A CaTiF6 powder, its preparation method and application

Abstract

The application provides a CaTiF6 powder, a preparation method and application thereof, and the preparation method comprises the following steps: (1) mixing a soluble titanium salt, a soluble fluorine salt and water under the condition of an ice water bath to perform a first precipitation reaction, and obtaining an intermediate product of a fluorotitanate salt through solid-liquid separation; (2) dissolving the fluorotitanate salt in step (1) in hot water to obtain a fluorotitanate salt aqueous solution; (3) mixing the fluorotitanate salt aqueous solution in step (2) and a soluble calcium salt to perform a second precipitation reaction, and obtaining the CaTiF6 powder through solid-liquid separation; the soluble fluorine salt in step (1) comprises any one or a combination of at least two of potassium fluoride, ammonium fluoride or sodium fluoride; when the soluble fluorine salt in step (1) is ammonium fluoride and / or sodium fluoride, anhydrous ethanol is added at the beginning of the first precipitation reaction. The raw materials used in the method are non-toxic, easily soluble in water and suitable for industrial production requirements, and are suitable for large-scale application.

Description

Technical Field

[0001] This invention belongs to the field of negative thermal expansion materials, and relates to a CaTiF6 powder, its preparation method and application. Background Technology

[0002] Negative thermal expansion (NTE) is an unusual physical property where a material shrinks in size when heated. It plays a crucial role in fundamental research and the regulation of thermal expansion in precision devices. Fluorides, as an important class of NTE materials, have attracted much attention due to their simple structure, making them ideal materials for studying NTE mechanisms. Among them, CaTiF6 is an example of an NTE-producing material. Ⅱ B Ⅳ As an important member of the F6 family (A and B are +2 and +4 valent metal ions, respectively), its excellent negative thermal expansion characteristics make it suitable as a filler for packaging substrates. This material can precisely control the thermal expansion performance of the packaging substrate, effectively reduce the degree of thermal mismatch between the substrate and the chip, avoid structural failure problems caused by thermal stress, thereby extending the service life of the device, reducing maintenance costs, and significantly improving the overall reliability of the device.

[0003] Currently, the main methods for preparing CaTiF6 powder are solid-state and solvothermal methods. For example, a research paper (Negative Thermal Expansion, Response to Pressure and Phase Transitions in CaTiF6, Inorg. Chem. 2018, 57, 11275-112) proposed a solid-state method for preparing CaTiF6. This method uses CaF2 and TiF4 as raw materials, grinds and mixes the materials in an equimolar ratio, dries them in a nitrogen atmosphere, presses them into shape, and then calcines them at high temperature to obtain a CaTiF6 off-white powder containing CaF2. However, CaF2 and TiF4 are expensive, and TiF4 is highly hygroscopic, increasing the difficulty of synthesis. Furthermore, solvothermal synthesis requires the introduction of excess HF to obtain high-purity CaTiF6, but HF is a toxic and highly corrosive substance. In addition, the reaction residue also requires special treatment, which undoubtedly places higher demands on the corrosion resistance of the reaction equipment and the safety control of the process, making it unfavorable for large-scale production.

[0004] CN116443925B proposes a method for preparing MNF6, a material with controllable thermal expansion. In this method, CaTiF6 is prepared using titanium dioxide (TiO2), calcium chloride (CaCl2), and hydrofluoric acid solution (an aqueous solution of HF) as initial raw materials. The precursor is obtained through solvent removal and crystallization in a sealed liquid phase, followed by pressing and molding, and then high-temperature calcination with ammonium fluoride. During the experiment, an excess of HF acid is used to ensure complete dissolution of TiO2, which is also unfavorable for large-scale production.

[0005] In addition, a research paper (Synthesis, electronic property, and negative thermal expansion in cubic CaTiF6, Nano Research, 2025, 18, 94907236) prepared CaTiF6 using CaCl2 and fluorotitanic acid (H2TiF6) as raw materials through co-precipitation and high-temperature sintering. However, the raw material H2TiF6 is also a toxic and highly corrosive colorless and transparent liquid, and is expensive, which is not conducive to industrial production.

[0006] Therefore, how to provide an environmentally friendly (non-toxic raw material), rapid, simple, and industrially suitable method for preparing CaTiF6 is an urgent technical problem to be solved. Summary of the Invention

[0007] To address the shortcomings of existing technologies, the present invention aims to provide a CaTiF6 powder, its preparation method, and its applications. The preparation method provided by this invention uses non-toxic, water-soluble raw materials suitable for industrial production; the preparation process is simple, and neither the preparation nor post-processing involves high-energy-consuming equipment, thus avoiding energy waste; the final emissions contain no harmful residues, and the process is clean. Furthermore, the CaTiF6 powder prepared using the method provided by this invention exhibits high crystallinity (high purity), high yield, and uniform size dispersion.

[0008] To achieve this objective, the present invention employs the following technical solution:

[0009] In a first aspect, the present invention provides a method for preparing CaTiF6 powder, the method comprising:

[0010] (1) Under ice-water bath conditions, soluble titanium salt, soluble fluoride salt and water are mixed to carry out the first precipitation reaction, and the intermediate product fluorotitanate is obtained after solid-liquid separation.

[0011] (2) Dissolve the fluorotitanate from step (1) in hot water to obtain an aqueous solution of fluorotitanate;

[0012] (3) The aqueous solution of fluorotitanate and the soluble calcium salt described in step (2) are mixed to carry out a second precipitation reaction, and the CaTiF6 powder is obtained after solid-liquid separation;

[0013] The soluble fluoride salt in step (1) includes any one or a combination of at least two of potassium fluoride, ammonium fluoride or sodium fluoride; when the soluble fluoride salt in step (1) is ammonium fluoride and / or sodium fluoride, anhydrous ethanol is added at the beginning of the first precipitation reaction.

[0014] In this invention, both the soluble fluoride salt and the soluble titanium salt are soluble in cold water or ice water, while the intermediate product fluorotitanate is almost insoluble in cold water or other polar solvents (such as anhydrous ethanol or an ethanol solution with a volume fraction of 75% or more). Therefore, using ice water or adding a large amount of other polar solvents to ice water as the reaction medium, the intermediate product can be separated from the reaction system and precipitated. It should be noted that compared to potassium fluoride, when the soluble fluoride salt is ammonium fluoride or sodium fluoride, the solubility of the intermediate product fluorotitanate produced by the precipitation reaction in water is improved, and the introduction of anhydrous ethanol is more conducive to the precipitation process. In the preparation of CaTiF6 powder, hot water can significantly increase the solubility of fluorotitanate, while calcium fluorotitanate (CaTiF6) is less soluble in water than the intermediate product fluorotitanate, so it can be separated by solid-liquid separation.

[0015] Furthermore, by preparing the intermediate product fluorotitanate in-house, this invention ensures the non-corrosiveness of the raw materials and allows for more controllable purity of the intermediate product fluorotitanate. The entire process requires only two precipitation steps to obtain CaTiF6 powder, and the raw materials used are all non-corrosive. The process is clean and eliminates the need for energy-intensive equipment such as calcination, making it suitable for industrial applications.

[0016] The following are preferred technical solutions of the present invention, but are not intended to limit the technical solutions provided by the present invention. The technical objectives and beneficial effects of the present invention can be better achieved and realized through the following preferred technical solutions.

[0017] Preferably, the molar ratio of titanium, fluorine and calcium in the soluble titanium salt, soluble fluoride salt and soluble calcium salt in step (1) and step (3) is 1:(6.04~6.1):(1~1.15), for example 1:6.04:1, 1:6.05:1.005, 1:6.06:1.01, 1:6.07:1.05, 1:6.08:1.08, 1:6.09:1.1, 1:6.1:1.13 or 1:6.1:1.15, etc.

[0018] Preferably, the soluble titanium salt in step (1) includes titanium oxysulfate and / or titanium oxysulfate hydrate.

[0019] Preferably, the soluble fluoride salt in step (1) is potassium fluoride.

[0020] Preferably, the order of mixing the soluble titanium salt, soluble fluoride salt and water in step (1) is as follows: first, the soluble titanium salt and soluble fluoride salt are dissolved independently in water to obtain an aqueous solution of soluble titanium salt and an aqueous solution of soluble fluoride salt, and then the aqueous solution of soluble titanium salt is added dropwise to the aqueous solution of soluble fluoride salt.

[0021] In this invention, when the aqueous solution of soluble titanium salt is added dropwise to the aqueous solution of soluble fluoride salt, the fluoride ions in the system are always in excess. When the titanium salt is added, the titanium ions will instantly combine with a large number of fluoride ions to form stable fluorotitanate ions, which is beneficial to increasing the rate of precipitation reaction. Furthermore, since the free titanium ions in the system are always at a low level, the hydrolysis of titanium ions can be avoided. At the same time, combined with the ice-water bath conditions, the sparingly soluble fluorotitanate can be precipitated from the reaction system in a timely manner, which is beneficial to the forward progress of the precipitation reaction.

[0022] Preferably, the dropping rate of the soluble titanium source aqueous solution into the soluble fluoride aqueous solution is 4 mL / min to 6 mL / min, for example, 4 mL / min, 4.5 mL / min, 5 mL / min, 5.5 mL / min or 6 mL / min.

[0023] Preferably, an acid is added to the aqueous solution of the soluble fluoride salt.

[0024] Preferably, acid is added simultaneously when the soluble titanium source aqueous solution is added dropwise to the soluble fluoride aqueous solution to adjust the pH of the system to 5.5-6.5, such as 5.5, 5.7, 6, 6.2 or 6.5.

[0025] In this invention, by adding acid to the reaction system as described above, a weakly acidic environment can be formed, which is beneficial to the dissolution of soluble titanium salts and can also neutralize the alkaline substances produced in the reaction, thereby increasing the reaction rate.

[0026] Preferably, the acid includes any one or a combination of at least two of dilute hydrochloric acid, dilute sulfuric acid, dilute nitric acid, dilute acetic acid, dilute formic acid, dilute sulfurous acid, ammonium nitrate, ammonium chloride, ammonium sulfate, ammonium hydrogen sulfate, or hydrogen peroxide.

[0027] Preferably, the temperature of the ice water bath in step (1) is 0℃~4℃, for example, 0℃, 1℃, 2℃, 3℃ or 4℃.

[0028] Preferably, step (1) of the first precipitation reaction includes: reacting for 20 min to 40 min under stirring, and then reacting for 1.5 h to 2.5 h under standing conditions. For example, reacting for 20 min, 25 min, 30 min, 35 min or 40 min under stirring, and then reacting for 1.5 h, 1.8 h, 2 h, 2.3 h or 2.5 h under standing conditions.

[0029] In this invention, stirring allows the raw materials to come into full contact and react to generate the intermediate product fluorotitanate precipitate.

[0030] Preferably, the solid-liquid separation method in step (1) is to alternately perform centrifugation and washing.

[0031] Preferably, the detergent used for washing is ice water.

[0032] In this invention, impurity ions in the solution can be removed by repeated centrifugation and washing.

[0033] Preferably, the temperature of the hot water in step (2) is 80℃~95℃, such as 80℃, 83℃, 85℃, 88℃, 90℃, 93℃ or 95℃.

[0034] Preferably, the soluble calcium salt in step (3) includes any one or a combination of at least two of calcium chloride, calcium nitrate, calcium nitrite, calcium bromide, calcium acetate, or calcium formate.

[0035] Preferably, the order of mixing the fluorotitanate aqueous solution and the soluble calcium salt in step (3) is as follows: first, the soluble calcium salt is dissolved in water to obtain a soluble calcium salt aqueous solution, and then the soluble calcium salt aqueous solution is added dropwise to the fluorotitanate aqueous solution.

[0036] Preferably, the dropping rate of the soluble calcium salt aqueous solution into the fluorotitanate aqueous solution is 1 mL / min to 3 mL / min, for example, 1 mL / min, 1.5 mL / min, 2 mL / min, 2.5 mL / min or 3 mL / min.

[0037] Preferably, step (3) of the second precipitation reaction includes: reacting at 80℃~95℃ with stirring for 20min~40min, then cooling to 0℃~4℃, and reacting under static conditions for 1.5h~2.5h. 20min~40min is for example 20min, 25min, 30min, 35min or 40min, etc., and 1.5h~2.5h is for example 1.5h, 1.8h, 2h, 2.3h or 2.5h, etc.

[0038] Preferably, the solid-liquid separation method in step (3) is to alternately perform centrifugation and washing.

[0039] In this invention, impurity ions in the product can be removed and the product purity can be improved by multiple centrifugal washing.

[0040] Preferably, after the solid-liquid separation in step (3), the solid product is dried to obtain the CaTiF6 powder.

[0041] Preferably, the drying includes vacuum drying.

[0042] Preferably, the pressure of the vacuum drying is ≤1 kPa, such as 0.2 kPa, 0.4 kPa, 0.6 kPa, 0.8 kPa or 1 kPa.

[0043] Preferably, the vacuum drying temperature is 110℃~150℃ and the time is ≤24h, for example, the temperature is 110℃, 120℃, 130℃, 140℃ or 150℃, and the time is 6h, 10h, 13h, 16h, 20h or 24h.

[0044] In a second aspect, the present invention provides a CaTiF6 powder prepared by the preparation method described in the first aspect.

[0045] Preferably, the crystallinity of the CaTiF6 powder is ≥90%, for example, 90%, 91%, 92%, 93%, 94%, 95% or 96%.

[0046] Preferably, the linear expansion coefficient of the CaTiF6 powder is ≤-7.5ppm / K, such as -7.5ppm / K, -7.52ppm / K, -7.54ppm / K, -7.56ppm / K, -7.58ppm / K, -7.6ppm / K, or -7.61ppm / K.

[0047] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values ​​included in the range.

[0048] Compared with the prior art, the present invention has the following beneficial effects:

[0049] The preparation method provided by this invention uses non-toxic, water-soluble raw materials that are suitable for industrial production. The preparation process is simple, and neither the preparation nor the post-processing involves high-energy-consuming equipment, thus avoiding energy waste. The final emissions contain no harmful residues, and the process is clean. Furthermore, the CaTiF6 powder prepared by the method provided by this invention has high crystallinity (high purity), high yield, and uniform size dispersion. Attached Figure Description

[0050] Figure 1 These are XRD patterns of the CaTiF6 powders prepared in Examples 1, 4-6, and Comparative Example 1. Detailed Implementation

[0051] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0052] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having”, and any variations thereof, in the specification and claims of this application are intended to cover non-exclusive inclusion.

[0053] Example 1

[0054] This embodiment provides a method for preparing CaTiF6 powder, the specific process of which is as follows:

[0055] S1. Preparation of potassium fluoride solution: Weigh 5.868 g (0.101 mol) of potassium fluoride (KF) into a polytetrafluoroethylene beaker, dissolve it in 100 mL of deionized water, and adjust the pH to ~6.0 with dilute hydrochloric acid;

[0056] S2. Preparation of titanium source solution: Weigh 2.699 g (0.0167 mol) of titanium oxysulfate monohydrate (TiO(SO4)·H2O) into a polytetrafluoroethylene beaker and dissolve it in 50 mL of deionized water;

[0057] S3. Preparation of calcium chloride solution: Weigh 1.855 g (0.0167 mol) of anhydrous calcium chloride (CaCl2) and dissolve it in 50 mL of deionized water;

[0058] S4. Place the polytetrafluoroethylene beaker containing the KF solution in an ice-water bath and stir (stirring speed 400 rpm). Add the titanium source solution dropwise into the potassium fluoride solution at a rate of 5 mL / min. At the same time, add dilute hydrochloric acid to the mixed solution to make the overall pH of the solution ~6.0.

[0059] S5. After the titanium source solution is added dropwise, keep the ice water bath and maintain the stirring speed for 30 minutes. Then let it stand in the ice water bath for 2 hours to obtain a white precipitate K2TiF6. Then centrifuge (centrifuge speed 4000 rpm, time 5 minutes), then wash with 50 mL of ice deionized water (2℃), and centrifuge again (repeat the centrifugation-washing operation three times).

[0060] S6. In a 90℃ water bath environment, with the stirring speed set to 400 rpm, the obtained white precipitate K2TiF6 was dispersed and dissolved in 2000 mL of deionized water to obtain a K2TiF6 solution. The stirring speed was increased to 800 rpm, and CaCl2 solution was added dropwise to the hot K2TiF6 solution at a rate of 2 mL / min. After the CaCl2 solution was added, the temperature was kept constant at 90℃ and stirred for 30 min. Then, while maintaining the stirring speed, the water bath temperature was lowered to near the ice water temperature (2℃) at a cooling rate of 5℃ / min. After that, stirring was stopped, and the mixture was allowed to stand in the ice water bath for 2 h to obtain a white precipitate. The obtained white precipitate was centrifuged and washed multiple times (centrifugation and washing conditions were the same as in S5). The centrifuged and washed sample was then dried in a 120℃ vacuum oven for 6 h, and 3.248 g of CaTiF6 powder was obtained.

[0061] Example 2

[0062] This embodiment provides a method for preparing CaTiF6 powder, the specific process of which is as follows:

[0063] S1. Preparation of potassium fluoride solution: Weigh 5.926 g (0.102 mol) of potassium fluoride (KF) into a polytetrafluoroethylene beaker, dissolve it in 100 mL of deionized water, and adjust the pH to ~5.5 with dilute hydrochloric acid;

[0064] S2. Preparation of titanium source solution: Weigh 2.699 g (0.0167 mol) of titanium oxysulfate monohydrate (TiO(SO4)·H2O) into a polytetrafluoroethylene beaker and dissolve it in 50 mL of deionized water;

[0065] S3. Preparation of calcium chloride solution: Weigh 2.041 g (0.0184 mol) of anhydrous calcium chloride (CaCl2) and dissolve it in 50 mL of deionized water;

[0066] S4. Place the polytetrafluoroethylene beaker containing the KF solution in an ice-water bath and stir (stirring speed 400 rpm). Add the titanium source solution dropwise into the potassium fluoride solution at a rate of 4 mL / min. At the same time, add dilute hydrochloric acid to the mixed solution to make the overall pH of the solution ~5.5.

[0067] S5. After the titanium source solution is added dropwise, keep the ice-water bath and maintain the stirring speed for 20 minutes. Then let it stand in the ice-water bath for 1.5 hours to obtain a white precipitate K2TiF6. Then centrifuge (centrifuge speed 4000 rpm, time 5 minutes), then wash with 50 mL of ice-cold deionized water (0℃), and centrifuge again (repeat the centrifugation-washing operation three times).

[0068] S6. In an 80℃ water bath environment, with the stirring speed set to 400 rpm, the obtained white precipitate K2TiF6 was dispersed and dissolved in 2000 mL of deionized water to obtain a K2TiF6 solution. The stirring speed was increased to 800 rpm, and CaCl2 solution was added dropwise to the hot K2TiF6 solution at a rate of 1 mL / min. After the CaCl2 solution was added, the temperature was kept constant at 80℃ and stirred for 20 min. Then, while maintaining the stirring speed, the water bath temperature was lowered to near the ice water temperature (0℃) at a cooling rate of 5℃ / min. After that, stirring was stopped, and the mixture was allowed to stand in the ice water bath for 1.5 h to obtain a white precipitate. The obtained white precipitate was centrifuged and washed multiple times (centrifugation and washing conditions were the same as in S5). The centrifuged and washed sample was then placed in a vacuum oven at 110℃ and dried for 24 h. 3.218 g of CaTiF6 powder was obtained by weighing.

[0069] Example 3

[0070] This embodiment provides a method for preparing CaTiF6 powder, the specific process of which is as follows:

[0071] S1. Preparation of potassium fluoride solution: Weigh 5.868 g (0.101 mol) of potassium fluoride (KF) into a polytetrafluoroethylene beaker, dissolve it in 100 mL of deionized water, and adjust the pH to ~6.5 with dilute hydrochloric acid;

[0072] S2. Preparation of titanium source solution: Weigh 2.699 g (0.0167 mol) of titanium oxysulfate monohydrate (TiO(SO4)·H2O) into a polytetrafluoroethylene beaker and dissolve it in 50 mL of deionized water;

[0073] S3. Preparation of calcium chloride solution: Weigh 2.122 g (0.0192 mol) of anhydrous calcium chloride (CaCl2) and dissolve it in 50 mL of deionized water;

[0074] S4. Place the polytetrafluoroethylene beaker containing the KF solution in an ice-water bath and stir (stirring speed 400 rpm). Add the titanium source solution dropwise into the potassium fluoride solution at a rate of 6 mL / min. At the same time, add dilute hydrochloric acid to the mixed solution to make the overall pH of the solution ~6.5.

[0075] S5. After the titanium source solution is added dropwise, keep the ice-water bath and maintain the stirring speed for 40 min. Then let it stand in the ice-water bath for 2.5 h to obtain a white precipitate K2TiF6. Then centrifuge (centrifuge speed 4000 rpm, time 5 min), then wash with 50 mL of ice-cold deionized water (4℃), and centrifuge again (repeat the centrifugation-washing operation three times).

[0076] S6. In a 95℃ water bath environment, with the stirring speed set to 400 rpm, the obtained white precipitate K2TiF6 was dispersed and dissolved in 2000 mL of deionized water to obtain a K2TiF6 solution. The stirring speed was increased to 800 rpm, and CaCl2 solution was added dropwise to the hot K2TiF6 solution at a rate of 3 mL / min. After the CaCl2 solution was added, the temperature was kept constant at 95℃ and stirred for 40 min. Then, while maintaining the stirring speed, the water bath temperature was lowered to near the ice water temperature (4℃) at a cooling rate of 5℃ / min. After that, stirring was stopped, and the mixture was allowed to stand in the ice water bath for 2.5 h to obtain a white precipitate. The obtained white precipitate was centrifuged and washed multiple times (centrifugation and washing conditions were the same as in S5). The centrifuged and washed sample was then dried in a 150℃ vacuum oven for 15 h, and 3.215 g of CaTiF6 powder was obtained by weighing.

[0077] Example 4

[0078] The difference between this embodiment and Embodiment 1 is that in step S1 of this embodiment, the amount of potassium fluoride used is 5.810g (0.100mol), and the pH of the potassium fluoride solution is adjusted to 6.0 with dilute sulfuric acid. The mass of CaTiF6 powder obtained in S6 is 3.221g.

[0079] All other preparation methods and parameters are consistent with those in Example 1.

[0080] Example 5

[0081] The difference between this embodiment and embodiment 1 is that in step S3 of this embodiment, 3.151g (0.0192mol) of calcium nitrate (Ca(NO3)2) is weighed and dissolved in 50mL of deionized water, and the mass of CaTiF6 powder obtained in step S6 is 3.238g.

[0082] All other preparation methods and parameters are consistent with those in Example 1.

[0083] Example 6

[0084] The difference between this embodiment and Embodiment 1 is that in step S1, the fluoride salt is replaced with 4.241g (0.101mol) of sodium fluoride (NaF), in step S3, anhydrous calcium chloride is replaced with 2.740g (0.0167mol) of calcium nitrate (Ca(NO3)2), in step S5, after stirring for 30min, 500mL of anhydrous ethanol is added to the mixture, and then it is left to stand in an ice-water bath for 2h. During washing, ice-cold deionized water is replaced with 50mL of anhydrous ethanol. Finally, it is dried in an oven at 60℃ for 30min. In step S6, 3.210g of CaTiF6 powder is obtained by weighing.

[0085] The remaining preparation methods and parameters are consistent with those in Example 1.

[0086] Example 7

[0087] The difference between this embodiment and Embodiment 1 is that in step S1 of this embodiment, the amount of potassium fluoride used is 5.810g (0.100mol);

[0088] The remaining preparation methods and parameters are consistent with those in Example 1.

[0089] Example 8

[0090] The difference between this embodiment and Embodiment 1 is that, in S4, potassium fluoride solution is added to the titanium source solution at a dropping rate of 5 mL / min.

[0091] The remaining preparation methods and parameters are consistent with those in Example 1.

[0092] Example 9

[0093] The difference between this embodiment and Embodiment 1 is that, in S6, the CaCl2 solution is added to the K2TiF6 solution all at once, instead of being added dropwise;

[0094] The remaining preparation methods and parameters are consistent with those in Example 1.

[0095] Example 10

[0096] The difference between this embodiment and Embodiment 1 is that dilute hydrochloric acid is not added in S4;

[0097] The remaining preparation methods and parameters are consistent with those in Example 1.

[0098] Example 11

[0099] The difference between this embodiment and embodiment 1 is that in S6, the water bath temperature is reduced to around 25°C at a cooling rate of 5°C / min, then stirring is stopped, and the water is left to stand at 25°C for 2.5 hours.

[0100] The remaining preparation methods and parameters are consistent with those in Example 1.

[0101] Comparative Example 1

[0102] This comparative example provides a method for preparing CaTiF6 powder, the specific process of which is as follows:

[0103] S1: In a dry nitrogen glove box, weigh 3.904g (0.05mol) of CaF2 and 6.193g (0.05mol) of TiF4 in a molar ratio of 1:1, and grind them evenly.

[0104] S2: Press the ground mixed powder at 5MPa for 5min to form a disc-shaped sample (10mm in diameter). Place the disc-shaped sample in a copper tube and seal it with argon arc welding. Then seal the sealed copper tube in a vacuum quartz ampoule.

[0105] S3: The quartz ampoule was placed in a muffle furnace and heated to 400°C, held at that temperature for 24 hours, then annealed at 350°C for 24 hours, and finally cooled naturally to room temperature to obtain 9.541g of product.

[0106] XRD analysis confirmed that the product was a mixture of CaF2 and CaTiF6. The content of each phase in the product was calculated according to the Rietveld method (see H.M. Rietveld, J. Appl. Cryst. 2, 65-71 (1969) and R.A. Young (ed.), "The Rietveld Method", International Union of Crystallography, Oxford University Press, New York 1993). The mass of CaTiF6 was 8.953 g, and the yield was 88.7%.

[0107] Comparative Example 2

[0108] The difference between this comparative example and Example 1 is that in S5, the ice-water bath is replaced with a 25°C water bath;

[0109] The remaining preparation methods and parameters are consistent with those in Example 1.

[0110] Comparative Example 3

[0111] The difference between this comparative example and Example 6 is that in step S5 of this comparative example, no anhydrous ethanol is added before standing in an ice-water bath, and 2.351g of CaTiF6 powder is obtained after drying.

[0112] The remaining preparation methods and parameters are consistent with those in Example 6.

[0113] Performance testing

[0114] XRD tests were performed on the samples prepared in Examples 1-11 and Comparative Examples 1-3, and their crystallinity was analyzed. The results are as follows: Figure 1 As shown in Table 1.

[0115] 2g of CaTiF6 powder prepared in Examples 1-11 and Comparative Examples 1-3 were weighed and compressed into tablets. The compression conditions were 5MPa for 5min, and the tablets were compressed into round cakes with a diameter of 10mm. The coefficient of thermal expansion of the compressed samples in the temperature range of 25℃~200℃ was measured using a thermomechanical analyzer. The results are shown in Table 1.

[0116] Table 1

[0117]

[0118] Depend on Figure 1 The XRD characterization results of Examples 1, 4-6 and Comparative Example 1 show that the peak positions of the samples prepared in Examples 1 and 4-6 are consistent with the standard spectrum, which indicates that pure phase CaTiF6 can be prepared by the method provided by the present invention. The peak intensities of Examples 1 and 4-6 are different, indicating that the CaTiF6 samples prepared in different examples have different crystal orientations.

[0119] A comparison of the data from Examples 1-3 and Comparative Examples 1-3 in Table 1 shows that the CaTiF6 samples prepared using the method of the present invention all have a thermal expansion coefficient below -7.5 ppm / K and a yield of over 95%. In particular, the sample of Example 1 has a thermal expansion coefficient below -7.6 ppm / K and a yield as high as 96.3%. However, the sample prepared using Comparative Example 1 has a higher thermal expansion coefficient, and both the crystallinity and yield show a significant decrease. This is because there is a small amount of loss during the grinding and transfer pressing process in Comparative Example 1. In addition, some CaF2 in the high-temperature sintering product does not react, resulting in a lower yield. In Comparative Example 2, because an ice-water bath was not used, the intermediate product fluorotitanate was not completely separated from the system, leading to a decrease in yield. In Comparative Example 3, sodium fluoride was used as the fluoride salt, but ethanol was not added during the precipitation process, resulting in the intermediate product also not being completely separated from the system, leading to a decrease in yield.

[0120] A comparison of the data from Examples 1 and 4-11 in Table 1 shows that in this invention, the types of fluoride and calcium salts, whether ethanol is added during the precipitation process when the type of fluoride salt changes, the molar ratio of fluoride and titanium, the order of addition of fluoride and titanium salts, whether acid is added during the process, the order of addition of calcium salts, and whether the preparation of CaTiF6 powder is carried out in an ice-water bath all affect the properties of the product. By controlling these factors within the preferred range of this invention, better results can be achieved. Specifically, the sample obtained in Example 6 showed an increase in the coefficient of thermal expansion and a decrease in crystallinity and yield. This is mainly because: in Example 6, ethanol was used to precipitate the intermediate product during sample preparation, resulting in a decrease in the crystallinity of calcium fluorotitanate. Since sodium fluorotitanate has a higher solubility than potassium fluorotitanate, when ethanol is used to precipitate the intermediate product, trace amounts of sodium fluorotitanate remain dissolved in water and are difficult to precipitate with ethanol, leading to a decrease in yield. The yield of the CaTiF6 sample obtained in Example 11 was less than 75%, mainly because KTiF6 has a certain solubility in room temperature solution, so some KTiF6 is difficult to precipitate to form CaTiF6.

[0121] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method for preparing CaTiF6 powder, characterized in that, The preparation method includes: (1) Under the conditions of ice-water bath at 0℃~4℃, the soluble titanium salt and the soluble fluoride salt are first dissolved in water independently to obtain the aqueous solution of soluble titanium salt and the aqueous solution of soluble fluoride salt. Then, the aqueous solution of soluble titanium source is added dropwise to the aqueous solution of soluble fluoride salt, and acid is added at the same time to carry out the first precipitation reaction. After solid-liquid separation, the intermediate product fluorotitanate is obtained. (2) Dissolve the fluorotitanate from step (1) in hot water at 80℃~95℃ to obtain an aqueous solution of fluorotitanate; (3) First, the soluble calcium salt is dissolved in water to obtain an aqueous solution of the soluble calcium salt. Then, the aqueous solution of the soluble calcium salt is added dropwise to the aqueous solution of the fluorotitanate in step (2) to carry out the second precipitation reaction. After solid-liquid separation, the CaTiF6 powder is obtained. The steps of the second precipitation reaction include: first reacting at 80℃~95℃ and stirring for 20min~40min, then cooling to 0℃~4℃, and reacting under static conditions for 1.5h~2.5h. The soluble fluoride salt in step (1) is any one or a combination of at least two of potassium fluoride, ammonium fluoride or sodium fluoride; when the soluble fluoride salt in step (1) is ammonium fluoride and / or sodium fluoride, anhydrous ethanol is added at the beginning of the first precipitation reaction; The soluble calcium salt in step (3) includes any one or a combination of at least two of calcium chloride, calcium nitrate, calcium nitrite, calcium bromide, calcium acetate, or calcium formate; The molar ratio of titanium, fluorine and calcium in the soluble titanium salt, soluble fluoride salt and soluble calcium salt in step (1) and step (3) is 1:(6.04~6.1):(1~1.15).

2. The preparation method according to claim 1, characterized in that, The soluble titanium salt in step (1) includes titanium oxysulfate.

3. The preparation method according to claim 1, characterized in that, The soluble fluoride salt mentioned in step (1) is potassium fluoride.

4. The preparation method according to claim 1, characterized in that, Step (1) The soluble titanium source aqueous solution is added to the soluble fluoride aqueous solution at a rate of 4 mL / min to 6 mL / min.

5. The preparation method according to claim 1, characterized in that, Step (1) While adding the soluble titanium source aqueous solution dropwise to the soluble fluoride aqueous solution, acid is added to adjust the pH of the system to 5.5~6.

5.

6. The preparation method according to claim 1, characterized in that, The acid in step (1) includes any one or a combination of at least two of dilute hydrochloric acid, dilute sulfuric acid, dilute nitric acid, dilute acetic acid, dilute formic acid or dilute sulfurous acid.

7. The preparation method according to claim 1, characterized in that, Step (1) The first precipitation reaction includes: reacting for 20 min to 40 min under stirring, and then reacting for 1.5 h to 2.5 h under standing conditions.

8. The preparation method according to claim 1, characterized in that, The solid-liquid separation method in step (1) is to alternately centrifuge and wash, and the washing detergent is ice water.

9. The preparation method according to claim 1, characterized in that, Step (3) The soluble calcium salt aqueous solution is added dropwise to the fluorotitanate aqueous solution at a rate of 1 mL / min to 3 mL / min.

10. The preparation method according to claim 1, characterized in that, The solid-liquid separation method described in step (3) involves alternating centrifugation and washing.

11. The preparation method according to claim 1, characterized in that, After solid-liquid separation in step (3), the solid product is dried to obtain the CaTiF6 powder.

12. The preparation method according to claim 11, characterized in that, The drying process includes vacuum drying.

13. The preparation method according to claim 12, characterized in that, The pressure of the vacuum drying process is ≤1 kPa.

14. The preparation method according to claim 12, characterized in that, The vacuum drying temperature is 110℃~150℃, and the time is ≤24h.

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