CN112340741A

CN112340741A - Wet gel block and efficient demolding method thereof

Info

Publication number: CN112340741A
Application number: CN202011231758.8A
Authority: CN
Inventors: 张晚林; 刘圆圆; 李文静; 李健; 黄红岩; 杨洁颖; 赵英民; 张昊
Original assignee: Aerospace Research Institute of Materials and Processing Technology
Current assignee: Aerospace Research Institute of Materials and Processing Technology
Priority date: 2020-11-06
Filing date: 2020-11-06
Publication date: 2021-02-09
Anticipated expiration: 2040-11-06
Also published as: CN112340741B

Abstract

The invention relates to a wet gel block and an efficient demoulding method thereof. The method comprises the following steps: coating a liquid perfluorocarbon oil thin layer on the inner surface of the mould; cooling the mold to solidify the thin liquid perfluorocarbon oil layer in the mold; placing the sol for preparing the aerogel in a mould for gel forming; heating the mold containing the wet gel mass in an oven to melt the thin layer of solid perfluorocarbon oil on the interior surface of the mold; and cooling the mold containing the wet gel block to room temperature, then soaking the interior of the mold with an organic solvent, and finally taking out the wet gel block contained in the mold after demolding. The invention can realize simple, efficient and rapid demoulding of the wet gel block, and the obtained wet gel block has complete appearance without crack and dimensional shrinkage and has demoulding success rate close to 100 percent. The demoulding method can greatly improve the finished product rate of the final aerogel product, accelerate the production speed, reduce the cost and greatly promote the application process of the aerogel.

Description

Wet gel block and efficient demolding method thereof

Technical Field

The invention belongs to the technical field of nano porous materials, relates to a wet gel block in aerogel preparation and an efficient demoulding method thereof, and particularly relates to an efficient demoulding method of a wet gel block in aerogel preparation with a fragile structure.

Background

Aerogel has attracted people's extensive research interest as a nanoporous material with excellent comprehensive properties. The obtaining of the complete block without cracks and with specific size is the premise that the aerogel can be widely applied in a plurality of fields such as heat prevention and insulation, sound insulation and noise reduction, energy conversion, biomedicine, high-energy physics, deep space exploration, national defense and military and the like. The most common preparation process of the aerogel usually comprises the steps of sol preparation, gel forming, gel aging, gel demolding, gel solvent replacement, supercritical drying of the gel and the like. The conventional inorganic ceramic aerogel such as silicon dioxide, aluminum oxide, zirconium oxide, titanium oxide and the like is formed by stacking oxide nano particles in a bead-like structure, the contact surface of the neck parts between the particles is small, so that the brittle mechanical properties and the structural strength of the particles are poor, and the blocks are often incomplete and have cracks in the preparation process. It is particularly noteworthy that for ultra-low density ceramic aerogels, the ultra-low density results in a much lower intrinsic structural strength.

At present, researchers mainly adjust and control sol-gel reaction parameters, optimize an aging process and a supercritical drying process, properly improve the skeleton strength of wet gel, and achieve the purpose of improving the condition that cracks are easily caused in the aerogel preparation process. After gel formation, aging, the wet gel needs to be released from the mold of a particular size so that the free mass of wet gel can be more fully solvent displaced and supercritical dried. Gel demoulding is used as another key intermediate link in the preparation process of the aerogel, and the completeness of the final aerogel and the yield of products are also determined by the quality of the effect. However, in the actual production, even if the surface of the mold is polished and sprayed, the surface still has a certain roughness, which causes the wet gel after molding to adhere to the surface of the mold. Generally, for the preparation of aerogel with higher density, the wet gel can be separated from the solvent and placed in the air for a certain time to cause a certain degree of natural shrinkage, and the relatively high skeleton strength of the aerogel can overcome the influence of the adhesive pull force of the mould surface on the wet gel, so that the gel block can keep integrity while the wet gel is separated from the mould. This strategy of demoulding by shrinkage, because of the uncontrollable shrinkage process, leads on the one hand to a low yield of crack-free aerogel blocks and on the other hand to an inefficient control of the size of the final aerogel. However, for the preparation of the ultra-low density aerogel, the wet gel skeleton strength is too weak, the adhesion force of the surface of the mold to the ultra-low density aerogel in the natural shrinkage process is difficult to overcome, and the success rate of obtaining a crack-free complete block is very low and even cannot be obtained in some cases.

In response, there is a need to develop a method for efficiently demoulding wet gel during the preparation of structurally fragile aerogel so as to obtain a complete, crack-free and size-controllable aerogel block, especially an ultra-low density aerogel block, at a high yield.

Disclosure of Invention

In order to solve the technical problems in the prior art, the invention provides a wet gel block and a high-efficiency demoulding method thereof. The invention can obtain the complete non-crack wet gel block and aerogel block with excellent yield, accurate size controllability and ultrahigh efficiency, and the demoulding method can be used for efficient demoulding of wet gel in the preparation of the fragile structure aerogel, and the wet gel obtained by demoulding can be used for preparing certain fragile structure inorganic ceramic aerogel, which cannot be realized by adopting other demoulding strategies.

The present invention provides in a first aspect a method for efficient demoulding of a wet gel mass, the method comprising the steps of:

(1) coating a liquid perfluorocarbon oil thin layer on the inner surface of the mould;

(2) cooling the mould treated in the step (1) to solidify the liquid perfluorocarbon oil thin layer in the mould into a solid perfluorocarbon oil thin layer;

(3) putting the sol for preparing the aerogel into the mold treated in the step (2) for gel forming to obtain a mold containing a wet gel block;

(4) heating the mold containing the wet gel mass in an oven to melt the thin layer of solid perfluorocarbon oil on the inner surface of the mold;

(5) and (3) cooling the mold containing the wet gel block processed in the step (4) to room temperature, then soaking the interior of the mold containing the wet gel block with an organic solvent, and finally demolding to obtain the wet gel block.

Preferably, the sol is one or more of sols used for preparing silica aerogel, alumina aerogel, zirconia aerogel and titania aerogel, preferably, the sol is one or more of sols used for preparing ultra-low density silica aerogel, ultra-low density alumina aerogel, ultra-low density zirconia aerogel and ultra-low density titania aerogel; and/or the liquid perfluorocarbon oil thin layer is formed by hot perfluorocarbon oil with the temperature of 30-70 ℃ and preferably 40 ℃.

Preferably, the perfluorocarbon oil is a mixture of perfluoropolyether oil and paraffin wax; the perfluoropolyether oil is one or more of GPL100, GPL104, GPL105, GPL106, GPL200, GPL201, GPL202, GPL203, GPL204 and GPL226 under DuPont Krytox series, and preferably, the perfluoropolyether oil is GPL 106.

Preferably, in the perfluorocarbon oil, the mass ratio of the perfluoropolyether oil to the paraffin wax is 1: (0.01-0.08) is preferably 1: 0.03.

Preferably, in step (1): coating hot perfluorocarbon oil on the inner surface of a mould by adopting one or more coating modes of dip coating, spin coating and spray coating to form a liquid perfluorocarbon oil thin layer; preferably, hot perfluorocarbon oil is applied to the inner surface of the mold by dip coating.

Preferably, the step of applying hot perfluorocarbon oil to the inner surface of the mold by dip coating comprises the substeps of:

(a) completely immersing the mould with the cleaned inner surface in hot liquid perfluorocarbon oil for 10-300 s, and taking out the mould;

(b) wiping up the perfluorocarbon oil adhered to the outer surface of the mold treated in the step (a), sucking away the excess perfluorocarbon oil adhered to the inner surface of the mold with an oil-absorbing paper, and then purging the inner surface of the mold with nitrogen gas to distribute a small amount of residual perfluorocarbon oil in a uniform ultra-thin layer on the inner surface of the mold.

Preferably, in the step (2), the cooling temperature of the mold is-80-10 ℃, the cooling time is 0.1-5 h, preferably, the cooling temperature of the mold is-20 ℃, and the cooling time is 1 h; and/or in the step (4), the heating temperature of the oven is 40-80 ℃, the heating time is 2-12 h, preferably, the heating temperature of the oven is 60 ℃, and the heating time is 6 h.

Preferably, the organic solvent is one or more of methanol, ethanol, acetonitrile, acetone, isopropanol, tert-butanol, n-pentanol, n-hexanol and cyclohexanol, and preferably, the organic solvent is ethanol; and/or in the step (5), after the mold containing the wet gel block processed in the step (4) is cooled to room temperature, soaking the mold containing the wet gel block into an organic solvent so that the organic solvent soaks the interior of the mold containing the wet gel block, wherein the volume of the organic solvent is 5-10 times of that of the mold containing the wet gel block.

In a second aspect, the present invention provides a wet gel mass demolded by the high efficiency demolding method of the first aspect of the invention; preferably, the wet gel mass has one or more of the following properties: the wet gel block has a complete shape and no cracks; the wet gel block has no size shrinkage and high size control precision; the yield of the wet gel block is high.

The invention provides in a third aspect a method of preparing an aerogel block, the method comprising: sequentially carrying out aging, solvent replacement and supercritical drying on the wet gel block obtained by demolding according to the efficient demolding method in the first aspect of the invention to obtain the aerogel block; preferably, the aerogel block is a silica aerogel block, an alumina aerogel block, a zirconia aerogel block, or a titania aerogel block; more preferably, the aerogel block is an ultra-low density silica aerogel block, an ultra-low density alumina aerogel block, an ultra-low density zirconia aerogel block, or an ultra-low density titania aerogel block.

Compared with the prior art, the invention at least has the following beneficial effects:

(1) compared with the wet gel demolding process in preparation of structurally fragile aerogel in the prior art, the wet gel demolding process has the advantages that the perfluorocarbon oil thin layer with low surface energy, good film forming property and stable chemical property is introduced to the surface of the mold for the first time, so that the wet gel block with fragile intrinsic structural strength is efficiently and quickly demolded; according to the invention, the characteristic that the perfluorocarbon oil can be reversibly solidified and melted according to the environmental temperature is utilized for the first time, so that the efficient and rapid demoulding of the wet gel block is realized, before the gel is formed, the liquid perfluorocarbon oil thin layer is cooled into a solid film (solid perfluorocarbon oil thin layer), a mould with a rough inner surface is isolated from the sol, and the inert perfluorocarbon oil cannot generate any influence on the gel process of the sol; after the gel is formed, the solid perfluorocarbon oil thin layer is melted into a liquid thin film (liquid perfluorocarbon oil thin layer), and the flowability of the liquid perfluorocarbon oil enables a small gap to exist between the mold and the wet gel, and the wet gel block does not have any adhesion with the mold, so that the wet gel block can be automatically separated, and the generation of cracks or cracks in the wet gel block caused by uneven stress caused by drying shrinkage or cutting operation adopted in the conventional demolding process is avoided.

(2) The wet gel demoulding method has universality on a gel system, can be used for efficient and rapid demoulding of wet gel blocks with fragile intrinsic structural strength, and is also suitable for efficient and rapid demoulding of other various types of wet gel blocks.

(3) The wet gel block obtained by the wet gel demoulding method has complete appearance, no crack or crack and accurately controlled size.

(4) According to the invention, by improving the demoulding process of the wet gel, the yield of aerogel blocks can be greatly improved, the production speed of products can be increased, the aim of reducing the production cost of the aerogel is finally achieved, the application of the aerogel in national production and life can be promoted to a greater extent, and the application process of the aerogel in various fields such as heat insulation, sound insulation and noise reduction, energy conversion, biomedicine, high-energy physics, deep space exploration, national defense and military and the like can be further promoted.

Drawings

FIG. 1 is a schematic diagram of the efficient stripping process of wet gel in the present invention.

FIG. 2 is a schematic representation of the structurally weak ultra low density silica wet gel made in example 1 of the present invention in a polytetrafluoroethylene mold.

FIG. 3 is a profile view of the structurally weak ultra low density silica wet gel prepared in example 1 of the present invention on the lower die plate after it is released from the PTFE mold.

FIG. 4 is a schematic view of a fragile ultra-low density silica Aerogel prepared in example 1 of the present invention placed on a sheet of paper filled with an Aerogel. The scale is used to measure the size of structurally weak ultra low density silica aerogel.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. It is to be understood that the embodiments described are only a few embodiments of the present invention, and not all embodiments. All other embodiments, which can be obtained by a person skilled in the art without any inventive step based on the embodiments of the present invention, are within the scope of the present invention.

(1) coating a thin layer of liquid perfluorocarbon oil on the inner surface of a mold (such as a polytetrafluoroethylene mold); in the present invention, for example, a thin layer of liquid perfluorocarbon oil is formed by coating an ultra-thin, film-forming, hot perfluorocarbon oil on the inner surface of a mold;

(2) cooling the mould treated in the step (1) to solidify the liquid perfluorocarbon oil thin layer in the mould into a solid perfluorocarbon oil thin layer; in the invention, for example, the mold coated with the liquid perfluorocarbon oil thin layer obtained by the treatment of the step (1) is transferred to a refrigerator for rapid cooling, and the liquid perfluorocarbon oil thin layer on the inner surface of the mold coated with the liquid perfluorocarbon oil thin layer is solidified to form a solid perfluorocarbon oil thin layer;

(3) placing the sol for preparing the aerogel into the mold treated in the step (2) for gel forming (for example, gel forming at room temperature) to obtain a mold containing a wet gel block; the invention does not specifically limit the sol system for preparing the aerogel, and the existing sol system commonly used for preparing the aerogel is adopted;

(4) heating the mold containing the wet gel mass in an oven to melt the thin layer of solid perfluorocarbon oil on the inner surface of the mold; in the present invention, for example, the mold containing the wet gel block can be placed in a metal mold and sealed, and then placed in an oven and heated to melt the thin layer of solid perfluorocarbon oil, and then the metal mold is disassembled to take out the mold containing the wet gel block; in the invention, preferably, the polytetrafluoroethylene mould containing the wet gel block is placed into a metal mould for sealing, and then is placed into an oven for heating so as to melt the solid perfluorocarbon oil thin layer, so that the problem that the solvent in the wet gel block is easy to volatilize and gel cracking is caused because the sealing performance of the polytetrafluoroethylene mould is not as good as that of the metal mould can be effectively avoided;

(5) cooling the mold containing the wet gel block processed in the step (4) to room temperature (for example, 10-30 ℃) and then soaking the interior of the mold containing the wet gel block with an organic solvent, and finally demolding to obtain the wet gel block; in the invention, for example, a mold containing the wet gel block is soaked in an organic solvent for 20-40 min so as to be convenient for taking out the wet gel block; in the invention, as the flowable perfluorocarbon oil liquid is arranged between the wet gel block and the mould, the gap between the wet gel block and the mould ensures that the wet gel block can be very easily demoulded, and the wet gel block with complete appearance, no crack or crack and no shrinkage in size can be easily obtained; meanwhile, the organic solvent is adopted for soaking, so that the organic solvent can fully enter a gap between the wet gel block and the die to play a lubricating role, and the demolding of the wet gel block is facilitated; in the invention, the obtained wet gel block is aged, replaced by a solvent and subjected to supercritical drying, so that the corresponding aerogel block (such as an ultra-low density silica aerogel block) with complete appearance and no cracks or fissures can be obtained.

As is known, the prior art mainly comprises a blade cutting method and a drying shrinkage method for demoulding the fragile wet gel, the demoulding success rate of the blade cutting method and the drying shrinkage method is not more than 40%, and the fatal problem is that the two methods cause uneven stress to a wet gel block in the demoulding process, so that the microstructure and the mechanical property of the wet gel are damaged. In addition, the planar dimensions of the crack-free aerogel blocks obtained by demolding in the prior art generally do not exceed 20cm × 20 cm. Compared with other existing wet gel demolding processes in preparation of structurally fragile aerogel, the wet gel block with fragile intrinsic structure strength is efficiently and quickly demolded by introducing the perfluorocarbon oil thin layer with low surface energy, good film forming property and stable chemical property on the surface of the mold for the first time; according to the invention, perfluorocarbon oil with reversible solidification and melting characteristics is used for the first time to isolate the gel block from the mold, so that the wet gel block is simply, efficiently and quickly demolded, the obtained wet gel block has the advantages of complete appearance, no crack, no size shrinkage, high size control precision, demolding success rate close to 100 percent and high yield of the wet gel block, in addition, the demolding method disclosed by the invention cannot cause any stress nonuniformity to the wet gel block, the demolding method disclosed by the invention has no any limitation on the size of the wet gel block, and the demolding method is also suitable for demolding of wet gel in the preparation of crack-free aerogel blocks with the plane size larger than 20cm multiplied by 20 cm. The wet gel block which is obtained by the demolding method and has fragile intrinsic structure strength but still complete appearance can be obtained, the corresponding aerogel block without any crack can be obtained after drying, the yield of the final aerogel product can be greatly improved, the production speed of the aerogel product is increased, the production cost of the aerogel product is reduced, and the application process of the aerogel in the fields of heat prevention and insulation, sound insulation and noise reduction, energy conversion, biomedicine, high-energy physics, deep space exploration, national defense and military and the like is greatly promoted.

The wet gel demoulding method has universality on a gel system, is suitable for efficient and rapid demoulding of various types of wet gel blocks, and is particularly suitable for efficient and rapid demoulding of wet gel blocks with fragile intrinsic structure strength, such as efficient demoulding of wet gel in preparation of inorganic ceramic aerogels such as silicon dioxide, aluminum oxide, zirconium oxide, titanium oxide and the like, and ultra-fragile ultra-low-density inorganic ceramic aerogels (such as the density of 20-60 mg/cm) with super-fragile structures such as silicon dioxide, aluminum oxide, zirconium oxide, titanium oxide and the like³Inorganic ceramic aerogel) in the preparation of a wet gel.

According to some preferred embodiments, the sol is one or more of sols used for preparing silica aerogel, alumina aerogel, zirconia aerogel, titania aerogel, preferably, the sol is one or more of sols used for preparing ultra-low density silica aerogel, ultra-low density alumina aerogel, ultra-low density zirconia aerogel, ultra-low density titania aerogel. The sol system for preparing the inorganic ceramic aerogel or the ultralow-density inorganic ceramic aerogel is not specifically limited, and the sol system commonly used for preparing the inorganic ceramic aerogel or the ultralow-density inorganic ceramic aerogel is adopted. In some embodiments of the present invention, the sol for preparing an aerogel is formed by: uniformly mixing methyl orthosilicate, methanol and water to obtain a mixed solution, then dropwise adding ammonia water (ammonia water solution) into the mixed solution, and then continuously stirring for 3-8 min to obtain sol for preparing the ultra-low density silica aerogel; preferably, the methyl orthosilicate, the methanol and the water are used in the following amounts in parts by mass: 3-4 parts of methyl orthosilicate, 50-70 parts of methanol and 1.5-3 parts of water, wherein the concentration of the ammonia water solution is 0.4-0.6 mol/L (0.4-0.6M), and the using amount is 5-8 mL; more preferably, 3.6 parts of methyl orthosilicate, 60 parts of methanol and 2 parts of water, wherein the concentration of the ammonia water solution is 0.5mol/L (0.5M) and the dosage is 6 mL.

According to some preferred embodiments, the thin liquid perfluorocarbon oil layer is formed from hot perfluorocarbon oil having a temperature of 30 to 70 ℃ (e.g., 30 ℃, 35 ℃, 40 ℃, 45 ℃, 50 ℃, 55 ℃, 60 ℃, 65 ℃ or 70 ℃), preferably 40 ℃.

According to some preferred embodiments, the perfluorocarbon oil is a mixture of perfluoropolyether oil and paraffin wax, and the freezing point of the perfluorocarbon oil is 10-15 ℃; the perfluoropolyether oil is one or more of GPL100, GPL104, GPL105, GPL106, GPL200, GPL201, GPL202, GPL203, GPL204 and GPL226 under DuPont Krytox series, and preferably, the perfluoropolyether oil is GPL 106.

According to some preferred embodiments, in the perfluorocarbon oil, the mass ratio of the perfluoropolyether oil to the paraffin wax is 1: (0.01-0.08) (e.g., 1:0.01, 1:0.02, 1:0.03, 1:0.04, 1:0.05, 1:0.06, 1: 0.07, or 1:0.08) is preferably 1: 0.03. In the present invention, it is preferable that the weight ratio of the perfluoropolyether oil to the paraffin wax in the perfluorocarbon oil is 1: (0.01-0.08), so that the solidifying point of the perfluorocarbon oil can be accurately adjusted, the solidifying point of the perfluorocarbon oil is 10-15 ℃, and reversible solidification and melting of the perfluorocarbon oil are facilitated; the invention finds that if the paraffin content is too low, the freezing point of the perfluorocarbon oil is too low, and if the paraffin content is too high, the freezing point of the perfluorocarbon oil is too high.

According to some preferred embodiments, in step (1): coating hot perfluorocarbon oil on the inner surface of a mould by adopting one or more coating modes of dip coating, spin coating and spray coating to form a liquid perfluorocarbon oil thin layer; preferably, hot perfluorocarbon oil is applied to the inner surface of the mold by dip coating.

According to some preferred embodiments, the application of hot perfluorocarbon oil to the inner surface of the mould by dip coating comprises the sub-steps of:

(a) completely immersing the mould with the cleaned inner surface in hot liquid perfluorocarbon oil for 10-300 s (for example, 10, 30, 50, 80, 100, 120, 150, 180, 200, 220, 250, 280 or 300s) and then taking out the mould;

(b) wiping the perfluorocarbon oil adhered to the outer surface of the mold treated in the step (a), sucking the redundant perfluorocarbon oil adhered to the inner surface of the mold by using an oil absorption paper, and then blowing the inner surface of the mold by nitrogen gas to ensure that the residual small amount of perfluorocarbon oil is distributed on the inner surface of the mold in a uniform ultrathin layer, preferably forming a liquid perfluorocarbon oil thin layer with the thickness of 0.1-2 mm on the inner surface of the mold. The invention has no strict requirement on the thickness of the liquid perfluorocarbon oil thin layer, and more preferably has the thickness within the range of 0.1-2 mm, if the liquid perfluorocarbon oil thin layer is too thin, the effect of facilitating demoulding is not achieved, and if the liquid perfluorocarbon oil thin layer is too thick, the liquid perfluorocarbon oil thin layer is not necessary; the invention can determine whether the thickness of the liquid perfluorocarbon oil thin layer is appropriate by, for example, visual observation or by means of a vernier caliper.

According to some specific embodiments, the dip-coating operation is to put the mold with the inner surface cleaned completely into the hot liquid perfluorocarbon oil which can be completely immersed in the hot liquid perfluorocarbon oil, soak the hot liquid perfluorocarbon oil for 10-300 s, then take out the mold, clean the perfluorocarbon oil on the outer surface of the mold, suck the redundant perfluorocarbon oil on the inner surface of the mold with an oil absorption paper, and then purge the inner surface with nitrogen gas, so that the residual small amount of perfluorocarbon oil is distributed on the inner surface of the mold in a uniform ultrathin layer.

According to some preferred embodiments, in step (2), the mold is cooled at-80 to 10 ℃ (e.g., -80 ℃, -70 ℃, -60 ℃, -50 ℃, -40 ℃, -30 ℃, -20 ℃, -10 ℃, 0 ℃ or 10 ℃) for 0.1 to 5 hours (e.g., 0.1, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5 or 5 hours), preferably at-20 ℃ for 1 hour; and/or in step (4), the heating temperature of the oven is 40-80 ℃ (for example, 40 ℃, 45 ℃, 50 ℃, 55 ℃, 60 ℃, 65 ℃, 70 ℃, 75 ℃ or 80 ℃), the heating time is 2-12 h (for example, 2, 4, 6, 8, 10 or 12h), and preferably the heating temperature of the oven is 60 ℃, and the heating time is 6 h.

According to some preferred embodiments, the organic solvent is one or more of methanol, ethanol, acetonitrile, acetone, isopropanol, tert-butanol, n-pentanol, n-hexanol, cyclohexanol, preferably, the organic solvent is ethanol; and/or in step (5), after cooling the wet gel mass-containing mold treated in step (4) to room temperature, soaking the wet gel mass-containing mold in an organic solvent having a volume 5 to 10 times (e.g., 5, 6, 7, 8, 9, or 10 times) that of the wet gel mass-containing mold so that the organic solvent soaks the interior of the wet gel mass-containing mold.

In a second aspect, the present invention provides a wet gel mass released by the efficient release method of the invention described in the first aspect.

According to some preferred embodiments, the wet gel mass has one or more of the following properties: the wet gel block has a complete shape and no cracks; the wet gel block has no size shrinkage and high size control precision; the yield of the wet gel block is high and approaches to 100%.

According to some more preferred embodiments, the wet gel mass is an intrinsic structural strength frangible wet gel mass that is intact in shape without any cracks; the wet gel block with weak intrinsic structural strength has no size shrinkage and high size control precision; the yield of the wet gel block with weak intrinsic structural strength is close to 100%.

The invention provides in a third aspect a method of preparing an aerogel block, the method comprising: the aerogel blocks are prepared by subjecting wet gel blocks (e.g., wet gel blocks having weak intrinsic structural strength but intact external shape) obtained by the high-efficiency mold-releasing method according to the first aspect of the present invention to aging, solvent displacement, and supercritical drying in this order. The aging, solvent replacement and supercritical drying conditions are not particularly limited, and the aging (for example, aging temperature is 30-60 ℃, aging time is 2-5 days), solvent replacement (for example, solvent replacement is performed by using ethanol as a solvent) and supercritical drying (for example, supercritical carbon dioxide drying) conditions commonly used for preparing the aerogel in the prior art are adopted.

According to the invention, the wet gel block which is prepared by the demolding method in the first aspect of the invention, has weak intrinsic structure strength, can still keep complete appearance, has no crack, no crack and no shrinkage in size, can be subjected to aging, solvent replacement and supercritical drying to obtain a corresponding aerogel block (such as an ultra-low density aerogel block) with complete appearance and no any crack or crack, and can further promote the application process of aerogel in various fields such as heat insulation, sound insulation and noise reduction, energy conversion, biomedicine, high-energy physics, deep space exploration, national defense and military and the like by improving the yield of aerogel products, accelerating the production speed of aerogel products and reducing the cost of aerogel products.

According to some preferred embodiments, the aerogel block is a silica aerogel block, an alumina aerogel block, a zirconia aerogel block, or a titania aerogel block; more preferably, the aerogel block is an ultra-low density silica aerogel block, an ultra-low density alumina aerogel block, an ultra-low density zirconia aerogel block, or an ultra-low density titania aerogel block.

The invention will be further illustrated by way of example, but the scope of protection is not limited to these examples.

Example 1

Weighing 30g of paraffin and 1000g of DuPont Krytox GPL106 perfluoropolyether oil into a metal box with the size of 100mm (length) × 100mm (width) × 60mm (height), uniformly mixing the paraffin and the 1000g of DuPont Krytox GPL106 perfluoropolyether oil by using a glass rod to obtain perfluorocarbon oil, putting the metal box into an oven with the temperature of 40 ℃, heating for 2h, then soaking an open cuboid polytetrafluoroethylene mould with the size of 70mm (length) × 40mm (width) × 20mm (height) into the perfluorocarbon oil with the temperature of 40 ℃ in the metal box for 60s, taking out the mould, wiping the perfluorocarbon oil on the outer surface of the mould completely, sucking the redundant perfluorocarbon oil on the inner surface of the mould by using oil absorption paper, then blowing the inner surface of the mould by using nitrogen flow to ensure that a small amount of residual perfluorocarbon oil is distributed on the inner surface of the mould in a uniform ultrathin layer, and forming a liquid perfluorocarbon oil thin layer with the thickness of 0.5mm on the.

Secondly, transferring the treated polytetrafluoroethylene mold to a freezer with the temperature of-20 ℃ for cooling for 1h to fully solidify the liquid perfluorocarbon oil thin layer on the inner surface of the mold, and then placing the polytetrafluoroethylene mold in a room with the temperature of 25 ℃ for 2h for later use.

③ adding 60g of methanol, 2g of water and 3.6g of methyl orthosilicate into a 100mL beaker, carrying out magnetic stirring uniformly at room temperature, then dropwise adding 6mL of 0.5M ammonia water solution, continuously stirring for 5min to obtain sol for preparing the ultra-low density silica aerogel, pouring the sol into a polytetrafluoroethylene mold of which the inner surface is a solid perfluorocarbon oil thin layer in the step II, and placing the mold for 1h at room temperature of 25 ℃ to form sol-gel in the mold.

And fourthly, placing the polytetrafluoroethylene mould containing the wet gel block into a metal mould, sealing the metal mould, and placing the metal mould into a 60 ℃ oven to heat for 6 hours. After the metal mold is cooled to room temperature (25 ℃), the metal mold is disassembled and the polytetrafluoroethylene mold containing the wet gel block is taken out, and the thin layer of perfluorocarbon oil on the inner surface of the mold is melted into liquid.

And fifthly, putting the polytetrafluoroethylene mold containing the wet gel block into a metal box filled with 500mL of ethanol, and soaking for 30min, wherein the wet gel block can be very easily demoulded due to a gap between the wet gel block and the polytetrafluoroethylene mold because of the flowable perfluorocarbon oil liquid, so that the wet gel block is complete in appearance, free of cracks and free of size shrinkage.

Sixthly, aging the wet gel block body for 3 days at the temperature of 40 ℃, and then performing ethanol solvent replacement and supercritical carbon dioxide drying to obtain the ultra-low density silicon dioxide aerogel block body with complete appearance, no crack and no crack.

The outline of the ultra-low density silica wet gel prepared in this example on the lower template after being released from the polytetrafluoroethylene mold is shown in fig. 3, and as can be seen from fig. 3, the obtained ultra-low density silica wet gel with a fragile structure has a complete outline, no cracks, and no shrinkage in size; as shown in fig. 4, it can be seen that the ultra-low density silica Aerogel block prepared in this embodiment has ultra-high transparency and the size reaches 7cm × 4cm, when the ultra-low density silica Aerogel block prepared in this embodiment is placed on an outline drawing of a piece of paper full of Aerogel (Aerogel); as can be seen from FIG. 4, the ultra-low density silica aerogel block prepared by the present example has a complete shape, no cracks and no cracks.

The measured density, room temperature thermal conductivity and dimensions of the ultra-low density silica aerogel block prepared in this example are shown in table 1, and it is specifically noted that the dimensions in the present invention refer to the planar area of the aerogel, i.e., the length × width dimensions, and there is no particular limitation on the thickness (height); this example also repeated the above steps (i) to (ii) 99 times to test the yield of ultra low density silica aerogel blocks, and the results are shown in table 1.

Example 2

Example 2 is essentially the same as example 1, except that:

weighing 10g of paraffin and 1000g of DuPont Krytox GPL106 perfluoropolyether oil into a metal box with the size of 100mm (length) × 100mm (width) × 60mm (height), uniformly mixing the paraffin and the 1000g of DuPont Krytox GPL106 perfluoropolyether oil by using a glass rod to obtain perfluorocarbon oil, putting the metal box into an oven with the temperature of 40 ℃, heating for 2h, then soaking an open cuboid polytetrafluoroethylene mould with the size of 70mm (length) × 40mm (width) × 20mm (height) and the inner surface of which is cleaned into the perfluorocarbon oil with the temperature of 40 ℃ in the metal box for 60s, taking out the mould, wiping the perfluorocarbon oil on the outer surface of the mould completely, sucking the redundant perfluorocarbon oil on the inner surface of the mould by using oil absorption paper, then blowing the inner surface of the mould by using nitrogen flow, and distributing a small amount of residual perfluorocarbon oil on the inner surface of the mould in a uniform ultrathin layer to form a liquid perfluorocarbon oil thin layer with the thickness of 0.5mm on.

Repeating the steps from (i) to (99) times in the example, the yield of the ultra-low density silica aerogel block obtained in the present example was as shown in table 1.

Example 3

Example 3 is essentially the same as example 1, except that:

weighing 80g of paraffin and 1000g of DuPont Krytox GPL106 perfluoropolyether oil into a metal box with the size of 100mm (length) × 100mm (width) × 60mm (height), uniformly mixing the paraffin and the 1000g of DuPont Krytox GPL106 perfluoropolyether oil by using a glass rod to obtain perfluorocarbon oil, putting the metal box into an oven with the temperature of 40 ℃, heating for 2h, then soaking an open cuboid polytetrafluoroethylene mould with the size of 70mm (length) × 40mm (width) × 20mm (height) and the inner surface of which is cleaned into the perfluorocarbon oil with the temperature of 40 ℃ in the metal box for 60s, taking out the mould, wiping the perfluorocarbon oil on the outer surface of the mould completely, sucking the redundant perfluorocarbon oil on the inner surface of the mould by using oil absorption paper, then blowing the inner surface of the mould by using nitrogen flow, and distributing a small amount of residual perfluorocarbon oil on the inner surface of the mould in a uniform ultrathin layer to form a liquid perfluorocarbon oil thin layer with the thickness of 0.5mm on.

Example 4

Example 4 is essentially the same as example 1, except that:

weighing 5g of paraffin and 1000g of DuPont Krytox GPL106 perfluoropolyether oil into a metal box with the size of 100mm (length) × 100mm (width) × 60mm (height), uniformly mixing the paraffin and the 1000g of DuPont Krytox GPL106 perfluoropolyether oil by using a glass rod to obtain perfluorocarbon oil, putting the metal box into an oven with the temperature of 40 ℃, heating for 2h, then soaking an open cuboid polytetrafluoroethylene mould with the size of 70mm (length) × 40mm (width) × 20mm (height) and the inner surface of which is cleaned into the perfluorocarbon oil with the temperature of 40 ℃ in the metal box for 60s, taking out the mould, wiping the perfluorocarbon oil on the outer surface of the mould completely, sucking the redundant perfluorocarbon oil on the inner surface of the mould by using oil absorption paper, then blowing the inner surface of the mould by using nitrogen flow, and distributing a small amount of residual perfluorocarbon oil on the inner surface of the mould in a uniform ultrathin layer to form a liquid perfluorocarbon oil thin layer with the thickness of 0.5mm on.

Example 5

Example 5 is essentially the same as example 1, except that:

weighing 100g of paraffin and 1000g of DuPont Krytox GPL106 perfluoropolyether oil into a metal box with the size of 100mm (length) × 100mm (width) × 60mm (height), uniformly mixing the paraffin and the 1000g of DuPont Krytox GPL106 perfluoropolyether oil by using a glass rod to obtain perfluorocarbon oil, putting the metal box into an oven with the temperature of 40 ℃, heating for 2h, then soaking an open cuboid polytetrafluoroethylene mould with the size of 70mm (length) × 40mm (width) × 20mm (height) and the inner surface of which is cleaned into the perfluorocarbon oil with the temperature of 40 ℃ in the metal box for 60s, taking out the mould, wiping the perfluorocarbon oil on the outer surface of the mould completely, sucking the redundant perfluorocarbon oil on the inner surface of the mould by using oil absorption paper, then blowing the inner surface of the mould by using nitrogen flow, and distributing a small amount of residual perfluorocarbon oil on the inner surface of the mould in a uniform ultrathin layer to form a liquid perfluorocarbon oil thin layer with the thickness of 0.5mm on.

Example 6

Example 6 is essentially the same as example 1, except that:

in the step (iv), the polytetrafluoroethylene mold containing the wet gel block is placed into an oven at 60 ℃ and heated for 6 hours, and the thin layer of perfluorocarbon oil on the inner surface of the mold is melted into liquid.

Example 7

Example 7 is essentially the same as example 1, except that:

in the first step, 540g of paraffin and 18000g of DuPont Krytox GPL106 perfluoropolyether oil are weighed and placed in a metal box with the size of 400mm (length) × 400mm (width) × 60mm (height) and uniformly mixed by a glass rod to obtain perfluorocarbon oil, the metal box is placed in an oven with the temperature of 40 ℃ and heated for 2h, then an open cuboid polytetrafluoroethylene mould with the size of 240mm (length) × 210mm (width) × 20mm (height) and the inner surface of which is cleaned is soaked in the perfluorocarbon oil with the temperature of 40 ℃ in the metal box for 60s, the mould is taken out, the perfluorocarbon oil on the outer surface of the mould is cleaned, the redundant perfluorocarbon oil on the inner surface of the mould is sucked away by oil suction paper, then the inner surface of the mould is blown by nitrogen flow, so that a small amount of residual perfluorocarbon oil is distributed on the inner surface of the mould in a uniform ultrathin layer, and a liquid perfluorocarbon oil thin layer with the thickness of 0.5mm is formed on the inner.

Step three, adding 1080g of methanol, 36g of water and 64.8g of methyl orthosilicate into a beaker, performing magnetic stirring uniformly at room temperature, then dropwise adding 108mL of ammonia water solution with the concentration of 0.5M, continuously stirring for 5min to obtain sol for preparing the ultra-low density silica aerogel, pouring the sol into a polytetrafluoroethylene mold with the inner surface being a solid perfluorocarbon oil thin layer in the step two, and placing for 3h at room temperature of 25 ℃ to mold the sol gel in the mold.

In the fifth step, the polytetrafluoroethylene mould containing the wet gel block is placed into a metal box filled with ethanol for soaking for 30min, wherein the dosage of the ethanol is 6 times of the volume of the polytetrafluoroethylene mould containing the wet gel block; because the flowable perfluorocarbon oil liquid is arranged between the wet gel block and the polytetrafluoroethylene mold, the wet gel block can be very easily demolded due to the gap between the wet gel block and the polytetrafluoroethylene mold, and the wet gel block with complete appearance, no crack and no shrinkage in size is obtained.

Table 1: test results of examples 1 to 7.

Finally, it should be noted that: the above examples are only intended to illustrate the technical solution of the present invention, but not to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; and such modifications or substitutions do not depart from the spirit and scope of the corresponding technical solutions of the embodiments of the present invention.

Claims

1. A method for efficiently demolding a wet gel block, the method comprising the steps of:

2. The high-efficiency demolding method as claimed in claim 1, wherein:

the sol is one or more of sol for preparing silica aerogel, alumina aerogel, zirconia aerogel and titania aerogel, preferably, the sol is one or more of sol for preparing ultra-low density silica aerogel, ultra-low density alumina aerogel, ultra-low density zirconia aerogel and ultra-low density titania aerogel; and/or

The liquid perfluorocarbon oil thin layer is formed by hot perfluorocarbon oil with the temperature of 30-70 ℃ and preferably 40 ℃.

3. The high-efficiency demolding method as claimed in claim 2, wherein:

the perfluorocarbon oil is a mixture consisting of perfluoropolyether oil and paraffin;

the perfluoropolyether oil is one or more of GPL100, GPL104, GPL105, GPL106, GPL200, GPL201, GPL202, GPL203, GPL204 and GPL226 under DuPont Krytox series, and preferably, the perfluoropolyether oil is GPL 106.

4. The high-efficiency demolding method as claimed in claim 3, wherein:

in the perfluorocarbon oil, the mass ratio of the perfluoropolyether oil to the paraffin is 1: (0.01-0.08) is preferably 1: 0.03.

5. The high-efficiency demolding method according to claim 2, wherein in step (1):

coating hot perfluorocarbon oil on the inner surface of a mould by adopting one or more coating modes of dip coating, spin coating and spray coating to form a liquid perfluorocarbon oil thin layer;

preferably, hot perfluorocarbon oil is applied to the inner surface of the mold by dip coating.

6. The efficient demolding method according to claim 5, wherein the step of coating the inner surface of the mold with the hot perfluorocarbon oil by dip coating comprises the substeps of:

7. The high-efficiency demolding method as claimed in any one of claims 1 to 6, wherein:

in the step (2), the cooling temperature of the die is-80-10 ℃, the cooling time is 0.1-5 h, and preferably the cooling temperature of the die is-20 ℃, and the cooling time is 1 h; and/or

In the step (4), the heating temperature of the oven is 40-80 ℃, the heating time is 2-12 h, preferably, the heating temperature of the oven is 60 ℃, and the heating time is 6 h.

8. The high-efficiency demolding method as claimed in any one of claims 1 to 6, wherein:

the organic solvent is one or more of methanol, ethanol, acetonitrile, acetone, isopropanol, tert-butanol, n-pentanol, n-hexanol and cyclohexanol, and preferably the organic solvent is ethanol; and/or

In the step (5), after the mold containing the wet gel mass treated in the step (4) is cooled to room temperature, the mold containing the wet gel mass is soaked into an organic solvent so that the organic solvent soaks the inside of the mold containing the wet gel mass, and the volume of the organic solvent is 5 to 10 times of the volume of the mold containing the wet gel mass.

9. A wet gel mass demolded by the high efficiency demolding method of any one of claims 1 to 8; preferably, the wet gel mass has one or more of the following properties:

the wet gel block has a complete shape and no cracks;

the wet gel block has no size shrinkage and high size control precision;

the yield of the wet gel block is high.

10. A method for preparing an aerogel block, the method comprising: subjecting a wet gel block obtained by demolding according to the high-efficiency demolding method of any one of claims 1 to 8 to aging, solvent replacement and supercritical drying in sequence to obtain the aerogel block; preferably, the aerogel block is a silica aerogel block, an alumina aerogel block, a zirconia aerogel block, or a titania aerogel block; more preferably, the aerogel block is an ultra-low density silica aerogel block, an ultra-low density alumina aerogel block, an ultra-low density zirconia aerogel block, or an ultra-low density titania aerogel block.