Microscopy in the Field of Materials Research

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Authors: Visittapong Yordsri, Chanchana Thanachayanont, Chabaiporn Junin, Nuttakorn Keratipaiboon, Pairat Tabai, Mana Rodchom, Samerkhae Jongthammanurak, Phetcharaporn Ninwilai, Supapan Seraphin, Chris Boothroyd
Abstract: Charcoal consists mostly of carbon materials prepared by carbonization, i.e., traditionally by pyrolysis [1,2] of wood pieces in a kiln. At a high enough temperature and an absence of oxygen [3], high-quality charcoal with low resistance can be produced. A possible application of the low-resistivity charcoal is as an electrode material for electrochemical devices. In this research, bamboo waste was used to produce low-resistance bamboo charcoal. During heating, the temperature gradually increased up to 700°C, was kept approximately constant overnight, and was left to cool down to room temperature. Then, the charcoal bamboo pieces were obtained. A rough temperature-resistivity map was constructed. The bamboo charcoals were divided into 3 resistivity ranges, namely, 20, 100 and 1000 ohm.cm-1. Transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectroscopy and microEDX (energy dispersive X-ray spectroscopy), were conducted for charcoal morphology and spectroscopic characterization [4-6]. The morphological results from SEM did not show any significant differences among bamboo charcoals with different resistivity. DF-STEM and EDS-STEM mapping revealed impurities inside the bamboo charcoal. Elemental analysis of micro areas showed weight percentage of carbon and other impurities in the bamboo charcoals. The 20 ohm.cm-1 bamboo charcoal was the best among all resistivity studied in terms of purity and main carbon structure. Decreasing the impurity content was found to be one of the essential parameters to obtain low resistivity bamboo charcoal. It was concluded that improving the stability and condition of the burning process in the conventional kiln was necessary in order to get a high yield of low resistance bamboo charcoals.
Authors: Nittaya Tamaekong, Sukon Phanichphant, Anurat Wisitsoraat, Chaikarn Liewhiran
Abstract: The p-CuxO core/n-ZnO shell heterostructure nanowire (NW) arrays were fabricated by thermal decomposition. Based upon the core/shell nanowire-based all oxide p-n junctions. The samples were analyzed by XRD, SEM, EDS and TEM. X-ray diffraction (XRD) analysis showed that the p-CuxO core/n-ZnO shell NW consisted of phase of p-CuxO and wurtzite phase of n-ZnO. The morphology analysis showed average diameter and length of nanowires of ̴ 50 to 200 nm and ̴ 10 to 30 µm, respectively. The EDS spectrum confirmed the presence of required elements in the p-CuxO core /n-ZnO shell NWs. It was found that Zn, O and Cu are distributed over the wire areas according to a ratio of 1:2 by atomic% ratio of Cu:Zn to get good core/shell structure. The TEM characterizations showed that the n-ZnO shell nanoparticles were comprised of n-ZnO polycrystalline nanoparticles (NPs) on the surface of p-Cu2O core NWs. The H2S gas sensing properties of the p-CuxO/n-ZnO NWs were evaluated in air containing dilute H2S gas at sensing temperatures (T) of 350°C. The response of 20.6 for p-CuxO/n-ZnO NW sensor to H2S gas was enhanced compared to that of the n-ZnO NW. The enhanced response of p-CuxO/n-ZnO NW sensor is due to increasing surface area, the increased amount of chemisorbed oxygen species on NP surface and the increased conductivity.
Authors: Bralee Chayasombat, Visittapong Yordsri, Vittaya Amornkitbamrung, Seksan Lowpa, Samuk Pimanpang, Wasan Maiaugree, Nattawat Ratchapolthavisin, Pikaned Uppachai, Santipap Mitravong, Chris Boothroyd, Chanchana Thanachayanont
Abstract: In this study, hydrothermal carbonization of carrot juice was conducted at 180 °C for 6 hours, followed by annealing at 500 °C for 6 hours. In the absence of a catalyst, hydrothermal carbonization of carrot juice produced hollow and solid carbon microspheres (CMS) with diameters ranging from 0.3 to 4.0 µm. SEM and TEM images of the CMS showed various morphologies and sizes. X-ray diffraction and Raman spectroscopy indicated the CMS had a disordered graphitic structure. A HAADF micrograph showed that although the majority of the CMS in this study were hollow, there were also solid spheres which had not previously been reported for hydrothermal carbonization. STEM EDS mapping of a solid CMS indicated approximately 95 wt% of C with traces of N, O, Si, P, S, Cl and K. The effect of the starting precursors on the hard sphere formation mechanism is discussed.
Authors: Yothin Chimupala, Rik Drummond-Brydson
Abstract: Titanium dioxide (B phase) with 1-D structures was successfully fabricated via a hydrothermal method with a subsequent ion-exchange process and calcination. P25, titanium isopropoxide (TTIP), rutile and also anatase were used as Ti precursors in the alkali hydrothermal system. TTIP promoted an elongation of nanorod morphology whereas the other precursors produced short nanorod structures. The different types of titanium precursors did not have any influence on the phase transformation during the fabrication process. Na2Ti6O13 was the primary intermediate product after washing the hydrothermal sample. H2Ti3O7 was the secondary intermediate phase obtained following proton-exchange of Na2Ti6O13 in HNO3 solution. Finally, the TiO2(B) phase was the product of calcination of the secondary intermediate product at 400°C for 5 hr. A phase transformation mechanism is presented based on an investigation of products at each of the steps. The effects of the synthesis conditions on tailoring of the crystal morphology are discussed. The growth direction of the TiO2(B) nanorods was investigated by HR-TEM and SADP. Finally, the metastable phase of TiO2(B) was shown to be transformed to anatase during thermal treatment at temperatures higher than 400°C.
Authors: Thanapat Autthawong, Bralee Chayasombat, Viratchara Laokawee, Nutpaphat Jarulertwathana, Takuya Masuda, Thapanee Sarakonsri
Abstract: Silicon-cobalt nanocomposites on NrGO, Si-Co/NrGO, were synthesized by the modified polyol method. Rice husk was used as the silicon source. The composites were primarily characterized by x-ray diffraction, scanning electron microscopy, and transmission electron microscopy equipped with energy dispersive spectroscopy. The small-sized particles of the silicon-cobalt product were effectively distributed on the NrGO. Finally, these anode materials were tested in lithium-ion batteries by haft-coin cell assembly. Electrochemical properties were measured and the result showed an initial capacity of 975 mAh g-1. This material is expected to be used as a high-performance anode, suitable for the next generation of anode materials in lithium-ion batteries.
Authors: Viratchara Laokawee, Nutpaphat Jarulertwathana, Thanapat Autthawong, Takuya Masuda, Yothin Chimupala, Suparin Chaiklangmuang, Thapanee Sarakonsri
Abstract: Silicon (Si) and Tin (Sn) are promising materials for anodes in lithium-ion batteries due to their high theoretical capacity and abundance of Si on earth. Si can be derived from rice husk which is the main agricultural byproduct in Thailand. However, the challenge of using these materials in lithium-ion batteries is the large volume expansion during charge-discharge process which leads to pulverization of electrodes. The effective solution is to combine these metals as composite with carbon supporter. Nitrogen-doped reduced graphene oxide (NrGO) has been used as carbon supporter in this research because of its high surface area, electrical conductivity and rate of electron transfer. To confirm phases of products, X-rays diffraction techniques (XRD) was measured. The results show that there were peaks of Si, Sn and carbon in XRD patterns. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to illustrate the morphology of prepared composites. From SEM and TEM results, there were small-sized particles of Si and Sn dispersed randomly on NrGO sheets. Furthermore, electrochemical properties of these products were measured to confirm their efficiency as anode materials in lithium-ion batteries by coin cell assembly. The prepared composite can deliver the highest initial capacity of 1600 mA h g-1 and expected to use as anode materials in the next generation lithium-ion batteries.
Authors: Voranuch Somsongkul, Surassawatee Jamikorn, Chanu Photiphitak, Thapanee Sarakonsri, Viratchara Laokawee, Nutpaphat Jarulertwathana, Naruephon Mahamai, Rawinunt Thanachayanont, Suchada Srisakuna, Chris Boothroyd, Taweechai Amornsakchai, Pasit Pakawatpanurat, Pennapa Muthitamongkol, Visittapong Yordsri, Chanchana Thanachayanont
Abstract: Dye sensitized solar cells (DSSCs) consist of photoanodes (dye adsorbed porous semiconductor film), electrolytes and counter electrodes. Nanostructured materials play important parts in both the photoanodes and the counter electrodes, while dyes are there to absorb photons and generate electron-hole pairs and electrolytes are there to transfer electrons from the photoanodes to the counter electrodes. In this study, to enhance light absorption and minimize electron-hole recombination, Ag nanoparticles and MgO nanolayer were coated on TiO2, respectively. To enable a long lifetime, i.e. avoiding liquid electrolyte leakage, quasi-solid-state (QSS) DSSCs were fabricated. PtSn nanoparticles were prepared by a simple chemical reduction method on graphene oxide (GO) to compare with conventional Pt catalyst on FTO substrates as counter electrodes. An average efficiency of the QSS DSSCs with PtSn/GO co-catalysts was found to outperform that of the QSS DSSCs with conventional Pt catalyst. A mixed microstructure of the PtSn/GO co-catalyst was observed. Although, PtSn2 and Pt2Sn3 phases were suggested by XRD, in a small region observed by EDX-STEM, it was found that C, O and Si were distributed uniformly on the graphene oxide film. Pt was also distributed uniformly, but the signal was low so there were only a few X-Ray counts across the image. There was no sign of Pt being concentrated in the particles. However, Sn was found to be concentrated in the particles without any other elements.
Authors: Natthaphol Chomsaeng, Bralee Chayasombat, Inthiraporn Insura, Kritsana Narkdee, Chanchana Thanachayanont
Abstract: Titanium dioxide nanotubes on titanium surface were prepared by electrolytic anodization in aqueous solution at constant voltages at room temperature for 2, 4 and 6 hours. Anodized titanium was heat treated in a furnace at 450 °C for 4 hours to convert amorphous structure to anatase and rutile crystalline structure. A scanning electron microscope was utilized for morphology investigation of the anodized titanium surfaces. For HF containing water media, porous surface on titanium was revealed after anodizing for 2 hours. Nanotubes (NT) were formed in this media at 4 and 6 hours anodizing time, the diameters of the tubes were approximately 70 to 100 nm. For HF/Na2SO4 aqueous solution, fine NTs, approximately 50 nm in diameter, were grown after 2 hours. However, the NTs obtained at anodizing time 4 and 6 hours were the same size, ranging from 100 to 120 nm. Anatase and rutile phases of TiO2 were formed in the anodized samples after annealing at 450 °C for 4 hours. The anodized samples were tested for their abilities to degrade Rhodamine B, to demonstrate their application as a material for waste water treatment. The Rhodamine B was degraded up to 41% in annealed sample anodized by electrolyte contained HF.
Authors: Namthip Kingnoi, Jiratchaya Ayawanna, Nattapol Laorodphan
Abstract: This work describes the performance of two glass-ceramic compositions, BaO-SiO2-B2O3 (Barium borosilicate glass: BaBS) and BaO-ZnO-SiO2-B2O3 (Barium zinc borosilicate glass: BaBS−Zn), used for joining YSZ ceramic electrolytes and Crofer22APU metallic interconnects in solid oxide fuel cells (SOFCs) working at 800°C for 50 h. ZnO had a negative effect on the thermal expansion coefficient (TEC) value of the BaBS-Zn glass-ceramic. XRD and SEM results revealed the formation of rod-shaped barium zinc silicate crystalline phases in the BaBS-Zn glass, which was accompanied by cracks and poor adherence at the YSZ/BaBS-Zn joint interface after working at 800°C for 50 h. The formation of cracks parallel to the interface between the Crofer22APU interconnect and the BaBS-Zn glass-ceramic sealant was observed due to the severe TEC mismatch. The BaBS glass–ceramic adhered well to the YSZ electrolyte as well as the pre-oxidized Crofer22APU without cracks. Chromium oxide scale developed between the pre-oxidized Crofer22APU/BaBS glass-ceramic joint interface with increasing the pre-oxidation temperature. This study shows that BaBS glass-ceramic is more effective than BaBS-Zn as a sealant for joining YSZ electrolytes and Crofer22APU metallic interconnects in SOFCs working at 800°C for 50 h.

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