非水解溶胶-凝胶法制备Cr掺杂α-Al_(2)O_(3)红色色料

Preparation of Chromium-Doped α-Al_(2)O_(3) Red Pigments by Non-Hydrolytic Sol-Gel Method

以无水三氯化铝(AlCl_(3))和三氯化铬(CrCl_(3))为原料,无水乙醇为溶剂和铝粉为还原剂,采用非水解溶胶-凝胶法制备Cr掺杂α-Al_(2)O_(3)红色色料,通过X射线衍射(XRD)、场发射扫描电镜(FE-SEM)、激光粒度仪和CIE-L*a*b*色度仪等测试手段研究了掺杂离子浓度、Al粉添加量、前驱体浓度和热处理温度对色料的相组成、形貌及呈色性能的影响。结果表明:在Cr^(3+)掺杂浓度为0%-5%(原子分数)范围内,随掺杂浓度增加,α-Al_(2)O_(3)的晶胞参数和晶胞体积均逐渐增大,说明Cr^(3+)成功固溶进入α-Al_(2)O_(3)晶格中。色料红度(a*)值随Cr^(3+)掺杂浓度增加呈现先增加后减少趋势,同时,提高前驱体浓度和还原剂的添加量有利于改善色料的呈色性能;随热处理温度增加,色料a*值先增加后趋于平稳,色料粒径逐渐增大;当Cr^(3+)掺杂浓度为4%(原子分数)、Al粉添加量(与CrCl_(3)摩尔比)为6∶1、前驱体浓度为0.4 mol·L^(-1)时,经1200℃热处理2 h,可制备呈色性能良好(a*=14.32)和粒径较小(平均粒度(D50)=7.85μm)的粉红色色料,其有望应用于陶瓷装饰领域。

Red ceramics pigments had pure bright color and intensive tinting capacity,which had been widely applied in the decora-tion fields of ceramic body,glaze and inkjet printing. Chromium(Cr)doped α-Al_(2)O_(3) materialshad drawn great attention due to its purebright color,excellent thermal and chemical stability,which were known as"ruby"or"ruby solution"and could be used as red ceram-ics pigments. Various synthesis methods had been reported for preparing Cr doped α-Al_(2)O_(3) red pigments,which included hydrothermalmethod,Pechini method and combustion method. However,the above-mentioned methods had many disadvantages,such as poor col-or performance,complicated operation and high equipment requirements. Hence,Cr doped α-Al_(2)O_(3) red pigments were prepared bynovel non-hydrolytic sol-gel(NHSG)method using anhydrous aluminum chloride(AlCl_(3))and chromic chloride(CrCl_(3))as raw materi-als,anhydrous ethanol as solvent and Al powders as reducing agents,respectively. The effects of doping concentration,Al powders ad-dition amount,precursor concentration and heat treatment temperature on the phase composition and coloration properties of pigmentswere investigated via X-ray diffraction(XRD),the automatic whiteness meter based on Commission International de I’Elcairage(CIE)system and ultraviolet and visible spectrophotometry(UV-Vis). In addition,the morphology,structure and particle size of pre-pared Cr doped α-Al_(2)O_(3) pigments were studied via field-emission scanning electron microscope(FE-SEM),high resolution transmis-sion electron microscope(HRTEM),and laser particle analyzer. XRD patterns showed that the relative intensity of the sample diffrac-tion peak was gradually weakened,and the angle of diffraction peak was gradually decreased with the increase of doping concentrationin the range of 0%-5%(atom fraction). Further,it could be found that the cell parameters and cell volume of sample gradually en-larged with boosted of Cr^(3+)doping concentration via Rietveld refinement,indicating that Cr^(3+)were successfully doped into α-Al_(2)O_(3) lat-tice. The a*value of pigments increased gradually and then decreased with the increase of doping content. When the addition contentsof Cr^(3+)were 4%,the samples exhibited good color property(a*=11.44). In addition,aluminum powder had strong reducibility,whichcould reduce CrCl_(3) to CrCl2. After non-hydrolysis polycondensation reaction,the raw materials could be uniformly mixed,which wasbeneficial to enhance doping efficiency. The formation of pure phase α-Al_(2)O_(3) was not affected after adding Al powder. As the amount ofAl powder increased,the L*value of the pigments first decreased and then increased,and the a*value first increased and then de-creased. When n(Al)/n(CrCl_(3))was 6∶1,the a*value of samples boosted to 12.45. The precursor concentration did not affect synthe-sized pure phase of α-Al_(2)O_(3). The L*value of the synthesized pigments fluctuated in the range of 59.42-66.29,and the b*value fluctu-ated in the range of-2.34 to-3.46 with the increase of the precursor concentration. The a*value of the pigments increased first andthen decreased with the increase of the precursor concentration. When the precursor concentration was 0.4 mol·L^(-1),the pigments ex-hibited excellent color property(a*= 14.32). Calcination temperature played an important role in the synthesis of pigments and colorproperty. XRD and DTA-TG results showed that the samples synthesized by NHSG method were composed of α-Al_(2)O_(3) and γ-Al_(2)O_(3) at1050 ℃. With the increase of the calcination temperature,γ-Al_(2)O_(3) was gradually transformed into α-Al_(2)O_(3). As the temperature in-creased to 1500 ℃,the samples were pure α-Al_(2)O_(3) phases and had high crystallinity. The a*value of the pigments gradually increasedand then tended to level off,as well as color saturation(Cab*)gradually increased with the increase of the heat treatment temperature.UV-Vis result indicated that the prepared samples had a strong reflectivity in the red light area(650 to 760 nm),indicating that theprepared Cr doped α-Al_(2)O_(3) pigments exhibited pink hue. The synthesized Cr doped α-Al_(2)O_(3) samples at 1100 °C were composed of ag-glomerate particles with a primary particle size of about 100 nm,which exhibited an irregular shape. It was found that the size of Crdoped α-Al_(2)O_(3) pigments also grually increased with the elevation of the heat treatment temperature via SEM images. When the heattreatment temperature enhanced to 1500 ℃,the particles tended to be partially sintered. TEM and HRTEM images showed that themorphology of the sample was irregular and the lattice stripes had no obvious defects,indicating that the prepared pigment at 1200 ℃had a higher degree of crystallinity. The laser particle analyzer showed that the particle size of the prepared pigment at 1200 ℃ exhibit-ed a unimodal distribution and narrow particle size distribution,where D10 was 2.17 μm,D50 was 7.85 μm and D90 was 15.9 μm,TheD90 of pigment particles was less than 20 μm,which could better meet the requirements of ceramic decoration. The excellent color per-formance(L*=66.29,a*=14.32,b*=-3.24,Cab*=14.68)of Cr doped α-Al_(2)O_(3) pigments with small particle sizes(D50=7.85 μm)couldbe obtained via NHSG method,making it be potential candidate in the application of industrial ceramic decoration.