CN1521770A - Fe2O3含量低于50摩尔%的Mn－Zn铁氧体 - Google Patents

Fe2O3含量低于50摩尔%的Mn－Zn铁氧体 Download PDF

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CN1521770A
CN1521770A CNA2004100039830A CN200410003983A CN1521770A CN 1521770 A CN1521770 A CN 1521770A CN A2004100039830 A CNA2004100039830 A CN A2004100039830A CN 200410003983 A CN200410003983 A CN 200410003983A CN 1521770 A CN1521770 A CN 1521770A
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小林修
山田修
伊藤清
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Minebea Co Ltd
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Abstract

一种Mn－Zn铁氧体，包括的基本组分为44.0－49.8摩尔％的Fe2O3，4.0－26.5摩尔％的ZnO，0.8摩尔％或更少的Mn2O3，余下的为MnO；含有0.20(不含0.20)－1.00质量％的CaO作添加剂；由于该Mn－Zn铁氧体中，Fe2O3的含量低于50.0摩尔％，并含有有限量的Mn2O3 (0.8摩尔％或更低)，甚至当CaO的含量超过0.20质量％时也不会产生反常的晶粒生长，可以得到高的电阻。因此可在如1MHz的高频段下实现优异的软磁性。

Description

Fe2O3含量低于50摩尔％的Mn-Zn铁氧体
技术领域
本发明涉及一种典型的软磁性氧化物磁材料，更具体地，涉及一种适于用作用于开关电源，各种电感元件，EMI对抗中的阻抗元件，电磁波吸收件等的低耗材料的Mn-Zn铁氧体。
背景技术
Mn-Zn铁氧体是典型的软磁性氧化物磁材料之一，通常包含的基本组分为：Fe2O3超过50.0摩尔％的化学计量，平均为52.0-55.0摩尔％；ZnO为10.0-24.0摩尔％；剩余部分由MnO组成，通常这样制造，按预定混合配比称量Fe2O3，ZnO和MnO生料粉末，将其混合，煅烧，研磨，调节组分，造粒，然后压成具有预定形状的生坯，将生坯于还原气氛中在1200-1400℃的温度下烧结2-4小时，气氛中的氧分压通过依据(1)式往炉中充入氮气来进行控制，然后在相同的气氛下冷却；
log P O 2 = - 14540 / ( T + 273 ) + b - - - ( 1 )
这里T是温度(℃)，PO2是氧分压，b是常数(通常设为7-8)。
通常，正如所知，Mn-Zn铁氧体中的锰(Mn)组分可以以Mn3+或者Mn2+存在，Mn3+和Mn2+之间的丰度比依赖于烧结时气氛中的氧分压，Mn3+显著破坏Mn-Zn铁氧体的软磁性。而且已知在Mn3+和Mn2+之间发生的电子转移会引起电阻的下降。因此，为了制造出具有优异的软磁性和高电阻的Mn-Zn铁氧体，必须控制烧结气氛(氧分压)以使Mn3+的生成最小化，并且考虑到工业可行的实质性，将上述(1)式中的常数b设在7-8之间。常数b设在7-8实际上意味着烧结时的氧分压必须控制在一个很窄的范围内，这使烧结步骤因生产成本上升而变得非常棘手。
在传统的Fe2O3含量超过50.0摩尔％的通用Mn-Zn铁氧体中，铁(Fe)组分可以Fe3+或Fe2+存在，当Mn-Zn铁氧体在上述还原气氛下烧结时，Fe3+被部分还原成Fe2+，Fe2+具有正的磁晶各向异性，可以抵消Fe3+的负的磁晶各向异性，因此提高了软磁性，但正像锰(Mn)组分那样，在Fe3+和Fe2+之间发生的电子转移会显著降低电阻。
近来，随着越来越多的具有更高性能和更小尺寸的电子设备的出现，形成的处理信号的频率更高了，所以需要有在高频段显示出优异磁特性的磁材料。用Mn-Zn铁氧体制成的磁芯，在较高的频率下涡电流会增加，因此会增加损耗。结果，为使Mn-Zn铁氧体在最高频的下起到作为磁芯材料的充分功能成为可能，需要使其电阻(电阻率)最大化。然而，由于传统的Mn-Zn铁氧体中Fe2O3含量超过50mol％(化学计量组分)，存在的Fe2+数量很大，这加速了Fe3+和Fe2+(离子)之间的电子转移。结果，电阻率低于大约1Ωm的数量级，所以Mn-Zn铁氧体的充分工作只能最高到几百kHz的频率，再往上，其起始磁导率显著降低，因此其作为软磁性材料的特性全部消失。
在此环境下，公开号为H07-230909和H10-208926的日本专利申请中公开了一种Fe2O3含量低于50.0摩尔％，并含有CaO和SiO2作添加剂以提高电阻的Mn-Zn铁氧体。
在上述公开号为H07-230909和H10-208926的日本专利申请中公开的Mn-Zn铁氧体被指定用作一种偏转轭的磁芯材料，所以倾向于仅仅能用到最高100kHz的频率(参照这些日本专利申请中的实施方案)，不能确保该Mn-Zn铁氧体可以在超过1MHz的高频段具有优异的磁性能(软磁性)。结果，该Mn-Zn铁氧体在超过1MHz的高频段不能成功地用作磁芯材料。上述公开号为H07-230909的日本专利申请表明在此Mn-Zn铁氧体中可以含有最高达0.50重量％的CaO和SiO2，但其中讨论的实施例包含的CaO少于0.10重量％，这样这些实施例中没有一个含有的CaO超过0.20质量％。并且，其中描述，可以加入适量的Mn2O3以使其与Fe2O3的总量在大约50.0摩尔％，但由于该Mn-Zn铁氧体含有的Fe2O3为45.0-48.5摩尔％，为达到50.0摩尔％，要加入1.4-5.0摩尔％的Mn2O3(即Mn3+)。如果包含了如此大数量的Mn3+，很难使Mn-Zn铁氧体同时满足软磁性和电阻的需要。
发明简述
本发明是考虑到上述问题而做出的，本发明的一个目的就是提供一种具有高电阻，并在超过1MHz的高频段下显示出优异软磁性的Mn-Zn铁氧体。
为了实现这一目的，在本发明的一个方面，Mn-Zn铁氧体包括的基本组分为：44.0-49.8摩尔％的Fe2O3，4.0-26.5摩尔％的ZnO，0.8摩尔％或更少的Mn2O3，剩余的为MnO，包含0.20(不含0.20)-1.00质量％的CaO作添加剂，具有的电阻率为1.5×104Ωm或更大，表面电阻为1.5×107Ω或更大。
在本发明的这一方面，FeO含量可以是0.2摩尔％或更低。
在本发明的这一方面，该Mn-Zn铁氧体可以进一步包含0.01-0.10质量％的SiO2作添加剂。
在本发明的这一方面，该Mn-Zn铁氧体可以进一步包含0.01-0.20质量％的V2O5，0.01-0.20质量％的MoO3，0.01-0.20质量％的ZrO2，0.01-0.20质量％的Ta2O5，0.01-0.20质量％的HfO2，0.01-0.20质量％的Nb2O5和0.01-6.00质量％的CuO中的至少一种作添加剂。
由此，由于依据本发明的该Mn-Zn铁氧体含有少于50.0摩尔％的Fe2O3以及有限数量(0.8摩尔％或更少)的Mn2O3，即使CaO含量超过了0.20质量％，也不会发生反常的晶粒生长，且可以得到高的电阻(电阻率为1.5×104Ωm或更高，表面电阻为1.5×107Ω或更大)。并且由于含有适量的TiO2和/或SnO2，可以将初始磁导率保持足够高，因此可在比如1 MHz的高频段下获得优异的软磁性。
具体实施方案
如上所述，当传统的Fe2O3含量高于50.0摩尔％的通用的Mn-Zn铁氧体在通过将(1)式中的常数b设定在7-8控制的还原气氛中烧结时，已知会破坏软磁性的Mn3+几乎不会产生，但会产生已知能显著降低电阻的Fe2+，因为超过50.0摩尔％的那些Fe2O3(即Fe3+)被还原了。另一方面，由于本发明中的Mn-Zn铁氧体包含的Fe2O3低于50.0摩尔％，具体地为44.0-49.8摩尔％，当该Mn-Zn铁氧体在通过将(1)式中的常数b设定在7-8控制的还原气氛中烧结时，Fe2+几乎不能生成。
Mn3+使晶格扭曲，因而显著降低了初始磁导率，并且引起电阻下降。本发明的Mn-Zn铁氧体包含0.8摩尔％或更低的Mn2O3(即Mn3+)，因而可以防止软磁性和电阻的破坏。
这样，本发明中的Mn-Zn铁氧体使得造成电阻显著降低的Fe2+的产生受到抑制，同样也抑制了引起软磁性的破坏和电阻下降的Mn3+的生成，因此成功获得了优异的软磁性和高的电阻。具体地，得到的电阻率为1.5×104Ωm或更高，表面电阻为1.5×107Ω或更大。Mn-Zn铁氧体中的铁组分，包括FeO(Fe2+)，通常用Fe2O3表示，并且由于如上所述Fe2+会极大地导致电阻的降低，FeO的含量优选设在0.2摩尔％或更低。
ZnO作为Mn-Zn铁氧体的一种基本组分，可以影响居里温度和饱和磁化强度。具体地，太小的ZnO含量会使初始磁导率降低，然而，太大的ZnO含量会引起居里温度和饱和磁化强度的降低。由于用在电源变压器中的铁氧体经常暴露在80-100℃的温度下，将居里温度和饱和磁化强度保持在很高是重要的，所以，如上所述，将ZnO的含量设在4.0-26.5摩尔％的范围。
如上所述，本发明的Mn-Zn铁氧体含有超过0.20质量％的CaO作添加剂。CaO会在晶粒边界上偏析，并引起电阻的提高，但当CaO含量超过0.20质量％时，会产生导致磁特性严重破坏的反常的晶粒生长。因此，为防止这种反常晶粒生长的产生，在传统的Mn-Zn铁氧体中，CaO的含量设在不大于0.20质量％。另一方面，在本发明的Mn-Zn铁氧体中，Fe2O3的含量设在49.8摩尔％(低于50.0摩尔％，即化学计量组分)或更低，同时将Mn2O3的含量设在微量(0.8摩尔％或更低)，而且按需要也可含有微量的FeO(0.2摩尔％或更低)。因此，甚至当CaO的含量超过0.20质量％时也不会产生反常的晶粒生长。为了提高电阻，CaO的含量优选设在大于0.50质量％，但太大的含量会引起软磁性的破坏，所以CaO的含量设定在0.20(不含0.20)-1.00质量％的范围内。SiO2也能有效地提高电阻，所以按需要可以包含0.01-0.10质量％的SiO2。
本发明的Mn-Zn铁氧体可以进一步包含V2O5，MoO3，ZrO2，Ta2O5，HfO2，Nb2O5和CuO中的至少一种作添加剂。这些组分能有效地帮助烧结作用并提高电阻，但当含量太小时并不十分有效，然而当含量太大时反而会引起反常的晶粒生长。因此，V2O5，MoO3，ZrO2，Ta2O5，HfO2和Nb2O5的含量优选设定在0.01-0.20质量％的范围，CuO的含量设在0.01-6.00质量％的范围。
本发明的Mn-Zn铁氧体可以在通过将(1)式中的常数b从7-12的范围内适当选择来控制氧分压的还原气氛中烧结并冷却。这意味着本发明的Mn-Zn铁氧体采用的气氛与传统Mn-Zn铁氧体采用的其中常数b通常选自7-8的范围的气氛相比可以方便地控制。结果，生产成本降低。此时，如果常数b设定超过了12，那么铁氧体中的Mn3+的含量就会超过0.8摩尔％，初始磁导率就会迅速下降。
在制造本发明的Mn-Zn铁氧体时，将基本组分Fe2O3，ZnO和MnO的原材料粉末按预定混合比进行称量，混合，煅烧和研磨。依据目标组分，煅烧进行的温度适当的确定在800-1000℃之间，用通用球磨，磨碎机或类似设备进行研磨。将经过如上处理的原材料粉末进一步与适量的CaO，SiO2以及其它可能需要的添加剂相混合，以得到具有目标组分的混合物粉末。依据一般的制造方法将该混合物粉末进行造粒，比如加入粘结剂，像聚乙烯醇，聚丙稀酰胺，甲基纤维素，聚环氧乙烷，甘油以及其它的相似剂，然后在如80MPa或更高的压力下将其压成生坯。在炉中将生坯在1000-1300℃的温度下，于通过充入惰性气体如氮气控制氧分压的气氛中烧结，并在相同的气氛中冷却。在烧结和冷却步骤中，(1)式中的常数b从7-12的范围内进行选择，这与烧结传统的Fe2O3含量超过50.0摩尔％的Mn-Zn铁氧体限定的7-8的范围相比具有显著宽松的可调性。结果，可以更容易地控制氧分压，并且由于在低于500℃的温度下，无论氧含量如何，氧化或者还原反应都是可以忽略的，所以在气氛的温度冷到500℃以下时，就不必依照(1)式来对气氛进行控制了。
实施例
按表1所示的组分制造9种不同的测试样品，其中包括2种对比样品。将原材料粉末Fe2O3，ZnO和MnO进行混合，用磨碎机搅拌，在空气中于850℃下煅烧2小时，用磨碎机研磨1小时，得到混合物粉末。然后，将CaO，SiO2，CuO，Nb2O5，V2O5和ZrO2粉末适当的加入到混合物粉末中调节组分，然后将调节后的混合物粉末用磨碎机搅拌1小时，加入聚乙烯醇造粒，在80MPa的压力下压成环形芯(生坯)，每个外径25mm，内径15mm，高度5mm。将生坯在1200℃下烧结2小时然后在炉中冷却，其中的气氛通过往炉中充入氮气来进行控制，以得到(1)式中常数b设在9时的氧分压。获得了本发明的样品1-7和对比样品1-2。
将如上制得的样品进行荧光X射线分析以得到各自的最终组分组成，滴定测量它们中的Mn2O3和FeO含量，如表1中所示。测量它们在1MHz下的初始磁导率，电阻率和表面电阻，结果在表1中列出。
表1
样品分类 基本组分(摩尔％)        滴定组分(摩尔％) 添加剂组分(摩尔％) 初始磁导率 电阻率(Ωm) 表面电阻(Ω)
    Fe2O3 (1)     MnO(2)     ZnO     Mn2O3     FeO     CaO     SiO2   其它
    对比样品1     51.0     36.8     12.2     1.2     0.8     0.10     0.04   -     40     1.1×101     1.2×102
    发明样品1     49.8     37.7     12.5     0.6     0.2     0.25     ″   -     720     1.6×104     1.7×107
    发明样品2     47.0     40.0     13.0     0.4     0.1     1.00     ″   -     820     6.1×104     8.5×107
    对比样品2     ″     ″     ″     ″     ″     1.50     ″   -     330     1.2×101     1.4×101
    发明样品3     ″     ″     ″     ″     ″     0.60     -   CuO：1.00     790     3.8×106     2.9×108
    发明样品4     ″     ″     ″     0.3     ″     ″     -   Nb2O5：0.05     800     3.5×105     2.7×108
    发明样品5     ″     ″     ″     ″     ″     ″     -   V2O5：0.05     890     3.6×106     2.6×108
    发明样品6     ″     ″     ″     0.2     ″     ″     0.04   ZrO2：0.05     830     3.4×105     2.6×108
    发明样品7     44.0     42.8     13.2     0.1     0     0.80     ″   -     810     4.4×104     3.2×108
注释：(1)Fe2O3指FeO和Fe2O3
      (2)MnO指Mn2O3和MnO
从表1可以看出，所有的发明样品1-7中含有低于0.8摩尔％的Mn2O3和0.2摩尔％或更低的FeO，并且具有超过700的初始磁导率和大于1.5×104Ωm的电阻率以及大于1.5×107Ω的表面电阻，这些证明获得了优异的软磁性和高的电阻。
另一方面，对比样品1由传统的Fe2O3含量大于50.0摩尔％的通用的Mn-Zn铁氧体制成，所以其具有的电阻显著降低，对比样品2含有大量的CaO，所以产生了反常的晶粒生长，其具有的初始磁导率显著降低。
尽管已依据具体的实施方案对本发明进行了阐释，应该明白本发明并不局限此，而是包括了在所附权利要求范围内的所有可能的更改和完善。

Claims (4)

1.一种Mn-Zn铁氧体：包括的基本组分为44.0-49.8摩尔％的Fe2O3，4.0-26.5摩尔％的ZnO，0.8摩尔％或更少的Mn2O3，余下的为MnO；含有0.20(不含0.20)-1.00质量％的CaO作添加剂；具有的电阻率为1.5×104Ωm或更大，表面电阻为1.5×107Ω或更大。
2.权利要求1中的Mn-Zn铁氧体，其中FeO的含量为0.2摩尔％或更少。
3.权利要求1或2中的Mn-Zn铁氧体，进一步包含0.01-0.10质量％的SiO2作添加剂。
4.权利要求1至3任意之一中的Mn-Zn铁氧体，进一步含有0.01-0.20质量％的V2O5，0.01-0.20质量％的MoO3，0.01-0.20质量％的ZrO2，0.01-0.20质量％的Ta2O5，0.01-0.20质量％的HfO2，0.01-0.20质量％的Nb2O5和0.01-6.00质量％的CuO中的至少一种作添加剂。
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