JPS61122129A - Conical alpha-ferric oxide particle and production thereof - Google Patents

Abstract

PURPOSE:To produce conical alpha-ferric oxide particle free from void and suitable as magnetic powder, etc., by heating an alkaline aqueous solution of amorphous ferric hydroxide in the presence of a specific hydroxycarboxylic acid (derivative). CONSTITUTION:An aqueous solution of ferric chloride, ferric sulfate, etc. is neutralized with an alkali, and the precipitated amorphous ferric hydroxide is filtered, and washed with water. The amorphous ferric hydroxide is dispersed in water, alkalinized with an alkali, added with 10<-3>-2X10<-2>mol (based on 1g-atom of Fe) of a hydroxycarboxylic acid (derivative) of formula (n is 5-15), and heated at about 100-250 deg.C. The produced red precipitate is separated by filtration, washed with water, and dried to obtain conical alpha-ferric oxide particle having a base diameter of <=1mum and a height of <=2mum and free from void.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to cone-shaped α-ferric oxide particles and a method for producing the same.

α-ferric oxide particles have been widely used as pigments and as intermediate raw materials for producing magnetic iron oxide powder. The acicular type is mainly known as a raw material for iron oxide powder.

Such α-ferric oxide has conventionally been produced by heating and dehydrating goethite, ie, α-Fe00H, at a temperature of about 150 to 400°C.

However, a large number of pores (dehydration pores) are generated in the α-ferric oxide particles obtained by this method. A large number of these particles remain in the iron particles, making them porous, and thus significantly reducing magnetic properties such as coercive force.In addition, in magnetic paints, many particles aggregate and agglomerate, reducing dispersibility. This results in deterioration of the magnetic recording characteristics of the magnetic recording medium.

Moreover, since goethite generally forms unique acicular aggregates, so-called tactoid particles, its particle morphology tends to change during the heating and dehydration process (as a result, the α-
Iron oxide particles have many branches and protrusions, and also have a strong tendency to aggregate with each other to form irregular shapes. in this way,
According to conventional methods, it is generally difficult to obtain α-ferric oxide particles that are substantially free of pores and have a uniform shape.

In order to solve the above-mentioned various problems in the production of α-ferric oxide, the present inventors have proposed Japanese Patent Publication No. 55-4694, Japanese Patent Publication No. 55-22416, Japanese Patent Publication No. 56-1
As described in Japanese Patent Application Laid-open No. 7290, Japanese Patent Application Laid-open No. 57-123831, etc., methods for producing α-ferric oxide that has substantially no pores have been proposed, but these methods Since the main purpose is to obtain α-ferric oxide suitable for producing magnetic iron oxide powder, the shape of the obtained α-ferric oxide is also limited to a needle shape.

Therefore, as a result of further intensive research into the production of α-ferric oxide, the present inventors found that α-ferric oxide was produced by heating an aqueous suspension of amorphous ferric hydroxide in alkaline conditions. The present invention was achieved by discovering that α-ferric oxide particles having a novel shape that was previously unknown can be obtained by using a specific oxycarboxylic acid as an additive in the method of be.

The α-ferric oxide particles according to the present invention are characterized by having a base diameter of 1 μm or less, a height of 2 μm or less, and a cone-like shape with substantially no pores, and have such a novel shape. According to the present invention, α-ferric oxide particles contain oxycarboxylic acid or a derivative thereof represented by the general formula (where n is an integer of 5 to 15) as an additive per gram of iron.
It is now produced by heating an aqueous suspension of amorphous ferric hydroxide in an alkaline coexistence of 10-3 to 2X10-'' moles per atom.

In the present invention, when heating an aqueous suspension of amorphous ferric hydroxide, an additive represented by the above general formula is allowed to coexist. Specific examples of such additives include norcabellad acid (n in the above general formula is 13) and agaritic acid (n in the above general formula is 15).

In order to obtain cone-shaped α-ferric oxide particles according to the present invention, the above-mentioned additives are added at 1% per 1g atom of iron.
It is necessary to coexist within the range of 0-3 to 2×10-” mole, and even if the amount outside this range is added,
The desired cone-shaped α-ferric oxide particles cannot be obtained.

Ferric hydroxide itself used in the present invention is not limited in any way in its manufacturing method. For example, by adding an alkali such as sodium hydroxide, potassium hydroxide, or ammonia to an aqueous solution of a ferric salt such as ferric chloride, ferric sulfate, or ferric nitrate, amorphous ferric hydroxide is formed as a precipitate. get.

Aqueous suspension of ferric hydroxide to use? The WJ liquid only needs to have a concentration that does not make stirring difficult when stirring in the presence of the above-mentioned additives, and the concentration of ferric hydroxide is usually 1.5 mol/iron equivalent. l or less, preferably 0.1 to
1 mole/7! is within the range of

The heating reaction of the aqueous suspension of ferric hydroxide is carried out under alkaline conditions. Therefore, the pH of the aqueous suspension is 7 or more, preferably 8 to 12.5-. The alkali is not particularly limited, but sodium hydroxide, potassium hydroxide, ammonia, etc. are usually used.

Further, during the reaction, pressure may be applied, but usually the suspension may be heated in a closed container without applying pressure. The reaction temperature is usually in the range of 100 to 250°C.

The α-ferric oxide particles according to the present invention, as described above,
Since it has an unprecedented new cone-like shape and approximately conical shape, for example, by manufacturing magnetic powder such as magnetic powder for perpendicular magnetic recording or non-oriented magnetic tape magnetic powder using this as a raw material,
Magnetic powder with unprecedented properties can be obtained, and it can also be used as a general pigment, and by appropriate blending, a coating composition with unprecedented properties can be obtained.

The present invention will be explained below with reference to Examples.

Example ferric chloride aqueous solution (iron concentration 16.7g/#) 34! to 1
A 0% aqueous sodium hydroxide solution was added to neutralize the slurry until the pH reached 7.5, thereby precipitating reddish brown amorphous ferric hydroxide. Next, this slurry containing ferric hydroxide was heated to 60° C., filtered, and washed with 2N warm water. The obtained ferric hydroxide was dispersed in water to form a suspension of 12, to which 7.8 g of agaritic acid (1.87 x 10-'' mol per 1 g of iron atom) was added, and 5% hydroxide was added. Aqueous sodium solution was added to adjust the pH to 12.25.

This suspension was transferred into a closed container, heated to a temperature of 150° C., and reacted with stirring for 2 hours. The generated red precipitate was filtered, washed with water, and then dried to obtain 71 g of red powder. This red powder was confirmed to be α-ferric oxide by xvA diffraction. Further, from the electron micrograph shown in the drawing, it was confirmed that these α-ferric oxide particles had a generally conical shape with an average base diameter of 0.2 μm and a height of 0.35 μm, with virtually no pores. Ta.

Comparative Example In the above example, 11.8g of agaritic acid (iron 1
α-ferric oxide particles were obtained by processing in exactly the same manner as in the above example except that 2.83 It was needle-like with a ratio of 4 and a major axis diameter of 0.8 μm.

[Brief explanation of the drawing]

The drawing is an electron micrograph (30,000 times magnification) showing the particle structure of α-ferric oxide according to the present invention.

Claims (2)

[Claims] (1) Cone-shaped α-ferric oxide particles having a base diameter of 1 μm or less, a height of 2 μm or less, and having substantially no pores. (2) As an additive, oxycarboxylic acid or its derivatives represented by the general formula ▲ mathematical formula, chemical formula, table, etc. ▼ (where n is an integer from 5 to 15) is added to 1 g of iron.
A base diameter of 1 μm or less and a height characterized by heating an aqueous suspension of amorphous ferric hydroxide in an alkaline state in which 10^-^3 to 2 x 10^-^2 moles per atom coexist. 2
A method for producing cone-shaped α-ferric oxide particles having a particle size of μm or less and having substantially no pores.