Method for producing porous member

Abstract

A method for producing a porous member, whereby a member having smaller microgaps can be produced, and additionally, the outermost surface alone can be made porous and a porous layer can be formed on the surface while maintaining the characteristics of portions in which no porous layer is formed, is provided.

Claims

1. A method for producing a porous member, which comprises: bringing a solid metal body (1) comprising a first component into contact with a solid metal material (2) comprising a compound, an alloy or a non-equilibrium alloy that simultaneously contains a second component and a third component having a positive heat of mixing and a negative heat of mixing, respectively, relative to the first component; performing heat treatment at a predetermined temperature for a predetermined length of time to interdiffuse the first component to the solid metal material (2), and the third component to the solid metal body (1); and selectively removing the first component and the third component from a portion of the solid metal material (2) in which the first component is diffused, thereby obtaining a member having microgaps.

2. The method for producing a porous member according to claim 1, wherein the portion of the solid metal material (2) in which the first component is diffused is exposed when the first component and the third component is selectively removed.

3. The method for producing a porous member according to claim 1, wherein the heat treatment is performed after the contact of the solid metal body (1) with the solid metal material (2), so that the first component and the third component are interdiffused for binding with each other.

4. The method for producing a porous member according to claim 3, wherein after the heat treatment is performed, a compound, an alloy or a non-equilibrium alloy formed by binding of the first component with the third component is selectively removed.

5. The method for producing a porous member according to claim 1, wherein after the heat treatment is performed, the first component and the third component are selectively eluted and removed by etching.

6. The method for producing a porous member according to claim 1, wherein the heat treatment is performed by maintaining a temperature corresponding to 50% or more of the melting point of the solid metal body (1) on the basis of the absolute temperature.

7. The method for producing a porous member according to claim 1, wherein the contact face of the metal body (1) with the metal material (2) and the contact face of the solid metal material (2) with the solid metal body (1) are mirror-finished in advance, and during the heat treatment, the contact face of the solid metal body (1) and the contact face of the solid metal material (2) are brought into close contact with each other.

8. The method for producing a porous member according to claim 1, wherein the first component comprises Li, Mg, Ca, Cu, Zn, Ag, Pb, Bi, a rare earth metal element, or, a mixture that is an alloy or a compound containing any one of them as a major component, the second component comprises any one of Ti, Zr, Hf, Nb, Ta, V, Cr, Mo, W, Fe, Co, Ni, C, Si, Ge, Sn, and Al, or, a mixture that is an alloy or a compound containing a plurality thereof, and the third component comprises any one of Li, Mg, Ca, Mn, Fe, Co, Ni, Cu, Ti, Zr, Hf, Nb, Ta, Cr, Mo, and W, or a mixture containing a plurality thereof.

9. The method for producing a porous member according to claim 1, wherein the first component comprises Mg, the third component comprises Ni, and the solid metal material (2) comprises a Ni-containing alloy.

10. A method for producing a porous member, which comprises bringing a solid metal body (1) comprising a second component into contact with a solid metal material (2) comprising a compound, an alloy or a non-equilibrium alloy that simultaneously contains a first component and a third component, performing heat treatment at a predetermined temperature for a predetermined length of time so as to interdiffuse the second component to the solid metal material (2) and the third component to the solid metal body (1), and selectively removing the second component and the third component from a portion of the solid metal material (2) in which the second component is diffused, thereby obtaining a member having microgaps, wherein the second component and the third component have a positive heat of mixing and a negative heat of mixing, respectively, relative to the first component, and the melting point of the first component on the basis of the absolute temperature corresponds to at least a half of the melting point of the second component on the basis of the absolute temperature.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a schematic perspective view showing the method for producing a porous member of an embodiment of the present invention.

(2) FIG. 2 shows a scanning electron micrograph of a metal body and a metal material after heat treatment, when the heat treatment of the method for producing a porous member of an embodiment of the present invention was performed at 460° C. for 12 hours, and the results of analyzing each element (Ni, Fe, Cr, and Mg) in a rectangular region by EDX.

(3) FIG. 3 shows (a) a scanning electron micrograph of a metal body and a metal material after heat treatment, (b) an enlarged micrograph of (a) at position A, (c) an enlarged micrograph of (a) at position B, and (d) an enlarged micrograph of (a) at position C, when the heat treatment of the method for producing a porous member of an embodiment of the present invention was performed at 460° C. for 12 hours.

(4) FIG. 4 shows: a scanning electron micrograph of a metal body and a metal material when (a) the heat treatment of the method for producing a porous member of an embodiment of the present invention was performed at 480° C. for each time length of heat treatment (6 hours, 12 hours, 24 hours, 48 hours, and 72 hours); and (b) a graph showing the relationship between the time for heat treatment and the thickness of the reaction region, when the heat treatment of the same was performed at 440° C., 460° C., and 480° C.

(5) FIG. 5 is an Arrhenius plot of the rate constant k of the temperature of each heat treatment found in FIG. 4(b).

(6) FIG. 6 shows (a) a scanning electron micrograph showing an area near the dealloying front of the reaction region, (b) a scanning electron micrograph showing the central part of the reaction region, and (c) an enlarged micrograph of a portion of (b), of a member produced by 12 hours of heat treatment at 460° C. and then performing etching according to the method for producing a porous member of an embodiment of the present invention.

(7) FIG. 7 shows (a) a scanning electron micrograph of, and (b) a graph showing the relationship between depth “x” from the dealloying front of the reaction region and the average ligament width “w” of a filamentary structure or a band structure in a member produced by 72 hours of heat treatment at 480° C. and then performing etching according to the method for producing a porous member of an embodiment of the present invention.

(8) FIG. 8 shows (a) a scanning electron micrograph of a coil spring made of HASTELLOY C-276, the metal material used in the method for producing a porous member of an embodiment of the present invention, (b) an enlarged micrograph of the surface of the coil spring, and (c) an enlarged micrograph of a portion of (b).

(9) FIG. 9 shows (a) a scanning electron micrograph of the surface of the coil spring, the metal material shown in FIG. 8 and (b) the results of analyzing each element (Ni, Mo, Cr, Fe and W) in the (a) region by EDX.

(10) FIG. 10 shows a scanning electron micrograph of the cross section of the coil spring, when Mg was deposited by vacuum deposition on the surface of the coil spring, the metal material shown in FIG. 8, and then heat treatment was performed at 460° C. for 12 hours according to the method for producing a porous member of an embodiment of the present invention.

(11) FIG. 11 shows (a) a scanning electron micrograph of the outermost surface of the coil spring, when etching was performed for the coil spring after heat treatment shown in FIG. 10 of the method for producing a porous member of an embodiment of the present invention, and (b) an enlarged micrograph of a portion of (a).

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(12) Hereafter, embodiments of the present invention are described below based on drawings with reference to examples.

(13) According to the method for producing a porous member of an embodiment of the present invention, firstly, as shown in FIG. 1(a), a solid metal body 11 comprising a first component and a solid metal material 12 comprising a compound, an alloy or a non-equilibrium alloy that simultaneously contains a second component and a third component having a positive heat of mixing and a negative heat of mixing, respectively, relative to the first component are used and brought into contact with each other.

(14) In a specific example shown in FIG. 1, pure magnesium (pure Mg) is used as the metal body 11, and (Fe.sub.0.8Cr.sub.0.2).sub.50Ni.sub.50 alloy is used as the metal material 12. At this time, the first component is Mg, the second component is Fe.sub.0.8Cr.sub.0.2, and the third component is Ni. Moreover, the contact face of the metal body 11 and the contact face of the metal material 12 are each polished flat in advance for mirror finishing, and thus are brought into close contact via the contact faces. For mirror finishing, an ion peeling process or the like can be employed.

(15) [Heat Treatment]

(16) Next, as shown in FIG. 1(b), a load is applied (loading) to the interface between the metal body 11 and the metal material 12 so as to prevent separation thereof during treatment, and then annealing is performed as heat treatment. Heat treatment is performed by maintaining the temperature corresponding to 75% to 85% of the melting point of the metal body 11 on the basis of the absolute temperature for 5 or more and 80 or less hours. Accordingly, depending on the heat of mixing relative to the first component that is the metal body 11, interdiffusion takes place so that the third component is diffused from the metal material 12 into the metal body 11, and the first component is diffused from the metal body 11 into the metal material 12. The second component of the metal material 12 has positive heat of mixing relative to the first component, so that the second component is not diffused to the metal body 11 side. Therefore, as shown in FIG. 1(c), in the metal material 12, a region is obtained as a reaction region (reaction layer) 13, in which portions comprising the first component and the third component and portions comprising the second component are mixed with each other in nanometer order. At this time, interdiffusion between solids slowly proceeds compared to the elution to a metal bath as described in Patent Literature 1, resulting in a condition where portions comprising the first component and the third component and portions comprising the second component are more finely mixed with each other.

(17) In a specific example shown in FIG. 1, the melting point of the metal body 11, Mg, is 650° C. (923K). Hence, when heat treatment is performed at about 420° C. to 510° C., interdiffusion takes place so that Ni is diffused from the metal material 12 into the metal body 11, and metal body 11, Mg, is diffused into the metal material 12. The metal material 12, Fe.sub.0.8Cr.sub.0.2, is not diffused to the metal body 11 side. In this manner, a reaction layer 13, in which Mg.sub.2Ni comprising Mg and Ni, and portions comprising Fe.sub.0.8Cr.sub.0.2 are mixed with each other in nanometer order in the metal material 12, can be obtained.

(18) FIG. 2 shows a scanning electron micrograph (SEM) when heat treatment was actually performed at 460° C. for 12 hours, and the results of analyzing each element (Ni, Fe, Cr, and Mg) by EDX (energy dispersive X-ray spectrometry). Furthermore, the results of performing composition analysis at positions A to D in FIG. 2 using a transmission electron microscope (TEM) are shown in Table 1. In addition, at the right end of Table 1, the chemical compositions of substances inferred on the basis of the composition analysis are indicated. In FIG. 2, positions A and B are located within a region of the metal body 11 before heat treatment, and positions C and D are located within a region of the metal material 12 before heat treatment.

(19) TABLE-US-00001 TABLE 1 Ni Fe Cr Mg A ND ND ND 100 pure Mg B 32.1 0.6 ND 67.3 Mg.sub.2Ni C 28.1 11.0 2.7 58.3 Fe.sub.0.8Cr.sub.0.2 + Mg.sub.2Ni D 50.0 40.7 9.3 ND Ni.sub.50(Fe.sub.0.8Cr.sub.0.2).sub.50

(20) As shown in FIG. 2 and Table 1, it was confirmed that only Mg was present at position A in the metal body 11 distant from the contact face for contact with the metal material 12, and the composition was not changed by heat treatment. It was also confirmed that Mg.sub.2Ni was present at position B in the metal body 11 near the contact face for contact with the metal material 12, and Ni was diffused from the metal material 12 into the metal body 11 by heat treatment, so as to bind with Mg. Furthermore, it was confirmed that Fe.sub.0.8Cr.sub.0.2 and Mg.sub.2Ni were present at position C in the metal material 12 near the contact face for contact with the metal body 11, and Mg was diffused from the metal body 11 into the metal material 12 by heat treatment, so as to bind with Ni. It was also confirmed that, Mg was not detected, but (Fe.sub.0.8Cr.sub.0.2).sub.50Ni.sub.50 was present at position D in the metal material 12 distant from the contact face for contact with the metal body 11, and the composition was not changed by heat treatment. As described above, it was confirmed that heat treatment caused interdiffusion to take place, whereby Ni was diffused from the metal material 12 into the metal body 11, and Mg of the metal body 11 was diffused into the metal material 12, and thus Mg and Ni were bound in the diffusion regions to form Mg.sub.2Ni.

(21) A scanning electron micrograph when heat treatment was similarly performed at 460° C. for 12 hours is shown in FIG. 3(a). In addition, enlarged micrographs at each position (A to C) in FIG. 3(a) are shown in FIG. 3(b) to (d). Positions A to C are located in the reaction layer 13 (the region between a pair of arrows on the left edge of FIG. 3(a)) in which the first component, Mg, was diffused, among the regions of the metal material 12 before heat treatment. Position B is located in the neighborhood of the center of the reaction layer 13. Position A is located near the contact face for contact with the metal body 11, the location of which is closer to the contact face than that of Position B. Position C is located in the neighborhood of the dealloying front where Mg is diffused; that is, Position C is located in the neighborhood of the boundary between the reaction layer 13 and regions in which the metal material 12 remains unchanged.

(22) As shown in FIG. 3(b) to (d), it was confirmed within the reaction layer 13 that Mg.sub.2Ni (bright portions in the Figure) and Fe.sub.0.8Cr.sub.0.2 (dark portions in the Figure) were mixed with each other in nanometer order of several hundred nanometers (nm) or less. In particular, it was confirmed in the neighborhood of the dealloying front where the first component, Mg, was diffused that, as shown in FIG. 3(d), Mg.sub.2Ni and Fe.sub.0.8Cr.sub.0.2 in filamentous forms were mixed with each other in nanometer order of 100 nm or less.

(23) The relationship between the time for heat treatment and the thickness of the reaction layer 13 was examined when heat treatment was performed at 440° C., 460° C., and 480° C., and then shown in FIG. 4. As shown in FIG. 4(a), a situation in which the reaction layer 13 was increased as the time for heat treatment passed can be confirmed. Furthermore, as shown in FIG. 4(b), the presence of a relationship represented by x.sup.2=k.Math.(t−t.sub.0) between the thickness “x” of the reaction layer 13 and the time “t” for heat treatment was confirmed. Here, “k” indicates the rate constant, and “t.sub.0” indicates the latent time taken for the reaction to start. Moreover, it was confirmed that as the temperature of heat treatment increased, the enlarging rate of the reaction layer 13 increased.

(24) An Arrhenius plot obtained by plotting the rate constant “k” of each temperature of heat treatment found in FIG. 4(b) is shown in FIG. 5. The activation energy E of interdiffusion due to heat treatment, which was found from FIG. 5, was 280 kJ/mol.

(25) [Etching Treatment]

(26) Next, after heat treatment, portions other than portions mainly composed of the second component are removed by etching from the reaction layer 13, and specifically, the first component and the third component are selectively removed by elution, thereby exposing portions mainly composed of the second component. When the first component and the third component bind with each other to form a compound, an alloy or a non-equilibrium alloy, this is selectively removed. Accordingly, a porous member mainly composed of the second component and having nanometer-sized microgaps can be produced. At this time, interdiffusion between solids produces a condition where portions comprising the first component and the third component and portions comprising the second component are finely mixed with each other, so as to be able to realize the smaller size of microgaps to be formed, compared to Patent Literature 1.

(27) In a specific example shown in FIG. 1, the metal material after heat treatment is immersed in an aqueous nitric acid solution, thereby removing Mg.sub.2Ni in the reaction layer 13. In this manner, a nanometer-sized member having microgaps mainly composed of Fe.sub.0.8Cr.sub.0.2 can be produced. Moreover, a nickel-free member having microgaps can be readily produced.

(28) Actually, after 12 hours of heat treatment at 460° C., the resultant was immersed in an aqueous nitric acid solution, subjected to etching, and then shown in FIG. 6. As shown in FIG. 6(a), in the neighborhood of the dealloying front of the reaction layer 13, a 100-nm-or-less, nanometer-order filamentary structure was confirmed. Moreover, as shown in FIGS. 6(b) and (c), a disordered nanoporous structure comprising a band structure having a width of 200 nm or less and having nanometer-order gaps was confirmed in the central part of the reaction region 13. It was confirmed by composition analysis using TEM that the structure was mainly composed of Fe.sub.0.8Cr.sub.0.2, from which most of Ni and Mg had been removed by etching. The gap size is about 1/10 the size of the metal member of Patent Literature 1.

(29) A member obtained by etching after 72 hours of heat treatment at 480° C. was examined for the relationship between the depth from dealloying front “x” of the reaction layer 13 and the average ligament width “w” of a filamentary structure or a band structure having microgaps and mainly composed of Fe.sub.0.8Cr.sub.0.2, and the results are shown in FIG. 7. As shown in FIG. 7, “w” was confirmed to decrease toward the dealloying front of the reaction layer 13, and to be almost proportional to “x” raised to the power of ½ (heat treatment time raised to the power of ¼). Accordingly, it can be said that the longer the time of being affected by diffusion, the larger the structure, and the larger the gaps.

Other Examples

(30) A 30-micron thick Ti.sub.50Cu.sub.50 (atom %) amorphous ribbon (metal material 12) was pressed at 20 MPa against a mirror-polished Mg plate (metal body 11), the resultant was heated to 480° C., that is, the temperature corresponding to 50% or more of the melting point of Mg, and then maintained. Therefore, a co-continuous-structured nanocomposite formation comprising portions that contain Cu (third component) and Mg (first component) as major components and portions that contain Ti (second component) as a major component was formed in the contact interface of the two. The formation was immersed in nitric acid to remove portions other than those containing Ti as a major component, and thus a porous metal member having gaps with a size of 100 nm or less was obtained. Furthermore, a 1-micron thick Mn.sub.85C.sub.15 (atom %) alloy thin film (metal material 12) was deposited on a 30-micron thick Ag foil (metal body 11) by a magnetron sputtering technique. The thin film was subjected to heat treatment in an argon atmosphere at 800° C., Mn was diffused from the alloy thin film to the Ag foil side, so that a co-continuous-structured nanocomposite formation comprising portions containing Ag (first component) and Mn (third component) as major components and portions containing C (second component) as a major component was formed in the interface. This was immersed in nitric acid to remove portions other than those containing C as a major component, thereby obtaining a porous carbon member having gaps with a size of 100 nm or less.

(31) Furthermore, a 1-micron thick Mn.sub.85C.sub.15 (atom %) alloy thin film (metal material 12) was deposited on the 30-micron thick Cu foil (metal body 11) by a magnetron sputtering technique. The thin film was subjected to heat treatment in an argon atmosphere at 800° C., Mn was diffused from the alloy thin film to the Cu foil side, and thus a co-continuous-structured nanocomposite formation comprising portions containing Cu (first component) and Mn (third component) as major components and portions containing C (second component) as a major component was formed in the interface. The formation was immersed in nitric acid to remove portions other than those containing C as a major component, thereby obtaining a porous carbon member having gaps with a size of 100 nm or less.

(32) An (Fe.sub.0.8Cr.sub.0.2).sub.50Ni.sub.50 alloy (metal material 12) was pressed at 20 MPa to a 30-micron thick Mg.sub.86Ni.sub.9Ca.sub.5 (atom %) metal glass ribbon (metal body 11), and then the temperature was increased to 140° C. or higher, which is the glass transition temperature of the metal glass ribbon. Therefore, the metal glass ribbon was transformed into a super cooled liquid, and then the viscous flow phenomenon caused the two to come into contact with no gaps regardless of their surface finishing state. Next, the resultant was heated to and maintained at 450° C., that is, the temperature corresponding to 50% or more of the melting point of the Mg.sub.86Ni.sub.9Ca.sub.5 alloy. In this manner, a co-continuous-structured nanocomposite formation comprising portions containing Mg (first component) and Ni (third component) as major components and portions containing Fe and Cr (second component) as major components was formed in the contact interface between the two. The resultant was immersed in nitric acid to remove portions other than those containing Fe and Cr as major components, thereby obtaining a porous metal member having gaps with a size of 100 nm or less.

(33) Using porous Cu having a specific surface area of 100 m.sup.2/g as a substrate (metal body 11), a Mn.sub.85C.sub.15 (atom %) alloy thin film (metal material 12) was uniformly deposited on the surface of nanoporous Cu by the CVD method. The resultant was subjected to heat treatment in an argon atmosphere at 800° C., Mn was diffused from the alloy thin film to the nanoporous Cu side, and thus a co-continuous-structured nanocomposite formation comprising portions containing Cu (first component) and Mn (third component) as major components and portions containing C (second component) as a major component was formed in the interface. The resultant was immersed in nitric acid to remove portions other than those containing C as a major component, so that a bimodal porous product composed of a macro structure that is the skeletal shape of porous Cu used as a substrate, and a micro structure that is nanoporous carbon. Accordingly, the surface area of C generated per gram of Cu could be increased to an area about 10 times the original surface area.

(34) In addition, according to the method for producing a porous member of an embodiment of the present invention, a reaction proceeds from the surface of the metal material 12 due to diffusion of the first component, so that only the surface of the metal material 12 can be reformed by stopping heat treatment in the middle thereof, and a member having microgaps only on the surface can be produced. Furthermore, the metal material 12 is formed into any shape such as a thin film or a hollow shape, and thus a member formed in an arbitrary shape having microgaps on the surface or throughout the member can also be produced.

(35) Mg (metal body 11; first component) was deposited by vacuum deposition on the surface of a coil spring (metal material 12) made of HASTELLOY C-276 (Ni.sub.57Cr.sub.16Mo.sub.16W.sub.4Fe.sub.5 (wt %) alloy), and then heat treatment was performed for 12 hours in an Ar gas atmosphere at 460° C. at which all compounds in the coil spring and Mg can maintain the solid phase. Scanning electron micrographs (SEM) of the coil spring made of HASTELLOY C-276 before vacuum deposition, and the results of analyzing each element (Ni, Mo, Cr, Fe, and W) by EDX (energy dispersive X-ray spectrometry) are shown in FIG. 8 and FIG. 9, respectively. In addition, a scanning electron micrograph of the cross section of the coil spring after heat treatment is shown in FIG. 10.

(36) As shown in FIG. 8 and FIG. 9, the coil spring made of HASTELLOY C-276 was confirmed to be a multiphasic alloy containing a p phase and a μ phase in which Mo (second component) was concentrated, and a γ phase in which Ni (third component) was concentrated. Further, as shown in FIG. 10, it was confirmed that reaction layer 13 was formed in the contact interface between a vapor-deposited Mg layer and the coil spring by heat treatment. Within the reaction layer 13, it was confirmed that the Ni component was selectively diffused (dealloyed) from the γ phase into Mg, and a co-continuous-structured nanocomposite formation was formed, in which portions (dark portions in the figure) containing Ni (third component) and Mg (first component) as major components, and portions (bright portions in the figure) in which Mo (second component) was concentrated because of depletion of Ni from the γ phase were mixed with each other in nanometer order.

(37) Heat treatment was performed and then the resultant was immersed in nitric acid, thereby performing etching to remove portions other than those containing Mo as a major component. Scanning electron micrographs of the outermost surface of the coil spring at this time are shown in FIG. 11. The p phase and the μ phase regions remained as fine grains on the outermost surface before heat treatment as shown in FIG. 8. However, as shown in FIG. 11, after heat treatment and after etching, only the portions containing Ni and Mg as major components were removed from the co-continuous nanocomposite formation formed in the original γ phase region. It was thus confirmed that a porous metal member having 10-nm-order gaps was obtained.

(38) As described above, according to the method for producing a porous member of an embodiment of the present invention, the steam of the first component was sprayed over the surface of the metal material 12 for adhesion, followed by heat treatment, so that a member having microgaps can also be produced. In this case, even if the metal material 12 has a complicated shape, a porous member can be relatively readily produced. Therefore, for example, a stent or the like having microgaps that are formed only on the surface can be produced.

REFERENCE SIGNS LIST

(39) 11 Metal body 12 Metal material 13 Reaction layer