JP7732156B2 - Iron-based powder for supplying iron ions - Google Patents

Description

The present invention relates to an iron-based powder for supplying iron ions that contribute to plant growth.

Iron is an essential nutrient for plant growth, playing a role in chlorophyll synthesis, energy production in mitochondria, and the conversion of nitrogen fertilizer into amino acids.

Plants absorb this iron as divalent ferric ions, but if there is a shortage of iron in the soil, it can cause poor growth of new shoots, as seen in the yellowing of rice plants, and result in reduced rice yields.
Taking paddy fields as an example, when fertilizer containing sulfate ions is used when there is a shortage of iron in the soil as described above, hydrogen sulfide is generated from the soil in the paddy fields, causing poor growth of rice roots and causing the rice plants to fall over due to reduced root penetration into the soil, and also reducing rice yields due to reduced absorption of nutrients from the soil.
In any case, in order to improve plant growth, it is necessary to provide a stable and continuous supply of divalent iron ions, and as a means for achieving this, attention has traditionally been focused on iron ion supplying materials.

For example, Patent Document 1 discloses an iron powder containing 80% or more by mass of iron and 0.4% to 1.5% by mass of oxygen, with 50% or more by mass of the total having a particle size of 100 μm to 10 mm, as a material for stably supplying divalent iron ions to plants.

Patent document 2 also discloses a plant growth promoter consisting of ferrous oxide and a chelating substance to enable plants to efficiently absorb iron.

JP 2015-119685 A Japanese Patent Application Laid-Open No. 2004-123677

In paddy fields and fields, where moisture is present, divalent iron ions dissolve from the spread iron powder, and at the same time, the surface of the iron powder is oxidized by oxygen dissolved in the water and oxygen in the air, producing mainly iron oxyhydroxide and iron oxide.

Since such iron oxyhydroxides and iron oxides act as passive compounds, the amount of divalent iron ions leaching from the iron powder decreases once the iron powder has oxidized to a certain extent. Furthermore, iron-reducing bacteria of the genus Geobacter and Anaeromyxobacter are present in soil (Monthly Modern Agriculture, October 2020 issue), and these iron-reducing bacteria reduce the trivalent iron in the above iron oxyhydroxides and iron oxides to divalent iron, which then leaches out as divalent iron ions, but this leaching takes time.

In other words, as described in Patent Document 1, when iron powder containing a large amount of metallic iron with a low oxygen concentration is spread, the surface of the iron powder is oxidized after spreading, and then iron-reducing bacteria reduce the oxidized portion. Therefore, although this contributes significantly to plant growth, it takes a relatively long time for the effect to be realized.

Furthermore, as described in Patent Document 2, when ferrous oxide is sprayed, the surface of the ferrous oxide (FeO) is first oxidized to iron oxyhydroxide or iron oxide before being reduced by iron-reducing bacteria, so the amount of divalent iron ions leached out is reduced, and even if they are leached out, it takes a long time to achieve the required amount.

The present invention aims to solve the above problems and provide an iron-based powder for supplying iron ions, which improves the growth conditions of plants (crops) by dissolving divalent iron ions, and thereby increases the yield of crops.

When a solid substance is subjected to mechanical energy such as crushing, impact, or friction, its crystalline properties change. When distortion occurs in the crystalline structure of the solid, it becomes chemically activated and more susceptible to chemical reactions.

Therefore, in order to solve the above-mentioned problems, the inventors have focused on the chemical activity of iron-based powders and conducted studies with the aim of promoting the elution of divalent iron ions from the iron-based powders, and as a result have found that divalent iron ions can be effectively eluted by controlling the half-width of the diffraction intensity curve corresponding to the (110) diffraction plane of the α-Fe crystal.
It was also found that the particle size of the chemically activated iron-based powder is not affected much by the particle size, and therefore the particle size of the iron-based powder does not necessarily have to be specified.

The present invention is based on the above findings and has the following gist and configuration.
1. An iron-based powder for supplying iron ions that contributes to plant growth,
The iron-based powder for supplying iron ions has a diffraction intensity curve corresponding to the (110) diffraction plane of an α-Fe crystal, and the diffraction peaks of the X-ray diffraction intensity curve obtained by using Cu-Kα rays of the iron-based powder constituting the iron-based powder for supplying iron ions have a half-width in the range of 0.03° to 3.00°.

2. The iron-based powder for supplying iron ions according to 1 above, wherein the median diameter _D50 is 50 μm or more and 10×10 ³ μm or less, and the maximum particle size is 80 μm or more and 30×10 ³ μm or less.

In accordance with the present invention, by limiting the range of the half-width of the diffraction intensity curve corresponding to the (110) diffraction plane of the α-Fe crystal of the iron-based powder, it is possible to provide an iron-based powder for supplying iron ions that has a high iron ion supply capacity that contributes to the growth of plants (crops).

Hereinafter, an embodiment of the present invention will be described.
[Among the diffraction peaks of X-ray diffraction using Cu-Kα rays of the iron-based powder constituting the iron-based powder for supplying iron ions, the half-width of the diffraction intensity curve corresponding to the (110) diffraction plane of the α-Fe crystal is in the range of 0.03° to 3.00°]
The reason why the iron-based powder for supplying iron ions of the present invention has a high iron ion supplying ability is presumed to be as follows.
In the case of iron-based powders, when mechanical energy is applied by pulverization using a pulverizer or mixing using a mixer, distortion occurs in the crystal structure of the iron-based powder particles, and oxygen reactivity is improved.
Here, the distortion of the crystal structure occurring within the iron-based powder particles can be evaluated from the value of the half-width of the X-ray diffraction intensity curve corresponding to the (110) plane of the α-Fe crystal derived from iron. The half-width increases as the non-uniform distortion occurring between the crystal lattice in which the atoms constituting the α-Fe crystal are three-dimensionally arranged and the adjacent crystal lattice increases.
The effect of improving oxygen reactivity increases with increasing strain. However, if the strain is too large, the effect of iron ion elution due to oxygen reaction caused by moisture in the cultivated land becomes significantly large, and although a large amount of iron ions are eluted in a short time after application, the elution period becomes short.
Since a continuous supply of iron ions is required for plant growth, it is necessary to continuously supply a stable amount of iron ions throughout the entire period from the early to late stages of growth, rather than supplying a large amount of iron ions in the early stages of growth.
Therefore, the half width is set to a range of 0.03° to 3.00°, preferably 0.05° to 3.00°, and more preferably 0.07° to 3.00°.

In the present invention, the half width is measured as follows.
First, X-ray diffraction measurement is performed on the iron-based powder for supplying iron ions using Cu-Kα radiation to obtain a diffraction intensity curve corresponding to the (110) diffraction plane of the α-Fe crystal. Next, the width of the diffraction intensity curve is determined at half the maximum intensity of the diffraction intensity. This width is defined as the half-value width in the present invention.

Growing plants using iron-based powder that meets the above characteristics can achieve effective iron ion elution and improve plant growth. Iron-based powder can be produced by any of the following methods: atomization (e.g., water atomization, gas atomization, etc.), pulverization, or oxide reduction. The atomization method involves spraying water or gas onto molten metal, pulverizing it, and then cooling and solidifying it. Either water atomization or gas atomization can be used. The oxide reduction method is a method for reducing iron oxide (mill scale) or iron ore powder that is generated on the surface of steel sheets during hot rolling, for example. The pulverization method is a method for crushing small metal pieces using a pulverizer.

"Iron-based powder" refers to a metal powder containing 50% or more by mass of Fe. The iron-based powder in the present invention preferably contains 50% or more by mass of metallic iron. Furthermore, the iron-based powder is preferably iron powder. Here, iron powder refers to a powder consisting of Fe and unavoidable impurities. Avoidable impurities such as C, S, O, N, Si, Mn, P, S, Cr, and Cu may be contained.

The method for measuring the metallic iron content of iron-based powders conforms to JIS A 5011-2 "Method for determining metallic iron content."

The iron-based powder preferably has a crystallinity of 90% by volume or more.
The crystallinity is calculated by the following method. First, the X-ray diffraction spectrum of the iron-based powder is measured by powder X-ray diffraction using characteristic X-rays of Cu-Kα. In the obtained X-ray diffraction spectrum, the crystallinity (Vcry) of the iron-based powder is calculated by the following formula (1) based on the area of a broad diffraction pattern derived from the amorphous phase (Amo.P) and the sum of the areas of multiple peaks derived from the crystalline phase (Cry.P).
Vcry (volume %) = Cry. P / (Amo. P + Cry. P) × 100 (1)

In the present invention, the median diameter _D50 and maximum particle diameter of the iron-based powder are not particularly limited as long as there are no problems with handling, but it is preferable that the median diameter _D50 is 50 μm or more. It is also preferable that the median diameter _D50 is 10× ¹⁰ μm or less. It is also preferable that the maximum particle diameter is 80 μm or more. It is also preferable that the maximum particle diameter is 30× ¹⁰ μm or less.

The particle size specification in Patent Document 1 mentioned above is limited to particle sizes that account for 50% or more by mass of the total iron powder, and is not an indicator of the particle size of the entire iron powder. In other words, Patent Document 1 allows for the mixing of extremely fine iron powder. However, if there is a large amount of extremely fine iron powder, it may be blown away by the wind during application and cultivation, reducing the amount actually applied to the soil, or the amount of iron powder in the soil available to plant roots may be reduced, resulting in insufficient effectiveness.

Furthermore, Patent Document 1 allows for the mixing of extremely coarse iron powder. If there is a large amount of extremely coarse iron powder, the specific surface area, which is the area per unit mass of the iron powder, will become small.

In other words, the leaching of divalent iron ions from iron powder in soil and the oxidation of iron powder proceed from the surface of the iron powder. Therefore, the larger the specific surface area of the iron powder, the greater the amount of divalent iron ions that will be leached, resulting in an iron ion leaching effect. On the other hand, if the specific surface area is small, there is a risk that sufficient iron ion leaching effect will not be achieved.

From the above considerations, it is preferable that the iron-based powder for supplying iron ions of the present invention has the following particle size.
That is, it is preferable that the median diameter (median value of particle diameter) _D50 of the iron-based powder for supplying iron ions is in the range of 50 μm or more and 10× ¹⁰ μm or less, and further that the maximum particle diameter is 80 μm or more. There is no particular upper limit to the maximum particle diameter, but for example, 30× ¹⁰ μm or less is preferable.
If the iron-based powder for supplying iron ions is excessively fine ( _D50 less than 50 μm or maximum particle size less than 80 μm), it may be blown away by the wind during application or cultivation, which may lead to a decrease in the amount of iron-based powder actually applied to the soil or a decrease in the amount of iron-based powder in the soil that can be used by plant roots.

On the other hand, if _D50 is greater than 10 × ¹⁰ μm or the maximum particle size is greater than 30 × ¹⁰ μm, the particles will be excessively coarse overall, resulting in a small specific surface area. Since the elution of divalent iron ions from the iron-based powder in soil and the oxidation of the iron-based powder both proceed from the surface of the iron-based powder, an excessively small specific surface area may reduce the amount of eluted divalent iron ions.
Therefore, it is preferable to satisfy the above-mentioned particle size regulations.

In the present invention, the _D50 and maximum particle size of powder are measured in accordance with JIS Z 8815 "General rules for sieving test methods."

To adjust the median diameter _D50 of the iron-based powder for supplying iron ions to 50 μm or more, the powder may be classified using a sieve.
On the other hand, in order to adjust the median diameter D ₅₀ of the iron-ion supplying iron-based powder to 10×10 ³ μm or less, specifically, the crushing conditions for the iron-based powder as raw material may be adjusted.

To adjust the maximum particle size of the iron-based powder for supplying iron ions to 80 μm or more, specifically, classification using a sieve may be carried out.
On the other hand, in order to adjust the maximum particle size of the iron-based powder for supplying iron ions to 30×10 ³ μm or less, specifically, the crushing conditions for the iron-based powder as a raw material may be adjusted.

[Production of iron-based powder]
The iron-based powder according to the present invention can be produced by subjecting an iron-based powder produced by a technique such as atomization, oxide reduction, or pulverization to a treatment for increasing the strain of the α-Fe crystals. First, the iron-based powder used in the present invention is preferably produced by water atomization, gas atomization, oxide reduction, or pulverization. Furthermore, the produced powder may be classified or mixed by various methods to prepare the iron-based powder according to the present invention.

Next, in the present invention, the iron-based powder obtained by the above-mentioned method must be subjected to a process to increase the distortion of the α-Fe crystals in the iron-based powder for supplying iron ions. This process is preferably carried out by applying mechanical energy using a mixer or a grinder. Mixers such as a V-type mixer, double cone mixer, conical blender, or agitator granulator, or grinders such as a ball mill, vibration mill, roller mill, jet mill, hammer mill, or disc mill can all be suitably used.

When using the above mixer or grinder, appropriate mixing or grinding conditions can be set to impart distortion to the α-Fe crystals and adjust the half-width to within the range of the present invention described above.

The iron-based powder used in this example was prepared by the following procedure.
In order to evaluate the ability of iron-based powders for supplying iron ions to plants, iron-based powders having particle sizes and the like shown in Table 1 were prepared. First, mill scale generated during hot rolling of steel was reduced to produce iron powder.
Next, a high-speed mixer (manufactured by EarthTechnica Corporation) was used as an agitation granulator to agitate 1 kg of each iron powder, thereby obtaining iron-based powders for supplying iron ions having particle sizes and the like shown in Table 1. All of the iron-based powders for supplying iron ions were iron powders. The agitation was carried out by using an agitator blade in a sample-loading container at a constant rotation speed of 500 rpm, while varying the agitation time.

The properties of the iron-based powder in this example were evaluated as follows.
The iron-based powders according to the examples were measured in accordance with JIS Z 8815 "General rules for sieving test methods," and the maximum particle size and the median diameter _D50, which is a representative value of the particle size, were determined from the particle size distribution based on mass.

Furthermore, the half-width of the X-ray diffraction intensity curve of the (110) plane of the α-Fe crystal powder was measured as follows.
That is, an X-ray diffractometer (SmartLab manufactured by Rigaku Corporation) was used to measure the iron-based powder to be measured using Cu-Kα characteristic X-rays (wavelength 1.54178 Å) at a scanning speed of 4°/min and a measurement angle in the range of 35° to 55°, thereby obtaining a diffraction intensity curve of the (110) plane of the α-Fe crystal in the iron-based powder. Then, the half-width was calculated from this diffraction intensity curve. More specifically, the measurement was performed in accordance with JIS K 0131 "General Rules for X-ray Diffraction Analysis."
Furthermore, using the above-mentioned method, it was confirmed that the iron-based powder according to the example had a metallic iron content of 50% or more and a crystallinity of 90% or more by volume.

To evaluate the ability to supply iron ions to plants, rice was cultivated in paddy fields as follows.
The iron-based powders according to Comparative Examples 1 to 8 and Invention Examples 1 to 12 were each spread at 10 kg ^per 100 m2 of paddy field, and rice cultivation was carried out, and the ability to supply iron ions to rice was evaluated based on the mass of harvested rice grains.
Conventional Example 1 was used when rice was grown without applying the iron-based powder, and the mass of harvested rice per unit area in this case was set to 100. The mass of harvested rice when each iron-based powder was used was shown as a mass ratio to Conventional Example 1. A larger value indicates a larger mass of harvested rice and a higher ability to supply divalent iron ions. In other words, the iron ion supply ability in this example was evaluated from the mass of harvested rice per unit area.
Table 1 shows the mass ratio of harvested rice per unit area as a result of the conventional example, comparative example, and inventive example.

As shown in Table 1, when the iron-based powders of Examples 1 to 12 of the invention, in which the half-width of the diffraction intensity curve of the (110) plane of α-Fe is 0.03° or more and 3.00° or less, are sprayed, the mass ratio of harvested rice grains is larger than when the iron-based powders of Conventional Example 1 and Comparative Examples 1 to 8 are sprayed.

Furthermore, when the iron-based powders of Examples ₃ , 6 to ¹² were sprayed, in which the half-width of the diffraction intensity curve of the (110) plane of α-Fe was 0.03° or more and 3.00° or less, the D50 was 50 μm or more and 10×10 ³ μm or less, and the maximum particle size was 80 μm or more and 30×10 3 μm or less, the mass ratio of the harvested rice grains was even greater than that of Examples 1, 2, 4 and 5.

When the iron-based powders of Examples 7 to 12 were sprayed, in which the half-width of the diffraction intensity curve of the (110) plane of α-Fe was 0.05° or more and 3.00° or less, the D ₅₀ was 50 μm or more and 10×10 ³ μm or less, and the maximum particle size was 80 μm or more and 30×10 ³ μm or less, the mass ratio of the harvested rice grains was even greater than that of Examples 3 and 6.

When the iron-based powders of Examples 9 to ¹² were sprayed, in which the half-width of the diffraction intensity curve of the (110) plane of α-Fe was 0.07° or more and 3.00° or less, and further the _D50 was 50 μm or more and 10×10 ³ μm or less, and the maximum particle size was 80 μm or more and 30×10 3 μm or less, the mass ratio of the harvested rice was even larger than that of Examples 7 and 8.

These results demonstrate that the performance of iron-based powders for supplying iron ions is influenced by the half-width of the diffraction intensity curve corresponding to the (110) diffraction plane of the powder's α-Fe crystals. Using the iron-based powder for supplying iron ions of the present invention makes it possible to efficiently supply divalent iron ions to plants, which is effective in increasing plant growth and yields.

Claims (2)

An iron-based powder for supplying iron ions that contributes to plant growth,
the iron-based powder for supplying iron ions contains 50% by mass or more of metallic iron,
The iron-based powder for supplying iron ions has a diffraction intensity curve corresponding to the (110) diffraction plane of an α-Fe crystal, and the diffraction peaks of the iron-based powder for supplying iron ions obtained by X-ray diffraction using Cu-Kα rays have a half-width in the range of 0.03° to 3.00°. 2. The iron-based powder for supplying iron ions according to claim 1, wherein the median diameter _D50 is 50 μm or more and 10×10 ³ μm or less, and the maximum particle size is 80 μm or more and 30×10 ³ μm or less.