• Journal of the Korean Ceramic Society
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• v.30 no.6
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• pp.499-509
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• 1993

Structures of hematite(${\alpha}$-Fe2O3), Ba-ferrite(BaFe12O19) and Zn2Y(Ba2Zn2Fe12O22) were studied by powder X-ray diffraction(XRD) method. Powder XRD patterns of the ferrites were analyzed with the Rietveld method, and the final refined R-factors were RWP<0.01 and RI<0.03. The lattice parameters refined with hexagonal crystal system were a=5.0342${\AA}$, c=13.746${\AA}$ for hematite, a=5.8928${\AA}$, c=23.201${\AA}$ for Ba-ferrite, and a=5.8763${\AA}$, c=43.567${\AA}$ for Zn2Y. In the hematite, the oxygen parameter is 0.3072 and the Fe-O distances in FeO6octahedron are 1.941${\AA}$ and 2.118${\AA}$, close to the single crystal data of Blake et al.. In the Ba-ferrite, the Fe atom in oxygen trigonal bipyramid is displaced 0.155${\AA}$ away from the BaO3 mirror plane into 4e position. In the Zn2Y, 75% of Zn is located at the oxygen terahedral site in S-block.

• Korean Journal of Materials Research
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• v.29 no.4
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• pp.252-257
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• 2019

Fabrication of soft magnetic composite powders for the $Fe_2O_3-Ca$ system by mechanical alloying(MA) has been investigated at room temperature. It is found that soft magnetic composite powders in which CaO is dispersed in ${\alpha}-Fe$ matrix are obtained by MA of $Fe_2O_3$ with Ca for 5 hours. Changes in magnetization and coercivity also reflect the details of the solidstate reduction process of hematite by pure metal of Ca during MA. The saturation magnetization of MA powders increases with increasing MA time and reaches a maximum value of 65 emu/g after 7 hours of MA. The average grain size of ${\alpha}-Fe$ in MA powders, estimated by diffraction line-width, gradually decreases with increasing MA time and reaches 52 nm after 5 hours of MA. It can also be seen that the coercivity of the 5-hour MA sample is fairly high at 190 Oe, suggesting that the grain refinement of already-produced ${\alpha}-Fe$ tends to clearly occur during MA.

• Bulletin of the Korean Chemical Society
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• v.9 no.6
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• pp.333-337
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• 1988

Spinel $CoFe_2O_4$ solid solutions containing up to 50 mol% CoO were synthesized with spectroscopically pure CoO and ${\alpha}-Fe_2O_3$ polycrystalline powders. The spinel structures of the $CoFe_2O_4$ solid solutions were analyzed from XRD patterns and the Mossbauer spectra showed that the quenched $CoFe_2O_4$ had a partially inversed spinel structure ($Co_{0.23}Fe_{0.77}$) < $Co_{0.77}Fe_{1.23}$ > $O_4$, while the slowly cooled $CoFe_2O_4$ was completely inversed spinel ($Co_{0.04}Fe_{0.96}$) <$Co_{0.96}Fe_{1.04}$ > $O_4$. The $CoFe_2O_4$ specimens containing 10, 20, 30 and 40 mol% CoO turned to be a mixture of corundum and spinel structures. Electrical conductivities were measured as a function of temperature from 300 to $900^{\circ}C$ under oxygen partial pressures from $10^{-3}$ to 1 atm. The temperature dependencies of the electrical conductivity show different behaviors in the low- and high-temperature regions. The average activation energies are 0.23 eV and 0.80 eV in the low- and high-temperature regions, respectively. It is suggested that $Co^{2+} {\to} CO^{3+} + e^-$ and $Fe^{2+} {\rightleftharpoons} Fe^{3+} + e^-$ are the main conduction mechanisms responsible for the electronic conduction in the low- and high-temperature regions, respectively.

• Journal of Magnetics
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• v.8 no.4
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• pp.138-141
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• 2003

$Ni_{0.65}Zn_{0.35}Fe_2O_4$thin films were prepared by using a sol-gel method. Their crystallographic, dielectric and magnetic properties were investigated as a function of Cu contents by means of an X-ray diffractometer (XRD), X-ray reflectivity, LCZ meter (NF2232), a vibrating sample magnetometer (VSM), and an atomic force microscope (AFM). From typical C-V measurements for $Ni_{0.65}Zn_{0.35}Fe_2O_4$ thin films on p-type silicon substrate, the surface charge density was calculated as 1.4 ${\mu}$C/$m^2$. The dielectric constant evaluated from the capacitance at the accumulation state was 28. The high $H_{c}$ and low $M_{sat}$ at x=0.0 and 0.1 were due to the growth of the ${\alpha}$-$Fe_2O_3$ phase having antiferromagnetic properties. The rapidly decreased $H_{c}$ and increased $M_{sat}$ at x=0.2 and 0.3 can be explained that the ${\alpha}$-$Fe_2O_3$ phases have completely disappeared at x=0.3 and so, non-magnetic defects are minimized. The $M_{sat}$ was slightly decreased and the $H_{c}$ was increased above at x=0.3 because the increase of grain boundary due to smaller grain size acts as defects during magnetization process.

• Journal of the Korean Ceramic Society
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• v.24 no.5
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• pp.431-436
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• 1987

High purity Al2O3 has been extracted from serlcite of clayminerals, selicite was treated by H2SO4(2N∼18N) solution, NH4OH treatment(PH8.5∼10.0) and metallic impurities such as Fe were removed by NaOH treatment. The tendency of extraction yield of ${\alpha}$-Al2O3 have been investigated by relating reaction time, acid concentration. Reaction products were analyzed by DT-TGA, chemical analysis and X-ray diffractometer. Prepared ${\alpha}$-Al2O3 power is fired in air at 1400$^{\circ}C$, 1600$^{\circ}C$ 2hr. The results are as follows; 1. The most suitable extracting conditions of ${\alpha}$-Al2O3 from Selicite were N-H2SO4, 120 min acidtreating time. 2. The optimum pH condition was 9.0. 3. Physical properties of sintered Al2O3 bodies were as follows. Relative density is 99%. Water absorption is 0.26%. Rock well hardness is 89.

• Proceedings of the IEEK Conference
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• 2001.10a
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• pp.106-110
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• 2001

Formation of stoichiometric lithium-, nickel-, and zinc- ferrites by calcining organo-metallic precursors a temperature below 40$0^{\circ}C$ is examined using DTA/TG, and XRD techniques. It attempts to simulate th immobilization of metal ions in industrial liquid influents (waste) through the synthesis of stoichiometric spinel ferrites (SSF). Two steps of the SSF formation during thermal treatments are noted. The transformation of magnetite to ${\gamma}$ - Fe$_2$O$_3$and subsequent first formation of SSF were observed at temperatures ranging from 200 to 45$0^{\circ}C$. Th formation of cation-containing ${\gamma}$-Fe$_2$O$_3$and subsequent second formation of the ferrite occurred at temperature ranges of < 45$0^{\circ}C$ and 500 to $650^{\circ}C$, depending on the heating rate used. Then the temperature range of 200t 45$0^{\circ}C$ is critical to the performance of the technique, because a calcination at the range would lead to a complete formation of SSF, avoiding the occurrences of ${\gamma}$-Fe$_2$O$_3$and ion-containing ${\gamma}$-Fe$_2$O$_3$. If not, so $\alpha$-Fe$_2$O$_3$would occur. And annealing at temperature above $650^{\circ}C$ must be employed by which solid-state reactio of $\alpha$-Fe$_2$O$_3$with metal ions (possibly metal oxides) to form SSF can be conducted.

• The Korean Journal of Mycology
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• v.17 no.3
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• pp.149-153
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• 1989

One strain of Aspergillus niger K-25 producing an acid-stable ${\alpha}-amylase$ was isolated from the soil. The optimum culture conditions were investigated. The production of the acid-stable ${\alpha}-amylase$ was enhanced when the strain was incubated in a medium containing soluble starch 3.5%, peptone 2%, $KH_2PO_4$ 0.5%, $MaSO_4{\cdot}7H_2O$ 0.25% and $FeCI_3$ 1.0% at pH 3 for 7 days. However, higher activity of acid-stable ${\alpha}-amylase$ was demonstrated on wheat bran culture. Amylase production was doubled when A. niger K-25 was incubated on the wheat bran supplemented with fumaric acid buffer (pH 3).

• Korean Journal of Materials Research
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• v.15 no.12
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• pp.760-764
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• 2005

The influences of the oxidant($O_2\;and\;O_3$) on the FeOOH formation were studied with fixed $FeSO_4{\cdot}7H_2O$ concentration (0.5M) and NaOH equivalent ratio(0.5). The characteristics of the synthesized powders were evaluateed by XRD, and equantitative phase analysis. $\alpha-FeOOH$ (Geothite) and/or $\gamma-FeOOH$ was promoted when $O_3$ was used as a oxidant which is stronger oxidizing agent than $O_2$.

• Korean Journal of Materials Research
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• v.8 no.7
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• pp.653-658
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• 1998

ZrO2, B2O3 및 AI을 사용하여 SHS법에 의한 붕화지르코늄을 합성을 하고 산화철과 알루미늄 분말의 첨가가 합성물의 치밀화에 미치는 영향에 대하여 검토하였다. 합성물중에 존재하는 결정상은 대부분이 ZrB2와 $\alpha$-AI2O3상이었다. 산화붕소와 알루미늄의 몰비가 1.0:3.3이상일 때 합성물의 치밀화는 크게 증가하였고, ZrB2 입자도$\alpha$-AI2O3용융상과 더불어 조대하였다. 산화철 1목에 대하여 알루미늄을 1-3몰을 첨가한 것과 산화철 1.5몰에 대하여 알루미늄을 3몰 첨가시 $\alpha$-AI2O3를 중심으로하는 슬라그상으로부터 용융상의 분이가 가능하였고, 이들 용융상에 존재하는 결정상은 ZrB2이외에 Fe, Fe2B, Zr2Fe상이었다. 용융상의 상대밀도는 산화철 1몰에 대하여 알루미늄을 1몰 첨가시 83.2%인 반면에 그 이상의 첨가량에 대해서는 치밀화는 크게 증가하여 알루미늄을 3몰 첨가한 경우 상대밀도는 93.7%로서 최대를 나타내었다.

• Journal of the Korean Magnetics Society
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• v.2 no.1
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• pp.22-28
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• 1992

Barium ferrite thin films were reactively deposited with Fe and BaO composite targets by a facing tergects sputtering unit. When thermally oxidized silicon wafers were used as substrates, minimum substrate heating of $750^{\circ}C$ was necessary for the perfect c-axis alignment in barium ferrite films. To lower the critical substrate temperature for the good c-axis alignment, such seed layers as ZnO, ${\alpha}-Fe_{2}O_{3}$ and ${\gamma}-Fe_{2}O_{3}$ were tested. The excellent c-axis algnment of BaM was obtained at a substrate temperature of $600^{\circ}C$ on ZnO seed layer whose (002) plane was parallel to the substrate surface. The magnetic properties of the BaM film showed saturation magnetization of 295 emu/cc, perpendicular coercivity of 1.7 kOe and squareness of 0.75. Optimum deposition rate of $230\;{\AA}/min$ was obtained with the composite target and this was 5 to 20 times higher than those of other investigators with oxide targets.