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hellen7256

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The representative geopolymerization product was fabricated through alkaline- or alkali-silicate-activated metakaolin, which has a wide range of compositions represented by M2O-mAl2O3-nSiO2, where (usually) m ≈ 1, 2 ≤ n ≤ 6, and M represents one or more alkali metals. To obtain geopolymers with a low Si/Al ratio and to overcome the disadvantages associated with the use of impure raw materials; amorphous Al2O3-SiO2 powder was first prepared through a sol-gel method in accordance with chemical compositions that were specifically designed in our work. The composition of the geopolymers is similar to that of the NaA zeolites when n = 2 and M = Na [15-16]. During this fabrication process, sodium silicate was used as an alkali activator (SiO2:Na2O molar ratio = 1.0), and the molar ratio of SiO2 in the synthetic powders to that of the sodium silicate was 1:1. Therefore, the chemical composition of the resulting geopolymers was Al2O3-2SiO2-Na2O. The zeolite crystal structure was obtained through the hydrothermal processing of Al2O3-2SiO2-Na2O at 90ºC for 6 h. The XRD patterns and the MAS NMR spectra of the calcined Al2O3-SiO2 powders, the chemosynthetic Al2O3-2SiO2-Na2O geopolymers, and the hydrothermal samples are presented in Fig. 2.
Traditional alkali-based geopolymers typically exhibit one “hump” centered at approximately 26.0° to 29.0° (2θ) in their XRD patterns [17-19]. However, the XRD pattern of the as-prepared Al2O3-2SiO2-Na2O geopolymer has one “hump” centered at approximately 28.5°, which indicates a trend of crystallization. The HRTEM results from the analysis of the Al2O3-2SiO2-Na2O geopolymer confirm the existence of nanoscale ordered structures within the amorphous geopolymer gel [15-16]. After the hydrothermal process, the XRD results indicate that the majority of the Al2O3-2SiO2-Na2O geopolymers transformed into NaA zeolite crystals with good crystallinity (see Fig. 2a). The most important observation from our results is that the crystalline zeolite seeds already exist in a solid geopolymer gel. Key evidence supporting this conclusion was also obtained from the MAS NMR spectra.

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1樓 2015-06-16 22:07:58

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jiangguofeng

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hellen7256: 金幣+30, 翻譯EPI+1, ★★★★★最佳答案, 謝謝 2015-06-17 21:40:53

典型的地質聚合產(chǎn)物是通過堿性的-或堿金屬-硅酸鹽-活化的偏高嶺土制造的，這種偏高嶺土具有寬泛的組分，表示為M2O-mAl2O3-nSiO2,式中（通常）m≈1, 2≤n≤6, M代表一種或多種堿金屬。為了獲得具有較小Si／鋁比的地質聚合物并為了克服使用不純的原料所帶來的缺點；首先，按照我們研究當中明確地設計的化學成分通過溶膠-凝膠法制備了非晶形Al2O3-SiO2粉末。當n=2并且M=Na時這種地質聚合物的組分與NaA分子篩相似[15-16]。在這種制造過程當中，硅酸鈉作為一種堿金屬活化劑( SiO2:Na2O摩爾比=1.0)使用并且合成的粉末中的SiO2對硅酸鈉的摩爾比為1:1。因此形成的地質聚合物的化學成分為Al2O3 - 2SiO2 - Na2O。這種分子篩晶體結構是通過Al2O3-2SiO2-Na2O于90℃熱液作用６小時而獲得的。焙燒的Al2O3-SiO2粉末、化學合成的Al2O3-2SiO2-Na2O地質聚合物和熱液樣品的X射線衍射圖和MAS NMR譜圖如圖2所示。
在X射線衍射圖中，傳統(tǒng)的堿基地質聚合物表現(xiàn)出典型的一個"駝峰"，其中心大約在26.0°到29.0°(2θ)[17-19]。然而，所制備的Al2O3 - 2SiO2 - Na2O地質聚合物的X射線衍射圖具有一個"駝峰"，其中心大約在28.5°處，這表明一種結晶的趨勢。 Al2O3-2SiO2-Na2O地質聚合物的高分辨率透射電子顯微鏡分析結果證實在非晶形地質聚合物凝膠之內存在納米級有序結構[15-16]。熱液作用之后，X射線衍射結果顯示大多數(shù)Al2O3-2SiO2-Na2O地質聚合物轉化成具有良好的結晶度的NaA分子篩結晶(詳見圖2a）。從我們的結果當中最重要的發(fā)現(xiàn)是結晶分子篩種子已經(jīng)存在于固體地質聚合物凝膠之中。還由魔角旋轉核磁共振譜圖中得到了支撐這種結論的關鍵證據(jù)。

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2樓2015-06-17 20:01:56

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