CN112280538B - Whisker toughened phase change heat storage microcapsule and preparation method thereof - Google Patents
Whisker toughened phase change heat storage microcapsule and preparation method thereof Download PDFInfo
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Abstract
The invention relates to a whisker toughened phase-change heat storage microcapsule and a preparation method thereof. The technical scheme is as follows: firstly, washing aluminum or aluminum-silicon alloy powder with an acid solution or an alkali solution and deionized water alternately, and drying; placing in pressurized water vapor, placing in a silica sol precursor, stirring, standing under vacuum condition, adjusting pH value, and filtering; and drying the filtered filter residue, then placing the dried filter residue in a muffle furnace, sintering the dried filter residue in an air atmosphere at 1050-1250 ℃, and naturally cooling the sintered filter residue along with the furnace to obtain the whisker toughened phase-change heat storage microcapsule. The invention has the characteristics of low cost of raw materials, simple preparation process and easy realization of industrial production; the prepared whisker toughened phase change heat storage microcapsule can improve the utilization rate and the utilization efficiency of heat, has high use temperature and long service life, and is suitable for high-temperature heat exchange of solar power plants and industrial furnaces and heat recovery of high-temperature industrial waste gas.
Description
Technical Field
The invention belongs to the technical field of phase change heat storage microcapsules. In particular to a whisker toughening phase change heat storage microcapsule and a preparation method thereof.
Background
The heat storage technology is a technology for storing heat energy by using a heat storage material to store temporarily unnecessary heat and release the heat when the heat is needed. The core of the heat storage technology is the preparation and application of heat storage materials, and the currently commonly used phase-change heat storage materials mainly comprise organic phase-change materials, inorganic phase-change materials, metals and alloys. The metal and the related alloy have the characteristics of large heat conductivity coefficient, high phase change latent heat, stable phase change temperature, small volume change in the phase change process and the like, and are ideal phase change heat storage materials. The Al-Si alloy corrodes containers and equipment after phase change melting, and needs to be effectively packaged to prepare a capsule structure, so that the capsule structure keeps high heat conductivity coefficient, heat storage density and thermal cycle stability, and is one of effective measures for solving the technical bottleneck of phase change heat storage.
Heat-storing capsules can be divided into macro-capsules (diameter larger than 1mm), micro-capsules (diameter 1 μm to 1mm) and nano-capsules (diameter less than 1 μm) according to capsule size (Liu C, Rao Z, ZHao J, et al. Review on nano-encapsulated phase change materials: Preparation, characterization and heat transfer enhancement. Nano Energy,2015,13: 814-. The microcapsule has received wide attention because of its advantages such as the heat-retaining density is big, heat exchange efficiency is high and preparation method is simple. In recent years, some researchers have conducted some studies on aluminum and aluminum-silicon alloys as phase change microcapsules, and have disclosed composite phase change heat storage capsules containing aluminum or aluminum-silicon alloys.
' an Al/Al2O3The heat-storage material and its preparation method (201010127955.5) patent technology, using aluminium powder as raw material, using atomized oxygen atmosphere to make cooling to prepare Al2O3A core-shell type composite phase change heat storage material coated with Al powder. The composite phase change heat storage material with the core-shell structure has high requirements on equipment, the preparation process is complex and difficult to control, and the prepared shell layer is thin, poor in thermal cycle performance and short in service life.
The patent technology of 'a high-temperature phase change heat storage microcapsule based on aluminum-silicon alloy and a preparation method thereof' (CN 108300426A) is characterized in that aluminum-silicon alloy powder, aluminum trichloride and ethyl acetate are mixed according to a proportion, a mixed solution of the aluminum-silicon alloy powder and absolute ethyl alcohol is added under the condition of water bath stirring, a mixed solution of the aluminum-silicon alloy powder and acetic acid is added, and the high-temperature phase change heat storage microcapsule based on the aluminum-silicon alloy is obtained after standing, filtering, washing, drying and sintering. In the literature (Nomura T, Sheng N, Zhu C Y, et al, microencapsulated phase change materials with high heat capacity and high cyclic purity for high-temperature thermal Energy transfer. applied Energy,2017,188:9-18.), an aluminum-silicon alloy powder was placed in boiling water and held for 3 hours, and then fired at 1200 ℃ to prepare alumina-coated aluminum-silicon alloy powder microcapsules. Literature (Cangjuan H, Huazhi G, Meijie Z, et al. thermal properties of Al–Si/Al2O3core-shell particles prepared by using stearic moisture method, journal of Alloys and Compounds,2019:152801) is put into pressurized water vapor for pre-corrosion, and then is sintered at high temperature to prepare the phase change heat storage microcapsule with the same structure and composition. In the method, an alumina shell layer is coated on the surface of aluminum or aluminum-silicon alloy, and the thermal cycle life of the microcapsule is short due to poor thermal shock resistance of alumina, so that the industrial application is limited.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and aims to provide a preparation method of the whisker toughened phase-change heat storage microcapsule, which has the advantages of low raw material cost, simple preparation process and easy industrial production; the whisker toughened phase change heat storage microcapsule prepared by the method can improve the utilization rate and utilization efficiency of heat and has high use temperature.
In order to achieve the purpose, the technical scheme adopted by the invention comprises the following specific steps:
and step one, alternately washing the aluminum powder or the aluminum-silicon alloy powder for 3-10 times by using an acid solution and deionized water, or alternately washing the aluminum powder or the aluminum-silicon alloy powder for 3-10 times by using an alkali solution and deionized water, then placing the washed aluminum powder or the aluminum-silicon alloy powder in a protective atmosphere, and drying for 3-12 h at the temperature of 80-120 ℃ to obtain the surface modified aluminum powder or the aluminum-silicon alloy powder.
And step two, placing the surface modified aluminum powder or aluminum-silicon alloy powder in pressurized steam, and keeping for 10-60 min to obtain the pretreated aluminum powder or aluminum-silicon alloy powder.
Step three, uniformly mixing tetraethoxysilane, absolute ethyl alcohol and water according to the mass ratio of tetraethoxysilane to absolute ethyl alcohol to water of 1 to (0.8-1.5) to (1-2) to prepare the silica sol precursor.
And step four, uniformly mixing the pre-treated aluminum powder or aluminum-silicon alloy powder and the aluminum fluoride according to the mass ratio of the pre-treated aluminum powder or aluminum-silicon alloy powder to the aluminum fluoride of 100 to (0.05-0.2) to obtain mixed powder.
And step five, according to the mass ratio of the silica sol precursor to the mixed powder of 100 to (20-30), placing the mixed powder into the silica sol precursor, stirring for 4-8 h at the temperature of 30-50 ℃, standing for 10-45 min under the condition that the vacuum pressure is 0.1-0.5 MPa, adding alkali to adjust the pH value to 9-11, and standing for 10-30 min to prepare the mixed slurry.
And step six, filtering the mixed slurry, and drying the filtered filter residue at 80-120 ℃ for 6-24 h to obtain the phase change heat storage microcapsule precursor.
Placing the phase change heat storage microcapsule precursor in a muffle furnace in an air atmosphere: heating from room temperature to 550-650 ℃ at the speed of 5-10 ℃/min, heating to 700-800 ℃ at the speed of 10-20 ℃/min, heating to 850-950 ℃ at the speed of 5-8 ℃/min, preserving heat for 3-6 h, heating to 1050-1250 ℃ at the speed of 3-5 ℃/min, and preserving heat for 1-3 h; cooling along with the furnace to obtain the whisker toughened phase change heat storage microcapsule.
The median diameter of the aluminum powder is 28-100 mu m; the Al content is more than 98 wt%.
The median diameter of the aluminum-silicon alloy powder is 28-100 mu m; the Si content in the aluminum-silicon alloy powder is less than 44 wt%, and the Al content is more than 54 wt%.
The acid solution is one of a dilute hydrochloric acid solution, a dilute nitric acid solution and a dilute sulfuric acid solution.
The alkali solution is sodium hydroxide solution or potassium hydroxide solution.
The protective atmosphere is argon or nitrogen.
The gauge pressure of the pressurized steam is 0.01 to 0.7 MPa.
C in the ethyl orthosilicate8H20O4The concentration of Si is more than or equal to 98 percent.
AlF of said aluminum fluoride3The content is more than or equal to 99.2 wt%.
Compared with the prior art, the invention has the following positive effects:
the invention takes aluminum powder or aluminum-silicon alloy powder as raw materials, and has low cost; in the preparation process, aluminum powder or aluminum-silicon alloy powder is alternately washed by acid solution or alkali solution and deionized water and dried; placing the mixture into pressurized steam, and then standing the mixture in a silica sol precursor; and drying the filtered filter residue, then placing the filter residue in a muffle furnace, generating the filter residue in an air atmosphere at 850-1250 ℃, and naturally cooling to obtain the whisker toughened phase change heat storage microcapsule. The preparation process is simple and easy for industrial production.
The invention adopts aluminum powder or aluminum-silicon alloy as the phase-change material, and aluminum in the aluminum powder or aluminum-silicon alloy is an amphoteric substance and is easy to react with water vapor to generate porous aluminum hydroxide. Then the pH value is adjusted to permeate into the nano SiO in the aluminum hydroxide gap2Depositing on the surface of the aluminum hydroxide to form aluminum hydroxide and nano SiO on the surface of the aluminum powder or the aluminum-silicon alloy powder2The initial shell layer of (a). When the melting point of the Al or Al-Si alloy is lower than the melting point in the high-temperature sintering process, part of aluminum hydroxide is decomposed to generate Al2O3The small crystal grains form loose coating on the aluminum powder or the aluminum-silicon alloy powder; continuously raising the temperature, expanding the loose shell layer together with the melt in the alloy melting and expanding process, and roasting O in the atmosphere2Diffusing into the surface of aluminum powder or aluminum-silicon alloy through loose shell layers, and reacting with molten aluminum to generate large-grain Al2O3(ii) a Because the balance of the melting speed of the alloy and the forming and growing speed of crystal grains is controlled, when the alloy is completely melted and fully expanded, Al2O3The small grains and part of the large grains form a complete shell layer which is coated on the surface of the aluminum powder or the aluminum-silicon alloy powder in a timing way; continued increase in temperature, Al2O3The large crystal grains continue to grow to form a rib belt mosaic structure, and part of small crystal grains Al2O3With nano SiO dispersed in the pores of the shell layer2In-situ reacting under the catalytic action of aluminium fluoride to form mullite whisker and its space network, and the rest unreacted small crystal grain Al2O3Then the spherical shear wall is embedded in the spatial network of the mullite whisker texture to form the spherical shear wall. The prepared whisker toughened phase change heat storage microcapsule is in a ribbed embedded shell structure formed by high-temperature sinteringHas high service temperature, good thermal shock stability and thermal cycle performance and long service life.
The mullite whiskers have the advantages of high strength and high heat conductivity coefficient, are distributed in a staggered manner to form a network structure, are inserted among the small-grain alumina, have the effect of a damper and can enhance the cold and heat cycle resistance of a shell layer. The prepared whisker toughened phase-change heat storage microcapsule can effectively prevent the heat storage capsule from leaking after aluminum or aluminum-silicon alloy is melted at high temperature due to shell layer fracture in the preparation or use process, and the aluminum or aluminum-silicon alloy has the characteristics of large heat conductivity coefficient, high phase-change heat and the like, so that the utilization rate and the utilization efficiency of heat can be effectively improved, and the whisker toughened phase-change heat storage microcapsule is suitable for high-temperature heat exchange of solar power plants and industrial furnaces and heat recovery of high-temperature industrial waste gas.
The whisker toughened phase change heat storage microcapsule prepared by the invention is detected as follows: the heat storage density is 136.8-385J/g, the heat conductivity coefficient is 50.5-156.8W/(m & lt K >); performing thermal cycle at 500-800 ℃ for 3000 times; the heat storage density retention rate is more than 85%.
Therefore, the invention has the characteristics of low cost of raw materials, simple preparation process and easy realization of industrial production; the prepared whisker toughened phase change heat storage microcapsule can improve the utilization rate and the utilization efficiency of heat, has high use temperature and long service life, and is suitable for high-temperature heat exchange of solar power plants and industrial furnaces and heat recovery of high-temperature industrial waste gas.
Detailed Description
The invention is further described with reference to specific embodiments, without limiting its scope.
A whisker toughening phase change heat storage microcapsule and a preparation method thereof. The preparation method of the specific embodiment comprises the following steps:
and step one, alternately washing the aluminum powder or the aluminum-silicon alloy powder for 3-10 times by using an acid solution and deionized water, or alternately washing the aluminum powder or the aluminum-silicon alloy powder for 3-10 times by using an alkali solution and deionized water, then placing the washed aluminum powder or the aluminum-silicon alloy powder in a protective atmosphere, and drying for 3-12 h at the temperature of 80-120 ℃ to obtain the surface modified aluminum powder or the aluminum-silicon alloy powder.
And step two, placing the surface modified aluminum powder or aluminum-silicon alloy powder in pressurized steam, and keeping for 10-60 min to obtain the pretreated aluminum powder or aluminum-silicon alloy powder.
Step three, uniformly mixing tetraethoxysilane, absolute ethyl alcohol and water according to the mass ratio of tetraethoxysilane to absolute ethyl alcohol to water of 1 to (0.8-1.5) to (1-2) to prepare the silica sol precursor.
And step four, uniformly mixing the pre-treated aluminum powder or aluminum-silicon alloy powder and the aluminum fluoride according to the mass ratio of the pre-treated aluminum powder or aluminum-silicon alloy powder to the aluminum fluoride of 100 to (0.05-0.2) to obtain mixed powder.
And step five, according to the mass ratio of the silica sol precursor to the mixed powder of 100 to (20-30), placing the mixed powder into the silica sol precursor, stirring for 4-8 h at the temperature of 30-50 ℃, standing for 10-45 min under the condition that the vacuum pressure is 0.1-0.5 MPa, adding alkali to adjust the pH value to 9-11, and standing for 10-30 min to prepare the mixed slurry.
And step six, filtering the mixed slurry, and drying the filtered filter residue at 80-120 ℃ for 6-24 h to obtain the phase change heat storage microcapsule precursor.
Placing the phase change heat storage microcapsule precursor in a muffle furnace in an air atmosphere: heating from room temperature to 550-650 ℃ at the speed of 5-10 ℃/min, heating to 700-800 ℃ at the speed of 10-20 ℃/min, heating to 850-950 ℃ at the speed of 5-8 ℃/min, preserving heat for 3-6 h, heating to 1050-1250 ℃ at the speed of 3-5 ℃/min, and preserving heat for 1-3 h; cooling along with the furnace to obtain the whisker toughened phase change heat storage microcapsule.
The median diameter of the aluminum powder is 28-100 mu m.
The median diameter of the aluminum-silicon alloy powder is 28-100 mu m.
The acid solution is one of a dilute hydrochloric acid solution, a dilute nitric acid solution and a dilute sulfuric acid solution.
The alkali solution is sodium hydroxide solution or potassium hydroxide solution.
The protective atmosphere is argon or nitrogen.
The gauge pressure of the pressurized steam is 0.01 to 0.7 MPa.
The aluminum-silicon alloy powder: the Si content is less than 44 wt%, and the Al content is more than 54 wt%.
In this embodiment:
the Al content of the aluminum powder is more than 98 wt%.
C in the ethyl orthosilicate8H20O4The concentration of Si is more than or equal to 98 percent.
AlF of said aluminum fluoride3The content is more than or equal to 99.2 wt%.
The detailed description is omitted in the embodiments.
Example 1
A whisker toughening phase change heat storage microcapsule and a preparation method thereof. The preparation method in this example is:
and step one, alternately washing the aluminum-silicon alloy powder for 3 times by using an acid solution and deionized water, then placing the washed aluminum-silicon alloy powder in a protective atmosphere, and drying for 3 hours at the temperature of 80 ℃ to obtain the surface modified aluminum-silicon alloy powder.
And step two, placing the surface modified aluminum-silicon alloy powder in pressurized steam, and keeping for 10min to obtain the pretreated aluminum-silicon alloy powder.
Step three, uniformly mixing tetraethoxysilane, absolute ethyl alcohol and water according to the mass ratio of tetraethoxysilane, absolute ethyl alcohol and water of 1: 0.8: 1 to prepare the silica sol precursor.
And step four, uniformly mixing the pre-treated aluminum-silicon alloy powder and the aluminum fluoride according to the mass ratio of the pre-treated aluminum-silicon alloy powder to the aluminum fluoride of 100: 0.05 to obtain mixed powder.
And step five, according to the mass ratio of the silica sol precursor to the mixed powder of 100: 30, placing the mixed powder into the silica sol precursor, stirring for 4 hours at the temperature of 30 ℃, standing for 10 minutes under the vacuum pressure of 0.1MPa, adding alkali to adjust the pH value to 9, and standing for 10 minutes to obtain the mixed slurry.
And step six, filtering the mixed slurry, and drying the filtered filter residue at 80 ℃ for 6 hours to obtain the phase change heat storage microcapsule precursor.
Placing the phase change heat storage microcapsule precursor in a muffle furnace in an air atmosphere: heating from room temperature to 550 ℃ at the speed of 10 ℃/min, heating to 700 ℃ at the speed of 20 ℃/min, heating to 850 ℃ at the speed of 5 ℃/min, preserving heat for 5h, heating to 1050 ℃ at the speed of 5 ℃/min, and preserving heat for 1 h; cooling along with the furnace to obtain the whisker toughened phase change heat storage microcapsule.
The aluminum-silicon alloy powder: the Si content is 38 wt%, and the Al content is 60 wt%; the median diameter of the aluminum-silicon alloy powder is 28 mu m.
The acid solution is a dilute hydrochloric acid solution.
The protective atmosphere is argon.
The gauge pressure of the pressurized steam was 0.01 MPa.
Example 2
A whisker toughening phase change heat storage microcapsule and a preparation method thereof. The preparation method in this example is:
and step one, alternately washing the aluminum-silicon alloy powder for 5 times by using an acid solution and deionized water, then placing the washed aluminum-silicon alloy powder in a protective atmosphere, and drying for 5 hours at the temperature of 90 ℃ to obtain the surface modified aluminum-silicon alloy powder.
And step two, placing the surface modified aluminum-silicon alloy powder in pressurized steam, and keeping for 30min to obtain the pretreated aluminum-silicon alloy powder.
Step three, uniformly mixing tetraethoxysilane, absolute ethyl alcohol and water according to the mass ratio of tetraethoxysilane to absolute ethyl alcohol to water of 1: 1.5 to prepare the silica sol precursor.
And step four, uniformly mixing the pre-treated aluminum-silicon alloy powder and the aluminum fluoride according to the mass ratio of the pre-treated aluminum-silicon alloy powder to the aluminum fluoride of 100: 0.08 to obtain mixed powder.
And step five, according to the mass ratio of the silica sol precursor to the mixed powder of 100: 30, placing the mixed powder into the silica sol precursor, stirring for 6 hours at 40 ℃, standing for 20 minutes under the condition that the vacuum pressure is 0.2MPa, adding alkali to adjust the pH value to 10, and standing for 20 minutes to obtain the mixed slurry.
And step six, filtering the mixed slurry, and drying the filtered filter residue at 90 ℃ for 10 hours to obtain the phase change heat storage microcapsule precursor.
Placing the phase change heat storage microcapsule precursor in a muffle furnace in an air atmosphere: heating from room temperature to 600 ℃ at the speed of 6 ℃/min, heating to 730 ℃ at the speed of 15 ℃/min, heating to 880 ℃ at the speed of 7 ℃/min, preserving heat for 3h, heating to 1100 ℃ at the speed of 5 ℃/min, and preserving heat for 2 h; cooling along with the furnace to obtain the whisker toughened phase change heat storage microcapsule.
The aluminum-silicon alloy powder: the Si content was 34 wt%, the Al content was 65 wt%; the median diameter of the aluminum-silicon alloy powder is 50 mu m.
The acid solution is a dilute nitric acid solution.
The protective atmosphere is argon atmosphere.
The gauge pressure of the pressurized steam was 0.08 MPa.
Example 3
A whisker toughening phase change heat storage microcapsule and a preparation method thereof. The preparation method in this example is:
and step one, alternately washing the aluminum-silicon alloy powder for 6 times by using an acid solution and deionized water, then placing the washed aluminum-silicon alloy powder in a protective atmosphere, and drying for 10 hours at the temperature of 100 ℃ to obtain the surface modified aluminum-silicon alloy powder.
And step two, placing the surface modified aluminum-silicon alloy powder in pressurized steam, and keeping for 50min to obtain the pretreated aluminum-silicon alloy powder.
Step three, uniformly mixing tetraethoxysilane, absolute ethyl alcohol and water according to the mass ratio of tetraethoxysilane to absolute ethyl alcohol to water of 1: 1.5: 2 to prepare the silica sol precursor.
And step four, uniformly mixing the pre-treated aluminum-silicon alloy powder and the aluminum fluoride according to the mass ratio of the pre-treated aluminum-silicon alloy powder to the aluminum fluoride of 100: 0.1 to obtain mixed powder.
And step five, according to the mass ratio of the silica sol precursor to the mixed powder of 100: 28, placing the mixed powder into the silica sol precursor, stirring for 5 hours at the temperature of 45 ℃, standing for 30 minutes under the vacuum pressure of 0.4MPa, adding alkali to adjust the pH value to 11, and standing for 20 minutes to obtain the mixed slurry.
And step six, filtering the mixed slurry, and drying the filtered filter residue for 15 hours at the temperature of 100 ℃ to obtain the phase change heat storage microcapsule precursor.
Placing the phase change heat storage microcapsule precursor in a muffle furnace in an air atmosphere: firstly heating from room temperature to 600 ℃ at the speed of 5 ℃/min, then heating to 750 ℃ at the speed of 10 ℃/min, then heating to 900 ℃ at the speed of 6 ℃/min, preserving heat for 5h, finally heating to 1200 ℃ at the speed of 4 ℃/min, and preserving heat for 2 h; cooling along with the furnace to obtain the whisker toughened phase change heat storage microcapsule.
The aluminum-silicon alloy powder: si content of 20 wt% and Al content of 77 wt%; the median diameter of the aluminum-silicon alloy powder is 67 mu m.
The acid solution is a dilute sulfuric acid solution.
The protective atmosphere is a nitrogen atmosphere.
The gauge pressure of the pressurized steam was 0.3 MPa.
Example 4
A whisker toughening phase change heat storage microcapsule and a preparation method thereof. The preparation method in this example is:
step one, alternately washing the aluminum-silicon alloy powder with an alkali solution and deionized water for 8 times, then placing the washed aluminum-silicon alloy powder in a protective atmosphere, and drying for 8 hours at the temperature of 110 ℃ to obtain the surface modified aluminum-silicon alloy powder.
And step two, placing the surface modified aluminum-silicon alloy powder in pressurized steam, and keeping for 40min to obtain the pretreated aluminum-silicon alloy powder.
Step three, uniformly mixing tetraethoxysilane, absolute ethyl alcohol and water according to the mass ratio of tetraethoxysilane to absolute ethyl alcohol to water of 1: 1.2: 1.5 to prepare the silica sol precursor.
And step four, uniformly mixing the pre-treated aluminum-silicon alloy powder and the aluminum fluoride according to the mass ratio of the pre-treated aluminum-silicon alloy powder to the aluminum fluoride of 100: 0.15 to obtain mixed powder.
And step five, according to the mass ratio of the silica sol precursor to the mixed powder of 100: 22, placing the mixed powder into the silica sol precursor, stirring for 7 hours at 48 ℃, standing for 40 minutes under the condition that the vacuum pressure is 0.3MPa, adding alkali to adjust the pH value to 10, and standing for 25 minutes to obtain the mixed slurry.
And step six, filtering the mixed slurry, and drying the filtered filter residue for 20 hours at the temperature of 110 ℃ to obtain the phase change heat storage microcapsule precursor.
Placing the phase change heat storage microcapsule precursor in a muffle furnace in an air atmosphere: firstly heating from room temperature to 650 ℃ at the speed of 8 ℃/min, then heating to 800 ℃ at the speed of 13 ℃/min, then heating to 950 ℃ at the speed of 8 ℃/min, preserving heat for 4h, finally heating to 1250 ℃ at the speed of 3 ℃/min, and preserving heat for 2 h; cooling along with the furnace to obtain the whisker toughened phase change heat storage microcapsule.
The aluminum-silicon alloy powder: the Si content is 18 wt%, and the Al content is 80 wt%; the median diameter of the aluminum-silicon alloy powder is 80 mu m.
The alkali solution is potassium hydroxide solution.
The protective atmosphere is a nitrogen atmosphere.
The gauge pressure of the pressurized steam was 0.5 MPa.
Example 5
A whisker toughening phase change heat storage microcapsule and a preparation method thereof. The preparation method in this example is:
and step one, alternately washing the aluminum-silicon alloy powder for 10 times by using an alkali solution and deionized water, then placing the washed aluminum-silicon alloy powder in a protective atmosphere, and drying for 12 hours at 120 ℃ to obtain the surface-modified aluminum-silicon alloy powder.
And step two, placing the surface modified aluminum-silicon alloy powder in pressurized steam, and keeping for 60min to obtain the pretreated aluminum-silicon alloy powder.
Step three, uniformly mixing tetraethoxysilane, absolute ethyl alcohol and water according to the mass ratio of tetraethoxysilane to absolute ethyl alcohol to water of 1: 1.5: 2 to prepare the silica sol precursor.
And step four, uniformly mixing the pre-treated aluminum-silicon alloy powder and the aluminum fluoride according to the mass ratio of the pre-treated aluminum-silicon alloy powder to the aluminum fluoride of 100: 0.2 to obtain mixed powder.
And step five, according to the mass ratio of the silica sol precursor to the mixed powder of 100: 20, placing the mixed powder into the silica sol precursor, stirring for 8 hours at 50 ℃, standing for 45 minutes under the condition that the vacuum pressure is 0.5MPa, adding alkali to adjust the pH value to 11, and standing for 30 minutes to obtain the mixed slurry.
And step six, filtering the mixed slurry, and drying the filtered filter residue for 24 hours at the temperature of 120 ℃ to obtain the phase change heat storage microcapsule precursor.
Placing the phase change heat storage microcapsule precursor in a muffle furnace in an air atmosphere: firstly heating from room temperature to 650 ℃ at the speed of 9 ℃/min, then heating to 780 ℃ at the speed of 18 ℃/min, then heating to 930 ℃ at the speed of 8 ℃/min, preserving heat for 6h, finally heating to 1250 ℃ at the speed of 3 ℃/min, and preserving heat for 3 h; cooling along with the furnace to obtain the whisker toughened phase change heat storage microcapsule.
The aluminum-silicon alloy powder: si content of 4 wt%, Al content of 95 wt%; the median diameter of the aluminum-silicon alloy powder is 100 mu m.
The alkali solution is sodium hydroxide solution.
The protective atmosphere is argon atmosphere.
The gauge pressure of the pressurized steam was 0.7 MPa.
Example 6
A whisker toughening phase change heat storage microcapsule and a preparation method thereof. The process is the same as example 1 except that the aluminum-silicon alloy powder is aluminum powder.
Example 7
A whisker toughening phase change heat storage microcapsule and a preparation method thereof. The process is the same as that of example 2 except that the aluminum-silicon alloy powder is aluminum powder.
Example 8
A whisker toughening phase change heat storage microcapsule and a preparation method thereof. The process is the same as example 3 except that the aluminum-silicon alloy powder is aluminum powder.
Example 9
A whisker toughening phase change heat storage microcapsule and a preparation method thereof. The process is the same as example 4 except that the aluminum-silicon alloy powder is aluminum powder.
Example 10
A whisker toughening phase change heat storage microcapsule and a preparation method thereof. The process is the same as example 5 except that the aluminum-silicon alloy powder is aluminum powder.
Compared with the prior art, the specific implementation mode has the following positive effects:
the specific embodiment takes the aluminum powder or the aluminum-silicon alloy powder as the raw material, so the cost is low; in the preparation process, aluminum powder or aluminum-silicon alloy powder is alternately washed by acid solution or alkali solution and deionized water and dried; placing the mixture into pressurized steam, and then standing the mixture in a silica sol precursor; and drying the filtered filter residue, then placing the filter residue in a muffle furnace, generating the filter residue in an air atmosphere at 850-1250 ℃, and naturally cooling to obtain the whisker toughened phase change heat storage microcapsule. The preparation process is simple and easy for industrial production.
In the specific embodiment, aluminum powder or aluminum-silicon alloy is adopted as the phase-change material, aluminum in the aluminum powder or aluminum-silicon alloy is an amphoteric substance and is easy to react with water vapor to generate porous aluminum hydroxide, and when the aluminum powder or aluminum-silicon alloy powder with the treated surfaces is placed in a silica sol precursor, solution molecules can easily permeate into the porous aluminum hydroxide to the surface of the aluminum powder or aluminum-silicon alloy powder under the vacuum condition because the silica sol precursor is liquid. Then the pH value is adjusted to permeate into the nano SiO in the aluminum hydroxide gap2Depositing on the surface of the aluminum hydroxide to form aluminum hydroxide and nano SiO on the surface of the aluminum powder or the aluminum-silicon alloy powder2The initial shell layer of (a). When the melting point of the Al or Al-Si alloy is lower than the melting point in the high-temperature sintering process, part of aluminum hydroxide is decomposed to generate Al2O3The small crystal grains form loose coating on the aluminum powder or the aluminum-silicon alloy powder; continuously raising the temperature, expanding the loose shell layer together with the melt in the alloy melting and expanding process, and roasting O in the atmosphere2Diffusing into the surface of aluminum powder or aluminum-silicon alloy through loose shell layers, and reacting with molten aluminum to generate large-grain Al2O3(ii) a Because the balance of the melting speed of the alloy and the forming and growing speed of crystal grains is controlled, when the alloy is completely melted and fully expanded, Al2O3The small grains and part of the large grains form a complete shell layer which is coated on the surface of the aluminum powder or the aluminum-silicon alloy powder in a timing way; continued increase in temperature, Al2O3The large crystal grains continue to grow to form a rib belt mosaic structure, and part of small crystal grains Al2O3With nano SiO dispersed in the pores of the shell layer2In-situ reacting under the catalytic action of aluminium fluoride to form mullite whisker and its space network, and the rest unreacted small crystal grain Al2O3Then the spherical shear wall is embedded in the spatial network of the mullite whisker texture to form the spherical shear wall. The prepared whisker toughened phase change heat storage microcapsule has high use temperature, good thermal shock stability and thermal cycle performance and long service life.
The mullite whiskers have the advantages of high strength and high heat conductivity coefficient, are distributed in a staggered manner to form a network structure, are inserted among the small-grain alumina, have the effect of a damper and can enhance the cold and heat cycle resistance of a shell layer. The prepared whisker toughened phase-change heat storage microcapsule can effectively prevent the heat storage capsule from leaking after aluminum or aluminum-silicon alloy is melted at high temperature due to shell layer fracture in the preparation or use process, and the aluminum or aluminum-silicon alloy has the characteristics of large heat conductivity coefficient, high phase-change heat and the like, so that the utilization rate and the utilization efficiency of heat can be effectively improved, and the whisker toughened phase-change heat storage microcapsule is suitable for high-temperature heat exchange of solar power plants and industrial furnaces and heat recovery of high-temperature industrial waste gas.
The whisker toughened phase change heat storage microcapsule prepared by the embodiment is detected as follows: the heat storage density is 136.8-385J/g, the heat conductivity coefficient is 50.5-156.8W/(m & lt K >); performing thermal cycle at 500-800 ℃ for 3000 times; the heat storage density retention rate is more than 85%.
Therefore, the specific implementation mode has the characteristics of low raw material cost, simple preparation process and easy realization of industrial production; the prepared whisker toughened phase change heat storage microcapsule can improve the utilization rate and the utilization efficiency of heat, has high use temperature and long service life, and is suitable for high-temperature heat exchange of solar power plants and industrial furnaces and heat recovery of high-temperature industrial waste gas.
Claims (10)
1. A preparation method of whisker toughening phase change heat storage microcapsules is characterized by comprising the following steps:
step one, alternately washing aluminum powder or aluminum-silicon alloy powder for 3-10 times by using an acid solution and deionized water, or alternately washing the aluminum powder or the aluminum-silicon alloy powder for 3-10 times by using an alkali solution and deionized water, then placing the washed aluminum powder or the aluminum-silicon alloy powder in a protective atmosphere, and drying for 3-12 h at the temperature of 80-120 ℃ to obtain surface-modified aluminum powder or aluminum-silicon alloy powder;
placing the surface-modified aluminum powder or aluminum-silicon alloy powder into pressurized steam, and keeping for 10-60 min to obtain pre-treated aluminum powder or aluminum-silicon alloy powder;
step three, uniformly mixing tetraethoxysilane, absolute ethyl alcohol and water according to the mass ratio of tetraethoxysilane to absolute ethyl alcohol to water of 1 to (0.8-1.5) to (1-2) to prepare a silica sol precursor;
step four, uniformly mixing the pre-treated aluminum powder or aluminum-silicon alloy powder and aluminum fluoride according to the mass ratio of the pre-treated aluminum powder or aluminum-silicon alloy powder to the aluminum fluoride of 100 to (0.05-0.2) to obtain mixed powder;
fifthly, according to the mass ratio of the silica sol precursor to the mixed powder of 100 to (20-30), placing the mixed powder into the silica sol precursor, stirring for 4-8 h at 30-50 ℃, standing for 10-45 min under the condition that the vacuum pressure is 0.1-0.5 MPa, adding alkali to adjust the pH value to 9-11, and standing for 10-30 min to prepare mixed slurry;
filtering the mixed slurry, and drying the filtered filter residue at the temperature of 80-120 ℃ for 6-24 hours to obtain a phase change heat storage microcapsule precursor;
placing the phase change heat storage microcapsule precursor in a muffle furnace in an air atmosphere: heating from room temperature to 550-650 ℃ at the speed of 5-10 ℃/min, heating to 700-800 ℃ at the speed of 10-20 ℃/min, heating to 850-950 ℃ at the speed of 5-8 ℃/min, preserving heat for 3-6 h, heating to 1050-1250 ℃ at the speed of 3-5 ℃/min, and preserving heat for 1-3 h; cooling along with the furnace to obtain the whisker toughened phase change heat storage microcapsule.
2. The preparation method of the whisker toughened phase-change heat storage microcapsule according to claim 1, wherein the median diameter of the aluminum powder is 28-100 μm; the Al content is more than 98 wt%.
3. The preparation method of the whisker toughened phase-change heat storage microcapsule according to claim 1, wherein the median diameter of the aluminum-silicon alloy powder is 28-100 μm; the Si content in the aluminum-silicon alloy powder is less than 44 wt%, and the Al content is more than 54 wt%.
4. The method for preparing whisker toughened phase-change heat storage microcapsules according to claim 1, wherein the acid solution is one of a dilute hydrochloric acid solution, a dilute nitric acid solution and a dilute sulfuric acid solution.
5. The preparation method of the whisker toughened phase-change heat storage microcapsule according to claim 1, wherein the alkali solution is a sodium hydroxide solution or a potassium hydroxide solution.
6. The method for preparing the whisker toughened phase-change heat storage microcapsule according to claim 1, wherein the protective atmosphere is argon or nitrogen.
7. The preparation method of the whisker toughened phase-change heat storage microcapsule according to claim 1, wherein the gauge pressure of the pressurized water vapor is 0.01 to 0.7 MPa.
8. The method for preparing whisker toughened phase-change heat storage microcapsule according to claim 1, wherein C in the tetraethoxysilane8H20O4The concentration of Si is more than or equal to 98 percent.
9. The method for preparing whisker toughened phase-change heat storage microcapsule according to claim 1, wherein the AlF of the aluminum fluoride3The content is more than or equal to 99.2 wt%.
10. A whisker toughened phase-change heat storage microcapsule, which is characterized by being prepared by the preparation method of the whisker toughened phase-change heat storage microcapsule according to any one of claims 1 to 9.
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