The Study Of Property And Ab Initio Calculation Of Chrome Oxide Greens

The chrome green is one of the main chromic salt industrial product. It is very important in the field of inorganic pigment because that it does not dissolve in acid or alkali; that it is stable in light, atmosphere and erosive gases such as SO2, H2S; that it is able to bear high temperature; that it has high cover power and high hue saturation.The chrome green produced by Chinese factories has many advantages and high yield. Compare with that of foreign factories, the gaps have been existed in chromatism and stability, but little explore was put to dig the essential reason that caused the difference. So this paper try to quest for the discrepancies among several pigments that come from Bayer Co. and Minfeng Co. on their properties, micro-structure and their causality through experiment and theory, in order to offer some help or reference for improving the quality of chrome green in China.Firstly, the differences of cell parameters, the components and content of main elements, chroma and chromatism etc. between samples of Bayer and Minfeng Co. were detected by X-ray diffraction analysis, photoelectron energy spectrum analysis, IR spectrum analysis, UV analysis, Electron Microscope analysis, TG and DSC analysis, laser partial size analysis, chroma and chromatism analysis. These differences are the main causations of the different hue of pigments.Secondly, on the base of the test results, the theoretic study of different models is carried out by ab initio calculation and DFT method. The results are that chromium-oxide octahedron is the active area that induce the pigments to exhibit green color and the changes of energy and electron density in this area should be take into account firstly; that the energy of Bayer-standard is not at the lowermost point in the five pigments; that in the range of the deviation among the lattice parameter a and c, the relation between the change of color and parameters is complex; that the little change of lattice parameters will bring obvious effect to properties of the pigments; that the increase of lattice parameters has more influence on properties of the pigments than that the decrease of it; that the properties of the pigments are more sensible to the change of the parameter a than to the change of the parameter c. When the Cr3+ is replaced by other metal ions, the calculation results indicate that the Fe3+ and Mn4+ will take different influence to the properties of the pigments because of their d electrons, but the Al3+and Ti4+will hardly affect the color of the pigments.Finally, in order to unearth the direct connection between the change of cell parameters and the field strength surrounding the Cr3+, the Dq and ΔE values of active units were calculated and analyzed by connecting ab initio calculation results with Crystal-Ligand Field Theory and analogizing Racah parameters properly. When the cell parameters increased, the B value which related to Ligand Field, theΔE value which related to the energy dispersion between d orbits, Dq value all will decrease. This will lead the absorbed wavelengh to move to red light, consequently the pigments exhibit the color more closed to blue. This deduction is approximately consistent with the experimental outcome.