| The study on all-reflective-film hollow-core waveguides is very important for the application of CO2 laser in many fields such as medical treatment, laser processing and so on. However, the preparation of all reflective films has aready become the first important factor in the research and development of the waveguides. Based on the infrared anomalous dispersion of compact alumina film, the character of alumina sols and the processing for fabricating compact alumina film were studied by using sol-gel method, combining dip-dropping, spin-coating method and electrophoretic deposition techniques.Alumina sols of different content were prepared by using Al(O-Sec-Bu)3 as precusor, water as solvent and nitric acid as peptizer. It's indicated that the zeta potential and total interaction energy of the colloidal particles are both at a maximum when the nitric acid concentration is 0.22mol/l for the alumina sols with a mol ratio of 1:50 between ASB and H2O,. The results show that the organic matter and solvent water in the alumina gels have been already wipped off after they were heat treated at 900℃ for 2 hours and 550℃ for 5 hours and the crystalline phase transformation occurs as r, and a -alumina in turn with the increase of temperature.At the same time, alumina polymeric sols were prepared by using Al(O-Sec-Bu)3 as precusor and Sec-BuOH as solvent. Then compact alumina films were fabricated by electrophoretic deposition. It was found that the zeta potential and average size of the colloidal particles increase earlier and drop later with the addition of Sec-BuOH and both of them reach the maximal values which are 790nm and 20mV respectively when the mol ratio between Sec-BuOH and ASB is 30. The film obtained the maximal thickness when the mol ratio of Sec-BuOH/ASB is 40 and the deposition time is 1 hour. The thickness of the film increases with the growth of voltage when deposited for certain time and increases with the enhancement of deposition time when deposited at certain voltage. Moreover, the rising rate falls with the prolongationof time.The effect of dropping speed, solid content of aluminum, dip-dropping cycles and heat-treatment rules on alunina film were also studied in the fabrication of compact alumina film by dip-dropping method. It's shown that the increase of solid content and decrease of dropping speed help to prepare homogeneous compact films. Microcracks and stresses will appear if the dropping speed, aluminum content and dropping cycles are too high. High temperature heat-treatment can eliminate and help to obtain compact thick film. In the study on spin coating, it can be resulted that decreasing spinning speed can heighten film thickness, capillary force resulted in shrinkage of the gel structure easily formed faultages inside the film. The capillary force can be dropped through vacuum drying process, and compact film with thickness of 6 u m was obtained by low spinning speed and few plating times.The general analysis of dip-dropping, spin-coating method and electrophoretic deposition techniques shows that the compaction degree of alumina film fabricated by the former two methods are higher than those prepared by the last one. Besides, spin-coating method is the most efficient and fast way to raise film thickness.
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