No abstract

In this research, zinc oxide (ZnO) nanoparticles were prepared through a chemical co-precipitation route using zinc acetate dihydrate and sodium hydroxide as the reactants. To study the variation in the properties of the nanoparticles, namely its phase, shape and size, the reaction temperature and stirring rate were varied during the synthesis process. From the X-ray diffraction profiles, the assynthesised samples were confirmed to be ZnO. Spherical and hexagonal-shaped particles were obtained when the temperature and stirring rate were varied. A rise in the synthesis temperature from 30 to 70°C caused insignificant changes to the average diameter of the particles, although their shape was altered from spherical to hexagonal. When the stirring rate was increased, the average diameter of the particles decreased. The average diameter of the sample calcined at 600°C for 1 hour recorded a slight increase while its X-ray diffraction profile depicted narrower peaks with higher intensity, indicating formation of a more stable phase of ZnO. Further study is needed to elucidate the effects of the particle shape and sizes on the thermoelectric transport properties.

The Zeeman effect of chlorine nuclear quadrupole resonance in polycrystalline samples of 2,6-, 2,5 and 3,5-dichloro.phenol has been investigated at room temperature in order to study the effect of hydrogen bonding on the electric field gradient asymmetry parameter q. While the two n.q.r. lines in 3,5dichlorophenol gave an asymmetry parameter of x 10 %, those in 2,6-and 2,5-dichlorophenol gave different values of q for the two chlorines. The chlorine atom which is ortho to the OH group and involved in hydrogen bonding (k, corresponding to the low frequency line) gave an asymmetry parameter of0.21 in 2,6dichlorophenol and 0.17 in 2,5-dichlorophenol while the other chlorine ( i e . , corresponding to the high frequency line) gave a lower value of 0.12 in 2,6-dichlorophenol and 0.11 in 2,5-dichlorophenol. These values of q are discussed in terms of hydrogen bonding and bond parameters.

N.q.r. in sodium chloroacetate has been investigated at temperatures from 77 K to room temperature (c.300 K). A single line has been observed throughout this temperature range. Torsional frequencies of the molecule have been calculated in the above temperature range from Bayer's theory. Also the temperature coefficient of the torsional frequencies has been calculated by Brown's method.