JPS62132380A - N-type thermoelectric element - Google Patents

Abstract

PURPOSE:To form a N-type thermoelectic element having excellent thermal resistance inexpensively by adding specific amount of aluminum oxide to zinc oxide. CONSTITUTION:Aluminum oxide is added to zinc oxide powder, the mixture is sufficiently mixed, pressure molded, and sintered in vacuum or reduced atmosphere to form a sintered material. The aluminum oxide content for the zinc oxide must be 0.02-2.0mol%. If the content is 0.02mol% or less, its specific resistance becomes excessively high so that the highest output power is remarkably reduced not to be practical. If the content is 2.0mol% or more, it specific resistance does not decrease as much as thermoelectric capacity decreases so that the highest output power is remarkably reduced. The thus obtained sintered material exhibits stable performance at 1,000 deg.C in oxidative atmosphere, and can be advantageously used for waste heat utilizing generator by combining a plurality parts consisting the materials and suitable P-type thermoelectric elements.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to an N-type thermoelectric element with excellent heat resistance that can be obtained using extremely inexpensive raw materials and processes, and is useful for power generation using waste heat, geothermal power generation, and solar thermal power generation. It is used for etc.

[Technical background of the invention and its problems]

Conventionally known thermoelectric elements include Di2Te3°Sb.
Most of them are mainly composed of intermetallic compounds such as , Te, , PbTa, and GeTe, which all use rare elements frequently, require high purity, have complicated manufacturing processes, and are extremely expensive. Furthermore, they tend to become unstable at high temperatures, and are generally used at temperatures below 300° C., and have been used for electronic cooling rather than for power generation.

In order for a thermoelectric element to be actually used for power generation using waste heat, etc., in addition to being heat resistant up to around 500° C., it is important that it be low cost.

[Purpose of the invention]

The present invention has been made to solve the above problems,
An object of the present invention is to provide an N-type thermoelectric element that is inexpensive and has excellent heat resistance.

[Summary of the invention]

Generally, the characteristics of thermoelectric materials are expressed by the following equation with a figure of merit of 2.

where ρ is the thermoelectric power (Seebeck coefficient), ρ is the specific resistance, and is the thermal conductivity.

In addition, as for the practical characteristics of thermoelectric elements in power generation, the open circuit voltage V and internal resistance R1 maximum output power Pmax are important, and respectively ■=α・ΔT ・・・・・・・・・・・・■R=ρ・−・ ・ ・ ・ ・ ・ ・ ・ ・ ・
It is expressed as 0Pmax=□・−・・・e−〈;1() R . Here, ΔT is the temperature difference between the high temperature Th and the low temperature Tc (ΔT=Th−Tc), Q is the length of the element, and S is the cross-sectional area of the element. From these formulas.

It can be seen that in order to extract a large amount of power, it is important to increase the open circuit voltage and reduce the internal resistance. It can be seen that the important physical properties of the material are high thermoelectric capacity and low specific resistance.

Oxides are generally known to have excellent heat resistance and high thermal lightning ability, but their specific resistance is high and many are used as insulators, and conductive oxides have low thermoelectric power. None of them could be used as thermoelectric elements.

The inventors investigated various additives for various oxides in order to significantly reduce the resistivity while maintaining the high thermoelectric power of the oxide. As a result, the addition of aluminum oxide to zinc oxide resulted in an extremely excellent N-type It was discovered that it can be used as a thermoelectric element.

The aluminum oxide content in zinc oxide in the present invention needs to be 0.02 to 2.0 mol%, and if the aluminum oxide content is less than 0.02 mol%, the specific resistance is too high and the maximum output power is significantly reduced. It becomes small and cannot be put to practical use. Further, if the temperature exceeds 2.0 moles, although the thermoelectric power decreases, the specific resistance does not decrease, and the maximum output power becomes extremely small.

In the present invention, it is appropriate to use a powder sintering method to form the device. Aluminum oxide powder is added to suboxide powder, mixed thoroughly, and then pressure molded and fired in a vacuum or in a reducing atmosphere to obtain a sintered body.The firing temperature ranges from 1000 to 1350°C. preferred, 1000
Below ℃, the specific resistance increases and the maximum output power decreases. At temperatures above 1350°C, zinc oxide begins to sublimate. A firing time of 30 minutes or more is sufficient. The sintered body thus obtained was heated to 1000°C in an oxidizing atmosphere.
It is an N-type thermoelectric element that exhibits stable performance even in 2008, and has excellent power characteristics.

The thermoelectric element of the present invention is mainly made of ordinary purity zinc oxide, which is extremely cheap as a raw material, so it is cheaper than conventional elements that use many rare elements, and it can be easily manufactured by a powder firing process. It is possible to significantly reduce costs.

[Embodiments of the invention]

Next, the present invention will be specifically explained using examples.

(Example 1) 0.1 mol% of aluminum oxide powder was added to zinc oxide powder, mixed for 1 hour in a bot mill, and then pressure-molded at 1 ton/d.
A sintered body was obtained by firing at 260°C for 30 minutes. The density of this sintered body was 5.38 g/cc. This sintered body was made into an element with a cross-sectional area of 1 d and a length of 1 m, and the high temperature side was heated to 450°C.
The open circuit voltage V and internal resistance R were measured with a temperature difference of 400°C with the low temperature side set at 50°C. Open end voltage is 126.8
mV, internal resistance is 3.7mΩ, maximum output power is 1.09
It became W. Thermoelectric power is 317μV/K, specific resistance is 37m
It is calculated as ΩG.

Also, set the high temperature side to 750℃ and the low temperature side to 50℃.

When a temperature difference of 700°C was applied, the open circuit voltage was 225.
4mV, internal resistance is 3.8mΩ, maximum output power is 3.3
4W was obtained. Thermoelectric power is 322μV/K, specific resistance is 3
．． It becomes 8mΩ mouth.

Similar measurements were performed after this element was heated in the atmosphere at 850°C for one week, but no change in thermoelectric properties was observed, indicating that it had excellent heat resistance.

(Example 2) 0.8 mol% of aluminum oxide powder was added to zinc oxide powder, mixed in a mortar for 30 minutes, and the resulting green compact was molded under pressure at 0.5 ton/- in a vacuum of to-3 Torr. 1100℃
A sintered body was obtained by firing for 1 hour. This sintered body was made into an element with a cross-sectional area of 1 d and a length of 1+ m+, and the high temperature side was heated to 450°C.
, when the low temperature side is set to 50℃ and a temperature difference of 400℃ is applied, the open circuit voltage is 99.2a+V, the internal resistance is 2.6+++Ω,
A maximum output power of 0.95W was obtained. Thermoelectric power is 248μ
V/K and specific resistance were 26 mΩ■.

(Comparative Example 1) Add 0.01 mole of aluminum oxide to zinc oxide powder, mix in a pot mill for 1 hour, pressurize at 1 ton/cJ, and then sinter at 1200°C in a vacuum of 10-' Torr for 1 hour. did. The obtained sintered body was made into an element with a cross section of fila J and a length of 1 m, and then heated to 450°C on the high temperature side and 5°C on the low temperature side.
When a temperature difference of 400° C. was applied, assuming that the temperature was 0° C., an open circuit voltage of 168.4 mV, an internal resistance of 138 mΩ, and a maximum output power of 0.0511 were obtained. The thermoelectric power is as high as 421μV/.

It has a large specific resistance of 1.38 Ωl, and the power that can be taken out is significantly small.

〔Effect of the invention〕

As detailed above, the N-type thermoelectric element of the present invention is extremely inexpensive in terms of raw materials and manufacturing process, and has excellent heat resistance. When applied to power generation using waste heat, it becomes possible to supply inexpensive energy, and the industrial value is significant.

Agent: Patent Attorney Noriyuki Chika Same Bamboo Flower Kikuo

Claims (1)

[Claims] Aluminum oxide (Al_
An N-type thermoelectric element containing 0.02 to 2.0 mol% of 2O_3).