A fluorite-derived structural oxide aerogel and its preparation method and application

Abstract

The present invention relates to a fluorite-derived structure oxide aerogel and its preparation method and application, belonging to the technical field of functional materials. To solve the problem that traditional oxide aerogels cannot stably serve in high-temperature and high-radiation environments for a long time, the present invention provides a fluorite-derived structure oxide aerogel, and the crystal structure of the aerogel is A2B7O 17 , where A is a rare earth element and B is a transition metal element. The aerogel of the present invention undergoes high-temperature heat treatment, and its reaction activity is reduced, which can reduce pore structure collapse and volume shrinkage during use in a high-temperature environment; the fluorite-derived crystal structure in the aerogel can absorb neutrons in a nuclear radiation environment and maintain a complete macro / micro morphology, enabling it to serve as an efficient thermal insulation material with high stability and long-term service in the high-temperature and strong-radiation environment of a nuclear reactor, broadening the application of oxide aerogels and having broad application prospects in the field of nuclear reactor thermal insulation materials.

Description

Technical Field

[0001] The invention belongs to the technical field of functional materials, and in particular relates to a fluorite-derived structural oxide aerogel and a preparation method and application thereof. Background Art

[0002] Thermal insulation materials play a vital safety role in nuclear reactors. They can effectively reduce the rate of heat transfer to the surrounding environment, reduce heat loss, improve energy efficiency, and protect equipment within the reactor from high temperature damage.

[0003] The internal environment of a nuclear reactor is extreme, with high temperature, high pressure and strong radiation, which places extremely high demands on the performance of thermal insulation materials. Nuclear radiation mainly affects the performance of thermal insulation materials by destroying the molecular structure of the material, causing chemical bond breakage, molecular deformation and atomic structure changes, including material embrittlement, changes in thermal conductivity, reduced fire resistance and impaired chemical stability.

[0004] Fluorite-derived structural oxides are oxides with structural characteristics similar to fluorite (calcium fluoride, CAF2) and have a stable cubic structure. They can maintain a disordered phase structure during the radiation process, resist radiation-induced amorphization, enhance radiation tolerance, and avoid cracking and failure of the material. β-phase fluorite-derived structural oxide ceramics are considered to be a highly promising material with broad application prospects in the field of high-radioactive nuclear waste solidification.

[0005] Although fluorite-derived structural oxide ceramics can maintain structural stability at high temperatures, their thermal conductivity is relatively high. This means that in high-temperature environments such as nuclear reactors, heat may be transferred through ceramic materials relatively quickly, limiting their thermal insulation effect. Moreover, fluorite-derived structural oxide ceramics generally have higher density and larger volume. In space-constrained environments such as nuclear reactors, overly heavy insulation materials may increase the burden on the structure and reduce overall efficiency.

[0006] Aerogel is a lightweight material with abundant nanoscale pores, high specific surface area and ultra-low thermal conductivity. However, common oxide aerogels are mostly SiO2 aerogel, Al2O3 aerogel, ZrO2 aerogel, etc. After high-temperature heat treatment, they become single-component oxide crystals. It is difficult to maintain a complete pore structure in a strong radiation environment, and it is impossible to achieve the coordination of radiation resistance and high-temperature thermal insulation. Summary of the invention

[0007] In order to solve the problem that traditional oxide aerogels cannot serve stably for a long time in a high temperature and high radiation environment, the present invention provides a fluorite-derived structured oxide aerogel and a preparation method and application thereof.

[0008] The technical solution of the present invention:

[0009] A fluorite-derived structured oxide aerogel, wherein the crystal structure of the aerogel is A2B7O 17 , where A is a rare earth element and B is a transition metal element.

[0010] Furthermore, the rare earth element is one of Y, Sc, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb or Lu, and the transition metal element is one of Ti, Zr or Hf.

[0011] A method for preparing a fluorite-derived structural oxide aerogel, comprising the following steps:

[0012] Step 1: Prepare gel:

[0013] Adding a rare earth element precursor and a transition metal precursor to a mixed solvent of deionized water and anhydrous ethanol, stirring in a water bath to obtain a mixed solution, adding glacial acetic acid to the mixed solution, stirring in a water bath, cooling to room temperature, adding epichlorohydrin, and stirring for a certain period of time to obtain gel I;

[0014] Step 2: Aging treatment:

[0015] The gel I obtained in step 1 is immersed in anhydrous ethanol, and the anhydrous ethanol is replaced regularly until aging is completed to obtain gel II;

[0016] Step 3: Supercritical drying:

[0017] The gel II obtained in step 2 is placed in a supercritical drying device, anhydrous ethanol is added to soak the gel II, nitrogen is introduced, the temperature is increased under a certain pressure, the pressure is increased after the temperature is increased to the drying temperature, and the temperature and pressure are maintained for a certain period of time to obtain a BO2-A2O3 composite aerogel;

[0018] Step 4: Heat treatment:

[0019] The BO2-A2O3 composite aerogel obtained in step 3 is placed in a heat treatment device, heated to a heat treatment temperature at a certain rate, and kept at the heat treatment temperature for a certain time to obtain a fluorite-derived structure oxide aerogel.

[0020] Furthermore, in step 1, the rare earth element precursor is a nitrate hydrate of a selected rare earth element; the transition metal precursor is a tetrachloride of a transition metal; the molar ratio of the rare earth element precursor to the transition metal precursor is 1:3.5; and the concentration of the transition metal tetrachloride in the mixed solution is 10%wt.

[0021] Furthermore, in step 1, the volume ratio of the deionized water to the anhydrous ethanol is 1:10; the added amounts of the glacial acetic acid and the epichlorohydrin are calculated based on the molar ratio of the transition metal precursor, glacial acetic acid and epichlorohydrin of 1:1.5:4.

[0022] Furthermore, the water bath stirring temperature in step 1 is 40° C., the water bath stirring time is 30 min, and the stirring time after adding epichlorohydrin is 2 to 10 min.

[0023] Furthermore, in step 2, the gel I is immersed in anhydrous ethanol at an ambient temperature of 45° C., and the anhydrous ethanol is replaced regularly every 12 hours, for a total of 6 times.

[0024] Furthermore, the gas pressure during the heating in step three is 3.5 MPa, the heating rate is 4°C / min, the drying temperature is 273°C, the gas pressure is increased by increasing the nitrogen pressure to 9 MPa, and the heat and pressure holding time is 2h.

[0025] Furthermore, the heating rate in step 4 is 5-10°C / min, the heat treatment temperature is 900-1200°C, and the insulation time is 30-60min.

[0026] An application of the fluorite-derived structural oxide aerogel provided by the invention in thermal insulation of a nuclear reactor.

[0027] Beneficial effects of the present invention:

[0028] The present invention efficiently obtains an oxide aerogel with a fluorite-derived structure through sol-gel, aging, supercritical drying, and high-temperature heat treatment. The obtained aerogel has a carbon content of 0.5 g / cm 3 Density below 100m 2 / g or more specific surface area, 0.05W / (m·K) or less thermal conductivity; the macroscopic appearance is a complete block.

[0029] The aerogel in the present invention has been subjected to a high temperature heat treatment at 900-1200°C, and the reaction activity is reduced, which can reduce the pore structure collapse and volume shrinkage when used in a high temperature environment; at the same time, the present invention is a multi-component oxide aerogel, and the aerogel forms a fluorite-derived crystal structure A2B7O 17， It can absorb neutrons in a nuclear radiation environment and maintain a complete macro / micro morphology. It can be used as a high-efficiency thermal insulation material with high stability and long service life in the high temperature and strong radiation environment of a nuclear reactor. It broadens the application of oxide aerogels and has broad application prospects in the field of nuclear reactor thermal insulation materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1This is a physical picture of the fluorite-derived structured oxide aerogel obtained in Example 1;

[0031] Figure 2 This is the XRD image of the fluorite-derived structured oxide aerogel obtained in Example 1;

[0032] Figure 3 This is a SEM image of the fluorite-derived structured oxide aerogel obtained in Example 1;

[0033] Figure 4 This is a SEM image of the fluorite-derived structured oxide aerogel obtained in Example 2;

[0034] Figure 5 This is a SEM image of the fluorite-derived structured oxide aerogel obtained in Example 3. DETAILED DESCRIPTION

[0035] The technical solution of the present invention is further described below in conjunction with the embodiments, but it is not limited thereto. Any modification or equivalent replacement of the technical solution of the present invention without departing from the spirit and scope of the technical solution of the present invention shall be included in the protection scope of the present invention. The process equipment or devices not specifically noted in the following embodiments are all conventional equipment or devices in the art. If not specifically specified, the raw materials used in the embodiments of the present invention can be obtained commercially; if not specifically specified, the technical means used in the embodiments of the present invention are all conventional means well known to those skilled in the art.

[0036] Example 1

[0037] This embodiment provides a fluorite derivative structure of Y2Hf7O 17 Oxide aerogel and preparation method thereof.

[0038] The crystal structure of the aerogel in this embodiment is Y2Hf7O 17 , the rare earth element is yttrium, and the transition metal element is hafnium.

[0039] The preparation method of the fluorite-derived structured oxide aerogel in this embodiment comprises the following steps:

[0040] Step 1: Prepare gel:

[0041] Weigh a rare earth element precursor, yttrium nitrate hexahydrate Y(NO3)3·6H2O, and a transition metal precursor, hafnium tetrachloride HfCl4, in a molar ratio of 1:3.5, add them to a mixed solvent of deionized water and anhydrous ethanol in a volume ratio of 1:10, and stir in a water bath at 40°C for 30 minutes to form a mixed solution, wherein the total concentration of yttrium nitrate hexahydrate and hafnium tetrachloride in the mixed solution is 10%wt;

[0042] Add glacial acetic acid to the obtained mixed solution at a molar ratio of HfCl4 to CH3COOH of 1:1.5, stir in a water bath at 40°C for 30 minutes, cool to room temperature, add epichlorohydrin to the mixed system cooled to room temperature at a molar ratio of HfCl4 to epichlorohydrin of 1:4, stir for 10 minutes to form gel I;

[0043] Step 2: Aging treatment:

[0044] Soak the gel I obtained in step 1 in anhydrous ethanol, place it in an environment of 45°C, replace the anhydrous ethanol every 12 hours, and replace it 6 times in total to obtain gel II;

[0045] Step 3: Supercritical drying:

[0046] The gel II obtained in step 2 was placed in a supercritical drying reactor, anhydrous ethanol was added to the reactor to soak the gel II, nitrogen was introduced to maintain a pressure of 3.5 MPa, and then the temperature was raised to a drying temperature of 273°C at a heating rate of 4°C / min, the exhaust valve was adjusted to maintain a pressure of 9 MPa, and the temperature and pressure were maintained for 2 hours. After the gas in the reactor was released and cooled to room temperature, the HfO2-Y2O3 composite aerogel was obtained;

[0047] Step 4: Heat treatment:

[0048] The HfO2-Y2O3 composite aerogel obtained in step 3 was placed in a muffle furnace and heated to a heat treatment temperature of 1100°C at a heating rate of 7°C / min. After being kept at this temperature for 40 minutes, a fluorite-derived structure of Y2Hf7O 17 of oxide aerogels.

[0049] Figure 1 This is a physical picture of the fluorite-derived structured oxide aerogel obtained in Example 1; the picture shows that the macroscopic appearance of the fluorite-derived structured oxide aerogel is a complete block.

[0050] Figure 2 This is the XRD picture of the fluorite-derived oxide aerogel obtained in Example 1. It can be seen that the aerogel forms a fluorite-derived crystal structure Y2Hf7O 17 , and its characteristic diffraction peak corresponds to PDF card 28-1450.

[0051] The fluorite derivative structure obtained in this embodiment is Y2Hf7O 17 The density of the oxide aerogel is 0.27 g / cm 3 , the specific surface area is 157.73m 2 / g, and its thermal conductivity is 0.027W / (m·K), which meets the requirements of lightweight and porous thermal insulation materials for nuclear reactors.

[0052] Example 2

[0053] This embodiment provides a fluorite derivative structure of Sc2Zr7O 17 Oxide aerogel and preparation method thereof.

[0054] The crystal structure of the aerogel in this embodiment is Sc2Zr7O 17 , the rare earth element is scandium, and the transition metal element is zirconium.

[0055] The preparation method of the fluorite-derived structured oxide aerogel in this embodiment comprises the following steps:

[0056] Step 1: Prepare gel:

[0057] The rare earth element precursor scandium nitrate hexahydrate Sc(NO3)3·6H2O and the transition metal precursor zirconium tetrachloride ZrCl4 were weighed in a molar ratio of 1:3.5, added into a mixed solvent of deionized water and anhydrous ethanol in a volume ratio of 1:10, stirred in a water bath at 40°C for 30 minutes to form a mixed solution, wherein the total concentration of scandium nitrate hexahydrate and zirconium tetrachloride in the mixed solution was 10%wt;

[0058] Add glacial acetic acid to the obtained mixed solution at a molar ratio of ZrCl4 to CH3COOH of 1:1.5, stir in a water bath at 40°C for 30 minutes, cool to room temperature, add epichlorohydrin to the mixed system cooled to room temperature at a molar ratio of ZrCl4 to epichlorohydrin of 1:4, stir for 10 minutes to form gel I;

[0059] Step 2: Aging treatment:

[0060] Soak the gel I obtained in step 1 in anhydrous ethanol, place it in an environment of 45°C, replace the anhydrous ethanol every 12 hours, and replace it 6 times in total to obtain gel II;

[0061] Step 3: Supercritical drying:

[0062] The gel II obtained in step 2 was placed in a supercritical drying reactor, anhydrous ethanol was added to the reactor to soak the gel II, nitrogen was introduced to maintain a pressure of 3.5 MPa, and then the temperature was raised to a drying temperature of 273°C at a heating rate of 4°C / min, the exhaust valve was adjusted to maintain a pressure of 9 MPa, and the temperature and pressure were maintained for 2 hours. After the gas in the reactor was released and cooled to room temperature, a ZrO2-Sc2O3 composite aerogel was obtained;

[0063] Step 4: Heat treatment:

[0064] The ZrO2-Sc2O3 composite aerogel obtained in step 3 was placed in a muffle furnace and heated to a heat treatment temperature of 1000°C at a heating rate of 5°C / min. After being kept at this temperature for 30 minutes, a fluorite-derived structure of Sc2Zr7O17 of oxide aerogels.

[0065] The fluorite derived structure obtained in this embodiment is Sc2Zr7O 17 The density of the oxide aerogel is 0.31 g / cm 3 , the specific surface area is 152.64m 2 / g, and thermal conductivity is 0.034W / (m·K).

[0066] Example 3

[0067] This embodiment provides a fluorite-derived structure of La2Ti7O 17 Oxide aerogel and preparation method thereof.

[0068] The crystal structure of the aerogel in this embodiment is La2Ti7O 17 , the rare earth element is lanthanum, and the transition metal element is titanium.

[0069] The preparation method of the fluorite-derived structured oxide aerogel in this embodiment comprises the following steps:

[0070] Step 1: Prepare gel:

[0071] Weigh a rare earth element precursor lanthanum nitrate hexahydrate La(NO3)3·6H2O and a transition metal precursor titanium tetrachloride TiCl4 in a molar ratio of 1:3.5, add them into a mixed solvent of deionized water and anhydrous ethanol in a volume ratio of 1:10, stir in a water bath at 40°C for 30 minutes to form a mixed solution, wherein the total concentration of lanthanum nitrate hexahydrate and titanium tetrachloride in the mixed solution is 10%wt;

[0072] Add glacial acetic acid to the obtained mixed solution at a substance ratio of TiCl4 to CH3COOH of 1:1.5, stir in a water bath at 40°C for 30 minutes, cool to room temperature, add epichlorohydrin to the mixed system cooled to room temperature at a substance ratio of TiCl4 to epichlorohydrin of 1:4, stir for 10 minutes to form gel I;

[0073] Step 2: Aging treatment:

[0074] Soak the gel I obtained in step 1 in anhydrous ethanol, place it in an environment of 45°C, replace the anhydrous ethanol every 12 hours, and replace it 6 times in total to obtain gel II;

[0075] Step 3: Supercritical drying:

[0076] The gel II obtained in step 2 was placed in a supercritical drying reactor, anhydrous ethanol was added to the reactor to soak the gel II, nitrogen was introduced to maintain a pressure of 3.5 MPa, and then the temperature was raised to a drying temperature of 273°C at a heating rate of 4°C / min, the exhaust valve was adjusted to maintain a pressure of 9 MPa, and the temperature and pressure were maintained for 2 hours. After the gas in the reactor was released and cooled to room temperature, the TiO2-La2O3 composite aerogel was obtained;

[0077] Step 4: Heat treatment:

[0078] The TiO2-La2O3 composite aerogel obtained in step 3 was placed in a muffle furnace and heated to a heat treatment temperature of 900°C at a heating rate of 5°C / min. After being kept at this temperature for 60 minutes, a fluorite-derived structure of La2Ti7O 17 of oxide aerogels.

[0079] The fluorite derived structure prepared in this embodiment is La2Ti7O 17 The density of the oxide aerogel is 0.33 g / cm 3 , the specific surface area is 148.72m 2 / g, and thermal conductivity is 0.038W / (m·K).

[0080] Figure 3 , Figure 4 , Figure 5 The SEM images of the fluorite-derived structured oxide aerogels obtained in Example 1, Example 2, and Example 3 respectively show that the examples prepared by the technology of the present invention have a typical rich nanoscale pore structure, which has a high specific surface area and low thermal conductivity and can effectively insulate in a high temperature environment.

Claims

1. A fluorite-derived structural oxide aerogel, characterized in that: The crystal structure of the aerogel is A2B7O 17 , where A is a rare earth element and B is a transition metal element; The steps of the preparation method of the fluorite-derived structured oxide aerogel are as follows: Step 1: Prepare gel: A rare earth element precursor and a transition metal precursor are added to a mixed solvent of deionized water and anhydrous ethanol, and stirred in a water bath to obtain a mixed solution, wherein the rare earth element precursor is a nitrate hydrate of a selected rare earth element; the rare earth element is one of Y, Sc, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb or Lu, and the transition metal element is one of Ti, Zr or Hf; the transition metal precursor is a tetrachloride of a transition metal; the molar ratio of the rare earth element precursor to the transition metal precursor is 1:3.5; the concentration of the transition metal tetrachloride in the mixed solution is 10wt%, glacial acetic acid is added to the mixed solution, stirred in a water bath at 40°C for 30min, and after cooling to room temperature, epichlorohydrin is added, and stirred for 2-10min to obtain gel I; Step 2: Aging treatment: The gel I obtained in step 1 is immersed in anhydrous ethanol, and the anhydrous ethanol is replaced regularly until aging is completed to obtain gel II; Step 3: Supercritical drying: The gel II obtained in step 2 is placed in a supercritical drying device, anhydrous ethanol is added to soak the gel II, nitrogen is introduced, the temperature is increased under a certain pressure, the pressure is increased after the temperature is increased to the drying temperature, and the temperature and pressure are maintained for a certain period of time to obtain a BO2-A2O3 composite aerogel; Step 4: Heat treatment: The BO2-A2O3 composite aerogel obtained in step 3 is placed in a heat treatment device, heated to a heat treatment temperature at a certain rate, and kept at the heat treatment temperature for a certain time to obtain a fluorite-derived structure oxide aerogel.

2. The fluorite-derived structured oxide aerogel according to claim 1, characterized in that: In step 1, the volume ratio of the deionized water to the anhydrous ethanol is 1:10; the added amounts of the glacial acetic acid and the epichlorohydrin are calculated based on the molar ratio of the transition metal precursor, glacial acetic acid and epichlorohydrin of 1:1.5:

4.

3. The fluorite-derived structured oxide aerogel according to claim 2, characterized in that: In step 2, the gel I is immersed in anhydrous ethanol at an ambient temperature of 45° C., and the anhydrous ethanol is replaced regularly every 12 hours, for a total of 6 times.

4. The fluorite-derived structured oxide aerogel according to claim 3, characterized in that: In step 3, the gas pressure during the heating is 3.5 MPa, the heating rate is 4°C / min, the drying temperature is 273°C, the gas pressure is increased by adjusting the nitrogen pressure to 9 MPa, and the heat and pressure holding time is 2h.

5. The fluorite-derived structured oxide aerogel according to claim 4, characterized in that: The heating rate in step 4 is 5-10°C / min, the heat treatment temperature is 900-1200°C, and the insulation time is 30-60min.

6. Use of the fluorite-derived structured oxide aerogel as claimed in claim 1 in thermal insulation of a nuclear reactor.

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