The Pr.O.F. project: orienting late High School students to University methodology in Chemistry and other Sciences

The P.r.O.F. project has been presented at the ECTN meeting and positively evaluated. The project aims to help high school students in the transition to University. It covers the areas of Chemistry, Physics, Biology and Mathematics. In the Chemistry section, methodological issues were emphasized. The specific subject, selected jointly by University and School teachers, was Solutions and Solubility. Short and long-time tests were performed to check the effectiveness of the intervention

"The influence of P2O5 on non-isothermal devitrification of 30Li2O*70SiO2 glass

The nucleation and crystal growth in 30 Li2O·70 SiO2 and 30 Li2O·69 SiO2· 1 P2O5 were studied by differential thermal analysis. The temperature of maximum nucleation rate, the activation energy for crystal growth and the crystallization mechanism were evaluated from DTA and DDTA curves. The influence of P2O5 on the devitrification process was also examine

Devetrification behaviour of Na2O*CaO*xSiO2 glasses

The effect of an increasing content of SiO2 in ternary glasses of compn. Na2O.CaO.xSiO2, where x = 2, 3, 4, 6, was investigated using DTA to evaluate the effect on the glass transition temp. and devitrification. The work is part of a more general study on the devitrification of soda-lime-silica glasses for glass-ceramic manuf. from cheap raw materials. Increasing the SiO2 content increased the glass transition temp. and thermal stability of the glass. Glasses with the compn. x = 4 and 6 softened remarkably before crystn. The glass with x = 2 underwent bulk crystn. with an activation energy of 95 kcal/mol from homogeneous bulk nuclei which developed with a max. nucleation rate at ∼550°

Nucleation and crystal growth in Na2O*SiO2 glass. A DTA study", Verres et Réfractaires 38, 589 (1984)

The curves obtained were used to evaluate the temperature at which maximum nucleation occurs, the activation energy of crystal growth and the crystallization mechanism. Comparison were made with the devitrification behaviour of a Na2O.2SiO2 glas

Glass transition temperature and devitrification behaviour of glasses in the Na2O*2SiO2-BaO*2SiO2 composition range", J.Mater.Sci.Letters 3,

DTA and DDTA measurements have been used. For more than 70 mol% Sodium disilicate surface crystallization alone occurs; at the eutectic at 70mol%, crystallization proved very difficult; and below 70mol%, bulk and surface crystallization occurred. Nucleation rates have been determine

Crystallization of glasses in the 2Na2O*CaO*3SiO2-Na2O*2CaO*3SiO2 composition range

The devitrification behaviour of specimens with compositions (2−x)Na2O(1+x)CaO·3 SiO2, O≤x≤ 1, was studied. The crystalline phases were identified by X-ray diffraction and the glass transition temperatures were determined by differential thermal analysis. The activation energies for the crystal growth were calculated from the inflection point temperatures detected on the derivation differential thermal analysis curves

Nucleation and crystal growth in Na2O*2CaO*3SiO2 glass. A DTA study

The non-isothermal devitrification of Na2O · 2 CaO · 3 SiO2 glass has been studied by differential thermal analysis in order to evaluate, from DTA curves, the temperature of maximum nucleation rate, Tm, and the activation energy values, Ec, for crystal growth. The temperature, Tm=580°C, is very close to the glass transition temperature, Tg=570°C, and the value of Ec=78 Kcal mole−1 for the surface crystal growth is nearly the same as the value Ec=89 kcal mole−1 for the bulk crystal growth; both are consistent with the activation energy for viscous flow. It is also pointed out that the nucleation rate—temperature curve and the crystallization rate—temperature curve are partially overlapped

Devitrification behaviour of glasses near the Na2O*2SiO2 composition

The influence of small substitutions of different cations for Na+ ions on the devitrification behaviour of Na2O·2 SiO2 glass has been investigated by differential thermal analysis. The stability of the glasses has been related to the glass transition temperature/liquidus temperature ratio and to the field strength of the cations

Nucleation In Glass-forming Systems - A Dta Study

A simple method recently proposed (ref. 1) for evaluating the temperature of maximum nucleation rate is applied to several different glass-forming systems. The results well agree with those obtained by means of traditional methods

Activation energy for the crystallization of glass from DDTA curves

A simple method, based on the measurements of two peak temperatures on a single derivative differential thermal analysis (DDTA) curve for determining the activation energy for bulk or surface crystallization in glasses is described. The devitrification of Li2O-2SiO2 glass has been investigated; the experimental results agree well with those obtained by alternative techniques and with the activation energy of viscous flow in the crystallization-range temperatures