Ionic conduction in space charge regions

The diffusion coefficients of several transition elements (Ti, V, Cr, Mn, Fe, Co, Ni, Cu, and Zn) and a few non-transition elements (Mg, Si, Ga, and Ge) in fcc and liquid Al are critically reviewed and assessed by means of the least-squares method and semi-empirical correlations. Inconsistent experimental data are identified and ruled out. In the case of the elements, for which plentiful experimental data are available in the literature, the least-squares analysis gives rise to the activation energies and pre-exponential factors in an Arrhenius equation. For the elements with limited experimental data or no data at all, the diffusion parameters are estimated from two semi-empirical correlations. In one correlation, the logarithmic pre-exponential factors are plotted against the activation energies for various elements in Al. In the other correlation, the activation energies are shown as a function of valences relative to Al. The diffusion coefficients calculated by using the evaluated diffusion parameters agree reasonably with the reliable experimental data. The proposed semi-empirical correlations are used to predict the diffusion coefficients of a few elements in liquid Al. A satisfactory agreement between the predicted and measured diffusion coefficients is obtained.

Diffusion coefficients of some solutes in fcc and liquid Al: critical evaluation and correlation

Massive charged particles create regions of intense damage (tracks) by passing through bulk samples of insulating materials. These tracks are shown to result from the positively charged region created by ionization. An approximate model of an ``ion explosion spike'' is proposed in which the mutual repulsion of the positive ions ejects them into the surrounding lattice. This model is shown to be generally consistent with a wide range of experimental fact. An additional damage mechanism appears to apply to polymers, in some of which tracks are produced by light projectiles such as α particles. The data here are shown to be consistent with tracks consisting primarily of broken bonds caused by decay of directly excited electrons.

Ion Explosion Spike Mechanism for Formation of Charged-Particle Tracks in Solids

We describe four criteria for the selection of alloying elements capable of producing castable, precipitation-strengthened Al alloys with high-temperature stability and strength: these alloying elements must (i) be capable of forming a suitable strengthening phase, (ii) show low solid solubility in Al, (iii) low diffusivity in Al, and (iv) retain the ability for the alloy to be conventionally solidified. With regard to criterion (i), we consider those systems forming Al3M trialuminide compounds with a cubic L12 crystal structure, which are chemically and structurally analogous to Ni3Al in the Ni-based superalloys. Eight elements, clustered in the same region of the periodic table, fulfill criterion (i): the first Group 3 transition metal (Sc), the three Group 4 transition metals (Ti, Zr, Hf) and the four latest lanthanide elements (Er, Tm, Yb, Lu). Based on a review of the existing literature, these elements are assessed in terms of criteria (ii) and (iii), which satisfy the need for a dispersion...

/pdf/criteria-for-developing-castable-creep-resistant-aluminum-7tojhsaie6.pdf

Criteria for developing castable, creep-resistant aluminum-based alloys - A review

http://physlab.phys.uoa.gr/org/pdf/tecto91.pdf

Latest aspects of earthquake prediction in Greece based on seismic electric signals, II☆

Diffusion of Solutes in Aluminum and Dilute Aluminum Alloys

Seismic electric signals from displacement of charged dislocations

The anomalously large excess ionic conductivity displayed by AgCl at high temperatures has been variously interpreted in terms of the onset of a second type of cation interstitialcy mechanism, or alternatively as due to a decrease in the Frenkel-defect formation energy with increasing temperature. A detailed measurement of the temperature dependence of the diffusivity of substitutional sodium-ion tracer in AgCl is here shown quantitatively to confirm the latter of these possibilities.

Temperature dependence of Frenkel-defect formation energy deduced from diffusion of sodium in silver chloride

The subsurface electric potential in oriented single crystals of silver chloride has been directly mapped out by a technique based on the equilibrium distribution of a very small concentration of a charged radiotracer. The potential was found to vary with depth according to the Gouy-Chapman solution of Poisson's equation, with screening lengths in the range 10\char21{}20 nm. The surfaces were all negative, relative to the deep interior, by 0.10\char21{}0.30 V, depending on temperature and surface orientation. The present results on the subsurface potential difference can be employed to resolve the Frenkel-pair formation enthalpy and entropy, as determined from transport measurements, into the formation enthalpies and entropies of the individual point defects comprising the pair. For the silver chloride (110) surface, for example, ${G}_{v}$=0.74 eV and ${G}_{i}$=0.37 eV at 150 \ifmmode^\circ\else\textdegree\fi{}C; the best values obtained to date for ${H}_{v}$, ${H}_{i}$, ${S}_{v}$, and ${S}_{i}$, are 0.77 eV, 0.70 eV, 0.79k, and 9.0k, respectively.

Lawrence Slifkin

Papers

Diffusion of Solutes in Aluminum and Dilute Aluminum Alloys

Seismic electric signals from displacement of charged dislocations

Temperature dependence of Frenkel-defect formation energy deduced from diffusion of sodium in silver chloride

Individual formation parameters of charged point defects in ionic crystals: Silver chloride.

A study of the high-temperature transport anomaly in AgBr, by diffusion of sodium tracer