JPH0433756B2 - - Google Patents

Description

Detailed Description of the Invention (Technical Field) The present invention relates to a method for producing high-density polycrystalline ferrite, particularly for recording on high-coercivity magnetic recording media such as metal tapes and vapor-deposited tapes in VTRs, FDDs, RDDs, etc. The present invention relates to a method for producing Mn--Zn ferrite having a high magnetic flux density and which can be suitably used in reproducing heads. (Prior art and its problems) Ferrite materials such as Mn-Zn ferrite have traditionally been used as materials for magnetic recording/reproducing heads of VTRs, etc. Generally, a ferrite raw material powder mixture containing 50 to 54% of ferric oxide in terms of molar ratio is calcined to reduce the ferrite conversion rate to approximately 80%.
% or higher, the calcined product is crushed and molded into a predetermined shape to obtain a molded product, which is first fired at a temperature of 1200°C or less under vacuum, and then reduced to approximately equilibrium oxygen content. It is manufactured by the so-called vacuum sintering method, which involves sintering at a temperature of 1250°C or higher under pressure (0.1 to 100% oxygen concentration) to control the ferrite particle size and magnetic properties.
In addition, in the firing process in the vacuum oven, the temperature was 900℃.
The ferrite conversion rate of the molded body was made to be 100% before and after, and the gas inside the molded body was removed and
The pores in the molded body are made to become closed pores by ℃. However, ferrite having the above iron oxide composition has a saturation magnetic flux density (B ₁₀ ) of
Since it is less than 5600G (Gauss), it could not be used as a ferrite for recording/reproducing heads of high coercivity magnetic recording media such as metal tapes. In addition, as one method for increasing the density of polycrystalline ferrite, a method of firing the above-mentioned compact under pressure using hot isostatic pressing (HIP) or hot pressing (HP) is also being considered. It is recognized that a fired ferrite body with a porosity of 0.01% or less can be obtained by this method, but in the case of a high-density polycrystalline ferrite body with a porosity reduced in this way, By being reheated to a temperature of ℃ or higher, the pores in the ferrite body are resuscitated, causing a phenomenon in which the ferrite body becomes a ferrite body with high porosity again. However, it was a problem to achieve single crystallization using the single crystallization method. On the other hand, in JP-A No. 59-64599, in terms of molar ratio,
61.5-65% ferric oxide, 10-20% zinc oxide,
A single-crystal ferrite has _been proposed that has a composition containing 28.5 to 15% manganese oxide and is grown from a melt (liquid phase) using the so-called Bridgman manufacturing method.
It has been revealed that it is possible to obtain ferrite that is over 5500G. In short, in order to use ferrite for the magnetic head of high coercive force magnetic recording media such as metal tapes, the saturation magnetic flux density of ferrite is generally required to be approximately 4 to 6 times the coercive force of the tape. For example, ferrite with a high saturation magnetic flux density is desirable, but the above-mentioned ferrite having a composition containing 50 to 54% of ferric oxide in terms of molar ratio was not able to fully meet this requirement. , a ferrite containing a high molar ratio of ferric oxide was proposed as shown in the above-mentioned Japanese Patent Application Laid-open No. 59-64599. That is, by increasing the content of ferric oxide in the ferrite to 60 mol% or more, the saturation magnetic flux density can be advantageously increased. However, in order to obtain a ferrite body with a ferric oxide content of more than 60 mol%, when a ferrite raw powder mixture with a high ferric oxide content is calcined in air, the ferrite changes. The ferrite conversion rate is about 40 to 60%, and when the calcined product with such a ferrite conversion rate is pulverized and the resulting molded body is fired using the above-mentioned sintering method under vacuum, ferrite is produced. The densification rate becomes approximately 100% at a temperature of around 1000°C, that is, the hematite in the fired body completely disappears, and therefore, it is not sufficiently densified even by subsequent sintering operations at temperatures above 1250°C. It was extremely difficult to reduce the porosity of the resulting sintered body to 0.01% or less. Moreover, since there are many pores in the resulting ferrite body, even if you try to single crystallize it using a single crystallization method using solid phase reaction, the temperature will be quite high, making it difficult to control single crystallization. In addition, there are inherent problems such as coarsening of crystal grains or generation of crystals with different orientations, and there is also a problem that a large amount of pores remain in the obtained single crystal. The present invention has been made against this background, and its object is to provide a head for high coercivity magnetic recording media with a saturation magnetic flux density (B ₁₀ ) of 5800G or more. Another purpose is to provide a method for advantageously producing high-density polycrystalline ferrite that can be suitably used in The purpose is to provide a method for producing high-density polycrystalline ferrite, and another objective is to provide a method for producing high-density polycrystalline ferrite. It is an object of the present invention to provide a method for advantageously producing high-density polycrystalline ferrite that solves the problem of pore resuscitation due to heating. (Solution Means) In order to achieve such an object, the present invention is characterized by having a molar ratio of ferric oxide of 60 to 68%, zinc oxide of 10 to 20%, and zinc oxide of 30 to 12%. A method for producing high-density polycrystalline ferrite by firing a ferrite material having a composition consisting of manganese and a hematite phase together with a ferrite phase, the method comprising: (a) heating the ferrite material with 0.01 to 50% oxygen; The hematite phase is gradually reduced in an atmosphere with a concentration of 1100 ~
(b) a first firing step in which the hematite phase is extinguished in a temperature range of 1250°C;
and a second firing step of performing densification by firing at atmospheric pressure at a temperature higher than 1250° C. in an atmosphere with an oxygen concentration of . In addition, the molar ratio of 60 to 68% ferric oxide, 10 to 20% zinc oxide, and 30 to 12% manganese oxide, obtained according to the manufacturing method of such high-density polycrystalline ferrite. The saturation magnetic flux density (B ₁₀ ) of high-density polycrystalline ferrite with a composition of
5800G (Gauss) or more, the porosity (P) as specified later is 0.01% or less, and the porosity does not substantially increase during heat treatment at a temperature of 1000°C or more. Therefore, it can be suitably used as a head for a high coercivity magnetic recording medium, and can also be suitably used as a ferrite material that does not impair the sliding characteristics of the magnetic head. Here, the fact that the porosity does not substantially increase means that the porosity before and after reheating is within the measurement error range and hardly changes. In this case, what is within the measurement error range is
Based on the accuracy of porosity measurement, it can be considered that the change is within a range of approximately ±50% of the measured value. Note that the first firing step in the method for producing high-density polycrystalline ferrite according to the present invention generally includes a plurality of temperature raising steps, and the final raising and lowering step brings the ferrite material to 1100%
It will be heated to a temperature of ~1250°C to substantially eliminate the hematite phase in the ferrite material. Further, in the first firing step, the ferrite material is usually heated to a temperature of at least 800° C. to reduce the hematite phase in the ferrite material. Further, according to a preferred embodiment of the present invention, the ferrite material has a composition consisting of 63 to 65% ferric oxide, 10 to 15% zinc oxide, and 27 to 20% manganese oxide in molar ratio. and the oxygen concentration in the firing atmosphere in the first firing step is 0.1 to 10%, and the oxygen concentration in the firing atmosphere in the second firing step is 1 to 20%. becomes. (Specific explanation and effects of the structure) By the way, the ferrite material used in the present invention has ferric oxide (Fe ₂ O ₃ ) of 60 to 68
A raw powder mixture of Mn-Zn ferrite having a composition of mol % and giving such a composition is calcined in accordance with a conventional method, and then pulverized to form a block. A molded body formed into an appropriate shape is used as the ferrite material. In addition,
Such a molded body is generally composed of 40 to 60% by weight of a ferrite phase, and the remaining 60 to 40% by weight of an unreacted phase mainly composed of a hematite phase. In addition, the composition of such a ferrite material is that of high-density polycrystalline ferrite obtained by firing it as it is, but the high-density polycrystalline ferrite with a high saturation magnetic flux density (B ₁₀ ) obtained according to the present invention Polycrystalline ferrite contains 60-68% ferric oxide (Fe ₂ O ₃ ), 10-20% zinc oxide (ZnO) and
Obtained using a ferrite material with a composition consisting of 30-12% manganese oxide (MnO), especially 63-65 mol% ferric oxide and 10-10 mol% zinc oxide.
A ferrite material having a composition of 15 mol% and 27 to 20 mol% of manganese oxide is preferably used, and thereby a high-density polycrystalline ferrite having a saturation magnetic flux density of 5800 G or more, preferably 6000 G or more can be advantageously obtained. It becomes. And a ferrite material (calcined product molded body) having a hematite phase together with such a ferrite phase.
First, He, Ar, or
Calculated under normal pressure in an atmosphere such as _N2 ,
The hematite phase in the ferrite material is gradually reduced, and the hematite phase is substantially eliminated in a temperature range of 1100 to 1250°C (first firing step). In other words, in this first firing step, the temperature and oxygen partial pressure (concentration ) will be adjusted. Note that if the oxygen concentration in the firing atmosphere is lower than 0.01%, the ferrite material will progress rapidly and the hematite phase will virtually disappear in the low temperature range, so the porosity of the ferrite material must be maintained sufficiently. Furthermore, when the oxygen concentration exceeds 50%, the progress of ferrite formation is slow, and the disappearance of the hematite phase is delayed until the second firing process, leaving coarse pores inside the fired body. There is a problem with it. Furthermore, if the hematite phase substantially disappears at a temperature below 1100°C, the ferrite material cannot be sufficiently densified in the second firing step, and the porosity of the final fired product will be sufficiently reduced. This becomes difficult. Furthermore, the disappearance of the hematite phase
If it is carried out at a temperature of 1250° C. or higher, there is a problem that coarse pores will be formed in the subsequent second firing step. Furthermore, as the firing temperature of the ferrite material in this first firing step, a temperature of 800°C or higher is generally used. However, if the temperature is lower than 800°C, the progress of ferrite formation is slow and an effective reduction reaction of the hematite phase cannot be induced. In such a first firing step, a method is adopted in which the ferrite material is fired using a temperature raising operation in which the temperature is raised stepwise or continuously. The firing temperature is increased step by step according to the stage temperature raising process, and in the final temperature raising process, the ferrite material is heated to a temperature of 1100 to 1250 °C,
The hematite phase in the ferrite material is made to disappear. More specifically, a preferred stepwise temperature raising operation in the first firing step of the present invention is a first temperature raising step in which the temperature is gradually raised from about 800°C to reach a temperature lower than 1200°C; This is followed by a first holding step consisting of holding the reached temperature for a predetermined time, followed by a second temperature raising step of raising the temperature to a predetermined temperature within the range of 1100 to 1250°C, and then holding the reached temperature for a predetermined time. and a second holding step of substantially eliminating the hematite phase. The temperature increase speed at that time is usually 150 to 800℃.
The heating rate will be approximately 200°C/hr, and the heating rate will be approximately 30 to 40°C/hr in both the first and second temperature raising steps. Next, the ferrite material whose hematite phase has been eliminated in the first firing step is
Furthermore, in the second firing step, the material is fired under normal pressure to further densify it. The firing atmosphere in this second firing step is 0.1~
An atmosphere with 100% oxygen concentration is used, and this oxygen concentration is necessary to ultimately reduce the porosity to 0.01% or less and to control the crystal grain size and magnetic properties of ferrite. It is something. Note that components other than oxygen in this firing atmosphere are inert gas components such as He, Ar, and _N2 .
Further, it is necessary to use a firing temperature exceeding 1250°C. This allows effective sintering to proceed, thereby making it possible to obtain a dense ferrite sintered body whose porosity is effectively reduced. The ferrite sintered body obtained through the first firing step and the second firing step according to the present invention is
It is a high-density polycrystalline ferrite with a porosity of 0.01% or less, and has excellent workability as a high-density ferrite for recording/reproducing heads.It also prevents chipping of the head and pores in the magnetic powder when sliding with the magnetic tape. It has the feature that it does not cause problems such as noise generation due to clogging. In addition, since it is a pressureless sintering method, it is cost-effective.
It is cheaper than the HIP method and hot press method, does not require large equipment, and has the characteristics of a simple process. Furthermore, pore resuscitation is effectively suppressed even by heat treatment at 1000℃ or higher. As a result, even if such a high-density ferrite (polycrystalline ferrite) is single-crystalized by a single-crystalization method using a solid-phase reaction, the porosity does not increase, and the pores of the resulting single crystal do not increase. The rate can also be reduced to 0.01% or less. Furthermore, the composition of the high-density polycrystalline ferrite obtained according to the present invention is changed from 60 to 68 mol% of ferric oxide, 10 to 20 mol% of zinc oxide, and 30 to 12 mol% of manganese oxide. By using Mn-Zn ferrite with a composition _of
High-density polycrystalline ferrite of 5800G or more, preferably 6000G or more can be obtained, and this can be advantageously used as a recording/reproducing head material for high-coercivity magnetic recording media such as metal tapes and vapor-deposited tapes. It's something you get. Note that the porosity in the present invention is expressed as a percentage of the area occupied by pores in an arbitrary cut surface of a sample, and is specifically determined as follows. That is, any cut surface of a given sample is polished, and the polished surface is inspected at 1000x magnification using a metallurgical microscope to determine the pore diameter: d and the number of pores in the field of view: n is measured, the porosity is measured from the pore area with respect to the total visual field area, and the porosity: P% is determined according to the following formula. P (%) = 〓 ⁱ π (d _i /2) ² n _i /measurement area x 100 However, d _i : Pore diameter (length) n _i : Pore diameter d _i Number of pores In addition, the ferrite conversion rate in the present invention and indicates the weight percent of the ferrite phase, or it is calculated by measuring the weight of the hematite phase at the time of preparation and the weight of the hematite phase after calcination, and assuming that all the disappeared hematite has become the ferrite phase. It is. Furthermore, the saturation magnetic flux density B ₁₀ indicates the saturation magnetic flux density in a magnetic field of 10 Oe. (Examples) In order to clarify the present invention more specifically, some examples of the present invention will be shown below, but the present invention should not be construed in any way limited by the description of such examples. It goes without saying that this is not the case. It should be noted that the present invention can be implemented in various embodiments in addition to the above-described specific explanation and the following examples, and as long as it does not depart from the spirit of the present invention, it is within the knowledge of those skilled in the art. It should be understood that all of the various embodiments that can be implemented based on these fall within the scope of the present invention. Example 1 A ferrite raw material powder mixture having a molar ratio of 61.0% ferric oxide, 27.0% manganese carbonate, and 12.0% zinc oxide obtained by roasting hydrothermally synthesized magnetite was heated in air to approx. 2 at a temperature of 1000℃
After being calcined for a period of time, it was crushed and molded into a predetermined shape. Then, the obtained molded body as a ferrite material was sintered under normal pressure as follows. That is, first, the temperature was raised at a rate of 150°C/hr from room temperature to 800°C, then at a rate of 40°C/hr from 800°C to 1000°C, and then at 1000°C for 4 hours. held. Note that during this firing, the firing atmosphere was a nitrogen atmosphere with an oxygen concentration of 0.1%. Then,
The first firing operation was continued by increasing the temperature at a rate of 40° C./hr and holding it at 1200° C. for 2 hours to eliminate the hematite phase in the compact. In addition, 1100℃
When the fired body immediately after heating up and the fired body after being held at 1200℃ for 2 hours were taken out midway and the cut surfaces inside the fired body were examined by X-ray diffraction, it was found that in the former case, hematite phase remained, whereas in the former case, the hematite phase remained. It was confirmed that the latter had a 100% ferrite phase, and that the hematite phase had disappeared during this time. Further, during this firing, the firing atmosphere was a nitrogen atmosphere with an oxygen concentration of 1%. Thereafter, the temperature was raised to 1300°C at a rate of 150°C/hr, and the temperature was maintained for 8 hours to carry out a second firing operation under normal pressure. Also,
During this firing, the firing temperature was set to a nitrogen atmosphere with an oxygen concentration of 5%, and after this firing, a cooling step of 1100°C or less was performed in a nitrogen atmosphere to obtain the desired fired ferrite body (polycrystalline body). Obtained. The obtained polycrystalline material has an average grain size of 9.8 μm and a porosity of
0.01%, discontinuous grain growth temperature: 1340°C. In addition, the obtained polycrystal was 5 mm x 5 mm x
It was cut into pieces of 10 mm and heat treated as follows, and the change in porosity after the heat treatment was examined. First, the temperature was raised from room temperature to 1100℃ at a rate of 300℃/hr.
The atmosphere during this time was nitrogen. After that, further
The temperature was raised to 1300°C at 300°C/hr and held for 2 hours. The atmosphere during this time was a nitrogen atmosphere with an oxygen concentration of 5%. Next, the temperature was lowered at a rate of 300°C/hr, and then cooled from 1100°C in a nitrogen atmosphere to obtain a heat-treated ferrite fired body. Example 2 In molar ratio, ferric oxide obtained by roasting hydrothermally synthesized magnetite: 62.5%, manganese carbonate: 26.5%,
A ferrite raw material powder mixture having a composition of zinc oxide: 11.0% was calcined in air at a temperature of about 1000°C for 2 hours, and then pulverized and molded into a predetermined shape. The obtained molded body was then fired under normal pressure as follows. In other words, from room temperature to 800℃, the temperature is 150℃/
hr heating rate and from 800℃ to 1000℃
The temperature was raised at a temperature increase rate of 40°C/hr, and the temperature was further maintained at 1000°C for 4 hours. Note that during this firing, the firing atmosphere was a nitrogen atmosphere with an oxygen concentration of 0.5%. Then, the temperature was increased at a rate of 40℃/hr, and further
The molded body was maintained at a temperature of 1220° C. for 2 hours to eliminate the hematite phase in the molded body. In addition, when we took out the fired body immediately after raising the temperature to 1100°C and the fired body after holding it at 1220°C for 2 hours, and examined the cut surface inside the fired body by X-ray diffraction, it was found that in the former, hematite phase remained. In contrast, in the latter case, it was 100% ferrite phase, and it was confirmed that the hematite phase had disappeared during this time. During this time, the atmosphere was a nitrogen atmosphere with an oxygen concentration of 1%. Next, the temperature was raised to 1300° C. at a heating rate of 150° C./hr, and maintained at that temperature for 8 hours to carry out the final normal pressure firing operation. During this firing, the firing atmosphere was a nitrogen atmosphere with an oxygen concentration of 3%. After firing, a cooling step of 1100° C. or lower was performed in a nitrogen atmosphere to obtain the desired fired ferrite body (polycrystalline body). The obtained polycrystalline material had an average grain size of 8.9 μm, a porosity of 0.008%, and a discontinuous grain growth temperature of 1350°C. In addition, the obtained polycrystalline body was 5 mm x 5 mm x 10
The sample was cut into pieces with a size of mm, and the heat treatment was performed in the same manner as in Example 1, and the change in porosity after the heat treatment was examined. Example 3 In terms of molar ratio, ferric oxide obtained by roasting hydrothermally synthesized magnetite: 63.5%, manganese carbonate: 22.5%,
A ferrite raw powder mixture having a composition of 14.0% zinc oxide was calcined in air at a temperature of about 1000° C. for 2 hours, and then pulverized and molded into a predetermined shape. The obtained molded body was then fired under normal pressure as follows. In other words, from room temperature to 800℃, the temperature is 150℃/
At increasing temperature of hr, and from 800℃ to 1000℃
The temperature was increased at a rate of 40°C/hr, and the temperature was further maintained at 1000°C for 4 hours. Note that during this firing, the firing atmosphere was a nitrogen atmosphere with an oxygen concentration of 1%. Thereafter, the temperature was increased to 1200°C at a rate of 40°C/hr, and the temperature was maintained at 1200°C for 2 hours to continue the firing operation and eliminate the hematite phase in the compact. In addition, when we took out the fired body immediately after raising the temperature to 1100°C and the fired body after holding it at 1200°C for 2 hours and examined the cut surface inside the fired body by X-ray diffraction, it was found that in the former, hematite phase remained. In contrast, in the latter case, it was 100% ferrite phase, and it was confirmed that the hematite phase had disappeared during this time. During this time, the firing atmosphere was a nitrogen atmosphere with an oxygen concentration of 1%. Next, a final atmospheric pressure firing operation was carried out by raising the temperature to 1350°C at a heating rate of 150°C/hr and holding at that temperature for 8 hours. Also,
During this firing, the firing atmosphere was a nitrogen atmosphere with an oxygen concentration of 1%. And after such firing,
The cooling process is carried out below 1100℃ in a nitrogen atmosphere.
The desired fired ferrite body (polycrystalline body) was obtained. This polycrystalline material had an average grain size of 10.2 μm, a porosity of 0.008%, and a discontinuous grain growth temperature of 1420°C. In addition, the obtained polycrystalline body was 5 mm x 5 mm x 10
Example 1
The same method as above was used to examine the change in porosity after heat treatment. Example 4 In terms of molar ratio, ferric oxide obtained by roasting hydrothermally synthesized magnetite: 65.0%, manganese oxide: 25.0%,
A ferrite raw powder mixture having a composition of 10.0% zinc oxide was calcined in air at a temperature of about 1000° C. for 2 hours, and then pulverized and molded into a predetermined shape. The obtained molded body was then fired under normal pressure as follows. In other words, from room temperature to 800℃, the temperature is 150℃/
hr heating rate and from 800℃ to 1050℃
The temperature was increased at a temperature increase rate of 40°C/hr, and the temperature was further maintained at 1050°C for 4 hours. Note that during this firing, the firing atmosphere was a nitrogen atmosphere with an oxygen concentration of 3.0%. After that, the temperature was increased at a rate of 40°C/hr, and
By holding the molded article at a temperature of 1220° C. for 2 hours, the hematite phase in the molded article was extinguished. In addition, 1100℃
When the fired body immediately after heating up and the fired body after being held at 1220°C for 2 hours were taken out midway and the cut surfaces inside the fired body were examined by X-ray diffraction, it was found that in the former case, hematite phase remained, whereas in the former case, the hematite phase remained. It was confirmed that the latter was 100% ferrite phase, and that the hematite phase had disappeared during this time. During this time, the firing atmosphere was a nitrogen atmosphere with an oxygen concentration of 1.0%. A final atmospheric pressure firing operation was then carried out by raising the temperature to 1350°C at a heating rate of 150°C/hr and holding at that temperature for 8 hours. Also, during this firing, the firing atmosphere has a low oxygen concentration.
A 1.0% nitrogen atmosphere was used. After the firing, a cooling step of 1100°C or lower is performed in a nitrogen atmosphere to obtain the desired fired ferrite body (polycrystalline body).
I got it. This polycrystalline material had an average grain size of 9.2 μm, a porosity of 0.009%, and a discontinuous grain growth temperature of 1380°C. In addition, the obtained polycrystalline body was 5 mm x 5 mm x 10
Example 1
The same method as above was used to examine the change in porosity after heat treatment. Example 5 In terms of molar ratio, ferric oxide obtained by roasting hydrothermally synthesized magnetite: 66.5%, manganese carbonate: 17.0%,
Zinc oxide: A ferrite raw powder mixture with a composition of 16.5% was heated in air at a temperature of about 1000℃ for 2 hours.
After being calcined for a period of time, it was pulverized into a predetermined shape. The obtained molded body was then fired under normal pressure as follows. In other words, from room temperature to 800℃, the temperature is 150℃/
hr heating rate and from 800℃ to 1000℃
The temperature was raised at a temperature increase rate of 40°C/hr, and the temperature was further maintained at 1000°C for 4 hours. Note that during this firing, the firing atmosphere was a nitrogen atmosphere with an oxygen concentration of 10%. After that, the temperature was increased at a rate of 40°C/hr, and
By maintaining the temperature at 1200° C. for 2 hours, the hematite phase in the molded body was extinguished. In addition, 1100℃
When the fired body immediately after heating up and the fired body after being held at 1200℃ for 2 hours were taken out midway and the cut surfaces inside the fired body were examined by X-ray diffraction, it was found that in the former case, hematite phase remained, whereas in the former case, the hematite phase remained. It was confirmed that the latter was 100% ferrite phase, and that the hematite phase had disappeared during this time. During this time, the firing atmosphere was a nitrogen atmosphere with an oxygen concentration of 3%. Next, the temperature was raised to 1350°C at a temperature increase rate of 150°C/hr, and the temperature was maintained for 8 hours to perform a final atmospheric pressure firing operation. During this firing, the firing atmosphere was a nitrogen atmosphere with an oxygen concentration of 0.5%. After the firing, a cooling step of 1100° C. or lower was performed in a nitrogen atmosphere to obtain the desired fired ferrite body (polycrystalline body). This polycrystalline material had an average grain size of 10.5 μm, a porosity of 0.008%, and a discontinuous grain growth temperature of 1410°C. In addition, the obtained polycrystalline body was 5 mm x 5 mm x 10
Example 1
The same method as above was used to examine the change in porosity after heat treatment. Example 6 In molar ratio, ferric oxide obtained by roasting hydrothermally synthesized magnetite: 67.5%, manganese carbonate: 20.5%,
A ferrite raw powder mixture having a composition of 12.0% zinc oxide was calcined in air at a temperature of about 1000° C. for 2 hours, and then pulverized and molded into a predetermined shape. The obtained molded body was then fired under normal pressure as follows. In other words, from room temperature to 800℃, the temperature is 150℃/
hr heating rate and from 800℃ to 1100℃
The temperature was raised at a temperature increase rate of 35°C/hr, and the temperature was further maintained at 1100°C for 4 hours. The firing atmosphere during this firing was a nitrogen atmosphere with an oxygen concentration of 20%. After that, the temperature was increased at a rate of 35℃/hr to 1250℃.
By holding the molded article at a temperature of 2 hours, the hematite phase in the molded article was extinguished. In addition, when we took out the fired body immediately after raising the temperature to 1100°C and the fired body after holding it at 1250°C for 2 hours and examined the cut surface inside the fired body by X-ray diffraction, it was found that in the former, hematite phase remained. In contrast, in the latter case, it was 100% ferrite phase, and it was confirmed that the hematite phase had disappeared during this time. During this time, the firing atmosphere is a nitrogen atmosphere with an oxygen concentration of 5%. Next, the temperature was raised to a temperature of 1370°C at a heating rate of 150°C/hr, and the temperature was maintained at that temperature for 8 hours to perform the final normal pressure firing operation. Further, during this firing, the firing atmosphere was a nitrogen atmosphere with an oxygen concentration of 0.3%. And after such firing, 1100℃
The following cooling process was performed in a nitrogen atmosphere to obtain the desired fired ferrite body (polycrystalline body). This polycrystal has an average grain size of 10.3μm and a porosity of 0.01.
%, discontinuous grain growth temperature: 1430°C. Further, this polycrystal was cut into a size of 5 mm x 5 mm x 10 mm, and the heat treatment was performed in the same manner as in Example 1, and the change in porosity after the heat treatment was examined. Comparative Example 1 Molar ratio: ferric oxide obtained by roasting hydrothermally synthesized magnetite: 58.0%, manganese carbonate: 24.0%,
A ferrite raw powder mixture having a composition of 18.0% zinc oxide was calcined in air at a temperature of about 1000° C. for 2 hours, and then pulverized and molded into a predetermined shape. The obtained molded body was then fired under normal pressure as follows. In other words, from room temperature to 800℃, the temperature is 150℃/
hr heating rate and from 800℃ to 1000℃
The temperature was raised at a temperature increase rate of 40°C/hr, and then maintained at a temperature of 1000°C for 4 hours. Note that during this firing, the firing atmosphere was a nitrogen atmosphere with an oxygen concentration of 0.05%. After that, the temperature was increased at a rate of 40℃/hr,
Then, it was maintained at a temperature of 1200°C for 2 hours. In addition,
Immediately after raising the temperature to 1100°C, the fired body was taken out midway and the cut surface inside the fired body was examined by X-ray diffraction, and it was confirmed that it was 100% ferrite phase, and that the hematite phase had already disappeared. did. During this time, the firing atmosphere was a nitrogen atmosphere with an oxygen concentration of 0.5%. Next, the temperature was raised to a temperature of 1350°C at a heating rate of 150°C/hr, and the temperature was maintained at that temperature for 8 hours, thereby carrying out a final atmospheric pressure firing operation. Note that during this firing, the firing atmosphere was a nitrogen atmosphere with an oxygen concentration of 10%. And after such firing, 1100
A cooling step below .degree. C. was performed in a nitrogen atmosphere to obtain the desired fired ferrite body (polycrystalline body). This polycrystal has an average grain size of 10.5μm and a porosity of 0.03.
%, discontinuous grain growth temperature: 1470°C. Further, this polycrystalline body was cut into a size of 5 mm x 5 mm x 10 mm, and the heat treatment was performed in the same manner as in Example 1, and the change in porosity after the heat treatment was examined. Comparative Example 2 In terms of molar ratio, ferric oxide obtained by roasting hydrothermally synthesized magnetite: 70.0%, manganese carbonate: 15.0%,
A ferrite raw material powder mixture having a composition of zinc oxide: 15.0% was calcined in air at a temperature of about 1000° C. for 2 hours, and then pulverized and molded into a predetermined shape. The obtained molded body was then fired under normal pressure as follows. In other words, from room temperature to 800℃, the temperature is 150℃/
hr heating rate and from 800℃ to 1000℃
The temperature was raised at a temperature increase rate of 40°C/hr, and then maintained at a temperature of 1000°C for 4 hours. Note that during this firing, the firing atmosphere was a nitrogen atmosphere with an oxygen concentration of 30%.
Thereafter, the temperature was increased at a rate of 40° C./hr, and the temperature was maintained at 1200° C. for 2 hours. In addition, 1200℃
The fired body that had been held for 2 hours was taken out midway through the process, and the cut surface inside the fired body was examined by X-ray diffraction, and it was confirmed that a hematite phase remained and that ferrite formation was not completed during this time. During this time, the atmosphere was a nitrogen atmosphere with an oxygen concentration of 1%. Next, the temperature was raised to a temperature of 1350°C at a heating rate of 150°C/hr, and the temperature was maintained at that temperature for 8 hours, thereby carrying out a final atmospheric pressure firing operation. Note that during this firing, the firing atmosphere was a nitrogen atmosphere with an oxygen concentration of 0.1%. And after such firing,
The cooling process is carried out below 1100℃ in a nitrogen atmosphere.
The desired fired ferrite body (polycrystalline body) was obtained. This polycrystalline material had an average grain size of 10.3 μm, a porosity of 0.05%, and a discontinuous grain growth temperature of 1460°C. Further, this polycrystalline body was cut into a size of 5 mm x 5 mm x 10 mm, and the heat treatment was performed in the same manner as in Example 1, and the change in porosity after the heat treatment was examined. Comparative Example 3 In terms of molar ratio, ferric oxide obtained by roasting hydrothermally synthesized magnetite: 52.5%, manganese carbonate: 31.0%,
A ferrite raw powder mixture having a composition of 16.5% zinc oxide was calcined in air at a temperature of about 1000° C. for 2 hours, and then pulverized and molded into a predetermined shape. The obtained molded body was then fired as follows. That is, from room temperature to 800°C, the heating rate is 150°C/hr, and from 800°C to 1000°C, the heating rate is 40°C.
The temperature was raised at a temperature increase rate of °C/hr, and further maintained at a temperature of 1000 °C for 4 hours. During this time, a vacuum atmosphere of 10 ^-3 torr or less was maintained. In addition, when the fired body kept at 1000℃ for 4 hours was taken out midway and the cut surface inside the fired body was examined by X-ray diffraction, it was found to be 100% ferrite phase, and the hematite phase had already disappeared. It was confirmed. Thereafter, the temperature was increased at a rate of 40° C./hr, and the temperature was maintained at 1200° C. for 2 hours. During this time, a vacuum atmosphere of 10 ^-3 torr or less was maintained. Next, the final calcination operation was performed by raising the temperature to 1350°C at a heating rate of 150°C/hr and maintaining that temperature for 8 hours. Note that during this firing, the atmosphere was a nitrogen atmosphere with an oxygen concentration of 1%. After the firing, a cooling step of 1100° C. or lower was performed in a nitrogen atmosphere to obtain the desired fired ferrite body (polycrystalline body). This polycrystalline material had an average grain size of 8.5 μm, a porosity of 0.008%, and a discontinuous grain growth temperature of 1420°C. Further, this polycrystalline body was cut into a size of 5 mm x 5 mm x 10 mm, and the heat treatment was performed in the same manner as in Example 1, and the change in porosity after the heat treatment was examined. Comparative Example 4 A ferrite raw material powder mixture having a molar ratio of 63.5% ferric oxide, 22.5% manganese carbonate, and 14.0% zinc oxide obtained by roasting hydrothermally synthesized magnetite was heated in air to approx. 2 at a temperature of 1000℃
After being calcined for a period of time, it was crushed and molded into a predetermined shape. The obtained molded body was then fired as follows. That is, from room temperature to 800°C, the heating rate is 150°C/hr, and from 800°C to 1000°C, the heating rate is 40°C.
The temperature was raised at a temperature increase rate of °C/hr, and then maintained at a temperature of 1000 °C for 4 hours. During that time, a vacuum atmosphere of 10 ^-3 torr or less was maintained. Thereafter, the temperature was increased at a rate of 40° C./hr, and the temperature was maintained at 1200° C. for 2 hours. During this time, a vacuum atmosphere of 10 ^-3 torr or less was maintained. In addition, when we took out the fired body immediately after raising the temperature to 1100℃ and examined the cut surface inside the fired body by X-ray diffraction method, we found that it was 100% ferrite phase, and the hematite phase had already disappeared. It was confirmed. Next, the final calcination operation was performed by raising the temperature to 1350°C at a heating rate of 150°C/hr and maintaining that temperature for 8 hours. The firing atmosphere was a nitrogen atmosphere with an oxygen concentration of 1%. After the firing, a cooling step of 1100° C. or lower was performed in a nitrogen atmosphere to obtain the desired fired ferrite body (polycrystalline body). This polycrystalline material has an average grain size of 9.8 μm, a porosity of 0.06%, and a discontinuous grain growth temperature:
It was 1500℃. Further, this polycrystalline body was cut into a size of 5 mm x 5 mm x 10 mm, and the heat treatment was performed in the same manner as in Example 1, and the change in porosity after the heat treatment was examined. Comparative Example 5 In terms of molar ratio, ferric oxide obtained by roasting hydrothermally synthesized magnetite: 63.5%, manganese carbonate: 22.5%,
A ferrite raw powder mixture having a composition of 14.0% zinc oxide was calcined in air at a temperature of about 1000° C. for 2 hours, and then pulverized and molded into a predetermined shape. The obtained compact was then pre-fired at a temperature of 1200° C. for 2 hours in a nitrogen atmosphere with an oxygen concentration of 10%. The temperature rise and fall at this time is 300
℃/hr, and a nitrogen atmosphere was used below 1100℃. Next, the following HIP treatment was performed. In order to prevent reduction, Mn-Zn ferrite powder with almost the same structure was filled around the pre-fired body.
Firing was performed as follows using Ar gas as a pressure medium. The treatment was carried out for 2 hours at a pressure of 1000 Kg/cm ² and a temperature of 1300°C. At this time, the temperature was raised and lowered at 300°C/hr, and the pressure was raised and lowered at about 1000°C. After HIP,
Annealing treatment was performed under the same conditions as those for pre-firing to obtain the desired ferrite sintered body. Performance comparison The characteristics of the various ferrite sintered bodies obtained in Examples 1 to 6 and Comparative Examples 1 to 5 above, namely, the porosity, the saturation magnetic flux density at 10 Oe, and the porosity after heat treatment were investigated, and the results were It is shown in Table 1 below. As is clear from the results in Table 1, the ferrite sintered bodies of Examples 1 to 6 according to the present invention have extremely high saturation magnetic flux densities and porosity of 0.01 or less. The porosity did not change even after the heat treatment, and it was confirmed that there was no resuscitation of pores. On the other hand, the ferrite sintered bodies of Comparative Examples 1 and 3 with a low mol% of iron oxide have a low saturation magnetic flux density, and when the mol% of iron oxide is high, the ferrite sintered bodies of Comparative Examples 2, 4, and 5 It is observed that the porosity becomes high like that of the body, and that the pores are revived by heating and the porosity increases. 【table】

Claims (1)

[Claims] 1 molar ratio of 60 to 68% ferric oxide and 10 to 20%
A method for producing high-density polycrystalline ferrite by firing a ferrite material having a composition of 30 to 12% zinc oxide and 30 to 12% manganese oxide and having a ferrite phase and a hematite phase, A first firing step in which the hematite phase is fired under normal pressure in an atmosphere with an oxygen concentration of 0.01 to 50% while gradually reducing the hematite phase, and the hematite phase is extinguished in a temperature range of 1100 to 1250°C; The ferrite material in which the
A method for producing high-density polycrystalline ferrite, comprising: a second firing step for densifying the ferrite. 2. The first firing step includes multiple temperature raising steps, and in the final temperature raising step, the ferrite material is heated to a temperature of 1100 to 1250°C, and the hematite phase in the ferrite material disappears. A method for producing high-density polycrystalline ferrite according to claim 1. 3. High-density recording according to claim 1 or 2, wherein in the first firing step, the ferrite material is heated to a temperature of at least 800°C to reduce the hematite phase in the ferrite material. Method for producing polycrystalline ferrite. 4 The ferrite material has a molar ratio of 63 to 65%
of ferric oxide, 10 to 15% zinc oxide, and 27 to 20% manganese oxide, and the oxygen concentration in the firing atmosphere in the first firing step is 0.1 to 10%. Claims 1 to 3, wherein the oxygen concentration in the firing atmosphere in the second firing step is 1 to 20%.
2. A method for producing high-density polycrystalline ferrite according to any one of paragraphs.