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17O enriched sodium borophosphate glasses were prepared from isotopically enriched NaPO3 and H3BO3. These glasses have been studied by 17O, 11B and 31P NMR including 17O and 11B multiple quantum magic angle sample spinning (MQMAS), 11B31P heteronuclear correlation (HETCOR) NMR and 11B 31P rotational echo double resonance (REDOR). For comparison, the crystalline borophosphates BPO4 and Na5B2P3O13 were included in the investigations. The latter compound shows three sharp 31P resonances at -0.2, -2 and -8 ppm and two BO4 sites that can only be resolved by MQMAS.
The 17O NMR spectra were recorded using both the static echo method at medium magnetic field (9.4 T) as well as MAS and MQMAS methods at high field (17.6 T). In total, five oxygen sites were identified in these borophosphate glasses: POP, NaOP, POB, BOB, NaOB. However, these five sites are not present simultaneously in any of the glasses. The 17O MQMAS spectra prove that POB links play a major role in borophosphate glasses. These results are confirmed by the complementary 11B MAS spectra that show the presence of asymmetric and symmetric trigonal groups BO3a and BO3s and two tetrahedral BO4 units. 11B 31P REDOR NMR is used to give independent information to assign the 11B lines to structural units present in the glasses. These REDOR measurements reveal that BOP bonds are present for each borate unit, including the BO3 groups. Particularly, a structural proposal for the two different BO4 resonances is given in terms of a different number of bonded phosphate tetrahedra. The 31P MAS spectra are usually broad and not well resolved. It is shown by 11B31P HETCOR NMR that a possible structural assignment of a 31P signal at about -20 ppm to Q2 units as in binary sodium phosphate glasses is wrong and that the phosphate tetrahedron belonging to this resonance must be connected to borate groups
Zinc aluminosilicate glasses are studied by Vickers indentation in order to reveal the effect of non-bridging oxygen (NBO) and incorporation of aluminium in the silica network on micromechanical properties. Therefore glasses of perzinc and peraluminous compositions as well as nominal NBO-free glasses on the meta-aluminous join are prepared by melt quenching.
To investigate the effect of environment on hardness, crack generation and propagation indentation was performed in air and in dry nitrogen atmosphere on HF etched surfaces. For constant silica fractions the increase in the Zn-to-Al ratio led to a characteristic step-like course of the micromechanical properties at the meta-aluminous composition.
The effect of the cation size is verified by comparing the results with those obtained in the calcia-alumina-silica system.
The effects of femtosecond laser pulse irradiation on the glass structure of alkaline silicate glasses were investigated by x-ray absorption near edge structure spectroscopy using the beamline of the Physikalisch-Technische Bundesanstalt at the electron synchrotron BESSY II in Berlin (Germany) by analyzing the magnesium Κ-edge absorption peak for different laser fluences. The application of fluences above the material modification threshold (2.1 J/cm²) leads to a characteristic shift of ~1.0 eV in the Κ-edge revealing a reduced (~3%) mean magnesium bond length to the ligated oxygen ions (Mg-O) along with a reduced average coordination number of the Mg ions.
Local structures of amorphous and quasicrystalline phases in Zr–Ti–Ni and Zr–Ti–Ni–Cu alloys have been studied by means of x-ray absorption spectroscopy. The amorphous phases show a high degree of icosahedral short-range order. In all investigated systems local order around Cu and Ni atoms was found to be nearly identical pointing to site substitution of Ni by Cu as the reason for an improved glass forming ability when Ni is partly substituted by Cu. The results strengthen an icosahedral cluster based approach for the structure of metallic glasses and indicate the importance of the medium-range order on glass formation.
Low melting zinc borate glasses awake interest to replace lead borate glasses in the silver metallization pastes for solar cells or microelectronics. In the current study, characteristic properties of alkali zinc borate glasses (X2O-ZnO-B2O3, X = Li, Na, K, Rb) were compared to an earth alkali zinc borate glass (CaO-ZnO-B2O3). Additionally, zinc oxide is partially substituted by lead oxide or cooper oxide in the borate glasses (Li2O-PbO-B2O3, Na2O ZnO CuO-B2O3). The alkali zinc borate glasses indicate less differences in Raman spectra, and thus in structural properties, in comparison to the Ca and Pb ions influence. LPbB (Tg = 401 °C) has a lower viscosity than LZB (Tg = 468 °C) and CaZB has the highest glass transition temperature (Tg = 580 °C). The Angell plot for the alkali zinc borate glasses shows a high fragility m = 80. Besides Tg, the density measured by means of the Archimedean principle, molar volume, and coefficient of thermal expansion (CTE) of the glasses were investigated. Trends could be found according to alkali ions or intermediate oxides. The density increases with decreasing alkali ion size from KZB (2.632 g/cm3) to LZB (2.829 g/cm3) and increases from LZB to LPbB (3.764 g/cm3). CTE ranges between 7.09 10-6 K-1 for CaZB and 11.5 10 6 K 1 for KZB and RZB. The differential thermal analysis (DTA) and X ray diffraction (XRD) indicate crystallization of various crystalline phases during heating with 5 K/min in most cases.
The structural properties of a borosilicate glass with nominal 16 mol% Na2O, 10 mol% B2O3 and 74mol% SiO2 and water contents between 0 and 8wt% H2O (0–22 mol% H2O)were investigated with IR, Raman and 11BMAS NMR spectroscopy. In addition to the pronounced OH stretching vibration band of weakly H-bonded species at 3580 cm−1 the MIR spectra show a triplet at 2900, 2350 and 1750 cm−1, similar as observed in water-bearing silicate glasses. These bands are assigned to OH groups and water molecules which are strongly H-bonded, to non-bridging oxygen. Water species contents determined from absorption bands in the NIR at 5200 cm−1 (molecular H2O), 4700 cm−1 (B\\OH), and 4500 cm−1 (Si\\OH) indicate that hydroxyl groups dominate up to ~6 wt% total H2O. Based on the absorption coefficients known from literature for silicate and borate glasses the B\\OH/Si\\OH ratio is estimated to be ≈0.8.
As indicated by density, Raman and NMR data the incorporation ofwater has strong structural impacts in particular at low water contents up to 3 wt% H2O. While the nominally dry glasses still contain a significant fraction (12%) of three-fold coordinated boron, almost all boron is four-fold coordinated in hydrous glasses. The increase of band components in the Raman spectra near 900 cm−1 relative to the region N 1050 cm−1 gives evidence for depolymerization of the network upon hydration. Fitting of the spectra with Gaussians implies that silica tetrahedra with two non-bridging oxygen (Q2) are preferentially formed by reactionwithwater on expense of tetrahedra linked to four tetrahedra (Q4).
The structural investigation of hydrated borate glasses provides new insights on the influence of water on boron speciation using spectroscopic methods. In the present study three soda–lime–borate glasses (NCBx with x = 5, 15 and 25 corresponding to xNa2O, 10CaO, 90 - xB2O3 in mol%) were prepared with water content up to 8 wt.%. The water speciation in the glasses was derived by near-infrared (NIR) spectroscopy while boron speciation was investigated by 11B MAS NMR (Magic Angle Spinning Nuclear Magnetic Resonance). For the three glasses effective molar absorption coefficients were determined experimentally for the bands at 5200 cm- 1 and 4600 cm- 1, corresponding to combination modes of H2O molecules and OH-groups, respectively. In contrast to silicate glasses, in which at most ~ 2 wt.% H2O are dissociated to OH-groups, the amount of dissociated H2O may even exceed 5 wt.% in borate glasses. The fraction of tetrahedral to total boron (N4 = BIV / BIV + BIII) is predominantly controlled by the ratio of Na2O + CaO / B2O3, but only weakly affected by the water content of the glasses. When increasing the H2O content from 0 to 8 wt.%, N4 increases from 25% to 26% for NCB5 and from 42% to 47% for NCB25 glasses.