A Mechanism for Strengthening Fluorine-Containing Lithium Aluminum Silicate Glass-Ceramics
A 0.4% difference in the unit cell volume of β-spodumene was found between the exterior surface and the interior of a fluorine-containing glass-ceramic. The smaller cell volume of the interior places the exterior in compression and is believed to be largely responsible for the increase in strength of this material over that of lithium aluminum silicates which do not contain fluorine. The stress calculated from these data is consistent with the measured strength values. The compressive layer was ∼140 μm thick and is depleted in fluorine. Experimental and calculated deflection data from thin surface slices taken from one side confirm the differential lattice volume-strengthening mechanism in fluorine-containing lithium aluminum silicate glass-ceramics.