Synthesis And Properties Of Neodymium Disilicate As A Ceramic Pigment And Its Ink With Allochroic Effect

In recent years, digital ink-jet printing technique has been used in the decoration of the building ceramic industry after screen printing and roller printing techniques. Ceramic ink-jet printing as an effective printing technique becomes an important issue for the economic growth in the building ceramic industry. At present, the domestic ink-jet printing equipment and decoration inks are widely used. Recent development of functional ceramic inks in China is still in its infancy although the ceramic inks such as subsidence glaze ink, flash ink, etc. are developed and applied to the building ceramic tiles in some developed countries. In this thesis, neodymium disilicate(Nd2Si2O7) as a ceramic pigment with allochroic effect was synthesized using different methods(i.e., the Pechini sol-gel method, the St?ber sol coated method, co-precipitation method and solide state reaction method). In addition, the allochroic Nd2Si2O7 ceramic ink was also prepared by a mechanical grinding/dispersion method with Nd2Si2O7 pigment synthesized under the optimization conditions as an allochroic pigment, a certain amount of organic solvent, wetting agent and dispersant, and applied to ceramic tiles with allochroic effect.Nd2Si2O7 powder was prepared by the Pechini sol-gel method with a mineralizer of Li Cl. The results show that the temperature for Nd2Si2O7 crystallization reduces to 200 oC in the presence of a mineralizer(i.e., Li Cl). Nd2Si2O7 powder exhibits different colors under different standard illuminants, implying that Nd2Si2O7 powder can be used as a functional ceramic pigment with allochroic effect. The mechanism of color change was also discussed according to the composition and structure of Nd2Si2O7 and standard illuminants. The results show that Nd2Si2O7 powders are easy to reflect the violet, blue and red light in the visible range. The violet color, blue color, red color and their combinations of the pigment appear under various light conditions. In addition, monodispersive spherical Si O2 particles were prepared by the St?ber sol method. The particle size of spherical Si O2 particles can be controlled via the adjustment of the contents of NH4 OH and H2 O. After coated the Nd3+ sol and fired at 1000 oC, the core-shell structured particles were obtained, which consisted of amorphous silica core and tetragonal crystalline Nd2Si2O7 shell. The particles obtained have the uniform spherical morphology of pure silica spheres with the monodispersity.Nd2Si2O7 powder was also prepared by a co-precipitation method. The influence of precipitants(i.e., NH4 OH, NH4HCO3 and(NH4)2CO) on the phase composition and thermal behavior of the prepared precursors was investigated. The result shows that NH4 OH as a precipitant can obtain an amorphous precursor, which can transform to the pure Nd2Si2O7 phase at 1200 oC for 5 h. The precursor with the surfactant PEG-10000 has less aggregates and better dispersion than the precursor without the surfactant. Also, the addition of the surfactant PEG-10000 can favor the dispersion of the resultant Nd2Si2O7 powder with the smaller grains. In addition, Nd2Si2O7 powder with the smaller grains has a more effective effect on the scattering of light, and Nd2Si2O7 powder with the greater grains shows a deeper color.Nd2Si2O7 powder was prepared by a solide state reaction method. The effects of soft mechano-chemical pretreatment and mineralizers on the reaction process of the prepared Nd2Si2O7 were investigated. The sample prepared with the raw material without mechano-chemical pretreatment and fired at 1200 oC only forms a certain amount of Nd4Si3O12. After the mechano-chemical pretreatment for 2 h and the subsequent themal treatment at 1100 oC, the raw material reacts completely, forming the sole crystalline phase of Nd2Si2O7. The result shows that the mechanically activation of the raw material can reduce the formation temperature of tetragonal Nd2Si2O7 and increase the crystallinity of Nd2Si2O7 due to the mechano-chemical effects. It is likely for H3BO3 as a mineralizer to cause the uneven distribution of Nd and Si elements in the reaction system, which is not conducive to obtain the sole Nd2Si2O7 phase. The only Nd4Si3O12 phase can be formed at 900-1100 oC in the presence of Na F or Ca F2 as a mineralizer. This implies that the addition of fluoride changes the reaction path of the system. The formation temperature of Nd2Si2O7 can be reduced to 350 oC at Li Cl of 5 wt.%. Therefore, Li Cl is one of optimal mineralizers in the synthesis.The tetragonal Nd2Si2O7 crystallization from polymeric xerogels was investigated by a non-isothermal differential thermal analysis method. The crystallization mechanism of the tetragonal Nd2Si2O7 was also discussed according to the calculation of the reaction kinetic parameters. The crystallization activation energies calculated by the Kissinger and the Ligero methods are 673 k J/mol for the xerogel without Li Cl and 586 k J/mol for the xerogel with 5 wt.% Li Cl. A low crystallization activation energy favors the low-temperature synthesis of Nd2Si2O7. The Avrami constant, n, is 3.97 for the tetragonal Nd2Si2O7 crystallization in the absence of Li Cl and 2.38 in the presence of 5 wt.% Li Cl. It is indicated that the crystallization of tetragonal Nd2Si2O7 from the xerogel synthesized without Li Cl could be due to the bulk and homogeneous crystallization processes, forming the spherulitic crystals, and the crystallization from the xerogel synthesized with 5 wt.% Li Cl could be due to the two-dimension crystallization process, forming the lamellar crystals.Nd2Si2O7 ink with allochroic effect was prepared by a mechanical grinding/dispersion method with Nd2Si2O7 ceramic pigment synthesized under optimimum conditions as a raw material. The organic ingredients of the prepared ceramic ink are organic solvent of 85 wt.%, wetting agent of 10 wt.% and dispersant B of 5 wt.%. The characterics of the prepared ceramic ink are the mean particle size of 279 nm, volume density of 1.35 g/cm3, solid content of 35%, p H value of 7.14, viscosity: of 24.83 m Pa.s and surface tension of 28.6 m N/m. In addition, the well-dispersive ink is stable with little aggregation for 10 days, showing the stability of the ink. Nd2Si2O7 ceramic ink prepared can be thus applied to the decoration of ceramic tiles due to these characterics in the application. The result shows that the ceramic tile presents a violet color under solar-light and appears a blue color under fluorescent lamp due to the allochroic effect.Finally, the thesis gives the major conclusions and some prospects for future work based on the experimental results and the corresponding mechanism analysis.