Preparation And Thermoelectric Properties Investigation Of SnSe Thermoelectric Materials

Thermoelectric material is a kind of new material which can directly convert heat into electric energy.It provides a feasible solution to the problem of energy shortage in the visible future.Because of its multi-energy valley valence band structure and ultra-low thermal conductivity,in the field of mesothermal thermoelectric materials,single crystal tin selenide?SnSe?has the highest ZT value,which can reach 2.62 at923K.But the complex preparation process,high cost and poor processability of single crystal SnSe make the large-scale industrial application become an extravagant hope.Nowadays,in order to solve above problems,polycrystalline SnSe materials have become the hotspot of researchers.In this paper,polycrystalline SnSe based thermoelectric materials were prepared by melting process and freezing grinding.High purity and stable Na_0.015Sn_0.985Se powders were obtained.Then,cellulose and SiC were used respectively as the second phase to improving the electrical and mechanical properties of Na_0.015Sn_0.985Se.It is expected to enhance phonon scattering and interface scattering,which further reduce the thermal conductivity of the material and improve the thermoelectric properties.At the same time,the mechanical properties of the materials were improved by the good mechanical properties of cellulose and SiC.The main contents of this paper are as follows:?1?A series of heat treatment processes,such as melting,quenching and annealing,are used to prepare Na_0.015Sn_0.985Se alloy ingots.Then the alloy ingot was ground into powder by freezing grinding process to avoid the oxidation of Na_0.015Sn_0.985Se material.The effects of freezing grinding technology on the morphology and thermoelectric properties of Na_0.015Sn_0.985Se were investigated by selecting different cycles and grinding rates.After experiments,a freezing grinding process with a cycle number of 5 and a grinding rate of 7 was determined.?2?Based on the above research,we hope to improve the thermoelectric and mechanical properties of Na_0.015Sn_0.985Se materials by using composite cellulose.In this paper,the influence of cellulose materials with different mass fraction?0.25%wt,0.50%wt,0.75%wt,1.00%wt?on the thermoelectric and mechanical properties of Na_0.015Sn_0.985Se has been investigated.It was found that the composite cellulose was not conducive to the improvement of the thermoelectric properties of Na_0.015Sn_0.985Se,but to the improvement of the mechanical properties of the materials.When the mass fraction of the composite cellulose is 0.75%wt,the flexural strength of the sample reaches 54.5 MPA,which is 127%higher than that of the matrix.?3?In order to improve the thermoelectric and mechanical properties of the materials at the same time,we have prepared the Na_0.015Sn_0.985Se samples with different mass fractions?1%wt,2%wt,3%wt,4%wt?of SiC.Because the composite SiC can enhance the phonon scattering and interface scattering to improve the thermoelectric properties of the composite thermoelectric materials,and the mechanical properties of the polycrystalline Sn Se thermoelectric materials can be improved by using the excellent mechanical properties of SiC.Based on the experimental data,the optimum ratio of SiC content and the variation trend of thermoelectric and mechanical properties with SiC content were determined.The thermoelectric properties of the samples with composite mass fraction of 1%wt are the best.At 773K,the ZT value in the vertical pressure direction is 0.91,which is more than 12%higher than that of the matrix.The flexural strength is 35 MPA,which is more than 45.8%higher than that of matrix.