Sol synthesis of the precursor of zirconium oxide in citric acid-ammonia solution

The precursor of zirconium oxide is synthesized by the sol-gel method by re acting zirconyl chloride octahydrate (ZrOCl2 . 8H(2)O) and citric acid in a mmonia solution. The ionized complex compounds (R(COO-+NH4)(3)) were first formed from the reaction of complex agent (citric acid) and ammonium hydrox ide. Zirconyl chloride octahydrate first hydrolyzed to produce zirconium te tranuclear complex molecule [Zr-4(OH)(8)(OH2)(16)(-OOC)(3)R](8+), which sub sequently produced a large complex molecule ([Zr-4(OH)(5)(OH2)(16)(OOC)(3)R ](5+) or [Zr-4(OH)(8) (OH2)(13)(-OOC)(3)R](5+)) through the polymerization of zirconium tetramer with the ionized complex agent. The effect of the rea ction conditions on the precursor solution's viscosity and average particle size were investigated in order to understand the kinetics of the reaction . A rational reaction mechanism is proposed satisfactorily to explain the f ormation and growth of the particles and viscosity of the sol.