With the increase in demand for titanium, the usage of titanium scrap has increased. It is necessary to develop a new technology to efficiently remove oxygen impurities in titanium scrap. However, it ...is extremely difficult to remove oxygen directly from a solid solution of oxygen and titanium; thus, there is no effective deoxidation method for titanium at the industrial scale. In this study, the authors thermodynamically analyzed and considered the feasibility of a new technology to remove oxygen dissolved in titanium by utilizing the vapor of rare earth metals which have high vapor pressures at high temperatures, such as samarium, europium, thulium, and ytterbium. It was elucidated that titanium with oxygen levels of < 500 mass ppm could be obtained by exploiting the deoxidation ability of samarium, thulium, and ytterbium combined with their ability to form oxychlorides. The oxygen level achieved through the proposed technology is lower than that obtained using metallic calcium vapor. Based on thermodynamic considerations, a new process to efficiently remove oxygen in titanium using rare earth metals with high vapor pressure based on their oxyhalide formation is proposed.
Metallic Ti has a strong affinity for O at high temperatures, and methods for removing O directly from Ti are limited. Recently, the authors developed a new sintering process that removes O from Ti ...using Y metal as a deoxidizing agent in molten salt. However, Y contaminated the sintered Ti body. To address this problem, the authors developed a new Ti deoxidation process using a metal filter. In this process, a Ti green made of Ti powder and Y metal are introduced with molten salt into the respective sides of a room divided by a Ti filter. O removed from the Ti green passes through the Ti filter and reacts with the Y metal. Meanwhile, the small solubility and diffusion coefficient of Y in
β
-Ti are expected to kinetically prevent Y contamination of the sintered Ti body. It was experimentally demonstrated that a sintered Ti product with a low-O-concentration (< 250 mass ppm O) can be produced while suppressing Y contamination (< 120 mass ppm Y) in the new process. The establishment of this process enables low-cost production of highly functional Ti products and the recycling of Ti scraps in the future.
In this work, the possibility of the direct removal of oxygen species from metallic Ti through the formation of rare-earth oxyfluorides has been investigated from a thermodynamic viewpoint. The ...deoxidation limit of
β
-Ti using rare-earth metals (M: Y, La, Ce, and Nd) as deoxidants was evaluated. It was found that Ti metal with an oxygen concentration of 200 mass ppm or less could be theoretically obtained under the M/MOF/MF
3
equilibrium at 1300 K (1027 °C), which suggested a possibility of reducing the oxygen content in Ti below 500 mass ppm utilizing a fluoride-based molten salt. Furthermore, a new deoxidation process, in which oxygen was removed in the form of MOF compounds using Mg deoxidant, was discussed as well. The obtained results revealed that the oxygen content in
β
-Ti could be theoretically reduced to a level below 1000 mass ppm using a MF
3
-containing molten salt equilibrated with Mg. Rare-earth metals and their alloys are usually produced by the electrolysis in a fluoride-based molten salt; hence, the modern industrial electrolysis techniques can be potentially utilized for deoxidizing Ti scrap.
Steel containers and instruments are used to hold and transport Mg melts. Thus, quantitative analysis of the dissolution of metallic elements from the steel materials into the liquid Mg is important ...for controlling the impurities in processes such as Mg alloy production and Ti smelting. When austenitic stainless steels containing Cr and Ni come in contact with a Mg or Mg alloy melt, a large amount of Ni and limited amounts of Fe and Cr dissolve into the melt. In this study, the composition of a Mg-Ni-based melt in equilibrium with SUS316 was investigated to determine the maximum amounts of impurities dissolved from SUS316 into the liquid Mg. Mg-Ni melts of different compositions were held in a closed crucible of SUS316 at 1073 K (800 °C) to 1273 K (1000 °C), and the compositions of the inner wall of the crucible and the Mg-Ni alloy were evaluated after quenching. Subsequently, the relationships between the solubility limit of element
i
(
i
: Ni, Fe, and Cr) in liquid Mg with the coexistence of SUS316,
C
sol
,
i
∗
(mass pct), and the temperature,
T
(K), were determined:
log
(
C
sol
,
Ni
∗
)
=
-
1.40
×
10
3
/
T
+
2.57
(
±
0.12
)
,
log
(
C
sol
,
Fe
∗
)
=
-
5.20
×
10
3
/
T
+
3.93
(
±
0.16
)
,
and
log
(
C
sol
,
Cr
∗
)
=
-
5.96
×
10
3
/
T
+
3.80
(
±
0.05
)
.
These solubility limits were compared with those estimated based on the available thermodynamic data for the SUS316 and Mg-
i
binary systems. The validity of the obtained data and the reliability of the previously reported thermodynamic data were also discussed.
Oxygen was directly removed from pure titanium and a Ti-6Al-4V alloy by electrolysis in molten MgCl
2
at 1173 K (900 °C), where the metal being refined was the cathode and a graphite rod was used as ...the anode. By applying a voltage of approximately 3 V between the electrodes, commercially pure titanium, containing 1200 mass ppm oxygen, and the Ti-6Al-4V alloy, containing 1400 mass ppm oxygen, were deoxidized to 500 mass ppm or less. Under certain conditions, extra-low-oxygen titanium (as low as 80 mass ppm oxygen) was obtained using this electrochemical technique. The results obtained in this study indicate that the electrochemical deoxidation of titanium in molten MgCl
2
is feasible and applicable not only to the refinement of primary metals, but also for upgrading machined titanium products and recycling metal scraps.
A novel method for removing the oxygen (O) in titanium (Ti) is proposed and developed, wherein holmium (Ho) and holmium chloride (HoCl3) are used as a deoxidant and flux, respectively. The reduction ...of O concentration in Ti to a level of below 200 mass ppm O (even reaching 110 mass ppm O) through the formation reaction of holmium oxychloride (HoOCl), i.e., O (in Ti) + 2/3 Ho + 1/3 HoCl3 → HoOCl, was confirmed. This result reveals that deoxidation of Ti using Ho in HoCl3 flux is effective, and low-O Ti can be obtained under Ho/HoOCl/HoCl3 equilibrium. This new deoxidation technique using Ho as a deoxidant can be applied to the refining of Ti scraps and the production of low-O content Ti powder in the future. The standard Gibbs energy of formation of HoOCl (ΔG°f,HoOCl) at 1300 K was experimentally determined to be – 744 ± 10 kJ mol−1. In addition, the value of ΔG°f,Ho2O3 was determined to be – 1503 ± 10 kJ mol−1, which is in good agreement with the reported data (– 1510 kJ mol−1). A potential diagram of the Ho–Cl–O system at 1300 K was newly drawn using the thermodynamic data determined through this study.
•The oxygen concentration of Ti was decreased to approximately 110 mass ppm.•These concentration levels are low compared to those of high-purity Ti sponge.•This new technique is expected to be used in the recycling of Ti scrap in the future.•The value of ΔG°f,HoOCl at 1300 K was experimentally determined for the first time.•A new potential diagram of the Ho–Cl–O system at 1300 K was constructed.
A novel technique for the continuous extraction of nickel (Ni) from Ni-based superalloy scraps using molten zinc (Zn) has been proposed, and its feasibility was experimentally demonstrated. The newly ...developed approach allows for extraction of Ni metal directly from superalloy scraps with simultaneous separation of the Zn from the resulting Zn-Ni alloy. The optimal conditions for the extraction of Ni and separation of valuable elements such as rhenium (Re), tantalum (Ta), and tungsten (W) were determined by varying major process parameters including the reaction time and configuration of the reaction chamber. The proposed method has been successfully utilized for the production of the superalloy containing 62.8 mass pct of Ni and 15.5 mass pct of refractory metals (Re, W, and Ta). Under certain conditions, 41 pct of the Ni contained in the superalloy could be extracted at 1173 K (900 °C) over 48 hours, producing an alloy containing 84.0 mass pct of Ni and 0.2 mass pct of the refractory metals.
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