Core TechnologyWet synthesis method

TODA KOGYO has been manufacturing and selling iron oxide since its founding in 1823, and has a long history and experience.
Using the synthesis and manufacturing technology that we have cultivated over many years, we have a lineup of various types of iron oxide with controlled properties, which are used in a wide range of applications such as pigments, catalysts, magnetic materials, raw materials for ferrite, and brake materials.
At TODA KOGYO, the thechnology controlling the important characteristics of powder design and particle design,“Type,” “Shape,” “Size,” “Distribution,” “Surface,” is called TSSDS control and inherited in new developments.
In addition to TSSDS control, we also have surface treatment technology of iron oxide particles with inorganic and organic materials, and can manufacture composite particles according to your needs.

List of properties of iron oxide

α-FeO(OH) (goethite)

• product
• product under development

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	product		product under development
shape	acicular	spindle	acicular	spindle
particle size (μm)	0.10～0.17、0.60～0.70	0.05～0.07	0.06～0.10	0.005～0.05
specific surface area 1) (m²/g)	100～150、15～20	110～140	150～190	120～280
True specific gravity	about 4.1	about 4.1	about 4.1	about 4.1
Oil absorption 2) (ml/100g)	35～45	35～40	35～45	35～45
refractive index	2.33	2.33	2.33	2.33
color phase	Yellow	Yellow	Yellow	Yellow
volume resistivity (Ω・cm)	10⁶～10⁷	10⁶～10⁷	10⁶～10⁷	10⁶～10⁷
electric charge amount (μC/g)
Types of magnetism	Antiferromagnetism	Antiferromagnetism	Antiferromagnetism	Antiferromagnetism

• 1) Measured by BET method.
• 2) Oil absorption amount can be adjusted depending on the grinding conditions.

α-Fe₂O₃ (hematite)

• product
• product under development

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	product			product under development
shape	granular	acicular	spindle	acicular	spindle
particle size (μm)	0.10～0.50	0.10～0.15	0.05～0.07	0.05～0.10	0.005～0.04
specific surface area 1) (m²/g)	2.0～11	50～55	110～130	50～110	60～140
True specific gravity	about 5.2	about 5.2	about 5.2	about 5.2	about 5.2
Oil absorption 2) (ml/100g)	15～25	35～40	35～40	35～40	25～35
refractive index	3.01	3.01	3.01	3.01	3.01
color phase	Red	Red	Red	Red	Red
volume resistivity (Ω・cm)	10⁶～10⁷	10⁶～10⁷	10⁶～10⁷	10⁶～10⁷
electric charge amount (μC/g)	about -5
Types of magnetism	Antiferromagnetism (weak ferromagnetism)	Antiferromagnetism (weak ferromagnetism)	Antiferromagnetism (weak ferromagnetism)	Antiferromagnetism (weak ferromagnetism)	Antiferromagnetism (weak ferromagnetism)

• 1) Measured by BET method.
• 2) Oil absorption amount can be adjusted depending on the grinding conditions.

Fe₃O₄ (magnetite)

• product
• product under development

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	product			product under development
shape	octahedral	hexahedral	spherical	octahedral, hexahedral,spherical, polyhedral, granular
particle size (μm)	0.23～1.5	0.20	0.15～0.25	0.01～1.5
specific surface area 1) (m²/g)	2.0～7.0	7.0	5.5～12	2.0～130
True specific gravity	about 5.2	about 5.2	about 5.2	about 5.2
Oil absorption 2) (ml/100g)	15～30	16～20	16～20	12～35
refractive index	2.42	2.42	2.42	2.42
color phase	Black	Black	Black	Black
volume resistivity (Ω・cm)	10¹～10²	10²～10⁴	10³～10⁸	10¹～10⁸
electric charge amount (μC/g)	about -5	about -5	about -5～+10	about -20～+10
Types of magnetism	ferrimagnetism	ferrimagnetism	ferrimagnetism	ferrimagnetism

• 1) Measured by BET method.
• 2) Oil absorption amount can be adjusted depending on the grinding conditions.

γ-Fe₂O₃ (maghemite)

• product under development

	product under development
shape	spherical
particle size (μm)	0.20
specific surface area 1) (m²/g)	6.5
True specific gravity	about 5.2
Oil absorption 2) (ml/100g)	17～20
refractive index
color phase	Brown
volume resistivity (Ω・cm)	10⁷
electric charge amount (μC/g)	about -5
Types of magnetism	ferrimagnetism

• 1) Measured by BET method.
• 2) Oil absorption amount can be adjusted depending on the grinding conditions.

Shape control technology of Iron oxide

Examples of the "Shape" control among the TSSDS controls in particle design are shown below.
TODA KOGYO manufactures various iron oxides by neutralizing aqueous solutions of iron salts with an alkali. This synthesis method in an aqueous solution is called wet synthesis, and is one of the core competencies of TODA KOGYO.
By changing the wet synthesis conditions according to the required functions and properties, the particle shape can be controlled to be spherical, octahedral, acicular, etc.

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  spherical (Fe₃O₄)

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  polyhedral (Fe₃O₄)

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  octahedral (Fe₃O₄)

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  hexahedral (Fe₃O₄)

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  acicular (α-FeOOH)

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  granular (Fe₃O₄)

Particle control technology of iron oxide

Examples of "Size" control among the TSSDS controls in particle design are shown below.
It is possible to control the particle size within the range of 0.005μm (5 nm) to 1.5μm (1500 nm), using the wet synthesis technology, our core competency.

Increase particle size

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  0.2μm (Fe₃O₄)

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  0.6μm (Fe₃O₄)

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  1.5μm (Fe₃O₄)

Decrease particle size

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  0.2μm (Fe₃O₄)

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  0.1μm (Fe₃O₄)

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  0.01μm (Fe₃O₄)

Magnetic properties control technology of iron oxide

Among iron oxides, Fe₃O₄ (magnetite) and γ-Fe₂O₃ (maghemite) have spinel-type crystal structures and show large magnetization.
The typical magnetic properties are listed in the table below.
The magnetic properties can also be controlled by controlling the particle shape and size.
In addition to wet synthesis, the magnetic properties can be adjusted by combining heat treatment technology.

Fe₃O₄ (magnetite)

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	product			product under development
shape	octahedral	hexahedral	spherical	octahedral, hexahedral,spherical, polyhedral, granular
Coercivity Hc (kA/m)	5.17～9.95	7.56	3.58～7.16	0.40～12.73
Coercivity Hc (Oe)	65～125	95	45～90	5～160
Residual magnetization σr (A･m²/kg)	5.9～10.0	9.0	3.3～10.0	0.5～8.0
saturation magnetization σs (A･m²/kg)	84.0～89.5	86.0	82.0～85.5	50.0～89.5

γ-Fe₂O₃ (maghemite)

	product under development
shape	spherical
Coercivity Hc (kA/m)	4.77
Coercivity Hc (Oe)	60
Residual magnetization σr (A･m²/kg)	5.5
saturation magnetization σs (A･m²/kg)	73.5

Grain size dependence between coercivity and saturation magnetization