JPH0455978B2 - - Google Patents

Description

Detailed Description of the Invention The present invention uses acicular goethite powder (α-FeOOH:
The present invention relates to an apparatus for producing Goethite (hydrous ferric oxide). In the case of magnetic materials, the particle morphology of the starting material is particularly important for the magnetic tape that is subsequently processed and manufactured.
It is said that it greatly influences the performance of products such as magnetic disks and magnetic cards, so-called magnetic recording media. In other words, in order to obtain the above-mentioned excellent effects as a recording medium, it is of course important that the magnetic powder has excellent magnetic properties. It is important that the surface condition of the magnetic coating film produced by coating it on a tape or card shape is extremely smooth and dense. In other words, as magnetic recording and reproducing equipment improves in performance and becomes smaller and lighter,
Improvements in various properties such as high sensitivity and frequency characteristics are required, and the magnetic powder used as the raw material is required to have high coercive force (Hc) and saturation magnetic flux density (σs), as well as dispersibility in magnetic paint. Excellent orientation and filling properties in the coating film are required, and the magnetic properties (Hc, Br) of the magnetic medium and the magnetic powder are uniformly distributed in the coating film, and the surface is smooth. In order to improve these properties, it is important that the magnetic powder has acicular crystals, uniform particle size, and no dendritic particles. In particular, it has recently been attracting attention as a material for the next high-density recording. The requirements for magnetic iron powder are even more demanding than those for conventional magnetic iron oxide, and it is extremely difficult to obtain powder with excellent dispersibility. In other words, even stricter synthesis conditions are required to produce goethite, which is the starting material for magnetic iron powder. A method for producing goethite particles with uniform particle size distribution is to use iron hydroxide (Fe(OH) ₂ ) prior to oxidation reaction.
In order to eliminate flocs, a non-oxidizing gas is introduced into the liquid in advance, and strong stirring is performed to uniformly disperse fine particles of iron hydroxide (Japanese Patent Application Laid-Open No. 1973-
21720), and as an actual synthesis method, a separate oxidation reaction is performed at low temperature to create fine seed crystals, which are added to the system and continued to react at 40 to 60°C to grow goethite crystals (especially 1972-22637)
Then, the oxidizing gas is supplied intermittently, that is, the cycle of supplying and stopping the oxidizing gas is repeated, and 1
By controlling the oxidation rate per cycle,
There is a method to make the particle size uniform (Japanese Patent Application Laid-Open No. 57-209834). However, in either method, oxygen dissolved in the reaction solution (concentration ) is uniformly dispersed within the system, and for this purpose the temperature within the system must also be uniform. The present invention solves these problems.
This relates to the structure of the reaction tank to make the system uniform.It has the characteristic that it can be applied to the various goethite production methods mentioned above, and is especially effective when the purpose is to enlarge the reaction system or produce fine particles. It is something that demonstrates the. In general, by eliminating variations in various factors within the reaction system,
In addition, in order to keep the reaction rate almost constant during a predetermined reaction time, the first idea is to increase the stirring efficiency and activate the convection between the upper and lower liquids in the tank. For various reaction mechanisms, in order to improve stirring efficiency,
When the rotation speed of the impeller is increased abnormally, a free cone-shaped cavity is generated around the rotation axis of the impeller, as shown in FIG. Also, in order to eliminate this defect, it is possible to install a baffle plate as shown in Figure 2 on the side of the reaction tank, but in this case too, if the rotation speed of the impeller is increased, the result will be as shown in the conceptual diagram of Figure 2. It is observed that the upper surface layer is undulating. In either case, air or unreacted oxidizing gas used in the reaction, which is released from the reaction liquid and remains in the upper space, is entrained from the upper part. In other words, the oxidation reaction of Fe(CH) ₂ will occur in the upper layer as well, making the reaction system non-uniform, and ultimately making it difficult to control the target α-FeOOH particle size, and further increasing the unevenness of the particle size. cause The present invention was developed with consideration given to the homogenization of the reaction, particularly to the prevention of the entrainment of excess air or oxidizing gas from the upper and surface layers as much as possible, as well as practical operability and ease of scale-up. That is, in the present invention, when manufacturing acicular goethite particles by contacting with an oxidizing gas and oxidizing a hydroxide suspension obtained by neutralizing a ferrous salt aqueous solution with an alkaline aqueous solution, By preventing the oxidizing gas from being entrained in the upper part of the reaction solution and allowing the oxidation reaction to occur only through contact with small bubbles of the oxidizing gas introduced into the reaction solution, the composition of the reaction solution can be made uniform, and particles In order to obtain well-shaped acicular goethite particles with a narrow distribution of length and axial ratio, the internal liquid of the reaction tank is To provide a reaction device for producing powder of acicular goethite particles, in which a disk-shaped baffle plate is provided directly below the surface in a direction perpendicular to the rotation of the liquid, and a spiral-shaped vertical plate is provided on the lower surface of the baffle plate. It is. First, the reaction apparatus of the present invention will be specifically explained. FIG. 3 shows a front sectional view of one example of the reaction tank of the present invention. In FIG. 3, 1 is a reaction tank, 2 is a heat exchange jacket provided in the reaction tank 1, and 3 is an oxidizing gas blowing pipe. 4 is a disk-shaped baffle plate, and in this figure, a vertical plate provided on the lower surface of the disk-shaped baffle plate is shown. 5 indicates a stirring blade. Figure 4 is -' in Figure 3.
This is a cross-sectional view showing one shape of a disc-shaped baffle plate. In the present invention, by welding the baffle plate 4 to the disc-shaped lid, it is possible to prevent the occurrence of ripples on the surface. Place this baffle plate 4 below the horizontal surface of the liquid, about 20~
The effect is achieved by inserting it at a distance of 30m/m. The stirring blade 5 can be arranged in multiple stages as shown in Fig. 3 to improve the stirring effect, depending on the structure of the tank, especially when the ratio of tank height/tank diameter is large or when the viscosity of the reaction liquid is high. can be increased. In this case too, the upper baffle plate causes ripples and
There is no formation of conical cavities, and the inside of the reaction tank can always be kept uniform. An example in which acicular goethite particles were produced using the reaction apparatus described above will be described with reference to the following examples. Example 1 Aqueous solution 12 of FeCl ₂ (Fe ²⁺ :
200 g/) and 720 ml of NiCl ₂ aqueous solution with a Ni ²⁺ concentration of 20 g/), and further NaOH aqueous solution (concentration 172.5
g/) is added to give the theoretical value of 6 in terms of alkali equivalent.
The amount was doubled (mol). First, maintain the melt temperature at 25℃ and add nitrogen gas to 1.25℃.
/min through the coil-shaped blowpipe (1m/mφ hole x 15 holes) at the bottom of the reaction tank shown in Figure 3, and while rotating the stirring blade at a speed of 500R/M, the dissolved While expelling oxygen, Fe
(OH) ₂ was generated. After 1 hour, the liquid temperature was raised to 40℃, and nitrogen was changed to air (flow rate was 1.0
/M), the oxidation reaction was started, and uniform fine needle-like crystals of α-FeOOH were obtained in about 2 hours, and the reaction was completed. FIG. 5 shows an electron micrograph of α-FeOOH, which had a particle size of about 0.4μ, an axial ratio of about 20, and had no branching and uniform particle size. Comparative Example 1 α-FeOOH was synthesized under the same reaction conditions as in Example 1 using the reaction tank shown in FIG. Figure 6 shows an electron micrograph of the obtained α-FeOOH.
It was observed that the dispersibility was poor. Comparative Example 2 Example 1 except that the reaction tank shown in Figure 1 was used.
α-FeOOH was synthesized under the same conditions as described above. [Evaluation test] Regarding α-FeOOH of Example 1, α-
After filtering and washing the FeOOH slurry with water, it was repulped again to a slurry concentration of 16 g/ml, and the α-
SiO ₂ was deposited on the surface of FeOOH. The amount of Si added is approximately 6%wt in terms of weight ratio to Fe (Si/Fe).
After filtering and washing with water, it was kept at 725°C in the air for 1 hour to change it to α-FeO ₃ and further reduced with hydrogen at 400°C to obtain α-Fe with a major axis of 0.20 μm and an axial ratio of 13. Table 1 shows the results of magnetic measurements of iron powders of Comparative Examples 1 and 2, which were treated under exactly the same conditions as Example 1. As is clear from the table, the magnetic iron powder obtained in Example 1 has a high coercive force (Hc) and excellent magnetic properties. 【table】

[Brief explanation of the drawing]

Fig. 1 is a conceptual diagram when a conventionally known reaction apparatus is used, Fig. 2 is a conceptual diagram when a normal baffle plate is provided in the reaction apparatus, and Fig. 3 is a conceptual diagram when a conventional reaction apparatus is used. A front sectional view of the device is shown, respectively. FIG. 4 is a sectional view taken along the line -' in FIG. 3. Fig. 5 shows an electron micrograph of magnetic iron powder synthesized from goethite obtained using the apparatus of the present invention, and Fig. 6 shows an electron micrograph of magnetic iron powder obtained in the same manner in a comparative example. show. The magnification is 27000 times each. In FIG. 3, symbols indicate the following contents. 1...
Reaction tank, 2... heat exchange jacket, 3... oxidizing gas blowing pipe, 4... disc-shaped baffle plate, 5... stirring blade.

Claims (1)

[Claims] 1. In a reaction tank equipped with an agitator and an oxidizing gas blowing pipe, a disc-shaped baffle plate is provided directly below the internal liquid level of the reaction tank in a direction perpendicular to the rotation of the liquid, and a disc-shaped baffle plate is installed on the bottom surface of the baffle plate. consists of a spiral vertical plate,
An apparatus for producing acicular goethite particles in which a void exists between the end surfaces of the baffle plate and the vertical plate on the reaction tank side and the inner wall of the reaction tank.