes that
are compatible with a particular cell design.
The braze alloys and the active braze seal formed thereof, generally have good
stability and chemical resistance within determined parameters at a determined temperature.
It is desirable (and in some cases, critical) that the braze seal retains its integrity and
properties during several processing steps while manufacturing and using the cell, for
example, during a glass-seal process for a ceramic-to-ceramic joint, and during operation of
the cell. In some instances, optimum performance of the cell is generally obtained at a
temperature greater than about 300 degrees Celsius. In one embodiment, the operating
temperature may be in a range from about 270 degrees Celsius to about 450 degrees Celsius.
0
In one embodiment, the glass-seal process is carried out at a temperature of at least about
1000 degrees Celsius. In some other embodiments, the glass-seal process is carried out in a
range of from about 1000 degrees Celsius to about 1200 degrees Celsius. Moreover, the
bond strength and hermeticity of the seal may depend on several parameters, such as the
composition of the braze alloy, thickness of the thin reaction layer, the composition of the
ceramic, and the surface properties of the ceramic.
In accordance with some embodiments of this invention, an energy storage
device includes a plurality of the electrochemical cells as disclosed in previous embodiments.
The cells are, directly or indirectly, in thermal and/or electrical communication with each
other. Those of ordinary skill in the art are familiar with the general principles of such
devices.
Some embodiments provide a method for joining a first component to a second
component by using a braze alloy composition. The method includes the step(s) of
introducing the braze alloy between the first component and the second component to form a
brazing structure. (The alloy could be deposited on one or both of the mating surfaces, for
example, as also described below). The brazing structure can then be heated to form an
active braze seal between the first component and the second component. In one
embodiment, the first component includes a ceramic; and the second component includes a
metal. The braze alloy composition includes copper, nickel, and an active metal element. At
least one additional alloying element, such as chromium, palladium, niobium, molybdenum,
cobalt, iron, and/or tungsten, may fiarther be added. The constituents of the braze alloy and
their respective amounts (and proportions) are described above.
In the general preparation of the braze alloy, a desired alloy powder mixture may
be obtained by combining (e.g., mixing and/or milling) commercial metal powders of the
constituents in their respecfive amounts. In some embodiments, the braze alloy may be
employed as a foil, a sheet, a ribbon, a preform, or a wire, or may be formulated into a paste
containing water and/or organic fluids. In some embodiments, the precursor metals or metal
alloys may be melted to form homogeneous melts, before being formed and shaped into
particles. In some cases, the molten material can be directly shaped into foils, preforms or
wires. Forming the materials into particles, initially, may comprise spraying the alloy melt
into a vacuum, or into an inert gas, to obtain a pre-alloyed powder of the braze alloy. In other
cases, pellets of the materials may be milled into a desired particle shape and size.
In one embodiment, a layer of the braze alloy is disposed on at least one surface
of the first component or the second component to be joined by brazing. The layer of the
braze alloy, in a specific embodiment, is disposed on a surface of the ceramic component.
The thickness of the alloy layer may be in a range between about 5 microns and about 100
microns. In some specific embodiments, the thickness of the layer ranges from about 10
microns to about 50 microns. The layer may be deposited or applied on one or both of the
surfaces to be joined, by any suitable technique, e.g. by a printing process or other dispensing
processes. In some instances, the foil, wire, or the preform may be suitably positioned for
bonding the surfaces to be joined.
In some specific embodiments, a sheet or foil of the braze alloy may be desirable.
As discussed previously, the braze alloys described herein are ductile and easy to process.
For example, the alloys can be easily rolled into sheets or foils. The thickness of sheets or
foils may vary between about 20 microns and about 200 microns.
In a typical embodiment, the method further includes the step of heating the
brazing structure at the brazing temperature. When the brazing structure is heated at the
brazing temperature, the braze alloy melts and flows over the surfaces. The heating can be
undertaken in a controlled atmosphere, such as ultra-high pure argon, hydrogen and argon,
ultra-high pure helium; or in a vacuum. To achieve good flow and wetting of the braze alloy,
the brazing structure is held at the brazing temperature for a few minutes after melting of the
braze alloy, and this period may be referred to as "brazing time". During the brazing process,
a load can also be applied on the samples.
The brazing temperature and the brazing time may influence the quality of the
active braze seal. The brazing temperature is generally less than the melting temperatures of
the components to be joined, and higher than the liquidus temperature of the braze alloy. In
one embodiment, the brazing temperature ranges from about 900 degrees Celsius to about
1500 degrees Celsius, for a time period of about 1 minute to about 30 minutes. In a specific
embodiment, the heating is carried out at a brazing temperature from about 1000 degrees
Celsius to about 1300 degrees Celsius, for about 5 minutes to about 15 minutes.
During brazing, the active metal element (or elements) present in the melt
decomposes, and forms a thin reactive layer at the interface of the ceramic surface and the
braze alloy, as described previously. The thickness of the reactive layer may range from
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about 0.1 micron to about 2 microns, depending on the amount of the active metal element
available to react with the ceramic, and depending on the surface properties of the ceramic
component. In a typical sequence, the brazing structure is then subsequently cooled to room
temperature; with a resulting, active braze seal between the two components. In some
instances, rapid cooling of the brazing structure is permitted.
Some of the embodiments of the present invention advantageously provide braze
alloys, which are chemically stable in the corrosive environment, relative to known braze
alloys, and are capable of forming an active braze seal for a ceramic-to-metal joint. These
braze alloys have high sodium corrosion resistance, and acceptable halide corrosion
resistance for many end uses. The formation of ceramic-to-metal seals for high temperature
cells (as discussed above) by active brazing simplifies the overall cell-assembly process, and
improves the reliability and performance of the cell. The present invention provides
advantages to leverage a relatively inexpensive, simple, and rapid process to seal the cell or
battery, as compared to currently available methods.
EXAMPLES
The examples that follow are merely illustrative, and should not be construed to
be any sort of limitation on the scope of the claimed invention. Unless specified otherwise,
all ingredients may be commercially available from such common chemical suppliers as
Alpha Aesar, Inc. (Ward Hill, Massachusetts), Sigma Aldrich (St. Louis, Missouri), Spectrum
Chemical Mfg. Corp. (Gardena, California), and the like.
Example 1
4 braze alloy compositions (samples 1-4) were prepared. For each braze sample,
individual elements were weighed according to the desired composition, as shown in Table 1.
These elements were arc-melted to provide an ingot for each composition. To ensure
homogeneity of the compositions, the ingots of the samples were triple-melted. The liquidus
temperature of the 3 samples (sample 1, 2, and 3) were measured using Differential Scanning
Calorimeter (DSC).
\ Table 1.
Braze
Samples
Sample 1
Sample 2
Sample 3
Sample 4
Braze alloy composition
. (weight percent)
Cu-3Ni-2Ti
Cu-10Ni-2Ti
Cu-20Ni-2Ti
Cu-1 OPd-15Ni-2Cr-0.5Mo-2Ti
Liquidus
temperature (°C)
1109
1130
1183
1150
(calculated)
The ingot of sample 1 was rolled into an approximately 50 micron-thick sheet.
The sheet of sample 1 was then placed between the surfaces of two alpha alumina pieces
(parts) to be joined. This assembly was then heated up to about 1200 degrees Celsius for
about 10 minutes, and then cooled to room temperature, to form a joint.
Figure 2 shows a cross-section SEM image 200 of an interface between the alpha
alumina 220 and braze sample 1, 240 at the joint. A reaction layer 260 was observed
between the braze sample 1 and alumina at the braze-ceramic interface, which indicates a
reaction between the braze alloy and the ceramic, and the formation of an active braze seal.
Inspection with Energy Dispersive Analysis of X-Rays (EDAX) suggested that the
composition of the reaction layer 260 included metallic and semi-metallic sub-oxides of
titanium (e.g., TiaO, TiO), which would have been formed by the reaction of the titanium in
braze sample 1, with alumina.
While only certain features of the invention have been illustrated and described
herein, many modifications and changes will occur to those skilled in the art. It is, therefore,
to be understood that the appended claims are intended to cover all such modifications and
changes as fall within the true spirit of the invention.
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ELEMENT LIST
10- a sodium-metal halide battery cell
20- an ion-conductive separator tube
30- a cell case
40-an anodic chamber
45- an anode material
50-a cathodic chamber
55- a cathode material
60- a ceramic collar
62-an upper portion of the collar
64-a lower portion of the collar
70- a top end of the tube
80-a cathode current collector assembly
90- a cap structure
100-aglass seal
110- a metal ring
120- an upper metal ring
130-an inner metal ring
140-active braze seal
150-active braze seal
200- a SEM image
220-alpha alumina
240-braze sample I
260-a reaction layer

We claim:
1. A braze alloy composition, comprising copper, nickel, and an active metal element,
wherein nickel is present in an amount less than about 30 weight percent, and the active metal
element is present in an amount up to about 10 weight percent, based on the total weight of
the braze alloy composition.
2. The braze alloy composition of claim 1, comprising from about 3 weight percent to
about 20 weight percent of nickel.
3. The braze alloy composition of claim 1, comprising from about 1 weight percent to
about 3 weight percent of the active metal element.
4. The braze alloy composition of claim 1, wherein the active metal element comprises
titanium, zirconium, hafnium, vanadium, or a combination thereof.
5. The braze alloy composition of claim 1, wherein the active metal element is titanium.
6. The braze alloy composition of claim 1, wherein the braze alloy further comprises an
additional alloying element selected from the group consisting of chromium, niobium,
cobalt, iron, molybdenum, tungsten, palladium, and a combination thereof.
7. An electrochemical cell, comprising a first component and a second component,
joined to each other by a braze alloy composition comprising copper, nickel, and an active
metal element, wherein nickel is present in an amount less than about 30 weight percent, and
the active metal element is present in an amount up to about 10 weight percent, based on the
total weight of the braze alloy composition.
8. The electrochemical cell of claim 7, wherein the braze alloy composition provides an
active braze seal that joins the first component to the second component.
9. The electrochemical cell of claim 7, wherein the first component comprises a metal,
and the second component comprises a ceramic.
10. An energy storage device, comprising a plurality of electrochemical cells as defined
in claim 7.