JP7272528B2 - CERAMIC BODY, MANUFACTURING METHOD THEREOF, AND TEMPERATURE INDICATE ARTICLE - Google Patents

Description

The present invention relates to a ceramic body having thermochromic properties (also referred to as a ceramic thermochromic body), a method for producing the same, and a temperature indicating article containing this ceramic body.

The change in color due to thermal energy is called the thermochromic phenomenon, and it is being researched in many fields because temperature changes can be intuitively felt from visual color changes. Many of the materials that exhibit the thermochromic phenomenon so far are organic materials and are limited to use at temperatures below 100°C. There was a restriction in the high temperature discoloration temperature range. For example, cooking utensils for heating such as earthenware pots and frying pans reach 200 to 300° C. in a short time after starting heating, so materials exhibiting strong thermochromic properties in this temperature range are desired.

As an inorganic thermochromic material expected to have heat resistance, a material using ferric oxide is known (Patent Document 1). Limited to this color change. A material using a bismuth oxide-based compound is also known (Patent Document 2). Furthermore, the present applicant has applied for a material using a barium titanate-based compound (Patent Document 3). Plate glass using vanadium oxide is at the stage of trial marketing, but its strong toxicity is a problem. Materials such as tellurium oxide have also been reported, but they have not yet been put to practical use due to the problem of toxicity at the research stage.

Japanese translation of PCT publication No. 2015-508106 Japanese Patent No. 5027983 JP 2018-141112 A

However, bismuth oxide-based compounds and vanadium oxide-based compounds have problems such as toxicity. was difficult to use. In particular, there is no known thermochromic ceramic body that can withstand heating at 1000° C. or higher and reversibly change color with changes in ambient temperature from about 25° C. to 500° C.

The present invention has been made to deal with such problems, and includes a ceramic thermochromic body that is less expensive than bismuth and vanadium and has almost no toxicity, a method for producing the same, and this ceramic body. The object is to provide a temperature-indicating article.

The ceramic body of the present invention is made of a ferrite compound and is a thermochromic ceramic body that reversibly changes color as the temperature rises from 25°C to 300°C.
The ferrite-based compound is a ferrite-based compound containing at least one selected from a compound having a spinel-type crystal structure, a compound having a perovskite-type crystal structure, and a compound having a garnet-type crystal structure,
The thermochromic property is characterized by a color change with a color difference (ΔE) of 4.0 or more at a temperature of 200° C. or higher and a color difference (ΔE) of 6.0 or more at a temperature of 300° C. or higher.

Among the ceramic bodies made of the ferrite-based compound of the present invention, (1) the compound having a spinel-type crystal structure is MFe ₂ O ₄ (where M is at least one selected from Li ₂ , Zn, and Mg). (2) the compound having a perovskite-type crystal structure is NFeO ₃ (where N is at least one element selected from La, Y, Gd, and Nd); and (3) the garnet The compound having a crystal structure of the type L ₃ Fe ₅ O ₁₂ (where L is at least one element selected from Y, Sm, Gd and Er).
Further, the MFe ₂ O ₄ is M(Fe _1-x Al _x ) ₂ O ₄ (where x=0 to 0.2 mol) in which part of Fe in MFe 2 O 4 is replaced with Al.

The method for producing a ceramic body of the present invention comprises: an iron compound selected from at least one of oxides, hydroxides and carbonates; It is characterized by comprising a step of mixing with N or the compound of L above, and a step of firing this mixture at 900 to 1300° C. in the air.

The temperature indicating article of the present invention is characterized by including the above ceramic body having reversible temperature indicating properties such that the color changes reversibly with temperature change.

The ceramic body of the present invention is a ferrite compound that exhibits a color difference (ΔE) of 4.0 or more at a temperature of 200° C. or higher and a color difference (ΔE) of 6.0 or more at a temperature of 300° C. or higher. , in the temperature range of 25° C. to 500° C., the color changes reversibly with changes in temperature. Therefore, it is easy to visually detect a change in temperature.

It is a figure which shows the thermochromic property of a ferrite. It is a figure which shows the thermochromic property of a spinel-type ferrite. FIG. 2 is a diagram showing thermochromic properties of substituted spinel ferrite; FIG. 2 is a diagram showing the thermochromic properties of perovskite ferrite; FIG. 2 is a diagram showing thermochromic properties of substituted perovskite ferrite;

Ferrite materials are generally magnetic materials, so they are widely used in storage media as electronic parts and motors as electric products, but they are not used as thermochromic materials and are hardly studied. do not have. However, in the course of researching the development of inorganic thermochromic materials with high heat resistance, such as transition metal-containing barium titanate, β-eucryptite, and β-spodumene, excellent thermochromic materials with precipitated ferrite crystals were found. found to exhibit sexuality. The present invention is based on such findings.

Ferrites are basically divided into spinel type (composition represented by _MFe2O4 ), perovskite type (composition represented by _NFeO3 ) _, garnet type (composition represented by _L3Fe5O12 ) and magnetoplumbite, depending on _their crystal structure _. There are four types of type (composition represented by RFe ₆ O ₁₉ ). Each of these ferrites further has various types depending on its composition.

Among the above ferrites, the ferrite that can be used in the present invention is a ferrite containing at least one selected from a compound having a spinel-type crystal structure, a compound having a perovskite-type crystal structure, and a compound having a garnet-type crystal structure. It is a system compound. Among these ferrite compounds, ferrite has a thermochromic property that changes color to a color difference (ΔE) of 4.0 or more at a temperature of 200° C. or higher and a color difference (ΔE) of 6.0 or more at a temperature of 300° C. or higher. Preferably, the color difference (ΔE) is 4.0 or more at 200°C and the color difference (ΔE) is 6.0 or more at 300°C, based on 25°C. Since the color difference (ΔE) is 4.0 or more at 200° C. or higher and 6.0 or more at 300° C. or higher, the color of ferrite changes remarkably or extremely remarkably with temperature changes.

For thermochromic properties, CIE-L ^* a ^* b ^* was calculated to quantify color change due to temperature (JIS Z 8781). Thermochromic properties are measured using a CR-300 color difference meter manufactured by Minolta Co., Ltd., measuring the Yxy value, and converting it to the CIE-L ^* a ^* b ^* color system, which is a more general color system. bottom. Formula 1 shows the conversion formula and the formula for calculating the color difference ΔE.

In the L ^* a ^* b ^* color system, L ^* represents brightness, L ^* =0 represents black, and L ^* =100 represents white. a ^* and b ^* indicate the color direction, +a ^* indicates the red direction, -a ^* indicates the green direction, +b ^* indicates the yellow direction, and -b ^* indicates the blue direction. Also, as the absolute value of each numerical value increases, the color becomes brighter, and as the absolute value decreases, the color becomes duller.

The change in color with respect to the value of the color difference ΔE is shown on the right as follows.
0 to less than 0.5: very slightly different by visual observation 0.5 to less than 1.5: slightly different 1.5 to less than 3.0: appreciably different 3.0 to less than 6.0: significantly different Different 6.0 to less than 12.0: Extremely different 12.0 or more: Become a different color system

A sample for measuring thermochromic properties was prepared by the following method. Predetermined amounts of iron oxide and other necessary ferrite-forming ingredients are mixed in a wet ball mill. For example, if the amount of the formulation is 20 g, 40 ml of water is added and mixed by a ball mill for about 8 hours. After drying the mixture at about 100° C., it was pulverized in a mortar and fired at 900 to 1300° C. for about 1 hour to synthesize various ferrites. This was pulverized in a wet ball mill, dried, press-molded, and heated in a circulation oven to obtain a sample for color difference measurement. The measurement temperature was 25°C to 300°C. The thermochromic property was examined by measuring the value at a predetermined temperature based on 25° C. in CIE-L ^* a ^* b ^* and calculating the color difference (ΔE).

Typical compositions of ferrite are Mg ferrite (MgFe ₂ O ₄ ) for spinel type, La ferrite (LaFeO ₃ ) for perovskite type, Y ferrite (Y ₃ Fe ₅ O ₁₂ ) for garnet type, and Sr for magnetoplumbite type. Ferrite (SrFe ₆ O ₁₉ ) was selected and blended at the blend ratio shown in Table 1. Using this mixture, a sample for measuring the thermochromic properties was prepared by the method described above, and the thermochromic properties were examined. The firing conditions are a temperature of 1200° C. and a time of 1 hour. The results are shown in FIG. Table 1 shows the measurement results of the color difference (ΔE) from 25°C to 300°C.

As shown in Table 1 and FIG. 1, spinel-type ferrite (MgFe ₂ O ₄ ), perovskite-type ferrite (LaFeO ₃ ), and garnet-type ferrite (Y ₃ Fe ₅ O ₁₂ ) exhibited excellent thermochromic properties. Spinel type ferrite and perovskite type ferrite were particularly excellent. Further, from the results of FIG. 1, it is understood that the thermochromic property is excellent when the color changes to a color difference (ΔE) of 4.0 or more at a temperature of 200° C. or higher and a color difference (ΔE) of 6.0 or more at a temperature of 300° C. or higher. rice field. Magnetoplumbite-type ferrite (SrFe ₆ O ₁₉ ), whose color change is less than this range, is inferior in thermochromic properties to spinel-type ferrites.

Table 2 shows the blending ratio of the spinel-type ferrite. Samples were prepared in the same manner as the ferrite examples shown in Table 1, and thermochromic properties were measured. However, the firing temperature was 1000° C. for Zn ferrite and Li ferrite, and 1200° C. for the others. FIG. 2 shows the thermochromic measurement results. Table 2 shows the measurement results of the color difference (ΔE) from 25°C to 300°C.

As shown in Table 2 and FIG. 2, among spinel ferrites, Li ferrite, Zn ferrite, and Mg ferrite exhibited excellent thermochromic properties. Compared to these, Mn ferrite, Ni ferrite, and Cu ferrite had low thermochromic properties.

The thermochromic properties of Zn ferrite and Mg ferrite in which a part of Fe of Mg ferrite was replaced with Al were measured. Table 3 shows the blending ratio of the substituted ferrite. A sample was prepared in the same manner as the ferrite example shown in Table 1. However, the firing temperature was 1000° C. for the substituted Zn ferrite and 1200° C. for the substituted Mg ferrite. FIG. 3 shows the thermochromic measurement results. Table 3 shows the measurement results of the color difference (ΔE) from 25°C to 300°C.

As shown in Table 3 and FIG. 3, by substituting a portion of Fe in Zn ferrite and Mg ferrite with Al, particularly by substituting a portion of Fe with 0 to 0.2 mol Al, thermochromic properties was found to improve.

Table 4 shows the mixing ratio of the perovskite-type ferrite. Samples were prepared in the same manner as the ferrite examples shown in Table 1, and thermochromic properties were measured. However, the firing temperature was 1300° C. for Y ferrite and La ferrite, and 1200° C. for Nd ferrite and Gd ferrite. FIG. 4 shows the thermochromic measurement results. Table 4 shows the measurement results of the color difference (ΔE) from 25°C to 300°C.

As shown in Table 4 and FIG. 4, it was found that Y ferrite, La ferrite, Nd ferrite, and Gd ferrite exhibit excellent thermochromic properties.

The thermochromic properties of perovskite-type ferrite having excellent thermochromic properties were measured by substituting a portion of Fe with Al. Table 5 shows the blending ratio of the substituted ferrite. A sample was prepared in the same manner as the ferrite example shown in Table 1. However, the firing temperature was 1300°C. FIG. 5 shows the thermochromic measurement results. Table 5 shows the measurement results of the color difference (ΔE) from 25°C to 300°C.

As shown in Table 5 and FIG. 5, it was found that substituting part of Fe in Y ferrite and La ferrite with Al reduces the thermochromic properties. However, when the substitution ratio was up to about 0.5 mol, thermochromic properties with a color difference (ΔE) of 6.0 or more were exhibited at 300° C. or higher.

The method for producing a ceramic body of the present invention includes the steps of (1) uniformly mixing ceramic raw materials for forming ferrite and (2) firing the mixture at 900 to 1300° C. in air. As raw materials, an iron compound selected from at least one of oxides, hydroxides, and carbonates, and a compound of M, N, or L selected from at least one of oxides and carbonates. is mentioned. As the mixing step, a known method used for pulverization and mixing, such as a ball mill, can be employed. A ball mill can also be used for pulverization after firing.

Since the above ceramic body changes color reversibly with changes in temperature, it is used alone or in combination with other materials as a powder, molded body, sintered body, thin film, or glaze. be able to. This ceramic body is an inorganic thermochromic body that can reversibly change color even at a high temperature of 200° C. or higher, unlike an organic thermochromic body. For this reason, the ceramic body of the present invention can be used for visualization of temperature (earthen pots, tempura pots, frying pans, etc.) by using it on the surface (glaze, etc.) of tableware and cooking utensils, and on the outer wall of bricks, tiles, etc., such as firing furnaces. It can be used to visualize dangerous areas by applying the material to high-temperature areas, and to visualize dangerous areas by applying high-temperature areas such as high-temperature pipes in chemical factories.

The temperature indicating article of the present invention includes the above ceramic body. For example, in the case of a glaze, the powder of the ceramic body is added to the base material of the glaze (95% by mass of frit for ceramics, 5% by mass of Gairome clay), and the solid content is about 10 to 400% by mass. , preferably about 10 to 100% by mass, and a slurry-like glaze can be produced by making an aqueous solution of about 60%. A temperature-indicating article having a glaze layer formed on the surface can be produced by applying this glaze to a fired body (ceramic base) as a base, drying it, and then firing it.

Since the ceramic body of the present invention reversibly changes its color in a high temperature range, it can be used for visualizing dangerous places such as installation in high temperature areas.

Claims (5)

A ceramic body made of a ferrite-based compound and having thermochromic properties that reversibly changes color as the temperature rises from 25°C to 300°C,
The ferrite-based compound is a ferrite-based compound containing at least one selected from a compound having a spinel-type crystal structure and a compound having a perovskite-type crystal structure,
The thermochromic property of the ceramic body is that the color changes to a color difference (ΔE) of 4.0 or more at 200° C. or higher and a color difference (ΔE) of 6.0 or more at 300° C. or higher. The compound having a spinel-type crystal structure is MFe ₂ O ₄ (where M is at least one element selected from Li ₂ , Zn, and Mg), and the compound having a perovskite-type crystal structure is NFeO _{3 .} 2. The ceramic body according to claim 1, wherein N is at least one element selected from La, Y, Gd and Nd. 2. M(Fe _1-x Al _x ) ₂ O ₄ (where x=0 to 0.2 mol) in which part of Fe in said MFe ₂ O ₄ is substituted with Al. A ceramic body as described. A method for manufacturing a ceramic body according to claim 2 ,
mixing an iron compound selected from at least one of oxides, hydroxides and carbonates with said M or said N compound selected from at least one of oxides and carbonates;
and firing the mixture at 900 to 1300° C. in air. A temperature indicating article comprising a ceramic body having a reversible temperature indicating property that reversibly changes color with temperature change,
A temperature indicating article, wherein the ceramic body is the ceramic body according to any one of claims 1 to 3.

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