JP2550160B2 - Method for producing ultrafine metal boride particles - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing ultrafine particles of a metal boride used as an electrically conductive composition of a thick film resistor.

[Conventional technology]

A conventional method for pulverizing a metal boride used as an electrically conductive composition of a thick film resistor that can be fired in a non-oxidizing gas atmosphere is described in JP-B-59-51721.
The raw material powder was mechanically ground, for example, by a vibration mill, and then sieved to obtain a desired particle size. However, in mechanical grinding, the particle size obtained by this grinding is limited, and the minimum particle size is about 0.2 μm,
The shapes are also irregular.

[Problems to be Solved by the Invention]

In the above-mentioned prior art, no consideration is given to the particle size and its shape, and when it is used as a thick film resistor, it is a problem that a stable resistor having a sheet resistance of several KΩ / □ or more cannot be obtained. I got it.

It is an object of the present invention to provide ultrafine metal boride particles having a particle size of 0.1 μm at the maximum and having a spherical and smooth surface.

Another object of the present invention is to use the metal boride ultrafine particles as an electrically conductive composition of a thick film resistor, and
It is to provide a thick film resistor paste which can obtain a stable resistance value in a wide range of 10 to 1 MΩ / □.

[Means for solving the problem]

In order to achieve the above object, the gas atmosphere in the system is nitrogen gas or a mixed gas atmosphere of nitrogen gas and an inert gas, both electrodes are obliquely arranged as a metal boride raw material, and an arc is formed between both electrodes. It is generated to generate ultrafine particles of the raw material.

[Action]

The gas atmosphere in the system is a non-oxidizing gas, both electrodes are diagonally arranged as a metal boride raw material, and an arc is generated between both electrodes.The arc heat generates a metal boride vapor from the raw material to generate ultrafine particles. To manufacture. At this time, since the metal boride, especially lanthanum hexaboride, is a strongly reducing substance, by changing the atmosphere gas to a non-oxidizing gas, it is possible to prevent the raw material from changing from boride to oxide.
In particular, since lanthanum hexaboride is very stable in a nitrogen gas atmosphere, it is desirable to use nitrogen gas or a mixed gas of an inert gas and nitrogen gas as the atmosphere gas. Also, by arranging both electrodes in an oblique direction, it is possible to reduce the arc pressure that can prevent the generation of metal boride vapor,
Ultrafine particles can be efficiently produced.

〔Example〕

An embodiment of the present invention will be described above with reference to FIGS.

In FIG. 1, 1 is a lanthanum hexaboride (LaB ₆ ) electrode, 2 is a LaB ₆ raw material, 3 is a water-cooled copper crucible, 4 is an arc,
Reference numeral 5 is a discharge power source, 6 is an atmosphere gas inlet, 7 is an ultrafine particle generating chamber, 8 is an ultrafine particle collecting section, 9 is a circulation pump, and 10 is an exhaust pump.

In the above structure, first the exhaust pump 10 generates the generation chamber 7
After the inside of the circulation passage system is evacuated, nitrogen gas is filled from the atmosphere gas inlet 6 up to about 0.1 MPa, and the circulation pump 9 circulates the inside of the system. Next, by supplying a current from the discharge power source 5 between the LaB ₆ electrode and the LaB ₆ raw material 2 placed on the water-cooled copper crucible 3 to generate an arc 4, the LaB ₆
The raw material 2 is evaporated by the arc heat, becomes ultrafine particles in the cooling process, and is conveyed to the collecting unit 8 together with the circulating gas and collected.

During the above operation, the other electrode 1 obliquely arranged on the LaB ₆ raw material 2 is made of LaB ₆ of the same material as the raw material, so that high purity LaB ₆ ultrafine particles can be obtained without mixing impurities in the ultrafine particles. It can be manufactured efficiently. At this time, by using the LaB ₆ raw material 2 as an anode and the LaB ₆ electrode 1 as a cathode to generate an arc, consumption of the LaB ₆ electrode is reduced as much as possible to continuously manufacture ultrafine particles.

As an example, nitrogen gas is used as the system atmosphere gas,
Under the condition of 200A-40V, LaB ₆ you pereto shape compacting the LaB ₆ powder have been conducted under manufacturing mechanical grinding specific surface area 5.4 m ² / g
Raw material and LaB ₆ powder obtained in the same way were sintered into rods.
It was prepared LaB ₆ fine particles using a LaB ₆ electrode. FIG. 2 is an X-ray diffraction pattern of the manufactured ultrafine particles, and FIG. 3 is an X-ray diffraction pattern of the same raw material powder. As is clear from the comparison, the pattern is the same as that of the raw material powder, and it can be seen that the manufactured ultrafine particles are LaB ₆ . The specific surface area is 83.0 m ²
As shown in the transmission electron micrograph of FIG. 4, about 5 g / Hr of ultrafine particles having a relatively uniform particle size and a nearly spherical shape were obtained. As a result of using these ultrafine particles as a thick film resistor, a stable resistance value was obtained in a wide range of 10 to 1 MΩ / □ as shown in FIG.

〔The invention's effect〕

According to the present invention, both electrodes are obliquely arranged as metal borides and ultrafine particles are produced in a non-oxidizing atmosphere, so that impurities are not mixed in, the particle size is relatively uniform, and the shape is It is possible to obtain spherical ultrafine particles. Further, by using the ultrafine particles, it is possible to obtain a thick film resistor in which a wide resistance value range can be stably obtained.

[Brief description of drawings]

FIG. 1 is a diagram of a production apparatus showing an embodiment of the present invention, FIG. 2 is a diagram showing an X-ray diffraction pattern of ultrafine particles, and FIG. 3 is a diagram showing an X-ray diffraction pattern of raw material powder. FIG. 4 is an electron micrograph system showing the particle structure of ultrafine particles, and FIG. 5 is a characteristic diagram of a thick film resistor using the ultrafine particles of the present invention. 1 ... LaB ₆ electrode, 2 ... LaB ₆ raw material, 3 ... water-cooled copper crucible, 4 ... arc, 5 ... discharge power supply, 6 ... atmosphere gas inlet, 7 ... ultrafine particle generation chamber, 8 ...... Ultrafine particle collection unit.

Claims (4)

(57) [Claims] 1. A method for producing ultra-fine particles using an arc heat source, wherein both electrodes are diagonally arranged as a metal boride raw material in a non-oxidizing gas atmosphere to generate an arc between both electrodes, and the raw material is produced. A method for producing ultrafine metal boride particles, which comprises producing ultrafine particles of 2. The method for producing ultrafine metal boride particles according to claim 1, wherein the non-oxidizing gas is nitrogen gas or a mixed gas of inert gas and nitrogen. 3. The method for producing ultrafine metal boride particles according to claim 1, wherein the metal boride raw material is lanthanum hexaboride. 4. A thick film resistance composition using the metal boride ultrafine particles according to claim 1.