Preparation and Characterization of Porous Ceramic Composites for Thermal Insulation

本研究主要在於利用膠粒製程以及直接發泡法，以雲母及G1A5玻璃(47BaO-21B2O3-27SiO2-5Al2O3, in mol%)粉體為主原料，來製備低熱傳以及可在1000 oC熱處理卻不會發生尺寸收縮之多孔陶瓷。本論文提出了製備此多孔陶瓷的最佳配方和製程參數。其中，發泡劑的種類、雲母/玻璃含量比、固含量、微波乾燥步驟、玻璃在雲母表面的潤濕行為、以及泡沫體的固化成型等均納入本實驗的考量，以得到具有最佳穩定性的陶瓷泡沫體。本實驗亦針對所製備出之多孔陶瓷燒結體執行孔隙率、孔徑尺寸、壓縮強度、氣體通透率以及熱傳導率等分析。其中一種多孔材在經過950oC持溫1小時的熱處理，於25oC、600oC以及800oC時之熱傳導率分別可達0.08 W/m K、0.14 W/m K與0.18 W/m K；同時該樣品具有的孔隙率、氣體通透率、壓縮強度與密度分別為91.2%、0.1 10-7 cm2、440 kPa與0.26 g/cm3。除此之外，實驗結果顯示當樣品的溫度介於室溫至800oC之間時，熱傳遞主要來自光子傳導和空氣傳導兩個機制。Direct forming of dispersive mica particulates and G1A5 (47BaO-21B2O3-27SiO2-5Al2O3, in mol%) glass powder was used to prepare ceramic foams with extremely low thermal conductivity and nearly no shrinkage by 1000oC treatment. Optimized formulation and processing parameters are proposed for the preparation of the ceramic foams. The effects of foaming agents, mica/glass ratio, solid content, microwave drying steps, wetting behavior of the glass on mica, and consolidation of the foam were investigated in consideration of foam stability. Besides, the properties of sintered foams, including porosity, pore size, compressive strength, permeability, and thermal conductivity were also analyzed. One ceramic foam which undergoes thermal treatment at the temperature as low as 950oC for 1 h is the best having a lowest thermal conductivity of 0.08 W/m K, 0.14 W/m K and 0.18 W/m K at the temperature of 25oC, 600oC and 800oC, respectively, as well as having a density of 0.26 g/cm3, porosity of 91.2%, gas permeability of 0.1 10-7 cm2, and compressive strength of 440 kPa. The results show that the photon conduction and air conduction are two dominated mechanisms of the foams from room temperature to 800oC