EP2387552A1

EP2387552A1 - Optically transparent glass and glass-ceramic foams, method for production thereof and use thereof

Info

Publication number: EP2387552A1
Application number: EP09779914A
Authority: EP
Inventors: Michael Scheffler; Christiane Ohl; Christina Olschewski; Viola Wilker; Franziska Scheffler
Original assignee: Otto Von Guericke Universitaet Magdeburg; Brandenburgische Technische Universitaet Cottbus
Current assignee: Otto Von Guericke Universitaet Magdeburg; Brandenburgische Technische Universitaet Cottbus
Priority date: 2009-01-16
Filing date: 2009-06-24
Publication date: 2011-11-23
Also published as: US20120028329A1; WO2010081561A1

Abstract

The present invention relates to an optically transparent glass foam or glass-ceramic foam and to a method for producing an optically transparent glass foam or glass-ceramic foam. A description is given of a method for producing optically transparent foams, the following steps being performed: a) mixing pre-ceramic Si polymer, glass powder and glass converters; b) heating the mixture to a temperature below the decomposition temperature of the pre-ceramic Si polymer to form a foam; c) heating the foam obtained to a temperature above the decomposition temperature of the pre-ceramic Si polymer; d) heating the product obtained to a temperature between 700°C and 1400°C to form glass; and e) cooling the product thus obtained to ambient temperature. A description is also given of the use for predominantly optical applications, such as for example as a carrier for photocatalysts, a carrier for enzymes/microbes which operate with light/sunlight in bioreactors, in environmental catalysis, biocatalysis and, for example, for the removal of VOCs from wastewater and air.

Description

OPTICALLY PERMANENT GLASS AND GLASS CERAMIC FOAMS, PROCESS FOR THEIR PRODUCTION AND THEIR USE

The invention relates optically to permeable foams, to processes for their preparation and to their use.

State of the art

Relevant processes for the production of glass foams

Methods for the production of glass foams are already known in the prior art. For example, G. Scarinci et al. (G. Scarinci, G. Brusatin, E. Bernardo: Glass Foams., In: M. Scheffler, P. Colombo (Editor): Cellular Ceramics: Structure, Manufacturing, Properties and Applications, 158-176, Wiley-VCH Verlag GmbH Co KGaA, Weinheim, ISBN: 3-527-31320-6, 2005) and L. Kern in US Pat. No. 1,898,839, filed in June 1930, glass foams and the production of glass foams. However, the glass foams produced by the disclosed methods are not suitable for optical applications. Criterion for use in optical applications is high light transmission of the material obtained.

M. Frosch, diploma thesis, University of Erlangen, 2007, proposes a method for producing a glass foam based on SiO 2. Here, a polymer sponge as described by K. Schwartzwalder and AV Somers in U.S. Patent 3,090,094 filed in February 1961 is coated with a polysiloxane and silica glass powder as a filler. In a complex thermal process, which is carried out stepwise at temperatures up to 1600 ⁰ C, the burnout of the organic template sponge and the sintering process of the resulting from the oxidation of the polysiloxane silicon dioxide to quartz glass or a quartz glass / cristobalite mixture. The material is characterized by a medium optical transparency. However, the high sintering temperatures have a disadvantageous effect on the preservation of the macroporous foam structure and the low mechanical strengths achieved.

Further, in the prior art of JD Torrey (Lecture 32nd International Conference & Exposure on Advanced Ceramics and Composites, Daytona Beach, FL, USA, 27.01.08-01.02.08), the use of glass powder with less high glass transition area than quartz glass has , described as a filler in the production of glass foams. Duranglas® was used as glass filling powder. However, a disadvantage of this method is that two glass phases of different composition are formed or remain adjacent to one another and the transmittance of light is lowered by the difference in the refractive index of both glasses.

Process for the preparation of polymer-derived ceramic foams

Polymer-derived ceramic foams are prepared by a variety of methods which have been the subject of numerous publications and papers, such as Bao, X., Nangrejo, M.R. & Edirisinghe, M.J., J. Mater. Sci., 1999, 34, 2495-2505; Gambaryan-Roisman, T., Scheffler, M., Buhler, P., Greil, P., Ceram. Trans.,

2000, 108, 121-130; Colombo, P., Bernardo, E., Comp. Be. Tech., 2003a, 63, 2353-2359; Scheffler M. and Colombo P. (eds.), Cellular Ceramics: Structure, Manufacturing, Properties and Applications, WILEY-VCH Weinheim, Germany, 2005 and Zeschky, J., Ceramic Foams of Filled Poly- silsesquioxanen, Dissertation, University of Erlangen, 2004.

In the course of these processes, a so-called green foam is first prepared by mixing a preceramic polymer, preferably a polysiloxane, with a filler and then either foaming it directly or converting it via a molding process into a crosslinked, infusible thermoset (see Colombo, p ., Bernardo, E., Comp. Sci. Tech., 2003a, 63, 2353-2359;

Gambaryan-Roisman, T., Scheffler, M., Buhler, P., Greil, P., Ceram. Trans., 2000, 108, 121-130; K. Schwartzwalder, A.V. Somers, U.S. Patent 3,090,094).

The thermoset obtained in this way is thermally transferred after the shaping / foaming in inert or reactive atmosphere in the so-called polymer-derived ceramic foam.

However, there is an urgent need for highly transparent glass and glass ceramic foams. Photocatalysts that can be activated by light are used in a variety of applications in the chemical industry and in environmental catalysis.

If such catalysts are provided for the acceleration of reactions in the liquid or gaseous phase and form themselves a solid, the fixation on a support is necessary. Such a carrier is subject to high requirements for its transmission of light with the catalyst-activating wavelength, but also to the permeability of flowing liquids and gases. For this purpose, monolithic glass and ceramic structures such as open-cell foams and honeycomb bodies are suitable. Object of the invention

The object of the present invention is to overcome the above-described disadvantages of the prior art.

In particular, it is an object of the present invention to provide a cellular support which is endowed with good flowability for gases and liquids and high optical transparency for much of the light of the wavelengths of the solar spectrum. Preference is given to a glass with a high silicate content of conventional composition.

Description of the invention

The object of the invention is achieved by the provision of an optically permeable glass foam or glass-ceramic foam which can be produced by the method according to the invention.

In order to overcome the above-mentioned problems of the prior art and to adapt the optical properties, a method has been developed in which a

Glass phase with the composition similar to or equal to the filler glass phase directly in the thermal conversion of a glass-filled, foamed, organosilicon polymer offset forms.

The object is thus achieved by a method as described in claim 1. Advantageous embodiments of the method according to the invention are characterized in the dependent subclaims. The invention relates to a process for the preparation of optically transparent foams, wherein the following steps are carried out: a) mixing of preceramic Si polymers, glass powders and glass transducers; b) heating the mixture to a temperature below the decomposition temperature of the preceramic Si polymer to form a foam; c) heating the resulting foam to a temperature above the decomposition temperature of the preceramic Si-polymer; d) heating the product obtained with glass formation to a temperature between 700 ⁰ C and 1400 ⁰ C; and e) cooling the product thus obtained to ambient temperature.

Preference is given to a process in which, after step a), an additional step f) is carried out, comprising: f) application and / or introduction of the mixture prepared in step a) and / or into an organic polymer foam body and subsequent drying of Body at elevated temperature if necessary.

Preference is further given to a process wherein the step c) is carried out at a temperature of 350 ⁰ C to 750 ⁰ C.

Particularly preferred is a method wherein the step d) is carried out at a temperature of less than 1100 ⁰ C.

Also preferred is a process in which step d) is carried out at the maximum temperature for 1 to 12 hours. Preference is also given to a process in which the products obtained are rapidly cooled by removal from the oven in step e).

Very particular preference is given to a process in which the products obtained are cooled in a fine cooling step in step e), wherein, starting from a temperature between 400 ⁰ C and 900 ⁰ C, a cooling rate between 0.1 K / min and 10 K. / min applies.

Particular preference is given to a process in which, in step a), at least one viscosity modifier or at least one catalyst or mixtures thereof is additionally added.

Particular preference is given to a process wherein the preceramic Si polymers are selected from the group consisting of polysiloxanes, polyorganosiloxanes, polysilsesquioxanes, silicone resins, silicone rubbers, polysilazanes and polycarbosilanes, the organic radicals of the Si polymers being selected from saturated, unsaturated, branched, unbranched, ring-shaped or open-chain radicals having 1 to 6 C atoms, aryl, aralkyl or alkylaryl radicals having up to 9 C atoms are selected.

Furthermore, a method in which the glass powder is selected from the group consisting of flat glass, window glass, container glass, bottle glass, commercial glass, incandescent glass, television flask glass, laboratory glassware, lead crystal glass, fiberglass, E glass or borosilicate glass is particularly preferred.

Particular preference is also a method, wherein the glass transducer from the group consisting of Na ₂ CO ₃ , H ₃ BO ₃ , K ₂ CO ₃ , Li ₂ CO ₃ , CaCO ₃ , MgCO ₃ , Al ₂ O ₃ and Na ₂ B ₄ O ₇ and their hydrous derivatives and is selected from the mixtures of the aforementioned compounds.

Preference is also given to a process in which the foams produced are infiltrated with a polymer selected from PMMA, PEEK or EVA.

Also preferred is a process wherein the foams produced are infiltrated with a glass that softens at lower temperatures than the glass foam.

An object of the invention is therefore a process by means of which a) a preceramic polymer, b) a glass filler powder and c) one or more components for modifying (glass transducers) the glass structure of filled-polymeric, cellular green bodies highly translucent Glass and glass ceramic foams with lying in the UV range, optical absorption edge directly without the detour of a low-viscosity melt phase of the glass components are formed.

The invention relates to a process which is characterized in that, for the production of an optically transparent glass foam or glass ceramic foam, an organosilicon preceramic polymer (eg polysiloxane of the general composition (RiR ₂ SiOi, ₅ ) _n , with Ri, R ₂ as an organic functional group , for example phenyl, methyl, vinyl or hydrogen, wherein Ri can also be equal to R ₂ , polysilsequioxanes, silicone resins, Silikonkau- tschuke, polysilazanes, polycarbosilanes) is used as SiO ₂ source.

Particularly preferred is a process which is characterized in that the organosilicon polymer is a glass powder and one or more typical Glaswandlerkomponenten, eg Na ₂ Cθ ₃ and its wasserhal- related relatives, H ₃ BO ₃ and their hydrous derivatives, K ₂ CO ₃ and its hydrous derivatives, Li ₂ CO ₃ , CaCO ₃ , MgCO ₃ , Al ₂ O ₃ , Na ₂ B ₄ O ₇ ^ OH ₂ O or those with a hermaphate function as a glass former and converters in compositions and concentrations typical of glass formation.

Preference is given to a process which is characterized in that an Si-organic monomer, typically a trialkoxyalkylsilane (for example trimethoxymethylsilane, triethoxymethylsilane), tetraalkoxysilanes (tetraethoxysilane, TEOS) can be added to adjust the viscosity.

Also preferred is a process which is characterized in that a catalyst such as, for example, oleic acid or aluminum acetylacetonate or the combination of both catalysts can be used for accelerated solidification of the offset.

Particularly preferred is a method which is characterized in that the conversion into an open-cell foam takes place directly by heating the offset.

Further preferred is a method characterized in that a polymeric template is coated with the offset containing the essential components and the offset is adhered to the template by a liquid-solid transition.

Particularly preferred is a method, which is characterized in that the introduced via preceramic polymer and / or polymer template organic constituents are removed by oxidation by a heat in air at 350 ⁰ C to 700 ⁰ C. Preference is furthermore given to a process which is characterized in that the thermal treatment for glass formation takes place at temperatures of less than or equal to 1100 ^° C.

Particularly preferred is a method which is characterized in that a holding stage of 1 to 12 hours at maximum temperature takes place.

Preference is furthermore given to a process which is characterized in that rapid cooling of the monolithic foam body takes place by removal from the furnace.

Particularly preferred is a method which is characterized in that a fine cooling step by conversion into a preheated oven with a temperature between 400 and 900 ⁰ C takes place and the cooling rates are set between 0.1 and 10 K / min.

Further preferred is a process characterized in that glass foams produced by the reticulate process are infiltrated with a polymer (e.g., PMMA, PEEK, EVA).

Particularly preferred is a method which is characterized in that glass foams produced by the reticulate method are infiltrated with a glass that softens at lower temperatures than the glass foam.

Another object of the present invention is an optically transparent glass foam or glass ceramic foam produced by the method according to the invention. Another object of the present invention is the use of the glass and glass ceramic foams of the invention for predominantly optical applications, such as photocatalysts, carriers for enzymes / microbes working in biorectors with light / sunlight, in environmental catalysis, biocatalysis and for example for removal of VOCs from waste water and air.

Brief description of the figures

Fig. 1 shows a schematic of the production of an optically transparent glass / glass-ceramic foam;

Fig. 2 shows absorption edges of erfindunsggemäßen glass foams.

Detailed description of the method according to the invention

The process according to the invention is used in two different ways to produce the highly transparent foams: a) as a direct foaming process (Gambaryan-Roisman, T., Scheffler, M., Buhler, P., Greil, P., Ceram. Trans.

2000, 108, 121-130) and b) as a special type of reticulate method according to Schwartzwalder (K. Schwartzwalder, A. V. Somers, U.S. Patent 3,090,094, 1963). Common to both is the process of glass formation to obtain the open cell foam structure.

As the SiO 2 -emiezing starting component constituting the later glass having the filler glass-like composition, there is used a silicon-based preceramic polymer of the polysiloxane, polysilsequioxane, silicone resin type, Silicone rubber, polysilazane or polycarbosilane. If this component (regardless of whether as a foam or compact body) in air at 800 to 1100 ⁰ C outsourced, there is oxidation of the organic components and volatilization thereof and the conversion of the present in the polymer silicon in SiO 2, the later main glass component. In order to generate with this SiO 2 a composition which corresponds to that of the glass filler powder, the glass transducers must be added. While the ratio of the mass of the polymer mP and the mass of the glass transducers mM is determined by the polymer used and the composition of the glass filler powder, the mass fraction of the glass filler powder mG can be varied to the sum of mP and mM, if the nomi - Average composition of the total glass should correspond on average to that of the glass powder. Alternatively, however, the proportion of glass transducers can be chosen within wide limits. The procedure is such that components a), b) and c) are weighed in and homogenized by means of a suitable mixer. Foaming then takes place, with process temperatures ranging from room temperature to a maximum of 320 ^° C., depending on the composition, depending on the process variant.

Furthermore, both process variants have in common that during / after foaming, combined with a liquid-solid transition, a thermal process for the conversion of the polymer / filler mixture is necessary. This thermal process has several functions:

i. the organic components are removed by oxidation, ii. SiO 2 is generated for glass formation with the glass transducer (s), iii. the activation energy / temperature for glass formation is provided. While i. is also necessary for the production of ceramic foams, the points ii. and iii. and their combination with the composition or use of components a), b) and c) in connection with the thermal conversion of preceramic polymers completely new.

Figure 1 demonstrates the process of making such a novel optical glass foam according to the present invention.

What is novel about the process according to the invention is that the silicon dioxide (SiO ₂ ) phase formed after the oxidation of the organic components from the preceramic polymer used for foaming (and the polyurethane foam, which serves as a cellular template in reticulum foams) directly into a glass properties of the glass properties Glass is similar in composition or the composition of the glass filler lent or equal. As a result, the sintering process of the glass particles with the newly formed glass is much easier, the thermal processes can at temperatures up to 1100 ° C (the production of glasses, which correspond to the composition of the filler powder used, is usually carried out at temperatures up to

1500 ⁰ C) carried out and the macrocellular structure of open-cell foams can be obtained. The process works regardless of whether a so-called green foam (foam after its formation and before thermal treatment) is produced by a direct foaming process or by a placeholder process (reticulate process, burnable spheres, salts). It is essential that the glass-forming SiO 2 component is formed by oxidation on site and the glass-converting component is already present and necessary for sintering with the filler powder Temperature can be reduced compared to conventional glass manufacturing.

The glass and glass-ceramic foams produced according to the invention are suitable as carriers for light-activatable

Catalysts, so-called photocatalysts, outstanding suitable. The foams produced according to the invention meet the high requirements in terms of their permeability to light with the wavelength activating the catalyst, but also to the permeability of flowing liquids and gases, in a special way. The products produced according to the invention are monolithic glass and ceramic structures as well as open-cell foams and honeycomb bodies.

In the present invention, a method is described which makes it possible to produce a cellular carrier with good flowability of gases and liquids and a high optical transparency for a large part of the light of the wavelengths of the solar spectrum. It is preferably a glass with a high silicate content of conventional composition.

embodiments

example 1

60 g of a preceramic polymer (H44, Wacker Siltronic) were mixed with 83.5 g of a glass powder having the composition 81% SiO ₂ , 13.1% B ₂ O ₃ , 4% Na ₂ O / K ₂ O, 1.9 % Al ₂ O ₃ (data in% by mass) with a particle size d ₅ o = 25 μm and

Weigh out 8.97 g of Na ₂ B ₄ O ₇ * 10H ₂ O and homogenize in an overhead shaker. Subsequently, the offset in the preheated oven at 270 ⁰ C was foamed (direct foaming by gas evolution from the components) and stored for 2 hours at this temperature. After cooling, the samples were cut to the desired size and 5 K / min heated to 550 ⁰ C, kept at this temperature for 4 hours and further heated to 1000 ⁰ C. Cooling took place after 2 to 4 hours by controlled fine cooling or quenching.

Example 2

77 g of H44 were weighed out with 59.3 g of a glass powder from Schott Glas AG (Duran®) with a particle size d ₅ o = 115 μm and 11.9 g Na ₂ B ₄ θ 7 * 10H 2 θ and homogenized in an overhead shaker. Subsequently, the offset was foamed in a preheated oven at 300 ⁰ C and paged for 4 hours at this temperature. After cooling, the samples were cut to the desired level and heated at 3 K / min to 550 ⁰ C, kept for 2 hours at this temperature and further heated to 1000 ⁰ C. Cooling took place after 2 to 4 hours by controlled fine cooling or quenching.

Example 3 66 g of H44 were mixed with 82.7 g of a glass powder from Corning, Inc. (Pyrex®) having a particle size dso = 15 μm and 4.7 g of Na ₂ B ₄ O ₇ * 10H ₂ O, 1.25 g Weighed B ₂ O ₃ (which was prepared by drying and mortars of H3BO3) and 0.95 g of Na ₂ CO 3 and homogenized in an overhead shaker. Subsequently, the offset in the preheated oven at 300 ⁰ C was foamed and stored for 2 hours at this temperature. After cooling, the samples were cut to the desired dimension and heated with 4 K / min to 550 ⁰ C, held for 3 hours at this temperature and continuing ter heated to 1000 ⁰ C. Cooling took place after 2 to 4 hours by controlled fine cooling or quenching.

Example 4

42.3 g of a methylpolysiloxane (MK, Wacker Siltronic) are introduced stepwise in the beaker by means of a magnetic stirrer with 20.1 g of methyltriethoxysilane (MTES, ABCR GmbH). solves. 78.5 g borosilicate glass 3.3 (Schott Glas AG) and 13.4 g borax are added to the suspension and homogenized. The catalyst used for crosslinking is 1.35 g of oleic acid, which is added a few minutes before the coating of the PU foam. The cut polyurethane foams (dimensions 3 cm * 3 cm * 5 cm) are immersed in the suspension and then dried in air. Thereafter, aging was carried out in a drying oven at 70 ^° C., annealing at 500 ^° C. for 5 hours or 550 ^° C. for 4 hours and heating to 980 ^° C. with a storage time of 3 hours.

Example 5

As in Example 4, but with repetition of the coating process after drying (coating, drying in air, drying at 70 ⁰ C, repeat process 3 to 6 times) and subsequent one-time intermediate temperature (500 to 550 ⁰ C) and high temperature treatment.

Example 6

For the glass foam produced according to Example 2, which is filled with Duranglas®, the absorption spectrum in the range from 200 to 800 nm was measured. FIG. 2 shows the comparison of the position of the absorption edges of a glass powder (Duran®), a window glass and a glass foam with Duranglas® of similar composition. It can be seen that the glass foam according to the invention according to Example 2 has almost the same absorption properties as the Duranglas® contained therein.

Claims

claims

A process for producing optically transparent foams, comprising the steps of: a) mixing preceramic Si polymer, glass powder and glass transducer; b) heating the mixture to a temperature below the decomposition temperature of the preceramic Si polymer to form a foam; c) heating the resulting foam to a temperature above the decomposition temperature of the preceramic Si polymer; d) heating the resulting product under glass formation to a temperature between 700 ⁰ C and 1400 ⁰ C; and e) cooling the product so obtained to ambient temperature.

2. The method according to claim 1, characterized in that after step a) performs an additional step f), comprising the: f) application and / or introduction of the mixture prepared in step a) and / or in an organic Polymer foam body and subsequent drying of the body at optionally elevated temperature.

3. The method according to claim 1 or 2, characterized in that one carries out step c) at a temperature of 350 ⁰ C to 750 ⁰ C.

4. The method according to any one of claims 1 to 3, characterized in that one carries out step d) at a temperature of less than 1100 ⁰ C.

5. The method according to any one of claims 1 to 4, characterized in that one carries out step d) the heating for 1 to 12 hours at the maximum temperature.

6. The method according to any one of claims 1 to 5, characterized in that one rapidly cools the products obtained by removal from the oven in step e).

7. The method according to any one of claims 1 to 5, characterized in that one cools the obtained products in a fine cooling step in step e), wherein, starting from a temperature between 400 ⁰ C and 900 ⁰ C, a cooling rate between 0, 1 K / min and 10 K / min applies.

8. The method according to any one of claims 1 to 7, characterized in that further added in step a) at least one viscosity modifier or at least one catalyst or mixtures thereof.

9. The method according to any one of claims 1 to 8, characterized in that the preceramic Si polymers are selected from the group consisting of polysiloxanes, polyorganosiloxanes, Polysilsequioxanen, silicone resins, silicone rubbers, polysilazanes and polycarbosilanes, wherein the organic radicals of the Si Polymers are selected from saturated, unsaturated, branched, unbranched, cyclic or open-chain radicals having 1 to 6 carbon atoms, aryl, aralkyl or alkylaryl radicals having up to 9 carbon atoms.

10. The method according to any one of claims 1 to 9, characterized in that the glass powder is selected from the group consisting of flat glass, window glass, container glass, bottle glass, economic glass, incandescent pen glass, television flask glass, laboratory glassware, lead crystal glass, fiberglass, e-glass or borosilicate glass.

11. The method according to any one of claims 1 to 10, characterized in that the glass transducer from the group consisting of Na ₂ CO ₃ , H ₃ BO ₃ , K ₂ CO ₃ , Li ₂ CO ₃ , CaCO ₃ , MgCO ₃ , Al ₂ O ₃ and Na ₂ B ₄ O ₇ and their hydrous derivatives and is selected from the mixtures of the aforementioned compounds.

12. The method according to claim 2, characterized in that infiltrating the foams produced with a polymer selected from PMMA, PEEK or EVA.

13. The method according to claim 2, characterized in that one infiltrates the foams produced with a glass that softens at lower temperatures than the glass foam.

14. An optically transparent glass foam or glass ceramic foam produced by the method according to claims 1 to 13.

Use of the optically transmissive glass foam or glass-ceramic foam according to claim 14 for optical applications, as a support for photocatalysts, as carriers for enzymes / microbes working in bio-reactors with light / sunlight, in environmental catalysis, biocatalysis and removal of VOCs from waste water and Air.