Structural and crystallization behavior studies on unfamiliar LiF–B2O3 glasses

Abstract

Glasses from the binary high LiF–B2O3 system with variable LiF contents (10–55 mol%) were prepared by normal melting-annealing technique. Optical, FTIR spectral properties were measured for the glasses in addition to thermal expansion parameters were derived to be able to convert glassy samples to their corresponding glass-ceramic derivatives. FTIR, X-ray diffraction and SEM were carried out for the prepared heat-treated glass-ceramics to derive their structural building groups and types of crystalline phases formed by controlled heat treatment regime. Optical spectra of the prepared glasses show only distinct UV absorption peaks which are related to unavoidable contaminated traces of impurities of Fe3+ ions. FTIR spectra reveal distinct extended vibrational bands within the mid-region 400-1600 cm−1 comprising both of triangular and tetrahedral borate groups (BO3, BO3F) beside the possibility of sharing of (LiF4) groups at high LiF content. Thermal expansion measurements indicate the changes of the dilatometric softening temperatures with the LiF content but with some derived variations depending on the constituents housing in the network structure. X-ray diffraction patterns data reveal the appearance of lithium borate crystalline phase at low LiF content and at high content both two crystalline phases of lithium borate Li2B4O7 (Diomignite) and LiB3O5 beside crystalline lithium fluoride (LiF) are identified. This result refers to the distinct action of both lithium ions (Li+) and fluoride ions (F−) as initiator to produce phase separation, ease of nucleation and followed by crystallization, similar to the behavior of Li2O within borate and silicate glasses. SEM images support the X-ray diffraction data revealing different crystalline phases with variable texture at high LiF content.