Neodymium disilicate powders were synthesized via a sol-precipitation method with different precipitants (i.e., ammonia, ammonium bicarbonate and urea) and subsequent sintering. The samples were characterized by X-ray diffraction. In addition, a theoretical relationship between neodymium ion concentrations in different precipitation equilibrium solutions was also investigated and analyzed based on thermodynamic equilibrium calculation. The results show that the precipitant type has an impact on the phase compositions of the precursors and the sintered products. In the synthesis, neodymium ions can be completely precipitated as amorphous neodymium hydroxide with ammonia as a precipitate at pH 8~9. For ammonium bicarbonate as a precipitate, the precursor type is related to both carbon concentration and pH value. The excessive hydroxide forms neodymium hydroxycarbonate in a heated urea solution. The possible formation mechanism of silicon sol in the presence of different precipitants was discussed.

Keywords: Precipitant, Precursor, Neodymium disilicate, Thermodynamis