KR20060073017A - Manufacturing method of thermoelectric materials - Google Patents

Abstract

The present invention The present invention relates to a method for manufacturing a thermoelectric device, which comprises mixing electrolytic iron powder and silicon powder having a purity of 99% or more in a molar ratio of 1: 2, melting the same in a high frequency melting furnace to synthesize FeSi ₂ ingots, and milling the synthesized ingot. After crushing through coarse powder, it was pulverized and mixed with a ball mill so that granules with an average particle size of 1 μm or less and 20 μm were granulated, dried by a spray dryer, and granulated. The granules were formed using a cold hydrostatic molding machine and then The molded body was sintered in a reducing atmosphere in an sintering furnace capable of controlling the atmosphere and then annealed in vacuo to obtain a thermoelectric material having better characteristics.

Thermoelectric element, cold hydrostatic molding, reducing atmosphere, annealing

Description

Manufacturing method of thermoelectric materials

The present invention relates to a method of manufacturing a thermoelectric element, and more particularly, to prepare a thermoelectric material having low thermal conductivity without mixing electrical particles and granules of different granules and granules having the same composition or particle size during manufacturing. It is.

In general, thermoelectric material is a metal or ceramic material having a function of directly converting heat into electricity or electricity directly into heat. Waste heat from incineration of waste, waste heat from turbine power generation, heat from automobile exhaust gas, combustion arrangement of city gas, and various industrial waste heat Application to thermoelectric power generation, thermoelectric cooling, and the like has attracted attention.

Thermoelectric power generation using thermoelectric materials is possible to generate power without moving parts by simply giving a temperature difference, and the structure is simple and trouble-free, so maintenance is useful, there is no noise, and there is a wide range of heat sources to use. In addition, thermoelectric cooling has the features and advantages of low temperature, low noise, selective cooling of minute parts, high thermal response sensitivity, precise temperature control, and no need for compressor or refrigerant.

The characteristics of the thermoelectric material can be generally evaluated by the performance index (Z) represented by the following [Formula 1].                         

[Equation 1]

Z = α ² σ / κ

α: Seebeck coefficient

σ: electrical conductivity

κ: thermal conductivity

The larger the performance index, the greater the potential difference, and thus, the thermoelectric material exhibits excellent characteristics. Therefore, for the application as a thermoelectric material from the above [Formula 1], a material having a high Seebeck coefficient and high electrical conductivity and low thermal conductivity is preferable. Here, the Seebeck coefficient is a material intrinsic property given as a function of temperature. The electrical and thermal conductivity can be optimized according to the shape and carrior concentration, crystal structure, bonding properties, and bonding strength of the material.

Particularly, in the case of powder sintered bodies, since the grain boundary of disordered structure exists, lattice thermal vibration of long wavelengths is scattered at grain boundaries, and lattice thermal vibrations of short wavelengths are respectively scattered at fine strains in crystals, which can lead to a decrease in thermal conductivity. have. However, in this case, there is a possibility that the electrical conductivity may be accompanied by the scattering of the carrior, and therefore, the necessity of precise microstructure control and non-bonding technology is emerging.

In addition, there is a method for lowering the thermal conductivity of the ceramic sintered body as a method of lowering the sintered density by controlling the sintering temperature, but at the same time, the electrical conductivity is lowered or the mechanical strength is poor, which makes it difficult to apply as a practical commercial device.

The present invention has been made in order to solve the above problems, the production of thermoelectric elements with low thermal conductivity without mixing the granules and granules of the same composition or particle size and starting materials of the assembly when the thermoelectric device is manufactured, the electrical conductivity is not lowered It is an object of the present invention to provide a thermoelectric device with better performance.

In the method of manufacturing a thermoelectric device of the present invention for achieving the above object, the electrolytic iron powder and silicon powder having a purity of 99% or more are mixed in a molar ratio of 1: 2 in a ratio of about 50:50 by weight and then melted in a high frequency melting furnace. FeSi ₂ ingots were synthesized, and the synthesized ingots were coarsely pulverized through a pulverizer, and then pulverized and mixed in a ball mill to have granules having an average particle size of 1 탆 or less and 20 탆. The granules are formed by using a cold hydrostatic molding machine, and then the molded bodies are sintered in a reducing atmosphere in a sintering furnace capable of controlling the atmosphere and annealed in vacuo.

In addition, the conditions for sintering the molded body in a reducing atmosphere in a sintering furnace are sintered by heating at a rate of 3 ° C./min. In an reducing atmosphere using Ar—H ₂ for 1 to 4 hours at 1110 to 1200 ° C., The conditions for annealing the sintered compacts in vacuum are for 5 to 20 hours at 750 to 850 캜.

In addition, when the ball mill is pulverized and mixed so that granules having an average particle size of 1 µm or less and 20 µm are granulated, 1 to 4 Wt% of polyvinyl algol is added by extrapolation, so that the proportion of the granulated powder is 1 to 40 vol%.

In the present invention, the purity of the electrolytic iron and silicon powder is preferably 99% or more. The reason is that when the purity falls below 99%, not only the grain growth is excessively promoted by the carbon or silica contained therein, but the sintering is excessively progressed, thus making it difficult to manufacture the thermoelectric element.

In addition, the sintering is preferably carried out in the reducing component atmosphere and the sintering temperature is preferably 1100 ~ 1200 ℃ but less than 1100 ℃ sintering is weak strength, exceeding 1200 ℃ excessive grain growth and excessive sintering porous body Difficult to get.

In addition, the reason for adding 1 to 4 Wt% of polyvinyl algol by the extrapolation is to improve moldability, and when the addition amount is less than 1% by weight, it is difficult to manufacture the molded product due to lack of moldability. Excess polyvinyl alcohol hardens the powder and makes it difficult to process. Most preferably 1% by weight.

Hereinafter, a method of manufacturing a hot device of the present invention will be described with reference to the following Examples.

EXAMPLE

In order to manufacture the porous thermoelectric device of the present invention, as a starting material, more than 99% of electrolytic iron powder and more than 99% of silicon powder are mixed in a molar ratio of 1: 2, and then melted in a high frequency melting furnace to synthesize FeSi ₂ ingot, The synthesized ingot is roughly pulverized by a pulverizer and then pulverized by a conventional ball mill to prepare fine particles having an average particle size of 1 탆 or less and granulated powder of 20 탆.

Polyvinyl alcohol (PVA) is added to the powder as a binder in an amount of 1 to 4 wt%, and the ratio of the granulated powder is changed to change the degree of pore formation. The compositions of Comparative Examples 1 and 2 to Inventive Example 3 of Table 1 were designed to have a range of 0 to 40 vol% added.

For each of the above compositions, the mixture was mixed for 6 hours in an ethanol solvent using a ball mill, dried in a spray dryer, and granulated. Then, the resultant was molded into a molding mold having a cross section of 20 mm x 40 mm using a hydraulic press. After pressure molding, the mold was molded at a pressure of 2.0 ton / cm 2 by cold isostatic press.

The molded specimen was sintered using Ar-H ₂ at a rate of 3 ° C./min. In a reducing atmosphere and maintained at 1150 ° C. for 3 hours. The sintered specimens were annealed at 800 ° C. for 10 hours in vacuo for semiconductorization, and then cut into 4 mm × 4 mm × 20 mm in size and used as final characterization specimens.

Sinterability, electrical conductivity, and thermal conductivity of the Comparative Examples 1, 2 to 3 were measured, and the results are shown in Table 1.

Table 1

Assembly (Vol%) Sinterability Conductivity (S / m) Thermal Conductivity (W / m.k) Comparative Example 1 0 Good 345 10 Inventive Example 1 10 Good 345 9 Inventive Example 2 20 Good 330 8 Inventive Example 3 30 Good 310 7 Comparative Example 2 40 Bad - -

As can be seen from Table 1, in the case of Inventive Examples 1 to 3, the sinterability is good and the thermal conductivity is lowered without significantly lowering the electrical conductivity, thereby showing excellent thermoelectric properties.

The thermoelectric device manufacturing method of the present invention as described above in the forming and sintering process of the thermoelectric element is mixed granules and granules of different granules and granules of the same composition or particle size, and then granulated using a spray dryer, the granules are cold-static After molding using a molding machine, the molded body was sintered in a reducing atmosphere in an sintering furnace capable of controlling the atmosphere, and annealed in vacuum to produce a thermoelectric element, thereby obtaining a thermoelectric material having better characteristics.

Claims (4)

Electrolytic iron powder and silicon powder with a purity of 99% or more are mixed in a molar ratio of 1: 2, and then melted in a high frequency melting furnace to synthesize FeSi ₂ ingots, and the synthesized ingots are roughly pulverized through a grinder and then averaged to their average particle size. Grind and mix with a ball mill to make granules of less than 1 ㎛ and granules of 20 ㎛, dry and granulate the spray dryer, and shape the granules by using a cold hydrostatic molding machine. A method of manufacturing a thermoelectric element, which is sintered in a reducing atmosphere and annealed in vacuo. According to claim 1, The conditions for sintering the molded body in a reducing atmosphere in the sintering furnace is heated at a rate of 3 ℃ / min. In the reducing atmosphere using Ar-H ₂ and maintained for 1 to 4 hours at 1110 ~ 1200 ℃ Thermoelectric element manufacturing method characterized in that the sintering. The method of claim 1, wherein the annealing of the sintered molded body in a vacuum is performed at 750 to 850 ° C. for 5 to 20 hours. The method according to claim 1, wherein when the ball mill is pulverized and mixed so that granules having an average particle size of 1 µm or less and 20 µm are granulated, 1 to 4 Wt% of polyvinyl algal is added by extrapolation, and the proportion of granulated powder is 1 to 40 vol%. Thermoelectric device manufacturing method characterized in that to be.