Preparation And Property Of Flaky Aluminium Composite Particles

Silica coated flaky aluminium powders (Al/SiO2), ferric oxide and silica coated flaky aluminium powders (Al/SiO2/Fe2O3) and Prussian blue and silica coated flaky aluminium powders (Al/SiO2/PB) were developed using common flaky aluminium pigments as subject by liquid method to meet the needs of waterborne coatings and powder coatings and to improve the color diversity. For good coating layer on alminium powder, the charge proportion between coating material and base, role of surfactants and main influencing factors of preparation process were investigated. Dispersibility, corrosive resistance and color feature of composite particles were characterized, and also, the application of three composite particles in waterborne coatings and powder coatings were studied.1. The preparation of Al/SiO2composite particles by sol-gel method and their characterization. Based on the theory of hydrolytic condensation of tetraethyl orthosilicate (TEOS) and electrostatic adsorption between Al particle and silica, the concentrations of water (nw:nTEOs), ethylenediamine (nE:nTEOs) and TEOS (nTEOs:nAl) were investigated deeply. Results of the tests indicated that the improvement of nw:nTEOS, nE:nTEOS and nTEOS:nAl help the coating efficiency (CE) and percentage of coating (PC) values and improve the corrosive resistance, however, exceptionally high concentration will lead to aggregation and therefore reduce the dispersibility. The optimum conditions are nw:nTEOS=11.6, nE:nTEOS=5.54×10-2, nTEOS:nAl=6.06×10-2and CE value is99.6%. Grain size of Al and Al/SiO2indicated that the composite particle have excellent dispersibility. Results of SEM、EDS and FTIR analyses proved that there is a layer of silica coating on the surface of flaky aluminium particle. The average roughness (Ra) is only3.9nm through AFM analysis. Average pore size and porosity are19.4nm and7.52%, indicating that the coating layer is dense.2. Adsorption of surfactants on Al/SiO2surface. According to the theory of electric attraction and hydrophobic force, the adsorbing of three surfactants on Al/SiO2surface was investigated. The results showed that the adsorption of cetyltri methyl ammonium bromide (CTAB) on Al/SiO2surface may be two layers, which one is obtained by electric attraction and the other is by hydrophobic force among the long-chain carbon. Quantity of adsorbing for sodium dodecyl sulfate (SDS) on Al/SiO2surface is poor. The structure of phosphate polyoxyethylene octyl phenol (PPOP) is affected by pH, therefore, it exhibits the characteristic of non-ionic surfactant or anionic surfactant. Adsorption of PPOP on Al/SiO2surface may be multilayer structure. The surface charge of Al/SiO2could be easily changed through the adsorption of surfactants.3. The preparation of Al/SiO2/Fe2O3composite particles by liquid precipitation and their characterization. The influence of parameters like surfactants, pH and so on were investigated during the coating of Fe2O3. The results showed that SDS and CTAB are harmful to CE, however, PPOP is very beneficial to the CE value which is95.5%under the best PPOP concentration. The particle size of Fe2O3increases with the increase of pH leading to the decrease of flop index (FI). Results of XRD indicated that the nano particle structure is amorphous and it will be transformed into α-Fe2O3through calcination at450℃. The gained Al/SiO2/Fe2O3is golden color and has excellent sparkle effect.4. The preparation of Al/SiO2/PB composite particles by liquid precipitation and their characterization. It can be seen that CTAB benefits PC and CE, however, pH and temperature influence the CE value little. The highest CE value is99.5%. SEM and XRD results showed that the layer is composed of nano cubic phase PB particles. Ra is16.9nm. Al/SiO2/PB composite particles are metallic blue and at least have three colors under different angles.5. Application of flaky aluminium composite particles in coatings. Compared with the product abroad, the performance of the three composite particles in waterborne coatings and powder coatings were tested systematically. The results showed that storage stability of the four is good, adhesion rate is above1according to national standard and anticorrosive of paint film with Al/SiO2or Al/SiO2/Fe2O3is better than product abroad. The anticorrosive of composite particles indicated that the stability of aluminium pigments in waterborne coating could be tested rapidly and quantitatively through sodium hydroxide of pH10. The gas volume less than1ml/g in10days at40℃could meet the stability about90days for the actual waterborne coatings, reducing the stability testing time for waterborne coating which contains aluminium pigments.