水热法制备高熵碳酸盐及其颜色特征

Preparation of High Entropy Carbonate by Hydrothermal Method and Its Color Properties

高熵碳酸盐固溶体因其鲜艳的色彩可被应用于颜料领域,同时其较高的近红外反射率也有用作隔热材料的潜能。本实验采用水热法,通过改变单一组元Cu、Fe和Mn,保持其他4组元为MgCoNiZn不变,制备出3种五元等摩尔高熵碳酸盐固溶体。利用X射线衍射仪、扫描电子显微镜、紫外–可见–近红外分光光度计、CIE 1976 L*a*b*色度坐标、Kubelka-Munk函数分析等对所合成的陶瓷粉体的晶体结构、颜色性能、反射性能等进行表征。结果表明,3种五元素组合均形成了单相高熵碳酸盐,且随着Cu^(2+)、Fe^(2+)、Mn^(2+)半径逐渐增大,晶格常数相应增大。通过组元的改变可以调节高熵碳酸盐的颜色,第5组元为Fe^(2+)时呈橙红色,Cu^(2+)时呈灰绿色,Mn^(2+)时呈浅紫色,相应的禁带宽度值也逐渐增大,吸收边缘相应的发生蓝移。此外还测得3种样品在780~2 500 nm波段具有不同的近红外反射率,最高可达78.64%,有望在高反射隔热材料领域进行应用开发。

Introduction In recent years,heat accumulation occurs with the emergence of the“heat island effect”.The high temperature can affects human living environment,and increases the energy consumption of refrigeration equipment.It is thus necessary to develop color thermal insulation materials with a high near-infrared reflectance.The existing components used for insulation coatings are mostly rare-earth transition metal composite oxides.However,a higher cost of using rare earth materials restricts the large-scale application to some extent.Transition metal high-entropy ceramic inorganic powder can be used as cheap raw materials,which has the advantages of multi-component characteristics(i.e.,great component adjustment space,unique entropy effect,and adjustable material properties.However,little work on the use as high reflective pigments has been reported yet.In this paper,high-entropy ceramic carbonate powders were prepared and the color of the powders was innovatively adjusted via changing the transition metal components.In addition,the phase,color and optical reflection properties of the prepared high-entropy ceramic carbonate powders with different element combinations were also analyzed.Methods For the hydrothermal preparation of high-entropy carbonate powders(i.e.,(Mg_(0.2)Co_(0.2)Ni_(0.2)Zn_(0.2)Cu_(0.2))CO_(3),(Mg_(0.2)Co_(0.2)Ni_(0.2)Zn_(0.2)Fe_(0.2))CO_(3),and(Mg_(0.2)Co_(0.2)Ni_(0.2)Zn_(0.2)Mn_(0.2))CO_(3)),pure MgSO_(4),CoSO_(4),NiSO_(4),ZnSO_(4),FeSO_(4),MnSO_(4),CuSO_(4) and Na_(2)CO_(3) were used as raw materials according to a stoichiometric coefficient ratio.Firstly,a certain proportion of five metal sulfate solids was mixed with deionized water in a beaker under stirring until fully dissolved.The sulfate solution was put into a sodium carbonate solution,and mixed under stirring.Afterwards,the mixture in a high-pressure reactor with a PTFE lining was heated at 160℃for 12 h for hydrothermal treatment.A high-entropy carbonate powder was obtained after centrifugation,washing,and drying.The phase composition of the powder was determined by a model Empyrean X-ray diffractometer(XRD,PANalytical Co.,The Netherlands).The microstructure of the powder was analyzed by a model SUPRA 55 field emission scanning electron microscope(FESEM,Carl Zeiss Co.,Germany).The UV visible near-infrared diffuse reflectance of the powder was characterized by a model LAMBDA 750 ultraviolet-visible-near infra-red spectrometer(UV-VIS-NIR,PerkinElmer Co.,USA).The near-infrared solar reflectance R*in the wavelength range of 780–2500 nm was calculated according to the national standard ASTMG159-98.The L*a*b*color parameters of the powder were determined by a model CS-5960GX spectrophotometer.Results and discussion Three types of five-component equimolar high-entropy carbonate solid solutions were prepared by a hydrothermal method.Based on the morphology characterizations,three high-entropy carbonates synthesized have the same crystal structure and the same spatial group as R3c.The diffraction peak gradually shifts towards a lower diffraction angle with the order of the components Cu,Fe,and Mn.This is because the radius of the element ions gradually increases,resulting in a corresponding increase in the crystal plane spacing.Moreover,there are significant differences in the morphology characteristics of three high-entropy carbonates,which are the result of the multiple effects of factors such as the number of extranuclear electrons,the Jahn Teller distortion,magnetism,and bond length of Cu,Fe,and Mn ions.The Jahn Teller distortion and para-magnetism of Cu lead to the formation of irregular spherical particles with surface density and particle aggregation in the MgCoNiZnCu carbonate solid solution.The ferromagnetism of Fe causes MgCoNiZnFe carbonate solid solution to form the spheres with dense and regular surface morphology.The combination of ion bonding bond length and antiferromagnetism of Mn results in the formation of loose aggregates of MgCoNiZnMn carbonate solid solutions.In addition,the colorimetric characterization indicates that the color of three high-entropy powders is different(i.e.,grayish green for MgCoNiZnCu,orange red for MgCoNiZnFe,and light purple for MgCoNiZnMn).The band gap value Eg gradually increases with the order of the component Fe,Cu,and Mn,and the absorption wavelength of the sample gradually decreases(i.e.,the absorption wavelengths are 497.14,393.99 nm and 242.71 nm,respectively),and the absorption edge gradually shifts blue.Three types of high-entropy carbonate solid solutions have a high near-infrared solar reflectance in the near-infrared band,with a maximum of 78.64%,which can be used as thermal insulation materials.Conclusions Three high-entropy carbonate powders with different elemental compositions were prepared by a hydrothermal method,and the phase composition,reflectance,and color properties of the synthesized powders were comprehensively investigated.The results showed that changing a single element in the compositions could change the color of the powder(i.e.,grayish green for MgCoNiZnCu,orange red for MgCoNiZnFe,and light purple for MgCoNiZnMn),and the color coordinate L*a*b*c*value also changed accordingly.Meanwhile,the bandgap width of the powder gradually increased from 3.11 eV to 3.40 eV and 5.49 eV with the order of the component Fe,Cu,and Mn.The three compositions of high-entropy carbonate powders had three different shades in the visible light region,and a high near-infrared solar reflectance(R*)of 78.64%.Therefore,the high-entropy carbonate powders prepared via changing the component element had the characteristics of stable structure,tunable color,and high near-infrared reflectance,having broad application prospects in architecture,automotive,and chemical engineering.