Abstract
Mg2Si is a promising eco-friendly thermoelectric material, and Ni is suited for electrical contact on it. In this study, Bi-doped Mg2Si ingots with Ni contacts were fabricated by co-sintering, and thermal stability was investigated by long-time (500 h, 500 cycles) temperature cycling from 25 °C to a peak temperature (Th = 400 and 450 °C) in N2. The as-sintered Ni/Mg2Si interfacial region is a multilayer consisting of Mg3Bi2, a series of MgxSiyNiz ternary compounds (ω, ν, ζ, and η-phases), and MgNi2. In the complex microstructure, the MgNi2 / η-phase interface was vulnerable to stress-induced voiding at Th = 450 °C, which arises from the mismatch of the thermal expansion coefficients. Interfacial voiding was avoided by adding 10 mol% Ag in Ni, which is probably due to the suppression of vacancy migration by the Ag-containing 2nd phase formation at the MgNi2/η-phase interface.
Highlights
In recent years, the regulations on greenhouse gases are being strengthened continuously, and the recovery of waste heat is becoming increasingly important as a viable means of raising the energy efficiency of fossil fuels
Ni powders were carefully loaded on top of the Mg2 Si powders to form a Ni/Mg2 Si/Ni structure, and the co-sintering was implemented by applying 150 MPa pressure at 800 ◦ C for 60 min using a hot press (HP) system
The points e and f belong to the Layer 3 and have slightly different contrast in the results suggest that both spots are ζ-phase (Mg3 Si7 Ni10 )
Summary
The regulations on greenhouse gases are being strengthened continuously, and the recovery of waste heat is becoming increasingly important as a viable means of raising the energy efficiency of fossil fuels. Thermoelectric generation (TEG) is an energy conversion technique based entirely on solid-state devices utilizing the Seebeck effect, and has many attractive features such as silent operation, long-term reliability, compactness, and scalability. Along with the potential advantages, thermoelectric technology has a few drawbacks to be resolved, among which the cost as well as the non-toxicity of the materials are very important requirements. In this regard, Mg2 Si is a very attractive material because it is inherently composed of non-toxic earth-abundant elements, which guarantees a low material cost. Mg2 Si-based materials are surely very promising for future thermoelectric applications
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