Korelace mezi aktivační energií strukturní relaxace a viskózního toku pro BaO-P2O5-Al2O3 skla

Viscosity and structural relaxation were studied by thermomechanical analysis for six Al2O3 -doped BaO-P2O5 glasses. The low-temperature viscosity data (10(7) - 10(11) Pa.s) were described and modeled by the Vogel-Fulcher-Tammann, Avramov-Milchev and Mauro-Yue-Ellison-Gupta-Allan equations. Temperature dependence of the activation energy of viscous flow was determined from the tangent of the extrapolated (in terms of the three viscosity equations) viscosity-temperature data-curves. Values of the activation energy of viscous flow were compared to the activation energies of volume relaxation determined from the exact physico-chemical description of the cyclic thermomechanical measurements performed over the glass transition region. In addition, differential scanning calorimetry was used to determine the activation energies of enthalpy relaxation. Good correspondence between the relaxation and viscosity activation energies was found in the respective temperature ranges. Good agreement was also confirmed for the viscosity and enthalpy fragilities, as well as for the indicator of the thermodynamic fragility.Viskozita a strukturní relaxace byly studovány pomocí TMA pro 6 vybraných skel systému BaO-P2O5-Al2O3. Z naměřených dat byly získány aktivační energie a vzájemně porovnány

Termodynamický model CaO-SiO2 skel

The CaO-SiO2 glass forming system is a typical example of a situation when the Shakhmatkin and Vedishcheva thermodynamic model cannot explain the experimentally determined Q-units distribution. As the system components are determined as stable crystalline phases found in the equilibrium phase diagram, the reason of the model failure is the missing system component representing the Q(3) structural unit. We suggested a solution to the problem by adding an artificial CaO center dot 2SiO(2) component and we proposed a method of estimating the Gibbs energy of this component. The method is based on the linear relationship found between the reaction Gibbs energy of the formation of the system components representing the different Qn units (n = 3, 2, 1, 0) divided by the number of non-bridging oxygen atoms in this particular component (i.e., 4-n) on one side and the n value on the other side. The method was qualified by the good coincidence of the model results with the MAS NMR experimentally determined Q-distribution. Moreover, the estimated value of Gibbs energy practically coincides with the optimised value obtained by minimising the sum of the squares of the d eviations between the experimental and calculated Q-distribution with respect to the molar Gibbs energy of CaO center dot 2SiO(2).Termodynamický model skel založených na systému CaO-SiO2 byl vytvořen na základě Shakhmatkin-Vedishcheva modelu a testován pomocí výsledků MAS NMR výsledků měření

Role modifikátorů na strukturní interpretaci skelného přechodu v MgO/BaO-Al2O3-P2O5 sklech

Thermomechanical analysis, differential scanning calorimetry and Raman spectroscopy were used to study the role of the modifying oxides on the glass transition behavior of the MgO/BaO-Al2O3-P2O5 glasses. In case of the volumetric changes associated with the glass-liquid transformation, a complex description combining the effects of viscosity, thermal expansion and structural relaxation was successfully applied to the thermomechanical data based on non-linear optimization of the involved variables. For the enthalpy relaxation data, a novel simulation-comparative method was developed to accurately determine the kinetic parameters of the Tool-Narayanaswamy-Moynihan relaxation model, overcoming the difficulties associated with the commonly encountered instrumental distortions of the experimental data. In most cases, the modifying oxides had the dominant role, as compared to the primarily cross-linking effect of the Al2O3 oxide, in determination of the physico-chemical properties of the studied glasses. Differences between the magnesium and barium phosphates were consistent with the concept of larger size Ba2+ ions leading to the higher disorganization and diversification of the phosphate glass matrix. Compositional trends in the measured quantities were correlated with the representation of the particular structural units occurring in the MgO/BaO-Al2O3-P2O5 glasses.TMA, DSC a Ramanova spektroskopie byly použity ke studiu vlivu modifikujících oxidů na skelný přechod MgO/BaO-Al2O3-P2O5 skel. Objemové změny asociované se skelným přechodem byly popsány kombinací efektu viskozity, teplotní expanze a strukturní relaxace. Entalpické změny byly analyzovány pomocí nové simulačně-srovnávací metody

Strukturní relaxace a viskozita MgO-P2O5 skel dopovaných Al2O3

Thermomechanical analysis and differential scanning calorimetry were used to study the viscosity and relaxation behavior of the Al2O3-doped magnesium phosphate glasses. Viscosity in the range (10(7) - 10(11)) Pa center dot s was described by the nowadays top performing multiparametric models. A fixed extrapolation of high-temperature viscosity according to the Eyring theory was applied with the exception of the Arrhenius equation. The activation energies of viscous flow were very close to the activation energy of enthalpy relaxation determined in terms of the Tool-Narayanaswamy-Moynihan model. On the contrary, the activation energy of volume relaxation was found to be much lower in comparison with the viscous flow activation energy. In general, the increase of the Al2O3 content leads to the increases of the viscosity, of the activation energies of viscous flow and structural relaxation (as well as of the kinetic fragilities calculated from these quantities), and of the temperatures characterizing the glass transition during the viscosity, volume, and enthalpy measurements. The phosphate chains interconnecting effect of the Al3+ ions was found to be much stronger than the influence of the MgO modifying oxide. However, the enthalpy changes during the relaxation processes seem to be primarily influenced by the MgO/P2O5 ratio. Consistence of the compositional interpretation of the obtained results indicates the benefits of the utilization of the correlation coefficients for attributing the structural units responsible for the changes of physico-chemical quantities.Relaxační chování Mg-fosfátových skel dotovaných Al2O3 bylo studováno pomocí termomechnické analýzy a diferenční skenovací kalorimetrie. Viskozity těchto skel byly studovány v rozsahu 10^7 až 10^11 Pa.s

CONTACTLESS THERMODILATOMETRY OF GLASS CULLET

Contactless dilatometry was used for the thermal analysis of a set of glass cullet samples collected in the surroundings (including the forest, gardens, etc.) of the Janstejn glass factory. The collected set of samples covered the time period of approximately one century. The glass composition was measured by X-ray fluorescence spectroscopy. A method of verifying the correctness of the contactless dilatometry results based on the Priven 2000 evaluation of thermal properties was proposed and verified

Termodynamický model a vysokoteplotní Ramanova spektra Na2O-B2O3 sklotvorných tavenin

The set of 33 baseline subtracted and thermally corrected Raman spectra of xNa(2)O center dot(1-x)B2O3 (x = 0.10, 0.15, 0.20, 0.25, 0.30, 0.40, and 0.50) glassforming melts measured at temperatures ranging from 501 degrees C to 1145 degrees C was analyzed. The real error estimated by Principal Component Analysis indicated 3-4 independent components. The Multivariate Curve Analysis (MCR) performed for three components resulted in the Raman spectra (so called loadings) and relative abundances (so called scores) of each component. The thermodynamic model of Shakhmatkin and Vedishcheva (SVTDM) was evaluated for each studied melt. Ten following system components were considered: Na2O, B2O3, 3Na(2)O center dot B2O3 (N3B), 2Na(2)O center dot B2O3 (N2B), Na2O center dot B2O3 (NB), Na2O center dot 2B(2)O(3) (NB2), Na2O center dot 3B(2)O(3) (NB3), Na2O center dot 4B(2)O(3) (NB4), Na2O center dot 5B(2)O(3) (NB5), and Na2O center dot 9B(2)O(3) (NB9). The Malfait's spectral decomposition was performed considering the equilibrium molar amounts of the components with highest abundance, i.e. B, NB, and NB4. The obtained partial Raman spectra were compared with the loadings obtained by MCR. The acceptable coincidence was found. The MCR adjusted scores were close to the SVTDM equilibrium molar amounts of system components considered in the Malfait's decomposition. The obtained results validate the correctness of the SVTDM. (C) 2019 Elsevier B.V. All rights reserved.Vysokoteplotní Ramanova spektra pro sklotvorné taveniny Na2O-B2O3 s obsahem Na2O 10 až 50 molárních procent byla změřena a analyzována ve spojení s termodynamickým modelem SVTDM

Efekt litia na skelně přechodové chování bioskla 45S5

Differential scanning calorimetry, thermomechanical analysis and Raman spectroscopy were used to study the role of the Li2O and P2O5 oxides on the structural relaxation phenomena in the Li-doped 45S5 Bioglass. The glass transition behavior was found to be similar for the enthalpy and volume manifestations of the relaxation motions. The Tool-Narayanaswamy-Moynihan (TNM) model was applied. An improved simulation-comparative methodology was used to determine the model relaxation parameters. The TNM model parameters and the selected glass transition characteristics (the glass transition temperature and the coefficients of thermal expansion) showed no statistically significant correlation with the particular elements present in the synthesized glasses. Hence, the information about the glasses composition was used to calculate the theoretical amounts of the Q(Si)(n) species in the Li-doped 45S5 glasses. It was found that practically all explored physico-chemical quantities related to the glass transition kinetics show a correlation with the content of Q(Si)(2) species that are responsible for the formation of the chain-like structures in the present glasses.Metody DSC, TMA a Ramanovy spektroskopie byly použity pro studium efektů Li2O a P2O5 na strukturní relaxaci Li-dopovaného bioskla 45S5. TNM model byl použit k popisu strukturní relaxace v oblasti skelného přechodu. TNM paramtery, teplota skelného přechodu a koefficient teplotní expanze nevykázaly žádnou významnou korelaci se složením syntetizovaných skel

Termokinetické chování Al2O3-PBO-B2O3 skel

Thermokinetic behavior of the Al2O3-PbO-B2O3 glassy system was investigated by means of differential scanning calorimetry, X-ray diffraction analysis and Raman spectroscopy. The glass transition kinetics was described in terms of the Tool-Narayanaswamy-Moynihan model. The compositional evolution of the relaxation parameters was explained in terms of the structural changes and movements of the characteristic structural units detected by Raman spectroscopy. Crystal formation in the studied glassy matrices was investigated in dependence on composition and particle size. The crystal growth was suppressed by increasing particle size as well as by increasing Al2O3 content; formation of crystalline boron oxides was replaced by formation of mixed Al2O3/PbO oxides and Pb4B2O7 phase. The nucleation-growth Johnson-Mehl-Avrami model and the empirical autocatalytic model of.Sestak and Berggren were used to describe the complex crystallization kinetics. The Avramov-.Sestak concept of temperature dependent activation energy was successfully applied and tested on the real-life experimental data. The corresponding methodology was critically reviewed.Termokinetické chování skel na bázi Al2O3-PBO-B2O3 bylo studováno technikami DSC, XRD a Ramanovou spektroskopií. Kinetika skelného přechodu byla popsána modelem TNM. Pro popis krystalizační kinetiky byly použity modely JMA a Sestak-Bergrren. Kompoziční trendy termokinetického chování byly popsány. Koncept Avramov-Šesták pro teplotní závislost aktivační energie byl úspěšně aplikován a testován