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Title: Phase equilibria studies of alloys relating to oxide nuclear fuels
Author: Gurler, Remzi
Awarding Body: The University of Birmingham
Current Institution: University of Birmingham
Date of Award: 1990
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Alloys of the elements Mo, Pd and Rh have been studied since complexes of these with Ru and Tc are found as metallic inclusions in irradiated oxide fuels, and it is considered that knowledge of the constitution of these multicomponent alloys may assist in understanding the history and character of such fuel. Samples were prepared either by arc melting or rapid solidification from Mo-Pd and Mo-Rh and ternary Mo-Pd-Rh systems. Rapid solidification was employed in an attempt to overcome the problem of slow diffusion in these systems particularly at lower temperatures. The usefulness of rapidly solidified materials in the constitutional investigation of these particular systems has been proved. Constitutional studies were made of binaries Mo-Pd and Mo-Rh using optical microscopy SEM analyses and X-ray diffraction methods. The phase boundaries in both binaries at temperatures ranging from 881 to 1100 °C were established satisfactorily. No intermediate phase was found at the temperatures of interest. Differences from published diagrams are suggested. An isothermal section of Mo-Pd-Rh ternary system was established at 1100 °C by constitutional studies employing the same techniques as utilised in the binary investigations. The section involves only the bcc fcc and hcp phases.T he bcc solid solution is restricted to the Mo comer while the fcc and hcp phases are stable over wide ranges of compositions. A three phase region (bcc + hcp + fcc ) is located near the Mo-Pd edge binary. The phase boundary composition limits found in the relevant binaries agree very well with those of the two-phase fields in the ternary . Thermodynamic coefficients for the phases in the relevant binaries Mo-Pd , Mo-Rh and Pd-Rh were derived by the assessment of available phase diagram and thermodynamic data using the Lukas program ; the resulting coefficients were input to reestablish the binaries. Very good agreement was found with the experimental phase diagrams and the comparison of integral molar free energies and the partial free energies of Mo with experimental values was very satisfactory. The coefficients established in the binary computations were combined with the lattice stability values of components and the ideal term to compute ternary isothermal sections-No ternary interaction terms were involved. The isothermals between 1373 - 2673 K were constructed. The isothermal calculated at 1373 K matches very well with the constitutionally established one except for the prediction of a more restricted hcp phase. The location of the three phase region is the same on both the experimental and calculated isothermal-Solidus , liquidus and secondary surfaces counters were constructed satisfactorily. Some attempts have been made to improve the 1373K isothermal section calculated employing the relevant binary coefficients only , by introducing ternary interaction terms. But these attempts were ineffective because of the lack of ternary thermodynamic values and insufficient ternary phase diagram data.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available