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Essential Oil Constituents of Swertia chirata Buch.-Ham.
Gyawali, Rajendra,Ryu, Keun-Young,Shim, Sung-Lye,Kim, Jun-Hyoung,Seo, Hye-Young,Han, Kyu-Jae,Kim, Kyong-Su The Korean Society of Food Science and Nutrition 2006 Preventive Nutrition and Food Science Vol.11 No.3
The essential oil of Swertia chirata Buch.-Ham. was extracted by solvent extraction (n-pentane:diethylether, 1:1) method using simultaneous distillation-extraction (SDE) apparatus and analyzed by gas chromatography-mass spectrometry (GC/MS). The yield of essential oil obtained from S. chirata was 236.47 mg/kg. Seventy seven compounds of the essential oil belonging to chemical classes of acid (4), alcohol (21), aldehyde (15), ester (3), furan (3), hydrocarbon (7), ketone (17) and miscellaneous (7) were tentatively identified. The major volatile compounds ranged in content order were as follows: undecanoic acid (28.63%), 2-buten-2-one (20.42%), camphor (18.40%), 2-heptadecanone (14.72%), and cedrol (13.07%).
Mechanical and tribological properties of Ni-W-TiB<sub>2</sub> composite coatings
Gyawali, Gobinda,Tripathi, Khagendra,Joshi, Bhupendra,Lee, Soo Wohn ELSEVIER SCIENCE 2017 JOURNAL OF ALLOYS AND COMPOUNDS Vol.721 No.-
<P><B>Abstract</B></P> <P>Pure Ni, Ni-W alloy, and Ni–W–TiB<SUB>2</SUB> composite coatings were prepared on the copper substrate by electrodeposition technique. Surface morphology and elemental composition of as prepared samples were observed and analyzed by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). X-ray diffraction (XRD) technique was used to analyze the crystallinity and phase composition of the samples. XRD patterns show a typical FCC Ni-W alloy phase of the Ni-W-TiB<SUB>2</SUB> composite coating. Vickers microhardness of Ni-W-TiB<SUB>2</SUB> composite coating is significantly improved as compared to pure Ni and Ni-W alloy coatings. Wear and coefficient of friction of the Ni-W-TiB<SUB>2</SUB> composite coating are found to be improved. Adhesive wear is found to be predominant in pure Ni, and Ni-W coating whereas abrasive nature of wear is obtained in Ni-W-TiB<SUB>2</SUB> composite coating. The Ni-W-TiB<SUB>2</SUB> composite coating exhibited improved scratch resistance over pure nickel and Ni-W coatings. The scratch resistance of the composite coating is influenced by W alloying and TiB<SUB>2</SUB> incorporation to the nickel matrix.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Ni-W-TiB<SUB>2</SUB> composites were prepared by electrochemical co-deposition method. </LI> <LI> Microstructure, scratch, friction and wear behaviors of the composites were studied. </LI> <LI> Enhanced scratch resistance of the Ni-W-TiB<SUB>2</SUB> were observed. </LI> <LI> Tribological properties of Ni-W-TiB<SUB>2</SUB> composites were significantly improved. </LI> </UL> </P>
Effect of Ultrasound on the Mechanical Properties of Electrodeposited Ni-SiC Nano Composite
Gyawali, Gobinda,Cho, Sung-Hun,Woo, Dong-Jin,Lee, Soo-Wohn Materials Research Society of Korea 2010 한국재료학회지 Vol.20 No.8
Nano sized SiC particles (270 nm) are easily agglomerated in nickel sulfamate electrolytic bath during a composite electrodeposition process. The agglomeration of nano particles in composite coatings can significantly reduce the mechanical properties of the composite coatings. In this study, Ni-SiC nano composite coatings were fabricated using a conventional electrodeposition process with the aid of ultrasound. Nano particles were found to be distributed homogeneously with reduced agglomeration in the ultrasonicated samples. Substantial improvements in mechanical properties were observed in the composite coatings prepared in presence of ultrasound over those without ultrasound. Ni-SiC composite coatings were prepared with variable ultrasonic frequencies ranging from 24 kHz to 78 kHz and ultrasonic powers up to 300 watts. The ultrasonic frequency of 38 kHz with ultrasonic power of 200 watt was revealed to be the best ultrasonic conditions for homogeneous dispersion of nano SiC particles with improved mechanical properties in the composite coatings. The microstructures, phase compositions, and mechanical properties of the composite coatings were observed and evaluated using SEM, XRD, Vickers microhardness, and wear test. The Vickers microhardness of composite coatings under ultrasonic condition was significantly improved as compared to the coatings without ultrasound. The friction coefficient of the composite coating prepared with an ultrasonic condition was also smaller than the pure nickel coatings. A synergistic combination of superior wear resistance and improved microhardness was found in the Ni-SiC composite coatings prepared with ultrasonic conditions.
A Thermally Reduced Graphite Oxide and Carbon Nanotube Composite for Supercapacitor Applications
Gyawali GHANASHYAM,정혜경 한국물리학회 2018 New Physics: Sae Mulli Vol.68 No.2
A thermally reduced graphite oxide and carbon nanotube (TRGO-CNT) composite is synthesized for supercapacitor applications by using a simple chemical method. The TRGO-CNT composite shows higher capacitance then the precursors (TRGO and CNT), and its impedance is lower than that of CNT, meaning that TRGO of high surface area connected with a CNT could provide highly efficient surface area and good connection for supercapacitor electrodes. Different weight ratios of TRGO to CNT are investigated, and the results show that the composite with more TRGO has better performance in the electrochemical measurements. Based on these findings, the proper TRGO amount is necessary for a high-performance supercapacitor. Neither CNT nor TRGO by itself can give the highest electrochemical performance for the supercapacitor; thus, the synergistic effect of TRGO and CNT is important.
Nitrogen-doped Molybdenum Disulfide to Catalyze Hydrogen and Oxygen Evolution Reactions
Gyawali Ghanashyam,Hae Kyung Jeong 한국물리학회 2022 새물리 Vol.72 No.4
Nitrogen-doped molybdenum disulfide (N-MoS2) was synthesized using melamine as the nitrogen source to be used as a catalyst for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). The as-synthesized N-MoS₂ had an atomic nitrogen composition of 13%, and it exhibited a low overpotential of −0.20 V at −10 mA/c㎠ for HER and 1.43 V at 10 mA/㎠ for OER, with small Tafel slope values of 97 and 117 mV/dec for HER and OER, respectively. The enhanced HER and OER performances observed as a result of the nitrogen doping of MoS₂ is attributed to N-MoS₂ being characterized by a higher electrochemical active surface area (9.1 × 10<SUP>−4</SUP> ㎠) and lower charge transfer resistance (8.1 Ω) than its precursor.
Sonochemical synthesis of solar-light-driven Ag@?-PbMoO<sub>4</sub> photocatalyst
Gyawali, G.,Adhikari, R.,Joshi, B.,Kim, T.H.,Rodriguez-Gonzalez, V.,Lee, S.W. Elsevier Scientific Pub. Co 2013 Journal of hazardous materials Vol.263 No.1
Ag@?-PbMoO<SUB>4</SUB> photocatalysts were synthesized by facile sonochemical method with different mol.% of Ag nanoparticles dispersed on the surface of PbMoO<SUB>4</SUB>. The synthesized powders were characterized by X-ray Diffraction (XRD) Spectroscopy, X-Ray Photoelectron Spectroscopy (XPS), Transmission Electron Microscopy (TEM), and Diffuse Reflectance Spectroscopy (UV-vis DRS) to investigate the crystal structure, morphology, chemical composition, and optical properties of the photocatalyst. Photocatalytic activities of the Ag@?-PbMoO<SUB>4</SUB> samples were evaluated by the degradation of Indigo Carmine (IC) dye under simulated solar light irradiation. It has been observed that the sample containing 0.3mol.% of Ag showed the best photocatalytic activity as compared to other samples. The results suggest that the dispersion of Ag nanoparticles on the surface of PbMoO<SUB>4</SUB> significantly enhances the photocatalytic activity of PbMoO<SUB>4</SUB>. Increase in photocatalytic activity of Ag@?-PbMoO<SUB>4</SUB> photocatalyst has been explained on the basis of surface plasmon resonance (SPR) effect caused by the silver nanoparticles present in the photocatalyst.
Gyawali, Gobinda,Lee, Soo Wohn American Scientific Publishers 2016 Journal of Nanoscience and Nanotechnology Vol.16 No.11
<P>Ag3PO4/MoS2 composite photocatalysts with 1 to 10 wt% of MoS2 have been synthesized by the microwave assisted hydrothermal process. Prepared Ag3PO4/MoS2 composites were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), UV-vis diffuse reflectance spectroscopy (DRS), and X-ray photoelectron spectroscopy (XPS). It was found that the as prepared Ag3PO4 revealed micron-sized particles, whereas Ag3PO4/MoS2 composites have shown a significantly reduced size of Ag3PO4 particles which were found to be deposited on the surface of MoS2. The Ag3PO4/MoS2 composites exhibited enhanced photocatalytic activity for the photocatalytic degradation of methyl orange (MO) under a simulated solar light condition. The photocatalytic reaction rate of Ag3PO4/3 wt% MoS2 composite is found to be the highest among all other samples. Furthermore, the photocatalytic stability of Ag3PO4/3 wt% MoS2 composite is significantly enhanced in comparison to bare Ag(3)PO4 photocatalyst.</P>