Demonstrating the Simplicity and In Situ Temperature Monitoring of the Mechanochemical Synthesis of Metal Chalcogenides Suitable for Thermoelectrics

Summary

Here, we present a protocol to synthesize two metal chalcogenides (Cu_1.8S and SnSe) suitable for thermoelectrics via an ultrafast (second-range), solvent-free, and one-step mechanochemical synthesis using elemental precursors. Simultaneously, we demonstrate the monitoring of the temperature in the jar during planetary ball milling in situ by the newly developed device.

Abstract

Mechanochemical synthesis is an extremely useful strategy to reach thermoelectric materials due to its solvent-free one-step character, as the targeted thermoelectricity (TE) materials in a nanocrystalline format can be prepared by mere high-energy milling of elemental precursors. Nevertheless, the subsequent densification method (e.g., spark plasma sintering or hot pressing) is required afterward, similarly to other synthetic methodologies. In this study, the simplicity of mechanochemical synthesis is presented for two selected metal chalcogenides, namely copper sulfide (Cu_1.8S, digenite) and tin selenide (SnSe, svetlanaite), which are known for high ZT values. These compounds can be prepared via a mechanically induced self-propagating reaction (MSR), which is a combustion-like process instantly yielding the products in a very short timeframe (within 1 min). The occurrence of MSR can be well-tracked by in situ temperature monitoring since an abrupt temperature increase occurs at the moment of MSR. We have developed a device which is capable of monitoring the temperature inside the milling jar every 80 ms during planetary ball milling, and it is therefore possible to very precisely track the moment of MSR ignition. The developed device presents an improvement in the monitoring capabilities in comparison with commercially available analogs. This contribution aims to provide a visual insight into all steps, with simple high-energy ball milling of elements to reach TE materials and in situ temperature monitoring being the central points.

Introduction

Statistically, more than 60% of energy in the world is lost, mostly as waste heat. Utilizing the waste heat for thermoelectricity (TE) applications has a great potential. TE offers a suitable method to convert waste heat into electrical energy. Special applications, like electrical energy sources in radioactive thermoelectric generators for space research and/or replacing the old Hg-Zn batteries in cardiac pacemakers, can be mentioned¹.

Among various TE materials, chalcogenides belong among the favorites, especially if they are composed of abundant and non-toxic elements. Chalcogenides with tellurium, lead,....

Protocol

1. Preparation of CuS mixture with the stoichiometry 1.6:1

1. Tare the weighing paper.
2. Weigh 7.6024 g of elemental copper and 2.3974 g of elemental sulfur powder to achieve the stoichiometry ratio of Cu and S at 1.6:1, with a total mass of 10 g.
3. Before milling, mix the Cu and S powder. After weighing, introduce both Cu and S powders into a plastic weighing dish and mix intensively with a spatula, until a powder of homogeneous color free from large lumps of sulfur is obtained........

Discussion

Mechanically induced self-propagating reactions (MSR) are an immediate transformation of precursors into products via an exothermic combustion-like process activated by mechanical action (similar to self-heat sustaining reactions where similar processes are activated by heat). The occurrence of MSR can often be identified by changes in the physical appearance of the product, a distinct smell at the moment of the reaction, or a scratching sound from the milling jar. However, empirical evidence suggests that these sen.......

Materials

Name	Company	Catalog Number	Comments
Copper	Pometon, Germany	7440-50-8	Red powder
D8 Advance diffractometer	Bruker, Germany	M88-E03036	X-ray instrument
DiffracPlus Evaluation package release	Bruker, Germany	DOC-M85-EXX002	Diffraction analysis software
Etaben	Mikrochem, Slovakia	64-17-5	solution
Jedit	Open Source software		Programmer's text editor
Project SAV 1.0			Software developed to record data from in situ temeprature monitoring
Pulverisette P7 planetary mill	Fritsch, Germany	07.5000.00	The milling device, utilized in the synthesis of Cu1.8S and SnSe
Selenium	Acros Organic, Germany	7782-49-2	Gray powder
Sulfur	Sigma Aldrich, Germany	7704-34-9	Yellow powder
Tin	Merck, Germany	7440-31-5	Gray powder
Topas Academic	Coelho Software		General non-linear least squares software driven by a scripting language. Its main focus is in crystallography, solid state chemistry and optimization.