JPH03115017A - Powder supply method and device - Google Patents

Abstract

PURPOSE:To prevent the crack generation and unequalization of an reaction layer at a powder supply device whose purpose is to form a reaction layer for a gas diffusion electrode, by arranging so that powder may be filled into a pipe body, and a powder filled layer may be dashed into pieces of mixture by advancing stirring blade bodies from one end at a fixed speed, and sending out of the pieces may be conducted by pressurized gas. CONSTITUTION:A filled layer 1 is formed by filling powder into a pipe body 2, and its left end is closed, and a slip pipe 5 and a pressurized gas supply pipe 6 are furnished on its right end through a seal body 3. A motor 4 and blade plates 8 are rotatably supported at the tip of the slip pipe 5. In this constitution, the motor 4 and blade bodies 8 are advanced rotatingly inside the pipe body 2 by means of the slip pipe 5, and the powder filled layer 1 is dashed to pieces and mixture is made. And, powder thus dashed and mixed is sent out through a sending out pipe 9 in the slip pipe 5 by means of pressurized gas from the supply pipe 6.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method and apparatus for supplying a constant amount of powder at a constant concentration to form, for example, a uniform reaction layer of a gas diffusion electrode.

(Prior art and its problems) Gas diffusion electrodes are widely used in fuel cells, secondary batteries, electrochemical reactors, and the like. The gas diffusion electrode is generally formed by bonding a water-repellent gas diffusion layer to a hydrophilic reaction layer, and bonding a current collector to the surface of the gas diffusion layer opposite to the reaction layer.

For example, the reaction layer of the gas diffusion electrode is generally made of hydrophilic carbon black, polytetrafluoroethylene (hereinafter referred to as PTFE), and water-repellent carbon black, and supports a catalyst if necessary. Several methods are known for forming the reaction layer, but all methods require uniform mixing of the powder substances.

Conventionally, the following two methods have been adopted.

The first method is called the filter trans method, in which the mixture of raw materials for the reaction layer is filtered on Millipore, the filtration surface is overlapped with carbon paper, and the filter is sandwiched between water-absorbing filter papers and pressed several times, and then, for example, nitrogen 300~3 in atmosphere furnace
This is a method of heat-treating at 50° C. for 10 minutes to obtain a reaction layer.

However, in this method, cracks occur on the surface of the reaction layer during heat treatment or firing, resulting in electrode defects such as electrolyte leakage when the gas diffusion electrode operates as an electrode in a fuel cell or the like. In order to avoid this, pressurized dehydration is required, and strong pressure is applied to the reaction layer, making it difficult to ensure sufficient porosity.

The second method is called the Claraday method, which eliminates the drawbacks of the filter transformer method.

That is, the raw material mixture for the reaction layer is filtered on a filter cloth to form a cake of a certain size, the cake is milled with a dry grinding device, and immediately introduced into a chamber containing carbon paper to form a cloud of the raw material in the chamber. In this method, the raw material is adhered to a carbon paper whose opposite side is maintained under negative pressure, pressure-molded, and then fired in the atmosphere to form a reaction layer.

Although this method has little risk of cracking, it is very difficult to uniformly control the particle size of the powder produced, and even with careful control using highly skilled techniques, there are limits to achieving uniformity. be. Conventionally, a mixer as shown in FIG. 2 has been used to form and supply the powder. The mixer fills the agglomerated powder C in a hollow body B in which a lid body A is installed, and supplies pressurized air into the hollow body from an air pump D through a flow meter E and a pressurizing pipe hole F. At the same time, the blade G installed at the bottom of the main body B is rotated to gradually crush the aggregated powder and transport the powder from the delivery pipe H to a predetermined location. However, with the passage of time, the powder concentration in the hollow body B decreases, and the powder concentration in the delivery pipe H also decreases, and the powder concentration at the predetermined location also decreases, resulting in a uniform concentration of powder. Can't get the body.

In addition to forming a reaction layer of a gas diffusion electrode, there is often a need to supply powder with a uniform concentration, and various industries are demanding methods and devices for supplying uniform powder.

OBJECTS OF THE INVENTION The present invention provides a uniform concentration powder supply method and apparatus, in particular for the formation of a reaction layer of a gas diffusion electrode, which avoids the drawbacks of the prior art, namely the occurrence of cracks and the formation of a non-uniform reaction layer; It is an object of the present invention to provide a powder supply method and apparatus useful for forming a reaction layer for a gas diffusion electrode that is uniform and has good performance.

(Means for Solving the Problems) The present invention provides, firstly, a stirring blade which is filled with powder in a cylindrical body and which enters the packed powder bed from one direction at a constant speed. The packed powder bed is gradually pulverized and mixed, and the pulverized powder having a uniform concentration is supplied to a predetermined location outside the cylindrical body from a delivery pipe whose one end is installed near the blade body using pressurized gas. The present invention is a powder supply method characterized by: and secondly, a powder supply device that can be used in the method.

The present invention will be explained in detail below.

The present inventor has discovered that the apparatus shown in FIG. 2 has a configuration in which the powder pulverized by the blades rises vertically against gravity, so that the powder is supplied to a predetermined location as the powder concentration in the hollow body decreases. In view of the fact that the powder concentration gradually decreases, a cylindrical body corresponding to the hollow body is installed, and the impeller enters the layer of powder filled in the cylindrical body from one direction and supplies gas. This makes it possible to always supply powder with an almost uniform concentration.

In the device of the present invention, unlike the conventional technology, the blade itself is moved in order to pulverize and mix the powder in the powder packed bed, so the power source such as a motor that rotates the blade is often moved as well. , the device itself is more complex than conventional devices.

When using the device of the present invention, powder such as carbon black is pulverized to a predetermined size, and if other additives such as synthetic resin are used, the additives are also finely pulverized, and both are uniformly ground. and fill it into the cylindrical body of the powder supply device main body.

One end of this powder packed bed is opened and the rotating blade is brought into contact with the open surface to pulverize and mix the powder packed bed, and the powder is sent from a delivery pipe installed near the blade. It is transported to a predetermined location outside the cylindrical body.

According to this device, by keeping the moving speed of the blade constant, the powder concentration in the powder packed bed does not change (by keeping the speed constant and the amount of powder supplied per unit time constant). Therefore, it is possible to make the concentration of the powder conveyed to the outside from the delivery pipe uniform.Furthermore, by moving the impeller to the other end of the powder packed bed, the entire powder packed bed can be uniformized. can be supplied without waste.

The concentration of the powder supplied to the outside from the delivery pipe can be set to an optimum value depending on the application by the moving speed of the blade and the supply speed of the pressurized gas.

When the present invention is used to form a reaction layer for a gas diffusion electrode such as a fuel cell, a mixture of fine hydrophilic carbon black powder or PTFE powder, or other catalyst particles may be added to the powder. As described above, the powder packed bed is pulverized and mixed, and then transported to the outside through a delivery pipe, and a carbon paper, for example, which is a base material of the reaction layer, is brought close to the tip of the delivery pipe. By moving the tip of the delivery pipe to scan over the carbon paper at a constant speed, a powder layer having a uniform concentration can be formed. Thereafter, the reaction layer can be provided through pressing or heating and baking steps.

By forming a uniform powder layer according to the present invention, the variation in concentration can be suppressed to within ±2%, and the resulting reaction layer for fuel cells can operate stably over a long period of time with almost no variation in performance. A fine powder layer is formed.

(Examples) Examples of the present invention will be described below, but the examples do not limit the present invention.

EXAMPLE A powder layer was formed on carbon paper using the powder supply device shown in FIG.

A seal body 3 is fitted to the other end side of the cylinder 2 with the left end of the packed bed 1 of powder closed. The slip pipe 5 and the pressurized gas supply vibro are fitted together, and a slip plate 7 is installed on the motor 4 with a slight gap between it and the cylinder body 2, and a slip plate 7 is attached to the other side of the slip plate 7. A blade body 8 made of resin is installed on the rotating body, and the slip plate 7 is slid on the inner surface of the cylinder body 2, so that the blade body 8 is brought into contact with the powder-filled bed l at a constant speed and The surface is gradually ground and mixed. One end of a delivery pipe 9 is located near the blade body 8, and the other end of the delivery pipe 9 passes through the inside of the slip pipe 5 and reaches the outside, and is located near the carbon paper (not shown). ing. Note that 10 is an air pump for supplying gas into the cylinder 2 from the pressurized gas supply vibro, and 11 is a flow meter for the gas.

In the cylinder 2 (inner diameter 25.4 mm) of the powder supply device constructed as described above, 70% by weight of hydrophilic carbon black with an average particle size of 450 particles carrying 10% by weight of a platinum catalyst and an average Filled with 1 g of mixed powder consisting of 30% by weight of PTFE with a particle size of 0.3 μm, the motor 4 was driven to rotate the blade body 8 and move the blade body at a speed of 50 m++n/min, and the diaphragm Air was supplied from the pressurized gas supply vibro at a rate of 212/min using a pump.

The other end of the delivery pipe 9 (not shown) has a side of 11c.
The above-mentioned mixed powder was deposited on the carbon paper by making the carbon paper 2 reciprocate once in 1 minute. After pressurizing the surface of the carbon paper with a sponge roll to bring the powder into close contact with the carbon paper, 50k
It was pressurized again at a pressure of g/cnf, and further fired for 10 minutes at 330° C. in a nitrogen atmosphere.

The carbon paper was divided into 5 pieces both vertically and horizontally to give a total of 25 pieces, and the weight distribution of the outer pieces was measured, and the variation was ±2% or less.

Comparative Example Using the mixer shown in Figure 2 as a powder supply device, using a diaphragm pump, and supplying air at 21/min from the pressurized gas supply vibro, the same mixed powder as in the example was fed under the same conditions. It was attached onto carbon paper. However, since the concentration of the supplied powder gradually decreased, it was necessary to move the delivery pipe back and forth seven times in seven minutes. 25 as in the example
As a result of cutting it into pieces and measuring the weight distribution for each month, the variation was less than ±3%. Also, 10% of the mixed powder remained.

(Effects of the Invention) In the present invention, a blade is brought close to the powder-filled bed filled in the cylinder from one direction to pulverize and mix the powder-filled bed. Therefore, the concentration of the supplied powder is not affected by gravity and is maintained almost constant regardless of the amount of the remaining powder packed bed.

This eliminates the inconvenience caused by non-uniformity in the concentration of powder supplied in the past, such as the need to repeat scanning many times when depositing mixed powder on carbon paper. , it becomes possible to form a uniform powder layer etc. in a short time.

[Brief explanation of drawings]

FIG. 1 is a conceptual diagram showing an embodiment of a powder supply device according to the present invention, and FIG. 2 is a schematic diagram showing a conventional powder supply device.

Claims (2)

[Claims] (1) Filling a cylinder with powder, gradually pulverizing and mixing the powder-filled bed with a stirring blade that enters the powder-filled bed from one direction of the powder-filled bed at a constant speed; A powder supply method characterized in that the pulverized powder having a uniform concentration is supplied to a predetermined location outside the cylindrical body from a delivery pipe whose one end is installed near the vane body using pressurized gas. (2) A cylindrical body filled with powder; a stirring blade that enters the powder-filled bed at a constant speed from one direction of the powder-filled bed to gradually crush and mix the powder-filled bed; A powder supply device comprising: a body; and a delivery pipe, one end of which is installed near the blade body, for conveying the powder of uniform concentration pulverized by pressurized gas to a predetermined location outside the cylinder body.