DE19634109A1 - Airgel- and plastic-containing, transparent composite material, process for its production and its use - Google Patents

Abstract

A transparent composite product containing 5 to 97 vol.- % transparent and translucid aerogel particles and at least one transparent or translucid plastic material, the production method and the product application are disclosed.

Description

The invention relates to novel composite materials of any shape high thermal insulation capacity, the 5 to 97 vol .-% transparent or translucent Airgel particles and at least one transparent or translucent plastic contain.

Conventional insulation materials based on polystyrene, polyolefins and Polyurethanes are made using blowing agents, such as. B. CFC's or CO₂ manufactured. The blowing agent trapped in the cells of the foam is responsible for the high thermal insulation capacity. Such blowing agents however pollute the environment as they slowly escape into the atmosphere. About that In addition, such foamed insulation materials are opaque.

Aerogels, especially those with porosities above 60%, are densities below 0.6 g / cm³, depending on the manufacturing process, are transparent, translucent or opaque and have an extremely low thermal conductivity. So you find Application as a heat insulation material, such as. B. in EP-A-0 171 722 described.

Aerogels in the broad sense, i.e. H. in the sense of "gel with air as a dispersant", are made by drying a suitable gel. Under the term "Airgel" in this sense includes aerogels in the narrower sense, xerogels and cryogels. A dried gel is called an airgel in the narrower sense if the Liquid of the gel at temperatures above the critical temperature and largely removed from pressures above the critical pressure becomes. If, on the other hand, the liquid of the gel becomes subcritical, for example below Removal of a liquid-vapor boundary phase is called that created gel as a xerogel.  

When using the term aerogels in the present application it is aerogels in the broad sense, d. H. in the sense of "gel with air as Dispersant ".

In addition, aerogels can also be basically divided into inorganic and divide organic aerogels, with inorganic aerogels since 1931 are known (S.S. Kistler, Nature 1931, 127, 741), whereas organic aerogels from a wide variety of starting materials, e.g. B. from melamine formaldehyde, have only been known for a few years (R.W. Pekala, J. Mater. Sci. 1989, 24, 3221).

The different processes for the production of aerogels by over- or Subcritical drying z. B. in EP-A-0 396076, WO 92/03378, the WO 94/25149, WO 92/20623 and EP-A-0 658513.

The aerogels obtained by supercritical drying are general hydrophilic or only briefly hydrophobic, whereas subcritically dried ones Aerogels due to their manufacturing process (silylation before drying) are permanently hydrophobic.

Also known are opaque, airgel-containing composite materials, which due to their low heat conduction can be used as thermal insulation materials. Such Composite materials are described, for example, in EP-A-0 340707 and EP-A-0 667 370, WO 96/12683, WO 96/15997 and WO 96/15998.

The commonality of these composite materials is that some of them contain transparent airgel granules, but the additional components are themselves opaque. As a result, the systems are overall opaque and cannot be use for transparent or translucent applications.

A transparent airgel and xerogel composite is described in DE-A-44 30 642 and DE-A-44 30 669 discloses.  

This composite is in the form of a mat that is an airgel or xerogel contains fibers distributed therein, the airgel or xerogel fragments passing through the fibers are held together.

Although good results have been achieved with such materials, disadvantages remain price type and the need to manufacture the systems in one step.

A transparent component with at least two panes arranged in parallel made of transparent material, in the space between which is fiber-reinforced Airgel plates or mats are located, for. B. in the German patent application 195 07 732.6. This measure increases the stability of the system significantly increased, but the complicated structure and the high price remain consist.

An alternative to the airgel-containing composites is described in CA-C-1 288313 C1, EP-A-018 955 and DE-A 41 06 192. According to these steps Airgel monoliths are placed between panes of glass in order to To improve the insulation effect due to the low thermal conductivity of the airgel and / or to improve the sound attenuation of such panes. The should Airgel monoliths e.g. T. be firmly connected to the glass plates.

In this way, almost crystal clear, transparent panes can be made achieve, but is due to the low mechanical stability of the aerogels one the effort for the production of appropriately large monoliths too high to others too complicated to handle when manufacturing the disks to be able to use such glass panes on a larger scale.

It is also known to make the space easier to manufacture and also easier to handle airgel granules. The disks are then however no longer crystal clear, but rather translucent, comparable to Frosted glass panes or structured glass panes. This is not an essential one Restriction because it has a number of uses such as Skylights exist where drop shadows are avoided by direct incidence of light should be such. B. Windows in factory, warehouse, exhibition or museum halls. However, such windows also have some disadvantages. So the granules can  condense over time, causing a change in the level in the window leads, which is undesirable. The compression can e.g. B. smaller as a result Shocks or by destroying airgel spheres, especially in the case of Evacuation takes place. Forces are between in the granulate Granules among themselves and / or between glass and Transfer granules only over very small contact areas. Thereby occur relatively high compressive and / or shear stresses, which lead to the destruction of Airgel grains can lead.

It was therefore proposed in DE-A-35 33 805 that the airgel granules between bring two foils between the glass panes and the space between the Evacuate slides. Due to the flexibility of the film, the surface can be between Foil and surface of the beads are enlarged, resulting in an improvement that leads to long-term stability. However, it is disadvantageous that the structure of the disks is very great is complicated. In addition, the additional layers of film reduce the Transparency.

Furthermore, vacuum panel systems filled with airgel are known, e.g. B. in the EP-A-0 468 124, EP-A-0 114687 and DE-A-33 47 619.

The disadvantage of vacuum panel systems, however, is that they are no longer available can be changed in shape or size at the place of use.

It was therefore an object of the present invention to provide a transparent, to develop heat-insulating composite material that is simple as well as in any Shape and size can be made and still in place at use its size is changeable.

This task is solved by a plastic-containing, transparent Composite material that contains 5 to 97 vol.% Transparent or translucent airgel Contains particles and at least one transparent or translucent plastic.  

The plastic forms a matrix that connects or encloses the airgel particles and runs as a continuous phase through the entire composite material.

With a content of airgel particles that are significantly below 5 vol .-% in the Composition would be due to the low proportion of airgel particles their positive properties are largely lost in the composition go. Such a composition would no longer have low densities and Have thermal conductivities.

A content of airgel particles that is significantly above 97% by volume would become one Plastic content of less than 3% by volume. In this case, its share would be too low to ensure that the airgel particles are adequately interconnected as well as to ensure mechanical pressure and bending strength.

The proportion of airgel particles is preferably in the range from 10 to 97% by volume and particularly preferably in the range from 40 to 95% by volume.

A particularly high proportion of airgel particles in the composite material can be by using a bimodal distribution of grain sizes.

Another option is to use a particularly high proportion of airgel particles in the To achieve composite material is the use of airgel particles, which is a have logarithmic distribution of grain size.

In order to achieve the highest possible degree of filling, it is also favorable if the Airgel particles are small in relation to the total thickness of the molded part.

So that the transparency of the composite material is as high as possible, the Airgel particles should be large enough. This allows the number of scattering centers keep it as low as possible by interfacing the airgel particles.

The size of the airgel particles is therefore preferably in the range of 250 μm up to 10 mm.  

In addition, it is important that the airgel granulate itself is as high as possible Has transparency. On the one hand, this is due to a structure that is as homogeneous as possible of the airgel, d. H. especially a narrow pore and Particle radius distribution, and on the other hand through the smoothest possible surface of airgel particles (no cracks, depressions, micro-cracks or dents).

Generally used aerogels for the invention Compositions are those based on metal oxides that are used for sol-gel Technology are suitable (C.J. Brinker, G.W. Scherer, Sol-Gel-Science, 1990, Chapter 2 and 3), such as Si or Al compounds, or those based organic substances that are suitable for the sol-gel technique, such as Melamine formaldehyde condensates (US-A-5 086085) or Resorcinol formaldehyde condensates (US-A-4 873218). The compositions can also be based on mixtures of the above materials. Prefers Aerogels containing Si compounds and in particular SiO₂- are used Aerogels.

To reduce the radiation contribution of thermal conductivity, the airgel IR Opacifiers, such as B. titanium dioxide, iron oxides or zirconium dioxide as well Mixtures of the same. It is important to ensure that this IR Opacifiers do not increase the transparency in the visible area of the airgel particles influence negatively.

In a preferred embodiment, the airgel particles have permanently hydrophobic surface groups. Suitable groups for permanent hydrophobization are, for example, silyl groups of the general formula -Si (R) _n , where n = 1, 2 or 3, preferably trisubstituted silyl groups, the radicals R generally being the same or different, independently of one another, a hydrogen atom or a non-reactive one , organic linear, branched, cyclic, aromatic or heteroaromatic radical, preferably C₁-C₁₈ alkyl or C₆-C₁₄ aryl, particularly preferably C₁-C₆ alkyl, cyclohexyl or phenyl, in particular methyl or ethyl. The use of trimethylsilyl groups is particularly advantageous for permanent hydrophobization of the airgel. These groups can be introduced as described in WO 94/25149, or by gas phase reaction between the airgel and, for example, an activated trialkylsilane derivative, such as. B. a chlorotrialkylsilane or a hexaalkyldisilazane (see R. Iler, The Chemistry of Silica, Wiley & Sons, 1979). Compared with OH groups, the hydrophobic surface groups produced in this way further reduce the dielectric loss factor and the dielectric constant. Airgel particles with hydrophilic surface groups can adsorb water depending on the air humidity, which means that the dielectric constant and the dielectric loss factor can vary with the air humidity. This is often not desirable for electronic applications. The use of airgel particles with hydrophobic surface groups prevents this variation since no water is adsorbed. The selection of the residues also depends on the typical application temperature.

Are airgel particles with hydrophobic surface groups in conjunction with If hydrophobic plastics are used, a hydrophobic one is obtained Composite material.

In addition, the thermal conductivity of the aerogels increases with increasing Porosity and decreasing density decreases. Therefore, aerogels are preferred Porosities over 60% and densities under 0.6 g / cm³. Are particularly preferred Aerogels with densities below 0.2 g / cm³.

Basically, all known plastics for the production of Composite materials according to the invention are suitable if these after production be transparent or translucent in the visible light wavelength range. It is not important whether the plastic is amorphous, semi-crystalline and / or is crystalline.

The plastic is either in liquid form, i.e. H. as liquid, melt, Solution, dispersion or suspension, used or as a solid powder used.  

Suitable transparent or translucent plastics are e.g. B. Polymethyl methacrylates (PMMA, e.g. Degalan®), cycloolefin copolymers (COC, e.g. B. Topas®, polyvinyl butyrals (e.g. Mowital®, polycarbonates and Polyethylene terephthalate (PET, e.g. Hostaglas®), with polyvinyl butyrals and Polymethyl methacrylates are preferred.

The plastic is generally in an amount of 3 to 95 vol .-% of Composite material used, preferably in an amount of 3 to 90 vol .-% and particularly preferably in an amount of 5 to 60% by volume. The selection of the Plastic is made depending on the desired mechanical and thermal Properties of the composite material. Mixtures can also be made from different plastics can be used.

When choosing the plastics, one also preferably chooses those Products that are essentially not inside the porous airgel particles penetration. The penetration of the plastic into the interior of the airgel particles besides the selection of the plastic material, it can also be done in various ways Parameters such as pressure, temperature or processing time can be influenced.

In addition, one preferably selects those plastics which are low Have thermal conductivity.

To avoid strong light scattering and associated reduced Transmission should also include the gusset between the airgel particles transparent plastic should preferably be filled as completely as possible.

This can help reduce the radiation contribution of thermal conductivity Composite material as long as it does not significantly impair transparency is, IR opacifiers such. B. titanium dioxide, iron oxides or zirconium dioxide as well Mixtures of the same contain, which is particularly suitable for applications at higher Temperatures and / or in evacuated systems is advantageous.  

In addition, the composite material can also fillers such. B. for coloring or Achieving special decorative effects included.

Furthermore, the composite material can also contain up to 85% by volume transparent fillers such as B. film snippets and / or fibers, for example to improve the mechanical properties. Preferably lies the proportion of fillers, based on the composite material, below 70% and particularly preferably in the range from 0 to 50% by volume.

Should the composite material be due to the plastic used and / or may be hydrophilic due to hydrophilic airgel particles a subsequent treatment is carried out, which makes the composite material hydrophobic Gives properties. All of them are suitable for this purpose to the person skilled in the art known substances that give the composite material a hydrophobic surface, such as B. paints, films, silylating agents, silicone resins, inorganic and / or organic binders.

Furthermore, so-called "coupling agents" can also be used for bonding will. They bring about better contact between the plastics and the surface of airgel particles and can also have a strong bond with both Airgel particles as well as with the plastic.

The molded articles produced according to the invention from airgel granules have preferably a density of less than 0.6 g / cm³ and preferably one Thermal conductivity of less than 100 mW / mK. The is particularly preferably Thermal conductivity below 50 mW / mK.

The fire class of the composite material obtained after drying is determined by determines the fire class of the airgel and the plastic. To one if possible maintain the favorable fire class of the composite material (flame retardant or non-flammable), the composite materials can still be used with suitable materials be concealed, such as B. window panes or silicone resin adhesives. Farther the use of fire protection agents known to the person skilled in the art is possible.  

In addition, all coatings known to those skilled in the art are also possible, the z. B. dirt-repellent, IR semi-transparent and / or hydrophobic.

Another object of the present invention was to provide a manufacturing method for the composite materials described above.

To produce the composite materials according to the invention, the airgel Particles connected to one another by means of at least one plastic. The Connection of the individual particles to one another can be quasi punctiform respectively. Such a surface coating can, for example, by Spraying the airgel particles with the plastic can be achieved. The coated particles are then, for example, filled into a mold and into the shape hardened.

Another object of the invention is therefore a method for manufacturing a composite material containing 5 to 97 vol .-% transparent or translucent Airgel particles and at least one transparent or translucent plastic, which is characterized in that airgel and plastic are mixed into the brings the desired shape and hardens.

In a preferred embodiment, the gusset volume is also added completely or partially filled with plastic between the individual particles. Such a composition can be prepared, for example, by the Airgel particles mixed with the plastic granulate.

The mixing can be carried out in any conceivable way. So is on the one hand, it is possible to insert the at least two components simultaneously into the Introduce mixing device, but on the other hand can also be one of the components submitted and the other (s) are then added.

The mixing device necessary for the mixing is also in no way limited. Any can be known to those skilled in the art for this purpose Mixing device can be used.  

The mixing process is carried out until it is approximately uniform Distribution of the airgel particles in the composition is present. The Mixing process both over the period and for example over the Speed of the mixing device can be regulated.

This is followed by the shaping and curing of the mixture in the mold, which depending on the type of plastic by heating and / or evaporating the used solvent and / or dispersant or, if using Melting, is done by cooling below the melting temperature of the plastic.

In a preferred embodiment, the mixture is pressed. It is the Specialist possible, the appropriate press and for the respective application select the appropriate press tool. Due to the high proportion of air in the Airgel-containing molding compounds use vacuum presses. In a preferred embodiment, the airgel-containing molding compounds Plates pressed. To prevent the molding compound from baking on the pressing tool, For example, to avoid press rams, Airgel-containing mixture with release paper or release film against the pressing tool be separated. The mechanical strength of the airgel-containing plates can by laminating screen fabrics, foils or glass panes onto the Plate surface can be improved. The sieve cloth, foils or glass panes can be added both afterwards and during the production of the composite material the airgel-containing plates are applied. The latter is preferred and can preferably in one step by inserting the sieve cloth, film or Glass panes in the mold and placing on the airgel-containing to be pressed Molding compound and subsequent pressing under pressure and temperature into one Airgel-containing composite panel.

The pressing generally takes place depending on the plastic used at pressures from 1 to 1000 bar and temperatures from 0 to 300 ° C in any shape instead.  

For composite materials that have a particularly high volume fraction of airgel Contain particles and the thermal conductivity is correspondingly poor, can additionally brought heat into the panels with the help of suitable radiation sources will. Coupled with the plastic used, as in the case of polyvinyl butyrals Microwaves, this radiation source is preferred.

The composite materials according to the invention are suitable after their curing due to their low thermal conductivity, for example as Thermal insulation materials.

Because of their transparency or translucency, they are also suitable for. B. as a window in factory, warehouse, exhibition or museum halls. Another one Area of application are skylights and so-called daylighting systems. Due to the simple production, any curved surfaces can also be used or other more complicated geometries. They are therefore suitable also especially for the production of skylights.

The invention is explained in more detail below on the basis of exemplary embodiments described without being restricted thereby.

The hydrophobic aerogels were analogous to that disclosed in DE-A 43 42 548 Process manufactured.

The thermal conductivities of the airgel granules were measured using a Heating wire method (see e.g. O. Nielsen, G. Rüschenpöhler, J. Groß, J. Fricke, High Temperatures-High Pressures, Vol. 21, 267-274 (1989)).

The thermal conductivities of the moldings were measured in accordance with DIN 52612.

The transparency of the moldings was determined using an apparatus consisting of a voltage measuring device (Keithley multimeter), a pyranometer (Lambrecht company, type CM3, sensitivity +/- 0.5%, 16.30 · 10 ^-6 V / Wm²) inside, matt white painted aluminum cubes and a halogen spotlight (500 W), measured. The moldings are placed directly in front of the round opening (⌀ 80 mm) of the aluminum cube painted matt white on the inside. The 400 mm halogen spotlight serves as the light source. The pyranometer placed in the aluminum cube behind a screen converts the detected light into a voltage. The transmission as a percentage of I₀ was determined by measuring the voltage without (I₀) and with the respective insulation board (I _D ).

Example 1a Shaped body made of 50 vol .-% airgel and 50 vol .-% polyvinyl butyral

50% by volume of hydrophobic airgel granules (solid density 130 kg / m³) and 50 vol .-% of a polyvinyl butyral powder (solid density 1100 kg / m³) intimately mixed. The percentage volume relates to the target volume of the Molded body. The hydrophobic airgel granulate has a grain size greater than 650 µm, a BET surface area of 640 m² / g and a thermal conductivity of 11 mW / mK. ®Mowital (Polymer F) (Hoechst AG, Frankfurt, Germany) with a grain size of around 50 µm.

The bottom of the mold with a base of 30 cm × 30 cm is with Release paper designed. The airgel-containing molding compound then becomes uniform spread out and covered with a release paper. It will be at 220 ° C for 30 Minutes to a thickness of 18 mm.

The molded body obtained has a density of 481 kg / m³ and a Thermal conductivity of 57 mW / mK. The transmission is 28%.

Example 1b Shaped body made of 50 vol .-% airgel and 50 vol .-% polyvinyl butyral

50% by volume of hydrophobic airgel granules (solid density 130 kg / m³) and 50 vol .-% of a polyvinyl butyral powder (solid density 1100 kg / m³) intimately mixed. The percentage volume relates to the target volume of the  Molded body. The hydrophobic airgel granulate has a grain size of less than 650 µm, a BET surface area of 640 m² / g and a thermal conductivity of 11 mW / mK. ®Mowital (Polymer F) (Hoechst AG, Frankfurt, Germany) with a grain size of around 50 µm.

The bottom of the mold with a base of 30 cm × 30 cm is with Release paper designed. Then the airgel-containing molding compound is evenly ver divides and covered the whole with a release paper. It will be at 220 ° C for 30 Minutes to a thickness of 18 mm.

The molded body obtained has a density of 510 kg / m³ and a heat conductivity of 59 mW / mK. The transmission is 20%.

Example 2 Shaped body made of 65 vol .-% airgel and 35 vol .-% polyvinyl butyral

There are 65 vol .-% hydrophobic airgel granules (solid density 130 kg / m³) and 35% by volume of a polyvinyl butyral powder (solid density 1100 kg / m³) intimately mixed. The percentage volume relates to the target volume of the Molded body. The hydrophobic airgel granulate has a grain size greater than 650 µm, a BET surface area of 640 m² / g and a thermal conductivity of 11 mW / mK. ®Mowital (Polymer F) (Hoechst AG, Frankfurt, Germany) with a grain size of around 50 µm.

The bottom of the mold with a base of 30 cm × 30 cm is with Release paper designed. Then the airgel-containing molding compound is evenly ver divides and covered the whole with a release paper. It will be at 220 ° C for 30 Minutes to a thickness of 18 mm.

The molded body obtained has a density of 539 kg / m³ and a Thermal conductivity of 32 mW / mK. The transmission is 31%.  

Example 3a Shaped body made of 50 vol.% Airgel and 50 vol.% Polymethyl methacrylate (PMMA)

50% by volume of hydrophobic airgel granules (solid density 130 kg / m³) and 50% by volume of a polymethyl methacrylate (solid density 1200 kg / m³) intimately mixed. The percentage volume relates to the target volume of the Molded body. The hydrophobic airgel granulate has a grain size greater than 650 µm, a BET surface area of 640 m² / g and a thermal conductivity of 11 mW / mK. As polymethyl methacrylate ®Degalan (PMMA) (DEGUSSA, Frankfurt, Germany) with a grain size of 50 µm.

The bottom of the mold with a base of 30 cm × 30 cm is with Release paper designed. Then the airgel-containing molding compound is evenly ver divides and covered the whole with a release paper. It will be at 220 ° C for 30 Minutes to a thickness of 18 mm.

The molded body obtained has a density of 615 kg / m³ and a Thermal conductivity of 59 mW / mK. The transmission is 25%.

Example 3b Shaped body made of 50 vol.% Airgel and 50 vol.% Polymethyl methacrylate (PMMA)

50% by volume of hydrophobic airgel granules (solid density 130 kg / m³) and 50% by volume of a polymethyl methacrylate (solid density 1200 kg / m³) intimately mixed. The percentage volume relates to the target volume of the Molded body. The hydrophobic airgel granulate has a grain size of less than 500 µm, a BET surface area of 640 m² / g and a thermal conductivity of 11 mW / mK. As polymethyl methacrylate ®Degalan (PMMA) (DEGUSSA, Frankfurt, Germany) with a grain size of 50 µm.  

The bottom of the mold with a base of 30 cm × 30 cm is with Release paper designed. Then the airgel-containing molding compound is evenly ver divides and covered the whole with a release paper. It will be at 220 ° C for 30 Minutes to a thickness of 18 mm.

The molded body obtained has a density of 628 kg / m³ and a Thermal conductivity of 64 mW / mK. The transmission is 17%.

Example 4 Shaped body made of 50 vol .-% airgel and 50 vol .-% cycloolefin copolymer (COC)

50% by volume of hydrophobic airgel granules (solid density 130 kg / m³) and 50% by volume of a cycloolefin copolymer (solid density 1200 kg / m³) intimately mixed. The percentage volume relates to the target volume of the Molded body. The hydrophobic airgel granulate has a grain size greater than 650 µm, a BET surface area of 640 m² / g and a thermal conductivity of 11 mW / mK. As a cycloolefin copolymer ®Topas (COC) (Hoechst AG, Frankfurt, Germany) with a grain size of around 250 µm.

The bottom of the mold with a base of 30 cm × 30 cm is with Release paper designed. Then the airgel-containing molding compound is evenly ver divides and covered the whole with a release paper. It will be at 220 ° C for 30 Minutes to a thickness of 18 mm.

The molded body obtained has a density of 585 kg / m³ and a Thermal conductivity of 62 mW / mK. The transmission is 25.6%.

Claims (13)

1. Composite material that contains 5 to 97 vol% transparent or translucent airgel Particles and at least one transparent or translucent plastic contains. 2. Composite material according to claim 1, characterized in that as Airgel particles SiO₂ airgel particles are used. 3. Composite material according to claim 1 or 2, characterized in that the airgel particles have hydrophobic surface groups. 4. Composite material according to at least one of claims 1 to 3, characterized characterized in that the airgel particles have porosities over 60% and densities have less than 0.6 g / cm³. 5. Composite material according to at least one of claims 1 to 4, characterized characterized in that as a plastic, a polymethyl methacrylate Cycloolefin copolymer, a polyvinyl butyral, a polycarbonate and / or a Polyethylene terephthalate is used. 6. Composite material according to claim 5, characterized in that as transparent plastic a polyvinyl butyral or a polymethyl methacrylate is used. 7. Composite material according to at least one of claims 1 to 6, characterized characterized in that the airgel particles and / or the composite material IR Contain opacifiers. 8. Composite material according to at least one of claims 1 to 7, characterized characterized in that the composite material contains fillers and / or fibers.   9. Composite material according to at least one of claims 1 to 8, characterized characterized in that the thermal conductivity is less than 100 mW / mK. 10. Composite material according to at least one of claims 1 to 9, characterized characterized in that the composite material on at least one side is coated. 11. Use of a composite material according to at least one of the Claims 1 to 10 for thermal insulation. 12. A method for producing an airgel according to at least one of the Claims 1 to 10, characterized in that airgel and Plastic mixes, brings them into the desired shape and hardens. 13. The method according to claim 11, characterized in that shaping and Hardening by pressing at a pressure of 1 to 1000 bar and one Temperature from 0 to 300 ° C take place.