Preparation,Properties And Application Of Doped-Yttrium Aluminum Garnet Near-Infrared Reflective Pigments In Substrates

Yttrium aluminum garnet(Y₃Al₅O₁₂)is an inorganic compound with promising applications in the field of fluorescence and lasers.In the cubic structure,Y³⁺ions occupy the c-site（YO₈）and Al³⁺ions can be present in both the a-site and d-site（Al O₆ and Al O₄）.Y³⁺and Al³⁺in Y₃Al₅O₁₂ structure can be replaced by other cations with similar radius,thus improving some of the original optical properties.So far,there have been few studies on the color characteristics and near-infrared reflective performance of doped Y₃Al₅O₁₂.In this experiment,three groups of samples with different metal ion-doped Y₃Al₅O₁₂ were prepared by the citric acid sol-gel method,and some typical samples were used as additives to prepare ceramic materials and modified resin materials.Various characterization techniques were used to investigate the crystal structure,optical properties,near-infrared reflectivity（NIR）and chemical stability of the samples.（1）The color of Y_3-xCe_xAl₅O₁₂（x=0.05,0.10,0.15,0.20）series powders changes from soft yellow to bright yellow with the increase of cerium ion doping amount and the morphology is a curved worm-like structure.According to the NIR performance test,Y_3-xCe_xAl₅O₁₂powders has high NIR solar reflectivity（88.94%,89.38%,90.06%,76.49%）,so the yellow powders can reflect most of the solar radiation and has great application potential in the field of NIR pigments.XPS data show that Ce ions exist in the form of mixed-valence(Ce³⁺and Ce⁴⁺).The substitution of Ce⁴⁺for Y³⁺introduces a point defect（Ce⁺）in Y₃Al₅O₁₂ lattice,or Ce⁴⁺does not enter the lattice but form the second phase,which results in cation vacancies in the Y₃Al₅O₁₂ lattice.According to Drude’s theory,the above two cases will increase the free carrier concentration,thus improving the near-infrared reflectivity.However,when x>0.15,the degree of lattice distortion increases,which increases the number of free electron traps and leads to a decrease in the free carrier concentration.Therefore,the NIR solar reflectance of Y_3-xCe_xAl₅O₁₂powder samples showed an overall trend of increasing and then decreasing.Compared with ordinary yellow pigment,Y_3-xCe_xAl₅O₁₂ has lower thermal conductivity,which can slow down the heat transfer to the interior.The temperature test experiment showed that the ceramic materials prepared from Y_2.9Ce_0.1Al₅O₁₂ pigment reduced the surface temperature by 7.5°C compared to the normal ceramic.（2）The Y₃Al_5-xFe_xO₁₂（x=0.5,1.0,1.5,2.0,3.0）particles have spherical or ellipsoidal morphology,and the particle size increases slightly with the increase of Fe³⁺doping amount,and the sample color is brown.When x increases from 0.5 to 3.0,the main phase of the samples gradually transforms the cubic yttrium aluminum garnet to hexagonal yttrium iron garnet.The near-infrared solar reflectance of Y₃Al_5-xFe_xO₁₂ pigment shows a downward trend（86.47%,84.79%,74.64%and 68.08%）.This is related to the lattice distortion caused by doping process.Crystal defects act as electron traps to absorb free carriers,leaving a small number of free electrons in the samples and a decrease in the number of collisions with infrared light.The addition of the high NIR reflectance pigment Y₃Al_5-xFe_xO₁₂ as a modifier to ASA plastics successfully improved the NIR solar reflectance of ASA from 33.04%to61.98%.The simulated box experiment demonstrated that the heat flux of ASA modified with8 wt%and 24 wt%Y₃Al₄Fe O₁₂ were reduced by 9.6%and 33.5%compared to the unmodified ASA.（3）The crystalline structure of Y₃Al_5-xCr_xO₁₂（x=0.01,0.05,0.10,0.20,0.30）sample is cubic phase.The particle morphology is granular or rod-shaped,and the particle size distribution is relatively uniform.As the doping concentration increases,the intensity of absorption peak in the visible region gradually increases,so the color property of the pigments deepens from light green to bean green.The crystallinity and average grain size of the samples gradually decreased with the increase of Cr³⁺doping,which caused by the escape of oxygen atoms due to high-temperature calcination or the supersaturation of Cr³⁺in the Y₃Al₅O₁₂lattice,and therefore the NIR reflectance of the samples showed a gradual decrease.When x=0.01,the near-infrared solar reflectivity of Y₃Al_4.99Cr_0.01O₁₂sample is the highest（91.47%）,and the color tone is relatively light.When x=0.10,the Y₃Al_4.9Cr_0.1O₁₂sample shows a satisfactory green color and high NIR solar reflectance（84.91%）.With the combination of color and reflectance properties,x=0.10 is considered as the best doping degree.Chromium doped yttrium aluminum garnet powders also have excellent thermal stability and chemical stability.Therefore,the pigment synthesized in this topic combines high NIR reflectivity,beautiful color and high resistance,which can make up for the deficiency of a single material,and is expected to be used as a colorant for ceramic materials and plastics in the field of heat insulation and energy saving.