JPS61158828A - Production of iron oxide fine powder - Google Patents

Abstract

PURPOSE:In producing iron oxide by neutralizing a ferrous salt with an alkali to give iron hydroxide, and introducing an oxidizing gas into it, a fine powder of iron oxide which can be sintered at lower temperature and becomes a sintering auxiliary at a low melting point is obtained by adding previously sodium silicate to the alkali. CONSTITUTION:A ferrous salt (e.g., ferrous chloride, ferrous sulfate, etc.) is neutralized with an alkali (e.g., ammonia water, sodium hydroxide, etc.) to give iron oxide, into which an oxidizing gas is introduced to produce iron oxide. In the operation, 3-20wt.% calculated as SiO2 based on iron oxide to be formed of sodium silicate is previously added to the alkali. The prepared iron oxide is made into a fine powder, consequently, a reaction is completed at a lower temperature during sintering, it can be processed into a sintering auxiliary at a lower melting point, and a sintered material having higher density can be obtained.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to a method for producing 111-particle iron oxide by neutralizing a ferrous salt aqueous solution with an alkali and oxidizing it with an oxidizing gas such as air. It is something.

<Prior art and its problems> Iron oxide is industrially produced by roasting iron sulfate obtained from steel plate pickling waste liquid from the steel industry and from the titanium industry.

Industrially obtained iron oxide is heat-treated by roasting, etc., so it is not dispersed in primary particles but in secondary particles.
They become secondary particles and exist in an aggregated state. In addition, the size of the 11th-order particles is several orders of magnitude larger, which is different from the particle diameter of the category of ultrafine particles that has recently been called ultrafine particles. It is a particle that does not have.

<Purpose of the Invention> The present inventors have developed iron oxide as a raw material for electronic materials and a sintering aid for powder metallurgy that can complete the reaction at a lower temperature or as a sintering aid with a low melting point from the viewpoint of energy saving. The present invention was achieved as a result of intensive research aimed at obtaining iron oxide that is suitable for use in iron oxides.

<Structure of the Invention> That is, the present invention involves neutralizing a ferrous salt with an alkali to form iron hydroxide, and then introducing an oxidizing gas to produce iron oxide. The present invention provides a method for producing particulate iron oxide, characterized in that 3 to 20% by weight of SiO2 is added to iron.

The present invention will be explained in more detail below.

In recent years, the trend toward finer particles of powders has become even stronger, and various types of powders are being studied. Melift is made into fine particles, which causes the melting point to drop and the catalytic effect to appear.
Various effects are expected, including the ability to obtain light sintered bodies. Iron oxide is also used as a raw material for electronic materials such as hard ferrite and soft ferrite.
It is thought that the effect of micronization is significant.

There are various methods for producing iron oxide, such as (1) roasting of iron salts, (2) wet synthesis in an aqueous solution, and (3) hydrothermal synthesis. Describing the characteristics of each method, (1) is a manufacturing method that is used industrially, but particles tend to aggregate, and it is very difficult to control the particle shape. In addition, (3) is a synthesis reaction at high temperature and high pressure, which poses safety issues, and from the perspective of particle shape control, depending on the generation conditions, hexagonal plate-shaped MrO may be produced, making it difficult to control grain growth. ,
It is very difficult to make it into fine particles.

The method according to the present invention is an application of the wet synthesis described in (2), and the present inventors have previously produced goethite, a raw material for metal magnetic powder, which is a magnetic recording medium, by this method. At that time, they discovered that metal ion impurities greatly affect the acicularity of goethite and have the effect of suppressing crystal growth.

Among them, when silicate compounds are added as impurities,
X-ray diffraction results showed that the particle shape became significantly smaller, and that when a certain amount or more was added, the particles became extremely fine. Moreover, the X-ray diffraction results revealed that these particles were amorphous. became.

As the ferrous salt, water-soluble ferrous salts such as ferrous chloride, ferrous sulfate and ferrous nitrate are preferred.

Further, as the alkali, hydroxides of alkali metals or alkaline earth metals such as aqueous ammonia and sodium hydroxide are preferable.

Air or the like is preferably used as the oxidizing gas.

Next, the silicate to be used as an additive is preferably a water-soluble silicate such as sodium silicate, and the amount of the silicate added is 3% to the iron oxide produced as SiO2.
The effect of micronization is significant in the range of 20% by weight. If the amount of silicate added is less than 3% by weight, some acicular goethite will be produced, which is insufficient as the amount to be added to produce particulate iron oxide. In addition, if the addition exceeds 20% by weight, the state of the aqueous solution such as the viscosity of the system changes, making complete oxidation impossible and having a negative effect on the generation of fine particles. For Si
It is 3 to 20% by weight as O2.

It is thought that the silicate present in ferrous hydroxide becomes a nucleus for the production of fine iron oxide particles and becomes fine particles to suppress crystal growth. If the amount is less than 3% by weight, the silicate acts as a nucleus for the formation of fine particles, but the suppressing effect is insufficient and the formation of needle-like crystals is considered.

It has also been found that the specific surface area of the fine particles of iron oxide obtained by the present invention increases as the amount of silicate added increases, as shown in FIG.

Practical example The present invention will be explained below based on examples.

(Example 1) Capacity: 59. Add 2IL of 5moi/4 sodium hydroxide to a glass flask under N2 gas atmosphere.Firstly, add about 4.88g of water-soluble sodium silicate (3wt% based on the iron oxide produced in terms of SiO2) and stir thoroughly. I did this. Furthermore, 2.5 l of ferrous chloride aqueous solution having a concentration of 0.4 mail/l was added, and the mixture was stirred for several hours with N2 gas. Thereafter, the temperature was raised to 40°C, air was introduced at a flow rate of 55 L/sin, and fine particles of iron oxide were obtained by air oxidation. The specific surface area of the produced iron oxide was measured by N2 gas adsorption method, and the result was 207 m''/g.

(Examples 2 to 6) In Example 1, the amount of water-soluble sodium silicate added was 5.1
Iron oxide was obtained under the same conditions except that the concentrations were 0, 15.17, and 20 wt%. The specific surface area was as shown in FIG.

(Examples 7 to 12) Using the fine particle iron oxide of Examples 1 to 6 as a raw material, 50 g of iron oxide
11.4 g of barium carbonate was mixed with the mixture, and after firing at 1250°C for 120 minutes, it was crushed to obtain calcined ferrite powder.Next, a molded body of 20Φ was prepared at a molding pressure of 2 T/cm2, and heated at 1150°C. A barium ferrite sintered body was produced under manufacturing conditions of 2 hours, and the sintered density was measured. The results are shown in Table 1.

(Comparative Example 1) Same as Examples 7 to 12, except that iron oxide obtained from iron steel washing resistant waste liquid (usually iron oxide obtained by the Ruessner method) was used as the raw material, and the sintered body formation temperature was 1270 ° C. A barium ferrite sintered body was created under the same conditions.

(Comparative Example 2) Iron oxide was obtained under the same conditions as in Example 1 except that the water-soluble sodium silicate was 0 wt %. Then, a barium ferrite sintered body was produced under the same conditions as in Comparative Example 1.

From the above examples, it can be seen that the products obtained in the examples of the present invention have a large specific surface area, that is, they are made into fine particles.

It can also be seen that the reaction temperature can be low because the particles are finely divided during sintering. It was also confirmed that the obtained sintered body had a high density.

Further, FIG. 2 shows an electron micrograph of the iron oxide obtained in Example 2, and it can be seen that fine particles of iron oxide have been changed.

Table 1 Density of prototype ferrite sintered body <Effects of the invention> In the present invention, by adding sodium silicate to ferrous salt in advance to produce iron oxide, the iron oxide obtained is made into fine particles. Therefore, the reaction can be completed at a lower temperature during sintering, or it can serve as a sintering aid due to its low melting point. Also,
A sintered body with high density can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a graph showing changes in the specific surface area of produced iron oxide with respect to the amount of added sodium silicate. FIG. 2 is a photograph substituted for a drawing showing the structure of particles, and is a transmission electron micrograph in the case of adding 5 wt % of sodium silicate (Example 2). FIG, l SiO2, 'Drinking amount (wt%/Fe2O3) F I
G, 2 pr

Claims (1)

[Claims] (1) After neutralizing the ferrous salt with an alkali to form iron hydroxide,
A method for producing particulate iron oxide, which comprises introducing an oxidizing gas and adding 3 to 20% by weight of SiO_2 to the iron oxide that produces sodium silicate in advance.