Preparation Of Spinel Ferrites With High Temperature Infrared Emissivity

The infrared radiation materials can enhance heat transfer by means of thermal radiation,which is beneficial to improve the temperature distribution in the heated area and reduce heat loss.Therefore,it has been widely used in industrial furnace energy saving,heat insulation coating,medical care,infrared heating,spacecraft thermal control and other aspects.It’s research,development and utilization are of great significance in promoting energy conservation,strengthening environmental protection and improving medical treatment.Therefore,as an energy-saving material with excellent photothermal conversion function,infrared radiation material has attracted the attention of scholars at home and abroad.The ferrite material with spinel structure has become one of the most concerned infrared radiation materials because of its high emissivity.The microstructure and macroscopic morphology of the material have a great influence on the free carrier concentration,free carrier mobility,band gap width,electromagnetic wave scattering,reflection and absorption characteristics,and further adjust the infrared emissivity of the material.Based on this,this paper studies the influence of different preparation methods and conditions on the infrared emissivity of CuFe₂O₄ on the basis of Mn-Fe-Co-Cu spinel structural materials,looks for the best components and preparation conditions of infrared radiation materials of spinel structures of different systems,and explores the key parameters affecting the infrared emissivity energy,providing theoretical basis and reference for the microscopic mechanism,material selection,preparation and application of high infrared radiation materials of spinel structures.The main research contents and results of this paper are as follows:（1）For the Mn-Fe-Co-Cu system materials that are widely studied at present,we successfully synthesized a series of Mn-Fe-Co-Cu spinel structural materials by solid phase method,and systematically characterized the microstructure and properties of the materials.The experimental results show that the crystal lattice vibration and electron transition can be enhanced by increasing the calcining temperature,and the emissivity can be improved.However,when the calcination temperature is too high,the lattice vibration and electron transition are weakened,so the emissivity is reduced.With the increase of MnO₂content and sintering time,the energy gap of the material can be reduced,the electron transition become easy,and the emissivity of the sample can be improved.But if it continues to increase,it will make electron transition difficult and emissivity decrease.With the increase of the test temperature,electron transition intensifies and emissivity increases.To sum up,the content of MnO₂was 50%,the maximam emissivity of product obtained by sintering at 1150 ^oC for 3h was from 0.649 to 0.970 at the test temperature of 40 ^oC to 800^oC in the 3～5μm band.This method requires high sintering temperature and high energy consumption in the preparation process.（2）In order to reduce the heat treatment temperature and improve the infrared emissity of CuFe₂O₄materials,we prepared CuFe₂O₄ferrite materials by sol-gel method.The experimental results showed that proper increasing the heat treatment temperature and drying temperature can increase the specific surface area of the materials and thus improve the emissivity.However,excessive heat treatment and drying temperature will lead to excessive grain size,decreased specific surface area and reduced emissivity.When CA/MC=1:1,citric acid can fully complexate with metal ions,so it can completely react with them and thus has a high emissivity.Proper extension of heat treatment time and increase of heat treatment times are beneficial to obtaining high emissivity.However,too long time and too many times will make the grain length too long,the interface absorption between grains will be reduced,and the emissivity will be reduced.When the drying temperature was 180^oC,CA/MC=1:1 and calcination at 800^oC for 6 h and the times of heat treatment was 2,the emissivity of 3～5μm band was from 0.479 to 0.920 at the test temperature of 40^oC to 800^oC.Compared with the solid-phase method,the sintering temperature is reduced from 1150^oC to 800^oC,which is conducive to high efficiency and energy saving.Although the emissivity is high,there is still space for further improvement.（3）In order to further improve the emissivity of CuFe₂O₄materials.Cu Fe₂O₄materials was synthesized by solvent thermal method with metal chloride as raw material,polyethylene glycol20000 as surfactant and sodium oxalate as precipitant.It was found that the crystallinity and purity of the products could be improved by increasing the heat treatment temperature,the energy gap could be narrowed,and then the emissivity could be increased.However,if the temperature is too high,the particle size will be too large and the specific surface area will be reduced,and the emissivity will be reduced.The increase of heat treatment time will increase the crystallinity of the product and contribute to the obtaining of high emissivity.However,if the time is too long,the grain size will be too large,the scattering between particles will become larger,the interface between particles will become smaller,the absorption between the interfaces will become smaller,and the emissity will be reduced.Different from the sol-gel method,the emissivity of CuFe₂O₄prepared by solvent thermal method decreases with the increase of heat treatment times.The the maximum emissivity of CuFe₂O₄was prepared by the solvent thermal temperature of 160^oC for 8 h and then at the treatment temperature of 1000^oC for 5 h,the emissivity of Cu Fe₂O₄in the band of 3～5μm was 0.678～0.965 at the test temperature of 40 ^oC～800^oC,which was positively correlated with the test temperature.Compared with the sol-gel method,the infrared emissivity was improved.（4）Because different physical and chemical properties of solvents will affect on the purity,morphology and particle size of the final product,so Cu Fe₂O₄material was successfully prepared by solvent/hydrothermal method with different solvents,and the effects of different solvents on the morphology,structure and performance of the material were studied.The experiments indicated that the change of solvent has no significant effect on the crystal structure of the final products,but has a great influence on the crystallinity,particle size and energy gap.A single organic solvent of ethylene glycol or glycerol is conducive to the formation of pure and high crystallinity CuFe₂O₄.The obtained products have larger particle size and smaller band gap width and larger emissivity.The water presence in solvent will lead to the appearance of heterogeneous phase in the product,reduce the crystallinity and size of the sampl,increase the energy gap and then reduce the emissivity.The crystallization and highest emissivity of CuFe₂O₄samples when the ethylene glycol was used as the solvent.When the test temperature was range from 40 ^oC to 800^oC,the emissivity increased from0.649 to 0.965,which was positively correlated with the test temperature.（5）Considering that surfactants also affect on the morphology,particle size and energy gap of final product.Therefore,different surfactants were used to prepare the CuFe₂O₄materials to explore the relationship between surfactant and crystal structure,microstructure and properties of the material.It is found that the type of surfactant has little effect on the structure of the product,but it can affect the crystallinity and microstructure.In addition,surfactant addition can significantly improve the emissivity of the product.When the test temperature was ranged from 40 ^oC to 800^oC and no surfactant,the emissivity value of CuFe₂O₄material was increased from 0.459 to 0.925.When CTMAB was used as surfactant,the emissivity value of CuFe₂O₄material was from 0.622 to 0.968,which was positively correlated with the test temperature.