JPH02218431A - Powder for plasma pulverizing and its supply method - Google Patents

Abstract

PURPOSE:To prevent the clogging of a nozzle by injecting a powder for pulverizing of plasma through the nozzle to a plasma-generated space kept at high temperature. CONSTITUTION:A plasma generating torch 3 is installed in one end and an arc jet 7 is formed by a conventional arc discharge generating means. A raw material powder together with a carrier gas is introduced into the arc jet 7 through a powder transferring apparatus 4 and a nozzle 2 in the radius direction, melted, evaporated, cooled by a cooling means in the downstream side, and recovered as a super fine powder. As the raw material powder to be pulverized super-finely, there are iron, cobalt, nickel, aluminum, zinc, copper, manganese, etc. By this method, production efficiency is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a powder for plasma atomization and a method for supplying the same to a plasma atomization process.

(Prior Art) Ultrafine particle powders of metals, metal oxides, and other compounds are required in many fields including magnetic powders for magnetic recording and powders for catalysts. Such ultrafine powder particles tend to aggregate to form secondary particles, and it is difficult to produce isolated ultrafine particles.

Gas evaporation methods have been known for the production of ultrafine particles. This is a method in which metals are melted in a vacuum and vaporized into ultrafine particles, which are then cooled and collected.
2-11896), however, this method has the problem that the raw material is limited to meltable metals or alloys, and also requires an ultra-high vacuum or has low productivity.

Other methods include methods for producing ultrafine powder using plasma. Typical examples are shown in Figures 1 to 4.
In the apparatus shown in the figure, a nozzle 2 for introducing the sample and carrier gas along the plasma central axis into one end of the plasma container 1;
A plasma-forming gas nozzle 3.4 is arranged surrounding it, and furthermore a high frequency coil is arranged around the vessel l.

In the apparatus of FIG. 2, the plasma-forming gas is introduced through a gas nozzle 3.4 at one end of the plasma vessel l, while the sample and carrier gas are introduced radially with respect to the plasma central axis through a nozzle 2 penetrating the side wall of the vessel l. Ru. In the apparatus shown in FIG. 3, a DC arc jet is formed by a central gas nozzle 6, and the sample and carrier gas are passed through nozzles 2 around the nozzle 6.
The plasma is introduced in the radial direction from the plasma, vaporized and dispersed by an arc jet, and then a high frequency plasma is formed by the high frequency coil 5. Figure 4 shows a device using DC plasma.
A DC arc jet 17 is formed by the plasma torch 13, and the sample and carrier gas are introduced radially through the nozzle 12 and vaporized and dispersed by the arc jet. The container l is preferably kept warm, and a heat insulating material 15 and a heat resistant material 16 are arranged inside. The material of the heat insulating material 15 is preferably fibrous carbon, alumina, zirconia, etc., and the material of the heat resistant material 16 is preferably graphite, boron nitride, tungsten, or other heat resistant alloy material.

(Problems with the prior art) All of these methods can form various ultrafine powders relatively well, but the exit of the sample introduction nozzle 2 is exposed to high heat, and the nozzle becomes narrow due to the molten sample, resulting in a decrease in efficiency. happens.

(Objective of the Invention) An object of the present invention is to provide a powder raw material and a method for supplying the same, which are free from the possibility of narrowing or clogging of a nozzle in a plasma pulverization method.

(Summary of the Invention) The above object of the present invention is to use metal, metal oxide, or other inorganic powder mixed with or surface coated with a sublimable substance such as carbon, and to introduce this into a plasma atomization device through a nozzle. This is achieved by

According to the present invention, even if the sublimable substance such as carbon starts to melt when the powder is exposed to the high temperature at the nozzle outlet,
It is possible to prevent powder from adhering to the nozzle outlet and to maintain the nozzle outlet in a clean state at all times. Therefore, it is possible to prevent a decrease in the production efficiency of ultrafine particle powder and maintain high productivity at all times.

(Detailed Description of the Invention) The following explanation will be made with particular reference to the plasma atomization device shown in FIG. Note that this is applicable when using a fine atomization device.

Now, the plasma atomization apparatus shown in FIG. 4 has a plasma generating torch 3 at one end, and forms an arc jet 7 by a conventional arc discharge generating means. The raw material powder is introduced into the arc jet 7 from the powder conveying device 4 through the radial nozzle 2 along with the carrier gas, where it is melted and evaporated, cooled by a cooling means (not shown) on the downstream side, turned into ultrafine particles, and recovered. be done.

The powder that is made into ultra-fine particles by this plasma atomization method includes:
Examples include metals such as iron, cobalt, nickel, aluminum, zinc, copper, and manganese, and metal compounds such as iron oxide, cobalt oxide, iron phosphate, aluminum oxide, copper oxide, and zinc oxide. These powders are melted and ultra-fine by arc and plasma.

Compounds and metal powders do not necessarily maintain their original powder state, such as by melting and amalgamating them to form alloys, solid solutions, or mixtures.

Carrier gas, arc and plasma gas are Ar
%Ns%H*, COIOs, Atr, etc. Carbon, boron nitride, aluminum nitride, sodium oxide, etc. can be used as the sublimable substance powder to be mixed with the raw material powder or to coat it, and the use of carbon is particularly preferable.The necessary conditions for the sublimable substance are as follows: It serves as a barrier to the nozzle wall of the molten raw material powder at the nozzle exit, and it sublimes due to the arc jet and plasma. All of the substances listed above satisfy this condition.

The object of the present invention can be better achieved if the raw material powder with the coated or mixed sublimation material is preferably preformed into granules. The method of granulation is by any conventional technique.

Examples and comparative examples of the present invention will be described below. In the following example, the nozzle block shown in FIG. 4 was used, and the sample introduction nozzle diameter was 10 mm.

Example 1 30 wt % of carbon black was added and mixed to iron oxide powder, and the mixture was made into granules by humidification and spray drying. When this was continuously introduced into an Ar-N plasma jet with an outlet of 19 KW at a rate of 1 g per minute, no powder or melt adhesion was observed at the inlet.

Example 2 5 wt% of carbon black was added to iron oxide powder, mixed and humidified, and this was continuously introduced into a 20 KW Ar-Nx plasma jet at a rate of 1 g per minute. No powder or melt adhesion was observed.

Example 3 25 wt% of carbon black was added to a mixed powder of iron oxide, cobalt oxide, and iron phosphate, and the mixture was made into granules by humidified play drying. This is the exit A of 17.5KW.
r - N s at a rate of 1 g per minute in the plasma jet,
When it was continuously introduced, no powder or melt adhesion was observed at the inlet.

Comparative Example A mixed powder of iron oxide, cobalt oxide and iron phosphate was made into granules by spray drying. Exit 17.5
When it was continuously introduced into KW's Ar-Nx plasma jet at a rate of 1 g per minute, melt adhered to the inlet, and after 50 minutes, the inlet was blocked by the melt.

Figures 1, 2 and 3 are explanatory diagrams showing three different types of plasma atomization equipment, and Figure 4 shows an example of an equipment for carrying out the method of the present invention. FIG.

15τ14 arm

Claims (4)

[Claims] (1) Powder for plasma pulverization mixed with or surface coated with a sublimable substance. (2) The powder for plasma pulverization according to item 1 above, wherein the sublimable substance is carbon. (3) A powder supply method, characterized in that the powder for plasma pulverization according to the above item 1 or 2 is introduced into a plasma space maintained at a high temperature through a nozzle. (4) The method for supplying powder according to item 3, wherein the powder for plasma pulverization is preformed into granules.