This review presents the historical temporal evolution of an atom-probe tomograph (APT) from its genesis (1973) from field-ion microscope images of individual tungsten atoms (1955). The capabilities of modern APTs employing either electrical or laser pulsing are discussed. The results of the application of APTs to specific materials science problems are presented for research performed at Northwestern University on the following problems: (a) the segregation of Mg at α-Al/Al3Sc heterophase interfaces, (b) phase decomposition in ternary Ni-Al-Cr and quaternary Ni-Al-Cr-Re alloys, and (c) 3-D nanoscale composition mapping of an InAs semiconductor nanowire whose growth was catalyzed by gold. These results demonstrate that it is now possible to obtain highly quantitative information from APT that can be compared with modeling, theory, simulations, and/or first-principles calculations.

Three-Dimensional Atom-Probe Tomography: Advances and Applications

Thermodynamics of solar-grade-silicon refining

https://iopscience.iop.org/article/10.1016/j.stam.2003.12.007/pdf

Removal of phosphorus by the solidification refining with Si–Al melts

Among currently known alternatives for renewable energy sources, solar power is generally regarded as having the most potential to satisfy the ever-growing demand While solar photovoltaic power is a well-established technology, its widespread uptake has been hindered by the prohibitively high price of units and thus electricity This is due mainly to the high cost of the silicon used to fabricate the devices This article presents a review of the development of established pyrometallurgical techniques as applied to refining metallurgical silicon to solar grade for the purposes of reducing reliance on expensive traditional silicon feedstock Four basic high-temperature methods—solvent refining, vaporization, electrorefining, and slag treatment—are described, and the limitations and advantages of each method are presented It is apparent that these techniques are very useful for removing impurities from silicon, but are often selective and not able to remove all problematic elements Therefore, refining may need to be as a sequence of steps, targeting specific elements each time, or as novel methods combining multiple techniques simultaneously Ultimately, the successful approach will have to achieve large-scale production by cost-effective means to replace current methods

https://tspace.library.utoronto.ca/bitstream/1807/93627/1/High%20Temp_TSpace.pdf

High-Temperature Refining of Metallurgical-Grade Silicon: A Review

The interaction between calcium and phosphorus in molten silicon was investigated for predicting the removal of phosphorus from silicon by an acid leaching treatment with calcium addition. In the present study, two immiscible liquids of silicon and lead were equilibrated, and the interaction parameter between calcium and phosphorus and the self-interaction parameter of phosphorus in molten silicon at 1723 K were determined. 

$$\varepsilon _{Ca in Si}^P = - 14.6( \pm 1.7) \varepsilon _{Ca in Si}^P = - 13.8( \pm 3.2)$$

In the derivation process, the following activity coefficients and the interaction parameters of metallic impurities in molten silicon and lead at 1723 K were also obtained: 

$$\begin{gathered} \ln \gamma _{Pb in Si}^0 = 3.73( \pm 0.010) \ln \gamma _{Si in Pb}^0 = 3.39( \pm 0.040) \hfill \\ \varepsilon _{Pb in Si}^P = - 4.08( \pm 0.80) \varepsilon _{Pb in Si}^P = - 23.8( \pm 18) \hfill \\ \varepsilon _{Pb in Si}^{Ca} = - 8.36( \pm 1.6) \varepsilon _{Si in Pb}^{Ca} = - 14.3( \pm 7.0) \hfill \\ \end{gathered} $$

The effect of the calcium addition to silicon improves the subsequent removal of phosphorus in the acid leaching treatment, and the increase in removal fraction of phosphorus was observed remarkably with the addition of calcium in silicon.

Thermodynamic study of the effect of calcium on removal of phosphorus from silicon by acid leaching treatment

Removal of phosphorus is one of the major problems on the purification of molten silicon for solar cell. The Gibbs energy change of phosphorus dissolution into molten silicon was determined in the temperature range from 1723 to 1848 K by equilibrating a molten silicon-phosphorus alloy in a controlled phosphorus partial pressure and is expressed by the following equations. 
$$\begin{gathered} \frac{1}{2}P_2 (g) = \underset{\raise0.3em\hbox{$\smash{\scriptscriptstyle-}$}}{P} (mass pct, in Si) \hfill \\ \Delta G^\circ = - 139,000{\text{ }}( \pm 2000){\text{ }} + {\text{ }}43.4{\text{ }}( \pm 10.1T){\text{ }}(J/mol) \hfill \\ \end{gathered} $$

 The possibility of removing phosphorus from silicon melts by vacuum treatment and the accompanying yield of silicon during the refining process are discussed.

Takahirio Miki

Papers

Thermodynamics of phosphorus in molten silicon