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hellen7256木虫 (小有名气)
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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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jiangguofeng
金虫 (著名写手)
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hellen7256: 金币+30, 翻译EPI+1, ★★★★★最佳答案, 谢谢 2015-06-17 21:40:53
hellen7256: 金币+30, 翻译EPI+1, ★★★★★最佳答案, 谢谢 2015-06-17 21:40:53
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典型的地质聚合产物是通过碱性的-或碱金属-硅酸盐-活化的偏高岭土制造的，这种偏高岭土具有宽泛的组分，表示为M2O-mAl2O3-nSiO2,式中（通常）m≈1, 2≤n≤6, M代表一种或多种碱金属。为了获得具有较小Si／铝比的地质聚合物并为了克服使用不纯的原料所带来的缺点；首先，按照我们研究当中明确地设计的化学成分通过溶胶-凝胶法制备了非晶形Al2O3-SiO2粉末。当n=2并且M=Na时这种地质聚合物的组分与NaA分子筛相似[15-16]。在这种制造过程当中，硅酸钠作为一种碱金属活化剂( SiO2:Na2O摩尔比=1.0)使用并且合成的粉末中的SiO2对硅酸钠的摩尔比为1:1。因此形成的地质聚合物的化学成分为Al2O3 - 2SiO2 - Na2O。这种分子筛晶体结构是通过Al2O3-2SiO2-Na2O于90℃热液作用６小时而获得的。 焙烧的Al2O3-SiO2粉末、化学合成的Al2O3-2SiO2-Na2O地质聚合物和热液样品的X射线衍射图和MAS NMR谱图如图2所示。 在X射线衍射图中，传统的碱基地质聚合物表现出典型的一个"驼峰"，其中心大约在26.0°到29.0°(2θ)[17-19]。 然而，所制备的Al2O3 - 2SiO2 - Na2O地质聚合物的X射线衍射图具有一个"驼峰"，其中心大约在28.5°处，这表明一种结晶的趋势。 Al2O3-2SiO2-Na2O地质聚合物的高分辨率透射电子显微镜分析结果证实在非晶形地质聚合物凝胶之内存在纳米级有序结构[15-16]。 热液作用之后，X射线衍射结果显示大多数Al2O3-2SiO2-Na2O地质聚合物转化成具有良好的结晶度的NaA分子筛结晶(详见图2a）。 从我们的结果当中最重要的发现是结晶分子筛种子已经存在于固体地质聚合物凝胶之中。 还由魔角旋转核磁共振谱图中得到了支撑这种结论的关键证据。 |
2楼2015-06-17 20:01:56
