ANTI-GREEN GROWTH TREATMENT METHOD FOR A BUILDING MATERIAL

Abstract

The present invention relates to a method for treating an anti-greening ceramic building material by depositing a coating which degrades organic deposits when exposed to sunlight, characterized in that it consists of depositing, before firing the building material and after shaping it, a layer of an oxide of a semiconductor, the degradation temperature of which is higher than the firing temperature of said building material.

Description

Description Title of the invention: METHOD FOR ANTI-GREENING TREATMENT OF A BUILDING MATERIAL Scope of the invention

[0001] = The development and proliferation of microorganisms on earthen roofs cooked foods can cause, in addition to an unsightly appearance, mechanical damage and chemical composition of the material. Thus, in addition to the unsightly appearance, the presence of micro- organisms on buildings cause physical and chemical damage to materials. Indeed, the algae and cyanobacteria present on the surface of materials can cause, for example, the dissolution of calcium carbonate in the case of stone or concrete buildings.

[0002] — Algae and cyanobacteria are the first colonizers of the envelope of buildings in humid areas. They colonize all surfaces where moisture is high. These microorganisms are present in the air in the form of spores, cells or filaments and, given sufficient light, moisture and nutrients, the ability to adapt their morphology and physiology to colonize different types of products mentioned above.

[0003] — The colonization of the substrate by microorganisms has an aspect dynamic. The bacteria rapidly colonize the surface of the material and are followed by the establishment of cyanobacteria and algae. This establishment can be divided into five steps which are as follows:

[0004] “the development of an organic biofilm that absorbs ions and molecules organic matter on the surface of the material, the transport of microorganisms to the surface and the formation of co-aggregates of Microorganisms, the reversible adhesion of microorganisms and aggregates, the co-adhesion of microorganisms and the irreversible adhesion of microorganisms to the surface of a material by the secretion of exo-polymers.

[0005] On buildings, the accumulation of microorganisms results in the presence of black or green dots in continental areas and red dots in areas coastal areas. These stains appear most often near outlet pipes, architectural defects and the fallout from drainage or ventilation pipes conditioning. The presence of microorganisms on the surface of buildings promotes the penetration of water into the porous network of the material, which initially leads to swelling and the appearance of cracks, followed by an increase in humidity levels in the material conducive to accelerating the colonization process To combat these microorganisms, current studies seek to give the surfaces of these products a self-cleaning property through two techniques. The first method involves modifying surface roughness by reproducing the micro- and nanostructures present on the surface of a lotus leaf. The microstructure was reproduced by imprinting, while the nanostructure was imparted by an organic deposition. Contact angle measurements validated the effect of the reproduced microstructure on the substrate's wettability. The second approach is based on the development of photocatalytic coatings based on semiconductor oxides. The measurement of photocatalytic activity made it possible to list the parameters of TiO; influencing this property and to highlight alternative oxides such as ZnO or SnO. The invention relates more specifically to this second approach. Photocatalysis is a natural phenomenon in which a substance, the photocatalyst (titanium dioxide), initiates a chemical reaction through the action of light, without degrading itself. Titanium dioxide is the photocatalyst commonly recommended for combating greening. When titanium dioxide nanoparticles are irradiated by UV and visible rays from the sun or artificial indoor lighting, they form reactive radicals by reacting with oxygen and water naturally present in the ambient air. The active radicals produced by this photocatalytic reaction decompose and destroy the vast majority of organic pollutants. The result of this decomposition is primarily water and CO₂, in infinitesimal quantities. State of the art In the state of the art, we know of various photocatalytic treatment solutions for the building envelope. In 2009, inventor Marielle Fassier notably defended a doctoral thesis in Ceramic Materials and Surface Treatments entitled "Interactions between the environment and terracotta: Role of surface roughness - Influence of coatings with photocatalytic properties". European patent EP1507751B1 is also known, concerning a molded ceramic body made from an oxidized ceramic base material and having a self-cleaning surface when sprayed or run off with water. The molded body has a porous oxidized ceramic coating that has a photocatalytic action and a specific surface area of ​​approximately 25 m² / g to approximately 200 m² / g, preferably approximately 40 m² / g to approximately 150 m² / g. This solution involves water-repellent treatment of the coating surface, with hardening that must not take place at a temperature exceeding 300°C. It is therefore not well suited to the preparation of building materials such as bricks or terracotta tiles requiring firing at much higher temperatures, exceeding 900°C. Document EP 0590477B1 describes a construction material, which may be, for example, an exterior wall material or a roofing material, in which a thin film of metal oxide having a photocatalytic effect is applied to the surface of the construction material. The metal oxide film is preferably applied by the sol-gel process. Preferably, a titanium dioxide thin-film material is produced using a titanium dioxide sol. French patent FR2775696 describes a process for obtaining a substrate with a photocatalytic coating on at least part of its surface. The coating consists of crystallized particles of an oxide of a metal A with photocatalytic properties, incorporated into the coating using a mineral binder containing an oxide of a metal B that also exhibits photocatalytic properties in its crystalline state. According to the process, the coating is deposited from liquid-phase dispersions containing: - on the one hand, the said crystallized particles of oxide of metal A, - on the other hand at least one organo-metallic compound precursor of the oxide of metal B of the binder, in a relative proportion A / B by weight referred to the weight of the metals entering respectively into the composition of oxide A and of the precursor(s) of oxide B between 60 / 40 and 40 / 60. This solution also has the disadvantage of a treatment temperature not exceeding 550°C. disadvantages of prior art Prior art solutions have several drawbacks. Firstly, titanium dioxide has a calcination temperature of approximately 600°C, from which an irreversible transformation of the anatase phase, which alone exhibits photocatalytic properties, to the rutile phase is observed. However, many building materials require firing at much higher temperatures, between 900°C and 1200°C. Therefore, with prior art solutions, it is only possible to apply a coating to the surface of the material after its production, resulting in poor adhesion and rapid leaching, causing the material to lose its properties when exposed to the elements. Secondly, prior art solutions to mitigate this drawback propose applying a hydrophobic coating, which is in complete contradiction with the fact that photocatalytic materials are hydrophilic in nature. Finally, public health studies suggest that exposure to titanium dioxide, in pul- This compound, with particle sizes smaller than 10 µm at specific concentrations, may promote the growth of precancerous intestinal lesions and immune system disorders, facilitating its penetration into the body. The carcinogenic risk of this compound cannot be ruled out, although the potential risk is more related to its use as a food additive. Solution provided by the invention To remedy these drawbacks, the Anti-greening treatment process for a mineral construction material, particularly ceramic, by depositing a coating that degrades organic deposits when exposed to sunlight, characterized in that it consists of depositing, before firing the construction material and after shaping it, a layer of an oxide of a semiconductor, the degradation temperature of which is higher than the firing temperature of said construction material. Preferably, the process includes a step of jointly baking the construction material coated with said layer of semiconducting oxide. Advantageously, the oxide of a semiconductor is doped or undoped titanium or zinc oxide According to one variant, the said oxide of a semiconductor is formed from a powder of which 90% of the particles have a diameter of less than 100 µm. According to one variant, the said oxide of a semiconductor is formed from a powder suspended in water and then sprayed onto the surface of the construction material. According to another variant, the process includes an additional step of applying a hydrophobic coating after the baking step. According to one variant, the said oxide of a semiconductor is mixed before spraying into a surface coating (silica, alumina, dye iron oxide, copper or titanium). The invention also relates to an anti-greening construction material characterized in that it consists of a ceramic coated with a layer of an oxide of a semiconductor, the degradation temperature of which is higher than the firing temperature of said construction material. The invention also relates to a semiconductor compound specifically intended for the implementation of the aforementioned process. Detailed description of the limitations (of realization) The present invention will be better understood upon reading the following description, concerning a non-limiting example of embodiment. * “inventi The present invention is based on the use of photo-activatable semiconductor compounds. For the purposes of this patent, "photo-activatable semiconductor" means a material whose band gap, constituting the separation between the valence band and the conduction band, is between 0.5 and 4 eV and preferably on the order of 3 eV. Such a material allows the release of electrons initially located in the valence band under the effect of the energy input of ultraviolet or visible radiation. A photoactivatable semiconductor must absorb radiation with energy at least equal to its band gap in order to cause an electron to move from the valence band to the conduction band. This results in the formation of a hole in place of the electron in the valence band: an electron-hole pair is created. These charge carriers can move within the semiconductor and participate in a chemical reaction. They can also recombine: the later the recombination occurs, the longer the electron-hole pair's lifetime and the more active the semiconductor. Such photoactivatable semiconductors also exhibit a superhydrophilic property, unlike prior art solutions designed for hydrophobic behavior The oxidation of organic molecules produces mineralization, that is, a transformation into carbon dioxide and water, or at least a degradation to form smaller, less adhesive molecules. The degradation of organic deposits can be direct or mediated by the formation of radicals in the presence of water or oxygen. When the construction material treated according to the invention is exposed to sunlight, the formation of an electron-hole pair in the photo-activatable semiconductor compound leads to a reduction of dioxygen, generating the superoxide anion. 02- : e- + QO; > *0,- And the autoprotolysis of water: HR20 2 H+ + OH- This reaction leads to the formation of the hydroxyl radical HO⁻ highly oxidizing: QOH— + h+ > HO+ The superoxide anion can also generate HO radicals via the following sequence of steps: e04—+ H+ > HODe 2 HOOe — H:O2 + O2 H2O; > 2 HO- (7) H:02 + e- — OH- + HD + Highly oxidizing HOe radicals can lead to the degradation of an organic molecule, denoted RH, according to the sequence of steps below: HOe + RH > Re + H30 Re +H0+ + ROH R-OH + HD+e — R'-CHO > R°-COOH R-COOH + h+ — R°-COO® + H+ > Re + COz(e) R'e + H0e + R'OH > R°-CHO — R-COOH — etc. (13) Direct transfers of h+ can also be observed according to a reaction known as the photo-Kolbe reaction, which, for formic acid (more precisely its conjugate base), has the following equation: HCOO- + h+ — CO.(g) + He The continuation of these reactions leads to total mineralization. Manufacturing of building materials The building material is produced from hydrated ceramics (cement, plaster, concrete, etc.), rocks (granite, marble, limestone, etc.), fired ceramics (brick, terracotta, porcelain, stoneware, etc.), or glass. They are intended for the construction of exterior and interior walls, floors in the form of tiles or paving stones, or roofing (tiles, slabs, etc.). The preparation is carried out according to classic industrial techniques, up to the drying stage. Next, a compound according to the invention, in the form of an aqueous solution, is sprayed onto the surface of the construction material, and it is then baked at a temperature above 800°C, typically between 900°C and 1200°C. The surface of the construction material is not subjected to any treatment modifying its relief specifically intended to modify its resistance to greening. The firing process jointly produces the firing of the ceramic and the sintering of the semiconductor coating with the surface layer of the building material. 2. Situation: The coating consists of semiconductor compounds, including doped semiconductor compounds, with a band gap between 0.5 and 4 eV; ty- a pinpoint of the order of 2.3 eV + 1.5 eV, and preferably of the order of 3 eV and a degradation temperature higher than the firing temperature of the ceramic constituting the construction material, and preferably higher than 800 °C. The degradation temperature is understood to be the temperature at which the compound loses its photocatalytic characteristics, in particular the transition temperature from one crystalline form to another crystalline form. Among the suitable semiconductors, we can notably consider: Titanium oxide Zinc oxide Iron oxide Oxide compounds based on bismuth, iron and molybdenum Oxide compounds based on calcium, copper, tantalum and titanium Tungsten oxide Semiconductor oxide composites: Cerium oxide — Silver carbonate — Zinc oxide Titanium oxide — Silver phosphate Silica-Silver Oxide Bismuth oxide — Silver oxide — Titanium oxide Titanium oxide —- Niobium oxide Titanium oxide — Tantalum oxide Titanium oxide — Tungsten oxide Titanium oxide — Zinc oxide Titanium oxide doped with silver, aluminum, cerium, iron, copper, to lanthanum, manganese, nitrogen Cerium-doped zinc oxide, copper

Claims

Demands

1. Method for the anti-greening treatment of a construction material ceramics by depositing a coating that causes a degradation of the organic deposits upon exposure to sunlight, characterized by which consists of depositing, before the building material is fired and after its shaping, a layer of a semiconductor oxide, whose degradation temperature is higher than the temperature of cooking of said building material.

2. Anti-greening treatment method according to claim 1, ca- characterized in that it includes a joint cooking stage of the building material coated with said semi-oxide layer driver.

3. Anti-greening treatment method according to claim 1, ca- characterized in that said oxide of a semiconductor is oxide of titanium or zinc, doped or undoped

4. Anti-greening treatment method according to claim 1, ca- characterized in that said oxide of a semiconductor is formed of a powder in which 90% of the particles have a diameter of less than 100 pm.

5. Anti-greening treatment method according to claim 1, ca- characterized in that said oxide of a semiconductor is formed of a powder suspended in water and then sprayed onto the surface of the building material.

6. Anti-greening treatment method according to claim 1, ca- characterized in that it includes an additional deposition step after the baking stage of a hydrophobic coating.

7. Anti-greening treatment method according to claim 1, ca- characterized in that said oxide of a semiconductor is mixed before spraying into a surface coating (silica, alumina, colorant) iron, copper or titanium oxide).

8. Anti-greening building material characterized in that it is consisting of a ceramic coated with a layer of an oxide of semiconductor, whose degradation temperature is higher than the cooking temperature of said building material.