Studies in Lithium Oxide Systems: I, Li ₂ O B ₂ O ₃ –B ₂ O ₃

Abstract

Phase relationships in the system Li 2 O, B 2 O 3 ‐B 2 O 3 were studied by the quenching method using twenty compositions. The crystalline phases encountered were ( a ) Li 2 O, B 2 O 3 , which melts congruently at 849°± 2°C., ( b ) Li 2 O.‐2B 2 O 3 , which melts congruently at 917°± 2°C., ( c ) a new compound, 2Li 2 O‐5B 2 O 3 , which melts incongruently at 856°± 2°C. and dissociates below 696°± 4°C., ( d ) Li 2 O.3B 2 O 3 , which melts incongruently at 834°± 4°C. and dissociates below 595°± 20°C., and ( e ) probably Li 2 O.4B 2 O 3 , which melts incongruently at 635°± 10°C. Reactions were sluggish at temperatures near 600°C., resulting in metastable relations. Hence phase equilibrium data relating to the lower stability limit of Li 2 O.3B 2 O 3 and to the upper stability limit of Li 2 O.4B 2 O 3 are considered to be tentative. Properties of the glasses and crystalline phases were studied. The refractive index of the glasses increased with the addition of Li 2 O up to 22%, but further additions up to 40% had no substantial effect. Glasses containing less than 30% Li 2 O were water soluble. Limited data on the density and thermal expansion of the glasses are presented. Li 2 OB 2 O 3 was euhedral, lath‐shaped, length‐fast, biaxial negative (2V = 27°), with n α = 1.540, n β = 1.612, n γ = 1.616. Li 2 O.2B 2 O 3 was uniaxial negative, with n e = 1.560, n w = 1.605. Li 2 O.3B 2 O 3 was biaxial negative (2V = 75° to 80°), with n α = 1.576, n β = 1.602, n γ = 1.605. X‐ray powder diffraction data for the five crystalline compounds are presented. Thermal expansion data for Li 2 O‐B 2 O 3 and Li 2 O.2B 2 O 3 and limited data on the fluorescent properties of the compounds are given. X‐ray diffraction data are also presented for Li 2 O.B 2 O 3 .4H 2 O and Li 2 O.‐5B 2 O 3 . 10H 2 O. Li 2 O B 2 O 3 was obtained by heating the first hydrate at 450° to 680° C. X‐ray diffraction showed Li 2 O.4B 2 O 3 and Li 2 O‐3B 2 O 3 to be the crystalline products obtained during heating the decahydrate at 500°C. and 600°C., respectively.