JP2010260935A - Powder containing composite particle, and method for producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide powder containing composite particles wherein growth of a hematite crystal is hardly generated even under a high temperature condition, and to provide a pigment hardly generating discoloration even under a high temperature condition and having various colors and glossiness. <P>SOLUTION: Powder containing composite particles wherein composite crystals each having a hematite crystal formed on a surface of a corundum particle are dispersed in inorganic glass is produced by dispersing corundum particles to be crystalline nuclear particles in molten inorganic glass containing iron element, cooling and solidifying the resultant dispersion body and then pulverizing the resultant solidified body. At this time, the hematite crystal is formed on the surface of the corundum particle by epitaxial growth. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a powder containing hematite crystals and a method for producing the same. The present invention also relates to a pigment made of such powder.

  Inorganic pigments containing iron oxide as a coloring component usually exhibit a dark red color, but pigments exhibiting various colors such as yellowish red, orange, red, and blackish red are produced due to differences in raw materials, shape, and manufacturing method. It is blended and used in paints as coloring materials for road surface displays, road sign displays, building materials, vehicles, and ceramics. In addition, glossy pigments are also used for applications that appeal to a sense of quality. A paint having various colors needs to be prepared by blending a plurality of pigments in accordance with the properties thereof, which is complicated in production and management. Therefore, it is required that various colors can be expressed by using only one kind of pigment.

  Patent Documents 1 and 2 disclose pigments having various colors ranging from yellowish red to blackish red, in which the surface of plate-like iron oxide particles is coated with alumina. These documents have a highly saturated color tone from orange to blue-red by adjusting the thickness of the iron oxide-coated plate-like particle layer and the thickness of the aluminum compound coating layer and utilizing light interference. Moreover, it is described that a red pigment having excellent stability can be obtained.

  However, these methods have the following drawbacks. First, in order to express various colors by light interference, it is necessary to adjust the thickness of the iron oxide plate-like particle layer and the aluminum layer on the order of several hundred nanometers. In order to heat with the heat shrinkage factor expected after precipitation, it is necessary to control the amount of the substance to be precipitated, which requires considerably complicated and sophisticated control. Further, when the precipitate is heated and crystallized, a large number of crystal nuclei are formed, so that the precipitate becomes polycrystalline, light is scattered, and the color tone is adversely affected. All the pigment production methods are sedimentation methods by neutralization reaction in an aqueous dispersion system, and waste liquid treatment is a heavy burden. Furthermore, although baking is performed at 900 ° C. or lower, at a temperature higher than this, the color easily changes to dark red close to black after baking, and the color before baking cannot be maintained. Therefore, if high-temperature baking at 900 ° C. or higher is performed, a product having a color before baking cannot be provided.

  Patent Document 3 describes a platelet-like two-layer pigment made of aluminum-containing iron oxide composed of a nucleus having a hematite structure and an outer layer having a spinel structure. The pigment is said to be capable of being adjusted to multiple shades. However, it must be produced by filtering and drying after acting a reducing agent in an aqueous suspension, which has a problem of waste liquid treatment. Patent Document 4 describes a method for producing aluminum-substituted hematite in which citric acid and ethylene glycol are added to a mixture of an iron compound and an aluminum compound to form a gel, which is then pyrolyzed and fired. The aluminum-substituted hematite thus obtained is said to be less likely to undergo particle growth even when heated at a high temperature, and exhibits a stable and clear color. However, a relatively large amount of water and organic substances must be used and dried or decomposed, which has problems in terms of energy and cost.

  Patent Document 5 describes a red composite pigment having a silica-based particle as a core and a hematite particle layer formed on the surface thereof, and is complexed with silica while maintaining a small hematite particle size and exhibiting a red color. This increases the particle size of the composite particles to improve dispersibility. Silica-based particles and hematite particles can be combined by a mechanochemical reaction to produce dry, or silica-based particles and hematite particles can be stirred in an aqueous alkali solution and produced wet. However, the composite pigment thus obtained cannot suppress crystal growth at high temperatures, and changes in color tone are unavoidable in applications where the pigments are used at high temperatures.

  In Non-Patent Document 1, material science research of Bizen ware pattern “bamboo” by the present inventors has been made, and the mechanism of the phenomenon of red color development at the part touching rice straw when baking Bizen ware is clear. Has been. According to it, during the firing of Bizen ware, a glass phase is formed on the surface due to the influence of potassium contained in rice straw, corundum particles are formed in it, and hematite crystals are subsequently epitaxially grown on the corundum particles. Has been confirmed.

JP-A-1-263157 Japanese Patent Laid-Open No. 6-1000079 JP-A 63-317559 JP 2004-43208 A JP 63-20367 A

Yasuhiro Kusano, Kazuhiro Yamaguchi, Minoru Fukuhara, Akira Doi, “Materials Science Study of Bizen ware pattern“ Tsubaki ”, Powder and Powder Metallurgy, Vol. 54, No. 2, p. 75-80, 2007

  The present invention has been made to solve the above problems, and an object of the present invention is to provide a powder containing composite particles in which hematite crystals hardly grow even under high temperature conditions. It is another object of the present invention to provide a method for easily producing the powder by a dry method in which no waste liquid is generated. It is another object of the present invention to provide a pigment having a variety of colors and gloss that hardly changes in color under high temperature conditions.

  The above problem is solved by providing a powder containing composite particles in which a composite crystal in which hematite crystals are formed on the surface of crystalline core particles is dispersed in an inorganic glass. At this time, the crystalline nucleus particles are preferably aluminum oxide particles. It is also preferred that hematite crystals are formed by epitaxial growth on the surfaces of the crystalline core particles. Moreover, it is also preferable that content of the sodium element contained in inorganic glass is 2 to 20 weight%. The above-mentioned problem can also be solved by providing a powder containing particles made of a composite crystal in which hematite crystals are formed on the surface of crystalline core particles. A preferred embodiment of the present invention is a pigment comprising the above powder.

  Moreover, the said subject is also solved by providing the manufacturing method of the said powder which disperse | distributes a crystalline nucleus particle | grain in the molten inorganic glass containing an iron element, and then it cools and solidifies and then grind | pulverizes. At this time, it is preferable that content of the iron element contained in the molten inorganic glass before hematite crystal is formed is 0.5 to 20% by weight.

  In the powder of the present invention, hematite crystals hardly grow even under high temperature conditions. Therefore, when used as a pigment, discoloration hardly occurs under high temperature conditions, and pigments having various colors and gloss can be provided. Further, since the powder production method of the present invention is a dry method that does not generate waste liquid, the environmental load is small and the production is easy.

In Example 1, it is the transmission electron micrograph which observed the corundum-hematite composite_body | complex.

  The powder of the present invention includes composite particles in which composite crystals in which hematite crystals are formed on the surfaces of crystalline core particles are dispersed in inorganic glass. In the composite particles obtained in this way, hematite crystals hardly grow even under high temperature conditions. Therefore, when used as a pigment, discoloration hardly occurs even under high temperature conditions, and it is suitable for coloring by baking.

The crystalline core particle is not particularly limited as long as it is a crystalline particle having a melting point higher than the softening point of inorganic glass, but is preferably aluminum oxide particles. Of these, corundum is preferably employed. This is because corundum is α-Al ₂ O ₃ and hematite, which is α-Fe ₂ O ₃ , easily grows on its surface. The average particle diameter of the crystalline core particles is usually about 1 to 15 μm.

  The composite crystal dispersed in the inorganic glass is one in which a hematite crystal is formed on the surface of the crystalline core particle. The color tone of the powder of the present invention varies depending on the size of the hematite crystal, and the color changes from reddish yellow to orange, red, and blackish red as the small hematite crystal increases. Therefore, powders exhibiting various colors can be obtained by controlling the dimensions of the formed hematite crystals. That is, in the powder manufacturing method of the present invention, various conditions that affect the dimensions of the resulting hematite crystals, such as the type of inorganic glass, the content of iron element in the inorganic glass, the heating temperature, and the cooling rate, are adjusted. By doing so, powders of various colors can be obtained. The hematite crystals formed on the surface of the crystalline core particles in this way hardly change in dimensions even when heated to a high temperature up to about 1200 ° C., and as a result, the color tone does not change. . This point is different from Bengala, which is simply an aggregate of hematite crystals, and darkens due to crystal growth by heating.

  The dimension of the hematite crystal is not particularly limited, but is about 10 nm to 10 μm. The hematite crystal is preferably formed on the surface of the crystalline core particle by epitaxial growth. The size of the hematite crystals produced at this time does not exceed the size of the crystalline core particles. That is, it is presumed that the color tone of the product can be controlled by changing the size of the crystalline core particles added to the glass powder.

Although the kind of inorganic glass in which the composite crystal is dispersed is not particularly limited, silicate glass is preferably used in terms of cost and ease of handling. That is, it contains a silicic acid (SiO ₂ ) component as a main component and usually contains 50% by weight or more, and further includes sodium oxide (Na ₂ O), potassium oxide (K ₂ O), magnesium oxide (MgO), calcium oxide ( A glass containing components such as CaO), aluminum oxide (Al ₂ O ₃ ), diboron trioxide (B ₂ O ₃ ), lead oxide (PbO) is preferable. It also contains iron ions that are not normally consumed for the growth of hematite crystals. Furthermore, inorganic glass may be produced by adding an element that can be substituted with an iron element, such as manganese, cobalt, zinc, nickel, or phosphorus, or that can be combined with an iron element. Diversity can be given to

  In order to lower the softening point of the inorganic glass, the inorganic glass preferably contains an alkali metal element or an alkaline earth metal element. And when the inorganic glass contains a sodium element and the content is 2 to 20% by weight, a powder excellent in color developability can be obtained. If the content of sodium element is less than 2% by weight, the color developability may be lowered, more preferably 3% by weight or more, and further preferably 5% by weight or more. On the other hand, when the content of sodium element exceeds 20% by weight, the water resistance of the glass may be lowered, and more preferably 16% by weight or less. In the case of containing potassium element instead of sodium element, as shown in Example 3 described later, a tendency for color developability to decline was observed. As shown in Non-Patent Document 1, in Bizen ware flames, vivid color development in glass containing potassium is recognized, but when heat treatment is performed at a lower temperature and for a shorter time than the firing process of Bizen ware. It has been found that color development is better when glass containing sodium element is used than when glass containing potassium element. Therefore, the content of potassium element is preferably 5% by weight or less, and more preferably 2% by weight or less. Moreover, the tendency for color development to fall was recognized also when there was much content of a calcium element. Therefore, the content of calcium element is preferably 5% by weight or less, and more preferably 2% by weight or less.

  The powder of the present invention is a powder containing composite particles in which composite crystals in which hematite crystals are formed on the surface of crystalline core particles are dispersed in inorganic glass. Since it is dispersed in the inorganic glass, unevenness on the pigment surface is reduced, and a pigment having gloss can be obtained. In addition, since the hematite crystals are coated on the inorganic glass, the acid resistance and reduction resistance of the pigment are improved. The ratio of the weight of the crystalline core particles to the weight of the glass is usually about 0.1 to 5 times. More preferably, it is 0.2 times or more and 2 times or less.

  On the other hand, a powder containing particles made of a composite crystal itself in which a hematite crystal is formed on the surface of crystalline core particles without being dispersed in inorganic glass is also an embodiment of the present invention. Such particles can be obtained, for example, by dissolving and removing the glass component using an aqueous solution that dissolves glass, such as hydrofluoric acid.

  The method for producing the powder of the present invention is not particularly limited. Preferably, the crystalline core particles are dispersed in the molten inorganic glass containing iron element, and then cooled and solidified, and then pulverized. Manufactured by. Conventional Bengala is often produced by a wet method, and its waste liquid treatment has been a problem. However, this production method is preferable from the viewpoint of the environment because no harmful waste liquid is produced.

  The composition of the molten inorganic glass containing an iron element is different from the inorganic glass contained in the powder described above in the content of the iron element. The content of the iron element contained in the molten inorganic glass before hematite crystals are formed is preferably 0.5 to 20% by weight. When the content of the iron element is less than 0.5% by weight, color developability may be lowered, more preferably 1% by weight or more, and further preferably 2% by weight or more. On the other hand, when the content of the iron element exceeds 20% by weight, hematite crystals may be formed in a multilayered manner around the crystalline core particles, more preferably 15% by weight or less, and further preferably 10% by weight or less. In general, the color becomes darker as the content of the iron element increases, so that the color tone can be adjusted by adjusting the content of the iron element.

  The manufacturing method of molten inorganic glass containing iron element is not particularly limited, and iron element is added to glass raw materials such as oxides and salts containing elements such as silicon, sodium, potassium, magnesium, calcium, aluminum, boron and lead. It can be prepared by mixing and heating and melting the contained oxide or salt. The compounds containing iron element used include iron oxide (II), iron oxide (III), iron sulfate (II), iron sulfate (III), iron nitrate (II), iron nitrate (III), iron chloride ( II), iron (III) chloride and the like are exemplified. Among these, iron oxide (II), iron oxide (III), iron sulfate (II), and iron sulfate (III) are preferable from the viewpoint of economy and ease of mixing. From the viewpoint of color development, iron (II) sulfate and iron (III) sulfate are preferred. The heating and melting temperature is usually about 1100 to 1500 ° C. The glass thus obtained is once cooled, pulverized, mixed with the crystalline core particles, and then heated and melted again to disperse the crystalline core particles in the molten inorganic glass containing the iron element. it can. Also, ready-made glass can be used as a raw material, and the shortage of iron element may be supplemented according to the content of iron element contained in the ready-made glass, and the powder of ready-made glass may be heated with corundum. . In this case, since waste glass is reused, there is an advantage from an environmental point of view.

  In addition, by mixing crystalline core particles together with oxides and salts containing iron element into the glass raw material, the crystalline core is directly incorporated into molten inorganic glass containing iron element by heating and melting only once. The particles can also be dispersed. In the case of producing by this method, the color developability may be slightly lowered, but since the heating operation is only required once, it is advantageous in terms of energy compared to the method of producing glass powder in advance. When manufacturing in this way, a part of the crystalline core particles may be melted to become a component of inorganic glass, and the remaining part may not be melted to form a composite with hematite crystals.

  The maximum temperature at which the crystalline core particles are dispersed in the molten inorganic glass containing iron element is preferably 800 to 1400 ° C. When the maximum temperature is lower than 800 ° C, the color developability may be lowered, more preferably 950 ° C or higher, and further preferably 1100 ° C or higher. On the other hand, when the maximum temperature exceeds 1400 ° C, the glass component may be deteriorated, more preferably 1350 ° C or less, and further preferably 1300 ° C or less. This temperature is usually maintained for about 0.1 to 24 hours and then cooled.

  When the molten inorganic glass containing the iron element and in which the crystalline core particles are dispersed is cooled, the darker the color is developed. From this, hematite crystals hardly precipitate in a molten state at a high temperature, and there seems to be a temperature range advantageous for crystal growth of hematite at a lower temperature. The cooling rate is preferably 50 ° C./min or less, more preferably 30 ° C./min or less, further preferably 10 ° C./min or less, and most preferably 5 ° C./min or less. Considering the production efficiency, the cooling rate is usually 0.1 ° C./min or more. It is possible to adjust the color tone by adjusting the cooling rate.

  The powder of the present invention can be obtained by pulverizing the solidified product obtained by cooling as described above. The grinding method is not particularly limited, and a known grinding method can be employed. The particle size is not particularly limited, and is adjusted to an appropriate particle size according to the application.

  The powder of the present invention is suitably used as a pigment. By adjusting the manufacturing conditions, various colors from reddish yellow to orange, red and blackish red can be easily obtained, and since it does not contain harmful heavy metals, It can be widely used for various applications such as roads, building materials, bridges, and automobiles. For example, it is particularly useful as a pigment for road yellow (orange) wires, which have conventionally been widely used with pigments containing harmful heavy metals such as chromium and lead. In addition, as described above, the powder of the present invention hardly changes its color tone even when heated to a high temperature of up to about 1200 ° C., so that it is heated to a high temperature of, for example, 900 ° C. or higher, or even 1000 ° C. or higher. It is suitable as a pigment to be used. Therefore, it is particularly suitably used for colored ceramics and the like that usually require a firing process at a high temperature, such as tiles, bricks, and ceramics. Furthermore, since the dimensions of the hematite crystal can be controlled, it is also promising as an electronic material or a magnetic material.

Example 1 (content of iron element)
Iron sulfate (II) (FeSO ₄ ) was added to 0.22 g of sodium carbonate (Na ₂ CO ₃ ), 4.81 g of silicon dioxide (SiO ₂ ), and 0.52 g of aluminum oxide (Al ₂ O ₃ ), respectively. 152 g, 0.304 g, and 0.76 g were added and mixed to prepare three types of glass raw materials having different compounding amounts of iron (II) sulfate. Here, although iron (II) sulfate was blended in the form of heptahydrate (FeSO ₄ · 7H ₂ O), the blending amount in this example describes the weight in terms of anhydride. This glass raw material was heated and melted at 1250 ° C. in the air atmosphere, and then maintained at the same temperature for 2 hours, and then cooled to synthesize a glass containing iron ions. The contents of elemental iron and sodium element in the synthesized glass were as shown in Table 1. These glasses are made into powder, and 0.5 g of corundum plate-like particles having a particle diameter of 1 to 10 μm are added to each 0.5 g and mixed well, and this mixture is heated at 1250 ° C. in an air atmosphere. And melted. At this time, the glass powder was in a liquid phase, but the corundum particles were dispersed without melting. Subsequently, by cooling the melt at a rate of 1 ° C./min, hematite crystals were formed around the corundum particles, and a solidified product in which the corundum-hematite composite was coated with glass was obtained.

  The appearance color of the obtained solidified product was observed, and the color according to the Munsell color system was measured. Further, the obtained solidified product was immersed in hydrofluoric acid to dissolve the glass component, and then the size of hematite bonded to the corundum particles was obtained by observing with a transmission electron microscope. At this time, the average value of the long diameter and the short diameter was determined for about 10 hematite particles, and the arithmetic average value was taken as the average particle diameter. These results are summarized in Table 1. FIG. 1 shows a transmission electron micrograph of the corundum-hematite composite from which the glass has been removed when the iron element content is 1.7% by weight. It can be seen that the hematite particles are epitaxially grown from the end faces of the corundum particles. An electron diffraction image of the hematite crystal is also shown in FIG. Moreover, although the powder obtained by pulverizing the three kinds of solidified materials thus obtained was heated at 1200 ° C. for 2 hours in an air atmosphere, no color change was observed visually. This point is different from Bengala, which changes to a dark color under similar heating conditions, and it can be seen that the powder of the present invention is excellent in heat resistance.

Example 2 (Cooling rate)
Add 0.285 g of iron (II) sulfate to 2.12 g of sodium carbonate (Na ₂ CO ₃ ), 4.81 g of silicon dioxide (SiO ₂ ) and 0.52 g of aluminum oxide (Al ₂ O ₃ ) and mix. A glass raw material was prepared. This glass raw material was heated and melted at 1250 ° C. in the air atmosphere, and then maintained at the same temperature for 2 hours, and then cooled to synthesize a glass containing iron ions. The iron element content in the synthesized glass was 1.6% by weight, and the sodium element content was 13.7% by weight. The glass was made into powder, 0.5 g of the same corundum as in Example 1 was added to each 0.5 g and mixed well, and the mixture was heated and melted at 1250 ° C. in an air atmosphere. At this time, the glass powder was in a liquid phase, but the corundum particles were dispersed without melting. Subsequently, by cooling the melt at four speeds of 1.0 ° C./min, 2.0 ° C./min, 5.0 ° C./min and 50 ° C./min, hematite crystals are formed around the corundum particles. Thus, a solidified product in which the corundum-hematite composite was coated with glass was obtained. The appearance color of the obtained solidified product was observed, and the color according to the Munsell color system was measured. These results are summarized in Table 2. Moreover, although the four kinds of solidified products thus obtained were heated at 1200 ° C. for 2 hours in an air atmosphere, no color change was observed visually.

Example 3 (Glass composition)
With respect to 2.76 g of potassium carbonate (K ₂ CO ₃ ), 4.81 g of silicon dioxide (SiO ₂ ) and 0.52 g of aluminum oxide (Al ₂ O ₃ ), 0.152 g and 0. 456 g and 0.76 g were added and mixed to prepare three types of glass raw materials (with potassium) having different compounding amounts of iron (II) sulfate. This glass raw material was heated and melted at 1250 ° C. in the air atmosphere, and then maintained at the same temperature for 2 hours, and then cooled to synthesize a glass containing iron ions. The contents of iron element and potassium element in the synthesized glass were as shown in Table 3.

Further, for a mixture of 1.70 g of sodium carbonate (Na ₂ CO ₃ ), 0.40 g of calcium carbonate (CaCO ₃ ), 4.81 g of silicon dioxide (SiO ₂ ), 0.52 g of aluminum oxide (Al ₂ O ₃ ), Iron sulfate (II) was added in an amount of 0.152 g, 0.456 g and 0.76 g, respectively, and mixed to prepare three types of glass raw materials (with sodium and calcium) having different compounding amounts of iron sulfate (II). This glass raw material was heated and melted at 1250 ° C. in the air atmosphere, and then maintained at the same temperature for 2 hours, and then cooled to synthesize a glass containing iron ions. The contents of iron element, sodium element and calcium element in the synthesized glass were as shown in Table 3.

  These 6 types of glass were made into powder, 0.125 g of the same corundum as in Example 1 was added to 0.5 g of each glass and mixed well, and this mixture was heated and melted at 1250 ° C. in an air atmosphere. At this time, the glass powder was in a liquid phase, but the corundum particles were dispersed without melting. Subsequently, by cooling the melt at a rate of 1.0 ° C./min, hematite crystals were formed around the corundum particles, and a solidified product in which the corundum-hematite composite was coated with glass was obtained. The appearance color of the obtained solidified product was observed, and the color according to the Munsell color system was measured. These results are summarized in Table 3. Moreover, although the six kinds of solidified materials thus obtained were heated at 1200 ° C. for 2 hours in an air atmosphere, no color change was observed visually.

Example 4 (heating temperature)
With respect to 2.12 g of sodium carbonate (Na ₂ CO ₃ ), 4.81 g of silicon dioxide (SiO ₂ ) and 0.52 g of aluminum oxide (Al ₂ O ₃ ), 0.152 g and 0. 456 g and 0.76 g were added and mixed to prepare three kinds of glass raw materials having different compounding amounts of iron (II) sulfate. This glass raw material was heated and melted at 1250 ° C. in the air atmosphere, and then maintained at the same temperature for 2 hours, and then cooled to synthesize a glass containing iron ions. Table 4 shows the contents of iron element and sodium element in the synthesized glass. The glass is powdered, 0.125 g of the same corundum as in Example 1 is added to 0.5 g of each glass and mixed well, and the mixture is mixed at 900 ° C., 1050 ° C., 1100 ° C. and 1250 ° C. in an air atmosphere. Heated to melt. At this time, the glass powder was in a liquid phase, but the corundum particles were dispersed without melting. Subsequently, by cooling the melt at a rate of 1 ° C./min, hematite crystals were formed around the corundum particles, and a solidified product in which the corundum-hematite composite was coated with glass was obtained.

Example 5 (one-step manufacturing method)
Sodium carbonate (Na ₂ CO ₃ ) 0.131 g, silicon dioxide (SiO ₂ ) 0.291 g, corundum 0.528 g and iron (II) sulfate 0.050 g were added and mixed well. It was melted by heating at ° C. At this time, the glass powder became a liquid phase, but some of the corundum particles were dispersed without melting. Subsequently, by cooling the melt at a rate of 1.0 ° C./min, hematite crystals were formed around the corundum particles, and a solidified product in which the corundum-hematite composite was coated with glass was obtained.

The appearance color of the obtained solidified product was orange, and the color according to the Munsell color system was 4.06YR5.72 / 4.49. Moreover, although the solidified material thus obtained was heated at 1200 ° C. for 2 hours in an air atmosphere, no color change was observed visually. Although the vividness of the color is slightly inferior to the method of mixing the corundum after producing the glass containing iron element in advance as in Example 1, coloring is possible even in a single heating operation. Cost advantage was recognized.

Claims (8)

  Powder containing composite particles in which composite crystals in which hematite crystals are formed on the surface of crystalline core particles are dispersed in inorganic glass.   The powder according to claim 1, wherein the crystalline core particles are aluminum oxide particles.   The powder according to claim 1 or 2, wherein hematite crystals are formed on the surfaces of the crystalline core particles by epitaxial growth.   The powder according to any one of claims 1 to 3, wherein the content of sodium element contained in the inorganic glass is 2 to 20% by weight.   A powder containing particles composed of composite crystals in which hematite crystals are formed on the surface of crystalline core particles.   A pigment comprising the powder according to any one of claims 1 to 5.   The method for producing a powder according to any one of claims 1 to 5, wherein the crystalline core particles are dispersed in a molten inorganic glass containing an iron element, followed by cooling and solidification, followed by pulverization. The method for producing a powder according to claim 7, wherein the content of the iron element contained in the molten inorganic glass before hematite crystals are formed is 0.5 to 20% by weight.