Heat capacities and derived thermodynamic properties of lithium,sodium,and potassium disilicates from T=(5 to 350)K in both vitreous and crystalline states

摘要

Cryogenic heat capacities determined by equilibrium adiabatic calorimetry from T=(6 to 350)K on Li,Na,and K disilicates in both crystalline and vitreous phases are adjusted to end member composition and the vitreous/crystal difference ascertained.The thermophys-ical properties of these and related phases are estimated,compared,and updated.The values at T= 298.15 K of {S°(T)- S°(0)}/R for stoichiometric compositions of alkali disilicate(M2O·2SiO2):vitreous,crystal:Li,16.30,14.65;Na,20.67,19.47;and K,23.26,23.00.Entropy differences confirm greater disorder in the vitreous compounds compared with the crystalline compounds.The entropy data also show that disorder increases with decreasing atomic mass of the alkali ion.