• Korean Journal of Soil Science and Fertilizer
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• v.49 no.1
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• pp.17-29
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• 2016

Though there is an abundant supply of nitrogen in the atmosphere, it cannot be used directly by the biological systems since it has to be combined with the element hydrogen before their incorporation. This process of nitrogen fixation ($N_2$-fixation) may be accomplished either chemically or biologically. Between the two elements, biological nitrogen fixation (BNF) is a microbiological process that converts atmospheric di-nitrogen ($N_2$) into plant-usable form. In this review, the genetics and mechanism of nitrogen fixation including genes responsible for it, their types and role in BNF are discussed in detail. Nitrogen fixation in the different agricultural systems using different methods is discussed to understand the actual rather than the potential $N_2$-fixation procedure. The mechanism by which the diazotrophic bacteria improve plant growth apart from nitrogen fixation such as inhibition of plant ethylene synthesis, improvement of nutrient uptake, stress tolerance enhancement, solubilization of inorganic phosphate and mineralization of organic phosphate is also discussed. Role of diazotrophic bacteria in the enhancement of nitrogen fixation is also dealt with suitable examples. This mini review attempts to address the importance of diazotrophic bacteria in nitrogen fixation and plant growth improvement.

• Journal of the Korean Society for Heat Treatment
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• v.15 no.2
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• pp.57-64
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• 2002

The 22%Cr-5%Ni-3%Mo duplex and 18%Cr-8%Ni austenitic stainless steels have been nitrogen permeated under the $1Kg/cm^2$ nitrogen gas atmosphere at the temperature range of $1050^{\circ}C{\sim}1150^{\circ}C$. The nitrogen-permeated duplex and austenitic stainless steels showed the gradual decrease in hardness with increasing depth below surface. The duplex stainless steel showed nitrogen pearlite at the outmost surface and austenite single phase in the center after nitrogen permeation treatment, while the obvious microstructural change was not observed for the nitrogen-permeated austenitic stainless steel. After solution annealing the nitrogen-permeated stainless steels(NPSA treatment) at $1200^{\circ}C$ for 10 hours, the hardness of the duplex and austenitic stainless steels was constant through the 2 mm thickness of the specimen, and the ${\alpha}+{\gamma}$ phase of duplex stainless steel changed to austenite single phase. Tensile strengths and elongations of the NPSA-treated duplex stainless steel remarkably increased compared to those of solution annealed (SA) duplex stainless steel due to the solution strengthening effect of nitrogen and the phase change from a mixture of ferrite and austenite to austenite single phase, while the NP-treated austenitic stainless steel displayed the lowest value in elongation due to inhomogeneous deformation by the hardness difference between surface and interior.

• Journal of the Korean Ceramic Society
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• v.35 no.3
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• pp.303-309
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• 1998

The fabrication of Al2O3/Al composite by pressureless infiltration was investigated by the change of Mg and Si content in Al alloy infiltration process and infiltration atmosphere. The effect of alloying elements infiltration atmosphere and interfacial reactants between Al alloy matrix and Al2O3 particles were in-vestigated in terms of bendingstrength and harness test,. The fabrication of Al2O3/Al composite by the vestigated in terms of bending strength and hardness test. The fabrication of Al2O3/Al composite by the pressureless infiltration was done in nitrogen atmosphere with Mg in Al alloy. It was successfully fabricated at $700^{\circ}C$ according to Mg contents in Al alloy and infiltration condition. Because Mg in the Al alloy and ni-trogen atmosphere of infiltratio condition produced Mg-N compound(Mg3N2) it decreased the wetting an-gle between molten Al alloy and Al2O3 particles by coating on surface of Al2O3 particles. The fracture strength of Al2O3/Al-Mg composite was 800MPa and Al2O3/Al-Si-Mg composite was 400MPa. Si in Al alloy decreased the interfacial strength between Al alloy matrix and Al2O3 particles.

• Progress in Superconductivity and Cryogenics
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• v.16 no.1
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• pp.6-8
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• 2014

The influence of quenching temperature, heating atmosphere and annealing time on superconducting characteristics has been studied for $LuBa_2Cu_3O_{7-z}$ compound which has been recently synthesized in a nearly phase-pure form. Resistivity measurements for the as-prepared sample heated at $300^{\circ}C$ in oxygen and subsequently quenched into liquid nitrogen revealed that there is no significant change in $T_c$. On the other hand, $T_c$ of the sample slightly increased when the sample was heated at $300^{\circ}C$ either in air or in $N_2$ atmosphere. It was also found that $T_c$ of the sample decreased when the annealing temperature in $N_2$ atmosphere increased above $400^{\circ}C$. The experimental results indicated that the as-prepared sample is under overdoped state. The enhanced superconducting transition observed in the samples after heating at $300^{\circ}C$ in air or $N_2$ atmosphere was discussed in conjunction with a slight removal of oxygen and ordering of oxygen atoms in the as-prepared sample.

• Journal of Adhesion and Interface
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• v.20 no.1
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• pp.9-14
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• 2019

The change of three different reagents for electrical conductive paint using aircraft coating with elapsing time of exposure to different condition was investigated. Three different reagents were poured into the vial bottles, stored in air condition and room temperature and observed with elapsing days. In addition, adhesion property of paint was tried using cross cut tape test after storage of $N_2$ atmosphere. The weight of each different reagent was measured along with elapsing time. To confirm the change of chemical component with exposure of air atmosphere, FT-IR was performed. The weight of part A and Part B decreased slightly whereas the weight of part C decreased rapidly and the precipitation was remained. The part B was cured after exposure of $N_2$ atmosphere and the 2250 cm-1 from FT-IR peak decreased slowly at the same time. It was considered that the water contained in air accelerated the reaction of -NCO functional groups and it caused the curing whereas $N_2$ atmosphere not contained water and it resulted in the retardancy of curing.

• Journal of the Korean Wood Science and Technology
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• v.36 no.6
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• pp.138-146
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• 2008

The chemical compositions, cell wall biopolymers and non-isothermal behavior of the stem biomass of Nicotiana Tabacum originated from tobacco industry were investigated in depth. On a weight basis, the contents of total ash and total sugar are 19.1% and 20.7% respectively. Lignin content was around 3% of tobacco stem biomass while pectin was over 7%. The holo-cellulose content in cell wall biopolymer was around 13% and the $\alpha$-cellulose constitutes 60% of the total holo-cellulose. The thermal behavior of stem biomass showed different patterns depending on either inert (nitrogen) or oxidizing (air) atmospheric condition. In the air atmosphere, the rapid thermal decompositions at around $473^{\circ}C$ and $581^{\circ}C$ were recorded as the peaks in DTG curve, while the peaks were not shown in the nitrogen atmosphere condition. The thermal analysis of the freeze dried soluble obtained from hot water extraction of tobacco stem biomass showed that the rapid thermal decomposition at around $581^{\circ}C$ in the air atmosphere was due to the residual char originated from the soluble fraction. The distinct difference in thermal decomposition between hemicellulose and cellulose were easily found in the DTG curve obtained in the nitrogen atmosphere.

• Journal of the Korean Ceramic Society
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• v.26 no.5
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• pp.637-644
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• 1989

Beta-sialon powder(Z=1) was synthesized by the simultaeous reduction and nitridation of the mixed powders of Hadong kaolin and silica. Silicon hydroxide was prepared from Si-alkoxide by a hydrolysis method and amorphous silica was obtained from the calcination of the prepared silicon hydroxide. Hadong kaolin was mixed with both the silicon hydroxide and amorphous silica, respectively. The average particle size was 4${\mu}{\textrm}{m}$ and the morphology of particle was rod-like and equiaxed in the case of beta-sialon powder prepared form Hadong kaolin and silicon hydroxide(COMPOSITION A), whereas the average particle size was 3${\mu}{\textrm}{m}$ and the morphology of particle was equiaxed in the case of beta-sialon powder prepared from Hadong kaolin and amorphous silica(COMPOSITION B). The synthesized beta-sialon powders were hot-pressed at 175$0^{\circ}C$ for 2 hours under 30 MPa in a nitrogen atmosphere after YAG composition(8wt%) was added to these powders as a sintering agent. The hot-pressed specimens were annealed a 140$0^{\circ}C$ for 4 hours in a nitrogen atmosphere. The mechanical properties of sintered bodies were investigated in terms of M.O.R., fracture toughness and hardness. The measured values are as follows. COMPOSITION A : M.O.R. 508MPa, KIC 3.5MN/m3/2, hardness 13.6GPa. COMPOSITION B : M.O.R. 653MPa, KIC 5.4MN/m3/2, hardness 13.5GPa.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09b
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• pp.1165-1166
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• 2006

An experiment was carried out to investigate the effect of Ba Stearate as a reducing agent on the magnetic and physical properties of anisotropic $BaFe_2-W$ type ferrite magnets. It was found that the magnetic properties of $BaO{\cdot}8.5Fe_2O_3$ were improved by adding 0.3 wt% of Ba Stearate, 0.5 wt% of $SiO_2$, and 0.5 wt% of CaO together. The optimum conditions for making magnets were as follows; semisintering condition: $1350^{\circ}C{\times}4.0$ h in nitrogen gas atmosphere, drying condition: $180^{\circ}C{\times}2.0$ h in air, sintering condition: $1160^{\circ}C{\times}1.5$ h in nitrogen gas atmosphere. Magnetic and physical properties of a typical sample were $J_m$ = 0.46 T, $J_r$ = 0.43 T, $H_{cJ}$ = 182.3 kA/m, $H_{cB}$ = 177.2 kA/m, $(BH)_{max}$ = 33.8 kJ/$m^3$, $T_C$ = $495^{\circ}C$ and $K_A$ = $2.65{\times}10^5\;J/m^3$ and $H_A$ = 1332 kA/m.

• Journal of Radiation Industry
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• v.4 no.3
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• pp.265-269
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• 2010

Silicon-based non-oxide ceramic carbide fiber is one of the leading candidate ceramic materials for engineering applications because of its excellent mechanical properties at high temperature and good chemical resistance. In this study, polycarbosilane(PCS) and zirconium butoxide were used as a precursor to prepare polyzirconocarbosilane (PZC) fibers. A polymer solution was prepared by dissolving PCS in zirconium butoxide (50/50 wt%). This solution was heated at $250^{\circ}C$ in a nitrogen atmosphere for 2 hour with stirring, and then dried in a vacuum oven for 48 hour. PZC fibers were fabricated using an electrospinning technique. The fibers were irradiated with an electron beam to induce structural crosslinking. Crosslinked PZC fibers were heat treated at $1,300^{\circ}C$ in a nitrogen atmosphere. The microstructures of PZC fibers were examined by SEM. Chemical structures of PZC fibers were examined by FT-IR and XRD. Thermal stability of PZC fibers was investigated by TGA.

• Journal of the Korean Ceramic Society
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• v.33 no.1
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• pp.41-48
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• 1996

Self-propagating High-temperature Synthesis of Ti+N system has been investigated using the cylindrical high pressure reactor. The nitrogen pressure was varied from 40 to 80 atmosphere and TiNx(x=0.55) powder produced by SHS process was used as a diluent in order to control the reaction. Both the velocity of surface reaction and the ratio of TiN synthesis increased with increasing the nitrogen pressure. As the amount of diluent increases the degree of conversion to titanium nitride increases. Homogenious TiN powder was obtained in the composition 50Ti+50TiN0.94(diluent)