The Preparation And Rheological Properties Of The Zinc-rich Coating From Sodium Silicate Modified With Inorganic Salt

The zinc-rich coating from sodium silicate solution is a kind of new-type anti-corrosion coating which is economic and effective for the steel material. The coating adhered to metal base body by use of physical chemistry action force occurred between the binder sodium silicate solution of coating and metal base body. The zinc-rich coating from sodium silicate solution has excellent properties of anti-corrosion, durability, lower cost and zero-VOC-emitting, so the manufacture of this waterborne coating has received considerable attention in modern industrial field.Although the zinc-rich coating from sodium silicate solution possesses some intriguing advantages, the application of the coating is limited by its poor water resistances, which affects the quality and anti-corrosion property of the final film. The aim of this thesis is to solve above problem and prepare high-performance zinc-rich coating from sodium silicate solution modified with aluminum chloride (AlCl 3 ) and ammonium dihydrogen phosphate (NH 4 H 2 PO 4 ). Through basic properties test, steady and dynamic rheological experimentation, model fitting,Fourie-transform spectra (FTIR) measurement and optical micrography observation, the following results were determined.1. Through research on water, heat, salt and impact resistance of the zinc-rich coating modified with aluminum chloride, the best composition was obtained as 40g( 36%)sodium silicate solution + 59.4g distilled water + 0.60g AlCl 3 +200g zinc pigment. This coating belonged to shear-thinning fluid. Kamal model could fit the curve of viscosity over time, and the relationship between the elastic and viscous moduli(G'and G'') and temperature could be fitted by multinomial. Both the elastic and viscous moduli increased as AlCl 3 dosage increases, and the complex viscosities depended strongly on the heating rate. FTIR measurement proved that there were chemical reactions among sodium silicate, modificator and zinc pigment, the forming mechanism was also analysed by the FTIR test. The optical micrography observation demonstrated that the anti-corrosion property of the film becomes better according to the best composition.2. The best composition of the zinc-rich coating modified with ammonium dihydrogen phosphate was 40g( 36%)sodium silicate + 59.8g distilled water + 0.20g NH 4 H 2 PO 4 +200g zinc pigment, the basic properties of this coating achieved and even exceeded the nation standard. NH 4 H 2 PO 4 could increase the thixotropic properties of zinc-rich coating system. The relationship between viscosity and shear rate could be fitted by the Williamson expression,η=η0 (T)+Kexp[B (T )?t] model was used to fit the curves of viscosity over time. The elastic and viscous moduli and the complex viscosities all increased when NH 4 H 2 PO 4 dosage increases, temperature sweep curves showed that at the beginning they risen with temperature, then went down. The dynamic and out of phase viscosities(n'and n'')depended strongly on the heating rate. FTIR test told us that the addition of NH 4 H 2 PO 4 promoted the formation of zinc silicate film. The optical micrography observation illustrated that the anti-corrosion property of the film became better according to the best formula, and we also analyzed the anti-corrosive property of the zinc-rich coating system modified with ammonium dihydrogen phosphate.These results have both theoritical and practical values for the production of the waterborne zinc-rich coating that satisfies the environmental requirement.