MATERIALS • PROCESSES • FINISHES
NANO-SILVER SINTERING
Researchers have developed a novel high-efficiency thermoelectric device design that uses silver nanoparticles as a welding filler
M
ultiple high-performance thermoelectric materials have been discovered over the past two decades. However, their
promise has remained largely unfilled due to a lack of efficient devices capable of converting the energy these materials produce into emission-free power. Now, an international team of scientists
from the University of Houston and the Harbin Institute of Technology have revealed a novel approach to constructing such thermoelectric modules that is expected to accelerate the development of advanced thermoelectric modules for power generation and other applications. Te key ingredient: Silver nanoparticles.
THERMOELECTRIC DEVICES SO FAR Termoelectric devices can convert heat directly into electricity due to the Seebeck effect, a phenomenon in which a temperature difference between two dissimilar electrical conductors or semiconductors produces a voltage difference between the two substances. Since they are compact and highly reliable, and operate without vibration
Silver nanoparticles connect the modules’ electrode and metallisation layers
Fig 1. The connection scheme can be applied to most thermoelectric device designs over a wide temperature range
and noise, these devices have key applications in aerospace and in other fields experiencing extreme conditions. In recent years, the performance
of different families of thermoelectric materials has been significantly improved. However, the development of thermoelectric devices with both high performance and high reliability remains difficult. Te key to developing thermoelectric devices lies in the design of two connection interfaces: the semiconductor-metal interface (the connection interface between the thermoelectric material and the contact layer) and the metal-metal interface (the bonding interface between the electrode and the contact layer). To ensure that the thermoelectric material performance does not decay, it is very important to realise connections that minimise interface resistance and thermal resistance while maintaining high connection strength. However, as the welding temperature
increases, problems such as thermoelectric material performance degradation, diffusion of elements between interfaces,
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and welding residual thermal stress become increasingly serious. Terefore, determining how to achieve both low- temperature connections and high- temperature service in thermoelectric devices to avoid the above problems is of great significance.
A NEW APPROACH WITH SILVER NANOPARTICLES Addressing this challenge to the development of thermoelectric devices, Professor Qian Zhang from the Harbin Institute of Technology, Professor Zhifeng Ren from the University of Houston, and their research groups proposed a novel connection design in which silver nanoparticles (Ag NPs) are used as a welding filler rather than using a traditional brazing alloy. Due to the nanoscale size of the Ag
NPs, their melting point is reduced while their specific surface energy is increased. Terefore, different metals can be bonded via sintering the Ag NPs at very low temperatures. By exploring the high-temperature mechanical properties
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