WO2008129185A1

WO2008129185A1 - Self-cleaning transparent wall in a heating chamber

Info

Publication number: WO2008129185A1
Application number: PCT/FR2008/050398
Authority: WO
Inventors: Alexandra Dekoninck; Catherine Jacquiod; Michaël BOURGEOIS
Original assignee: Saint-Gobain Glass France
Priority date: 2007-03-12
Filing date: 2008-03-10
Publication date: 2008-10-30
Also published as: FR2913682B1; FR2913682A1

Abstract

The invention relates to a transparent wall in a heated chamber, having a transparent, mineral surface coating that is non porous or pores with a maximum size of 300 nm and containing accessible catalytic particles with a size of between 1 and 200 nm; the invention also relates to a method for manufacturing the same and to any heated chamber comprising this wall.

Description

SELF CLEANING TRANSPARENT WALL FOR HEATED ENCLOSURE

The present invention relates to maintaining the cleanliness of transparent walls of heating chambers such as oven, roaster, fireplace insert ...

The documents US 2002 0192472, US 2004 0005469, US 2004 0105985 and US 2004 0209072 describe hydrophobic coatings on the internal face of such transparent walls, frequently constituting a door. Dirt resulting from combustion or cooking fumes, greases, adhere less easily than in the absence of the hydrophobic coating. Cleaning, for example with water, is also easier than in the absence of the coating.

On the other hand, the documents FR 2 848 290, US 4,029,603 and US 2004 0253432 describe catalytic furnace walls based on porous oxides in which are dispersed oxide particles. The catalytic layer has the property of oxidatively degrading grease and soot at the operating temperature of the heating chamber. The soils are then easier to remove, for example by washing with water, because their adhesion is lower after oxidation. In addition, at least some of the dirt is already removed by this oxidation. However, the catalytic layers are non-transparent ceramic layers.

The invention therefore aims to provide a transparent wall of a heating enclosure having greater ease of cleaning and able to degrade at least a portion of fat and soot by catalytic oxidation at the operating temperature of the heated enclosure. Thus, a combination of easier restoration and slower degradation of transparency is aimed at.

For this purpose, the subject of the invention is a transparent wall of a heating enclosure, distinguished by the fact that it comprises a non-porous transparent mineral surface coating or having pores of sizes at most equal to 300 nm and containing accessible catalytic particles and sizes of between 1 and 200 nm. The catalytic particles are chosen so as to oxidatively degrade the grease and soot at the operating temperature of the heating chamber. The operating temperature of a catalytic furnace does not exceed 275 ° C., that of a pyrolysis furnace does not exceed 500 ^° C. The catalytic particles are therefore necessarily active at lower temperatures than these maximums.

Of course, it is also important for the surface coating to withstand at least these maximum temperatures.

The term transparent is to be understood here in a general sense as referring to a wall through which the contents of the oven are readily visible from the outside.

The wall of the invention further exhibits slower fouling and greater ease of cleaning as a catalyzed furnace wall. It makes it possible to get rid of pyrolysis, which consumes much more energy, and in some countries is subject to restrictive or expensive regulations (complex safety systems, such as locking oven doors), or even prohibited.

In a preferred embodiment of the wall of the invention, the coating is mesoporous, and the mesopores are accessible throughout the thickness of the coating.

The mesoporous, mesoporous terms refer to pores with diameters between 2 and 50 nm. This porosity dimension, combined with the small size of the catalytic particles contributes to the transparency of the coating, which is not diffusing.

Mesopores are advantageous in that they increase the contact area between the materials to be oxidized and the catalytic particles, especially since the mesopores are accessible throughout the thickness of the coating.

The wall of the invention is preferably made of glass or glass ceramic.

In a particularly interesting embodiment of the invention, the wall is removable: it can be replaced by a clean wall if necessary. On the other hand, the wall of the invention may be frontal and then constitute in particular a door; it can be a rear, side wall, upper or lower.

The surface coating comprises a mesoporous transparent mineral matrix based on at least one compound of at least one of Si, W, Sb, Ti, Zr, Ta, V, B, Pb, Mg, Al, Mn. Co, Ni, Sn, Zn, In, Fe and Mo, optionally covalently bound with elements such as O, S, N, C or the like. Preferably, use is made of a mineral matrix of SiO ₂ , TiO ₂ , Al ₂ O ₃ , ZrO ₂ , SnO ₂ , Fe ₂ Os, alone or in a mixture of several of them, in which the catalytic particles are dispersed.

The catalytic particles consist of at least one metal, in particular Pd, Pt, Au and / or at least one metal oxide, preferably an oxide of Ce, Cu, Mn, Ag, Co, Fe, Ni, Mo , Zn, Cr, V, W, Zr, Ti, La, Nb, Ta, alone or in mixtures of several of them.

The catalytic particles are advantageously of sizes at most equal to 60 nm.

The thickness of the surface coating is preferably between 30 nm and 1 μm, particularly preferably at most 600 nm. A thickness of less than 30 nm does not provide a desired degree of oxidation degradation to a sufficient degree. On the other hand, although a thickness of 1 μm, and even greater is perfectly suitable both for catalytic functionality and for transparency and optical quality, it seems that it is not necessary, because the penetration of products to degrade is more difficult at increasing depth in the coating. The inventors have thus found that coating thicknesses of at most 600 nm, or even 500 nm in some cases, already make it possible to obtain at least the greater part, or almost all, of the catalytic effect.

The wall of the invention further advantageously has a light transmission at least equal to 70% and a blur at most equal to 1, 5%, these criteria being a guarantee of good transparency.

Another object of the invention resides in a method of manufacturing a wall as described above, which method comprises: the preparation of a liquid composition comprising at least one precursor of the material constituting the mesoporous structure of the surface coating and at least one organic structuring agent,

the precipitation of the precursor around the organic structuring agent and the growth of molecules derived from the precursor,

the addition to the liquid composition of the catalytic particles, the application of the composition to the surface to be coated, and

the elimination of the organic structuring agent.

For the manufacture of the wall of the invention, the preparation of the liquid composition advantageously comprises: the preparation of an oxide precursor sol (in particular of silica), the ripening of the soil, then the mixture with the structuring agent .

Indeed, the soil ripening allows a preliminary condensation of the oxide precursor which promotes the structuring of the condensed oxide coating on the support surface in large areas. Advantageous ripening conditions include maintaining the soil at a temperature of 40 to 60 ^° C. for a period of 30 minutes to 24 hours, the curing time being shorter the higher the temperature.

In this case, the oxide precursor is advantageously a hydrolyzable compound, such as a halide or an alkoxide, the structuring agent is advantageously chosen from cationic surfactants, preferably of the quaternary ammonium type such as cetylthmethylammonium bromide, or not ionic, including di-block or triblock copolymers based for example on ethylene oxide or propylene oxide.

The elimination step of the organic structuring agent advantageously coincides with the thermal cycle of the quenching to which the wall is subjected.

The invention also relates to an oven, a roasting pan, a fireplace insert or other heating enclosure having a transparent wall as described above.

The invention will be described below using non-limiting examples. Examples

The following compositions for the treatment of glass substrates are prepared.

Composition 1 witness

9.9 g of tetraethoxysilane (TEOS), 8.34 g of absolute ethanol and 4.29 g of demineralized water + HCl at pH 1 are mixed. The mixture is stirred until clear and then heated to 60 ^° C. for 1 hour. A mixture is obtained.

On the other hand, 3.85 g of a polyoxyethylene-polyoxypropylene block copolymer marketed by BASF under the trade name Pluronic PE 6800 and 40.29 g of absolute ethanol are mixed. It is heated slightly until the copolymer is dissolved. We obtain the mixture B.

Mixture A is added to mixture B. Composition 2

50 g of a 20% CeO ₂ dispersion are added to the composition.

NYACOL (registered trademark of NYACOL Nanotechnologies

Inc.) colloidal ceria nitrate at pH 1.5.

The size of the CeO ₂ particles is 10-20 nm.

The molar ratio CeO ₂ / Si is 1, 22. Composition 3

Same composition 2, replacing TEOS with 8.47 g of methyltriethoxysilane (MTEOS).

The CeO ₂ / Si molar ratio of 1, 22 is retained.

The deposition of these compositions is carried out on three samples of 12 cm × 10 cm of sodocalcic flat glass by immersion (dip coating). The glass is previously cleaned with cerium oxide.

The soaking rate is 10 cm / min.

One side of each sample is obscured by an adhesive.

The following heat treatment is applied to the samples:

- rise from 25 ⁰ C to 100 ⁰ C at 5 ° C / minute,

Bearing at 100 ^° C. for 24 hours,

- rise from 100 ⁰ C to 175 ⁰ C at 6 ° C / minute, plateau at 175 ⁰ C for 2 hours,

- rise of 175 ⁰ C at 400 ⁰ C at 0.5 ° C / minute, - Bearing at 400 ⁰ C for 12 hours.

Thus, samples 1 to 3 (numbers corresponding to those of the compositions) with coatings of approximately 300 nm thickness are obtained. Analysis by Field Scanning Electron Microscope (15 kV). The coatings are mesoporous and have a network of interconnected pores of sizes centered around 4 nm.

On the other hand, the sample 4 is obtained by platinum salt doping of a sample identical to the sample 2. The doping is carried out in the following manner by a post-impregnation process.

With an ammonia solution (2 drops of 28% NH ₃ in 40 ml of demineralized water), an aqueous solution of tetraammine platinum II nitrate at 5.10 ^-3 mol / l is adjusted to pH 8.

The sample is soaked for one minute in the platinum salt solution. Then the plates are dried with compressed air. Two rinses with distilled water are carried out for one minute. The sample is dried at room temperature for about 15 hours. Then it is calcined at 450 ^° C. for 2 hours, after a rise at 2 ° C./minute.

The CeO ₂ / Si molar ratio of 1, 22 is retained. The average thickness of the layer for sample 4 is the same as that of sample 2.

The grafted Pt density measured by microprobe analysis (Pt-M _{01 line} at 15 kV) is 1.76 ± 0.02 μg / mm ² .

50 μl of olive oil and 0.05 g of jam are placed on each sample and then placed in an oven at 275 ^° C. for 3 hours.

The samples are allowed to cool.

They are then subjected to 17 successive washing steps as described in the table below, and the effectiveness of the cleaning after each step is evaluated.

The washing uses a soft cloth, a yellow sponge (soft), a green sponge (abrasive), hot water at 40 ⁰ C, dishwashing liquid (15 ml of mild detergent in 5 I of hot water to 40 ^° C), an abrasive product (40% abrasive but not scouring powder and 40% water), a spray oven (aerosol with soda). Table: Steps of the cleaning test

Sample 1 is the most difficult to clean.

The traces of cooked oil and jam are clearly visible after step 17.

For the other samples, it is already noted after the first cleaning step a high efficiency of the mesoporous layers on the oil. Activity on sugar (jam) remains low.

After the first step, sample 3 appears to be more effective than sample 2 on the oil. The oil is removed from sample 4 after the fourth cleaning step.

This sample 4 seems to be the most effective for sugar. This has almost disappeared after the cleaning step, while there remains substantially more on the sample 2.

Thus, the wall of the invention makes it easier to clean glass against all the usual soiling inside furnaces, especially at temperatures of catalytic furnaces, lower than those of pyrolysis furnaces.

Claims

1. Transparent wall of heating enclosure, characterized in that it comprises a non-porous transparent mineral surface coating or having pores of sizes at most equal to 300 nm and containing accessible catalytic particles and sizes of between 1 and 200 nm.

2. Wall according to claim 1, characterized in that the coating is mesoporous, and in that the mesopores are accessible throughout the thickness of the coating.

3. Wall according to one of the preceding claims, characterized in that it consists of glass or glass ceramic.

4. Wall according to one of the preceding claims, characterized in that it is removable.

5. Wall according to one of the preceding claims, characterized in that it is a front wall, including a door, a rear wall, side, upper or lower.

6. Wall according to one of the preceding claims, characterized in that the surface coating comprises a transparent mesoporous mineral matrix of SiO ₂ , TiO ₂ , Al ₂ O ₃ , SnO ₂ , Fe ₂ O ₃ or ZrO ₂ alone or in mixtures of several of them, in which the catalytic particles are dispersed.

7. Wall according to one of the preceding claims, characterized in that the catalytic particles consist of at least one metal and / or at least one metal oxide alone or in mixtures of several of them.

8. Wall according to one of the preceding claims, characterized in that the catalytic particles consist of Pd, Pt, Au, an oxide of Ce, Cu, Mn, Nb, Ta, Ag, Co, Fe, Ni, Mo, Zn, Cr, V, W, Zr, Ti, La, alone or in mixtures of several of them.

9. Wall according to one of the preceding claims, characterized in that the catalytic particles are of sizes at most equal to 60 nm.

10. Wall according to one of the preceding claims, characterized in that the thickness of the surface coating is between 30 nm and 1 micron.

11. Wall according to one of the preceding claims, characterized in that the thickness of the surface coating is at most 600 nm.

12. Wall according to one of the preceding claims, characterized in that it has a light transmission at least equal to 70% and a blur at most equal to 1, 5%.

13. A method of manufacturing a wall according to one of the preceding claims, comprising: the preparation of a liquid composition comprising at least one precursor of the material constituting the mesoporous structure of the surface coating and at least one organic structuring agent, the precipitation of the precursor around the organic structuring agent and the growth of molecules derived from the precursor, the addition in the liquid composition of the catalytic particles, the application of the composition to the surface to be coated, and the elimination of the agent organic structuring.

14. The method of claim 13, characterized in that the removal of the organic structuring agent coincides with the thermal cycle of quenching which is subjected to the wall.

Oven, roasting pan, chimney insert or other heating enclosure having a transparent wall according to one of claims 1 to 12.