• Journal of Magnetics
• /
• v.8 no.3
• /
• pp.118-120
• /
• 2003

As an alternative promising way of producing high coercivity Sr-ferrite for a permanent magnet application, intensive mechanical milling process was applied to the raw materials of the Sr-ferrite with different composition. Synthesising reactivity for the Sr-ferrite of the mechanically milled raw material containing $SrCO_3$, $La_2O_3$, $Fe_2O_3$, $Co_3O_4$, and $SiO_2$ was inferior to that of the raw material containing $SrCO_3$ and $Fe_2O_3$, The Sr-ferrite prepared from mechanically milled raw materials had profoundly improved magnetic properties compared to the Sr-ferrite prepared by conventional method. Beneficial effect of the substituting ($La_2O_3$, $Co_3O_4$) and additive ($SiO_2$) oxides for improving the magnetic properties was not exploited in the Sr-ferrite prepared from the mechanically milled raw material. The Sr-ferrite powder prepared from the mechanically milled raw materials was magnetically isotropic in nature.

• Journal of the Korean Ceramic Society
• /
• v.28 no.6
• /
• pp.471-477
• /
• 1991

Effects of ZnO, PbO and SiO2 on the grain growth and magnetic properties of Sr-ferrite were investigated. (1) Addition of ZnO to Sr-ferrite increased remanence, but decreased coercivity and maximum energy product. (2) Addition of PbO up to 0.5 wt% increased (B$.$H)max of Sr-ferrite, but addition more than 0.5 wt% decreased (B$.$H)mzx (3) SiO2 addition to the 0.5 wt% PbO doped Sr-ferrite decreased remanence and increased coercivity. The coercivity increase in due to the grain refinement effect of SiO2. But addition of SiO2 more than 0.5 wt% invoked a decrease of coercivity and (B$.$H)max of Sr-ferrite due to abnormal grain growth. Sr-ferrite magnet having maximum energy product of 3.7MGOe was fabricated by using the roasting product of Pyrrhotite.

• Proceedings of the Korean Magnestics Society Conference
• /
• 2002.12a
• /
• pp.90-91
• /
• 2002

영구자석 재료용 Sr-ferrite의 제조에 mechanical alloying (기계적 합금화)기술을 적용해서 초미세 결정립으로 구성된 고보자력의 Sr-ferrite를 제조해서 높은 보자력을 실현할 수 있는 것으로 보고하고 있다[1]. 그러나 이 새로운 방법으로 제조한 Sr-ferrite는 높은 보자력을 갖기는 하지만, 대단히 미세한 결정립들이 결합하여 입자를 구성하고 있어 자장을 가해서 입자를 배향시키기가 어렵다. 따라서 이 재료는 등방성 분말로 밖에 이용할 수 없는 결정적인 문제점이 있다. (중략)

• Journal of the Speleological Society of Korea
• /
• no.79
• /
• pp.77-81
• /
• 2007

In this paper deals with behavior of the magnetic abrasive using Sr-Ferrite on polishing charateristiccs in a internal finishing of staninless steel pipe a tying magnetic abrasive polishing. The magnetic polishing is the useful method to finish some machinery fabrications by using magnetic power. This method is one of the precision techniques and has in aim for clean technology in the transportation of the pure gas in the clean pipes. The magnetic abrasive polishing method is not so common in the field of machine that it is not known to widely. There are rarely researcher in this field because of non-effectiveness of magnetic abrasive. Therefore, in this paper we deals with the development of the magnetic abrasive with the use of Sr-Ferrite. In this development, abrasive grain SiC has been made by using the resin bond fabricated at low temperature. And magnetic abrasive powder was fabricated from the Sr-Ferrite which was crushed into 200 mesh. The XRD analysis result shows that only SiC abrasive and Sr-Ferrite crystal peaks were detected, explaining that resin bond was not any more to contribute chemical reaction. From MACRO analysis, we found that SiC abrasive and Sr-Ferrite were strongly bonding with each other.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2002.07a
• /
• pp.82-85
• /
• 2002

High-quality Sr-ferrite sintered magnets have been studied by using mill scale added SrCO$_3$ and oxidents before oxidation process. The pre-added SrCO$_3$ powders were improved the degree of oxidation and crush of mill scale and the magnetic properties of Sr-ferrite sintered magnets. The small added NaNO$_3$ oxidant was also highly improved the degree of oxidation and crush of mill scale and the magnetic properties of Sr-ferrite sintered magnets; 3805 G of remanent flux density, 3240 Oe of intrinsic coercivity, and 3.45 MGOe of maximum energy product.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2001.11b
• /
• pp.284-287
• /
• 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.

• Journal of the Korean Ceramic Society
• /
• v.31 no.10
• /
• pp.1181-1187
• /
• 1994

Sr-ferrite powders were synthesized by molten salt method. The process of powder formation was investigated by controlling the size and shape (sphere and acicular) of starting materials. The morphology of resulting ferrite was plate-like regardless of the shape of starting materials, Fe2O3 powders. As a result, the formation of Sr-ferrite in the molten salt was proceeded by solution-precipitation.

• Journal of the Korean Ceramic Society
• /
• v.34 no.5
• /
• pp.453-460
• /
• 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.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 1998.06a
• /
• pp.49-52
• /
• 1998

Preparation of hexagonal strontium-ferrite by modified spray co-roasting(MSC:H) which is expected to shorkn the length of the process and to elevate the magnetic properties of hard ferrite was studied. We prapared $Fe_2O_3/SrCO_3$ mixture powders by MSCR after stirring ionized $FeCI_2$ in distilled water with solid state $SrCO_3$. And then calcined the mixture powders up to $1150^{\circ}C$ for Sr-ferrite powders It is possible to prepare hexaferrite powders with high saturation magnetization (Ms > 69 emu/g) , coercivity (Hc > 4000 Oe) The nlagnetic values of saturation magnetization iire higher than those achieved by the conventional technique.

• Journal of the Korean Ceramic Society
• /
• v.40 no.2
• /
• pp.191-197
• /
• 2003

Sr ferrites with various compositions were applied to the decomposition of $CO_2$ to mitigate the greenhouse effect. In the reduction reaction of Sr ferrites up to 80$0^{\circ}C$, starting temperature was lower with increasing of Sr content in Sr ferrite. However, the reactivity was higher with decreasing Sr content. In the $CO_2$ decomposition reaction with reduced Sr ferrites, the amount of CO and C were depended on the ratio of Sr and Fe in Sr ferrite. With increasing Sr content. larger amount of C were deposited on the surface of ferrite. Therefore, in order to apply Sr ferrites for the decomposition of $CO_2$, it is necessary to control the ratio of Sr and Fe according to the conditions used.