Purification of High-Purity Tin via Vertical Zone Refining

Abstract

The present investigation delves into the potential of vertical zone refining as an effective purification technique for achieving high-purity tin (Sn) metal. The utilization of vertical zone refining offers distinct advantages over traditional horizontal zone refining, as it allows for enhanced control over the molten zone and solid–liquid interface, ultimately leading to superior impurity separation efficiency. The present study reveals that the solute partition coefficients (k0) of various impurity elements, such as Zn, Ag, Al, Mg, Ca, Ni, In, Co, Cu, As, Pb, Fe, and Bi, during the vertical zone refining process consistently demonstrate values below one. Notably, the partition coefficient of Sb deviates slightly from the others, being greater than one but approaching one. The authors achieve exceptional levels of purity in both the bottom and middle regions of the rod by subjecting the Sn melt to nine passes of vertical zone refining at a heating temperature of 405 °C and a downward pulling rate of 10 µm/s, resulting in purities exceeding 6N4. Furthermore, by evaluating the effective partition coefficients (keff), it was determined that impurity elements, such as Cu and Bi, closely approach their equilibrium partition coefficients, reaching values of approximately 0.492 and 0.327, respectively. To further enhance the purity of Sn metal and maximize product yield, we propose the utilization of electrolytic refining and vacuum distillation, with particular emphasis on the efficient separation of five specific elements, including Cu, Fe, As, Pb, and Sb. By elucidating these findings, this study not only contributes valuable insights into the efficacy of vertical zone refining as a purification technique for high-purity tin metal, but also offers important recommendations for refining strategies and impurity element separation.

A Review on the Zone Refining Process Technology toward Ultra‐Purification of Gallium for GaAs/GaN‐based Optoelectronic Device Applications

“…The distillation process has been successfully used for the production of high pure metals and percentage of purity can reach up to 5N level. [ 1,139–143 ] However, a combination of vacuum distillation and zone melting process can upgrade the purify even up to 7N. [ 140 ] Zone melting: Zone melting is a method of impurity segregation by melting.…”

“…[ 17–21 ] This process is used to ultra‐purify many metals and materials. [ 11,23,139,144–146 ] It is the most efficient purification method as it can purify materials even up to 13N, without any other associate refining technique. [ 146 ] Purification efficiency can be improved by optimizing the molten zone length, zone travel rate, and stirring of the zone. Czochralski method: This is a very useful technique to grow bulk single crystals of materials having large diameters.…”

“…Let us now explore all these parameters of zone refining which the vital in improving efficiency. These include refining the material vertically or horizontally named as the vertical and horizontal zone refining system respectively, [ 139,171 ] ideal zone width and precise temperature control, [ 177 ] travel speed along with molten zone stirring, minimizing recontamination from auxiliary equipment [ 16 ][ 178 ] and cost analysis. Some parameters are interdependent on each other.…”

“…Figure a depicts a vertical zone refining system for producing high‐purity tin. [ 139 ] When employing a horizontal refining method, the material to be purified is supported horizontally in a crucible or boat. The molten zone is set up to pass along the material bar, either by moving the crucible through the hot zone or by creating a hot zone to encircle and pass over the bar.…”

The Spin–Orbit Effect on the Electronic Structures, Refractive Indices, and Birefringence of X2PO4I (X = Pb, Sn, Ba and Sr): A First-Principles Investigation

“…Post-transition metal cations, including Pb 2+ , Sn 2+ , Bi 3+ , and Sb 3+ , have a wide variety of applications in electrochemical energy storage [1,2] high-temperature superconductivity [3][4][5], catalysis [5][6][7], gas sensors [8][9][10], birefringent material [11][12][13][14], nonlinear optical crystals [15][16][17][18], etc. By analyzing many existing studies, it was found that the introduction of post-transition metal cations containing stereochemically active lone-pair electrons is a good strategy to enhance optical properties.…”