Among many nano materials and chemical materials, zinc oxide nanomaterials have attracted researchers’ interest because of their high efficiency, low cost, easy preparation, and variable morphology. The purpose of this study is to explore the fabrication and conductive process of nano ZnO varistors under the simulation of an animation plane form. In this study, the chemical vapor deposition method was used to prepare nano ZnO. Then, ZnO nanomaterials were mixed with deionized water to form a suspension. Under the action of a micromechanical stirrer, impurities were removed by heat treatment, and then different amount of water was added to obtain a nano ZnO electrode. The conductive process and electrochemical properties of the nano ZnO electrode were investigated and analyzed. The results show that the pressure ratio of the varistor increases obviously after adding nano ZnO. In the range of 0–30%, the pressure ratio of the ZnO varistor increases with the increase in nano ZnO content. When
In the rapid development of chemical materials, pressure-sensitive zinc oxide valves are important equipment of zinc oxide thermometers. The properties of nano ZnO varistors mainly depend on the microstructure, material composition, and the function of raw materials. It represents a semiconductor valve plate with nonlinear bolt current intensity and is sensitive to electromotive force change. If the voltage is lower than the specified threshold voltage, the resistance value will rise and the current will hardly flow. However, if this threshold voltage exceeds (rheostat voltage), the resistance will change strongly and the current will immediately increase. Therefore, it is necessary to study the effect of ZnO particle size on the electrical properties of pressure-sensing valve discs.
Nano ZnO has many unique properties of nano materials, such as electrical conductivity, piezoelectricity, gas sensitivity, antibacterial, UV absorption, and scattering. Due to the advantages of nano ZnO, such as light, electricity, magnetism, and sensitivity, it is used in gas sensors, thrusters, semiconductor materials, piezoelectric materials, antibacterial materials, UV shielding materials, thrusters, efficient catalysts, magnetic materials, thin film materials, and conductive materials.
According to the previous solid-state reaction method, Yang prepared ZnO-based varistor ceramics by immobilizing La2O3 and doping Y2O3 differently. He used X-ray diffraction (XRD), scanning electron microscopy (SEM), and direct current tests to study the phase composition, microstructure, and electrical properties of the materials. XRD and SEM analyses showed the Y2O3 phase,
In this study, the crystal structure and characteristics of ZnO are introduced firstly, and then the material, application, and mechanism of nano ZnO pressure-sensing valve discs are explained. This study illustrates the symptoms of planar animation. The preparation methods of six kinds of nano ZnO were summarized in detail. In this study, the calculation of electrochemical performance of nano ZnO pressure-sensing valve discs includes a resistance equation and nonlinear coefficient
Electrical conductivity is one of the important properties of ZnO. At room temperature, the resistivity of ZnO may reach below 0.068 Ω cm. The conductivity of ZnO is closely related to its crystal structure [
Atomic structure of nano ZnO.
Nano ZnO is a white hexagonal crystal or powder, odorless, nontoxic, and delicate. A new type of high-performance micro inorganic material with a particle size of 1–100 nm was prepared. It is also known as zinc oxide. The relative density is 5.606 g/cm3, the refractive index is 2.008∼2.009, and the melting point is 1975°C. It is soluble in acid, sodium hydroxide, and ammonium chloride and insoluble in water, ethanol, and ammonia. It is an amphoteric oxide, which absorbs carbon dioxide and water from the air to form zinc carbonate. It turns yellow when heated and white after cooling. It does not allow ultraviolet light to penetrate and will not turn black when exposed to hydrogen sulfide [
It is used as a voltage regulator in TV receiver, CRT application equipment, lighting equipment, particle accelerator, and TV monitoring [
It is used as an overvoltage protection component in CNC lathe, automobile engine, loader, starter, copier, and telephone.
It is used as an overvoltage protection device in generator magnetization protection equipment and track system flash protection equipment [
The band gap of ZnO is about 3.2 eV. At 27°C, the composite stoichiometric nano ZnO valve plate must have insulation, but due to the existence of inherent defects, it becomes an extra energy space area where the cycle is disturbed. The existence of these extra energy spaces will lead to the formation of aggressive zinc atoms. The activation energy of the attacking zinc atoms is low, most of which are ionized at 27°C. This is one of the reasons for the conductivity of ZnO conductive ceramics at room temperature. If there are no impurity ions, these conductive electrons mainly come from the ionization of interstitial zinc atoms, which presents the atomic electron conduction characteristics of nano ZnO. When metal oxide impurities are introduced into zinc oxide, these metal ions act as donors or acceptors (which is different from the type of zinc oxide that forms solid solution and metal ions) and the conductivity of zinc oxide is greatly different [
The annual power change of varistor zinc oxide valve discs is mainly due to the increase of leakage, the decrease of no-load voltage, and the absolute condition of voltage current function after long DC voltage or large impulse current [
“Plane” refers to surfing without ups and downs, where two connecting lines are on the same plane. In the field of art and design, “planarization” has two sides. On the other hand, “planarization” refers to the material plane of art and design works and the limitation of objective conditions. In other words, the material of the work is medium sized. Designers or artists use a variety of methods to create and express art in space [
In order to obtain a pure planarization effect and abstract the abstract meaning of concrete and objective things, we refine and simplify the visual elements of traditional modeling, such as normal transformation, spatial distance method, and light and shadow change, to create creators in the art process. Because of the integration of aesthetic feelings and objective things, it will bring a peaceful impression to the audience’s psychological level [
In the process of artistic creation, the creators give up the concept of traditional modeling, combine the basic elements such as pure point, line, surface, and color into unreasonable expression, and use bright morphological symbols to explain the spiritual connotation and realize the plane characteristics—very powerful visual effects.
In the process of artistic creation, the creator transforms various forms of expression space and three-dimensional space into plane graphics and color blocks for layout and combination, such as digital, traditional, and so on. The collage combination method can create simple, bright, and unique style of image effects [
Metal compound materials vaporize at a high temperature and then change the particles in the gas phase to obtain the required nano materials. The characteristics of this method are strong controllability and single product. The most important thing is that the quality of the extracted materials is very good, which can be used to observe and test the properties of materials [
In this method, the reagents are distributed into the solution according to a certain proportion at a high temperature and high pressure in a closed container and cooled at room temperature; the crystalline precipitate obtained from the reaction is cleaned and finally dried to obtain the required nano products. The hydrothermal process has the following advantages: simple equipment, simple operation, high uniformity, and high performance. The disadvantage is that the reaction time is long, the experimental process cannot be directly monitored, and the product cannot be controlled.
In this way, the mixed material of ZnO and valve plate materials is heated in a special environment to cause a reduction reaction. The zinc vapor is used as a catalyst to oxidize it into liquid state and then oxidized to solid form to create a solid rosette. In addition, according to the pretreatment of the experimental substrate, ZnO nanomaterials can be prepared by this process without catalysts [
The mechanism of this process is that under the laser irradiation, the target becomes water vapor. The steam is very hot and dense. In the case of transporting the gas, it condenses into nanostructures under the influence of liquid catalyst nanoparticles. Continuous growth in different environments and its growth diameter are limited by catalyst nanoclusters [
These two processes are similar to the hydrothermal process, that is to say, transparent colloidal solution is formed after liquid-phase reaction and nanoparticles are prepared by different treatment processes. Each of these two methods has its own advantages and disadvantages. The nanoparticles prepared by sol-gel method have high uniformity and high-purity particles, but they must undergo long time combustion and synthesis. The monodisperse interface of nanoparticles prepared by the microemulsion method is good [
The principle of this method is to use soluble salt solution NH3-H2O and other substances under certain conditions. After a chemical reaction is formed and precipitated, the extra anions are washed away by precipitation, and finally, the precipitate is heated to obtain zinc oxide.
In the same measuring circuit, Scotty’s contact voltage current ratio remains unchanged regardless of the length of ZnO nanoribbons associated with the circuit [
The current equation of hot electron emission theory is as follows:
Since the limit value of
The experimental formula is expanded, and the change of crystal resistance of nano ZnO materials is combined into a formula:
It can be seen from the formula that the resistance characteristics of nano ZnO do not conform to the classical Ohm’s law. This shows that the resistance of the material varies linearly with the length.
After integration, we can get
Measuring instruments: analytical balance and ordinary balance. Powder mixing unit: QM-ISP04 planetary drilling rig. Drying/heat treatment equipment: electric constant temperature drying oven and KXX-12-16A resistance furnace. Test device: MY-3 KV propeller tester. Microstructure analysis device: JSM-59000LV scanning electron microscope, X-650 scanning electron microscope, X’pertPro X-ray diffractometer, and V4150 electron spectrometer.
This is the main raw material accounting for more than 90% of all raw materials. In addition to using high-purity raw materials as much as possible, the qualified standards for the composition, shape, particle size, processing temperature, and bulk density of zinc oxide raw materials must be formulated. Zinc oxide powder was purchased for this study.
There are many kinds of additives (5–8) and are of a small amount (less than 5 mol in total), which are the basis of excellent electrical performance of zinc oxide pressure-sensing valve discs.
Table
Material composition.
Number | Component% | ||||||
---|---|---|---|---|---|---|---|
Bi2O3 | Sb2O3 | Cr2O3 | Co2O3 | MnO2 | ZnO | Nd2O3/CeO2/La2O3 | |
1 | 0.7 | 1.0 | 0.5 | 0.8 | 0.5 | Allowance | 0 |
2 | 0.7 | 1.0 | 0.5 | 0.8 | 0.5 | Allowance | 0.02 |
3 | 0.7 | 1.0 | 0.5 | 0.8 | 0.5 | Allowance | 0.04 |
4 | 0.7 | 1.0 | 0.5 | 0.8 | 0.5 | Allowance | 0.06 |
5 | 0.7 | 1.0 | 0.5 | 0.8 | 0.5 | Allowance | 0.08 |
6 | 0.7 | 1.0 | 0.5 | 0.8 | 0.5 | Allowance | 0.1 |
The varistor voltage
The nano ZnO bubbles are fused with ionic water to form a mixture, which is stirred at a uniform speed under the function of the instrument to disperse the mixture evenly. Then zinc oxide was evenly distributed on the surface of ITO by spray equipment, and ITO was removed after cooling the heating plate.
The specific electrode design process is as follows: The suspension was obtained by placing a 0.02 g ZnO nano electrode in 20 mL ionic water. Place six pieces of clean ITO on the heating plate under the spraying device and seal both sides of ITO glass with a transparent tape. The reason is that nano ZnO will not cover the whole ITO surface, and the content of nano ZnO will increase during the electrochemical test. After the heating plate is heated to 100°C, the distance between the spray gun and the spray gun is connected to 15 cm. Spray air provides spray power, inserts zinc oxide into the center of the container, and sprays the spray suspension in a mist form. After the ITO is cooled, heat treatment at 450°C for one hour to remove impurities, and drop solutions with different contents to obtain nano zinc oxide materials/ ITO electrode are performed.
The repeatability of DPV was measured by using a 40
Repeatability and stability of graphene/ZnO nanomaterials/ITO electrodes.
From Figure
The sintering temperature is 1150. Table
Conductivity of samples with different holding time.
Holding time (hours) | 1 mA varistor gradient (V/mm) | U1 mA/U0.1 mA |
---|---|---|
2 | 446.27 | 1.224 |
2.5 | 375.96 | 1.089 |
3 | 332.16 | 1.157 |
3.5 | 309.45 | 1.201 |
4 | 262.87 | 1.297 |
The sintering temperature is 1150. The variation of the electrical properties of the ZnO varistor valve piece with 1 mA varistor potential gradient and pressure ratio (U1 mA/U0.1 mA) with insulation pairs is shown. Figure
Effect of holding time on voltage gradient and voltage ratio of ZnO varistors.
It can be seen from Figure
In the process of preparation, temperature is the main stage. The components of this stage of material will undergo sufficient physical and chemical changes, so as to obtain compact sintered body without raw or over burning. Prolonged holding time can make the reaction between additives and between additives and zinc oxide complete, and the homogeneity of each phase is good, which is conducive to the recrystallization of the liquid phase and can promote the grain growth, so the varistor potential gradient decreases. In addition, with the increase in holding time, the grain distribution is more uniform and the ceramic structure is more compact, so the nonlinear coefficient increases and the pressure ratio decreases. However, if the holding time is too long, the volatilization of Bi203 in raw materials will be intensified, which will affect the quality of grain boundary layers. As a result, porosity increases, bulk density decreases, resistivity decreases, and nonlinear coefficient and other electrical properties deteriorate.
When nano ZnO is added into the varistor, the varistor voltage increases significantly. In the range of 0 to 30%, with the increase of nano ZnO, the influence voltage of pressure-sensitive ZnO varistors increases. When
A 3D image of the ZnO nanobelt obtained through a scanning microscope shows that it is 30 microns wide and 1.5 microns thick and the surface of the sample is very smooth. The physical contact between the surface of ZnO nanoribbons and the platinum-plated conductive probe was established using atomic force microscope (AFM) contact mode. Thus, a closed circuit was formed to measure the current voltage curve. One of the characteristics of AFM is that it can select the contact position with ZnO nanobelts, so that a constant force can be maintained in the measurement to reduce the system error. When one end of the circuit is grounded, the voltage applied to the ZnO nanoribbon is negative. The type of thermoelectric elements is defined, the temperature is set at room temperature, and the isotropic and anisotropic characteristics of zinc oxide are simulated using software. Figure
Planar form of conducting process of nano ZnO valve sheet.
It can be seen from Figure
TEM and XRD spectra of conductive ZnO powder heat treated at 500°C for 1.5 h in H2 atmosphere were studied. The distribution of ZnO particles is spherical, the particle size is relatively uniform, and the particle size is between 30 nm and 40 nm. There is a certain degree of agglomeration between the particles, which is consistent with the SEM observation. It can be seen from the XRD spectra that the sample is a single hexagonal system. When the spectrum is locally enlarged, the diffraction peaks of doping m3+ can be found at the places of 2e 59.3470 and 65.2390, but the intensity is very weak, which indicates that the dissolution amount of ZnAl204 is very small. The average particle size calculated from the half peak width of the formula is about 36 nm, which is also roughly consistent with the observation of TEM photos, indicating that each particle is basically composed of single crystal. As shown in Figure
XRD spectrum of conductive ZnO powder.
It can be seen from Figure
When nano ZnO is added to the valve disc with high sensitivity, the voltage of the varistor will increase greatly. In the range of up to 30 wt%, the varistor voltage of the ZnO pressure-sensitive valve disc increases greatly with the increase in nano ZnO content. When adding 0–30% nano ZnO into the induction valve, the pressure ratio increases with the increase in nano ZnO content; within 10%, with the increase in nano ZnO dosage, the leakage current of the varistor zinc oxide valve plate decreases; in the range of 10% to 30%, with the increase in nano ZnO content, the leakage current increases; because nano ZnO is added to the pressure valve plate, ZnO particle size is reduced.
When the sintering temperature is 1150°C, the pressure gradient of the varistor ZnO valve disc is larger and the pressure ratio is the smallest. The best sintering temperature is 50°C. When the constant temperature state is 2.5 hours, the induced voltage potential of the material is the highest and the voltage ratio is the smallest, so two 2.5 hours is the best constant temperature state. The potential radius of the varistor zinc oxide valve plate increases sharply and the leakage current decreases with the addition of diluted upper oxide Nd2O3 CeO2 La2O3. In principle, the pressure ratio does not change but slightly decreases.
In this study, an experimental device was installed to measure the voltammetric characteristics of ZnO nanobelts. The results show that there is a specific ratio between the resistance of the chemical bond and the material length and nonlinearity. The change in the conductivity of ZnO nanomaterials was analyzed by a finite element method. Under isotropic conditions, the current density distribution of nano ZnO varistors is very uniform. Under the anisotropic condition, the current density is mostly distributed on the surface of nano ZnO varistors. Nano zinc/ITO electrodes have good electrochemical performance. The sensitivity of the electrode to LD is 0.32
No data were used in the study.
The authors declare that they have no conflicts of interest.
This work was supported by the 2018 Gansu Provincial Science and Technology Plan Project “Research and Creation of Western Type Film and Television Brands in the Context of the Belt and Road Initiative,” project number: 18CX1ZA011, and the 2017 Lanzhou Jiaotong University School-Level Youth Project “Building a Multi-Ethnic Dunhuang Silk Road under the Belt and Road” Strategy Featured Film and Television Brands, project number: 2017023.