• Progress in Superconductivity and Cryogenics
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• v.7 no.3
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• pp.9-12
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• 2005

[ $Y_1Ba_2Cu_3O_{7-8}$ ] (YBCO) coated conductor has been fabricated by batch-type process using oxide-precursor-based metal-organic deposition (MOD) method. The batch-type process can be scaled up more simply to Produce long-length YBCO conductor than the reel-to-reel process. Also, it has less handling problems and is adequate to the ambient gas environment. In this work, YBCO oride powder was used as a starting precursor for MOD method. After reel-to-reel dip coating process, me ter-long-buffered metal tape was wound around a cylinder and underwent calcination and annealing processes. Annealed YBCO films showed good c-axis alignment and dense surface morphology with no cracks, but exhibited very low critical current density of $10^5\;A/cm^2$.

• Journal of Powder Materials
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• v.17 no.3
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• pp.209-215
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• 2010

Mesoporous alumina particles were prepared by spray pyrolysis using cetyltrimethyl-ammonium bromide (CTAB) as a structure directing agent and the effect of Al precursor types on the texture properties was studied using $N_2$ adsorption isotherms, small-angle X-ray scattering (SAXS), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The surface area and the microstructure of alumina particles were significantly influenced by the Al precursor type. The largest BET surface area was obtained when Al chloride was used, whereas alumina particles prepared from Al acetate had the largest pore volume. According to small-angle X-ray scattering (SAXS) analysis, the alumina powders prepared using nitrate and acetate precursors had a clear single SAXS peak around $2{\theta}=1.0{\sim}1.5^{\circ}$, indicating that regular mesopores with sponge-like structure were produced. On the basis of TEM, SAXS, and $N_2$ isotherm results, the chloride precursor was most profitable to obtain the largest surface area ($265\;m^2/g$), whereas, the nitrate precursor is useful for the preparation of non-hollow mesoporous alumina with regular pore size, maintaining high surface area (${\sim}233\;m^2/g$).

• Journal of Magnetics
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• v.20 no.1
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• pp.21-25
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• 2015

Fine Nd-Fe-B-type particles were prepared by ball milling of different types of Nd-Fe-B precursor materials, such as die-upset magnet, HDDR-treated material, and sintered magnets. Coercivity dependence on the grain and particle size of the powder was investigated. Coercivity of the milled particles was reduced as the particle size decreased, and the extent of coercivity loss was dependent upon the precursor material. Coercivity loss in the finely milled particles was attributed to the surface oxidation. The extent of coercivity loss in the fine particles was closely linked to grain size of the precursor materials. Coercivity loss was more profound for the fine particles with larger grain size. Contrary to the fine particles from the sintered magnets with larger grain size the fine particles (~10 um) from the die-upset magnet and HDDR-treated material with much finer grain size still retained high coercivity (> 10 kOe for die-upset magnet, > 4 kOe for HDDR-treated material).

• The Korean Journal of Ceramics
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• v.6 no.1
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• pp.32-36
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• 2000

Pyrolytic preparations of Ti-Al-N ceramics from three blended precursors were investigated. The precursors were prepared stirring ($HA1N^{i}Pr_m$ and an aminolysis product of $Ti(NMe_2)_4$ with $MeHNCH_2CH_2$NHMe in $C_6/H_6$ . IR and $^1H\;NMR $analyses suggested that essentially no Ti-N-Al bonds were present in the precursors. Pyrolysis of the precursors under $NH_3-N_2$led to the formation of brown solids with ceramic yields of about 30%, and the Ti-Al ratios in the pyrolyzed products were close to those of the precursors. XRD analysis of the pyrolyzed product from the precursor with Ti:Al=5:1 indicated the formation of a NaCl-type compound as the only crystalline phase. Pyrolysis of the precursor with Ti:Al=2:1 led to the formation of AlN besides the major NaCl-type compound. A ceramic composite containing AlN and the NaCl-type compound was formed by pyrolysis of the precursor with Ti:Al=1:2.

• Korean Journal of Materials Research
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• v.13 no.4
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• pp.251-258
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• 2003

The effects of the salt and the precursor pH on the synthesizing behavior and the morphology of mullite have been studied. Two kinds of mullite precursor sols were prepared by the dissolution of two kinds of salt (aluminum nitrate enneahydrate, Al($NO_3$)$_3$ㆍ$9H_2$O; type I and aluminum sulfate 14∼18 water, (SO$Al_4$)$_3$$\cdot$$14∼18H_2$O; type II) into the mixture of colloidal silica sol, respectively. Precursor pH of the sols was controlled to the acidic (pH= 1.5∼2) and basic (pH= 8.5∼9) conditions. The co-products with nitrate and sulfate were completely eliminated at $500^{\circ}C$ and $850^{\circ}C$, respectively, which was confirmed by TG/DTA results. The synthesizing temperature of mullite phase was found to be above $1200^{\circ}C$ for pH= 1.5∼2 and above $1300^{\circ}C$ for pH= 8.5∼9 in type I. However, in type II, the synthesizing temperature of mullite was decreased to $850^{\circ}C$ for pH= 1.5∼2 and $1100^{\circ}C$ for pH= 8.5∼9. The grain size of the mullite synthesized at pH= 8.5∼9 was larger than that at pH= 1.5∼2 in overall heat-treated temperatures, showing smaller grain size in type II. Aspect ratio of the mullite grains was more increased at pH= 1.5∼2 than pH= 8.5∼9 in type I, showing similar aspect ratio at both pH conditions in type II. It was found that the synthesizing temperature and grain size were predominantly governed by the initial precursor pH and decomposition of the salt, with minor effect on the grain morphology.

• Korean Journal of Microbiology
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• v.13 no.3
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• pp.123-137
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• 1975

Sexual reproduction of paramecia have been accomplished through conjugation between individuals which have opposite mating type substances on their cilia when they were starved. Using selfing clone in which mating takes place, I examined whether a mating type change in indicidual cells required new protein and new mRNA synthesis or not and also shether there is a precursor relationship between both of the complementary mating type substances in their synthetic pathway. I found that 1. Mating type change needs new protein(s) and new mRNA synthesis. 2. Mating type substances are synthesized sequentially from mating type XIII to XIV 3. There might be a common precursor pool from which the mating type XIII substnace is synthesized and then complementary mating type XIV is fromed by addition of small group to the mating type XIII substance.

• Bulletin of the Korean Chemical Society
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• v.34 no.12
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• pp.3565-3569
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• 2013

A home-made pinhole-type glass nozzle was employed to generate vibronically excited but jet-cooled benzyl-type radicals from precursor 2-fluoro-4-chlorotoluene with a large amount of carrier gas He, from which the visible vibronic emission spectrum was recorded with a long-path monochromator. From an analysis of the spectrum observed, it was found that two benzyl-type radicals, 2-fluorobenzyl and 2-fluoro-4-chlorobenzyl radicals, were formed from the precursor in corona discharge. The possible pathway for the production of benzyl-type radicals that can explain the spectroscopic observation is herein proposed. In addition, the electronic energy of the $D_1{\rightarrow}D_0$ transition and the vibrational mode frequencies in the $D_0$ state of the 2-fluoro-4-chlorobenzyl radical were determined for the first time.

• Journal of the Korean Ceramic Society
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• v.54 no.3
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• pp.222-227
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• 2017

Flake-type micro hollow silica was synthesized by precipitation method using an $Mg(OH)_2$ inorganic template and sodium silicate and ammonium sulfate as the silica precursors. We investigated the effects of the silica precursor concentration on the shape, shell thickness, and surface of the hollow silica. When the concentration of the silica precursor was 0.5 M, the hollow silica had a smooth and translucent thin shell, but the shell was broken. On the other hand, the shell thickness of the hollow silica changed in the range of 12 nm to 18 nm with the increase of the precursor concentration from 0.7 M to 1.1 M. Simultaneously, unintended spherical silica satellites were created on the shell surface. The number of satellites and the size rose according to the increased concentration of silica precursor. The reason for the formation of spherical silica satellites is that the $NH_4OH$ nucleus generated in the synthesis of hollow silica acted as another silica reaction site.

• Korean Journal of Materials Research
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• v.18 no.3
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• pp.137-142
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• 2008

Blue-emitting BAM:Eu phosphor powders were formed by post-treatment of precursor powders with hollow or dense morphologies. The morphologies of the precursor powders obtained by spray pyrolysis were controlled by changing the preparation conditions and by changing the type of spray solution. The effects of the morphologies of the precursor powders on the characteristics of the BAM : Eu phosphor powders reacted with $AlF_3$ flux were investigated. Precursor powders with a spherical shape and a hollow morphology produced BAM : Eu phosphor powders with a plate-like morphology, a fine size and a narrow size distribution. On the other hand, precursor powders with a spherical shape and dense morphology produced BAM : Eu phosphor powders with a plate-like morphology and a large size. $AlF_3$ flux improved the photoluminescence intensities of the BAM : Eu phosphor powders. The photoluminescence intensity of the fine-sized BAM : Eu phosphor powders with a plate-like morphology was 90% of the commercial product under vacuum ultraviolet conditions.

• Macromolecular Research
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• v.12 no.3
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• pp.263-268
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• 2004

We have synthesized a water-soluble polyimide precursor, poly(amic acid) amine salt (PAD), from pyromellitic dianhydride (PMDA), 4,4'-oxydianiline, and N,N -dimethylethanolamine (DMEA) and have investigated in detail its properties with respect to the degree of salt formation (D$\_$sf/). The maximum value of D$\_$sf/ we obtained upon precipitation of the precursor solution into acetone was 79%. We synthesized a PAD having a D$\_$sf/ of 100% (PAD100) by the solid state drying of an organic solution. The precursors showed different solubility depending on the D$\_$sf/ to make up to 4 wt% solutions in water containing a small amount of DMEA. PAD100 is completely soluble in pure water. We investigated the imidization behavior of PAD in aqueous solution using various spectroscopic methods, which revealed that PAD 100 has faster imidization kinetics relative to that of the poly(amic acid)-type precursors. The resulting polyimide films prepared from an aqueous precursor solution possess almost similar physical and thermal properties as those prepared from N-methyl-2-pyrrolidone(NMP) solution. Therefore, we have demonstrated that PAD can be used as a water-based precursor of polyimide; this procedure avoids the use of toxic organic solvents, such as NMP.