Microstructure, Thermal Conductivity, and Temperature-Dependent Infrared Emissivity of Divalent Transition Metal Ions Doped A-Cordierite Ceramics

Abstract

The pure a -cordierite (MAS) and divalent transition metal ions doped a -cordierite powders (Mg 1.8 M 0.2 )Al 4 Si 5 O 18 ( M= Ni, Co, and Zn , named MASNi 0.2 , MASCo 0.2 , and MASZn 0.2 ) were synthesized by the sol-gel technique. Further, the powders were compacted by cold isostatic pressing and then sintered to produce the crystallized bulk ceramics. The relationships between doped ions, microstructure, thermal conductivity, thermal expansion, and infrared emissivity were studied and analyzed. The results show that substituting divalent transition metal ion s for a portion of magnesium ions can effectively increase the α-cordierite ceramic emissivity at 3 –20 μm, attributing to the enhanced lattice vibration and the unique 3 d orbital energy level splitting after introducing transition metal ions. Significantly, the average emissivity of MASNi 0.2 ceramic has a maximum of ~0.99 in the wave band of 10 – 20 μm at 500 ° C, an increase of about 24% compared to that of pure α-cordierite. Moreover, divalent transition metal ions doping can efficaciously decrease the thermal conductivity by improving phonon scattering of the sintered ceramic due to the increase of lattice distortion. The ions doping causes structural change owing to the difference of ionic radius between the doped and magnesium ions, influencing the thermal expansion performance.

Keywords: -cordierite, Thermal conductivity, Thermal expansion, Infrared emissivity, Divalent ions.