On the melting behaviour of calcium monoxide under different atmospheres: a laser heating study

The melting behaviour of calcium monoxide, a very common geological compound produced whenever lime-based minerals are heated to high temperature in contact with air or CO2, has been revisited by quasi-containerless laser heating under controlled atmosphere. This is an experimental technique recently developed and applied to other refractory materials. This approach allowed a direct observation of the melting / freezing point dependence on the environment in which samples were heated across the fusion /solidification transition. The current results prove that the large discrepancy existing in the literature data for the melting temperature of CaO is most probably attributable to the influence of the environmental oxidising / reducing conditions on the melting behaviour itself. The CaO melting / freezing point measured in this work is (3222 ± 25) K in an oxidising environment, in agreement with previous research carried out under similar conditions and the JANAF table recommendation. The fusion /solidification transition in a reducing atmosphere occurs at a slightly, but systematically lower, more poorly reproducible temperature, with an average value of (3192  40) K. In the latter case, a more abundant formation of colour centres was noticed, corresponding to a higher concentration of oxygen defects in the refrozen and quenched CaO samples. The present study shows that the melting behaviour of calcia is dependent on the experimental atmosphere and the creation of oxygen defects in the re-solidified material. In the light of such conclusions, it is suggested that also pseudo-binary phase diagrams including CaO as one end member should be reassessed by taking into account possible deviations from the exact O/M stoichiometry in mixed oxides susceptible to the creation of oxygen defects at temperatures close to melting.

MANARA Dario;  BÖHLER Robert;  CAPRIOTTI Luca;  QUAINI Andrea;  BAO Zhaoui;  BOBORIDIS Konstantinos;  LUZZI L.;  JANSSEN Arne;  POEML Philipp;  ELOIRDI Rachel;  KONINGS Rudy; 

2014-02-18

ELSEVIER SCI LTD

JRC79915

0955-2219,   

http://www.sciencedirect.com/science/article/pii/S0955221913005918,    https://publications.jrc.ec.europa.eu/repository/handle/JRC79915,   

10.1016/j.jeurceramsoc.2013.12.018,