Preparation And Properties Of Complex Inorganic Pigments Copper Chrome Black

In this paper, a composite inorganic environmental protection pigment copper chromite black were prepared by homogeneous precipitation method, co-precipitation method and Sol-Gel method. And on the basis of Sol-Gel method, ions doped samples were studied to show the influence on the copper chromite black pigments. Additionally, copper chromite black pigments were characterized by X-ray diffraction, thermal analysis technology, UV-VIS Spectrophotometer, TEM, laser particle analyzer and coloring power test.For the copper chromite black pigment samples prepared by homogeneous precipitation method, the additive amount of urea, pH in the solution, surfactant, calcination temperature and other impact factors were studied to show influence on the preparation of pigments, and crystal morphology, particle size and distribution, heat resisting property and coloring power were also discussed. In the Sol-Gel method, except for the factors mentioned above, Cu-Cr ratio was also studied. The results show that copper chromite black pigments with average size of about 50nm were obtained by homogenous precipitation method, and add PEG400 as dispersant can markedly improve the dispersion of pigment samples. But the pigment samples prepared by Sol-Gel method can get even smaller particles with the average size less than 30nm. Besides, samples prepared by the latter can get the crystal transformation temperature lower than the former, and pigment samples synthesized by both methods have high heat resisting property.In the research on the ions doping based on the copper chromite black pigments; two kinds of ions were studied. The first kind is chromophoric ions; the other is colourless ions. In chromophoric ions doping research, Fe3+, Co2+and Ni2+were taken into account and the roles these ions playing in the pigment samples were mainly discussed. The results show that Fe3+impacts bad on the coloring power of the pigments while Co2+and Ni2+have opposite effects. They can improve the coloring power significantly and also obtain chromatic color. As far as colourless ions are concerned, Zn2+and Mg2+were chosen to study the influence on the microstructure such as lattice parameters. Research has shown that both ions have relatively big influence on the lattice parameters of the copper chromite black pigment samples. With the increase amount of doped ions, phase transition was happened on the pigment samples. The tetragonal copper chromite turned to cubic phase.In addition, copper chromite black pigments also prepared by co-precipitation method, the core of this method is preparing ammonium hydroxide copper chromite first and then put it into muffle furnace to calcinate. By this means, with the temperature of 500℃is enough. After calcination, the samples were washed by hot dilute hydrochloric acid and then washed by hot distilled water. In consequence, copper chromite crystal exists in cubic phase at lower temperature while exists in tetragonal phase at higher temperatures. But after washed by acid, the cubic phase turned to tetragonal phase. And experiment shows that cubic phase samples have bad heat resisting property.As a kind of non-toxic and environmental protection pigment, hexavalent chromium content of the pigment samples calcinated at different temperatures were characterized. Results show that hexavalent chromium content has a great relationship with the crystallinity of the pigment samples. When the crystallinity is lower, the hexavalent chromium content is higher. But when the copper chromite crystal formed completely, chromium ions were inserted into spinel lattices, so the samples were very stable that trivalent chromic ions were hard to be oxidized to hexavalent valence. Besides, Cu-Cr ratio also plays a great important role in the hexavalent chromium content. If total chromium is far beyond theoretical content, it is easier to be oxidized to hexavalent valence. But, by and large, hexavalent chromium content is far less than any national and international standards; this proves copper chromite black pigment to be a kind of non-toxic and environmental protection pigment.