A series of borophosphate glasses with the composition (65-x) B2O3 + 15 P2O5 + 20 Na2O + x CaO (x = 0, 2.5, 5, 7.5, 10, and 15 mol%) synthesized by melt-quenching technique. XRD analysis confirmed the amorphous nature of the glass. FTIR spectroscopy was used to investigate structural changes in the borophosphate glass with varying CaO content. In the zero-calcium oxide sample, bands were observed between 500 and 650 cm−1 (B-O-B), 1050 cm−1 (P-O-P), 1465–1471 cm−1 (H–O–H), and 3215–3446 cm−1 (O–H). With CaO incorporation, notable shifts and new bands emerged. Broader bands from 400 to 1600 cm−1 in higher CaO contents indicated the presence of metallic bonds, network depolymerization, and structural rearrangements confirming the role of CaO as a network modifier. Physical parameters systematically evaluated, revealing a densification trend with increasing CaO content. Density fluctuated between 2.163 and 2.532 g cm−3, while molar volume fluctuated between 46.34 and 39.05 cm3 mol−1, indicating tighter atomic packing. OPD fluctuated from 69.73 to 62.58 mol L−1, suggesting enhanced structural compactness. Optical absorption spectra analyzed using a UV–Vis–NIR spectrometer, together with Urbach energy evaluation, revealed a redshift in the absorption edge, while the optical band gap varied from 2.470 to 3.162 eV with increasing CaO content. These variations are attributed to modifications in the glass network structure, including possible changes in the concentration of non-bridging oxygen atoms. The metallization criterion calculated from refractive index and band gap values fluctuated from 0.351 to 0.397 by increasing CaO, indicating higher metallic character; these findings point to a tunable electronic structure. The thermal stability of the glass was determined by means of differential scanning calorimetry/thermogravimetric analysis (DSC/TGA). From the DSC/TGA curve, the glass transition temperature (Tg), crystallization temperature (Tc), and melting temperature (Tm) have been identified and thermal stability is also calculated. The tailored compositional design significantly affects bioactivity, positioning these borophosphate glasses as promising candidates for bone regeneration.

Thermal and structural effects of calcium in borophosphate bioactive glasses

期刊论文
发表日期：

2026年5月9日

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Gailan A. Saber,
Saman Q. Mawlud

摘要

A series of borophosphate glasses with the composition (65-x) B₂O₃ + 15 P₂O₅ + 20 Na₂O + x CaO (x = 0, 2.5, 5, 7.5, 10, and 15 mol%) synthesized by melt-quenching technique. XRD analysis confirmed the amorphous nature of the glass. FTIR spectroscopy was used to investigate structural changes in the borophosphate glass with varying CaO content. In the zero-calcium oxide sample, bands were observed between 500 and 650 cm⁻¹ (B-O-B), 1050 cm⁻¹ (P-O-P), 1465–1471 cm⁻¹ (H–O–H), and 3215–3446 cm⁻¹ (O–H). With CaO incorporation, notable shifts and new bands emerged. Broader bands from 400 to 1600 cm⁻¹ in higher CaO contents indicated the presence of metallic bonds, network depolymerization, and structural rearrangements confirming the role of CaO as a network modifier. Physical parameters systematically evaluated, revealing a densification trend with increasing CaO content. Density fluctuated between 2.163 and 2.532 g cm⁻³, while molar volume fluctuated between 46.34 and 39.05 cm³ mol⁻¹, indicating tighter atomic packing. OPD fluctuated from 69.73 to 62.58 mol L⁻¹, suggesting enhanced structural compactness. Optical absorption spectra analyzed using a UV–Vis–NIR spectrometer, together with Urbach energy evaluation, revealed a redshift in the absorption edge, while the optical band gap varied from 2.470 to 3.162 eV with increasing CaO content. These variations are attributed to modifications in the glass network structure, including possible changes in the concentration of non-bridging oxygen atoms. The metallization criterion calculated from refractive index and band gap values fluctuated from 0.351 to 0.397 by increasing CaO, indicating higher metallic character; these findings point to a tunable electronic structure. The thermal stability of the glass was determined by means of differential scanning calorimetry/thermogravimetric analysis (DSC/TGA). From the DSC/TGA curve, the glass transition temperature (T_g), crystallization temperature (T_c), and melting temperature (T_m) have been identified and thermal stability is also calculated. The tailored compositional design significantly affects bioactivity, positioning these borophosphate glasses as promising candidates for bone regeneration.