The thermal expansion, density and molar volume of some binary borate glasses were measured before and after exposure to a
gamma-ray dose of 103 kGy. The expansion curves for all glasses, which were measured from room temperature to above the softening temperature,
displayed similar characteristics. Increase of the lead oxide content decreased the thermal coefficient of expansion, but
the effects of different alkali metal cations were shown to depend on their ionic radii. The various proposed mechanisms of
thermal expansion are dealt with. The experimental results could be explained by considering the bond strengths, the polarizing
powers of the different cations and the damage produced by radiation. The possible compaction of the structure due to irradiation
is also discussed.
Differential scanning calorimetry (DSC) and thermomechanical analysis (TMA) were used to study the thermal behaviour of (50-x)Na2O-xTiO2-50P2O5 and 45Na2O-yTiO2-(55-y)P2O5 glasses. The addition of TiO2 to the starting glasses (x=0 and y=5 mol% TiO2) resulted in a nonlinear increase of glass transition temperature and dilatation softening temperature, whereas the thermal
expansion coefficient decreased. All prepared glasses crystallize under heating within the temperature range of 300–610°C.
The contribution of the surface crystallization mechanism over the internal one increases with increasing TiO2 content. With increasing TiO2 content the temperature of maximum nucleation rate is also gradually shifted from a value close to the glass transition temperature
towards the crystallization temperature. X-ray diffraction measurements showed that the major compounds formed by glass crystallization
were NaPO3, TiP2O7 and NaTi2(PO4)3. The chemical durability of the glasses without titanium oxide is very poor, but with the replacement of Na2O or P2O5 by TiO2, it increases sharply.
The effect of replacing SrO by BaO on the glass transition temperature and on devitrification behaviour in a series of glasses in the strontium tetragermanate — barium tetragermanate composition range has been studied by differential thermal analysis, X-ray diffraction and Fourier-transform infrared spectra. All glasses studied exhibit internal crystal nucleation. The progressive replacing of SrO by BaO causes the decrease of the glass transition temperature. Solid solutions between SrGe4O9 and BaGe4O9 were found to crystallize in glass containing both SrO and BaO. The effect of the specific surface of the glass samples on devitrification processes has been also pointed out.
Authors:F. Branda, A. Costantini, A. Buri, and A. Tomasi
In this paper a thermoanalytical study of the kinetic parameters and mechanism of the devitrification process of CaO·SiO2, 1.6CaO·0.4MgO·2SiO2 and 1.4CaO·(0.6/3)Y2O3·2SiO2 is reported. The experimental results suggest that, in the studied glasses, a surface nucleation process is operative; however,
in finely powdered samples, that soften and efficiently sinter before devitrifying, surface nuclei behave as bulk nuclei.
In this case lamellar crystalline structures are obtained.
Authors:L. Abbas, L. Bih, A. Nadiri, Y. El Amraoui, H. Khemakhem, and D. Mezzane
Thermal and chemical durability studies of the phosphate glasses belonging to the binary MoO3-P2O5 and the ternary K2O-MoO3-P2O5 systems are reported. The chemical resistant attack tests carried out on the free alkaline MoO3-P2O5 glasses show that the glass associated with the P/Mo ratio 2 has the high chemical durability. It shows also a high glass
transition temperature value. The above findings are interpreted in terms of the cross-link density of the glasses and the
strength of the M-O bonds (M=P, Mo).
The influence of K2O addition on the properties (density, Tg, durability) of this binary high water resistant glass is studied. It is found that the chemical durability along with the
other physical properties are reduced by the incroporation of K2O in the glass matrix. The results were explained by assuming the formation of non-bridging oxygens and weak bonds. The mechanism
of the dissolution of these glasses is proposed.
Authors:J. Rincon, J. Cáceres, C. González-Oliver, D. Russo, A. Petkova, and H. Hristov
A study of three Spanish and one Bulgarian basaltic rock demonstrated that, after thermal treatment at temperatures higher
than 800C, crystallization of pyroxenes, anorthite and magnetic occurred. Following sintering of the original basalts and
powdered original glasses, the same crystalline phases were nucleated and grown in the resulting glass-ceramics. Chemical
and DTA/TG analyses suggested similar behaviour for the synthesized Canarian basalt glasses, which are located in the tephrite-basanite
field, and different behaviour for the trachy-andesite Canarian and the basaltic-andesite Bulgarian basalt glass. In consequence
of the high sensitivity of the specific heat to phase transformations, Cp(T) and TMA experiments allowed a distinction between the tephrite-basanite and trachy-andesite Canarian glasses on the basis
of their different thermal behaviour.
Besides a short introduction to historical data on inorganic and polymeric glasses, some aspects of the glassy-state are analyzed:
particularly, induced entropy changes, characteristics of the glass transformation and a novel anharmonicity vibrational approach.
The horizons and scientific prospects for the nano- and non-crystalline states are discussed.
Authors:S. Lendvayová, K. Moricová, E. Jóna, J. Kraxner, M. Loduhová, V. Pavlík, J. Pagáčová, and S. C. Mojumdar
traditional silicate glass, numerous new glass systems have been developed under the demand of modern industrial applications [ 1 – 3 ].
Therefore, it is very important to evaluate the thermal stability of glasses against crystallization [ 4 – 6