In Situ Synchrotron X‐ray Diffraction Studies of the Mechanochemical Synthesis of ZnS from its Elements

Abstract

Mechanochemistry, as a synthesis tool for inorganic materials, became an ever-growing field in material chemistry. The direct energy transfer by collision of the educts with the milling media gives the possibility to design environmentalfriendly reactions. Nevertheless, the underlying process of energy transfer and hence the kinetics of mechanosynthesis remain unclear. Herein, we present in situ synchrotron X-ray diffraction studies coupled with pressure measurements performed during the formation of ZnS and the subsequent phase transition (PT) from the hexagonal to the cubic modification. Milling Zn and S 8 results in the sublimation of S 8 , observed by a sudden pressure increase. Simultaneously, the hexagonal metastable ZnS-modification (wurtzite) forms. Via detection of the pressure maximum, the exact start of the wurtzite formation can be determined. Immediately after the formation of wurtzite, the structural PT to the thermodynamic stable cubic modification sphalerite takes place. This PT can be described by the Prout-Tompkins equation for autocatalytic reactions, similar to thermally induced PT in sulfur vapor at high temperatures (T > 1133 K). The increase in the reactivity of the wurtzite formation is explained by the reaction in sulfur vapor and the induction of defect structures by the collisions with the milling media.

Zeitaufgelöste In‐Situ‐Untersuchungen von mechanochemischen Reaktionen

“…Manometrische Messungen, d. h. die Messung von Druckänderungen im Verlauf der Reaktion, werden seit vielen Jahrzehnten in der mechanochemischen Forschung eingesetzt. [29,34,[59][60][61] [62] Thermometrie. Thermische Messungen während mechanisch-chemischer Experimente werden seit vielen Jahren durchgeführt.…”

“…Im Falle des Kugelmahlens von Zn und S 8 konnte XRD nur Veränderungen in der kristallographischen Struktur aufzeigen. Nur durch den gleichzeitigen Einsatz manometrischer Messungen konnten die Autoren zu dem Schluss kommen, dass sich eine Reaktionsphase (S 8 ) während des Mahlens verflüchtigte und dadurch eine reaktive Zwischenphase bildete, die die Bildung des Endprodukts vorantrieb [62] …”

Time‐Resolved In Situ Monitoring of Mechanochemical Reactions

“…In view of the far-reaching applications of mechanochemistry as a "chemical innovation that will change our world", [5] interest is quickly growing in the use of TRIS [12] Copyright 2021, Nature Publishing Group. b) Relative pressure during the ball milling of Zn and S 8 , [62] Copyright 2015, Wiley-VCH. c) XANES data for the mechanochemical formation of gold nanoparticles.…”

“…I) a) Typical XRD measurement for a reaction between bis(2‐nitrophenyl)‐ and bis(4‐chlorophenyl)disulfide, [12] Copyright 2021, Nature Publishing Group. b) Relative pressure during the ball milling of Zn and S 8 , [62] Copyright 2015, Wiley‐VCH. c) XANES data for the mechanochemical formation of gold nanoparticles.…”

Methods for Monitoring Milling Reactions and Mechanistic Studies of Mechanochemistry: A Primer

“…The Weidenthaler group has combined the use of real-time synchrotron XRPD and pressure monitoring to study the mechanochemical reaction of zinc metal and elementary sulfur (S 8 ) to form zinc sulfide (ZnS) in a shaker mill. The real-time XRPD results demonstrated rapid formation of the hexagonal ZnS (wurtzite) phase followed by transformation into the thermodynamically stable cubic form (sphalerite) . Simultaneously with the appearance of the wurtzite phase, a significant jump in pressure was observed, indicating that the reaction proceeds through impact-induced vaporization of sulfur.…”