General knowledge of coating: ultrasonic preparation of nano powder

Core tips: 1 Introduction Ultrasonic wave refers to the mechanical wave with the frequency range of lokhz-106 ­ kHz The wave speed is generally about 1500m / s and the wavelength is 10cm-0.01cm, which exceeds the upper limit of people's hearing Ultrasonic wave is a kind of wave form, which can be used as the carrier of detecting and loading information; meanwhile, ultrasonic wave is also an energy form, which can accelerate chemical reaction or trigger new reaction channels The ultrasonic wave interacts with the medium in the process of propagation and produces the ultrasonic effect Interaction between ultrasonic and medium Paint knowledge | precautions for wall paint color selection Recommended introduction: when painting the wall, the owner sometimes has difficulty in choosing what color of the wall paint to paint In fact, there is no ugly color in the wall paint, only the disharmonious color matching The use of wall color contains the knowledge of health Too strong color will stimulate people's perception, make people have a sense of fidgety, affect people's mental health Grasp the basic principles of wall color and paint a colorful space 1、 Wall paint color selection notice 1 Light color is generally used for the top surface Light colors make people feel light, dark colors make people feel heavy Usually, the treatment of rooms is from top to bottom, from shallow to deep For example, the ceiling and walls of rooms are white and Home of coatings: 1 Introduction ultrasonic wave refers to the mechanical wave with the frequency range of lokhz-106 ­ kHz, the wave speed is generally about 1500m / s, and the wave length is 10cm-0.01cm, which exceeds the upper limit of people's hearing Ultrasonic wave is a kind of wave form, which can be used as the carrier of detecting and loading information; meanwhile, ultrasonic wave is also an energy form, which can accelerate chemical reaction or trigger new reaction channels The ultrasonic wave interacts with the medium in the process of propagation and produces the ultrasonic effect The interaction between ultrasonic and medium can be divided into thermal mechanism, mechanical mechanism and cavitation mechanism The research of ultrasonic technology is a new frontier subject With the development of science and technology, the cross penetration of related technical fields and the improvement of high-power ultrasonic equipment make it possible for ultrasonic technology to be widely used in many fields such as chemistry, chemical industry, medical treatment and medicine The high energy of ultrasonic plays an important role in material chemistry, which cannot be achieved by optical, electrical and thermal methods The huge energy released from ultrasound in liquid is beyond the reach of other methods, let alone the effect of ultrasonic quantitative control In the synthesis of macromolecular materials and the degradation of plastics, the application of ultrasound is still in its infancy, while the application of ultrasound in emulsion synthesis of macromolecular solution and cell division of macromolecular is more successful Ultrasound also has great potential in material synthesis The preparation of nano materials by ultrasonic method has achieved some goals which can not be achieved by laser, ultraviolet irradiation and thermoelectricity, and has a good prospect 2 The mechanism of ultrasonic wave interaction with the medium in the process of propagation, phase and amplitude change, which can change the state, composition, structure and properties of the medium This kind of change is called ultrasonic effect The interaction between ultrasonic and medium can be divided into thermal mechanism, mechanical mechanism and cavitation mechanism 2.1 thermal mechanism when ultrasonic wave propagates in the medium, its vibration energy is absorbed by the medium and converted into heat continuously, which makes the medium temperature rise This mechanism is called thermal mechanism 2.2 mechanical mechanism when the frequency is low, the absorption coefficient of medium is small, the action time of ultrasonic is short, and the generation of ultrasonic effect is not accompanied by obvious thermal effect At this time, the ultrasonic effect can be attributed to the mechanical effect Ultrasonic is also a form of mechanical energy transmission The mechanical parameters in the process of wave motion, such as the origin displacement, vibration speed, acceleration and sound pressure, can show the ultrasonic effect 2.3 cavitation is one of the main mechanisms of sonochemical effect of ultrasound Acoustic cavitation refers to a series of dynamic processes, such as oscillation, growth, contraction and even collapse of vesicles, in which tiny vesicles are activated by sound waves The phenomenon includes two aspects, that is, the group of bubbles produced by intense ultrasound in liquid and the special movement of bubbles under the action of intense ultrasound When ultrasonic field is applied in the liquid, when the ultrasonic intensity is large enough, a group of bubbles will be produced in the liquid, which are called "acoustic cavitation bubbles" These bubbles are affected by ultrasonic at the same time When they experience the sparse phase and the compressed phase of ultrasonic, the bubbles grow, contract, re: grow, re shrink, and finally crack at high speed after several periodic oscillations The temperature of gas phase reaction can reach (5000K), the temperature of liquid phase reaction is about 1900k, and the local pressure is 5.05x Above 107pa, the temperature change rate is as high as l09k / s, producing strong current, accompanied by strong shock wave and jet with speed as high as 400km / h, which has achieved good impact on the liquid-solid surface, especially leading to strong mutual collision and aggregation between molecules These conditions are enough to open the strong bond (376.8-418.6kl / mol) and promote the "aqueous combustion" reaction This leads to many mechanical, thermal and biological effects Micro bubbles or bubbles attached to solid particles, micro dust or container surface as well as in the slit, because of their uneven structure, cause a small area of strength weakening in the liquid, in which the separated gas can form this kind of micro bubble core According to the intensity of response to sound field, acoustic cavitation is generally divided into two types: steady-state cavitation and transient cavitation The sonochemistry in liquid mainly depends on the physical effects of rapid heating and cooling caused by the implosion of cavitation bubble The characteristics of implosion temperature and reaction are easy to change acoustic frequency, acoustic intensity, ambient temperature, static pressure, ambient gas and other factors The heat produced by the implosion of cavitation bubble can decompose water into hydrogen radicals and oxyhydrogen radicals In the process of rapid cooling, hydrogen radicals and oxygen radicals recombine to hydrogen oxide and hydrogen molecules When the "hot spot" is produced by the implosion of cavitation bubbles in various solutions, the solution molecules at the "hot spot" may be excited to a high-energy state When these molecules return to the ground state, they will radiate visible light, which is the sonoluminescence process At the same time, the effect of ultrasound on liquid can also be used to increase the chemical activity of liquid compounds and promote the emulsification of two immiscible liquids The surface acoustic cavitation of small solid particles in liquid is related to the dynamic characteristics of cavitation bubble implosion When the cavitation in liquid occurs near the surface of small solid particles, the implosion of cavitation bubbles is quite different from the spherical symmetry observed when there is only liquid phase The pressure generated by ultrasonic field is distorted on the surface of small solid particles, so the implosion near the surface of solid particles is significantly asymmetric This process will make the brittle solid powder disperse and be able to Increase the chemical activity of solid surface, make them have good catalysis Ultrasound is a useful tool in almost all cases of liquid-solid reaction In addition, ultrasonic wave can spread well in liquid, so it is suitable for industrial production The application of ultrasound in the preparation of nano powder materials nano powder (particle size 1-100nm) is composed of nano particles, which lies in the middle of macro matter, micro atom and molecule Because of its surface effect, volume effect, quantum size effect, macro tunnel effect, optical effect, electronic effect, volume effect and special chemical and catalytic properties, nano materials are regarded as the interdisciplinary growth point and cross century "hot spot" research field, known as "the most promising materials in the 21st century", and are widely used in chemical industry, electronics, metallurgy, aerospace , biology, medicine and other fields show broad application prospects Usually, the preparation methods of rice noodles include chemical vapor deposition (CVD), chemical vapor synthesis (CVS), co precipitation, hydrolysis, homogeneous precipitation, oxidation hydrolysis, reduction, sol gel, hydrothermal synthesis, evaporation, microemulsion (reverse micelles), template method, etc In recent years, acoustic cavitation method is becoming a new technology to prepare new materials with different properties The special physical and chemical environment caused by acoustic cavitation provides a new way for scientists to prepare nano materials Various nanostructured materials with high boiling point catalytic properties, such as nanostructured metals, alloys, carbon and sulfur compounds, nanocolloids and nanostructured support catalysts, can be obtained by sonochemical decomposition of VOC precursors in high boiling point solvents The research team of Suslick, a famous sonochemist, has done a lot of work in the preparation and synthesis of nanostructured materials For example, when the decane solution of Fe (CO) 5 is irradiated by ultrasound at O ℃, dark black iron powder can be produced According to the elemental analysis, the mass fraction of iron in the powder is 96% The results of scanning electron microscopy (SEM) and perspective electron microscopy (TEM) show that the material is a aggregation of particles with a particle size of about 4-6nm Magnetic research shows that it is a very soft ferromagnetic material with Curie temperature as high as 580k Lin Jingu et al Injected a set of specially designed ultrasonic particle preparation device with the solution of carbonyl iron Fe (CO) 5 and hexacarboxyl chromium Cr (CO) 6 dissolved in decalin, decomposed for 3.5H under the ultrasonic power of 120W and the frequency of 20kHz, and obtained the alloy nano powder of Fe-Cr with the particle size of l7-28nm Wang Juxiang et al Developed the ultrasonic electrolysis method to prepare nanometer metal powder By controlling certain solution concentration, ultrasonic power, electrolysis conditions, current density and other conditions, copper and nickel powder were obtained below 10 μ m This method has the characteristics of simple process, low cost, non-toxic and pollution-free It is a new method to prepare ultrafine metal powder When the high-energy ultrasonic wave propagates in the liquid, not only the cavitation effect but also the acoustic flow effect is produced The particles less than 10 μ m are uniformly dispersed in the solution and wetted at the same time, so as to obtain fine particles with good structure and enhance the aluminum matrix composite powder For the first time, Chen Xuemei used the ultrasonic method to prepare Nano-Al2O3 powder by precipitation method, and the Al2O3 powder with a particle size of 12 nm was prepared by the ultrasonic radiation process The results show that ultrasonic radiation can effectively refine the precipitated particles of precursor nh4al (OH) 2CO3 and inhibit the aggregation of precursor particles through cavitation of liquid medium Ultrasonic radiation retards the process of precursor to gel transformation, and obtains a three-dimensional porous network skeleton structure containing smaller water and bound water Wang Jian and others, using anhydrous tin chloride as raw material, obtained nano SnO2 by sol-gel method under the action of ultrasonic wave, and characterized their structures by TEM and XRD Under suitable conditions, the average particle size of nano SnO2 powder is 20 nm, the particle is spherical, the particle size is uniform, the flow performance is good, the product structure is tetragonal cassiterite structure, the purity is more than 95% Ultrasound plays an important role in controlling particle size and preventing agglomeration Guoweilin et al Prepared nano titanium dioxide with different crystal shapes under mild conditions by sonochemical method The results show that nanocrystals with good dispersion can be obtained in aqueous solution Ultrasound can promote polycondensation reaction, resulting in a lot of "hot spots" due to cavitation effect in the generated gel, and further reaction can lead to a large number of tiny nuclei forming.