Elasticity and structure of the compounds in the wollastonite (CaSiO3)–Na2SiO3 system: from amorphous to crystalline state

Abstract

The elastic properties and structure of four potential bioactive compounds in the CaSiO3-Na2SiO3 system were characterized by Raman and Brillouin spectroscopy at ambient conditions. The increase of Na2O content in the Na2O-CaO-SiO2 glass with the same silica content and hence polymerization was found to lower the elastic moduli with accompanied decrease of Q(0) and Q(2) species, increase of Q(1) species and negligible change of Q(3) species, corresponding to a lower and higher equilibrium constant for the disproportional reactions [Formula: see text] and [Formula: see text] (without balance), respectively. The composition-dependent variation in the shear modulus (G) of the Na2O-CaO-SiO2 glass can be attributed to the concentration change of Q(2) and probably Q(4) species; while bulk modulus (K) ascribed to the cohesion factor. The elastic moduli of the corresponding crystalline phases in this system also lower with the increase of Na2O content following two general criteria as a function of Na2O/CaO molar ratio: (1) K decreases faster than G for both the amorphous and crystalline phases and (2) both K and G decreases faster for the crystals than the glasses.

Structural variations of bioactive glasses obtained by different synthesis routes

“…Very similar bands were found for the crystalline phase that was derived from the glass of the CaSiO 3 -Na 2 SiO 3 system with the Na 2 O:CaO:2SiO 2 molar ratio, which was quite close to that occurring in the 45S5 bioglass. In particular, the most intense band at 985 cm −1 can be assigned to Q 2 Si species in the chain or ring crystalline silicates [48]. This suggests that the above-mentioned signals can be attributed to crystalline sodium calcium silicate Na 2 Ca 2 Si 3 O 9 phase (combeite), as identified by the XRD (Fig.…”

Alkali activation of a novel calcium‐silicate hydraulic binder with CaO/SiO2 = 1.1

“…The latter spectrum is simply characterized by 2 distinct signals, a broader one, corresponding to the amorphous component of the sample, with chemical shifts spanning from −65 to −95 ppm and a narrow feature at approximately ‐83.5 ppm, which is assigned to the presence of pseudowollastonite (α‐Ca 3 Si 3 O 9 ) . The amorphous spectral component of the anhydrous sample has a Q n structural unit distribution typical of calcium metasilicate glasses, ranging from Q 0 to Q 3 groups and a negligible or nonexistent amount of Q 4 units …”

“…Anhydrous material powders and the corresponding dried pastes after 28 days of hydration were analyzed by solidstate NMR analysis using a TecMag (Redstone)/Bruker 300 "wide bore" spectrometer with a 7 mm solid-state probe operating at 59.595 MHz for 29 Si observation and at 78.216 MHz for 27 Al observation. Only the samples hydrated for 28 days were chosen for NMR analysis due to the limited time of access to the NMR facilities and because XRD analysis showed that the main phase changes already occurred by 28 days.…”

“…cylindrical zirconia rotors. The chemical shifts were referenced to external samples of tetrakis(trimethylsilyl)silane (trimethylsilyl groups, Si(CH 3 ) 3 , d = À9.8 ppm) for 29 Si and a-O 3 Al 2 (d iso approximately at 12 ppm, octahedral co-ordination of Al) for 27 Al observations. More than 2000 scans were accumulated during NMR experiments, being these spectra collected under magic-angle spinning (MAS) with a rate of approximately 3.3 kHz for 29 Si and 5.2 kHz for 27 Al observations.…”

“…The chemical shifts were referenced to external samples of tetrakis(trimethylsilyl)silane (trimethylsilyl groups, Si(CH 3 ) 3 , d = À9.8 ppm) for 29 Si and a-O 3 Al 2 (d iso approximately at 12 ppm, octahedral co-ordination of Al) for 27 Al observations. More than 2000 scans were accumulated during NMR experiments, being these spectra collected under magic-angle spinning (MAS) with a rate of approximately 3.3 kHz for 29 Si and 5.2 kHz for 27 Al observations. For the singlepulse 29 Si NMR experiments, a pulse length of 2.5 ls, corresponding to a 50°magnetization flip angle, and a recycling time delay of 20 seconds were selected, while for the 27 Al NMR measurements, a pulse length of 1 ls, corresponding to a 30°magnetization flip angle, and a relaxation delay time of 1 second were selected.…”