A combined experimental and theoretical study of enthalpy of phase transition and fusion of yttria above 2000 °C using “drop-n-catch” calorimetry and first-principles calculation

Abstract

Drop-n-catch" calorimetry was performed on Y 2 O 3 spheroids of 2-3 mm in diameter, prepared by laser melting of powders. Samples were aerodynamically levitated in a splittable nozzle levitator in air or argon flow, laser heated from ~2200 to 3000 °C and dropped into a calorimeter at 25 °C, thus measuring their enthalpy as a function of temperature. The fusion enthalpy of cubic Y 2 O 3 was derived from the step in the temperature-enthalpy curve as 119 ± 10 kJ/mol. Calculations performed using density functional theory and molecular dynamics techniques produced the value 127 ± 3 kJ/mol Y 2 O 3. This combined methodology enables accurate determination of the enthalpies of fusion and phase transition of refractory oxides, including those containing lanthanides and actinides.

Phase transformations in oxides above 2000°C: experimental technique development

“…For Y 2 O 3 , the step in enthalpy corresponds to the sum of the pre-melting phase transformation and the enthalpy of fusion. The obtained value, 119 ± 10 kJ/mol, is within the uncertainty of previously reported values and in agreement with results of ab initio molecular dynamic (AIMD) simulations [37]. The DnC technique was then employed for fusion enthalpy measurements of ZrO 2 , HfO 2 , Lu 2 O 3 , and Yb 2 O 3 ( Table 1).…”

Measurements of Density of Liquid Oxides with an Aero-Acoustic Levitator

“…In Table 1 the density and thermal expansion coefficient values for liquid oxides measured in this work are listed together with four types of previously published density data: (i) measurements in aerodynamic levitator by Granier and Heurnault’s [ 59 ], Kohara et al [ 65 ], and Kondo et al [ 66 ]; (ii) measurements with the electrostatic levitator on board of International Space Station [ 36 , 37 ]; (iii) refinement from pair distribution function analysis (PDF) of synchrotron X-ray scattering [ 62 ]; (iv) ab initio molecular dynamic computations [ 60 , 63 ].…”

Combined computational and experimental investigation of high temperature thermodynamics and structure of cubic ZrO2 and HfO2

“…Our combined approaches are easy to generalize from HfO 2 and ZrO 2 to a broader range of systems. Indeed, we have applied the same combined experimental and computational methods to a wide range of oxides (e.g., Y 2 O 3 18 , La 2 Zr 2 O 7 41 , and several rare earth oxides). In addition, the computational method has been employed to study dozens of systems 45 , including oxides 46 , carbides, such as the Hf-Ta-C-N system 47 , and metals 48 .…”

“…Fusion enthalpies for ZrO 2 and HfO 2 were measured using drop and catch calorimetry. The technique and apparatus were described in detail elsewhere 17 , 18 . Schematic diagrams and photographs are provided in Supplementary Information together with data from all experiments.…”

“…The combination of experimental and computational method offers a unique opportunity for corroboration that is essential given the challenges associated with each approaches. On the experimental side, the difficulties lie in thermal gradients unavoidable in conditions of uniaxial laser heating of aerodynamically levitated samples used for calorimetry 17 , 18 and X-ray diffraction 19 – 21 . On the computational side, the difficulties reside in reaching sufficiently large system sizes and sufficiently long simulation times while still using accurate electronic structure calculations as well as ensuring proper modeling of all forms of excited states (defect formation and diffusion, potential anharmonic phonons and electron excitations).…”