In‐situ determination of the HfO₂–Ta₂O₅‐temperature phase diagram up to 3000°C

Abstract

The previously unknown experimental HfO 2 -Ta 2 O 5 -temperature phase diagram has been elucidated up to 3000°C using a quadrupole lamp furnace and conical nozzle levitator system equipped with a CO 2 laser, in conjunction with synchrotron X-ray diffraction. These in-situ techniques allowed the determination of the following: (a) liquidus, solidus, and invariant transformation temperatures as a function of composition from thermal arrest experiments, (b) determination of equilibrium phases through testing of reversibility via in-situ X-ray diffraction, and (c) molar volume measurements as a function of temperature for equilibrium phases. From these, an experimental HfO 2 -Ta 2 O 5 -temperature phase diagram has been constructed which is consistent with the Gibbs Phase Rule.

Reply to comments: “In‐situ determination of the HfO2‐Ta2O5‐temperature phase diagram up to 3000°C”

“…In the comment on "In Situ Determination of the HfO 2 -Ta 2 O 5 -Temperature Phase Diagram up to 3000°C," Fedorov 1 praises the outstanding work performed by McCormack et al 2 in combining high temperature X-ray synchrotron diffraction and a conical nozzle levitator equipped with CO 2 laser to obtain reliable data in the HfO 2 -Ta 2 O 5 system up to the melting point (3000°C). Fedorov 1 then comments on the sketched phase fields that results from this data.…”

“…As Fedorov 1 states, the correct curvature of the monotectic phase field between T-Ta 2 O 5 and L+T-Ta 2 O 5 would be autocorrected from CALPHAD calculations. As stated, McCormack et al 2 have not performed any CALPHAD calculations on this system. The phase fields were solely constructed by satisfying the Gibbs phase rule as explicitly stated 2 .…”

“…As stated, McCormack et al 2 have not performed any CALPHAD calculations on this system. The phase fields were solely constructed by satisfying the Gibbs phase rule as explicitly stated 2 . Figures 1 and 2 shows Figure 3 and Figure 5, respectively from McCormack et al 2 , with the phase fields adjusted according to Fedorov's 1 recommendations.…”

“…The phase fields were solely constructed by satisfying the Gibbs phase rule as explicitly stated 2 . Figures 1 and 2 shows Figure 3 and Figure 5, respectively from McCormack et al 2 , with the phase fields adjusted according to Fedorov's 1 recommendations. It is important to stress that CALPHAD calculations still need to be performed to optimize these phase fields.…”

“…The phase fields represented here are akin to "Massalski's" diagrams 5 , that is, they have been sketched to match the experimental data and should not be directly used for CALPHAD modeling. The authors of McCormack et al 2 advise when using their paper for CALPHAD analysis, to only use actual data points, not the sketched phase fields, in addition to other thermochemical data such as enthalpies of formation and heat capacities.…”