| Nano-alumina has been widely used in the fields of composite material such as high strength alumina ceramic, coating, rubber, plastic, wear well reinforcing material etc. with many excellent performances. However, nanoparticles were attributed to thermodynamically unstable system, with large surface area, increasing number of surface atoms, lack of atomic coordinate, high surface energy, particles were easily form a connection interface with a lager size aggregates. Agglomeration of nanoparticles is a major problem restricting its application.The interaction of nano particles and theory of dispersion stability in aueous phase were summarized, and the surface electrical properties and dispersion of nano-alumina aqueous suspension were studied in this pater. By the determination of zeta potential, particle size distribution, sedimentation test and adsorption test, the method of dispersion, dispersion time, dispersing agent and the amount of dispersant on the dispersion stability of suspension were investigated. The synergy between combination surfactant was researched by means of recomposing surfactant. The effect of adsorption and dispersion were characterized using FTIR and SEM; the characterizing results were coincided with experimental results. It is determined that the best condition for the dispersity and stability aqueous suspension of nano-alumina.The main results are as following:1. The dispersion and stabilization of nano-alumina in aqueous system were studied. The Van der Waals' forces between agglomerate particles were opened in the high energy microenvironment which was formed by the ultrasonic cabitation. The best dispersion time was 20min. In the acidic conditions, the surface of nano-alumina was positively charged and negative charge in alkaline conditions. The isoelectric point of alumina is about at pH8.4; the surface charge density of particles was high in the area of pH 2.97-5.1 and 10.0-12.14.2. The influence of dispersant sodium dodecyl sulfate SDS, cetyltrimethyl-ammonium bromide CTAB, polyethyleneglycol PEG and arabicgum GA to the dispersion and stability of nano-alumina aqueous suspension was discussed. Zeta potential of the suspension was changed significantly for the adding of dispersant. When using dispersant as CTAB, the maximum absolute of zeta potential was 57.02mV and average size of particles was minimum at pH=4.0; the maximum adsorbing capactity of alumina surface was 37.78μmol·g-1 with the concertration of CTAB was 6.2mmol·L-1. The effect of adsorption was good. The electrostatic repulsion between particles was strong and dispersion stability was optimal.3. The effect of synergy between combination surfactants to the dispersion stability of nano-suspension was reseatched by recomposing surfactant of ionic and nonionic surfactant. The surface of particles showed different electricity properties with the variation of pH for the adding of combination surfactants, and then has an affect on the dispersion. With the adding of combination surfactant of nonionic surfactant PEG and cationicsurfactant CTAB, the zeta potential was always positive with no the isoelectric point. The maximum absolute of zeta potential was 70.14mV. The surface of alumina shows good adsorption and the the maximum adsorbing capacity was 37.78μmol·g-1. The dispersion of nano-alumina was improved obviously compared with adding single dispersant and no dispersant.4. The FTIR characterization results indicated that the dispersant was authentically adsorbed on the surface of alumina. The stracture and potential distribution of the particle surface were altered, and the steric hindrance and electrostatic repulsion were formed by the chemical adsorption between the dipersant and the surface of alumina. Therefore, the effect of dipersion was improved. The SEM characterization results indicated that particles were separated because of electrostatic repulsion at pH3.0 and was seriously aggerated at isoelectric point pH8.4 with no dispersant; the size of the coacervate was effectively reduced and dispersion of particles was improved obviously; particles were evenly dispersed and the effect of dispersion was preferable with the adding of combination surfactant PEG and CTAB. Results were coincided with experimental results. |
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