JP5554509B2 - Method for producing chromite bulk material - Google Patents

Description

The present invention can be used as a measurement sample for grasping various physical properties of a chromite (FeCr ₂ O ₄ ) phase formed as a subscale when Cr-containing steel is oxidized, or can be used as various materials. The present invention relates to a method for manufacturing a bulk material.

  In the manufacturing process of steel products, an oxide film (scale) is formed on the surface of the steel material, 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 the scale material may generate scale flaws. . 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 problems caused by scale, it is necessary to grasp dynamic behavior such as scale formation behavior and 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 necessary to examine 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.], but the steel material is Cr-containing steel. As a subscale, FeCr ₂ O ₄ (chromite) is formed. It is known that the subscale formed on the surface of the Cr-containing steel is difficult to remove by pickling as compared with the normal scale formed on the normal steel, and therefore it takes time to descale. Therefore, it is considered that if the physical properties of the subscale formed on the surface of the Cr-containing steel are grasped, the descaling time can be shortened and the productivity can be improved (Non-patent Document 1).

  In order to grasp the physical properties of the scale at high temperature, it is necessary to prepare a single sample of Fe-based oxide or subscale and measure the physical properties such as hardness, Young's modulus (elastic constant), linear expansion coefficient at high temperature. Conceivable.

However, chromite formed as a subscale on the surface of Cr-containing steel is an inner layer scale that is formed as a secondary layer when the Fe-based oxide is formed as an outer layer scale. is there. When Fe is oxidized during the rolling process, it forms relatively stable Fe-based oxides such as FeO, Fe ₃ O ₄ , and Fe ₂ O _{3. When} these Fe-based oxides are formed, The equilibrium oxygen pressure varies depending on the temperature, and usually increases in the order of FeO, Fe ₃ O ₄ , and Fe ₂ O ₃ . Therefore, Fe ₂ O ₃ is formed on the surface of the steel material having a high oxygen potential (oxygen partial pressure), and a layered scale is formed in the order of Fe ₂ O ₃ , Fe ₃ O ₄ , and FeO from the surface toward the ground iron. . Among these scales, the oxygen potential (oxygen partial pressure) is further lower than the equilibrium oxygen pressure when FeO is formed in the iron region inside the FeO layer formed at the deepest position. However, when Cr is present in the iron region inside the FeO layer, Cr is oxidized and reacts with nearby FeO to form a composite compound, that is, FeCr ₂ O ₄ (chromite). This chromite layered is called a subscale.

  Thus, chromite is a scale (subscale) that is formed as a sub-scale as the inner scale when the Fe-based oxide is formed as the outer scale, and is formed at the interface between the outer scale and the ground iron. Therefore, it is very difficult to prepare a chromite single sample. On the other hand, since chromite is formed as an inner layer scale, it is considered that the physical properties of the entire scale including the outer layer scale (Fe-based oxide) are affected. In order to grasp the characteristics and mechanical properties), it is considered to be extremely important to grasp the physical properties (for example, physical properties and mechanical properties) of chromite.

Mikako Takeda et al., “Effects of Cr and Heating Conditions on Scale Microstructure and Adhesion”, Kobe Steel Technical Report, 2006, 12, p. 22-25

  The present invention has been made paying attention to the above-mentioned circumstances, and its purpose is to establish a technique capable of producing a single chromite sample having a size capable of measuring mechanical properties and a high density. . Another object of the present invention is to establish a method capable of producing a simple sample with high chromite purity.

  The method for producing a chromite bulk material according to the present invention that has solved the above problems includes a step of molding a mixed powder of paraffin and chromite powder passing through a 150-mesh sieve, and an obtained molded body. Including a step of sintering, the content of the paraffin is 1 to 5% by mass with respect to the whole mixed powder, the molding is performed at a pressure of 196 to 392 MPa, and the sintering is performed at 1100 to 1500 ° C. Has a gist. The sintering is preferably performed in an inert gas atmosphere.

According to the present invention, when producing a chromite bulk material (single sample) by sintering a compacted body of chromite (FeCr ₂ O ₄ ) powder, paraffin is mixed into the chromite powder and pressure conditions at the time of molding. Since the temperature conditions during sintering are appropriately controlled, a chromite bulk material having a size capable of measuring mechanical properties and a high density can be produced. Moreover, if the atmosphere at the time of sintering a molded object is further controlled, the chromite purity of the resulting bulk material can be further enhanced.

  By using the chromite bulk material obtained in the present invention, the mechanical properties of the chromite phase (for example, hardness, Young's modulus, linear expansion coefficient, etc.) can be measured, so that the physical properties of the subscale in a high temperature state can be grasped. To help. Moreover, the chromite bulk material obtained by this invention can also be used as various raw materials.

FIG. FIG. 3 is an XRD chart of the bulk material shown in FIG. FIG. 15 is an XRD chart of the bulk material shown in FIG. FIG. 3 is a graph showing the results of measuring the hardness of each bulk material.

  The inventors of the present invention have made extensive studies in order to establish a method capable of producing a chromite simple substance sample that is large enough to measure mechanical properties and has a high density. As a result, it was found that a mixed powder of paraffin and chromite powder can be used as a raw material, molded under an appropriate pressure condition, and then sintered under an appropriate condition, thereby completing the present invention.

That is, if Cr-containing steel is heated, a scale containing chromite can be formed on the surface, but chromite as a bulk material cannot be produced only by following this method. , Young's modulus and linear expansion coefficient of chromite cannot be measured. Chromite (FeCr ₂ O ₄ ) is a composite oxide formed by the reaction of FeO and Cr ₂ O _3, but even if the Cr-containing steel is heated to form FeCr ₂ O ₄ , it remains at room temperature. During cooling, FeCr ₂ O ₄ may separate into two phases of FeO and Cr ₂ O ₃ . For example, after forming a FeCr ₂ O _4, even if an attempt is prepared frozen metastable phase of FeCr ₂ O ₄ by increasing the cooling rate to room temperature, a portion in the middle cooling can cause two-phase separation is there. Moreover, although chromite itself is marketed in the form of a powder, a chromite simple substance sample having a size capable of measuring mechanical properties is not commercially available and is not used as various materials.

Accordingly, the present inventors have focused on the powder metallurgy technique and studied a method for producing a single sample of chromite. as a result,
(1) a step of molding a mixed powder of paraffin and chromite powder passing through a 150 mesh sieve;
(2) including a step of sintering the obtained molded body,
The paraffin content is adjusted to a range of 1 to 5% by mass with respect to the entire mixed powder,
The molding is performed at a pressure of 196 to 392 MPa,
It has been clarified that if the sintering is performed at 1100 to 1500 ° C., a chromite bulk material (single sample) having a size capable of measuring mechanical properties and a high density can be produced. Hereinafter, each process will be described in detail in order.

[(1) Molding process]
In the present invention, it is important to use a mixed powder of paraffin and chromite powder as a raw material. That is, when the present inventors examined, even if it tried to sinter the molded object obtained by shape | molding using only a chromite powder, the bulk material was not able to be formed. On the other hand, a molded body obtained by molding using a mixed powder obtained by mixing paraffin into chromite powder could be sintered and a bulk material could be formed. It is thought that paraffin acted as a binder that binds the chromite powder. Since the paraffin volatilizes during sintering and does not remain in the bulk material, the purity of chromite is not reduced.

  The chromite powder can be obtained from, for example, Wako Pure Chemical Industries. In addition, since commercially available chromite is in the form of powder, mechanical properties such as Young's modulus and linear expansion coefficient cannot be measured.

  In the present invention, a powder that passes through a 150 mesh sieve is used as the chromite powder. When powder that does not pass through a 150-mesh sieve (that is, powder that remains on the sieve) is used, the powder itself is large, so that the gap between the powders becomes large when molded, and the density of the molded body decreases. Therefore, a high-density bulk material cannot be manufactured. Therefore, in this invention, the powder which passes a 150 mesh sieve is used as a chromite powder.

  The chromite powder passing through the 150 mesh sieve is obtained by classifying commercially available chromite powder using a 150 mesh sieve and collecting the powder passing through the sieve. Moreover, you may grind | pulverize using a mortar, a ball mill, a jet mill, an auto mill etc. as needed before classification.

  The paraffin needs to be contained in an amount of 1 to 5 mass% with respect to the entire mixed powder. If the paraffin content is too small, the binder effect is not exhibited, and a bulk material cannot be formed. On the other hand, when the content of paraffin is too large, paraffin cannot be completely removed from the bulk material during sintering, pores are formed in the bulk material, the density of the bulk material becomes small, and the mechanical properties cannot be measured.

  In the present invention, paraffin refers to alkanes (chain saturated hydrocarbons) distributed between about 16 to 40 carbon atoms.

  The chromite powder passing through the 150 mesh sieve and the paraffin may be mixed uniformly using, for example, a mortar.

In the present invention, a mixed powder of paraffin and chromite powder passing through a 150 mesh sieve is molded to obtain a molded body. The molding pressure is 196 to 392 MPa (2.0 to 4.0 tonf / cm ² ). To do. When the molding pressure is less than 196 MPa (2.0 tonf / cm ² ), the pressure becomes insufficient and a molded body cannot be formed. Accordingly, the molding pressure is 196 MPa (2.0 tonf / cm ² ) or more. However, if the molding pressure exceeds 392 MPa (4.0 tonf / cm ² ), the stress remaining in the molded body increases, and cracks occur in the bulk material in the subsequent sintering step, and the bulk material cannot be obtained. Accordingly, the molding pressure is set to 392 MPa (4.0 tonf / cm ² ) or less.

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 chromite powder as uniformly and densely as possible, and both ends of the tube are made of neoprene rubber. Stop with a stopper and seal. If this sample is CIP-molded at a hydrostatic pressure of 196 to 392 MPa (2.0 to 4.0 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]
The molded body is sintered at 1100 to 1500 ° C. If the sintering temperature is less than 1100 ° C., the sintering is insufficient, the density of the bulk material cannot be increased, and the mechanical properties cannot be measured. Therefore, sintering is performed at 1100 ° C. or higher, preferably 1200 ° C. or higher. However, when the sintering temperature exceeds 1500 ° C., chromite is melted and a bulk material cannot be formed. Therefore, sintering is performed at 1500 ° C. or lower, preferably 1400 ° C. or lower.

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

  Since the sintering time is affected by the sintering temperature, it cannot be uniformly defined, and the sintering may be performed while taking into consideration the sintering temperature so that the density can be measured. The sintering time may be, for example, 10 to 120 minutes. 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 sintering atmosphere is not particularly limited, and may be any of, for example, an inert gas atmosphere, an oxygen-containing atmosphere (for example, an air atmosphere), a vacuum atmosphere, or the like.

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

The vacuum atmosphere may be set to a pressure of 0.13 Pa (1 × 10 ⁻³ Torr) or less, for example.

However, in an oxygen-containing atmosphere, a portion of chromite is oxidized to form Cr ₂ O ₃ or Fe ₂ O _3, so that the chromite purity tends to decrease. Further, in a vacuum atmosphere, oxygen in the atmosphere is reduced, so that part of chromite is reduced, Fe is generated, and chromite purity tends to decrease. Therefore, in the present invention, it is recommended that the sintering atmosphere be an inert gas atmosphere. By sintering in an inert gas atmosphere, the purity of the chromite bulk material can be increased as compared with sintering in an oxygen-containing atmosphere or a vacuum atmosphere.

The chromite bulk material obtained by sintering has a high density of 2 g / cm ³ or more in the as-sintered state.

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

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited by the following examples, but may be appropriately modified within a range that can meet the purpose described above and below. Of course, it is possible to implement them, and they are all included in the technical scope of the present invention.

  The following experiment 1 examined the molding pressure, the following experiment 2 examined the blending amount of paraffin, the following experiment 3 examined the sintering conditions, and the following experiment 4 examined the mechanical properties (hardness) of the bulk material.

[Experiment 1]
Commercially available FeCr ₂ O ₄ powder (manufactured by Wako Pure Chemical Industries) was pulverized in a mortar and classified using a 150 mesh sieve. Paraffin (manufactured by Wako Pure Chemical Industries, Ltd.) was blended with the FeCr ₂ O ₄ powder that passed through the sieve as a binder to obtain a mixed powder. The blending amount of paraffin was 2.0% by mass with respect to the mass of the entire mixed powder. The mixed powder was charged into a cylindrical mold and pressure was applied to produce a molded body of φ30 mm × 120 mm. The molding pressure is 147 MPa (1.5 tonf / cm ² ), 196 MPa (2.0 tonf / cm ² ), 294 MPa (3.0 tonf / cm ² ), 392 MPa (4.0 tonf / cm ² ), or 441 MPa (4.5 tonf) / Cm ² ). As a result, when the molding pressure was 147 MPa, the molded body collapsed when removed from the mold. On the other hand, when the molding pressure was 196 MPa or more, the molded body taken out from the mold did not collapse and a stable molded body could be formed.

  Next, the molded body taken out from the mold was sintered in an Ar atmosphere at 1300 ° C. for 1 hour to obtain a bulk material. In the sintering, the heating rate at the time of raising the temperature to 1300 ° C. was 600 ° C./hour, and the cooling after sintering at 1300 ° C. for 1 hour was carried out by cooling in a sintering furnace. As a result of visual observation of the obtained bulk material, cracks were generated in the bulk material obtained at a molding pressure of 441 MPa, and part of the collapse of the bulk material was also confirmed. On the other hand, in the bulk material obtained with a molding pressure of 196 to 392 MPa, generation of cracks was not observed, and it was visually confirmed that a good bulk material could be produced.

The apparent density of the obtained bulk material was measured by the Archimedes method. As a result, the density of the bulk material obtained by sintering the molded body obtained by molding at 196 MPa is 2.56 g / cm ³ , and obtained by sintering the molded body obtained by molding at 294 MPa. The bulk material has a density of 3.47 g / cm ³ , 392 MPa, and the bulk material obtained by sintering a molded body obtained by molding at 392 MPa has a density of 3.92 g / cm ³ , 441 MPa. The density of the bulk material obtained by sintering the molded body was 4.08 g / cm ³ .

[Experiment 2]
In Experiment 1 above, mixed powders with different binder blending amounts were prepared to produce molded bodies. The amount of paraffin used as the binder is 0.5% by mass, 1.0% by mass, 2.0% by mass, 3.0% by mass, 4.0% by mass, and 5.% by mass with respect to the total mass of the mixed powder. It was set to 0% by mass or 5.5% by mass. The mixed powder was charged into a cylindrical mold and molded at a molding pressure of 294 MPa (3.0 tonf / cm ² ) to produce a molded body of φ30 mm × 120 mm.

Next, the molded body was taken out from the mold and sintered under the same conditions as in Experiment 1 above. As a result, when the blending amount of the binder was 0.5% by mass, a bulk material could not be obtained due to insufficient binder. On the other hand, when the blending amount of the binder was 5.5% by mass, the binder could not be removed during sintering, pores were formed in the bulk material, and the density of the bulk material was lowered. The density of this bulk material was 0.36 g / cm ³ . On the other hand, when the blending amount of the binder is 1.0 to 5.0% by mass, a bulk material having a density of 3.11 to 4.2 g / cm ³ was obtained.

[Experiment 3]
In Experiment 1, a molded body having a diameter of 30 mm × 120 mm was manufactured by molding at a molding pressure of 294 MPa (3.0 tonf / cm ² ).

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

The obtained bulk material was measured by XRD (X-ray diffraction), and the phase of the bulk material was identified. The identification results are shown in Table 1 below for each bulk material. In Table 1, “◯” means that the diffraction peak was detected to such an extent that it could be identified, and “−” means that the diffraction peak was not detected to the extent that it could be identified. In the bulk material used in this experiment, FeCr ₂ O ₄ , Cr ₂ O ₃ and Fe were detected, but no other phases were detected.

No. shown in Table 1. The XRD chart of the bulk material No. 2 is shown in FIG. An XRD chart of 14 bulk materials is shown in FIG. As is apparent from FIG. In the bulk material No. 2, only the diffraction peak derived from FeCr ₂ O ₄ was confirmed. On the other hand, as is apparent from FIG. In the 14 bulk material, in addition to the diffraction peak derived from FeCr ₂ O ₄ , a diffraction peak derived from Fe was also observed.

The following table 1 can be considered as follows. No. Nos. 2 to 5 and 8 to 11 are examples sintered in an inert atmosphere. From the obtained bulk material, only a diffraction peak derived from FeCr ₂ O ₄ was detected, and high purity chromite (FeCr ₂ O ₄ ) Bulk material was obtained.

No. In 12 and 13, a chromite bulk material is obtained. However, since sintering was performed in an air atmosphere, a diffraction peak derived from Cr ₂ O ₃ was detected in addition to the diffraction peak derived from FeCr ₂ O ₄ from these bulk materials. From the peak intensity ratio, the purity of chromite (FeCr ₂ O ₄ ) It was found to be lower than the purity of bulk materials of 2-5 and 8-11.

No. In 14 and 15, a chromite bulk material is obtained. However, since sintering was performed in a vacuum atmosphere, a diffraction peak derived from Fe was also detected from these bulk materials in addition to the diffraction peak derived from FeCr ₂ O ₄ . From the peak intensity ratio, the purity of chromite (FeCr ₂ O ₄ ) It was found to be lower than the purity of bulk materials of 2-5 and 8-11.

On the other hand, no. Only the diffraction peak derived from FeCr ₂ O ₄ was detected from the bulk material 1, and a chromite (FeCr ₂ O ₄ ) bulk material was obtained. However, since the sintering temperature was too low, the sintering was insufficient, and the density of the bulk material was 0.42 g / cm ³ , the strength was low, and it could not be used as a test piece for measuring mechanical properties.

No. Only the diffraction peaks derived from FeCr ₂ O ₄ were detected from the bulk materials 6 and 7, but a chromite (FeCr ₂ O ₄ ) bulk material was obtained. However, no. The bulk material No. 6 was deformed as a result of partial melting because the temperature during sintering was too high, and could not be used as a test piece for measuring mechanical properties. No. The bulk material No. 7 has a sintering temperature of No. 7. Since it was higher than 6, the bulk material was completely melted and could not be used as a test piece for measuring mechanical properties.

[Experiment 4]
In Experiment 3, a molded body of φ30 mm × 120 mm was manufactured by molding at a molding pressure of 294 MPa (3.0 tonf / cm ² ).

  Next, the molded body was taken out of the mold and sintered by heating at 1300 ° C. for 1 hour in an Ar atmosphere to obtain a bulk material. In the sintering, the heating rate at the time of raising the temperature to 1300 ° C. was 10 ° C./min, and the cooling after sintering at 1300 ° C. for 1 hour was carried out by cooling in a sintering furnace. As a result of visual observation of the obtained bulk material, generation of cracks was not recognized.

The obtained bulk material was subjected to XRD (X-ray diffraction) measurement under the same conditions as in Experiment 3, and the phase of the bulk material was identified. As a result, only the diffraction peak derived from FeCr ₂ O ₄ was detected from the bulk material, and it was found that a chromite (FeCr ₂ O ₄ ) bulk material with high purity was obtained.

  Next, the hardness (Vickers hardness) of the obtained bulk material was measured at room temperature (25 ° C.), 400 ° C., 600 ° C., 800 ° C., or 1000 ° C. The hardness was measured according to JIS Z 2244 using an MQ type high-temperature microhardness meter made by Nippon Optical. The measurement results are shown by ■ in FIG.

As comparison objects, FeO bulk material, Fe ₃ O ₄ bulk material, Fe ₂ O ₃ bulk material, and Fe ₂ SiO ₄ bulk material were produced under the following conditions, and the hardness of each bulk material was measured in the same manner as described above. The measurement results are shown in FIG. 3 by Δ for FeO, □ for Fe ₃ O ₄ , ◇ for Fe ₂ O ₃ , and ● for Fe ₂ SiO ₄ .

<< FeO bulk material >>
Commercially available pure Fe powder (“Atmel 300NH (trade name)” manufactured by Kobe Steel) and Fe ₃ O ₄ powder (“Wako Pure Chemical Industries, Ltd.“ tradenamed iron trioxide reagent (trade name) ”, purity 95% or more) Were mixed so that the mass ratio of Fe powder: Fe ₃ O ₄ powder was 0.8: 1, mixed for 3 hours, put into a square mold and molded by applying pressure, 55 mm × 55 mm × An 8 mm ^t molded body was produced. The molding pressure was 147 MPa (1.5 ton / cm ² ), and CIP molding was performed.

The obtained molded body was pre-sintered by holding at 1100 ° C. for 1 hour in an Ar atmosphere. The pre-sintered body is placed in a graphite mold and pressed at a pressure of 50 MPa, and held in a vacuum atmosphere (on the order of 1 × 10 ⁻⁴ Torr) at 900 ° C. for 1 hour to perform press molding. Was made. As a result of XRD (X-ray diffraction) measurement of the obtained bulk material and performing phase identification of the bulk material, no diffraction peaks other than FeO were detected.

<Fe ₃ O ₄ bulk material>
Put commercially available Fe ₃ O ₄ powder (“Wood Iron Oxide Reagent (trade name)” manufactured by Wako Pure Chemical Industries, Ltd., purity 95% or more) into a square mold and mold it by applying pressure, 55 mm × 55 mm A molded body of × 8 mm ^t was produced. The molding pressure was 294 MPa (3.0 tonf / cm ² ), and CIP molding was performed.

The obtained molded body was sintered at 1100 ° C. for 1 hour in an Ar atmosphere to produce a bulk material. As a result of XRD (X-ray diffraction) measurement of the obtained bulk material and phase identification of the bulk material, diffraction peaks other than Fe ₃ O ₄ were not detected.

"Fe ₂ O ₃ bulk material"
A commercially available Fe ₂ O ₃ powder (manufactured by Wako Pure Chemical Industries, Ltd.) was put into a square mold and molded by applying pressure to produce a molded body of 55 mm × 55 mm × 8 mm ^t . The molding pressure was 294 MPa (3.0 tonf / cm ² ), and CIP molding was performed.

The obtained molded body was sintered in the air at 1100 ° C. for 1 hour to produce a bulk material. As a result of measuring the XRD (X-ray diffraction) of the obtained bulk material and identifying the phase of the bulk material, no diffraction peaks other than Fe ₂ O ₃ were detected.

<< Fe ₂ SiO ₄ bulk material >>
Iron olivine (“FAYALITE (trade name)” manufactured by Wako Pure Chemical Industries, Ltd.), a massive natural mineral that is commercially available, is pulverized in a mortar, classified using a 150 mesh sieve, and passed through the sieve. A powder was obtained. The obtained iron olivine powder was put into a square mold and molded by applying pressure to produce a molded body of 55 mm × 55 mm × 8 mm ^t . The molding pressure was 147 MPa (1.5 ton / cm ² ), and CIP molding was performed.

The obtained molded body was sintered in a vacuum atmosphere (1 × 10 ⁻⁵ Torr or less) at 1130 ° C. for 1 hour to produce a bulk material. As a result of XRD (X-ray diffraction) measurement of the obtained bulk material and performing phase identification of the bulk material, no diffraction peaks other than Fe ₂ SiO ₄ were detected.

  As is clear from FIG. 3, it can be seen that there is a difference in hardness depending on the type of the bulk material. Therefore, although the scale is composed of various oxides, it can be seen that the hardness (mechanical characteristics) varies depending on the type of oxide.

Claims (2)

Including a step of molding a mixed powder of paraffin and a chromite powder passing through a 150-mesh sieve, and a step of sintering the obtained molded body,
The content of the paraffin is 1 to 5% by mass with respect to the entire mixed powder,
The molding is performed at a pressure of 196 to 392 MPa,
Said sintering is performed at 1100-1500 degreeC, The manufacturing method of the chromite bulk material characterized by the above-mentioned.   The manufacturing method according to claim 1, wherein the sintering is performed in an inert gas atmosphere.

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