The Preparation Of Nanometer Nature Barite And Its Application Research In Coil Coating

Nanometer nature barite have been successfully synthesized by a novel wet grinding technique, using crude micron barite as source material, and the samples were characterized. The dispersibility and electrokinetic properties of barite nanoparticles have been investigated in water. After the barite nanoparticles were modified using several methods, barite nanoparticles/epoxy composite paint film was prepared and its anti-corrosion mechanism was studied. This dissertation is consisted of seven related parts:(1) Nanometer nature barite have been successfully prepared by new grinding technology, using crude micron barite as source material. The samples were characterized by X-ray diffraction (XRD), N₂ adsorber, transmission electron microscopy and Malvern laser granulometer.(2) Zeta potential, particle size and viscosity of barite nanoparticles in aqueous suspension as a function of pH and concentration of dispersant NaPAA were studied. These results showed electrosteric stabilisation by addition of an anionic polyelectrolyte (NaPAA) shifted the isoelectric point (IEP) to lower pH. Higher dissociated polymer was adsorbed to the positively charged surfaces of barite nanoparticles with 2wt % NaPAA at pH 8.5. So, Particle size and viscosity of barite nanoparticles in aqueous suspension was low.(3) A series of zeta potential measurements have been performed to determine the isoelectric point (iep), potential-determining ions (pdi), and the effect of mono-, di-, and trivalent electrolytes on the zeta potential of barite nanoparticles. Barite nanoparticles yield an isoelectric point at pH 7.8. Multivalent anions exert a greater influence on the zeta potential of barite nanoparticles than monovalent anions. Monovalent anions can only compress the EDL and reduce the zeta potential, while di- and trivalent anions may be adsorbed specifically in the IHP of the stern, and are capable of even reversing the sign of the zeta potential of barite nanoparticles. A model is proposed to illustrate the accommodation of mono- and multivalent ions in the EDL, and the thickness of the double layer were calculated for mono- (1/k₁), di-(1/k₂), and trivalent ions (1/k₃), respectively.(4) Surface modification of barite nanoparticles was investigated with cationic surfactant dodecyltrimethylammonium bomide (DTAB). Results showed that most of DTAB may be adsorbed onto the surface of barite nanoparticels, the surface free energy of barite nanopaticles was reduced, the dispersibility of barite nanoparticels in petronol system was improved, indicating that the surface performance of barite nanoparticles has been changed from hydrophilicity to hydrophobicity after modification.(5) Surface modification of barite nanoparticles was investigated using Al₂O₃/stearate as modified agent. The surface free energy of the modified barite nanopaticles was 4.4×10^-3N/m, which was 1/20 times than barite nanopaticles without modified. The viscosity of modified barite nanopaticles was decreased in petronol system. In addition, the sample was characterized by XPS, FT-IR, and Zeta potential test.(6) The effect of dosage of barite nanoparticles on the mechanical behaviour and salt spray test of the paint films have been investigated in detail. The performances of composite paint film adding 1.0% modified barite nanoparticles were improved largely, the T-bending was improved from 4T to 2T, and the corrosion resistance increased 20% with its retardation time from 720h to 1096h before showing blisters. Moreover, barite nanoparticles dispersed uniformly in the paint film was characterized by SEM images.(7) Using the particle blending model, the nine kinds of epoxy coatings modified by barite nanoparticles and barite micronparticles, in which the A is 0.4, 0.5, 0.6, 0.7, were prepared. Corrosion resistance mechanism of coatings was studied by electrochemical technology and Mott-Schottky analysis. Results showed the impedance of the modified coating by barite nanoparticles was bigger than the impedance of the modified coating by barite microparticles. It indicates that the corrosion behavior of the barite nanoparticles modified coating is better than the barite microparticles modified coating. There is semi-conducting behavior in inactivation process of the nanoparticles composite coating.