An x-ray photoelectron spectroscopic study of the chemical states of fluorine atoms in calcium silicate glasses

Abstract

X-ray photoelectron spectroscopy has been used to examine the chemical states of fluorine in the glasses of composition xCaF2(50 – x)CaO · 50SiO2 (x = 5, 10, 15, 20, and 25 mol %) and xCaF2(50 – x/2)CaO(50 – x/2)SiO2 (x = 5, 10, 15, and 20 mol %). The analysis of the F1s spectra indicated that Ca2+ and F- ions introduced as CaF2 are favorably located among the Si–O skeleton forming Ca–F clusters. The fraction of the bridging and nonbridging oxygen atoms was derived from the O1s spectra, and the network of the fluorine-containing glasses was concluded to depend only on the ratio CaO/SiO2.

Effect of Fluorine on Silicate Network for CaO-CaF2-SiO2 and CaO-CaF2-SiO2-FeOx Glasses.

“…The binding energies are close to that of CaF 2 crystal (684.3 eV, 13) 685.1 eV 20) ) rather than that of F-containing VAD SiO 2 glass (687.1 eV). 13) It has been reported that the fluorine in the VAD SiO 2 glass form covalent Si-F bonds. 21) Consequently, it can be concluded that the fluorine is dominantly coordinated with Ca 2ϩ in the present composition ranges of the CaO-SiO 2 -CaF 2 and CaO-SiO 2 -CaF 2 -FeO x glasses.…”

“…tion of the F1s XPS spectra range from 683.4 to 684.9 eV. The binding energies are close to that of CaF 2 crystal (684.3 eV, 13) 685.1 eV 20) ) rather than that of F-containing VAD SiO 2 glass (687.1 eV). 13) It has been reported that the fluorine in the VAD SiO 2 glass form covalent Si-F bonds.…”

“…This is so-called halo pattern confirming that the samples are amorphous. 13,20) and F-containing SiO 2 glass due to the vapor phase axial deposition method (VAD) 13) are indicated in both figures. The spectra for all samples give symmetrical peaks and have been fitted with single Gaussian functions.…”

“…The structure of silicate glasses containing CaF 2 has been predicted from the data obtained by means of viscosity [2][3][4] and cryoscopic measurements, 5) and studied more directly using spectroscopic measurements such as infrared absorption, [6][7][8][9] Raman, 10,11) X-ray photoelectron 12,13) and 19 F nuclear magnetic resonance spectroscopies. 14,15) The conclusions deduced from the above reports can be classified into three conflicting views:…”

“…10,12) (iii) Fluorine is present as F Ϫ coordinated with Ca 2ϩ and does not contribute to the breakage of Si-O bonds irrespective of glass compositions. 9,11,13) Consequently, there is no consensus on the structure of silicate glasses containing CaF 2 . In order to judge the above views, it is necessary to accumulate more reliable data for the structures of glasses having different compositions to determine the relationship between the structural role of fluorine and the glass composition.…”