JP5780851B2 - Method for producing iron-silicon alloy - Google Patents

Description

The present invention relates to a method for producing an iron-silicon alloy used in the process of producing β-iron silicide (βFeSi ₂ ), semiconductors, and the like used for optical elements such as optical sensors, light-emitting elements, solar cells, and thermoelectric elements.

  Conventionally, as a method for producing this kind of iron silicon alloy, first, raw materials such as Fe and Si are mixed, melted in a high frequency furnace and cast into a mold, and then an iron silicide alloy ingot is prepared. It is pulverized into a powder of about 2 μm by a stamp mill and a ball mill, and after the binder is mixed with this powder, it is cold pressed and molded, and then the molded body is sintered and subsequently subjected to β heat treatment to produce a thermoelectric power generation material. (For example, refer to Patent Document 1).

Japanese Patent Publication No. 2-1381

However, in such a conventional method for producing an iron-silicon alloy, a mixture of FeSi, unreacted Si, Fe, and a small amount of αFeSi ₂ is synthesized when the raw material is melted at a high temperature (1200 ° C. or higher). In order to form a grain boundary, it is necessary to pulverize and re-sinter the melted iron silicide alloy.
As a result, the number of processes is large, and it takes time for manufacturing and also requires heat treatment for a long time. Therefore, there is a problem that energy consumption is increased, making it unsuitable for mass production and costly.
Furthermore, since a high-frequency furnace and a mold used for the melting process and a stamp mill and a ball mill used for the crushing process are required, there is a problem that the manufacturing equipment becomes expensive and the cost is increased.
In addition, the powder sintering method by cold pressing must granulate the powdered raw material again to an appropriate size or remove the fine powder, resulting in poor raw material yield and oxidation in the raw material. Since substances, adsorbed gases, and the like deteriorate the characteristics of the thermoelectric conversion element, there are problems that an extra step is required to remove them and that quality control of the raw materials must be strictly performed.
Therefore, it is conceivable that the raw material powder is pressurized and simultaneously heated and sintered by a hot press method instead of the cold press powder sintering method.
However, the hot press method requires very high pressure and temperature to increase the sintering density, which makes the production equipment expensive and requires a long sintering time, which causes problems in terms of running cost and productivity. In addition, similarly to the cold pressing method, there is a problem that appropriate quality control of the raw material is necessary.

  An object of the present invention is to deal with such problems, and aims to produce high-purity iron-silicon alloys, β-iron silicides, and semiconductors without going through a melting step and a pulverizing and mixing step. It is what.

The present invention in order to achieve the above object, a filling step of filling the raw material and to the iron powder and divorced powder into sintered, wherein the iron powder filled in the sintering mold and the silicon powder A sintering step of sintering the mixed powder of the above by a pulse current sintering method,
The silicon powder is chips having an average particle size of 0.1 to 10 μm discharged when the wafer is cut and separated from the Si ingot, and the sintering step is performed by applying a DC pulse while pressing the mixed powder. Thus, a sintered body containing αFeSi ₂ as a main component was produced.

In the present invention having the above-mentioned features, a DC pulse energization is performed by filling iron powder having a particle size of 10 μm or less and silicon powder having a particle size of 10 μm or less into a sintering mold and pressurizing the powder by a pulse current sintering method. As a result, plasma discharge is generated, and ions are moved at high speed by electric field action, and the oxide and adsorbed gas in the powder are effectively removed, and the quality based on αFeSi ₂ is good and Since a dense sintered body can be obtained, it is possible to produce a high-purity iron silicon alloy that can be converted into β-iron silicide, a semiconductor, or the like without going through a melting step or a pulverizing and mixing step.
As a result, the number of processes can be reduced and manufacturing time can be shortened compared to conventional methods that require a melting process and a pulverizing and mixing process, and energy required for the melting process and the pulverizing and mixing process can be reduced. Reduction can be achieved, and it becomes possible to produce in larger quantities.
Furthermore, since the manufacturing equipment used for a melting process and a grinding | pulverization mixing process is unnecessary, the cost can be reduced further.
In addition, the pulse current sintering method can be fired in a shorter time than the powder sintering method by the hot press method, improving running costs and productivity, and dense sintering at a relatively low temperature in a short time. Since a body is obtained, it can be used as an optical element that has been difficult to use due to crystallinity problems.

Hereinafter, embodiments of the present invention will be described in detail.
A method for producing an iron-silicon alloy according to an embodiment of the present invention includes a filling step of filling a sintered mold with iron powder having a particle size of 10 μm or less and silicon powder having a particle size of 10 μm or less, A sintering step of sintering the filled mixed powder by a pulse current sintering method.

In the filling step, iron powder having an average particle diameter of 10 μm or less and silicon powder having an average particle diameter of 10 μm or less are prepared as raw materials, and these are mixed in desired amounts, and then filled into a sintering mold. Alternatively, iron powder and silicon powder are filled into the sintering mold in a desired amount and mixed.
In the sintering step, the mixed powder filled in the sintering mold is subjected to direct current pulse energization while being pressed by a pulse current sintering method, so that sintering with αFeSi ₂ (α iron silicide) as a main component is performed. The body is made.
Further, as a subsequent step of the sintering step, it is possible to include a β treatment step for obtaining βFeSi ₂ (β iron silicide) by subjecting the sintered body to a β heat treatment.

In the pulse current sintering method, a direct current pulse current of, for example, several hundred amperes to several thousand amperes is passed through the mixed powder in the sintering mold, and the powder is sintered by direct heat generation due to discharge between particles or Joule heat of the sintering mold. This is a kind of pressure sintering method, and is also called a direct current pulse current sintering method or a discharge plasma sintering method.
As an example of an apparatus used for carrying out the pulse electric current sintering method (DC pulse electric current sintering method, discharge plasma sintering method), a sintering mold installed in a chamber and a filling in the sintering mold A pressing mechanism for pressing the mixed powder and an electrode for allowing a DC pulse current to flow through the mixed powder. By applying a direct current pulse current from the power source to the mixed powder through this electrode, a plasma discharge is generated between the particles of the mixed powder, and heat sintering is performed between the particles.

The amount of pressurization of the mixed powder by the pressurizing mechanism is preferably 10 MPa or more, preferably 20 MPa or more and 60 MPa or less.
The heating temperature of the mixed powder by the electrode is preferably controlled in the range of, for example, 500 ° C to 1500 ° C, preferably in the range of 850 ° C to 1200 ° C.
Furthermore, as a sintering environment of the sintering type, for example, it is preferable to reduce the pressure to 10 Pa or less or to sinter in an inert gas.

According to such a method for producing an iron-silicon alloy according to an embodiment of the present invention, iron powder and silicon powder having a particle size of 10 μm or less are mixed and filled in a sintering mold in the filling step, and the sintering is performed in the sintering step. Direct current pulse energization is performed while the mixed powder filled in the mold is pressed by a pulse current sintering method.
As a result, plasma discharge is generated, and ions are moved at high speed by electric field action, and the oxide and adsorbed gas in the mixed powder are effectively removed, and the quality based on αFeSi ₂ is good and A dense sintered body is obtained.
Therefore, it is possible to produce a high-purity iron-silicon alloy that can be converted into β-iron silicide (βFeSi ₂ ), a semiconductor, or the like even if the melting step and the pulverizing and mixing step, which are indispensable in Patent Document 1 described above, are omitted. it can.
Furthermore, when chips having an average particle diameter of 0.1 to 10 μm discharged when cutting and separating a wafer from an Si ingot are used as silicon powder, a pulverizer such as a ball mill or a planetary ball mill is used. Therefore, there is an advantage that it can be obtained easily and inexpensively, and the waste material can be effectively used as a raw material, so that it is environmentally friendly and economical.

  In particular, when the mixed powder is pressurized to 20 MPa or more, a direct current pulse is applied to the mixed powder, and the powder is heated and sintered within a range of 850 ° C. to 1200 ° C. or less. There is an advantage that can be produced reliably.

The iron-silicon alloy obtained in this way is obtained by subjecting the sintered body to β heat treatment in the β treatment step as a subsequent step of the sintering step, thereby obtaining high-purity β iron silicide.
Accordingly, there is an advantage that high-purity β-iron silicide can be produced even if the melting step and the pulverizing and mixing step, which are indispensable in Patent Document 1 described above, are omitted.
As specific examples of the β heat treatment, the sintered body is subjected to heat treatment at about 700 to 900 ° C. under reduced pressure for about 10 hours or more, or heat treatment at about 700 to 900 ° C. for about 200 hours or more by argon substitution. It is preferable to do.

In the filling step, it is also possible to add a small amount of a doping material (dopant) such as Mn or Co to the mixed powder made of iron powder and silicon powder having a particle size of 10 μm or less as the raw material.
That is, when direct current pulse energization is performed while the mixed powder to which the doping material is added is pressed by a pulse current sintering method, a p / n junction is directly formed in the sintered body.
Thereby, there is an advantage that a p-type or n-type semiconductor can be produced without increasing the number of steps.

Furthermore, it is possible to heat-treat after laminating a dope material such as Mn or Co on the surface of the sintered body by, for example, coating.
That is, when a dope material is applied to the surface of the sintered body and then heat-treated, an n-type or p-type semiconductor is formed.
This has the advantage that a p-type or n-type semiconductor can be produced.

Claims (3)

A filling step of filling iron powder and divorced powder into sintered as a raw material,
A sintering step of sintering the mixed powder of the iron powder and the silicon powder filled in the sintering mold by a pulse current sintering method,
The silicon powder is a chip having an average particle size of 0.1 to 10 μm discharged when the wafer is cut and separated from the Si ingot,
The method for producing an iron-silicon alloy is characterized in that in the sintering step, a sintered body containing αFeSi ₂ as a main component is produced by applying direct current pulse while pressing the mixed powder. As a step after the sintering step, the manufacturing method according to claim 1 Symbol placement iron silicon alloy, characterized in that it comprises the sintered body was heat-treated β of obtaining β-iron disilicide β treatment step. The process according to claim 1 Symbol placement iron silicon alloy, wherein the heat-treated by stacking doped material on the surface of the sintered body.