| With the development of the modern science and technology, many progresses have been made on the preparation technology and new kind of ceramic pigments. Compared with the traditional red pigments, Ce1-xPrxO2 nano-crystallite red ceramic pigment has higher temperature resistance, lower toxicity and wider coloration range. It is a good candidate for the replacement of traditional toxic pigments. Low-temperature combustion synthesis (LCS), hydrothermal method and microemulsion process are all new technologies for powder preparation. The new technology provides new processing for the preparation of nano-crystallites pigments for the key materials of ink-jet printers controlled by computer.Ce1-xPrxO2 nano-crystallites red pigments were prepared by low-temperature combustion synthesis at the ignited temperature of about 250°C with a later hydrothermal treatment, using Ce(NO3)3·6H2O and Pr6O11 as raw materials. The influence of fuel categories, the mole ratio of fuel/cerium nitric, the content and the state of doped Pr ions and the mineralizer categories on the the crystallites structure and properties of prepared pigments were investigated. The later hydrothermal treatment and the heat process of the prepared powders were also studied.The Ce1-xPrxO2 nano-size ceramic pigments powders were also prepared by a W/O microemulsion system and a co-precipitation-hydrothermal method using Ce(NO3)3·6H2O, Pr6O11 as raw materials and ammonia as the precipitation agent. The influence of the annealing conditions on the preparation of Ce1-xPrxO2 powders was also investigated.DSC, XRD, SEM, TEM, XPS, Laser Raman spectra and CIE color measurements were used to analyze the valence of praseodymium and cerium in Ce1-xPrxO2 crystal structure. The mechanism of the color and the grain growth of Ce1-xPrxO2 red pigments were also discussed.The results show, for many fuels, such as CO(NH2)2, (COOH)2·2H2O, CH3COONH4, C6H8O7, C6H12O6, CH3COOC2H5 and NH4NO3 et al, CH3COONH4 and C6H8O7 are suitable for the preparation of Ce1-xPrxO2 nano-size red pigments by LCS process. Compared with citric acid, the as-prepared powders have better crystallites and color performance by using acetic ammonium as fuel; and the more Pr ions entered into 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 LCS process. The particle size of the resulted powders is about 200nm ~ 300nm.The LCS resulted Ce1-xPrxO2 (x=0~0.5) nano-crystallite powders have the color range from pink to red-brown, with diffrent doping amount of Pr ions. In a certain area (x<0.3), the crystallite size of the powders decreasees with the increases of the content of Pr, when x is in the range of 0.3~0.5, the content of Pr has not notable effect on the crystallite size. The parameter a* increase firstly with the increase of x and reaches maximum when x=0.05; and then decrease when x is in the range of 0.3~0.5. This infers that the content of Pr has not notable effect on parameter a* in this range. In the research condition, the crystallites size of powders are in the range of 9~41nm. The content of Pr has little effect on ignited temperature; but decomposition temperature of oxidant in the combustion reaction has important influence on ignited temperature.Pr ions were doped in CeO2 crystal latice for the preparation of Ce1-xPrxO2 crystallites by using Pr6O11 and Pr(NO3)4 respectively. Results show that the crystallites of sample prepared from Pr(NO3)4 grow up more perfectly; and the chromatic performance is greatly improved. Content of Pr ions doped in solid solution is close to doping amount of the experiment. Na2CO3, CaF2, NaF, H3BO3, LiF and NaClO3 were used as mineralizer respectively. The influence of these mineralizers on the structure and performance of the Ce1-xPrxO2 nano-crystallites was investigated. It is found that the value a*of the powders is notablely improved by using mineralizers. The red value improvment of these six mineralizers conform to the order of NaClO3>LiF> H3BO3>NaF>CaF2>Na2CO3. Therefore, NaClO3 is the best one for preparation of Ce1-xPrxO2.A later heat treatment and a later hydrothermal process of Ce1-xPrxO2 nano-crystallite powders prepared by LCS were done. Result show that, the parameter a* is up to 26.95 by the treatment of the powders at 1200oC for 2 hours. The crystallization and the color performance of the samples after hydrothermal treatment are improved obviously. The particle distributions of the powders are more uniform at alkaline condition with filling ratio is 60%. Keeping a long hydrothermal treatment time is useful for the uniformity of the crystallites, which avoids the particle aggregation and improves the color performance of samples.A W/O microemulsion system composed of OP-emolsifier / water / cyclohexane / 1-Pentanol was adopted to prepare ultrafine Ce1-xPrxO2 powders. The influence of the annealing conditions on the preparation of Ce1-xPrxO2 powders was investigated. The results show that preparation temperature has not notable effect on the crystal structure and morphology of the as-prepared powders; but has an effect on the size of the particles. With the increase of temperature, the particles aggregation becomes stronger and the particle size increases. A fluorite structure of Ce1-xPrxO2 was found when the temperature is above 600°C. With the increase of temperature, content of Pr ions doped in solid solution is close to the doping amount.Ce1-xPrxO2 nano-size powders were prepared by a co-precipitation-hydrothermal method using Ce(NO3)3·6H2O, Pr6O11 as raw materials and ammonia as the precipitation agent. Results show that the average crystallite size of Ce1-xPrxO2 powders is 12 nm; the average particle size is 18 nm. The powders exhibit light-red color and quadrate morphologies and no particle aggregation is exhibited. With the increase of hydrothermal treatment temperature, the solubility of praseodymium in the crystal lattice of CeO2 increases; but not all of praseodymium is dissolved into the crystal lattice of CeO2. With the increase of hydrothermal treatment time, the red value of Ce1-xPrxO2 powders firstly increase and then decrease. The growth process of Ce1-xPrxO2 powder is a dynamic dissolution-deposition process of cerium and praseodymium ions. In research condition, with the increase of hydrothermal treatment temperature, the solubility of praseodymium in the crystal lattice of CeO2 is more close to the doping content. The optimal condition of the hydrothermal time is 20 hours which the solution pH of 9~10. After calcining at 800oC for 4 hours, the color of the Ce1-xPrxO2 powders change from light red to red brown; and the powders show faceted polyhedral morphologies with improved crystallization. The valences of Ce and Pr and chromatic mechanism of the Ce1-xPrxO2 red pigments were investigated. The results show that all samples have a fluorite structure monophse in our research, and the crystallite size is smaller than 41 nm. With the increase of Pr content, the concentration of oxygen vacancies increase. There are trivalent Pr and tetravalent Ce in Ce1-xPrxO2 crystal lattice. The red value a* and the color saturation value C* is firstly increase and then decrease with the increase of the content of Pr. The chromatic performance of Ce1-xPrxO2 red pigments samples reache optimum while x is 0.05. The substitution of Ce4+ by Pr3+ will form oxygen vacancies, which cause the distortions and the defections of CeO2 crystal lattice. Therefore, the pigments can absorb the light with wavelength of less then approximate 600nm and present the red tonality.The mechanism of hydrothermal synthesis of Ce1-xPrxO2 powders was investigated. The results show that the growth process of Ce1-xPrxO2 Crystallites is a dissolution-deposition process of cerium and praseodymium ions. Crystallites particles make an orientation movement from solution to the surface of crystallites, resulting in the formations of planar crystallites nucleuses in the boundary layer. Molecules will diffuse from the solution to the nucleus surface and deposit at the edge of the step offered by the planar crystallite,forming a layer structure. The continue growth of crystallites will need new planar crystallite nucleus, which is provided by the edge distortions appeared at the never-disappeared steps. The steps will grow along the edge distortion, resulting in the growth of continuous crystallites. |
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