Study On Preparation Of ZrSiO₄ Film Via Sol-Gel Method

Zirconium silicate film was prepared on silicon carbide substrate via sol-gel method by using zirconium acetate as zirconium source,tetraethoxysilane as silicon source,lithium fluoride as mineralizer,nitric acid as peptizing agent and acetyl acetone as chelating agent,respectively.On this basis,the silane coupling agent3-aminopropyltriethoxysilane?APTES?was introduced into the sol to enhance the adhesion strength between the film and substrate,resulting in the increase of the coating cycle.Futhermore,impurities ZrO₂ in film was stabilized by introduced Y³⁺into the sol which not only reduces the phase transformation stress,but also enhances the stability of the film and oxidation resistance property.Effects of sol process,chelating agent amount,pH value,precursor concentration,aging time,deposition parameters and heat treatment on the quality of ZrSiO₄ film were studied by means of DTA-TG,XRD,SEM,EDS,AFM and FTIR.The experimental results indicated that:The stable zirconium silicate sol can be prepared through acid catalytic process with nitric acid as peptizer and under the concentration of chelating agent acetyl acetone with higher than 0.47 mol·L^-1 and at pH of 1.The ZrSiO₄ precursor was coated on substrate under the concentration of 0.4 mol·L^-1,over 24 h ageing time,lift speed of 1 mm·s^-1.After dryed at 60 ^oC for 2 h and calcined at 900 ^oC for 0.5 hour,a smooth and crack-free zirconium silicate film was obtained.The peptizer nitric acid improved the stability of sol,and thus the dense zirconium silicate film can be prepared.When the concentration of ZrSiO₄ precursor is lower than 0.4 mol·L^-1,dense zirconium silicate film was not obtained.If the precursor concentration is higher than this value,the crack of the film is increased with increaseing the sol viscosity,which causes the poor oxidation resistance performance.Aging time is also one of the great important factors to influence the film microstructure.As shown in SEM results,when the aging time was less than 24 h,unhomogenous sol affected the smoothness of the film surface,resulting in the formation of small particles.Above this value,a moderate thickness film without any crack was achived,which has high corrosion resistance property.Introduction of the APTES into the sol can improve the bonding force between substrate and film.FT-IR results show that the Si-C bands were inhanced in the gel,resulting in the close relation between organic and inorganic materials.The AFM results indicate that the film is more smooth and dence after inctroducing the APTES agent.When APTES amount is 0.04 mol·L^-1,the film coating cycle was enhanced from 2 to 4times.Sample with 4 times coating has good oxidation resistance,and only 0.03%mass loss after 102 h cyclic oxidation under 1300 ^oC,less than 0.08%of the blank sample and0.16%of the uncoated sample.The phase transformation stress of ZrO₂ impurites is the main reason to the crack of ZrSiO₄ film.When 1%precursor molar mass of yttrium nitrate was introduced to zirconium silicate sol,a more stable ZrSiO₄ film was achieved,which exhibits less crack after high temperature treatment.Above up,this method broadens the range to prepare ZrSiO₄ sol for the film application,and also give a new thought for the preparation and application of composite oxidation film through sol-gel method.