JPS6354041B2 - - Google Patents
Info
- Publication number
- JPS6354041B2 JPS6354041B2 JP59062569A JP6256984A JPS6354041B2 JP S6354041 B2 JPS6354041 B2 JP S6354041B2 JP 59062569 A JP59062569 A JP 59062569A JP 6256984 A JP6256984 A JP 6256984A JP S6354041 B2 JPS6354041 B2 JP S6354041B2
- Authority
- JP
- Japan
- Prior art keywords
- metallic iron
- main component
- acicular
- magnetic particles
- metal magnetic
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 claims description 158
- 229910052751 metal Inorganic materials 0.000 claims description 70
- 239000002184 metal Substances 0.000 claims description 70
- 239000006249 magnetic particle Substances 0.000 claims description 68
- 229910052742 iron Inorganic materials 0.000 claims description 62
- 239000002245 particle Substances 0.000 claims description 44
- SZVJSHCCFOBDDC-UHFFFAOYSA-N iron(II,III) oxide Inorganic materials O=[Fe]O[Fe]O[Fe]=O SZVJSHCCFOBDDC-UHFFFAOYSA-N 0.000 claims description 42
- 239000000843 powder Substances 0.000 claims description 14
- 239000007864 aqueous solution Substances 0.000 claims description 13
- 125000002887 hydroxy group Chemical group [H]O* 0.000 claims description 12
- 239000003960 organic solvent Substances 0.000 claims description 10
- 239000007858 starting material Substances 0.000 claims description 10
- 239000006185 dispersion Substances 0.000 claims description 8
- 229910021506 iron(II) hydroxide Inorganic materials 0.000 claims description 8
- NCNCGGDMXMBVIA-UHFFFAOYSA-L iron(ii) hydroxide Chemical compound [OH-].[OH-].[Fe+2] NCNCGGDMXMBVIA-UHFFFAOYSA-L 0.000 claims description 8
- 230000001590 oxidative effect Effects 0.000 claims description 8
- UQSXHKLRYXJYBZ-UHFFFAOYSA-N iron oxide Inorganic materials [Fe]=O UQSXHKLRYXJYBZ-UHFFFAOYSA-N 0.000 claims description 7
- 238000004519 manufacturing process Methods 0.000 claims description 7
- NDLPOXTZKUMGOV-UHFFFAOYSA-N oxo(oxoferriooxy)iron hydrate Chemical compound O.O=[Fe]O[Fe]=O NDLPOXTZKUMGOV-UHFFFAOYSA-N 0.000 claims description 5
- 238000010438 heat treatment Methods 0.000 claims description 4
- 239000013078 crystal Substances 0.000 claims description 3
- 239000010408 film Substances 0.000 description 43
- 230000005415 magnetization Effects 0.000 description 25
- 238000000034 method Methods 0.000 description 17
- 238000007254 oxidation reaction Methods 0.000 description 17
- 239000007789 gas Substances 0.000 description 16
- 230000003647 oxidation Effects 0.000 description 15
- HEMHJVSKTPXQMS-UHFFFAOYSA-M Sodium hydroxide Chemical compound [OH-].[Na+] HEMHJVSKTPXQMS-UHFFFAOYSA-M 0.000 description 12
- 239000011248 coating agent Substances 0.000 description 11
- 238000000576 coating method Methods 0.000 description 11
- YXFVVABEGXRONW-UHFFFAOYSA-N Toluene Chemical compound CC1=CC=CC=C1 YXFVVABEGXRONW-UHFFFAOYSA-N 0.000 description 9
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 8
- 230000015572 biosynthetic process Effects 0.000 description 8
- 239000001301 oxygen Substances 0.000 description 8
- 229910052760 oxygen Inorganic materials 0.000 description 8
- 230000009467 reduction Effects 0.000 description 8
- 239000000243 solution Substances 0.000 description 7
- 238000006243 chemical reaction Methods 0.000 description 6
- 238000001035 drying Methods 0.000 description 6
- BAUYGSIQEAFULO-UHFFFAOYSA-L iron(2+) sulfate (anhydrous) Chemical compound [Fe+2].[O-]S([O-])(=O)=O BAUYGSIQEAFULO-UHFFFAOYSA-L 0.000 description 6
- JEIPFZHSYJVQDO-UHFFFAOYSA-N iron(III) oxide Inorganic materials O=[Fe]O[Fe]=O JEIPFZHSYJVQDO-UHFFFAOYSA-N 0.000 description 6
- 230000007246 mechanism Effects 0.000 description 6
- 239000000463 material Substances 0.000 description 5
- 229910044991 metal oxide Inorganic materials 0.000 description 5
- 150000004706 metal oxides Chemical class 0.000 description 5
- 238000006068 polycondensation reaction Methods 0.000 description 5
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 5
- 239000003513 alkali Substances 0.000 description 4
- ZWEHNKRNPOVVGH-UHFFFAOYSA-N 2-Butanone Chemical compound CCC(C)=O ZWEHNKRNPOVVGH-UHFFFAOYSA-N 0.000 description 3
- KWYUFKZDYYNOTN-UHFFFAOYSA-M Potassium hydroxide Chemical compound [OH-].[K+] KWYUFKZDYYNOTN-UHFFFAOYSA-M 0.000 description 3
- 238000002441 X-ray diffraction Methods 0.000 description 3
- 230000008859 change Effects 0.000 description 3
- 230000000052 comparative effect Effects 0.000 description 3
- 230000000694 effects Effects 0.000 description 3
- 239000000696 magnetic material Substances 0.000 description 3
- 239000006247 magnetic powder Substances 0.000 description 3
- 150000002739 metals Chemical class 0.000 description 3
- 230000008569 process Effects 0.000 description 3
- 238000003756 stirring Methods 0.000 description 3
- CSCPPACGZOOCGX-UHFFFAOYSA-N Acetone Chemical compound CC(C)=O CSCPPACGZOOCGX-UHFFFAOYSA-N 0.000 description 2
- MYMOFIZGZYHOMD-UHFFFAOYSA-N Dioxygen Chemical compound O=O MYMOFIZGZYHOMD-UHFFFAOYSA-N 0.000 description 2
- CWYNVVGOOAEACU-UHFFFAOYSA-N Fe2+ Chemical compound [Fe+2] CWYNVVGOOAEACU-UHFFFAOYSA-N 0.000 description 2
- 230000001070 adhesive effect Effects 0.000 description 2
- 239000010953 base metal Substances 0.000 description 2
- 238000004040 coloring Methods 0.000 description 2
- 230000003247 decreasing effect Effects 0.000 description 2
- 238000010586 diagram Methods 0.000 description 2
- 229910001882 dioxygen Inorganic materials 0.000 description 2
- 238000001493 electron microscopy Methods 0.000 description 2
- 239000011790 ferrous sulphate Substances 0.000 description 2
- 235000003891 ferrous sulphate Nutrition 0.000 description 2
- 229910000359 iron(II) sulfate Inorganic materials 0.000 description 2
- 239000007788 liquid Substances 0.000 description 2
- 239000007791 liquid phase Substances 0.000 description 2
- 239000012071 phase Substances 0.000 description 2
- 239000006104 solid solution Substances 0.000 description 2
- 238000005406 washing Methods 0.000 description 2
- 229910006540 α-FeOOH Inorganic materials 0.000 description 2
- DKPFZGUDAPQIHT-UHFFFAOYSA-N Butyl acetate Natural products CCCCOC(C)=O DKPFZGUDAPQIHT-UHFFFAOYSA-N 0.000 description 1
- DGAQECJNVWCQMB-PUAWFVPOSA-M Ilexoside XXIX Chemical compound C[C@@H]1CC[C@@]2(CC[C@@]3(C(=CC[C@H]4[C@]3(CC[C@@H]5[C@@]4(CC[C@@H](C5(C)C)OS(=O)(=O)[O-])C)C)[C@@H]2[C@]1(C)O)C)C(=O)O[C@H]6[C@@H]([C@H]([C@@H]([C@H](O6)CO)O)O)O.[Na+] DGAQECJNVWCQMB-PUAWFVPOSA-M 0.000 description 1
- CTQNGGLPUBDAKN-UHFFFAOYSA-N O-Xylene Chemical compound CC1=CC=CC=C1C CTQNGGLPUBDAKN-UHFFFAOYSA-N 0.000 description 1
- 239000000853 adhesive Substances 0.000 description 1
- 238000005273 aeration Methods 0.000 description 1
- 229910052782 aluminium Inorganic materials 0.000 description 1
- 230000000903 blocking effect Effects 0.000 description 1
- 238000007664 blowing Methods 0.000 description 1
- 229910052804 chromium Inorganic materials 0.000 description 1
- 239000011651 chromium Substances 0.000 description 1
- 229940090961 chromium dioxide Drugs 0.000 description 1
- IAQWMWUKBQPOIY-UHFFFAOYSA-N chromium(4+);oxygen(2-) Chemical compound [O-2].[O-2].[Cr+4] IAQWMWUKBQPOIY-UHFFFAOYSA-N 0.000 description 1
- AYTAKQFHWFYBMA-UHFFFAOYSA-N chromium(IV) oxide Inorganic materials O=[Cr]=O AYTAKQFHWFYBMA-UHFFFAOYSA-N 0.000 description 1
- 238000004140 cleaning Methods 0.000 description 1
- 238000007796 conventional method Methods 0.000 description 1
- 238000001816 cooling Methods 0.000 description 1
- 238000005260 corrosion Methods 0.000 description 1
- 230000007797 corrosion Effects 0.000 description 1
- 238000000635 electron micrograph Methods 0.000 description 1
- 238000001704 evaporation Methods 0.000 description 1
- 229960002089 ferrous chloride Drugs 0.000 description 1
- 229910001448 ferrous ion Inorganic materials 0.000 description 1
- 239000010419 fine particle Substances 0.000 description 1
- 230000004907 flux Effects 0.000 description 1
- 230000020169 heat generation Effects 0.000 description 1
- 229910052595 hematite Inorganic materials 0.000 description 1
- 239000011019 hematite Substances 0.000 description 1
- FUZZWVXGSFPDMH-UHFFFAOYSA-N hexanoic acid Chemical compound CCCCCC(O)=O FUZZWVXGSFPDMH-UHFFFAOYSA-N 0.000 description 1
- XLYOFNOQVPJJNP-UHFFFAOYSA-M hydroxide Chemical compound [OH-] XLYOFNOQVPJJNP-UHFFFAOYSA-M 0.000 description 1
- 230000006872 improvement Effects 0.000 description 1
- 239000011261 inert gas Substances 0.000 description 1
- 150000002505 iron Chemical class 0.000 description 1
- NMCUIPGRVMDVDB-UHFFFAOYSA-L iron dichloride Chemical compound Cl[Fe]Cl NMCUIPGRVMDVDB-UHFFFAOYSA-L 0.000 description 1
- LIKBJVNGSGBSGK-UHFFFAOYSA-N iron(3+);oxygen(2-) Chemical compound [O-2].[O-2].[O-2].[Fe+3].[Fe+3] LIKBJVNGSGBSGK-UHFFFAOYSA-N 0.000 description 1
- 229910052745 lead Inorganic materials 0.000 description 1
- 230000000670 limiting effect Effects 0.000 description 1
- 229910052749 magnesium Inorganic materials 0.000 description 1
- 229910052748 manganese Inorganic materials 0.000 description 1
- 230000001404 mediated effect Effects 0.000 description 1
- 229910052759 nickel Inorganic materials 0.000 description 1
- 230000036961 partial effect Effects 0.000 description 1
- 230000001681 protective effect Effects 0.000 description 1
- 230000002829 reductive effect Effects 0.000 description 1
- 239000002002 slurry Substances 0.000 description 1
- 229910052708 sodium Inorganic materials 0.000 description 1
- 239000011734 sodium Substances 0.000 description 1
- 239000000725 suspension Substances 0.000 description 1
- 239000010409 thin film Substances 0.000 description 1
- 229910052718 tin Inorganic materials 0.000 description 1
- 229910052719 titanium Inorganic materials 0.000 description 1
- 239000008096 xylene Substances 0.000 description 1
- 229910052725 zinc Inorganic materials 0.000 description 1
Landscapes
- Paints Or Removers (AREA)
- Manufacture Of Metal Powder And Suspensions Thereof (AREA)
- Powder Metallurgy (AREA)
- Magnetic Record Carriers (AREA)
- Hard Magnetic Materials (AREA)
Description
【発明の詳細な説明】
本発明は、金属鉄を主成分とする針状晶金属磁
性粒子粉末の粒子表面に緻密で密着性のよい薄い
マグネタイト被膜を生成させることにより、空気
中に安定して取り出すことができ、しかも、空気
中に取り出した後の酸化による飽和磁化σsの減少
が防止される等の酸化安定性に優れた金属鉄を主
成分とする針状晶金属磁性粒子粉末の製造法に関
するものである。
近年、磁気記録再生用機器の小型軽量化が進む
につれて、記録媒体に対する高性能化の必要性が
益々生じてきている。すなわち、高密度記録、高
出力特性、殊に、周波数特性の向上が要求され
る。磁気記録媒体に対する上記のような要求を満
足させる為に適した磁性材料の特性は、大きな飽
和磁化と高い保磁力を有することである。
ところで、従来から磁気記録媒体に用いられて
いる磁性材料は、マグネタイト、マグヘマイト、
二酸化クロム等の磁性粉末であり、これらの磁性
粉末は飽和磁化σs70〜85emu/g、保磁力Hc250〜
500Oeを有するものである。
殊に、上記酸化物磁性粒子粉末のσsは最大85e
ｍｕ／ｇ程度であり、一般にはσs70〜80emu／ｇで
あることが再生出力並びに記録密度に限度を与え
ている主因となつている。更に、Coを含有して
いるCo―マグネタイトやCo―マグヘマイト磁性
粉末も使用されているが、これらの磁性粒子粉末
は保磁力Hcが400〜800Oeと高いという特徴を有
するが、これに反して飽和磁化σsが60〜80emu/g
と低いものである。
最近、高出力並びに高密度記録に適する特性を
備えた磁性粒子粉末すなわち、大きな飽和磁化と
高い保磁力を有する磁性粒子粉末の開発が盛んで
あり、そのような特性を有する磁性粒子粉末に
は、Fe2O3を主成分とする針状晶酸化第二鉄粒子
を還元性ガス中で加熱還元することにより得られ
る金属鉄を主成分とする針状晶金属磁性粒子粉末
がある。
上述するように金属鉄を主成分とする針状晶金
属磁性粒子粉末は現在、最も要求されている磁気
記録材料としての特性、すなわち、飽和磁化σsが
著しく大きく（例えば、90〜200emu/g）、保磁力
Hcが高い（例えば、600〜2000Oe）という特徴
を有しており、磁気記録媒体として塗布した場
合、大きい残留磁束密度Brと高い保磁力Hcを有
する為、高密度記録、高出力特性が得られるので
注目をあびており、近年実用化がなされている。
上述した通り、金属鉄を主成分とする針状晶金
属磁性粒子粉末は、同きな飽和磁化と高い保磁力
を有するものであるが、磁気記録媒体用に使用さ
れる金属鉄を主成分とする針状晶金属磁性粒子粉
末は1μｍ以下の非常に微細な粒子である為、粒
子の表面活性が非常に大きく、還元後に空気中に
取り出すと、空気中の酸素と急激に反応し、発熱
発火するという極めて不安定なものである。ま
た、同時に上記酸化反応により酸化物になつてし
まう為、大幅な磁気特性、殊に飽和磁化の減少を
きたし、目的とする高保磁力、高飽和磁化の磁性
粒子粉末を得ることができない。
従来、金属鉄を主成分とする針状晶金属磁性粒
子粉末をその特性を損なうことなく安定して空気
中に取り出す方法として各種の試みがなされてお
り、代表的な方法としては、
(1) 金属鉄を主成分とする針状晶金属磁性粒子粉
末を有機溶媒に浸漬する方法。
(2) 金属鉄を主成分とする針状晶金属磁性粒子粉
末を酸素分圧を調整した雰囲気中で処理する方
法。
がある。
いずれの場合にも、金属鉄を主成分とする針状
晶金属磁性粒子の粒子表面に酸化被膜を形成させ
るものである。
しかしながら、上記の方法による場合には、酸
化被膜の形成が十分ではなく、従つて、空気中に
取り出した後、金属鉄を主成分とする針状晶金属
磁性粒子は、空気により徐々に酸化されて、飽和
磁化σsが著しく減少してしまうという欠点があつ
た。
本発明者は、上述したところに鑑み、空気中に
安定して取り出すことができ、しかも、空気中に
取り出した後の酸化による飽和磁化σsの減少が防
止された酸化安定性の優れた金属鉄を主成分とす
る針状晶金属磁性粒子粉末を得るべく、種々検討
を重ねた結果、本発明に到達したのである。
即ち、本発明は、Fe2O3を主成分とする針状晶
酸化第二鉄粒子を出発原料とし、該出発原料を還
元性ガス中で加熱還元して得られた金属鉄を主成
分とする針状晶金属磁性粒子を有機溶剤中で浸漬
処理し、別した後、20℃〜50℃の温度範囲で乾
燥し、次いで、該粒子を水酸化第一鉄を含む水溶
液中に分散させ、該分散液のOH基濃度0.05〜3.0
ｍｏｌ／、50〜100℃の温度範囲において非酸化性
雰囲気中で処理することにより、上記金属鉄を主
成分とする針状晶金属磁性粒子の表面にマグネタ
イト被膜を生成させることよりなる金属鉄を主成
分とする針状晶金属磁性粒子粉末の製造法であ
る。
本発明の構成、効果を説明すれば以下の通りで
ある。
先ず、本発明の基礎とする諸知見について述べ
る。
本発明者は、前述した従来技術に鑑みて、空気
中に安定して取り出すことができ、しかも、空気
中に取り出した後の酸化による飽和磁化σsの減少
が防止された酸化安定性に優れた金属鉄を主成分
とする針状晶金属磁性粒子粉末を得る為には、粒
子表面に形成される金属酸化物被膜が空気等によ
る酸化を完全に阻止することができる程十分なも
のであり、且つ、金属鉄を主成分とする針状晶金
属磁性粒子粉末の特性を損なわないものでなけれ
ばならないと考えた。そして、このような金属酸
化物被膜の特性としては、できるだけ緻密で密着
性がよく薄いものが好ましいと考え、金属酸化物
被膜の種類及び製造方法について種々検討を重ね
た。
色材協会誌49巻11号（1976年）の659〜668ペー
ジには「さび発生のメカニズム」について詳述さ
れているが、その中に「さび層形成の過程におい
て電子伝導性のよいFe3O4が地金に密着し、これ
が均一に全面分布すれば安定した保護性被膜とな
る」また、「密着さび層は黒紫色を帯びSQメータ
ーで測定すると数10Ω〜数100Ωの電子伝導性を
持ち、地金に密着したFe3O4であることがわか
る」という記載が見られる。
本発明者は、この記載内容に着目し、緻密で密
着性のよい薄い金属酸化物被膜の種類としては、
マグネタイト被膜が最適であると考えたのであ
る。
そこで、本発明者は、緻密で密着性のよい薄い
マグネタイト被膜を形成する技術について種々検
討を重ねた結果、Fe2O3を主成分とする針状晶酸
化第二鉄粒子を出発原料とし、該出発原料を還元
性ガス中で加熱還元して得られた金属鉄を主成分
とする針状晶金属磁性粒子を有機溶剤中で浸漬処
理し、別した後、20℃〜50℃の温度範囲で乾燥
し、次いで、該粒子を水酸化第一鉄を含む水溶液
中に分散させ、該分散液のOH基濃度0.05〜3.0m
ｏｌ／、50〜100℃の温度範囲において非酸化性雰
囲気中で処理した場合には、粒子表面に緻密で密
着性のよい薄いマグネタイト被膜を形成すること
ができるので、空気中に安定して取り出すことが
でき、しかも、空気中に取り出した後の酸化によ
る飽和磁化σsの減少が防止された酸化安定性に優
れた金属鉄を主成分とする針状晶金属磁性粒子粉
末を得ることができるという新しい知見を得たの
である。
次に、本発明におけるマグネタイト被膜の生成
機構について述べる。
本発明者は、長年に亘り、酸化鉄の製造及び開
発にたずさわつているものであるが、その過程で
アルカリ水溶液（OH基を多く含んだ溶液）中で
Fe2O3にFe（OH）2を作用させた場合には、(1)の反
応式に従つてマグネタイトが生成されるという知
見を既に得ている。
Fe2O3＋Fe（OH）2→Fe3O4 ……(1)
このマグネタイトの生成機構は、Fe2O3とFe
（OH）2とがOH基を媒介して縮重合反応を生起
し、Fe2O3中に第一鉄イオンが拡散していくため
と考えている。
本発明によつて金属鉄を主成分とする針状晶金
属磁性粒子粉末の粒子表面に生成された金属酸化
物被膜を生成機構は、上述した(1)式により説明す
ることができる。
即ち、本発明は、金属鉄を主成分とする針状晶
金属磁性粒子を有機溶剤中で処理し、別した後
乾燥してから、金属鉄を主成分とする針状晶金属
磁性粒子の粒子表面では、有機溶媒を徐々に蒸発
させることによつて金属鉄を主成分とする針状晶
金属磁性粒子と空気とを穏やかに接触させること
によつて酸化物被膜（Fe2O3）が生成されている
ものと考えられる。
次いで、酸化物被膜（Fe2O3）が形成された金
属鉄を主成分とする針状晶金属磁性粒子は、水酸
化第一鉄を含む水溶液中に分散させ、該分散液の
OH基濃度0.05〜3.0mol/、50〜100℃の温度範
囲において非酸化性雰囲気中で処理されるから、
粒子表面に生成された酸化物被膜（Fe2O3）とFe
（OH）2とがOH基を媒介して縮重合反応を生起
し、マグネタイト被膜が生成されたものと考えら
れる。
本発明におけるマグネタイト被膜の生成機構
は、上述した通り、粒子表面に生成された酸化物
被膜（Fe2O3）とFe（OH）2とがOH基を媒介して
縮重合反応するのであるから、Fe（OH）2のFe2+
が粒子表面に生成された酸化物被膜（Fe2O3）中
に拡散していくものと考えられ、、従つて、緻密
で密着性のよい薄いマグネタイト被膜が形成され
るものと考えられる。
尚、従来、水溶液中で金属鉄を主成分とする針
状晶金属磁性粒子の粒子表面にマグネタイト被膜
を生成するものとしては、例えば、特公昭56−
12282号公報及び特開昭58−161704号公報に記載
の方法がある。
特公昭56−12282号公報に記載の方法は、金属
鉄を主成分とする針状晶金属磁性粒子を、温度５
℃〜70℃であり、〔OH-〕濃度が0.01〜18規定で
ある水酸化ナトリウム水溶液に懸濁させた後、該
懸濁液の温度を60℃〜100℃に調整し、次いで酸
素含有ガスを通気することによりマグネタイト被
膜を生成するものであるが、その生成機構は、金
属鉄を主成分とする針状晶金属磁性粒子を水酸化
ナトリウム水溶液に懸濁させることにより粒子表
面では、水酸化ナトリウム水溶液中に溶存してい
るわずかな酸素により酸素消費型の腐食反応Fe
＋2H+＋1/2O2→Fe2+＋H2Oが生起し、粒子表面
に生成されたFe2+は水溶液中のOH-と結合して
Fe（OH）2となり、更に、酸素含有ガスを通気す
ることにより、上記Fe（OH）2が酸化されてマグ
ネタイト被膜が生成されるものである。
特開昭58−161704号公報に記載の方法は、金属
鉄を主成分とする針状晶金属磁性粒子を液相ない
し気相中で酸素ガス量を調節しながら酸化処理し
て上記金属鉄を主成分とする針状晶金属磁性粒子
の表面に酸化被膜を形成し、次に、この処理粒子
を第一鉄塩とアルカリとを含む水溶液中に分散さ
せこれに酸化性ガスを吹き込んで反応させること
により、マグネタイト被膜を生成させるものであ
る。
上記特開昭58−161704号公報に記載の発明にお
ける被膜の生成機構について考察すると、金属鉄
を主成分とする針状晶金属磁性粒子を液相ないし
気相中で酸素ガス量を調節しながら酸化処理する
ことにより、粒子表面にマグネタイト被膜を形成
し、次いで該マグネタイト被膜が形成された粒子
を第一鉄塩とアルカリとを含む水溶液中に分散さ
せこれに酸化性ガスを吹き込んで反応させること
により、粒子表面に生成させた前記マグネタイト
被膜を粒子の外部に向かつてエピタキシヤル成長
させるものであると考えられる。
金属鉄を主成分とする針状晶金属磁性粒子の粒
子表面にマグネタイト被膜を生成するという上記
従来技術は、上述した通りいずれも酸化反応であ
るから、酸素含有ガスを通気する等の工程が必要
であるが、本発明による場合には、OH基を媒介
とする縮重合反応であるから、酸素含有ガスを通
気する等の工程を必要としない。
また、前出特開昭58−161704号公報詰載の発明
によれば、金属鉄を主成分とする針状晶金属磁性
粒子の粒子表面にマグネタイト被膜を生成させた
後、必ずアセトン洗浄をしており、これはマグネ
タイト被膜の十分な生成が行われていなかつた為
であろうと考えられる。
今、本発明者が行つた数多くの実験例からその
一部を例示して説明すれば次の通りである。
図１は、金属鉄を主成分とする針状晶金属磁性
粒子を空気中に取り出した時の飽和磁化σsの経時
による減少率を温度50℃、相対湿度80％の条件下
において飽和磁化の変化する前後における差
（Δσs）を変化前の飽和磁化で除した値を百分率
で示したものである。
図１中、曲線ａは、金属鉄を主成分とする針状
晶金属磁性粒子の粒子表面に本発明に方法により
マグネタイト被膜を生成した場合、曲線ｂは、金
属鉄を主成分とする針状晶金属磁性粒子を有機溶
剤に取り出した場合である。
図１から明らかな通り、本発明により得られた
金属鉄を主成分とする針状晶金属磁性粒子粉末
は、空気中に安定して取り出すことができ、しか
も、空気中に取り出した後の酸化による飽和磁化
σsの減少が防止された酸化安定性に優れたもので
あるから、非常に緻密で密着性のよい薄い被膜が
形成されていることを示すものであり、この被膜
の組成は、前述の色材協会誌の記載から明らかな
ように、マグネタイトであることが理解できる。
更に、本発明方法により得られた金属鉄を主成分
とする針状晶金属磁性粒子粉末の飽和磁化が大き
いことからもマグネタイトであることが理解でき
る。
次に、本発明方法実施にあたつての諸条件につ
いて述べる。
本発明においてFe2O3を主成分とする針状晶酸
化第二鉄粒子とは針状晶α―、β―、γ―含水酸
化第二鉄粒子、針状晶ヘマタイト粒子、針状晶マ
グネタイト粒子、針状晶マグヘマイト粒子並びに
これら粒子に従来から金属鉄を主成分とする針状
晶金属磁性粒子粉末の生成に際し添加されるCo、
Mg、Al、Cr、Zn、Ni、Ti、Mn、Sn、Pb等の
Fe以外の異種金属を含むものをいう。
これら出発原料として還元性ガス中で加熱還元
して得られたものは、針状晶金属鉄磁性粒子粉末
及びこれにFe以外の異種金属が固溶したもので
あり、本発明においてはこれらを金属鉄を主成分
とする針状晶金属磁性粒子粉末と総称した。
また、マグネタイト被膜は、出発原料の種類に
よつて当然にFe以外の異種金属が固溶したマグ
ネタイト被膜となるが、本発明においてはこれら
すべてをマグネタイト被膜と総称した。
本発明における有機溶剤としては、トルエン、
キシレン、メチルエチルケトン、酢酸ブチル等を
使用することができる。
本発明における有機溶剤処理後の乾燥温度は、
20℃〜50℃である。
乾燥温度は、金属鉄を主成分とする針状晶金属
磁性粒子の粒子表面に生成されたFe2O3被膜の厚
さに関与するものであり、20℃以下である場合に
は、Fe2O3被膜の生成が十分ではなく、50℃以上
である場合には、Fe2O3被膜の厚さが必要以上に
厚くなり飽和磁化σsの低下を招来することとな
る。
本発明における水酸化第一鉄を含む水溶液は、
第一鉄塩として硫酸第一鉄、塩化第一鉄を、アル
カリとして水酸化ナトリウム、水酸化カリウム等
を用いて生成することができる。本発明における
金属鉄を主成分とする針状晶金属磁性粒子の水酸
化第一鉄による処理は、水酸化第一鉄を含む水溶
液に分散させるか、又は、アルカリ中に分散させ
た後、第一鉄塩を添加するいずれの方法でもよ
い。
本発明におけるOH基濃度は、0.05〜3.0mol/
である。
0.05mol/以下である場合には、縮重合反応
が十分生起せず、マグネタイト被膜の生成が十分
ではない。
3.0mol/以上である場合もマグネタイト被膜
を生成させることはできるが、必要以上に添加す
る意味はなく、後の水洗工程で多量の水を必要と
する為、工業的、経済的ではない。
本発明における分散液の温度は、50〜100℃で
ある。分散液の温度は、処理時間に関与するもの
であり、温度を50℃以下とすれば、本発明におけ
るマグネタイト被膜の生成が難しく、生成すると
しても極めて長時間の処理を必要とする。
本発明方法を非酸化性雰囲気下で行うのは、分
散液中の水酸化第一鉄の酸化を防止するためであ
る。
何故ならば、第一鉄が水酸化物のとき始めて前
出(1)式の反応が生起するからである。
上記した通りの本発明によれば、金属鉄を主成
分とする針状晶金属磁性粒子の粒子表面に緻密で
密着性のよい薄いマグネタイト被膜を生成させる
ことにより、空気中に安定して取り出すことがで
き、しかも、空気中に取り出した後の酸化による
飽和磁化σsの減少が防止される等の酸化安定性に
優れた金属鉄を主成分とする針状晶金属磁性粒子
粉末を得ることができるので、現在最も要求され
ている高出力、高密度記録用磁性材料として好適
である。
また、本発明は、金属鉄を主成分とする針状晶
金属磁性粒子の粒子表面にマグネタイト被膜を生
成させるにあたり、空気等の酸素含有ガス吹き込
む等の工程が必要ではなく、工業性、経済性の面
で非常に有利である。
更に、本発明によれば、金属鉄を主成分とする
針状晶金属磁性粒子の粒子表面に生成されたマグ
ネタイト被膜は、緻密で密着性がよい為、マグネ
タイト被膜を生成した後はそのまま別、水洗、
乾燥するのみで空気中に安定して取り出すことが
できるという効果を有するものである。
次に、実施例並びに比較例により本発明を説明
する。
尚、以下の実施例並びに比較例における粒子の
軸比（長軸：短軸）、長軸はいずれも電子顕微鏡
写真から測定した数値の平均値で示した。
磁気特性の値は、試料振動型磁力計を用いて外
部磁場10KOeの下で測定した結果である。
また、酸化安定性は、温度50℃、相対湿度80％
の雰囲気で、７日間放置した後の飽和磁化減少率
（％）で示した。
実施例 １
出発原料として平均値で長軸0.8μ、長軸：短軸
＝10：１の針状晶α―FeOOH粒子を用い、該針
状晶α―FeOOH粒子粉末1500ｇを回転型レトル
ト容器中に投入し、駆動回転させながらH2ガス
を毎分40の割合で通気し、還元温度400℃で還
元して、金属鉄を主成分とする針状晶金属磁性粒
子粉末を生成した。
次いで、H2ガスをN2ガスに置換して冷却した
後、上記金属鉄を主成分とする針状晶金属磁性粒
子粉末を不活性ガスで十分置換された取り出し容
器に取り出した後、空気との接触を遮断してトル
エン溶液10に撹拌しながら投入した後、別
し、35℃で60分間乾燥して粒子表面に酸化被膜が
生成された金属鉄を主成分とする針状晶金属磁性
粒子粉末を得た。
上記酸化被膜が生成された金属鉄を主成分とす
る針状晶金属磁性粒子粉末1000ｇを2.3―Ｎの水
酸化ナトリウム水溶液９に撹拌しながら投入
し、次いで、0.358molの硫酸第一鉄と水を投入
して全量を10（OH基濃度2.0mol/）とした
後、得られた分散液を100℃に昇温保持し、可及
的に空気の混入を防止して良く撹拌しながら５時
間後にスラリーを取り出し、水洗、別し、60℃
で乾燥して金属鉄を主成分とする針状晶金属磁性
粒子粉末を得た。
図２は、得られた金属鉄を主成分とする針状晶
金属磁性粒子粉末のＸ線回折図である。
図２中、ピークＡはマグネタイトのピークを示
し、ピークＢは金属鉄のピークを示す。
得られたマグネタイト被膜を有する金属鉄を主
成分とする針状晶金属磁性粒子粉末は電子顕微鏡
観察の結果、長軸0.7μｍ、長軸：短軸＝８：１で
あつた。
また磁気特性は、飽和磁化σs128emu/g、保磁
力Hc1250Oe、飽和磁化の減少率4.0％であつた。
実施例 ２〜15
出発原料の種類、還元温度、有機溶剤の種類、
乾燥温度、第一鉄塩の種類並びに量、OH基濃
度、温度を種々変化させた以外は実施例１と同様
にして金属鉄を主成分ととする針状晶金属磁性粒
子粉末を得た。
主要製造条件及び諸特性を表１に示す。
実施例２〜15で得られた金属鉄を主成分とする
針状晶金属磁性粒子粉末は、Ｘ線回折の結果、い
ずれもマグネタイトと金属鉄のピークを示してい
た。
比較例 １
実施例１において得られた粒子表面に酸化被膜
が生成された金属鉄を主成分とする針状晶金属磁
性粒子粉末は、電子顕微鏡観察の結果、長軸0.8μ
ｍ、長軸：短軸＝８：１であつた。
また、磁気特性は、飽和磁化σs135emu/g、保
磁力Hc1320Oe、飽和磁化の減少率22％であつ
た。
【表】DETAILED DESCRIPTION OF THE INVENTION The present invention creates a thin magnetite film that is dense and has good adhesion on the particle surface of acicular metal magnetic particles whose main component is metallic iron, so that they are stable in the air. A method for producing acicular metal magnetic particles whose main component is metallic iron, which can be taken out and has excellent oxidation stability, such as preventing a decrease in saturation magnetization σs due to oxidation after being taken out into the air. It is related to. In recent years, as magnetic recording and reproducing equipment has become smaller and lighter, there has been an increasing need for higher performance recording media. That is, high-density recording, high output characteristics, and especially improvement in frequency characteristics are required. The characteristics of a magnetic material suitable for satisfying the above requirements for a magnetic recording medium are that it has a large saturation magnetization and a high coercive force. By the way, magnetic materials conventionally used in magnetic recording media include magnetite, maghemite,
Magnetic powder such as chromium dioxide, these magnetic powders have saturation magnetization σs70~85emu/g and coercive force Hc250~
It has 500Oe. In particular, the σs of the above oxide magnetic particles is at most 85e.
mu/g, and generally σs is 70 to 80 emu/g, which is the main reason for limiting the reproduction output and recording density. Furthermore, Co-magnetite and Co-maghemite magnetic powders containing Co are also used, but these magnetic particle powders have a high coercive force Hc of 400 to 800 Oe. Magnetization σs is 60-80emu/g
This is low. Recently, there has been active development of magnetic particles with characteristics suitable for high output and high density recording, that is, magnetic particles with large saturation magnetization and high coercive force. There is an acicular metal magnetic particle powder whose main component is metallic iron, which is obtained by heating and reducing acicular ferric oxide particles whose main component is Fe 2 O 3 in a reducing gas. As mentioned above, acicular metal magnetic particles mainly composed of metallic iron currently have the most required properties as a magnetic recording material, that is, the saturation magnetization σs is extremely large (for example, 90 to 200 emu/g). , coercive force
It is characterized by a high Hc (e.g. 600 to 2000 Oe), and when coated as a magnetic recording medium, it has a large residual magnetic flux density Br and a high coercive force Hc, so high density recording and high output characteristics can be obtained. Therefore, it has attracted attention and has been put into practical use in recent years. As mentioned above, acicular metal magnetic particles mainly composed of metallic iron have similar saturation magnetization and high coercive force; The acicular metal magnetic particles are very fine particles of 1 μm or less, so the surface activity of the particles is very high, and when taken out into the air after reduction, it rapidly reacts with oxygen in the air, causing heat generation and ignition. This is extremely unstable. At the same time, since the oxidation reaction turns into an oxide, the magnetic properties, especially the saturation magnetization, are significantly reduced, making it impossible to obtain the desired magnetic particles with high coercive force and high saturation magnetization. In the past, various attempts have been made to stably extract acicular metal magnetic particles containing metallic iron as a main component into the air without impairing their properties.The representative methods include (1) A method of immersing acicular metal magnetic particles whose main component is metallic iron in an organic solvent. (2) A method of processing acicular metal magnetic particles whose main component is metallic iron in an atmosphere with a controlled oxygen partial pressure. There is. In either case, an oxide film is formed on the surface of the acicular metal magnetic particles containing metallic iron as a main component. However, in the case of the above method, the formation of an oxide film is not sufficient, and therefore, after being taken out into the air, the acicular metal magnetic particles whose main component is metal iron are gradually oxidized by the air. However, there was a drawback that the saturation magnetization σs decreased significantly. In view of the above, the present inventor has developed a metal iron with excellent oxidation stability that can be stably taken out into the air and which prevents the saturation magnetization σs from decreasing due to oxidation after being taken out into the air. The present invention was achieved as a result of various studies in order to obtain acicular metal magnetic particles containing as a main component. That is, the present invention uses acicular ferric oxide particles containing Fe 2 O 3 as a main component as a starting material, and uses metallic iron obtained by heating and reducing the starting material in a reducing gas as a main component. The acicular metal magnetic particles are immersed in an organic solvent, separated and dried at a temperature range of 20°C to 50°C, and then the particles are dispersed in an aqueous solution containing ferrous hydroxide, OH group concentration of the dispersion: 0.05 to 3.0
mol/, by processing in a non-oxidizing atmosphere in a temperature range of 50 to 100°C to form a magnetite coating on the surface of the acicular metal magnetic particles whose main component is metal iron. This is a method for producing acicular metal magnetic particles as a main component. The structure and effects of the present invention will be explained as follows. First, various findings on which the present invention is based will be described. In view of the above-mentioned prior art, the present inventors have discovered a material with excellent oxidation stability that can be stably taken out into the air and which prevents a decrease in saturation magnetization σs due to oxidation after being taken out into the air. In order to obtain acicular metal magnetic particles whose main component is metallic iron, the metal oxide coating formed on the particle surface is sufficient to completely prevent oxidation by air, etc. In addition, it was thought that the powder must not impair the characteristics of the acicular metal magnetic particles whose main component is metallic iron. Considering the characteristics of such a metal oxide film, it is preferable that it be as dense as possible, have good adhesion, and be as thin as possible, and various studies have been conducted on the types and manufacturing methods of the metal oxide film. Pages 659 to 668 of the Journal of the Japan Coloring Materials Association Vol. 49, No. 11 (1976) provides a detailed explanation of the ``mechanism of rust formation,'' and it includes ``In the process of rust layer formation, Fe 3 , which has good electronic conductivity, If O 4 adheres to the base metal and is uniformly distributed over the entire surface, it will form a stable protective film.''Also, ``The adhesive rust layer has a blackish-purple color and has an electronic conductivity of several tens to hundreds of ohms when measured with an SQ meter.'' It can be seen that it is Fe 3 O 4 that has a strong bond and adheres to the base metal.'' The present inventor paid attention to the contents of this description, and the types of thin metal oxide films that are dense and have good adhesion are as follows:
They thought that a magnetite coating would be optimal. Therefore, as a result of various studies on techniques for forming a thin magnetite film that is dense and has good adhesion, the inventors of the present invention have developed a method using acicular ferric oxide particles containing Fe 2 O 3 as the main component as a starting material. The acicular metal magnetic particles containing metallic iron as a main component obtained by thermally reducing the starting material in a reducing gas are immersed in an organic solvent, separated, and then heated in a temperature range of 20°C to 50°C. Then, the particles are dispersed in an aqueous solution containing ferrous hydroxide, and the OH group concentration of the dispersion is 0.05 to 3.0 m.
When treated in a non-oxidizing atmosphere in the temperature range of 50 to 100℃, a thin magnetite film with dense and adhesive properties can be formed on the particle surface, so it can be stably taken out into the air. Moreover, it is possible to obtain acicular metal magnetic particles whose main component is metallic iron, which has excellent oxidation stability and which prevents a decrease in saturation magnetization σs due to oxidation after being taken out into the air. I gained new knowledge. Next, the generation mechanism of the magnetite film in the present invention will be described. The present inventor has been involved in the production and development of iron oxide for many years, and in the process, he encountered problems in an alkaline aqueous solution (a solution containing many OH groups).
We have already obtained the knowledge that when Fe(OH) 2 is reacted with Fe 2 O 3 , magnetite is produced according to the reaction formula (1). Fe 2 O 3 + Fe(OH) 2 →Fe 3 O 4 ...(1) The formation mechanism of this magnetite is that Fe 2 O 3 and Fe
It is thought that this is because (OH) 2 causes a polycondensation reaction via OH groups, and ferrous ions diffuse into Fe 2 O 3 . The mechanism for forming the metal oxide film on the particle surface of the acicular metal magnetic particle powder containing metallic iron as a main component according to the present invention can be explained by the above-mentioned equation (1). That is, in the present invention, acicular metal magnetic particles containing metallic iron as a main component are treated in an organic solvent, separated and dried, and then processed into particles of acicular metal magnetic particles containing metallic iron as a main component. On the surface, an oxide film (Fe 2 O 3 ) is formed by gradually evaporating the organic solvent and gently bringing the acicular metal magnetic particles, which are mainly composed of metallic iron, into contact with air. It is thought that this has been done. Next, the acicular metal magnetic particles mainly composed of metallic iron on which an oxide film (Fe 2 O 3 ) has been formed are dispersed in an aqueous solution containing ferrous hydroxide, and the dispersion is
Because it is processed in a non-oxidizing atmosphere with an OH group concentration of 0.05 to 3.0 mol/ and a temperature range of 50 to 100°C,
Oxide film (Fe 2 O 3 ) generated on the particle surface and Fe
It is thought that (OH) 2 caused a polycondensation reaction via the OH group, resulting in the formation of a magnetite film. As mentioned above, the formation mechanism of the magnetite film in the present invention is that the oxide film (Fe 2 O 3 ) generated on the particle surface and Fe(OH) 2 undergo a polycondensation reaction via OH groups. , Fe(OH) 2 , Fe2 +
It is thought that the particles diffuse into the oxide film (Fe 2 O 3 ) formed on the particle surface, and therefore, a thin magnetite film that is dense and has good adhesion is formed. Conventionally, as a method for forming a magnetite film on the particle surface of acicular metal magnetic particles containing metallic iron as a main component in an aqueous solution, for example,
There are methods described in JP-A No. 12282 and JP-A-58-161704. In the method described in Japanese Patent Publication No. 56-12282, acicular metal magnetic particles containing metallic iron as a main component are heated at a temperature of 5.
After suspending in an aqueous sodium hydroxide solution with a temperature of 70°C to 70°C and an [OH - ] concentration of 0.01 to 18N, the temperature of the suspension was adjusted to 60°C to 100°C, and then an oxygen-containing gas was added. A magnetite coating is produced by aerating the particles, and the mechanism of its formation is that acicular metal magnetic particles containing metallic iron as the main component are suspended in an aqueous sodium hydroxide solution. Oxygen-consuming corrosion reaction due to a small amount of oxygen dissolved in sodium aqueous solution
+2H + +1/2O 2 →Fe 2+ +H 2 O is generated, and the Fe 2+ generated on the particle surface combines with OH - in the aqueous solution.
The Fe(OH) 2 becomes Fe(OH) 2 and further, by passing an oxygen-containing gas, the Fe(OH) 2 is oxidized and a magnetite film is generated. The method described in JP-A No. 58-161704 involves oxidizing acicular metal magnetic particles containing metallic iron as a main component while controlling the amount of oxygen gas in a liquid phase or gas phase to remove the metallic iron. An oxide film is formed on the surface of the acicular metal magnetic particles that are the main component, and then the treated particles are dispersed in an aqueous solution containing ferrous salt and an alkali, and an oxidizing gas is blown into the solution to cause a reaction. This produces a magnetite film. Considering the film formation mechanism in the invention described in JP-A No. 58-161704, it is found that acicular metal magnetic particles containing metal iron as a main component are grown in a liquid phase or a gas phase while adjusting the amount of oxygen gas. A magnetite coating is formed on the particle surface by oxidation treatment, and then the particles with the magnetite coating formed thereon are dispersed in an aqueous solution containing a ferrous salt and an alkali, and an oxidizing gas is blown into the solution to cause a reaction. It is thought that this causes the magnetite coating formed on the particle surface to grow epitaxially toward the outside of the particle. The above-mentioned conventional techniques for producing a magnetite film on the particle surface of acicular metal magnetic particles containing metallic iron as a main component are all oxidation reactions as described above, and therefore require steps such as aeration of oxygen-containing gas. However, in the case of the present invention, since the polycondensation reaction is mediated by OH groups, there is no need for steps such as passing oxygen-containing gas through the reaction. Furthermore, according to the invention disclosed in the above-mentioned Japanese Patent Application Laid-Open No. 58-161704, after a magnetite film is formed on the surface of the acicular metal magnetic particles whose main component is metal iron, cleaning with acetone must be carried out. This is thought to be because the magnetite film was not sufficiently formed. The following is a description of some of the many experimental examples conducted by the present inventor. Figure 1 shows the rate of decrease in saturation magnetization σs over time when acicular metal magnetic particles containing metallic iron as the main component are taken out into the air. The value obtained by dividing the difference (Δσs) before and after the change by the saturation magnetization before the change is expressed as a percentage. In FIG. 1, curve a represents the case where a magnetite film is formed on the particle surface of acicular metal magnetic particles mainly composed of metallic iron, and curve b represents the case where a magnetite film is formed on the particle surface of acicular magnetic particles mainly composed of metallic iron. This is a case where crystalline metal magnetic particles are taken out in an organic solvent. As is clear from FIG. 1, the acicular metal magnetic particle powder containing metallic iron as a main component obtained by the present invention can be stably taken out into the air, and is not oxidized after being taken out into the air. This indicates that a very dense and thin film with good adhesion is formed because it has excellent oxidation stability and prevents the decrease in saturation magnetization σs due to As is clear from the description in the Coloring Materials Association magazine, it can be understood that it is magnetite.
Furthermore, it can be understood that the acicular metal magnetic particles obtained by the method of the present invention, which are mainly composed of metallic iron, have a large saturation magnetization, and therefore are magnetite. Next, various conditions for carrying out the method of the present invention will be described. In the present invention, acicular ferric oxide particles containing Fe 2 O 3 as a main component include acicular α-, β-, γ-hydrated ferric oxide particles, acicular hematite particles, and acicular magnetite. particles, acicular crystal maghemite particles, and Co, which is conventionally added to these particles when producing acicular metal magnetic particles whose main component is metallic iron.
Mg, Al, Cr, Zn, Ni, Ti, Mn, Sn, Pb etc.
This refers to materials containing dissimilar metals other than Fe. These starting materials obtained by heating reduction in a reducing gas are acicular crystal metal iron magnetic particle powder and a solid solution of different metals other than Fe in this powder, and in the present invention, these are used as metal iron magnetic particles. It was collectively called acicular metal magnetic particle powder whose main component is iron. Further, depending on the type of starting material, the magnetite coating naturally becomes a magnetite coating in which different metals other than Fe are dissolved in solid solution, but in the present invention, all of these are collectively referred to as the magnetite coating. Examples of the organic solvent in the present invention include toluene,
Xylene, methyl ethyl ketone, butyl acetate, etc. can be used. The drying temperature after organic solvent treatment in the present invention is
The temperature is between 20°C and 50°C. The drying temperature is related to the thickness of the Fe 2 O 3 film formed on the particle surface of the acicular metal magnetic particles whose main component is metallic iron, and if the drying temperature is 20°C or less, the Fe 2 O 3 film is If the production of the O 3 film is not sufficient and the temperature is 50° C. or higher, the thickness of the Fe 2 O 3 film becomes thicker than necessary, resulting in a decrease in saturation magnetization σs. The aqueous solution containing ferrous hydroxide in the present invention is
It can be produced using ferrous sulfate or ferrous chloride as the ferrous salt, and sodium hydroxide, potassium hydroxide, etc. as the alkali. In the present invention, the acicular metal magnetic particles containing metallic iron as a main component are treated with ferrous hydroxide by dispersing them in an aqueous solution containing ferrous hydroxide or in an alkali. Any method of adding iron salt may be used. The OH group concentration in the present invention is 0.05 to 3.0 mol/
It is. If it is 0.05 mol/or less, the polycondensation reaction will not occur sufficiently, and the magnetite film will not be sufficiently formed. Although it is possible to form a magnetite film at a concentration of 3.0 mol/or more, there is no point in adding more than necessary, and a large amount of water is required in the subsequent water washing process, which is not industrially or economically viable. The temperature of the dispersion liquid in the present invention is 50 to 100°C. The temperature of the dispersion liquid is related to the processing time, and if the temperature is set to 50° C. or lower, it is difficult to produce the magnetite film in the present invention, and even if it is produced, an extremely long processing time is required. The reason why the method of the present invention is carried out under a non-oxidizing atmosphere is to prevent oxidation of ferrous hydroxide in the dispersion. This is because the reaction of formula (1) above occurs only when ferrous iron is a hydroxide. According to the present invention as described above, by forming a thin magnetite film that is dense and has good adhesion on the particle surface of acicular metal magnetic particles whose main component is metallic iron, they can be stably taken out into the air. Moreover, it is possible to obtain an acicular metal magnetic particle powder mainly composed of metallic iron, which has excellent oxidation stability, such as preventing a decrease in saturation magnetization σs due to oxidation after being taken out into the air. Therefore, it is suitable as a magnetic material for high-output, high-density recording, which is currently most required. In addition, the present invention does not require a process such as blowing oxygen-containing gas such as air when forming a magnetite film on the particle surface of acicular metal magnetic particles containing metallic iron as a main component, and is industrially and economically efficient. It is very advantageous in terms of Furthermore, according to the present invention, the magnetite film formed on the particle surface of the acicular metal magnetic particles containing metallic iron as a main component is dense and has good adhesion, so that after the magnetite film is formed, it can be separated as it is. washing with water,
This has the effect that it can be stably taken out into the air just by drying. Next, the present invention will be explained with reference to Examples and Comparative Examples. In addition, the axial ratio (long axis: short axis) and long axis of particles in the following Examples and Comparative Examples are both shown as average values of numerical values measured from electron micrographs. The magnetic property values are the results measured under an external magnetic field of 10 KOe using a sample vibrating magnetometer. In addition, oxidation stability is measured at a temperature of 50°C and a relative humidity of 80%.
It is expressed as the saturation magnetization reduction rate (%) after being left for 7 days in an atmosphere of Example 1 Using acicular α-FeOOH particles with an average major axis of 0.8 μ and a major axis:minor axis ratio of 10:1 as a starting material, 1500 g of the acicular α-FeOOH particles were placed in a rotary retort container. H 2 gas was passed through at a rate of 40°C per minute while driving and rotating, and reduction was carried out at a reduction temperature of 400°C to produce acicular metal magnetic particles containing metallic iron as a main component. Next, after cooling by replacing H 2 gas with N 2 gas, the acicular metal magnetic particle powder containing metallic iron as a main component is taken out into a container that has been sufficiently replaced with inert gas, and then replaced with air. The acicular crystalline metal magnetic particles whose main component is metallic iron are obtained by blocking contact with the toluene solution 10 and adding it to the toluene solution 10 with stirring, then separating it and drying it at 35°C for 60 minutes to form an oxide film on the particle surface. A powder was obtained. 1,000 g of the acicular metal magnetic particles containing metallic iron as the main component on which the oxide film has been formed are added to a 2.3-N sodium hydroxide aqueous solution 9 with stirring, and then 0.358 mol of ferrous sulfate and water are added. was added to bring the total amount to 10 (OH group concentration 2.0 mol/), and the resulting dispersion was heated and maintained at 100°C for 5 hours while stirring well while preventing air from entering as much as possible. After that, take out the slurry, wash it with water, separate it, and store it at 60℃.
The powder was dried to obtain acicular metal magnetic particles containing metallic iron as a main component. FIG. 2 is an X-ray diffraction diagram of the obtained acicular metal magnetic particles whose main component is metallic iron. In FIG. 2, peak A indicates the peak of magnetite, and peak B indicates the peak of metallic iron. The obtained acicular metal magnetic particles having a magnetite coating and having metallic iron as a main component were observed by electron microscopy to have a long axis of 0.7 μm and a ratio of long axis to short axis of 8:1. The magnetic properties were a saturation magnetization σs of 128 emu/g, a coercive force of Hc of 1250 Oe, and a reduction rate of saturation magnetization of 4.0%. Examples 2 to 15 Types of starting materials, reduction temperatures, types of organic solvents,
Acicular metal magnetic particles containing metallic iron as a main component were obtained in the same manner as in Example 1, except that the drying temperature, type and amount of ferrous salt, OH group concentration, and temperature were varied. Table 1 shows the main manufacturing conditions and various characteristics. As a result of X-ray diffraction, the acicular metal magnetic particles mainly composed of metallic iron obtained in Examples 2 to 15 all showed peaks of magnetite and metallic iron. Comparative Example 1 As a result of electron microscopy observation, the acicular metal magnetic particle powder mainly composed of metallic iron with an oxide film formed on the particle surface obtained in Example 1 was found to have a long axis of 0.8μ.
m, major axis: minor axis = 8:1. The magnetic properties were as follows: saturation magnetization σs 135 emu/g, coercive force Hc 1320 Oe, and saturation magnetization reduction rate 22%. 【table】
図１は、金属鉄を主成分とする針状晶金属磁性
粒子を空気中に取り出した時の飽和磁化σsの経時
による変化を示したものである。図２は、実施例
１で得られた金属鉄を主成分とする針状晶金属磁
性粒子粉末のＸ線回折図である。
FIG. 1 shows the change over time in the saturation magnetization σs when acicular metal magnetic particles containing metallic iron as a main component are taken out into the air. FIG. 2 is an X-ray diffraction diagram of the acicular metal magnetic particles obtained in Example 1 and containing metallic iron as a main component.
Claims (1)
を出発原料とし、該出発原料を還元性ガス中で加
熱還元して得られた金属鉄を主成分とする針状晶
金属磁性粒子を有機溶剤中で浸漬処理し、別し
た後、20℃〜50℃の温度範囲で乾燥し、次いで、
該粒子を水酸化第一鉄を含む水溶液中に分散さ
せ、該分散液のOH基濃度0.05〜3.0mol/、50〜
100℃の温度範囲において非酸化性雰囲気中で処
理することにより、上記金属鉄を主成分とする針
状晶金属磁性粒子の粒子表面にマグネタイト被膜
を生成させることを特徴とする金属鉄を主成分と
する針状晶金属磁性粒子粉末の製造法。1 Acicular crystal metal containing metallic iron as a main component obtained by using acicular ferric oxide particles containing Fe 2 O 3 as a main component as a starting material and reducing the starting material by heating in a reducing gas The magnetic particles are immersed in an organic solvent, separated, dried at a temperature range of 20°C to 50°C, and then
The particles are dispersed in an aqueous solution containing ferrous hydroxide, and the OH group concentration of the dispersion is 0.05 to 3.0 mol/, 50 to
Mainly composed of metallic iron, characterized in that a magnetite film is formed on the particle surface of the acicular metal magnetic particles mainly composed of metallic iron by processing in a non-oxidizing atmosphere in a temperature range of 100°C. A method for producing acicular metal magnetic particle powder.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP59062569A JPS60204803A (en) | 1984-03-29 | 1984-03-29 | Production of magnetic particle powder of acicular crystal metal consisting essentially of metallic iron |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP59062569A JPS60204803A (en) | 1984-03-29 | 1984-03-29 | Production of magnetic particle powder of acicular crystal metal consisting essentially of metallic iron |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JPS60204803A JPS60204803A (en) | 1985-10-16 |
| JPS6354041B2 true JPS6354041B2 (en) | 1988-10-26 |
Family
ID=13204053
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP59062569A Granted JPS60204803A (en) | 1984-03-29 | 1984-03-29 | Production of magnetic particle powder of acicular crystal metal consisting essentially of metallic iron |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JPS60204803A (en) |
-
1984
- 1984-03-29 JP JP59062569A patent/JPS60204803A/en active Granted
Also Published As
| Publication number | Publication date |
|---|---|
| JPS60204803A (en) | 1985-10-16 |
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