Fluidized state gelation of ceramic microspheres: Feasibility study of a continuous process and analysis of the chemical dehydration phenomena

A continuous gelation process for producing aluminum and zirconium hydroxid e microparticles was conceived and tested in a lab-scale apparatus, Fluidiz ed state was devised as an appropriate hydrodynamic configuration to mainta in the reacting sol microdrops suspended: stable non-coalescing spherical g el particles in a size range quite below 100 mu m were produced via gelatio n. The microspheres produced by a subsequent calcination step showed a diam eter ranging between 2 mu m and 20 mu m. This powder, without further size classification, was an optimal product to manufacture test specimens by sin tering. Measurements on the mechanical properties, such as toughness, flexu ral strength and hardness, classified the test bars as a very promising cer amic material. In order to enlighten the chemical drying phenomenon and dev ise the main governing mechanisms acting in the gelation reaction, an extre mely simplified experimental system was set. A single drop of sol was depos ited into a given amount of the dehydrating liquid medium and observed by a n optical microscope; image analysis permitted us to identify the gel forma tion, the size reduction kinetics, as well as secondary phenomena.