The efficiency of thermal power conversion into electric power is characterized by the value Z, the formula for which is shown as follows:
Z = α²·σ/κ
σ – specific conductivity [Ohm-1cm-1]
α – thermal electromotive force [mkV/K]
κ – thermal conductivity [W/(m·К)]
For its production of the advanced efficiency thermoelectric material, THERMOINTECH Company uses the patented method of melt-quenching in liquid. High speed of the melt drip cooling and its volume restriction results in strong overcooling of the crystallization front and creation of conditions for the X-ray amorphous structure formation inside the drip. The presence of the amorphized structure becomes an additional obstacle to the distribution of thermal phonons, but does not affect the charge carrier. As a result, it enables to reduce the lattice component of the thermal conductivity significantly without reducing the electrical conductivity, thus increasing the efficiency of Z thermoelectric material.
Studies conducted by THERMOINTECH Company with the aid of a scanning electron microscope LEO 1420 show that the application of different types of cooling liquids makes it possible to change the cooling speed and, accordingly, to control the formation of X-ray amorphous structure. The figure above shows photographs of granules received during the ultra-rapid solidification resulting in the uncharacteristic crystallization for thermoelectric materials with the formation of concentric circles on the surface or a unique granules formula.
The X-ray amorphous structure is found inside such granules. The structure contains small-sized, chaotically crystallized multidirectional plates of the thermoelectric material.
The Figures show solid solution granules on the basis of the bismuth telluride received during the slower quenching of the liquid. Notwithstanding the fancifulness of granules forms, one can see that the crystallization does not result in the formation of the amorphous structure in the considerable volume.
Using the liquid quenching technology, it is possible to receive materials on the basis of bismuth telluride, with the average integral factor of quality within the temperature range from +60 to +280 Сº
for Р-type from 2,0×10-3 to 2,4×10-3 К-1
for N-type from 1,7×10-3 to 1,9×10-3 К-1
Comparison of temperature dependences of electrophysical properties of thermoelectric materials received by the liquid quenching and according to the official procedure for N-type.
Comparison of temperature dependences of electrophysical properties of thermoelectric materials received by the liquid quenching and according to the standard procedure for P-type.
The application of thermoelectric materials received according to the liquid quenching technology makes it possible to receive the efficiency ratio of the thermoelectric conversion more than 6.6% when the item operates in the normal temperature mode.