With the rapid development of our national economy, the development of energy decreasing, and coal, oil and natural gas mining and processing caused serious environmental pollution, thermoelectric materials as a kind of environmental protection and energy exchange has a wide application prospect and materials, has attracted much attention.
At present, low thermoelectric efficiency and high cost are still the key to restrict the large-scale production and application of thermoelectric materials. With the progress of science and the modernization process, believe that the performance of thermoelectric materials will be further improved, the preparation process will become more and more mature, thermoelectric materials will become a new hot research field of new materials in china.
Overview of thermoelectric materials technology
Thermoelectric material (also called thermoelectric material, thermoelectric materials) is a kind of functional material which uses the internal carrier motion of solid to realize the direct conversion of heat energy and electric energy.
In 1834, the French physicist Pelte discovered the thermoelectric effect, will be connected to the conductor of different materials, and through the current, the contact point of the different conductors - nodes, will absorb or emit heat. In 1838, Russian physicist Lenz made more visibility experiment: using metal bismuth and antimony form when the current node along one direction through the nodes, the nodes in the water will solidify into ice; if the reverse current direction, cemented on node of ice will melt into the water immediately.
Although the scientific community found on Pell McNair Lenz very seriously, but because of the metal thermoelectric conversion efficiency is very low, the discovery is not quickly into practical application. It was not until 1950s that some semiconductor materials with excellent thermoelectric conversion performance were found. Thermoelectric refrigeration and thermoelectric power generation technology became a hot research topic.
Development of thermoelectric power generation technology
What is the use of thermoelectric power generation, waste heat, waste heat steam, waste heat, solar heat such as heat, and thermoelectric power larger features, using a thermal effect (first Sebek effect, or Seebeck effect), convert heat directly into a way of generating electricity.
Two different types of thermoelectric conversion material N and P is combined with one end and the other end of the high temperature condition, and give open at low temperature due to the high temperature end of the heat stimulation is strong, electron and hole concentration than the low temperature end in this high, the carrier concentration gradient, hole and electron diffusion to low end to the open end of temperature, forming potential in low temperature. If a plurality of groups of P type and N type thermoelectric materials are connected to form a module, a sufficiently high voltage can be obtained to form a thermoelectric generator.
According to the classification of the use of heat sources, thermoelectric generator can be divided into radioisotope thermoelectric generator, nuclear reactor thermoelectric generator, hydrocarbon fuel thermoelectric generator, low thermal thermoelectric generator, etc.. While the lower heat thermoelectric generator, the various forms of low temperature heat (including heat heat) directly into electrical energy conversion thermoelectric generator, the hot surface temperature is generally below 400 DEG C, typical thermoelectric materials are using bismuth telluride (Bi2Te3). In addition, there are two kinds of low dimensional thermoelectric materials has good application prospect, one is CsBi4Te6, which is actually the interstitial Bi2Te3, the other is a selenium (Se) doped HfTe5 in the temperature range of T<220K, the Seebeck coefficient is far beyond the Bi2Te3.
Development of thermoelectric material preparation technology
Thermoelectric materials can be prepared by single crystal growth process in principle, but the single crystal process requires sophisticated equipment, and the operation is complex, high cost. Therefore, thermoelectric materials are often used in practice. In general, the preparation of thermoelectric materials is a powder metallurgy method and a zone melting method. The thermoelectric materials prepared by powder metallurgy have lower thermal conductivity and higher mechanical strength, but decrease the conductivity. Relatively speaking, it is possible to use the zone melting method to prepare the material with higher conductivity, but also improve the thermal conductivity of the material.
In recent years, the mechanical alloying (MA), the mixed sintering (PIES), extrusion and spark plasma sintering (SPS) have been developed. In general, PbTe and SiGe alloys were prepared by powder metallurgy process, and Bi2Te3 and its alloys were prepared by zone melting method and hot pressing or extrusion process.
Development of thermoelectric material structure
A P column and a N column are connected by a metal plate to form a basic unit of a semiconductor thermoelectric element by doping the thermoelectric material into P type and N type semiconductor.
At present, the common structure of the cone type thermoelectric couple arm of thermoelectric, thermoelectric, coaxial ring arm of thermoelectric cascade of infinite. Cone type thermoelectric couple arm of thermoelectric of infinite cascade with studies of nano science and technology development, thermoelectric materials is one of the key countries in Europe and the full development of nano technology, whether in theoretical or experimental research has great space. Nano materials have interface and quantum confined effect is greater than the bulk material, the nano structure materials with new physical properties, and the phenomenon of the new interface, which is expected to enhance the ZT value of thermoelectric materials encountered bottleneck breakthrough improvement, so nano technology is regarded as the search for thermoelectric materials with high ZT value I hope.
Overview of thermoelectric materials industry
Thermoelectric material is a kind of functional materials can be heat and power conversion, the Seebeck effect found in 1823 and 1834 found that the Parr effect for thermoelectric energy conversion.