Disclosure of Invention
The invention aims to provide a method for preparing a cesium tungsten bronze material under normal pressure, which is used for preparing the cesium tungsten bronze material within 1 hour by taking tungsten hexachloride as a tungsten source and cesium hydroxide as a cesium source at 40-78 ℃ under normal pressure for the first time.
The invention also provides a cesium tungsten bronze material prepared by the method.
In order to achieve an object of the invention, the invention adopts the following technical scheme:
a method for preparing a cesium tungsten bronze material under normal pressure comprises the following steps:
dissolving tungsten hexachloride and cesium hydroxide in ethanol at normal pressure and 40-78 ℃, uniformly mixing, and adding acetic acid to obtain a reaction solution; stirring and reacting for 10-30min, centrifuging, washing, precipitating and drying to obtain the cesium tungsten bronze material.
In a specific implementation process, the preparation process of the reaction solution comprises the following steps:
dissolving tungsten hexachloride in ethanol at 40-78 deg.C under normal pressure, stirring to obtain yellow solution, stirring for 2-10min, adding cesium hydroxide, stirring for 2-5min, adding acetic acid, and stirring to obtain reaction solution.
The purity of tungsten hexachloride used in the present invention was 99%, the purity of cesium hydroxide was 99.9%, and the cesium tungsten bronze material prepared was a deep blue powder.
Preferably, the concentration of the tungsten hexachloride in the reaction liquid is 2-15mg/mL; the concentration of the cesium hydroxide is 0.7-2.5mg/mL.
Preferably, the volume ratio of ethanol to acetic acid in the reaction solution is 4:1-12.
Preferably, the purity of the ethanol is analytically pure and the purity of the acetic acid is analytically pure.
Preferably, the centrifugal washing comprises an alcohol washing and a water washing process. The water used was ultrapure water having a resistivity of 18.2 M.OMEGA.cm.
Preferably, the drying is in air at 30-50 ℃ for 24h.
It should be noted that the preparation process of the cesium tungsten bronze material provided by the invention is carried out under normal pressure, the whole reaction and drying temperature does not exceed 80 ℃, and the whole preparation process can be completed within 1h, compared with the reaction temperature of 800 ℃ in the traditional high-temperature reduction method and the reaction time of dozens of hours at 200 ℃ in the hydrothermal method, the reaction temperature is reduced, the reaction time is greatly shortened, the reaction conditions are greatly simplified, the production efficiency is improved, and the resources are saved.
In order to realize the second purpose of the invention, the following technical scheme is adopted:
the cesium tungsten bronze material prepared by the preparation method.
Preferably, the cesium tungsten bronze material is a nanoparticle aggregate of 10-20 nm.
Preferably, the cesium tungsten bronze material has a light transmittance of near infrared light of 10% in the range of 1100-2000 nm.
The cesium tungsten bronze material prepared by the method has good infrared ray absorption performance, the light transmittance of near infrared light is rapidly reduced to 10% from 18% in the wavelength range of 800-1100nm, and the light transmittance of near infrared light is basically maintained at 10% in the wavelength range of 1100-2000 nm.
The invention has the following beneficial effects:
the invention provides a preparation method of a cesium tungsten bronze material, which takes tungsten hexachloride as a tungsten source, cesium hydroxide as a cesium source, ethanol as a solvent and acetic acid as a reactant and can be completed within 1 hour under the conditions of normal pressure and the temperature lower than 80 ℃. The preparation equipment is simple, the operation is simple, the preparation time is short, and the method can be applied to large-scale production.
In addition, the cesium tungsten bronze material prepared by the preparation method provided by the invention has good infrared ray absorption performance, the light transmittance of near infrared light is rapidly reduced from 18% to 10% in the wavelength range of 800-1100nm, and the light transmittance of near infrared light is basically maintained at 10% in the wavelength range of 1100-2000 nm.
Detailed Description
In order to more clearly illustrate the invention, the invention is further described below with reference to preferred embodiments and the accompanying drawings. It is to be understood by persons skilled in the art that the following detailed description is illustrative and not restrictive, and is not to be taken as limiting the scope of the invention.
In the present invention, the preparation methods are all conventional methods unless otherwise specified. The starting materials used are available from published commercial sources unless otherwise specified, and the percentages are by mass unless otherwise specified.
Example 1
Weighing 0.2-0.4 g of tungsten hexachloride, dissolving the tungsten hexachloride in 40-60 mL of ethanol, stirring for 2-10min under the condition of constant-temperature water bath at 40 ℃, weighing 0.05-0.07 g of cesium hydroxide, dissolving the cesium hydroxide in the solution, and continuously stirring for 2-5 min. And measuring 5mL of acetic acid, quickly adding the acetic acid into the reaction solution, continuously stirring for 20min, centrifuging, washing and drying to obtain the dark blue cesium tungsten bronze material. Taking a proper amount of powder sample for XRD detection. The obtained spectrum is basically consistent with a standard spectrum (JCPDS 83-1334). And re-dispersing a small amount of dried sample in pure water (with the resistivity of 18.2M omega cm), spotting on a silicon wafer for scanning electron microscope observation, and observing by using a scanning electron microscope to obtain a sample formed by aggregating nano particles with the particle size of 10-20 nm. The energy spectrum (EDS) proves that the material contains cesium, tungsten and oxygen components. And (3) taking a proper amount of powder sample to perform ultraviolet visible near infrared spectrum test, and under an integrating sphere mode, measuring that the light transmittance of near infrared light of the sample is below 18% at the wavelength of 800-1100nm, and the light transmittance of the near infrared light is basically maintained at 10% at the wavelength of 1100-2000 nm.
Example 2
Weighing 0.2-0.4 g of tungsten hexachloride, dissolving the tungsten hexachloride in 40-60 mL of ethanol, stirring for 2-10min under the condition of a constant-temperature water bath at 60 ℃, weighing 0.05-0.07 g of cesium hydroxide, dissolving the cesium hydroxide in the solution, and continuously stirring for 2-5 min. 10mL of acetic acid is measured and quickly added into the reaction solution, and after the stirring is continued for 10min, the mixture is centrifugally washed and dried to obtain the dark blue cesium tungsten bronze material. Taking a proper amount of powder sample for XRD detection, obtaining a spectrogram as shown in figure 1, and showing that the spectrogram is basically consistent with a standard spectrogram (JCPDS 83-1334). And re-dispersing a small amount of dried sample in pure water (with the resistivity of 18.2M omega cm), spotting on a silicon wafer for scanning electron microscope observation, and observing by using a scanning electron microscope to obtain a sample formed by aggregating nano particles with the particle size of 10-20 nm. The energy spectrum (EDS) proves that the material contains cesium, tungsten and oxygen components. And (3) taking a proper amount of powder sample to perform ultraviolet visible near infrared spectrum test, and under an integrating sphere mode, measuring that the light transmittance of near infrared light of the sample is below 18% at the wavelength of 800-1100nm, and the light transmittance of the near infrared light is basically maintained at 10% at the wavelength of 1100-2000 nm.
Example 3
Weighing 0.4-0.6 g of tungsten hexachloride, dissolving the tungsten hexachloride in 40-60 mL of ethanol, stirring for 2-10min under the condition of a constant-temperature water bath at 50 ℃, weighing 0.07-0.09 g of cesium hydroxide, dissolving the cesium hydroxide in the solution, and continuously stirring for 2-5 min. And measuring 5mL of acetic acid, quickly adding the acetic acid into the reaction solution, continuously stirring for 10min, centrifuging, washing and drying to obtain the dark blue cesium tungsten bronze material. Taking a proper amount of powder sample for XRD detection. The obtained spectrum is substantially consistent with a standard spectrum (JCPDS 83-1334). And re-dispersing a small amount of dried sample in pure water (with the resistivity of 18.2M omega cm), spotting on a silicon wafer for scanning electron microscope observation, and observing by using a scanning electron microscope to obtain a sample formed by aggregating nano particles with the particle size of 10-20 nm. The energy spectrum (EDS) proves that the material contains cesium, tungsten and oxygen components. And (3) taking a proper amount of powder sample to carry out ultraviolet visible near infrared spectrum test, wherein the light transmittance of the near infrared light of the tested sample is below 18% at the wavelength of 800-1100nm and is basically maintained at 10% at the wavelength of 1100-2000nm in an integrating sphere mode.
Example 4
Weighing 0.4-0.6 g of tungsten hexachloride, dissolving the tungsten hexachloride in 60-80 mL of ethanol, stirring for 2-10min under the condition of a constant-temperature water bath at 50 ℃, weighing 0.07-0.09 g of cesium hydroxide, dissolving the cesium hydroxide in the solution, and continuously stirring for 2-5 min. 10mL of acetic acid is measured and quickly added into the reaction solution, and after the stirring is continued for 20min, the mixture is centrifugally washed and dried to obtain a dark blue cesium tungsten bronze material. Taking a proper amount of powder sample for XRD detection. The obtained spectrum is substantially consistent with a standard spectrum (JCPDS 83-1334). And re-dispersing a small amount of dried sample in pure water (with the resistivity of 18.2M omega cm), spotting on a silicon wafer for scanning electron microscope observation, and observing by using a scanning electron microscope to obtain a sample formed by aggregating nano particles with the particle size of 10-20 nm. The energy spectrum (EDS) proves that the material contains cesium, tungsten and oxygen components. And (3) taking a proper amount of powder sample to carry out ultraviolet visible near infrared spectrum test, wherein in an integrating sphere mode, the light transmittance of the near infrared light of the tested sample is rapidly reduced from 18% to 10% at the wavelength of 800-1100nm, and the light transmittance of the near infrared light is basically maintained at 10% at the wavelength of 1100-2000 nm.
Example 5
Weighing 0.4-0.6 g of tungsten hexachloride, dissolving the tungsten hexachloride in 60-80 mL of ethanol, stirring for 2-10min under the condition of a constant-temperature water bath at 60 ℃, weighing 0.09-0.12 g of cesium hydroxide, dissolving the cesium hydroxide in the solution, and continuously stirring for 2-5 min. And measuring 10mL of acetic acid, quickly adding the acetic acid into the reaction solution, continuously stirring for 10min, centrifuging, washing and drying to obtain the dark blue cesium tungsten bronze material. Taking a proper amount of powder sample for XRD detection. The obtained spectrum is basically consistent with a standard spectrum (JCPDS 83-1334). Another small amount of dried sample is re-dispersed in pure water (resistivity 18.2M Ω · cm), and spotted on a silicon wafer for scanning electron microscope observation, and then the sample is observed by a scanning electron microscope, and the obtained sample is formed by aggregating nano particles with the particle size of 10-20nm, as shown in fig. 2. As shown in fig. 3, the material was confirmed to contain cesium, tungsten, and oxygen components by energy spectroscopy (EDS). And (3) taking a proper amount of powder sample to carry out ultraviolet visible near infrared spectrum test, wherein in an integrating sphere mode, the light transmittance of the near infrared light of the tested sample is rapidly reduced from 18% to 10% at the wavelength of 800-1100nm, and the light transmittance of the near infrared light is basically maintained at 10% at the wavelength of 1100-2000 nm.
Example 6
Weighing 0.4-0.6 g of tungsten hexachloride, dissolving the tungsten hexachloride in 80-100 mL of ethanol, stirring for 2-10min under the condition of a constant-temperature water bath at 60 ℃, weighing 0.12-0.15 g of cesium hydroxide, dissolving the cesium hydroxide in the solution, and continuously stirring for 2-5 min. 10mL of acetic acid is measured and quickly added into the reaction solution, and after the stirring is continued for 20min, the mixture is centrifugally washed and dried to obtain a dark blue cesium tungsten bronze material. Taking a proper amount of powder sample for XRD detection. The obtained spectrum is substantially consistent with a standard spectrum (JCPDS 83-1334). And re-dispersing a small amount of dried sample in pure water (with the resistivity of 18.2M omega cm), spotting on a silicon wafer for scanning electron microscope observation, and observing by using a scanning electron microscope to obtain a sample formed by aggregating nano particles with the particle size of 10-20 nm. The energy spectrum (EDS) proves that the material contains cesium, tungsten and oxygen components. A proper amount of powder samples are taken to carry out ultraviolet visible near infrared spectrum test, under the mode of an integrating sphere, the light transmittance of near infrared light of the tested samples is rapidly reduced from 18 percent to 10 percent when the wavelength is 800-1100nm, and the light transmittance of the near infrared light is basically maintained at 10 percent when the wavelength is 1100-2000nm, as shown in figure 4.
Example 7
Weighing 0.4-0.6 g of tungsten hexachloride, dissolving the tungsten hexachloride in 80-100 mL of ethanol, stirring for 2-10min under the condition of a constant-temperature water bath at 78 ℃, weighing 0.12-0.15 g of cesium hydroxide, dissolving the cesium hydroxide in the solution, and continuously stirring for 2-5 min. 10mL of acetic acid is measured and quickly added into the reaction solution, and after the stirring is continued for 20min, the mixture is centrifugally washed and dried to obtain a dark blue cesium tungsten bronze material. Taking a proper amount of powder sample for XRD detection. The obtained spectrum is substantially consistent with a standard spectrum (JCPDS 83-1334). And re-dispersing a small amount of dried sample in pure water (with the resistivity of 18.2M omega cm), spotting on a silicon wafer for scanning electron microscope observation, and observing by using a scanning electron microscope to obtain a sample formed by aggregating nano particles with the particle size of 10-20 nm. The energy spectrum (EDS) proves that the material contains cesium, tungsten and oxygen components. And (3) taking a proper amount of powder sample to carry out ultraviolet visible near infrared spectrum test, wherein in an integrating sphere mode, the light transmittance of the near infrared light of the tested sample is rapidly reduced from 18% to 10% at the wavelength of 800-1100nm, and the light transmittance of the near infrared light is basically maintained at 10% at the wavelength of 1100-2000 nm.
Example 8
Weighing 0.6-0.8 g of tungsten hexachloride, dissolving the tungsten hexachloride in 60-80 mL of ethanol, stirring for 2-10min under the condition of a constant-temperature water bath at 50 ℃, weighing 0.07-0.09 g of cesium hydroxide, dissolving the cesium hydroxide in the solution, and continuously stirring for 2-5 min. Measuring 15mL of acetic acid, quickly adding the acetic acid into the reaction solution, continuously stirring for 30min, centrifuging, washing and drying to obtain the dark blue cesium tungsten bronze material. Taking a proper amount of powder sample for XRD detection. The obtained spectrum is substantially consistent with a standard spectrum (JCPDS 83-1334). And dispersing a small amount of dried sample in pure water again (the resistivity is 18.2M omega cm), spotting on a silicon wafer for scanning electron microscope observation, and observing by using a scanning electron microscope to obtain the sample which is formed by aggregating nano particles with the particle size of 10-20 nm. The energy spectrum (EDS) proves that the material contains cesium, tungsten and oxygen components. And (3) taking a proper amount of powder sample to carry out ultraviolet visible near infrared spectrum test, wherein in an integrating sphere mode, the light transmittance of the near infrared light of the tested sample is rapidly reduced from 18% to 10% at the wavelength of 800-1100nm, and the light transmittance of the near infrared light is basically maintained at 10% at the wavelength of 1100-2000 nm.
Example 9
Weighing 0.6-0.8 g of tungsten hexachloride, dissolving the tungsten hexachloride in 60-80 mL of ethanol, stirring for 2-10min under the condition of a constant-temperature water bath at 50 ℃, weighing 0.12-0.15 g of cesium hydroxide, dissolving the cesium hydroxide in the solution, and continuously stirring for 2-5 min. And measuring 10mL of acetic acid, quickly adding the acetic acid into the reaction solution, continuously stirring for 20min, centrifuging, washing and drying to obtain the dark blue cesium tungsten bronze material. Taking a proper amount of powder sample for XRD detection. The obtained spectrum is substantially consistent with a standard spectrum (JCPDS 83-1334). And re-dispersing a small amount of dried sample in pure water (with the resistivity of 18.2M omega cm), spotting on a silicon wafer for scanning electron microscope observation, and observing by using a scanning electron microscope to obtain a sample formed by aggregating nano particles with the particle size of 10-20 nm. The energy spectrum (EDS) proves that the material contains cesium, tungsten and oxygen components. And (3) taking a proper amount of powder sample to carry out ultraviolet visible near infrared spectrum test, wherein in an integrating sphere mode, the light transmittance of the near infrared light of the tested sample is rapidly reduced from 18% to 10% at the wavelength of 800-1100nm, and the light transmittance of the near infrared light is basically maintained at 10% at the wavelength of 1100-2000 nm.
Example 10
Weighing 0.8-1.0 g of tungsten hexachloride, dissolving the tungsten hexachloride in 60-80 mL of ethanol, stirring for 2-10min under the condition of a constant-temperature water bath at 60 ℃, weighing 0.12-0.15 g of cesium hydroxide, dissolving the cesium hydroxide in the solution, and continuously stirring for 2-5 min. Measuring 15mL of acetic acid, quickly adding the acetic acid into the reaction solution, continuously stirring for 30min, centrifuging, washing and drying to obtain the dark blue cesium tungsten bronze material. Taking a proper amount of powder sample for XRD detection. The obtained spectrum is substantially consistent with a standard spectrum (JCPDS 83-1334). And re-dispersing a small amount of dried sample in pure water (with the resistivity of 18.2M omega cm), spotting on a silicon wafer for scanning electron microscope observation, and observing by using a scanning electron microscope to obtain a sample formed by aggregating nano particles with the particle size of 10-20 nm. The energy spectrum (EDS) proves that the material contains cesium, tungsten and oxygen components. And (3) taking a proper amount of powder sample to carry out ultraviolet visible near infrared spectrum test, wherein in an integrating sphere mode, the light transmittance of the near infrared light of the tested sample is rapidly reduced from 18% to 10% at the wavelength of 800-1100nm, and the light transmittance of the near infrared light is basically maintained at 10% at the wavelength of 1100-2000 nm.
Example 11
Weighing 0.8-1.0 g of tungsten hexachloride, dissolving the tungsten hexachloride in 60-80 mL of ethanol, stirring for 2-10min under the condition of a constant-temperature water bath at 78 ℃, weighing 0.12-0.15 g of cesium hydroxide, dissolving the cesium hydroxide in the solution, and continuously stirring for 2-5 min. Measuring 15mL of acetic acid, quickly adding the acetic acid into the reaction solution, continuously stirring for 30min, centrifuging, washing and drying to obtain the dark blue cesium tungsten bronze material. Taking a proper amount of powder sample for XRD detection. The obtained spectrum is substantially consistent with a standard spectrum (JCPDS 83-1334). And re-dispersing a small amount of dried sample in pure water (with the resistivity of 18.2M omega cm), spotting on a silicon wafer for scanning electron microscope observation, and observing by using a scanning electron microscope to obtain a sample formed by aggregating nano particles with the particle size of 10-20 nm. The energy spectrum (EDS) proves that the material contains cesium, tungsten and oxygen components. And (3) taking a proper amount of powder sample to carry out ultraviolet visible near infrared spectrum test, wherein in an integrating sphere mode, the light transmittance of the near infrared light of the tested sample is rapidly reduced from 18% to 10% at the wavelength of 800-1100nm, and the light transmittance of the near infrared light is basically maintained at 10% at the wavelength of 1100-2000 nm.
Example 12
Weighing 0.8-1.0 g of tungsten hexachloride, dissolving the tungsten hexachloride in 80-100 mL of ethanol, stirring for 2-10min under the condition of a constant-temperature water bath at 70 ℃, weighing 0.12-0.15 g of cesium hydroxide, dissolving the cesium hydroxide in the solution, and continuously stirring for 2-5 min. 10mL of acetic acid is measured and quickly added into the reaction solution, and after the stirring is continued for 20min, the mixture is centrifugally washed and dried to obtain a dark blue cesium tungsten bronze material. Taking a proper amount of powder sample for XRD detection. The obtained spectrum is basically consistent with a standard spectrum (JCPDS 83-1334). And re-dispersing a small amount of dried sample in pure water (with the resistivity of 18.2M omega cm), spotting on a silicon wafer for scanning electron microscope observation, and observing by using a scanning electron microscope to obtain a sample formed by aggregating nano particles with the particle size of 10-20 nm. The energy spectrum (EDS) proves that the material contains cesium, tungsten and oxygen components. And (3) taking a proper amount of powder sample to carry out ultraviolet visible near infrared spectrum test, wherein in an integrating sphere mode, the light transmittance of the near infrared light of the tested sample is rapidly reduced from 18% to 10% at the wavelength of 800-1100nm, and the light transmittance of the near infrared light is basically maintained at 10% at the wavelength of 1100-2000 nm.
Example 13
Weighing 0.8-1.0 g of tungsten hexachloride, dissolving the tungsten hexachloride in 80-100 mL of ethanol, stirring for 2-10min under the condition of a constant-temperature water bath at 60 ℃, weighing 0.09-0.12 g of cesium hydroxide, dissolving the cesium hydroxide in the solution, and continuously stirring for 2-5 min. Measuring 15mL of acetic acid, quickly adding the acetic acid into the reaction solution, continuously stirring for 30min, centrifuging, washing and drying to obtain the dark blue cesium tungsten bronze material. Taking a proper amount of powder sample for XRD detection. The obtained spectrum is substantially consistent with a standard spectrum (JCPDS 83-1334). And re-dispersing a small amount of dried sample in pure water (with the resistivity of 18.2M omega cm), spotting on a silicon wafer for scanning electron microscope observation, and observing by using a scanning electron microscope to obtain a sample formed by aggregating nano particles with the particle size of 10-20 nm. The energy spectrum (EDS) proves that the material contains cesium, tungsten and oxygen components. And (3) taking a proper amount of powder sample to carry out ultraviolet visible near infrared spectrum test, wherein in an integrating sphere mode, the light transmittance of the near infrared light of the tested sample is rapidly reduced from 18% to 10% at the wavelength of 800-1100nm, and the light transmittance of the near infrared light is basically maintained at 10% at the wavelength of 1100-2000 nm.
Example 14
Weighing 0.8-1.0 g of tungsten hexachloride, dissolving the tungsten hexachloride in 80-100 mL of ethanol, stirring for 2-10min under the condition of a constant-temperature water bath at 70 ℃, weighing 0.12-0.15 g of cesium hydroxide, dissolving the cesium hydroxide in the solution, and continuously stirring for 2-5 min. Measuring 15mL of acetic acid, quickly adding the acetic acid into the reaction solution, continuously stirring for 20min, centrifuging, washing and drying to obtain the dark blue cesium tungsten bronze material. Taking a proper amount of powder sample for XRD detection. The obtained spectrum is substantially consistent with a standard spectrum (JCPDS 83-1334). And re-dispersing a small amount of dried sample in pure water (with the resistivity of 18.2M omega cm), spotting on a silicon wafer for scanning electron microscope observation, and observing by using a scanning electron microscope to obtain a sample formed by aggregating nano particles with the particle size of 10-20 nm. The energy spectrum (EDS) proves that the material contains cesium, tungsten and oxygen components. And (3) taking a proper amount of powder sample to carry out ultraviolet visible near infrared spectrum test, wherein in an integrating sphere mode, the light transmittance of the near infrared light of the tested sample is rapidly reduced from 18% to 10% at the wavelength of 800-1100nm, and the light transmittance of the near infrared light is basically maintained at 10% at the wavelength of 1100-2000 nm.
Example 15
Weighing 0.8-1.0 g of tungsten hexachloride, dissolving the tungsten hexachloride in 80-100 mL of ethanol, stirring for 2-10min under the condition of a constant-temperature water bath at 78 ℃, weighing 0.12-0.15 g of cesium hydroxide, dissolving the cesium hydroxide in the solution, and continuously stirring for 2-5 min. 10mL of acetic acid is measured and quickly added into the reaction solution, and after the stirring is continued for 20min, the mixture is centrifugally washed and dried to obtain a dark blue cesium tungsten bronze material. Taking a proper amount of powder sample for XRD detection. The obtained spectrum is substantially consistent with a standard spectrum (JCPDS 83-1334). And re-dispersing a small amount of dried sample in pure water (with the resistivity of 18.2M omega cm), spotting on a silicon wafer for scanning electron microscope observation, and observing by using a scanning electron microscope to obtain a sample formed by aggregating nano particles with the particle size of 10-20 nm. The energy spectrum (EDS) proves that the material contains cesium, tungsten and oxygen components. And (3) taking a proper amount of powder sample to carry out ultraviolet visible near infrared spectrum test, wherein in an integrating sphere mode, the light transmittance of the near infrared light of the tested sample is rapidly reduced from 18% to 10% at the wavelength of 800-1100nm, and the light transmittance of the near infrared light is basically maintained at 10% at the wavelength of 1100-2000 nm.
It should be understood that the above-mentioned embodiments of the present invention are only examples for clearly illustrating the present invention, and are not intended to limit the embodiments of the present invention, and it will be obvious to those skilled in the art that other variations or modifications may be made on the basis of the above description, and all embodiments may not be exhaustive, and all obvious variations or modifications belonging to the technical solutions of the present invention are within the scope of the present invention.