The effect of substituting La2O3 to CaO at constant O/Si ratio, has been studied on thermal properties and non-isothermal devitrification behaviour of CaO.SiO2 glass. Differential thermal Analysis (DTA) and X-ray Diffraction Analysis have been used. Glass transformation temperatures, T-g, and softening temperatrues, T-g, curves versus composition are well explained by admiting that La+3 ions enter the glass structure with an average coordination number greater than the one of Ca+2 ions; however La+3 ions appear to succeed in working out their own coordination only when similar to 40% of CaO is substituted. In samples devitrified during a UTA run, CaO.SiO2 crystals form until similar to 50% CaO amount is substituted (x=1). The addition of La2O3 appears to stabilize, in the temperature range 900-1000 degrees C, the aCaO.SiO2 form, which in the binary CaO-SiO2 system is reported to be stable only above 1125 degrees C. Ca3La6(SiO4)(6) crystals form when similar to 60% CaO is substituted (x=1.4). In all devitrified samples, containing La2O3, another crystalline phase forms whose reflections were not identified by means of JCPDS cards. When La2O3 is substituted To CaO the tendency to devitrify appears to be lowered and so also the crystal growth activation energy, as a consequence of the shift of devitrification peaks towards higher temperatures. Devitrification involves a mechanism of surface nucleation; in samples that soften and sinter before devitrifying, surface nuclei behave as bulk nuclei.

Thermal properties and devitrification behaviour of (2-x)CaO center dot x/3La(2)O(3)center dot 2SiO(2) glasses / Costantini, Aniello; R., Fresa; A., Buri; Branda, Francesco. - In: SILICATES INDUSTRIELS. - ISSN 0037-5225. - ELETTRONICO. - 61:(1996), pp. 171-175.

Thermal properties and devitrification behaviour of (2-x)CaO center dot x/3La(2)O(3)center dot 2SiO(2) glasses

COSTANTINI, ANIELLO;BRANDA, FRANCESCO
1996

Abstract

The effect of substituting La2O3 to CaO at constant O/Si ratio, has been studied on thermal properties and non-isothermal devitrification behaviour of CaO.SiO2 glass. Differential thermal Analysis (DTA) and X-ray Diffraction Analysis have been used. Glass transformation temperatures, T-g, and softening temperatrues, T-g, curves versus composition are well explained by admiting that La+3 ions enter the glass structure with an average coordination number greater than the one of Ca+2 ions; however La+3 ions appear to succeed in working out their own coordination only when similar to 40% of CaO is substituted. In samples devitrified during a UTA run, CaO.SiO2 crystals form until similar to 50% CaO amount is substituted (x=1). The addition of La2O3 appears to stabilize, in the temperature range 900-1000 degrees C, the aCaO.SiO2 form, which in the binary CaO-SiO2 system is reported to be stable only above 1125 degrees C. Ca3La6(SiO4)(6) crystals form when similar to 60% CaO is substituted (x=1.4). In all devitrified samples, containing La2O3, another crystalline phase forms whose reflections were not identified by means of JCPDS cards. When La2O3 is substituted To CaO the tendency to devitrify appears to be lowered and so also the crystal growth activation energy, as a consequence of the shift of devitrification peaks towards higher temperatures. Devitrification involves a mechanism of surface nucleation; in samples that soften and sinter before devitrifying, surface nuclei behave as bulk nuclei.
1996
Thermal properties and devitrification behaviour of (2-x)CaO center dot x/3La(2)O(3)center dot 2SiO(2) glasses / Costantini, Aniello; R., Fresa; A., Buri; Branda, Francesco. - In: SILICATES INDUSTRIELS. - ISSN 0037-5225. - ELETTRONICO. - 61:(1996), pp. 171-175.
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11588/467572
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