JP2003213352A - Method for manufacturing functional porous structure - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a porous structure in which functional fine particles are uniformly dispersed over the whole of a porous body by applying heat treatment to the porous body as a starting material containing components to be the functional fine particles. <P>SOLUTION: The porous body which is composed of an element Z having high affinity and an element Y as a matrix and has 0.1 to 95.0% porosity, is heated in an atmosphere containing an element X to allow the element X to selectively react with the element Z, by which the porous structure in which a compound Z-X is dispersed finely and uniformly can be manufactured. In this way, the porous structure provided with various functionalities according to the kinds of the compound Z-X, such as the oxides, nitrides, fluorides and hydrides of various metals, can be obtained. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a porous structure in which fine particle or plate-like compounds exhibiting various functions are dispersed and deposited inside or on the surface of a porous body.

[0002]

2. Description of the Related Art A fine particle-dispersed composite functional material is manufactured by mixing fine particles having a predetermined function with a metal or alloy powder constituting a matrix, molding the obtained mixture into a predetermined shape, and then firing the mixture. There is. However, according to this manufacturing method, it is difficult to uniformly disperse the functional fine particles in the matrix. By the way, in a composite functional material in which catalyst particles having a large specific surface area are dispersed, the smaller the particle size of the functional fine particles, the more effectively they contribute to the catalytic reaction, but the fine particles having an extremely fine particle size are likely to aggregate. Therefore, the functional fine particles are distributed as large-sized aggregated particles in a state of being mixed with the metal or alloy powder forming the matrix,
It cannot be expected that the reaction activity resulting from the ultrafine graining will be improved.

In order to avoid aggregation of the functional fine particles in the powder mixing-sintering method, there is a method of internally oxidizing an alloy containing a metal element to be an oxide (functional fine particles). The present inventor also introduced that functional materials such as conductive materials, contact materials, and high-strength materials can be obtained by dispersing and depositing oxide particles in a matrix by internal oxidation under specific conditions (JEMS NEWS, No. 1). 28 (1986), pages 1-5).

[0004]

When the internal oxidation method is used, finely divided functional oxide can be dispersed in the matrix. However, when the metal material having a flat shape is internally oxidized, the reaction for producing the functional fine particles is limited to the surface layer of the metal material, and the functional fine particles cannot be deposited inside the metal material. Therefore, the additional element inside the metal material is likely to remain unreacted. Moreover, the functional fine particles are likely to grow to a large particle size due to the heating during the formation reaction, and the effective specific surface area of the functional fine particles does not become larger than the planned value. As a result, there is a limit to the functionality that can be imparted, and there is also a limit to the improvement in functionality due to the functional fine particles having an extremely fine particle size. Further, since the functional fine particles are generated by internal oxidation, it cannot be applied to disperse and deposit the functional fine particles other than the oxide.

[0005]

The present invention has been devised to solve such a problem, and by using a porous body as a starting material containing a component which becomes functional fine particles, A porous structure that enables deposition of functional fine particles not only on the surface layer of the body but also has a large surface area and significantly improves the effect of functional fine particles, and is lightweight and capable of achieving high strength based on a dispersion strengthening mechanism. The purpose is to provide.

In order to achieve the object, the method for producing a porous structure of the present invention comprises an element Z having a large affinity with an element X in the vapor phase and an element Y forming a matrix, and the concentration of the element Z is 0. Porosity 0.1 to 9 at 0.0001 to 70 atom%
A porous body of 5.0% was prepared, which was insufficient for forming a compound of the element Y and the element X, but was porous under an atmosphere containing a partial pressure of the element X which was sufficient for forming a compound of the element Z and the element X. The body is heated to deposit a compound of the element Z and the element X in the form of particles or a plate on the surface and / or inside of the porous body.

In a porous structure in which oxides are dispersed and deposited as functional fine particles, oxygen O is an element X, Si, Mn,
P, Al, Zn, Ti, Ni, Cr, Co, Fe, B
e, Mg, Cd, In, Zr, Sn, Ce, Ca, G
a, B, Sb, Tl, Pb, Nb, Ta, Bi, Li,
Mo, W, V, Pb. 1 or 2 obtained from Hf
More than one kind of metal is used as element Z, and unlike element Z, Ag, Cu,
Ni, Fe, Pd, Co, Au, Pt, Cr, Mo,
W, Ti, Zr, Hf, V, Nb, Ta, Ge, Sn,
One or more metals selected from Pb are used for the element Y.

In a porous structure in which nitride is dispersed and deposited as functional fine particles, nitrogen N is used as element X, Ti, Zr,
One or more metals selected from Al, Fe, Cr, Mo, V, and Si are used as the element Z, and unlike the element Z, Ag, C
u, Ni, Fe, Pd, Co, Au, Pt, Cr, M
One or more metals selected from o and W are used for the element Y.

In the porous structure in which fluoride is dispersed and deposited as the functional fine particles, fluorine F is added to the element X, Be and M are added.
element Z is one or more metals selected from g, Ca, Al, Ti, Si, and Cr, and unlike element Z, Ag, C
u, Ni, Fe, Pd, Co, Au, Pt, Cr, M
One or more metals selected from o, W, Ti, and Zr are used for the element Y.

In a porous structure in which hydride is dispersed and deposited as functional fine particles, hydrogen H is added to element X, and La and C are added.
a, Li, Ti, K, Na, U, Mg, Ni, Co,
1 selected from V, Fe, Mn, Ce, Al, Y, Zr
Species or two or more species as element Z, different from element Z, Ag, C
u, Ni, Fe, Pd, Co, Au, Pt, Cr, M
One or more metals selected from o, W, Ti, Zr, and Mg are used for the element Y.

[0011]

When a porous body composed of the element Z having a high affinity and the element Y serving as a matrix is heated in an atmosphere containing the element X, the element X in the atmosphere reacts with the element Z in the surface layer of the porous body to form an oxide, Functional fine particles such as nitride, fluoride and hydride are generated. The formation reaction of the functional fine particles proceeds at the contact interface between the element X in the atmosphere and the porous body. However, since it is a porous body having a large number of voids into which atmospheric gas can penetrate, the surface layer portion of the porous body is of course. , Functional fine particles are deposited even inside. Therefore, a porous structure having an extremely large specific surface area of the functional fine particles can be obtained. Moreover, there is a high degree of freedom in selecting functional fine particles such as oxides, nitrides, fluorides and hydrides.

The element X in the vapor phase in the normal state includes oxygen O, nitrogen N, fluorine F, hydrogen H and the like. An element Y that serves as a matrix and an element Z that has a large affinity are selected according to the element X, and oxides, nitrides, fluorides, which are formed after the heat treatment,
A porous structure having a function derived from the compound ZX such as hydride can be obtained. The functions derived from the compound Z-X include photocatalyst, chemical catalyst, selective substance separation ability, conductivity improvement, insulation property imparting, magnetic property imparting, mechanical property enhancing,
It has various functions such as heat resistance, corrosion resistance, and chemical resistance depending on the type of compound Z-X.

In order to impart such a function, it is necessary that the concentration of the element Z contained in the starting material be 0.0001 atomic% or more. When the concentration of the element Z is less than 0.0001 atom%, the action of the compound Z-X becomes insufficient.
However, when the element Z is contained at a concentration of 70 atomic% or more,
The compound Z-X produced by the heat treatment tends to agglomerate, which hinders the uniform dispersion of fine particles. Further, in order to efficiently proceed the reaction between the element X and the element Z in the atmosphere during the heat treatment, it is necessary to set the porosity of the porous body to 0.1% or more. However, if the porosity exceeds 95.0%, the skeleton of the porous body cannot be maintained.

The porous material used as the starting material is manufactured by a unidirectional solidification method, a molten metal foaming method, an interparticle infiltration casting method, an investment casting method, a plating method, a powder metallurgy method, a sputter deposition method or the like. For example, in the unidirectional solidification method, the molten metal is injected into a mold partially equipped with a cooling plate, and the molten metal is cooled along a unidirectional heat flow path through the cooling plate, thereby aligning the growth direction of dendrites. , Create innumerable gaps between dendrite arms. In the molten metal foaming method, a physical method of injecting and stirring an inert gas or carbon dioxide gas into the molten metal, and a foaming agent such as titanium hydride or zirconium hydride is added to the molten metal to decompose the hydride. There is a chemical method of foaming by utilizing the generated hydrogen gas. In the latter case, after adjusting the viscosity of the molten metal poured into the mold, a foaming agent is added to foam the molten metal, thereby producing innumerable bubbles inside the molten metal.

In the interparticle permeation method, small spheres of glass or sodium chloride are packed in a mold, molten metal is impregnated into the gaps, and after solidification, the small spheres are removed. In the investment casting method, the voids such as polyurethane foam are filled with a refractory slurry, the polyurethane foam is removed after drying and firing, the molten metal is vacuum-cast into a manufactured mold, and then the mold is removed to obtain a porous body. The plating method is a method of electroplating Ni or the like on the surface of a skeleton such as polyurethane foam, and after plating, polyurethane is similarly removed.

The sputter deposition method utilizes the fact that a metal thin film sputter-deposited in an inert gas on a water-cooled substrate is heated to near the melting point and the mixed inert gas expands and foams. The powder metallurgy method includes a slurry foaming method in which a mixed powder slurry containing a foaming agent is fired, and an atmospheric pressure sintering in which metal powder is sintered at atmospheric pressure without hot isostatic processing or cold isostatic processing. Method, a sponge method in which a metal powder slurry is soaked in polyurethane foam, dried and sintered.

[0017]

Example 1 After high-frequency melting of a Ni alloy containing 2.0 atomic% of Ti in an inert atmosphere, the molten alloy was cast into a mold equipped with a water-cooled copper hearth on the bottom surface to dissipate heat through the water-cooled copper hearth. The alloy melt was unidirectionally solidified by. The fully solidified Ni alloy has a porosity of 30% with lotus root-like pores due to the cast structure in which the dendrite extends upward from the water-cooled copper hearth.
It was a porous body of. Nickel oxide powder, nickel powder,
The Ni alloy porous body was embedded in a mixed powder bed in which equal amounts of alumina powders were mixed, and the mixture was kept at 1050 ° C. for 2 hours in an Ar stream, then kept at 550 ° C. for 10 hours, and then gradually cooled to room temperature.

When the heat-treated porous body was observed with a scanning electron microscope, fine particles uniformly dispersed inside the porous body were detected. As a result of X-ray diffraction, peaks of anatase type and rutile type TiO ₂ were detected in addition to the peak of Ni. Since the anatase-type TiO ₂ is deposited, it is presumed that the porous structure exhibits a photocatalytic action.

Then, salad oil was dropped onto the porous structure at a rate of 0.1 mg / cm ² , and the surface of the porous body was irradiated with 1 mW / cm ² of ultraviolet light for 6 hours. The decrease amount A of the salad oil was determined from the weight change of the porous body measured before and after irradiation with ultraviolet light. For comparison, with respect to the porous body not subjected to the heat treatment, salad oil was dropped and irradiated with ultraviolet light in the same manner, and the decrease amount B of the salad oil was determined from the weight change before and after the irradiation with ultraviolet light. When the reduction amounts A and B were compared, the A / B ratio was 59 or more, and it was confirmed that the photocatalytic action by the anatase-type TiO ₂ was efficiently expressed.

It can be seen that the porous structure exhibits an excellent antifouling action because the amount of salad oil reduced is extremely large. In addition, Ni, which has excellent catalytic activity for chemical reactions such as hydrogenation, dehydrogenation reaction, reductive desulfurization, reductive alkylation, reductive amination, and redox reaction, is used as the base material of the isoporous structure. It is also expected to be used as an excellent composite catalyst in combination with the photocatalytic action of TiO ₂ .

[0021]

Example 2 Fe-6.4 atomic% Ni in an inert atmosphere
-14.4 atomic% Cr-15.0 atomic% Pt-5.0 atomic% Ti alloy was subjected to high frequency melting, and the molten alloy was cast in the same mold as in Example 1 and unidirectionally solidified. The obtained ingot is P
It was a Fe-Ti alloy porous body having a porosity of 60% in which fine particles of t were dispersed. The Fe—Ti alloy was embedded in a mixed powder bed in which equal amounts of iron oxide powder, iron powder, and alumina powder were mixed, and heat treatment was performed at 950 ° C. for 12 hours. Iron oxide is decomposed by this heat treatment, and the generated oxygen causes Fe-
The solute Ti contained in the Ni alloy is oxidized, and Fe--N
Fine-grained TiO ₂ was deposited on the surface and inside of the i alloy. Then, the temperature was maintained at 500 ° C. for 10 hours and then gradually cooled to room temperature.

X-ray diffraction of the heat-treated Fe-Ti alloy (porous structure) revealed that solute elements such as Ti and Cr were fine particles of anatase type oxide having a photocatalytic action. A porous structure was incorporated into the exhaust gas system of an automobile to quantify the NO _x component contained in the exhaust gas.
The quantitative result was the exhaust gas in which the NO _x concentration was reduced by 17% by volume as compared with the exhaust gas system in which the conventional catalyst was incorporated.

In order to further enhance the catalytic action of Pt, instead of 15 atomic% of Pt added to the starting alloy, an internal oxidation-treated Fe-Ti alloy porous body is formed into an emulsion in which Pt fine particles having a particle size of 5 to 10 nm are suspended. Soaked. The Fe-Ti alloy porous body after the emulsion dipping and dried, was subjected to the same heat treatment, the porous structures Pt particles and anatase TiO ₂ on the surface of the porous body, Cr ₂ O ₃ are uniformly dispersed can be obtained It was When this porous structure was used as an exhaust gas purifying catalyst, NO _x of exhaust gas was obtained under the same test conditions.
The concentration was reduced by 27%. This result shows that anatase type Ti
It is shown that O ₂ , Cr ₂ O ₃ and Pt fine particles are combined to exhibit an excellent exhaust gas purification function.

[0024]

Example 3 Mg powder was mixed with Ag powder in an amount of 30.0 atomic%, and the mixed powder was sintered at 450 ° C. to prepare a porous Ag—Mg alloy having a porosity of 75%. This Ag-Mg alloy is placed in a fluorine gas (F ₂ ) atmosphere,
Hold at 700 ° C. for 2 hours. Ag-M cooled to room temperature
Observation of the g alloy with a scanning electron microscope revealed that fine particles were uniformly dispersed inside the alloy. As a result of X-ray diffraction, a peak of MgF ₂ was detected. Therefore, it can be said that the heat-treated Ag—Mg alloy is a porous structure in which chemical resistance is improved by dispersing the MgF ₂ fine particles. Further, since Ag having excellent bactericidal action and catalytic activity is used as the base material, it can be used as a catalyst which maintains catalytic activity for a long period of time even when exposed to a harsh environment.

[0025]

Example 4 Zr powder was mixed with Mg powder at a ratio of 60.0 atomic%, and the mixed powder was sintered at 475 ° C. to obtain a Mg-Zr alloy porous body having a porosity of 85%. Mg-Z
The r alloy porous body was heated in a hydrogen stream at 530 ° C. for 1 hour and then gradually cooled to room temperature. When the produced porous structure was observed with a scanning electron microscope, fine particles were uniformly dispersed inside the Mg—Zr alloy. From the results of X-ray diffraction, it was found that the fine particles were ZrH ₂ . When the hydrogen release pressure of the porous structure was measured, it was 1 atm hydrogen release pressure at 290 ° C. This result indicates that the Mg-Zr-based porous structure is an excellent hydrogen storage material.

[0026]

INDUSTRIAL APPLICABILITY As described above, in the present invention, the alloy porous body containing the element Z having a high affinity is heat-treated in the atmosphere containing the element X, so that the compound Z--X is converted into the porous structure. Evenly dispersed. O, N, F, H
Etc. are used as the element X, and an oxide, a nitride, a fluoride, and a hydride are dispersed and deposited, respectively, to obtain a compound Z-
Functionality derived from X is imparted. Moreover, since the porous body is used as the starting material, the specific surface area of the precipitated compound fine particles becomes extremely large and the function of the compound Z-X is fully exhibited, so that a highly functional porous structure can be obtained. .

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Hirohito Hira             2-274 Shinonokaze, Midori-ku, Nagoya-shi, Aichi             14 (72) Inventor Mamoru Mabuchi             Independent trip to 1-1 Hirate-cho, Kita-ku, Nagoya City, Aichi Prefecture             Central Research Institute, National Institute of Advanced Industrial Science and Technology             Within

Claims (5)

[Claims] 1. A normal state is composed of an element Z having a large affinity with an element X in a vapor phase and an element Y serving as a matrix. The concentration of the element Z is 0.0001 to 70 atomic%, and the porosity is 0.1 to 95.
A porous body of 0% is prepared, and the porous body is prepared in an atmosphere containing a partial pressure of the element X which is insufficient for forming the compound of the element Y and the element X but is sufficient for forming the compound of the element Z and the element X. A method for producing a porous structure having functionality, which comprises heating to deposit a compound of an element Z and an element X in the form of particles or a plate on the surface and / or inside of the porous body. 2. When oxygen O is converted to element X, Si, M
n, P, Al, Zn, Ti, Ni, Cr, Co, Fe,
Be, Mg, Cd, In, Zr, Sn, Ce, Ca, G
a, B, Sb, Tl, Pb, Nb, Ta, Bi, Li,
Mo, W, V, Pb. 1 or 2 obtained from Hf
More than one kind of metal is used as element Z, and unlike element Z, Ag, Cu,
Ni, Fe, Pd, Co, Au, Pt, Cr, Mo,
W, Ti, Zr, Hf, V, Nb, Ta, Ge, Sn,
The production method according to claim 1, wherein one or more metals selected from Pb are used for the element Y. 3. When nitrogen N is changed to element X, Ti, Z
1 selected from r, Al, Fe, Cr, Mo, V, Si
Element or two or more metals as element Z, which is different from element Z
g, Cu, Ni, Fe, Pd, Co, Au, Pt, C
The production method according to claim 1, wherein one or more metals selected from r, Mo and W are used for the element Y. 4. When fluorine F is converted to element X, Be, M
element Z is one or more metals selected from g, Ca, Al, Ti, Si, and Cr, and unlike element Z, Ag, C
u, Ni, Fe, Pd, Co, Au, Pt, Cr, M
The production method according to claim 1, wherein one or more metals selected from o, W, Ti, and Zr are used for the element Y. 5. When hydrogen H is converted to element X, La, C
a, Li, Ti, K, Na, U, Mg, Ni, Co,
1 selected from V, Fe, Mn, Ce, Al, Y, Zr
Species or two or more species as element Z, different from element Z, Ag, C
u, Ni, Fe, Pd, Co, Au, Pt, Cr, M
The manufacturing method according to claim 1, wherein one or more metals selected from o, W, Ti, Zr, and Mg are used for the element Y.