Developing 3D printer for thermoelectrical material and module fabrication

A significant portion of the energy we use on Earth dissipates into the atmosphere as waste heat. It is possible to directly generate electricity from this unused heat energy. The most ideal technology for this purpose is thermoelectric (TE) generators based on thermoelectric materials. These TE generators, which have many advantages over solar and wind energy sources, face a major problem: their efficiency is not yet at the desired level. Although their efficiency has reached around 17% today, to compete with solar and wind panels, their efficiency needs to reach 25-30%. Therefore, the main goal of research in this field globally is to increase the efficiency of these materials, create modules from them, or develop different application areas. The focus of this study is to synthesize high-efficiency TE materials using different preparation techniques (such as solid-state reaction, arc melting, and fast quenching) and theoretical approaches (such as PGEC, PLEC, and nano structuring) and then develop their technological applications by producing modules. TE materials and modules are produced through long, energy-consuming, and somewhat costly production processes. One of the low-cost and fast production methods for TE materials and modules is the 3D printing technique. The aim of this thesis is to produce high-efficiency materials using both classical methods and the 3D printing technique and compare them. In the first stage of this thesis study, nano composite compounds were synthesized and their structural and thermoelectric properties were examined, followed by the development of a special printer for 3D printing. In the final stage, different shapes of TE compounds were printed with the 3D printer. For nano composite TE compounds, a certain amount of nano Fe3.25Co0.75Sb12 compounds was added to the nano Cu2Se compound, and their TE properties were examined. When nano Cu2Se1-x(FeCoSb)x (x=0.0-0.5) was doped with FeCoSb at different ratios, it was observed that 0.5% nano FeCoSb doping reduced the electrical conductivity of the compound but significantly increased the Seebeck coefficient, resulting in a 15% increase in the zT value. Another work done in this thesis study is the development of a functional 3D printer that allows easy module production from TE compounds. The developed functional 3D printer ensures a homogeneous mixture of TE materials (N or P type) produced in fluid form and subsequently produces TE modules in the desired geometric shape. TE modules produced on A4 printer paper with the 3D printer were produced in various sizes: large (8x8 cm) and small (3x3 cm), butterfly shape (4x1 cm), hexagonal form (4x2 cm), IUC logo (1.5x4 cm), and classic (vertical) modules (1.5x4 cm). The open-circuit voltages produced by these modules were measured by applying a strip heater to one surface of the developed modules based on temperature difference. Temperature differences of approximately 10, 30, and 60 K were applied, and it was observed that the open-circuit voltage produced by all modules increased with the temperature difference. The highest open-circuit voltage was obtained as 80 mV and 16 mV at 60 K for large (8x8 cm) and small (3x3 cm) modules, respectively. The highest open-circuit voltages for the same temperature differences were obtained as 12 mV, 8 mV, and 7 mV for the logo form module, hexagonal, and classic (vertical) module, respectively. The higher open-circuit voltage obtained in art forms such as butterfly and logo form is due to the higher temperature difference between surfaces because of their shapes. The open-circuit voltage produced by the modules produced with the 3D printer was lower compared to classic (rigid ceramic plate) modules. This is due to the higher number of legs used in rigid modules, the high Seebeck voltage because the TE legs are in solid form, and the uniform contact of the heat source with the modules thanks to the ceramic plate, which was not achieved in the 3D-printed modules. In conclusion, various shapes of Bi-Sb-Te based TE modules were successfully produced with a 3D printer that has features such as software-supported automatic control system, simultaneous dispensing, and sintering process, and it was demonstrated that rapid and low-cost module production is possible with this method. Another conclusion obtained from this thesis is that more efficient TE modules can be produced by optimizing the dispensing nozzles according to the type of TE compound, the sintering time, and the viscosity of the TE materials.