The Thermodynamics of Oxygen in Reactive Metals

Influence of oxygen content on grain growth in Pr–Fe–B/Nd–Fe–B sintered magnets

“…9, may be associated with the solution of oxygen in the respective RE-rich phases; gases such as oxygen (as well as hydrogen and nitrogen) are soluble in all the rare earths, being present in the form of atoms (rather than molecules) that occupy interstitial sites within the metal lattice [36], where further changes in oxygen content results in a change in the chemical composition of the remaining liquid, leading to a decrease in the eutectic melting temperature at the ternary eutectic point. During the cooling process after the sintering treatment, the chemical composition of the remaining liquid changes along the monovariant curve (e 1 U 3 -Pr-Fe-B [5] and e 5 E 2 -Nd-Fe-B [37]): where (e 1 /e 5 ) ≈ L ⇔ + , and (U 3 /E 2 ) ≈ L ⇔ RE-rich phase + + , in the respective systems.…”

Direct oxygen removal technique for recycling titanium using molten MgCl2salt

“…By submerging Ti wires and small pieces in Ca-saturated CaCl 2 , Ti samples has been deoxidized to a level of 50 mass ppm (see also Table 3). 5,19 In the Ca-halide ux deoxidation method, the ultimate limit of deoxidation depends on the nal O concentration in the ux, which means that the purity of the ux and the initial O content of the Ti will rule the deoxidation limit. To decrease the deoxidation limit set by a CaO , an electrochemical method was developed (electrochemical deox.…”

“…Based on the thermodynamic calculation shown in Fig. 4, 5,11,50 when a MgO is decreased to the level of 10 À2 in the presence of metallic Mg at 1200 K, the chemical potential of O 2 (p O 2 ) in the system is decreased to $10 À45 atm, and Ti containing 0.018 mass% (180 mass ppm) O can be obtained. In other words, when Ti is deoxidized down to commercial O levels for high-grade Ti (0.05 mass% O, or 500 mass ppm) using Mg as reductant, a MgO at 1200 K must be decreased to the level of 0.025. the electrochemical deoxidation of Ti in MgCl 2 is shown in Fig.…”

“…Because the principle of electrochemical deoxidation of Ti has been reported in detail previously, 5,21 the deoxidation process is only briey outlined here. A solid Ti-O solution is deoxidized by Mg in the following reaction:…”

“…O removal directly from Ti and its alloys to levels below 0.1 mass% (1000 mass ppm) is very difficult because O dissolves in Ti to form an interstitial solid solution, and because Ti has a strong affinity with O. 5,6 Table 2 lists some effective methods for direct removal of O from Ti and from TiAl. 2, For example, the deoxidation of solid Ti by reaction with chemically active Ca dissolved in CaCl 2 in the temperature range of 1273 to 1473 K has been examined.…”