Article and method

Abstract

A method of providing an article having a set of directional channels, including a first directional channel, therein is described. The method comprises preparing a mixture including particles comprising a first material and a first binding agent. The method comprises providing an article precursor by surrounding a pattern comprising a second material with the mixture. The method comprises heating the article precursor thereby coalescing the particles to provide the article. The method comprises removing the pattern by reacting the second material to form a gaseous product, thereby providing the set of directional channels in the article, wherein the set of directional channels corresponds with the removed pattern. Such an article is also described.

Claims

1. A method of providing an article having a set of directional channels, including a first directional channel, therein, the method comprising: preparing a mixture including particles comprising a first material and a first binding agent; providing an article precursor by surrounding a pattern comprising a second material with the mixture; heating the article precursor thereby coalescing the particles to provide the article; and removing the pattern by reacting the second material to form a gaseous product, thereby providing the set of directional channels in the article, wherein the set of directional channels corresponds with the removed pattern; wherein the heating comprises heating the article precursor in the presence of oxygen at a first temperature for a first period, wherein removing the pattern is by reacting the second material and/or combusting the second material to form the gaseous product; and wherein the heating comprises heating the article precursor in the presence of oxygen at a second temperature for a second period, thereby oxidizing the particles to provide oxidized particles, wherein coalescing the particles comprises coalescing the oxidized particles; and wherein the method further comprises heating the oxidized particles in an absence of oxygen and/or in a reactant or in a vacuum at a third temperature for a third period, thereby reducing the oxidized particles to provide the article having the set of directional channels therein.

2. The method according to claim 1, comprising: coating the pattern with particles of the first material and a second binding agent, before surrounding the pattern with the mixture.

3. The method according to claim 1, wherein the first material comprises a metal and/or alloy thereof, and/or an oxide thereof and/or mixtures thereof.

4. The method according to claim 1, wherein the particles have a size in a range from 5 μm to 250 μm.

5. The method according to claim 1, wherein the second material comprises a polymeric composition comprising a thermoplastic polymer.

6. The method according to claim 1, wherein the first binding agent comprises an adhesive; a fatty acid; and/or a solvent.

7. The method according to claim 1, wherein the second binding agent comprises an adhesive or plastic glue.

8. The method according to claim 1, wherein the pattern comprises a set of fibers or filaments.

9. The method according to claim 8, comprising arranging the set of fibers.

10. The method according to claim 1, wherein the first directional channel has a cross-sectional dimension in a range from 20 μm to 1000 μm and/or a length in a range from 1 mm to 1000 mm.

11. The method according to claim 1, wherein a volume of the set of directional channels is in a range from 5% to 70% of the volume of the article.

12. The method according to claim 1, wherein a density of the article, excluding the set of directional channels, is in a range of from 60% to 95% of the density of the first material.

13. The method according to claim 1, wherein the article comprises and/or is a heat exchanger.

14. An article having a set of directional channels, including a first directional channel, therein, the article formed from coalesced particles comprising a first material, wherein a volume of the set of directional channels is in a range from 20% to 60% of the volume of the article.

15. The method according to claim 1, wherein the first material comprises a metal and/or alloy thereof, wherein the metal is Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu or Zn.

16. The method according to claim 1, wherein heating the article precursor thereby coalescing the particles and removing the pattern are concurrent.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) For a better understanding of the invention, and to show how exemplary embodiments of the same may be brought into effect, reference will be made, by way of example only, to the accompanying diagrammatic Figures, in which:

(2) FIG. 1 schematically depicts a method of providing an article having a set of directional channels therein, according to an exemplary embodiment;

(3) FIG. 2 schematically depicts a method of providing an article having a set of directional channels therein, according to an exemplary embodiment;

(4) FIG. 3 shows an optical micrograph of cross-section of an article having a set of directional channels therein, according to an exemplary embodiment;

(5) FIG. 4 shows an optical micrograph of a longitudinal cross-section of the article of FIG. 3; and

(6) FIG. 5 shows an optical micrograph of cross-section of an article having a set of directional channels therein, according to an exemplary embodiment.

DETAILED DESCRIPTION OF THE DRAWINGS

Example Method 1

(7) FIG. 1 schematically depicts a method of providing an article having a set of directional channels therein, according to an exemplary embodiment.

(8) The article has the set of directional channels, including a first directional channel, therein.

(9) At S101, a mixture including particles comprising a first material and a first binding agent is prepared.

(10) At S102, an article precursor is provided by surrounding a pattern comprising a second material with the mixture.

(11) At S103, the article precursor is heated thereby coalescing the particles to provide the article.

(12) At S104, the pattern is removed by reacting the second material to form a gaseous product, thereby providing the set of directional channels in the article, wherein the set of directional channels corresponds with the removed pattern.

(13) The method may include any of the steps described herein, for example with respect to the first aspect.

Example Method 2

(14) FIG. 2 schematically depicts a method of providing an article having a set of directional channels therein, according to an exemplary embodiment. Particularly, in this example, the method is of providing a porous copper article having a set of directional channels therein.

(15) At S201, a mixture including particles comprising a first material and a first binding agent is prepared. Particularly, Cu (i.e. the first material) particles are mixed with a binder (ethanol or PVA glue) (i.e. the first binding agent) to form a Cu particle slurry (i.e. the mixture). The Cu particle slurry is made by mixing Cu powder and the binder (ethanol or PVA glue, approximately 20 vol. % of the Cu powder).

(16) At S202, an article precursor is provided by surrounding a pattern comprising a second material with the mixture.

(17) Firstly, polylactic acid (PLA) fibres (i.e. the pattern) are coated with Cu powder (i.e. the particles comprising the first material) using a binder (i.e. a second binding agent). The PLA fibres are painted with PVA glue and then dredged in Cu powder so that the PLA fibres are fully surrounded by Cu particles in order to improve integrity of the channels in the final product.

(18) Secondly, the coated PLA fibres are subsequently embedded (i.e. surrounded) in the Cu particle slurry, thereby providing the article precursor. The Cu coated PLA fibres are embedded in the slurry layer by layer in a mould.

(19) In more detail, a thin layer of Cu powder slurry is spread in a mould. The coated PLA fibres are uniformly laid on the thin layer of Cu powder slurry. Then, another layer of Cu powder slurry is spread over these coated PLA fibres, ensuring filling the gaps between the coated PLA fibres. This layering process is repeated until a desired thickness is reached. The coated PLA fibres are preferably arranged in the mould straight and directional (i.e. mutually aligned and/or mutually spaced apart, whereby an arrangement of the directional channels is predetermined and/or controlled). A volume fraction of the channels in the Cu matrix is controlled by the quantity of the PLA fibres in the material and can be up to 0.7. The channel diameter is controlled by the diameter of the PLA fibres, e.g. ranging from 100 μm to 1000 μm.

(20) In this example, S203 and S204 are concurrent. At S203, the article precursor is heated thereby coalescing the particles to provide the article and at S204, removing the pattern by reacting the second material to form a gaseous product, thereby providing the set of directional channels in the article, wherein the set of directional channels corresponds with the removed pattern. Particularly, the article precursor is heated in the atmosphere (i.e. air, in the presence of oxygen) at 650° C. for 30 mins so as to oxidize the Cu particles, sinter the oxidized Cu particles and decompose the PLA fibres to form a sintered directional porous CuO.

(21) At S205, the oxidised particles are heated in an absence of oxygen and/or in a reactant or in a vacuum at a third temperature for a third period, thereby reducing the oxidised particles to provide the article having the set of directional channels therein. Particularly, the sintered directional porous CuO is heated in a vacuum (<4×10.sup.−2 mBar) at 1000° C. for 6 hours in order to reduce the CuO to Cu.

(22) The method may include any of the steps described herein, for example with respect to the first aspect.

(23) This process may be used to produce materials having micro-channel structure and these micro-channels are independent and may have controllable channel diameters. Commonly, the volume fraction of channels in the Cu matrix can be up to 70%. The volume fraction of channels is varied depending on the quantity of the PLA fibres in the material.

(24) The metallic particles may comprise copper or copper oxide. The metallic particles may have any particle sizes depending upon the application that the material is to be used for and the pore size required, and preferably within the range from 5 to 75 microns. There are no particular limitations on the form of powder.

(25) Preferably, the quantity of PLA fibres additive in the material may be up to 70 vol % and this will approximately relate to the production of a material with a volume fraction of channels in the Cu matrix up to 70%. The solid density of the Cu matrix may be greater than 85%. The small interstices or voids between the metal particles result from partial sintering.

(26) The addition of the binder helps to evenly coat the metallic powder on the PLA fibres and to ensure homogeneous distribution of the coated PLA fibres in the metallic powder slurry. For coating the metallic powder on the PLA fibres, the binder may be PVA glue. For distributing the coated PLA fibres in the metal particle slurry, PVA glue or ethanol may be used as the binder to mix with Cu powder for high channel volume fraction (>60%) or low channel volume fraction (<60%), respectively. Preferably, the quantity of the binder in the slurry is about 30%.

(27) The directional porous Cu may be used to produce a wide range of products in a number of different fields. In particular, the material may be used in heat transfer and thermal management applications. For example, directional porous Cu may be in conjunction with a cooling liquid and provide a heat sink material for cooling apparatus such as miniaturized and highly integrated electronic chips and power devices.

(28) Example Article 1

(29) FIG. 3 shows an optical micrograph of cross-section of an article 10 having a set of directional channels 100 therein, according to an exemplary embodiment. Particularly, FIG. 3 is an optical micrograph of the article 10, specifically directional porous Cu (i.e. a first material), showing a cross section perpendicular to the set of directional channels 100.

(30) FIG. 4 shows an optical micrograph of a longitudinal cross-section of the article 10 of FIG. 3. Particularly, FIG. 4 is an optical micrograph the article 10, showing a cross section parallel to the set of directional channels 100.

(31) The article 10 has the set of directional channels 100, including a first directional channel 100A, therein. The article 10 is formed from coalesced particles 1000 comprising the first material, wherein a volume of the set of directional channels 100 is in a range from 5% to 70%, preferably from 20% to 60% of the volume of the article.

(32) The article 10 was provided as described above with respect to Example method 2. 170 pieces of PLA fibres with diameter of 390 μm were painted in PVA glue and then dredged in copper powder with particle size <20 μm. The copper powder slurry was formed by mixing copper powder with ethanol (30 vol. %). The coated PLA fibres were embedded in the Cu powder slurry layer by layer in mould with dimension of 2×3×0.5 cm.sup.3. The preform was heated in the atmosphere at 650° C. for 30 mins. The preform was then moved to a vacuum furnace and sintered in a vacuum atmosphere (<4×10.sup.−2 mBar) at 1000° C. for 6 hours. As a result, directional channels with a diameter of 390 μm in the Cu matrix were obtained. The volume fraction of the channels in Cu matrix was about 20%.

(33) The open channels of the material as produced in this experiment can be seen in FIGS. 3 and 4. FIG. 3 is the transverse sectional view (perpendicular to the channel direction) and shows that the channels in the material have the same diameter as the PLA fibres and are uniformly distributed. FIG. 4 is the longitudinal sectional view (parallel to the channel direction) and shows that the channels in the material are straight and open. The solid density of the sintered Cu matrix in FIGS. 1 and 2 is over 85%.

(34) Example Article 2

(35) FIG. 5 shows an optical micrograph of cross-section of an article 20 having a set of directional channels 200 therein, according to an exemplary embodiment. Particularly, FIG. 5 is an optical micrograph of a sample of the directional porous Cu material (i.e. the article 20), showing a cross section perpendicular to the channels.

(36) The article 20 was provided as described above with respect to Example method 2. 440 pieces of PLA fibres with diameter of 450 μm were painted in PVA glue and then dredged in copper powder with particle size <20 μm. The copper powder slurry was formed by mixing copper powder with PVA glue (30 vol. %). The coated PLA fibres were embedded in the Cu powder slurry layer by layer in mould with dimension of 2×3×0.5 cm.sup.3. The preform was heated in the atmosphere at 650° C. for 30 mins. The preform was then moved to a vacuum furnace and sintered in a vacuum atmosphere (<4×10.sup.−2 mBar) at 1000° C. for 6 hours. As a result, directional channels with a diameter of 450 μm in the Cu matrix were obtained. The volume fraction of the channels in Cu matrix was about 70%.

(37) The open channels of the material as produced in this experiment can be seen in FIG. 5.

(38) Heat Transfer

(39) Table 1 shows heat transfer coefficients and pressure drops for conventional copper microchannels, porous copper manufactured by a Lost Carbonate Sintering (LCS) process, and directional porous copper according to an exemplary embodiment, measured under the same test conditions (water flow rate: 2 l min.sup.−1). The test data shows that the directional porous copper has both an excellent heat transfer coefficient, comparable to LCS porous metals, and a reduced pressure drop, comparable to conventional microchannels.

(40) TABLE-US-00001 TABLE 1 Heat transfer coefficients and pressure drops for conventional copper microchannels, porous copper manufactured by a Lost Carbonate Sintering (LCS) process, and a directional porous copper according to an exemplary embodiment Key performance indicators under Heat transfer Pressure forced water Diameter Porosity coefficient drop cooling μm % kW m.sup.−2 K.sup.−1 kPa Cu 500 14  25 microchannels LCS porous Cu 425-710 67 23 188 Directional 450 20 24  23 porous Cu

(41) Although a preferred embodiment has been shown and described, it will be appreciated by those skilled in the art that various changes and modifications might be made without departing from the scope of the invention, as defined in the appended claims and as described above.

(42) In summary, the invention provides a method of providing an article having a set of directional channels, including a first directional channel, and such an article. In this way, the article may be provided having channels which are open, independent and directional. In this way, channel diameter, quantity and distribution in the article may be controlled. In this way, an arrangement of the directional channels may be predetermined and/or controlled, by the pattern. In this way, an article having a relatively large volume fraction of directional channels, as a fraction of the volume of the article may be provided.

(43) Attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

(44) All of the features disclosed in this specification (including any accompanying claims and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at most some of such features and/or steps are mutually exclusive.

(45) Each feature disclosed in this specification (including any accompanying claims, and drawings) may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

(46) The invention is not restricted to the details of the foregoing embodiment(s). The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.