Date of Award
1988
Degree Type
Dissertation
Degree Name
Doctor of Philosophy
Abstract
High temperature (T) and pressure (p) investigations of electrical and thermal transport processes in solid and liquid Fe serve as basic input to: (a) geomagnetic dynamo models and (b) a better understanding of the complex electronic structures of d-band transition metals.;The electrical resistivity ({dollar}\rho{dollar}) of pure Fe was measured in both solid and liquid states at p up to 70 kb. A modified four-wire technique was developed to eliminate the parasitic potentials inherent to many of the common methods of current and potential lead attachment. p-coefficients of resistivity decrease linearly with T at a rate of 2.7 {dollar}\times{dollar} 10{dollar}\sp{lcub}-6{rcub}{dollar}(kb K){dollar}\sp{lcub}-1{rcub}{dollar} in the solid followed by a sharp drop to a T-independent value of -8.4 {dollar}\times{dollar} 10{dollar}\sp{lcub}-3{rcub}{dollar}kb{dollar}\sp{lcub}-1{rcub}{dollar} in the liquid. T-coefficients of resistivity (TCR) in the liquid for p below 52 kb agree well with several previous investigations at 1 atm. However, it appears that the discrete increase in the TCR from 1.5 {dollar}\times{dollar} 10{dollar}\sp{lcub}-4{rcub}{dollar}K{dollar}\sp{lcub}-1{rcub}{dollar} to 5 {dollar}\times{dollar} 10{dollar}\sp{lcub}-4{rcub}{dollar}K{dollar}\sp{lcub}-1{rcub}{dollar} for p above 52 kb is associated with the different parent solid structures.;Assuming dominant electronic heat conduction, the Wiedemann-Franz Law was used, in conjunction with the {dollar}\rho{dollar}(T,p) data, to calculate the thermal conductivity of solid and liquid Fe at high p.;The thermoelectric power (S) of Fe was determined from thermal emf measurements of twisted Fe/Pt-10%Rh thermocouples. S values for both solid and liquid Fe at p up to 70 kb indicate that the effects of p and T can be correlated with changes in slope of the density of states function ({dollar}\partial{dollar}N({dollar}\in{dollar})/{dollar}\partial{lcub}\in{rcub}{dollar}) at the Fermi energy ({dollar}\varepsilon\sb{lcub}\rm F{rcub}{dollar}). The strong T-dependence of S in bcc-Fe is associated with {dollar}\varepsilon\sb{lcub}\rm F{rcub}{dollar} changes in a local N({dollar}\in{dollar}) minimum, resulting in rapid variations in {dollar}\partial{dollar}N({dollar}\varepsilon\sb{lcub}\rm F{rcub}{dollar})/{dollar}\partial{lcub}\in{rcub}{dollar}. In the liquid region, {dollar}\partial{dollar}N({dollar}\varepsilon\sb{lcub}\rm F{rcub}{dollar})/{dollar}\partial{lcub}\in{rcub}\ >0{dollar} at low p, consistent with existing calculations, but is {dollar}<{dollar}0 at high p. This corroborates the structural correlation interpreted from the TCR data.;With the unlikelihood that {dollar}\rho{dollar} and S of the outer core are radically different than those of pure liquid Fe, the possibility of thermoelectric effects is explored as a contributing factor in the generation and interaction of electrical and fluid velocity fields in the outer core.
Recommended Citation
Secco, Richard Andrew, "Electrical, Thermal, And Thermoelectrical Properties Of Solid And Liquid Iron At High Pressures" (1988). Digitized Theses. 1752.
https://ir.lib.uwo.ca/digitizedtheses/1752