Chai Yan Ng

The formation of WO3 nanorods using the surfactant-assisted hydrothermal reaction

Monoclinic tungsten oxide (WO3) nanorods were grown using the hydrothermal method on a seeded W foil. The seed layer was formed by thermal oxidation of W foil at 400°C for 30 min. Cetyltrimethylammonium bromide (CTAB) or hexamethylamine (HMT) was used in the reactive hydrothermal bath, along with sodium tungstate dihydrate (Na2WO4.2H2O) and hydrochloric acid (HCl). The concentration of CTAB was varied from 0.01 M to 0.07 M and the concentration of HMT was varied from 0.01 M and 0.05 M. The result showed that CTAB-assisted hydrothermal reaction produced WO3 nanorods with 4–7 nm diameter, and provided that CTAB concentration was less than 0.07 M. WO3 nanorods could not be obtained when CTAB concentration was 0.07 M. Columnar structured WO3 was produced with the presence of HMT in the hydrothermal bath. This was due to decomposition of HMT to form hydroxyl ions (OH−) that inhibited the growth of nanorods. Cyclic voltammetry (CV) analysis showed better electrochromic property of WO3 nanorods compared to columnar structured WO3.

The Effects of Combustion Agents on the Formation of Bi-Based Compounds Synthesized Using the Soft Combustion Method

In this work, 20 % Pr doped bismuth sodium titanate (PBNT) powders were synthesized using the soft combustion technique. Three combustion agents; polyethylene glycol 200, citric acid and glycine with 0.2, 2.0 and 5.0 mol were used to aid combustion process. A single phase PBNT was obtained with the addition of 5 mol % citric acid. For most compounds, secondary phases presence such as Bi4Ti3O12 and Bi2Ti2O7. In general, crystallite size increased with increasing sintering temperature that was due to diffusion of ions at high temperature. Dielectric properties increased with increasing densities. The optimum properties were obtained for PBNT synthesized using 5 mol % citric acid sintered at 1100°C for 3 hours which gave the highest dielectric constant (1153.20), acceptable loss tangent (0.1074) and high relative density (95.03).