الفهرس 
Chapter 1Only 14 pages are availabe for public view
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Abstract
The co-precipitation method was used as a facile approach to prepare two different metal oxides nanoparticles, viz. Cr2O3 NPs and Co3O4 NPs, with large quantities. Alcohol assisted room temperature synthesis procedure was also used to prepare MnO2 NPs. The synthesized MnO2 NPs. Cr2O3 NPs, Co3O4 NPs, and MnO2 NPs were characterized by XRD, TEM, SEM, BET, FTIR, and TGA.
The XRD of Cr2O3 NPs provided a good agreement with reference pattern in the Rhombohedra phase. No obvious XRD peaks arising from impurities or other phases referring to the high purity of the as-prepared crystalline Cr2O3NPs. The XRD of Co3O4 NPs had a good agreement with reference pattern in cubic phase and no other XRD peaks were identified and this indicates the high purity of the as-prepared crystalline Co3O4NPs. The XRD of MnO2 NPs lacks the presence of well-defined peaks. The low intensity and broadening of peaks give good evidence for the amorphous nature of MnO2 was is mainly due to reaction of ethanol with KMnO4, yielding MnO2 particles instantly with small particles size.
The TEM and SEM studies of Cr2O3 NPs illustrated the size of particles in the range of 14-29 nm. The morphology of Cr2O3 NPs was spherical and irregular shape was obtained with some agglomerated forms. The TEM and SEM studies of Co3O4 NPs defined the size of particles as 14-50 nm. The morphology of Co3O4 NPs was found as a combination of sphere and cubic structures which are characterized by irregular shape and some agglomeration. The TEM and SEM of MnO2 NPs refer to particle size in the range of 2-29 nm. The morphology of was MnO2 NPs was spherical and exhibited irregular shape. Some agglomeration was found due to very small size of particles.
Determination of surface area values by the BET method of Cr2O3 NPs, Co3O4 NPs, and MnO2 NPs were identified as 38.9 m2/g, 32.2m2/g, and 59.1m2/g, respectively. These metal oxides nanoparticles were characterized as mesoporous materials.
The FTIR spectrum of Cr2O3 NPs reveals the presence of the corresponding vibration bands of Cr–O only and this could be used to account for the successful removal of impurity contents during calcinations and high purity of the as-grown Cr2O3 NPs. The high intensity of FTIR bands indicates the good crystalline nature of the materials. The FTIR spectrum of Co3O4 illustrated the corresponding vibration bands of
111
Co–O only and this means the successful preparation of high purity Co3O4NPs. High intensity of Co3O4 bands indicates the good crystalline nature of the materials. The FTIR of MnO2 NPs exhibited the vibration bands of Mn–O with low intensity due to the amorphous nature of this material. The absorption bands of water were also characteried due to the nanocrystalline stucture.
The TGA studies of Cr2O3 NPs and Co3O4 NPs showed no considerable weight loss up to 600°C. It simply indicated that Cr2O3 and Co3O4 were thermally stable in nature and we can use these synthesized NPs up to 600° C. The TGA of MnO2 NPs showed high percentage of water due to high surface to volume ratio.
The shielding properties of Cr2O3 NPs, Co3O4 NPs, and MnO2 NPs were aimed to study in this thesis and several general conclusion points and trends can be outlined. First, the observed decrease in count rates as the film thickness values of Cr2O3 NPs, Co3O4 NPs, and MnO2 NPs increase. Second, the relationship between the disk thickness and count rate was found to be in an exponential relationship. Third, the linear attenuation coefficient decreased with the increase in energy of γ- ray. Similarly, the mass attenuation coefficient decreased with increasing the energy. Fourth, the shielding efficiency of γ – ray photon using Co3O4 NPs was higher than Cr2O3 NPs and MnO2 NPs which may be attributed to the high density. Fifth, the shielding efficiency of Cr2O3 NPs and MnO2 NPs were almost the same due to their closet density values. Sixth, the calculated linear attenuation coefficient values of bulk materials were higher than the experimental linear attenuation coefficient of nanomaterials due to the density of bulk materials is higher than the density of nanomaterials. At low energy of γ- ray mass attenuation coefficient of bulk materials is much larger than mass attenuation coefficient of nanomaterials. This is because photo-absorption is much more probable at lower energies.