Method for low-temperature synthesis of ultrafine flaky chrome-alumina red ceramic pigment

Abstract

The application discloses a method for synthesizing superfine flaky chromium-aluminum red ceramic pigments at low temperature. The method uses boehmite and a chromium source as raw materials, does not add any mineralizer, mixes and ball grinds the raw materials at room temperature according to a certain mass ratio, and obtains the superfine chromium-aluminum red pigments with excellent color rendering performance, uniform particle size distribution and good dispersibility through heat treatment. The superfine chromium-aluminum red pigments are suitable for fields with high requirements for particle size, such as ceramic inkjet printing. The raw materials are low in price, the preparation process is simple, the superfine chromium-aluminum red pigments are synthesized at low temperature, the preparation period is short, the energy consumption is low, and the superfine chromium-aluminum red pigments are easy to mass-produce.

Description

A method for low-temperature synthesis of ultrafine flake-shaped chromium aluminum red ceramic pigment Technical Field

[0001] This invention relates to the field of inorganic non-metallic materials technology, and in particular to a low-temperature preparation method for an ultrafine flake-shaped chromium aluminum red ceramic pigment with excellent coloring properties. Background Technology

[0002] As an important branch of ceramic pigments, corundum-based (α-Al₂O₃) ceramic pigments have a history of over a thousand years. Due to their excellent thermal and chemical stability, high refractive index, and optical transparency, α-Al₂O₃ matrix materials have attracted widespread attention from researchers. Chromium aluminum red (Cr-doped α-Al₂O₃) ceramic pigment is a Cr... 3+ Substitution of Al in part of the matrix α-Al2O3 3+ The solid solution material formed during the process exhibits a pinkish hue and thermochromic properties, making it suitable for applications in high-temperature reversible thermochromic sensors and ceramic pigments. Currently, methods for preparing chromium aluminum red ceramic pigments mainly include solid-state methods, hydrothermal methods, the Pechini method, and combustion methods. For example, using Al2O3, Cr2O3, and Y2O3 as raw materials, and NaCl and CaCO3 as composite mineralizing agents, the aluminum-based red pigment chromium yttrium aluminum red (Cr-YAlO3) with excellent coloring properties was prepared by solid-state method at 1300℃. Alternatively, using Al(NO3)3·9H2O and Cr(NO3)3·9H2O as raw materials, a precursor was obtained through hydrothermal reaction at 120℃ for 24 hours, followed by heat treatment at 1200℃ for 2 hours to obtain rod-shaped Al... 2-x Cr x O3 pigment, when the doping amount is 5%, produces ceramic pigments with the best coloring performance, with chromaticity values ​​of L* = 89.00, a* = 7.88, and b* = 3.88. Using Al(NO3)3·6H2O and Cr(NO3)3·6H2O as raw materials, chromium-doped corundum-type pigments are synthesized using the Pechini method. When 4% Cr is doped with α-Al2O3, its chromaticity values ​​are L* = 73.30, a* = 13.50, and b* = -0.20. Using a non-hydrolyzable sol-gel method, with anhydrous AlCl3 and CrCl3 as raw materials, anhydrous ethanol as solvent, and aluminum powder as reducing agent, Cr... 3+When the doping concentration is 4%, the chromium aluminum red ceramic pigment obtained after heat treatment at 1200℃ for 2 hours exhibits excellent coloring properties, with a redness value (a*) of 14.32 and an average particle size of approximately 7.85 μm. However, the above preparation methods all have some drawbacks, such as expensive raw materials, high synthesis temperature for solid-phase methods (even with the addition of mineralizers, 1300℃ is still required for synthesis), and the need for liquid-phase methods, which require not only 1200℃ but also the use of organic solvents and difficulties in wastewater treatment during the preparation process. Furthermore, the above methods for preparing red corundum-based ceramic pigments still suffer from problems such as large pigment particle size and poor coloring properties. Therefore, developing a simple and efficient method to prepare Cr-doped α-Al₂O₃ red ceramic pigments that combine ultrafine particle size and high coloring performance is of great significance. Summary of the Invention

[0003] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method for low-temperature synthesis of ultrafine flake-shaped chromium aluminum red ceramic pigment. Using boehmite and chromium source as raw materials, the mixture is ball-milled at room temperature according to a certain mass ratio, and then heat-treated to obtain ultrafine chromium aluminum red pigment. This method achieves the production of chromium aluminum red pigment with excellent coloring performance, uniform particle size distribution and good dispersibility using low-cost raw materials, simple and easy-to-control preparation process and short production cycle, which is beneficial for large-scale industrial production.

[0004] The objective of this invention is achieved through the following technical solution:

[0005] This invention provides a method for low-temperature synthesis of ultrafine flake-shaped chromium aluminum red ceramic pigment, comprising the following steps:

[0006] (1) Boehmite (γ-AlOOH) and chromium source were mixed according to a molar ratio of aluminum source to chromium source = 1:0.01 to 0.2, and then dry-milled using a high-speed vibrating ball mill at a speed of 380 to 1200 r / min for 48 to 72 h to obtain Cr / α-Al2O3 precursor.

[0007] (2) The Cr / α-Al2O3 precursor is placed in a crucible and heated to 1000-1200℃ at a rate of 3-5℃ / min for 2-8 hours. The pink powder obtained after cooling to room temperature is the chromium aluminum red ceramic pigment.

[0008] In the above scheme, the chromium source of the present invention is chromium oxide (Cr2O3), chromium chloride (CrCl3), chromium acetate ((CH3COO)3Cr), or chromium nitrate (Cr(NO3)3). The morphology of the chromium aluminum red ceramic pigment of the present invention is flake-like, with an average particle size of 1-2 μm, and chromaticity values ​​of L* = 70.60-71.98, a* = 8.42-11.03, and b* = -4.47--1.89.

[0009] The present invention has the following beneficial effects:

[0010] This invention employs a solid-state method to synthesize ultrafine, flake-like Cr-doped α-Al₂O₃ red ceramic pigment at low temperatures without the use of any mineralizing agents, exhibiting excellent coloring properties. This method is simple, involves low-temperature synthesis, has a short preparation cycle, low energy consumption, and is easy to mass-produce. The aluminum source boehmite (γ-AlOOH) and the ball milling process are crucial in this invention. Boehmite, which is readily available and inexpensive, is selected as the raw material. Utilizing the 15 wt.% water inherent in the γ-AlOOH structure, a mechanically induced dehydration reaction occurs during ball milling. The water released during the decomposition of γ-AlOOH into α-Al₂O₃ forms cracks in the aggregated system, promoting its breakage. The released water hydroxylates the surface of α-Al₂O₃, forming chemical bonds with Cr. This allows for the rapid preparation of a high-purity, homogeneous, and well-bonded Cr / α-Al₂O₃ precursor at room temperature, which is beneficial for Cr production at lower temperatures. 3+ By doping into the α-Al2O3 lattice, an ultrafine Cr-doped α-Al2O3 red ceramic pigment with high color rendering performance, a particle size of 1-2 μm, uniform particle size distribution, and good dispersibility is finally synthesized, which is suitable for fields with high requirements for particle size, such as ceramic inkjet printing. Attached Figure Description

[0011] The present invention will now be described in further detail with reference to the embodiments and accompanying drawings:

[0012] Figure 1 is the XRD pattern of the Cr-doped α-Al2O3 chromium aluminum red ceramic pigment prepared according to an embodiment of the present invention;

[0013] Figure 2 is a SEM image of the Cr-doped α-Al2O3 chromium aluminum red ceramic pigment prepared according to an embodiment of the present invention. Detailed Implementation

[0014] Example 1:

[0015] This embodiment describes a method for low-temperature synthesis of ultrafine flake-shaped chromium aluminum red ceramic pigment, the steps of which are as follows:

[0016] (1) Using boehmite (γ-AlOOH) as the aluminum source and Cr2O3 as the chromium source, 20g of boehmite and 2.5g of Cr2O3 were mixed according to the molar ratio of aluminum source to chromium source = 1:0.1. The mixture was then dry-milled using a high-speed vibrating ball mill at a speed of 380r / min according to the ratio of ball to material = 2:1 for 72h to obtain the Cr / α-Al2O3 precursor.

[0017] (2) The above Cr / α-Al2O3 precursor is placed in a crucible and placed in an electric furnace. The temperature is increased to 1000℃ at a rate of 5℃ / min and held for 4h. After cooling to room temperature, the resulting pink powder is the Cr-doped α-Al2O3 chromium aluminum red ceramic pigment.

[0018] Example 2:

[0019] This embodiment describes a method for low-temperature synthesis of ultrafine flake-shaped chromium aluminum red ceramic pigment, the steps of which are as follows:

[0020] (1) Using boehmite (γ-AlOOH) as the aluminum source and chromium trichloride as the chromium source, 50g of boehmite and 7.9g of chromium trichloride were mixed according to the molar ratio of aluminum source to chromium source = 1:0.06. The mixture was then dry-milled using a high-speed vibrating ball mill at a speed of 380r / min according to the ratio of ball to material = 2:1 for 48h to obtain the α-Al2O3 precursor.

[0021] (2) The above α-Al2O3 precursor is placed in a crucible and placed in an electric furnace. The temperature is increased to 1100℃ at a rate of 5℃ / min and held for 6h. After cooling to room temperature, the resulting pink powder is the Cr-doped α-Al2O3 chromium aluminum red ceramic pigment.

[0022] Example 3:

[0023] This embodiment describes a method for low-temperature synthesis of ultrafine flake-shaped chromium aluminum red ceramic pigment, the steps of which are as follows:

[0024] (1) Using boehmite (γ-AlOOH) as the aluminum source and Cr2O3 as the chromium source, 50g of boehmite and 12.66g of Cr2O3 were mixed according to the molar ratio of aluminum source: chromium source = 1: 0.2. The mixture was then dry-milled using a high-speed vibrating ball mill at a speed of 380r / min according to the ratio of ball to material = 2: 1 for 48h to obtain the α-Al2O3 precursor.

[0025] (2) The above α-Al2O3 precursor is placed in a crucible and placed in an electric furnace. The temperature is increased to 1200℃ at a rate of 5℃ / min and held for 2 hours. After cooling to room temperature, the resulting pink powder is the Cr-doped α-Al2O3 chromium aluminum red ceramic pigment.

[0026] Example 4:

[0027] This embodiment describes a method for low-temperature synthesis of ultrafine flake-shaped chromium aluminum red ceramic pigment, the steps of which are as follows:

[0028] (1) Using boehmite (γ-AlOOH) as the aluminum source and chromium nitrate Cr(NO3)3 as the chromium source, 20g of boehmite and 6.28g of Cr(NO3)3 were mixed according to the molar ratio of aluminum source: chromium source = 1: 0.08. The mixture was then dry-milled using a high-speed vibrating ball mill at a ball: material ratio of 2: 1 and a speed of 380r / min for 72h to obtain the α-Al2O3 precursor.

[0029] (2) The above α-Al2O3 precursor is placed in a crucible and placed in an electric furnace. The temperature is increased to 1100℃ at a rate of 5℃ / min and held for 2 hours. After cooling to room temperature, the resulting pink powder is the Cr-doped α-Al2O3 chromium aluminum red ceramic pigment.

[0030] The Cr-doped α-Al2O3 chromium aluminum red ceramic pigment prepared in the embodiments of the present invention, as shown in Figure 1, is a pure phase corundum type chromium aluminum red pigment; as shown in Figure 2, it has a flake-like morphology, good dispersibility, and an average particle size of 1 μm.

[0031] The color rendering performance was tested as follows:

[0032] The CIE-L*a*b* parameters of the Cr-doped α-Al2O3 ceramic pigment prepared in the embodiments of the present invention were characterized using a fully automatic whiteness meter. First, a black tube and a standard white plate were used for calibration. Then, the pigment powder was placed in a mold and pressed into a sheet (30*2mm). The colorimetric value was calculated using the whiteness meter, and the results are shown in Table 1, demonstrating excellent color rendering performance.

[0033] Table 1. Coloring properties of chromium aluminum red ceramic pigments prepared according to the embodiments of the present invention.

[0034]

Claims

1. A method for preparing ultrafine flake-shaped chromium aluminum red ceramic pigment by low-temperature synthesis, characterized in that... The process includes the following steps: (1) mixing boehmite and chromium source in a molar ratio of aluminum source to chromium source = 1:0.01-0.2, and then dry grinding them using a high-speed vibrating ball mill at a speed of 380-1200 r / min for 48-72 h to obtain a Cr / α-Al2O3 precursor; the chromium source is chromium oxide, chromium chloride, chromium acetate, or chromium nitrate; (2) placing the Cr / α-Al2O3 precursor in a crucible and heat-treating it to 1000-1200℃ at a rate of 3-5℃ / min for 2-8 h, and then cooling it to room temperature to obtain the desired product. The pink powder is chromium aluminum red ceramic pigment. Utilizing the 15 wt.% water inherent in the boehmite γ-AlOOH structure, a mechanically induced dehydration reaction occurs during ball milling. The water released during the decomposition of γ-AlOOH into α-Al2O3 forms cracks in the aggregated system, promoting system fragmentation. The released water also hydroxylates the α-Al2O3 surface, forming chemical bonds with Cr. This allows for the rapid preparation of a high-purity, homogeneous, and well-bonded Cr / α-Al2O3 precursor at room temperature, which is beneficial for Cr production at lower temperatures. 3+ The chromium aluminum red ceramic pigment is doped into the α-Al2O3 lattice; the morphology of the pigment is flake-like, with an average particle size of 1-2 μm and chromaticity values ​​of L* = 70.60-71.98, a* = 8.42-11.03, and b* = -4.47--1.89.

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