Micronization And Ce Modification Of Pr-ZrSiO₄ Pigment Using For Ceramic Ink-jet Printing

Currently,ink-jet printing is popular in the building ceramics industry.The corresponding ceramic inks,as the most consumed material in the ink-jet printing processes,has received much attention from researchers.Ceramic pigments are the key material of ceramic inks.In the process of ceramic ink-jet printing,in order to prevent the ink-jet nozzle from being blocked by the solid particles,the median diameter of the pigment particles needs to be between 200⁵00nm,and the maximum particle size should be smaller than 1?m.The Pr-doped zircon pigment,as one of the three zircon-based pigments,is the only widely used yellow pigment in the ceramic inks.However,most of the commercial Pr-doped zircon pigments are synthesized by solid-state reaction method,causing the particle size located at the micrometer scale.The pigment particles must be ultra-finely milled in order to meet the requirements of ink-jet printing.However,it has been found that the coloring ability of Pr-ZrSiO₄ pigment will significantly reduce after ultrafine milling.In order to achieve the same coloring ability,it has to increase the amount of Pr-ZrSiO₄ pigment in the ceramic inks,which will increase the cost of the ceramic inks,and on the other hand,waste the mineral resources.Based on the above,it is necessary to systematically investigate the milling process of Pr-ZrSiO₄ pigment,analyze the reason for its color deterioration,find ways to avoid the color deterioration.On the other hand,in view of the color deterioration during the grinding process,it is necessary to find a method to improve the color strength or keep it unchanged.As is known that,the rare-earth doping method is one of an effective material modification methods.Thus,this study attempts to improve the color intensity and color grade by means of co-doping of Pr and Ce.First,the milling process of Pr-ZrSiO₄ pigment was studied by means of ball milling and stirred media milling.The Pr-ZrSiO₄ pigment particles were milled to different particle sizes by adjusting the milling parameters.The milled pigments were analyzed by means of XRD,SEM,EDS,XPS and UV-VIS-NIR diffuse reflectance spectra.As the particles are micronized to the submicron scale,the color of Pr-ZrSiO₄ pigment decline significantly from a bright reddish yellow to a pale yellow.Micronization remarkably refined the grains size,however,it did not change the phase composition of the pigment,nor did it cause a detectable amorphous phase in the pigment.In addition,there is no element loss in the milled samples,and micronization did not change the valence state of Pr.There are three main reasons for the decline of color strength after micronization:First,micronization increases the crystal defects of Pr-ZrSiO₄,which can destroy the coordination structure formed by the Pr ions and their ligands and thus reduce the color strength of the pigment.Second,as the particle size decreases to half of the wavelength of incident light,the scattering of visible light is enhanced,resulting in an increase in the brightness of the samples,which slightly diminish the color saturation.Third,Pr is nonuniform distributed in the unmilled pigment particles?i.e.,enriched in the particles'surface layer?.Micronization causes the micron-sized large particles to be dissociated into submicron-sized small particle groups,and the interior of the large particles is exposed after micronization,so that the area ratio of the original large particles'outer surface is reduced in any exposed surface of the newly formed small particle groups,i.e.,the ratio of the area with high Pr concentration is decreased.The color of the Pr-ZrSiO₄ pigment is sensitive to the content of Pr,thus it results in a significant color deterioration in the milled pigments.Furthermore,we also studied the modification of Pr-ZrSiO₄ pigment by Ce.Firstly,the Pr-ZrSiO₄ pigment was synthesized by solid-state reaction method.The effects of calcination temperature,holding time,the addition amount of Pr and mineralizers were studied.Base on the above experimental results,a series of Pr and Ce co-doped ZrSiO₄ pigment were synthesized and characterized.The prepared?Pr_x,Ce_y?-Zr_1-x-ySiO₄ pigments mainly consists of zircon phase and is well crystallized.Only a specific amount of Pr was incorporated into ZrSiO₄ lattice,and the dopant Pr that was not incorporated into the ZrSiO₄ lattice was stabilized in the samples in the form of NaPrF₄.The dissolving of Pr into the ZrSiO₄ lattice decreased as the amount of Ce increased,which caused the b*value to slightly decrease.Compared with Pr,Ce was almost completely incorporated into the ZrSiO₄ lattice and homogeneously distributed within the pigment particles.The dopant Ce induced a significant increase in the a*value,and thus caused the color of the samples to gradually change from yellow to orange.The enhanced red tone was caused primarily by an increase in absorption of light with wavelengths between 500⁵65 nm.After being applied in the ceramic glaze,the samples still presented a reddish-yellow tone,therefore,Ce can be used to improve the color tone of the Pr-ZrSiO₄ pigment.