• 한국세라믹학회지
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• 제34권5호
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• pp.453-460
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• 1997

Sr-ferrite having magnetoplumbite structure is similar to Ba-ferrite in magnetic characteristics, but better magnetic characteristics for using motor application. To improve remanence magnetic flux density(Br) and coercive force(iHc), it is necessary that sintered ferrites must have high density and grain size less than 1 $\mu$m. By varying n values in SrO.nFe2O3 basic composition, calcination temperature, and BaO addition, Sr-ferrite powder and sintered specimen was prepared. The n values, calcination temperature, and BaO addition affected secondary phase formation, particle size, and particle shape. BaO addition enhanced Fe2O3 secondary phase and hexagonal shape particle. Fe2O3 phase reduced sintered density which greatly decreased Br.

• 한국세라믹학회지
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• 제24권1호
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• pp.17-22
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• 1987

This study is to detect the synthetic condition for the formation of Sr-Ferrite(SrFe12O19) by hydrothermally reaction. Mixed suspension of SrCl26H2O and FeCl3 6H2O were fixed on pH and were subjected to autoclavings at various temperature(150∼300$^{\circ}C$), reaction time(2hrs.∼48hrs.). The Sr-Ferrite powders were synthesized at 150$^{\circ}C$ for 36hrs, 200$^{\circ}C$ for 4hrs and 250$^{\circ}C$ for 2hrs. Synthesized powders were increased particle sizes at longer reaction time and higher reaction temperature. It has hexagonal ferrite M-type structure and has high purity of SrO.5.6 Fe2O3 composition.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2001년도 추계학술대회 논문집 Vol.14 No.1
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• pp.284-287
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• 2001

Multi-pole anisotropic Sr-ferrite sintered magnets has been studied by powder injection molding under applied magnetic field. The orientation of anisotropic Sr-ferrite powders higher than 80% during injection molding is achieved at the following conditions; apparent viscosity lower then 2500 poise in 1000 $sec^{-1}$ shear rate and applied magnetic field higher then 4 kOe. For the high fluidity and strength of injection molded compact, and the effective binder removal without defects during solvent extraction and thermal debinding, the optimum multi-binder composition is paraffin wax(PW)/carnauba wax(CW)/HDPE = 50/25/25 wt%. The rate of binder removal is proportional to the mean particle size of Sr-ferrite powders whereas it is inversely proportional to the content of Sr-ferrite powders and the sample thickness. The high magnetic properties of Sr-ferrite sintered magnets are; 3.8 kG of remanent flux density, 3.4 kOe of intrinsic coercivity, and 1.2 kG of surface flux density (l-mm-thick) in the direction of applied magnetic field.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2001년도 추계학술대회 논문집
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• pp.284-287
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• 2001

Multi-pole anisotropic Sr-fertile sintered magnets has been studied by powder injection molding under applied magnetic field. The orientation of anisotropic Sr-ferrite powders higher than 80% during injection molding is achieved at the following conditions; apparent viscosity lower then 2500 poise in 1000 sec$\^$-1/ shear rate and applied magnetic field higher then 4 kOe. For the high fluidity and strength of injection molded compact, and the effective binder removal without defects during solvent extraction and thermal debinding, the optimum multi-binder composition is paraffin wax(PW)/carnauba wax(CW)/HDPE = 50/25/25 wt%. The rate of binder removal is proportional to the mean particle size of Sr-ferrite powders whereas it is inversely proportional to the content of Sr-ferrite powders and the sample thickness. The high magnetic properties of Sr-ferrite sintered magnets are; 3.8 kG of remanent flux density, 3.4 kOe of intrinsic coercivity, and 1.2 kG of surface flux density (1-mm-thick) in the direction of applied magnetic field.

• 한국세라믹학회지
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• 제42권10호
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• pp.672-677
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• 2005

In this study we prepared the Sr-ferrite powders and magnet by a molten salt method using the (NaCl+KCl) salt mixture. Starting materials of $Fe_{2}$$O_{3}$ and Sr$Co_{3}$ were mixed as the molar ratio of 5.70:1, and 0.08 mol$ \% $ $Al_{2}$$O_{3}$, 0.10 mo1$ \% $ Si$O_{2}$ and 0.12 mo1$ \% $ CaO were added as additives. Sr-ferrite powders synthesized at the reaction temperatures of 800$\∼$1200$ ^{\circ}C $ showed the typical M-type hexagonal ferrite phase, and hexagonal plate-like morphology with uniform distribution of 1$\∼$3 $\mu$m particle size. The bulk density of the sintered Sr-ferrite magnet prepared with powders by the molten salt method showed the maximum density of 4.82 g/$cm^{3}$ at the sintering temperature of 1200$^{\circ}C $. The maxima of remanent flux density (Br, 45 emu/g) and coercive force (iHc, 3.75 kOe) occurred at the sintering temperatures of 1150$ ^{\circ}C$ and 1200$^{\circ}C $.

• 자원리싸이클링
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• 제7권4호
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• pp.43-49
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• 1998

다양한 hard ferrite용 국산 산화철(${\alpha}Fe_2O_3$)의 분체특성이 Sr-ferrite의 자기특성에 미치는 영향을 조사하였다. 산화철의 평균입도와 입도분호는 철강 냉연공장의 염산폐액 정제방법에 따라 서로 구분되었으며, Sr-ferrite의 자기특성과 미세조직에 큰 영향을 주었다. Ruthner 산화철의 응집현상은 Sr-ferrite의 포화자화를 감소시켰으며, Chemirite(CY) 산화철의 $0.80{\mu}\textrm{m}$이상의 조대한 입자는 Sr-ferrite의 고유보자력을 감소시켰다. 평균입도가 $0.14\mu\textrm{m}$로 가장 작은 Chemirite 포항2냉연(EP) 산화철을 사용하여, 5.8mol, $1150^{\circ}C$/1시간의 하소조건에서 제조된 Sr-ferrite는 포화자화가 68.2emu/g, 고유보자력이 4300Oe인 최적의 자기특성을 나타내었다.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1994년도 하계학술대회 논문집 C
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• pp.1314-1316
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• 1994

$0.36[wtx]Sio_2$ and $0.1[wtx]H_3BO_3$ were added to strontium ferrite magnets of the magnetoplumbite phase SrO $5.7Fe_2O_3$. This experiment was carried out to investigate the effects of particle size distribution as a function of milling time(20,30,40,50,60,70 hours) on the magnetic properties of SrO $5.7Fe_2O_3$ ferrite magnet. The B-H Curve, density and the degree of orientation were measured. The optimal conditions of making magnets and properties of a typical sample are the following : The milling time was 60 hours. Magnetic and physical properties are $B_r$=4000[G], $_BH_c$=3330[Oe], $_IH_c$=3525[Oe], (BH)max=3.786 [MGOe], density= $5.0063g/cm^2$, orientation factor f=0.813.

• 한국자기학회지
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• 제5권5호
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• pp.740-744
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• 1995

For the fabrication of a multi-pole anisotropic Sr-ferrite magnet by powder injection molding, it is important to control effectively the alignment of magnetic powders during the injection molding process. The effect of the fluidity of powder/binder mixture on the powder alignment was studied with changing the particle sizes and the volume fraction of Sr-ferrite magnetic powders. The critical volume fraction of Sr-ferrite powders increases from 58 vol.% to 64 vol.% as the mean powder size increases from $0.8\;\mu\textrm{m}$ to $1.2\;\mu\textrm{m}$. A Sr-ferrite powder alignment greater than 80 % is achieved at the conditions of an apparent viscosity lower than 1000 poise at $1600\;sec^{-1}$ shear rate, an applied magnetic field higher than 4 kOe, and a powder volume fraction 8 vol.% lower than the critical fraction. The powder alignment obtained during the injection molding process is not much affected by the subsequent processes of debinding and sintering, showing the magnetic properties of 3.8 kG of remanent flux density and 3.37 kOe of intrinsic coercivity.

• 자원리싸이클링
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• 제12권6호
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• pp.19-25
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• 2003

제철소 냉연 공정의 염산 폐액에서 ruthner process 공법으로 제조된 산화철을 사용하여 2차 배소 온도변화에 따른 산화철의 분체 특성을 조사하였고, 산화철과 스트론튬을 건식 혼합 및 가소후 Sr-ferrite 자석을 제조하여 자기적 물리적 특성을 조사하였다. Ruthner proces의 산화철을 2차 배소를 실시한 경우, Cl- 함량이 적고 분체 특성이 안정적인 배소온도는 $800^{\circ}C$ 부근으로, 평균 입자(APS)는 1.5 $mu extrm{m}$, apparent bulk density(ABD)는 1.4 g/$m\ell$ 이며, Cl- 함유량은 0.05% 이하를 나타내었다. Ruthner process에서 제조된 산화철을 vibrating disk mill에서 1차 분쇄를 실시한 경우, Sr-ferrite magnet의 보자력(HcJ)은 229 kA/m에서 251 kA/m로 향상하였다. Sr-ferrite magnet의 소결 온도 변화에 따른 잔류자속밀도와 보자력의 희귀식은 Br≒-0.258HcJ＋494의 함수 관계를 나타내고 있으며, 성형 중 가한 자장 방향과 수직방향에 따른 수축비는 산화철의 2차 배소 온도 $800^{\circ}C$까지는 1.6으로 안정적인 판상형으로 결정 성장을 나타내고 있으나, 그 이상의 온도로 2차 배소한 산화철을 사용한 경우에는 소결에서 결정이 더 커진 것으로 판단된다.

• 한국자기학회지
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• 제27권1호
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• pp.23-29
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• 2017

시료 크기별 자화 역전과 자기 상호작용이 보자력에 미치는 영향을 조사한 결과, 자구생성보다 자벽고착에 의한 자화 역전 현상이 지배적인 시료일수록 보자력과 각형비가 컸다. 이와 같은 현상은 자벽이 낟알 경계면이나 시료 내부에 존재하는 고착점에 강하게 포획되기 때문인 것으로 판단된다. 한편 자기 상호작용을 분석한 결과, 시료의 크기에 무관하게 모든 시료는 쌍극자 상호작용이 지배적인 상호작용 기구이며, 쌍극자 상호작용이 강한 시료일수록 보자력이 작았다. 따라서 보자력은 자화 역전 현상, 자기 상호작용 기구와 세기에도 깊이 관련됨을 알 수 있다.