Sythesis, Morphology And Structure Of Chromium Oxide Nanoparticles

Nanoparticles usually exhibit unique optical, electric, magnetic and catalytic characteristics due to their surface effect, small scale effect, macroscopic quantum tunneling effect and so on, which result in potential applications greatly. As a kind of inorganic and multifunctional material, Cr2O3 nanoparticles have attracted considerable interests because of their particular characters such as high melting point, large rigidity, wear and corrosion resistance. Although a lot of methods have been used to synthesize Cr2O3 nanoparticles, most of the processes are complex or high-cost. In this thesis, a simple and low-cost method for the synthesis of Cr2O3 nanoparticles with controllable size and morphology is described. The synthesis mechanism and influencing factors of the process are investigated. The relation between the lattice parameters, particle size and morphologies is discussed.By the chelate reaction of chromium trioxide (CrO3) and polymer molecules of poly vinyl alcohol (PVA) in aqueous solution, spherical Cr2O3 nanoparticles with good dispersivity, narrow distribution of particle size have been obtained. Series of Cr2O3 nanoparticles with different particle size and morphologies were acquired by changing the mass ratio (PVA/CrO3). The formation of Cr2O3 is analyzed in terms of the thermal gravimetry and differential thermal analysis (TG-DTA), fourier transform infrared specrroscopy (FT-IR) and powder X-ray diffraction (XRD). The effect of the reactive temperature, stirring time and annealing temperature on the dispersivity, morphology and size of Cr2O3 particles were discussed, and the optimal preparation condition was confirmed. We measured the lattice parameters of the typical sample such as spherical Cr2O3 nanoparticles with the different particle size, the virgulate and plate-like Cr2O3 nanoparticles using XRD. The main conclusions are as follows.1. The single phase crystallized Cr2O3 nanoparticles can be obtained by the chelate reaction of chromium trioxide (CrO3) and polymer molecules of poly vinyl alcohol (PVA). The optimum preparation conditions:At the room temperature, when the color of reaction solution changes to gray green, stirring should be stopped. After cooling down and aging for about 24h, the precursor samples were obtained after drying at 75℃. Finally, the precursor was annealed at 750℃.2. By changing the mass ratio (PVA/CrO3), spherical Cr2O3 nanoparticles were obtained with the average particle size of 50nm,75nm and 100nm, respectively. At the same time, the virgulate and plate-like submicron Cr2O3 particles were prepared. The mass ratio is the most important factor to control the particle size and morphology of Cr2O3.3. Typical samples with different particle sizes and morphologies were studied by measuring lattice parameters precisely using XRD. The relation between lattice parameters and morphology is as follows:For the spherical Cr2O3 nanoparticles, the lattice parameters a and c and volume are become smaller with decreasing particle size. Compared to virgulate particles, the lattice parameters c of the plate Cr2O3 particle is large.4. We prepared crystalline and amorphous Cr2O3 nanoparticles with ellipsoidal morphology by by aqueous reduction method. The grain size of the amorphous Cr2O3 nanoparticles was smaller than crystalline. The reason is probably the raising of annealing temperature.