Currently, various electronic instruments, home audio and video equipment and microcomputer, etc., in order to prevent the equipment from the external power supply cord, transmission of noise and signal lines or air surge voltage, as well as the human body electrostatic factors lead to wrong operation or semiconductor devices are broken down, is the use of ZnO varistor for protection.
However ZnO varistor is purely resistive element, although has good pressure sensitive features, but because of the small dielectric constant, dielectric loss, high frequency noise absorption and the steep pulse surge response speed slow, limiting its development and application, makes the improvement of the reliability of the instruments are affected.
After 1983 YalIllaoka _7 】 【 in reducing atmosphere, etc Complete donor doping nanometer strontium titanate is a semiconducting ceramics, on its surface coated with Na and Na: o pulp and secondary processing in oxidizing atmosphere, the nanometer strontium titanate with pressure sensitive properties of ceramic grain boundary layer capacitor, it not only has excellent dielectric property and significant nonlinear volt-ampere characteristics, but also absorbs 1000 ~ ~ 3000 cm2 such high surge capability, so the material with large capacity and the function of the pressure sensitive resistor capacitor.
In the field of low voltage work, ZnO pressure sensitive resistor can be replaced, and various electrical functions can overcome the deficiency of ZnO pressure sensitive resistance. So people call this pressure sensitive resistor srTi03 multi-functional ceramics (MFC). This new component has a capacitor-capacitor function with a large capacity under low voltage (the capacitance is greater than 0. After the voltage is above some critical value, the function of the pressure-sensitive resistor (the non-linear coefficient of the voltage is greater than 15, the surge current can reach l 800 ~ cm2).
- 5 thermosensitive element Currently used the most positive temperature coefficient (PTC) thermal element is (srBa) Ti03 thermal element, the PTC effect is directly related to ferroelectricity, resistivity correspond to the Curie temperature of mutations. In order to meet different USES, PTC materials and components are required to have different Curie temperatures: for example, the temperature of Curie is about 50 when the color – colored erector is used. C, the PTC of physiotherapy equipment requires Curie temperature of 35 to 60. C high temperature heating body requires Curie temperature in 300-400. C.
The nano-titanate strontium is used as the peaking agent, which can reduce the temperature of the residence of PTC ceramics . In addition. (Pb) ‘s r Ti03 system heat sensitive materials with negative temperature coefficient (NTc) and positive temperature coefficient (PTC) characteristics, as to prevent the surge current components, over-voltage automatic protection and temperature detection and control, etc have broad application prospects. State 2. The oxygen vacancy in the crystal lattice of the 6 oxygen sensitive material l state is in the lattice of materials. When the atmosphere concentration changes, the oxygen vacancy also changes, resulting in the change of the material resistance, which can be used as an oxygen sensitive material. The semiconductor oxygen sensor has been widely used in combustion management, environmental protection, safety and explosion-proof, metallurgy, food industry and gas separation.
Oxide semiconductor oxygen sensor spirit for a short oxygen sensitive response when asked, high sensitivity, small volume, simple structure, does not need to reference the advantages of oxygen electrode, nurtures the hope instead of semiconductor oxygen concentration cell type 2. 7 sites humidity-sensitive material 1 doping elements (such as Sr, K, etc.) after nanometer strontium titanate, will absorb the water in the surrounding atmosphere, make the electronic conductivity and dielectric constant to improve, so that the conductivity increased. So nano titanate sawing materials can be used as humidity sensitive materials to control the humidity around electronic devices. In these application fields, strontium titanate powders are prepared first, then the powder is applied directly as materials, or as raw materials to further process the components. Therefore, the preparation of strontium titanate ultrafine powders is a prerequisite for the application of strontium titanate functional materials and directly affects the properties of materials.
Three existing ultrafine strontium titanate powder preparation technology and the existing problems of traditional strontium titanate preparation methods for high temperature solid instead should method, with the development of the related industries, the performance of the powder requirements to higher and higher, the uniformity of particles must be strictly controlled, such as purity, particle size and the stoichiometric ratio. The traditional method for the preparation of strontium titanate powders prepared by the legal system is not sufficient to meet the above requirements, and a lot of chemical liquid phase powder preparation methods have been developed.
Wanfang data process engineering journal 3. 1 high temperature solid instead should method [J high temperature solid instead should method is a traditional method of preparation of strontium titanate powder, usually within the S (or SrC03) and Ti02 powder in a ball mill machine mixing, pelleting, high temperature (1000. C above) calcined in a few hours to a few hours, and then through the ground at the end of the line to the strontium titanate powder. The law generally need to be done at high temperatures, can appear, which wastes energy and particle growth, is not conducive to forming superfine powders.
In addition, the following problems are also present: (a) the solid reaction should be carried out on the particle interface, often with incomplete reaction and uneven composition; (b) solid phase doping is difficult to mix uniformly, especially trace doping (O. It is impossible to achieve full mixing uniformity when it is 1% ~ 1%. 3. 2 Sol Gel method (Sol – Gel) 【 l deputy Sol Gel method refers to metal organic or inorganic compounds by a Sol Gel solution is dry, then through calcination methods of oxide (or heat treatment). A Sol Gel method materials including metal alkoxide, acetate, acetyl acetone, nitrate, chloride salt, etc.; the metal alkoxide, easy to use with distilling and recrystallization technology, soluble in ordinary organic solvents, easy hydrolysis characteristics, it is widely used in of powder prepared by Sol – Gel;
The disadvantage is that the metal alcohol salt is expensive, and the commonly used solvent is poisonous. Currently, this method is used for industrial production of alumina, cobalt oxide and other powder systems. It is still in the research and exploration stage to use sol-gel method. The basic process is, first of all in titanium alkoxide and strontium salt (including strontium organic compounds) as raw materials, organic compound as chelate, alcohol as solvent, to the preparation of homogeneous sol, gel, after drying, calcination for several hours at 9000 c available to ultrafine strontium titanate powder. The key to this method is the homogenous gel, which is formed by the formation of the polypolymer in the system. The strontium ion is adsorbed in the gel body due to electrostatic effect.