Abstract
A new precipitation method by use of a tubular reactor was proposed for the continuous production of inorganic salt fine particles. A various inorganic salts such as lanthanum phosphate, cerium phosphate, iron phosphate, lead phosphate, barium carbonate, lead sulfate, barium sulfate, lead sulfide, copper sulfide, zinc sulfide, and nickel sulfide were prepared in the aqueous phase. The tubular reactor made of silicone rubber tube of 3.0 mm in inner diameter was used. Two reactant solutions of the constituent cation and anion of the target salt were continuously fed and mixed at the inlet of the reactor. Typical liquid residence time was 110 s. The mixing part of the reactor was placed at 0°C whereas the remaining part was at 30°C. The particle size ranged from 50 nm to 5µm. In a single run, however, monodispersed particle diameter distribution was attained for most inorganic salts by the application of the proposed method. Spherical particles were obtained in case of sulfides and lanthanoid phosphates. A small amount of acicular particles were formed in case of phosphate preparation except for lead phosphate. Barium sulfate particles exhibited complicated shape formed by competitive aggregation and crystal growth. Clear crystal planes were observed at the surface of barium sulfate, lead sulfate, and barium carbonate. Besides temperature, the most significant factor to determine the particle yield and shape was pH. When a polyprotic acid was used as anion source, the particle yield changed with varying pH in accordance with the fraction of the first dissociation product of the acid.
