Study On The Influence Of Interlayer Spacing And Layer Thickness Of Layered Oxides On Their Thermal Properties

Layered oxide materials are a class of oxide materials with a layered structure.This material shows anisotropic in thermal conductivity,and the thermal conductivity perpendicular to the layer is much smaller than that parallel to the layer.This makes the layered oxide materials very promising for thermal insulation applications.However,the thermal stability of the layered oxide decreases after ion exchange and ion intercalation processing;the effect of the microstructure of the layered oxide?such as interlayer spacing and layer thickness?on its thermal conductivity remain unclear;the preparation of oriented coatings or bulks are difficult.These facts hinder the application of the layered oxides in thermal insulation.Therefore,in this thesis,K_0.8Li_0.27Ti_1.73O₄ and KCa₂Nb₃O₁₀ are used as precursors to adjust the interlayer spacing and layer thickness to explore the effect of the interlayer spacing and layer thickness of oxides on their thermal properties.The research results obtained in this paper are as follows:?1?Li⁺,Na⁺,K⁺and Cs⁺ion intercalated titanates with different interlayer spacings were prepared by protonation,ion exchange and calcination at 200°C,and the interlayer spacing increases with the increase of intercalated ion size.In third chapter,three methods were tried to prepare samples with orientation.The spin coating method can prepare oriented samples.However,the organic molecules in the solvent easily enter the interlayer during sample processing,which disturbs the accuracy of subsequent tests.The titration method can also prepare samples with orientation,but it is difficult to make the sample distribution even during titration.The sedimentation method can yield coatings with good orientation,uniformity and thickness,and the samples are easily compressed into oriented pellet samples without substrate after sedimentation.?2?The four alkali metal ion intercalated titanates have different thermal stability.The thermal stability depends on the intercalated ions,and the thermal stability increases with the increase of the intercalated ion size.Li⁺ion intercalated titanate shows lowest thermal stability,and it loses its original layered structure before 400°C,and the Cs⁺ion intercalated titanate demonstrates the highest thermal stability,and its original layered structural vanish at about 800°C.The thermal conductivity at room temperature of four alkali metal ion intercalated titanates without interlayer water decreases as the intercalation ion size increases.K⁺ions and Cs⁺ion intercalated titanates were calcined at 200-1000°C,and then the room temperature thermal conductivity of the calcined samples was investigated.It was found that the room temperature thermal conductivity of the calcined samples increased with the increase of calcination temperature.?3?In fifth chapter,two methods were studied to synthesize layered niobates with different thicknesses.The indirect synthesis method can only synthesize a 4KCNNO and lower order niobates,and the direct synthesis method can synthesize a high order niobates up to 6KCNNO.an excess of 20%mol K₂CO₃ and 5%mol Na₂CO₃ is necessary for the direct method to synthesize pure 5KCNNO.On the other hand,an excess of 20%mol K₂CO₃ and 10%mol Na₂CO₃ is required for for the direct synthesis of pure 6KCNNO.The room temperature thermal conductivity of niobates increased with the increase of host layer thickness.