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Mat. Res. Soc. Symp. Proc. Vol. 581 © 2000 Materials Research Society

at room temperature the precipitate was collected and washed with isopropanol. Basic magnesium chloride nanorods were then transformed into magnesium hydroxide nanorods by base (NaOH) treatment at 60 'C in a mixed solvent of ethanol and water (3:1). Lastly the dried magnesium hydroxide nanorods were heated in flowing oxygen slowly to 900 'C and calcined at 900 'C for one hour to finish the conversion to crystalline magnesium oxide nanorods. The morphology and structure of the products were examined by field-emission scanning electron microscopy (SEM) (LEO 982) and transmisson electron microscopy (TEM) (Philips EM420 and JEOL 2010) equipped with energy dispersive X-ray (EDX) spectroscopy to evaluate the chemical composition. The phase analysis was performed using powder X-ray diffraction (XRD) (Scintag XDS2000). RESULTS AND DISCUSSION

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Figure 1. (a) - (c) SEM images of the precursor, the intermediate product after base treatment, and the final product after calcination, respectively. (d) - (f) Corresponding powder XRD patterns of products from each of the step in (a) - (c).

Figure 1 shows typical SEM images of the products from each step and their corresponding powder XRD patterns. The SEM data show clearly that they all have similar rod-like morphology with aspect ratios of at least 50 and relatively good uniformity. XRD patterns show that they are Mg 2(OH) 3C1-4H 20, Mg(OH) 2 and MgO, respectively, and that no second phase is present. This demonstrates a successful transformation from hydrated basic magnesium chloride nanorods to magnesium oxide nanorods via intermediate magnesium hydroxide nanorods. In general, the diameters of MgO nanorods range from 40 nm to 200 nm with an average of 120 nm and the lengths usually are 10 gim or longer. The nanorods have rectangular cross section and are straight and uniform in diameter along the axis. EDX spectroscopy measurements of these rods show no other heavy elements, such as Cl, other than Mg. Powder XRD pattern (figure 1(f)) can be indexed as cubic MgO structure. Together with the EDX measurement, it shows very high phase purity of these nanorods. In addition, from the SEM images it can be seen that particulate impurities are rarely found. Therefore the products are very pure (>95%) crystalline MgO nanorods. Figure 2 shows a TEM image of a single MgO nanorod. The rod surface looks rough at this magnification. To determine whether the rods are single-crystalline or polycrystalline, electron diffraction patterns were recorded on a number of nanorods. Figure 3 shows three most commonly seen electron diffraction patterns. The arrows in the patterns indicate the direc