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. 2023 Aug 1;16(15):5406.
doi: 10.3390/ma16155406.

Experimental Investigation of Phase Equilibria of the Ho-Ir-O Ternary System at 1073 K

Viera Homolová  1 , Lucia Čiripová  1 , Ondřej Zobač  2 , Adéla Zemanová  2 , Ladislav Falat  1
Affiliations

Experimental Investigation of Phase Equilibria of the Ho-Ir-O Ternary System at 1073 K

Viera Homolová et al. Materials (Basel). .

Abstract

An experimental study of the phase equilibria of the Ho-rich part of the Ho-Ir-O ternary system at 1073 K by means of x-ray diffraction, differential scanning calorimetry, and scanning electron microscopy has been carried out. Ho-hcp and four binary compounds, namely Ho3Ir, Ho5Ir2, Ho5Ir3, and Ho2O3, were identified in the Ho-Ir-O model alloys after long-term annealing (350-1220 h). No solubility of iridium in Ho2O3 oxide and Ho-hcp was observed. No ternary phase was found. Based on the experimental results, an isothermal section of the Ho-rich part of the Ho-Ir-O system at 1073 K was constructed. In addition, the microstructure of as-cast alloys was studied. An irregular eutectic consisting of faceted Ho-phase in Ho3Ir phase was observed in the alloys with Ho-hcp + Ho3Ir + Ho2O3 phase composition, and the temperature of the eutectic reaction Ho-hcp + Ho3Ir ↔ liquid was determined.

Keywords: Ho-Ir-O system; eutectic microstructure; isothermal section; phase diagram; phase equilibria.

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Conflict of interest statement

The authors declare no conflict of interest. The funders had no role in the design of the study, in the collection, analysis, or interpretation of data, in the writing of the manuscript, or in the decision to publish the result.

Figures

Figure 1
Figure 1
Experiment scheme: SEM—scanning electron microscopy, XRD—X-ray diffraction, DSC—differential scanning calorimetry.
Figure 2
Figure 2
Microstructure of the alloys without annealing with EDX spectra of observed particles (a) alloy 1 (67Ho-5Ir-28O at %), (b) alloy 2 (57Ho-7Ir-36O at %), (c) alloy 3 (59.6Ho-11.4Ir-29O at %), (d) alloy 5 (57.5Ho-9Ir-33.5O at %), (e) detail of the eutectic in alloy 5 (57.5Ho-9Ir-33.5O at %), (f) alloy 6 (55Ho-23Ir-22O at %), and (g) alloy 8 (61Ho-19Ir-20O at %).
Figure 2
Figure 2
Microstructure of the alloys without annealing with EDX spectra of observed particles (a) alloy 1 (67Ho-5Ir-28O at %), (b) alloy 2 (57Ho-7Ir-36O at %), (c) alloy 3 (59.6Ho-11.4Ir-29O at %), (d) alloy 5 (57.5Ho-9Ir-33.5O at %), (e) detail of the eutectic in alloy 5 (57.5Ho-9Ir-33.5O at %), (f) alloy 6 (55Ho-23Ir-22O at %), and (g) alloy 8 (61Ho-19Ir-20O at %).
Figure 3
Figure 3
DSC heating curves of the alloys (a) alloy 2 (57Ho-7Ir-36O at %), and (b) alloy 3 (59.6Ho-11.4Ir-29O at %).
Figure 4
Figure 4
Microstructure of the alloys after annealing at 1073 K: (a) alloy 1 (67Ho-5Ir-28O at %) with EDX spectra of identified phases; (b) alloy 2 (57Ho-7Ir-36O at %); (c) alloy 5 (57.5Ho-9Ir-33.5O at %); (d) alloy 7 (61Ho-16Ir-23O at %), and (e) alloy 6 (55Ho-23Ir-22O at %) with EDX spectra of identified phases.
Figure 4
Figure 4
Microstructure of the alloys after annealing at 1073 K: (a) alloy 1 (67Ho-5Ir-28O at %) with EDX spectra of identified phases; (b) alloy 2 (57Ho-7Ir-36O at %); (c) alloy 5 (57.5Ho-9Ir-33.5O at %); (d) alloy 7 (61Ho-16Ir-23O at %), and (e) alloy 6 (55Ho-23Ir-22O at %) with EDX spectra of identified phases.
Figure 5
Figure 5
XRD patterns of the investigated alloys: (a) alloy 3 (59.6Ho-11.4Ir-29O at %); (b) alloy 7 (61Ho-16Ir-23O at %); (c) alloy 8 (61Ho-19Ir-20O at %); and (d) alloy 4 (55Ho-17Ir-28O at %).
Figure 5
Figure 5
XRD patterns of the investigated alloys: (a) alloy 3 (59.6Ho-11.4Ir-29O at %); (b) alloy 7 (61Ho-16Ir-23O at %); (c) alloy 8 (61Ho-19Ir-20O at %); and (d) alloy 4 (55Ho-17Ir-28O at %).
Figure 6
Figure 6
The suggested Ho-rich part of the isothermal section of the Ho-Ir-O phase diagram at 1073 K. The composition of the investigated alloys is marked by stars.
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