Optical-optical Conversion, Heat-optical Conversion, And Thermal Conduction Properties Of Magnetoplumbite Hexaaluminate

Energy saving and emission reduction is the urgent requirements of sustainable development for society and economic. As one of the most important high energy consumption equipment, industrial furnace is significant in energy saving. In this paper, development of novel high-temperature LnMeAl₁₁O₁₉ thermal insulation material with low thermal conductivity and its application in high-temperature heat conduction have been proposed to fulfil energy saving and consumption reducing of high-temperature industrial furnace.The optimized high temperature solid state reaction process conditions for rare earth ions Ln3+（La, Ce, Nd, Sm, Eu, Gd） and transition metal ions Me2+（Mn, Co, Ni, Zn） replacement LaMgAl₁₁O₁₉ powder were 1550°C and 1600°C for 5 h, respectively. The results show that the grain sizes of platelet LnMeAl₁₁O₁₉ increased with the increasing synthesis temperatures, and their lattice parameters decreased with the decreasing ionic radius of Ln3+ ions, while increased with the decreasing relative atomic mass of Me2+ ions.Rare earth ions Ln3+ and transition metal ions Me2+ replaced LnMeAl₁₁O₁₉ ceramics were prepared by pressureless sintering method in air, and the mechanical and thermal physic properties of LnMeAl₁₁O₁₉ material were studied in detail. When the ionic radius of Ln3+ ions decreased or the relative atomic mass of Me2+ ions increased, the mechanical properties of LaMgAl₁₁O₁₉ material improved, while its thermal physic properties decreased. The main mechanism was found to be the improvement of phonon scatting and bulk density, due to the lattice volume shrinkage by ions replacement. Among the rare earth replaced LnMgAl11O19 materials, GdMgAl11O19 obtained the lowest thermal conductivity, which was investigated to be 1.91- 1.78 W/m?K in the range from room temperature to 800°C. LaZnAl11O19 showed the most optimal properties in the transition metal ions replaced LaMeAl11O19 materials, and its bending strength and fracture toughness were 163.3 MPa and 3.3 MPa?m1/2, respectively.The optical-optical conversion properties for different rare earth ions Ln3+（Ln3+: Pr3+, Sm3+, Dy3+, Ho3+, Er3+, Tm3+） doped or co-doped LaMgAl₁₁O₁₉ material were investigated. The results show that the optical conversion, optical conversion spectra and lifetime all depend on the characteristic energy level transition of 4f electrons in rare earth ions. The energy transfer behaviours between Sm3+â†'Eu3+, Tm3+â†'Dy3+ and Er3+â†'Sm3+ were also confirmed obviously, in which emission reabsorption and resonance energy levels are the main energy transfer mechanism. Moreover, the concentration quenching and temperature quenching for optical conversion were found and the main reason was considered to be cascade energy transfer and intercrossing relaxation between activator ions.The influence of material composition and temperature on the high-temperature infrared heat-optical conversion properties of LaMgAl₁₁O₁₉ series materials has also been investigated. The results indicate that the doped or co-doped rare earth ions and transition metal ions had obvious influence on the average infrared emissivity for LaMgAl₁₁O₁₉ materials. LaMgAl₁₁O₁₉:Er3+, Sm3+ and LaZnAl11O19 show better average infrared emissivity（800 °C） than pure LaMgAl₁₁O₁₉ material, which were calculated to be 0.906 and 0.915, respectively. And the heat-optical conversion spectra intensity and emissivity in infrared wavelengths increased greatly with rising temperature. Moreover, the LaMgAl₁₁O₁₉ materials could effectively reduce the thermal conduction of the traditional alumina ceramic materials, when they were brushed on the surface of alumina ceramic. These research achievements show that LaMgAl₁₁O₁₉ series materials have significant potential application in novel low thermal conductivity thermal insulation material for the working surface of industrial furnace lining materials.