JP2009143784A - Method for producing magnetite bulk material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing a magnetite bulk material giving a bulk material with a high density and high magnetite purity. <P>SOLUTION: This method comprises a step of molding a Fe<SB>3</SB>O<SB>4</SB>powder to obtain a molded body and a step of sintering the resulting molded body, where the molding may be conducted under a pressure of 98-294 MPa and the sintering may be conducted at 1,000-1,300°C in an inert atmosphere. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for producing a magnetite bulk material that can be used as a measurement sample for grasping various physical properties of a magnetite phase or used as various materials.

  In the manufacturing process of steel products, an oxide film (scale) is formed on the surface, which causes the quality and performance of the product to deteriorate and the production yield to decrease. For example, if the removal of the thick primary scale formed in the heating furnace is incomplete and it is subjected to rolling with a part remaining, the scale may be broken or pushed in, and scale flaws may occur in the steel material. . Further, due to the secondary scale, mechanical descaling (MD) property may be poor or plating property may be poor. Thus, the scale greatly affects the surface properties of the steel material. Therefore, in order to solve the problem caused by the scale, it is only necessary to grasp the dynamic behavior such as the scale formation behavior and the scale fracture / deformation behavior during the rolling process. In particular, in order to grasp the fracture / deformation behavior of the scale during the rolling process, it is only necessary to grasp the physical properties (for example, physical characteristics and mechanical characteristics) of the scale in a high temperature state.

By the way, the scale is usually composed of an Fe-based oxide [for example, FeO (wustite), Fe ₃ O ₄ (magnetite), Fe ₂ O ₃ (hematite), etc.]. Therefore, in order to grasp the physical properties of the scale at high temperatures, it is considered to prepare a simple sample of such an Fe-based oxide and measure the physical properties such as hardness, Young's modulus (elastic constant) and linear expansion coefficient at high temperatures. It is done. In particular, magnetite (Fe ₃ O ₄ ) is a main oxide constituting the scale and is considered to have a great influence on the physical properties of the scale.

  As a technique for evaluating the physical properties of magnetite, Non-Patent Document 1 discloses that a steel sheet is heated to form a scale on the surface of the steel material, and the Vickers hardness of the magnetite layer is measured at 1000 ° C. in the exposed scale cross section. Is disclosed. However, since the technology disclosed in Non-Patent Document 1 is not for producing a single sample having a high magnetite purity (hereinafter sometimes referred to as a bulk), the Vickers hardness of the magnetite layer can be measured. Other mechanical properties (for example, Young's modulus and linear expansion coefficient of magnetite) cannot be measured.

On the other hand, although it is not a technique for providing a bulk material with high magnetite purity, Patent Document 1 describes that a synthesized magnetite powder is molded and fired to obtain a magnetite sintered body.
Materials Science Forum Vols.522-523 (August 2006) pp.469-476 JP 2003-20286 A

  Patent Document 1 describes that a synthesized magnetite powder is molded and fired to obtain a magnetite sintered body. However, this Patent Document 1 does not describe specific conditions for producing a magnetite sintered body. Therefore, the magnetite purity of the sintered body obtained in Patent Document 1 is unknown.

This is because Fe forms oxides such as FeO, Fe ₃ O ₄ , and Fe ₂ O _{3. As a} result of studies by the present inventors, the equilibrium oxygen pressure forming each oxide has a rank depending on the temperature. Depending on the sintering temperature, the magnetite (Fe ₃ O ₄ ) used as a raw material is easily oxidized to form hematite (Fe ₂ O ₃ ), or reduced to form wustite (FeO). It has been found that a sintered body having a high purity may not be obtained.

  The present invention has been made in view of such a situation, and an object of the present invention is to provide a method capable of producing a bulk material having a high magnetite purity and a size capable of measuring mechanical properties and having a high density. It is in.

The method for producing a magnetite bulk material according to the present invention that has solved the above problems includes a step of obtaining a molded body by molding Fe ₃ O ₄ powder, and a step of sintering the obtained molded body, The molding is performed at a pressure of 98 to 294 MPa, and the sintering is performed at 1000 to 1300 ° C. in an inert gas atmosphere. The sintering is preferably performed for 10 to 120 minutes.

  After sintering, the sintered density of the magnetite bulk material obtained by further hot pressing can be further increased. The hot pressing is preferably performed at 39.2 to 78.5 MPa at 700 to 1000 ° C. in an inert gas atmosphere or a vacuum atmosphere of 0.13 Pa or less.

According to the present invention, a bulk material having high magnetite purity and high density can be produced by using Fe ₃ O ₄ powder as a raw material and sintering a molded body obtained by molding the powder under appropriate conditions. Moreover, when the obtained magnetite bulk material is further hot pressed, the density of the bulk material can be further increased.

  If the magnetite bulk material obtained by the present invention is used, the mechanical properties (eg, Young's modulus and linear expansion coefficient) of magnetite can be measured, which is useful for grasping the physical properties of the scale at a high temperature. Moreover, the magnetic bulk material obtained by this invention can also be used as various raw materials.

The inventors of the present invention have made extensive studies in order to produce a bulk material having a high magnetite purity and a high density. As a result, it has been found that a high-density bulk material with high magnetite purity can be produced by using Fe ₃ O ₄ powder as a raw material and sintering a molded body obtained by molding the powder under appropriate conditions, thereby completing the present invention.

Magnetite itself is commercially available in the form of a powder, but a single magnetite sample that is large enough to measure mechanical properties is not commercially available and is not used as various materials. Therefore, the present inventors pay attention to powder metallurgy technology, and form a molded body by molding Fe ₃ O ₄ powder, and if this molded body is sintered under appropriate conditions, the magnetite purity is high and the density is high. I have been researching the possibility of producing bulk materials. as a result,
(1) a step of obtaining a molded body by molding Fe ₃ O ₄ powder;
(2) including a step of sintering the obtained molded body,
The molding is performed at a pressure of 98 to 294 MPa (molding load of 1.0 to 3.0 tonf / cm ² ), and the sintering is performed in an inert gas atmosphere at 1000 to 1300 ° C., and the magnetite purity is high. It became clear that high-density bulk materials could be manufactured. Hereinafter, each process will be described in detail in order.

[(1) Step of obtaining a molded body]
In the present invention, it is important to use Fe ₃ O ₄ powder as a raw material. This is because a high-purity magnetite bulk material can be produced by sintering a molded body obtained by molding Fe ₃ O ₄ powder under predetermined conditions.

Fe ₃ O ₄ powder can be obtained from, for example, Wako Pure Chemical Industries. As the Fe ₃ O ₄ powder, the particle size (maximum diameter), it is preferable to use a powder of approximately 10 to 200 [mu] m. If the particle diameter is less than 10 μm, the handleability is poor, and the surface area becomes too large, so that oxidation and reduction are easily performed in the sintering process. Classification is also difficult. Preferably it is 50 micrometers or more. On the other hand, if the particle diameter exceeds 200 μm, the particle diameter is too large, so that the bulk material cannot be densified. Preferably it is 100 micrometers or less.

In the present invention, an Fe ₃ O ₄ powder is molded to obtain a molded body, and it is important that the molding pressure is 98 to 294 MPa (1.0 to 3.0 tonf / cm ² ). If the molding pressure is less than 98 MPa (1.0 tonf / cm ² ), the load becomes insufficient and a molded body cannot be formed. Accordingly, the molding pressure is 98 MPa (molding load 1.0 tonf / cm ² ) or more. However, when the molding pressure exceeds 294 MPa (3.0 tonf / cm ² ), the stress remaining in the molded body increases, and cracks are generated in the bulk material in the subsequent sintering process, and a good bulk material cannot be obtained. . Therefore, the molding pressure is 294 MPa (3.0 tonf / cm ² ) or less.

The method for molding the Fe ₃ O ₄ powder is not particularly limited, and press molding or CIP molding may be performed.

The type of mold used for molding is not particularly limited, and a mold or a rubber mold may be used. When a rubber mold is used, CIP molding may be performed. For example, when producing a cylindrical molded body, a neoprene rubber tube is cut to a desired length, and this is filled with Fe ₃ O ₄ powder as uniformly and densely as possible, and both ends of the tube are neoprene rubber. Stop with a metal stopper and seal. If this sample is subjected to CIP molding at a hydrostatic pressure of 98 to 294 MPa (1.0 to 3.0 tonf / cm ² ), a cylindrical molded body can be produced. In addition, the shape of a molded object is not specifically limited, The shape of various test pieces may be sufficient, and plate shape and block shape may be sufficient.

[(2) Sintering step]
In this invention, although the said molded object is sintered, it is important to perform this sintering at 1000-1300 degreeC by inert gas atmosphere. By making the sintering atmosphere an inert gas atmosphere, it is possible to prevent the Fe ₃ O ₄ powder from being oxidized or reduced during the sintering.

As the inert gas, pure Ar gas, pure N ₂ gas, pure He gas, or a gas obtained by mixing these gases may be used. In order to reduce the cost, it is preferable to use pure Ar gas or pure N ₂ gas.

As will be apparent from the examples described later, when the sintering atmosphere is an oxygen-containing atmosphere (for example, air), part of Fe ₃ O ₄ is oxidized to produce Fe ₂ O ₃ . Accordingly, the magnetite purity is lowered. In addition, if the sintering atmosphere is a vacuum atmosphere of 0.13 Pa (1 × 10 ⁻³ Torr) or less, the oxygen partial pressure becomes too low. Therefore, at the sintering temperature (1000 to 1300 ° C.), Fe ₃ O ₄ Part is reduced to produce FeO. Therefore, a bulk material with high magnetite purity cannot be produced.

In the present invention, the sintering temperature needs to be 1000 to 1300 ° C. If the sintering temperature is less than 1000 ° C., the sintering is insufficient, the density of the bulk material cannot be increased, and the mechanical properties cannot be measured. Accordingly, the sintering temperature is set to 1000 ° C. or higher. Preferably it is 1050 degreeC or more, More preferably, it is 1100 degreeC or more. However, when the sintering temperature exceeds 1300 ° C., part of the Fe ₃ O ₄ powder is oxidized by oxygen inevitably contained in the sintering atmosphere, and Fe ₂ O ₃ is generated. Accordingly, the sintering temperature is 1300 ° C. or lower. Preferably it is 1250 degrees C or less.

  In sintering, the rate of temperature rise until reaching the sintering temperature may be, for example, 100 to 1200 ° C./h.

  Since the sintering time is affected by the sintering temperature, it cannot be uniformly defined, and the sintering time may be determined in consideration of the sintering temperature so as to obtain a density at which mechanical properties can be measured. The sintering time may be, for example, 10 to 120 minutes. This is because if the sintering time is too short, the sintering tends to be insufficient, and if the sintering time is too long, it is economically wasteful. A more preferable lower limit of the sintering time is 15 minutes, and a more preferable upper limit is 90 minutes. In addition, what is necessary is just to cool in a sintering furnace when cooling to room temperature after sintering.

  The magnetite bulk material obtained by sintering is a high-density material having a sintered density of 90% or more in the as-sintered state, as will be apparent from Examples described later.

  In the present invention, it is preferable to perform hot pressing after sintering. By performing hot pressing, the sintered density of the magnetite bulk material obtained by sintering can be further increased.

[(3) Hot press]
The hot pressing is preferably performed in an inert gas atmosphere or a vacuum atmosphere of 0.13 Pa (1.0 × 10 ⁻³ Torr) or less. By performing hot pressing in an atmosphere from which oxygen is removed as much as possible, it is possible to prevent Fe ₃ O _{4 from} being oxidized or reduced, so that the density can be increased without degrading the purity of the magnetite bulk material. As described above, when sintering is performed in a vacuum atmosphere, since the sintering temperature is high, part of Fe ₃ O ₄ is reduced, but hot pressing is performed at a lower temperature than sintering. Even if hot pressing is performed in a vacuum atmosphere, no reduction occurs.

As the inert gas, pure Ar gas, pure N ₂ gas, pure He gas, or a gas obtained by mixing these gases may be used. In order to reduce the cost, it is preferable to use pure Ar gas or pure N ₂ gas.

The temperature and pressure when performing hot pressing are not particularly limited, but the temperature is preferably 700 to 1000 ° C., and the pressure is preferably 29.4 to 78.5 MPa (molding load 300 to 800 kgf / cm ² ).

  When the hot press temperature is 700 ° C. or higher, a high-density magnetite bulk material is easily obtained. However, when the hot press temperature exceeds 1000 ° C., cracks may occur in the magnetite bulk material itself or the mold. Therefore, the hot press temperature is preferably 1000 ° C. or lower.

What is necessary is just to set a hot press pressure according to hot press temperature so that the density of a magnetite bulk material may become high. For example, it is preferable to set it as 29.4-78.5 MPa (300-800 kgf / cm < ² >). By setting the hot press pressure to 29.4 MPa (300 kgf / cm ² ) or more, a high-density magnetite bulk material can be easily obtained. The hot press pressure is preferably 39.2 MPa or more (400 kgf / cm ² or more). However, when the hot press pressure exceeds 78.5 MPa (800 kgf / cm ² ), cracks may occur in the magnetite bulk material itself or the mold. Accordingly, the hot press pressure is preferably 78.5 MPa (800 kgf / cm ² ) or less.

In particular, when hot pressing is performed at a relatively low temperature (about 700 to 800 ° C.), the sintered density of the magnetite bulk material is reduced by pressing the pressure to about 39.2 MPa or more (about 400 kgf / cm ² or more). It can be 95% or more. On the other hand, when hot pressing is performed at a relatively high temperature (about 900 to 1000 ° C.), the magnetite bulk material is sintered by pressing the pressure to about 29.4 MPa or more (about 300 kgf / cm ² or more). The density can be 95% or more.

  The hot press time is affected by the temperature and pressure during hot pressing and cannot be defined uniformly, but may be, for example, 30 to 120 minutes. This is because if the hot pressing time is too short, the effect of improving the density is not sufficiently exhibited, and if the sintering time is too long, it is economically wasteful. A more preferable lower limit of the hot press time is 40 minutes, and a more preferable upper limit is 110 minutes.

  Hot pressing may be performed by putting a magnetite bulk material obtained by sintering into an arbitrary mold. In addition, when putting a magnetite bulk material in arbitrary metal mold | dies, what is necessary is just to machine this magnetite bulk material according to a metal mold | die shape beforehand.

  Although the material of the metal mold | die used when performing a hot press is not specifically limited, In consideration of ensuring heat resistance and not reacting with a molded object, it is preferable to use a graphite metal mold.

  If further hot pressing is performed after sintering, as will be apparent from the examples described later, the sintered density can be further increased, and for example, a high-density magnetite bulk material of 95% or more can be produced.

  If the magnetite bulk material obtained by the present invention is used, the hardness of magnetite can be measured, the Young's modulus and linear expansion coefficient can be measured, and the mechanical properties of magnetite can be examined. By examining the mechanical properties of magnetite in detail, it becomes possible to grasp the scale fracture and deformation behavior during the rolling process. Moreover, the magnetite bulk material obtained by this invention can be used as various raw materials.

  Hereinafter, the present invention will be described in more detail with reference to experimental examples, but the following experimental examples are not intended to limit the present invention, and may be implemented with appropriate modifications within a range that can meet the purpose described above and below. These are all possible and are within the scope of the present invention.

[Experiment 1]
Powdered iron trioxide reagent (manufactured by Wako Pure Chemical Industries, Ltd.) is charged into a cylindrical mold (φ10 mm × 10 mm) and a square mold (55 mm × 55 mm × 8 mm ^t ), respectively, and molded by applying pressure. did. The molding pressure is 49 MPa (0.5 tonf / cm ² ), 98 MPa (1.0 tonf / cm ² ), 196 MPa (2.0 tonf / cm ² ), 294 MPa (3.0 tonf / cm ² ), or 392 MPa (4.0 tonf). / Cm ² ).

As a result, when the pressure at the time of molding is 49 MPa (0.5 ton / cm ² ), the molded body is taken out from the mold regardless of whether it is a cylindrical mold or a square mold. Collapsed. On the other hand, when the pressure during molding is 98 MPa (1.0 tonf / cm ² ) or more, the molding taken out from the mold can be performed using either a cylindrical mold or a square mold. The body did not collapse and it was confirmed that a stable molded body was formed.

  Next, the molded body taken out from the mold was heated and sintered at 1300 ° C. for 1 hour in a pure Ar gas atmosphere to obtain a bulk material (sintered body). In the sintering, the heating rate at the time of raising the temperature to 1300 ° C. was 300 ° C./h, and the cooling after sintering at 1300 ° C. for 1 hour was carried out by cooling in a sintering furnace.

As a result of visually observing the obtained bulk material, cracks were generated in the bulk material obtained by setting the pressure during molding to 392 MPa (4.0 tonf / cm ² ). The collapse of the material was also confirmed visually. On the other hand, in the bulk material obtained at a molding pressure of 98 to 294 MPa (1.0 to 3.0 tonf / cm ² ), generation of cracks was not observed, and it was visually confirmed that a good bulk material could be produced. Confirmed.

[Experiment 2]
Powdery iron trioxide reagent (manufactured by Wako Pure Chemical Industries, Ltd.) was charged into a cylindrical mold (φ10 mm × 10 mm) and molded by applying a pressure of 147 MPa (1.5 tonf / cm ² ). As a result, it was confirmed that none of the molded bodies taken out from the mold was disintegrated and a stable molded body was formed.

The molded body taken out from the mold was sintered by heating in the atmosphere shown in Table 1 below at the temperature shown in Table 1 for the time shown in Table 1 below to obtain a bulk material (sintered body). In sintering, the rate of temperature increase when the temperature was raised to the sintering temperature shown in Table 1 below was set to 300 ° C./h, and cooling after sintering was performed by allowing to cool in a sintering furnace. In Table 1, the sintering atmosphere of “vacuum” means that sintering was performed at a gas partial pressure of 0.13 Pa (1 × 10 ⁻³ Torr) or less. The sintering atmosphere “pure Ar” means that sintering was performed in a pure Ar gas atmosphere at normal pressure. The sintering atmosphere of “pure N ₂ ” means that sintering was performed in a pure N ₂ gas atmosphere at normal pressure. The “atmosphere” as the sintering atmosphere means that the sintering was performed in an atmospheric atmosphere at normal pressure.

The obtained bulk material was measured by XRD (X-ray diffraction), and the oxide species constituting the bulk material were examined. Table 1 below shows the detected oxide species for each bulk material. In Table 1, “◯” means that the diffraction peak was detected to such an extent that the oxide species can be identified, and “−” means that no diffraction peak was detected to the extent that the oxide species could be identified. . In the bulk material used in this experiment, Fe ₂ O ₃ , Fe ₃ O ₄ , and FeO oxide species were detected, but other oxide species were not detected.

The following table 1 can be considered as follows. No. Only the diffraction peak derived from Fe ₃ O ₄ among the oxide species was detected from the bulk material 1 and a high purity magnetite bulk material was obtained, but the sintering time was somewhat short, so that the sintering was insufficient. The strength of the bulk material was slightly lowered and could not be used as a test piece for measuring mechanical properties.

No. From the bulk materials of 2 to 5, 11 to 14, only the diffraction peak derived from Fe ₃ O ₄ among the oxide species was detected, and a magnetite bulk material with high purity was obtained. In addition, No. It is thought that the magnetite purity of the bulk materials of 2 to 5, 11 to 14 is 95% or more.

No. 6 to 10 are sintered in a vacuum atmosphere of 0.13 Pa (1 × 10 ⁻³ Torr) or less, so the oxygen partial pressure becomes too low and a part of Fe ₃ O ₄ is reduced to produce FeO. Was. Therefore, a bulk material with high magnetite purity cannot be produced.

No. In addition to the diffraction peaks derived from Fe ₃ O ₄ among the oxide species, diffraction peaks derived from other oxide species were also detected from 15 to 20 bulk materials. From the peak intensity ratio, the magnetite purity was considered low. Therefore, no. Bulk materials of 15 to 20 could not be used as test pieces for measuring mechanical properties.

[Experiment 3]
Powdered iron trioxide reagent (manufactured by Wako Pure Chemical Industries, Ltd.) was charged into a disk-shaped mold (φ180 mm × 20 mm) and molded by applying a pressure of 147 MPa (1.5 tonf / cm ² ). As a result, it was confirmed that none of the molded bodies taken out from the mold was disintegrated and a stable molded body was formed.

  Next, the molded body taken out from the mold was sintered under the same conditions as in Experiment 1 to obtain a bulk material (sintered body). As a result of visual observation of the obtained bulk material, generation of cracks was not recognized, and a good bulk material could be produced.

The obtained bulk material was machined into a square block of 90 mm × 90 mm × 20 mm, and then put into a graphite mold having an inner diameter of 90 mm × 90 mm, and subjected to temperature and pressure to 0.13 Pa (1 × 10 ⁻³ Torr) Hot pressing was performed for 60 minutes in the following vacuum atmosphere.

The bulk material obtained by hot pressing was subjected to XRD (X-ray diffraction) measurement, and the oxide species constituting the bulk material were examined. As a result, only the diffraction peak derived from Fe ₃ O ₄ among the oxide species was detected from the bulk material, and it was found that a magnetite bulk material with high purity was obtained.

Moreover, the apparent density of the magnetite bulk material obtained by hot pressing was measured by the Archimedes method. On the other hand, since the value of the true density of magnetite is 5.18 g / cm ³ , the sintered density was calculated from the apparent density and the true density by the following formula. The measurement results of the sintered density of the magnetite bulk material when hot pressing is performed while changing the temperature and pressure are shown in FIG.
Sintering density = (apparent density of magnetite bulk material) ÷ (true density of magnetite)

The following can be considered from FIG. When hot pressing is performed at 700 ° C., the sintered density of the magnetite bulk material can be 95% or more by pressurizing to about 39.2 MPa (400 kgf / cm ² ) or more. On the other hand, when hot pressing is performed at 900 to 1000 ° C., the sintered density of the magnetite bulk material can be 95% or more by pressurizing to about 29.4 MPa (300 kgf / cm ² ) or more. That is, if hot pressing is performed at 700 ° C. or higher and 39.2 MPa (400 kgf / cm ² ) or higher, the sintered density can be 95% or higher. In addition, even when hot pressing is performed in a pure Ar gas atmosphere or a pure N ₂ gas atmosphere instead of a vacuum atmosphere, no phase transformation of Fe ₃ O ₄ is observed, and a high purity and high density magnetite bulk material is obtained. It was. On the other hand, when hot pressing was performed in an air atmosphere instead of a vacuum atmosphere, hematite (Fe ₂ O ₃ ) was generated on the surface of the bulk material, and the purity of the bulk material was reduced.

[Experiment 4]
In Experiment 3, the hardness (Vickers hardness) of the magnetite bulk material obtained by hot pressing was measured at room temperature or 1000 ° C. For the hardness measurement, an MQ type high temperature micro hardness tester manufactured by Nippon Optical Co., Ltd. was used, and the measurement was performed according to JIS Z 2244. The measurement results are shown in Table 2 below (No. 21).

As a comparison object, a test material obtained by cutting high-purity iron having a purity of 99.99% into a size of 10 mm × 20 mm × 3 mm was used, and the test material was heated at 1000 ° C. for 30 minutes in an oxygen atmosphere. As a result, a comparative sample whose surface was oxidized was produced. A scale having a thickness of about 600 μm was generated in the comparative sample. The sample for comparison was processed to expose the scale cross section, and the hardness (Vickers hardness) measurement was performed at room temperature or 1000 ° C. at the portion where Fe ₃ O ₄ was formed in a layered form. The measurement results are shown in Table 2 below (No. 22).

It can be considered as follows from Table 2 below. Whether measured at room temperature or 1000 ° C., the hardness of the magnetite bulk material is almost the same as the hardness of the portion where Fe ₃ O ₄ is formed in a layered manner in the scale produced in the comparative sample. It was. Therefore, from the results of hardness measurement, it can be seen that the obtained magnetite bulk material is composed of high-density and high-purity magnetite.

[Experiment 5]
In Experiment 3 above, the magnetite (Fe ₃ O ₄ ) bulk material obtained by hot pressing was machined into a square block shape having a size of 3.5 mm × 3.5 mm × 20 mm to obtain a specimen. . About the obtained specimen, the linear expansion coefficient from room temperature to 1000 degreeC was measured using the thermomechanical analysis (TMA) apparatus, and the thermal expansion coefficient was computed. The result of the calculated thermal expansion coefficient is shown in FIG. As reference data, a hematite (Fe ₂ O ₃ ) bulk material was prepared, and the coefficient of thermal expansion was calculated by measuring the linear expansion coefficient by the same method as shown in FIG. In FIG. 2, the result of the magnetite bulk material is indicated by a solid line, and the result of the hematite bulk material is indicated by a dotted line.

  As is clear from FIG. 2, it was confirmed that there was a difference in the temperature change of the linear expansion coefficient between the magnetite bulk material and the hematite bulk material, and it was confirmed that the thermal expansion coefficients of these materials were different from each other.

FIG. 1 is a graph showing the results of calculating the sintered density of the magnetite bulk material in Experiment 3. FIG. 2 is a graph showing the results of calculating the thermal expansion coefficient in Experiment 5.

Claims (4)

The method includes a step of molding a Fe ₃ O ₄ powder to obtain a molded body, and a step of sintering the obtained molded body. The molding is performed at a pressure of 98 to 294 MPa, and the sintering is performed in an inert gas atmosphere. Then, the manufacturing method of the magnetite bulk material characterized by performing at 1000-1300 degreeC.   The said sintering is a manufacturing method of Claim 1 performed in 10 to 120 minutes.   The manufacturing method according to claim 1, wherein hot pressing is further performed after sintering.   The manufacturing method according to claim 3, wherein the hot pressing is performed at 39.2 to 78.5 MPa at 700 to 1000 ° C in an inert gas atmosphere or a vacuum atmosphere of 0.13 Pa or less.

Images