A controllable thermal expansion material MNF6 and its preparation method
MNF6 materials prepared through cheap raw materials and simple solid-phase sintering method solve the problem of high preparation cost of existing negative thermal expansion fluoride, and achieve low-cost and stable thermal expansion performance. They are suitable for LED light emission, integrated circuits and aerospace engineering and other fields.
Patent Information
- Application Number
- CN202310346261.8
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2023-04-03
- Publication Date
- 2025-08-01
- Estimated Expiration
- 2043-04-03
AI Technical Summary
The existing thermally expanded fluoride materials are harsh and expensive to prepare, which limits their applications in LED light emission, integrated circuits and aerospace engineering.
The controlled thermal expansion material MNF6 is prepared by cheap raw materials and a simple solid-phase sintering method. The MNF6 material with a cubic phase structure is obtained by mixing metal salts and oxide precursors in a hydrofluoric acid solution, and then sintering under a coated NH4F or NH4HF2 powder.
It realizes a low-cost controlled thermal expansion material, has stable thermal expansion performance, is suitable for industrial production, avoids thermal cracks and performance damage, and is suitable for phosphors, battery electrodes and electronic circuit board substrates.
Smart Images
Figure CN116443925B_ABST
Abstract
Description
Technical Field
[0001] The present invention belongs to the field of thermal expansion materials, and particularly relates to a controllable thermal expansion material MNF6 and a preparation method thereof. Background Art
[0002] The harms caused by positive thermal expansion can be seen everywhere, such as broken glass under exposure to the sun. Negative thermal expansion goes against the common thermal expansion and contraction phenomenon, and is a type of material whose length or volume decreases with the increase in temperature. Such materials can be used in combination with positive thermal expansion materials to offset the harms caused by the thermal expansion of materials. With the progress of technology, more and more fields require related matrix materials to have specific thermal expansion properties. Therefore, the development of materials with controllable thermal expansion coefficients has great application prospects and significance in the manufacturing of precision instruments such as LED lighting, integrated circuits, and aerospace engineering.
[0003] It is reported that fluorides have excellent applications in fields such as luminescence, energy storage, optical fibers, and fuel cells. However, the vast majority of materials in these fields are positive thermal expansion materials, which will expand after long-term heating, affecting the use performance of the materials. There are also a small number of fluorides that are negative thermal expansion materials. However, although the reported negative thermal expansion fluorides can also be prepared by conventional solid-phase sintering methods, the preparation conditions are harsh and the prices are expensive. For example, to synthesize CaTiF6 and CaHfF6, under a dry nitrogen atmosphere, the raw materials (CaF2 and TiF4 / HfF4) with a molar ratio of 1:1 are ground and pressed into tablets. Subsequently, the tablet-shaped raw materials are placed in a copper tube, and the copper tube is welded and sealed under an argon atmosphere. Then, the copper tube is sealed in a vacuum quartz ampoule and heated. For CaTiF6, it is heated at 400°C for 24 hours; for CaHfF6, it is heated at 850°C for 24 hours. Moreover, the TiF4 / HfF4 raw materials are extremely easy to absorb water, and the prices are as high as hundreds of yuan per gram. These disadvantages greatly limit the application of fluoride negative thermal expansion materials. Therefore, it is also very meaningful to develop fluoride negative thermal expansion materials with low cost and simple preparation methods. Summary of the Invention
[0004] In order to overcome the deficiencies existing in the prior art, the purpose of the present invention is to provide a controllable thermal expansion material MNF6 and a preparation method thereof. The preparation method of the present invention has low cost and simple preparation method.
[0005] To achieve the above purpose, the technical solution adopted by the present invention is as follows:
[0006] A controllable thermal expansion material, whose molecular formula is MNF6, where M = Ca, Mn, Fe, Co, Ni or Zn; N = Ti, Zr or Hf, has a symmetric crystal structure. At room temperature, the crystal structure of MNF6 is cubic phase, and the space group is Fm -3 m .
[0007] Preparation method, the preparation steps are as follows:
[0008] (1) Preparing a precursor: mixing an M source and a N source in a molar ratio of M:N=1:1, heating and stirring the M source and the N source under sealed conditions to completely dissolve them in a hydrofluoric acid solution to obtain a mixed solution, and then evaporating and crystallizing to obtain a precursor; wherein the M source is an inorganic acid salt of metal M, and the N source is an oxide of metal N;
[0009] (2) Proceed as follows (i) or (ii):
[0010] (i) placing the precursor powder directly or after being pressed into a sheet into a copper tube, and covering the upper surface of the precursor with a layer of NH4F or NH4HF2 powder, and sealing the copper tube;
[0011] (ii) placing the precursor powder directly or after being pressed into a tablet in a crucible, and covering the upper surface of the precursor with a layer of NH4F or NH4HF2 powder;
[0012] (3) Place the copper tube or crucible of step (2) into a muffle furnace, sinter the CaTiF6 precursor at 200-400°C for 1-6 hours, and sinter the precursors of other substances at 500-900°C for 1-6 hours, and cool to room temperature to obtain the controllable thermal expansion material MNF6.
[0013] Preferably, the M source is MCO3 or MCl2, and the N source is NO2.
[0014] Preferably, in step (1), the temperature of heating and stirring is 60-80°C.
[0015] Preferably, in step (1), the temperature of evaporation crystallization is 60-80°C.
[0016] Preferably, in step (1), the molar volume ratio of M source: hydrofluoric acid solution is 20 mmol: (15-30) mL.
[0017] Preferably, in step (1), the concentration of the hydrofluoric acid solution is 40-60 wt%.
[0018] The controllable thermal expansion material of the present invention can be applied to phosphors, battery electrodes or electronic circuit board substrates.
[0019] Compared with the prior art, the present invention has the following beneficial effects:
[0020] The present invention adopts a method of pre-treating cheap raw materials and then performing simple solid-phase sintering to prepare the product, which is more cost-effective in synthesis. The linear thermal expansion coefficient of MNF6 prepared by the present invention is in the range of +3.52×10 -6 / K ~ -7.87×10 -6 / K, as the temperature rises, since the ranges of the thermal expansion coefficients in each axial direction inside it are the same, this material will not generate thermal cracks or even be damaged due to uneven heating; the thermal expansion material provided by the present invention has a low cost, is suitable for industrial production, and is expected to be applied in high-tech fields such as LED lighting, integrated circuit packaging, and aerospace engineering.
[0021] The present invention also has the following beneficial effects:
[0022] (1). Existing isotropic negative thermal expansion materials such as ZrW2O8, A2M3O 12 etc. When the temperature changes, these materials will have microcracks caused by local thermal stress and will undergo phase changes, affecting the performance of the device. However, the thermal expansion material MNF6 of the present invention is a single phase and there is no problem of material performance damage caused by phase changes;
[0023] (2). Existing single-phase isotropic negative thermal expansion materials such as FeNi 36 , TbCo 1.9 Fe 0.1 etc. Their negative thermal expansion temperature ranges are all near room temperature, while the thermal expansion range of MNF6 of the present invention is from room temperature to 400 °C, crossing the constraint of room temperature;
[0024] (3). The present invention can prepare thermal expansion materials with different thermal expansion coefficients and different chemical properties according to actual needs, indicating that the regulation of metal sites can meet the needs of specific working conditions / components for thermal expansion coefficients. Description of the Drawings
[0025] Figure 1 : Appearance diagram of the CaZrF6 sample obtained in Example 1.
[0026] Figure 2 : XRD patterns of the precursor (a) and CaZrF6 (b) obtained in Example 1.
[0027] Figure 3 : Room temperature crystal structure diagram of the CaZrF6 sample obtained in Example 1 (M = Ca; N = Zr).
[0028] Figure 4 : Linear thermal expansion diagram of the CaZrF6 sample obtained in Example 1.
[0029] Figure 5 : Thermogravimetric diagram of the CaZrF6 sample obtained in Example 1.
[0030] Figure 6 : Linear thermal expansion diagram of the MNF6 samples obtained in Examples 2 - 4. Detailed Embodiments
[0031] To make the present invention clearer and more explicit, the following further details the present invention. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.
[0032] Example 1
[0033] A preparation method of a thermal expansion material is as follows:
[0034] (1) Weigh 20 mmol of CaCl2 and 20 mmol of ZrO2 respectively, mix them in a plastic beaker, add 20 mL of hydrofluoric acid solution (40 wt%), seal the plastic beaker with plastic wrap, and stir for 5 h by heating in a water bath at 80 °C; then remove the plastic wrap, evaporate and crystallize at 80 °C until the mixed solution is completely crystallized; dry the crystallized solid at 80 °C for 6 h to obtain the S1-precursor.
[0035] (2) Take an appropriate amount of S1-precursor powder and press it into a cylindrical block with a diameter of 10 mm and a height of about 3 mm. Put the block into a copper tube, evenly cover a layer of NH4F powder on the upper surface of the block, and then seal the copper tube; then place the copper tube in a muffle furnace and sinter at 800 °C for 1 h, and cool to room temperature to obtain the thermal expansion material CaZrF6, which is named S1-CaZr.
[0036] Example 2
[0037] A preparation method of a thermal expansion material is as follows:
[0038] (1) Weigh 20 mmol of CaCl2 and 20 mmol of TiO2 respectively, mix them in a plastic beaker, add 20 mL of hydrofluoric acid solution (40 wt%), seal the plastic beaker with plastic wrap, and stir for 5 h by heating in a water bath at 80 °C; then remove the plastic wrap, evaporate and crystallize at 80 °C until the mixed solution is completely crystallized; dry the crystallized solid at 80 °C for 6 h to obtain the S2-precursor.
[0039] (2) Take an appropriate amount of S2-precursor powder and press it into a cylindrical block with a diameter of 10 mm and a height of about 3 mm. Put the block into a copper tube, evenly cover a layer of NH4F powder on the upper surface of the block, and then seal the copper tube; then place the copper tube in a muffle furnace and sinter at 250 °C for 1 h, and cool to room temperature to obtain the thermal expansion material CaTiF6, which is named S2-CaTi.
[0040] Example 3
[0041] A preparation method of a thermal expansion material is as follows:
[0042] (1) Weigh 20 mmol of MnCl2, FeCl2, CoCl2, and ZnCl2 in sequence. Then, mix them with 20 mmol of ZrO2 respectively and put them into a plastic beaker. Add 15 mL of hydrofluoric acid solution (40 wt%). Seal the plastic beaker with plastic wrap and stir for 5 h by heating in a water bath at 80 °C. Then, remove the plastic wrap and evaporate and crystallize at 80 °C until the mixed solution is completely crystallized. Dry the crystallized solid at 80 °C for 6 h to obtain the S2-precursor.
[0043] (2) Take an appropriate amount of S3-precursor powder and press it into a cylindrical block with a diameter of 10 mm and a height of about 3 mm. Put the block into a copper tube, evenly cover a layer of NH4F powder on the upper surface of the block, and then seal the copper tube. Then, place the copper tube in a muffle furnace and sinter at 750 °C for 1 h. Cool to room temperature to obtain the thermal expansion materials MnZrF6, FeZrF6, CoZrF6, and ZnZrF6 in sequence, and name them S3-MnZr, S3-FeZr, S3-CoZr, and S3-ZnZr in sequence.
[0044] Example 4
[0045] A preparation method of a thermal expansion material is as follows:
[0046] (1) Weigh 20 mmol of CaCl^2, MnCl^2, and FeCl^2 in sequence. Then, mix them with 20 mmol of HfO^2 respectively, add 15 mL of hydrofluoric acid solution (40 wt%). Seal the plastic beaker with plastic wrap and stir for 5 h by heating in a water bath at 80 °C. Then, remove the plastic wrap and evaporate and crystallize at 80 °C until the mixed solution is completely crystallized. Dry the crystallized solid at 80 °C for 6 h to obtain the S4-precursor.
[0047] (2) Take an appropriate amount of S4-precursor powder and press it into a cylindrical block with a diameter of 10 mm and a height of about 3 mm. Put the block into a copper tube, evenly cover a layer of NH4F powder on the upper surface of the block, and then seal the copper tube. Then, place the copper tube in a muffle furnace and sinter at 800 °C for 1 h. Cool to room temperature to obtain the thermal expansion materials CaHfF6, MnHfF6, and FeHfF6 in sequence, and name them S4-CaHf, S4-MnHf, and S4-FeHf in sequence.
[0048] Product characterization and thermal expansion performance test
[0049] Figure 1 It is the appearance diagram of the CaZrF6 sample obtained in Example 1. It can be observed that the surface of the fabricated device is smooth and dense, which will not affect the subsequent performance test.
[0050] Figure 2XRD pattern of the CaZrF6 sample (S1-CaZr) obtained in Example 1. It can be found that the XRD diffraction peak pattern of CaZrF6 is consistent with the CaZrF6 standard card, and no other impurity phases appear. Only the peak positions are different, indicating that the negative thermal expansion material explored in the present invention is a single phase, and the preparation conditions are correct and will not affect subsequent performance tests.
[0051] Figure 3 It is the crystal structure diagram of the CaZrF6 sample obtained after refinement of the XRD data according to Figure 1 It can be observed that this structure is composed of MF6 polyhedra and NF6 polyhedra connected by sharing F atoms (M = Ca; N = Zr), with high symmetry. The structure is cubic phase, and the space group is Fm -3 m . More importantly, the lengths and properties of the three axes of the cubic phase material are the same, so this structure exhibits isotropic thermal expansion behavior. The crystal structures of the other samples prepared in Examples 2-4 of the present invention are the same as Figure 1 .
[0052] Figure 4 Linear thermal expansion diagram of the CaZrF6 sample (S1-CaZr) obtained in Example 1. It can be observed that in the temperature range of RT~400 °C, the length of the CaZrF6 bulk sample decreases with the increase of temperature, and the linear thermal expansion coefficient is -7.87×10 -6 / K, indicating that it has negative thermal expansion performance.
[0053] Figure 5 Thermogravimetric diagram of the CaZrF6 sample (S1-CaZr) obtained in Example 1. It can be observed that in the temperature range of RT~800 °C, the mass of the CaZrF6r sample hardly changes with the increase of temperature, indicating that it has good thermal stability.
[0054] Figure 6 Linear thermal expansion diagrams of the CaTiF6 sample (S2-CaTi) obtained in Example 2, the MZrF6 samples (S3-MnZr, S3-FeZr, S3-CoZr, and S3-ZnZr) obtained in Example 3, and the MHfF6 samples (S4-CaHf, S4-MnHf, and S4-FeHf) obtained in Example 4. Among them, S3-MnZr and S4-MnHf basically coincide, so they are omitted. It can be observed that in the temperature range of RT~400 °C, the length of the CoZrF6 sample increases with the increase of temperature (the linear thermal expansion coefficient is +3.52×10 -6 / K). The length of the ZnZrF6 bulk sample remains basically unchanged as the temperature increases, while the lengths of other samples decrease as the temperature increases. For example, the linear thermal expansion coefficient of the CaHfF6 bulk sample is -7.59×10 -6 / K, indicating that the MNF6 series samples have a controllable thermal expansion coefficient. In addition, there are no inflection points in the thermal expansion data of all samples, indicating that there is no phase change.
Claims
1. A method for preparing a controllable thermal expansion material, characterized in that, The molecular formula of the controllable thermal expansion material is MNF6, where M = Ca, Mn, Fe, Co, Ni or Zn; N = Ti, Zr or Hf, and it has a symmetric crystal structure. At room temperature, the crystal structure of MNF6 is a single cubic phase, and the space group is Fm -3 m ; The preparation steps are as follows: (1) Preparation of the precursor: Mix the M source and the N source in a molar ratio of M:N = 1:
1. Under sealed conditions, heat and stir the M source and the N source at 60-80°C until they are completely dissolved in the hydrofluoric acid solution to obtain a mixed solution. Subsequently, evaporate and crystallize at 60-80°C to obtain the precursor. Among them, the M source is an inorganic acid salt of metal M, and the N source is an oxide of metal N. Among them, the concentration of the hydrofluoric acid solution is 40-60 wt%, and in terms of the molar volume ratio, M source:hydrofluoric acid solution = 20 mmol:(15-30) mL; (2) Proceed in the following manner (i) or (ii): (i) Place the precursor powder directly or after pressing it into a tablet in a copper tube, and cover the upper surface of the precursor with a layer of NH4F or NH4HF2 powder, and seal the copper tube; (ii) Place the precursor powder directly or after pressing it into a tablet in a crucible, and cover the upper surface of the precursor with a layer of NH4F or NH4HF2 powder; (3) Put the copper tube or crucible in step (2) into a muffle furnace. Sinter the precursor of CaTiF6 at 200-400°C for 1-6 h, and sinter the precursors of other substances at 500-900°C for 1-6 h. Cool to room temperature to obtain the controllable thermal expansion material MNF6.
2. The preparation method of the controllable thermal expansion material according to claim 1, characterized in that: The M source is MCO3 or MCl2, and the N source is NO2.