WO2009049427A1

WO2009049427A1 - Open cell, porous material, and a method of, and mixture for, making same

Info

Publication number: WO2009049427A1
Application number: PCT/CA2008/001863
Authority: WO
Inventors: Dominic Pilon; Alain Harvey; Mario Patry
Original assignee: Metafoam Technologies Inc.
Priority date: 2007-10-19
Filing date: 2008-10-20
Publication date: 2009-04-23
Also published as: EP2214851A1; CA2702997A1; WO2009049397A1; KR20100098507A; CN101903125A

Abstract

The porous material of the present invention is produced toy heating a dry powder mixture, containing mainly an organic solid hinder and inorgnnic particles and containing no foaming agent. The mixture is heated to melt the organic binder. The resulting solid structure comprising inorganic particles embedded in an organic binder is then heated to eliminate the organic binder, and finally healed again Io melallurgically bond the remaining inorganic tri-dimensional network into a rigid structure having interconnected pυrosiiy.

Description

OPEN (JELL. PUKUUS MATERIAL, AND A METHOD OF, AND MIXTlIRF. FOR, MAKING SAME

CKOSS RF.FERF.NCr. TO RELATED APPLICATIONS The present application claims the benefit of priority to International Patent Application

No. PCT/CA2007/001874 filed October 19, 2007 with die Canadian Receiving Office entitled "Heat Management Devices Using Inorganic foam" (hereinafter "the "874 application"). (The '874 application is incorporated by reference herein.) HELD OF THE INVENTION

The present invention relates to porous materials, methods of making porous materials, ami mixtures for making porous materials.

BACKOROLWD OF THE TMVFNTTON Porous metal or ceramic materials are currently used for the fabrication of devices such as filters, heat exchangers, sound absorbent, electrochemical cathodes, fuel cells, catary.it supports, fluid treatment units, lightweight structures and biυmaterials. The structures (open/closed porosity, pore size distribution and shape, density) and properties (permeability, thermal, electrochemical and mechanical properties) required greatly depend on the application. Closed porosity is generally soυubt for lightweight structure while open pυrosily is particularly sought when surface exchange is involved or when permeability or pore connectivity is required.

Different approaches have been proposed for the fabrication of such porous materials.

Reviews of manufacturing methods and characterization of porous metal and ceramic materials are given in United States Patent No. 6,660,224 (hereinafter "the '224 patent") and the documents referred k> therein. (The '224 patent and all the documents referred to therein are incorporated herein by reference.)

In particular, the invention described in Ae '224 patent is a porous material thai is produced by heating a dry powder mixture containing mainly an organic solid binder and inorganic particles. The mixture is foamed while the organic' binder is melted. Foaming comes from a foaming agent in the powder mixture. The resulting solid foamed structure that comprises the inorganic particles embedded in the organic binder is next heated to cure and then eliminate Uic organic binder and final Iy io sinter the remaining inorganic three-dimensional network into a rigid structure having interconnected porosity.

As is more fully described in the '874 application, some embodiments of the porous material described in the '224 patent arc particularly well suited for use in working-liqiiid-phasc- change heat transfer devices, such as heat pipes and vapor chambers. Notwithstanding ιhι- atlvaneerncni prcscrtiwi hy ilic use of such material* m such devices, there are some executions of working-liquid-phase-ehange heat transfer devices that lequiie a porous material with an even greater wicking capacity and smaller pore size than is possible to obtain hy lollnwiπg the methods described in the '224 patent. No other suitable method exists for producing such materials.

SUMMARY OF THE INVENTION

It is an object of the present invention to ameliorate at least some of the inconvenience.- prescni I" 'he prior art. Tt is also an object of the present invention to provide an open cell porous material, and a method of, and mixture for, making same, where the material is suitable for use in certain workiπg-liquid-phase-chauge heal transfer devices.

Thus, in one aspect, as embodied ftπd broadly described herein, the invention provides a method for making an open cell porous structure, comprising: (a) Providing a dry flowablc powder mixture including (i) a first predetermined amount of inorganic particles having a firsi melting temperature, (ii) a second predetermined amount of a binding agent having a decomposition temperature, the decomposition temperature being lower than the first melting temperature, and (iii) an absence of foaming agent (in. no forming agent), (b) Heating the mixture to a temperature lower than the decomposition temperature at least to cure the binding agent to obtain a solid structure (if the binder is not a liquid ftr a gel it will first melt and surround the inorganic particles before being cured), (c) Heating the solid structure to the decomposition temperature to decompose the binding agent and obtain a non-mctallurgically- bonded open cell porous strucluic. '(A inclallurgically-hondcd material is one that is held together by direct metal atom to metal atom bonds. In the present step after the binder is heated Io lhc decomposition temperature, the metal is oxidized and it is the oxygen atoms that are interconnecting the metal atoms and bonding the structure together.) It is highly preferred that the binder be cleanly decomposed, i.e. that it leaves no residue behind after its decomposition, (d) Healing the uoπ-ineiallurgically-bonded open cell porous structure to a temperature lower than the first melting temperature Io mclalluryieally bond the inorganic particles and obtain a solid metallurgically bonded open cell porous structure. It is preferred that healing the non- metallurgically-bondcd open cell porous slruekire Io a temperature lower than the first melting temperature lυ meiallurgieally bond the inorganic particles and obtain a solid metallurgically bonded open cell porous structure comprises heating the πe-π-metallurgically-bonded open cell porous structure to a temperature lower than the first melting temperature tu sinter the inorganic particles and obtain a solid sintered open cell porous structure. Sintering is usually accomplished by healing the structure to a temperature between 70% and 90% of the melting temperature of the metal to be sintered- Sintering in most esses will not eliminate the oxygen atoms bul will create direct metal atom to metal atom bonds. The present inventors have realized that in certain situations, contrary to what is lauβhl in the '224. patent, it is possihle to carry out a method similar to that described in the '224 patent, without having any foaming agent present Ln the mixture. It had been thought that if no foaming agent were present in the mixture there would not have been enough space for the gas produced by the decomposition of llie binder agent to exit the material being formed. Thus, lhe binder agent decomposition gases would build up wrihin the material and damage or destroy the malerinl owing to pressure and/or combustion of the gases.

Surprisingly, the present inventors have observed than in some situations, particularly where the material to be made is of reduced thickness (e.g. less than 2 mm), damage or destruction of material does not occur notwithstanding the fact that there is no foaming agent present in lhc mixtuie from which die material is being produced. The absolute Iimil for any particular material before damage or destruction occurs will vary depending on the shape of the material, tins composition of the inorganic particles from which the material is being produced, and the nature and type of binding agent being used. Simple visual inspection of the material will allow one to determine whether the limit has been passed. Owing to the absence of foaming agent, the voids present in materials of the '224 patent that are created by the foaming agent are not present in materials of the present invention. Therefore, the capillary radius of capillaries of materials of the present invention is smaller (i.e. in the order of between 50 100 microns) versus those in the materials of (he '224 patent (i.e. greater than 100 microns); the permeability of materials of the present invention is lower (i.e. in the order of between 9.4xlO^"12 m² to 1.3x10^"" m² than that of the materials of the '224 patent (Le, higher than 1.3x 10^"" m²). Materials of the present invention thus have a significantly greater wicking strength and an equivalent or inferior pumping speed than materials of the '224 patent. Materials of the present invention can thus he used in applications («._'.#. certain executions of wnrking-liquid-phase-chaπge heat transfer devices) for which materials of lhe ^:224 patent are not appropriate.

Furthermore, materials of the present invention are dillerent lhan eonventional sintered powder materials. The capillary radius of capillaries of materials of the present invention is higher (i.e. in the order of between SO 100 microns) versus those in conventional sintered powder materials (i.e. lower than 50 microns); the permeability of materials of the present invention is higher (i.e. in the order of between 9.'4χ.lQ^*12 m² to J .3x10 " ttt² l.lιaπ that of

Cuπvcπlioiiat sintered powder materials (i.e. lower lhan 9.4x.lO'¹² m^J). Materials of the present invention thus have a tower wicking strength and significantly higher pumping speed than conventional sintered powder materials. Materials of the present invention can thus be used in applications (e g. certain executions of working-liquid-phase-change heat transfer devices) for which conventional sintered powder materials are not appropriate.

Preferably, the first predetermined amount of inorganic particles is between about U) wt % to about 90 wt % inclusive of a total weight of the mixture. More preferably, the first predetermined ainouni is between about 40 wi % ID about 90 wt % inclusive of the total weight of the mixture. Still more preferably, the first predetermined amount is between about 55 wt % to about 80 wt % inclusive. Most preferably it is between 60 wt % to about 75 wl % inclusive. The first predetermined amount is selectable by persons skilled in the art according to the final use of the material to be made. For instance, for applications where a high thermal conductivity is required, it is likely thai lirst predetermined amount will be at the relatively high end of the ranges disclosed (e.g. about 75 wl % or highet). For applications where low density is required, it likely the first predetermined amount will be at the relatively low end of llκ ranges disclosed (e.g. about 60 wt % or lower).

It is preferred that the second predetermined amount of binder agent be between πbout 10 wl % to about 90 wt % inclusive of the total wciAbl of the mixture. More preferably, the second predetermined amount is between about 20 wl % to about 35 wl % inclusive. In mixtures where only the inorganic particles and the binding agent arc present (e.g. metallic particles and a thermoset binding agent), the wt % of the binding agent will he directly related to the wt % of the inorganic particles. In other mixtures (e.g. metallic particles, a thermoplaslic resin, and a curing agent), the binding agent will likely be the vast majority of the wt % of the mixture that is nut inorganic particles.

Preferably, the inorganic particles consist essentially of iioii-rnelallic particles (preferably ceramic particles), metallic particles, or combinations thereof. The selection will depend on the final use to which the material being made is put, and lhus lhe required characteristics thereof (e.g. thermal conductivity, electrical conductivity, wicking capacity, absorptive capacity, etc.). Where the mixture contains metallic particle?, it is preferred (hat the particles be at least one of metal particles and metal alloy particles. In some such cases it is preferred that the metallic particles be metallic particles of at least one transition metal, and preferably at least one transition metal selected from the group consisting of scandium, titanium, vanadium, chromium, manganese, iron, coball, nickel, copper, ytlrium, zirconium, niobium, molybdenum, ruthenium, rhodium, palladium, silver, hafnium, tantalum, tungsten, rhenium, osmium, indium, platinum, and gold. More preferably, the metallic particles arc ai least one selected from the group consisting of copper, nickel, iron, titanium, copper-based alloy particles, nickel-based alloy particles, iron-based alloy particles, and titanium-based alloy particles. Most preferably the metallic particles are ai least one. uf copper and copper-based alloy particles. These materials are preferred given their ability to be (relatively) easily sintered.

Tt is also preferred that for some applications the inorganic- particles consist essentially of coated particles. The particles may be coated hy chemical reaction {e.g. an aluminum particle will generally oxidize in an oxidizing environment to produce an aluminum particle with an aluminum oxide coating {i.e. outer layer)) or by mechanical deposition («.#. a copper particle mechanic-ally coated with a silver-based brazing agent)

Tt is also preferred that the binding agent be a thcπnoscl resin or a thermoplastic polymer. Suitable resins and polymers are well known in the art. La such cases, it is preferred that the binding agent be blended with fhe other components) of the mixture by dry mixing or milling. Where the binding agent is a thermoplastic polymer, it is preferred that the binding agent be cured with the aid of a curing agent, or alternatively by an irradiation cross-linking treatment, or a. liμhl-expυsure cross-linking treatment

It is also preferred that the mixture farther include at least one additional agent adapted to minimise segregation and dusting and to improve the flownbility of the mixture. Such agents are well known in the art. Λn example would be a fine silica power that is added to the mixture in a very small amount {e.g. less than 0.01 wt %) where the mixture is to be injection molded or extrusion molded.

Tl is picferrcd lhat the mixture be subject to successive increases of temperature during execution of (b), (c), and (d) set forth above. For methods carried out in a continuous process, it is preferred that the temperature be increased in a stepwise manner.

It is preferred that (a), (b), (c), and (d) set forth above he carried one of continuously, ϊcquunlially, partially continuously and partially sequentially.

It is also preferred that pressure be applied tυ the mixture at least one of k-lbre and during the heating thereof in (b), (c) or (d) as set ibrth above. Pressure can be used for various purposes depending on at which point in the process the preςsure is being applied. Kor example, pressure in the order of 206 kPa to 278 kPa (30 to 40 psi), applied via an hydraulic press exerting force on the mold containing the mixture, can be used before (b) in order to ensure a smooth finish to the final materia! to be made As another example, pressure in the ordet of 7 kPa ( 1 psi), applied via the application of a perforated flat plate, cau be applied during (c) to ensure that the final material will be flat and not warp. As another example, pressure in the order 890 kPa

(129 psi), -applied during (d) via the application of force to the mold in which the triatrial is being made, can be applied to ensure that bonding of the material to a substrate (e g. a copper plate occurs (see below). As a linal example, pressure can also be used during extrusion or injection molding, if these arc pail of the process. The selection of lhe amount of pressure, how ii is applied, and when it is applied, is within the understanding αl^'lhosc skilled in the art.

It is also preferred that the method further comprise shaping the mixture, preferably before it is heated. Tn such cases it is preferred that the shaping be carried out via at least one of molding, deposition, lamination, and CXIΓUMUII. Each of these processes is well known in the art. In addition, at any one of various stages in the process, the intermediate or final structure can be machined through (he use of a numhci of conventional machining l.cdmk|iιes.

In some cases, it is also preferred that the method further comprise providing a substrate, and that the mixture be disposed on the substrate prior to (d). The presence of and selection of a substrate will depend on the application to which the material to he made is being put. For example, the substrate may be a cupper plulc where the material will be used in a vapor chamber. The copper plate provides good thermal conductive properties as well as mechanical support for the material, enabling it Io helter serve its intended function irt lhe vapor chamber.

It is also preferred that the mixtures further comprise at least one spacing ayent. As is well known in the art, a spacing agent is added to mixtures to occupy Space during lhe formation of the materials, which will create a void in the material when the spacing agent is removed. An example is a salt, that is not affected by the application of heat during the manufacturing process, but that can be removed Horn die final material by being dissolved in uπ appropriate liquid (i.e. by leaching), usually water. In the eonlexl of lhe present invention, it is preferred that the at least one spacing agent be a scaffold. It is also preferred thai ihc ai leasl one spacing agent be removed by at least one of thermal decomposition and leaching.

In some instances i( is preferred that the mixture further comprise at least one brazing agent to metallurgical^ bond the inorganic particles, as is described in international patent application I¹CT/CA2OO7/OOO679 filed April 23, 2007 entitled "Open Cell Porous Material and Method for Producing Same" published as WO 2007/121575 Al on November 1, 2007 (which is incorporated herein by reference). Brazing is usually used in place of sintering (as opposed to in addition U>). A bra/ing agent creates a solid solder-like bond hetween adjacent particles which results in n material having generally improved mechanical properties. Typically, brazing is achieved at a tower temperature and in a shorter time than a conventional sintering step, and can thus lead to reduced manufacturing time and reduced energy costs. Many conventional brazing agents exist Typically brazing agents are silver, copper or eadmium-based powders.

Further, ϊτι additional aspects, as embodied and broadly described herein, the invention, provides an open cell porous structure made according to the methods described hereinabove, as well as to a mixture as described above used therein.

Embodiments of the present invention each have at least one of the above-mentioned objects and/or aspects, but do not necessarily have all of them. It should he understood that some aspects oi^" the present invention that have resulted from attempting to attain the above- mentioned objects may not satisfy these objects and/or may satisfy other objects not specifically recited herein.

DETAILED DESCRIPTION

The porous material according to (he present invention is produced from a dry flownble powder mixture comprising a base material and a binding agent, eaeh provided in predetermined amounts, and having an absence ftf tf.e. no) foaming agent. The base material includes inorganic particles having a first melting temperature, the binding agent is preferably, bυ( not exclusively, an organic binder having a decomposition temperature lower than the first melting temperature and having clean bum out characteristics. All of these materials arc readily available from appropriate commercial suppliers. As it will be readily understood, the exact amount of each constituent of the mixture is determined, prior to the execution of the method of the present invention, based on the physical and chemical properties of the inorganic particles and of the binding agent, and based on the desired properties of the finished open cell porous structure. Consequently, the exact composition of the mixture will vary according to the nature of the base material and of the binding agent.

Tlie inorganic particles comprise metallic particles, metallic alloy particles, ceramic particles, coated particles and/or a combination thereof. In the case of metallic and metallic alloy particles, the metal or metals are preferably transition metals (e.g. copper, nickel, iron) as defined by the periodic table of elements. The inorganic particles will have a first melting temperature. The inorganic particle content may be between about 10 to about 90 wt % inclusive of the total weight of the mixture (preferably between about 40 Io about 90 wt % inclusive, more preferably between about 55 wt % to 80 wt % inclusive, still more preferably between about 60 wt % to 75 wt % inclusive). The exact amount of the Inorganic particles and the choice thereof will be determined by the skilled addressee depending on the requirements of the application for which the open cell porous material is being manufactured.

The hinder used in the mixture is preferably an organic binder provided in a dry llowable powdered form and with clean bum out characteristics. The binder can be a thermoplastic polymer, a theπnoset resin and/or a combination thereof. The binder can also he an inorgnnic binder, a synthetic binder or a mixture of, organic and/or inorganic and/or synthetic binders. The binder may be provided in solid form (preferably powder particles), in semi-solid funn, HI liquid form, in gel form or in semi-liquid form. The binder has a decomposition temperature lower than the first melting temperature of the inorganic particles in order to prevent premature melting of the inorganic panicles during the decomposition step. Though the binder content in the mixture may vary from about 10 to about 90 wt % of (he (olal weight of the mixture, the exact amount thereof will be determined by the skilled addressee depending on the nature of the inorganic puilielvs and on the requirements of the npplication for which the open cell porous material is being manufactured. Most preferably, the binder should no decomposition products in the porous structure. However, some residues can be accepted if they do not negatively affect the final properties of the final product or if they improve some of Hs properties.

Optionally, the mixture may comprise a curing agent {e.g. a cross-linking) agent to induce faster Curing of the hinder during or after the curing step and improve lhc mechanical strength of the cured structure before the decomposition of the binder. Optionally, the mixture may also comprise other additives such as a lubricant to ease shaping, molding or demolding, or flowing agents to improve the flowability of the powder when all the constituents arc in powdered form.

The organic binder can be blended with the other constituent using various techniques such as, but not limited to, mixing, milling, mixing the binder in suspension or in solution in a liquid, blending the binder in molten, liquid, gel or semi-liquid form with the inorganic particles and the other additives. Whichever mixing technique is used, the resulting product should be a curable mixture.

In oΛcr variants, a spacing agent may be added to the mixture to provide additional porosity and to improve pore connect ivjiy. A spacing agent is removed after curing to leave voids in the structure after decomposition of the binder or after sintering. The spacing agent can be removed by thermal decomposition after curing or by leaching after curing, decomposition of lhc binder Or sintering. The spacing agcvil can be parlidcs or a scaffold. When particles are used, they arc admixed with the rest of the mixture. In one non limitative example, the spacing agent can be polymeric particles admixed with the mixture. In this ς;asc, the spacing agent concentration can vary from about 5 to 50 wt % inclusively, but preferably between 10 and 30 wt % inclusively. When a scaffold is used, its porous structure is filled with the mixture used to produce the porous material. The scaffold is, tor example, a polymeric foam, that can be filled with the mixture and removed by theππal decomposition or by leaching, It is also contemplated to add additional binder in amount varying between 0.05 wt % to

5 wt %, but preferably between 0.05 wt % to 1 wt %, in the mixture. This adUniunal binder may be generally used to bind different constituents of the mixture together in such n. wny thnt the final product is less prone to segregation and/or dusting. The additional binder may be added at different steps of the mixing procedure, cither before mixing the inorganic particles with the binder, after the binder addition, after the lubricant addition, after the flowing agent addition or after the addition of any combination υflhosc constituents. Whichever mixing technique is used, the resulting product should be a curable mixture.

Tlic resulting mixture may be shaped using methods such as molding, deposition, lamination or extrusion. The product is then heated at a moderate temperature to melt the binder, if the latter is not already in liquid, gel or icπii-ljquid form, and to initiate the curing of the mixture, Optionally, pressure may be applied Io the mixture before or during heating the mix lure.

The porosity and structure of the resulting open cell porous material will depend on the particle size, shape, density and content of the inorganic particles; the content and viscosity of the hinder, as well as the processing conditions. However, in most cases the material will haw two pore groups, namely a first pore group and a second pore group. The first pore group has an average pore UM in the range from about 20μm to about 200μrπ, preferably in the range from about 40μm to aboul ISOμiπ and most prvfciahly from about 60μm to about lOOμm. In each case the standard deviation is in the range from about lOμm to about IGOμm. The first pore size group constitutes from about 50% to about 80% of the void volume of the metallic porous structure. The second pore group has an average pore size in the range from about 25Unni to about 15μm, preferably in the range from about SQOiim to about 15μm and most preferably from about 500αiϊι to about lOum. Iu each case the standard deviation is in the range from aboul 200nm to about lϋμm. The second pore size group constitutes from about 20% to about 50% of the void volume of the metallic porous structure. The capillary radius will be an average of the two pυre groups, thus on average, relatively low because of the second pore group. The first pore group will lead to a high permeability. Hence the structure provides a high permeability and low capillary radius leading to a high pumping speed. K) Materials can be cured in a mold Io provide three-dimensional porous stiiictuies

The mixture can be cured on or in a substrate to ptoducc a coating or to produce composiU; structures. Curing can be done ll>r example on a plate, on a rod, in or outside a tube or cylinder, in or on other porous structure (mcsli, beads, (bam for example) or any other substrate, The material can be machined after curing, decomposition oi^'lhc binder or sintering. hυnctionally grnded materials can be produced using mixtures with variable composition. Graded layered structures can be produced for example by deposing layers of mixtures with different composition. Functionally jζradetl materials can also be produced by controlling the thermal gradient during curing in order to control material curing and pore t>uc distribution. Optionally, the mechanical strength of the cured structure may be further increased, before decomposition of the binder and Sintering, by using externally assisted eruss-linking techniques such as irradiation or light exposure.

After curing and optionally cross-linking, the cured mixture is treated at a suttϊeiently high temperature to decompose the binder. The atmosphere (with or without the presence of oxygen), duration and leinperauue of the thetmal treatment should preferably allow a clean decomposition of the binder. Hinder decomposition should preferably not deteriorate the three- dimensional structure of the Cured mixture. If gas pressure generated during binder decomposition is too great, cracking in or destruction of the still unmetallurgically-boπdcd structure may occur. Oxidizing or reducing conditions during the thermal treatments may be chosen to optimize binder decomposition. After decomposition, the cured structure is composed of open cell metal (usually oxidized metal), and/or metal alloy (usually oxidized metal alloy), and/or ceramic material particles.

Sintering (metallurgical bonding) is done after the decomposition of (he binder to create bonds between the inorganic particles of the cured mixture. Sintering conditions (temperature, time and atmosphere) should be such that the inorganic particles do not melt to create the bond between them; conditions should be such that the material particles adhere to each other through a bond mainly created by solid-state diffusion to form a strong metallurgical joint between them. Effective solid-state diffusion occurs between material panicles when they are heated, for a certain lime, at temperatures slightly under the inching temperature of the material particles. Sintering is generally done in reducing atmosphere for metal particles to avoid the formation of surface oxides on the structure and to reduce lhe oxides that were present prior to sinteruig.

Mechanical strength may be adjusted for the application. The choice, size, nature and/oι physical state of the inorganic particles and of the binder content will have a .substantial U influence of the physical properties (e.g. mechanical strength) of the produced open cell porous material.

Additional treatment can be done on the porous material produced. The internal surface of the structure can be modified for example by heat treatment, chemical treatment or deposition of coatings using various state of the art deposition techniques. The external surfaces of the structure can be modified for example by a stumping, etching, embossing, or grooving leelumjuc and by state of the art surface coating techniques. The structure.- tan be integrated in other products and/or to other structures using different state of the art techniques such as diffusion bonding, press fitting, welding, brazing, sintering or gluing. The invention is not so limited.

H>

Rxamnle 1

In a first specific example, n metallic open cell porous structure, with copper (Cn) as the base material, was produced from a mixture having the formulation presented the table below.

TABLE 1

15

The different constituents were dry-mixed together until the mixture became humυμenwus. After mixing, the mixture was poured into a mould and cured at 110"C in air for 2 hours. After curing, the material was submitted for the decomposition of the binding agent in a furnace at 650⁰C for 4 hours in u dry air stream. Finally, the material was sintered in a

20 75%Ar/25%H₂ atmosphere for 2 hours at HK)O⁰C (The melting temperature of copper is 1080-C)

Example 2

In a second specific example, a metallic open cell porous structure, with nickel (Ni) as 5 the base materia), was produced from a mixture having the formulation presented the table below.

O TΛBLC 2

The different constituents were dry-mixed together until the mixture hecame homogeneous. After mixing, the mixture was poured into a mould and cured at I IO^βC in air for

2 hours. After curing, the material was submitted for rhc decomposition of the binding agem in a furnace at 650⁰C for 4 hows in a dry air stream. Finally, the material was sintered in A

75%Ar/25%Tl2 atmosphere for 2 hour at 1300⁰C.

Kxample 3

In u third specific example, u metallic open cell porous structure, with iron (Fe) as the base material, was produced from a mixture liaving the formulation presented the table below.

TABLE 3

The different constituents were dry-mixed together until the mixture became homogeneous. After mixing, the mixture was poured into a mould and cured at 1 H)⁰C in air for 2 hours. Alter curing, the material was submitted for the decomposition of the binding agent in a furnace at 6.1O⁰C 1'or 4 hours in a dry air stream. Finally, thy material was sintered in a 75%Ar/25%TI₂ atmosphere for 2 hours at 1400⁰C.

Example 4 lii a fourth specific example, a metallic open cell porous structure, with copper (Cu) as the base material, was produced from a mixture having the formulation presented in the table below.

The different constituents were dry-mixed together until the mixture became homogeneous. AΛcr πiixmy, ihu mixture was poured imo a mould and cured at 110"C in air for 2 hours. After curing, the material was submitted for the decomposition of the binding agent in a furnace at 6S0"C for 4 hours in a dry air stream. Finally, lhe material was brazed in a 75%Ar/25%H> atmosphere for I hour at 785'C.

Although various embodiments have been illustrated, this was lor the purpose of describing, but not limiting, the invention Various modifications will become apparent to those skilled in the art and arc within the scope of this invention, which is defined mote particularly by the rtUaehed claims.

Claims

1. A method for making an open cell porous structure, comprising: a) providing a dry flowable powder mixture including i) a first predetermined amount of inorganic particles having a first melting temperature, ii) a second predetermined amount of a binding agent having a decomposition temperature, the decomposition temperature being lower than the first melting temperature, and i i i) an absence of foam i ng agent; b) heating the mixture to a temperature lower than the decomposition temperature at least to cure the binding agent to obtain a solid structure; and c) heating the solid structure to at least the decomposition temperature to decompose the binding agent and to obtain a non-metallurgically-bυnded open cell porous sirυckire; and d) heating the non-metallurgically-bonded open cell porous structure to a temperature lower than the first melting temperature sufficient to mctalliirgioally bond the inorganic particles to obtain Ά sob^'d metallurgical ly-bonded open cell porous slructurv.

2. A method for making an open cell porous structure as claimed in claim 1, wherein ihc first predetermined amount is between about 10 wt % to about 90 wt % inclusive of a total weight of the mixiurc.

J. Λ method for making an open cell porous structure as claimed in claim 2, wherein the first predetermined amount is between about 55 vvt % to about 80 wt % inclusive of the total weight of the mixture.

4. A method for making an open cell porous structure as claimed in claim 3, wherein the first predetermined amount is between about 60 wt % tn about 75 wt % inclusive of the total weight of the mixture.

5. A method for making an open cell porous structure as claimed in claim 3, wheiein the second predetermined amount is between about 20 wt % to about 35 wt % inclusive of the tolal weight of the mixture.

6. Λ method for making an open cell porous structure as claimed in any one of claims 1 to 5, wherein the inorganic particles consist essentially of ceramic particles.

7. A method for making an open eel! porous structure as claimed in any one of claims 1 to 5, wherein the inorganic particles consist essentially υf metallic particles.

8. Λ method for making an open cell porous structure as claimed in claim 7. wherein the at least one transition metal is al least one seleeled from the group consisting of scandium, titanium, vanadium, ehrυuiiurπ, ιnξui|>mie8e, iron, cobalt, nickel, copper, yttrium, zirconium, niobium, molybdenum, ruthenium, rhodium, palladium, silver, hafnium, tantalum, tungsten, rhenium, osmium, iridium, platinum, and gold.

9. A method tor making an open cell porous structure as claimed in claim 7, wherein the metallic particles arc al least one selected from ihe group consisting of copper, nickel, iron, titanium, copper-based alloy particles, nickel-bnsed alloy particles, iron-based alloy particle*, titanium-based alloy particles, and copper-based alloy particles.

10. Λ method for making an open cell porous structure as claimed in claim 7, wherein the metallic particles are at least one of copper and copper-based alloy particles.

1 1. A method for making an open cell porous structure as claimed in any one of claims I to

10, wherein the inorganic particles consistent essentially of coated particles.

12. Λ method for making an open cell porous structure as claimed in any one of claims 1 to

1 1 , wherein the binding agent is cured with the aid of a curing agent

13. A method for making an open cell porous structure aς clnimed in any one of claims 1 to

12, wherein the binding a^eut is a Ihcππoset resin.

14. A method for making an open cell porous -.iruUure as claimed in any one of claims I to 12, wherein the binding agent is a thermoplastic polymer.

15. A method for making an open cell porous structure as claimed in claim 14, wherein the S thermoplastic polymer is cured with the aid of one of a curing agent, nil irradiation cross-linking treatment, and A Hghi-gxposure cπjss-linkiπg treatment.

16. A method for making an open cell porous structure as claimed in any one of claims 1 to

15, wherein the mixture further includes at least one additional agcni βOaplcd Io minimize0 segregation and dusting and to improve the flowability of the mixture.

17 A method tor making an open cell poitws slrucluic as claimed in any one of claims I to

16, wherein pressure is applied to the mixture at least one ol" before and during the heating thereof in b . C . or d. 5

18. A method for making an open cell porous structure as claimed in any one of claims 1 tu

17, further comprising shaping I he mixlurc prior Io healing.

19. A method for making an open cell porous structure as claimed in any otiu of claims 1 to0 18, further comprising providing a substrate, and wherein the mixture is disposed on the substrate prior to heating.

20. A mclhυd for making an open cull porous structure as claimed in any one of claims 1 Io

19, wherein the mixture further comprises at least one spacing agent. 5

21. A method for making an open cell porous structure as claimed in any one of claims 1 lυ

20, wherein healing the non-rnetallurgically-boiided open cell porous structure to a temperature lower than lhc first inciting temperature sufficient to metallurgically bond the inorganic particles to obtain a solid open cell porous structure comprises heating the non»metallurgically-bonded0 open cell porous structure lυ a temperature lower than the first melting temperature sufficient to sinter the inorganic particles to obtain a solid open cell porous structure.

22. A method lor making an open cell porous, structure as claimed in any one of claims I to 20, wherein the mixture further include* a. bπt/ing agent tor metallurgically bonding the inorganic particles.

23. Λn open cell porous structure made according to the method as claimed ύi any one of claims 1 to 22.

24. A dry ilowable powder mixture for making open cell porous, ^uttures, the mixture uorπpriiriinjj: a first predetermined amount of inorganic particles having a first mulling temperature; a second predetermined amυunl of a binding agent having a decomposition temperature, the decomposition temperature being lower than the first melting temperature.

25. Λ mixture as claimed in claim 24, wherein the first predetermined amount is between about 10 wt % to about 90 wt % inclusive of a total weight of the mixture.

26. A mixture as claimed in claim 25, wherein the first predetermined amount is between about 55 wt % to about 80 wt % inclusive of the total weight ol^" the mixture.

27. Λ mixture as claimed in claim 26, wherein the first predetermined amount is between about 60 wt % to about 75 wt % inclusive of the total weight of the mixture.

2K. A mixture as claimed in claim 2(\ wherein the second predetermined amount varies from about 20 wt % to about .15 wt % of the total weight of the mixture.

29. A mixture as claimed in any one of claims 24 to 28, wherein the inorganic panicles consist essentially of ceramic particles.

30. A mixture as claimed in any one of dflims 24 to 2SJ, wherein the inorganic particles consist essentially of metallic particles.

31. A mixture as claimed in claim 30, wherein the at least one transition metal i_. one selected from the group consisting of scandium, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, yttrium, zirconium, niobium, molybdenum, ruthenium, rhodium, palladium, silver, hafnium, tantalum, tungsten, rhenium, osmium, indium, platinum, and gold.

32. A mixture as claimed in claim 30, wherein the metallic particles are ai least one selected liυm the group consisting of copper, nickel, iron, titanium, copper-bnsed alloy particles, nickel- based alloy particles, iron-based alloy particles, and titanium-based alloy particles.

33. Λ mixture as claimed in claim 30, wherein the metallic particles are one of copper and copper-based alloy particles.

34. A mixture as claimed in any one of claims 24 to .1.1, wherein the inorganic pnrtieles consist essentially of coated particles.

35. Λ mixture as claimed in any one of claims 24 to 34, further comprising a curing agent for assisting in curing the binding agent

36. Λ mixture as claimed in any one of claims 24 to 35, wherein the binding agent is a thermoset resin.

37. A mixture as claimed in any ouc of claims 24 to 35, wherein the binding agent is a thermuplastu: pυlymtr.

3X- A mixture as claimed in any one of claims 24 to 37, wherein the m UIu re further comprises at least one additional agent adapted tυ minimize segregation and dusting and to improve the flowabilily of the nib-lute.

39. A mixture as claimed in any one of claims 24 to 38, wherein the mixture further comprises a lubricating agent to assist in at least one of shaping, molding and demoldiπg.

40. A mixture as claimed in any one of claims 24 to 39, wherein the mixture further comprises a brazing agent for metallurgical Iy bonding lhe inorganic particles.