JPH0319171B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to goethite (α-FeOOH) containing zinc, which has a completely new particle form in the form of discs, and a method for producing the same. The platy goethite of the present invention can be used as a yellow pigment, a raw material for magnetic powder, a pigment for reinforcing paint films, a raw material for two-dimensionally oriented ferrite, a reinforcing material for composite materials (reinforced resin), and the like. [Prior Art] Goethite, which is originally called goethite, has the property of growing into euhedral acicular particles. Therefore, many methods for producing goethite are already known, but goethite obtained by known methods is needle-shaped, and these goethites are mainly used for yellow pigments and magnetic powders for longitudinal (in-plane horizontal magnetic) recording. It is widely used as a raw material for electronic materials. It is important for pigments, including their particle morphology, to have high dispersibility, heat resistance (weather resistance), etc. when turning them into paints. Furthermore, it is important for magnetic powder for longitudinal recording to have high acicularity, uniform particles, and good dispersibility. In addition, in recent years, with the demand for higher density magnetic recording, perpendicular magnetic recording has been developed in place of longitudinal recording, and barium ferrite is known as one of the magnetic powders. It is desired that the magnetic powder be disc-shaped and have uniform particles. In addition to the conventional acicular goethite, there is a method for producing granular goethite such as rice grains and pea grains, for example,
58-49693, JP 58-49694, JP 53-28158, JP 50-65499, JP 49-42597, JP 49-42598, etc. However, there is no proposal for a plate-shaped goethite or its production method, and it is difficult to obtain plate-shaped goethite using the proposed method. [Problems to be solved by the invention] Goethite has the property of growing into acicular particles as euhedral, and although granular goethite has been proposed, it is generally acicular and the particles are Goethite with a disc-like shape and its manufacturing method have not been found. If disk-shaped goethite particles can be obtained instead of needle-shaped, granular, etc. goethite particles, it is expected that new applications will be developed in the fields of pigments, electronic materials, composite materials, etc. that take advantage of the characteristics of the disk-shaped structure. Ru. An object of the present invention is to provide a plate-shaped goethite and a method for producing the same. Another object of the present invention is to provide a plate-shaped goethite containing zinc that has well-organized particles and good heat resistance, and a method for producing the same. [Means for Solving the Problems] As a result of continuing research into improving the particle morphology, particle size distribution, dispersibility, etc. of goethite, the present inventors found that
(1) When a ferric salt and an alkali hydroxide are reacted to produce ferric hydroxide, which is a precursor of goethite, an oxyalkylamine is added to produce ferric hydroxide, and this water When ferric oxide is hydrothermally treated, it is surprisingly possible to obtain plate-shaped goethite with a completely different particle form from the conventional one; (2) when a zinc compound is added when producing the ferric hydroxide; ,
The inventors have discovered that the heat resistance of plate-shaped goethite is improved and that it is possible to obtain plate-shaped goethite with well-organized particles, leading to the present invention. In the present invention, the particle form is a disc-shaped α containing zinc.
- FeOOH, platy goethite characterized by a particle size (disc diameter) of 0.01 to 1 μm and a platy ratio (particle size/thickness) in the range of 1 to 10, and ferric salt and hydroxide A zinc compound is added to an alkali in the presence of an oxyalkylamine in an aqueous medium to produce ferric hydroxide, and the resulting slurry of ferric hydroxide is hydrothermally treated to form a disc containing zinc. The present invention relates to a method for producing disc-shaped goethite, which is characterized by producing goethite. The disc-shaped goethite of the present invention and its manufacturing method will be explained in more detail. In the present invention, as the ferric salt, ferric sulfate, ferric chloride, ferric nitrate, etc. are generally used, and among these, ferric chloride is preferred.
As the alkali hydroxide, sodium hydroxide, potassium hydroxide, etc. are preferably used. As a method of reacting a ferric salt and an alkali hydroxide in a medium, a method of reacting a ferric salt aqueous solution with an alkali hydroxide aqueous solution is generally suitable. At this time, it is appropriate to adjust the concentration of the ferric salt aqueous solution to 0.1 to 1 mol/h, and the concentration of the alkali hydroxide aqueous solution to 0.3 to 5 mol/h.
It is appropriate to adjust it so that In addition, the amount of alkali hydroxide used for ferric salt is 1 to 1.
It is preferable to use about 5 times equivalent amount. In obtaining the disc-shaped goethite of the present invention,
In particular, when a ferric salt and an alkali hydroxide are reacted in an aqueous medium to produce ferric hydroxide, which is a precursor of goethite, a zinc compound is added in the presence of an oxyalkylamine. It is important to generate ferric oxide. The oxyalkylamine is dissolved in a solvent,
For example, it can be used by dissolving it in a solvent such as water, by dissolving it in an aqueous alkali hydroxide solution, or by adding it directly into the system.
The amount used is usually 15 to 80 times the mole of the ferric salt, preferably 30 to 80 times, particularly 35 to 75 times the mole. If the amount of oxyalkylamine added is too small, it tends to become plate-like, become granular, or have a wide particle size distribution, and if it is added too much, α-
Fe ₂ O ₃ is easily generated and it is not economical. As the oxyalkylamine, those in which the alkyl group has 2 to 6 carbon atoms are suitable, and typical examples thereof include ethanolamine, γ-propanolamine, β-propanolamine, diethanolamine, triethanolamine, isobutanolamine, etc. Among these, ethanolamine is preferred. As the zinc compound, water-soluble zinc sulfate, zinc chloride, zinc nitrate, etc. are generally preferably used, but acid-, alkali-, etc.-soluble zinc compounds can also be used. The zinc compound may be added after being dissolved in an aqueous solution of a ferric salt, a zinc ion-containing solution may be prepared and added, or the zinc compound may be added directly into the system. The amount of the zinc compound added is preferably such that the zinc content in the platy goethite is 0.1 to 10 at%, preferably 0.5 to 7 at%, based on the iron atoms. A method is adopted in which a zinc compound is added so that the amount of zinc ions relative to ferric ions becomes the above-mentioned amount. If the amount of zinc compound added is too large, it becomes difficult to form a plate shape, loses its shape, or becomes elongated, and if the amount added is too small, the effect of improving heat resistance may not be sufficiently expressed. , the particle size distribution width also tends to widen. The reaction temperature when producing ferric hydroxide by reacting a ferric salt with an alkali hydroxide in the presence of an oxyalkylamine and adding a soluble zinc compound is 50°C or lower, preferably -10°C or lower. +45℃
It is preferable to increase the effect of adding oxyalkylamine and to control the plate ratio, particle morphology, etc. If the temperature is too high, the particles tend to become long, α-Fe ₂ O ₃ is mixed in, and the variation in particle morphology becomes large. If the temperature is too low, part of the solution freezes and the particles become microscopic. , the disc ratio becomes smaller, but there is no particular advantage in making it too low. Further, the reaction time is not particularly limited, but is generally appropriately selected from the range of 1 to 20 hours. A slurry of ferric hydroxide obtained by the reaction of a ferric salt and an alkali hydroxide can produce plate-shaped goethite even if it is immediately treated with hydrothermal treatment. When ripened, it becomes easier to obtain disk-like particles with uniform morphology. As a maturing method, generally employed is a method of leaving the product at 0 to 80°C for about 5 to 30 hours with stirring or without stirring. In addition, in order to enhance the hydrothermal treatment effect, it is necessary to
It is desirable to perform the hydrothermal treatment at a pH of 10 or more, preferably 10.5 to 14. To adjust the pH of the slurry to 10 or higher, for example, the slurry containing ferric hydroxide may be filtered, washed, or after removing the supernatant liquid, an alkali such as sodium hydroxide or potassium hydroxide may be added to the slurry. This method is convenient. Hydrothermal treatment temperature is 100-250℃, preferably 120℃
~230°C is preferred. If the hydrothermal treatment temperature is too low, it will take a long time to convert to goethite, and the particles will become elongated and have a large variation in morphology. If the hydrothermal treatment temperature is too high, α-
Fe ₂ O ₃ may be generated. The hydrothermal treatment time is not particularly limited, but is generally about 0.5 to 5 hours. Further, an autoclave is generally suitably employed for the hydrothermal treatment. By the hydrothermal treatment, the ferric hydroxide in the slurry is converted into highly dispersible platy goethite having an unprecedented particle morphology. As a method for recovering plate-shaped goethite particles from the slurry after hydrothermal treatment, conventional methods such as washing with water, filtration, drying, etc. can be employed. In the present invention, the plate-shaped goethite particles recovered after hydrothermal treatment are found to have α
-It is confirmed that it is a crystal of FeOOH. Also, particle diameter (disc diameter), disc ratio (particle diameter/thickness)
etc. can vary over a wide range depending on the manufacturing conditions as described below, but when observing and measuring the shape, distribution, etc. of plate-shaped goethite particles using a transmission electron microscope (TEM), the particle morphology is found to be plate-shaped. More specifically, it has a hexagonal disc shape or a shape similar to it, the particle size is in the range of 0.01 to 1 μm, and the disc ratio is in the range of 1 to 1 μm.
The particles are well aligned within the range of 10, and the particle size and disc ratio are also within a narrow range. In addition, in a hexagonal disk shape or a form similar to it, the ratio of the lengths of the short side and the long side of the six sides (long side/short side) is 3 or less, and most of the particles are 1.5 or less. In addition, the average particle diameter and average platelet ratio (average value of 30 randomly measured particles) are:
It can be controlled within the range of 0.03 to 0.5 μm and 1 to 7, and all particles are within ±50% of the average particle diameter. Further, according to differential thermal analysis, the dehydration temperature of the plate-shaped goethite of the present invention is 250° C. or higher, and even 260° C. or higher, indicating that it has excellent heat resistance. [Example] Example 1 A solution of 50 g of ferric chloride [FeCl ₃ 6H ₂ O] and 0.25 g of zinc chloride [ZnCl ₂ ] dissolved in 1 part of distilled water and kept at 8°C was mixed with 75 g of sodium hydroxide and 0.25 g of zinc chloride [ZnCl 2 ]. Dissolve 500 ml of monoethanolamine (45 times the mole of ferric chloride) in distilled water 2 and heat at 8°C.
The solution was added dropwise to a solution maintained at about 10°C, and reacted with sufficient stirring while maintaining the temperature at about 10°C, to obtain a ferric hydroxide slurry. After leaving this slurry at 30°C for about 20 hours to age, remove the supernatant liquid, wash with a 10% sodium hydroxide aqueous solution to adjust the pH of the slurry to 11, and place the slurry in an autoclave with a volume of 500 ml. Prepared for 150
Hydrothermal treatment was performed at ℃ for 1 hour to obtain a plate-shaped goethite slurry. The plate-shaped goethite slurry is washed with water, filtered,
After drying, a powdery plate-like goethite was obtained. The zinc content in the platy goethite powder was determined by fluorescent X-rays and was found to be 0.9 atomic % based on iron atoms. Furthermore, a transmission electron microscope (TEM) photograph (50,000 times) of the obtained plate-shaped goethite powder is shown in FIG. Moreover, analysis by X-ray diffraction confirmed that this disc-shaped goethite had an α-FeOOH structure. Transmission electron microscopy (TEM) of platy goethite
The particle size (disc diameter), disc ratio (particle diameter/thickness), particle size distribution, etc. were measured. In addition, differential thermal analysis was performed on the platy goethite powder to measure the thermal decomposition temperature. These results are shown in Table 1 together with the specific surface area measurement results. Note that the average particle diameter and average platelet ratio in Table 1 are average values for 30 particles. Examples 2 to 6 The amount of monoethanolamine used in Example 1 was changed from 45 times the mole to 60 times the amount of ferric chloride (Example 2), and the zinc content in Example 1 was changed to 2 at%.
(Example 3), the hydrothermal treatment temperature in Example 1 was changed from 150°C to 180°C (Example 4), β-propanolamine was used instead of monoethanolamine in Example 1. A platy goethite was obtained in the same manner as in Example 1 except that 20 times the mole of diethanolamine was used in place of monoethanolamine in Example 1 (Example 6). Table 1 shows the results measured in the same manner as in Example 1.

〔Effect of the invention〕

The present invention is a plate-shaped goethite containing zinc, which is a completely new particle form for goethite, and a method for producing the same. Plate-shaped goethite containing zinc has uniform particles and excellent heat resistance. In addition, this goethite can not only be used for the same purposes as conventional acicular and granular goethite, but also heat-resistant yellow iron oxide, yellow transparent iron oxide, iron oxide for ultraviolet absorption, pigments for reinforcing paint films, two-dimensional It can be used in a wide range of fields including raw materials for oriented ferrite, reinforcing materials for composite materials, and raw materials for magnetic powder for perpendicular magnetic recording.

[Brief explanation of drawings]

FIG. 1 is an electron micrograph showing the particle morphology of the zinc-containing platy goethite obtained in Example 1 of the present invention, which is enlarged 50,000 times.

Claims (1)

[Claims] 1. Particles containing zinc in the form of discs containing α-
A disc-shaped goethite that is FeOOH and has a particle diameter (disc diameter) of 0.01 to 1 μm and a disc ratio (particle diameter/thickness) in the range of 1 to 10. 2. The platy goethite according to claim 1, wherein the content of zinc is 0.1 to 10 atomic % based on iron atoms. 3. The plate-shaped goethite according to claim 1, wherein the plate shape is a hexagonal plate shape or a shape similar to the hexagonal plate shape. 4. The plate-shaped goethite according to claim 1, wherein the content of zinc is 0.5 to 7 atomic % based on iron atoms, and the plate shape is a hexagonal plate shape or a form similar thereto. 5 Add a zinc compound to a ferric salt and an alkali hydroxide in an aqueous medium in the presence of an oxyalkylamine to generate ferric hydroxide, and hydrothermally treat the resulting slurry of ferric hydroxide. A method for producing plate-shaped goethite, which comprises producing plate-shaped goethite containing zinc. 6. Production of platy goethite according to claim 5, wherein the amount of the zinc compound added is such that the zinc content in the platy goethite is 0.1 to 10 atomic % based on iron atoms. Law. 7. The method for producing platy goethite according to claim 5, wherein the amount of oxyalkylamine is 15 to 80 times the mole of the ferric salt.