• Journal of Microbiology and Biotechnology
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• 제23권7호
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• pp.1004-1014
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• 2013

Six nonpathogenic fungal strains isolated from alkaline soils of Buenos Aires Province, Argentina (Acremonium murorum, Aspergillus sidowii, Cladosporium cladosporoides, Neurospora tetrasperma, Purpureocillium lilacinum (formerly Paecilomyces lilacinus), and Westerdikella dispersa) were tested for their ability to produce keratinolytic enzymes. Strains were grown on feather meal agar as well as in solid-state and submerged cultures, using a basal mineral medium and "hair waste" as sole sources of carbon and nitrogen. All the tested fungi grew on feather meal agar, but only three of them were capable of hydrolyzing keratin, producing clear zones. Among these strains, P. lilacinum produced the highest proteolytic and keratinolytic activities, both in solid-state and submerged fermentations. The medium composition and culture conditions for the keratinases production by P. lilacinum were optimized. Addition of glucose (5 g/l) and yeast extract (2.23 g/l) to the basal hair medium increased keratinases production. The optimum temperature and initial pH for the enzyme production were $28^{\circ}C$ and 6.0, respectively. A beneficial effect was observed when the original concentration of four metal ions, present in the basal mineral medium, was reduced up to 1:10. The maximum yield of the enzyme was 15.96 $U_c/ml$ in the optimal hair medium; this value was about 6.5-fold higher than the yield in the basal hair medium. These results suggest that keratinases from P. lilacinum can be useful for biotechnological purposes such as biodegradation (or bioconversion) of hair waste, leading to a reduction of the environmental pollution caused by leather technology with the concomitant production of proteolytic enzymes and protein hydrolyzates.

• Carbon letters
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• 제22권
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• pp.60-69
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• 2017

Nitrogen-doped carbon nanosheets with a developed porous structure were prepared from polyurethane foams by hydrothermal carbonization following $ZnCl_2$ chemical activation. Scanning electron microscopy, thermogravimetric analysis, Fourier transform infrared spectroscopy, solid state $^{13}C$ nuclear magnetic resonance (NMR) spectra and X-ray photoelectron spectroscopy were used to characterize the nitrogen-doped carbon nanosheet structure and composition. The removal of Cr(VI) by the N-doped carbon nanosheets was investigated. The results showed that the maximum removal capacity for chromium of 188 mg/g was found at pH=2.0 with PHC-Z-3. pH had an important effect on Cr(VI) removal and the optimal pH was 2.0. Moreover, amino groups and carboxyl groups in the nitrogen-doped carbon nanosheet played important roles in Cr(VI) removal, and promoted the reduction of Cr(VI) to Cr(III).

• 한국분말재료학회지
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• 제28권1호
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• pp.31-37
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• 2021

This study explores reducing the oxygen content of a commercial Ti-48Al-2Cr-2Nb powder to less than 400 ppm by deoxidation in the solid state (DOSS) using Ca vapor, and investigates the effect of Ca vapor on the surface chemical state. As the deoxidation temperature increases, the oxygen concentration of the Ti-48Al-2Cr-2Nb powder decreases, achieving a low value of 745 ppm at 1100℃. When the deoxidation time is increased to 2 h, the oxygen concentration decreases to 320ppm at 1100℃, and the oxygen reduction rate is approximately 78% compared to that of the raw material. The deoxidized Ti-48Al-2Cr-2nb powder maintains a spherical shape, but the surface shape changes slightly owing to the reaction of Ca and Al. The oxidation state of Ti and Al on the surface of the Ti-48Al-2Cr-2Nb powder corresponds to a mixture of TiO2 and Al2O3. As a result, the peaks of metallic Ti and Ti suboxide intensify as TiO2 and Al2O3 in the surface oxide layer are reduced by Ca vapor deposition.

• 한국자동차공학회논문집
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• 제22권4호
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• pp.152-159
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• 2014

Urea solution as a reductant of SCR has been widely used to reduce NOx emissions from diesel engine. But it has lots of problems which are freezing at low temperature due to liquid state, deposition of solid formation in the exhaust, dosing device, and complex package such as mixers for uniform concentration of ammonia. In order to overcome these obstacle, ammonium carbonate which is one of solid ammonium materials to produce ammonia gas directly by sublimation process is considered. Simple reactor with visible widow was designed to predict equilibrium temperature and pressure of ammonium carbonate. To simulate real operation conditions under automobile environment, several cycles of heating and cooling condition were settled, two different re-solidification materials were extracted from the reactor and visible window. Analytical study is performed to characterize these unknown materials by XRD(X-Ray Diffraction), FT-IR(Fourier Transform Infrared Spectroscopy), and EA(Elemental Analyzer). From analytical results, re-solidification materials from heating and cooling cycles are very similar to original material of ammonium carbonate.

• Bulletin of the Korean Chemical Society
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• 제35권7호
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• pp.2057-2064
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• 2014

Thermochemical sulfate reduction (TSR) was conducted in autoclave on the system of crude oil and $MgSO_4$ at different temperatures. Gas chromatography pulsed flame photometric detector (GC-PFPD) was used to detected the composition of organic sulfur compounds in oil phase products. The results of the analysis indicate that with increased temperature, the contents of organic sulfur compounds with high molecular weight and thermal stability, such as benzothiophenes and dibenzothiophenes, gradually became dominated. In order to gain greater insight into the formation and distribution of organic sulphur compounds from TSR, positive ion electrospray Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) was used in detecting the detailed elemental composition and distribution of them. The mass spectra showed that the mass range of sulfur compounds was 200-550 Da. Four sulfur class species, $S_1$, $N_1S_1$, $O_1S_1$ and $O_2S_1$, were assigned in the positive-ion spectrum. Among the identified sulfur compounds, the $S_1$ class species was dominant. The most abundant $S_1$ class species increase associated with the DBE value and carbon number increasing which also indicates the evolution of organic sulfur compounds in TSR is from the labile series to the stable one. In pure blank pyrolysis experiments with crude oil cracking without TSR, different composition and distribution of organic sulfur compounds in oil phase products were seen from mass spectra in order to evaluate their pyrolysis behaviors without $MgSO_4$. FT-IR and XRD were used in analyzing the products of solid phases. Two distinct crystallographic phases MgO and $MgSO_4$ are found to coexist in the products which demonstrated the transformation of inorganic sulfur compounds into organosulfur compounds exist in TSR.

• Computers and Concrete
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• 제21권1호
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• pp.67-74
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• 2018

A differential scheme based micromechanical framework is proposed to obtain the effective properties of the saturated concrete repaired by the electrochemical deposition method (EDM) considering the interfacial transition zone (ITZ) effects. The constituents of the repaired concrete are treated as different phases, consisting of (micro-)cracks, (micro-)voids and (micro-)pores (occupied by water), deposition products, intrinsic concrete made up by the three traditional solid phases (i.e., mortar, coarse aggregates and their interfaces) and the ITZs. By incorporating the composite sphere assemblage (CSA) model and the differential approach, a new multilevel homogenization scheme is utilized to quantitatively estimate the mechanical performance of the repaired concrete with the ITZs. The CSA model is modified to obtain the effective properties of the equivalent particle, which is a three-phase composite made up of the water, deposition products and the ITZs. The differential scheme is employed to reach the equivalent composite of the concrete repaired by EDM considering the ITZ effects. Moreover, modification procedures considering the ITZ effects are presented to attain the properties of the repaired concrete in the dry state. Results in this study are compared with those of the existing models and the experimental data. It is found that the predictions herein agree better with the experimental data than the previous models.

• 전기전자학회논문지
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• 제27권1호
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• pp.25-29
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• 2023

폴리실라잔 고체 전해질 층과 은(Ag) 활성 전극의 공정이 멤리스터의 전기적 특성에 미치는 영향을 살펴보았다. 더 높은 온도에서 어닐링된 고체 전해질을 갖는 멤리스터가 더 낮은 온도에서 어닐링된 고체 전해질을 갖는 소자보다 더 높은 set voltage 및 더 나은 메모리 유지 특성을 보였다. 어닐링 온도 증가에 따른 set voltage의 증가 및 메모리 유지 특성의 향상은 각각 고체 전해질 층 내부의 빈 공간의 감소 및 균일도 증가 때문인 것으로 사료된다. 고체 전해질 층을 비교적 높은 온도에서 어닐링 할지라도, 폴리실라잔 용액의 농도가 지나치게 높은 경우에는 멤리스터의 저저항상태가 유지되지 못했다. 마지막으로, 용액공정으로 형성한 Ag 활성 전극을 갖는 멤리스터는 진공공정으로 형성한 Ag 활성 전극을 갖는 소자와 달리 WORM 특성을 갖는 것으로 나타났다. 이러한 WROM 특성은 용액공정 Ag 활성 전극에 존재하는 형태적 결함 때문인 것으로 사료된다.

• 한국산학기술학회논문지
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• 제12권11호
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• pp.5376-5383
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• 2011

본 연구의 목적은 연소 배기가스로부터 포집된 이산화탄소를 다시 일산화탄소 또는 탄소로 전환하여 산업에 다시 활용하고자 하는 탄소순환형 기술개발이다. 이산화탄소는 화학적으로 안정한 분자로써 쉽게 분해되지 않기 때문에 낮은 온도에서 반응이 일어날 수 있는 적합한 금속계 산화물(활성화제)의 선택이 필요하다. 따라서 본 연구에서는 Ni-Fe 전이금속산화물을 사용하여 $CO_2$를 CO나 C로 전환하고자 하였다. 시료는 고상법과 수열합성을 이용해 제조된 분말을 사용하여 각각 이산화탄소 분해특성 연구를 수행하였다. 이산화탄소의 분해 특성을 관찰하기 위해 TPR/TPO와 TGA 장치를 사용하였다. TPR/TPO를 이용한 수소의 환원면적은 NiO의 함량이 15wt%일 때 높게 나타났고, $CO_2$에 의한 흡착분해 곡선면적은 NiO의 함량이 5wt%일 때 우수한 성능을 나타내었다. 그러나 TGA를 이용한 실험결과에서는 고상법에 의해 제조된 시료 중 NiO의 함량이 2.5wt%일 때 수소에 의한 흡착환원이 28.47wt% 발생하였고, $CO_2$에 의한 산화량의 경우 26.95wt%로 가장 높게 나타났다. 그리고 이산화탄소의 분해효율이 94.66%로 우수한 산화 환원 특성을 나타내었다.

• 한국세라믹학회지
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• 제48권4호
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• pp.303-306
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• 2011

[ $V_2O_5$ ]doped Karrooite pigments were synthesized by the solid state method to get stabilized brown pigment in oxidation and reduction atmosphere. Optimum substitution condition and limited dopant with $V_2O_5$ for Karrooite pigment was investigated. With calcination at $1250^{\circ}C{\sim}1400^{\circ}C$, compositions were designed varying $V_2O_5$ molar ratio by increasing 0.02mole to the formula $Mg_1-xTi_2-xM_{2x}O_5$(x = 0.01~0.09 mole). Synthesized pigments were analyzed by XRD, Raman spectroscopy and UV-vis. When $V_2O_5$ was doped from 0.01 to 0.05 mole, single phase of Karrooite was observed at temperature $1300^{\circ}C$ and soaking time 4h by Raman spectroscopy. However, it was found that excess $VO_2$ peak appeared with 0.07 and 0.09 mole of $V_2O_5$ doped to $MgTi_2O_5$. This result indicated that the maximum limit of solid solution is 0.05 mole $V_2O_5$. Karrooite pigments were applied as a ceramic pigment to achieve brown colors in lime magnesia glaze and lime barium graze at both of oxidation and reduction atmosphere. CIE color coordinates are $L^*$ = 40.34, $a^*$ = 9.94, $b^*$ = 21.40 in lime magnesia glaze.

• Bulletin of the Korean Chemical Society
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• 제19권6호
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• pp.661-666
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• 1998

Active reaction sites and electrochemical O2 reduction kinetics on La_{1-x}Sr_xMnO_{3+{\delta}} (x=0.1-0.4)/YSZ (yttria-stabilized zirconia) electrodes are investigated in the temperature range of 700-900 ℃ at $Po_2=10^{-3}$-0.21 atm. Results of the steady-state polarization measurements, which are formulated into the Butler-Volmer formalism to extract transfer coefficient values, lead us to conclude that the two-electron charge transfer step to atomically adsorbed oxygen is rate-limiting. The same conclusion is drawn from the $Po_2$-dependent ac impedance measurements, where the exponent m in the relationship of $I_o$ (exchange current density) ∝ $P_{o_{2}}^m$ is analyzed. Chemical analysis is performed on the quenched Mn perovskites to estimate their oxygen stoichiometry factors (δ) at the operating temperature (700-900 ℃). Here, the observed δ turns out to become smaller as both the Sr-doping contents (x) and the measured temperature increase. A comparison between the 8 values and cathodic activity of Mn perovskites reveals that the cathodic transfer coefficients $({\alpha}_c)$ for oxygen reduction reaction are inversely proportional to δ whereas the anodic ones $({\alpha}_a)$ show the opposite trend, reflecting that the surface oxygen vacancies on Mn perovskites actively participate in the $O_2$ reduction reaction. Among the samples of x= 0.1-0.4, the manganite with x=0.4 exhibits the smallest 8 value (even negative), and consistently this electrode shows the highest ${\alpha}_c$ and the best cathodic activity for the oxygen reduction reaction.