When the colloidal casting processing technique wa s used to mold ,the hardening time of silica sol shell without NH4Cl aqueous solution was 38 hrs. Where as the hardening time of silica sol shell with addition of NH4Cl aqueous solution was only 1hr , and a gas with pungent smell was generated at the meantime . The results show that NH4Cl aqueous solution plays a role in accelerating silica sol shell2hardening , and a chemical reaction take s place and thus emit s NH3 . The
hardening mechanism of NH4Cl aqueous solution in silica sol shell molding wa s studied through analyzing the silica sol structure , coagulation principle , thermodynamics and dynamics