Phosphate/oxyfluorophosphate glass crystallization and its impact on dissolution and cytotoxicity

Fluorine loss determination in bioactive glasses by laser‐induced breakdown spectroscopy (LIBS)

“…Nevertheless, it has been widely shown that in bioactive glasses, fluoride complexes modifier cations (Ca 2+ , Na + etc.) exclusively, and does not form Si‐F bonds, as confirmed by 19 F‐ and 29 Si MAS NMR spectroscopy and molecular dynamics simulations 6,19,46,47,54,55 . Thus, fluorine loss in the present glasses is more likely to occur via formation of HF from the reaction of water vapor with metal fluorides (CaF 2 in our case) at high temperatures, as illustrated by the following reactions 53 :…”

“…However, those glasses were melted for 1 h at 1430°C, which is lower than the melting temperatures in the present work (Table 1). In ref 19 . fluorine losses in SiO 2 ‐free glasses in the system P 2 O 5 ‐CaO‐Na 2 O‐CaF 2 were determined by EPMA and with a fluoride ion probe, giving 18% and ~21% fluorine loss, respectively.…”

“…Fluorine losses in glasses are strongly dependent on the composition. While in bioactive glasses in the system SiO 2 ‐P 2 O 5 ‐CaO‐CaF 2 fluorine losses are typically in the range between 5 and 23%, 2,19 in oxyfluoride glasses much higher fluorine losses between 30 and 40% have been reported 11,12,20‐22 ; in the system SiO 2 ‐TiO 2 ‐SrO‐SrF 2 even as high as 63% 23 . The use of lids on the crucibles during melting as well as pre‐calcined raw materials (decreasing the water content, thereby avoiding the fluoride loss as HF) is highly recommended to increase fluorine retention during melting 4,12 …”

“…More recent publications reported on wavelength‐dispersive x‐ray fluorescence (WD‐XRF) spectrometry 13,25 . Here, an electron probe micro analyzer (EPMA) equipped with five wavelength dispersive x‐ray analyzers (WDX) was used to determine the fluoride content with an accuracy of ±0.1 at% 13,19 . The measurements were performed at the surface of polished bulk samples, showing that a certain amount of sample preparation is required.…”

“…Fluorine can be also determined by quantitative solid-state nuclear magnetic resonance (NMR). 31 However, typical disadvantages are weighing imprecisions, as only about 20-50 mg of sample is used to fill the rotor, and, depending on the probe, the presence of 19 F background signals, the suppression of which requires additional measurements. Moreover, a potential systematic error may arise if the relaxation times of the sample and the employed standard differ, the correction of which requires additional measurements, as well.…”