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高分子材料论文翻译求助
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Morphology of multilayer film The morphology of each layer film was investigated with AFM. The results are displayed in Fig. 1. The Films have no microcracks and are individually consistent in color. It is known that the titanium dioxide film is achromatous and barium ferrite film is brown. The consistent in color of each layer film shows that the composite film is uniform. With the increase of layer, the color of composite film becomes heavier. The morphology of each layer film is different to others. The one layer film is looked not very even. Some cavities appear in it. The size of cavities changes from 60 to 180 nm. The grains in the one layer film are not homogeneous. The size changes from 30 to 120 nm. Compared with the one layer film, the surface of the two and three layer film is bettered. The cavity is few, and the grains are relative uniform in the two layer film. The size of grains changes from 30 to 60 nm. In the three layer film, some big grains appear, with the maximum size of 240 nm. The substrate and layer number are important factors to affect the growth of films. The first layer film grows on the quartz glass plate. The difference in structure makes the film to grow difficultly. So the defects easily appear and grains are unordered. However, the second layer film grows on the base of the first layer film. The growth conditions are improved for the second layer film. It can grow better under the direction of the first layer film. With the increase of layer number, some grains have chance to grow big in three dimensions. In the three layer film, some grains even grow to 240 nm. Additionally, the TiO2and ferrite grains can not be distinguished in the composite film. Crystalline structure of multilayer film In the course of preparing substituted BaFe12O19using sol–gel method, the intermediate results including Fe2O3, BaCO3and BaFe2O4will appear. If they react heavy with TiO2during the formation of multilayer film, the expected magnetic materials, substituted barium ferrites will not form. XRD is used to inves- tigate the crystalline structure of composite film and its pattern is shown in Fig. 2. The composite film is composed of rutile titanium dioxide and M-type hexagonal barium ferrite. The diffraction peaks of Al2O3and Cr2O3are not found on the pattern, which shows that all of Al3+and Cr3+ions have entered the lattice of BaFe12O19. It is concluded that the mixed sols basically react into the substituted BaFe12O19and TiO2 during the calcination process. The substituted barium ferrite can be synthesized via titanium dioxide as a matrix using sol–gel method. In addition, there are two unknown weak diffraction peaks on XRD pattern, which can not be recognized by standard cards. Maybe, a little part of Fe, Ti and O elements still reacted into an unstoichiometric compound. Microwave absorption property of multilayer film Microwave attenuation materials are required to absorb microwave energy in a broad frequency range. Single material is not easy to realize it. Substituted barium ferrites are selected to prepare composite multilayer film with TiO2. These films are arranged according to the frequencies of their microwave absorption peaks. The absorption frequencies of BaFe10.1Al1.9O19 are the highest, so the composite layer containing BaFe10.1Al1.9O19is treated as the first layer nearby the substrate. The absorption frequencies of BaFe11.4Cr0.6O19 are the lowest, and then the composite layer containing it is on the top. Theomposite layer containing BaFe10.5Al1.5O19is in the middle. This arrangement can make more microwave energy to enter the multilayer film and to be absorbed. The microwave loss spectrum of composite multilayer film is shown in Fig. 3. The microwave loss spectra of BaFe10.1Al1.9O19, BaFe10.5Al1.5O19 and BaFe11.4 Cr0.6O19 powders are simultaneously displayed as a comparison. The microwave absorption property of the compos- ite multilayer film is excellent. The largest loss efficiency is close to –40 dB. The frequency range with the loss above –10 dB is more than 7 GHz. It is an ideal microwave absorption material. Because of the variable absorption frequency, each layer film can absorb microwave energy in different frequency band. The multilayer film assembles the achievements of each layer. Moreover, the compounding of ferrites with TiO2is helpful for the microwave absorption. Barium ferrite is a magnetic material, and TiO2is a nonmag- netic material. After they are compounded together, electromagnetic properties of magnetic material can be changed. It is known that almost all of ferrites have little dielectric loss. Now the compounding with TiO2 can improve the dielectric losses of substituted barium ferrites. Additionally, the size of most grains in multilayer film belongs to nanometer scope, which is attributed to the surround of TiO2particles. The ferrite grains with single magnetic domain structure can notgrow big and convert into multi-domain structure, due to the block of TiO2particles, which also increase the microwave absorbing. |
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