SE533051C2 - Silica aerogel body as transparent panel in energy windows - Google Patents

Description

533 051 2 provide a body, e.g. a panel, of an improved silica aerogel material, such as based on e.g. thermal conductivity, with a predetermined and predetermined shape and size.

Summary of the Invention The above object is achieved by means of a body of a silica gel material which is porous and comprises nanoparticles, the body having a density in the range of 60-300 kg / m 2; has a thermal conductivity Å of less than 0.020 W / (m * K) when measured at a density of 150 kg / m3 and a temperature of about 20 ° C; -preferably is crack-free; and - is transparent and has a total transparency of at least 90%; and - has a refractive index in the range 1.017-1.060, when measured at a thickness of 14 mm and as a non-enclosed body.

The body or silica aerogel material of which it is composed according to the present invention has a very low thermal conductivity. At a density of 150 kg / m3 and a temperature of about 20 ° C and in the non-evacuated state, ie a state where there is still air left in the pores of the material, the thermal conductivity (thermal conductivity) is below 0.020 W / (m * K), which is to be compared with 0,021 W / (m * K) for the airgel material described in SE 422 045, the latter per se measured at a higher density of 240 kg / ma but still in an evacuated state (airless condition for the pores), which in itself means a significantly lower thermal conductivity than in the case of non-evacuated condition. For comparison, it can be said that for vacuum the thermal conductivity is 0.022 W / (m * K) at about room temperature.

Specific Embodiments of the Invention There are many different possible uses for a body, such as a panel, according to the present invention. Depending on the intended application, the silica aerogel material of the present invention may be given different properties suitable for the specific application. An inherent property of a silica gel material according to the present invention is the possibility of a high transparency of the material. This means that the material 533 051 3 according to a specific embodiment can maintain a high level of clarity, which means that it is suitable for use in applications where both light can penetrate and that one should be able to see through the material almost as well as for ordinary window glass. This in turn means that a panel according to the present invention can be used in energy window applications, which are also transparent, but also energy-saving because the thermal conductivity is so low for the material. As stated above, the following applies to the body according to the present invention: - is transparent and has a total transparency of at least 90%; and - has a refractive index in the range 1.017-1.060, when measured at a thickness of 14 mm and as a non-enclosed body.

Transparency in the field of optics is synonymous with transparent and translucent, ie clear. The transparency of a material can be divided into the transparency that can be derived from light or radiation that penetrates directly through the material, so-called normal incidence, and light or radiation that is scattered in the material, but penetrates thereafter, so-called diffused light or diffused light. The total transparency can be defined as the transparency that is derived from both direct light penetration and penetration of scattered or diffused light.

However, the bodies of the present invention can be made to have properties other than high transparency. One such example is a body which is translucent in that glass fibers are involved in the silica gel material or in that the surface of the body is heat treated or roughened.

Such treatment can be done, for example, by surface treatment by spraying with water or by burning on the surface.

By a translucent material is meant a material that lets light through but is not transparent. There are applications where translucent bodies could be very useful. One such example is for panels in energy windows in, for example, a bathroom where you are happy to let light through, but do not want any transparency. The incorporation of, for example, glass fibers in the panel material also increases the mechanical stability of materials, which of course may be desirable in certain applications. The glass fibers 533 051 4 which can be mixed in can have different shapes, such as, for example, nets, rods or chips. Heat-treating the surface to make the material translucent can be done by overheating the surface, which causes the pores to "crash" and the surface to rise.

In addition to glass fibers, there are many other substances or materials which, for certain application purposes, may be advantageous to incorporate into the material of the present invention. Examples of such are wavelength shifters and light filters. This can be done, for example, to cause the color of the material to change. There is, of course, some bluishness in a standard panel according to the present invention. With the help of, for example, a wavelength shifter, the blue light that the standard panel material normally emits could be shifted to another color, such as green light. Furthermore, a wavelength shifter could be mixed in to lower the proportion of diffused light, by reducing the scattering of the light, and thus have the effect that the proportion of directly penetrating light increases.

Therefore, according to a specific embodiment of the present invention, a wavelength shifter is involved in the silica aerogel material.

As mentioned above, other materials may also be included in the material of the present invention. For example, the body can also be opaque in that carbon fiber, glass wool, mineral wool and / or rock wool are mixed into the silica airgel material.

By an opaque material is meant in this respect a material that is opaque, which means that light does not pass through the material and that of course you can not then see through the material either. By mixing carbon fibers, glass wool, mineral wool and / or rock wool in the silica aerogel material according to the present invention, the mechanical stability of the material is increased, but on the other hand the transparency is completely lost. Opaque bodies, such as panels, can advantageously be used as insulation material as a low thermal conductivity and mechanical stability are important while transparency is uninteresting.

There are also other purely procedural possible measures, ie in addition to mixing substances, to implement to increase certain properties that may be important for different types of applications. As mentioned above, evacuation of the material, which means that substantially all of the air remaining in the pores of the material is expelled, is a possible method which means that the thermal conductivity of the present material can be further improved. According to a specific embodiment of the present invention, the body is evacuated and is super-insulating and has a thermal conductivity A which is 0.007 W / (m * K) or lower, when measured at a density of 150 kg / ms and a temperature of about ° C. This is a value of the thermal conductivity that is significantly lower than both the vacuum and the material described in SE 422 045. Since the thermal conductivity varies with the density, it may be of interest to regulate the obtained density of the material for certain applications. As stated, the density of the silica aerogel material of the present invention may be between 60 and 300 kg / m 3, such as between 80 and 250 kg / m 3, but in a number of applications the desired density is between 100 and 200 kg / m 3, as in the range 125 -175 kg / m3, eg at about 150 kg / m3.

There are further other properties which may be desirable to impart to the material of the present invention. According to a specific embodiment of the present invention, the silica aerogel material is further water resistant in that a silane compound is bound in the silica aerogel material. This can be an advantage because the material thus becomes easier to handle. An example of silane compounds that may be bound is hexamethyldisilazane (HMDS).

The body of the present invention may further be enclosed in a surrounding material. This is also something that can make, for example, panels according to the present invention easier to handle and transport. Therefore, according to a specific embodiment of the present invention, an enclosing material surrounds the body. According to another embodiment of the invention, the enclosing material is selected from the group consisting of transparent materials, plastic foils, glass sheets and plastic sheets. The type of enclosing material used depends, of course, on the desired application. For example, when an enclosed body with high transparency is what is desired, the enclosing material must of course also be transparent, for example a transparent plastic foil. Another possibility is to use a glass material to enclose the body. In the case where a panel of a silica aerogel material according to the present invention is enclosed between two insulating glasses, these insulating glasses may, for example, be colored. This is to reduce the impression of the blue misty appearance that might otherwise occur from the silica aerogel material. For an enclosed opaque body, on the other hand, non-transparent materials can of course be used, such as plastic foils in this case as well.

By body is meant according to the present invention a geometric body.

As indicated above, panels are highly conceivable geometric bodies according to the present invention. According to a specific embodiment of the present invention, therefore, the body is a panel, for example a panel having a thickness of up to 5 cm. According to another specific embodiment of the present invention, the body is a tubular cup-shaped body. Panel according to the present invention further refers to geometric shapes where length and width are greater than the thickness. According to the present invention, completely different thicknesses, lengths and widths are possible. According to a specific embodiment, the panel has a size of up to 1.5 m * 2 m (width * length), such as eg 600 mm * 1200 mm (width * length).

The present invention also describes a process for producing a silica aerogel body which is porous and comprises nanoparticles.

This process may comprise the steps of: - supplying recipe starter components to a mixer, the recipe starter components comprising at least one silane compound, an alcohol selected from the group consisting of methanol, ethanol and propanol and a catalyst which is either ammonia or titanium lactate; mixing in the mixer under temperature control to form a sun gel which, by polymerization, transforms into a wet gel; filling the wet gel into at least one mold; - retention of the wet gel in the mold; shaping the mold and transferring the wet gel to a transport device; supplying the conveying device and supernatant wet gel to an autoclave to which autoclave either supercritical carbon dioxide or liquid carbon dioxide is added successively, to effect extraction where evaporation of alcohol from the wet gel in the autoclave is carried out, to initially form a silica airgel; Emptying the autoclave and further processing the silica aerogel in a heating process at 200 ° C or higher to further evaporate alcohol and form a substantially alcohol-free silica aerogel material; the discharge of the formed substantially non-alcoholic silica aerogel material from the heating process and any further processing of the formed substantially non-alcoholic silica aerogel material for molding to the desired shape and size, wherein addition of additional recipe components is optionally performed at either the mixture in the mixer, during the extraction process or during the heating process.

In connection with the description of the procedure above, the following explanations of certain terms and parts may be important to understand.

A sun gel is by definition a suspension consisting of a solvent and a sol which is then allowed to polymerize and aggregate to form a gel. The solvent, in this case methanol, ethanol or propanol, can then be evaporated off and the result is a porous material.

An example of a material for a mold in this case is, for example, glass, but there are other materials that are equally conceivable.

The step of retaining the wet gel in the mold can be carried out, for example, by immersing the mold in a water bath and holding it there for about 1-3 days.

According to the present invention, it could also be possible to accelerate the polymerization during the residence step. This could, for example, be possible by treating the wet gel with radiation, such as UV light, or ultrasound or by heat treatment.

An example of the demolding step is that said mold is immersed in a demolding bath containing solvent, then the top of the mold is removed so that the wet gel releases from the mold and floats up in the solvent, when the wet gel then becomes heavier from admixture from the solvent. which is placed in the demoulding bath between the wet gel and the mold after the wet gel has floated up in the solvent. In this case, the solvent is suitably the same solvent used in the remainder of the process.

The transport device described above can be of different types.

There are various examples that are conceivable. A grille has been tested and this can 533 05? 8 according to this method work perfectly for certain application types. However, small marks may appear in the gel where the grid holds it up. For other applications, such as in the manufacture of transparent panels for window applications, this is not fully acceptable and then other types of transport devices should be used, such as a support plane, eg a membrane, which is gas permeable. In addition, there are other techniques that could be possible to use in accordance with the present invention. This is, for example, transporting the gel on an air bed that keeps the gel floating. Also in the autoclave, technology can be used which ensures that the gel does not have to rest against a transport device such as a grid or a supporting plane. This could, for example, be to direct a gas inflow of suitable gas, for example an inert gas, with sufficient force to keep the gel floating. Furthermore, devices having units which alternately hold the gel together would also be possible. These technical solutions reduce or eliminate the risk of deformation of the gel and also ensure that carbon dioxide in the autoclave comes into contact with all parts and sides of the gel.

It is therefore often important at the demoulding step that the wet gel does not change in terms of structure and shape and therefore the transport device or transport technique should therefore be chosen carefully. In this respect, the remaining part of the process can also be important. Furthermore, by having a vertical arrangement for future steps, ie when panels are manufactured, such as during transport and supply to the autoclave, instead of a horizontal arrangement, the problem of deformation of panels can be reduced.

The evaporation of alcohol carried out in the autoclave, which autoclave is filled with the alcohol in question, can be done either with the aid of supercritical carbon dioxide or liquid carbon dioxide. An example of how this can be done is with supercritical carbon dioxide at eg from 90 bar to 150 bar and at from 45 ° C to 80 ° C or with liquid carbon dioxide at eg 50-70 bar and a temperature of 10- ° C. This step is much simpler and much safer than the alcohol stripping step described in SE 422 045.

According to the present invention, the process for producing a silica aerogel body which is porous and comprises nanoparticles may also comprise the following steps: supplying recipe starter components to a mixer, the recipe starter components comprising at least one silane compound, an alcohol selected from the group consisting of methanol, ethanol and propanol and a catalyst which is either ammonia or titanium lactate; mixing in the mixer under temperature control to form a sun gel which, by polymerization, transforms into a wet gel; filling the wet gel into at least one mold; - retention of the wet gel in the mold; direct supply of the mold to an autoclave to which autoclave either supercritical carbon dioxide or liquid carbon dioxide is added successively, to effect extraction where evaporation of alcohol from the wet gel in the autoclave is carried out, for the initial formation of a silica airgel; emptying the autoclave and further processing the silica airgel in a heating process at 200 ° C or higher to further evaporate alcohol and form a substantially alcohol-free silica airgel material; the discharge of the formed substantially non-alcoholic silica aerogel material from the heating process and any further processing of the formed substantially non-alcoholic silica aerogel material for molding to the desired shape and size, wherein addition of additional recipe components is optionally performed at either the mixture in the mixer, during the extraction process or during the heating process.

The procedure described above means that the step of demoulding the wet gel does not have to be performed before the extraction step in the autoclave. However, this of course places new demands on the mold as it must be kept in the autoclave. Also in this case it is conceivable that a conveying device is inserted at the bottom of the mold, such as a conveying device in the form of a supporting plane, for example a membrane, which is gas-permeable, for use at a later stage during and possibly after extraction. tion in the autoclave. Deformation of the mold is done in this case after the extraction or after the heating process.

As described above, the subsequent heating process is carried out at a temperature above 200 ° C. The temperature chosen depends largely on the desired final material for the silica aerogel body. According to the present invention 533 Cl5't, the heating process can be carried out, for example, at 250 ° C-350 ° C, which is sufficient for the solvents contemplated by the present invention. This means that the heating process according to the present invention is considerably less energy-intensive than that described in SE 422 045 where a temperature range of between 500 ° C and 750 ° C is relevant, ie to achieve a similar effect.

There are also other possible solvents that can be used in general to prepare a silica gel material. This is, for example, ethyl acetate-acetate. However, this is not something that is desirable because the heating process must then be carried out at over 400 ° C for the silica aerogel material to be clear again, after being brownish at a couple of hundred degrees due to the solvent used. In addition, this known process means that HF is used as a catalyst in the formation of the sun gel, which is also not desirable.

However, there are applications according to the present methods when an elevated temperature is desirable in the heating process. This can, for example, be to achieve shrinkage or glazing of the material, which means a uniform shape change of the material and which can provide increased mechanical stability. According to the present invention, therefore, the heating process can be carried out at at least 500 ° C to effect shrinkage of the substantially alcohol-free silica aerogel material. The shrinkage increases with increasing temperature and if a stronger shrinkage of the material is desired, the heating process can thus be carried out at, for example, at least 700 ° C.

Sealing of the pores on the surface can also be performed on the material of the present invention. In other words, this could be called glazing or shrinking the surface only. This can be done with different types of technology, such as by “sputtering”, which is also called sputtering or cathode sputtering in Swedish, of the surface or by heat heating the surface.

Furthermore, what is stated above for the final evaporation of alcohol in connection with the first process alternative is also valid for the second alternative according to the present invention.

In the case of catalysts which can be used according to the present invention, this process can be run both basic and acidic. In the acidic case, possible alternatives are HF, HCl and H2SO4, but where HF is the one that is at least 533 051 11 desirable. However, it is preferred to use basic catalysts, such as ammonia or titanium lactate. An example of a commercially available titanium lactate catalyst that can be used in the present processes is further Tyzor®. Different types of mixers can be used in the present processes, such as a Sulzer® mixer.

According to the present invention, it is possible to produce silica aerobic bodies, such as, for example, panels or tubular cup-shaped bodies. According to a specific embodiment of the present methods, therefore, the formed silica gel body is panel-shaped or tubular. According to another embodiment of the present methods, the silica gel body formed is finally enclosed in an enclosing material. This can be done for eg panels, but also other shapes.

According to a process variant of the present invention, the recipe starting components comprise at least one silane compound which is tetramethylorthosilicate (TMOS), also called tetramethoxysilane, or a mixture of tetramethylorthosilicate (TMOS) and tetraethylorthosilicate (TEOS), the latter also called tetraethoxys. As mentioned above, any additional recipe components are added during either the mixing in the mixer, during the extraction or during the heating process. Examples of such possible additional recipe components are carbon fibers, rock wool, glass wool, mineral wool, glass fibers, wavelength shifters, iron, titanium or tin compounds, boron compounds and silane compounds, or a mixture thereof. Several of these are described above, but in the case of various possible metal compounds, such as various metal salts, only a number of which are specified above, these are mixed in to effect dyeing of the silica aerogel material of the present invention. In addition to these, there are also other possible admixture components or prescription components. Examples of such peas are dendrimers. Other examples are ethylene glycol or boron oxide, which could be mixed in to break some bonds in the silica aerogel material. This could be done, for example, to increase the elasticity of the material according to the present invention, and as an example, such components could be mixed in already at the mixing step of the process. 533 05? A specific embodiment is furthermore the use of a transparent panel in an energy window.

Conclusions The present invention describes a body of a silica aerogel material which has excellent properties, such as a very low thermal conductivity, ie is very insulating. Furthermore, various specific embodiments are described in which the body, such as a panel, according to the present invention has been given various advantageous properties, such as high transparency, increased mechanical stability and increased handling and transport possibilities, the latter being done by the panel being enclosed in a enclosing material.

Furthermore, the present invention describes methods for producing a shaped silica gel material, such as, for example, a panel, which are both relatively energy-efficient and safe in comparison with the prior art.

Claims (11)

10 15 20 25 30 533 D51 13 PATENT CLAIMS A body of a silica aerogel material which is porous and comprises nanoparticles, the body - having a density in the range of 60-300 kg / ms; has a thermal conductivity Å of less than 0.020 W / (m * K) when measured at a density of 150 kg / ml and a temperature of about 20 ° C; - preferably is crack-free; and - is transparent and has a total transparency of at least 90%; and - has a refractive index in the range 1.017-1.060, when measured at a thickness of 14 mm and as a non-enclosed body. A body according to claim 1, wherein a wavelength shifter is involved in the silica aerogel material. Body according to claim 1 or 2, wherein the body is evacuated and is super-insulating and has a thermal conductivity A which is 0.007 W / (m * K) or lower, when measured at a density of 150 kg / m 3 and a temperature of approx. 20 ° C. A body according to any one of claims 1-3, wherein the silica aerogel material is water resistant stent in that a silane compound is bound in the silica aerogel material. A body according to any one of claims 1-4, wherein an enclosing material surrounds the body. A body according to claim 5, wherein the enclosing material is selected from the group consisting of transparent materials, plastic foils, glass sheets and plastic splices. A body according to any one of the preceding claims, wherein the body is a panel. 10 533 051 14 Body according to any one of the preceding claims, wherein the body is a panel having a thickness of up to 5 cm. Body according to any one of the preceding claims, wherein the body is a panel having a size of up to 1.5 m * 2 m (width * length). A body according to any one of claims 1-6, wherein the body is a tubular cup-shaped body. Use of a transparent panel according to any one of claims 7-9 in an energy window.