Study On Synthesis Of Thermoelectric Materials Of Bi-Sb Alloy Films By Electrochemical Method

Semiconductor thermoelectric module can be applied to power generation of thermal powerplants, automobile exhaust and waste heat，as it is energy saving and environmental protectionand can transform heat to electricity directly without chemical reaction and mechanicalmovement， thus possessing broad application foreground. Bi（1-x）SbxRY. is performancematerials of low-temperature and electrodeposition is one of the important preparations of it.However, both the change of deposition conditions and electrodeposition solution will affectthe composition and organizational structure of the deposited film. Systematic research onelectrochemical deposition processes and the relationship between electrodepositionparameters and microstructure of Bi-Sb alloy has scientific significance and application value.The electrochemical behavior of Bi（Ⅲ）, Sb （Ⅲ） in electrolytic solution system wasdetermined with BiCl3and SbCl3as the main salt, and on the basis of above, influence oftemperature, pH value, concentration of salts, additive and doping rare earth element on thecontent of Bi, Sb in electrodeposition film and the apparent morphology of material wereinvestigated. DSC curve of the material in heat treatment process was determined throughthermal analysis，its structure and morphology were characterized by XRD，SEM, accordinglyfor the functional rule among the electrochemical, the structure and thermoelectric propertiesof material. All these possess the theoretical guidance for preparation of Bi2Sb3alloy films byelectrochemical method. The main contents of this thesis include following:1.Calculate the Sb （Ⅲ） concentrations of various existing forms in the system of Sb（Ⅲ）-HCl-H₂O，taking the total concentration of Sb（Ⅲ）5×10^-5mol/L as example，thethermodynamic calculations on the basic assumptions of the same total content of Sb （Ⅲ） indifferent pH. And the results indicate that, SbO+is the mainly existing form of Sb （Ⅲ）, n（SbO+）/n（Sbtotal）>99.8%while1.30<pH <4in the system of Sb（Ⅲ）-HCl-H₂O.2. Based on the results of thermodynamic calculation, the solutions were preparedaccordance with the Method of Equivalent Molarity according to the co-reaction of citric acidand Sb （Ⅲ）.The ratio of citric acid to Sb （Ⅲ） in the complex is1:1and the stability constant of the complexes were9.4×10⁵tested by UV spectrophotometry, when pH is2.5.3. Determine the salts of electrolyte are SbCl3and BiCl3in theory and study theinfluence law of various additives on the electrodeposition process through the exploring thepolarization curve of the Sb-Bi alloy electrodeposition. On this basis, we identify the suitablecondition of electrodeposition and that boric acid is1.0g, citric acid is1.5².5g, sodiumcitrate is2.0².5g, Sodium chloride is2.0².5g, thiourea is0.01g, tartaric acid is0.1g inelectrolyte solution of50ml.4. Electrochemical preparation of film thermoelectric material Bi-Sb is studied in thispaper. The effects of different electrodeposition conditions of temperature, pH, potential range,scan rate and the main concentration on the composition of Bi-Sb alloy film were investigatesby titration and atomic absorption spectrometry. Then the orthogonal test was conducted andthe optimum forming technics were selected accordingly based on analysis, of which pH is0¹, the temperature is30³5℃, the concentration of main salt is0.4⁰.4and the depositionpotential range is-0.5^-0.7V.5. The morphology of Bi-Sb alloy film prepared under the appropriate condition abovewere analysed, and DSC showed that lanthanum and cerium doping improves the oxidationresistance of the Bi-Sb alloy film. SEM results indicated that doping of La, Ce had ansignificant influence on fineness and uniformity of crystalline grain, and the effect of Ladoped is better than Ce doped obviously. X-ray diffraction analysis showed that the Bi-Sballoy film is mainly consist of Bi-Sb.