CN110894167A

CN110894167A - Nano porous heat insulation material and preparation method thereof

Info

Publication number: CN110894167A
Application number: CN201911261076.9A
Authority: CN
Inventors: 刘爱林
Original assignee: Shanghai Xidian New Material Technology Co Ltd
Current assignee: Shanghai Xidian New Material Technology Co Ltd
Priority date: 2019-09-26
Filing date: 2019-12-10
Publication date: 2020-03-20
Also published as: CN110898689B; CN110804205B; CN110898688B; CN110804205A; CN110938271B; CN110951106B; CN110898681A; CN110898689A; CN110898681B; CN110938271A; CN110951106A; CN110898688A

Abstract

The invention discloses a nano porous heat insulation material and a preparation method thereof. The preparation method of the heat insulation material with the nano porous structure comprises the steps of dissolving raw materials for preparing inorganic hydrosol in water to form a prefabricated body with the water content of 5-40 wt%; the inorganic hydrosol comprises at least one of silicon dioxide sol, titanium dioxide sol, aluminum oxide sol and zinc oxide sol; heating the preform to vaporize the water and maintain its form substantially unchanged; the volume of the material is increased by bulking until the required porosity is reached, and the heat insulation material with the nano porous skeleton structure is obtained.

Description

Nano porous heat insulation material and preparation method thereof

Technical Field

The invention belongs to the field of processing and application of heat insulation materials, and mainly relates to a heat insulation material with a nano porous structure and a preparation method thereof.

Background

The existing heat insulation and preservation material is generally a special gel which replaces liquid in the gel with gas and does not change the network structure or volume of the gel per se, and is a product after hydrogel or organic gel is dried. It has the features of nano level porous structure, high porosity, etc. and is one of the known solid materials with low density. Such insulation was first made in the 30's of the 20 th century by professor Kistler. The preparation process is complicated and long, the price is high, the product is easy to be crisp and the like, and the product does not attract attention for a long time. With the rapid development of sol-gel technology since the 70 s of the 20 th century, the research and development of inorganic heat insulating materials mainly composed of silica and synthetic polymer heat insulating materials represented by condensation polymers of resorcinol/formaldehyde and melamine/formaldehyde have attracted much attention. The porous structure with a large number of nanometer sizes in the heat-insulating material endows the material with ultrahigh porosity (80-99.8%) and high specific surface area (100-1600 m)²(0.004-0.500 g/cm) and ultralow density³) The characteristics of the material are the same, so that the material has wide application prospects in various fields of optics, electricity, acoustics, heat, catalysis and the like.

According to patent CN108793172A, when the reagent is prepared, TEOS, MTMS and APTES are mixed to obtain a mixed reagent A, acetonitrile and deionized water are mixed to obtain a mixed reagent B, and then the temperature of the mixed reagents A and B is reduced to 0 ℃; mixing the two cooled reagents, aging at room temperature to obtain wet gel, sequentially exchanging the wet gel with ethanol and acetonitrile solvent, soaking in acetonitrile solution of hexamethylene diisocyanate, transferring into acetonitrile solution, and keeping the temperature at 70 deg.C for 7 ℃2h, then putting the wet gel into acetonitrile solution for solvent exchange, and finally passing the wet gel through CO₂And (5) performing supercritical drying to obtain the isocyanate enhanced silicon dioxide porous material. The method comprises the steps of reacting silicon dioxide with sodium hydroxide to generate modified sodium silicate by CN109650396A, and using ethanol/water as a solvent; adding inorganic acid to neutralize the modified sodium silicate solution to generate modified silica sol and remove inorganic salt by-products, wherein the modified silica sol generates modified silica gel at a certain temperature and pressure; and (3) carrying out solvent exchange on the modified silica gel by using a nonpolar solvent, and drying to obtain the hydrophobic porous material. Proposed by 109721059a, the uniformly mixed a system and gel core particles were mixed in a sealed state to obtain a precursor, and the precursor was dried. After the precursor is dried, silicic acid is shrunk to form silicon dioxide, and simultaneously, the white carbon black and the silicon micropowder are used as gel core particles to adsorb the silicon dioxide obtained after shrinkage, so that the silicon dioxide porous material with the pompon-shaped porous structure is formed. CN108423685A provides a method for preparing a super-hydrophobic silica porous material under normal pressure, which comprises six steps of sol preparation, sol gelation, gel aging, gel solvent exchange, surface hydrophobic modification and normal pressure drying. CN109650395A proposes a method for preparing a silicon dioxide porous material by a sublimation method, which comprises the steps of dissolving a sublimation substance in an alcohol-water solvent to obtain a transparent solution, adding a silicon source and an alkali catalyst into the solution, uniformly mixing, standing to form gel, aging the gel, and carrying out vacuum sublimation on the aged gel to remove the sublimation substance to obtain the silicon dioxide porous material.

The existing preparation processes of the nano porous material are all improved aiming at the sol preparation process of the porous material, no innovation is provided on the drying method, and aiming at the problems existing in the processes, the invention actively researches and innovates based on long-term practical experience and rich professional knowledge, and finally invents a method for preparing the nano porous material with the porosity of more than 80 percent by high-temperature puffing so as to solve the defects in the prior art.

Disclosure of Invention

The invention aims to provide a heat insulation material with a nano porous structure and a preparation method thereof.

In a first aspect, the invention provides a preparation method of a heat insulation material with a nano porous structure.

The preparation method of the nano porous heat insulation material comprises the following steps: forming an inorganic hydrosol preform having a water content of 5-40 wt%; heating the preform to vaporize the water and maintain its form substantially unchanged; the volume of the material is increased by bulking until the required porosity is reached, and the heat insulation material with the nano porous structure is obtained. The inorganic hydrosol comprises at least one of silicon dioxide sol, titanium dioxide sol, aluminum oxide sol and zinc oxide sol.

In one scheme, raw materials for preparing inorganic hydrosol are dissolved in water to form a prefabricated body with the water content accounting for 5-40 wt% of the total amount; heating the preform to vaporize the water and maintain its form substantially unchanged; the volume of the material is increased by bulking until the required porosity is reached, and the heat insulation material with the nano porous skeleton structure is obtained. In a preferred embodiment, the silica sol is prepared by aqueous silicate solution. As a more specific technical scheme, a raw material containing water-soluble silicate is dissolved in water to form a preform with the water content of 5-40 wt% of the total amount; heating the preform to vaporize the water and maintain its form substantially unchanged; the volume of the material is increased by bulking until the required porosity is reached, and the heat-insulating and heat-preserving material with the nano porous framework structure is obtained.

The method disclosed by the invention can ensure that the porosity of the prepared heat insulation material with the nanoscale aperture is 80-99.8%. The aperture size is adjustable within the range of 0.5-999 nm.

The preform is allowed to contain a suitable amount of water which vaporizes at a temperature to cause the preform to expand to form a hole. Too high water content easily causes too large pore diameter or uneven pore diameter distribution, too low water content easily causes insufficient puffing degree or unsuccessful puffing, so that the water content is controlled within a certain range, which is beneficial to uniform pore diameter distribution and pore diameter control of the material, and the heat preservation and heat insulation performance of the material is improved. The material volume is kept unchanged, namely, the material is not expanded when water is vaporized, and the pore size distribution can be controlled. The maintenance of its form means that the water is vaporized without puffing. Maintaining the morphology can be accomplished by controlling the volume of the material constant during the vaporization of the solvent by the heating.

The water-soluble silicate includes, but is not limited to, alkali metal silicates such as sodium silicate and potassium silicate.

The expansion may be such that the volume of the material expands in any one, two or three directions of XYZ. The requirements, operation processes, equipment or molds are different. The method can ensure that the porosity of the prepared heat insulation material with the nano-scale aperture is 80-99.8%. And the volume increasing process of the materials in the puffing process is a gradual change process under a controllable state. The material expansion process is preferably achieved by passing the material under controlled conditions through a die having a gradual design of volume. Also, puffing may be accomplished by puffing the material in a die, and by controllably moving the upper and/or lower dies. Alternatively, bulking can be achieved by controlling the speed of rotation of the rollers to move the material controllably by maintaining the gap between the rollers (or heated roller and pressure belt) constant so that the material is compressed and then pulled off the rollers (or heated roller and pressure belt) during movement. The pressure during puffing is gradually reduced from 30-0 MPa.

In a preferred embodiment, the raw material further comprises a water-soluble resin. The resin can increase the toughness and strength of the material. The addition amount of the resin is preferably 30-100 wt% of the solid content of the inorganic raw material. The source of the water-soluble resin is not particularly limited, and the water-soluble resin can be prepared by the existing method or can be obtained by commercial purchase. "Water-soluble resin" refers to a resin that is water-soluble. The resin is selected from water-soluble phenolic resin, water-soluble epoxy resin, water-soluble melamine formaldehyde resin, water-soluble urea formaldehyde resin, water-soluble unsaturated polyester resin, water-soluble polyurethane resin, water-soluble acrylic resin, polyacrylamide, sodium polyacrylate, polyethylene glycol, polyvinyl alcohol, polymaleic anhydride, polyethyleneimine, polyethylene oxide, polyethylene chloride, starch, water-soluble natural gum, methyl cellulose, hydroxyethyl cellulose and sodium carboxymethyl cellulose.

In a preferred scheme, the raw materials are dissolved by water with the solid content of 0.5-10 times of the weight to obtain a mixed solution; and reducing the water content of the obtained mixed solution until the water content reaches the required content. In a more preferable scheme, a water-soluble silicate raw material is dissolved by water with the solid content of 0.5-10 times of the weight to obtain a mixed solution; and reducing the water content of the obtained mixed solution until the water content reaches the required content. The water content of the mixed liquid can be reduced by adopting a heating mode. The manner and apparatus of heating are not limited as long as the content of water is reduced to a desired content. The rate of water reduction is slower at lower heating temperatures, but the heating temperature is not too high to avoid forward puffing. Preferably, the heating temperature is 25-200 ℃. The excessive solvent is used for dissolving the raw materials, so that the raw materials can be fully dissolved, the water can be uniformly dispersed in the raw materials, and the swelling of the product is facilitated to form more uniform pore size distribution. Or replacing part of water with anhydrous ethanol, and placing into a heating container to reduce water content. The use amount of the absolute ethyl alcohol is 1-4 times of the weight of the raw materials. It is to be understood that the starting materials referred to in this disclosure refer to the starting materials used to prepare the inorganic hydrosol, such as the water-soluble silicate starting material (which may be water glass).

As another technical scheme, the preparation method of the heat insulation material with the nano porous structure comprises the steps of dissolving raw materials containing water-soluble silicate (and/or water-soluble resin) and a curing agent in water to form a prefabricated body with the water content accounting for 5-40 wt% of the total amount; heating the preform to vaporize water and maintain its form; and then expanding the volume of the material until the required porosity is reached to obtain the heat insulation material with the nano porous skeleton structure. In the case where a curing agent and/or a water-soluble resin is added, the "raw materials" include the curing agent and/or the water-soluble resin in addition to the raw materials for preparing the inorganic hydrosol.

In the above technical scheme, the preparation process of the preform may be that water-soluble silicate (and/or water-soluble resin) is dissolved by water and is uniformly mixed with a curing agent to obtain a mixed solution; finally, the water content of the obtained mixed solution is reduced until the water content reaches the required content.

By controlling the heating temperature and/or the amount of curing agent added, the material can be allowed to begin to cure substantially after expansion. The addition of the curing agent can promote the water-soluble silicate (and/or the water-soluble resin) to have no flowability (the viscosity of the material is increased) at the glass transition temperature, so that the pore size and the pore size distribution are prevented from being influenced due to the better flowability of the material after the material is expanded, and the strength and the waterproof performance of the material can be improved. In some embodiments, the curing agent comprises at least one of a phosphate, a sodium fluorosilicate, an inorganic acid. The phosphate salts include, but are not limited to, aluminum tripolyphosphate, silicon phosphate, sodium phosphate, and the like. Preferably, the mass of the curing agent is 1-30 wt% of the water-soluble silicate (and/or water-soluble resin) aqueous solution.

The heating temperature for heating the preform to vaporize water is preferably in excess of the boiling point of water. More preferably, the heating temperature is 140 to 400 ℃. It should be understood that during the heating process (before puffing), the water is ensured to be vaporized under the condition of the water content at the moment, so that the pore-forming of the material by puffing is facilitated at the later stage to form the nano-porous material with uniform pore size distribution. The heating time can be reduced when the heating temperature is high. The control of the addition amount of the curing agent and the water content of the preform can ensure that the preform can keep a skeleton structure in the heating process.

In a preferred embodiment, the preform is heated to vaporize water while being pressurized. Pressurization is not necessary because pressure is generated by vaporization of water during heating. The pressurization pressure is adjusted according to the water content, the temperature of heating and the desired pore size. The water is vaporized by heating and pressurizing, and the volume of the material is kept unchanged. The pressure is then slowly released (puffing), i.e. reduced, increasing the volume of the material to a given porosity. The range of pressurization is preferably higher than the saturated vapor pressure of water used to disperse the sodium silicate (or sodium silicate and curing agent) under the heating conditions. The decompression time is controlled to complete the puffing and to form the specified porosity and pore size distribution. Too rapid a pressure reduction tends to result in too large a pore size and a non-uniform pore size distribution. Too slow a pressure reduction tends to cause expansion failure or too low porosity. Preferably, the pressurizing pressure is 0.01-20 MPa. In one embodiment, the pressure reduction time is preferably 0.5 to 10 seconds in order to achieve a pore diameter of 100nm or less and a porosity of 80% or more.

In a preferred embodiment, the preform heating process and the preform expanding process are performed using a system for preparing a material having a nanoporous structure including a hot press roll. The preform is preferably fed into the manufacturing system at a predetermined rate as a sheet, heated between two rolls and subjected to some compression and water vaporization. The preform is extruded substantially without puffing (equivalent to puffing in a closed space) between the rollers as the preform contacts the rollers on both sides, and puffing occurs during subsequent venting away from the rollers. The increase in expanded volume occurs as the sheet exits the twin roll gap to achieve the desired porosity. At this time, the volume of the material is further increased to 10 times, 20 times or even 50 times of the original volume. The sheet thickness is preferably made to be well above the twin roll gap by 10-40% so that it is somewhat squeezed as it enters between the rolls. The time for vaporization of the solvent as the material is heated in the nip between the rolls can be controlled by controlling the roll speed, and the rate at which the material exits the rolls (i.e., controlling the puffing process) can also be controlled. In a preferable scheme, the thickness of the sheet is preferably 0.5-5 mm, and the temperature of the double-roller hot press is preferably 230-300 ℃; the speed of the double rollers is preferably 0.4-10 m/min; the twin roll gap is preferably 0.5-6mm (in the case where no particular mention is made, the twin roll gap is the minimum distance between the twin rolls).

In a preferred embodiment, the preform is fed into a system for producing a material having a nanoporous structure comprising a screw extrusion section, heated to vaporize water, then fed into a conveying section while maintaining its morphology, and then fed into a bulking unit of increasing volume to bulk the material to achieve a desired porosity. The volume increasing process of the material in the puffing process is a gradual change process under a controllable state. The bulking unit can be a fixed-size die with gradually changed die volume, so that the bulking process of the material is changed into a gradual change process.

In a preferred embodiment, the preform is fed into a molding press having a variable volume container, and the expansion process is controlled by controlling the volume change of the container to achieve the desired porosity. The puffing unit can be a die consisting of an upper die and a lower die with fixed sizes, and the upper die and/or the lower die can move relatively in a controllable way to realize puffing. Specifically, the pressure relief speed can be controlled by controlling the demolding speed, so that the pressure during puffing is controlled to be slowly reduced, the material is uniformly puffed under the condition of pressure, and the porosity can be controlled. The pressure during puffing is gradually reduced from 20-0 MPa.

In a preferred embodiment, the preform is fed into an injection molding machine having a variable volume container, and the expansion process is controlled by controlling the volume change of the container to achieve the desired porosity. The puffing unit can be a die consisting of an upper die and a lower die with fixed sizes, and the upper die and/or the lower die can move relatively in a controllable way to realize puffing.

Preferably, the pore size is controlled by controlling at least one of the water content, heating temperature, pressurization pressure, and depressurization (expansion) rate.

According to the preparation method, water is uniformly dispersed in the material framework, so that the later-stage water is heated and vaporized to enable the material to be puffed to form holes, and the pore size of the material can be controlled by controlling the temperature and puffing.

Compared with the prior art, the invention has the beneficial effects that:

1. the puffing and drying technology used in the method of the invention provides a brand new idea for drying the porous material. But also is beneficial to industrialized production.

2. The solvent used in the invention has low cost and meets the actual production requirement.

3. The method is carried out on the basis of the existing equipment without other additional equipment.

4. The method has the advantages of simple and feasible process, low cost, environmental protection and environment friendliness, and belongs to an environment-friendly technology.

In a second aspect, the invention also provides the heat insulation material with the nano-porous structure, which is obtained by the preparation method, and the heat insulation material is provided with a framework formed by the raw materials, nano-scale pores are uniformly distributed in the framework, and the pore size is adjustable within the range of 0.5-999 nm. As described above, the raw material may be a single water-soluble silicate (in this case, the skeleton structure is a silica skeleton), or may be a water-soluble silicate and a water-soluble resin (in this case, the skeleton structure is a skeleton formed of silica and a resin); it is also possible that both further include a curing agent (in this case, the skeleton structure is silica, and/or a skeleton formed by the resin and the curing agent).

The silica heat insulation material with the nano porous structure has excellent mechanical property and heat insulation performance.

Drawings

FIG. 1 is a photograph of example 1 after drying of water glass without addition of a curing agent;

FIG. 2 is a photograph of a nanoporous material made from water glass without the addition of a curing agent in example 1;

FIG. 3 is a photograph of an aluminum phosphate water glass after drying in example 2 by adding aluminum phosphate to the water glass;

FIG. 4 is a photograph of a nanoporous material produced in example 2 after the addition of aluminum phosphate to water glass;

FIG. 5 is a photograph showing the dried materials of example 3 in which 8%, 30%, and 50% of polyurethane was added to water glass;

FIG. 6 is a photograph of a nanoporous material obtained by adding 8% polyurethane to water glass in example 3;

FIG. 7 is a photograph of a nanoporous material obtained in example 3 after adding 30% polyurethane to water glass;

FIG. 8 is a photograph of a nanoporous material obtained in example 3 after adding 50% polyurethane to water glass.

Detailed Description

The present invention is further illustrated by the following examples, which are to be understood as merely illustrative and not restrictive.

The preparation method of the silica thermal insulation material with a nano-porous structure is shown below.

First, a preform is prepared. The preparation process of the preform may be: raw materials for preparing the inorganic hydrosol are dissolved in water to form an inorganic hydrosol preform having a water content of 5 to 40 wt%.

As one of specific technical schemes for preparing the preform, water is uniformly dispersed in water-soluble silicate to obtain the preform which takes the water-soluble silicate as a raw material and has a proper amount of water uniformly dispersed therein. The water content in the preform is 5-40% of the weight of the preform. When the water is in the content range, the later-stage puffing control is facilitated. Too high a water content tends to result in too large a pore size or an uneven pore size distribution, while too low a water content tends to result in unsuccessful puffing. Therefore, the water content is controlled in a certain range, which is beneficial to the uniform distribution of the pore diameter of the material and the control of the pore diameter size, and the heat preservation and insulation performance of the material is improved.

With respect to the preparation of the preform, in one embodiment, the water-soluble silicate is dissolved in water and directly mixed to prepare the preform. In another embodiment, the preparation of the preform may comprise the following two steps: (1) firstly, dissolving water-soluble silicate with excessive water to obtain a mixed solution. (2) The resulting mixture is then reduced in water. The mixing may be performed by a mixing device such as a mixer or a blender. The water-soluble silicate, the curing agent and water may also be mixed by mechanical action under heating. Mixing can be achieved using equipment with high temperature capabilities such as internal mixers, roll mills, high temperature kneaders, twin-cone extruders, twin-screw extruders, twin-roll presses, and the like. The large amount of water allows the water-soluble silicate to dissolve relatively quickly and uniformly.

It is understood that in the above or subsequent embodiments, the water-soluble silicate feedstock (or silicate feedstock) may also be replaced by other inorganic materials conventionally used in the nanoporous materials (more than 80% porosity) industry. The inorganic hydrosol comprises at least one of silicon dioxide sol, titanium dioxide sol, aluminum oxide sol and zinc oxide sol.

) In addition, the raw material may further contain a water-soluble resin. The addition amount of the resin is 30-100 wt% of the solid content of the inorganic raw material for preparing the inorganic hydrosol.

As a second technical scheme for preparing the preform, water and a curing agent are uniformly dispersed in water-soluble silicate, so that the preform which takes the water-soluble silicate and the curing agent as main raw materials and has a proper amount of water uniformly dispersed therein is obtained. The water is used for making holes and can be vaporized at a certain temperature to enable the prefabricated body to be expanded and formed into holes. The water resistance and the curing performance of the prepared material can be improved by using the curing agent.

With respect to the preparation of the preform, in one embodiment, a water-soluble silicate (inorganic raw material) is dissolved with water and directly mixed with an appropriate amount of a curing agent to prepare a preform. In another embodiment, the preparation of the preform may comprise the following two steps: firstly, dissolving the water-soluble silicate by using excessive water, and uniformly mixing the water-soluble silicate with the curing agent to obtain a mixed solution. (2) The resulting mixture is then reduced in water. The mixing may be performed by a mixing device such as a mixer or a blender. The water-soluble silicate, the curing agent and water may also be mixed by mechanical action under heating. Mixing can be achieved using equipment with high temperature capabilities such as internal mixers, roll mills, high temperature kneaders, twin-cone extruders, twin-screw extruders, twin-roll presses, and the like. The large amount of water allows the water-soluble silicate to dissolve relatively quickly and uniformly. The silicate may be dissolved in 0.5 to 10 times by weight of water. The amount of the water solvent is different according to the dissolution performance of the material. The amount of water is preferably 1-3 times (the silicate is dissolved by water based on the weight of the silicate material, and then the amount of water is reduced to a suitable amount, the mass of the curing agent can be 1-30 wt% based on the weight of the silicate aqueous solution, if the mass of the curing agent is too low, the curing effect may be poor or the curing may be uneven, and if the mass of the curing agent is too high, the material may begin to cure before swelling or may cure when swelling is insufficient.

The preform includes a suitable amount of water which can be vaporized by heating to promote the subsequent expansion of the material to form a nanoporous material (with a porosity of greater than 80%). The inorganic raw materials are fully dissolved by using water, so that the water is uniformly dispersed in the prepared prefabricated body, and the uniformity of later-stage puffing pore size distribution is facilitated. Furthermore, direct drying and setting of the preform can have an effect on the pore size of the material, or the pore size is difficult to control. The method disclosed by the invention has the advantages that the pore size of the material can be regulated and controlled by heating the preform with a certain solvent content, controlling the heating vaporization temperature of the preform with a certain solvent content and the subsequent speed of pressure release in the puffing process, and the porosity of the prepared nano-porous material reaches more than 80%. Compared with the process for preparing the nano porous material with the porosity of more than 80% by freeze drying and supercritical drying, the method disclosed by the invention is more convenient, quicker, more economical and has adjustable pore diameter.

In the step (2) of the preparation of the above preform, in one example, water may be reduced by applying a certain temperature to the resulting mixed liquid. The heating temperature can be adjusted at 25-200 ℃ according to different water contents. It should be understood that while the boiling point of water is 100 ℃, the water will not be completely evaporated as long as the time is short enough to reach a specific water content range. The heating temperature is too low, the water is slowly reduced, and the industrial chain time is prolonged; if the heating temperature is too high, the water in the preform is vaporized and expanded in advance, and the pore diameter distribution of the product cannot be controlled to be uneven. It will be appreciated that in the process of the invention, machines such as twin screw extruders may be used to reduce the water content, and that these machine temperatures are increased without puffing the material.

In the step (2) of the preparation of the above preform, any apparatus capable of reducing the water content to effect drying may be used. In another embodiment, the water of the resulting solution may be reduced by an instrument with a high temperature function. The apparatus used for controlling the moisture content may be a parallel twin-screw extruder, a conical twin-screw extruder, an open mill, an internal mixer, a drying cabinet, a microwave oven, a freeze dryer, a pressure sprayer, an impinging stream dryer, or the like. Methods used to reduce water content include, but are not limited to, atmospheric drying, reduced pressure drying, spray drying, ebullient drying, freeze drying, infrared drying, microwave drying, moisture absorption drying, impingement drying, sonic drying, displacement drying, steam drying, ice slurry drying, airless drying, pulse combustion drying, and the like. The industrial mass production can be realized by using the instrument, so that the limitation of the production quantity is avoided.

The invention can select proper curing agent according to different materials. In some embodiments, curing agents include, but are not limited to, aluminum tripolyphosphate, silicon phosphate, phosphates such as sodium phosphate, and sodium fluorosilicate, inorganic acids, and the like.

And then, carrying out porosity treatment on the intermediate (prefabricated body) to obtain the heat insulation material with the nano porous structure. The porosification treatment refers to a treatment in which water is vaporized to generate pores in a material. Specifically, the prefabricated body is heated to vaporize water and keep the volume or the shape of the prefabricated body unchanged, then the volume is increased to reach the required porosity by expanding and releasing pressure, and the prefabricated body is naturally cooled to obtain the heat insulation material with the nano porous structure.

The preform is heated, and sufficient time is ensured during heating to vaporize the water in the preform and maintain the volume of material constant. The pressure is then controllably relieved, i.e., reduced (water vaporization pressure), to increase the volume of the material to a desired porosity. And then cooling to keep the structure stable, and preparing the heat-insulating material with the nano porous structure. And the volume increases as the water vaporizes causing the material to expand.

The temperature to be heated during the porosification treatment of the intermediate (preform) may be selected depending on the kinds of materials and curing agents. In a preferred embodiment, the temperature of heating should exceed the boiling point of water. If the temperature is too low, the later expansion rate of the material is too low; if the temperature is too high, the pore diameter of the material is too large, thereby affecting the heat insulation performance of the material. In some embodiments, the heating temperature is in the range of 140-400 ℃. In a more preferred embodiment, the heating temperature is in the range of 230 to 300 ℃.

The heating time for the preform porosification treatment is preferably controlled so that water is vaporized at the heating temperature. The lower the water content and the higher the temperature, the shorter the heating time. In this heating process, water may be completely vaporized, but a small amount of water may remain, only having a certain influence on the thermal conductivity of the material, as long as the thermal conductivity is satisfactory.

In some embodiments, the preform may also be pressurized simultaneously with the heating to vaporize the water. The water is vaporized by pressurizing while heating, and the volume of the material is kept constant to regulate the pore structure, such as uniform pore distribution and pore size. The pressure can be controlled to be higher than the saturated vapor pressure of water at this time temperature and the volume of the material is made constant. Then the subsequent pressure release is carried out to realize the expansion. In some embodiments, the pressurization pressure is 0.01 to 20 MPa. In a more preferred embodiment, the pressurization pressure is 0.1 to 10 MPa.

After the water is vaporized, slowly releasing the pressure, namely expanding. In the process, the pressure in the material is gradually reduced, and the volume of the material is gradually increased. It should be understood that the process of increasing the volume of the material during puffing should be controlled to be gradual under a controlled state. The swelling process is used to increase the volume of the material to achieve a specified porosity. In the pressure relief process, because the water is in a gas state at this time and the material still has certain fluidity, the water vapor pressure promotes the volume increase of the material, so that the material is expanded. With respect to the pressure relief time, it is desirable to complete the expansion and to provide a suitable porosity and uniform pore size distribution. The rate of pressure reduction is preferably such that material expansion is achieved and the desired porosity is achieved. In some embodiments the time for pressure release is not less than 0.4 seconds. Too fast a pressure reduction tends to result in too large pore sizes and non-uniform pore size distribution. But too slow a pressure reduction tends to cause puffing failure or too low porosity. It should be understood that small amounts of water may remain at the time of initial pressure release, as long as the thermal conductivity is within the desired range.

The present invention can control the pore structure, such as pore size and/or uniformity of pore size distribution, by controlling at least one of water content, heating temperature, puffing rate.

In some embodiments, the preform is sent to a system for preparing a material having a nanoporous structure comprising a heated press roll for porosification.

When the production system of the material having a nanoporous structure including the hot press roll is used, the intermediate material sent to the production system of the material having a nanoporous structure including the hot press roll is preferably a sheet. The sheet can be processed in any manner, including extrusion through a twin-screw extruder, and can also be formed by a twin-roll hot press. The processing temperature for forming the sheet should be lower than the puffing temperature, preferably, the processing temperature for forming the sheet is lower than the boiling point of water, and more preferably, the processing mode for forming the sheet is cold pressing at normal temperature. The thickness of the sheet is preferably 10 to 40% higher than the gap between the twin rolls (the minimum distance between the twin rolls is not particularly specified). Since the sheet thickness is higher than the twin roll nip, when the sheet is fed into a system for preparing a material having a nanoporous structure comprising a hot press roll until the sheet is separated from the twin roll nip (i.e., the minimum distance between the twin rolls), the sheet is subjected to temperature and twin roll compression (i.e., heat and pressure) so that water is vaporized; and after the sheet exits the twin roll gap, the volume of material increases as the pressure is released as the distance between the rolls increases (i.e., the pressure is slowly relieved), and bulking is achieved. When the preparation system of the material with the nano-porous structure comprising the hot press roller is adopted, the pressurizing pressure can be controlled by controlling the gap of the double rollers, and the pressure reducing speed and the pore morphology can be controlled by controlling the rotating speed of the double rollers, so that the size of the pore diameter and the uniformity of the pore diameter distribution can be controlled. Wherein, the slow pressure relief is realized by the gradual increase of the double-roller gap, and the pressure is reduced as the double-roller gap is increased. It will be appreciated that the higher the water content and the higher the temperature, the lower the speed of rotation of the twin rolls. Since the higher the temperature, the higher the water content and the higher the fluidity of the material, the lower the speed of rotation of the twin rolls, the formation of large bubbles in the insulating material can be avoided. In a specific embodiment, the water content in the preform is 10 to 20 wt% based on the total weight. The heating temperature of the preform is preferably 230 to 300 ℃. Furthermore, the rotation speed of the twin rolls can be less than 40m/min, and preferably, the rotation speed of the twin rolls is 0.4-10 m/min. The gap between the two rollers can be 0.5-6 mm. The larger the gap between the two rolls, the higher the expansion ratio and the higher the porosity, the better the thermal insulation and the lower the thermal conductivity, while ensuring that the material can be brought into contact with the rolls.

In some embodiments, the preform heating process and the preform bulking process are performed using a system for preparing a material having a nanoporous structure comprising a heated press roll. The material is heated and extruded to some extent between the two rollers to vaporize water, and the vaporization degree of water is preferably controlled to 90-100%. The degree of vaporization of water in the material between the rolls is related to the desired pore size and porosity of the final product. The higher the degree of vaporization, the larger the pore size and the higher the porosity. And because the water fully dissolves the material and is uniformly distributed in the material, the nano-scale holes left after the water is vaporized are uniformly distributed in the material. The pressure created by the vaporized water as the sheet exits the twin roll gap causes the material to expand and increase in volume to achieve the desired porosity. The volume of the material can be further increased to 10 times, 20 times or even 50 times of the original volume. The volume of the material is gradually increased in the puffing process, and the pressure of the material is gradually released. The sheet thickness is preferably made to be suitably larger than the twin roll gap by 10 to 40% so that it is subjected to a certain squeezing when it enters between the twin rolls. The time for vaporization of the solvent as the material is heated in the nip between the rolls can be controlled by controlling the roll speed, as well as the rate at which the material exits the rolls (i.e., controlling the puffing process). In a preferred embodiment, the temperature of the double-roller hot press is preferably 230 to 300 ℃ and the speed of the double rollers is preferably 0.4 to 10m/min when the thickness of the sheet is 0.5 to 5 mm. The sheet material can be placed in iron sheets and between the twin rolls in order to allow sufficient heating. Two pieces of release paper of the same specification as the iron sheet may be prepared for better release.

In some embodiments, the preform is fed into a system for producing a material having a nanoporous structure comprising a screw extrusion section, heated to vaporize water, then fed into a conveying section while maintaining its morphology, and then fed into a bulking unit of increasing volume to increase the bulked volume of the material to achieve a desired porosity. The volume increasing process of the material in the puffing process is a gradual change process under a controllable state. The bulking unit can be a fixed-size die with gradually changed die volume, so that the bulking process of the material is changed into a gradual change process.

In some embodiments, the intermediate is fed to a molding press for porosification. The intermediate is fed into a closed container placed between an upper die and a lower die of a die press. The shape of the intermediate body can be adjusted according to the shape of the closed container. The puffing unit can be a die consisting of an upper die and a lower die with fixed sizes, and the upper die and/or the lower die can move relatively in a controllable way to realize puffing. The upper part can be driven to move towards the direction far away from the lower part along with the movement of the upper die, so that the volume of the accommodating part is gradually changed. When the molding press is used, the porosity of the material is controlled by controlling the interval between the upper and lower molds, that is, the volume change of the receiving portion.

In some embodiments, the intermediate is fed to an injection molding machine for voiding. The molding press has basically the same principle as the puffing principle of an injection molding machine, and the difference is that the injection molding machine injects materials into a closed container in an injection mode.

In some embodiments, the intermediate is fed to a drum vulcanizer for porosification. The drum vulcanizer works in a similar manner to the two-roll hot press except that the two rolls are replaced by a heated roll and a pressure belt. The preform is heated and pressurized in a region where the gap between the heating roller and the pressure belt is kept constant, to vaporize water. In this region, since the gap distance is kept constant, the heated material maintains a state in which the shape is constant, and swelling does not occur. The material then continues to be conveyed to the increasingly spaced gap regions (i.e., the expansion units) where the material expands as the spacing of the regions increases. In some embodiments, the temperature of the heating roller is 140 ℃ to 400 ℃, and the rotating speed of the heating roller is 0.4-10 m/min.

Compared with the prior art, the preparation method has the beneficial effects that:

1. the puffing and drying technology adopted by the method of the invention provides a brand new idea for drying the heat insulation material. Compared with freeze drying and supercritical drying preparation processes, the method is more convenient, faster, more economical and has adjustable aperture. Both supercritical carbon dioxide drying and vacuum freeze drying require gel formation prior to drying and subsequent drying. The present invention does not require the step of forming a gel.

2. The method is carried out on the basis of the existing equipment without other additional equipment.

3. The method has simple and feasible process and lower cost, and is beneficial to industrial production.

The heat insulation material prepared by the preparation method can be in the forms of plates, films, blocks, powder, particles and the like. Therefore, the material obtained by the preparation method of the invention has the advantages of abundant types, convenient preparation and low cost, and can meet the requirements of various complex geometric shapes, mechanics and thermal properties.

The existing heat insulation and preservation material has the difficult problem of forming, wet gel with large water content (the water content is needed for the material with certain porosity) is prepared firstly, in the drying process of the wet gel, the existence of a gas-liquid interface generates large capillary force, and the anisotropy of a gel framework caused by incomplete and uniform pore diameter of the gel finally shows that the framework receives larger stress in macroscopical view, so that the framework is contracted and cracked, the network structure is collapsed, and the prepared porous material is often powder or particles and is difficult to form into a complete block. In the technical scheme of the invention, the moisture content of the prefabricated body is only 5-40%, and the prefabricated body is instantly subjected to high temperature and directly vaporized, so that capillary force cannot damage a gel framework.

In addition, in the preparation method, organic solvents such as alcohols are not introduced, so that the requirements on equipment such as tightness, explosion resistance and static electricity resistance are reduced, the cost is reduced, the production safety is improved, and the high cost caused by recycling the organic solvents such as alcohols is avoided.

In some embodiments, the thermal insulation material has a porosity of 80-99.8%. The porosity in the present invention is tested by the following method: p ═ V₀-V)/V₀*100％＝(1-ρ₀ρ) × 100%, wherein: p-porosity of material,%; v₀Volume or apparent volume, cm, of material in its natural state³Or m³；ρ₀Bulk density of the material, g/cm³Or kg/m³(ii) a V-Absolute dense volume of material, cm³Or m³(ii) a Rho-material density, g/cm³Or kg/m³。

In some embodiments, the density of the thermal insulation material is 0.004-0.5 g/cm³. The density in the present invention is measured by the following method: p is m/abt 10⁴Rho-density, kg/m³(ii) a m-dry mass of sample, g; a is the length of the sample, mm; b-width of the sample, mm; t-thickness of the pattern, mm.

In some embodiments, the thermal insulation material has a specific surface area of 100-2000 m²(ii) in terms of/g. The specific surface area of the invention is obtained by testing the specific surface area of V-Sorb 2800P and a pore size analyzer.

In some embodiments, the thermal insulation material has a thermal conductivity of 0.018-0.04W/mk. The thermal conductivity is obtained by testing the thermal conductivity by a transient hot wire method through a thermal conductivity tester.

The heat insulation material has a nano porous network structure, can effectively inhibit gas heat conduction and solid heat conduction, realizes heat insulation in all aspects, and has good mechanical property and lower density.

In summary, the heat insulating material of the present invention uses a water-soluble silicate (e.g., water glass) which is inexpensive and readily available as a raw material, and a silica heat insulating material is obtained by a simple reaction route and a method of controlling pressure release. Moreover, the heat insulation material has good heat insulation efficiency, low heat conductivity and good high-temperature scour resistance, is mainly used in the technical fields of light heat-proof/high-temperature heat-insulation heat-protection systems and the like, and has important application value.

The present invention will be described in detail by way of examples. It is also to be understood that the following examples are illustrative of the present invention and are not to be construed as limiting the scope of the invention, and that certain insubstantial modifications and adaptations of the invention by those skilled in the art based on the foregoing description are intended to be within the scope of the invention. The specific process parameters and the like of the following examples are also merely examples of suitable ranges, i.e., those skilled in the art can select from the suitable ranges through the description herein, and are not limited to the specific values exemplified below. In the case where the present invention is not specifically described, the addition ratio and the content refer to mass.

The water glass in the following examples is a sodium silicate solution with a solid content of 42% and is available from the national pharmaceutical group chemical agents limited. Aluminum tripolyphosphate (analytically pure) was purchased from Shanghai Michelin Biotech, Inc. Water-soluble polyurethane, shanghai Lingfeng Chemicals, ltd. Silicon phosphate (analytically pure) purchased from Shih Corp Biotech, Inc. of Hubei. Sulfuric acid (analytically pure) was purchased from Nanjing chemical reagents, Inc. Sodium fluorosilicate (analytically pure) was purchased from Shanghai Michelin Biotech, Inc. All other reagents used were analytically pure and were purchased directly without further purification.

Example 1

Weighing 100g of water glass (the water glass refers to a sodium silicate solution, the solid content of the sodium silicate is 42%, the same below), putting the sample into a conical double-screw extruder, reducing the water content of the sample to 20 wt% (the water accounts for the total mass of the raw materials, the same below) at the temperature of 110 ℃ and the rotating speed of 60r/min, and drying the water glass as shown in figure 1. Taking out part of the dried sample, making into a sample with thickness of 2mm and volume of 1.1cm³The sheet of (2) is placed in a release paper (placed in the release paper to prevent the sample from sticking to the device). And opening the double-roller press, setting the temperature at 230 ℃, the rotating speed at 4m/min and the roller gap at 1.5mm, and placing the sheet into the roller for expansion molding after the set temperature is reached. And (3) placing the mixture into a double-roller hot press for high-temperature puffing for about 1min, and then finishing the puffing to obtain the nano porous material. The thickness of the material at this time was 3mm and the volume was 19.8cm³. The material is fully contacted with the double rollers and is uniformly heated, the gap adjusted by the double rollers is smaller than the thickness of the material before puffing, and the length and the width of the material are greatly changed due to the pressure.

The nanoporous material after being subjected to the double-roller hot-pressing high-temperature puffing for 1min is shown in fig. 2.

And (3) putting the porous material cut into the regular shape into an oven at 180 ℃ for drying for 4-6 hours, wherein the weight is marked as m, and the length and the width are marked as a and b. The height h was measured with a vernier caliper, the volume V was abh, and the density ρ was m/abh. The density rho of the porous material is measured to be 2.36/(11)6×0.3)＝0.12g/cm³。

Obtaining porosity P ═ 1-rho/rho by consulting the data_{Sodium silicate}) X 100% of sodium silicate, wherein the density of sodium silicate is 2.33g/cm³The porosity P is (1-0.12/2.33) × 100 is 95%.

The porous material prepared by the method has high porosity, but poor strength and toughness.

Example 2

The difference from the foregoing example 1 is that 100g of water glass was weighed in a container in the foregoing step 1 while 30% (this ratio refers to the ratio of the mass of aluminum phosphate as a curing agent to the mass of water glass, the same applies hereinafter) of aluminum phosphate (powder) was added to prepare a porous material. The sample is put into a conical double-screw extruder, the water content is reduced to 20 wt% under the conditions of 110 ℃ and 60r/min of rotating speed, and the dried aluminum phosphate water glass is shown in figure 3. The two-roll press was opened, the set temperature was 230 ℃, the rotational speed was 4m/min, the roller gap was 1.5mm, and the porous material obtained after high temperature expansion by the two-roll press was as shown in fig. 4. The thickness of the material was changed from 2mm to 4mm and the volume was changed from 0.9cm before entering the two-roll hot press and before exiting the two-roll hot press³It became 6.4cm³。

The density ρ of the material prepared in this example was 2.24/(5.7 × 2.8 × 0.4) ═ 0.35g/cm, as measured by the above method³. Obtaining porosity P ═ 1-rho/rho by consulting the data_{Sodium silicate}) X 100% of sodium silicate, wherein the density of sodium silicate is 2.33g/cm³. The porosity P is (1-0.35/2.33) × 100% is 85%.

The porosity of the porous material prepared by the embodiment is reduced compared with that of the porous material prepared by the embodiment 1, but the strength is obviously improved.

Example 3

1. Three portions of 100g of water glass are weighed. And then respectively weighing 8 percent, 30 percent and 50 percent of water-soluble polyurethane (the solid content is 35 percent) (the mass of the polyurethane solution accounts for the mass of the water glass solution) into the water glass, and uniformly stirring.

2. And (3) opening the double-screw extruder, opening a temperature control switch, setting the temperature to be 100 ℃, rotating at the speed of 60r/min, slowly pouring the feed liquid into the feed inlet, and taking out the extruded sample at the discharge outlet.

3. Two iron sheets with the length of 15cm, the width of 17cm and the thickness of 0.2mm are prepared for being heated sufficiently, two pieces of demoulding paper with the same specification are prepared, a double-roller hot press is opened, the temperature is set to be 180 ℃, the rotating speed is 5m/min, the gap between the double rollers is 1.4-1.5 mm, a sample is placed into the demoulding paper, the demoulding paper is placed into the iron sheets, and then the sample is placed into an inlet of the double-roller hot press for preheating for about two minutes.

4. And after preheating, putting the iron sheet into a double roller for hot pressing for about 2min to obtain the nano porous material.

FIG. 6 is a photograph of a nanoporous material obtained by adding 8% polyurethane to water glass in example 3; FIG. 7 is a photograph of a nanoporous material obtained in example 3 after adding 30% polyurethane to water glass; FIG. 8 is a photograph of a nanoporous material obtained in example 3 after adding 50% polyurethane to water glass. It can be seen that the surface of the sample added with 8% of polyurethane is full of gloss, has certain strength and is not easy to break, but the toughness is slightly poor; the samples with 30% and 50% polyurethane added have high toughness and certain strength.

And (3) drying the porous material with the regular shape in an oven at 180 ℃ for 4-6 hours, wherein the weight is marked as m, and the length and the width are marked as a and b. The height h was measured with a vernier caliper, the volume V was abh, and the density ρ was m/abh. Finding P ═ 1-rho/rho by consulting the data_{Composite material}) X 100% of sodium silicate, wherein the density of sodium silicate is 2.33g/cm³The density of the polyurethane was 1.005g/cm³。

When the addition amount of the polyurethane aqueous solution is 8%, the density rho of the porous material sample

＝1.88/(7.5×5.7×0.4)＝0.11g/cm³. The thickness before puffing is 2mm, and the thickness after puffing is 4 mm. Volume before puffing is 1.1cm³Volume after puffing 17.1cm³. When the ratio of the polyurethane (solid content) to the solid content of the mixed solution was 8% × 35%/(8% × 35% + 92% × 42%)×2.33))×100％＝95％。

When the amount of the aqueous polyurethane solution added is 30%, the density ρ of the porous material sample

＝1.97/(5.5×3.0×0.35)＝0.34g/cm³. The thickness before puffing is 2mm, and the thickness after puffing is 3.5 mm. Volume before puffing is 1.0cm³Volume after puffing 5.8cm³. The ratio of the polyurethane (solid content) to the solid content of the mixed solution was 30% x 35%/(30% x 35% + 70% x 42%): 26%, and the ratio of the sodium silicate (solid content) to the solid content of the mixed solution was 70% x 42%/(30% x 35% + 70% x 42%): 74%, and the porosity P (30%): 1-0.34/(26% x 1.005+ 74% x 2.33)) × 100%: 83%.

When the amount of the aqueous polyurethane solution added is 50%, the density ρ of the porous material sample

＝2.01/(5.1×3.0×0.31)＝0.43g/cm³. The thickness before puffing is 2mm, and the thickness after puffing is 3.1 mm. Volume before puffing is 0.9cm³Volume after puffing is 4.7cm³. The ratio of the polyurethane (solid content) to the solid content of the mixed solution was 50% × 35%/(50% × 35% + 50% × 42%) to 45%, and the ratio of the sodium silicate (solid content) to the solid content of the mixed solution was 50% × 42%/(50% × 35% + 50% × 42%) to 55%, and the porosity P (50%) was 1 to 0.43/(45% × 1.005+ 55% × 2.33)) × 100% to 75%.

Example 4

And (3) swelling the water glass into a nano silicon dioxide porous material. Weighing 100g of water glass, weighing 2.1g of aluminum tripolyphosphate according to 5% of solid content of the water glass, mixing the water glass and the aluminum tripolyphosphate in a 500mL beaker, fully stirring the mixture by using a glass rod until the mixture is uniformly mixed, pouring the uniformly mixed solution into a twin-screw extruder at 110 ℃ and 80r/min at a constant speed to ensure that the water content is 15% of sodium silicate, and placing the extruded material in a normal-temperature flat-plate tablet press at 10kg/cm²The obtained uniform flaky material passes through a double-roller hot press with the temperature of 180 ℃, the gap of 3mm and the double-roller speed of 2m/min at a constant speed for 10s, and finally the nano silicon dioxide porous material with the porosity of 93 percent is obtained.

Example 5

The same process flow as in example 4 is adopted to swell the water glassAnd (5) forming the nano silicon dioxide porous material. Weighing 100g of water glass, weighing 4.2g of aluminum tripolyphosphate according to 10% of solid content of the water glass, mixing the water glass and the aluminum tripolyphosphate in a 500ml beaker, fully stirring the mixture by using a glass rod until the mixture is uniformly mixed, pouring the uniformly mixed solution into a twin-screw extruder at 110 ℃ and 80r/min at a constant speed to ensure that the water content is 15% of sodium silicate, and placing the extruded material in a normal-temperature flat-plate tablet press at 10kg/cm²The obtained uniform flaky material passes through a double-roller hot press with the temperature of 180 ℃, the gap of 3mm and the double-roller speed of 2m/min at a constant speed for 10s, and finally the nano silicon dioxide porous material with the porosity of 90% is obtained.

Example 6

The same process flow as in example 4 was used to expand water glass into a nano-silica porous material. Weighing 100g of water glass, weighing 4.2g of silicon phosphate according to 10% of solid content of the water glass, mixing the water glass and the silicon phosphate, putting the mixture into a 500ml beaker, fully stirring the mixture by using a glass rod until the mixture is uniform, pouring the uniformly mixed solution into a twin-screw extruder at 110 ℃ and 80r/min at a constant speed to ensure that the water content is 5% of sodium silicate, putting the extruded material into a normal-temperature flat-plate tablet press, and putting the extruded material into a flat-plate tablet press at 10kg/cm²The obtained uniform flaky material passes through a double-roller hot press with the temperature of 200 ℃, the gap of 3mm and the double-roller speed of 2m/min at a constant speed for 10s, and finally the nano-silica porous material with the porosity of 88% is obtained.

Example 7

The same process flow as in example 4 was used to expand water glass into a nano-silica porous material. Weighing 100g of water glass, weighing 4.2g of silicon phosphate according to 10% of solid content of the water glass, mixing the water glass and the silicon phosphate, putting the mixture into a 500ml beaker, fully stirring the mixture by using a glass rod until the mixture is uniform, pouring the uniformly mixed solution into a double-screw extruder at 120 ℃ and 90r/min at a constant speed to ensure that the water content is 30% of sodium silicate, putting the extruded material into a flat-plate tablet press at normal temperature and using the tablet press at 10kg/cm²The obtained uniform flaky material passes through a double-roller hot press with the temperature of 260 ℃, the gap of 3mm and the double-roller speed of 1.7m/min at a constant speed for 10s, and finally the nano-silica porous material with the porosity of 94 percent is obtained.

Example 8

The same process flow as in example 4 was used to expand water glass into a nano-silica porous material. Weighing 100g of water glass, weighing 4.2g of aluminum tripolyphosphate according to 20% of solid content of the water glass, mixing the water glass and the aluminum tripolyphosphate in a 500ml beaker, fully stirring the mixture by using a glass rod until the mixture is uniformly mixed, pouring the uniformly mixed solution into a twin-screw extruder at 105 ℃ and 80r/min at a constant speed to ensure that the water content is 20% of sodium silicate, and placing the extruded material in a normal-temperature flat-plate tablet press at 10kg/cm²The obtained uniform flaky material passes through a double-roller hot press with the temperature of 180 ℃, the gap of 2mm and the double-roller speed of 4m/min at a constant speed for 10s, and finally the nano silicon dioxide porous material with the porosity of 89% is obtained.

Example 9

The same process flow as in example 4 was used to expand water glass into a nano-silica porous material. Weighing 100g of water glass, weighing 6.3g of aluminum tripolyphosphate according to 15% of solid content of the water glass, mixing the water glass and the aluminum tripolyphosphate in a 500ml beaker, fully stirring the mixture by using a glass rod until the mixture is uniformly mixed, pouring the uniformly mixed solution into a twin-screw extruder at 110 ℃ and 80r/min at a constant speed to ensure that the water content is 10% of sodium silicate, and placing the extruded material in a normal-temperature flat-plate tablet press at 10kg/cm²The obtained uniform flaky material passes through a double-roller hot press with the uniform speed of 280 ℃, the gap of 3mm and the double-roller speed of 6m/min at the cold pressing time of 10s, and finally the nano silicon dioxide porous material with the porosity of 91% is obtained.

Example 10

The same process flow as in example 4 was used to expand water glass into a nano-silica porous material. Weighing 100g of water glass, weighing 2.1g of sodium fluosilicate according to 5 percent of solid content of the water glass, mixing the water glass and the sodium fluosilicate, putting the water glass and the sodium fluosilicate into a 500ml beaker, fully stirring the water glass and the sodium fluosilicate by using a glass rod until the water glass and the sodium fluosilicate are uniformly mixed, pouring the uniformly mixed solution into a double-screw extruder at 110 ℃ and 80r/min at a constant speed to ensure that the water content is 40 percent of the sodium silicate, putting the extruded material into a flat-plate tablet press at normal temperature and using the²The obtained uniform flaky material is subjected to cold pressing for 10s, and the obtained uniform flaky material passes through a die at a constant speed of 300 ℃, a gap of 4mm and a double-roller speed of 1.5And (3) performing a double-roller hot press at the speed of m/min to finally obtain the nano silicon dioxide porous material with the porosity of 94%.

Example 11

The same process flow as in example 4 was used to expand water glass into a nano-silica porous material. Weighing 100g of water glass, weighing 4.2g of aluminum phosphate according to 10% of solid content of the water glass, mixing the water glass and the aluminum phosphate in a 500ml beaker, fully stirring the water glass and the aluminum phosphate by using a glass rod until the water glass and the aluminum phosphate are uniformly mixed, pouring the uniformly mixed solution into a conical double-screw extruder at 110 ℃ and 80r/min at a constant speed to ensure that the water content is 10% of the sodium silicate, and placing the extruded material in a normal-temperature flat-plate tablet press at 10kg/cm²The obtained uniform flaky material passes through a double-roller hot press with the uniform speed of 280 ℃, the gap of 3mm and the double-roller speed of 4m/min at the cold pressing time of 10s, and finally the nano silicon dioxide porous material with the porosity of 90% is obtained.

Example 12

The same process flow as in example 4 was used to expand water glass into a nano-silica porous material. Weighing 100g of water glass, weighing 8.4g of 10% dilute sulfuric acid according to 20% of solid content of the water glass, mixing the water glass and the dilute sulfuric acid in a 500ml beaker, fully stirring the water glass and the dilute sulfuric acid by using a glass rod until the water glass and the dilute sulfuric acid are uniformly mixed, pouring the uniformly mixed solution into a conical double-screw extruder at 110 ℃ and 80r/min at a constant speed to ensure that the water content is 10% of sodium silicate, and placing the extruded material in a normal-temperature flat-plate tablet press at 10kg/cm²The obtained uniform flaky material passes through a double-roller hot press with the uniform speed of 280 ℃, the gap of 2mm and the double-roller speed of 4m/min at the cold pressing time of 10s, and finally the nano-silica porous material with the porosity of 88% is obtained.

The test data for examples 1-12 and comparative examples 1-4 are shown in Table 1.

TABLE 1 TABLE of Performance parameters for examples 1-12 and comparative examples 1-4

Comparative example 1

Porous bodies were prepared by weighing 100g of water glass in a container while adding 30% aluminum phosphate (powder)A material. Putting the sample into a conical double screw, and drying the water content of the mixed solution of the water glass and the aluminum phosphate to 3 wt% under the conditions of 180 ℃ and 60r/min of rotating speed. And opening the double-roller press, setting the temperature at 230 ℃, the rotating speed at 4m/min and the roller gap at 0.7mm, and performing high-temperature puffing by using the double-roller press to obtain the porous material. The thickness before puffing is 1mm, and the thickness after puffing is 1.2 mm. Volume before puffing is 0.7cm³Volume after puffing 1.1cm³。

The density p of the material prepared in this example was 1.56/(4.5 × 2.1 × 0.12) and 1.40g/cm, measured according to the above method³. Finding P ═ 1-rho/rho by consulting the data_{Sodium silicate}) X 100% of sodium silicate, wherein the density of sodium silicate is 2.33g/cm³The porosity P is (1-1.40/2.33) × 100 is 40%.

Comparative example 1 it can be seen that when the water content before puffing is too low, the porosity of the resulting porous material is low.

Comparative example 2

100g of water glass was weighed in a container while 30% aluminum phosphate (powder) was added to prepare a porous material. Putting the sample into a conical double screw, and drying the water content of the mixed solution of the water glass and the aluminum phosphate to 45 wt% under the conditions of 110 ℃ and 60r/min of rotating speed. And opening the double-roller press, setting the temperature at 230 ℃, the rotating speed at 4m/min and the roller gap at 1.5mm, and performing high-temperature puffing by using the double-roller press to obtain the porous material. The thickness before puffing is 2mm, and the thickness after puffing is 5 mm. Volume before puffing is 0.8cm³Volume after puffing 5.9cm³。

The density p of the material prepared in this example was 1.76/(5.1 × 2.3 × 0.5) ═ 0.30g/cm, as measured by the above-mentioned method³. Finding P ═ 1-rho/rho by consulting the data_{Sodium silicate}) X 100% of sodium silicate, wherein the density of sodium silicate is 2.33g/cm³The porosity P is (1-0.30/2.33) × 100 is 87%. Comparative example 1 it can be seen that, although the porosity is higher, there are significant macropores, which are caused by the higher water content in the preform.

Comparative example 3

100g of water glass was weighed in a container while 2% aluminum phosphate (powder) was added to prepare a porous material.And (3) putting the sample into a conical double-screw extruder, and drying the water content of the mixed solution of the water glass and the aluminum phosphate to 20 wt% under the conditions of 110 ℃ and 60r/min of rotating speed. And opening the double-roller press, setting the temperature at 230 ℃, the rotating speed at 4m/min and the roller gap at 1.5mm, and performing high-temperature puffing by using the double-roller press to obtain the porous material. The thickness before puffing is 2mm, and the thickness after puffing is 4 mm. Volume before puffing is 1.2cm³Volume after puffing 6.2cm³。

The density p of the material prepared in this example was 2.66/(6.5 × 2.4 × 0.4) ═ 0.42g/cm, as measured by the above-mentioned method³. Finding P ═ 1-rho/rho by consulting the data_{Sodium silicate}) X 100% of sodium silicate, wherein the density of sodium silicate is 2.33g/cm³The porosity P is (1-0.42/2.33) × 100 is 82%. Comparative example 2 it can be seen that with the addition of a smaller amount of curing agent, the material is brittle.

Comparative example 4

100g of water glass was weighed in a container while adding 40% aluminum phosphate (powder) to prepare a porous material. And (3) putting the sample into a conical double-screw extruder, and drying the water content of the mixed solution of the water glass and the aluminum phosphate to 20% under the conditions of 110 ℃ and 60r/min of rotating speed. And opening the double-roller press, setting the temperature at 230 ℃, the rotating speed at 4m/min and the roller gap at 1.5mm, and performing high-temperature puffing by using the double-roller press to obtain the porous material. The thickness before puffing is 2mm, and the thickness after puffing is 2.7 mm. Volume before puffing is 1.1cm³Volume after puffing is 1.9cm³。

The density p of the material prepared in this example was 2.98/(3.6 × 2.0 × 0.27) ═ 1.51g/cm, as measured by the above-mentioned method³. Finding P ═ 1-rho/rho by consulting the data_{Sodium silicate}) X 100% of sodium silicate, wherein the density of sodium silicate is 2.33g/cm³The porosity P is (1-1.51/2.33) × 100 is 35%. Comparative example 1 can find that the curing agent is added in too much amount, which causes the water glass to be cured too fast, thereby causing the material to have low porosity and affecting the heat insulation performance of the material.

Claims

1. A preparation method of a heat insulation material with a nano porous structure is characterized in that,

dissolving raw materials for preparing inorganic hydrosol in water to form a prefabricated body with the water content of 5-40 wt%; the inorganic hydrosol comprises at least one of silicon dioxide sol, titanium dioxide sol, aluminum oxide sol and zinc oxide sol;

heating the preform to vaporize the water and maintain its form substantially unchanged;

the volume of the material is increased by bulking until the required porosity is reached, and the heat insulation material with the nano porous skeleton structure is obtained.

2. The production method according to claim 1, wherein the raw material further comprises a water-soluble resin.

3. The production method according to claim 1 or 2, characterized in that the production of the preform comprises:

dissolving the raw materials with water with the solid content of 0.5-10 times of the weight to obtain a mixed solution;

the water content of the resulting mixture is reduced to the desired level.

4. The method according to claim 3, wherein the water content of the resulting solution is reduced by heating, and the heating temperature is preferably 25 to 200 ℃.

5. The production method according to any one of claims 1 to 4, wherein the heating temperature of the preform exceeds the boiling point of water, preferably the heating temperature of the preform is 140 to 400 ℃.

6. The production method according to any one of claims 1 to 5, wherein the preform is heated to vaporize water while being pressurized at a pressure higher than the saturated vapor pressure of water under the heating condition.

7. The method according to any one of claims 1 to 6, wherein the volume increase of the material in the puffing process is a gradual process in a controlled state.

8. The method according to any one of claims 1 to 7, wherein the pore size is controlled by controlling at least one of water content, heating temperature, and puffing rate.

9. The preparation method according to any one of claims 1 to 8, wherein the raw materials further comprise a curing agent which is formed by the raw materials and contains 1 to 30wt% of an aqueous solution.

10. The heat insulation material with the nano-porous structure obtained by the preparation method according to any one of claims 1 to 9, characterized by comprising a framework formed by the raw materials, wherein nano-scale pores are uniformly distributed in the framework, and the pore size is adjustable within the range of 0.5 to 999 nm.