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Cu3.21Bi4.79S9 was synthesized from Cu, Bi and S element powders using mechanical alloying method. The formation of Cu3.21Bi4.79S9 was identified using XRD and the changes of morphologies of the mixtures of Cu, Bi, and S powders during milling were observed using table top SEM. The milled powders were sintered using Hot-isostatic pressing at 230°C with a pressure of 50 MPa. Electrical resistivity and Seebeck coefficient of sintered samples were measured using ZEM-3 (Electrical resistivity and Seebeck Coefficient measuring System). Cu3.21Bi4.79S9 and some secondary phases were found in the 5h milled powder but single phase Cu3.21Bi4.79S9 was only obtained after milling for 15 h. A minimum electrical resistivity of sintered Cu3.21Bi4.79S9 sample was found to be 0.66 Ω.m at 170°C. We observed that a n- to p-type conversion at temperature of around 75 °C. However, a maximum n-type Seebeck coefficient of Cu3.21Bi4.79S9 was of -214 μV/K at 45 °C. The Seebeck coefficient decreases with increasing temperature and it reaches zero value at around 75 °C and then p-type Seebeck coefficient increases with increasing the temperature. The maximum p-type Seebeck coefficient was observed of 202 μV/K at 170°C.

During the last three decades, there has been growing interest in applying thermoelectric technology to improve the efficiency of waste heat recovery .This study reports an estimation of the amount of power produced by a thermoelectric generator (TEG) placed between the flue gas duct and fresh air duct of an industrial thermal oil heater to recover waste heat. A plate fin heat sink is used to transfer the heat from flue gas to the thermoelectric generator. The effects of various design parameters and flow parameters were investigated in order to maximize the power generation. Then the best suited conditions were applied to new a thermoelectric generator module based on recently developed Bi2Te3, PbTe and TAGS thermoelectric group materials. A thermoelectric generator based on p-type (Bi,Sb) 2 Te 3 and n-type hot forged Bi 2 Te 3 generates 4.4 W, which is about 19% improvement in output power compared to a commercial module (HZ-2). For a proposed system, in a biomass fired thermal oil heater, the estimated annual power generation could be around 181,209 kWh. The thermal efficiency of the TEG modules based on recently developed thermoelectric materials could be enhanced by up to 8.18%. The specifications of plate fin heat sinks as well as thermoelectric properties of the p-n materials of the system have a substantial impact on the performance of the TEG module.