• The Korean Journal of Ceramics
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• v.5 no.2
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• pp.142-147
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• 1999

The interaction between commercial $Si_3N_4$ powder and two types of additives (nitrate and oxide additives) during the sintering of $Si_3N_4$ was investigated. The nitrates solution or oxide particles were added as a sintering additives. The surface of mixed powder was observed with FT-IR, TG, and HREM. DTA was used to characterize the reactivity of the powders. The formation of crystalline phases and phase transformation were analyzed by XRD. The adsorption of the additives on the surface of silicon nitride was confirmed in the nitrate salts. It was shown that the adsorption occurred by interaction between the amorphous $SiO_2$ layer on the $Si_3N_4$ surface and metal cations $(Al^{3++\; and \;Y^{3+})$ and anions $(NO_3\;^-\; or\; OH^-)$, resulting in a higher degree of homogeneous distribution of additives.

• Journal of Powder Materials
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• v.8 no.1
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• pp.55-60
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• 2001

Mechanical alloying technique was applied to prepare hard magnetic $Sm_2Fe_{17}N_x$ compound powders. Staring from pure Fe and Sm powders, the formation process of hard magnetic $Sm_2Fe_{17}N_x$ phase by mechanical alloying and subsequent solid state reaction was studied. As milled powders were found to consist of Sm-Fe amorphous and $\alpha$-Fe phases in all compositions of $Sm_xFe_{100-x}$(x = 11, 13, 15, 17). The effects of starting composition on the formation of $Sm_2Fe_{17}$ intermetallic compound was investigated by heat treatment of mechanically-alloyed powders. When Sm content was 15 at.％, heat-treated powders consisted of nearly $Sm_2Fe_{17}$ single phase. For preparation of hard magnetic $Sm_2Fe_{17}N_x$ powders, additional nitriding treatment was performed under $N_2$ gas flow at 45$0^{\circ}C$. The increase in the coercivity and remanence was proportional to the nitrogen content which increased drastically at first and then increased gradually as the nitriding time was extended to 3 hours.

• Journal of Pharmaceutical Investigation
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• v.16 no.2
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• pp.55-67
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• 1986

Inclusion complexation of tiaprofenic acid (TPA) with cyclodextrins $({\alpha}-,\;{\beta}-,\;{\gamma}-CyDs)$ in aqueous solution and in solid phase was investigated by solubility method, measurement of partition coefficient, ultra-violet, circular dichroism, infrared spectroscopies, powder X-ray diffractometry and differential scanning calorimetry. Investigations were made to prepare inclusion complexes of TPA with ${\beta}-CyD$ in solid powdered form by coprecipitation, freeze-drying, spray-drying and co-pulverization methods. The coprecipitation, freeze-drying and spray-drying methods were successful in obtaining inclusion complexes. The results showed that the latter two methods might be originally superior to the former in obtaining powdered inclusion completes. Especially, it was shown by powder X-ray diffractometry that spray-dried ${\beta}-CyD$ alone, TPA-spray-dried ${\beta}-CyD$ physical mixture, and spray-dried $TPA-{\beta}-CyD$ complex were amorphous. The dissolution behaviours of $TPA-{\beta}-CyD$ systems prepared by above four methods were compared with those of TPA alone and $TPA-{\beta}-CyD$ physical mixture, and the rates of dissolution of TPA in pH 1.2 buffer were greatly enhanced by inclusion complexation and copulverization.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2007.11a
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• pp.440-441
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• 2007

For this study, terbium-doped yttrium aluminum garnet (YAG:Tb) phosphor powders were prepared via the combustion process using the varous reagents. The characteristics of the synthesized nano powder were investigated by means of X-ray diffraction (XRD), Scanning Electron Microscope(SEM), and photoluminescence (PL). Single-phase cubic YAG:Tb crystalline powder was obtained at $1000^{\circ}C$ by directly crystallizing it from amorphous materials, as determined by XRD techniques. The SEM image showed that the resulting YAG:Tb powders had uniform sizes and good homogeneity. The photoluminescence spectra of the YAG:Tb nanoparticles were investigated to determinethe energy level of electron transition related to luminescence processes. There were three peaks in the excited spectrum, and the major one was a broad band of around 274 nm. Also, the YAG:Tb nanoparticles showed two emission peaks in the range of 450~500 nm and 525~560 nm, respectively, and had maximum intensity at 545 nm.

• Journal of Ocean Engineering and Technology
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• v.27 no.6
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• pp.95-99
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• 2013

Lead zirconate titanate (PZT) thick films with a thickness of $10-20{\mu}m$ were fabricated on silicone substrates using an aerosol deposition method. The starting powder, which had diameters of $1-2{\mu}m$, was observed using SEM. The average diameter ($d_{50}$) was $1.1{\mu}m$. An XRD analysis showed a typical perovskite structure, a mixture of the tetragonal phase and rhombohedral phase. The as-deposited film with nano-sized grains had a fairly dense microstructure without any cracks. The deposited film showed a mixture of an amorphous phase and a very fine crystalline phase by diffraction pattern analysis using TEM. The as-deposited films on silicon were annealed at a temperature of $700^{\circ}C$. A 20-${\mu}m$ thick PZT film was torn out as a result of the high compressive stress between the PZT film and substrate.

• Korean Journal of Materials Research
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• v.31 no.1
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• pp.23-28
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• 2021

The purpose of this study is to prepare WO3 nanopowders by high-energy milling in mixture gas (7 % H2+Ar) with various milling times (10, 30, and 60 min). The phase transformation, particle size and light absorption properties of WO3 nanopowders during reduction via high-energy milling are studied. It is found that the particle size of the WO3 decreases from about 30 ㎛ to 20 nm, and the grain size of WO3 decreases rapidly with increasing milling time. Furthermore, the surface of the particles due to the pulverization process is observed to change to an amorphous structure. UV/Vis spectrophotometry shows that WO3 powder with increasing milling times (10, 30, 60 min) effectively extends the light absorption properties to the visible region. WO3 powder changes from yellow to gray and can be seen as a phenomenon in which the progress of the color changes to blue. The characterization of WO3 is performed by high resolution X-ray diffractometry, Field emission scanning electron microscopy, Transmission electron microscopy, UV/Vis spectrophotometry and Particle size analysis.

• Korean Journal of Materials Research
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• v.11 no.5
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• pp.345-353
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• 2001

The present study was carried out to investigate the effect of zirconium addition to $Al_3$Nb intermetallic on the crystal structural modification and microstructural characterization of $Al_3$Nb intermetallic. Elemental Al, Nb, Zr powders and arc melted $Al_3$Nb and $Al_3$Zr intermetallic mixed powders were used as starting materials. MA was carried out in an attritor rotated with 300 rpm for 20 hours. The behavior of MA between two starting materials was some-what different in which the value of internal strain of the elemental powders was higher than that of the intermetallic powder. The intermetallic powder was much more disintegrated during the MA processing. In the case of the elemental powders, AlNb$_2$ phase were transformed to Al(Nb.Zr)$_2$ as a result of ternary addition of Zr element. With the successive heat treatment at 873K for 2 hours, the Al(Nb.Zr)$_2$ phase was transformed to more stable $Al_3$(Nb.Zr) phase. This transformation was clearly confirmed by the identification of X-ray peak position shift. On the other hand, in the carte of the intermetallic powder, there was no evidence of phase transformation to other ternary intermetallic compounds or amorphous phases, even in the case of additional heat treatment. However, nano-sized intermetallic with $Al_3$Nb and $Al_3$Zr were just well distributed instead of phase transformation.

• Progress in Superconductivity and Cryogenics
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• v.21 no.1
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• pp.18-24
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• 2019

This study was carried out to investigate the effect of milling of boron (B), which is one of raw materials of $MgB_2$, on the critical current density ($J_c$) of $MgB_2$. B powder used in this study is semi-amorphous B (Pavezyum, Turkey, 97% purity, 1 micron). The size of B powder was reduced by planetary milling using $ZrO_2$ balls (a diameter of 2 mm). The B powder and balls with a ratio of 1:20 were charged in a ceramic jar and then the jar was filled with toluene. The milling time was varied from 0 to 8 h. The milled B powders were mixed with Mg powder in the composition of (Mg+2B), and the powder mixtures were uniaxially pressed at 3 tons. The powder compacts were heat-treated at $700^{\circ}C$ for 1 h in flowing argon gas. Powder X-ray diffraction and FWHM (Full width at half maximum) were used to analyze the phase formation and crystallinity of $MgB_2$. The superconducting transition temperature ($T_c$) and $J_c$ of $MgB_2$ were measured using a magnetic property measurement system (MPMS). It was found that $B_2O_3$ was formed by B milling and the subsequent drying process, and the volume fraction of $B_2O_3$ increased as milling time increased. The $T_c$ of $MgB_2$ decreased with increasing milling time, which was explained in terms of the decreased volume fraction of $MgB_2$, the line broadening of $MgB_2$ peaks and the formation of $B_2O_3$. The $J_c$ at 5 K increased with increasing milling time. The $J_c$ increase is more remarkable at the magnetic field higher than 3 T. The $J_c$ at 5 K and 4 T was the highest as $4.37{\times}10^4A/cm^2$ when milling time was 2 h. The $J_c$ at 20 K also increased with increasing milling time. However, The $J_c$ of the samples with the prolonged milling for 6 and 8 h were lower than that of the non-milled sample.

• The Korean Journal of Ceramics
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• v.3 no.2
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• pp.116-123
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• 1997

A chemically stabilized $\beta$-cristobalite, which is stabilized by stuffing cations of $Ca^{2+}$ and $Al^{3+}$, was prepared by a solution-polymerization route employing Pechini resin or PVA solution as a polymeric carrier. The polymeric carrier affected the crystallization temperature, morphology of calicined powder, and particle size distribution. In case of the polyvinyl alcohol (PVA) solution process, a fine $\beta$-cristobalite powder with a narrow particle size distribution (average particle size : 0.3$\mu\textrm{m}$) and a BET specific surface area of 72 $\m^2$/g was prepared by an attrition-milling for 1 h after calcination at 110$0^{\circ}C$ for 1h. Wider particle size distribution and higher specific surface area were observed for the $\beta$-cristobalite powder derived from Pechini resin. The cubie(P1-to-tetraganalb) phase transformation in polynystalline $\beta$-cristobalite was induced at approximately 18$0^{\circ}C$. Like other materials showing transformation toughening, a critical size effect controlled the $\beta$-to-$\alpha$ transformation. Densifed cristobalite sample had some cracks in its internal texture after annealing. The cracks, occurred spontaneoulsy on cooling, were observed in the sample with an average grain sizes of 4.0 $\mu\textrm{m}$ or above. In case of the sintered cristobalite having a composition of CaO.$2Al_2O_3$.40SiO$_2$, small amount of amorphous phase and slow grain growth during annealing were observed. Shear stress-induced transformation was also observed in ground specimen. Cristobalite having a composition of CaO.2Al2O3.80SiO2 showed a more sensitive response to shear stress than the CaO.$2Al_2O_3$.40SiO$_2$ type cristobalite. Shear-induced transformation resulted in an increase of volume about 13% in $\alpha$-cristobalite phase on annealing for above 10 h in the case of the former composition.

• Proceedings of the IEEK Conference
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• 2001.10a
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• pp.409-412
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• 2001

The high purity manganese oxides were made from the dust, generated in AOD process that produces a medium-low carbon ferromanganese and collected in the bag filter. Manganese oxide content in the dust was about 90%, and its phase was confirmed as Mn₃O₄. In the extraction of manganese, because of remaining amorphous MnO₂, the dust was reduced to MnO by roasting with charcoal. The pulp density of the reduced dust can control pH of the solution more than 4 and then Fe ion is precipitated to a ferric hydroxide. Because a ferric hydroxide co precipitates with Si ion etc, Fe, Si ion was removed f개m the solution. Heating made water to be volatized and nitrates was left in reactor Then nitrates were a liquid state and stirring was possible. Among the nitrates in reactor, only the manganese nitrate which have the lowest pyrolysis temperature pyrolyzed into β-MnO₂powder and NO₂(g) at the temperature less than 200℃. When the pyrolysis of manganese nitrate has been completed about 90%, injection of water stopped the pyrolysis. Nitrates of impurity dissolved and the spherical high purity β-MnO₂powders were obtained by filtering and washing. Mn₂O₃or Mn₃O₄ powder could be manufactured from β-MnO₂powder by controlling the heating temperature. Lastly, a manufactured manganese oxide particle has 99.97% purity.