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Development of high-temperature oxide melt solution calorimetry for p-block element containing materials Mykola Abramchuk1,2 , Kristina Lilova2, Tamilarasan Subramani1,2, Ray Yoo1, Alexandra Navrostky1,2,a) 1

Peter A. Rock Thermochemistry Laboratory and NEAT ORU, University of California Davis, Davis, California 95616, USA School of Molecular Sciences and Center for Materials of the Universe, Arizona State University, Tempe, Arizona 85287, USA a) Address all correspondence to this author. e-mail: [email protected] 2

Received: 30 April 2020; accepted: 2 July 2020

Understanding the thermodynamic stability of materials plays an essential role in their applications. The hightemperature oxide melt solution calorimetry is a reliable method developed to experimentally measure formation enthalpy. Until now, it has been mostly used for the characterization of oxide materials. We introduce modifications in the experimental technique which makes it suitable for a wide range of non-oxide compounds. The modified methodology was used to measure the heat effects associated with the oxidative dissolution of almost all p-elements of groups III, IV, V, and VI and verified by calculating the standard enthalpies of formation of the corresponding oxides at 298 K. The results presented serve as a compelling database for pure p-elements, which will provide a very straightforward way of calculating the formation enthalpies of non-oxide systems based on high-temperature calorimetric experiments.

INTRODUCTION The high-temperature oxide melt solution calorimetry (HT OMSC) is a powerful experimental tool to determine thermodynamic properties of solid-state inorganic materials [1]. In this method, a given material and its constituent components are dropped from room temperature into a molten salt solvent at high temperature in a Calvet-type calorimeter (Fig. 1). The sample is dissolved in the molten salt, resulting in a heat effect called drop solution enthalpy (ΔHds). The obtained values of ΔHds for reactants and products are used to calculate the formation enthalpy via thermochemical cycles [1, 2, 3]. Over five decades, HT OMSC was predominantly applied to various multicomponent oxides and related systems, such as spinels and olivines [4, 5, 6], sulfates [7], phosphates [8, 9], ceramics for nuclear waste immobilization [10, 11], perovskites [12, 13], and layered oxides [14]. Several exceptions include studies of the heat of mixing between binary sulfides and selenides and the investigation of the energetics of nitrides and related materials [15, 16, 17, 18, 19, 20, 21]. Guo et al. studied the phase stability of uranium silicides through HT OMSC and transposed temperature drop calorimetry, in which a similar experimental setup was used without the solvent [22]. Zaikina et al. [23] determined the enthalpy of transition

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between three allotropes of germanium by HT OMSC and differential scanning calorimetry (DSC) methods. The results revealed a good agreement between the two methods, thus suggesti