Authors:Jinn-Shing Lee, C.-K. Hsu, and Chin-Wang Huang
The effects of Al2O3 and SiO2 additives on the crystallization of calcium phosphate glasses were studied. When the Al2O3 content was higher than 7 mol%, surface devitrification occurred in the glasses. However, for glasses with Al2O3 contents higher than 10 mol%, bulk devitrification predominanted. For the glasses with SiO2, a surface devitrification mechanism predominanted. Non-isothermal DTA techniques were applied in order to establish the
devitrification mechanism, and the kinetic parameters of crystal growth were obtained. The parameter m depends on the mechanism
and morphology of devitrification of calcium phosphate, glass containing SiO2 as additive, the values of m being lower than 1.2. These results indicate that the devitrification is controlled by the reaction
at the glass-crystal interface, or occurs from surface nuclei.
Authors:S Grujić, N Blagojević, M Tošić, V Živanović, and B Božović
effect of replacing 20 mol% of GeO2 by TiO2
on the properties of potassium germanate glass was investigated. The structure
and devitrification behaviour of glasses were studied by Fourier transform
infrared spectroscopy (FTIR), differential thermal analysis (DTA) and X-ray
diffraction (XRD). It was observed that potassium titanium germanate has a
higher glass transition temperature and a higher thermal stability vs. crystallization.
The presence of two exothermic peaks on the DTA curve of potassium germanate
glass indicates the complex crystallization process. The XRD pattern of this
glass heated at the temperature of the first crystallization peak indicated
that the GeO2 and K2Ge7O15
were formed. Only the K2TiGe3O9
phase was identified, in a case when potassium titanium germanate glass was
heated at the temperature of the crystallization peak.
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.
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.
The thermal properties and devitrification behaviour of substituted InF3 glasses were studied by means of differential thermal analysis. A comparison of various simple quantitative methods to assess
the level of stability of multicomponent fluoride glass systems was also made. Most of these methods are based on critical
temperatures. In this paper, a new parameter,kd(T), is introduced to the stability criteria. The stabilities of several substituted InF3 glasses were evaluated experimentally and correlated with the activation energies of crystallization via this new kinetic
criterion and compared with those evaluated by other criteria.
Authors:P. Kavouras, Th. Kehagias, K. Chrissafis, Ph. Komninou, and Th. Karakostas
Three batch compositions of pure oxides (SiO2,
Fe2O3, PbO, Na2O)
with equivalent SiO2, Fe2O3
and PbO contents and a gradually increased Na2O content
were vitrified through heating in a high temperature electric furnace and
subsequent quenching. The resulting vitreous products were thermally treated
in order to study the devitrification behaviour, under conditions designated
from differential thermal analysis experiments. Depending on the Na2O
content, crystal phase separation gave rise to the growth of acmite and hematite
or maghemite. A uniformly phase separated glass-ceramic material, with crystallites
of similar size and population density, was produced from devitrification
of the vitreous product with the higher Na2O content.
Authors:Hugo R. Fernandes, Dilshat U. Tulyaganov, Ashutosh Goel, and José M. F. Ferreira
2 O 3 + K 2 O introduction on devitrificationbehaviour of glass L 23 S 77 . As is evident from Fig. 2c , the crystallisation curve for glass G3 is shallower and exhibits a considerable shift to high temperature with respect to glass L 23 S 77