A thermodynamic study of the influence of the thermal treatments (annealing), below the glass transition temperature, on the
thermal behavior and enthalpy of maltitol glass was carried out by differential scanning calorimetry (DSC). An enthalpic effect
(exothermal) produced by the isothermal treatment of the quenched glass was found and measured.
The origin of the thermal effect was assigned to a physicochemical transformation of molecular associations in the solid (glass).
To achieve a correct description of the thermodynamic functions of glasses, another parameter, in addition to T and P, is introduced, namely the degree of advance of the above mentioned transformation.
Crystallization and glass-transition phenomena were studied for amorphous chlorobenzene (CB)/toluene (TL) binary systems as
the function of composition. Samples were prepared by vapor-deposition onto cold substrates, and their structural changes
due to temperature elevation were monitored with Raman scattering and light transmission. It was found that the crystallization
temperature (Tc) of CB-rich amorphous samples increases as the TL concentration is increased. This is similar to the linear dependence of
glass-transition temperatures (Tg) of many organic compounds on the concentration of additive. Also found was that Tc of TL-rich supercooled-liquids decrease as the CB concentration is increased. Issues related to the two kinds of Tc are discussed briefly.
Authors:V. Živanović, S. Grujić, M. Tošić, N. Blagojević, and J. Nikolić
The crystallization of K2O·TiO2·3GeO2 glass under non-isothermal condition was studied. In powdered glass with particle sizes less than 0.15 mm, surface crystallization
was dominant and an activation energy of crystal growth of Ea,s=327±50 kJ mol−1 was calculated. In the size range 0.15 to 0.45 mm, both surface and volume crystallization occurred. For particle sizes >0.45
mm, volume crystallization dominated with spherulitic morphology of the crystals growth and Ea,v=359±64 kJ mol−1 was calculated.
Structural and thermal properties of the 20Li2O-80TeO2 glass were studied using X-ray diffraction analysis and differential scanning calorimetry techniques to understand and control
the crystallization process on this glass. The γ-TeO2, α-TeO2 and α-Li2Te2O5 phases were identified during the crystallization in this glass. Activation energies and Avrami exponent n were calculated
from non-isothermal measurements for glasses with different particle size. The mean values
Authors:M. Chromcíková, M. Liška, and M. Martišková
A simple mathematical model of thermal polishing of rough glass surface as observed by light beam thermal analysis (LBTA)
is presented. The rough surface is represented by a triangular profile used for calculation of the light beam intensity attenuation
and an equivalent rectangular profile is used for the modeling of the time course of the thermal polishing. Computational
results obtained for the NBS 711 viscosity standard glass showed that the characteristic temperature, obtained from the series
of LBTA experiments after extrapolation to zero starting surface roughness, does not represent the glass transition temperature,
but it corresponds to the viscosity value of about 109 dPa.s. The validity of the proposed model was confirmed by the comparison of simultaneous LBTA and viscosity measurements
of CaO-Y2O3-Al2O3-SiO2 glasses.
The relation between change of the specific heat (ΔCp) accompanying the glass transformation and the chemical composition of glasses (Na2O, CaO, MgO)-Al2O3-SiO2 system has been studied. The exchange of modifiers in the glass structure causes the ΔCp increase in the sequence Na>Ca>Mg. Change the glass network composition by introducing Al into it makes smaller increase
of the ΔCp values. It has been shown that degree of ΔCp value changes is dependent on the iconicity/covalence of chemical bonds of cations with oxygen of glass structure network.
Crystallization, morphology and mechanical properties of a spodumene-diopside glass ceramics with adding different amount
of CaO and MgO in Li2O-Al2O3-2SiO2 were investigated. With CaO and MgO addition, the crystallization temperature (Tp) decreased, the value of Avrami constant (n) decreased from 3.2±0.3 to 1.4±0.2, the activation energy (E) increased from 299±3 kJ mol−1 to 537±5 kJ mol−1. The crystalline phases precipitated were h-quartz solid solution, β-spodumene and diopside. The mechanism of crystallization of the glass ceramics changed from bulk
crystallization to surface crystallization. The grain sizes and thermal expansion coefficients increased while flexural strength
and fracture toughness of the glass-ceramics increased first, and then decreased. The mechanical properties were correlated
with crystallization and morphology of glass ceramics.
EN 410 ( 2011 ): Glass in building. Determination of luminous and solar characteristics of glazing
ISO 15099 ( 2003 ): Thermal performance of windows, doors and shading devices – Detailed calculations
separate overlapping transitions when one transition goes into the reversing signal and the other into the nonreversing signal. But what if both go into the reversing signal such as a melting transition overlapping a glass transition due to a phase