A foamed ceramic having a low density, fine pore size

Abstract

The present application relates to the technical field of foamed ceramics, and particularly relates to a foamed ceramic with low density and fine pore size. The foamed ceramic is added with a foaming agent capable of generating gas in a sintering process, and the foamed ceramic formed after sintering has a plurality of pores. In terms of mass percentage, the chemical composition of the foamed ceramic contains 2.7-6.7% of potassium element; and the mass ratio of potassium element to sodium element is 0.95-2.3; and the half-ball temperature of the foamed ceramic is 1352-1410 DEG C. Through improvement on the formula system, especially limiting the ratio of K element to Na element to 0.95-2.3, and controlling the sintering system of the foamed ceramic, the foamed ceramic has suitable incipient melting point and high-temperature viscosity, the high-temperature zone has a certain liquid phase, the liquid phase amount cannot be too low, the pores formed after foaming are not combined and connected, and the foamed ceramic with low density and fine pore size is obtained.

Description

Technical Field

[0001] This invention relates to the field of foamed ceramics technology, and more particularly to a foamed ceramic with low density and fine pore size. Background Technology

[0002] Currently, the production technology of foamed ceramic sheets has matured, and the resulting foamed ceramic sheets generally exhibit a positive correlation between density and pore size. This is mainly because the sintering temperature of existing foamed ceramics is mostly around 1140-1160℃. Due to this relatively high sintering temperature and unreasonable high-temperature viscosity, the pores are prone to rupture after foaming, resulting in larger pores and low-density cells. Therefore, finished foamed ceramic products have low density (generally around 650 kg / m³). 3 When the following characteristics are present, the pores will inevitably be larger; conversely, high density (generally around 1000 kg / m³) will result in larger pores. 3 The pore size of foamed ceramic materials (as described above) is much finer. Furthermore, in traditional sintering processes, the heating curve rises sharply from the mid-temperature zone to the high-temperature zone, resulting in intense foaming. Because the internal temperature of the board remains high during subsequent cooling, foaming continues, easily leading to uneven foaming. This results in pore size deviations between the face and bottom of the foamed ceramic board, creating a stress difference between them. When the board is cut, bending deformation may occur, and excessive deformation can even cause cracking. Moreover, differences in pore size between the middle and top / bottom of the cut surface lead to uneven heat dissipation, excessive thermal stress, and varying cooling efficiency. After being left to stand for 2-6 hours or even longer after exiting the kiln, cracks may appear on the board.

[0003] However, in the production of foamed ceramics, there is limited research on how to adjust the formulation system and sintering process to ensure sufficient foaming of the foaming agent, thereby reducing the density of the foamed ceramics without creating excessively large pores. Therefore, this paper proposes a foamed ceramic with low density and fine pore size. Summary of the Invention

[0004] The main objective of this invention is to provide a foamed ceramic with low density and fine pore size, aiming to improve the technical problem that existing low-density foamed ceramics mostly have large pore size characteristics, making it impossible to obtain low-density, fine-pore-size foamed ceramics.

[0005] To achieve the above objectives, this invention proposes a foamed ceramic with low density and fine pore size, which contains a foaming agent that generates gas during sintering. The foamed ceramic formed after sintering has a number of pores. The chemical composition of the foamed ceramic contains 2.7-6.7% potassium by mass percentage, and the mass ratio of potassium to sodium is 0.95-2.3. The hemispherical temperature of the foamed ceramic is 1352-1410℃.

[0006] This method adjusts the proportion of alkali metals, especially potassium and sodium, in the raw materials of foamed ceramics to give it high potassium and low sodium characteristics. Specifically, the mass ratio of potassium to sodium is 0.95-2.3. This allows the hemispherical temperature of the foamed ceramic to be controlled at 1352-1410℃, thereby adjusting the viscosity of the high-temperature zone of the foamed ceramic to form a certain liquid phase in the high-temperature zone. The amount of liquid phase cannot be too low, resulting in a large number of micropores after foaming. These micropores do not merge or connect with each other, thus giving the foamed ceramic low-density fine pore characteristics. Furthermore, the overall impact resistance, toughness, weather resistance, and strength of the foamed ceramic are better.

[0007] When the potassium-sodium ratio is too high, the firing temperature of the formula will be too high, resulting in less liquid phase in the powder, high viscosity at high temperatures, which is not conducive to the encapsulation of gas generated during high-temperature foaming, or even the inability to encapsulate the gas, leading to gas expulsion and inconsistent pore size. When the potassium-sodium ratio is too low, the sodium content will be too high, resulting in low viscosity of the powder at high temperatures. Under high-temperature foaming conditions, the foaming gas encapsulated in the liquid phase is easily broken due to its low viscosity, causing several small pores to become large pores. This results in enlarged bubbles and larger pores. With a fixed potassium-sodium ratio, extending the high-temperature foaming time (delaying the heating rate) will lead to larger overall pores. Shortening the heating rate will result in insufficient oxidation time for the powder, leading to the generation of oxidation bubbles and resulting in pores of varying sizes. Therefore, it is necessary to strictly control the potassium-sodium ratio in this scheme within the above-mentioned range.

[0008] Preferably, by mass percentage, the foamed ceramic comprises the following raw materials: 24-50% low-temperature flux, 4-5% clay, 6-30% sand, 10-50% plastic waste, 7-10% magnesia or talc, and 0-1% wollastonite; the firing temperature of the foamed ceramic is 1187-1193℃.

[0009] Preferably, the density of the foamed ceramic is 520-655 g / cm³. 3 The pore size is ≤1mm. After firing according to the above formula and its corresponding firing regime, a first type of low-density, fine-pore foamed ceramic can be obtained. Among the four formulas, this foamed ceramic has a relatively high density and high strength.

[0010] Preferably, the chemical composition of the foamed ceramic contains 2.7-4.9% potassium; the mass ratio of potassium to sodium is 0.95-1.6; and the hemispherical temperature of the foamed ceramic is 1352-1359℃ (temperature state point under a high-temperature microscope, the spherical temperature is around 1245-1285℃; the leveling temperature is around 1435-1460℃). Under the above-mentioned potassium-sodium mass ratio and hemispherical temperature constraints, the obtained foamed ceramic has lower density, smaller and more uniform pore size, and higher strength.

[0011] Preferably, by mass percentage, the foamed ceramic comprises the following raw materials: 19-25% plastic waste, 20-27% sand, 5-15% clay, 33-36% barren waste, 5-10% magnesia clay or talc, and 0.5-4% calcium fluoride or boron mud; the firing temperature of the foamed ceramic is 1163-1170℃.

[0012] Preferably, the density of the foamed ceramic is 390-420 g / cm³. 3 The pore size is 1-1.5 mm. After firing according to the above formula and its corresponding firing regime, a second type of low-density, fine-pore foamed ceramic can be obtained.

[0013] Preferably, by mass percentage, the foamed ceramic comprises the following raw materials: 34-55% plastic waste, 30-44% barren waste, 0-27% low-temperature flux, 4-10% magnesia or talc, 0-9% sand, and 0-3% waste ceramic fiber paper; the firing temperature of the foamed ceramic is 1160-1165℃.

[0014] Preferably, the density of the foamed ceramic is 370-415 g / cm³. 3 The pore size is 0.5-1 mm. After firing under the above-mentioned formula and firing regime, a third type of low-density, fine-pore foamed ceramic can be obtained.

[0015] Preferably, by mass percentage, the foamed ceramic comprises the following raw materials: 15-20% low-temperature flux, 55-65% plastic waste, 4-12% sand, 0-2% waste ceramic fiber paper (fragments of aluminosilicate fiber paper that have lost their toughness after high-temperature calcination), 4-10% talc or magnesia, 0-3% cordierite, and 0-3% wollastonite; the firing temperature of the foamed ceramic is 1160-1165℃.

[0016] Preferably, the density of the foamed ceramic is 530-560 g / cm³. 3 The pore size is <0.5mm. After firing according to the above formula and its corresponding firing regime, a fourth type of low-density, fine-pore foamed ceramic can be obtained.

[0017] In summary, this solution provides the above four different raw material formulations and their corresponding firing regimes, enabling the produced foamed ceramics to be used in different scenarios and thus have a wider range of applications. In the specific formulations mentioned above, plastic waste includes tailings from mining (such as Xiaming tailings, Shirong tailings, Xitai tailings, Quanzhe processing tailings, and Xizhi processing tailings), washed mud, or pressed mud. Inferior waste includes cutting slag (cutting slag is the scrap material from the cutting of foamed ceramic blanks), waste powder (waste powder refers to the unsintered powder generated during the feeding and powder spraying granulation process of foamed ceramics in the kiln front section), ceramic polishing slag (ceramic polishing slag is the waste generated from polishing and grinding the edges of fired building ceramic bricks), and waste soil (construction slag). Low-temperature flux includes potassium feldspar or zirconium white frit.

[0018] Among them, the raw materials for preparing foamed ceramics can be clinker with more glass phase, such as foamed ceramic (waste) cutting slag, ceramic polishing slag, mining tailings and other bulk solid wastes, or strong flux materials such as calcium fluoride and boron mud can be introduced into the formula to reduce the firing temperature of foamed ceramics, facilitate rapid oxidation and decomposition of organic matter, and reduce the firing pressure in the oxidation zone at the front of the kiln.

[0019] Preferably, based on the total amount of raw materials for the foamed ceramic, the raw materials for the foamed ceramic further include: 0-1.2% desizing agent and 0-0.25% green body reinforcing agent. A green body reinforcing agent to improve strength can also be added to the foamed ceramic raw materials to improve the green body strength of the powder, thereby preventing breakage during powder transportation. The desizing agent can effectively desiccate the foamed ceramic raw materials, making the particle size distribution of the powder more reasonable, improving the fluidity of the raw materials in the molten state, and improving the overall performance of the foamed ceramic.

[0020] Based on the total amount of raw materials of the foamed ceramic, the amount of foaming agent added is 0.45-0.6%; the foaming agent is at least one of silicon carbide, manganese oxide, ferric oxide, ferric oxide, calcite calcium carbonate or dolomite.

[0021] The above-mentioned low-density, fine-pore foamed ceramic is prepared by the following steps: the raw materials of the foamed ceramic are crushed to obtain powder, the powder is mixed according to the mass percentage and then distributed, and after sintering, the low-density, fine-pore foamed ceramic is obtained.

[0022] Preferably, during sintering, the temperature is raised from 1100℃ to the maximum temperature and held at the maximum temperature for 30-40 minutes, with a heating rate of 0.3-0.5℃ / min. In the firing curve of the foamed ceramics produced by this method, the heating rate is very gradual, meaning the overall temperature fluctuation of the firing zone is small. This reduces the pressure on subsequent cooling, facilitates rapid cooling, and results in higher quality foamed ceramic products.

[0023] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0024] 1. The foamed ceramic of the present invention has the characteristics of low density and fine pore size. The main improvement is in the formulation system, especially in limiting the ratio of K to Na to 0.95-2.3. Some strong flux-type clinker is also introduced into the raw materials. At the same time, the firing process of the foamed ceramic is controlled to keep the hemispherical temperature of the foamed ceramic at 1352-1410℃ and to control the high-temperature viscosity of the powder during high-temperature foaming, so that there is a certain liquid phase in the high-temperature zone, and the amount of liquid phase cannot be too low, so that the pores formed after foaming do not merge and connect.

[0025] 2. This solution enables low-temperature rapid firing of foamed ceramics, with a sintering temperature of 1100-1145℃. The overall temperature fluctuation of the sintering zone is small, and the heating rate is set below 0.5℃ / min. As a result, the foamed ceramic products obtained are of good quality, with low density and (small) fine pores. Compared with traditional foamed ceramic products, the density is reduced, which greatly helps the transport load of the products, reduces transportation costs, enhances the competitiveness of the products, and improves the overall impact resistance, toughness, weather resistance, and strength. Attached Figure Description

[0026] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0027] Figure 1 This is a comparison chart of foamed ceramic products. Product A on the left is conventional foamed ceramic, while product B on the right is the low-density, fine-pore foamed ceramic of this solution.

[0028] The realization of the purpose, functional features and advantages of this application will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0029] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0030] Furthermore, the technical solutions of the various embodiments can be combined with each other, but only if they are feasible for those skilled in the art. If the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such combination of technical solutions does not exist and is not within the scope of protection claimed by this invention.

[0031] A process for preparing foamed ceramics with low density and fine pore size includes the following steps: the raw materials of the foamed ceramics are crushed to obtain powder, the powder is mixed according to the mass percentage and then distributed, and after sintering, the foamed ceramics with low density and fine pore size are obtained.

[0032] The foamed ceramic contains 2.7-6.7% potassium by mass percentage; and the mass ratio of potassium to sodium is 0.95-2.3; the hemispherical temperature of the foamed ceramic is 1352-1410℃. (Preferably, the foamed ceramic contains 2.7-4.9% potassium by mass percentage, the mass ratio of potassium to sodium is 0.95-1.6; the hemispherical temperature of the foamed ceramic is 1352-1359℃.)

[0033] The foamed ceramic comprises, by weight percentage, the following raw materials: 24-50% low-temperature flux, 4-5% clay, 6-30% sand, 10-50% plastic waste, 7-10% magnesia or talc, and 0-1% wollastonite; the firing temperature of the foamed ceramic is 1187-1193℃. The density of the obtained foamed ceramic is 520-655 g / cm³. 3 The pore diameter is ≤1mm.

[0034] Alternatively, by weight percentage, the foamed ceramic comprises the following raw materials: 19-25% plastic waste, 20-27% sand, 5-15% clay, 33-36% lean waste, 5-10% magnesia or talc, and 0.5-4% calcium fluoride or boron mud; the firing temperature of the foamed ceramic is 1163-1170℃. The density of the obtained foamed ceramic is 390-420 g / cm³. 3 The pore diameter is 1-1.5 mm.

[0035] Alternatively, by weight percentage, the foamed ceramic comprises the following raw materials: 34-55% plastic waste, 30-44% lean waste, 0-27% low-temperature flux, 4-10% magnesia or talc, 0-9% sand, and 0-3% waste ceramic fiber paper; the firing temperature of the foamed ceramic is 1160-1165℃. The density of the obtained foamed ceramic is 370-415 g / cm³. 3 The pore diameter is 0.5-1mm.

[0036] Alternatively, by weight percentage, the foamed ceramic comprises the following raw materials: 15-20% low-temperature flux, 55-65% plastic waste, 4-12% sand, 0-2% waste ceramic fiber paper, 4-10% talc or magnesia, 0-3% cordierite, and 0-3% wollastonite; the firing temperature of the foamed ceramic is 1160-1165℃. The density of the obtained foamed ceramic is 530-560 g / cm³. 3 The pore diameter is <0.5mm.

[0037] Based on the total amount of raw materials of the foamed ceramic, the raw materials of the foamed ceramic further include: 0-1.2% of desizing agent and 0-0.25% of green body reinforcing agent; the amount of foaming agent added is 0.45-0.6%; the foaming agent is at least one of silicon carbide, manganese oxide, ferric oxide, ferric oxide, calcite calcium carbonate or dolomite.

[0038] The technical solution of the present invention will be further described in detail below with reference to specific embodiments. It should be understood that the following embodiments are only used to explain the present invention and are not intended to limit the present invention.

[0039] The specific chemical composition of each raw material used in the preparation of foamed ceramics in the following embodiments is detailed in the table below (by mass percentage, in %):

[0040]

[0041]

[0042] Note: The chemical composition of the raw materials in the table above is less than 100% mainly due to the presence of other undetected impurities or elements. The total amount of zirconium white frit is less than 100% because it also contains small amounts of zirconium, zinc, and barium components; the total amount of calcium fluoride is less than 100% because it also contains fluorine components.

[0043] For the first formulation of foamed ceramic (24-50% low-temperature flux, 4-5% clay, 6-30% sand, 10-50% plastic waste, 7-10% magnesia or talc, 0-1% wollastonite), the following examples are provided:

[0044] The remaining process parameters for the following embodiments are as follows: heating from 1100℃ to the firing temperature at a rate of 0.3℃ / min, holding at the firing temperature for 35 minutes, and the powder obtained from the raw materials of the above formula having a moisture content of less than 5.5%, a bulk density of ≥0.87, and a particle size distribution of 0.5% for particles larger than 20 mesh, 35% for particles between 20 and 40 mesh, 64% for particles between 40 and 100 mesh, and 0.5% for particles smaller than 100 mesh.

[0045] Example 1

[0046]

[0047] The foamed ceramic with low density and fine pore size prepared in Example 1 was subjected to performance testing. The specific test results are shown in the table below:

[0048]

[0049] The test results of Example 1 above show that the density of the foamed ceramic obtained under this formula can be controlled between 520-605 g / cm³. 3 Furthermore, foamed ceramics have smaller pore sizes and relatively higher strength.

[0050] When the raw material is replaced with talc instead of magnesia clay, and no wollastonite is added, the overall density of the foamed ceramic is lower, and can be controlled at 570 g / cm³. 3 the following.

[0051] For the second formulation of foamed ceramics (19-25% plastic waste, 20-27% sand, 5-15% clay, 33-36% lean waste, 5-10% magnesia or talc, 0.5-4% calcium fluoride or boron mud), the following examples are provided (the remaining process parameters are the same as in Example 1):

[0052] Example 2

[0053]

[0054] Comparative Example 1

[0055] The main difference from Example 2 is that it does not contain the raw material calcium fluoride.

[0056]

[0057] The foamed ceramics with low density and fine pore size prepared in Example 2 and Comparative Example 1 were subjected to performance testing. The specific test results are shown in the table below:

[0058] The test results of each group in Example 2 above show that the introduction of calcium fluoride, a strong fluxing agent, can significantly reduce the firing temperature to 1170℃ or below. The reduced firing temperature, combined with the introduction of more quartz sand to appropriately increase the silicon content, results in a lower overall density of the foamed ceramic, ranging from 390-420 g / cm³. 3 Within this range, the aperture is also relatively small.

[0059] The test results of Comparative Example 1 show that the firing temperature of the formula without calcium fluoride is too high, the foaming effect is poor, and there are large and small pores with uneven pore size.

[0060] For the third formulation of foamed ceramics (34-55% plastic waste, 30-44% lean waste, 0-27% low-temperature flux, 4-10% magnesia or talc, 0-9% sand, and 0-3% waste ceramic fiber paper), the following examples and comparative examples are provided (the remaining process parameters are the same as in Example 1):

[0061] Example 3

[0062]

[0063] Example 4

[0064]

[0065]

[0066] Example 5

[0067]

[0068] Example 6

[0069]

[0070]

[0071] Example 7

[0072]

[0073] Comparative Example 2

[0074] All parameters and preparation steps in this comparative example are consistent with those in Example 3, except that the raw materials for preparing the foamed ceramic are different. By mass percentage, the raw materials include: 45% polishing slag, 15% waste soil, 15% quartz, 25% Banks sodium sand, and 0.4% silicon carbide; wherein, the potassium content in the foamed ceramic is 2.4%, and the potassium-sodium ratio is 0.74%.

[0075] The potassium-to-sodium ratio in this comparative example is outside the range of this scheme, and the ratio is too small.

[0076] Comparative Example 3

[0077] All parameters and preparation steps in this comparative example are consistent with those in Example 3, except that the raw materials for preparing the foamed ceramic are different. By mass percentage, the raw materials include: 45% polishing slag, 15% waste soil, 15% quartz, 25% potassium feldspar, and 0.4% silicon carbide; wherein, the potassium content in the foamed ceramic is 5.12%, and the potassium-sodium ratio is 2.83%.

[0078] The potassium-to-sodium ratio in this comparative example is outside the range of this scheme, and the ratio is too large.

[0079] Comparative Example 4

[0080] All raw materials and preparation steps in this comparative example are consistent with those in Example 3, except that the heating rate during sintering is different, as detailed in the table below:

[0081] Heating rate (°C / min) Comparative Example 4-1 1 Comparative Example 4-2 0.6 Comparative Example 4-3 0.15 Comparative Example 4-4 0.1 Comparative Example 4-5 1.5

[0082] The foamed ceramics prepared in Examples 3-7 and Comparative Examples 2-4 were subjected to performance testing. The specific test results are shown in the table below:

[0083]

[0084]

[0085] The test results of Examples 3-7 show that the potassium-sodium ratio corresponding to the raw materials with the third ratio described above can be controlled within the range of 0.95-1.6, and the amount of liquid phase obtained is relatively suitable. The hemispherical temperature of the foamed ceramic is also moderate. Therefore, it is possible to obtain a product with relatively low density (density of 420 g / cm³). 3 Foamed ceramics with relatively fine pore size (less than 1 mm) and uniform pore size distribution, and relatively high strength.

[0086] The test results of Comparative Examples 2 and 3 show that when the raw materials of the foamed ceramic are adjusted to a potassium-sodium ratio that exceeds the range specified in this scheme, the obtained foamed ceramic cannot simultaneously maintain the characteristics of low density, fine pore size and high strength.

[0087] The test results of Comparative Example 4 show that the foamed ceramics of this scheme need to be heated steadily during sintering; otherwise, the degree of foaming cannot be well controlled, and the obtained foamed ceramics will not have the characteristics of low density and fine pore size.

[0088] For the fourth formulation of foamed ceramics (15-20% low-temperature flux, 55-65% plastic waste, 4-12% sand, 0-2% waste ceramic fiber paper, 4-10% talc or magnesia, 0-3% cordierite, 0-3% wollastonite), the following examples are provided (process parameters are the same as in Example 1):

[0089] Example 8

[0090]

[0091]

[0092] The foamed ceramic with low density and fine pore size prepared in Example 8 was subjected to performance testing. The specific test results are shown in the table below:

[0093]

[0094] As can be seen from the test results of Example 8 above, the firing temperature corresponding to the above formula is relatively low. The pore size of the foamed ceramic obtained under this special formula and firing temperature can be maintained at 0.5 mm or less, with finer pore size. At the same time, the density of the foamed ceramic is also relatively low, and the overall strength is relatively high.

[0095] The above description is merely a preferred embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural transformations made using the contents of the present invention under the inventive concept of the present invention, or direct / indirect applications in other related technical fields, are included within the patent protection scope of the present invention.

Claims

1. A foamed ceramic with low density and fine pore size, comprising a foaming agent that generates gas during sintering, wherein the foamed ceramic formed after sintering has a plurality of pores, characterized in that, The foamed ceramic contains 2.7-4.9% potassium by mass percentage; the mass ratio of potassium to sodium is 0.95-1.6; and the hemispherical temperature of the foamed ceramic is 1352-1359℃. The foamed ceramic comprises the following raw materials by weight percentage: The composition includes 19-25% plastic waste, 20-27% sand, 5-15% mud, 33-36% barren waste, 5-10% magnesia clay or talc, and 0.5-4% calcium fluoride or boron mud; the firing temperature of the foamed ceramic is 1163-1170℃. or, The composition includes 34-55% plastic waste, 30-44% barren waste, 0-27% low-temperature flux, 4-10% magnesia clay or talc, 0-9% sand, and 0-3% waste ceramic fiber paper; the firing temperature of the foamed ceramic is 1160-1165℃. or, The composition includes 15-20% low-temperature flux, 55-65% plastic waste, 4-12% sand, 0-2% waste ceramic fiber paper, 4-10% talc or magnesia clay, 0-3% cordierite, and 0-3% wollastonite; the firing temperature of the foamed ceramic is 1160-1165℃.

2. The foamed ceramic with low density and fine pore size according to claim 1, characterized in that, Based on the total amount of raw materials of the foamed ceramic, the raw materials of the foamed ceramic also include: 0-1.2% desizing agent and 0-0.25% green body reinforcing agent.

3. A foamed ceramic with low density and fine pore size according to claim 1, characterized in that, Based on the total amount of raw materials of the foamed ceramic, the amount of foaming agent added is 0.45-0.6%; the foaming agent is at least one of silicon carbide, manganese oxide, ferric oxide, ferric oxide, calcite calcium carbonate or dolomite.

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