Thermal storage ceramics, composite thermal storage materials and preparation methods for encapsulating energy storage PCM

Abstract

The present invention relates to a thermal storage ceramic, composite thermal storage material, and preparation method for encapsulating energy storage PCM. The thermal storage ceramic has honeycomb pores for encapsulating phase change material. The raw materials of the thermal storage ceramic include a base powder and an admixture accounting for 5-10% of the total mass of the base powder. The base powder comprises 75-96% alumina and 4-25% kaolin. The admixture is a micro-nanoscale magnesium oxide-yttrium oxide composite powder with a core-shell structure, prepared by flame spray pyrolysis of magnesium and yttrium sources. The present invention uses yttrium oxide-magnesium oxide powder with a core-shell structure to promote the densification of the ceramic matrix and improve the thermal conductivity of the encapsulated matrix. The ceramic encapsulated matrix of the present invention has the advantages of high heat storage density, high thermal conductivity, and good long-term thermal shock resistance. The thermal storage ceramic obtained by encapsulating the phase change material has the advantages of a wide operating temperature range and can meet the requirements of multi-stage temperature zone heat storage and heat release.

Description

Technical Field

[0001] The present invention relates to the field of new energy storage materials, and in particular to a heat storage ceramic for encapsulating energy storage PCM, a composite heat storage material and a preparation method thereof. Background Art

[0002] Solar high-temperature thermal power generation technology converts solar energy into high-temperature heat, which is then converted into electricity. This technology system includes concentrating solar heat, heat storage, and power generation systems. The heat storage system stores the collected solar heat and steadily releases it in the absence of sunlight to maintain system stability and continuity. Because the heat storage system must operate efficiently and stably at high temperatures for a long time, the materials used to store heat must not only have high heat storage density and high thermal conductivity, but also exhibit excellent resistance to high temperatures, corrosion, and thermal shock.

[0003] Sensible and latent heat composite thermal storage materials composed of ceramics, molten salts, and alloys have the advantages of high heat storage density, high operating temperature, and long service life. They have become one of the research hotspots in the field of solar high-temperature thermal utilization. The Chinese invention patent "A composite phase change thermal storage material and its preparation method" (CN202011497616.6) uses talc, sillimanite, and alumina as matrix materials, and nitrates, carbonates, and chlorides as phase change materials (PCM). After sintering at 1300-1500°C, the ceramic composite phase change thermal storage material is obtained. The system has a heat storage density of 647-835 kJ / kg and a thermal conductivity of 5.7-7.3 W (m·K). -1 , the operating temperature is 250-450°C; China's invention patent "A composite phase change heat storage capsule and its preparation method" (CN202211509511.7) uses KCl-Na2SO4 eutectic salt as a composite phase change heat storage material and modified alumina ceramic as a shell layer. The composite heat storage material is sintered at 700-720°C. The system has a heat storage density of 220.6kJ / kg and an operating temperature of 522°C; China's invention patent "A preparation method and use of Al2O3-Al composite packaging material" (CN202210601520.2) uses aluminum powder, alumina powder, and CuO-TiO2 powder as raw materials. The Al2O3-Al composite packaging material is sintered at 750-850°C to encapsulate Al-12Si-Sr alloy. The heat storage density of the prepared heat storage system is 179.58kJ / kg and the room temperature thermal conductivity is 13.48W (m·K) -1 , operating temperature is less than 800℃.

[0004] The packaging materials used in the above-mentioned patents have problems such as low heat storage density, low thermal conductivity, and poor thermal shock resistance of the packaging matrix, resulting in low heat storage / release cycle efficiency of the energy storage system and a short service life of the system, which cannot meet the demand for high-performance heat storage systems in actual applications. Summary of the Invention

[0005] The purpose of the present invention is to overcome the above technical deficiencies and provide a thermal storage ceramic, a composite thermal storage material and a preparation method for encapsulating energy storage PCM, so as to solve the technical problems of low thermal storage density or poor thermal shock resistance of thermal storage ceramics in the prior art.

[0006] In order to achieve the above technical objectives, the technical solution provided by the present invention is:

[0007] In a first aspect, the present invention provides a heat storage ceramic for encapsulating energy storage PCM, the heat storage ceramic having honeycomb pores for encapsulating phase change materials; the raw materials of the heat storage ceramic include a base powder and an admixture accounting for 5 to 10% of the total mass of the base powder; wherein, in terms of mass percentage, the base powder includes 75 to 96% alumina and 4 to 25% kaolin; the admixture is a micro-nanoscale magnesium oxide-yttrium oxide composite powder with a core-shell structure prepared by flame spray pyrolysis of a precursor solution prepared by adding a magnesium source and a yttrium source to a solvent.

[0008] In a second aspect, the present invention provides a method for preparing a heat storage ceramic for encapsulating energy storage PCM, comprising the following steps: S1, adding a magnesium source and a yttrium source to a solvent to prepare a precursor solution, and preparing a micro-nanoscale magnesium oxide-yttrium oxide composite powder with a core-shell structure as an additive from the precursor solution by flame spray pyrolysis; S2, uniformly mixing the additive with the base powder to obtain a mixed powder; S3, forming and shaping the mixed powder into a green body to obtain a ceramic green body with honeycomb holes; S4, drying the ceramic green body and sintering it to obtain a heat storage ceramic for encapsulating energy storage PCM.

[0009] In a third aspect, the present invention provides a composite heat storage material encapsulating energy storage PCM, using the above-mentioned heat storage ceramic as a ceramic encapsulation matrix, wherein a phase change material is encapsulated in the ceramic encapsulation matrix, and the phase change material occupies 40-60% of the honeycomb pore volume.

[0010] In a fourth aspect, the present invention provides a method for preparing a composite heat storage material encapsulating an energy storage PCM, comprising the following steps: first, sealing one end of a ceramic packaging substrate with a high-temperature packaging adhesive, then loading a phase change material into the honeycomb pores of the ceramic packaging substrate at 1150-1250°C; and finally, sealing the other end of the ceramic packaging substrate with a high-temperature packaging adhesive to obtain a composite heat storage material.

[0011] Compared with the prior art, the present invention has the following beneficial effects:

[0012] The present invention adopts yttrium oxide-magnesium oxide powder with a core-shell structure as an additive, which can, on the one hand, act as a sintering aid to promote the densification of the ceramic matrix, and on the other hand, effectively improve the thermal conductivity of the packaging matrix; at the same time, the ceramic packaging matrix prepared by the present invention has a corundum-mullite multiphase structure, and in particular, the second phase mullite and other structures therein have the effect of toughening and improving thermal shock resistance; therefore, the ceramic packaging matrix has the advantages of high heat storage density, high thermal conductivity, and good long-term thermal shock resistance; the heat storage ceramic obtained by encapsulating the phase change material has the advantages of a wide operating temperature range and can meet the requirements of multi-stage temperature zone heat storage / release. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 This is an SEM image of the yttrium oxide-magnesium oxide composite powder prepared by the present invention;

[0014] Figure 2 This is a cross-sectional SEM image of the ceramic package substrate prepared by the present invention;

[0015] Figure 3 is the XRD spectrum of the corundum-mullite based ceramic packaging matrix;

[0016] Figure 4 Schematic diagram of a corundum-mullite-based ceramic packaging substrate and its encapsulated PCM. DETAILED DESCRIPTION

[0017] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0018] This invention provides a thermal storage ceramic encapsulating a multi-stage coupled energy storage PCM and its preparation method. This coupled energy transmission system, formed by the interaction of multiple phase-change materials, addresses the problems of existing energy storage systems, such as low operating temperatures, narrow operating temperature ranges, low heat storage / release cycle efficiency, low heat storage density of the encapsulation matrix and phase-change materials, low thermal conductivity, poor thermal shock resistance, and short lifespan. The invention develops a multi-stage coupled heat storage / release system that meets the requirements of next-generation energy storage, as well as a thermal storage material with high heat storage density, high thermal conductivity, excellent thermal shock resistance, and a long lifespan.

[0019] In a first aspect, the present invention provides a thermal storage ceramic for encapsulating an energy storage PCM, wherein the thermal storage ceramic has honeycomb pores for encapsulating a phase change material;

[0020] The raw materials for ceramic packaging include a base powder and an admixture accounting for 5 to 10% of the total mass of the base powder; wherein, by mass percentage, the base powder includes 75 to 96% alumina and 4 to 25% kaolin, preferably 75 to 85% alumina and 15 to 25% kaolin;

[0021] The additive is prepared by adding magnesium source and yttrium source into solvent to prepare precursor solution, and then preparing micro-nano magnesium oxide-yttrium oxide composite phase powder with core-shell structure through flame spray pyrolysis method.

[0022] Preferably, the heat storage ceramic is a corundum-mullite based heat storage ceramic, wherein the particle size of the corundum particles is 2 to 4.5 μm, and the particle size of the mullite particles is 4 to 5.5 μm.

[0023] Preferably, the alumina is industrial grade α-Al2O3 and the kaolin is Longyan kaolin.

[0024] Preferably, the magnesium source is magnesium nitrate, the yttrium source is yttrium nitrate, and the solvent is ethanol; in terms of mass percentage, the precursor solution includes 15-30% yttrium nitrate, 25-40% magnesium nitrate, and 30-60% ethanol.

[0025] In a second aspect, the present invention provides a method for preparing a thermal storage ceramic for encapsulating an energy storage PCM, comprising the following steps:

[0026] S1, powder preparation: including precursor preparation and composite powder preparation; specifically, a magnesium source and a yttrium source are added to a solvent to prepare a precursor solution, and the precursor solution is flame spray pyrolysis to prepare a micro-nanoscale magnesium oxide-yttrium oxide composite powder with a core-shell structure as an admixture;

[0027] S2, raw material preparation: mainly includes mixing raw materials; specifically, mixing the admixture and the base powder in proportion to obtain a mixed powder;

[0028] S3, green body forming: the mixed powder is subjected to green body forming (including green body plasticization and green body forming) and shaping to obtain a ceramic green body with honeycomb pores;

[0029] S4, ceramic preparation: the ceramic green body is dried and then sintered at a sintering temperature not higher than 1650° C. to obtain a heat storage ceramic for encapsulating the energy storage PCM.

[0030] Preferably, in the flame spray pyrolysis method of step S1, methane is used as the combustion-supporting gas to atomize and ignite the precursor solution, the effective sintering height of the flame is 25-35 cm, and the effective sintering temperature range is 900-1100°C.

[0031] Preferably, in step S2, after the admixture is mixed with the base powder, the admixture is placed in a high-energy ball mill and ground for 15 to 30 minutes to mix them uniformly.

[0032] Preferably, in step S3, the green body forming includes mud kneading, aging, extrusion molding and cutting; wherein the mud kneading is carried out in a vacuum mud kneader; and the aging time is 24 to 48 hours.

[0033] Further preferably, the mud kneading is to sieve the mixed powder, add a certain amount of binder solution, and use a vacuum mud kneading machine to knead the mud; wherein the mesh number of the sieve is 100-200 mesh, PVA is used as the binder, and the amount of binder solution added is 3-8wt% of the total mass of the mixed powder after sieving.

[0034] More preferably, the extrusion molding and cutting process involves extruding the aged clay through an extruder and then cutting it to form a honeycomb-shaped encapsulated ceramic body with increasing pore diameters from the inside out, wherein the extruder pressure is 3 to 5 MPa. More preferably, the honeycomb pores have a pore diameter range of 5 to 25 cm, a pore size ratio range of 1:1 to 5:1, a porosity of 60 to 85%, and a body height of 30 to 50 cm.

[0035] It is understood that the shape of the honeycomb holes in the present invention can be circular holes or polygonal holes, such as square, pentagonal or hexagonal holes, and the specific shape can be selected according to the situation; the aperture or side length of the honeycomb holes ranges from 5 to 25 cm.

[0036] Further preferably, the honeycomb holes are distributed in concentric circles around the axis of the ceramic packaging substrate.

[0037] Preferably, in step S3, microwave shaping is used for shaping, the power of microwave shaping is 2-6 kW, the frequency is 2200-2600 MHz, and the microwave shaping time is 15-20 min.

[0038] Preferably, in step S4, drying is carried out at 80-100° C. for 18-22 hours.

[0039] Preferably, in step S4, sintering includes a heating process, a heat preservation process and a cooling process, wherein the heating process refers to heating from room temperature to 1550-1650°C; the heat preservation process is to keep the temperature at 1550-1650°C for 1-3 hours; the cooling process refers to from the highest temperature to 1150-1250°C, and the material is packaged at 1150-1250°C.

[0040] Further preferably, during the heating process, the heating rate from room temperature to 1000°C is 5-8°C / min, and the heating rate from 1000°C to the maximum temperature is 3-5°C / min; the cooling rate during the cooling process is 5-8°C / min; and during the heating process, when the temperature is less than 1000°C, the temperature is kept warm for 20-30 minutes per 100°C, and when the temperature is ≥1000°C, the temperature is kept warm for 30-60 minutes per 100°C.

[0041] In a third aspect, the present invention provides a composite heat storage material encapsulating energy storage PCM, using the above-mentioned heat storage ceramic as a ceramic encapsulation matrix, in which a phase change material is encapsulated, and the phase change material occupies 40-60% of the honeycomb pore volume.

[0042] Preferably, the pore size of the honeycomb holes on the ceramic packaging substrate ranges from 5 to 25 cm, and the porosity is 60 to 85%; along the radial direction of the cross section of the ceramic packaging substrate from the outside to the inside, the honeycomb holes are evenly distributed and the pore size increases successively or the adjacent pore size is equal. When there are multiple types of phase change materials encapsulated, the phase change temperature of the phase change materials increases successively or is equal.

[0043] Preferably, the encapsulated phase change material includes one or more of (59.5-53.5wt%) MgCl2-(46.5-40.5wt%) NaCl, (80-70wt%) Al-(30-20wt%) Si, (60-50wt%) Mg2Si-(50-40wt%) Si and 100wt% Na2O.

[0044] In a fourth aspect, the present invention provides a method for preparing a composite heat storage material encapsulating energy storage PCM. First, a high-temperature encapsulation adhesive is used to seal one end of a ceramic encapsulation substrate. Then, a phase change material is loaded into the honeycomb pores of the ceramic encapsulation substrate at 1150-1250°C. Finally, a high-temperature encapsulation adhesive is used to seal the other end of the ceramic encapsulation substrate to obtain a composite heat storage material.

[0045] Further preferably, the packaging specifically includes: placing molten salts and alloys with different melting points into the honeycomb holes of a ceramic packaging substrate with one end closed in sequence according to their heat storage capacity, and then using a high-temperature packaging adhesive to seal the other end of the honeycomb holes on the ceramic packaging substrate.

[0046] Preferably, the high-temperature packaging adhesive comprises, by mass fraction, 20-23 wt % of aluminum dihydrogen phosphate, 10-17 wt % of β-Al 2 O 3 , 20-25 wt % of silicon powder, and 35-50 wt % of water.

[0047] The main mechanism of action and advantages of the present invention include:

[0048] (1) The corundum-mullite composite ceramic packaging matrix prepared by the present invention has the advantages of high heat storage density, high thermal conductivity, and good thermal shock resistance. The reason why the ceramic packaging matrix has high heat storage density and high thermal conductivity is related to the yttrium oxide-magnesium oxide powder with a core-shell structure. On the one hand, during the ceramic sintering process, yttrium oxide-magnesium oxide acts as a sintering aid to promote the densification process of the ceramic matrix. On the other hand, the core-shell coating effect of the high thermal conductivity yttrium oxide-magnesium oxide can effectively improve the thermal conductivity of the packaging matrix. The second phase mullite contained in the ceramic packaging matrix not only has an important toughening effect on the matrix, but also makes the matrix have high thermal shock resistance in the long-term heat storage-release cycle.

[0049] (2) The multi-stage coupled heat storage / release system prepared by the present invention has a wide operating temperature range, and the energy storage system can meet the advantages of multi-stage temperature zone heat storage / release. Since the system uses molten salts and alloys with high phase change latent heat and different melting points such as MgCl2-NaCl, Al-Si, Mg2Si-Si, and Na2O as phase change materials, the system can meet the requirements of high operating temperature (>1000℃), wide operating temperature range (585~1210℃), and multi-stage temperature zone heat storage / release in practical applications. On this basis, by optimizing the aperture design, a coupled high-efficiency energy transmission system is formed between multiple phase change materials, and a heat storage ceramic system with excellent heat storage / release capacity is obtained.

[0050] The present invention is further described in detail below through specific examples.

[0051] Example 1:

[0052] A method for preparing a thermal storage ceramic encapsulating a multi-stage coupled energy storage PCM comprises the following steps:

[0053] (1) Precursor preparation: A precursor solution was prepared using 20 wt% yttrium nitrate, 35 wt% magnesium nitrate as solute and 45 wt% ethanol as solvent.

[0054] (2) Preparation of composite powder: The precursor solution is placed in a glass container, and a rubber tube is used as a liquid guide tube. The precursor solution is sprayed from an ultrasonic atomizing nozzle at a rate of 20 mL / min. Methane is used as a combustion-supporting gas to ignite the atomized liquid to form a flame temperature field with a height of about 30 cm (the sintering temperature is about 1100°C at this time); after the atomized powder is cooled, it enters a micro-nano dust collector to obtain micro-nano-scale magnesium oxide-yttrium oxide composite powder.

[0055] See also Figure 1 The yttrium oxide-magnesium oxide composite powder prepared by the present invention has a core-shell structure and a particle size of 0.5 to 4 μm.

[0056] (3) Raw material mixing: Industrial-grade α-Al2O3 and Longyan kaolin are used as the main raw materials, and micro-nano-scale magnesium oxide-yttrium oxide composite powder with a core-shell structure is used as an additive. The raw materials are weighed and mixed according to their mass ratio, and then ground in a high-energy ball mill for 15 minutes to obtain a uniformly mixed powder. The raw material powders and their mass fractions are as follows: 81.03wt% of industrial-grade α-Al2O3 and 18.97wt% of Longyan kaolin, totaling 100wt%, forming a base powder; the added magnesium oxide-yttrium oxide composite powder accounts for 7wt% of the base powder.

[0057] (4) Plasticizing the blank: adding a binder solution to the mixed powder prepared in step (3), wherein the amount of the binder solution is 4% of the mixed powder, to obtain a plasticized powder; wherein the mass fraction of PVA in the binder solution is 5%; and granulating to obtain a plasticized blank.

[0058] (5) Blank forming: The plasticized blank prepared in step (4) is placed in a vacuum clay kneader for clay kneading. After aging for 24 hours, the clay is extruded and cut into a packaged ceramic blank with an aperture ratio of 2:3:4:5 (the aperture increases from the outside to the inside), a porosity of 75%, and a height of 35 cm. The obtained packaged ceramic blank is then microwave-shaped and dried to obtain a ceramic green body with honeycomb pores; wherein the extruder extrusion pressure is 4 MPa, the microwave shaping power is 4 kW, the frequency is 2400 ± 50 MHz, and the microwave shaping time is 15 minutes.

[0059] (6) Drying the green body: The ceramic green body formed in step (5) is placed in a drying oven and dried at 95° C. for 20 h to obtain a green body.

[0060] (7) Ceramic sintering: The green body dried in step (6) is placed in a silicon-molybdenum rod furnace, and the furnace temperature is raised from room temperature to 1000°C at a heating rate of 5°C / min, and then raised from 1000°C to 1650°C at a heating rate of 3°C / min. After holding the temperature for 2 hours, the furnace temperature is lowered to 1200°C at a cooling rate of 5°C / min. During the heating process, when the temperature is less than 1000°C, the temperature is kept at 100°C for 30 minutes each, and when the temperature is ≥1000°C, the temperature is kept at 100°C for 60 minutes each. After sintering, a corundum-mullite-based ceramic packaging substrate is obtained.

[0061] See also Figure 2 The cross-sectional SEM image of the corundum-mullite-based ceramic packaging matrix prepared by the present invention shows that the flaky grains are corundum with a particle size of 2 to 4.5 μm, the long rod-shaped grains are mullite with a particle size of 4 to 5.5 μm, and yttrium oxide and magnesium oxide are evenly distributed between the grains.

[0062] See also Figure 3, XRD spectrum of the corundum-mullite based ceramic packaging matrix prepared by the present invention, the main crystal phase of the ceramic matrix is corundum, and the secondary crystal phase is mullite.

[0063] (8) Material packaging: Molten salts and alloys with mass fractions of (59.5%) MgCl2-(40.5%) NaCl, (80%) Al-(20%) Si, (60%) Mg2Si-(40%) Si, and 100% Na2O are placed in the corundum-mullite-based ceramic packaging matrix prepared in step (7) in order from the outside to the inside. The filling amount of molten salt and alloy is 1 / 2 of the honeycomb pore volume of the ceramic packaging matrix. The ceramic packaging matrix is packaged using a high-temperature packaging adhesive (prepared by mixing 20wt% aluminum dihydrogen phosphate, 10wt% β-Al2O3, 20wt% silicon powder and 50wt% deionized water). One side of the matrix is packaged first, and after the molten salt and alloy are placed in the ceramic packaging matrix, the other side is packaged to obtain a heat storage ceramic that encapsulates a multi-stage coupled energy storage PCM.

[0064] The room temperature thermal conductivity of the heat storage ceramic matrix prepared by the present invention is 22.64W (m·K). -1 (Refer to the national standard thermal conductivity GB / T10294-2008), the bulk density was measured by static weighing method and was 3.7g / cm 3 , porosity is 0.5%, water absorption is 0.2%, and the flexural strength is measured to be 225 MPa by the three-point bending test method (referring to the national standard: GB5101-2003). There is no cracking after 40 thermal shock cycles from 1100°C to room temperature (air cooling) (referring to the standard (GB / T 30873-2014)). Field emission scanning electron microscopy (EPMA) detection shows that the prepared corundum-mullite-based ceramic packaging matrix has good corrosion resistance.

[0065] The thermal storage ceramics after PCM is encapsulated in a corundum-mullite based ceramic encapsulation matrix have a phase transition temperature of 442°C for the ceramic encapsulation matrix / MgCl2-NaCl composite thermal storage material and a system heat storage density of 1125 kJ / kg; a phase transition temperature of 844°C for the ceramic encapsulation matrix / Al-Si composite thermal storage material and a system heat storage density of 1297 kJ / kg; a phase transition temperature of 946°C for the ceramic encapsulation matrix / Mg2Si-Si composite thermal storage material and a system heat storage density of 1467 kJ / kg; and a phase transition temperature of 1210°C for the ceramic encapsulation matrix / Na2O composite thermal storage material and a system heat storage density of 1663 kJ / kg.

[0066] Comparative Example 1

[0067] The only difference between Comparative Example 1 and Example 1 is that untreated micro-nanoscale magnesium oxide and yttrium oxide (the molar ratio is the same as that in Example 1, i.e., the mass ratio calculated therefrom is 6.8:6.2) are directly mixed as an admixture; the other steps and conditions are the same as those in Example 1.

[0068] The room temperature thermal conductivity of the prepared heat storage ceramic matrix is 8.3W (m·K). -1 , the volume density is 3.5g / cm 3 , porosity is 1.12%, water absorption is 0.7%, and flexural strength is 175MPa.

[0069] Compared with Example 1, under the same other steps and conditions as Example 1, Comparative Example 1 directly mixes untreated micro-nanoscale magnesium oxide and yttrium oxide to replace the core-shell structured magnesium oxide-yttrium oxide composite powder in Example 1. The porosity and water absorption of the obtained ceramic packaging matrix increase, while the thermal conductivity, bulk density and flexural strength all decrease, indicating that the use of the core-shell structured magnesium oxide-yttrium oxide composite powder in the present invention is beneficial to improving the heat storage performance and mechanical properties of the obtained ceramic packaging matrix.

[0070] Comparative Example 2

[0071] The only difference between Comparative Example 2 and Example 1 is that 100 wt% of α-alumina is used as the base powder and mixed with core-shell micro-nanoscale magnesium oxide and yttrium oxide fired by flame spraying; other steps and conditions are the same as Example 1.

[0072] The room temperature thermal conductivity of the prepared heat storage ceramic matrix was 12.1 W (m·K) -1 , the volume density is 3.54g / cm 3 The porosity is 3.74%, the water absorption is 2.58%, and the flexural strength is 98 MPa. After 28 thermal shock cycles from 1100°C to room temperature (air cooling), some samples cracked.

[0073] Compared with Example 1, when other steps and conditions are the same as those in Example 1, the base powder of Comparative Example 2 is entirely composed of α-alumina, and the porosity and water absorption of the obtained ceramic packaging matrix increase, and due to the disappearance of the mullite phase, the flexural strength of the matrix decreases significantly. After 28 thermal shock cycles, the sample cracks, indicating that the present invention uses kaolin as a secondary base powder, and the mullite crystal phase that can be combined with alumina at high temperature is beneficial to the improvement of the matrix strength and greatly improves the service life of the matrix as a heat storage ceramic.

[0074] See also Figure 4The present invention can also encapsulate multiple phase change materials at the same time. According to the law of heat storage / release cycle, in order to effectively improve the storage / release efficiency of the heat storage system, the present invention is designed to increase the pore size from the outside to the inside or make adjacent pores equal. When there are multiple phase change materials encapsulated, the phase change material with a low phase change temperature is encapsulated in the small pores, and the material with a high phase change temperature is encapsulated in the large pores. For example, MgCl2-NaCl is encapsulated in the outer small pores, Al-Si is encapsulated in the second layer of pores, Mg2Si-Si is encapsulated in the third layer of pores, and Na2O is encapsulated in the innermost large pores.

[0075] In summary, the room temperature thermal conductivity of the ceramic package substrate prepared by the present invention is 16.36~22.64W(m·K) -1 , the volume density is 3.7~3.8g / cm 3 The porosity is 0.5-0.7%, the water absorption is 0.2-0.4%, the flexural strength is 203-257 MPa, and there is no cracking after 40 thermal shock cycles from 1100°C to room temperature. The test results show that the prepared corundum-mullite-based ceramic packaging matrix has good corrosion resistance, mechanical properties and thermal shock stability, and far exceeds the national standard of "Refractory Materials" (GB / T 30873-2014). For the heat storage system after PCM is encapsulated in corundum-mullite-based ceramics, the ceramic encapsulation matrix / MgCl2-NaCl composite thermal storage material can be used for medium-temperature heat storage at 442-585°C, with a heat storage density of 1125-1354.8 kJ / kg; the ceramic encapsulation matrix / Al-Si composite thermal storage material can be used for high-temperature heat storage at 585-946°C, with a heat storage density of 1297-1459.9 kJ / kg; and the ceramic encapsulation matrix / Mg2Si-Si and ceramic encapsulation matrix / Na2O composite thermal storage materials can be used for ultra-high-temperature heat storage at 946-1210°C, with heat storage densities of 1467-1663 kJ / kg, respectively.

[0076] The specific embodiments of the present invention described above do not limit the scope of protection of the present invention. Any other corresponding changes and modifications made based on the technical concept of the present invention should be included in the scope of protection of the claims of the present invention.

Claims

1. A thermal storage ceramic for encapsulating energy storage PCM, characterized in that: The heat storage ceramic has honeycomb pores for encapsulating phase change materials; the raw materials of the heat storage ceramic include a base powder and an admixture accounting for 5 to 10% of the total mass of the base powder; wherein, by mass percentage, the base powder includes 75 to 96% alumina and 4 to 25% kaolin; The additive is prepared by adding a magnesium source and a yttrium source into a solvent to prepare a precursor solution, and then preparing a micro-nanoscale magnesium oxide-yttrium oxide composite powder with a core-shell structure by flame spray pyrolysis; The main crystal phase of the heat storage ceramic is corundum, and the secondary crystal phase is mullite.

2. The heat storage ceramic for encapsulating energy storage PCM according to claim 1, characterized in that: Alumina uses industrial grade α-Al2O3 and kaolin uses Longyan kaolin.

3. The thermal storage ceramic for encapsulating energy storage PCM according to claim 1, characterized in that: The magnesium source is magnesium nitrate, the yttrium source is yttrium nitrate, and the solvent is ethanol; calculated by mass percentage, the precursor solution includes 15-30% of yttrium nitrate, 25-40% of magnesium nitrate, and 30-60% of ethanol.

4. The method for preparing the thermal storage ceramic for encapsulating energy storage PCM according to any one of claims 1 to 3, characterized in that: The following steps are involved: S1, adding a magnesium source and a yttrium source to a solvent to prepare a precursor solution, and preparing a micro-nanoscale magnesium oxide-yttrium oxide composite powder having a core-shell structure as an admixture from the precursor solution by flame spray pyrolysis; S2, mixing the admixture and the base powder uniformly to obtain a mixed powder; S3, the mixed powder is formed and shaped into a green body to obtain a ceramic green body with honeycomb pores; S4, the ceramic green body is dried and then sintered to obtain a heat storage ceramic for encapsulating the energy storage PCM.

5. The method for preparing the thermal storage ceramic for encapsulating energy storage PCM according to claim 4, characterized in that: In the flame spray pyrolysis method of step S1, methane is used as the combustion-supporting gas to atomize and ignite the precursor solution, and the effective sintering height of the flame is 25 to 35 cm; In step S3, the green body forming includes clay kneading, aging, extrusion molding and cutting; wherein the clay kneading is carried out in a vacuum clay kneading machine; the aging time is 24 to 48 hours; The shaping is done by microwave, the power of the microwave shaping is 2-6kW, the frequency is 2200-2600MHz, and the microwave shaping time is 15-20min.

6. The method for preparing the thermal storage ceramic for encapsulating energy storage PCM according to claim 4, characterized in that: In step S4, drying is carried out at 80-100° C. for 18-22 hours; sintering includes a heating process, a heat preservation process and a cooling process, wherein the heat preservation process is carried out at 1550-1650° C. for 1-3 hours.

7. The method for preparing the thermal storage ceramic for encapsulating energy storage PCM according to claim 6, characterized in that: During the heating process, the heating rate from room temperature to 1000°C is 5-8°C / min, and the heating rate from 1000°C to the maximum temperature is 3-5°C / min; the cooling rate during the cooling process is 5-8°C / min; and during the heating process, when the temperature is less than 1000°C, the temperature is kept at 100°C for 20-30 minutes each time, and when the temperature is ≥1000°C, the temperature is kept at 100°C for 30-60 minutes each time.

8. A composite heat storage material encapsulating energy storage PCM, characterized by: The heat storage ceramic according to any one of claims 1 to 3 is used as a ceramic packaging matrix, wherein a phase change material is encapsulated in the ceramic packaging matrix, and the phase change material occupies 40 to 60% of the volume of the honeycomb pores.

9. The composite heat storage material encapsulating energy storage PCM according to claim 8, characterized in that: The honeycomb pores on the ceramic package substrate have a pore size range of 5 to 25 cm and a porosity of 60 to 85%. The honeycomb pores are evenly distributed along the radial direction of the cross section of the ceramic package substrate from the outside to the inside, and the pore sizes increase sequentially or the adjacent pore sizes are equal. When multiple phase change materials are encapsulated, the phase change temperatures of the phase change materials increase sequentially or are equal. The phase change material includes one or more of (59.5-53.5%)MgCl2-(46.5-40.5%)NaCl, (80-70%)Al-(30-20%)Si, (60-50%)Mg2Si-(50-40%)Si and 100%Na2O.

10. The method for preparing a composite heat storage material encapsulating energy storage PCM according to claim 8, characterized in that: The following steps are involved: First, a high-temperature packaging adhesive is used to seal one end of the ceramic packaging substrate, and then a phase change material is loaded into the honeycomb pores of the ceramic packaging substrate at 1150-1250°C; finally, a high-temperature packaging adhesive is used to seal the other end of the ceramic packaging substrate to obtain a composite heat storage material.

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