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首页> 外文期刊>European Journal of Glass Science and Technology, PartB. Physics and Chemistry of Glasses >Calorimetric study of glasses and liquids in the polyamorphic system Y_2O_3-Al_2O_3
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Calorimetric study of glasses and liquids in the polyamorphic system Y_2O_3-Al_2O_3

机译：Y_2O_3-Al_2O_3多晶体系中玻璃和液体的量热研究

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Liquids in the Y_2O_3-Al_2O_3 system exhibit liquid state 'polyamorphism'with a transition occurring between two liquid phases ( in the supercooled state) with the same chemical composition but different density and strucure. Differential scanning and high temperature solution calorimertry experientnts were performed on Y_2O_3-Al_2O_3 glasses quenched from polyamporphic liquids to establish the thermodynamic properties of the high and low density amorphous phases (HDA, LDA) and the energetic factors that drive the liquid-liquid phase transition. Glasses produced from the high density, high temperature liquid by rapid quenching show the onset of a glass transition for the HDA form at 1120-1150 K. The HDA liquid is highly 'fragile' with a nonArrhenian temperature dependence consistent with its large configuratonal entropy. The HDA-LDA transition occurs at 1450 -1575 K, depending upon the composition, during quenching experiments. The HDA form can be recovered metastably to ambient conditions providing samples for calorimetric study. Transition to the more stable LDA 'polyamorp' then occurs when the HDA form is heated above its glass transition. This transitio is observed as an exothermic signature in heat capacity traces at 1211-1277 K. The glass transition for the LDA polyamorph occurs at approx 1320-1480 K. It is broader than that observed for the HDA form, indicating a 'stronger' (less fragile) liquid state, associated with smaller configurational entropy. Heats of solution measured in molten 2PbO.B_2O_3 at 1073 K indicate a large enthalpy difference between the HDA and LDA phases (DELTAH deg = 182 (+-) 5 kJ/mol at 298 K). The transition enthalpy is strongly temeprature dependent and DELTAH (LDA=HDA) is 30-50 kJ/mol at the liquid-liquid transition temperature (1450-1575 K depending on the composition).
机译：Y_2O_3-Al_2O_3系统中的液体表现出液态“多态性”，在化学成分相同但密度和结构不同的两个液相（过冷状态）之间发生转变。在由多两性液体淬火的Y_2O_3-Al_2O_3玻璃上进行了差示扫描和高温溶液热解实验，以建立高密度和低密度非晶相（HDA，LDA）的热力学性质以及驱动液相-液相转变的能级因子。由高密度，高温液体通过快速淬火制得的玻璃显示出HDA形式在1120-1150 K时发生了玻璃化转变。HDA液体具有高度“易碎性”，并且与非阿累尼昂温度相关，并且具有较大的结构熵。在淬火实验中，取决于组成，HDA-LDA转变发生在1450 -1575K。 HDA形式可以恢复到环境条件，为热量分析提供样品。然后，当将HDA形式加热到其玻璃化转变温度以上时，便会转变为更稳定的LDA“聚氨纶”。在1211-1277 K处的热容曲线中观察到该过渡是放热特征。LDA多晶型物的玻璃化转变发生在大约1320-1480K。它比HDA形式观察到的宽，表明“更强”（较小的脆性）液态，并具有较小的构型熵。在1073 K下在熔融2PbO.B_2O_3中测得的溶液热表明HDA和LDA相之间的焓差很大（在298 K下DELdegh度= 182（±）5 kJ / mol）。转变焓强烈依赖于温度，在液-液转变温度（1450-1575 K，取决于组成）下，DELTAH（LDA = HDA）为30-50 kJ / mol。

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