Research Of Ceramic Precursor Coatings:Synthesis And Properties

As a kind of organic silicon ceramic precursor,polysilazane has many advantages:stable main chain structure,high surface energy,good adhesion,non-toxic and non-polluted,etc.,which give it promising applications in the field of coating materials.However,polysilazane has poor performances after curing and crosslinking in low temperature,and its ceramic yield was low in high temperature after pyrolysis,which greatly limits its development.In this paper,liquid silazane precursor resin(LSZ)with low viscosity at room temperature(about 3 cP)was synthesized by co-ammonolysis of chlorosilane.And liquid polysilazanes(PSZ)were synthesized by the prepolymerized chain extention of LSZ with hexamethylenediisocyanate(HDI)through nucleophilic addition reaction.In the prepolymerization,with the increase of HDI amount,the viscosity of PSZ was gradually increased till the product became a gel-like solid;when HDI amount was not higher than 10wt%(relative to the mass fraction of matrix,the same below),PSZ was stable as liquid for ever,or else PSZ would turn to a solid after standing as a liquid for 48 h.With the increase of the amount of HDI,PSZ ceramic yield significantly increased(LSZ pure ceramic yield 22.6%,HDI amount of 5wt%ceramic yield of 43.2%,20wt%ceramic yield of 58.7%).Polysilazane(ViLSZ)was synthesized by co-ammonolysis of chlorosilane.Then the influence of HDI and nickel acetylacetonate(NiACAC)on curing and ceramics were studied.The results showed that,after adding HDI,there was almost no influence on curing and ceramics,while NiACAC content was 1wt%,the curing temperature reduced 151℃ compared to pure ViLSZ and ceramic yield increased 21.1%.Scanning electron microscope(SEM)of ViLSZ after ceramization showed that the section was continuous and dense ceramic structure.APP and SiC were composited with ViLSZ to prepare fire-resistant coatings.Performance study showed that,when the content of APP and SiC were all 5wt%,the curing temperature decreased 35℃(relative to pure ViLSZ),thermal expansion coefficient increased from-9%to 50%,increased by about four times,which is very favorable for the fire-resistant coatings.The SEM figures showed,APP and SiC distributed evenly in ViLSZ without appearing different phases,which showed a good compatibility.ViLSZ coatings flaked off a little after outer flame burning in 3min of alcohol lamp,and the section was continuous,dense structure;after adding APP and SiC,coating flaking rarely,showed that the integrity improved by APP and SiC.PFDTES was composited with ViLSZ to prepare silicone water-resistant coatings.It showed that,wiht the addtion of PFDTES,the adhesion between coatings and substrate was reduced;but the wear resistance and toughness were increased.When the PFDTES content was 20wt%,the contact angle increased by about 10°.