Preparation method and crystalline state transformation method for spherical and sheet-like CRF 33h 2o micro-nano powder

Abstract

Disclosed are a preparation method and crystalline state transformation method for spherical and sheet-like CrF 3·3H 2O micro-nano powder. The preparation method comprises: slowly adding an HF acid solution to Cr2AlB2 powder, and stirring and reacting at 25-40ºC for 4-20 h, wherein the mass fraction of the HF acid solution is 20-45%; after the reaction is complete, centrifugally washing the obtained solution successively with deionized water and absolute ethanol to neutrality; and freeze-drying the obtained precipitate to obtain spherical CrF 33H2O powder and ultrasonically treating the powder in an ethanol solution until the powder is fully expanded to form a two-dimensional sheet-like material. In the present method, on the basis of a selective etching reaction of hydrofluoric acid for Cr2AlB 2, spherical CrF33H2O micro-nano powder is prepared. By adjusting the reaction conditions, CrF33H2O micro-nano powder having uniform morphology and relatively narrow particle size distribution can be obtained, and crystalline state transformation of CrF33H2O can be realized by means of heat treatment.

Description

A method for preparing spherical and sheet-like CrF3·3H2O micro / nano powders and their crystal transformation. Technical Field

[0001] This invention belongs to the field of materials preparation technology, specifically relating to a method for preparing spherical and sheet-like CrF3·3H2O micro / nano powders and their crystalline transformation. Background Technology

[0002] With the rapid development of modern technology, the research and development of new materials has played a crucial role in promoting progress in various fields such as industry, electronics, and energy. Among them, transition metal fluorides, due to their unique physicochemical properties, such as high electronegativity, high ionic conductivity, and excellent thermal and chemical stability, have become a research hotspot in the field of materials science. Transition metal fluorides have shown broad application prospects in batteries, capacitors, magnetic materials, catalysts, and anti-corrosion coatings. CrF3·3H2O, as an important chromium-based fluoride, has the molecular structure of chromium trihydrate fluoride and has potential application value in catalytic reactions, magnetic materials, and anti-corrosion coatings. However, current conventional methods for preparing CrF3·3H2O micro / nano powders have some shortcomings, such as complex preparation processes, harsh reaction conditions, uneven product morphology, and wide particle size distribution, which limit its widespread application in high-performance materials.

[0003] Existing methods for preparing CrF3·3H2O mainly include solution chemistry, sol-gel, coprecipitation, and solid-state reaction methods. While these methods can produce CrF3·3H2O powder, the complexity of the reaction conditions and the difficulty in controlling the morphology often result in unparalleled uniformity and controllable size in the micro- and nano-sized powders. Furthermore, these methods typically require lengthy reaction processes, increasing energy consumption and increasing the risk of crystallization defects, thus affecting the material's performance in practical applications. In addition, although polycrystalline CrF3·3H2O performs well in some applications, amorphous materials often exhibit superior performance in specific fields, such as magnetic materials and catalysts. Amorphous materials, due to the lack of long-range ordered atomic arrangement, typically possess higher surface area, more uniform active site distribution, and better corrosion resistance. Therefore, this research aims to develop a simple and effective process that can not only prepare uniformly morphological CrF3·3H2O micro- and nano-sized powders but also achieve a crystalline transformation through heat treatment.

[0004] Current technologies for preparing CrF3·3H2O micro / nano powders still face certain limitations and challenges in terms of their morphology and crystallinity. Developing a simple and efficient preparation method that can achieve the crystallization transformation of the material by controlling heat treatment conditions will provide new ideas and technical support for the research and application of novel functional materials. Summary of the Invention

[0005] This invention provides a method for preparing CrF3·3H2O micro / nano powders, and a pathway for controlling their crystallization state. It also yields spherical or sheet-like CrF3·3H2O powders with micro / nano structures, as well as corresponding amorphous CrF3 powders and crystalline Cr2O. 2.4 With Cr2O3 powder: This material is suitable for the development of high-performance coating materials, lubricants, catalysts and other functional materials.

[0006] I. Preparation of spherical CrF3·3H2O micro / nano powders

[0007] This invention provides a method for preparing spherical CrF3·3H2O micro / nano powders by reacting Cr2AlB2 with hydrofluoric acid. The specific method is as follows:

[0008] (1) Slowly add HF acid solution to Cr2AlB2 powder and stir at 100-350 r / min at 25-40℃ for 4-20 h; the mass fraction of HF acid solution is 20-45%.

[0009] The particle size of Cr2AlB2 powder is controlled below 50 micrometers. The concentration of Cr2AlB2 powder in HF acid solution is 0.04–0.1 g / mL.

[0010] (2) After the reaction is complete, the resulting solution is washed with deionized water and anhydrous ethanol by centrifugation until neutral; the centrifugation speed is 3000-5000 r / min.

[0011] (3) The precipitate was freeze-dried at -60℃ to -80℃ to obtain spherical CrF3·3H2O powder.

[0012] II. Preparation method of two-dimensional sheet-like CrF3·3H2O

[0013] Spherical CrF3·3H2O micro-nano powders were ultrasonically treated in an ethanol solution to fully expand them and form two-dimensional sheet-like CrF3·3H2O micro-nano powder materials.

[0014] III. Methods for the Crystallization Transformation of CrF3·3H2O Micro / Nano Powder

[0015] 1. Heat-treat spherical or two-dimensional sheet-like CrF3·3H2O micro / nano powder at a temperature of 160-300℃ for more than 30 minutes to remove the water of crystallization and obtain amorphous spherical or sheet-like CrF3 powder.

[0016] 2. Spherical or two-dimensional sheet-like CrF3·3H2O micro / nano powders are heat-treated in an oxygen-deficient environment at a temperature of 400℃~1000℃ for more than 30 minutes to form Cr2O with oxygen vacancies.2.4 Spherical or sheet-like materials;

[0017] Spherical or two-dimensional sheet-like CrF3·3H2O micro / nano powders are heat-treated in an atmospheric environment at a temperature of 400℃~1000℃ for a time of more than 30 minutes to form sheet-like materials with oxygen vacancies in Cr2O3.

[0018] The transformation from spherical to plate-like shape can be completed first, followed by the amorphous transformation; alternatively, the crystalline transformation can be completed first, followed by the conversion from spherical to plate-like material. The process of completing the crystalline transformation first, followed by the conversion from spherical to plate-like material, is as follows:

[0019] 1. Crystallization transformation method of spherical CrF3·3H2O micro / nano powder

[0020] (1) A method for transforming spherical CrF3·3H2O micro / nano powder from a polycrystalline state to an amorphous state through heat treatment, specifically including the following steps:

[0021] The prepared spherical CrF3·3H2O micro / nano powder was subjected to heat treatment at a temperature of 160-300℃ to remove the water of crystallization and obtain amorphous CrF3 powder; the heat treatment time was greater than 30 minutes.

[0022] (2) Spherical CrF3·3H2O micro / nano powder is transformed into polycrystalline Cr2O3 or Cr2O 2.4

[0023] The prepared spherical CrF3·3H2O micro / nano powders were heat-treated in an oxygen-deficient or atmospheric environment at temperatures ranging from 400℃ to 1000℃ to form Cr2O with oxygen vacancies. 2.4 Or Cr2O3; heat treatment time greater than 30 minutes.

[0024] 2. Preparation method of two-dimensional sheet-like CrF3·3H2O

[0025] The prepared spherical crystalline CrF3·3H2O micro / nano powder or amorphous CrF3 powder is ultrasonically treated in an ethanol solution to fully expand it and form two-dimensional sheet-like CrF3·3H2O micro / nano powder material or two-dimensional sheet-like amorphous CrF3 powder material.

[0026] IV. Preparation of Spherical CrF3·3H2O Micro / Nano Powder and Its Crystal Transformation Mechanism in this Invention

[0027] The preparation of CrF3·3H2O micro / nano powders is mainly based on the selective etching reaction of Cr2AlB2 with hydrofluoric acid (HF). Cr2AlB2 is a layered transition metal carbide and boride composite material. In its structure, chromium atoms have strong chemical bonds with aluminum and boron atoms, and the stability of these bonds varies in acidic media. During the reaction, HF reacts chemically with the aluminum and chromium in Cr2AlB2 to generate chromium fluorides and other byproducts. The specific reaction steps can be summarized as follows: 1. HF first attacks the aluminum in Cr2AlB2, generating AlF3 and H2; 2. As the reaction proceeds, the chromium in Cr2AlB2 gradually transforms into CrF3 and combines with water molecules in the solution to form CrF3·3H2O. By controlling the reaction conditions (acid concentration, reaction temperature and time, drying temperature, etc.), the crystallization process of CrF3·3H2O can be adjusted to gradually form spherical micro / nano powder structures. The formation of the spherical morphology is mainly related to the surface tension in the solution and the particle growth kinetics. Under suitable conditions, CrF3·3H2O particles gradually form spherical micro / nano structures through a uniform nucleation and growth process. By adjusting the reaction conditions, CrF3·3H2O micro / nano powders with uniform morphology and narrow particle size distribution can be obtained.

[0028] The crystal transformation of CrF3·3H2O is achieved through heat treatment. The core of heat treatment lies in controlling the temperature and holding time to transform the material from a polycrystalline to an amorphous state. The mechanism can be divided into the following aspects: 1. Lattice disturbance during heating: During heating, the CrF3·3H2O lattice absorbs heat energy, leading to increased lattice vibration. When the heating temperature reaches a certain level, the atomic positions in the lattice become unstable, gradually losing long-range order. This disorder of atomic arrangement is the main reason for the formation of the amorphous state; 2. The effect of surface energy and internal stress: At the micro-nano scale, CrF3·3H2O powder has a large specific surface area, which makes surface energy significantly affect the thermodynamic behavior of the material. As the temperature increases, the energy difference between the powder's interior and surface further intensifies, causing an increase in internal stress. This internal stress promotes the collapse of the crystal structure, leading to the transformation of the material from an ordered polycrystalline state to a disordered amorphous state. 3. Removal of water molecules: At higher temperatures, the water of crystallization in CrF3·3H2O may be partially or completely removed, a process that further disrupts the crystal lattice. The removal of water of crystallization not only alters the stability of the crystal structure but may also lead to the formation of voids or defects within the crystal, creating conditions conducive to amorphization. As the temperature continues to rise, the remaining fluoride continues to decompose, the oxidation process intensifies, and under high-temperature conditions, the crystal lattice gradually becomes ordered, forming Cr2O. 2.4 And chromium oxide Cr2O3.

[0029] This invention provides a novel method for preparing spherical CrF3·3H2O micro / nano powders based on the selective etching reaction of Cr2AlB2 with hydrofluoric acid (HF). By adjusting the reaction conditions, spherical CrF3·3H2O micro / nano powders with uniform morphology and narrow particle size distribution can be obtained, and these powders can be easily transformed into two-dimensional sheet-like materials. Furthermore, the crystallization of CrF3·3H2O can be achieved through heat treatment. The spherical or sheet-like structure can increase the specific surface area of ​​the material, which helps to enhance the reaction activity in catalytic or electrode materials. In addition, the uniformly shaped spherical particles have better flowability and are easier to disperse evenly, making them suitable for coating or 3D printing processes. The two-dimensional sheet-like materials exhibit excellent lubrication properties in tribological applications, reducing the coefficient of friction and extending service life. Attached Figure Description

[0030] Figure 1 shows the X-ray diffraction pattern of CrF3·3H2O powder prepared in Example 1 of this invention.

[0031] Figure 2 is a scanning electron microscope image of the spherical CrF3·3H2O powder in Example 1 of the present invention.

[0032] Figure 3 is the XRD pattern of amorphous CrF3 powder after amorphization in Example 3 of the present invention.

[0033] Figure 4 is a TEM image of the amorphous CrF3 powder after amorphization in Example 3 of the present invention.

[0034] Figure 5 is a TEM image of the lamellar amorphous CrF3 powder after ultrasonic treatment in Example 4 of the present invention.

[0035] Figure 6 shows the XRD patterns of the powders after high-temperature heat treatment in Examples 5 and 6 of the present invention. Detailed Implementation

[0036] The present invention will be further explained and described below with reference to specific embodiments.

[0037] Example 1

[0038] (1) Weigh 5 grams of Cr2AlB2 powder, put it into an agate mortar and grind and sieve it, and control the particle size to be below 50 micrometers.

[0039] (2) Transfer the powder obtained from grinding to a polytetrafluoroethylene beaker, measure 100 ml of HF acid solution with a mass fraction of 20%, and slowly pour it into the beaker;

[0040] (3) At a temperature of 25℃, the speed of the magnetic stirrer was set to 350 r / min and the reaction duration was set to 4 hours;

[0041] (4) After the reaction was completed, the powder was washed at least 3 times by centrifugation with deionized water at a speed of 3000 r / min, then washed with anhydrous ethanol until the pH value was close to 7, and finally freeze-dried at -60℃ for 8 hours to obtain spherical CrF3·3H2O powder.

[0042] Crystallinity tests were performed using X-ray diffraction, and Figure 1 shows that the CrF3·3H2O powder possesses a good crystalline phase. Scanning electron microscopy was used to observe the powder morphology; Figure 2 shows a uniform spherical structure and particle size distribution, indicating a consistent material morphology and narrow particle size distribution. The morphology of the material significantly affects its performance and applications. Spherical or lamellar structures can increase the specific surface area of ​​the material, which helps to enhance the reaction activity in catalytic or electrode materials. Furthermore, spherical particles have better flowability and are easier to disperse uniformly, making them suitable for processing such as coatings or 3D printing.

[0043] (5) By continuing ultrasonic treatment of the spherical CrF3·3H2O powder for 20 minutes, unfolded lamellar CrF3·3H2O material can be obtained. Two-dimensional lamellar materials exhibit excellent lubrication performance in tribological applications, reducing the coefficient of friction and extending service life. Morphology optimization can simultaneously enhance the mechanical strength and electrical and thermal conductivity of the material, making it suitable for a wide range of high-performance applications.

[0044] Example 2

[0045] (1) Weigh 5 grams of Cr2AlB2 powder, put it into an agate mortar and grind and sieve it, and control the particle size to be below 50 micrometers.

[0046] (2) Place the powder obtained from grinding into a polytetrafluoroethylene beaker, measure 100 ml of HF acid solution with a mass fraction of 40%, and slowly pour it into the beaker;

[0047] (3) Set the reaction temperature to 40℃, the magnetic stirrer speed to 100r / min, and the reaction time to 4 hours;

[0048] (4) After the reaction was completed, the powder was washed at least three times by centrifugation with deionized water at 3000 r / min, then washed with anhydrous ethanol until the pH value was close to 7, and finally freeze-dried at -60℃ for 8 hours to obtain spherical CrF3·3H2O powder. X-ray diffraction tests were performed, and the results were consistent with those of Example 1.

[0049] Example 3

[0050] (1) Take the spherical CrF3·3H2O powder prepared in Example 1;

[0051] (2) Place the powder in a vacuum tube furnace and heat treat it under a protective atmosphere (argon); set the furnace temperature to 180°C and the holding time to 4 hours.

[0052] (3) After heat treatment, the sample is naturally cooled to room temperature in the furnace to avoid thermal shock damage and to obtain amorphous CrF3 powder.

[0053] X-ray diffraction analysis was performed to confirm the transition from polycrystalline to amorphous state. Figure 3 shows that the characteristic peaks of the powder crystals weakened after heat treatment, indicating an amorphization trend. The morphology of the heat-treated powder was analyzed using transmission electron microscopy, and Figure 4 shows the characteristics of the amorphous structure.

[0054] Example 4

[0055] (1) Take the spherical CrF3·3H2O powder prepared in Example 2;

[0056] (2) Place the powder in a vacuum tube furnace and heat treat it in a vacuum environment; set the furnace temperature to 250°C and the holding time to 6 hours.

[0057] (3) After heat treatment, the sample is naturally cooled to room temperature in a vacuum to obtain spherical amorphous CrF3 powder.

[0058] (4) Continue to sonicate the spherical amorphous CrF3 powder for 20 minutes to obtain unfolded lamellar amorphous CrF3 powder material.

[0059] Figure 5 shows the morphology of the spherical unfolded sheets after ultrasonic treatment, and the structural characterization is consistent with that of Example 3.

[0060] Example 5

[0061] (1) Take the spherical CrF3·3H2O powder prepared in Example 2;

[0062] (2) Place the powder in a vacuum tube furnace and heat treat it under vacuum conditions. Set the furnace temperature to 800℃ and the holding time to 2 hours.

[0063] (3) After the heat treatment is completed, allow the sample to cool naturally to room temperature in a vacuum.

[0064] X-ray diffraction tests showed that the main substance after heat treatment at 800℃ in a vacuum environment was Cr2O containing oxygen vacancies. 2.4 Furthermore, the characteristic peaks of powder crystallization are obvious (as shown in Figure 6 (left)).

[0065] Example 6

[0066] The heat treatment in the vacuum environment of Example 5 was replaced with heat treatment in the atmospheric environment, while all other aspects remained the same as in Example 5, resulting in Cr2O3 containing oxygen vacancies. X-ray diffraction tests showed that the main substance after heat treatment at 800℃ in the atmospheric environment was Cr2O3 containing oxygen vacancies, and the characteristic peaks of powder crystallization were obvious (as shown in Figure 6 (right)).

Claims

1. A method for preparing spherical CrF3·3H2O micro / nano powder, characterized in that: HF acid solution was slowly added to Cr2AlB2 powder and stirred at 25-40℃ for 4-20 h; the mass fraction of HF acid solution was 20-45%; after the reaction, the resulting solution was washed with deionized water and anhydrous ethanol by centrifugation until neutral; the precipitate was dried to obtain spherical CrF3·3H2O powder.

2. The preparation method of the spherical CrF3·3H2O micro-nano powder according to claim 1, characterized in that: The particle size of the Cr2AlB2 powder is controlled to be below 50 micrometers.

3. The preparation method of the spherical CrF3·3H2O micro-nano powder according to claim 1, characterized in that: The concentration of the Cr2AlB2 powder in the HF acid solution is 0.04–0.1 g / mL.

4. The preparation method of the spherical CrF3·3H2O micro-nano powder according to claim 1, characterized in that: Stirring speed: 100-350 r / min; centrifugation speed: 3000-5000 r / min.

5. [Amended according to Rule 26 11.06.2025] The preparation method of the spherical CrF3·3H2O micro-nano powder according to claim 1, characterized in that: The product is dried using a freeze-drying method at a temperature of -60℃ to -80℃.

6. A method for preparing two-dimensional sheet-like CrF3*3H2O micro-nano powder from the spherical CrF3*3H2O micro-nano powder according to claim 1, characterized in that: Spherical CrF3·3H2O micro-nano powders were ultrasonically treated in an ethanol solution to fully expand them and form two-dimensional sheet-like CrF3·3H2O micro-nano powder materials.

7. A method for amorphous state transformation of the CrF3-3H2O micro-nano powder according to claim 1 or 6, characterized in that: Spherical or two-dimensional sheet-like CrF3·3H2O micro / nano powders are heat-treated at a temperature of 160-300℃ for more than 30 minutes to remove the water of crystallization and obtain amorphous spherical or sheet-like CrF3 powders.

8. A method for amorphous state transformation of the CrF3-3H2O micro-nano powder according to claim 1 or 6, characterized in that: The spherical or two-dimensional flaky CrF3·3H2O micro-nano powder is heat treated in an oxygen-free environment, the heat treatment temperature is 400-1000℃, the heat treatment time is greater than 30 minutes, and the spherical or flaky material with oxygen vacancies Cr2O 2.4 is formed. Spherical or two-dimensional sheet-like CrF3·3H2O micro / nano powders are heat-treated in an atmospheric environment at a temperature of 400℃~1000℃ for a time of more than 30 minutes to form sheet-like materials with oxygen vacancies in Cr2O3.

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