JPS609081B2 - Manufacturing method of spheroidized subgrain - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing metal particles, and particularly to a method for producing fine spherical metal particles simply and efficiently.

As a method for manufacturing spherical metal particles, a physical spheroidization method has been proposed in which the shape is modified by dropping metal particles into a cooling medium or by transporting metal particles obtained by gas mist through a spral tube. .

However, when producing metal particles by dropping into a cooling medium, small particle sizes cannot be obtained;
The particles with a mesh size or larger account for nearly 90%, and this method is not suitable as a method for producing fine metal particles with a mesh size of 100 mesh or smaller.

In addition, although the above-mentioned method of passing the metal solution through a spiral tube after transferring the gas has some effect in eliminating sharp protrusions, it is still insufficient to be called spherical. Not only does the structure of the device become complicated, but operation management is also complicated.

Therefore, the conventionally proposed methods cannot be said to be satisfactory for obtaining fine spherical metal particles. Incidentally, in recent years, there has been a strong demand for producing fine spherical particles of metal such as zinc, cadmium, lead, steel, etc. for the purpose of improving the quality of powder compacts. For example, alkaline batteries are becoming increasingly smaller and thinner, and as a measure to extend battery life, it is desired that the zinc used in electrode moldings be fine particles and spherical. It is difficult to produce such fine, spherical metal particles using the methods described above, and it is necessary to establish a new method. The present invention has established a method for easily manufacturing fine spherical metal particles in order to eliminate the drawbacks of the above-mentioned prior art and to meet the demands in this field.

The inventor of the present invention has carefully observed and studied the formation of metal particles in the gas vaporization method, in which a metal solution is dispersed into pongee droplets using a mist gas. It was discovered that the key to the success or failure of spheroidization is that spheroidization is inhibited when the amount of oxide exceeds a predetermined amount. The metal solution falling from the metal storage container is atomized by the mist gas and dispersed as droplets, and as it falls through the metal particle collection hopper, it solidifies and accumulates at the bottom, but in the process, metal It is necessary to suppress the chance of bonding of the solution and oxygen to below a predetermined limit. For this purpose, it is necessary to maintain not only the oxygen concentration in the falsified gas but also the oxygen concentration in the metal particle collection hopper below a predetermined limit. Although the upper limit of the oxygen concentration depends on the metal in question, it is generally set at 8% based on the observation of the degree of spheroidization.

In this way, the present invention provides a method for producing metal particles, which comprises dispersing a metal solution into droplets using mist gas, allowing them to fall through a metal particle collection hopper and collecting them in a bottle, in which the oxygen concentration in the mist gas is reduced. The present invention also provides a method for producing metal particles, characterized in that the oxygen concentration in the atmosphere within the metal particle recovery hopper is 8% or less.

The present invention will be described in detail below. The metals targeted in the present invention include all metals in general from which metal particles can be produced by the rolling method, but metals that have a high affinity for oxygen, such as zinc, cadmium, lead, or alloys thereof, are particularly targeted. be done.

The metal solution is maintained at a predetermined temperature in a storage container installed on the metal particle collection hopper and released through a nozzle provided at the bottom of the storage container, and immediately after release, it is dispersed into fine droplets by a mist gas.

The dispersed pongee droplets solidify as they fall within the hopper, and are collected as metal particles at the bottom of the hopper. The temperature of the metal melt should be as close to the melting point as possible, but it must be within a temperature range that allows atomization.

For example, in the case of manufacturing zinc particles for batteries, the purest zinc (9
9.99% Zn) was used, and the solution temperature was 450-60
It is considered to be 0:00. Since the temperature of the solution is correlated with the solidification time of the atomized droplets, if the fine droplets are not sufficiently solidified when they collide with the hopper wall, they are likely to become flattened or distorted by the impact. It is desirable to select the port body temperature in consideration of other factors of the equipment so as to obtain coagulated particles of If the hopper has a large volume and the time required for the dispersed pongee droplets to collide with the hopper wall is relatively long, the solution temperature can be increased. However, since the use of a large hopper is undesirable because it requires bulky equipment, it is preferable to keep the solution temperature low. Preferably, the side wall of the hopper has a curved surface.

This is because, as mentioned above, if the atomized metal is not sufficiently cooled before it hits the side wall, it is likely to deform, so the curved surface reduces the impact as much as possible. The higher the atomization gas pressure is, the better in order to obtain pongee grains, but if it is set too high, the dispersed droplets may hit the side walls and deform, or the droplets may become flat due to pressure impact, which is not preferable.

In order to obtain as uniform and fine atomization effect as possible, it is necessary to select an appropriate pressure, taking into consideration the dimensions of the discharge nozzle at the bottom of the reservoir, etc. For example, in the case of zinc, it generally ranges from 1 to 5k9/ground, with 2k9/ground being preferred. According to the present invention, the oxygen concentration of the mist gas must be suppressed to 8% or less.

This is to minimize the chance of contact between the metal solution and oxygen. As the atomizing gas, atomizing gas,
C02 gas, argon and other inert gases are used. Particularly important in the present invention is to control the oxygen concentration in the atmosphere within the metal particle collection hopper, where the particles remain in an unsolidified state after atomization, to 8% or less.

In conventional equipment, the free air atmosphere inside the hopper was poorly controlled or little consideration was given, and the oxygen concentration was not strictly limited, which was a major reason why spherical metal particles could not be obtained. It seems that there was. In the conventional apparatus, ambient air easily enters between the solution reservoir and the recovery hopper, and it is assumed that the oxygen concentration in the atmosphere inside the hopper is quite high. Therefore, in the present invention, it is necessary that the inside of the hopper has a structure that is well sealed from the outside. Appropriate sealing means must be provided at the connection between the solution reservoir and the hopper and at the metal particle collection port. Thus, the dispersed droplets are atomized under minimal oxygen contact.
Contact with oxygen is minimized until they have solidified, and then they become spheroidized due to surface tension with little oxide formation.

If the amount of oxide exceeds a predetermined amount, it will adversely affect the surface tension, viscosity, etc. of the droplets, and a sufficient spheroidizing effect will not be achieved. In this way, minimizing the contact between the metal and oxygen during the period from atomization to solidification of the metal solution is the most important requirement in order to obtain more spherical metal particles. Such careful consideration had not been given.

As mentioned earlier, the upper limit of the oxygen concentration depends on the degree of oxygen affinity of the target metal, but it is sufficient if it is 8% or less (including zero) for all metals. Something was discovered.

This limit value was determined by measuring bulk specific gravity of various metals and understanding the degree of spheroidization through microscopic observation. For example, in the case of zinc, which has a strong affinity for oxygen, the following results were obtained. The bulk density increases as the metal grains are of regular size and become spherical, and provides a very clear indication of the properties of the metal grains. was judged to be excellent.

As can be seen from the comparison between Reference Photos 1 and 2, the spheroidization effect due to the decrease in oxygen concentration is truly amazing.
Compared to conventional products, which were elongated and irregularly shaped, by strictly controlling the oxygen concentration, rectified spheroidal metal particles with a large bulk specific gravity can be obtained.

Further, the metal particles produced according to the present invention are usually fine particles with a mesh size of 100 to 200, which is generally required. In addition to the above considerations, the temperature of the atomizing gas also affects the final metal particulate product.

The rapid cooling effect of the mist gas on the metal falling from the reservoir nozzle is not fully understood, but it is thought to be related to factors such as viscosity and local solidification, resulting in good spheroidization. Not done. Therefore, the use of a warmed-up mist gas also has a favorable effect on the objectives of the present invention. However, it is not preferable to use a false mist gas that is too high in temperature because it will actually delay the solidification of the metal droplets and will also raise the temperature of the exhaust gas, making it impossible to use simple dust collection equipment such as bag filters. Next, examples and comparative examples using molten zinc will be described.

Example Zinc particles for an Alka IJ battery were manufactured using room temperature nitrogen + oxygen gas adjusted to a predetermined oxygen concentration as the atomizing gas.

The aim was to produce spherical particles of 100 to 200 mesh with a bulk specific gravity of 3.320 or more. The implementation conditions and results are as follows; as can be seen from the table above, the oxygen concentration was
% or less, zinc grains having a bulk specific gravity of 3.20 or more are produced, which means that zinc grains that are highly sized and spheroidized are produced. Furthermore, in contrast to the method of dropping into a cooling medium, fine particles of 100 to 200 mesh, which are particularly required for alkaline batteries, were produced at a high occupancy rate. The bulk specific gravity of the zinc particles thus produced according to the present invention is about 1. Since the kalpa pitch becomes larger, it makes a significant contribution to increasing the capacity of small batteries such as alkaline batteries. In addition, in alkaline batteries,
Conventionally, zinc wire could not be obtained with a uniform grain size, and the majority of the wires were long and thin (reference photo 1), so zinc wire was cut into uniform shapes, but with the present invention, It is also a great advantage that spherical objects of a certain size can be manufactured continuously by a simple spraying method without relying on such troublesome methods. Furthermore, zinc grains used as a raw material for batteries do not like oxygen as an impurity component, but the present invention also binds zinc grains with a small amount of oxygen at the same time.
This is one of the preferable results of the present invention. The above also applies to cadmium particles for cadmium batteries. As explained above, the present invention enables gas atomization by strictly controlling contact with oxygen throughout the entire process from atomization to solidification, which was rarely considered in the past. This method makes it possible to easily and efficiently produce fine spherical metal particles.

Claims (1)

[Claims] 1. In a method for manufacturing zinc particles, which consists of dispersing zinc solution into fine droplets using atomized gas, and then allowing them to fall and be collected in a zinc particle recovery hopper, the oxygen concentration in the atomized gas and the oxygen in the atmosphere inside the zinc particle recovery hopper are A method for producing spheroidized zinc particles, which is characterized by producing spheroidized zinc particles by controlling the concentration to 8% or less.