Synthesis Of Yttrium Manganate-Based Powders And Preparation Of Thermal Insulation Coatings

Heat transfer under high temperature is mainly based on short-wave infrared radiation.The application of near-infrared reflective/infrared radiant heat insulation materials can effectively protect the substrate materials,which is an effective method for energy conservation and efficiency enhancement in high-temperature industry.Yttrium manganate?YMnO₃?has relatively high melting point?2067 K?and good near-infrared reflection performance.Therefore,it has broad application prospects as a kind of heat-insulating and energy-saving material used in high-temperature fields.In this work,YMnO₃-based powders were synthesized by the molten salt synthesis?MSS?method and the traditional solid-state reaction method.The corresponding coatings were prepared using the synthesized powders as the functional fillers.The near-infrared reflection and infrared radiation properties of powders and coatings were analyzed.The correlation between the microstructures of YMnO₃-based materials and their infrared functional properties was discussed.The main results were as follows:?1?YMnO₃ powders mainly in orthorhombic structure can be prepared via a facile MSS method at 700°C.The powders with good dispersivity in short prismatic shape were obtained,which had relatively high reflectivity in the near-infrared band.After the powders were heat-treated at higher temperatures,the orthorhombic structure was transformed into hexagonal structure,and the near-infrared reflectivity was significantly enhanced.After being doped with Fe ions,the reflectivity of the orthorhombic yttrium manganate-based powders in the 1000-2000 nm band was decreased.?2?YMn_1-xFe_xO₃?x=0,0.05,0.10,0.15,0.20?and YMn_1-xTi_xO₃?x=0.05,0.10?powders synthesized by the traditional solid-state method possessed hexagonal structure after being calcined at 1300°C.The near-infrared reflectivity of the powders after being doped with Fe and Ti ions was reduced.?3?Using the obtained YMnO₃-based powders with different crystalline structure and compositions as fillers,high-solid-content coatings with good stability were obtained.The reflectivity of the orthorhombic YMnO₃ coatings with higher doping amount of Fe ions was increased slightly in the 1500-2200 nm band,which was related to the sizes and morphologies of the filler powders.Fe ion-doping increased the emissivity of the orthorhombic YMnO₃ coatings in the 8-14?m band.This was due to the increase in the amount of Mn³⁺-Mn⁴⁺ion pairs,which led to the easier electronic transition.?4?Both Fe and Ti ion-doping reduced the reflectivity in the near-infrared band of the hexagonal YMnO₃ coatings to a certain extent.After being doped with Fe ions,the infrared emissivity of the coatings in the 8-14?m band was reduced,which was related to the decreased content of Mn³⁺-Mn⁴⁺ion pairs.Compared with Fe ion-doped coatings,coatings with higher doping amount of Ti ions had higher infrared emissivity in the 8-14?m band,which might be due to the electronic transition between Mn³⁺-Mn⁴⁺ions.