Patent Application
20160091225
The instant invention relates to materials and their thermal applications in different purposes. More specifically, it relates to the employment of a selective absorbing coating obtained at room temperature and deposited on metal, used for harnessing solar energy and converting it into thermal energy. Said coating improves the efficiency in the collection of thermal energy, optimizing visible and near infrared light harnessing and minimizing heat emission of the metal towards environment.
The object of the instant invention is to present the process for obtaining a solar and/or artificial radiation selective absorbing coating at room temperature which can operate in the temperature range from 0° C. to 300° C. and its application on metallic substrates with different shape and geometry configurations such as smooth, rough, porous, tubular or laminar, as non-limiting exemplary embodiments of the instant application, generating heat through solar radiation and/or artificial illumination.
It also relates to different uses and applications that can be given to it, for example, such technology can be used to coat metal fibers used in the manufacture of coats, jackets, sweaters, hats, gloves, fabric for tents, shoes, boots, etc. without limiting the scope of the present application, specifically as an inner linning (interlining) which is constructed in each of the clothing designs or applications that can integrate it so that these garments have the capacity to absorb solar and/or artificial radiation, convert it into heat, keep the calorific energy and transmit said energy to the human body.
In the field of solar energy, the selective absorbing coatings efficiently capture solar radiation in the spectral region of high intensity visible light and near infrared. Consequently, a selective coating will absorb and retain a substantial amount of solar radiation, while a non-selective surface, such as an ordinary black body, will lose a high percentage of the energy absorbed by re-radiation.
Absorbers with black surfaces absorb 95% of incident solar radiation. The reflection loss is only 5%. However, black surfaces give off much of this energy in the form of thermal radiation and wasting 45% of the absorbed energy. Thus, the total yield of the collectors with black coatings is less than 50%. For high solar absorption applications, the selective coating must be thermally stable around 400° C., ideally in the air and have an absorbency greater than 0.95 and a thermal emittance below 0.15 at 400° C.
The object of the selective absorbing coatings is to increase the efficiency of solar collectors and are generally used in thermosolar applications. Said coatings have a large power of absorption of solar energy and low emissivity characteristics in order to reduce energy losses through thermal radiation in the remote infrared region. Whatever their application, the selective absorbing coatings play an essential part in increasing the efficiency of heat absorbing materials.
There are two magnitudes denominated absorbance (α) in the UV_VIS region of the spectre (200-1000 nm) and emittance (ε) in the infrared region (1-15 μm) used for evaluating the efficiency of selective absorbing coatings. The greater a and the smaller c, the higher is the efficacy of the coating.
The selective coatings for the efficient absorption of solar energy and its conversion into heat are characterized because they have a reflectance spectrum that changes abruptly according to the wavelength value. Thus, with wavelength values below certain value (about 2 μm, corresponding to the infrared region), the intensity of solar radiation is null or with a very low value (about 5%), while with wavelengths greater than this value the intensity reaches a very high value (greater than 90%) which corresponds to the infrared spectral region. This ensures that the heat acquired by the metallic element is not lost through thermal radiation.
Several patents and patent applications related to solar selective coatings are known. Usually, the coatings are made of a metal, dielectric or ceramic material substrate, at least one reflecting metallic layer and at least one anti-reflection layer and their direct application is in absorbing pipes for parabolic-trough solar collectors and in absorbing sheets for solar panels, such as those described in patents ES2316321B2, ES2317796B2 and patent application WO2012172148A1. The main advantage is an absorbance greater than 95% and an emittance lower than 0.20 in the range from 400° C. to 550° C. However, their compositions and methods for obtaining thereof are very complex and thus would not be economically sound in industries such as: food, textile, among others, because of their high production costs and thus the high price of the final product would be high for such markets.
Specifically, the inventions described in patents ES2317796B2 or ES2316321B2, report very acceptable absorbance values but their emittance values are not so favorable, leading to a selectivity ratio of α/ε 400° C.=0.975/0.15 and α/ε 400° C.=0.975/0.08.
Patent ES2317796B2 patent discloses a selective coating for solar applications with a reflective coating in the infrared region between two aluminum oxide layers, which allows any material of the reflective layer to not diffused in the infrared region in the superimposed absorption layer; causing it to have a high absorption capacity α>95.5% and a reduced emissivity with ε<9% at an operating temperature of 550° C. under vacuum for a period of time of 250 hours, reporting a selectivity ratio of α/ε=10.61; but at medium and low temperatures there are no reported results, or absorption operation and implementation capacity.
Meanwhile patent application WO2012172148A1 refers to a selective absorbing coating to visible and infrared radiation comprising: (a) a first non diffusing barrier layer (2); (b) an IR reflective metallic layer (3) of at least one metallic element selected from a group consisting of Au, Ag, Al, Cu, Ti and Pt; (c) at least one second non diffusing barrier layer (4) formed by oxidation of the layer (3); (d) an absorbent structure in the UV-VIS comprising at least a first film (5) and a second film (6) of cermet, which itself comprises a metal fraction of a metal selected from Pt, Cr, Mo, W, Zr, Nb, Ta and Pd, or any alloy thereof, and a ceramic comprising a free oxygen nitride constituted by a metallic oxide selected from aluminum, silicon and chromium; and (e) an antireflective dielectric layer in the UV-VIS region comprising a nitride of at least one metal selected from silicon, aluminum and chromium. Another object of the invention is the method for obtaining such a coating and its use in solar thermal collectors.
The ES2316321 patent reports that the methods for obtaining a selective coating in which the different layers of the coating are deposited by techniques of physical vapor deposition in vacuum (PVD, physical vapor deposition) such as are thermal evaporation, electron gun, ionic implantation or “sputtering”, by chemical vapor deposition (CVD) or through electrolytic baths, being the sputtering technique preferred for this purpose. It also has a refractive index of between 1.4 and 2.4 of the dielectric material layers of the absorbent multilayered structure comprising metallic oxides and/or nitrides of metallic elements.
The U.S. Pat. No. 4,104,134 describes a process for obtaining an aluminum absorber panel through a chemical bath in an aqueous solution with an alkaline cleaner from 5 to 10 minutes at a temperature of 60° C. and 80° C. to be then immersed in a brilliant solution from 5 and 10 minutes at 82° C. and 93° C.
Patent application WO2002072918 suggests a process and method for stripping a metal piece after welding to increase its corrosion resistance, indicating that the novelty of the invention resides in using an acid and an alkaline stripping agent for the process containing heavy metals and subsequently adding sodium hydroxide to the process for a chemical precipitation; afterwards, in the passivation process for creating an anticorrosion protective layer to the metal, it is possible to maintained a temperature above 35° C.
The EP Patent 0317838 defines a method of manufacturing an ultra-black coating; detailing that the process of preparation is carried out through a chemical bath in electrolytic solution of phosphorus and nickel alloy to form the coating based, which is immersed generally at temperatures of between 80 and 95° C. from 1 to 5 hours. For the black finish, it is required to soak it into a nitric acid solution between a 20° C. to 100° C. temperature from 5 seconds to 5 minutes, depending on the phosphorus content in the base, which indicates that usually at a concentration of 1 to 1 of phosphorus to nitric acid at a temperature of 50° C. the coating base blackens, the typical process temperature varies from 30 to 80° C. with a time from 5 seconds to 5 minutes, achieving a very stable coating with excellent mechanical strength, moisture resistance, and a spectrum reflectance from 0.1-0.4%, a wavelength width from 380-1800 nm and a wavelength range of 0.1% or less.
Particularly, in each one of these patents a large number of selective coatings have been described that use cermets formed by some of the following metals: Cu, Ni, Co, Pt, Cr, Mo, W, Al or Ag; and as ceramic matrix, the following compounds: SiO, SiO2, Al2O3, AlN or MgO. In order to improve their efficacy, these cermets must be covered with a layer of a material having very good transparent qualities such as the following oxides: Cr2O3, MoO3, WOx, HfOx or SiO2, where said layer acts as anti-reflection layer. Additionally, the cermet must be deposited on the metal acting as infrared mirror, which is usually achieved with Ag, Cu, Al, Au or Pt.
Unlike the state of art, the present invention introduces a method for obtaining a coating at room temperature, and the invention presented is not comprised of multiple layers. Nevertheless, very good results are obtained in the absorbent and reflective properties of the material. On the other hand, in any patent application or patent granted in our knowledge, it is proposed depositing a selective coating into fibers, threads, wires or metallic mesh with minimum thickness from 0.03 mm, which expands the applicability of the invention to other industries mainly textiles for making clothing that use solar selective coatings that provide solar and artificial radiation absorbent qualities.
The following patents disclose the background in the use of metallic fibers where we have found the following methods, processes and fiber products that integrate solar selective coatings.
The document U.S. Pat. No. 8,187,984 B2, Temperature sensitive intelligent textiles, relates to a textile fabric that includes a smooth surface with one or more regions (layers) of material having a variable behavior of thermal expansion or contraction, adjusting the insulation performance of the textile fabric in response to ambient conditions, yet the patent does not teach the use of radiation-absorbing coatings.
The document KR101386765, Electrically conductive fiber of graphene and method of production thereof, relates to a method for manufacturing a graphene electronic conductive fiber coated using a cotton thread of modified surface and the grapheneosin solution. The electronic conductive fiber manufactured by such method has very high conductivity, thereby being used for the intelligent electronic fiber (e-textile and e-fiber); but its application is limited to the transmission of electricity.
The document KR101373633, Method for manufacturing a conductive metal fiber, that has a higher elastic resistance, method of manufacturing products with the metal fiber composition with use of the same. The document relates to a method for manufacturing a fiber of a complex conductive metal that can be applied to an intelligent textile, made by combining the use of technologies such as electricity, computers, and electronics technology. In order to increase the limit of elasticity of the fiber by collecting multiple pieces of a first twisted thread twisted into a thread and a conductive fiber. The method for manufacturing the conductive complex fiber comprises the steps of: a first process that manufactures the fiber by winding the thread with the coated conductive fiber; a second process that makes the first twisted stranded thread; and a third process that produces fiber reinforced having a higher creep strength for winding the thread onto the surface of multiple pieces of the first coated stranded thread. This patent reflects the intention to bring to market intelligent fibers that integrate advanced technology for making clothing.
Finally, the document WO 2010129923 A2 entitled Pattern for controlling heating in materials, relates to method and apparatus using an array of heat elements coupled to a base material to maintain close body heat, while maintaining the desired transfer properties of the base material. In some embodiments, the material elements that manage or control the heat include elements that reflect or conduct heat; the mainly used materials are aluminum as reflective and can be glued, sewn or ironed to the clothes so that they can be addressed into the body of a wearer or away from the same in the inside of the garment; its method of preparation involves the sputtering technique for the precipitation of the material onto the fabric; unlike the present invention, this patent must be superimposed by the inner layer of the clothing to reflect infrared from the body, and it does not have the ability to absorb heat as the present invention does.
Overall, the patents discussed, analyze and give detail in the method of making intelligent textile fibers with different applications; however no one deepens on the ability to use a selective coating method that will provide to mesh fibers, threads, fibers, and metallic wire, capacity to absorb solar and artificial radiation and to generate heat. At the same time, these patents propose processes that cannot be done at room temperature, which involves high costs processes. Finally, unlike prior art documents, this invention discloses a method for deposing a selective coating into fibers or metallic meshes in thicknesses from 0.03mm without affecting the substrate.
The present invention relates to an absorbent and selective coating of solar and/or artificial and infrared radiation. In the present invention, the term radiation is to be understood broadly and without limitation, as the total electromagnetic spectrum, including sunlight, ultraviolet, infrared and artificial lighting, also called selective surface, which refers to a material or coating exhibiting optical selectivity; said coating material has optical properties which extremely vary from one spectral region to another, and it is characterized by its production process at room temperature. In the present invention, the term ambient temperature should be understood as the temperature from the 20° C. to 40° C., including standard room temperature of 25° C. Said coating is and may be permanently secured or fixed to a base material in a plurality of forms, such as, without limiting the scope of the methods: by chemical solution, cathodic spraying (sputtering), thermal evaporation, electrochemical and spray or sol-gel.
This coating acts as a heat trap, as it absorbs solar and/or artificial radiation and transforms it into heat. It also has the ability to reflect infrared radiation generated by a body.
Said coating comprises a substrate (1 and 10) of metallic material, that may present, without limitation, certain dielectric or ceramic characteristics, and at least a metallic layer (2 and 12) providing low emittance properties and because of its features it has various uses, for example as selective absorbent on metallic surfaces or substrates for thermosolar applications, in the textile industry.
The substrate (1 and 10) of metallic material may have surfaces of various shapes, geometry and texture configurations, including, without limitation, smooth, rough, porous, tubular, sheet, wire, threads, filaments, meshes, spheres and this without limiting the type of base material that can be used, provided it complies with the basic features for the material or selective absorbing coating adheres to and coat the surface maintaining the physical and chemical properties and performance (12).
For the above mentioned uses and applications, the solar and/or artificial radiation selective absorbing coating operates within the temperature range from 0° C. to 300° C., in the case of solar thermal applications, generating a range in the ratio of selectivity from α/ε=5.33 to α/ε=4.23 between such temperatures; enough for its employment in devices generating heat through solar radiation or artificial illumination.
The steps in the process of obtaining the proposed invention comprises (a) at least one cleaning stage, (b) at least one first stage of immersion and standing in aqueous solution, (c) at least one first rinsing stage, (d) at least one second stage of immersion in aqueous solution and (e) at least one second rinsing stage.
In said cleaning stage, the metallic substrate or surface to be coated is cleaned with solvents that are selected from the group comprising, without limiting the scope of the invention, the following substances:
A mixture of silicates, phosphates, carbonates and sulfates, to remove impurities such as dust and some greases;
Trichloroethylene for removing greases and oils that may be present on the metallic surface;
Acetone, for removing inorganic greases and polymer coatings that are different from oxides.
After the cleaning stage, the substrate to a stripping process in an aqueous solution of hydrofluoric acid is subjected in a concentration range of 0% to 5% plus nitric acid at a concentration ranging from 5% to 15%.
After the cleaning stage, the substrate is subjected to a stripping process in a hydrofluoric acid aqueous solution at a concentration ranging from 0% to 5% plus nitric acid at a concentration ranging from 5% to 15%. In a period of time from 8 to 16 minutes, the surface to be coated is allowed to stand immersed in the solution.
Then, the water rinsing stage is conducted (distilled water may be used).
After the cleaning stage and immersion in aqueous solution, in the second immersion stage, the pre-treated substrate is immersed in a chromic acid aqueous solution at a concentration ranging from 200 g/L to 300 g/L and sulfuric acid at a concentration ranging from 350 g/L to 450 g/L, during 9 to 10.5 hours obtaining coatings 3 blue, 4 gray, 5 black, 6 blue-purple according to
This coating is generated by applying the indicated ranges and with a room temperature, between 20° C. and 40° C., and at a humidity ranging from 0% RH to 80% RH, preferably between 20-80% RH, because out of this range precipitation would be generated in the solution.
Once obtained the first coatings, chromic acid solution can be kept at room temperature and used repeatedly for more coatings without affecting the absorption properties of coatings to be developed afterwards, which presents big savings on the cost of the solution.
Finally, the substrate with the coating is withdrawn and is submitted to a rinsing stage that can be conducted with water or with an impurity removing liquid.
Then, the metal substrate (1, 10) is coated with one single layer (2, 12) of chromium oxide having simultaneously reflecting and anti-reflecting characteristics.
The process may employ a step (f) or additional polishing process, to improve the coating, whereas sheets, tubes and spheres can be polished (2), however, if this additional step is not used, as in the case of wires, threads, fabric or metallic fiber, this does not drastically reduced absorbance values.
The usage of acetone is not mandatory in this procedure, this component ensures the cleaning of the metallic substrate (1) but it does not affect the efficacy values obtained.
The absorption level in the wavelength from 0.25 to 1.0 μm is in the range from 80 to 89%, the reflectance level in the wavelength from 2 to 15 μm which is in the range from 15 to 21%.
The thickness of the obtained film of chromium oxide is 100 nm to 200 nm.
Also and despite it is performed with hydrofluoric acid and nitric acid in the pretreatment and chromic acid to the pre-treated substrate to generate the selective coating at room temperature, the process allows its application on metallic substrate with thicknesses smaller than 0.03 mm up to thicknesses greater than 1.2 mm keeping their absorbance and reflectance properties for the applications described (12, 16, 17, 18, 19, 20).
A variation is that the present invention can be depose equally on reels of fiber, filament or metallic wire before being woven into a fabric woven with points or planes, without limiting the scope of the woven fabric, and having the same properties.
The tests conducted on the selective absorbing coating with a typical optical test of reflectance generate a high reflectance spectrum result such as the one shown in
The tests performed in
According to
As it can be observed, the instant invention has the advantage of being a simple process that however has not been previously used for solving situations of cost reduction implemented in industries where process heat is required in the manufacturing process and where fossil fuels are mainly used, and it is thus considered a novelty for its simplicity but with a technical degree of good results.
Another advantage is that solvents and solutions can be reused, thus optimizing the use of these supplies.
Also in
A big advantage is that the present invention integrated on mesh, thread, wire or metallic fabric functions as a protective shield against ultraviolet rays as the tests conducted to measure the transmittance indicate that it only allows 27.6% of ultraviolet light incident on the same as shown in
Another advantage is that it can be applied into substrates with thicknesses below 0.03 mm (10, 11, 12) and can be applied to configurations where selective coatings have never been applied as in the case of fibers, wire, threads or metallic meshes for use in textiles wherein jackets (16), trousers, scarves, shirts, hats (19), shoes (17) gloves (18), mittens and mitts, sleeping bags, tents (20), without limiting the scope of the invention, can be made up, and that in conjunction with insulating textiles enhance absorption and retention of body heat and solar radiation.
Thus, one of the main uses of the selective coating obtained at room temperature is on fibers, threads, wire and/or metallic meshes (10) and an example of its direct industrial application is for making jackets (16), sweaters, hats (19), gloves (18), fabric for tents (20), shoes (17) boots (17) among others without limiting the scope of the invention. Unlike the application on other substrates for other uses it does not require additional procedures in order to integrate the invention into fabrics with different characteristics, qualities and compositions as an interlining (14); the union of these absorb solar radiation, convert it into heat and maintain heat (26), which is equivalent to the use of bulky garments without the need of having thermal insulation around the garment to protect from the cold. The main advantages of a fabric of the present invention are: lighter textiles and garments, less bulky, externally generated heat and retention thereof in the garment, convenience, added value for the producer of textiles and superior aesthetics.
| Number | Date | Country | Kind |
|---|---|---|---|
| MX/A/2014/001213 | Jan 2014 | MX | national |
This application is a continuation-in-part of U.S. application Ser. No. 14/895,362 filed Dec. 2, 2015, entitled, RADIATION SELECTIVE ABSORBING COATING AND PROCESS FOR OBTAINING THE SAME AT ROOM TEMPERATURE, pending, the content of which is incorporated herein by reference, which is a US national stage entry of PCT/MX2014/000173 filed Nov. 4, 2014, under the International Convention, which claims priority over Mexican patent application No. MX/a/001213 filed Jan. 29, 2014.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 14895362 | Dec 2015 | US |
| Child | 14958237 | US |
