Thanusit Burinprakhon

NANOSIZE POWDERS OF SILVER-DOPED SODIUM COBALT OXIDE SYNTHESIZED BY POLYMERIZED COMPLEX METHOD

Nanosized powders used for the preparation of bulk Na1.5Co2O4 and Ag-doped Na1.5Co2O4 nanosized crystalline grains were synthesized by the polymerized complex (PC) method. X-ray diffraction analysis revealed that the nondoped and Ag-doped PC products were composed of Co3O4 and Na2CO3 phases. After a subsequent calcination at 800°C, the nondoped PC product was converted to powder of single phase γ-NaxCo2O4, whereas the Ag-doped PC products remained as mixed phases of Co3O4 and Na2CO3 and Ag2O with a small trace of γ-NaxCo2O4. SEM and TEM investigations showed that all the calcined products were powders of about 200–500 nm particle size.

Thermoelectricity of p-NCO and n-ZAO Thin Films

Thin films of sodium cobalt oxide and zinc aluminium oxide were prepared onto ceramic substrates by a bipolar pulsed-dc magnetron sputtering system using a NaCoO2 target and a ZnAlO target, respectively, under an argon atmosphere. Energy dispersive spectroscopy analysis revealed that the as-deposited films from the NaCoO2 target comprised Na, Co, O elements, while those from the ZnAlO target contained Zn, Al, O elements. Cross-sectional view estimation by the scanning electron microscope indicated that the as-deposited Na-Co-O (NCO) and Zn-Al-O (ZAO) films had the thickness of 0.63 μm and 0.58 μm, respectively. X-ray diffraction analysis showed that the NCO thin films were grown in amorphous phase while the ZAO thin films exhibited hexagonal structure. From thermoelectric properties measurement, the p-NCO and n-ZAO films were found to exhibit the thermoelcectric power factor of 0.03 and 14.39 μW/mK2, respectively. A thermoelectric module made from three pairs of the p-n thin film stripes provided the open-circuit voltage up to 26.0 mV for a temperature difference of 79.3 K. However, the module was unable to produce useful electrical current due to its high internal series resistance contributed from the NCO films.

NANOCRYSTALLINE DIAMOND FILMS ON HIGH SPEED STEEL BY MICROWAVE PLASMA CHEMICAL VAPOR DEPOSITION

Nanocrystalline diamond films were deposited on high speed steel substrates by microwave plasma chemical vapor deposition. The best hardness improvement was about 130% of the substrate hardness, using -150 V substrate bias deposition conditions. Raman peaks of nanocrystalline diamond at 1190 cm-1 and of graphite nanoclusters at 1522 cm-1 wereobserved in this sample. Scanning electron microscope images show crystallite grains of different sizes between 25–250 nm.