FURTHER INVESTIGATION OF THE STABILIZATION OF BETA-CRISTOBALITE

Chemical stabilization of beta-cristobalite has been achieved using tw o methods: (1) incorporating ''stuffing'' cations Na, Ca, Cu, and Sr i nto the cavities in the tectosilicate framework, as previously reporte d, and (2) without ''stuffing'' cations, by substituting AlPO4 into th e framework. XRD, TEM, FTIR, DSC, and solid-state variable-temperature Si-29 NMR confirm that stabilization occurs by both methods. Dynamic disorder, characteristic of the beta-cristobalite structure above the alpha <-- --> beta phase transition, was observed via TEM in the NaAlO 2-, CaAl2O4-, and CuAl2O4-stabilized cristobalites at room temperature . For AlPO4-stabilized material intergrowths of AlPO4 regions with a t ridymite-type structure suppress the beta- --> alpha-cristobalite phas e transition.