Low Thermal Conductivity and Radiation of Porous Ceramics
|Keywords:||氧化鋁;氧化鋯;孔隙率;熱傳導;光譜分析;水合;Al2O3;ZrO2;porosity;thermal conductivity;FTIR;hydration||Issue Date:||2008||Abstract:||
摘要 本研究主要採用膠粒分散及打泡法，將氣泡均勻分散在陶瓷漿料中，經適當的微波乾燥及燒結步驟，製備出孔隙率在85 %以上的多孔陶瓷，並使用不同材料種類、觀察微結構，了解這些因素對於熱傳導之影響。實驗中，分別以SDS和valeric acid當作起泡劑，利用直接泡沫法(Direct Foaming Method, DFM)做出孔隙率高達85 % ~ 95%的多孔氧化鋁，氧化鋯及雲母。經由掃描式電子顯微鏡(SEM-EDX)分析，發現製出的多孔陶瓷氣胞平均尺寸在17 um到80 um之間，且包含緻密與不緻密的兩種氣胞壁。利用熱機械性質分析(TMA)觀察不同孔隙率的多孔陶瓷對燒結溫度的影響。光學部份，經由快速傅立葉轉換紅外線光譜儀(FTIR)分析多孔陶瓷在1000 cm-1到4000 cm-1被散射的情況，及比較孔隙率、晶粒與氣胞壁對衰減係數之影響。在熱傳導分析部份，以熱線法(hot-wire method)自行組裝熱傳分析儀器，利用標準樣品做校正後，量測分析比較多孔陶瓷的孔隙率、晶粒大小、氣胞壁緻密度、以及固溶物與氧空缺對熱傳導係數的影響。本研究製備95 %孔隙率的氧化鋁有最佳隔熱性，其在室溫的熱傳係數為0.05 W/m*oC，在800oC為0.17 W/m*oC。
This study used colloidal dispersion and direct foaming method to distributed bubbles uniformly in ceramic slurry. After microwave drying and appropriate sintering, the porous ceramics with porosity 85 ~ 95 % were made. The effects of material and porous structure on thermal conductivity are investigated in this study. Porous Al2O3, ZrO2 and mica with porosity higher than 85 % are foamed by the direct foaming method with SDS and valeric acid as surfactants. The gas cells of porous ceramics in an average bubble size with the range of 17 um to 80 um were characterized by scanning electron microscope equipped with energy dispersive spectroscopy (SEM-EDX). Two different cell walls with dense and non-dense profiles exist in the porous samples. Thermal mechanical analysis (TMA) was used to analyze the sintering behaviors of porous ceramics with different porosities. Light scattering between 1000 cm-1 and 4000 cm-1 were investigated by Fourier Transform Infrared Spectroscopy (FTIR). The instrumental set-up for measuring thermal conductivity by a hot-wire method was calibrated by the standard sample. The thermal conductivities of porous ceramics with different porosity, grain size, cell walls, and defects are observed and compared to each other. Consequently, small k value of 0.05 W/m*oC at room temperature and 0.17 W/m*oC at 800oC of one Al2O3 foam with the porosity of 95 % can be reached in this study.
|Appears in Collections:||材料科學與工程學系|
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