CN111498906B - Transparent heat-shielding material, transparent heat-shielding microparticle dispersion, and production method and use thereof - Google Patents

Transparent heat-shielding material, transparent heat-shielding microparticle dispersion, and production method and use thereof Download PDF

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CN111498906B
CN111498906B CN201910647213.6A CN201910647213A CN111498906B CN 111498906 B CN111498906 B CN 111498906B CN 201910647213 A CN201910647213 A CN 201910647213A CN 111498906 B CN111498906 B CN 111498906B
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transparent heat
shielding
nitrogen
tungsten
heat
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CN111498906A (en
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金平实
纪士东
孙光耀
李�荣
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Shanghai Institute of Ceramics of CAS
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Shanghai Institute of Ceramics of CAS
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    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
    • C01G41/00—Compounds of tungsten
    • C—CHEMISTRY; METALLURGY
    • C03—GLASS; MINERAL OR SLAG WOOL
    • C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
    • C03C27/00—Joining pieces of glass to pieces of other inorganic material; Joining glass to glass other than by fusing
    • C03C27/06—Joining glass to glass by processes other than fusing
    • C03C27/10—Joining glass to glass by processes other than fusing with the aid of adhesive specially adapted for that purpose
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2002/00—Crystal-structural characteristics
    • C01P2002/50—Solid solutions
    • C01P2002/52—Solid solutions containing elements as dopants
    • C01P2002/54—Solid solutions containing elements as dopants one element only
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2002/00—Crystal-structural characteristics
    • C01P2002/70—Crystal-structural characteristics defined by measured X-ray, neutron or electron diffraction data
    • C01P2002/72—Crystal-structural characteristics defined by measured X-ray, neutron or electron diffraction data by d-values or two theta-values, e.g. as X-ray diagram
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2004/00—Particle morphology
    • C01P2004/01—Particle morphology depicted by an image
    • C01P2004/03—Particle morphology depicted by an image obtained by SEM
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2004/00—Particle morphology
    • C01P2004/01—Particle morphology depicted by an image
    • C01P2004/04—Particle morphology depicted by an image obtained by TEM, STEM, STM or AFM
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02A—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE
    • Y02A40/00—Adaptation technologies in agriculture, forestry, livestock or agroalimentary production
    • Y02A40/10—Adaptation technologies in agriculture, forestry, livestock or agroalimentary production in agriculture
    • Y02A40/25—Greenhouse technology, e.g. cooling systems therefor

Abstract

The invention provides a transparent heat-shielding material, a transparent heat-shielding microparticle dispersion, a preparation method and an application thereof. The transparent heat shielding material is a transparent materialHas the chemical formula MxWO3‑δWherein M is at least one element selected from alkali metals, alkaline earth metals and rare earth elements, x is at least 0.1 and at most 1, W is tungsten, O is oxygen, and δ is at least 0.5. According to the invention, nitrogen is doped in the traditional tungsten bronze structure, so that nitrogen enters a tungsten-oxygen skeleton structure to replace part of oxygen, thereby causing distortion of crystal lattices, reducing the crystal lattices, and increasing the stability of the structure because doped metal ions are not easy to escape.

Description

Transparent heat-shielding material, transparent heat-shielding microparticle dispersion, and production method and use thereof
Technical Field
The invention belongs to the field of functional new nano materials, and particularly relates to a transparent heat-shielding material, transparent heat-shielding nano powder and a transparent heat-shielding microparticle dispersion, which can be widely applied to the application fields of heat-shielding coatings, heat-shielding films, heat-shielding glass and various photo-thermal conversion materials.
Background
The wavelength range of sunlight is about 300-2500 nm, wherein the wavelength range of visible light is 380-780 nm, and the wavelength of near infrared is 780-2500 nm. In building and vehicle glass components, the near infrared part of sunlight is greatly shielded while the high visible light transmittance is kept, so that the energy conservation and emission reduction are facilitated, and the comfort of living space is improved.
In the agricultural field, with the increasing warming of the climate, crops in the form of greenhouses or mulch films stop growing and even die in hot seasons due to excessive temperatures. Meanwhile, the lack of manpower and the aging of the population of the agriculture also put higher requirements on the working environment.
In the field of a plurality of heat storage and heat preservation materials, such as heat storage fibers or fabric products, the heat storage and heat preservation of human bodies and organisms can be realized efficiently by absorbing sunlight and converting the sunlight into far infrared heat radiation.
Thus, there is a great potential need in the marketplace for transparent heat shielding materials and products. Among them, a novel transparent infrared heat-shielding coating, film, sheet, fiber product, which is formed by combining an inorganic nano heat-shielding material with a resin, has been gradually expanding the market size and application field.
Conventional inorganic nano-grade heat-shielding materials include transparent conductive materials (such as ITO, ATO, etc.), or lanthanum hexaboride (LaB)6) And the recently discovered series of transparent heat-shielding materials with tungsten bronze structure (doped tungsten bronze) are superior to those with tungsten bronze structureHigh visible light transmittance and excellent heat-shielding, heat-storing and heat-insulating properties are widely noted.
For example, patent document 1 discloses a method for producing a tungsten oxide-based transparent heat shielding material having excellent properties, which is represented by the general formula MxWyOz, wherein M is at least one selected from the group consisting of alkali metals, alkaline earth metals, rare earth elements, Zr, Cr, Mn, Fe, Ru, Co, Rh, Ir, Ni, Pd, Pt, Cu, Ag, Au, Zn, Cd, Al, Ga, In, Tl, Si, Ge, Sn, Pb, Sb, B, F, P, S, Se, Br, Te, Ti, Nb, V, Mo, Ta, and Re.
Also, patent document 2 discloses a tungsten bronze structure heat shielding nanopowder doped with a metal element, the doping element being one or a mixture of several elements selected from Li, Na, K, Rb, Cs, Be, Mg, Ca, Sr, Ba, Al, Ga, In, Tl, Ge, Sn, Pb, As, Sb, Bi, Se, Te, Ti, Mn, Fe, Co, Ni, Cu or Zn.
However, in a heat-shielding product formed of a heat-shielding material of tungsten bronze structure and a resin, such as a heat-shielding laminated film or laminated glass, a problem of insufficient stability of optical properties is found during use, as manifested by various degrees of change or deterioration of optical properties with the increase of use time, specifically as manifested by local discoloration under ultraviolet irradiation and discoloration originating from the edges of the product in a moist heat environment.
Detailed research results (see non-patent documents 1 to 4) show that the mechanism of performance deterioration is due to reversible photochromism (coloration) caused by cesium deficiency generated on the surface of CWO particles and reaction with hydrogen elements, or performance failure (discoloration) caused by oxidation of the surface of CWO particles in a hot and humid environment, in a composite material (e.g., PET heat shielding film) formed with a resin by fine particles of a metal-doped tungsten bronze structure (e.g., cesium tungsten bronze CWO).
Prior art documents:
patent documents:
patent document 1: japanese patent JP 2005-187323A;
patent document 2: chinese patent CN 107200357A;
non-patent documents:
non-patent document 1: adachi, y.ota, h.tanaka, m.okada, n.oshimura, a.tofuku, chromatographic in vivo in process of bacillus-coped tungsten fibers, j.appl.phys.114(19) (2013)11.
Non-patent document 2: yunxiang Chena, b,1, Xianzhe Zeng, Yijie Zhou, Rong Li, Heliang Yao, Xun Cao, Ping Jin, Core-shell structured CsxWO3@ ZnO with excellent activity and high performance on near-concerned shielding, Ceramics International 44(2018)2738-,
non-patent document 3: yijie Zhou, ab Ning Li, ab yunchuun Xin, a Xun Cao, Shidong Ji and Ping Jin, CsxWO3nanoparticle-based organic polymer transporter hairs low haze, high near in-free shielding reliability and excellent photoresist stability, j.
Non-patent document 4: xianzhe Zeng, Yijie Zhou, Shidong Ji, Hongjie Luo, Heliang Yao, Xiao Huang and Ping Jin, The preparation of a high performance required shifting Cs xWO3/SiO2 composition reacting and research on optical stability unit ultrasonic analysis, J.Mater.chem.C. 2015,3,8050 and 8060.
Disclosure of Invention
Therefore, an object of the present invention is to provide a novel tungsten-doped bronze heat shielding material having stable properties, which solves the problem of unstable optical properties of the material and the resin product.
The inventor finds that for the tungsten bronze structure doped with the same metal, such as cesium tungsten bronze, the size ratio of cesium ions to a network lattice constant is improved by reducing the lattice constant of a tungsten-oxygen network crystal structure containing cesium, so that the escape of the cesium ions can be effectively limited, and the stability of the material is improved.
In addition, the forbidden band width of the traditional doped tungsten bronze structure is larger, namely the ultraviolet shielding capability is lower. Excessive UV irradiation is detrimental to the shielding ability and life of the heat-shielding resin product, and excessive UV-shielding additives are added, or cause an increase in cost and a decrease in optical and mechanical properties.
Therefore, the forbidden bandwidth of the doped tungsten bronze structure is reduced, the red shift of the absorption end is realized, the ultraviolet absorption rate of the structure can be increased, and the color change caused by the photo-induced coloring in the heat shielding resin is effectively inhibited while the ultraviolet shielding efficiency is increased.
Thus, the inventor designs a new doped tungsten bronze structure, which can simultaneously realize the reduction of the lattice constant and the red shift of the absorption end.
In a first aspect, the present invention provides a transparent heat shield material obtained by forming a film of the formula MxWO3-δWherein M is at least one element selected from alkali metals, alkaline earth metals and rare earth elements, x is at least 0.1 and at most 1, W is tungsten, O is oxygen, and δ is at least 0.5.
According to the invention, nitrogen is doped in the traditional tungsten bronze structure, so that nitrogen enters a tungsten-oxygen skeleton structure to replace part of oxygen, thereby causing distortion of crystal lattices, reducing the crystal lattices, and increasing the stability of the structure because doped metal ions are not easy to escape.
Meanwhile, nitrogen doping and oxygen substitution change the forbidden band width of the original crystal structure, so that the forbidden band width is reduced, the absorption end is red-shifted, and the ultraviolet shielding performance is improved.
Preferably, the components of the transparent heat shielding material are represented by the general formula MxWOyNzN is nitrogen, and 2.5. ltoreq. y + z. ltoreq.3.
Preferably, 0.001 ≦ z ≦ 0.5.
Preferably, the ratio of z to y is 1/4 or less, preferably 1/10 or less, more preferably 1/20 or less.
In a second aspect, the present invention provides a method for preparing any one of the above transparent heat shielding materials, comprising the following steps:
and (3) keeping the temperature of the mixture of the tungsten source and the M metal source in the MxWOyNz formula at 450-750 ℃ for 2-8 hours in a vacuum state with a nitrogen-containing atmosphere.
In a third aspect, the present invention provides a method for preparing any one of the above transparent heat shielding materials, comprising the following steps:
stirring and drying the solution in which the nano tungsten oxide powder and the M metal source in the MxWOyNz formula are uniformly dispersed to obtain a precursor;
and preserving the heat of the precursor for 1-8 hours at 400-700 ℃ in a vacuum state with a nitrogen-containing atmosphere.
Preferably, the tungsten source is selected from at least one of tungsten oxide, tungstic acid and ammonium tungstate, and ammonium tungstate is preferred.
Preferably, the M metal source is a carbonate of the M element, preferably cesium carbonate.
Preferably, the nitrogen-containing atmosphere is ammonia gas, nitrogen gas or a mixed gas thereof, or a mixed gas of the above gas and hydrogen gas.
In a fourth aspect, the present invention provides transparent heat shielding fine particles, wherein the transparent heat shielding fine particles are made of any one of the above transparent heat shielding materials, and the diameter of the transparent heat shielding fine particles is in a range of 1nm to 1000 nm.
In a fifth aspect, the present invention provides a transparent heat shielding fine particle dispersion in which the transparent heat shielding fine particles are dispersed in a medium.
Preferably, the medium is selected from any one of a liquid containing a resin, a transparent resin film sheet, a glass substrate, a chemical fiber, and a woven fabric.
The medium can be selected from a variety of transparencies, such as resin, glass, aerogel, and the like. Among them, the resin-based media are high in transparency, various in form and easy to process, and the media are preferably various resin-based media, and preferably resin media with high transparency, such as PET (polyethylene terephthalate), PE (polyethylene), EVA (ethylene-vinyl acetate copolymer), PVB (polyvinyl butyral), PI (polyimide), PC (polycarbonate) and the like.
According to the present invention, a transparent heat shielding material, transparent heat shielding fine particles, and a transparent heat shielding fine particle dispersion having stable properties can be provided.
Drawings
FIG. 1 is an XRD (X-Ray Diffraction) Diffraction spectrum of a nitrogen-doped cesium tungsten bronze powder according to an embodiment of the present invention.
Fig. 2 is a transmission electron micrograph of the nitrogen-doped cesium tungsten bronze powder according to the embodiment of the present invention.
Fig. 3 is a scanning electron micrograph of the nitrogen-doped cesium tungsten bronze powder according to the embodiment of the present invention.
Fig. 4 is a transmittance spectrum of a heat shielding laminated glass according to an embodiment of the present invention.
Detailed Description
The present invention is further illustrated by the following examples, which are to be understood as merely illustrative and not restrictive.
The transparent heat shielding material of one embodiment of the invention is obtained by doping nitrogen in a tungsten bronze structure. The tungsten bronze structure can be represented by the chemical formula MxWO3-δWherein M is one or more elements selected from alkali metals, alkaline earth metals and rare earth elements, x is 0.1 ≦ x ≦ 1, W is tungsten, O is oxygen, and δ is 0 ≦ δ 0.5.
The stability of the doped tungsten bronze structure is related to the ionic radius of the doping element, such as in an alkali metal doped tungsten bronze structure, the larger the ionic radius of the alkali metal, the more stable the structure. Thus, where M comprises an alkali metal, the alkali metal is preferably cesium.
In some embodiments, the transparent heat shielding material is of the formula MxWOyNzN is nitrogen, and 2.5. ltoreq. y + z. ltoreq.3.
The tungsten bronze structure before being doped with N may be in an oxygen deficient state. After N is doped, N can replace the position of O and can also occupy oxygen vacancy. In some embodiments, y + z ≧ 3- δ.
Although the performance of tungsten bronze is improved by proper amount of nitrogen doping, the difficulty of large amount of doping exists in the process, and the stability can be influenced by excessive distortion of the crystal structure due to excessive doping amount. Therefore, the nitrogen to oxygen ratio (i.e., z/y) after doping should not exceed 1/4, preferably does not exceed 1/10, and more preferably does not exceed 1/20. On the other hand, the nitrogen to oxygen ratio (i.e., z/y) after doping is preferably 1/100 or more, which ensures improved tungsten bronze performance.
In some embodiments, 0.001 ≦ z ≦ 0.5.
The transparent heat shielding fine particles according to an embodiment of the present invention are formed of the transparent heat shielding material.
The diameter of the transparent heat-shielding fine particles may be 1nm to 1000nm, preferably 10nm to 100nm, and more preferably 20nm to 50 nm. Because, although the micro-particles with the diameter ranging from 1nm to 1000nm can form transparent heat-shielding materials and products with the medium, the over-large particle size is easy to generate diffuse reflection to visible light, and the transparency of the products is reduced; on the other hand, if the particle size is too small, the particles are not easily crushed and are more difficult to be uniformly dispersed in a medium.
The transparent heat-shielding fine particles are dispersed in a medium to form a transparent heat-shielding fine particle dispersion. The medium may be a transparent body.
In some embodiments, the transparent heat-shielding fine particles are uniformly dispersed in a liquid containing a resin to obtain an aqueous or solvent-based transparent heat-shielding coating.
The transparent heat-shielding coating is coated on a substrate, and a transparent heat-shielding coating film can be obtained.
In some embodiments, the transparent heat-shielding fine particles are uniformly dispersed or coated in the glass substrate to obtain the transparent heat-shielding glass.
In some embodiments, the transparent heat-shielding microparticles are uniformly dispersed in a transparent resin film (e.g., PET, PE, PI, PVB, or EVA), or a resin sheet (PC), to obtain a transparent heat-shielding film or sheet article.
In some embodiments, the transparent heat-shielding particles are uniformly dispersed in chemical fibers (such as terylene, chinlon, acrylon, clolon, vinylon, spandex, polyolefin stretch yarn, and the like) to obtain heat-storage and heat-preservation fibers and textile (clothing, quilt, filler, and the like) products.
Hereinafter, a method for producing a transparent heat shielding material according to an embodiment of the present invention will be described as an example.
In some embodiments, a mixture of a tungsten source and an M source (M is any one or more of an alkali metal, an alkaline earth metal, and a rare earth element) is heat-treated in a vacuum state with a nitrogen-containing atmosphere to obtain a transparent heat shield material.
The tungsten source (raw material containing tungsten element) is preferably a substance containing both tungsten element and oxygen element, and for example, may be selected from at least one of tungsten oxide, tungstic acid, ammonium tungstate, and the like, and more preferably a substance further containing nitrogen element, such as ammonium tungstate. The tungsten element is combined with oxygen to form a crystal skeleton with a tungsten bronze structure in the synthesis process, and a doped metal element is introduced into a polyhedral vacancy of the skeleton to generate infrared absorption. Because ammonium tungstate contains ammonium groups, namely nitrogen elements, the nitrogen elements existing in the starting raw materials are beneficial to doping of nitrogen. And the solubility of the ammonium tungstate in water is high, which is beneficial to the uniform mixing and chemical reaction of the raw materials.
The M source (raw material containing M element) may be selected from salts containing no metal other than M, such as carbonate, chloride, sulfate, and organic acid salt of M element. When the M element is an alkali metal, the M source is preferably an alkali metal carbonate, because the carbonate is cheap and good, has high solubility in water, can form a high-concentration ionic dispersion liquid, and promotes the raw materials to realize uniform mixing and chemical reaction. In a more preferred embodiment, the M source is cesium carbonate, which has high stability due to the large ionic radius of cesium in cesium tungstate.
And uniformly mixing the tungsten source and the M source to obtain a mixture. The method can be that the tungsten source and the M source are directly mixed evenly; or preparing the tungsten source and the M source into solutions respectively, uniformly mixing the solutions, and drying the mixed solution.
The resulting mixture was placed in a reaction apparatus. The reaction apparatus is preferably a dynamic reaction apparatus such as a rotary kiln, which allows the reaction to be more complete and uniform. Vacuumizing the reaction device, and introducing gas containing nitrogen element, such as ammonia gas, nitrogen gas or mixed gas thereof; alternatively, hydrogen gas may be added to the above gas as necessary to form a reducing mixed gas. The total gas flow rate can be 10-1000 standard milliliters per minute. The volume ratio of the nitrogen-containing gas to the hydrogen gas can be (1-99): (99-1). Keeping the reaction device in a vacuum state, heating the reaction device from room temperature to 450-750 ℃, and preserving heat for 2-8 hours. In this process, the rotary kiln is preferably started.
After the heating process is finished, the furnace is kept in a rotation state and is cooled to be near the room temperature, and reaction products are taken out to obtain the transparent heat shielding material.
The obtained transparent heat-shielding material is crushed to the particle size range of 1 nm-1000 nm, and then the transparent heat-shielding particles are obtained.
In some embodiments, tungsten source nanopowder is used as a raw material, so that transparent heat shielding microparticles with nanometer size can be directly obtained without pulverization.
The tungsten source nanopowder is preferably a nano tungsten oxide powder having a particle size of preferably less than 100nm, more preferably less than 50 nm.
The M source may be as described above and will not be described further herein.
Dissolving the M source in a solvent to prepare a solution. The solvent used can be at least one selected from water, alcohol and ether, preferably methanol or ethanol, and is easy to volatilize, thereby being beneficial to improving the drying efficiency; the volatilized alcohol can be reused through a recovery system, reducing environmental load.
And dispersing the tungsten source nano powder into the M source solution, uniformly mixing, stirring for a period of time such as 5-120 minutes, and then drying to obtain the nano precursor.
And placing the obtained nano precursor in a reaction device. The reaction apparatus is preferably a dynamic reaction apparatus such as a rotary kiln, which allows the reaction to be more complete and uniform. Vacuumizing the reaction device, and introducing gas containing nitrogen element, such as ammonia gas, nitrogen gas or mixed gas thereof; alternatively, hydrogen gas may be added to the above gas as necessary to form a reducing mixed gas. The total gas flow rate can be 10-1000 standard milliliters per minute. The volume ratio of the nitrogen-containing gas to the hydrogen gas can be (1-99): (99-1). Keeping the reaction device in a vacuum state, heating the reaction device to 400-700 ℃ from room temperature, and preserving heat for 1-8 hours. In this process, the rotary kiln is preferably started.
After the heating process is finished, the furnace is kept in a rotation state and is cooled to be near the room temperature, and reaction products are taken out to obtain the transparent heat shielding particles with nanometer sizes.
In the embodiment of the invention, before the formation of the tungsten bronze crystal, the heating is carried out in the vacuum state of the nitrogen element-containing atmosphere, the heating is started from room temperature to the highest temperature and is kept for a certain time, and the nitrogen element-containing atmosphere and the vacuum state are always kept in the cooling process, so that the sufficient nitrogen doping is easily realized. Once the tungsten bronze crystal is formed, for example, the tungsten bronze crystal is subjected to a heat treatment in a nitrogen-containing atmosphere, sufficient nitrogen doping, if any, is difficult to achieve, and the doping amount is far smaller than that of the present invention under the same heat treatment conditions.
The present invention will be described in detail by way of examples. It is also to be understood that the following examples are illustrative of the present invention and are not to be construed as limiting the scope of the invention, and that certain insubstantial modifications and adaptations of the invention by those skilled in the art may be made in light of the above teachings. The specific process parameters and the like of the following examples are also merely one example of suitable ranges, i.e., those skilled in the art can select the appropriate ranges through the description herein, and are not limited to the specific values exemplified below.
Example 1
0.652kg of cesium carbonate and 3.132kg of ammonium paratungstate are mixed and put into a rotary heating furnace with the volume of 50L, the furnace door is closed, ammonia gas is introduced after vacuum pumping is carried out by a vacuum unit, the flow rate is kept at 100SCCM (standard milliliter per minute), and a certain vacuum state is kept in the whole synthesis process; starting a furnace rotating device, heating the furnace to 750 ℃ from room temperature within 2 hours, and preserving heat for 4 hours at the temperature; stopping heating, and naturally cooling the furnace to be near the room temperature; opening a rotary furnace door to discharge, and obtaining the determined cesium tungsten bronze powder.
The obtained powder has a single-phase cesium tungsten bronze crystal structure (fig. 1) as determined by powder XRD. By performing a more detailed comparison analysis of XRD diffraction peaks, the diffraction peak positions are slightly shifted toward high angles (for example, the (200) lattice diffraction position located in the vicinity of 27.8 ° is shifted toward high angles by about 0.2 °) as compared with the stoichiometric hexagonal cesium tungsten bronze (cs0.33wo3) diffraction peak, and it can be considered to be caused by lattice constant distortion due to nitrogen doping.
The above reaction process can be represented by the following reaction formula:
(NH4)10(H2W12O42)·4H2O+Cs2CO3+NH3→Cs0.33WO3:N+NH3+H2O
the water vapor and the like gradually generated during the reaction are gradually evacuated from the vacuum during the initial stage of heating. Adding a nitrogen-containing raw material and nitrogen elements in an ammonia atmosphere into the cesium tungsten bronze crystal lattice formation reaction process from room temperature, and gradually heating to finally form a nitrogen-doped cesium tungsten bronze crystal structure.
Important reasons for achieving nitrogen doping are: 1) adopting a nitrogen-containing tungsten source, 2) heating in a vacuum state containing ammonia gas before forming the cesium tungsten bronze crystal, 3) starting heating from room temperature to the highest temperature and keeping for a certain time, and keeping the powder in an ammonia gas atmosphere and vacuum state all the time in the cooling process. It is obvious that once the cesium tungsten bronze crystal is formed, it is difficult to achieve sufficient nitrogen doping, for example, in heat treatment of the cesium tungsten bronze crystal in a nitrogen-containing atmosphere.
FIG. 2 is a transmission electron micrograph of the obtained powder, which was in the form of particles having a particle diameter of several hundred nanometers.
Example 2
Completely dissolving 0.325kg of cesium carbonate in methanol to obtain a cesium carbonate methanol solution; 1.391kg of nano tungsten oxide (commercially available WO)3Average grain diameter of 50nm) is put into the solution, stirred and dried to obtain a cesium tungsten bronze precursor; adding the obtained cesium tungsten bronze precursor into a 50L rotary furnace, closing a furnace door, vacuumizing by using a vacuum unit, introducing mixed gas of nitrogen and hydrogen (7:3), keeping the total flow of the mixed gas at 100SCCM, and keeping the furnace at a certain vacuum degree in the whole synthesis process; starting a furnace rotating device, heating the furnace to 500 ℃ from room temperature within 2 hours, and preserving heat for 8 hours at the temperature; stopping heating, and naturally cooling the furnace to be near the room temperature; opening a rotary furnace door to discharge, and obtaining the determined nitrogen-doped cesium tungsten bronze powder.
Powder XRD analysis showed that the obtained powder had a single-phase cesium tungsten bronze crystal structure with an XRD spectrum similar to that of fig. 1. The above reaction process can be represented by the following reaction formula:
Cs2CO3+CH3OH+WO3+N2+H2→Cs0.33WO3:N+N2+H2+CO2
FIG. 3 is a scanning electron micrograph of the obtained powder, which is composed of nitrogen-doped cesium tungsten bronze nanocrystals with an average particle size of about 60nm, and whose morphology and particle size distribution are similar to those of nano tungsten oxide containing tungsten as a raw material. The nanometer tungsten oxide is used as a raw material, and cesium ion alcohol solution is used for uniform dispersion and heat treatment at a lower temperature, so that the obtained nitrogen-doped cesium tungsten bronze nanometer powder basically keeps the original nanometer size. The preparation method can directly use the nanometer powder to obtain the nanometer heat-shielding product without a crushing process.
Example 3
200G of the nitrogen-doped cesium tungsten bronze nano-powder obtained in example 2 and 15kg of a plasticizer (3G8) were uniformly mixed by a stirrer, and the mixed liquid was gradually added to 35kg of PVB powder through a funnel and sufficiently mixed in a horizontal mixer, and then plasticized at 160 ℃ by a twin-screw extruder, and a PVB heat-shielding intermediate film (0.38 mm. times.1 m. times.100 m) containing nitrogen-doped cesium tungsten bronze nano-particles was obtained by extrusion molding.
Example 4
An appropriate amount of the PVB heat-shielding interlayer film obtained in example 3 was cut, placed between two pieces of glass (3mm × 30mm × 30mm), placed on a heating table, kept at 95 ℃ under pressure for a certain time, and cooled to obtain PVB heat-shielding laminated glass.
The optical transmittance of the heat-shielding laminated glass (N-CWO) obtained in example 4 was measured by a spectrophotometer, and compared with that of a cesium tungsten bronze heat-shielding laminated glass (CWO) obtained by the same method as in examples 3 and 4 using cesium tungsten bronze nanopowder not doped with nitrogen (except that only hydrogen gas was used during heating to avoid nitrogen doping, the production method was the same as in example 2), and the results are shown in fig. 4.
As shown in fig. 4, the heat-shielding laminated glass using nitrogen-doped cesium tungsten bronze has a high infrared blocking ratio, and also realizes partial red shift of the absorption end.
Example 5
The two heat-shielding laminated glasses shown in fig. 4 were placed in a high-temperature high-humidity (90 ℃/90% relative humidity) laboratory cabinet, and the transmittance spectra were taken out every 24 hours and measured, and compared with the original spectra in fig. 4.
The comparison shows that the transmittance of the CWO laminated glass is increased by about 2% after the CWO laminated glass is placed for 24 hours, while the transmittance of the N-CWO laminated glass is only increased by 0.5% after the N-CWO laminated glass is placed for 72 hours. As mentioned previously, the increase in transmittance is caused by the escape of cesium atoms due to the surface oxidation of cesium tungsten bronze particles. It is evident that nitrogen doping increases the oxidation resistance of the cesium tungsten bronze particles.
Example 6
100g of the nitrogen-doped cesium tungsten bronze nano powder obtained in the example 2, 2g of a dispersing agent and 200g of toluene are added into a sand mill, the mixture is kept for 5 hours at the rotating speed of 2600r/min, and the mixture is taken out to obtain a nitrogen-doped cesium tungsten bronze dispersion liquid.
25g of the dispersion was weighed and mixed with 75g of silicone resin, 4g of polymerization inhibitor and 1g of BYK-385N to obtain dispersion A.
50g of toluene is weighed, 10g of ultraviolet absorbent and 5g of stabilizer are added, and after uniform dissolution, dispersion liquid B is obtained.
The transparent heat-shielding coating can be obtained by uniformly mixing the material A and the material B before coating operation. The coating is coated on a transparent substrate (glass or polymer) by spraying, blade coating and the like, and the transparent heat-shielding glass or transparent heat-shielding coating plate is obtained after curing.
Comparative example 1
100g of cesium carbonate and tungstic acid are weighed according to the molar ratio of Cs to W of 0.33, are fully mixed by using an automatic mortar, and are heated at 600 ℃ for 120 minutes in a reducing atmosphere (Ar: H2 is 97:3 volume ratio), after the reactants are cooled to room temperature, the temperature is raised to 800 ℃ in a pure Ar atmosphere again, and the temperature is maintained for 60 minutes, so that a cesium bronze product is obtained, and the cesium bronze product has a Cs0.33WO3 hexagonal crystal structure through XRD measurement, and the (200) lattice diffraction position of the cesium bronze product, which is positioned near 27.8 degrees, is consistent with a theoretical value.
The above reaction can be described by the following reaction formula:
Cs2CO3+H2WO4+H2→Cs0.33WO3+H2O+CO2
heating the obtained powder in an NH3 atmosphere with the flow rate of 500 ml/min at 450 ℃ for 60 minutes to obtain a cesium tungsten bronze powder product, wherein the (200) lattice diffraction position of the cesium tungsten bronze powder product, which is positioned near 27.8 degrees, is slightly shifted to a high angle through XRD measurement, the shift amount is about 0.05 degrees, which shows that the cesium tungsten bronze powder product after subsequent heat treatment is doped with nitrogen, and the reaction formula can be expressed by the following formula:
Cs0.33WO3+ NH3 → Cs0.33WO3: N + NH3 (heating temperature 450 ℃ C.)
However, compared with the case of examples 1 and 2 in which the reactant precursor was heated in a nitrogen-containing vacuum from room temperature, the XRD diffraction peak was shifted to a much smaller degree, meaning that the amount of nitrogen doped in comparative example 1 was much smaller than that in examples 1 and 2. A cesium tungsten bronze product obtained in comparative example 1 was subjected to the heat-shielding laminated glass prepared in the same manner as in example 4 and tested in the same manner as in example 5. The results show that the heat-shielding laminated glass transmittance increases by 1.2% after 72 hours of standing.

Claims (8)

1. A method for preparing a transparent heat-shielding material is characterized in that the transparent heat-shielding material is prepared by adopting a chemical formula MxWO3-δWherein M is at least one element selected from alkali metals, alkaline earth metals and rare earth elements, x is at least 0.1 and at most 1, W is tungsten, O is oxygen, and δ is at most 0.5; the components of the transparent heat-shielding material are represented by the general formula MxWOyNzWherein N is nitrogen, 2.5 ≦ y + z ≦ 3, and a ratio of z to y is 1/100 or more and 1/4 or less;
the preparation method of the transparent heat-shielding material comprises the following steps:
keeping the temperature of a mixture of a tungsten source and an M metal source at 450-750 ℃ for 2-8 hours in a vacuum state with a nitrogen-containing atmosphere, and keeping the powder in an ammonia atmosphere and vacuum state all the time in the cooling process; the tungsten source is ammonium tungstate, and the M metal source is carbonate of M element; the nitrogen-containing atmosphere is ammonia gas.
2. A method for preparing a transparent heat-shielding material is characterized in that the transparent heat-shielding material is prepared by adopting a chemical formula MxWO3-δWherein M is at least one element selected from alkali metals, alkaline earth metals and rare earth elements, x is at least 0.1 and at most 1, W is tungsten, O is oxygen, and δ is at most 0.5; the components of the transparent heat shielding material are represented by the general formula MxWOyNzWherein N is nitrogen, 2.5 ≦ y + z ≦ 3, and a ratio of z to y is 1/100 or more and 1/4 or less;
the preparation method of the transparent heat shielding material comprises the following steps:
stirring and drying a methanol solution in which nano tungsten oxide powder and an M metal source are uniformly dispersed to obtain a precursor, wherein the M metal source is carbonate of an M element;
preserving the heat of the obtained precursor for 1-8 hours at 400-700 ℃ in a vacuum state with a nitrogen-containing atmosphere; the nitrogen-containing atmosphere is a mixed gas of nitrogen and hydrogen.
3. The production method according to claim 1 or 2, wherein the ratio of z to y is 1/100 or more and 1/10 or less.
4. The method according to claim 3, wherein the ratio of z to y is 1/100 or more and 1/20 or less.
5. The method of claim 1 or 2, wherein the M metal source is cesium carbonate.
6. Transparent heat shielding fine particles, wherein the material of the transparent heat shielding fine particles is prepared by the preparation method according to any one of claims 1 to 5, and the diameter of the transparent heat shielding fine particles is in the range of 1nm to 1000 nm.
7. A transparent heat-shielding fine particle dispersion comprising the transparent heat-shielding fine particle according to claim 6 dispersed in a medium.
8. The transparent heat shielding fine particle dispersion according to claim 7, wherein the medium is selected from any one of a resin-containing liquid, a transparent resin film sheet, a glass substrate, a chemical fiber, and a woven fabric.
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