This application relates to a low-alpha-
ray silica and its preparation method. The method involves adding a high-purity
sodium sulfate solution to water glass, followed by the sequential addition of dilute
sulfuric acid solutions of varying concentrations for aging. The resulting precipitate is then calcined to obtain low-alpha-
ray silica with Th ≤ 5 ppb and U ≤ 5 ppb. The
sodium sulfate solution optimizes the
precipitation process in two ways: first, it increases the
ionic strength of the solution, compresses the colloidal double layer, and disrupts the metastable state of the
system, thus promoting the aggregation and
crystallization of the target precipitate; second,
sulfate ions preferentially complex or inhibit the
precipitation tendency of
impurity cations based on the
common ion effect; furthermore, the dilute
sulfuric acid solution promotes the reaction and rapid
precipitation of
silicate ions with
hydrogen ions, causing the Th and U ions encapsulated in the precipitate to precipitate out, thereby reducing the
impurity content in the solution. This low-alpha-
ray silica, due to its extremely low Th and U content and good
thermal conductivity, can be widely used in high-performance and special-purpose
chip packaging fields.