JP3750156B2 - Manufacturing method of iron disilicide - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to a method for producing β-phase iron disilicide, which is a promising material as a thermoelectric conversion element.
[0002]
[Prior art]
Thermoelectric conversion materials are attracting attention as energy sources that do not emit environmental pollutants, do not emit noise, and are maintenance-free. Currently, thermoelectric cooling elements are mainly produced commercially, but the market for thermoelectric power generation is expected to be gradually formed. β-phase iron disilicide is particularly noted for its excellent oxidation resistance and heat resistance, no toxicity, low cost raw materials, and a relatively high Seebeck coefficient at 200 to 900 ° C.
[0003]
Iron disilicide is used as a thermoelectric conversion material of a sintered body or a thin film. The present invention relates to a powder for sintered iron disilicide or a method for producing a sintered body. A conventional method for manufacturing a sintered body of iron disilicide includes melting a raw material containing iron and silicon at a high temperature and solidifying it as an ingot to obtain an eutectic of an ε phase and an α phase. In this method, the powder obtained by pulverization and pressure forming is sintered at 1100 ° C. or higher, and then subjected to heat treatment for a long time in a β-phase stable region to form a β phase.
[0004]
However, this conventional method has a high energy consumption due to melting at high temperature and requiring a long heat treatment to produce β-phase iron disilicide (for example, special effects). (Kaisho 5-56781).
[0005]
On the other hand, in recent years, a method for producing β-phase iron disilicide by a mechanical alloying method has been proposed. French Patent Specification No. 8,809,896 (1988) discloses a method for producing carbide or silicide by mechanically alloying a transition metal element or the like with carbon or silicon. Among them, as for iron silicide, it is described in the Examples that a powder of iron and silicon (atomic ratio 1: 2) treated with a vibration ball mill for 24 hours was a mixture of α, β and ε phases.
[0006]
Japanese Patent Laid-Open No. 6-81076 discloses a method for producing β-phase iron disilicide comprising a step of grinding and mixing iron and silicon raw material powder, a step of forming, and a step of sintering. According to this method, a sintered body obtained by hot pressing at 950 ° C. after pulverizing iron and silicon powder for 100 hours with a ball mill was a mixture of β and ε phases.
[0007]
JP-A-6-92619 discloses a method for producing iron disilicide by mechanically alloying iron and silicon raw material powder (molar ratio 1: 2.1 to 1: 3.5) and then heat-treating. Has been. According to this method, a powder of iron and silicon (1: 2.2 to 1: 3.0) was treated with a vibration ball mill for 10 hours, then molded and then heat treated at 900 ° C. for 80 to 100 hours. It was a mixture of β and ε phases, and the ε phase was 2 to 10%.
[0008]
[Problems to be solved by the invention]
The above three inventions based on the mechanical alloying method have the advantage that the amount of energy consumption is small in that the high temperature melting is not required as compared with the above melting method. On the other hand, however, there is a problem that the obtained sintered body contains an ε phase in addition to the β phase. Since the β phase is effective for the thermoelectric conversion characteristics, it is preferable to suppress the generation of the ε phase as much as possible.
An object of the present invention is to suppress the generation of the ε phase in the mechanical alloying method, and further to shorten the time required for the mechanical alloying to increase the production efficiency.
[0009]
[Means for Solving the Problems]
As a result of intensive studies to solve the above problems, the present inventors have used a mixed powder having an Fe: Si atomic ratio of more than 1: 2.0 and not more than 1: 3.0, and the raw material iron is reduced. It has been found that when a powder in which an α phase and an ε phase are generated by performing mechanical alloying until it is consumed to 20% or less is heat-treated, an iron disilicide sintered body substantially having a β phase is obtained. The present invention has been completed.
[0010]
Further, the present inventors have found that in a mechanical alloying method, in which we found that allowed to produce a relatively short period of time α phase and ε phase by the use of a de Isukumiru.
[0011]
That is, the present invention provides [1] a method for producing β-phase iron disilicide in which iron and silicon-containing powder are mechanically alloyed and then heat treated.
(1) The raw material is prepared so that the atomic ratio of iron and silicon contained in the raw material powder is more than 1: 2.2 and 1: 3.0 or less,
(2) Forming α-phase and ε-phase iron silicide by mechanical alloying using a disk mill until the raw material iron is consumed to 20% or less, then (3) forming, heat-treating and sintering A method for producing a β-phase iron disilicide sintered body , characterized in that a body is obtained .
[0012]
[2] The method for producing a β-phase iron disilicide sintered body according to the above item [1], wherein a raw material to which a substitution metal element is added instead of a part of the raw iron or silicon is used.
[0014]
The iron, silicon, and substitutional metal elements that are the raw material powders in the present invention are industrial grade powders, preferably those having a purity of 99% by weight or more, more preferably those having a purity of 99.9% by weight or more. It is done. It is a well-known fact that the thermoelectric conversion characteristics depend on the type and amount of metal added to the iron disilicide, and therefore it is preferable that the purity of the powder is high in order to avoid unexpected impurities.
[0015]
The feed ratio of iron and silicon in the raw material powder is such that the atomic ratio of iron to silicon or the atomic ratio of (iron + substitution metal element) to silicon exceeds 1: 2.2 and is within a range of 1: 3.0 or less. There must be. When the amount of silicon is less than 1: 2.2, the ε-phase after firing increases, which is not preferable. When it exceeds 1: 3.0, a component of silicon is present after firing, so that the purity of iron disilicide decreases.
[0016]
The metal element for substitution in the present invention is to give semiconductor characteristics by substituting a part of iron or silicon, and is made of Mn, Cr, V, Al, etc. to make a p-type semiconductor, and an n-type semiconductor. Therefore, it can be substituted with Co, Ni, Pt or the like. The ratio of substitution may be a known level, and is exemplified by 0.5 to 10 atomic%.
[0017]
In the present invention, mechanical alloying refers to generating fine particles, amorphization, solid solution, chemical reaction, etc. by applying mechanical pulverization or grinding force to a substance. As for mechanical alloying, research examples are increasing in recent years, and there are detailed descriptions in, for example, “Organic / Inorganic Mechanochemistry” (Kubo, Industrial Data Center, 1993).
[0018]
Conventionally, rotary ball mills, vibration ball mills, planetary ball mills, and the like are known as devices for performing mechanical alloying. Among them a device used in the mechanical alloying of the present invention uses a large de Isukumiru impact force. Conventionally, a disk mill has been used as a grinding device for obtaining a sample for analysis. We propose to use this for material synthesis. Usually, the disc mill is composed of three combinations of vessel, ring, and stone, and there are 50 cc, 100 cc, etc. as the volume of the vessel. Materials include tungsten carbide, stainless steel, alumina, zirconia and the like.
[0019]
The amount of powder charged into the disk mill is not necessarily specified, but is preferably around 30% by volume of the vessel volume. The time for performing mechanical alloying is the time until most of the charged iron is consumed, and depending on the type of raw material, for example, 20 to 60 minutes is exemplified. In the present invention, until iron is almost consumed, the iron diffraction line (2θ = 44.7) is compared with before and after pulverization by powder X-ray diffraction (source: CuKα) until it becomes 20% or less. Means.
[0020]
When iron and silicon are mechanically alloyed, the ε-phase diffraction line (2θ = 45.2) and the above-mentioned iron diffraction line are close to each other, so the iron decreases and the ε-phase increases. The diffraction line becomes the shoulder of the diffraction line of the ε phase, and the diffraction intensity cannot be read accurately. Therefore, for the sake of convenience, the standard of 20% or less is set.
[0021]
There is no particular limitation on the atmospheric gas pressure in mechanical alloying.
The gas component is not particularly limited, and examples thereof include an inert gas, oxygen, nitrogen, or a mixed gas thereof.
[0022]
The method of the present invention is characterized in that a powder in which an α phase and an ε phase are generated is heat treated by mechanical alloying. Therefore, it is necessary that powder X-ray diffraction lines of α phase (2θ = 17.3) and ε phase (2θ = 45.2) exist in the powder after mechanical alloying.
[0023]
In the present invention, the heat treatment refers to holding for a certain period of time below the decomposition temperature of β-phase iron disilicide. Although it changes with metal elements for substitution, the temperature range of 850-950 degreeC is mentioned, for example. This heat treatment includes a cold-pressed product, a hot press, a hot isostatic press, and the like.
[0024]
The atmosphere of the heat treatment is preferably under vacuum, and an inert gas, nitrogen, oxygen, or a mixed gas thereof is also used.
[0025]
【Example】
The present invention will be illustrated in more detail by the following examples, but the present invention is not limited to these examples.
Further, in the following examples, the existence ratio of the ε phase by X-ray diffraction of the heat-treated formed body or powder is the ε phase (2θ = 2θ = 2) = the diffraction intensity of the β phase (2θ = 29.1) is 100. The ratio of the diffraction intensity of 45.2) is expressed as a percentage.
[0026]
Example 1
16.23 g of iron powder (manufactured by High Purity Chemical Co., Ltd., purity 99.9%, particle size of 300 mesh or less) and silicon powder (made by Rare Metallic, purity 99.99%, particle size of 150 mesh or less) 18.77 g Was loaded into a disk mill (Herzog, Vessel 100 cc, tungsten carbide) (Fe: Si = 1: 2.3), and after nitrogen substitution, it was subjected to mechanical alloying three times for 15 minutes. From the powder X-ray diffraction of the obtained powder, the iron residue was 20% or less, and an α phase and an ε phase were detected. 4.00 g of the obtained powder was formed into a diameter of 13 mm and a height of 12 mm with a cold press (press pressure 3.4 t / cm ² ), and under vacuum (2 × 10 ⁻⁴ mmHg) at 900 ° C. for 4 hours. Heat treatment was performed. From the X-ray diffraction of the obtained molded product, it was β phase, and ε phase was not detected.
[0027]
Example 2
In Example 1, iron powder 14.78 g, manganese powder (manufactured by Furuuchi Chemical Co., Ltd., purity 99.9%, particle size 300 mesh or less) 1.44 g, silicon powder 18.78 g were charged (Fe: Mn : Si = 0.94: 0.06: 2.3), and a sintered compact was obtained in the same manner as in Example 1 except that the cold pressing pressure was 1.0 t / cm ² . The ε phase in the sintered body was 1%.
[0028]
Example 3
A sintered body was obtained in the same manner as in Example 2 except that the charged powder composition in Example 2 was changed to Fe: Mn: Si = 0.97: 0.03: 2.3. The ε phase in the sintered body was 1%.
[0029]
Example 4
In the same manner as in Example 2, 8.00 g of powder obtained by mechanical alloying was formed into a diameter of 20 mm and a height of 9 mm with a hot press machine (900 ° C., 1 hour, pressure 1.0 t / cm ² , Atmosphere argon). From the X-ray diffraction of the obtained molded product, it was β phase, and ε phase was not detected.
[0030]
Example 5
In Example 1, 15.73 g of iron powder, 0.51 g of cobalt powder (manufactured by Furuuchi Chemical Co., Ltd., purity 99.9%, particle size of 300 mesh or less), and 18.76 g of silicon powder were charged (Fe: Co : Si = 0.94: 0.06: 2.3), and a sintered compact was obtained in the same manner as in Example 1 except that the cold pressing pressure was 1.0 t / cm ² . The ε phase in the sintered body was 1% .
[ 0034]
Comparative Example 1
In Example 1, mechanically alloyed powder was obtained in the same manner as in Example 1 except that mechanical alloying was performed twice for 15 minutes and 5 minutes. From the X-ray diffraction of the obtained powder, the iron residue was 53%, and the α phase was detected. 1.5 g of this powder was put in a quartz container and baked under vacuum (2 × 10 ⁻⁴ mmHg) at 900 ° C. for 4 hours. From the X-ray diffraction of the obtained powder, 29% of ε phase was present in addition to β phase.
[0035]
Comparative Example 2
16.58 g of powder (made by High Purity Chemical Co., Ltd., purity 99.9%, particle size 300 mesh or less) and 19.42 g of silicon powder (made by Rare Metallic, purity 99.99%, particle size 150 mesh or less) A rotating ball mill (stainless steel mill diameter: 120 mm, length: 120 mm, stainless steel ball diameter: 9.5 mm) was charged (Fe: Si = 1: 2.33), and after nitrogen substitution, mechanical alloying was performed at 95 rpm for 200 hours. From the X-ray diffraction of the obtained powder, the iron residue was 53%, and no α phase was detected. This powder was formed into a diameter of 13 mm and a height of 13 mm with a cold press (pressing pressure: 1.0 t / cm ² ) and heat-treated for 4 hours under vacuum (2 × 10 ⁻⁴ mmHg). From the X-ray diffraction of the obtained molded body, 35% of ε phase was present in addition to β phase.
[0036]
【The invention's effect】
According to the method of the present invention, high-temperature melting is not required, heat treatment may be performed at a relatively low temperature, and a short time is required, so that production efficiency is remarkably improved. Further, the obtained iron disilicide has a very small ε phase and is almost regarded as a β phase single phase, and therefore is suitable as a thermoelectric property material.

Claims (2)

In the method for producing β-phase iron disilicide, mechanically alloying a powder containing iron and silicon and then heat-treating,
(1) The raw material is prepared so that the atomic ratio of iron and silicon contained in the raw material powder is more than 1: 2.2 and 1: 3.0 or less,
(2) Forming α-phase and ε-phase iron silicide by mechanical alloying using a disk mill until the raw material iron is consumed to 20% or less, then (3) forming, heat-treating and sintering A method for producing a β-phase iron disilicide sintered body , characterized in that a body is obtained . The method for producing a β-phase iron disilicide sintered body according to claim 1, wherein a raw material to which a substitution metal element is added instead of a part of the raw material iron or silicon is used.