| Thermoelectric materials are a function material which can convert thermal energy into electrical energy directly. Thermoelectric devices not only can convert the waste heat in industrial to electricity directly but also can be used as refrigeration equipment in some special working environment. The development and application of thermoelectric devices have attracted more and more attentions due to its advantages such as causing lighter environmental pollution, lower noise, lighter weight and smaller volume, giving more stable working performance and so on. As a kind of low temperature thermoelectric material, Bismuth Sulfide(Bi2S3) has a pretty low thermal conductivity at room temperature. Compared with Bi2Te3, the abundant and cheap element sulfur was used to replace the expensive rare element tellurium in Bi2S3, which has greatly reduced the material cost, and have great significance on the study of thermoelectric materials. In this dissertation, pure Bi2S3 with different components were consolidated into bulk ceramic by Spark Plasma Sintering(SPS) technique,the microstructure and thermoelectric properties of the Bi2S3 based materials were studied systematically. The main contents of this dissertation are as following:1. Bi2S3 powders with spherical structure were synthesized successfully by using hydro-thermal method and then pressed into bulk sample by applying Spark Plasma Sintering technique. The impact of temperature and surfactant on the morphology of Bi2S3 were investigated systematically. The results showed that the grain size reduced with increasing temperature. The grain size of Bi2S3 reduced sharply when added 12 m L of ethylene glycol, with the increased addition of dodecylbenzene sulfonic acid the morphology of spherical structure gradually changed to round cookie morphology. The maximal ZT value of Bi2S3 sample was 0.1 at 575 K, and the change tendency of thermoelectric properties of Bi2S3 samples was almost the same as literature reports.2. Bi Cl3/Bi2S3 composite powders with round cookie structure were synthesized successfully by hydrothermal method, combined with the Spark Plasma Sintering technique. The effect of Bi Cl3 content on the Bi Cl3/Bi2S3 composite thermoelectric properties was investigated systematically. The surface of the composite bulk was compact with no cracks, which was beneficial for us to obtain reliable results. Appropriate Bi Cl3 added in Bi2S3 not only reduced the thermal conductivity, but also enhanced the electrical conductivity. The ZT value of the composite sample increased with increasing temperature, the maximal ZT value of Bi2S3 with 0.25 % Bi Cl3 was 0.63 at 724.3 K, which was about three times of pure Bi2S3 of 0.22.3. Ag2S/Bi2S3 composite powders with spherical structure were synthesized successfully by adopting hydrothermal method and then pressed into bulk by employing Spark Plasma Sintering technique. The effect of Ag2 S contents on the Ag2S/Bi2S3 composite morphology and thermoelectric properties were investigated systematically. The results showed that with the increasing of Ag2 S content in Ag2S/Bi2S3 composite, the spherical structure gradually turned into round cookie structure, however, it still kept the hierarchical structure characteristics. The thermal conductivity of Ag2S/Bi2S3 composite samples was lower than that of pure Bi2S3 sample. The maximal ZT value of Bi2S3 sample composed of with 3 % Ag2 S was 0.23 at 724 K, which was more than twice of that value of pure Bi2S3.4. Dual composites sample of Bi2S3 with Ag2 S and Bi Cl3 dual composites sample were synthesized successfully by applying hydrothermal method and Spark Plasma Sintering technique. The effect of Ag2 S and Bi Cl3 contents on the thermoelectric properties of dual composite sample was investigated systematically. The electrical conductivity of the composite sample was increased obviously. The maximal ZT value of Bi2S3 sample compounded with 5 % Ag2 S and 1% Bi Cl3 was 0.59 at 724.3 K, which was nearly five times of that of Bi2S3 with 5 % Ag2 S. |
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