TECHNICAL FIELD
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The present invention relates to a high purity manganese (Mn) manufactured from a commercially available electrolytic manganese (Mn) and a manufacturing method thereof.
BACKGROUND ART
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A method for manufacturing a commercially available metal Mn is an electrolytic process in an ammonium sulfate electrolytic bath. In a commercially available electrolytic Mn obtained by this method, contained are about 100 to 3000 ppm of sulfur (S) and several hundred ppm of carbon (C). Several hundred ppm of chlorine (Cl) is also contained, and about several thousand ppm of oxygen (O) is further contained as it is an electrodeposit out of an aqueous solution.
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As a method for removing S, O from the above electrolytic Mn, the sublimation purification method is well known among conventional technologies. However, the sublimation purification method has disadvantages such as very expensive instrumentation and very poor yield. Further, even though the sublimation purification method can reduce S and O, a metal Mn obtained from the purification method will be subject to contamination due to the material of a heater, the material of a condenser and the like in a sublimation purification apparatus. For this reason, disadvantageously, it is not suitable as a raw material for electronic devices.
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As a prior art, the following Patent Document 1 describes a method for removing S in metal Mn in which, at a melting temperature of a Mn oxide compound such as MnO, Mn3O4 and MnO2 and/or metal Mn, a material to be converted into such a Mn oxide, for example Mn carbonate, is added, and metal Mn to which a Mn compound has been added is melted under an inert atmosphere, and maintained in a molten state preferably for 30 to 60 minutes to give a S content of 0.002%.
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However, Document 1 does not contain any description about the contents of oxygen (O), nitrogen (N), carbon (C) and chlorine (Cl), and does not provide a solution for a problem that is caused when these materials are contained.
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The following Patent Document 2 describes a method for electrowinning metal Mn, and a method for electrowinning metal Mn characterized in that used is an electrolytic solution prepared by dissolving an excess amount of a high purity metal Mn in hydrochloric acid, filtering out undissolved materials to obtain a solution, neutralizing the solution by the addition of an oxidizing agent, filtering out the resulting precipitates, and then adding a buffering agent. It also describes a more preferable method for electrowinning metal Mn with the use of an electrolytic solution prepared by further adding metal Mn to a hydrochloric acid solution of a metal Mn, filtering out undissolved materials to obtain a solution, adding hydrogen peroxide and aqueous ammonia to the solution, filtering out precipitates formed under weakly acidic or neutral pH, and then adding a buffering agent.
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Although Document 2 describes that S content in a high purity Mn is reduced to 1 ppm, it does not have any description about the contents of oxygen (O), nitrogen (N), carbon (C) and chlorine (Cl), and does not provide a solution for a problem that is caused when these materials are contained.
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The following Patent Document 3 describes a method for manufacturing a high purity Mn, and a method in which an ion-exchange purification method using a chelating resin is applied to an aqueous Mn chloride, and then the resulting purified aqueous Mn chloride is highly purified by the electrowinning method. It is described that, in a dry process, a high purity Mn can be obtained from solid phase Mn by the vacuum sublimation purification method (Mn vapor obtained by sublimation of solid phase Mn is selectively condensed and deposited as a purified material at a cooling unit due to the difference in vapor pressures).
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Further, Document 3 describes that the total concentration of sulfur (S), oxygen (O), nitrogen (N) and carbon (C) is 10 ppm or less.
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However, Document 3 does not contain any description about the content of chlorine (Cl) which has a deleterious effect on the manufacture of semiconductor components. Mn chloride is used as a raw material, and therefore, disadvantageously, chlorine may be contained at a high concentration.
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The following Patent Document 4 describes a method for manufacturing a low-oxygen Mn material in which a Mn material with oxygen reduced to 100 ppm or less can be obtained by performing induction skull melting to a Mn raw material under an inert gas atmosphere, and the Mn raw material is preferably subjected to an acid wash before induction skull melting in view of further reducing oxygen. Although Document 4 has a description about the reduction of oxygen (O), sulfur (S) and nitrogen (N) in a high purity Mn, it does not have any description about the content of the other impurities, and does not provide a solution for a problem caused when these materials are contained.
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The following Patent Document 5 describes a Mn alloy material for magnetic materials, a Mn alloy sputtering target, and a magnetic thin film. Also described is that the oxygen content is 500 ppm or less, the S content is 100 ppm or less, and further, the total content of impurities (elements other than Mn and alloy components) is preferably 1000 ppm or less.
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Further, the Document describes a method for removing oxygen (O) and sulfur (S) by adding, as deoxidizing/desulfurizing agents, Ca, Mg, La and the like to a commercially available electrolytic Mn and then performing high frequency melting. It also describes that vacuum distillation is performed after preliminary melting in order to achieve higher purification of Mn.
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With regard to the above Mn raw material, it is described that, in Example 3, a deoxidizing/desulfurizing agent is added, and then high frequency melting is performed to give an oxygen content of 50 ppm and a sulfur content of 10 ppm (Table 3 of Patent Document 5). In Example 7, vacuum distillation is performed after preliminary melting to give an oxygen content of 30 ppm and a sulfur content of 10 ppm (Table 7 of Patent Document 5). Moreover, in these Examples, about 10 to 20 ppm of Si and about 10 to 30 ppm of Pb are contained.
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However, the purity of Mn manufactured according to the following Patent Document 5 is at a 3N level, and a high purity Mn, such as that obtained from the present invention, could not be achieved. Further, in Example 3 of the following Patent Document 5, high frequency melting is performed after adding a deoxidizing/desulfurizing agent. Therefore, disadvantageously, a deoxidizing/desulfurizing agent may contaminate Mn to reduce the purity. In the case of Example 7, vacuum distillation is performed after preliminary melting. Therefore, disadvantageously, a manufacturing cost is high because 99% or more of the molten Mn is volatilized.
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The following Patent Document 6 describes a method for manufacturing a high purity Mn material, and a high purity Mn material for forming a thin film. In this case, it is described that after crude Mn is subjected to preliminary melting at 1250 to 1500° C., vacuum distillation is performed at 1100 to 1500° C. to obtain a high purity Mn material. The degree of vacuum when performing vacuum distillation is preferably 5×10−5 to 10 Torr.
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In a high purity Mn obtained as described above, the total impurity content is 100 ppm or less, oxygen (O): 200 ppm or less, nitrogen (N): 50 ppm or less, sulfur (S): 50 ppm or less, and carbon (C): 100 ppm or less. This is followed by examples in which the oxygen content is 30 ppm, and other elements are contained less than 10 ppm in Example 2 (Table 2). However, even in this case, the impurity level has not reached the intended level.
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In addition, the following Patent Document 7 describes a sputtering target comprising a high purity Mn alloy. Patent Document 8 describes a method for recovering Mn using sulfuric acid. Patent Document 9 describes a method for manufacturing metal Mn in which Mn oxide is subjected to heat reduction. However, none of the above describes desulfurization in particular.
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In view of the above, the present inventors have proposed a method for manufacturing a high purity Mn, comprising leaching a Mn raw material in acid, filtering out residues and using the filtrate for the cathode side in electrolysis; the above method for manufacturing a high purity Mn, further comprising degassing the above electrolytic Mn to reduce the CI content in the above electrolytic Mn to 100 ppm or less; and the method for manufacturing a high purity Mn, further comprising degassing the above electrolytic Mn material, and performing melting under an inert atmosphere to manufacture Mn where Cl≦5. 10 ppm, C≦5 50 ppm, S<50 ppm, and O<30 ppm (see Patent Document 10).
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This method is effective for producing a high purity Mn. An object of the present invention is to provide a manufacturing method capable of achieving a higher purity and reducing cost. Another object is to provide a high purity Mn.
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Patent Document 1: Japanese Patent Application Laid-Open No. S53-8309
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Patent Document 2: Japanese Patent Application Laid-Open No. 2007-119854
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Patent Document 3: Japanese Patent Application Laid-Open No. 2002-285373
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Patent Document 4: Japanese Patent Application Laid-Open No. 2002-167630
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Patent Document 5: Japanese Patent Application Laid-Open No. H11-100631
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Patent Document 6: Japanese Patent Application Laid-Open No. H11-152528
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Patent Document 7: Japanese Patent Application Laid-Open No. 2011-068992
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Patent Document 8: Japanese Patent Application Laid-Open No. 2010-209384
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Patent Document 9: Japanese Patent Application Laid-Open No. 2011-094207
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Patent Document 10: Japanese Patent Application Laid-Open No. 2013-142184
SUMMARY OF INVENTION
Technical Problem
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An object of the present invention is to provide a high purity Mn manufactured from a commercially available electrolytic Mn and a manufacturing method thereof. In particular, the present invention aims to provide a high purity Mn that has a significantly lower impurity content and is manufactured at a lower cost as compared with the conventional technology.
Solution to Problem
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The present invention can achieve the foregoing object by providing the following invention.
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1) A method for manufacturing a high purity Mn, the method comprising: placing a Mn raw material in a magnesia crucible to perform melting with the use of a vacuum induction melting furnace (VIM furnace) at a melting temperature of 1240 to 1400° C. under an inert atmosphere of 500 Torr or less; then adding calcium (Ca) in a range between 0.5 and 2.0% of the weight of Mn to perform deoxidation and desulfurization; casting the resultant in an iron mold after the completion of the deoxidation and desulfurization to manufacture an ingot; then placing the Mn ingot in a skull melting furnace; reducing pressure to 10−5 Torr or less with a vacuum pump; starting heating and keeping the Mn in a molten state for 10 to 60 minutes; and then ending the melting reaction for obtaining a high purity Mn.
2) A high purity Mn refined via vacuum induction melting (VIM) and skull melting, wherein a total amount of B, Mg, Al, Si, S, Ca, Cr, Fe, and Ni as impurity elements is 50 ppm or less, and the purity excluding gas components is 4N5 (99.995%) or higher.
3) A high purity Mn refined via vacuum induction melting (VIM) and skull melting, wherein a total amount of B, Mg, Al, Si, S, Ca, Cr, Fe, and Ni as impurity elements is 50 ppm or less, the purity excluding gas components is 4N5 (99.995%) or higher, and contents of oxygen (O) and nitrogen (N) as gas components are each less than 10 ppm.
4) A high purity Mn, wherein a total amount of B, Mg, Al, Si, S, Ca, Cr, Fe, and Ni as impurity elements is 50 ppm or less, and the purity excluding gas components is 4N5 (99.995%) or higher.
5) A high purity Mn, wherein a total amount of B, Mg, Al, Si, S, Ca, Cr, Fe, and Ni as impurity elements is 50 ppm or less, the purity excluding gas components is 4N5 (99.995%) or higher, and contents of oxygen (O) and nitrogen (N) as gas components are each less than 10 ppm.
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Note that each instance of the unit “ppm” used herein means “wtppm”. Except for nitrogen (N) and oxygen (O) which are gas component elements, analytical values for the concentration of each element were analyzed with the GDMS (Glow Discharge Mass Spectrometry) method. Moreover, gas component elements were analyzed using an oxygen/nitrogen analyzer from LECO Corporation. The term “gas component elements” as used herein refers to hydrogen (H), oxygen (O), nitrogen (N), and carbon (C). The same applies hereinafter.
Advantageous Effects of Invention
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According to the present invention, it is possible to achieve the following effects.
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(1) A high purity Mn, in which the total amount of impurity elements B, Mg, Al, Si, S, Ca, Cr, Fe and Ni is 50 ppm or less, and which has a purity of 4N5 (99.995%) or higher, and can be obtained. Further a high purity Mn, in which the contents of 0 and N as gas components are each less than 10 ppm, can be obtained.
(2) Without the need for special equipment, a common furnace can be used for manufacturing a high purity Mn at a lower cost and higher yield as compared with the conventional distillation method.
(3) Moreover, when the high purity Mn of the present invention is used to produce a sputtering target, it is possible to obtain a target with lower generation of particles.
BRIEF DESCRIPTION OF DRAWINGS
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FIG. 1 This shows a schematic diagram of a sequence of process steps from a step of subjecting the Mn raw material to VIM (vacuum induction melting) and then skull melting through to the manufacture of highly refined Mn.
DESCRIPTION OF EMBODIMENTS
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Embodiments of the present invention are now explained in detail.
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Commercially available (a 2N level) flaky electrolytic Mn can be used as a raw material in the method for manufacturing a high purity Mn according to the present invention. However, there is no particular limitation for the type of the raw material since the method is not affected by the purity of the raw material.
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When manufacturing a high purity Mn, first, a Mn raw material is placed in a magnesia crucible, and subjected to melting with the use of a vacuum induction melting furnace (VIM furnace) at a melting temperature of 1240 to 1400° C. under an inert atmosphere of 500 Torr or less. If the temperature is lower than 1240° C., Mn does not melt and the VIM treatment cannot be performed.
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If the temperature is higher than 1400° C., suspended solids of oxides and/or sulfides in the molten Mn are re-melted into the molten Mn due to the high temperature. Therefore, the concentrations of magnesium (Mg), calcium (Ca), oxygen (O) and sulfur (S) after the VIM step will be in an order of hundreds of ppm to thousands of ppm, and the intended purity in the present invention ultimately cannot be achieved. Results are shown in Table 2.
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Then, Ca in a range of 0.5 to 2.0% of the weight of Mn was gradually added to this molten Mn to perform deoxidation and desulfurization. After the completion of deoxidation and desulfurization, the resultant is cast in an iron mold to manufacture an ingot. After cooling the ingot, slags adhered to the ingot are removed.
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The obtained Mn ingot is subsequently loaded in a skull melting furnace, the pressure is reduced to 10−5 Torr or less with a vacuum pump to start heating, the Mn is kept in a molten state for 10 to 60 minutes, and then the melting reaction is ended to obtain high purity Mn.
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In the case of Mn obtained by this manufacturing method, obtained is a high purity Mn having a purity of 4N5 (99.995%) or higher except for gas components in which the total amount of B, Mg, Al, Si, S, Ca, Cr, Fe and Ni as impurity elements is 50 ppm or less.
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In addition, it is possible to obtain high purity Mn in which the total amount of B, Mg, Al, Si, S, Ca, Cr, Fe, and Ni as impurity elements is 50 ppm or less, and contents of O and N as gas components are each less than 10 ppm.
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In particular, since the existence of O or N in electronic devices using manganese (Mn) will result in the formation of oxides or nitrides, the properties of Mn itself will deteriorate. Furthermore, the formation of oxides or nitrides may have an influence (deterioration of properties) on a material in complex with or alloyed with Mn, and/or an influence (deterioration of properties) on a material adjacent to the Mn-containing material by the diffusion of O or N therein. Therefore, the existence of Mn capable of reducing the contents of O and N is extremely effective.
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The outline of these process steps is shown in FIG. 1.
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A common skull melting device may be used during the skull melting process step. Generally speaking, skull melting is characterized in that contamination from the furnace does not occur since a skull furnace is cooled and the raw material loaded in the furnace is melted via induction heating.
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For refining Mn, it could be said that the concept of eliminating S and O by VIM treatment using calcium (Ca), subsequently using a skull furnace to eliminate Mg and Ca that increased excessively, and ultimately attaining the high purification of Mn did not exist in conventional technologies.
EXAMPLE
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The present invention is now explained with reference to the following Example. However, this Example is described for facilitating the understanding of the invention, and the present invention shall not be limited to this Example or Comparative Example.
Example 1
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Commercially available flaky electrolytic Mn (purity 2N: 99%) was used as a starting raw material. The impurities of the raw material Mn were as follows; specifically, B: 15 ppm, Mg: 90 ppm, Al: 4.5 ppm, Si: 39 ppm, S: 280 ppm, Ca: 5.9 ppm, Cr: 2.9 ppm, Fe: 11 ppm, Ni: 10 ppm, O: 720 to 2500 ppm, and N: 10 to 20 ppm.
(VIM Step)
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The above Mn raw material was placed in a magnesia crucible, and melting was performed using a vacuum induction melting furnace (VIM furnace) at a melting temperature of 1300° C. under an inert atmosphere of 200 Torr or less. Then, calcium (Ca) in 1 wt % of the weight of Mn was gradually added to this molten Mn to perform deoxidation and desulfurization. After the completion of the deoxidation and desulfurization, the resulting molten Mn was cast in an iron mold to manufacture an ingot. After cooling the ingot, slags adhered to the ingot were removed.
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The impurities of the ingot after melting were as follows; specifically, B: 14 ppm, Mg: 160 ppm, Al: 1.2 ppm, Si: 16 ppm, S: 16 ppm, Ca: 520 ppm, Cr: 2.5 ppm, Fe: 3.6 ppm, Ni: 1.3 ppm, O: less than 10 ppm, and N: less than 10 ppm. The results are shown in Table 1.
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As shown in Table 1, Ca is increased in the cast Mn due to the calcium reduction step. Mg is also increased considerably because Mg is a constituent element of the magnesia crucible and susceptive to reduction by Ca, and a portion thereof contaminates the cast Mn. Meanwhile, the results reveal that S, O and Ni are significantly decreased, and other elements are also decreased.
(Skull Melting Step)
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Next, the Mn ingot obtained from the VIM treatment was loaded in a water-cooled crucible, the crucible was placed in a skull melting furnace, and pressure was reduced to 10−5 Torr or less with a vacuum pump to perform induction heating. After confirming the melting of the Mn ingot as a raw material, the molten state thereof was maintained for 30 minutes and the melting was then ended to obtain a solidified Mn.
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The impurities of this Mn ingot were as follows; specifically, B: 8.1 ppm, Mg: 1.9 ppm, Al: 1.7 ppm, Si: 16 ppm, S: 2.7 ppm, Ca: 9.4 ppm, Cr: 1.1 ppm, Fe: 3.6 ppm, Ni: 1.1 ppm, O: less than 10 ppm, and N: less than 10 ppm.
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The results are similarly shown in Table 1. As shown in Table 1, after the skull melting, it can be seen that Ca and Mg, which increased in the primary VIM step, have decreased considerably. Moreover, S has also been decreased. Thus, it is considered that volatile impurities were eliminated via skull melting.
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By performing VIM treatment, in which the foregoing deoxidizing/desulfurizing agent was added, and skull melting treatment, it was possible to highly purify the electrolytic Mn raw material having a purity of 2N to a purity level of 4N5 excluding gas component elements.
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TABLE 1 |
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|
| |
|
|
|
(wtppm) |
| |
|
Raw |
Primary |
Secondary |
| |
|
material |
melting |
melting |
| |
|
Mn |
(VIM) |
(skull melting) |
| |
|
| |
| |
B |
15 |
14 |
8.1 |
| |
Mg |
90 |
160 |
1.9 |
| |
Al |
4.5 |
1.2 |
1.7 |
| |
Si |
39 |
16 |
16 |
| |
S |
280 |
16 |
2.7 |
| |
Ca |
5.9 |
520 |
9.4 |
| |
Cr |
2.9 |
2.5 |
1.1 |
| |
Fe |
11 |
3.6 |
3.6 |
| |
Ni |
10 |
1.3 |
1.1 |
| |
O |
2200 |
<10 |
<10 |
| |
N |
20 |
<10 |
<10 |
| |
|
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TABLE 2 |
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|
| |
|
Raw |
Primary |
Primary |
| |
|
material |
melting |
melting |
| |
|
Mn |
(VIM) |
(VIM) |
| |
|
| |
| |
Mg |
90 |
150 |
500 |
| |
S |
280 |
10 |
150 |
| |
Ca |
5.9 |
600 |
1100 |
| |
O |
2200 |
15 |
500 |
| |
N |
20 |
20 |
20 |
| |
Heating |
|
1400 |
1450 |
| |
temperature |
|
|
|
| |
(° C.) |
| |
|
INDUSTRIAL APPLICABILITY
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According to the present invention, Mn having ultra-high purity can be obtained by a relatively simple manufacturing process at a reduced manufacturing cost. Therefore, it is useful as: a metal Mn used for wiring materials, electronic component materials such as magnetic materials (magnetic recording heads), and semiconductor component materials; and a sputtering target material for forming a thin film thereof, in particular a Mn-containing thin film. Since the present invention can be manufactured with a common furnace without the need for special equipment, and a high purity Mn can be obtained at a lower cost and higher yield as compared with the conventional distillation method, it can be said that it has high value regarding industrial utility.
