The melting curves of tin, uranium, cadmium, thallium and indium metals under pressure

Melting Is Well-Known, but Is It Also Well-Understood?

Contrary to continuous phase transitions, where renormalization group theory provides a general framework, for discontinuous phase transitions such a framework seems to be absent. Although the thermodynamics of the latter type of transitions is well-known and requires input from two phases, for melting a variety of one-phase theories and models based on solids has been proposed, as a generally accepted theory for liquids is (yet) missing. Each theory or model deals with a specific mechanism using typically one of the various defects (vacancies, interstitials, dislocations, interstitialcies) present in solids. Furthermore, recognizing that surfaces are often present, one distinguishes between mechanical or bulk melting and thermodynamic or surface-mediated melting. After providing the necessary preliminaries, we discuss both types of melting in relation to the various defects. Thereafter we deal with the effect of pressure on the melting process, followed by a discussion along the line of type of materials. Subsequently, some other aspects and approaches are dealt with. An attempt to put melting in perspective concludes this review.

New Approach for Trace Thallium Removal in High Purity Ammonium Rhenate Solution by P204 Extraction

Thallium (Tl) is an extremely toxic rare metal to the eco-environment. Trace thallium impurity in ammonium perrhenate is harmful to the high-temperature mechanical properties of rhenium metal used for aeroengine single crystal blade. The di(2-ethylhexyl) phosphoric acid (P204) extraction to remove thallium in ammonium perrhenate solution without additive was innovatively proposed. The migration behavior of trace thallium with the concentration of P204, saponification degree and organic/aqueous phase (O/A) ratio, distribution law of thallium in the extraction system of P204, and mechanism of thallium removal were revealed. It was found Tl removal was rapidly increased to 98.5%, at conditions of P204 0.75 mol/L saponified 70% by ammonia, Tl 3.27 mg/L, O/A 1:1, T 298.15 ± 2 K, 250 rpm, and 3 min. McCabe-Thiele Tl extraction equilibrium isotherms indicates Tl concentration of raffinate less than 18.7 μg/L, a theoretical extraction of two stages and a theoretical stripping of two stages are required when both O/A work lines were at 1.0. Therefore, the method of the P204 solvent extraction system can effectively extract Tl in the forms of TlA(org), TlA3(org), TlOHA2(org), and Tl(OH)2A(org). Meanwhile, the new approach can be a promising process for ammonium rhenate refining.