CN109019614B - Rare earth toughened silicon aerogel precursor - Google Patents
Rare earth toughened silicon aerogel precursor Download PDFInfo
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- CN109019614B CN109019614B CN201810786244.5A CN201810786244A CN109019614B CN 109019614 B CN109019614 B CN 109019614B CN 201810786244 A CN201810786244 A CN 201810786244A CN 109019614 B CN109019614 B CN 109019614B
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- C01B33/00—Silicon; Compounds thereof
- C01B33/113—Silicon oxides; Hydrates thereof
- C01B33/12—Silica; Hydrates thereof, e.g. lepidoic silicic acid
- C01B33/14—Colloidal silica, e.g. dispersions, gels, sols
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- C01B33/00—Silicon; Compounds thereof
- C01B33/113—Silicon oxides; Hydrates thereof
- C01B33/12—Silica; Hydrates thereof, e.g. lepidoic silicic acid
- C01B33/14—Colloidal silica, e.g. dispersions, gels, sols
- C01B33/141—Preparation of hydrosols or aqueous dispersions
- C01B33/142—Preparation of hydrosols or aqueous dispersions by acidic treatment of silicates
- C01B33/143—Preparation of hydrosols or aqueous dispersions by acidic treatment of silicates of aqueous solutions of silicates
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- C01B33/113—Silicon oxides; Hydrates thereof
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- C01B33/16—Preparation of silica xerogels
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Abstract
The invention discloses a silicon aerogel precursor which is carried out in normal temperature and normal pressure environment, has short process time, is suitable for industrialization and can improve the toughness and the heat-resisting temperature of silicon aerogel. The preparation method of the silicon aerogel precursor comprises the following steps: (1) preparing a mixed solution of a silicon source and a solvent, (2) sol, (3) gel, (4) aging, (5) solvent replacement and (6) surface modification; a preparation method of rare earth toughening solid silicon aerogel is characterized by placing a prepared silicon aerogel precursor into a drying kettle, filling nitrogen into the drying kettle to remove oxygen until the oxygen content in the drying kettle is less than 3%, and then carrying out microwave vacuum drying on the material in the drying kettle; drying to obtain solid powdery silica aerogel.
Description
The application is a divisional application of Chinese invention patent with patent application number 201610995966.2 (application date: 2016, 11, 12 and the name: a preparation process of rare earth toughened silicon aerogel precursor and solid silicon aerogel).
Technical Field
The invention relates to the technical field of aerogel, in particular to a rare earth toughened silicon aerogel precursor.
Background
Silica aerogel is a light nano-porous material with a controllable structure, and has many excellent properties, such as high porosity, high specific surface area, low density, low thermal conductivity, and the like.
The preparation of aerogels generally consists of sol, gel processes and supercritical drying processes. In the sol and gel process, through controlling the hydrolysis and polycondensation reaction conditions of the solution, nanoclusters with different structures are formed in the solution, the clusters are adhered to each other to form gel, and the periphery of the solid skeleton of the gel is filled with the liquid reagent left after the chemical reaction. In order to prevent the damage of the material structure caused by the surface tension in the micro-pores in the drying process of the gel, a supercritical drying process is adopted for treatment, the gel is placed in a pressure container for heating and boosting, so that the liquid in the gel is changed into supercritical fluid, a gas-liquid interface disappears, the surface tension does not exist any more, and at the moment, the supercritical fluid is released from the pressure container, so that the low-density aerogel material with the porous, disordered and nano-scale continuous network structure can be obtained. But the supercritical drying equipment has high requirement, consumes a large amount of energy, is dangerous to operate, greatly increases the cost of the aerogel, and is not beneficial to large-scale production.
Therefore, the supercritical drying method for preparing the silica aerogel brings the defects of high production cost and long preparation process time; in recent years, some relevant reports and patent documents about preparation of silica aerogel under normal temperature and temperature difference pressure are provided by research and development personnel, but most of the reports and patent documents are in the laboratory preparation stage, the process is long, the process implementation range is too narrow, and large-scale industrial production and application cannot be realized. In addition, the aerogel has a net structure, the edges of the structure are thin and brittle, and the aerogel is easy to collapse under external pressure, so that the thermal conductivity is reduced; in addition, the silica aerogel has low use temperature, and is generally stable when used at the temperature of below 500 ℃. The internal structure of the silica aerogel changes above 500 ℃, which leads to a sharp drop in thermal conductivity. This will affect the further development and utilization of aerogels.
Disclosure of Invention
The invention aims to provide a silicon aerogel precursor which is carried out in the environment of normal temperature and normal pressure, has short process time, is suitable for industrialization and can improve the toughness and the heat-resisting temperature of silicon aerogel, aiming at the technical defects in the prior art.
The technical scheme adopted for realizing the purpose of the invention is as follows: a preparation method of a rare earth toughened silicon aerogel precursor comprises the following steps:
(1) preparation of a mixed solution of a silicon source and a solvent
Filling sodium silicate with the mole number of 3.0-4.0 into a reaction kettle, adding deionized water with the mass of 1-3 times that of the sodium silicate for dilution, stirring the reaction kettle at the speed of 80-200 revolutions per minute for 30 minutes, and filtering the mixture through a 200-mesh sieve to obtain a sodium silicate solution;
the water solution of sodium silicate is commonly called water glass, which is composed of alkali metal and silicon dioxide in different proportions, and has a chemical formula of R2O. nSiO2, wherein R2O is alkali metal oxide, n is the ratio of the mole number of the silicon dioxide to the mole number of the alkali metal oxide, and is called the mole number of the water glass, and the most common is sodium silicate water glass Na 2O. nSiO 2;
(2) sol gel
Taking acid A, adding metal salt A and rare earth acid salt A into the acid A, uniformly mixing, and adding into the sodium silicate solution obtained in the step (1) in a spraying manner; rapidly stirring the materials in the reaction kettle at the speed of 1200-2000 rpm while spraying, controlling the pH value of the sodium silicate solution to be 1.5-3.0, and controlling the average pore diameter to be 15-30 nanometers to obtain sol, wherein the time of the step is 60-120 minutes;
(3) gel
Taking sodium hydroxide or ammonia water, adding deionized water to dilute until the pH value is 10-11.5, and adding the sodium hydroxide or ammonia water into a reaction kettle in a spraying manner; rapidly stirring the materials in the reaction kettle at the speed of 1200-2000 rpm while spraying, stopping spraying when the pH value of the materials in the reaction kettle is 4.5-5.5 to obtain gel, wherein the time for the step is 80-180 minutes;
(4) aging of
Continuously stirring the mixture in the reaction kettle for 3 to 10 hours at the speed of 20 to 50 revolutions per minute, aging the materials in the reaction kettle, and controlling the temperature of the materials in the reaction kettle to be 35 to 50 ℃; the prior art generally adopts a standing mode for aging, takes 3-5 days, and does not stir the gel, because the prior art generally considers that the aging process needs standing, and the standing can facilitate the structural growth of the aerogel;
(5) solvent replacement
Continuously stirring in the reaction kettle for 60-180 minutes, and simultaneously adding a displacement solvent with the same volume as the aged material in the reaction kettle in the step (4) to displace the residual water; in the prior art, the structure of the stirring tank is damaged, the stirring tank cannot be used for stirring during replacement, and standing treatment is adopted, so that the consumed time is long; the preparation method provided by the invention can stir for 60-180 minutes during solvent replacement, can greatly shorten the replacement period, and does not damage the microstructure;
(6) surface modification
Continuously stirring in the reaction kettle, and continuously adding the coupling agent with the same volume as the aged material in the reaction kettle in the step (4); stirring for 60-180 min to obtain the silica aerogel precursor coated with the replacement solvent and the coupling agent.
The coupling agent added in the surface modification in the step (6) replaces water in the aerogel micropores, and the coupling agent is filled in the aerogel micropores, so that the stability of the micropore structure can be improved, and the average of the pore size is improved; in addition, the hydrophobic and hydrophilic functions of the aerogel can be adjusted by adding different coupling agents for surface modification.
In the step (2), the acid A is sulfuric acid, hydrochloric acid, oxalic acid or nitric acid, and is adjusted to be 6-15 mol/L by deionized water.
In the step (2), the metal salt A is zirconium A acid salt or aluminum A acid salt.
In the step (2), the rare earth A acid salt is cerium salt A, yttrium salt A or lanthanum salt A.
The metal salt A and the rare earth A acid salt are liable to absorb moisture and cause inaccurate metering, so that in order to accurately quantify the amounts to be added, the metal salt A and the rare earth A acid salt are added in a molar ratio of 100: 1 to 6; in the step (2), the mole ratio of the oxide of the metal salt A to the silicon oxide in the sodium silicate is 2-5: 100, respectively; for example, the metal salt of a is aluminum sulfate, calculated as its oxide, i.e., in a molar ratio of alumina to silica in sodium silicate of 2 to 5: 100.
the replacement solvent in the step (5) is one or more of methanol, acetone, n-hexane and heptane.
The stirring in the step (5) or the step (6) is carried out in a reaction kettle;
the stirring is realized by providing rapid forward stirring (a high-speed shearing disc) for the center of the reaction kettle and providing a baffle plate at the periphery of the center of the reaction kettle.
In the step (6), the coupling agent is one or more of hexamethyldisilazane, bis (trimethylsilyl) acetamide, methoxytrimethylsilane, dimethoxydimethylsilane, phenyltriethoxysilane, phenyltrimethoxysilane, vinyltrimethoxysilane, methyltriethoxysilane or methyltrimethoxysilane.
The preparation method of the rare earth toughened solid silicon aerogel is characterized by comprising the following steps: putting the prepared silicon aerogel precursor into a drying kettle, filling nitrogen into the drying kettle to remove oxygen until the oxygen content in the drying kettle is less than 3%, and then performing microwave vacuum drying on the material in the drying kettle; drying at 85-135 deg.C under negative pressure of 0.08-0.12 mpa to obtain solid powdered silica aerogel. The silica aerogel precursor is coated with a displacement solvent and a coupling agent, belongs to hydroxide, and is changed into solid powdery oxide after microwave drying.
Preferably, the microwave vacuum drying time is 50-80 minutes, and the microwave frequency is 2450MHz +/-10 MHz.
The working principle of the invention is as follows: in the preparation method of the silicon aerogel precursor, the metal salt A and the rare earth A acid salt are added in the gelling process, so that the effects of toughening and improving the heat resistance of the silicon aerogel can be achieved; the aging and solvent replacement steps are carried out under the stirring state, so that the reaction efficiency is greatly improved, the process time is shortened, and the method is suitable for industrialization; the process for preparing the solid powdery silica aerogel by using the silica aerogel precursor is carried out by adopting a negative pressure microwave drying method, and microwaves can directly penetrate into a micropore structure of the silica aerogel, so that a heat conduction mode from inside to outside is realized; the microwave can generate microcosmic vibration on the materials in the microporous structure, thereby effectively avoiding the occurrence of agglomeration; under negative pressure, the boiling point, evaporation point or vaporization point of the solvent in the micropores decreases.
Compared with the prior art, the invention has the beneficial effects that:
(1) in recent years, some relevant reports and patent documents about preparation of silica aerogel under normal temperature and differential pressure exist in the prior art, but most of the reports and patent documents stay in a laboratory preparation stage, the process is long, and the process implementation range is too narrow, so that large-scale industrial production and application are difficult to realize; the invention provides a preparation method under normal temperature and normal pressure, which changes the relative static process in the prior art, applies stirring in the key process, accelerates the realization of the hydrolysis, polycondensation and modification of aerogel, realizes the process of synthesizing aerogel precursor within 30 hours, provides a method for industrially preparing rare earth toughening silicon aerogel in batches, and provides the premise for the mass production and use of aerogel;
(2) one of the reasons for hindering the development of aerogels is that aerogels have a network structure, but the edges of the structure are thin and brittle, have low compressive strength, and are easily collapsed under pressure, resulting in unstable performance; according to the invention, rare earth A acid salt and metal salt A are added, so that the toughness of the material is improved, and the strength of the silica aerogel is improved;
(3) the silica aerogel prepared by the prior art has low use temperature, is generally stable when used below 500 ℃, and can cause the internal structure change of the silica aerogel above 500 ℃ to reduce the heat conductivity coefficient; according to the invention, rare earth A acid salt and metal salt A are added, so that the temperature resistance of the material is improved, and the heat resistance temperature of the silica aerogel is increased;
(4) in the prior art, the commonly adopted methods such as high-temperature sintering, drying and the like in the process of preparing the solid-state silicon aerogel can cause structural collapse or sintering agglomeration in the material sintering process, reduce the specific surface area of the material and greatly influence the heat conductivity coefficient of the material; according to the invention, the silicon aerogel precursor is subjected to microwave vacuum drying, microwaves can directly penetrate into the microporous structure of the aerogel, and a heat conduction mode from inside to outside is realized; under the negative pressure state, the boiling point, the evaporation point or the gasification point of the solvent in the micropores can be reduced; the microwave can generate micro vibration on the materials in the microporous structure, thereby effectively avoiding the phenomena of structural collapse or sintering agglomeration of the materials caused by high-temperature sintering, drying and other methods, and effectively improving the specific surface area and the heat conductivity coefficient of the materials;
(5) and nitrogen is filled for protection during microwave vacuum drying, and the negative pressure low temperature is used for safely recycling the replacement solvent or the coupling agent so as to reduce the manufacturing cost. Nitrogen is filled for protection during microwave vacuum drying, and the microwave vacuum drying is carried out under the state of negative pressure and low temperature; the microwave vacuum drying gasifies the replacement solvent or the coupling agent in the microporous structure in a negative pressure state, liquefies the replacement solvent or the coupling agent in a low-temperature state, and can realize safe recycling so as to reduce the process cost.
Detailed Description
The present invention will be described in further detail with reference to specific examples. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
Example 1:
the present invention will be described in detail with reference to the following examples:
(1) preparation of a mixed solution of a silicon source and a solvent
And (3) filling water glass with the mole number of 3.0 into a reaction kettle, diluting with deionized water with the mass of 2.5 times, stirring for 30 minutes at 180 revolutions per minute, and filtering through a 200-mesh sieve to obtain a water glass solution.
(2) Sol gel
Taking 8mol/L sulfuric acid, and adding zirconium sulfate salt (the molar ratio of the zirconium sulfate salt to the silicon oxide of the water glass solution is 5: 100 in terms of zirconium oxide) and yttrium sulfate salt (the molar ratio of the yttrium sulfate salt to the aluminum oxide is 1: 100 in terms of yttrium oxide); after uniform mixing, spraying and adding the water glass solution obtained in the step (1), rapidly stirring at 1300 rpm while spraying, stopping spraying when the pH value is controlled to be 1.5, and controlling the spraying time to be 100 minutes; a sol is obtained.
(3) Gel
And (3) spraying a sodium hydroxide solution with the pH value of 11, adding the sodium hydroxide solution into the sol obtained in the step (2), rapidly stirring at 1300 rpm while spraying, stopping spraying until the pH value is 5, and taking 120 minutes to obtain the gel.
(4) Aging of
The gel is continuously stirred for 10 hours in the reaction kettle at the speed of 40 r/min, and the temperature of the gel in the reaction kettle is controlled to be 45 ℃.
(5) Solvent replacement
And adding a replacement solvent n-hexane with the same volume as the aged material while stirring in the reaction kettle, and stirring for 2 hours.
(6) Surface modification
Adding a coupling agent with the same volume as the aged material into the reaction kettle; the coupling agent is dimethoxy dimethyl silane, and the silica aerogel precursor coated with the replacement solvent and the coupling agent is obtained after stirring for 150 minutes and surface modification.
A preparation method of rare earth toughened solid silicon aerogel comprises the following steps: and (2) performing microwave vacuum drying on the silicon aerogel precursor coated with the replacement solvent and the coupling agent, wherein nitrogen in a drying kettle is used for removing oxygen until the oxygen content is less than 3%, the negative pressure is 0.08mpa, the temperature is 95 ℃, the microwave frequency is controlled within the range of 2450MHZ +/-10 MHZ, and the toughened silicon aerogel solid powder is obtained in 55 minutes.
The product is detected to have an average pore diameter of 26nm, a specific surface area of 588 square meters per gram, a loose specific gravity of 0.057g/cm, super hydrophobicity, flame retardance, a heat conductivity coefficient of 0.021W/M.K, a heat-resistant temperature of 880 ℃ and a compressive strength of 0.118 Mpa.
Example 2:
the present invention will be described in detail with reference to the following examples:
(1) preparation of a mixed solution of a silicon source and a solvent
And (3) filling water glass with the mole number of 3.2 into a reaction kettle, diluting with deionized water with the mass of 3 times, stirring for 30 minutes at 200 revolutions per minute, and filtering through a 200-mesh sieve to obtain a water glass solution.
(2) Sol gel
Taking 10mol/L nitric acid, and adding aluminum salt hydrochloride (the molar ratio of aluminum oxide to silicon oxide in the water glass solution is 2: 100 in terms of aluminum oxide) and lanthanum salt hydrochloride (the molar ratio of lanthanum salt hydrochloride to aluminum oxide is 3: 100 in terms of lanthanum oxide); after uniform mixing, spraying and adding the mixture into the water glass solution obtained in the step (1), rapidly stirring at 1200 rpm while spraying, and controlling the pH value to 2.5, wherein the spraying time is controlled to be 100 minutes; a sol is obtained.
(3) Gel
And (3) spraying an ammonia water solution with the pH value of 10.5, adding the ammonia water solution into the sol obtained in the step (2), rapidly stirring at 1200 rpm while spraying, stopping spraying until the pH value is 4.5, and taking 150 minutes to obtain gel.
(4) Aging of
Continuously stirring the reaction kettle for 5 hours at the speed of 30 r/min, and controlling the temperature of gel in the reaction kettle to be 50 ℃;
(5) solvent replacement
While stirring in the reaction kettle, the displacement solvent methanol with the same volume as the aged material is added to displace the residual moisture.
(6) Surface modification
Adding a coupling agent with the same volume as the aged material into the reaction kettle; the coupling agent is vinyl trimethoxy silane, and the surface of the vinyl trimethoxy silane is modified by stirring for 100 minutes to obtain a silicon aerogel precursor coated with a replacement solvent and the coupling agent.
A preparation method of rare earth toughened solid silicon aerogel comprises the following steps: and (3) performing microwave vacuum drying on the silicon aerogel precursor coated with the replacement solvent and the coupling agent, wherein nitrogen in a drying kettle is used for removing oxygen until the oxygen content is less than 2%, the negative pressure is 0.09mpa and 110 ℃, the microwave frequency is controlled within the range of 2450MHZ +/-10 MHZ, and the toughened silicon aerogel solid powder is obtained in 50 minutes.
The product is detected to have an average pore diameter of 28nm, a specific surface area of 568 square meters per gram, a loose specific gravity of 0.056g/cm, super hydrophobicity, flame retardance, a heat conductivity coefficient of 0.0198W/M.K, a heat resistance temperature of 920 ℃ and a compressive strength of 0.122 Mpa.
Example 3:
the present invention will be described in detail with reference to the following examples:
(1) preparation of a mixed solution of a silicon source and a solvent
And (3) putting water glass with the mole number of 4.0 into a reaction kettle, diluting with deionized water with the mass of 3 times, stirring for 30 minutes at 80 revolutions per minute, and filtering through a 200-mesh sieve to obtain the water glass solution.
(2) Sol gel
Adding 15mol/L nitric acid into aluminum oxalate salt (calculated by alumina, the molar ratio of the aluminum oxalate salt to the silicon oxide in the water glass solution is 3: 100) and lanthanum oxalate salt (calculated by lanthanum oxide, the molar ratio of the lanthanum oxalate salt to the aluminum oxide is 6: 100); after uniform mixing, spraying and adding the mixture into the water glass solution obtained in the step (1), rapidly stirring at the speed of 1800 rpm while spraying, controlling the pH value to 2.5, and controlling the spraying time to be 100 minutes; a sol is obtained.
(3) Gel
And (3) spraying a sodium hydroxide solution with the pH value of 11.5, adding the sodium hydroxide solution into the sol obtained in the step (2), rapidly stirring at 1200 rpm while spraying, stopping spraying until the pH value is 5.5, and taking 80 minutes to obtain the gel.
(4) Aging of
Continuously stirring the reaction kettle for 5 hours at the speed of 50 revolutions per minute, and controlling the temperature of gel in the reaction kettle to be 35 ℃;
(5) solvent replacement
While stirring in the reaction kettle, adding a displacement solvent acetone with the same volume as the aged material to displace the residual water.
(6) Surface modification
Adding a coupling agent with the same volume as the aged material into the reaction kettle; the coupling agent is a mixture of hexamethyldisilazane, bis (trimethylsilyl) acetamide and methoxytrimethylsilane, the weight of which is one third of that of hexamethyldisilazane, the mixture is stirred for 180 minutes, and the surface of the mixture is modified to obtain the silica aerogel precursor coated with the replacement solvent and the coupling agent.
A preparation method of rare earth toughened solid silicon aerogel comprises the following steps: and (2) performing microwave vacuum drying on the silicon aerogel precursor coated with the replacement solvent and the coupling agent, wherein nitrogen in a drying kettle is used for removing oxygen until the oxygen content is less than 1%, the negative pressure is 0.12mpa, the temperature is 80 ℃, the microwave frequency is controlled within the range of 2450MHZ +/-10 MHZ, and the toughened silicon aerogel solid powder is obtained after 60 minutes.
The product is detected to have an average pore diameter of 27nm, a specific surface area of 575 square meters per gram, a loose specific gravity of 0.058g/cm, super hydrophobicity, flame retardance, a heat conductivity coefficient of 0.0202W/M.K, a heat resistance temperature of 725 ℃ and a compressive strength of 0.125 Mpa.
Example 4:
the present invention will be described in detail with reference to the following examples:
(1) preparation of a mixed solution of a silicon source and a solvent
And (3) filling water glass with the mole number of 3.5 into a reaction kettle, diluting with deionized water with the mass of 2.5 times, stirring for 30 minutes at 120 revolutions per minute, and filtering through a 200-mesh sieve to obtain a water glass solution.
(2) Sol gel
Taking 6mol/L nitric acid, adding zirconium nitrate salt (calculated by zirconia, the molar ratio of the zirconium nitrate salt to the silicon oxide in the water glass solution is 4: 100) and cerium nitrate salt (calculated by cerium oxide, the molar ratio of the cerium nitrate salt to the zirconium oxide is 4: 100); after uniform mixing, spraying and adding the mixture into the water glass solution obtained in the step (1), rapidly stirring at the speed of 2000 rpm while spraying, controlling the pH value to be 5, and controlling the spraying time to be 120 minutes; a sol is obtained.
(3) Gel
And (3) spraying an ammonia water solution with the pH value of 10.5, adding the ammonia water solution into the sol obtained in the step (2), rapidly stirring at 1300 rpm while spraying, stopping spraying until the pH value is 4.5, and taking 180 minutes to obtain the gel.
(4) Aging of
Continuously stirring the reaction kettle for 8 hours at the speed of 20 r/min, and controlling the temperature of gel in the reaction kettle to be 40 ℃;
(5) solvent replacement
The displacement solvent (acetone, n-hexane and heptane, one third by weight of a mixture) was added in the same volume as the aged material while stirring in the reaction kettle to displace the remaining water.
(6) Surface modification
Adding a coupling agent with the same volume as the aged material into the reaction kettle; the coupling agent is a mixture of phenyltriethoxysilane, phenyltrimethoxysilane and methyltrimethoxysilane, the weight of which is one third of that of the mixture, and the mixture is stirred for 60 minutes to obtain the silicon aerogel precursor coated with the replacement solvent and the coupling agent after surface modification.
A preparation method of rare earth toughened solid silicon aerogel comprises the following steps: and (3) performing microwave vacuum drying on the silicon aerogel precursor coated with the replacement solvent and the coupling agent, wherein nitrogen in a drying kettle is used for removing oxygen until the oxygen content is less than 3%, the negative pressure is 0.10mpa, the temperature is 100 ℃, the microwave frequency is controlled within the range of 2450MHZ +/-10 MHZ, and the toughened silicon aerogel solid powder is obtained after 30 minutes.
The product is detected to have an average pore diameter of 24nm, a specific surface area of 558 square meters per gram, a loose specific gravity of 0.061g/cm3, super hydrophobicity, flame retardance, a heat conductivity coefficient of 0.0196W/M.K, a heat resistance temperature of 729 ℃ and a compressive strength of 0.121 MPa.
The foregoing is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, various modifications and decorations can be made without departing from the principle of the present invention, and these modifications and decorations should also be regarded as the protection scope of the present invention.
Claims (4)
1. The rare earth toughened silicon aerogel precursor is characterized by being prepared by the following steps:
(1) preparation of a mixed solution of a silicon source and a solvent
Filling sodium silicate with the mole number of 3.0-4.0 into a reaction kettle, adding deionized water with the mass of 1-3 times that of the sodium silicate for dilution, stirring the reaction kettle at the speed of 80-200 revolutions per minute for 30 minutes, and filtering the mixture through a 200-mesh sieve to obtain a sodium silicate solution;
(2) sol gel
Taking acid A, adding metal salt A and rare earth acid salt A into the acid A, uniformly mixing, and adding into the sodium silicate solution obtained in the step (1) in a spraying manner; rapidly stirring the materials in the reaction kettle at the speed of 1200-2000 rpm while spraying, controlling the pH value of the sodium silicate solution to be 1.5-3.0, and controlling the average pore diameter to be 15-30 nanometers to obtain sol; in the step (2), the acid A is sulfuric acid, hydrochloric acid, oxalic acid or nitric acid;
(3) gel
Taking sodium hydroxide or ammonia water, adding deionized water to dilute until the pH value is 10-11.5, and adding the sodium hydroxide or ammonia water into a reaction kettle in a spraying manner; rapidly stirring the materials in the reaction kettle at the speed of 1200-2000 rpm while spraying, and stopping spraying when the pH value of the materials in the reaction kettle is 4.5-5.5 to obtain gel;
(4) aging of
Continuously stirring the mixture in the reaction kettle for 3 to 10 hours at the speed of 20 to 50 revolutions per minute, aging the materials in the reaction kettle, and controlling the temperature of the materials in the reaction kettle to be 35 to 50 ℃;
(5) solvent replacement
Continuously stirring in the reaction kettle for 60-180 minutes, and simultaneously adding a displacement solvent with the same volume as the aged material in the reaction kettle in the step (4) to displace the residual water;
(6) surface modification
Continuously stirring in the reaction kettle, and continuously adding the coupling agent with the same volume as the aged material in the reaction kettle in the step (4); stirring for 60-180 minutes to obtain a silicon aerogel precursor coated with a displacement solvent and a coupling agent;
the metal salt A in the step (2) is zirconium A acid salt or aluminum A acid salt;
in the step (2), the molar ratio of the metal salt A to the rare earth A acid salt is 100: 1 to 6;
in the step (2), the mole ratio of the oxide of the metal salt A to the silicon oxide in the sodium silicate is 2-5: 100.
2. the rare earth toughened silicon aerogel precursor according to claim 1, wherein the substitution solvent in step (5) is one of methanol, acetone, n-hexane or heptane.
3. The rare earth toughened silicon aerogel precursor according to claim 1, wherein the stirring in step (5) or step (6) is rapid forward stirring in the center of the reaction vessel, and baffles are provided at the periphery of the center of the reaction vessel.
4. The rare earth toughened silicon aerogel precursor according to claim 1, wherein the synthesis time of the rare earth toughened silicon aerogel precursor is less than 30 hours.
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| CN110563435B (en) * | 2018-06-06 | 2022-07-01 | 厦门稀土材料研究所 | Rare earth-based aerogel material with radiation shielding effect and heat insulation performance as well as preparation and application thereof |
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