Study On Preparation And Chromatic Performance Of Doped Alumina-based Ceramic Pigment With Controlled Morphology

It’s a hot reseach field to design and build a new nano-ceramic pigment withcontrolled morphology. The aluminum ceramic pigment is one important branchof ceramic pigment and alumina is an excellent matrix construct material due tochemical stability, high temperature resistance and so on, especially, differentmethods to prepare nanosized alumina with different morphologys has alreadybeen researched. In this study, in-situ doping alumina-based ceramic pigmentswith various morphology were synthesized by traditonal hydrothermal andmicrowave hydrothermal, which can provide a new thought and theoretical basisfor the application of alumina-based nano-structured functoinal materials in theceramic pigment, also, the relationship of morphology and chromaticperformance was researched.In the paper, the purpose of Cr in-situ doping and morphology controlledhave been successfully achieved by two hydrothermal methods with rod-like andsphere-like morphology alumina as matrix, the γ-Al₂O₃-based and α-Al₂O₃-basedceramic pigments were obtained as a result of different calcinations temperaturesat900C and1200C, respectively. The products were characterized by X-raypowder diffraction （XRD）, energy dispersive spectrometer （EDS）, fouriertransform infrared （FTIR）, electronic microscopy （SEM）, transmission electronmicroscopy （TEM）, ultraviolet-visible diffuse reflectance spectroscopy （UV-Vis）and CIE-L_*a_*b_*1976color scales. The analysis on phase, morphology andchromatic performance of precursor and pigment were got that showed theinteraction among the three and the amount of doping metal, the relationshipamong morphology, structure and chromatic performance was also beenobserved. Besides, chrome green pigment and chrome aluminium red pigment were prepared by high temperature solid-state method in order to compare withthe morphology and choromatic performance of pigment by the former twomethods. In the end, rare earth element Ce-doped alumina-based ceramicpigments were initally prepared by hydrothermal methods.The experimental results are shown as follows:（1）The in-situ Cr-doped NH₄Al（OH）₂CO₃（AACH） with rod-likemorphology and pink colour has been successfully prepared by traditionalhydrothermal method using aluminium nitrate, chromic nitrate as raw materials,with incrasing amount of chromium, which has morphology trend as follows,fibrousâ†'rodsâ†'some rods incompleted and some small particlesâ†'shorter rodand more small particles. The γ-Al₂O₃-based and α-Al₂O₃-based ceramicpigments are obtained after calcined at900C and1200C, whoes morphologyare still rod-like. The colour of the former pigment appears yellow-green togreen trend, a*and the colour saturation C increase but L*decreased with anincrease in amount of chromium. For the latter pigment, the trend of colour ispink to green, the corresponding a*is positive and then becomes negative, Cpresents the tendency of increase first and reduction afterwards, also, L*reducesas the chromium amount increases. On condition that Cr doping amount islow（the molar ratio of Cr and Al<5%）, the in-situ Cr-doped AlOOH withmicrosphere-like morphology and light-green colour also have been obtained bymicrowave hydrothermal using aluminium chloride, chromium chloride, sodiumhydroxide, ethyl acetate as raw materials and CTAB as surfactant. The resultsindicate that chromium phase occures with an increase in Cr-doped amount,meanwhile, small particles are observed in SEM. After the same heat treatment,the γ-Al₂O₃-based and α-Al₂O₃-based ceramic pigments are also obtained withstill microsphere morphology. As the Cr-doped amount increases, the colourtrends of the two pigments are yellow-green to green and pink to green. L*, a*,b*also have the same tendency with rod-like morphology, but have differentvalue range, which indicates that morphology have certain effect on chromaticperformance.（2）The chrome green pigment synthesized by solid-phase method has thesimilar chromatic performance to the best products prepared by the twohydrothermal methods, but the chrome alumium red pigment has much better chromatic performance than the pink pigment prepared by hydrothemal methods.（3）CeO/Al₂O₃micro-nanostructured pigment has been prepared bytraditional hydrothermal method which is composed of fiber-like morphologyAl₂O₃and partical-like morphology CeO₂. CeO₂particles are absorbed onalumina which leads to a light yellow colour.