JPH0812309A - Element crystal superfine particulate encapsulated in carbon wall capsule - Google Patents

Abstract

PURPOSE:To produce crystal superfine particulates of 3d transition metal element encapsulated in a carbon wall capsule and stabilized by executing arc discharge between a cathode of pure carbon and an anode using a carbon composite electrode containing 3d transition metal element. CONSTITUTION:Powder of a simple substance, a compound such as carbide, oxide or carbonate, or an alloy of an element selected from among 3d transition metals in an amount of 2-15wt.%, a carbon substrate adhesive and graphite at need at mixed to form a carbon composite electrode. The mixture is pre- heated to 100-140 deg.C for 3-12 hour in the atmosphere and heat treated at 600-1500 deg.C for 0.3-3 hour in vacuum in an arc discharge furnace. By using this carbon composite electrode as an anode and a pure carbon as a cathode, a direct current arc discharge is executed for 1-10min in a gaseous helium atmosphere whose pressure is lower than the atmosphere in the arc discharge furnace. Soot generated at periphery of the electrode is captured and separated to obtain the superfine particulates of the element crystal encapsulated in the capsule having a multi-layer carbon wall. The average grain size is 5-1000nm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to single crystal ultrafine particles encapsulated in a carbon wall envelope. Single crystal ultrafine particles encapsulated in the carbon wall envelope of the present invention, due to its reactivity,
It is expected to be used as a material for hydrogen storage materials, superconducting materials, electronic materials, magnetic materials, magnetic recording materials, optical materials, sintered materials, catalyst materials, sensor materials, and the like.

[0002]

2. Description of the Related Art Conventionally, single crystal ultrafine particles have been produced by two methods, a gas phase method and a solid phase method. The gas phase method is a method in which a liquid material is vaporized and a mixed gas of methane and argon is introduced into laser light or plasma, or a solid material is sputtered to produce ultrafine particles. On the other hand, the solid phase method is a method of pulverizing a solid raw material into ultrafine particles.

[0003] However, in general, single crystal ultrafine particles are difficult to handle because they are unstable in the atmosphere. In order to stabilize ultrafine particles, surface treatment methods such as stabilization treatment and encapsulation with a special compound are known, but the method is complicated, and the deceptive method used for surface treatment Since the compound is mixed in the ultrafine particles, it is difficult to use the compound as a material.

[0004]

Accordingly, it is desired to provide single crystal ultrafine particles which are stabilized so as not to adversely affect the use of ultrafine particles as a material.

[0005]

The inventor of the present invention has conducted intensive studies on the above-mentioned problems, and as a result, has found that a direct current arc between a positive electrode, which is a carbon composite electrode containing an element selected from 3d transition metals, and a pure carbon negative electrode. It has been found that, if the carbon composite electrode is used as an electrode in causing an electric discharge or in an AC arc discharge, ultrafine particles of a single crystal encapsulated in a multilayer carbon wall envelope can be produced, and the present invention Was completed.

That is, the gist of the present invention resides in single crystal ultrafine particles of an element selected from 3d transition metals, which are included in a multilayer carbon wall envelope.

The element constituting the single crystal ultrafine particles is 3d
It is a transition metal.

[0008] The ultrafine particles are usually isotropic (spherical), but can also be elongated (spheroidal). The converted average particle diameter of the ultrafine particles is usually 5 to 1000 nm, preferably 5 to 1000 nm.
To 100 nm, more preferably 5 to 30 nm. In the case of an elongated sphere, the ratio of the long axis to the single axis is usually 1 to 100
It is. The elementary ultrafine particles are a single crystal, a single crystal, or a multiple twin.

The single crystal ultrafine particles are of a size exhibiting at least metallic properties, and usually consist of 10 ⁴ or more atoms. The upper limit of the number of atoms of the single crystal ultrafine particles is usually 10 ¹² .

[0010] An envelope body containing single crystal ultrafine particles usually has a multilayer wall of 5 to 50 layers. The envelope is usually isotropic, but may be cylindrical.

The single crystal ultrafine particles encapsulated in the multilayer carbon wall envelope can be produced by the method described below. First, a manufacturing method using DC arc discharge will be described.

The form of the 3d transition metal element contained in the carbon composite electrode is not particularly limited, and may be used as a simple substance, a compound such as a carbide, oxide or carbonate, or an alloy. Specifically, cobalt, nickel, iron, cobalt-
Nickel alloy, cobalt oxide, cobalt carbonate, nickel oxide, nickel carbonate, iron oxide and the like are used.

The carbon composite electrode can be formed by molding a mixture of a simple substance of an element, a powder of a compound or alloy such as a carbide, an oxide or a carbonate, and a carbon substrate adhesive.
The above mixture may be further mixed with graphite, if necessary. In the case of a carbon positive electrode having a deceptive composite matrix structure, the amount of the elemental element is usually 2 to 15% by weight, preferably 10 to 12% by weight, based on the positive electrode composite matrix portion.
It is.

The carbon composite electrode can be formed by forming a hole in the center of a pure carbon electrode and filling the inside with a simple substance, carbide or alloy of an element capable of forming carbide, or a mixture thereof. . In the case of a carbon composite electrode having a deceptive packing structure, the ratio of the sectional area of the hole to the sectional area of the electrode is usually about 25%. When a mixture is used for the filler, 30% by weight based on the whole mixture is the upper limit for maintaining the tackiness of the mixture. In addition, usually, the shape of the carbon composite electrode is cylindrical.

The carbon composite electrode is usually placed in a vacuum of 1 × 10 ⁻³ Torr or less in a vacuum of 600 to 1500 before arc discharge.
C. for 0.3 to 3 hours.

The above-mentioned heat treatment is preferably performed in an arc discharge furnace. This is because, after the heat treatment, the electrode can be used as a positive electrode for direct current arc discharge without exposing the electrode to the atmosphere, thereby avoiding denaturation of the electrode surface that occurs when the electrode is exposed to the air. Further, in the case of a carbon composite electrode having a packing structure, in order to reduce the loss during the heat treatment of the filling material, the heat treatment may be performed by bringing the filling surface into contact with the opposite negative electrode.

Prior to the above heat treatment, it is preferable to perform preheating of the carbon composite electrode. And in the atmosphere 100
When preheating is performed at ~ 140 ° C for 3 to 12 hours, the mixture is solidified and subsequent handling of the electrode is facilitated. In a vacuum of 1 × 10 ⁻⁵ Torr, 500 to 700
When preheating at 24 ° C. for 24 to 70 hours, the yield of elemental ultrafine particles contained in the carbon wall envelope is further improved. In particular, the carbon composite electrode of the present invention containing a simple substance, a carbide, or an alloy of an element is preferable since a deceptive effect can be obtained by a short heat treatment as compared with the case of a carbon composite electrode containing an oxide. The deceptive effect is presumed to be based on the removal of impurities contained in the adhesive.

The DC arc discharge is performed by causing a DC arc discharge between a positive electrode and a negative electrode, which are carbon composite electrodes kept at an appropriate distance, in an arc discharge furnace. When an electrode having a packing structure is used as the carbon composite electrode, DC arc discharge is performed with the filling surface facing the negative electrode. The material of the negative electrode is usually pure carbon.

In DC arc discharge, conditions such as discharge power, atmosphere, pressure, time, and distance between electrodes are appropriately selected with reference to the ratio of the weight of the deposit on the negative electrode to the consumption weight of the carbon composite electrode. Power is typically 0.4-2k
W, atmosphere is usually a rare gas, preferably helium gas, pressure is usually below atmospheric pressure, time is usually
1 to 10 minutes.

When helium gas is used as the atmosphere, since the pressure does not affect the ratio of the weight of the deposit on the negative electrode to the weight of the carbon composite electrode, the discharge conditions can be easily set. Typical conditions for DC arc discharge include a helium atmosphere, a pressure of 100 Torr, and a discharge power of 0.6 k.
The condition of W is mentioned.

By performing the DC arc discharge, a cylindrical deposit grows on the cathode, and soot is generated around the positive and negative electrodes. The cathode deposit is cylindrical,
The cylinder has a dual structure in which the outside is relatively hard and gray, and the inside is relatively soft and black. By collecting soot and performing a separation operation, ultrafine particles of elemental single crystals encapsulated in an envelope (super fullerene) having a multilayer carbon wall can be obtained.

The envelope usually has a multilayer wall of 5 to 50 layers. The shape of the obtained ultrafine elemental single crystal particles is usually isotropic, but may also be elongated. The converted average particle diameter of the obtained ultrafine particles is usually 5 to 1000 nm.
It is. The element single crystal ultrafine particles are single crystal, single crystal or multiple twin.

The envelope having a multilayer carbon wall can be decomposed by irradiation with an electron beam or the like. Encapsulated elementary single crystal ultrafine particles include hydrogen storage materials, superconducting materials, electronic materials, magnetic materials, magnetic recording materials, optical materials, sintered materials,
When producing a catalyst material and a sensor material, it can be easily used as a stable material in the atmosphere.

Since the encapsulant has a multilayered carbon wall, it blocks oxygen and the like having high reactivity with carbides. As a result, it is presumed that the encapsulated ultrafine particles of elemental single crystals can stably exist. .

In another manufacturing method, ultrafine particles of an elementary single crystal encapsulated in a carbon wall envelope are manufactured by using an AC arc discharge. That is, except that the carbon composite electrode described in the manufacturing method using DC arc discharge is used, and an AC arc discharge is caused between them, the same method as described in the manufacturing method using DC arc discharge is used. Ultrafine particles of elemental single crystals encapsulated in the wall envelope can be produced.

In this case, since the carbon composite electrode is used for both electrodes, the yield of the encapsulating body containing the elementary single crystal ultrafine particles with respect to the consumption amount of the carbon composite electrode is not changed. The amount of the ultrafine particles obtained by the above method is about twice as large as that in the case of DC arc discharge.

[0027]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to the following examples unless it exceeds the gist of the present invention.

Example 1 Cobalt simple substance Co (Kanto Chemical Co., Ltd., purity 99.0%)
And reducing graphite bond (Amco, 551-R)
(Trade name)) were mixed at a weight ratio of about 0.3: 1. This was filled in a hole of 3 mm in diameter and 4 cm in length formed in a carbon rod (external diameter: 6 mm, length: 8 cm, purity: 99.999%, Nippon Carbon Co., Ltd.).

Next, the above-mentioned carbon rod was placed in the atmosphere for 120 hours.
After heating for 3 hours at ° C., in a vacuum of 1 × 10 ^-5 Torr 6
Heating was performed at 00 ° C. for 24 hours to obtain an anode. In the arc discharge furnace, the charged portion of the anode is installed so as to face the cathode of pure carbon, and the two are kept in contact with each other, and 1 × 10 ⁻³ To
Heated at 1200-1450 ° C. in rr vacuum for 1 hour.

Next, both electrodes are kept in a non-contact state, and 30 A
Arc discharge was caused under the condition of a constant current of 15 to 20 V. About 8 minutes of discharge, 4 cm on the cathode
Soot was formed around the positive and negative electrodes of a cylindrical deposit with a length of. The weight ratio of sediment to soot was about 1.5: 1. The cylindrical sediment had a structure that could be clearly identified from its longitudinal section. That is, the outside was relatively hard and gray, and the inside was relatively soft and black. The weight ratio of the black part to the gray part was about 1: 4.

Further, a small amount of the encapsulant having a multi-layered carbon wall enclosing a crystal was observed in the black portion, and a large amount was observed in the soot. In particular, it was found that about 80% of the encapsulant having multiple carbon walls present in the soot contained crystals. The yield of the envelope having the multilayered carbon wall enclosing the crystal is 41% by weight based on the consumption of the composite electrode, and most of the crystal has β-C
o, a very small amount was confirmed to be Co ₃ C.

Elemental analysis of black matter and soot by electron beam X-ray analysis showed that only cobalt was observed. Further, as a result of analysis of carbon and oxygen, it was confirmed that carbon was present but oxygen was hardly present. From a transmission electron micrograph (bright field image) of this substance, lattice fringes of crystals were observed inside the envelope having about 10 layers of carbon walls.

As a result of analyzing the encapsulated crystalline substance by an electron diffraction method and an X-ray diffraction method, the crystal structure of the substance occupying most of the substance is face-centered cubic, and the lattice constant is a = 3.5.
44 ± 0.003 °. This agreed with the literature value for the β-Co crystal with an accuracy of 1.7%. Further, the crystal structure of a very small amount of substance is orthorhombic, and the lattice constants are a = 4.573 ± 0.046 ° and b = 5.137 ±.
0.051 ° and c = 6.758 ± 0.068 °. These agreed with the literature values for the Co ₃ C crystal with an accuracy of 1.7%. α-Co and Co ₂ C were examined as candidate substances other than β-Co and Co ₃ C, but no agreement in lattice constant with literature values was found within the precision of the experiment. From the above, most of the encapsulated crystalline material is β-Co crystal, and a very small amount is Co-crystal.
It was identified as a ₃ C crystal.

After heating the above composite electrode at a temperature of 1300 to 1450 ° C. and a degree of vacuum of 10 ⁻³ Torr for 10 to 60 minutes (no arc discharge), the mixture inside the electrode was examined with an electron microscope. As a result, generation of an envelope having a multilayered carbon wall enclosing the crystal was observed. Its production rate tended to increase with increasing heating temperature and heating duration. Under the conditions of about 1450 ° C. and 10 to 20 minutes, the wrapping body having the multilayered carbon wall containing the crystal was only about 8% by weight based on the consumption of the composite electrode. As a result of electron beam diffraction and X-ray diffraction, it was found that most of the crystal in this case was β-Co and a very small amount was Co ₃ C.

Example 2 Cobalt oxide Co ₃ O ₄ (Kanto Chemical Co., Ltd., purity 99.9)
5%) and reducing graphite bond (Amco, 551)
-R (trade name)) was mixed at a ratio of about 0.3: 1 by weight. The preparation of the composite electrode, heat treatment and arc discharge conditions were as follows: heating at 600 ° C. in vacuum of 1 × 10 ⁻⁵ Torr
It is the same as Example 1 except that it was set to 0 hours. The discharge for about 8 minutes produced a 4 cm long cylindrical deposit on the cathode and soot around the positive and negative electrodes. The weight ratio of sediment to soot was about 1.5: 1.

The above-mentioned cylindrical sediment had a structure that could be clearly identified from its longitudinal section. That is, the outside was relatively hard and gray, and the inside was relatively soft and black. The weight ratio of the black part to the gray part is about 1: 4
Met. A small amount of the enveloping body having a multilayered carbon wall containing crystals was observed in the black portion, and a relatively large amount was found in the soot. About 70% of the encapsulants having multiple carbon walls present in the soot contained crystals. The yield of the envelope having multiple layers of carbon walls enclosing the crystal was about 26% by weight based on the consumption of the composite electrode.
Most of the crystals were analyzed by the same analysis as in Example 1 to obtain β-C
o, a very small amount was confirmed to be Co ₃ C.

Example 3 Cobalt carbonate CoCO ₃ (Kanto Chemical Co., Ltd., 43% to 4%)
8% Co) and reducing graphite bond (Amco, 551-R (trade name)) were mixed at a weight ratio of about 0.3: 1. The preparation of the composite electrode, the heat treatment, and the arc discharge conditions are the same as in Comparative Example 1. After about 8 minutes of discharge, a 4 cm long cylindrical deposit on the cathode, positive and negative
Soot was formed around the negative electrodes. The weight ratio of sediment to soot was about 1.5: 1.

The above-mentioned cylindrical deposit had a structure that could be clearly identified from its longitudinal section. That is, the outside was relatively hard and gray, and the inside was relatively soft and black. The weight ratio of the black part to the gray part was about 1: 4. A small amount of the encapsulant having a multilayered carbon wall enclosing the crystal was found in the black portion, and a relatively large amount was found in the soot. Approximately 70% of the encapsulants having multiple carbon walls in soot contain crystals
Met. The yield of the envelope having the multilayered carbon wall enclosing the crystal was about 16% by weight based on the consumption of the composite electrode. Most of the crystals were confirmed to be β-Co and a very small amount was Co ₃ C by the same analysis as in Example 1.

Example 4 Nickel simple substance Ni (Kanto Chemical Co., Ltd., purity: 99.0%)
And reducing graphite bond (Amco, 551-R)
(Trade name)) were mixed at a weight ratio of about 0.3: 1. The preparation of the composite electrode, heat treatment, and arc discharge conditions were the same as in Example 1. The discharge for about 8 minutes produced a 4 cm long cylindrical deposit on the cathode and soot around the positive and negative electrodes. The weight ratio of sediment to soot is about 1.
5: 1.

The above-mentioned cylindrical sediment had a structure that could be clearly identified from its longitudinal section. That is, the outside was relatively hard and gray, and the inside was relatively soft and black. The weight ratio of the black part to the gray part was about 1: 4. A small amount of the encapsulant having a multilayered carbon wall enclosing the crystal was found in the black portion, and a relatively large amount was found in the soot. In particular, it was found that about 80% of the encapsulant having multiple carbon walls present in the soot contained crystals. The yield of the envelope having the multilayered carbon wall enclosing the crystal was 41% by weight based on the consumption of the composite electrode, and the crystal was identified as Ni as described below.

Elemental analysis of black matter and soot by electron beam X-ray analysis showed that only nickel was observed. Further, as a result of analyzing carbon and oxygen, it was confirmed that carbon was present but oxygen was scarcely present. From a transmission electron micrograph (bright field image) of this substance, lattice fringes of crystals were observed inside the envelope having about 10 layers of carbon walls.

As a result of analyzing the encapsulated crystalline substance by electron beam diffraction and X-ray diffraction, the crystal structure was face-centered cubic and the lattice constant was a = 3.533 ± 0.003 °.
Was asked. These agreed with the literature values for the Ni single crystal with an accuracy of 0.3%. Ni ₃ C was examined as a candidate substance other than Ni, but no agreement in lattice constant with literature values was found within the precision of the experiment. From the above, the included crystalline substance was identified as a Ni crystal.

After heating the above composite electrode at a temperature of 1300 to 1450 ° C. and a degree of vacuum of 10 ⁻³ Torr for 10 to 60 minutes (no arc discharge), the mixture inside the electrode was examined with an electron microscope. As a result, generation of an envelope having a multilayered carbon wall enclosing the crystal was observed. Its production rate tended to increase with increasing heating temperature and heating duration. Under the conditions of about 1450 [deg.] C. and 10 to 20 minutes, the yield of the encapsulating body having the multi-layered encapsulating carbon wall was only about 8% by weight based on the consumption of the composite electrode. As a result of electron beam diffraction, it was found that the crystal in the above case was also Ni.

Example 5 Nickel oxide NiO (Kanto Chemical Co., Ltd., purity 97.0)
%) And reducing graphite bond (Amco, 551-
R (trade name)) were mixed at a weight ratio of about 0.3: 1. The preparation of the composite electrode, heat treatment, and arc discharge conditions were the same as in Example 2. The discharge for about 8 minutes produced a 4 cm long cylindrical deposit on the cathode and soot around the positive and negative electrodes. The weight ratio of sediment to soot is about 1.
5: 1.

The above-mentioned cylindrical sediment had a structure that could be clearly identified from its longitudinal section. That is, the outside was relatively hard and gray, and the inside was relatively soft and black. The weight ratio of the black part to the gray part was about 1: 4. A small amount of the encapsulant having a multilayered carbon wall enclosing the crystal was found in the black portion, and a relatively large amount was found in the soot. About 70% of the encapsulants having multiple carbon walls present in the soot contained crystals. The yield of the envelope having the multilayered carbon wall enclosing the crystal was about 40% by weight based on the consumption of the composite electrode. The crystal was identified as Ni by the same analysis as in Example 4.

Example 6 Nickel carbonate NiCO ₃ (Kanto Chemical Co., Ltd., 45% to 5%)
0% Ni) and reducing graphite bond (Amco 551-R (trade name)) were mixed at a weight ratio of about 0.3: 1. The preparation of the composite electrode, heat treatment, and arc discharge conditions were the same as in Example 2. The discharge for about 8 minutes produced a 4 cm long cylindrical deposit on the cathode and soot around the positive and negative electrodes. The weight ratio of sediment to soot was about 1.5: 1.

The above-mentioned cylindrical sediment had a structure that could be clearly identified from its longitudinal section. That is, the outside was relatively hard and gray, and the inside was relatively soft and black. The weight ratio of the black part to the gray part was about 1: 4. A small amount of the encapsulant having a multilayered carbon wall enclosing the crystal was found in the black portion, and a relatively large amount was found in the soot. Approximately 70% of the encapsulants having multiple carbon walls in soot contain crystals
Met. The yield of the envelope having the multilayered carbon wall enclosing the crystal was about 25% by weight based on the consumption of the composite electrode. The crystal was identified as Ni by the same analysis as in Example 4.

Example 7 A simple substance of Fe (Kanto Chemical Co., Ltd., purity: 98.0%) and a reducing graphite bond (Amco, 551-R (trade name)) were added in a weight ratio of about 0.3: 1. At a rate of The preparation of the composite electrode, heat treatment, and arc discharge conditions were the same as in Example 1. The discharge for about 8 minutes produced a 4 cm long cylindrical deposit on the cathode and soot around the positive and negative electrodes. The weight ratio of sediment to soot was about 1.5: 1.

The above-mentioned cylindrical sediment had a structure that could be clearly identified from its longitudinal section. That is, the outside was relatively hard and gray, and the inside was relatively soft and black. The weight ratio of the black part to the gray part was about 1: 4. A small amount of the encapsulant having a multilayered carbon wall enclosing the crystal was found in the black portion, and a relatively large amount was found in the soot. In particular, it was found that about 80% of the encapsulant having multiple carbon walls present in the soot contained crystals. The yield of the envelope having multiple carbon walls enclosing the crystal is 41% by weight based on the amount of consumption of the composite electrode, and the crystal is mostly α-
Fe and a small amount were confirmed to be γ-Fe.

Elemental analysis of black matter and soot by electron beam X-ray analysis showed that only iron was observed. Furthermore, as a result of analyzing carbon and oxygen,
It was confirmed that carbon was present but oxygen was hardly present. From a transmission electron micrograph (bright field image) of this substance, lattice fringes of crystals were observed inside the envelope having about 10 layers of carbon walls. In addition, before photographing with a transmission electron microscope, in order to make the image clear, 1450 is used.
The sample was heated at 0 C for 1 hour.

As a result of analyzing the encapsulated crystal substance by electron beam diffraction and X-ray diffraction, the crystal structure of the substance occupying most of the substance is body-centered cubic, and the lattice constant is a = 2.8.
66 ± 0.003 °. This agreed with the literature value for α-Fe with an accuracy of 1.1%. Further, the crystal structure of the minute amount of the substance was face-centered cubic, and the lattice constant was determined to be a = 3.560 ± 0.014 °. This agreed with the literature value for γ-Fe with an accuracy of 1.1%. Nine types of iron carbide phases other than α-Fe and γ-Fe were examined, but the agreement of the lattice constant with the literature value within the precision of the experiment was not recognized. From the above, most of the included crystalline substance was identified as α-Fe, and a very small amount was identified as γ-Fe.

After heating the above composite electrode at a temperature of 1300 to 1450 ° C. and a degree of vacuum of 10 ⁻³ Torr for 10 to 60 minutes (no arc discharge), the mixture inside the electrode was examined with an electron microscope. As a result, generation of an envelope having a multilayered carbon wall enclosing the crystal was observed. Its production rate tended to increase with increasing heating temperature and heating duration. Under the conditions of about 1450 [deg.] C. and 10 to 20 minutes, the yield of the encapsulating body having the multi-layered encapsulating carbon wall was only about 8% by weight based on the consumption of the composite electrode. As a result of electron diffraction, most of the crystals in the above case were also α-F
e, a very small amount was found to be γ-Fe.

Example 8 A weight ratio of iron oxide Fe ₂ O ₃ (Kanto Chemical Co., Ltd., purity 99.0%) and reducing graphite bond (Amco 551-R (trade name)) was about 0. The mixture was mixed at a ratio of 3: 1. Preparation of composite electrode, heat treatment and arc discharge conditions were as in Example 2.
Is the same as About 8 minutes of discharge, 4c on the cathode
Soot was formed around the m-length cylindrical deposit and the positive and negative electrodes. The weight ratio of sediment to soot was about 1.5: 1.

The above-mentioned cylindrical deposit had a structure that could be clearly identified from its longitudinal section. That is, the outside was relatively hard and gray, and the inside was relatively soft and black. The weight ratio of the black part to the gray part was about 1: 4. A small amount of the encapsulant having a multilayered carbon wall enclosing the crystal was found in the black portion, and a relatively large amount was found in the soot. About 70% of the encapsulants having multiple carbon walls present in the soot contained crystals. The yield of the envelope having multiple layers of carbon walls enclosing the crystal was about 26% by weight based on the consumption of the composite electrode.
Most of the crystals were found to be α-F by the same analysis as in Example 7.
e, a very small amount was confirmed to be γ-Fe.

[0055]

The ultrafine particles of a single crystal encapsulated in the carbon wall envelope of the present invention are expected to be applied in various technical fields.

Claims (1)

[Claims] 1. Single crystal ultrafine particles of an element selected from 3d transition metals encapsulated in a carbon wall envelope.