Abstract
Thermoelectrics is one promising way of increasing the efficiency of machines and devices by reusing some of the waste heat produced. One obstacle for commercialization is the need to coat the materials to prevent sublimation and oxidation of the thermoelectric materials. Such coatings were designed for PbI2 doped PbTe using a (SiO2)0.68(PbO)0.3(B2O3)0.01(Na2O)0.01 based glass designed for operation at 500 °C. In this research various conditions of the coating process were examined. The effect of the atmosphere on the bonding and densification of the coating was studied using argon, vacuum and air. From the three air shows, the best bonding characteristics were from a better flow of glass and increased bonding between the oxidized PbTe layer and glass. This also created a PbO rich glass in the interface between the glass and the PbTe sample. The effect of 0, 3, and 6 wt. % NaCl additive to the solution was tested and showed that NaCl achieves better coverage due to high green body density, reaction of NaCl with the glass and removal of remaining CO2 from the glass in the form of decomposing Na2CO3. In addition, when testing the time and temperature, it was shown that the temperature of 520 °C was the minimum needed for high densification of the glass, but a duration shorter than 30 min did not allow for bonding of the glass to the substrate despite adequate densification. Finely, to obtain a well bonded coating with full coverage over the sample, the glass was coated with 6% NaCl in air at 520 °C for 30 min.
Highlights
In the pursuit of providing efficient and practical energy conversion methods, heat to energy recovery, using thermoelectric materials is one of the most promising technologies.Thermoelectric devices provide passive energy regeneration, while turning heat into electricity without any moving parts or control of operations
Some measure of glass was detected with additional phases
This is common in Na containing glass powders [26] since Na2 CO3 can start decomposing above 400 ◦ C into Na2 O
Summary
In the pursuit of providing efficient and practical energy conversion methods, heat to energy recovery, using thermoelectric materials is one of the most promising technologies.Thermoelectric devices provide passive energy regeneration, while turning heat into electricity without any moving parts or control of operations. Some challenges remain due to the need to operate at high temperatures, and the high sensitivity of most thermoelectric materials to oxidation and sublimation. One such major hurdle is overcoming degradation due to a high temperature exposure to the atmosphere, as marked in the figure. Most high temperature thermoelectric generators need to be encased in Metals 2020, 10, 284; doi:10.3390/met10020284 www.mdpi.com/journal/metals
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