Preparation method of mullite foamed ceramic with controllable porosity

Abstract

The present invention discloses a porosity controllable mullite foam ceramic preparation method, which comprises: preparing an aluminum source-silicon source solution, the aluminum source-silicon source solution comprises an inorganic aluminum source, an organic aluminum source and a silicon source; hydrolyzing the aluminum source-silicon source solution to prepare a mullite foamed ceramic precursor sol stock solution; concentrating the mullite foamed ceramic precursor sol stock solution to obtain a mullite foamed ceramic precursor sol solution; foaming the mullite foamed ceramic precursor sol solution in a porosity controllable foaming device to obtain a solid foamed ceramic precursor; freeze-drying the solid foamed ceramic precursor to obtain a foamed precursor dry blank; and sintering the foam precursor dry blank to obtain the mullite foam ceramic, the preparation of the mullite foamed ceramic with high porosity, open pores, controllable porosity and high mullite content and purity is realized.

Description

Technical Field

[0001] The invention relates to the field of mullite foam ceramics, and in particular to the technical field of a method for preparing mullite foam ceramics with controllable porosity. Background Art

[0002] Foam ceramics combine the characteristics of foam materials and ceramic materials, and have the advantages of low density, high specific surface area, high specific strength, high temperature resistance, corrosion resistance, and wear resistance. They can be widely used in the fields of filtration, adsorption, catalysis, and thermal insulation.

[0003] The preparation processes of foam ceramics mainly include the addition of pore-forming agents, organic foam impregnation and direct foaming. The addition of pore-forming agents can adjust the size and shape of pores, but the porosity is low, generally below 50%. The organic foam impregnation method can prepare foam ceramics with high porosity and open pores, but the porosity is uncontrollable, resulting in uncontrollable strength of the material, and the operation is complicated.

[0004] Therefore, how to prepare foam ceramics with high porosity and open pores, controllable porosity, and high purity of mullite content has become a difficult problem that needs to be solved urgently in this field. Summary of the invention

[0005] In order to solve the above technical problems, a method for preparing mullite foam ceramics with controllable porosity is provided to prepare foam ceramics with high porosity and open pores, and mullite foam ceramics with controllable porosity and high purity of mullite content.

[0006] According to the present invention, a method for preparing a mullite foam ceramic with controllable porosity is provided, comprising the following steps:

[0007] preparing an aluminum source-silicon source solution, wherein the aluminum source-silicon source solution comprises an inorganic aluminum source, an organic aluminum source, and a silicon source;

[0008] The aluminum source-silicon source solution is hydrolyzed to prepare a mullite foam ceramic precursor sol stock solution;

[0009] The mullite foam ceramic precursor sol stock solution is concentrated to obtain a mullite foam ceramic precursor sol solution;

[0010] The mullite foam ceramic precursor sol solution is foamed in a porosity controllable foaming device to obtain a solid foam ceramic precursor;

[0011] freeze-drying the solid foam ceramic precursor to obtain a foam precursor dry blank;

[0012] The foam precursor dry blank is sintered to obtain the mullite foam ceramic.

[0013] Compared with the prior art, the beneficial effect of the present invention is that, by preparing an aluminum source-silicon source solution, the aluminum source-silicon source solution includes an inorganic aluminum source, an organic aluminum source, and a silicon source, so that the mullite foam ceramic precursor sol solution does not contain a dispersant, a foaming agent, and a coagulant, and the mullite foam ceramic component prepared is high in purity, avoiding the problem of lowering the heat resistance temperature caused by the introduction of impurity metal elements such as Na, K, Ca, and Mg, and achieving a heat resistance temperature of the mullite foam ceramic close to the theoretical upper temperature limit of 1650-1750° C. for the application of mullite ceramics;

[0014] The mullite foam ceramic precursor sol solution is obtained by concentrating the mullite foam ceramic precursor sol stock solution; the mullite foam ceramic precursor sol solution is foamed in a porosity controllable foaming device to obtain a solid foam ceramic precursor, so that the prepared mullite foam ceramic has high porosity, open pores, and controllable porosity;

[0015] The solid foam ceramic precursor is freeze-dried to obtain a foam precursor dry blank, which is beneficial to volatilize small molecules in the solid foam ceramic precursor without causing damage or cracking of the solid foam ceramic precursor.

[0016] Further, preparing the aluminum source-silicon source solution comprises the following steps:

[0017] Adding an inorganic aluminum source into deionized water to dissolve it, thereby obtaining an inorganic aluminum source solution;

[0018] Then, an organic aluminum source and a silicon source are added into the inorganic aluminum source solution and stirred to obtain an aluminum source-silicon source solution;

[0019] The mass ratio of the inorganic aluminum source, the organic aluminum source, and the silicon source is (3-6): (8-12): (4-7).

[0020] The beneficial effect of adopting the previous step is that the mullite foam ceramic precursor sol solution does not contain dispersant, foaming agent, and coagulant, and the mullite foam ceramic component prepared has high purity, avoiding the problem of lowering the temperature resistance due to the introduction of impurity metal elements such as Na, K, Ca, and Mg.

[0021] Furthermore, the process for preparing the mullite foam ceramic precursor sol solution comprises the following steps:

[0022] The aluminum source-silicon source solution is placed at room temperature for hydrolysis for 24-28 hours; and then heated at 60-70° C. for hydrolysis for 16-40 hours to obtain a mullite foam ceramic precursor sol stock solution.

[0023] The beneficial effect of adopting the previous step is that the aluminum source-silicon source solution is placed at room temperature for hydrolysis for 24-28 hours; and then heated at 60-70°C for hydrolysis for 16-40 hours, so that the aluminum source and the silicon source are slowly hydrolyzed, while avoiding precipitation caused by excessive hydrolysis. In addition, it avoids excessively high temperature during the hydrolysis process, which leads to excessive activity of the hydrolyzed material, and precipitation and other problems in the subsequent concentration process of the mullite foam ceramic precursor sol solution.

[0024] Furthermore, the process for preparing the mullite foam ceramic precursor sol solution comprises the following steps:

[0025] According to Formula 1 and Formula 2, the mass m of the mullite component in the mullite foam ceramic precursor sol solution added to the foaming accommodation space is calculated by the preset required porosity β of the mullite foam ceramic. 莫 , the volume V of the foaming accommodation space of the porosity controllable foaming device 模 、Theoretical density of mullite ρ 莫 =3.03g / cm 3 -3.16g / cm 3 , the mass m of the mullite foam ceramic precursor sol solution added to the foaming accommodation space 溶 , the solid content c of the mullite foam ceramic precursor sol solution is obtained 溶 ;

[0026] Formula 1:

[0027]

[0028] Formula 2:

[0029] m 莫 =m 溶 ×c 溶 ;

[0030] Through the c 溶 The mass of alumina and silicon oxide in the inorganic aluminum source, organic aluminum source and silicon source added to the mullite foam ceramic precursor sol stock solution is obtained by concentrating the mullite foam ceramic precursor sol stock solution.

[0031] The beneficial effect of the above step is that the method can realize the preparation of mullite foam ceramics with a preset porosity; that is, the solid content c of the mullite foam ceramic precursor sol stock solution when the mullite foam ceramics with a preset required porosity are obtained in the porosity controllable foaming device with preset parameters can be obtained by formula 1 and formula 2. 溶 , while passing c 溶The mass of the mullite foam ceramic precursor sol solution after concentrating the mullite foam ceramic precursor sol stock solution is obtained; thereby, the mullite foam ceramic with a preset porosity can be obtained.

[0032] Further, the porosity controllable foaming device comprises a foaming device;

[0033] The foaming device is provided with a foaming accommodating space inside and a heating accommodating space sleeved outside the foaming accommodating space;

[0034] The surface of the foaming device is provided with a feeding port, and the feeding port is connected with the foaming accommodating space; the feeding port is detachably connected with a cover body; a sealing member is provided between the cover body and the feeding port;

[0035] The heat accommodating space is connected to the heat source through a pipeline.

[0036] The beneficial effect of adopting the previous step is that a quantitative amount of mullite foam ceramic precursor sol solution is added to the foaming accommodating space through the feeding port according to the preset porosity to be achieved, and then the feeding port is sealed by the cover body, and the mullite foam ceramic precursor sol solution in the foaming accommodating space is heated by adding a heat source into the heating accommodating space and controlling the temperature, so that the mullite sol is decomposed and foamed by heat in the foaming accommodating space, and bubbles are mixed into the sol; at the same time, the activation energy of water under hydrothermal conditions is greatly enhanced, and the sol particles undergo a series of reactions such as rapid hydrolysis, expansion, cross-linking and gelation under the action of water molecules, and the unreleased gas is wrapped inside before the gel is solidified, thereby expanding, and part of the gas generated after the gel is solidified is slowly discharged to obtain a mullite foaming precursor.

[0037] Furthermore, the porosity controllable foaming device also includes a pressure control device;

[0038] The surface of the foaming device is also provided with a first air outlet, and the first air outlet is connected to the pressure control device through a first air pipeline;

[0039] The first gas transmission pipeline is provided with a one-way control valve;

[0040] The pressure control device is provided with a gas accommodating space inside, and the pressure control device is provided with a first air inlet, a second air inlet, and a second air outlet;

[0041] The first air inlet and the first air outlet connect the foaming accommodating space with the gas accommodating space through the first air delivery pipeline;

[0042] The second air inlet hole connects the air source with the gas containing space through a second air pipeline, and the second air pipeline is provided with a second control valve;

[0043] The second air outlet is provided with an exhaust pipeline, and the exhaust pipeline is provided with a first control valve;

[0044] A pressure sensor is arranged in the gas accommodating space.

[0045] The beneficial effect of adopting the above step is that the first air inlet and the first air outlet connect the foaming accommodating space with the gas accommodating space through the first gas transmission pipeline, so that the mullite foam ceramic precursor sol solution in the foaming accommodating space undergoes hydrothermal reaction foaming, expansion, and solidification, and the excess gas is discharged from the solidified material into the gas accommodating space, thereby achieving that the internal pores of the obtained mullite foam ceramic are through holes;

[0046] The one-way control valve is provided on the first gas transmission pipeline, which can control the time of opening the channel between the foaming accommodating space and the gas accommodating space, that is, the foaming accommodating space is connected with the gas accommodating space after the volume of the foaming accommodating space is fully expanded, and the gas in the gas accommodating space is prevented from flowing into the foaming accommodating space after the valve is opened;

[0047] The gas source is connected to the gas accommodating space through the second gas inlet hole and the second gas supply pipeline, and the second gas supply pipeline is provided with a second control valve; the second gas outlet hole is provided with an exhaust pipeline, and the exhaust pipeline is provided with a first control valve; the pressure in the gas accommodating space is controlled within a certain range, so that the gas pressure in the foaming accommodating space can be within a certain range, and at the same time, the gas is transferred from the foaming accommodating space to the gas accommodating space; finally, the gel state of the foaming accommodating space is achieved, the pores in the mullite foam ceramic precursor will not collapse, and most of the internal pores are through holes.

[0048] Further, the process of preparing the solid foam ceramic precursor comprises the following steps:

[0049] According to the preset mass msol of the mullite foam ceramic precursor sol solution to be added to the foaming accommodating space, the mullite foam ceramic precursor sol solution with the mass msol is added to the foaming accommodating space of the porosity controllable foaming device through the feeding port, and then the cover body is connected to the feeding port;

[0050] The heat source introduces a heating substance into the heating accommodation space through a pipeline to heat the mullite foam ceramic precursor sol solution in the foaming accommodation space; preferably, the heating process in the foaming accommodation space is to increase the temperature to 170°C-200°C at a heating rate of 2-10°C / min, and keep the temperature at 170°C-200°C for 12-24h;

[0051] During the heating process of the sol solution of the raw stone foam ceramic precursor in the foaming accommodation space, hydrolysis, expansion, cross-linking and gelation reactions are carried out to obtain a solid foam ceramic precursor.

[0052] The beneficial effect of adopting the previous step is that the mullite foam ceramic precursor sol solution is heated in the foaming accommodating space by adding a heat source into the heating accommodating space and controlling the temperature to heat the mullite foam ceramic precursor sol solution in the foaming accommodating space, so that the mullite sol is thermally decomposed and foamed in the foaming accommodating space, and bubbles are mixed into the sol; at the same time, the activation energy of water under hydrothermal conditions is greatly enhanced, and the sol particles undergo a series of reactions such as rapid hydrolysis, expansion, cross-linking and gelation under the action of water molecules, and the unreleased gas is wrapped inside before the gel solidifies, thereby expanding, and part of the gas generated after the gel solidifies is slowly discharged to obtain a mullite foaming precursor, thereby obtaining a solid foam ceramic precursor; and the final mullite foam ceramic with a preset porosity is achieved, thereby achieving controllable internal porosity of the mullite foam ceramic.

[0053] Further, the process of preparing the solid foam ceramic precursor comprises the following steps:

[0054] According to the preset mass msol of the mullite foam ceramic precursor sol solution to be added to the foaming accommodating space, the mullite foam ceramic precursor sol solution with the mass msol is added to the foaming accommodating space of the porosity controllable foaming device through the feeding port, and then the cover body is connected to the feeding port;

[0055] Adding gas into the gas containing space inside the pressure control device through a gas source, and when the gas containing space reaches a preset pressure, stopping adding gas into the gas containing space;

[0056] Then the heat source introduces a heating substance into the heating accommodation space through a pipeline to heat the mullite foam ceramic precursor sol solution in the foaming accommodation space;

[0057] The mullite foam ceramic precursor sol solution in the foaming accommodation space undergoes hydrolysis, expansion, cross-linking and gelation reactions during the heating process;

[0058] When the mullite foam ceramic precursor sol solution in the foaming accommodating space is foamed and fills the foaming accommodating space, the one-way control valve provided on the first gas transmission pipeline is opened;

[0059] At the same time, the pressure in the gas containing space is controlled at a preset pressure by controlling the second control valve provided in the second gas transmission pipeline and the first control valve provided in the exhaust pipeline;

[0060] When the mullite foam ceramic precursor sol solution in the foaming accommodating space is completely reacted, a solid foam ceramic precursor is obtained.

[0061] The beneficial effect of adopting the previous step is that the above method is conducive to achieving that the internal pores of the obtained mullite foam ceramic are through holes.

[0062] Further, the inorganic aluminum source includes one or more of aluminum nitrate, aluminum chloride, and aluminum sulfate;

[0063] The organic aluminum source includes one or more of aluminum isopropoxide, aluminum sec-butoxide, and aluminum carboxylate;

[0064] The silicon source includes tetramethyl silicate and / or tetraethyl silicate.

[0065] Furthermore, the process of preparing the foam body dry blank comprises the following steps:

[0066] The solid foam ceramic precursor is pre-frozen at -22 to -18°C for 1.8 to 2.2 hours, and then frozen at -40 to -25°C for 24 to 36 hours;

[0067] Then, the temperature is raised from -40 to -25°C to room temperature at a rate of 4.5-5.5°C / h to thaw, thereby obtaining a foam precursor dry blank;

[0068] and / or

[0069] The process for preparing the mullite foam ceramic comprises the following steps:

[0070] The foam precursor dry blank is heated from room temperature to 80-120°C at a heating rate of 9-10°C / min; from 80-120°C to 300-350°C at a heating rate of 4-5°C / min; from 300-350°C to 1000-1200°C at a heating rate of 1-2°C / min.

[0071] The beneficial effect of adopting the above step is that the process of preparing the foam body dry blank is conducive to slowly volatilizing the volatiles in the solid foam ceramic precursor, while avoiding the problem of damage, cracks or internal pore collapse of the solid foam ceramic precursor;

[0072] By heating the foam precursor dry blank from room temperature to 80-120°C at a heating rate of 9-10°C / min, it is beneficial to realize the rapid volatilization of small molecular volatiles and form through holes. By heating from 80-120°C to 300-350°C at a heating rate of 4-5°C / min, the volatiles of larger molecules are slowly decomposed, and slowly volatilize on the basis of the through holes formed by the small molecular volatiles, thereby not causing the problem of cracking or damage of mullite foam ceramics. By heating from 300-350°C to 1000-1200°C at a heating rate of 1-2°C / min, ceramicization is realized. Compared with conventional mullite ceramics that need to be sintered at 1350-1450°C, the sintering temperature is lowered, thereby reducing the production cost. DETAILED DESCRIPTION

[0073] In order to better understand the technical solution of the present invention, the present invention is further described below in conjunction with specific embodiments.

[0074] Embodiment 1:

[0075] According to this embodiment, a method for preparing a mullite foam ceramic with controllable porosity is provided, comprising the following steps:

[0076] An aluminum source-silicon source solution is prepared, wherein the aluminum source-silicon source solution comprises an inorganic aluminum source, an organic aluminum source, and a silicon source; the preparation of the aluminum source-silicon source solution comprises the following steps:

[0077] Adding an inorganic aluminum source into deionized water to dissolve it, thereby obtaining an inorganic aluminum source solution;

[0078] Then, an organic aluminum source and a silicon source are added into the inorganic aluminum source solution and stirred to obtain an aluminum source-silicon source solution;

[0079] The mass ratio of the inorganic aluminum source, the organic aluminum source and the silicon source is 4.5:10:5.5; the inorganic aluminum source includes aluminum nitrate; the organic aluminum source includes aluminum isopropoxide; and the silicon source includes tetramethyl silicate.

[0080] The aluminum source-silicon source solution is hydrolyzed to prepare a mullite foam ceramic precursor sol stock solution; the preparation process comprises the following steps:

[0081] The aluminum source-silicon source solution was placed at room temperature for hydrolysis for 36 hours; and then heated at 65° C. for hydrolysis for 28 hours to obtain a mullite foam ceramic precursor sol stock solution.

[0082] The mullite foam ceramic precursor sol stock solution is concentrated to obtain a mullite foam ceramic precursor sol solution; the preparation process of the mullite foam ceramic precursor sol solution comprises the following steps:

[0083] According to Formula 1 and Formula 2, the preset porosity β of mullite foam ceramic, the mass m of mullite component in the mullite foam ceramic precursor sol solution added to the foaming accommodation space, the volume V of the foaming accommodation space of the porosity controllable foaming device, and the theoretical density ρ of mullite are 3.03 g / cm 3 -3.16g / cm 3 , presetting the mass msolution of the mullite foam ceramic precursor sol solution added to the foaming accommodation space, and obtaining the solid content csolution of the mullite foam ceramic precursor sol stock solution;

[0084] Formula 1:

[0085]

[0086] m 莫 =m 溶 ×c 溶 ;

[0087] The mass of the mullite foam ceramic precursor sol solution after concentrating the mullite foam ceramic precursor sol stock solution is obtained by measuring the mass of the alumina and the silicon oxide in the inorganic aluminum source, the organic aluminum source and the silicon source added to the C solution and the mullite foam ceramic precursor sol stock solution;

[0088] The porosity controllable foaming device comprises a foaming device; the foaming device is provided with a foaming accommodating space inside and a heating accommodating space sleeved outside the foaming accommodating space;

[0089] The surface of the foaming device is provided with a feeding port, which is communicated with the foaming accommodating space; the feeding port is detachably connected with a cover body; a sealing member is provided between the cover body and the feeding port; and the heat accommodating space is connected with a heat source through a pipeline.

[0090] The mullite foam ceramic precursor sol solution is foamed in a porosity controllable foaming device to obtain a solid foam ceramic precursor;

[0091] The process of preparing a solid foam ceramic precursor comprises the following steps:

[0092] According to the preset mass msol of the mullite foam ceramic precursor sol solution to be added to the foaming accommodating space, the mullite foam ceramic precursor sol solution with the mass msol is added to the foaming accommodating space of the porosity controllable foaming device through the feeding port, and then the cover body is connected to the feeding port;

[0093] The heat source passes the heating material into the heating accommodation space through the pipeline to heat the mullite foam ceramic precursor sol solution in the foaming accommodation space; the heating process in the foaming accommodation space is to increase the temperature to 185°C at a heating rate of 6°C / min and keep the temperature at 185°C for 18 hours;

[0094] During the heating process of the sol solution of the raw stone foam ceramic precursor in the foaming accommodation space, hydrolysis, expansion, cross-linking and gelation reactions are carried out to obtain a solid foam ceramic precursor.

[0095] The solid-state foam ceramic precursor is freeze-dried to obtain a foam precursor dry blank; the process for preparing the foam precursor dry blank comprises the following steps:

[0096] The solid foam ceramic precursor was pre-frozen at -20°C for 2 h and then frozen at -32°C for 30 h;

[0097] Then, the temperature was raised from -32°C to room temperature at a rate of 5°C / h to thaw, thereby obtaining a dry foam precursor.

[0098] The foam precursor dry blank is sintered to obtain the mullite foam ceramic; the process for preparing the mullite foam ceramic comprises the following steps:

[0099] The foam precursor dry blank was heated from room temperature to 100°C at a heating rate of 9.5°C / min; from 100°C to 320°C at a heating rate of 4.5°C / min; and from 320°C to 1150°C at a heating rate of 1.5°C / min.

[0100] Example 2

[0101] The same contents as those in Example 1 are not described in detail here. The differences between this embodiment and Example 1 are as follows:

[0102] The porosity controllable foaming device also includes a pressure control device;

[0103] The surface of the foaming device is also provided with a first air outlet, and the first air outlet is connected to the pressure control device through a first air pipeline;

[0104] The first gas transmission pipeline is provided with a one-way control valve;

[0105] The pressure control device is provided with a gas accommodating space inside, and the pressure control device is provided with a first air inlet, a second air inlet, and a second air outlet;

[0106] The first air inlet and the first air outlet connect the foaming accommodating space with the gas accommodating space through the first air delivery pipeline;

[0107] The second air inlet hole connects the air source with the gas containing space through a second air pipeline, and the second air pipeline is provided with a second control valve;

[0108] The second air outlet is provided with an exhaust pipeline, and the exhaust pipeline is provided with a first control valve; and a pressure sensor is provided in the gas containing space.

[0109] The process of preparing a solid foam ceramic precursor comprises the following steps:

[0110] According to the preset mass msol of the mullite foam ceramic precursor sol solution to be added to the foaming accommodating space, the mullite foam ceramic precursor sol solution with the mass msol is added to the foaming accommodating space of the porosity controllable foaming device through the feeding port, and then the cover body is connected to the feeding port;

[0111] Adding gas into the gas containing space inside the pressure control device through a gas source, and when the gas containing space reaches a preset pressure, stopping adding gas into the gas containing space;

[0112] Then, the heat source introduces a heating substance into the heating accommodation space through a pipeline to heat the mullite foam ceramic precursor sol solution in the foaming accommodation space; the heating process in the foaming accommodation space is to increase the temperature to 195° C. at a heating rate of 8° C. / min and keep the temperature at 195° C. for 14 hours;

[0113] The mullite foam ceramic precursor sol solution in the foaming accommodation space undergoes hydrolysis, expansion, cross-linking and gelation reactions during the heating process;

[0114] When the mullite foam ceramic precursor sol solution in the foaming accommodating space is foamed and fills the foaming accommodating space, the one-way control valve provided on the first gas transmission pipeline is opened;

[0115] At the same time, the pressure in the gas containing space is controlled at a preset pressure by controlling the second control valve provided in the second gas transmission pipeline and the first control valve provided in the exhaust pipeline;

[0116] When the mullite foam ceramic precursor sol solution in the foaming accommodating space is completely reacted, a solid foam ceramic precursor is obtained.

[0117] The mass ratio of the inorganic aluminum source, the organic aluminum source and the silicon source is 5:11:6; the inorganic aluminum source includes aluminum chloride; the organic aluminum source includes aluminum sec-butoxide; and the silicon source includes tetraethyl silicate.

[0118] The aluminum source-silicon source solution is hydrolyzed to prepare a mullite foam ceramic precursor sol stock solution; the preparation process comprises the following steps:

[0119] The aluminum source-silicon source solution was placed at room temperature for hydrolysis for 27 hours; and then heated at 68° C. for hydrolysis for 38 hours to obtain a mullite foam ceramic precursor sol stock solution.

[0120] The solid foam ceramic precursor was pre-frozen at -21 °C for 1.9 h and then frozen at -38 °C for 25 h;

[0121] Then, the temperature was raised from -38°C to room temperature at a rate of 4.6°C / h to thaw, thereby obtaining a dry foam precursor.

[0122] The foam precursor dry blank was heated from room temperature to 115°C at a heating rate of 9.8°C / min; from 115°C to 345°C at a heating rate of 4.8°C / min; and from 345°C to 1150°C at a heating rate of 1.8°C / min.

[0123] Example 3

[0124] The same contents as those in Example 1 are not described in detail here. The differences between this embodiment and Example 1 are as follows:

[0125] The porosity controllable foaming device also includes a pressure control device;

[0126] The surface of the foaming device is also provided with a first air outlet, and the first air outlet is connected to the pressure control device through a first air pipeline;

[0127] The first gas transmission pipeline is provided with a one-way control valve;

[0128] The pressure control device is provided with a gas accommodating space inside, and the pressure control device is provided with a first air inlet, a second air inlet, and a second air outlet;

[0129] The first air inlet and the first air outlet connect the foaming accommodating space with the gas accommodating space through the first air delivery pipeline;

[0130] The second air inlet hole connects the air source with the gas containing space through a second air pipeline, and the second air pipeline is provided with a second control valve;

[0131] The second air outlet is provided with an exhaust pipeline, and the exhaust pipeline is provided with a first control valve; and a pressure sensor is provided in the gas containing space.

[0132] The process of preparing a solid foam ceramic precursor comprises the following steps:

[0133] According to the preset mass msol of the mullite foam ceramic precursor sol solution to be added to the foaming accommodating space, the mullite foam ceramic precursor sol solution with the mass msol is added to the foaming accommodating space of the porosity controllable foaming device through the feeding port, and then the cover body is connected to the feeding port;

[0134] Adding gas into the gas containing space inside the pressure control device through a gas source, and when the gas containing space reaches a preset pressure, stopping adding gas into the gas containing space;

[0135] Then, the heat source introduces a heating substance into the heating accommodation space through a pipeline to heat the mullite foam ceramic precursor sol solution in the foaming accommodation space; the heating process in the foaming accommodation space is to increase the temperature to 175°C at a heating rate of 3°C / min and keep the temperature at 1750°C for 22 hours;

[0136] The mullite foam ceramic precursor sol solution in the foaming accommodation space undergoes hydrolysis, expansion, cross-linking and gelation reactions during the heating process;

[0137] When the mullite foam ceramic precursor sol solution in the foaming accommodating space is foamed and fills the foaming accommodating space, the one-way control valve provided on the first gas transmission pipeline is opened;

[0138] At the same time, the pressure in the gas containing space is controlled at a preset pressure by controlling the second control valve provided in the second gas transmission pipeline and the first control valve provided in the exhaust pipeline;

[0139] When the mullite foam ceramic precursor sol solution in the foaming accommodating space is completely reacted, a solid foam ceramic precursor is obtained.

[0140] The mass ratio of the inorganic aluminum source, the organic aluminum source and the silicon source is 4:9:4.5; the inorganic aluminum source includes aluminum chloride and aluminum sulfate; the organic aluminum source includes aluminum sec-butoxide and aluminum carboxylate; and the silicon source includes tetramethyl silicate and tetraethyl silicate.

[0141] The aluminum source-silicon source solution is hydrolyzed to prepare a mullite foam ceramic precursor sol stock solution; the preparation process comprises the following steps:

[0142] The aluminum source-silicon source solution was placed at room temperature for hydrolysis for 25 hours; and then heated at 62° C. for hydrolysis for 18 hours to obtain a mullite foam ceramic precursor sol stock solution.

[0143] The solid foam ceramic precursor was pre-frozen at -19 °C for 2.1 h and then frozen at -28 °C for 35 h;

[0144] Then, the temperature was raised from -26°C to room temperature at a rate of 5.3°C / h to thaw, thereby obtaining a dry foam precursor.

[0145] The foam precursor dry blank was heated from room temperature to 90°C at a heating rate of 9.2°C / min; from 85°C to 310°C at a heating rate of 4.2°C / min; and from 310°C to 1050°C at a heating rate of 1.2°C / min.

[0146] The above description is only a preferred embodiment of the present application and an explanation of the technical principles used. Those skilled in the art should understand that the scope of the invention involved in the present application is not limited to the technical solution formed by a specific combination of the above technical features, but should also cover other technical solutions formed by any combination of the above technical features or their equivalent features without departing from the inventive concept. For example, the above features are replaced with (but not limited to) technical features with similar functions disclosed in the present application.

Claims

1. A method for preparing mullite foam ceramic with controllable porosity, characterized in that: The following steps are involved: preparing an aluminum source-silicon source solution, wherein the aluminum source-silicon source solution comprises an inorganic aluminum source, an organic aluminum source, and a silicon source; The aluminum source-silicon source solution is hydrolyzed to prepare a mullite foam ceramic precursor sol stock solution; The mullite foam ceramic precursor sol stock solution is concentrated to obtain a mullite foam ceramic precursor sol solution; The mullite foam ceramic precursor sol solution is foamed in a porosity controllable foaming device to obtain a solid foam ceramic precursor; freeze-drying the solid foam ceramic precursor to obtain a foam precursor dry blank; The foam precursor dry blank is sintered to obtain the mullite foam ceramic.

2. The method for preparing the mullite foam ceramic with controllable porosity according to claim 1, characterized in that: The preparation of the aluminum source-silicon source solution comprises the following steps: Adding an inorganic aluminum source into deionized water to dissolve it, thereby obtaining an inorganic aluminum source solution; Then, an organic aluminum source and a silicon source are added into the inorganic aluminum source solution and stirred to obtain an aluminum source-silicon source solution; The mass ratio of the inorganic aluminum source, the organic aluminum source, and the silicon source is (3-6): (8-12): (4-7).

3. The method for preparing the mullite foam ceramic with controllable porosity according to claim 1, characterized in that: The process for preparing the mullite foam ceramic precursor sol solution comprises the following steps: The aluminum source-silicon source solution is placed at room temperature for hydrolysis for 24-28 hours; and then heated at 60-70° C. for hydrolysis for 16-40 hours to obtain a mullite foam ceramic precursor sol stock solution.

4. The method for preparing the mullite foam ceramic with controllable porosity according to claim 2, characterized in that: The preparation process of the mullite foam ceramic precursor sol solution comprises the following steps: According to Formula 1 and Formula 2, the mass m of the mullite component in the mullite foam ceramic precursor sol solution added to the foaming accommodation space is calculated by the preset required porosity β of the mullite foam ceramic. 莫 , the volume V of the foaming accommodation space of the porosity controllable foaming device 模 、Theoretical density of mullite ρ 莫 =3.03g / cm 3 -3.16g / cm 3 , the mass m of the mullite foam ceramic precursor sol solution added to the foaming accommodation space 溶 , the solid content c of the mullite foam ceramic precursor sol solution is obtained 溶 ; Formula 1: Formula 2: m 莫 =m 溶 ×c 溶 ; Through the c 溶 The mass of alumina and silicon oxide in the inorganic aluminum source, organic aluminum source and silicon source added to the mullite foam ceramic precursor sol stock solution is obtained by concentrating the mullite foam ceramic precursor sol stock solution.

5. The method for preparing the mullite foam ceramic with controllable porosity according to claim 4, characterized in that: The porosity controllable foaming device comprises a foaming device; The foaming device is provided with a foaming accommodating space inside and a heating accommodating space sleeved outside the foaming accommodating space; The surface of the foaming device is provided with a feeding port, and the feeding port is connected with the foaming accommodating space; the feeding port is detachably connected with a cover body; a sealing member is provided between the cover body and the feeding port; The heat accommodating space is connected to the heat source through a pipeline.

6. The method for preparing the mullite foam ceramic with controllable porosity according to claim 5, characterized in that: The porosity controllable foaming device also includes a pressure control device; The surface of the foaming device is also provided with a first air outlet, and the first air outlet is connected to the pressure control device through a first air pipeline; The first gas transmission pipeline is provided with a one-way control valve; The pressure control device is provided with a gas accommodating space inside, and the pressure control device is provided with a first air inlet, a second air inlet, and a second air outlet; The first air inlet and the first air outlet connect the foaming accommodating space with the gas accommodating space through the first air delivery pipeline; The second air inlet hole connects the air source with the gas containing space through a second air pipeline, and the second air pipeline is provided with a second control valve; The second air outlet is provided with an exhaust pipeline, and the exhaust pipeline is provided with a first control valve; A pressure sensor is arranged in the gas accommodating space.

7. The method for preparing the mullite foam ceramic with controllable porosity according to claim 5, characterized in that: The process of preparing a solid foam ceramic precursor comprises the following steps: According to the preset mass m of the mullite foam ceramic precursor sol solution added to the foaming accommodation space 溶 , the mass is m 溶 The mullite foam ceramic precursor sol solution is added into the foaming containing space of the porosity controllable foaming device through the feeding port, and then the cover body is connected to the feeding port; The heat source passes a heating substance into the heating accommodation space through a pipeline to heat the mullite foam ceramic precursor sol solution in the foaming accommodation space; During the heating process of the sol solution of the raw stone foam ceramic precursor in the foaming accommodation space, hydrolysis, expansion, cross-linking and gelation reactions are carried out to obtain a solid foam ceramic precursor.

8. The method for preparing mullite foam ceramic with controllable porosity according to claim 6, characterized in that: The process of preparing a solid foam ceramic precursor comprises the following steps: According to the preset mass msol of the mullite foam ceramic precursor sol solution to be added to the foaming accommodating space, the mullite foam ceramic precursor sol solution with the mass msol is added to the foaming accommodating space of the porosity controllable foaming device through the feeding port, and then the cover body is connected to the feeding port; Adding gas into the gas containing space inside the pressure control device through a gas source, and when the gas containing space reaches a preset pressure, stopping adding gas into the gas containing space; Then the heat source introduces a heating substance into the heating accommodation space through a pipeline to heat the mullite foam ceramic precursor sol solution in the foaming accommodation space; The mullite foam ceramic precursor sol solution in the foaming accommodation space undergoes hydrolysis, expansion, cross-linking and gelation reactions during the heating process; When the mullite foam ceramic precursor sol solution in the foaming accommodating space is foamed and fills the foaming accommodating space, the one-way control valve provided on the first gas transmission pipeline is opened; At the same time, the pressure in the gas containing space is controlled at a preset pressure by controlling the second control valve provided in the second gas transmission pipeline and the first control valve provided in the exhaust pipeline; When the mullite foam ceramic precursor sol solution in the foaming accommodating space is completely reacted, a solid foam ceramic precursor is obtained.

9. The method for preparing the mullite foam ceramic with controllable porosity according to claim 2, characterized in that: The inorganic aluminum source includes one or more of aluminum nitrate, aluminum chloride, and aluminum sulfate; The organic aluminum source includes one or more of aluminum isopropoxide, aluminum sec-butoxide, and aluminum carboxylate; The silicon source includes tetramethyl silicate and / or tetraethyl silicate.

10. The method for preparing mullite foam ceramic with controllable porosity according to claim 6, characterized in that: The process of preparing the foam body dry blank comprises the following steps: The solid foam ceramic precursor is pre-frozen at -22 to -18°C for 1.8 to 2.2 hours, and then frozen at -40 to -25°C for 24 to 36 hours; Then, the temperature is raised from -40 to -25°C to room temperature at a rate of 4.5-5.5°C / h to thaw, thereby obtaining a foam precursor dry blank; and / or The process for preparing the mullite foam ceramic comprises the following steps: The foam precursor dry blank is heated from room temperature to 80-120°C at a heating rate of 9-10°C / min; from 80-120°C to 300-350°C at a heating rate of 4-5°C / min; from 300-350°C to 1000-1200°C at a heating rate of 1-2°C / min.

Images