Characterization Of Pr-CeO₂ Rare-Earth Ceramic Red Pigments Prepared By Low-Temperature Combustion Synthesis & Hydrothermal Method

Ce_1-xPr_xO₂(Pr-CeO₂) red pigments were prepared from Ce(NO₃)₃·6H₂O and Pr6O11 by low-temperature combustion synthesis with treatment of hydrothermal method.The paper studied the influence of fuel categories and the mole ratio of Fuel/Cerium nitric on the reaction parameter, the crystallite structure and performance of prepared pigments. The crystallite structure and performance of prepared pigments after hydrothermal treatment also be studied, and the hydrothermal conditions are to find a optimal condition; some parameters in the low-temperature combustion synthesis, such as the state of doped Pr ion and the mineralizer categories are optimized to find suitable parameters of the low-temperature combustion synthesis for Ce_1-xPr_xO₂ red pigment; Ce_1-xPr_xO₂ red pigments with different praseodymium content are synthesized by low-temperature combustion method. The valence of cerium and praseodymium ion of samples and the color mechanism of Ce_1-xPr_xO₂ red pigments are discussed.The ignited temperature of the precursor was characterized by differential scanning calorimeter (DSC). The crystal structure and morphology of prepared pigments were investigated by X-ray Diffractometry(XRD),scan electron microscopy(SEM) and transmission electron microscopy(TEM). The valence of praseodymium in the Ce_1-xPr_xO₂ red pigment has studied by X-ray Photoelectron Spectroscopy (XPS) analysis. The concentration of oxygen vacancies has studied by Laser Raman Spectrometer(Raman), The color of the red pigments was studied by CIELAB color parameter measurement. Results show that: for many fuels, such as CO(NH₂)₂,(COOH)₂·2H₂O,CH₃COONH₄,C₆H₈O₇,C₆H₁₂O₆,CH₃COOC₂H₅ and NH₄NO₃, CH₃COONH₄ and C6H8O7 are the suitable fuels for Ce_1-xPr_xO₂ red pigment synthesized by LCS. Compared with citric acid as fuel, product with acetic ammonium as fuel have better crystallites, color performance and more Pr ion incorporated in CeO2 crystal lattice. The optimal mole ratio of Fuel/Cerium nitric is 2:1 with acetic ammonium as fuel and 3:1 with citric acid as fuel by the LCS. Their grain size is about 200nm to 300nm. The sample with soaking for 2h at 600℃have better crystal structure and red tonality compared with LCS method alone, Synchronously, More Pr ion is incorporated in CeO₂ crystal lattice.Pr ions was doped in CeO₂ with the forms of Pr₆O₁₁ and Pr(NO₃)₄ for prepared Ce_0.95Pr_0.05O₂ pigments, respectively. The results show that the crystallite of sample doped by Pr(NO₃)₄ grows up more perfectly, and the chromatic performance is greatly improved. Content of Pr ion doped in solid solution is close to doping amount of the experiment. Na₂CO₃,CaF₂,NaF,H₃BO₃,LiF,NaClO₃ were used as mineralizer, respectively. The influence of these mineralizers on the structure and performance of the Ce_1-xPr_xO₂ nano crystallite red pigment was investigated. It is found that the color of the powder is notablely improved after mineralizer used. The color perfecting of these six mineralizers conform to the order of Na₂CO₃< CaF₂< NaF< H₃BO₃3. NaClO₃ is the optimum to synthesize Ce_0.95 Pr_0.05O₂.The crystallization and the color performance of samples after hydrothermal treatment are improved obviously. The particle distributions are more uniform; at filling ratio 60%, alkaline condition, keeping a long hydrothermal treatment time is helpful for the uniformity of powder, so the particle aggregation are improved, accordingly, the color performance of samples are improved.Ce_1-xPr_xO₂ red pigment samples with different doping amount of Pr ions were prepared by low-temperature combustion synthesis. The valences of Ce and Pr and chromatic mechanism of the Ce_1-xPr_xO₂ red pigment was investigated. The results show that all samples have single a fluorite structure in our research work, and the crystallite size is smaller than 20 nm. With the increasing of Pr content, the concentration of oxygen vacancies is consistent increase. There are trivalent Pr and tetravalent Ce in Ce_1-xPr_xO₂ crystal. The red value and the color saturation value is firstly increase and then decrease with the increase of the content of Pr. While x is 0.05, chromatic performance of Ce_1-xPr_xO₂ red pigment sample is optimal. Pr³⁺ substituted Ce⁴⁺ formed oxygen vacancies, which caused the distortions and the defections of the crystal lattice. Therefore, the pigments can absorb the light with wavelength of approximate 600nm and present the red tonality.