Study On Low Temperature Catalytic Conversion And Coating Performance Of Polysilazane

The technology of preparing coatings using polymer ceramic precursors has garnered significant interest among researchers.The method has the advantages of flexible processing,wide range of application and excellent corrosion,high temperature and oxidation resistance of the prepared coatings.In this method,the precursor type plays a decisive role.Polysilazane is the main material for precursor conversion coating technology,and it can be used to obtain inorganic silicon oxide/silicon nitride coatings or organic-inorganic hybrid coatings under high temperature and vacuum ultraviolet(VUV)irradiation conditions,which have important applications in aerospace and microelectronics fields.However,the application of the current conversion method is limited or difficult to scale up production.In order to solve this problem,the following research has been carried out :Perhydropolysilazane(PHPS),which does not contain organic groups,was used to investigate the role of amino silanes on its conversion process.After conducting the experiment,it was found that the addition of 3-aminopropyltriethoxysilane(KH 550)had a significant catalytic effect.With a dosage of only 5 wt%(relative to the mass of PHPS),the rapid conversion of PHPS was achieved at 80 ℃ and 90% RH,with a conversion rate of 95% in just10 minutes.In contrast,iminosilanes,such as bis(trimethoxysilylpropyl)amine(Dynasylan(?)1124)and n-butylaminopropyltrimethoxysilane(Dynasylan(?) 1189),showed a weak catalytic effect,resulting in relatively low conversion rates of PHPS even after 10 minutes.Nonaminosilanes,including n-Propyltrimethoxysilane(PTMS)and Methyltrimethoxysilane(MTMS),did not exhibit any catalytic effect.Based on these findings,we proposed the catalytic conversion mechanism: the amino group’s nucleophilic attack promotes the hydrolytic condensation reaction of the Si-H and Si-N bonds in the PHPS structure,the catalytic efficiency is higher when the amino group is more basic and nucleophilic.The properties of the KH 550 catalytic PHPS conversion coating were thoroughly examined.Structural tests revealed that the coating was primarily composed of silicon oxide.The coating exhibited excellent performance,with the volume shrinkage of 0.89% calculated from the thickness variation,the density of 1.9g/cm3,and the refractive index of 1.451.The surface was flat and smooth,with the surface roughness of 0.293 nm.The coating demonstrated good optical transparency(>90%),and the adhesion to the substrate was 5B.Additionally,the coating exhibited outstanding mechanical properties,with a pencil hardness of 9H,a nanoindentation hardness of 3.09 GPa,and a modulus of elasticity of 30.06 GPa.The catalytic conversion of organic polysilazane(OPSZ)by amino silanes was investigated,and the basic properties of the conversion coatings were examined.The study revealed that the catalytic efficiency of KH 550 for OPSZ was hindered by the spatial site blocking effect caused by the organic groups present in OPSZ side chain.To effectively promote the conversion of OPZ 181 at 80 ℃ and 90%RH,the ratio of polymethyl(hydrogen)/polydimethylsilazane(OPZ 181)to KH 550 needed to be greater than2:1.The structural test results indicated that the OPZ 181 coating obtained by the catalytic transformation method is an organic-inorganic hybrid coating with a predominantly Si-O-Si structure and containing-CH3 organic groups.The test results of the comprehensive performance of the coating showed that the coating has good mechanical properties with the pencil hardness of 6H,the nanoindentation hardness of 0.7 GPa and the modulus of 5.7 GPa.The H/E and elastic recovery rate(We)of the coating reached 0.1 and 60% or more,respectively,indicating that the coating has good hard flexible properties.The coating’s hardness on polyethylene terephthalate(PET)film was up to 2H,and the coating showed impressive bending resistance.After lamination with PET substrate,the coating could endure more than10,000 bends at a bending radius of 1 cm and still remain intact,indicating its potential to achieve hard and tough protection coatings on flexible substrates.The surface of coating was flat and smooth.The coating demonstrated good optical transparency(>90%),and the adhesion to the substrate was 5B.The coating had a low surface energy due to the presence of-CH3 and the water contact angle >90°,which provided good hydrophobic properties.The coating had excellent anti-fouling properties and could effectively prevent contamination by water-based graffiti pens,oil-based graffiti pens and ink.