| Copper chrome black (CuCr2O4) pigment is a kind of pigments which mixedwith metal oxide spinel crystal structure, due to it owns some excellent propertiessuch as excellent hiding power, chemical resistance, high temperature resistance,outdoor stability and non-proliferation, it has been widely applied in ceramics, enamel,paint and plastics fields. The main prepared methods include high-temperaturesolid-phase method and hydroxide precipitation. The disadvantages ofhigh-temperature solid-phase method are non-uniform and inadequate reaction, highimpurity content of the product, irregular crystal form, the high energy consumptionand so on; while these disadvantages that complex process, coarse product particles,uneven distribution of particle size and the impurity product exists in the hydroxideprecipitation method. Therefore, in order to improve product quality of copper chromeblack, expand product use and reduce production costs, the research about the newprepared methods of copper chrome black is essential. In this paper, copper chromiteblack pigment were prepared by Stearic acid sol-gel self-propagating combustionmethod, molten salt method and propylene oxide sol-gel method, and the structureand related properties of products also were systematically studied.The copper chromite black pigment was successfully prepared by the sol-gelself-propagating combustion method, which selected copper nitrate and chromiumnitrate as reactant, stearic acid as a gelling agent. The effects of the ratio of reactant onthe gel preparation, calcination temperature and the holding time on the formation ofcopper chromite black crystal. In order to characterize precursor, heat-differentialthermal analysis and infrared spectroscopy were used, and the structure of the productwere characterized by scanning electron microscopy and X-ray diffraction. Theexperimental results show that copper chromite black pigment with the high purity,regular crystalline form, small particle size and a narrow distribution with an averageparticle size of60-80nm could obtained, which the related conditions included thatthe molar ratio of copper nitrate and chromium nitrate was1:2, the molar ratio ofstearic acid and mental salts was1.25to1.50:1, the calcination temperature was800degrees, holding time was3hours. It’s cost lower than selected citric acid as a gellingagent, and compared to high-temperature solid-phase method and alcohol-watercoprecipitation, it owns lower calcination temperature and energy consumption.Molten salt method also can successfully synthesize the copper chromite black,which selected copper oxide and chromium trioxide as reactant, sodium and potassiumchloride as molten salt solvent. First of all, it need mixed of the reactant andthe molten salt by using high energy ball milling, and then calcined the mixture. Theeffects of calcination temperature, holding time and the amount of molten on thecrystal type formation of copper chromite black were researched, X-ray diffractioncharacterized its structure. The results showed that the copper chrome black particlewith small size distribution and uniform crystalline structure could prepared just whenthe mole ratio of molten salt medium and reactant was1.5:1, the calcinationtemperature was850degrees, holding time was four hours; with increasing thecalcination temperature, crystalline of product become more perfect, but the particlesize increases, and the agglomeration phenomenon began to appear; the amount ofmolten salt can affect the diffusion and contact with each other of reactant, increasingthe amount of molten salt can contribute to the formation and growth of copperchromite black crystals; holding time have less effect on the formation of crystalline,but with increasing it the grain became larger and agglomeration produce.The copper chromite black pigment was successfully synthesised by propyleneoxide sol-gel method, which selected chloride of copper and chromium as reactant,propylene oxide as a gelling agent, ethanol as solvent. The effects of the dosage ofpropylene oxide, calcination temperature and holding time on the synthesised pigmentwere explored, and the crystalline and morphology of product were analyzed. Theresults showed that when the molar ratio of propylene oxide and the metal ions is3:1,the gel could quickly form and the stage of gel was uniform and stable; the copperchromite black nanoparticles could be synthesized at700degrees for2hours, whichdispersed uniformly without agglomeration and the distribution of particle size isconcentrated in the range of50to60nanometers.Free copper and chromium ion levels of copper chromite black samples whichprepared by stearic acid sol-gel method, molten salt method and propylene oxide lowtemperature sol-gel method were measured. According to experimental results, itrevealed that free copper and chromium ion levels were directly related to thecrystallization degree; When the calcination temperature reached at the temperature ofcrystal transformation, soluble chromium and copper ions which existed in the samples are lower than the national standard (GB8978–1996), it would not pollutedthe environment in the process of application. |
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