JPH06264103A - Production of superfine particle of oxidation resistant intermetallic compound and its assemblage - Google Patents

Abstract

PURPOSE:To provide the superfine particles of a high-temp. oxidation resistant intermetallic compd. having high purity and excellent crystallinity by aggregating the clusters formed by melting and evaporating a blank material consisting of a reference metallic element and additive element by a plasma arc under prescribed conditions. CONSTITUTION:The reference metallic element (for example, Cu) having a b.p. bP1(K) and the additive element (for example, Al) having a b.p. bP2(K) are prepd. and the relation bP2/bP1 between these b.p. is specified to 0.8 to 1.25. The components of the elements mentioned above are adjusted to prepare the blank material 1 forming the intermetallic compd. by a gaseous phase reaction. The blank material 1 is then melted by the plasma arc in an inert atmosphere G to evaporate the clusters 3 of the intermetallic compd. compsn. These clusters 3 are aggregated, by which liquid drops 4 are formed.

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 ultrafine particles of oxidation resistant intermetallic compound and aggregates thereof.

[0002]

2. Description of the Related Art Conventionally, as ultrafine particles, for example, Cu ultrafine particles disclosed in JP-A-2-294417 are known.

[0003]

The ultrafine particles have a large specific surface area, strong activity, and extremely high reactivity.
Therefore, ultrafine particles have been attempted to be applied to an exhaust gas purifying catalyst element of an automobile engine in order to effectively utilize the specificity.

However, the conventional Cu ultrafine particles are not suitable for use as the catalyst element because they are significantly oxidized in the atmosphere at a temperature of about 100 ° C. and have no high temperature oxidation resistance.

In view of the above, it is an object of the present invention to provide a method for producing the above ultrafine particles having excellent high temperature oxidation resistance and aggregates thereof.

[0006]

The ultrafine particles of the oxidation resistant intermetallic compound according to the present invention have a boiling point of the reference metal element of bp1.
(K) and the boiling point of one or more additional metal elements is b
When p2 (K), the mutual relationships of the boiling points are 0.8
It is characterized in that 0 <bp2 / bp1 <1.25, and is composed of an intermetallic compound by a gas phase reaction between the reference metal element and the added metal element.

The method for producing an aggregate of oxidation resistant intermetallic compound ultrafine particles according to the present invention comprises a reference metal element having a boiling point of bp1 (K) and one or more additive elements having a boiling point of bp2 (K). And their boiling points are 0.80 <
bp2 / bp1 <1.25, and prepare a material whose composition is adjusted so that an intermetallic compound is formed by a gas phase reaction between the reference metal element and the added metal element, and use the material as the reference metal. By plasma arc melting in an atmosphere containing a gas inert to the element and the additional metal element, evaporation of clusters of a large number of intermetallic compounds containing the reference metal element and the additional metal element, and then the above-mentioned It is characterized in that the formation of droplets due to cluster aggregation is revealed.

[0008]

Since the ultrafine particles are composed of an intermetallic compound, they have excellent high temperature oxidation resistance, and the mutual relationships of boiling points are specified as described above and obtained by a gas phase reaction. Therefore, it has high purity, good crystallinity, and excellent high-temperature stability.

Furthermore, in the intermetallic compound ultrafine particles,
Since each element on the surface is arranged in a regular manner, the intermetallic compound ultrafine particle surface has a unique geometrical property different from the ultrafine particle surface composed of a simple metal, and the bonding form between atoms is a metal. Unlike ultrafine particles composed of a simple substance, therefore, the intermetallic compound ultrafine particles have unique electronic properties.

When the intermetallic compound ultrafine particles having such characteristics are used as a catalyst element for purifying exhaust gas of an automobile engine, they exhibit excellent catalytic activity and high temperature durability at high temperatures.

Since the intermetallic compound ultrafine particles have a surface having unique geometrical properties as described above, various sensors whose sensitivity, selectivity, etc. are influenced by the surface state, such as gas, temperature, It is effective as a constituent material for sensors such as humidity.

Further, since the intermetallic compound ultrafine particles have a unique electronic property as described above, they have a large crystal magnetic anisotropy, and are therefore effective as a hard magnetic material.

According to the above manufacturing method, an aggregate of ultrafine particles made of an intermetallic compound can be easily obtained in one melting step. Further, since the boiling points of the reference metal element and the added metal element are close to each other, the particle size of the intermetallic compound ultrafine particles can be easily controlled by the melting temperature, and further the intermetallic compound ultrafine particles in the gas phase reaction can be controlled. Since they are manufactured, the particles do not aggregate.

However, the relationship between the boiling points is bp2 / bp1.
When ≦ 0.80, the boiling point bp2 of the added metal element is lower than the boiling point bp1 of the reference metal element, and the difference between the two boiling points becomes large, so that the evaporation rate of the added metal element becomes faster than that of the reference metal element. . As a result, clusters containing the reference metal element and clusters containing the added metal element are separately formed, and since these clusters do not aggregate, that is, do not collide, fuse, or grow, the clusters containing the reference metal element aggregate with each other. Due to the mutual aggregation of the clusters including and the added metal element, ultrafine particles made of a simple metal corresponding to these elements can be obtained, and ultrafine particles made of an intermetallic compound cannot be obtained. On the other hand, when bp2 / bp1 ≧ 1.25, the evaporation rate of the reference metal element becomes faster than that of the added metal element, so that the same phenomenon as described above occurs.

[0015]

[Examples] Ultrafine particles of intermetallic compounds having oxidation resistance (hereinafter referred to as IMC ultrafine particles in this column) have a reference metal element and one or more additive metal elements, and are formed by a gas phase reaction of these elements. It is composed of intermetallic compounds. Since it is an intermetallic compound by a gas phase reaction, the boiling point of the reference metal element is bp1 (K, Kelvin temperature, the same applies hereinafter).
And the boiling point of the added metal element is bp2 (K), the relationship between the boiling points is 0.80 <bp2 / bp1.
<1.25. The particle size D of the IMC ultrafine particles is D ≦ 20
It is 0 nm.

In the production of the IMC ultrafine particles, a reference metal element having a boiling point of bp1 (K) and a boiling point of bp2
(K) one or more additive elements, the mutual boiling points of which are 0.80 <bp2 / bp1 <1.25, and the intermetallic compounds are formed by a gas phase reaction between the reference metal element and the additive metal element. By preparing a material whose composition is adjusted so that a compound is formed, and melting the material by plasma arc melting in an atmosphere containing a gas inert to the reference metal element and the added metal element, A method is adopted in which evaporation of a large number of clusters of intermetallic compound composition containing an additive metal element and subsequent formation of droplets by cluster aggregation are revealed.

FIG. 1 shows the formation mechanism of IMC ultrafine particles in the above manufacturing method.

In FIG. 1 (a), when the material 1 is plasma-arc melted using the electrode 2 in an atmosphere containing an inert gas G, the gas G is dissociated (G ⁺ ) into an atomic state by the arc plasma. , Melted into the melted raw material 1, then released as molecules (G) from within the raw material 1, and this dissolution and release are repeated. At the time of this discharge, many clusters 3 are actively evaporated from the material 1. This cluster 3 has an IMC composition containing a reference metal element and an additive metal element. This is because the evaporation rates of both elements are almost equal due to the mutual relationship of the boiling points.

In FIG. 1B, since the clusters 3 have substantially the same composition, they are aggregated, that is, collided, fused and grown to form spherical droplets 4 of ultrafine particle size of 200 nm or less, By solidifying it, IMC ultrafine particles are obtained.

A specific example will be described below.

FIG. 2 shows an apparatus used for producing an aggregate of IMC ultrafine particles. The manufacturing apparatus has a main chamber 5 and a sub-chamber 6 continuously provided below the main chamber 5, and both chambers 5 and 6 communicate with each other via a duct 7 and a nozzle 8 attached to the lower end thereof. To do. A tungsten electrode 2 inserted in the main chamber 5 and a Cu hearth 9 installed in the main chamber 5 are connected to a power supply 10. A movable substrate 11 is provided in the sub chamber 6.
Are arranged to face the nozzle 8. The main chamber 5 is connected to the atmospheric gas supply source 12, while the sub chamber 6 is connected to the vacuum pump 13.

C as an alloy material composed of Cu and Al
u ₅₀ Al ₅₀ alloy material (numerical value is atomic%) was selected. In this case, the reference metal element is Cu and the added metal element is Al. The boiling point bp1 of Cu is 2836K, the boiling point bp2 of Al is 2793K, and the relationship bp2 / bp1 between these boiling points is 0.98. Cu and A
As the gas inert to l, two kinds of argon gas and hydrogen gas are used.

Next, an example of manufacturing an aggregate of IMC ultrafine particles using the above manufacturing apparatus will be described.

(1) 30 to 50 g of Cu in the hearth 9
₅₀ Al ₅₀ alloy material 1 was added.

(2) The vacuum pump 13 is operated to evacuate the main chamber 5 and the sub-chamber 6 until the atmospheric pressure in the chambers 5 and 6 reaches 1 × 10 ⁻⁴ Torr, and then the atmospheric gas supply source 12 Was operated to supply argon gas and hydrogen gas into the main chamber 5. The argon gas and the hydrogen gas in the main chamber 5 flow into the sub chamber 6 through the duct 7 and the nozzle 8 by the operation of the vacuum pump 13 and then flow out from the sub chamber 6, so that the atmospheric pressure in the main chamber 5 is 300. ~
The supply amounts of the argon gas and the hydrogen gas from the atmospheric gas supply source 12 were adjusted so that the steady state was 600 Torr.

(3) Tungsten electrode 2 and hearth 9
A voltage was applied between them to generate an arc discharge, and the alloy material 1 was plasma-arc melted under the condition of an arc current of 100 to 300A. This melting evaporates the cluster 3 of IMC composition containing Cu and Al, and the cluster 3 aggregates to form droplets, and then the droplets are cooled.
The MC ultrafine particles 14 are formed, and the IMC ultrafine particles 14 are formed.
Was ejected from the nozzle 8 through the duct 7 onto the substrate 11 and deposited there, whereby an aggregate of IMC ultrafine particles 14 having a particle size D of D ≦ 200 nm was obtained.

FIG. 3 shows the X-ray diffraction result of IMC ultrafine particles. Based on FIG. 3, the surface spacing d and the relative intensity (I / I
_When the IMC ultrafine particles were identified in order to obtain ₁ ), it was found that the IMC ultrafine particles consisted of only IMC Al ₄ Cu ₉ .

Next, in order to investigate the oxidation resistance of the IMC ultrafine particles, the IMC ultrafine particles are heated in the air from room temperature to 750 ° C. at a temperature raising rate of 10 ° C./min, and heated at a predetermined temperature. When the fine particles were weighed and the weight increase rate due to the oxidation was obtained, the results shown in FIG. 4 were obtained. For comparison, data of Cu ultrafine particles having a particle diameter D ≦ 200 nm and commercially available Cu powder having a particle diameter D ≦ 74 μm are also shown in FIG.

As is apparent from FIG. 4, the IMC ultrafine particles are hardly oxidized in the heating temperature range of normal temperature to about 300 ° C., and the oxidation progresses extremely slowly in the heating temperature range of about 300 to about 500 ° C. In the heating temperature range of about 500 to about 650 ° C., the oxidation proceeds slightly faster, and about 650 to 75
In the heating temperature range of 0 ° C, there is a tendency that the oxidation proceeds rapidly.

In the case of Cu ultrafine particles, the heating temperature is about 100 ° C.
In the case of commercially available Cu powder, the oxidation proceeds rapidly at a heating temperature of about 200 ° C.

From these facts, IMC ultrafine particles are C
It is clear that it has excellent high-temperature oxidation resistance as compared to u ultrafine particles and the like.

Next, the following NOx purification test was conducted on the IMC ultrafine particles in order to investigate the function as a catalyst element for purifying exhaust gas of an automobile engine.

In the preparation of the catalyst, the IMC ultrafine particles were mixed with γ-Al ₂ O ₃ particles so that the amount of the IMC ultrafine particles was 10% by weight, and they were sufficiently mixed, A method of molding the mixed particles into pellets and then firing the molded product was adopted.

In the NOx purification test, the catalyst tank supporting 1 g of the catalyst was loaded with N 2 at a reaction temperature of 500 ° C.
Helium gas containing 2000 ppm of O was flowed at a flow rate of 100 ml / min for a predetermined time, and the gas passing through the catalyst tank was analyzed by gas chromatography to determine the NO conversion rate. For comparison, a catalyst similar to the above was prepared using the Cu ultrafine particles as a catalyst element, and a NOx purification test similar to the above was performed.

Table 1 shows the NOx purification test results for each catalyst.

[0036]

[Table 1] It can be seen from Table 1 that the catalyst using the IMC ultrafine particles 1 as a catalyst element exhibits excellent catalytic activity and that it lasts for a long time. On the other hand, a catalyst using Cu ultrafine particles as a catalyst element has extremely low catalytic activity because the element has poor high temperature oxidation resistance.

Next, the relationship between various alloy materials and IMC ultrafine particles obtained by using them will be described.

(A) When Cu-Al alloy material is used The reference metal element is Cu and the boiling point bp1 is 2836K. The added metal element is Al and the boiling point bp2 is 2
It is 793K. Therefore, bp2 / bp1 is 0.98 as described above. Table 2 shows the types of alloy materials and IMC of ultrafine particles.

[0039]

[Table 2] In Table 2, when the Cu ₅₀ Al ₅₀ alloy material is used, the ultrafine particle IMC becomes an Al ₄ Cu ₉ single phase as described above.

(B) When Cu-Sn alloy material is used The reference metal element is Cu and the boiling point bp1 is 2836K. The added metal element is Sn and the boiling point bp2 is 2
It is 876K. Therefore, bp2 / bp1 is 1.01
It is. Table 3 shows the types of alloy materials and IMC of ultrafine particles.
It is as follows.

[0041]

[Table 3]In Table 3, Cu₆₀Sn₄₀When alloy material is used,
IMC of particles is almost Sn _FiveCu₆It becomes a single phase.

(C) When Cu-Ge alloy material is used The reference metal element is Cu and the boiling point bp1 is 2836K. The additive metal element is Ge, and the boiling point bp2 is 3.
It is 107K. Therefore, bp2 / bp1 is 1.09
It is. Table 4 shows the types of alloy materials and IMC of ultrafine particles.
It is as follows.

[0043]

[Table 4] In Table 4, when the Cu ₇₅ Ge ₂₅ alloy material is used, the IMC of the ultrafine particles is substantially GeCu ₃ single phase.

(D) When Cu-Si alloy material is used The reference metal element is Cu and the boiling point bp1 is 2836K. The added metal element is Si and the boiling point bp2 is 3
It is 540K. Therefore, bp2 / bp1 is 1.24
It is. Table 5 shows the types of alloy materials and IMC of ultrafine particles.
It is as follows.

[0045]

[Table 5] (E) When using Cu-Ga alloy material The reference metal element is Cu and the boiling point bp1 is 2836K. The additive metal element is Ga, and the boiling point bp2 is 2.
It is 478K. Therefore, bp2 / bp1 is 0.87
It is. Table 6 shows the types of alloy materials and IMC of ultrafine particles.
It is as follows.

[0046]

[Table 6] In Table 6, when the Cu ₇₀ Ga ₃₀ alloy material is used, the IMC of the ultrafine particles becomes a Ga ₄ Cu ₉ single phase.

(F) When using Al-Ni alloy material The reference metal element is Al and the boiling point bp1 is 2793K. The additive metal element is Ni and the boiling point bp2 is 3
It is 187K. Therefore, bp2 / bp1 is 1.14
It is. Table 7 shows the types of alloy materials and IMC of ultrafine particles.
It is as follows.

[0048]

[Table 7] (G) When using an Al-Fe alloy material The reference metal element is Al and the boiling point bp1 is 2793K. The additive metal element is Fe and the boiling point bp2 is 3
It is 135K. Therefore, bp2 / bp1 is 1.12
It is. Table 8 shows the types of alloy materials and IMC of ultrafine particles.
It is as follows.

[0049]

[Table 8] (H) When using an Al-Cr alloy material The reference metal element is Al and the boiling point bp1 is 2793K. The additive metal element is Cr and the boiling point bp2 is 2
It is 945K. Therefore, bp2 / bp1 is 1.05
It is. Table 9 shows the types of alloy materials and IMC of ultrafine particles.
It is as follows.

[0050]

[Table 9] IMC ultrafine particles containing two kinds of additive metal elements I
Examples of MC include quasicrystalline Al ₆₅ Cu ₂₀ Fe ₁₅ (numerical value is atomic%). In this case, the reference metal element is Cu (bp1 = 2836K), and the additive metal element is A
l (bp2 = 2793K) and Fe (bp2 = 313)
5K). The bp2 / bp1 between Cu and Fe is 1.10, and the bp2 / bp1 between Cu and Al is 0.98 as described above.

As a similar IMC, Cu ₂ SnX is used.
(However, X is any one of Fe, Cu and Ni). In this case, the reference metal element is Cu
(Bp1 = 2836K), and the additive metal element is Fe
(Bp2 = 3135K), Co (bp2 = 3201K)
And any one of Ni (bp2 = 3187K) and Sn
(Bp2 = 2876K). B between Cu and Sn
p2 / bp1 is 1.01, Cu and Fe as described above.
Bp2 / bp1 between them is 1.10 as described above, bp2 / bp1 between Cu and Co is 1.12, and Cu and Ni.
The bp2 / bp1 between them is 1.12. The IMC ultrafine particles are effective as a hard magnetic material.

Another binary alloy material in which the reference metal element is Cu, for example, a Cu--Zn alloy material (Zn bp2
= 1180K) and Cu-Mg alloy material (Mg b
p2 = 1363K), even if the composition is adjusted to the IMC forming composition, bp2 / bp1 is bp2 / bp1 ≦.
Since it is 0.8, IMC ultrafine particles cannot be produced. In addition, for example, Cu-Ti alloy material (Ti
Bp2 = 3562K), Cu-Y alloy material (Yb
p2 = 3611K), Cu-La alloy material (La b
p2 = 3730K) and Cu-Ce alloy material (Ce
Bp2 = 3699K), the composition is IMC
Even if the composition is adjusted, bp2 / bp1 is bp2 / bp
Since 1 ≧ 1.25, IMC ultrafine particles cannot be produced.

The material in the present invention is not limited to the alloy material described above, and it is also possible to use a mixed powder of the powder of the reference metal element and the powder of one or more additive metal elements.

[0054]

EFFECTS OF THE INVENTION Since the ultrafine particles according to the present invention are composed of an intermetallic compound, they have excellent high temperature oxidation resistance and high temperature stability, and have a unique geometrical surface and a unique electronic property. Therefore, it is effective as a catalyst element for purifying exhaust gas of an automobile engine, a constituent material of various sensors, a hard magnetic material, and the like.

According to the manufacturing method of the present invention,
It is possible to easily obtain an aggregate of the intermetallic compound ultrafine particles having the above-mentioned characteristics in a single melting step without aggregation, and it is also easy to control the particle diameter of the particles.

[Brief description of drawings]

FIG. 1 is an explanatory view showing a formation mechanism of intermetallic compound ultrafine particles.

FIG. 2 is a schematic view of an intermetallic compound ultrafine particle aggregate manufacturing apparatus.

FIG. 3 is an X-ray diffraction diagram of intermetallic compound ultrafine particles.

FIG. 4 is a graph showing a relationship between a heating temperature and a weight increase rate due to oxidation.

[Explanation of symbols]

 1 Material 2 Electrode 3 Cluster 4 Droplet 9 Hearth 10 Power Supply 12 Atmosphere Gas Supply Source 14 Intermetallic Compound Ultrafine Particle

 ─────────────────────────────────────────────────── ─── Continuation of front page (71) Applicant 000005326 Honda Motor Co., Ltd. 2-1-1 Minami-Aoyama, Minato-ku, Tokyo (72) Inventor Ken Masumoto 3-8-22, Uesugi, Aoba-ku, Sendai-shi, Miyagi (72) ) Inventor Akihisa Inoue Kawauchi Muzen, Aoba-ku, Sendai City, Miyagi Prefecture 11-806 (72) Inventor Masashi Yamaguchi 1-16-23, Izumizaki, Taichiro-ku, Sendai City, Miyagi Prefecture Inventor Katsutoshi Nozaki, Wako City, Saitama Prefecture Central 1-4-1 Stock Company Honda Technical Research Institute

Claims (2)

[Claims] 1. The boiling point of the reference metal element is bp1 (K), and the boiling point of one or more added metal elements is bp2 (K).
, The boiling point relationship is 0.80 <bp2
/Bp1<1.25, and is composed of an intermetallic compound obtained by a gas phase reaction between the reference metal element and an additive metal element, which is an oxidation resistant intermetallic compound ultrafine particle. 2. A reference metal element having a boiling point of bp1 (K) and one or more additive elements having a boiling point of bp2 (K), and the mutual relationships of the boiling points are 0.80 <bp2 / b.
A material having p1 <1.25 and having a component adjusted so that an intermetallic compound is formed by a gas phase reaction between the reference metal element and the added metal element is prepared, and the material is used as the reference metal element and By plasma arc melting in an atmosphere containing an inert gas for the additive metal element, evaporation of a cluster of a large number of intermetallic compound compositions containing the reference metal element and the additive metal element, and then the cluster of A method for producing an aggregate of oxidation-resistant intermetallic compound ultrafine particles, which comprises causing formation of droplets by aggregation.