Significant reduction of thermal conductivity of intermetallic Mg2Si thermoelectric material from carbon fiber inclusion

Abstract

Thermoelectric power generation, which utilizes dispersed waste heat energy, has garnered interest as a durable and eco-friendly power source. Mg2Si-based alloys show great potential as thermoelectric materials for converting energy in the intermediate to high temperature range. The thermoelectric performance of Mg2 has been improved using techniques such as impurity doping, nano-structuring, and alloying. Additionally, they have the potential to lead to a decrease in the weight of thermoelectric generators, which is a crucial characteristic for the automotive industry. To decrease the thermal conductivity of silicide-based materials, one can modify phonon scattering by introducing nanosized crystalline grains. This work investigates the impact of Carbon Fiber-doping and small quantities of the isoelectronic impurity carbon fiber (CF) on the thermal characteristics of magnesium silicide (Mg2Si). The study focused on examining the impact of different levels of Carbon fiber doping on Mg2Si (specifically, Mg2Si:CF=1:x where x represents the doping amount of 0.0025, 0.005, 0.0075, 0.01, and 0.05 ratio).

This work produced compact polycrystalline samples of Mg2Si by Spark Plasma Sintering techniques. The materials' shape, content, and structure were studied using SEM, EDS, and XRD investigations following each step of the process. This work presents an analysis of the thermal conductivity of the samples which analysis using Laser flash analysis techniques. However, CF did decrease the thermal conductivity significantly and we achieved lowest thermal conductivity till date for Mg2Si. Approximately, 68.44% thermal conductivity reduced by doped Mg2Si at room temperature compared to undoped Mg2Si we produced in our laboratory as well as 53.61% reduction compared to reported Mg2Si undoped samples[1]. Additionally, thermal conductivity of 5 wt.% CF Mg2Si showed up to 30.67% reduction at room temperature and 56.92% reduction at 773 K compared to reported Sb and C co-doped Mg2Si.