Ultra-fine Aluminum Hydroxide Particles In The Drying Process Reunion

The technology for ultra-fine aluminium hydroxide production by hydro-chemical method is often charactered with simple process and abundant material on a mild reaction condition and can be readily applied in industrial scale, while the particles are easily agglomerated in the precipitation or drying process. The particle agglomeration can be controlled with the addition of surfactant or under special precipitation conditions. The principle of particle agglomeration in the drying process is rarely reported. In this paper the particle agglomeration in ultra-fine powder was studied in detail. The results showed that the particles agglomerated greatly if the particle size was fine or the temperature was high. And the finer particles would agglomerated firstly, and then the larger ones agglomerated in the drying process. Water in the powder was given off at a constant rate in the drying process. The results also indicated that the rate of particle loss due to agglomeration became fast even though the particle size is more than 2.0μm at 80°C.On the contrast the particle loss was slow and the particles which is less than 0.5μm was agglomerated in drying process at 40°C. It was difficult for the ultra-fine particles to be agglomerated and the particle loss was less than 6% with the addition of surfactant, while above 99% particles were disappeared in the drying process without any surfactant. The analysis of IR indicated that the free OH bond was increased and the free hydrogen bond appeared at 1310cm^-1 but binary or multi OH bond was reduced with the addition of surfactant. The results of BET and SEM showed that the pore diameter of the powder was not uniform, some of the pore diameter was more than 3μm and the powder existed in hard block without surfactant. In contrast, the pore diameter of the powder appeared uniform and the agglomeration of the particle became less with the addition of surfactant. The pore mainly account for open mino-pore and medium-pore, which favored the diffusion of water in wet-powder in drying process with addition of surfactant. The intension of interface was decreased with the addition of surfactant which was advantageous for the reduction of the multi-division collapse of pore due to capillary function. The addition of surfactant can change the particle surface and intensify the spacial obstruction, resulting in less hydrogen bond among particles to be formed. At the same time, the addition of surfactant can change the interaction among the particles and reduce the interfacial intension, leading to the decrease of interaction among particles and capillary function. And thus the particle agglomeration was decreased.