Ceramic sintering aid and application thereof

Abstract

The invention relates to the field of ceramic material preparation, in particular to a ceramic sintering aid and application thereof. The ceramic sintering aid comprises the following components in parts by weight: 2-10 parts of bismuth oxide and 1-5 parts of ferric oxide. Liquid phase sintering of bismuth oxide can cause abnormal growth of crystal grains, so that in ceramic doped with bismuth oxide and lithium carbonate, excessive glass phases are formed due to cooling of a high-temperature liquid phase, and the coefficient of thermal expansion of a ceramic matrix is relatively large. By using the sintering aid, the density of the ceramic is greatly improved, the content of a glass phase in the ceramic is reduced, and the high-density honeycomb ceramic heat accumulator can be produced by a simple process.

Description

Technical Field

[0001] The invention relates to the field of ceramic material preparation, and in particular to a ceramic sintering aid and application thereof. Background Art

[0002] Production practice and a large number of studies have shown that low porosity and high density ceramic structures have excellent performance. High density means that the grains in the ceramic are closely arranged, and it is not easy to form destructive breakthrough points when subjected to external loads or corrosive substances. At the same time, the improvement of mechanical properties is manifested as better thermal shock resistance. Overall, the service life of high-density ceramics is greatly improved.

[0003] There are currently two methods to promote ceramic sintering densification. One is to change the sintering method. Generally speaking, the sintering products of hot pressing (HP), hot isostatic pressing (HIP), spark plasma sintering (SPS) and other methods have a high degree of densification, but they often require higher temperatures and pressures, while the density of pressureless sintering products is relatively low. In addition, ceramic densification can be promoted by adding sintering aids. The action mechanism of additives can be divided into solid solution formation, liquid phase formation and second phase action.

[0004] Patent CN116535218 discloses a high-purity dense silicon carbide ceramic material and its solid phase sintering method and application. Silicon carbide powder, sintering aid, and liquid organic resin are used as raw materials. A green body is prepared under a pressure of 250MPa in a cold isostatic press. The green body is subjected to three-stage sintering treatments of vacuum sintering, normal pressure sintering, and pressure sintering to obtain a high-purity dense silicon carbide ceramic material. This patent prepares a high-purity dense silicon carbide ceramic with a density of 93.6% and an open porosity of 0.20%, but the cost is relatively high.

[0005] Patent CN111960818A discloses a low-temperature sintered ceramic material and its preparation method, which uses a mixture of lithium carbonate and bismuth oxide with a low eutectic point as a flux to achieve low-temperature sintering of energy storage ceramic materials. However, liquid phase sintering will bring certain negative effects, such as the introduction of a glass phase with a large thermal expansion coefficient; the formed glass phase will reduce the thermal conductivity of the ceramic and affect the heat recovery efficiency of the honeycomb ceramic; too much liquid phase will cause abnormal grain growth and deteriorate the mechanical properties of the ceramic; and the carbon dioxide produced by the decomposition of lithium carbonate will also prevent the ceramic from being dense. Summary of the invention

[0006] The purpose of the present invention is to provide a ceramic sintering aid for improving the density of ceramics and application thereof.

[0007] In order to achieve the above object, the technical solution of the present invention is as follows:

[0008] A ceramic sintering aid comprises, by weight, 2-10 parts of bismuth oxide and 1-5 parts of ferric oxide.

[0009] The combined action of bismuth oxide and ferric oxide promotes the dense sintering of ceramics, thereby solving the problem of a large amount of glass phase in the ceramics during the bismuth oxide liquid phase sintering process, which increases the thermal expansion coefficient of the ceramics.

[0010] In one of the preferred embodiments, the ceramic sintering aid comprises, by weight, 5-7 parts of bismuth oxide and 1-3 parts of ferric oxide.

[0011] In one of the preferred embodiments, the ceramic sintering aid comprises: 5-7 parts of bismuth oxide and 2 parts of ferric oxide.

[0012] In one of the preferred embodiments, the ceramic sintering aid comprises: 6 parts of bismuth oxide and 2 parts of ferric oxide.

[0013] In one preferred embodiment, the ceramic sintering aid also includes 1-5 parts of nano-alumina.

[0014] High-temperature liquid phase crystallization is induced by nano-alumina and the corresponding cooling system.

[0015] In a preferred embodiment, the aluminum oxide particle size is 20-100 nm.

[0016] When the nano-alumina particle size is in the range of 20nm-100nm, the ceramic sample is denser and has a lower thermal expansion coefficient than the ceramic sample without adding nano-alumina, indicating that in this range, nano-alumina can effectively induce glass phase crystallization. If the particle size is too small, it will lead to agglomeration or overburning, while if the particle size is too large, it will fail to induce crystallization and will be difficult to sinter.

[0017] Based on the same inventive concept, the present invention also claims protection for a ceramic heat storage body, the raw materials of which include the above-mentioned ceramic sintering aid.

[0018] In a preferred embodiment, a ceramic sintering aid is added to the ceramic raw material powder for mixing.

[0019] In a preferred embodiment, the raw materials of the ceramic thermal storage body include: 40-60 parts of bauxite powder, 2-6 parts of cordierite powder, 1-4 parts of kaolin, 0.5-1.5 parts of pyroxene powder, 20-35 parts of mullite powder, 2-4 parts of potassium feldspar, 4-9 parts of raw talc, 1-3 parts of dispersant, 1-3 parts of grinding aid, 2-10 parts of bismuth oxide and 1-5 parts of ferric oxide.

[0020] In a preferred embodiment, the raw materials of the ceramic thermal storage body include: 40-60 parts of bauxite powder, 2-6 parts of cordierite powder, 1-4 parts of kaolin, 0.5-1.5 parts of pyroxene powder, 20-35 parts of mullite powder, 2-4 parts of potassium feldspar, 4-9 parts of raw talc, 1-3 parts of dispersant, 1-3 parts of grinding aid, 2-10 parts of bismuth oxide, 1-5 parts of ferric oxide, and 1-5 parts of nano alumina.

[0021] In a preferred embodiment, the alumina content in the bauxite powder is >80wt%.

[0022] In a preferred embodiment, the dispersant includes one or more of sodium acrylate, ammonium polyacrylate, sodium citrate, and triethanolamine.

[0023] In a preferred embodiment, the grinding aid includes one or more of glycerol, propylene glycol, sodium metasilicate, and polyethylene glycol.

[0024] Based on the same inventive concept, the present invention also claims a method for preparing the ceramic thermal storage body, comprising the following steps:

[0025] S1, mixing the raw materials and then ball milling them to obtain a mixture; then adding a kneading aid and kneading them to obtain a kneaded mud segment;

[0026] S2, refining, pressing, drying, cutting, firing and cooling the kneaded mud segment to obtain the ceramic thermal storage body.

[0027] In a preferred embodiment, the kneading aid comprises, by weight, 1-4 parts of cellulose, 1-3% of palm oil, 0.3-1 parts of polyethylene oxide, and 10-20 parts of water.

[0028] In a preferred embodiment, the kneading speed is 20-40 revolutions per minute, and the kneading time is 20-30 minutes.

[0029] In a preferred embodiment, the ball milling speed is 10-40 revolutions per minute, and the ball milling time is 6-10 hours.

[0030] In a preferred embodiment, the viscosity of the cellulose is 8-12 mPa. . s.

[0031] In a preferred embodiment, the molecular weight of the polyethylene oxide is 1-8 million.

[0032] In a preferred embodiment, the refining is to put the kneaded mud segment into a vacuum mud kneading machine and refine it at a vacuum degree of 0.06-0.09 to obtain a refined mud segment.

[0033] In a preferred embodiment, the pressing is to press the refined mud segment using a mold to obtain a wet blank.

[0034] In a preferred embodiment, the drying is to dry the wet blank at 80-100° C. to obtain a dry blank.

[0035] In a preferred embodiment, the cutting is to cut both ends of the dry blank, and the cutting size is 1-1.2 times the length of the finished product to obtain a cut dry blank.

[0036] In a preferred embodiment, the firing is to fire the cut dry blank at 1150° C.-1600° C. for 1-3 hours to obtain a ceramic thermal storage body.

[0037] In a preferred embodiment, the cooling is staged cooling, including: when the temperature is greater than 850°C, cooling at a rate of 5-10°C / min; when the temperature is between 800-850°C, cooling at a rate of 1-5°C / min; after the temperature is lower than 800°C, cooling to room temperature at a rate of 20-30°C / min.

[0038] A suitable cooling strategy can promote the nucleation and growth of bismuth oxide induced on the surface of nano-alumina. In the system of the present invention, this segmented cooling method is optimal.

[0039] The present invention will be further explained below:

[0040] Bismuth oxide has a low melting point and can form a liquid phase during the ceramic sintering process to promote particle rearrangement and fill pores; the trivalent iron ions in ferric oxide are close to the radius of the aluminum ions in the ceramic matrix, forming a solid solution in the ceramic to cause lattice distortion and promote mass transfer. During the sintering process of ceramics, the composite addition of bismuth oxide and ferric oxide has both the advantages of liquid phase sintering and the strengthening effect of element solid solution on mass transfer, which can effectively promote the sintering density of ceramics. At the same time, the introduction of nano-alumina and an appropriate cooling system can effectively inhibit the formation of glass phase. During the cooling process of ceramics, nano-alumina can provide a large number of nucleation sites for the liquid phase, and the cooling system can make the high-temperature liquid phase precipitate in the form of crystals. Compared with the glass phase, the crystals have a lower thermal expansion coefficient, higher mechanical properties and better corrosion resistance. In summary, the composite addition of bismuth oxide and ferric oxide supplemented by the induced crystallization of nano-alumina and the cooling system can obtain a high-density ceramic with superior performance.

[0041] The beneficial effects of the present invention are:

[0042] The sintering aid of the present invention, namely the composite addition of bismuth oxide and ferric oxide, has both the advantages of liquid phase sintering and the strengthening effect of element solid solution on mass transfer, and can greatly improve the density of ceramics.

[0043] Furthermore, the present invention further adds nano-alumina and adopts a suitable cooling system to reduce the content of the glass phase in the ceramic, thereby producing a highly dense honeycomb ceramic thermal storage body under a simple process. DETAILED DESCRIPTION

[0044] The specific implementation modes of the present invention are further described in detail below through the description of embodiments.

[0045] Example 1

[0046] Effect of Bismuth Oxide on Ceramics Properties

[0047] A high-density honeycomb ceramic heat storage body is made of the following basic raw materials in parts by weight (kg): 50 parts of bauxite powder with an aluminum oxide content of>80%, 3 parts of cordierite powder, 2 parts of Suzhou kaolin, 0.5 parts of pyrope powder, 25 parts of mullite powder, 3.5 parts of potassium feldspar, and 4 parts of raw talc, and then a dispersant of 5% of the total weight of the basic raw material powder and a grinding aid of 2% of the total weight of the basic raw material powder are added, and bismuth oxide addition amounts of 0%, 2%, 4%, 6%, 8%, and 10% of the total weight of the basic raw material are selected respectively for addition, and the performance of the samples is tested.

[0048] The preparation method of honeycomb ceramics is as follows:

[0049] Weigh each raw material by weight, put the raw material into a ball mill, and mill it at a speed of 30 revolutions per minute for 6 hours to obtain a mixture; add the mixture into a kneader, and add 2% of HPMC by weight of the mixture. 100,000 viscosity cellulose, 2% 28 degree palm oil, 8% 5 million molecular weight polyethylene oxide, 13% deionized water, the kneading machine speed is set to 30 revolutions per minute, kneading for 20 minutes to obtain a kneaded mud segment; the kneaded mud segment is put into a vacuum mud kneading machine, and refined at a vacuum degree of 0.07 to obtain a refined mud segment; a mold is used to press the desired product to obtain a wet blank; the wet blank is dried to obtain a dry blank; the two ends of the dry blank are cut, and the cutting size is 1.20 times the length of the finished product to obtain a cut dry blank; the cut dry blank is put into a kiln and fired at 1150°C, and then a segmented cooling strategy is adopted, when the temperature is greater than 850°C, it is cooled at a rate of 5-10°C / min; it is slowly cooled at a rate of 1-5°C / min in the range of 800-850°C; after it is lower than 800°C, it is accelerated to cool to room temperature (20-30°C / min) to obtain a finished product. The ceramics with different bismuth oxide addition amounts were pressed into cake, rectangle and cylinder shapes. After calcination, the true density of the ceramics was measured using cake-shaped samples; the sintering line shrinkage, compressive strength and water absorption of the ceramics were measured using rectangles; the thermal expansion coefficient of the ceramics was measured using cylinders. The data results are shown in Table 1:

[0050] Table 1 Effect of different contents of bismuth oxide on ceramic properties

[0051]

[0052] As shown in Table 1, with the increase of bismuth oxide addition, the true density of ceramics shows an upward trend, the shrinkage of sintering lines shows an upward trend, and the water absorption rate shows a downward trend, indicating that the density of ceramics is gradually improved. Due to its low melting point, bismuth oxide can form a liquid phase at a lower temperature. During the liquid phase sintering process, the liquid phase can penetrate into the gaps between ceramic particles and fill the gaps through the dissolution-precipitation mechanism, making the ceramic material more dense. At the same time, the liquid phase can also promote the rearrangement and plastic deformation of ceramic particles, further increasing the density of the material. However, the liquid phase sintering process will bring some negative effects, such as an increase in the thermal expansion coefficient of ceramics, a decrease in the mechanical properties of ceramics, and a decrease in the thermal conductivity of ceramics. The increase in the thermal expansion coefficient is mainly because the liquid phase is too supercooled during the cooling process, resulting in the inability to crystallize, and exists in the ceramic matrix as a glass phase with a larger thermal expansion coefficient. When the amount of liquid phase is too large, it will cause abnormal growth of grains, resulting in a significant decrease in the mechanical properties of ceramic materials (such as fracture toughness, flexural strength, etc.). During the abnormal growth of grains, some grains will quickly swallow up the surrounding grains, resulting in excessively fast grain boundary movement, even faster than the speed of pore discharge, leaving a large number of pores inside the grains, reducing the density of the material. At the same time, the grain size distribution of the ceramic material becomes extremely uneven, with both abnormally grown coarse grains and small grains that have not grown fully. This uneven microstructure will affect the overall performance of the material.

[0053] In summary, when the addition amount of bismuth oxide is 6-10wt%, the density of the ceramic is the highest, but there is a large amount of glass phase in the ceramic, resulting in a large thermal expansion coefficient.

[0054] Example 2

[0055] Effect of Iron Oxide on Ceramics Performance

[0056] The only difference between this embodiment and embodiment 1 is that bismuth oxide is not used as the additive, but ferric oxide is added in an amount of 1%, 2%, 3%, 4% and 5% of the total mass of the base raw material powder.

[0057] The samples were tested for true density, sintering line shrinkage, water absorption, compressive strength, thermal expansion coefficient, etc. The test results are shown in Table 2:

[0058] Table 2 Effect of different contents of ferric oxide on ceramic properties

[0059]

[0060]

[0061] From the data, we can see that ferric oxide can increase the true density and sintering line shrinkage of ceramics and reduce the water absorption rate of ceramics, which shows that ferric oxide can effectively improve the density of ceramics. However, the addition of ferric oxide will also cause the thermal expansion coefficient to increase too quickly, which will deteriorate the thermal shock resistance of ceramics.

[0062] Example 3

[0063] Effect of Bismuth Oxide + Ferric Oxide Composite Additive on Ceramics Properties

[0064] A high-density honeycomb ceramic heat storage body, the difference between this embodiment and embodiment 1 is only the additive: the mass percentage of the fixed bismuth oxide + ferric oxide composite additive is 8% of the total mass of the basic raw material powder, and the bismuth oxide is gradually replaced by ferric oxide. The ceramic sample was tested, and the test results are shown in Table 3.

[0065] Table 3 Effect of different contents of bismuth oxide + ferric oxide on ceramic properties

[0066]

[0067] From the perspective of the shrinkage rate and water absorption rate of the ceramic sintering line after the composite additives, the synergistic effect of bismuth oxide + ferric oxide is greater than the effect of the additives alone. The sintering line shrinkage rate and compressive strength of 4% bismuth oxide + 4% ferric oxide are greater than those of the ceramic sample with 8% bismuth oxide, while the water absorption rate is smaller, indicating that the composite additive has a more obvious effect on promoting ceramic densification. However, since alkali metal oxides are generally not corrosion-resistant, and excessive sintering line shrinkage will cause the ceramic to deform greatly during the sintering process and easily crack. Therefore, the composition of the composite additive is 5-7% bismuth oxide + 1-3% ferric oxide in the total mass of the base raw material powder.

[0068] Example 4

[0069] Effect of Nano-alumina Addition on Ceramics Properties

[0070] As a common ceramic material, nano-alumina has a high surface area, good thermal stability and good chemical compatibility with bismuth oxide. During the rapid cooling process, bismuth oxide easily forms an amorphous glass phase, and the glass phase will cause the mechanical strength and thermal stability of the ceramic to decrease. Nano-alumina can be used as a heterogeneous nucleating agent to provide a large number of nucleation sites during the melting and cooling of bismuth oxide, thereby significantly reducing the nucleation free energy barrier, promoting the direct crystallization of bismuth oxide from the liquid phase to form a stable crystalline phase, and avoiding the formation of an amorphous glass phase. In this embodiment, the additive formula is selected as 6% bismuth oxide + 2% ferric oxide, and 1-5% of the total mass of the powder is added. Nano-alumina has a particle size of 50nm. At the same time, a segmented cooling strategy is adopted. When the temperature is greater than 850°C, it is cooled at a rate of 5-10°C / min; in the range of 800-850°C, it is slowly cooled at a rate of 1-5°C / min to promote the surface of nano-alumina to induce bismuth oxide nucleation and growth; after the crystal is formed, it is accelerated to cool to room temperature (20-30°C / min). The performance of the sample is tested. The test results are shown in Table 4:

[0071] Table 4 Effect of nano-alumina induced high temperature liquid phase crystallization on ceramic properties

[0072]

[0073] It can be seen from the data in the table that with the increase of nano-alumina content, the compressive strength of the ceramic increases significantly, while the thermal expansion coefficient gradually decreases, indicating that through the induction of nano-alumina and the new cooling system, the bismuth oxide and the remaining liquid phase in the ceramic are effectively crystallized. Nano-alumina has a high specific surface area and surface energy. When introduced as a seed, it can provide a large number of nucleation sites for bismuth oxide. These sites help to reduce the free energy barrier of nucleation of bismuth oxide during the cooling process and significantly increase the nucleation rate. By promoting the crystallization of bismuth oxide, nano-alumina helps to improve the density and crystal phase purity of ceramics, thereby enhancing the mechanical strength, hardness and impact resistance of ceramics. At the same time, the crystal structure usually has higher thermal stability and thermal shock resistance than the amorphous state. Therefore, after the crystallization of bismuth oxide, the overall thermal stability of the ceramic is significantly improved. In addition, the dispersed nano-alumina exists between the grains as a second phase substance, which can cooperate with ferric oxide to inhibit grain growth and refine the grains, thereby obtaining a fine-grained structure of the ceramic. When a load is applied to the ceramic matrix, the dispersed second phase substance can also inhibit crack expansion and improve the mechanical properties of the ceramic. However, when the addition amount is greater than 5%, the ceramic performance begins to decline - the true density, sintering line shrinkage and compressive strength begin to decline; the water absorption rate and thermal expansion coefficient begin to rise. When the addition amount is too much, the nanoparticles may agglomerate, and at the same time, due to the high melting point of alumina, it is more difficult to sinter the ceramic to a dense state at the same temperature, resulting in a decline in the ceramic performance.

[0074] Example 5

[0075] Effect of Nano-alumina Particle Size on Ceramics Properties

[0076] If the particle size of nano-alumina is too small, it will lead to agglomeration and over-burning; if the particle size is too large, it will not play the role of inducing crystallization. In order to screen out the appropriate particle size, this embodiment selects nano-alumina with a particle size of 10nm, 20nm, 50nm, 100nm, and 150nm, which accounts for 5wt% of the total mass of the powder, and mixes them into the ceramic. At the same time, a segmented cooling strategy is adopted. When the temperature is greater than 850℃, it is cooled at a rate of 5-10℃ / min; in the range of 800-850℃, it is slowly cooled at a rate of 1-5℃ / min to promote the nucleation and growth of bismuth oxide induced on the surface of nano-alumina; after the crystal is formed, it is accelerated to cool to room temperature (20-30℃ / min). Its performance is shown in Table 5:

[0077] Table 5 Effect of nano-alumina particle size on ceramic properties

[0078]

[0079] From the data in the table, we can see that when the particle size of nano-alumina is in the range of 20nm-100nm, the ceramic sample has a higher density and a lower thermal expansion coefficient than the ceramic sample without adding nano-alumina, and 50nm is the best. This shows that in this range, nano-alumina can effectively induce glass phase crystallization, while too small will lead to agglomeration or over-burning, and too large will fail to induce crystallization and be difficult to sinter.

[0080] Example 6

[0081] Effect of Cooling System on Ceramic Properties

[0082] The cooling system plays a vital role in the crystallization of high-temperature liquid phase. The high-temperature liquid phase in ceramics is mainly composed of two parts, one part is composed of impurity elements in the ceramics, and the other part is bismuth oxide liquid phase. Considering that the melting point of oxidation is 850℃, the ceramic cooling process is divided into three stages (sintering temperature - 850℃; 850℃-800℃; 800℃-room temperature), and different cooling rates are applied to each stage to study the effect of the cooling system on the performance of ceramics. Table 6 shows the different cooling systems designed:

[0083] Table 6 Cooling system

[0084] Cooling system Sintering temperature -850℃ 850℃-800℃ 800℃-Room temperature System 1 Cooling with furnace Cooling with furnace Cooling with furnace System 2 5-10℃ / min Cooling with furnace Cooling with furnace System 3 5-10℃ / min 5-10℃ / min Cooling with furnace System 4 5-10℃ / min 1-5℃ / min Cooling with furnace System 5 5-10℃ / min 1-5℃ / min 20-30℃ / min

[0085] In this embodiment, ceramic samples prepared by using 6% bismuth oxide + 2% ferric oxide + 5% nano-alumina were selected and different cooling systems were used, and the rest was the same as in Example 1. The following table shows the influence of the cooling system on the ceramic properties:

[0086] Table 7 Effect of cooling system on ceramic properties

[0087]

[0088] As shown in the table, the extremely slow cooling rate in the range of 850℃-800℃ has a significant effect on the performance of ceramics. At the same time, the slow cooling rate above 850℃ can also improve the performance of ceramics to a certain extent, because slow cooling in this temperature range can partially crystallize the liquid phase formed by impurity elements. However, after the temperature is less than 800℃, rapid cooling can prevent excessive grain growth. Therefore, the most suitable cooling system is: cooling at a rate of 5-10℃ / min when the temperature is greater than 850℃; slow cooling at a rate of 1-5℃ / min in the range of 800-850℃ to promote the nucleation and growth of bismuth oxide induced on the surface of nano-alumina; after the crystal is formed (i.e. below 800℃), accelerate cooling to room temperature (20-30℃ / min).

[0089] Comparative Example 1

[0090] A high-density and high-thermal expansion honeycomb ceramic heat storage body is made of the following raw materials in parts by weight (kg): 50 parts of bauxite powder with an aluminum oxide content of>80%, 3 parts of cordierite powder, 2 parts of Suzhou kaolin, 0.5 parts of pyrope powder, 25 parts of mullite powder, 3.5 parts of potassium feldspar, 4 parts of raw talc, 5% of the total weight of the powder as a dispersant, 2% of the total weight of the powder as a grinding aid, and 6% by weight of the total weight of the powder as bismuth oxide and lithium carbonate in a molar ratio of 1:1.

[0091] The preparation method of honeycomb ceramics is as follows:

[0092] Weigh each raw material by weight, put the raw material into a ball mill, and mill it at a speed of 30 revolutions per minute for 6 hours to obtain a mixture; add the mixture into a kneader, and add 2% of HPMC by weight of the mixture. 100,000 viscosity cellulose, 2% 28 degree palm oil, 8% 5 million molecular weight polyethylene oxide, 13% deionized water, the kneading machine speed is set to 30 revolutions per minute, kneading for 20 minutes to obtain kneaded mud segments; the kneaded mud segments are put into a vacuum mud kneading machine, and refined at a vacuum degree of 0.07 to obtain refined mud segments; a mold is used to press the desired product to obtain a wet blank; the wet blank is dried to obtain a dry blank; both ends of the dry blank are cut, and the cutting size is 1-1.20 times the length of the finished product to obtain a cut dry blank; the cut dry blank is put into a kiln and fired at 1150°C, and then a segmented cooling strategy is adopted, when the temperature is greater than 850°C, it is cooled at a rate of 5-10°C / min; it is slowly cooled at a rate of 1-5°C / min in the range of 800-850°C; after it is lower than 800°C, it is accelerated to cool to room temperature (20-30°C / min) to obtain a finished product. The ceramics with different bismuth oxide addition amounts were pressed into cake, rectangle and cylinder shapes. After calcination, the true density of the ceramics was measured using cake-shaped samples; the sintering line shrinkage, compressive strength and water absorption of the ceramics were measured using rectangles; the thermal expansion coefficient of the ceramics was measured using cylinders. The data results are shown in Table 8:

[0093] Table 8 Various properties of ceramics with bismuth oxide and lithium carbonate added at a molar ratio of 1:1 with a total powder mass of 6 wt%

[0094]

[0095] Under the same conditions, the true density of Example 4 is higher and the thermal expansion coefficient is lower. Bismuth oxide and lithium carbonate can form a material with a low melting point, but its mechanism of action is only liquid phase sintering, and too much liquid phase will cause abnormal growth of grains. At the same time, lithium carbonate will also decompose carbon dioxide at high temperature, so that the ceramic porosity will rise, and the ceramic densification process will be slow. In general, the higher the porosity, the lower the thermal expansion coefficient of the ceramic will be, but in the ceramics doped with bismuth oxide and lithium carbonate, the glass phase formed by cooling down the high-temperature liquid phase is too much, resulting in a larger thermal expansion coefficient of the ceramic matrix. Relatively speaking, in Example 4, there are both the advantages of liquid phase sintering and the enhanced mass transfer effect of element solid solution. At the same time, nano alumina and cooling system can effectively induce glass phase crystallization, showing more superior compactness and thermal shock resistance.

[0096] The present invention uses sintering aids to greatly improve the density of ceramics, while using nano-alumina and adopting a suitable cooling system to reduce the content of the glass phase in the ceramics, and can produce a high-density honeycomb ceramic thermal storage body under a simple process.

[0097] The above description is only a specific implementation of the present invention. Each example does not limit the essential content of the present invention. Those skilled in the art may modify or deform the aforementioned specific implementation without departing from the essence of the present invention.

Claims

1. A ceramic sintering aid, characterized in that: Calculated by weight, it comprises: 2-10 parts of bismuth oxide and 1-5 parts of ferric oxide.

2. The ceramic sintering aid according to claim 1, characterized in that: The ceramic sintering aid comprises: 5-7 parts of bismuth oxide and 1-3 parts of ferric oxide.

3. The ceramic sintering aid according to claim 1, characterized in that: The ceramic sintering aid also includes 1-5 parts of nano alumina.

4. The ceramic sintering aid according to claim 3, characterized in that: The aluminum oxide particle size is 20-100 nm.

5. A ceramic heat storage body, characterized in that: The raw materials include the ceramic sintering aid described in any one of claims 1 to 4.

6. The ceramic heat storage body according to claim 5, characterized in that: The raw materials of the ceramic heat storage body include: 40-60 parts of bauxite powder, 2-6 parts of cordierite powder, 1-4 parts of kaolin, 0.5-1.5 parts of pyrope powder, 20-35 parts of mullite powder, 2-4 parts of potassium feldspar, 4-9 parts of raw talc, 1-3 parts of dispersant, 1-3 parts of grinding aid, 2-10 parts of bismuth oxide and 1-5 parts of ferric oxide.

7. The ceramic thermal storage body according to claim 6, characterized in that: The dispersant includes one or more of sodium acrylate, ammonium polyacrylate, sodium citrate, and triethanolamine; the grinding aid includes one or more of glycerol, propylene glycol, sodium metasilicate, and polyethylene glycol.

8. The method for preparing a ceramic thermal storage body according to any one of claims 5 to 7, characterized in that: The following steps are involved: S1, mixing the raw materials and then ball milling them to obtain a mixture; then adding a kneading aid and kneading them to obtain a kneaded mud segment; S2, refining, pressing, drying, cutting, firing and cooling the kneaded mud segment to obtain the ceramic heat storage body.

9. The preparation method according to claim 8, characterized in that: The kneading aid comprises, by weight, 1-4 parts of cellulose, 1-3 parts of palm oil, 0.3-1 parts of polyethylene oxide, and 10-20 parts of water.

10. The preparation method according to claim 8, characterized in that: The cooling is staged cooling, including: When the temperature is greater than 850°C, cool at a rate of 5-10°C / min; when the temperature is between 800-850°C, The temperature is controlled to be cooled at a rate of 1-5°C / min. After the temperature is lower than 800°C, the temperature is cooled to room temperature at a rate of 20-30°C / min.

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