Method and composition for metallizing a refractory material by coating the refractory material

Abstract

The present invention is directed to a coating composition and its employment in a metallization process that facilitates bonding of brazing filler metals to treated refractory surfaces, such as ceramics. The coating can be applied in preselected areas of the refractory surface to define the target area for brazing. It is believed that when compositions of the present invention are employed with brazing or soldering filler metals, strong bonds between two non-metallic refractory bodies, or between a non-metallic refractory body to ferrous and non-ferrous metal can be attained. In one embodiment, the present invention is a coating composition applied to a refractory material prior to brazing, the composition being comprised of a group IVB transition metal component selected from the group consisting of a group UVB transition metal, a hydride thereof, mixtures of group IVB metals and/or hydrides thereof, a binder material, and a fluid carrier. For example, the group IVB transition metal component may be a group IVB transition metal selected from among titanium, zirconium, hafnium, and thorium, hydrides of these group IVB transition metals, and mixtures of these group members. In one embodiment, the group IVB transition metal component is titanium, titanium hydride, or mixtures thereof.

Description

BACKGROUND OF THE INVENTION

[0002] Refractory materials such as ceramic materials are often utilized in applications requiring the joining of such materials to either other ceramic materials or to metal components. For example, in the automotive industry, ceramic is utilized many parts including in wear pads that are joined to metal parts to prolong the service life of such parts. In another example, technical ceramics are used in many electrical and electronic applications such as power grid tubes, vacuum interrupters, semi-conductor packaging, multilayer substrates, ball grid arrays, power dissipation packages, and sensor packages. In the use of non-metallic refractory materials such as ceramics, it has been traditionally difficult to join them together or to join them to metal materials. Conventionally, metallization processes have been required to be performed on the ceramic prior to joining the ceramic to itself or to a metal body because existing brazing formulations typically do not adequately wet the refractory surface. Typically, these processes involve multi-step processes that form a bridge between the refractory material surfaces and braze filler metals, solder metals, or conductive/protective metals used to construct circuits on refractory materials.

[0003] One example of a conventional metallization process relating to ceramic as the refractory body involves four major steps:

[0004] 1. applying the desired area of the refractory material, which is to be metallized (usually screened on), with a molybdenum or molybdenum/manganese paste and then air drying or drying in an infrared oven (e.g. at about 90C to about 100C for about 10 to about 15 minutes);

[0005] 2. firing the product of step 1 above in a controlled atmosphere (e.g. wet hydrogen) kiln at about 1200° C. to about 1500° C.;

[0006] 3. cleaning, etching and nickel plating either with electroless or electrolytic process the product of step 2 above, re-firing to sinter nickel into the molybdenum/manganese coating; and

[0007] 4. adding brazing filler metal in the form of wire, foil, ring, preform or powdered metal in between the metallized sections of the refractory body or bodies and then heating or firing to a temperature above the liquidus of the brazing filler metal in an oxygen free environment such as argon, dry hydrogen, ammonia gas, or vacuum.

[0008] For electronic currents application, there can be additional steps of cleaning and activating the nickel layer and over plating with gold, silver, copper, or tin.

[0009] Another composition and method used in metallizing is disclosed in U.S. Pat. No. 5,340,012, which is incorporated by reference herein.

SUMMARY OF THE INVENTION

[0010] The present invention relates to coating compositions and their employment in a metallization process that facilitates bonding of brazing filler metals to treated refractory surfaces, such as ceramics. The coating can be applied in preselected areas of the refractory surface to define the target area for brazing. It is believed that when compositions of the present invention are employed with brazing or soldering filler metals, strong bonds between non-metallic refractory bodies to non-metallic refractory bodies and non-metallic refractory bodies to ferrous and non-ferrous metal materials can be attained. On this aspect, as well as other aspects of the invention, the teachings of U.S. Pat. No. 5,340,012 are incorporated herein by reference.

[0011] In one embodiment, the present invention is a coating composition applied to a refractory material prior to brazing, the composition being comprised of a group IVB transition metal component selected from the group consisting of a group IVB transition metal, a hydride thereof, mixtures of group IVB metals and/or hydrides thereof, a binder material, and a fluid carrier. For example, the group IVB transition metal component may be a group IVB transition metal selected from among titanium, zirconium, hafnium, and thorium, hydrides of these group IVB transition metals, and mixtures of these group members. In one embodiment, the group IVB transition metal component is titanium, titanium hydride, or mixtures thereof.

[0012] Suitable binder materials used in the present invention include, but are not limited to hydrocarbon resins, modified hydrocarbon synthetic resins, gum rosins, tall oil rosins, wood rosins, modified rosin, acrylic polymer, natural and synthetic waxes, synthetic rubber like polyisobutylene, thermoplastic mixture of polybutylene and paraffin, water or solvent soluble cellulosic polymers, water soluble resins such as acrylic acid polymers, polyolefin and linear primary alcohols. Some gellant material like triblock, radial block and multiblock copolymers, optionally in conjunction with a diblock copolymer may also be employed. In one embodiment, the binder is a hydrocarbon resin. In another embodiment, it may be a hydrogenated hydrocarbon resin and styrene block copolymer.

[0013] The fluid carrier employed in the present invention may include, but is not limited to aliphatic hydrocarbon solvents, aromatic hydrocarbon solvents, alcohols, ketones, esters, glycol, glycol ether, glycerin, water. The fluid carrier of choice will depend on its compatibility with the binder of choice. Paraffinic hydrocarbons and hydro treated light petroleum distillate hydrocarbon solvents can be used herein.

[0014] In another embodiment, the coating composition includes about 10 to 90 weight percent of titanium or titanium hydride metal powder and 90 to 10 percent binder and fluid carrier having hydrogenated hydrocarbon resins (available from Hercules), styrene block copolymer and treated light petroleum distillate hydrocarbon fluid carrier (available from Penreco).

[0015] In one embodiment, the coating composition of the present invention, having an ink-like to paste-like consistency, can be applied though a screen. The consistency of the composition can be varied to achieve the desired shape and fineness of details. For example, the composition can be applied to the entire refractory surface by suitable coating techniques including, but not limited to, brushing, rolling and/or spraying. In another example, in selective applications for rim sealing/joining or in the formation of electrical/electronic circuit traces, a suitable mask can be used to control the coated treated areas.

[0016] Surface coating ceramics with this composition may allow more control of active metal concentration for interfacial compound development and subsequently joint strength. As a result, active metal depletion should be substantially reduced at ceramic surfaces and the deterioration of the braze material's physical properties attributable to excessive active metal concentrations (i.e. 8% or greater) should also be substantially reduced.

[0017] In another embodiment, screen-printing or stenciling with the composition, followed by a metallization/brazing process with suitable brazing filler metals may enable formation of circuit traces on refractory substrates.

[0018] In one example, the composition of the present invention is suited for use with oxide ceramics like alumina, zirconia, silica, etc. In addition, most nitrides, carbides, diamonds (synthetic or natural), graphite or carbon, and sapphire (or similar gemstones) can be joined without the need for prior metallizing procedures.

[0019] After drying the refractory material containing the coating of the present invention, the coated treated surfaces can be directly joined with any suitable brazing filler metal, employing conventional brazing/soldering processes and conventional equipment. For example, the coated treated surface can be brazed/metallized by heating in a substantially oxygen-free environment (e.g. argon, dry hydrogen and/or vacuum) to a temperature above the liquidus of the brazing filler metal or solder metal.

[0020] In one embodiment, the coating composition and corresponding process of the present invention can be used with commercially available brazing filler metals and in commercially available heating equipment.

[0021] In another embodiment of the present invention, the following metallization process can be used where ceramics are the refractory body:

[0022] 1. coating (e.g. by brushing or screening) a refractory surface (e.g. the ceramics surface) to be metallized with the composition of the present invention. The coating is then dried, either air dried at ambient conditions or at elevated temperatures of about 120° C. to about 150° C. for about 10-20 minutes in order to accelerate drying;

[0023] 2. applying a brazing filler metal in a preselected form (such as in the form of either a wire, foil, strip, shim, ring, preform or powdered metal) to the refractory body (e.g. ceramic body) and brazing at suitable substantially oxygen-free conditions (e.g. in vacuum, argon, or dry hydrogen atmosphere) at a temperature appropriate for the selected brazing filler metal.

[0024] It is believed that the drying step removes fluid carrier, leaving a coating of Group IVB transition metal component and binder on the refractory material. After applying the brazing filler metal material and undertaking the brazing step, the binder volatizes, removing binder. The inclusion of the group IVB transition metal component, as applied by the method which utilizes the composition of the present invention, is believed to improve the strength of the braze joint.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0025] The present invention is a coating composition applied to a refractory material prior to brazing, the composition being comprised of (1) a group IVB transition metal component selected from the group consisting of a group IVB transition metal, a hydride of a group IVB transition metal, and mixtures of these group members, (2) a binder material, and (3) a fluid carrier. For example, the group IVB transition metal component may be selected from among titanium, zirconium, hafnium, and thorium, or hydrides of these group IVB transition metals, and mixtures of these group members. In another embodiment, the group IVB metal component is titanium, or titanium hydride. In one embodiment, the group IVB metal component is titanium, zirconium, hydrides of titanium and zirconium, and mixtures thereof.

[0026] Suitable binder materials include, but are not limited to hydrocarbon resins, modified hydrocarbon synthetic resins, gum rosins, tall oil rosins, wood rosins, modified rosin, acrylic polymer, natural and synthetic waxes, synthetic rubber like polyisobutylene, thermoplastic mixture of polybutylene and paraffin, water or solvent soluble cellulosic polymers, water soluble resins such as acrylic acid polymers, polyolefin and linear primary alcohols. Some gellant material like triblock, radial block and multiblock copolymers, optionally in conjunction with a diblock copolymer. In one embodiment, the binder is a hydrocarbon resin. In yet another embodiment, the binder is hydrogenated hydrocarbon resin and styrene block copolymer.

[0027] A fluid carrier is employed in the composition. A non-exhaustive list of fluid carriers includes aliphatic hydrocarbon solvents, aromatic hydrocarbon solvents, alcohols, ketones, esters, glycol, glycol ether, glycerin, water. The fluid carrier of choice will depend on its compatibility with the binder of choice. The present invention uses both a paraffinic hydrocarbon fluid carrier and hydro treated light petroleum distillate hydrocarbon fluid carrier.

[0028] In another embodiment, the composition includes about 10 to 90 weight percent of group IVB transition metal component, in a powder form and about 90 to 10 percent binder and fluid carrier.

[0029] In another embodiment, the composition includes about 10 to 90 weight percent of titanium or titanium hydride metal powder and about 90 to 10 percent binder and fluid carrier. These compositions have the consistency suited for brushing, rolling, spraying or screening and stencilling the refractory surface.

[0030] As used herein, the term “binder” refers to a material or materials that, when present in the compositions of the present invention (1) facilitates the binding of the group IVB transition metal component to the refractory body, ferrous body, or non-ferrous body, or (2) helps maintain the group IVB transition metal component in a stable suspension within the fluid carrier, or (3) performs both of these functions.

[0031] As used herein, the term “fluid carrier” refers to a fluid material that serves as a carrying agent for the group IVB transition metal component and the binder. The fluid carrier is volatizable at temperatures lower than the temperatures at which brazing or soldering will be effected. In some instances, the carrier may be a solvent for at least one of the group IVB transition metal component and the binder.

[0032] Binders include, but are not limited to, hydrogenated hydrocarbon resins (available from Hercules under the trade name Regal Rez), di- and tri-block copolymers based on thermoplastic rubbers, such as styrene block copolymers (available from Penreco). Other suitable fluid carriers include, but are not limited to, isoparaffinic hydrocarbons available under the Isopar tradename from Exxon and hydrogenated light distillates available under the Conosol tradename from Penreco.

[0033] In another example, Versagel and Synergel, available from Penreco, are suited for use in the compositions of the present invention.

[0034] In one embodiment, after the composition is applied to the refractory surface, the fluid carrier is removed from the composition by air drying and/or heating so that a coating of the Group IVB transition metal component binder remain on the refractory surface. Subsequently, after the brazing filler metal is applied and brazing is undertaken, the binder, volatizes at temperatures below the brazing temperature leaving little or no residue and thus, does not interfere or contaminate the braze joint.

[0035] Examples of Suitable Compositions for the Present Invention

[0036] The following chart show examples of various coating compositions of the present invention. It is understood that these are merely exemplary of suitable materials that may be employed with the present invention.

Ingredient	Trade Name	Weight %
Active Metal-
Titanium powder,		10 to 90%
zirconium powder,
hafnium, thorium, or any
Group IVB elements, and
hydrides of these elements.
Mixtures of above
elements are also suitable.
Binder-
Di or tri block copolymers	Available from the	1-50%
based on thermo-plastic	Penreco Division of
rubbers such as styrene	Pennzoil
block copolymers.
Fluid carrier-
Isoparaffinic	Isopar G	15-50%
Hydrocarbon
Fluid carrier-
Hydrogenated light	Conosol 145	15-50%
distillate
Binder-
Modified hydrocarbon	Regalrez 1126 Resin	1-10%
synthetic resins

[0037] In another embodiment, active metals from the Group UVB including combinations of elements such as titanium and zirconium are used to form a eutectic with a lower liquidus temperature or to meet other special requirements. In yet another embodiment, the particle size of the group IVB transition metal powder can be a sufficient size to go through a 325 mesh screen (i.e., −325) although other mesh sizes may be effective.

[0038] In a further embodiment, the type and/or amount of fluid carrier in the composition of the present invention is selected so as to adjust the viscosity of the composition of the present invention. As shown in the chart above, one type of fluid carrier or a combination of two or more fluid carriers may be used in the composition of the present invention. For example, an isoparaffinic hydrocarbon may be used alone or combined with another fluid carrier such as hydrogenated light distillate fluid carrier. In yet another example, a plurality of the fluid carriers, which are disclosed in the chart, may be combined at any appropriate ratio so as to result in the desired viscosity and/or sufficient carrier properties of the composition.

[0039] In one embodiment, titanium or titanium hydride metal powder, having a mesh size of about ˜325 is mixed with binder. A mixture may comprise about 35 weight percent titanium and 65 weight percent binder, having hydrogenated hydrocarbon resins (Hercules), and/or styrene block copolymer and treated light petroleum distillate hydrocarbon fluid carrier (Penreco). This mixture has a consistency for brushing, rolling or spraying the refractory surface.

[0040] In one example, the mixtures are coated on refractory body in an amount sufficient to apply the group IVB transition metal in a percent range that is between about 2 percent and about 8 weight percent of the combined weight of the braze alloy and group IVB transition metal, with about 4 to 6 percent group IVB transition metal being well suited for this application.

[0041] In another embodiment, titanium or titanium hydride metal powder having a mesh size of about 325 mesh or smaller (44 micron or smaller) is mixed with the binder. A mixture may comprise about 65% weight titanium and 35% weight percent binder having hydrogenated hydrocarbon resins (Hercules), styrene block copolymer and treated petroleum distillate hydrocarbon fluid carrier (Penreco). This mixture has a consistency for screening or stenciling for coating refractory body.

[0042] The present invention is used in conjunction with one or more brazing filler metals. A brazing filler metal is a metal alloy that is used to join refractory material. Suitable brazing filler material include, but are not limited to, conventional braze alloy such as a silver-copper eutectic composition (e.g. 72% silver and 28% copper), a silver-copper alloys include from about 50 to 85 weight percent silver, and from about 15 to 50 weight percent copper, alloys of silver-copper-nickel, or silver-copper-indium (e.g. silver-copper-nickel alloys comprising from about 50 to 85 weight percent silver, from 15 to 50 weight percent copper and from about 0.2 to 2.5 weight percent nickel, while the silver-copper-indium alloys comprising from about 50 to 70 weight percent silver, from about 15 to 35 weight percent copper, and from about 10 to 20 weight percent indium), or the eutectic alloys of these metals.

[0043] In another embodiment, a wide range of other conventional brazing filler alloys can be included when used for joining similar or dissimilar base materials or components. For example, alloys containing copper, nickel, tin, silver, gold, molybdenum, cobalt, or palladium, along with additives such as boron or the like. Other examples of brazing filler material include nickel base materials and gold-nickel alloys and semi-amorphous materials.

[0044] The brazing filler material used with the present invention can be of any suitable shape and form. For example, the brazing filler material can be in the form of wire, foil, strip, shim, ring, preform or powdered metal.

[0045] The composition of the present invention is suited for use with oxide ceramics like alumina, zirconia, silica, etc. In addition, most nitrides, carbides, diamonds (synthetic or natural), graphite or carbon, and sapphire (or similar gemstones) can be joined without the need for prior metallizing procedures.

EXAMPLE

[0046] A composition having an ink-like consistency has the following formulation:

[0047] All percentages are by weight:

[0048] Titanium powder—35%

[0049] Binder: (Regal Rez)—6.5%

[0050] Di- or tri-block copolymers based on thermoplastic rubbers such as styrene block

[0051] copolymers in a hydrogenated light hydrocarbon distillate—16.25%

[0052] Fluid carrier (Isopar) 42.25%

[0053] A composition with a paste-like consistency, suited for stenciling and screening, had the following formulation:

[0054] All percentages are by weight:

[0055] Titanium—55%

[0056] Isopar fluid carrier—5%

[0057] Binder (Regal Rez)—19.4%

[0058] Di- or tri-block copolymers based on thermoplastic rubbers such as styrene block

[0059] copolymers in a hydrogenated light hydrocarbon distillate—28.6%

[0060] The Regal Rez is dissolved into the fluid carrier or di- or tri-block copolymers based on thermoplastic rubbers such as styrene block copolymers in a hydrogenated light hydrocarbon distillate using any standard mixing process. Heat can be used to expedite the process, but it is not necessary. Titanium is added to the above mixture to form a smooth, homogeneous mixture.

Claims

1. A coating composition applied to a refractory material, the coating composition comprised of: (a) a group IVB transition metal component selected from the group consisting of a group IVB transition metal, a group IVB transition metal hydride, and mixtures thereof; (b) a binder; and (c) a fluid carrier.

2. The coating composition of claim 1 wherein the group IVB transition metal, or hydride thereof, is selected from the group consisting of titanium, zirconium, hafnium, thorium, and mixtures thereof.

3. The coating composition of claim 1 wherein the binder material is selected from the group consisting of hydrocarbon resins, modified hydrocarbon synthetic resins, gum rosins, tall oil rosins, wood rosins, modified rosin, acrylic polymer, natural and synthetic waxes, synthetic rubber like polyisobutylene, thermoplastic mixture of polybutylene and paraffin, water or solvent soluble cellulosic polymers, water soluble resins such as acrylic acid polymers, polyolefin and linear primary alcohols, gellant materials including triblock, radial block and multiblock copolymers, optionally in conjunction with a diblock copolymer.

4. The coating composition of claim 1 wherein the binder material is comprised of hydrogenated hydrocarbon resin and styrene block copolymer.

5. The coating composition of claim 1 comprised of a group IVB transition metal component selected from the group consisting of about 10 to 90 weight percent of titanium and titanium hydride metal powder and 90 to 10 weight percent binder having hydrogenated hydrocarbon resins and styrene block copolymers.

6. The coating composition of claim 1 wherein the fluid carrier is selected from the group consisting of aliphatic hydrocarbon solvents, aromatic hydrocarbon solvents, alcohols, ketones, esters, glycol, glycol ether, glycerin, water, paraffinic hydrocarbon solvents, hydro treated light petroleum distillate hydrocarbon solvents, and mixtures thereof.

7. The coating composition of claim 1 wherein the group IVB transition metal component has a mesh size of about −325.

8. A method of coating a refractory surface comprised of the step of applying the coating composition of claim 1 to the surface of a refractory material by brushing, spraying or rolling though a masking stencil.

9. A method of coating a refractory surface comprised of the step of applying the coating composition of claim 1 to the surface though a masking stencil.

10. The method of claim 1 wherein the refractory surface is an oxide ceramic selected from the group consisting of alumina, zirconia, silica, nitrides, carbides, diamonds, graphite, carbon, and sapphire.

11. A method for metallizing a refractory material comprised of the steps of: (a) coating a refractory surface with the composition of claim 1; (b) drying the composition; (c) applying a brazing filler metal in a preselected form to the refractory material; and (d) brazing at preselected conditions at a temperature appropriate for the selected brazing filler metal.

12. The method of claim 11 wherein the composition is dried at ambient conditions.

13. The method of claim 11 wherein the composition is dried at elevated temperatures of about 120 to about 150° C. for 10-20 minutes.

14. The method of claim 11 wherein the brazing filler metal is in the form of one of a wire, foil, strip, shim, ring, preform or powdered metal.

15. The method of claim 11 wherein the brazing step is effected in an oxygen-free environment selected from the group consisting of vacuum, argon, and dry hydrogen.

16. Coated and joined refractory bodies comprised of at least two refractory bodies coated with the composition of claim 1 and joined together with a brazing filler metal alloy.

17. The coated and joined refractory bodies of claim 16 wherein the group IVB transition metal is present in an amount of between about 2 weight percent to about 8 weight percent of the combined weight of the group IVB transition metal and braze filler metal alloy.

18. Coated and joined refractory bodies comprised of a refractory body joined to a ferrous or non-ferrous metal body, wherein the bodies are coated with the composition of claim 1 and joined together with a brazing filler metal alloy.

19. The coated and joined refractory bodies of claim 18 wherein the group IVB transition metal is present in an amount of between about 2 weight percent to about 8 weight percent of the combined weight of the group IVB transition metal and braze filler metal alloy.