Method for preparing tetragonal phase zirconium dioxide stable at room temperature by ammonium chloride reduction strategy

Abstract

The invention discloses a method for preparing tetragonal phase zirconium dioxide stable at room temperature by an ammonium chloride reduction strategy. The method comprises the following steps: preparing a zirconium hydroxide precursor through inorganic zirconium salt and ammonia water precipitation, carrying out solid-phase mixing on the zirconium hydroxide precursor and ammonium chloride according to a certain ratio through a ball milling method, and carrying out high-temperature annealing to construct the tetragonal phase zirconium dioxide stable at room temperature. The method is simple and efficient, and the synthesized t-ZrO2 is high in purity, relatively stable at normal temperature, not prone to phase change or structure change, good in thermal stability and chemical stability and beneficial to long-time storage.

Description

Technical Field

[0001] This invention relates to a method for preparing room-temperature stable tetragonal zirconium dioxide using an ammonium chloride reduction strategy, belonging to the field of nanomaterial preparation. Background Technology

[0002] Zirconia (ZrO2) possesses high stability, corrosion resistance, and high-temperature tolerance, leading to its widespread application in interface materials, electrocatalysts, and sensors. ZrO2 exhibits diverse crystal structures, commonly including monoclinic (m-ZrO2), tetragonal (t-ZrO2), and cubic (c-ZrO2). Thermodynamically, at room temperature, the monoclinic phase of ZrO2 is stable, while the tetragonal and cubic phases are metastable. Among these, t-ZrO2 exhibits higher ionic conductivity, higher surface activity, and a greater oxygen vacancy concentration than other phases, making it a promising candidate for applications in various industrial and technological fields. Therefore, stabilizing ZrO2 to the tetragonal phase at room temperature is of significant importance.

[0003] In recent years, the preparation of t-ZrO2 via hydrothermal synthesis, sol-gel method, and hydrothermal oxidation has been widely reported. However, these synthesis methods are complex and costly, making large-scale production difficult. Therefore, finding a simple, efficient, environmentally friendly, room-temperature stable method for synthesizing t-ZrO2 is of great significance. Calcination is a commonly used technique for preparing tetragonal zirconium dioxide. Zhang Hui's team (Influence of Calcination Temperature on the Structural Properties of ZrO2 Microspheres in Quasi-Gas Phase Reaction Method, Acta Chimica Sinica, 2005, Vol. 63, No. 22, 2098-2102) used a quasi-gas phase reaction method to prepare ZrO2 microspheres with high sphericity at 600℃ to 800℃. These microspheres possess a uniform porous structure and nanocrystals, making them suitable for the construction of photonic crystals. The team led by Yu Jianchang (Synthesis of Mesoporous Zirconia Nanocrystals via Anionic Surfactant-Assisted Template Approach, Acta Chimica Sinica, 2005, Vol. 63, No. 15, 1429-1432) synthesized worm-like mesoporous zirconia using anionic surfactant templates and organozirconia alkoxides. After removing the template at 500℃, stable tetragonal zirconia nanocrystals were formed. Existing calcination methods have optimized the structure and properties of t-ZrO2 through different templates and conditions, but still have the following shortcomings:

[0004] (1) High energy consumption and high cost: These methods usually require high temperature and long processing time, resulting in high energy consumption and production costs;

[0005] (2) Difficulty in achieving room temperature stability: Existing calcination methods have poor stability at room temperature and usually require high-temperature calcination, which poses a challenge to the stability of some applications and materials;

[0006] (3) Template removal problem: When using the template method, incomplete template removal may affect the structure and properties of the final material;

[0007] (4) Impure phase: Existing methods may not be able to completely control the phase composition of the product, resulting in the presence of non-tetragonal impurity phases in the generated zirconium oxide, which affects the purity and performance of the material.

[0008] Therefore, although the current calcination method can effectively prepare t-ZrO2, its complexity, high cost, energy consumption, poor room temperature stability, difficulty in template removal, and impure product phase still need improvement. Currently, there are no literature reports on the application of ammonium chloride in the calcination synthesis of t-ZrO2. Summary of the Invention

[0009] The purpose of this invention is to provide a method for preparing room-temperature stable tetragonal zirconium dioxide using an ammonium chloride reduction strategy.

[0010] The technical solution to achieve the purpose of this invention is as follows:

[0011] A method for preparing room-temperature stable tetragonal zirconium dioxide using an ammonium chloride reduction strategy includes the following steps:

[0012] (1) Preparation of zirconium hydroxide precursor: Under stirring and oil bath heating at 70±5℃, ammonia water was slowly added dropwise to an aqueous solution of inorganic zirconium salt. After the reaction was completed, the solution was filtered while hot. The precipitate was washed with water, centrifuged and dried to obtain zirconium hydroxide precursor.

[0013] (2) Preparation of tetragonal zirconium dioxide: The zirconium hydroxide precursor and ammonium chloride were ball-milled and thoroughly mixed. The mixed solid sample was placed in a muffle furnace and annealed at a high temperature of 300-500℃ to obtain room temperature stable tetragonal zirconium dioxide (t-ZrO2). The chemical equation is as follows:

[0014]

[0015] Preferably, in step (1), the inorganic zirconium salt is zirconium nitrate or zirconium chloride.

[0016] Preferably, in step (1), the molar ratio of inorganic zirconium salt to ammonia is 1:4, and ammonia is added dropwise until pH = 8.

[0017] Preferably, in step (1), the drying conditions are: drying in an oven at 100℃ for 12 to 24 hours.

[0018] Preferably, in step (2), the molar ratio of zirconium hydroxide precursor to ammonium chloride is 1:5.

[0019] Preferably, in step (2), the heat treatment conditions are: heating rate of 5-10℃ / min, and holding time of 4-6h.

[0020] This invention involves mixing zirconium hydroxide precursor and ammonium chloride and annealing at high temperature. On one hand, ammonium chloride acts as a molten salt, its decomposition creating interstitial spaces that disperse the metal oxide. On the other hand, it decomposes at high temperatures, producing ammonia and hydrogen chloride, which create a reducing atmosphere in the reaction system. In this oxygen-deficient environment, ammonium chloride does not react directly with the metal oxide, but rather influences its structure by inducing the overflow of lattice oxygen atoms and the formation of vacancies on the metal oxide surface. This reduction process facilitates the formation of defects in the metal oxide, thereby promoting the formation of pure-phase metal oxides.

[0021] Compared with the prior art, the present invention has the following advantages:

[0022] (1) Universality of Synthesis Conditions: Traditional methods typically require strict control over the type of zirconium salt, temperature, pH, and precipitation rate. However, this invention, through the addition of ammonium chloride and a reduction strategy, allows for the use of different zirconium salts (such as zirconium chloride and zirconium nitrate) at a wide pH range (8-10), a relatively low but wide temperature range (300-500℃), and without the need to control the precipitation rate. This significantly optimizes the synthesis conditions, helps save energy and reduce production costs, and facilitates large-scale production applications.

[0023] (2) High-purity product: Pure t-ZrO2 product can be obtained by adding ammonium chloride during heat treatment. In contrast, traditional methods often retain some m-ZrO2.

[0024] (3) Product stability: The obtained t-ZrO2 is relatively stable at room temperature and is not prone to phase change or structural change. It has good thermal and chemical stability, which is conducive to long-term storage. Attached Figure Description

[0025] Figure 1 A schematic flowchart of a method for preparing room-temperature stable tetragonal zirconium dioxide using an ammonium chloride reduction strategy.

[0026] Figure 2 The image shows the XRD pattern of the t-ZrO2 sample in Example 1.

[0027] Figure 3 The image shows the Raman spectrum of the t-ZrO2 sample in Example 1.

[0028] Figure 4 The images show (a) TEM, (b) HRTEM, and (c) SAED images of the t-ZrO2 sample in Example 1.

[0029] Figure 5 The image shows the XRD pattern of the t-ZrO2 sample in Example 2.

[0030] Figure 6 The XRD patterns are of the t-ZrO2 samples in Examples 3-5.

[0031] Figure 7 The image shows the XRD pattern of the m-ZrO2 sample in Comparative Example 1.

[0032] Figure 8 The Raman spectrum of the m-ZrO2 sample in Comparative Example 1 is shown.

[0033] Figure 9 The images show (a) TEM, (b) HRTEM, and (c) SAED images of the m-ZrO2 sample in Comparative Example 1.

[0034] Figure 10 The image shows the XRD pattern of the sample in Comparative Example 2.

[0035] Figure 11 The image shows the XRD pattern of the m-ZrO2 sample in Comparative Example 3.

[0036] Figure 12 The image shows the XRD pattern of the m-ZrO2 sample in Comparative Example 4.

[0037] Figure 13 The XRD pattern of the sample in Comparative Example 5 is shown. Detailed Implementation

[0038] The present invention will be further described below with reference to specific embodiments and accompanying drawings.

[0039] Example 1

[0040] (1) Weigh 6.87g of Zr(NO3)4·5H2O, dissolve it in 100ml of deionized water, heat it to 70℃ with stirring in an oil bath, and slowly add NH3·H2O until pH=8. Allow it to precipitate completely, and filter it while hot. Centrifuge the residue, wash it 2-3 times with deionized water, and dry it overnight at 100℃ to obtain the Zr(OH)4 precursor.

[0041] (2) Weigh 100 mg of Zr(OH)4 precursor and 1 g of NH4Cl, and ball mill for 10 min to mix thoroughly. Place the mixed solid sample in a muffle furnace, heat at a rate of 5 °C / min to 500 °C and hold for 4 h to obtain t-ZrO2. The obtained product is named t-ZrO2-500.

[0042] Figure 2 The image shows the XRD pattern of t-ZrO2-500. Figure 2 It can be seen that the XRD characterization of t-ZrO2-500 in Example 1 shows that the prepared sample is precisely matched with the t-ZrO2 standard card (PDF#50-1089), indicating the formation of the product t-ZrO2. Figure 3The Raman spectral peak of the catalyst synthesized by introducing NH4Cl is at 149 cm⁻¹. (This is the Raman spectral peak of t-ZrO₂-500.) -1 270cm -1 312cm -1 462cm -1 635cm -1 640cm -1 It conforms to the active vibrational mode of t-ZrO2. Figure 4 The three images are TEM, HRTEM, and SAED characterization test results of t-ZrO2-500. Figure 4 (a) It can be seen that the particles in the obtained t-ZrO2-500 are relatively dispersed; such as Figure 4 As shown in (b) and 4(c), the interplanar spacing of the t-ZrO2-500 sample prepared in Example 1 is 0.293 nm, which corresponds to the (011) crystal plane of t-ZrO2. SAED characterization of the (121), (020), and (011) crystal planes of t-ZrO2 provides further support for the crystal characteristics of t-ZrO2-500.

[0043] Example 2

[0044] This embodiment is basically the same as Example 1, except that Zr(NO3)4·5H2O is replaced with ZrCl4, and the resulting product is named t-ZrO2-500-C.

[0045] Figure 5 The image shows the XRD pattern of t-ZrO2-500-C. Figure 5 It can be seen that the XRD characterization of t-ZrO2-500-C in Example 2 shows that the prepared sample is precisely matched with the t-ZrO2 standard card (PDF#50-1089), indicating the formation of the product t-ZrO2.

[0046] Example 3

[0047] This embodiment is basically the same as Embodiment 1, except that the heat treatment temperature is changed from 500℃ to 300℃, and the resulting product is named t-ZrO2-300.

[0048] Figure 6 The image shows the XRD pattern of t-ZrO2-300. Figure 6 As can be seen, XRD characterization of the sample in Example 3 showed that the prepared sample was precisely matched with the t-ZrO2 standard card (PDF#50-1089), indicating the formation of the product t-ZrO2.

[0049] Example 4

[0050] This embodiment is basically the same as Embodiment 1, except that the heat treatment temperature is changed from 500℃ to 400℃, and the resulting product is named t-ZrO2-400.

[0051] Figure 6 The image shows the XRD pattern of the t-ZrO2-400 sample. Figure 6 It can be seen that the XRD characterization of the t-ZrO2-400 sample in Example 4 showed that the prepared sample was precisely matched with the t-ZrO2 standard card (PDF#50-1089), indicating the formation of the product t-ZrO2.

[0052] Example 5

[0053] This embodiment is basically the same as Embodiment 1, except that the heat treatment temperature is changed from 500℃ to 450℃, and the resulting product is named t-ZrO2-450. Figure 6 The image shows the XRD pattern of sample t-ZrO2-450. Figure 6 It can be seen that the XRD characterization of the t-ZrO2-450 sample in Example 5 showed that the prepared sample was precisely matched with the t-ZrO2 standard card (PDF#50-1089), indicating the formation of the product t-ZrO2.

[0054] Comparative Example 1

[0055] This comparative example is basically the same as Example 1, except that NH4Cl is not added, and the resulting product is named m-ZrO2-500.

[0056] Figure 7 The image shows the XRD pattern of m-ZrO2-500. Figure 7 It can be seen that the XRD characterization of m-ZrO2-500 in Comparative Example 1 shows that the prepared sample is precisely matched with the m-ZrO2 standard card (PDF#37-1484), indicating the formation of the product m-ZrO2. Figure 8 The Raman spectral peak of the sample synthesized without the addition of NH4Cl is at 180 cm⁻¹. (This is the Raman spectral peak of m-ZrO₂-500.) -1 220cm -1 305cm -1 339cm -1 376cm -1 474cm -1 613cm -1 634cm -1 It conforms to the active vibrational mode of m-ZrO2. Figure 9 The three images are TEM, HRTEM, and SAED characterization test results of m-ZrO2-500, respectively. Figure 9(a) It can be seen that the particles in the obtained m-ZrO2-500 are relatively aggregated; such as Figure 9 As shown in (b) and 9(c), the interplanar spacing of the m-ZrO2-500 sample is 0.316 nm, which corresponds to the (111) crystal plane of m-ZrO2. SAED characterization of the (220), (111), and (110) crystal planes of m-ZrO2 provides further support for the crystal characteristics of the m-ZrO2-500 sample.

[0057] Comparative Example 2

[0058] This comparative example is basically the same as Example 1, except that the heat treatment temperature of 500℃ is changed to 250℃, and the resulting product is named ZrO2-250.

[0059] Figure 10 The image shows the XRD pattern of the ZrO2-250 sample. Figure 10 It can be seen that the ZrO2-250 sample in Comparative Example 2 was characterized by XRD and the prepared sample was exactly matched with the NH4Cl standard card (PDF#07-0007), indicating that the target reaction could not occur at 250℃.

[0060] Comparative Example 3

[0061] This comparative example is basically the same as Example 1, except that the heat treatment temperature of 500℃ is changed to 600℃, and the resulting product is named m-ZrO2-600.

[0062] Figure 11 The image shows the XRD pattern of sample t-ZrO2-600. Figure 11 It can be seen that the XRD characterization of the m-ZrO2-600 sample in Comparative Example 3 shows that the prepared sample matches the m-ZrO2 standard card (PDF#37-1484), indicating that the product m-ZrO2 was generated.

[0063] Comparative Example 4

[0064] This comparative example is basically the same as Example 1, except that ammonium chloride is replaced with ammonium fluoride. Since ammonium fluoride is volatile, the ball milling time is changed to 3 minutes. The resulting product is named m-ZrO2-F-500.

[0065] Figure 12 The image shows the XRD pattern of sample m-ZrO2-F-500. Figure 12 As can be seen, XRD characterization of the m-ZrO2-F-500 sample in Comparative Example 4 showed that the prepared sample matched the m-ZrO2 standard card (PDF#37-1484), indicating that the product m-ZrO2 was generated.

[0066] Comparative Example 5

[0067] This comparative example is basically the same as Example 1, except that ammonium chloride is replaced with ammonium fluoride. Since ammonium fluoride is volatile, the ball mill is replaced with a mortar and pestle for 3 minutes, and the temperature is adjusted to 400°C. The resulting product is named ZrO2-F-400.

[0068] Figure 13 The image shows the XRD pattern of sample ZrO2-F-400. Figure 13 It can be seen that, according to XRD characterization of the ZrO2-F-400 sample in Comparative Example 5, the prepared sample is similar to Zr(F,O). 2.706 The standard card (PDF#39-1215) was a precise match, indicating that the target reaction could not occur under these conditions, and that some oxygen atoms in the sample were replaced by fluorine atoms, resulting in impurity phases.

Claims

1. A method for preparing room-temperature stable tetragonal zirconium dioxide using an ammonium chloride reduction strategy, characterized in that, Includes the following steps: (1) Preparation of zirconium hydroxide precursor: Under stirring and oil bath heating at 70±5 ℃, ammonia water was slowly added dropwise to an aqueous solution of inorganic zirconium salt. After the reaction was completed, the solution was filtered while hot. The precipitate was washed with water, centrifuged and dried to obtain zirconium hydroxide precursor. (2) Preparation of tetragonal zirconium dioxide: The zirconium hydroxide precursor and ammonium chloride were ball-milled and mixed thoroughly. The mixed solid sample was placed in a muffle furnace and annealed at high temperature of 300~500 °C to obtain room temperature stable tetragonal zirconium dioxide.

2. The method according to claim 1, characterized in that, In step (1), the inorganic zirconium salt is zirconium nitrate or zirconium chloride.

3. The method according to claim 1, characterized in that, In step (1), the molar ratio of inorganic zirconium salt to ammonia is 1:4, and ammonia is added dropwise until pH = 8.

4. The method according to claim 1, characterized in that, In step (1), the drying conditions are: drying in an oven at 100 ℃ for 12~24 h.

5. The method according to claim 1, characterized in that, In step (2), the molar ratio of zirconium hydroxide precursor to ammonium chloride is 1:

5.

6. The method according to claim 1, characterized in that, In step (2), the heat treatment conditions are: heating rate of 5~10℃ / min, and holding for 4~6 h.

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