Preparation And Properties Of Waterborne Nano Ceramic Coatings

Traditional inorganic silicate coatings use water as the main dispersant,which shrinks greatly during the curing process and is prone to cracks.At the same time,it is affected by soluble ions and has poor water resistance.In this thesis,sodium silicate and potassium silicate are used as the main film-forming materials to prepare organic-inorganic composite coatings and inorganic coatings to solve the problems of brittleness,cracking,poor water resistance and corrosion resistance of potassium silicate and sodium silicate coatings.(1)A self curing sodium silicate/potassium silicate inorganic waterborne coating was prepared by using sodium silicate and self-made potassium silicate as film-forming materials,adding glass powder and other additives.The effects of potassium silicate with different modulus,potassium silicate and sodium silicate with different mass ratio and different silicate content on the properties of the coating were studied.The results of test and analysis show that the potassium silicate solution with SiO₂/K₂O molar ratio of 5.5 has better storage stability due to less silicate colloidal particles and active silicon hydroxyl groups.When Na/K=2:5 and silicate content is35%,the combination between pigments and fillers and potassium silicate and sodium silicate solution is closer,and the compactness of the coating is good,which can well weaken the diffusion and migration of corrosive medium in the coating.(2)Zinc powder modified self curing sodium silicate potassium silicate inorganic waterborne coating was prepared by adding zinc powder,aluminum oxide and other additives to sodium silicate and self-made potassium silicate.The effects of zinc powder on the mechanics,static contact angle,microstructure and corrosion resistance of the coating were studied.XRD results show that zinc silicate peak appears in the coating with zinc powder,indicating that zinc powder reacts with silicate,and the generated zinc silicate network structure can improve the adhesion strength and wear resistance of the coating.SEM results show that with the addition of zinc powder,the coating surface becomes denser and smoother.At the same time,there are abundant zinc powder particles under the thin layer of reaction products,which can provide effective cathodic protection for electrochemical reaction.The corrosion resistance of the coating was studied by polarization technology and electrochemical impedance spectroscopy(EIS).The results show that due to the high self-corrosion potential of zinc powder,it is easier to be corroded than iron(substrate),which improves the cathodic protection of the coating.(3)Using sodium silicate(Na₂SiO₃)as inorganic component,methyl trimethoxy siloxane(MTMS)as silane coupling agent and silicone acrylate emulsion as organic component,Na₂SiO₃-MTMS-silicone acrylic emulsion was prepared by mechanical blending.Na₂SiO₃-MTMS-silicone acrylate emulsion is used as film forming material,titanium dioxide,glass powder as filler,sodium fluosilicate(Na₂SiF₆)as curing agent,together with other auxiliaries to prepare self curing high water resistant silicate coating.The effects of Na₂SiF₆,low melting point glass powder and silicone acrylic emulsion on the appearance,adhesion,hardness,wear resistance and corrosion resistance of the coating were studied.When the dosage of silicone acrylic emulsion is30%and the amount of Na₂SiF₆is 0.5%,the mechanical properties of the coating are the best.The results show that silicone acrylic emulsion filled in the voids of Si-O and Si-O-Si network structure can not only enhance corrosion resistance,but also increase the flexibility and stability of the coating.Sodium fluosilicate as a curing agent can reduce the residual moisture in the coating,resulting in a more rigid silicate gel network due to loss of water,while the water resistance of the coating is also improved.