A heat-reflective ceramic pigment, its preparation method and application

Abstract

This invention discloses a heat-reflective ceramic pigment, its preparation method, and its application. The general chemical formula of the heat-reflective ceramic pigment is Nd. x Cr 1‑x Fe y TiO 3.5+1.5y Where: 0.15≤x≤0.45, 0.5≤y≤0.7. This invention achieves high reflectivity of ceramic pigments in the visible-near-infrared band by forming isoelectric substitution through rare earth doping and utilizing the radius difference between ions to create lattice distortion defects. Simultaneously, Cr is used to adjust the color of the pigment, resulting in a yellowish hue and a beige heat-reflective ceramic pigment. Furthermore, by utilizing foaming and expansion technology and employing non-ionic foaming agents such as fatty acid esters, a loose and porous structure is formed during the dehydration process of the precursor, achieving uniform dispersion of the ceramic pigment precursor. This effectively solves the problem of precursor agglomeration affecting the poor dispersibility of the fired pigment, thereby improving the dispersibility and heat reflection effect of the pigment.

Description

Technical Field

[0001] This invention belongs to the field of ceramic pigment technology, specifically relating to a heat-reflective ceramic pigment, its preparation method, and its application. Background Technology

[0002] Building heating and cooling are major contributors to global environmental problems such as the greenhouse effect and ozone depletion. Therefore, building energy conservation has become a global concern. Traditional methods primarily utilize new wall materials such as aerated concrete blocks, hollow concrete blocks, porous fly ash bricks, and autoclaved aerated concrete bricks to achieve building wall insulation. However, numerous studies have shown that while external wall insulation technology is highly effective in reducing heating energy consumption in northern regions, its effect on reducing air conditioning energy consumption in southern regions is not significant.

[0003] Using near-infrared reflective coatings on building exteriors is an effective method for building energy conservation. White is the most common and easiest to prepare reflective materials; for example, titanium sphene, zirconium oxide, alumina, calcium silicate, and titanium dioxide all have high reflectivity. However, white is a limited color, failing to meet people's color needs and thus restricting its application. Beige is a common design for exterior wall decoration, and while there are many types of beige materials available, very few offer high heat reflectivity.

[0004] Therefore, developing a beige ceramic colorant with good heat reflection effect has broad market prospects. Summary of the Invention

[0005] The present invention aims to solve at least one of the technical problems existing in the prior art. To this end, the present invention proposes a heat-reflective ceramic pigment, its preparation method, and its application. The ceramic pigment is beige in color and has good heat reflection effect in the visible-near infrared band.

[0006] To address the aforementioned technical problems, a first aspect of the present invention provides a heat-reflective ceramic pigment, wherein the general chemical formula of the heat-reflective ceramic pigment is Nd. x Cr 1-x Fe y TiO 3.5+1.5y Where: 0.15≤x≤0.45, 0.5≤y≤0.7.

[0007] Specifically, rare earth and transition metal ions possess diverse electronic structures, thus playing unique roles in the fields of light and heat. This invention achieves high reflectivity of ceramic pigments in the visible-near infrared band by forming isoelectric substitution through rare earth doping and utilizing the radius differences between ions to create lattice distortion defects. Simultaneously, Cr is used to adjust the color of the pigment, making it yellowish, thereby obtaining a beige heat-reflective ceramic pigment.

[0008] In some embodiments of the present invention, the maximum particle size of the heat-reflective ceramic pigment is no greater than 20 μm. Fine-particle-size ceramic pigments have higher activity, which not only improves the color development effect of the pigment but also enhances its heat-reflective properties.

[0009] A second aspect of the present invention provides a method for preparing the above-mentioned heat-reflective ceramic pigment, comprising the following steps:

[0010] (1) Dissolve tetrabutyl titanate in anhydrous ethanol to obtain solution A;

[0011] (2) Add soluble iron salt, soluble chromium salt and soluble neodymium salt to solution A according to the stoichiometric ratio of the general chemical formula, mix, and obtain solution B;

[0012] (3) Add citric acid to the solution B and mix to obtain solution C;

[0013] (4) The solution C is heated in a water bath, fatty acid ester is added, and the mixture is continuously stirred to emulsify and foam. After drying, the expanded precursor is obtained.

[0014] (5) Grind, calcine, re-grind and sieve the precursor to obtain the heat-reflective ceramic colorant.

[0015] Specifically, during the precursor preparation process, due to gradual evaporation and dehydration, the precursor condenses into a hardened block, which is difficult to break. Simultaneously, the calcined powder is prone to forming large, hard agglomerates, thus affecting the performance of the pigment. This invention utilizes foaming and expansion technology, employing a non-ionic foaming agent, fatty acid ester, to create a loose, porous structure in the precursor during dehydration. This ensures uniform dispersion of the precursor, thereby guaranteeing the dispersibility of the calcined pigment and improving its reflective properties.

[0016] In some embodiments of the present invention, in step (2), the concentration of solution A is 0.1-0.5 mol / L. Preferably, the concentration of solution A is 0.1-0.2 mol / L.

[0017] In some embodiments of the present invention, in step (2), the soluble iron salt is an iron nitrate, sulfate or hydrochloride, such as ferric nitrate, ferric sulfate, ferric chloride, etc.; preferably ferric nitrate.

[0018] In some embodiments of the present invention, in step (2), the soluble chromium salt is a nitrate, sulfate or hydrochloride of chromium, such as chromium nitrate, chromium sulfate, chromium chloride, etc.; preferably chromium nitrate.

[0019] In some embodiments of the present invention, in step (2), the soluble neodymium salt is a neodymium nitrate, sulfate or hydrochloride, such as neodymium nitrate, neodymium sulfate, neodymium chloride, etc.; preferably neodymium nitrate.

[0020] In some embodiments of the present invention, in step (3), the amount of citric acid added is not less than three times the amount of tetrabutyl titanate.

[0021] In some embodiments of the present invention, in step (3), the amount of citric acid added is 3-4 times the amount of tetrabutyl titanate.

[0022] In some embodiments of the present invention, in step (4), the amount of fatty acid ester added is 1-3 wt% of anhydrous ethanol.

[0023] In some embodiments of the present invention, in step (4), the temperature of the water bath heating is 85-90°C.

[0024] In some embodiments of the present invention, in step (5), the maximum calcination temperature is 1250-1300℃.

[0025] In some embodiments of the present invention, in step (5), the heat preservation time at the highest temperature is 30-90 minutes.

[0026] A third aspect of the present invention provides an exterior wall ceramic tile, wherein the raw materials for preparing the exterior wall ceramic tile include the above-mentioned heat-reflective ceramic pigments, or include heat-reflective ceramic pigments prepared by the above-mentioned preparation method.

[0027] Compared with the prior art, the above-described technical solution of the present invention has at least the following technical effects or advantages:

[0028] (1) This invention achieves high reflectivity of ceramic pigments in the visible-near infrared band by forming isopotential substitution through rare earth doping and forming lattice distortion defects by taking advantage of the radius difference between ions; at the same time, Cr is used to adjust the color of the pigments to make the pigments yellow, thus obtaining beige heat-reflective ceramic pigments.

[0029] (2) This invention utilizes foaming and expansion technology and adopts non-ionic foaming agent fatty acid ester to form a loose and porous structure during the dehydration process of the precursor, thereby achieving uniform dispersion of ceramic pigment precursor and effectively solving the influence of precursor agglomeration on poor dispersion of fired pigment, thus improving the dispersion and heat reflection effect of pigment.

[0030] (3) The method for preparing heat-reflective ceramic pigments of the present invention is simple and conducive to large-scale industrial production. Detailed Implementation

[0031] The present invention will now be described in detail with reference to embodiments to facilitate understanding of the invention by those skilled in the art. It is particularly important to note that the embodiments are merely illustrative of the invention and should not be construed as limiting the scope of protection of the invention. Non-essential improvements and adjustments made to the invention by those skilled in the art based on the above description should still fall within the scope of protection of the invention. Furthermore, all raw materials mentioned below, unless otherwise specified, are commercially available products; all process steps or preparation methods not mentioned in detail are process steps or preparation methods known to those skilled in the art.

[0032] Example 1

[0033] A heat-reflective ceramic colorant with the chemical formula Nd 0.15 Cr 0.85 Fe 0.7 TiO 4.55 The maximum particle size is no greater than 20 μm. The preparation method of this heat-reflective ceramic colorant includes the following steps:

[0034] (1) According to the chemical formula Nd 0.15 Cr 0.85 Fe 0.7 TiO 4.55 Weigh out tetrabutyl titanate, ferric nitrate, chromium nitrate and neodymium nitrate. First, add 0.1 mol of tetrabutyl titanate to a beaker containing 500 mL of anhydrous ethanol, stir and mix well to obtain solution A.

[0035] (2) Add 0.07 mol ferric nitrate, 0.085 mol chromium nitrate and 0.015 mol neodymium nitrate to solution A in sequence, stir and mix well to obtain solution B;

[0036] (3) Add 0.35 mol of citric acid to solution B, stir and mix well to obtain solution C;

[0037] (4) Place the beaker of solution C in an 85°C water bath, add 4g of fatty acid ester to solution C, and stir continuously to emulsify and foam; when solution C gradually evaporates, stop stirring and continue heating in the water bath until dry to obtain the expanded precursor.

[0038] (5) Grind the precursor, calcine it at 1250°C for 90 minutes, cool and grind it, and pass it through a 500-mesh sieve to obtain the heat-reflective ceramic colorant of this embodiment.

[0039] Example 2

[0040] A heat-reflective ceramic colorant with the chemical formula Nd 0.45 Cr 0.55 Fe 0.5 TiO 4.25The maximum particle size is no greater than 20 μm. The preparation method of this heat-reflective ceramic colorant includes the following steps:

[0041] (1) According to the chemical formula Nd 0.45 Cr 0.55 Fe 0.5 TiO 4.25 Weigh out tetrabutyl titanate, ferric nitrate, chromium nitrate and neodymium nitrate. First, add 0.1 mol of tetrabutyl titanate to a beaker containing 600 mL of anhydrous ethanol, stir and mix well to obtain solution A.

[0042] (2) Add 0.05 mol ferric nitrate, 0.055 mol chromium nitrate and 0.045 mol neodymium nitrate to solution A in sequence, stir and mix well to obtain solution B;

[0043] (3) Add 0.4 mol of citric acid to solution B, stir and mix well to obtain solution C;

[0044] (4) Place the beaker of solution C in a 90°C water bath, add 10g of fatty acid ester to solution C, and stir continuously to emulsify and foam; when solution C gradually evaporates, stop stirring and continue heating in the water bath until dry to obtain the expanded precursor.

[0045] (5) Grind the precursor, calcine it at 1300℃ for 30 minutes, cool and grind it, and pass it through a 500-mesh sieve to obtain the heat-reflective ceramic pigment of this embodiment.

[0046] Example 3

[0047] A heat-reflective ceramic colorant with the chemical formula Nd 0.3 Cr 0.7 Fe 0.5 TiO 4.25 The maximum particle size is no greater than 20 μm. The preparation method of this heat-reflective ceramic colorant includes the following steps:

[0048] (1) According to the chemical formula Nd 0.3 Cr 0.7 Fe 0.5 TiO 4.25 Weigh out tetrabutyl titanate, ferric nitrate, chromium nitrate and neodymium nitrate. First, add 0.1 mol of tetrabutyl titanate to a beaker containing 500 mL of anhydrous ethanol, stir and mix well to obtain solution A.

[0049] (2) Add 0.05 mol ferric nitrate, 0.07 mol chromium nitrate and 0.03 mol neodymium nitrate to solution A in sequence, stir and mix well to obtain solution B;

[0050] (3) Add 0.3 mol of citric acid to solution B, stir and mix well to obtain solution C;

[0051] (4) Place the beaker of solution C in an 88°C water bath, add 6g of fatty acid ester to solution C, and stir continuously to emulsify and foam; when solution C gradually evaporates, stop stirring and continue heating in the water bath until dry to obtain the expanded precursor.

[0052] (5) Grind the precursor, calcine it at 1280°C for 60 minutes, cool and grind it, and pass it through a 500-mesh sieve to obtain the heat-reflective ceramic colorant of this embodiment.

[0053] Example 4

[0054] A heat-reflective ceramic colorant with the chemical formula Nd 0.3 Cr 0.7 Fe 0.6 TiO 4.4 The maximum particle size is no greater than 20 μm. The preparation method of this heat-reflective ceramic colorant includes the following steps:

[0055] (1) According to the chemical formula Nd 0.3 Cr 0.7 Fe 0.6 TiO 4.4 Weigh out tetrabutyl titanate, ferric nitrate, chromium nitrate and neodymium nitrate. First, add 0.1 mol of tetrabutyl titanate to a beaker containing 500 mL of anhydrous ethanol, stir and mix well to obtain solution A.

[0056] (2) Add 0.06 mol of ferric nitrate, 0.07 mol of chromium nitrate and 0.03 mol of neodymium nitrate to solution A in sequence, stir and mix well to obtain solution B;

[0057] (3) Add 0.35 mol of citric acid to solution B, stir and mix well to obtain solution C;

[0058] (4) Place the beaker of solution C in a 90°C water bath, add 5g of fatty acid ester to solution C, and stir continuously to emulsify and foam; when solution C gradually evaporates, stop stirring and continue heating in the water bath until dry to obtain the expanded precursor;

[0059] (5) Grind the precursor, calcine it at 1250°C for 72 minutes, cool and grind it, and pass it through a 500-mesh sieve to obtain the heat-reflective ceramic colorant of this embodiment.

[0060] Comparative Example 1

[0061] The main difference between Comparative Example 1 and Example 4 is that the heat-reflective ceramic pigment does not contain Nd in its chemical composition; its chemical formula is CrFe. 0.6 TiO 4.4 The maximum particle size is no greater than 20 μm. The preparation method of this heat-reflective ceramic colorant includes the following steps:

[0062] (1) According to the chemical formula Nd 0.3 Cr 0.7 Fe 0.6 TiO 4.4 Weigh out tetrabutyl titanate, ferric nitrate and chromium nitrate. First, add 0.1 mol of tetrabutyl titanate to a beaker containing 500 mL of anhydrous ethanol, stir and mix well to obtain solution A.

[0063] (2) Add 0.06 mol of ferric nitrate and 0.1 mol of chromium nitrate to solution A in sequence, stir and mix well to obtain solution B;

[0064] (3) Add 0.35 mol of citric acid to solution B, stir and mix well to obtain solution C;

[0065] (4) Place the beaker of solution C in a 90°C water bath, add 5g of fatty acid ester to solution C, and stir continuously to emulsify and foam; when solution C gradually evaporates, stop stirring and continue heating in the water bath until dry to obtain the expanded precursor;

[0066] (5) Grind the precursor, calcine it at 1250℃ for 72 minutes, cool and grind it, and pass it through a 500-mesh sieve to obtain the heat-reflective ceramic pigment of this comparative example.

[0067] Comparative Example 2

[0068] The main difference between Comparative Example 2 and Example 4 lies in the higher Nd content in the chemical composition of the heat-reflective ceramic pigment, whose chemical formula is Nd. 0.5 Cr 0.5 Fe 0.6 TiO 4.4 The maximum particle size is no greater than 20 μm. The preparation method of this heat-reflective ceramic colorant includes the following steps:

[0069] (1) According to the chemical formula Nd 0.5 Cr 0.5 Fe 0.6 TiO 4.4 Weigh out tetrabutyl titanate, ferric nitrate, chromium nitrate and neodymium nitrate. First, add 0.1 mol of tetrabutyl titanate to a beaker containing 500 mL of anhydrous ethanol, stir and mix well to obtain solution A.

[0070] (2) Add 0.06 mol of ferric nitrate, 0.05 mol of chromium nitrate and 0.05 mol of neodymium nitrate to solution A in sequence, stir and mix well to obtain solution B;

[0071] (3) Add 0.35 mol of citric acid to solution B, stir and mix well to obtain solution C;

[0072] (4) Place the beaker of solution C in a 90°C water bath, add 5g of fatty acid ester to solution C, and stir continuously to emulsify and foam; when solution C gradually evaporates, stop stirring and continue heating in the water bath until dry to obtain the expanded precursor;

[0073] (5) Grind the precursor, calcine it at 1250℃ for 72 minutes, cool and grind it, and pass it through a 500-mesh sieve to obtain the heat-reflective ceramic pigment of this comparative example.

[0074] Comparative Example 3

[0075] The main difference between Comparative Example 3 and Example 4 lies in the lower Fe content in the chemical composition of the heat-reflective ceramic pigment, whose chemical formula is Nd. 0.3 Cr 0.7 Fe 0.2 TiO 3.8 The maximum particle size is no greater than 20 μm. The preparation method of this heat-reflective ceramic colorant includes the following steps:

[0076] (1) According to the chemical formula Nd 0.3 Cr 0.7 Fe 0.2 TiO 3.8 Weigh out tetrabutyl titanate, ferric nitrate, chromium nitrate and neodymium nitrate. First, add 0.1 mol of tetrabutyl titanate to a beaker containing 500 mL of anhydrous ethanol, stir and mix well to obtain solution A.

[0077] (2) Add 0.02 mol ferric nitrate, 0.07 mol chromium nitrate and 0.03 mol neodymium nitrate to solution A in sequence, stir and mix well to obtain solution B;

[0078] (3) Add 0.35 mol of citric acid to solution B, stir and mix well to obtain solution C;

[0079] (4) Place the beaker of solution C in a 90°C water bath, add 5g of fatty acid ester to solution C, and stir continuously to emulsify and foam; when solution C gradually evaporates, stop stirring and continue heating in the water bath until dry to obtain the expanded precursor;

[0080] (5) Grind the precursor, calcine it at 1250℃ for 72 minutes, cool and grind it, and pass it through a 500-mesh sieve to obtain the heat-reflective ceramic pigment of this comparative example.

[0081] Comparative Example 4

[0082] The main difference between Comparative Example 4 and Example 4 lies in the higher Fe content in the chemical composition of the heat-reflective ceramic pigment, whose chemical formula is Nd. 0.3 Cr 0.7 The preparation method of FeTiO5, with a maximum particle size of no more than 20 μm, for this heat-reflective ceramic colorant includes the following steps:

[0083] (1) According to the chemical formula Nd 0.3 Cr 0.7 FeTiO5: Weigh out tetrabutyl titanate, ferric nitrate, chromium nitrate and neodymium nitrate. First, add 0.1 mol of tetrabutyl titanate to a beaker containing 500 mL of anhydrous ethanol, stir and mix well to obtain solution A.

[0084] (2) Add 0.1 mol of ferric nitrate, 0.07 mol of chromium nitrate and 0.03 mol of neodymium nitrate to solution A in sequence, stir and mix well to obtain solution B;

[0085] (3) Add 0.35 mol of citric acid to solution B, stir and mix well to obtain solution C;

[0086] (4) Place the beaker of solution C in a 90°C water bath, add 5g of fatty acid ester to solution C, and stir continuously to emulsify and foam; when solution C gradually evaporates, stop stirring and continue heating in the water bath until dry to obtain the expanded precursor;

[0087] (5) Grind the precursor, calcine it at 1250℃ for 72 minutes, cool and grind it, and pass it through a 500-mesh sieve to obtain the heat-reflective ceramic pigment of this comparative example.

[0088] Comparative Example 5

[0089] The main difference between Comparative Example 5 and Example 4 is that no fatty acid ester was added during the preparation of the heat-reflective ceramic pigment, whose chemical formula is Nd. 0.3 Cr 0.7 Fe 0.6 TiO 4.4 The maximum particle size is no greater than 20 μm. The preparation method of this heat-reflective ceramic colorant includes the following steps:

[0090] (1) According to the chemical formula Nd 0.3 Cr 0.7 Fe 0.6 TiO 4.4 Weigh out tetrabutyl titanate, ferric nitrate, chromium nitrate and neodymium nitrate. First, add 0.1 mol of tetrabutyl titanate to a beaker containing 500 mL of anhydrous ethanol, stir and mix well to obtain solution A.

[0091] (2) Add 0.06 mol of ferric nitrate, 0.07 mol of chromium nitrate and 0.03 mol of neodymium nitrate to solution A in sequence, stir and mix well to obtain solution B;

[0092] (3) Add 0.35 mol of citric acid to solution B, stir and mix well to obtain solution C;

[0093] (4) Place the beaker of solution C in a 90°C water bath and stir continuously; when solution C gradually evaporates, stop stirring and continue heating in the water bath until dry to obtain the precursor;

[0094] (5) Grind the precursor, calcine it at 1250℃ for 72 minutes, cool and grind it, and pass it through a 500-mesh sieve to obtain the heat-reflective ceramic pigment of this comparative example.

[0095] Performance testing

[0096] The thermal reflectivity of the thermochromic ceramic pigment samples prepared in Examples 1-4 and Comparative Examples 1-5 was tested. The testing procedure was as follows: the pigment was added to ordinary ceramic glaze (addition amount of 5 wt%), and the glaze was applied to the surface of the ceramic tile blank and fired at 1200℃ to obtain ceramic tiles; the thermal reflectivity of the glaze layer on the surface of the ceramic tile was tested. Specifically, the thermal reflectivity test was conducted according to Part 1 of standard GJB 5023.1A-2012, Test Methods for Reflectivity and Emissivity of Materials and Coatings, with a test wavelength of 400-2500 nm. The results are shown in Table 1.

[0097] Table 1:

[0098] sample Chemical formula Pigment dispersibility Pigment color Reflectance (%) Example 1 <![CDATA[Nd 0.15 Cr 0.85 Iron 0.7 TiO 4.55 ]]> Good dispersion, no aggregation beige 84 Example 2 <![CDATA[Nd 0.45 Cr 0.55 Iron 0.5 TiO 4.25 ]]> Good dispersion, no aggregation beige 85 Example 3 <![CDATA[Nd 0.3 Cr 0.7 Iron 0.5 TiO 4.25 ]]> Good dispersion, no aggregation beige 87 Example 4 <![CDATA[Nd 0.3 Cr 0.7 Iron 0.6 TiO 4.4 ]]> Good dispersion, no aggregation beige 86 Comparative Example 1 <![CDATA[CrFe 0.6 TiO 4.4 ]]> Good dispersion, no aggregation Reddish-brown 65 Comparative Example 2 <![CDATA[Nd 0.5 Cr 0.5 Iron 0.6 TiO 4.4 ]]> Good dispersion, no aggregation Light brown 72 Comparative Example 3 <![CDATA[Nd 0.3 Cr 0.7 Iron 0.2 TiO 3.8 ]]> Good dispersion, no aggregation brownish-yellow 70 Comparative Example 4 <![CDATA[Nd 0.3 Cr 0.7 FeTiO5]]> Good dispersion, no aggregation Light brown 65 Comparative Example 5 <![CDATA[Nd 0.3 Cr 0.7 Iron 0.6 TiO 4.4 ]]> Poor dispersion, severe aggregation beige 72

[0099] As shown in Table 1, the ceramic pigments prepared in Examples 1-4 of the present invention have good uniformity and dispersion, no agglomeration, are yellowish-white, and have a reflectivity of 84-87%, exhibiting good reflectivity of visible and near-infrared light.

[0100] Compared to Example 4, Comparative Example 1 has a reddish-brown color and a significantly lower reflectance because the ceramic pigment does not contain Nd in its chemical composition.

[0101] Compared to Example 4, Comparative Examples 2-4 show that the pigments in ceramic colorants are light brown, brownish-yellow, and light brown, respectively, and their reflectivity is also lower than that in Example 4, since the content of Nd or Fe in the chemical composition of the ceramic colorants is not within the protection scope of this invention. This indicates that the type and amount of doping elements have a significant impact on the color and reflectivity of the colorants.

[0102] Compared to Example 4, Comparative Example 5 showed that the ceramic pigment did not contain fatty acid esters during preparation, resulting in decreased pigment dispersibility and severe agglomeration. Although the pigment was beige, its reflectivity decreased significantly due to agglomeration.

[0103] For those skilled in the art, several simple deductions or substitutions can be made without departing from the inventive concept, without requiring creative effort. Therefore, any simple improvements made to this invention by those skilled in the art based on the disclosure of this invention should be within the scope of protection of this invention. The above embodiments are preferred embodiments of this invention, and all processes similar to this invention and equivalent changes should fall within the scope of protection of this invention.

Claims

1. A heat-reflective ceramic color, characterized in that, The chemical general formula of the heat-reflecting ceramic colorant is Nd x Cr 1- x Fe y TiO 3.5+1.5y wherein: 0.15≤ x ≤0.45, 0.5≤ y ≤0.7; The heat-reflecting ceramic colorant is prepared by a preparation method comprising the following steps: (1) dissolving butyl titanate in anhydrous ethanol to obtain solution A; (2) adding soluble iron salt, soluble chromium salt and soluble neodymium salt in stoichiometric ratio of the chemical formula to the solution A, mixing to obtain solution B; (3) adding citric acid to the solution B, mixing to obtain solution C; (4) performing water bath heating on the solution C, adding fatty acid ester, continuously stirring, performing emulsification and foaming, drying to obtain the expanded precursor; (5) performing grinding, calcining, re-grinding and sieving on the precursor to obtain the heat-reflecting ceramic colorant.

2. The heat-reflective ceramic color of claim 1, wherein, The maximum particle size of the heat-reflecting ceramic colorant is not more than 20 μm.

3. The heat-reflective ceramic color of claim 1, wherein, In step (2), the concentration of the solution A is 0.1-0.5 mol / L.

4. The heat-reflective ceramic color of claim 1, wherein, In step (2), the soluble iron salt is nitrate, sulfate or hydrochloride of iron; and / or, the soluble chromium salt is nitrate, sulfate or hydrochloride of chromium; and / or, the soluble neodymium salt is nitrate, sulfate or hydrochloride of neodymium.

5. The heat-reflective ceramic color of claim 1, wherein, In step (3), the adding amount of the citric acid is not less than 3 times of the mass of butyl titanate.

6. The heat-reflective ceramic color of claim 1, wherein, In step (4), the adding amount of the fatty acid ester is 1-3 wt% of the anhydrous ethanol.

7. The heat-reflective ceramic color of claim 1, wherein, In step (4), the temperature of the water bath heating is 85-90 ℃.

8. The heat-reflective ceramic color of claim 1, wherein, In step (5), the highest temperature of the calcining is 1250-1300 ℃; and / or, the holding time at the highest temperature is 30-90 minutes.

9. An external wall ceramic tile, characterized by, The preparation raw material of the external wall ceramic tile comprises the heat-reflecting ceramic colorant according to any one of claims 1-8.