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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Effect of Boehmite Crystallite Size and Steaming on Alumina Properties
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Effect of Boehmite Crystallite Size and Steaming on Alumina Properties

机译：勃姆石微晶尺寸和汽蒸对氧化铝性能的影响

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摘要

Boehmite and pseudoboehmite were studied in order to find the effect of their individual properties upon the properties of transitional alumina and a.-A1203 produced thereof; the influence of steaming on these properties was also considered. Samples were characterized by X-ray powder diffraction, crystalline structure refinement, scanning electron microscopy, thermoanalysis, and nitrogen adsorption. Boehmite and pseudoboehmite had the same crystalline structure but different crystallite dimensions. Differences between lattice parameters’ (only 0.0052 nm along the b axis) are so small that the assumption of many authors that pseudoboehmite has intercalated water in its crystalline structure cannot be supported. Small crystallites with larger active areas, increased by crystal faces perpendicular to (020) planes, explain the larger amounts of desorbed water that pseudoboehmite exhibits compared to boehmite while drying. The hydrogen-bond length in boehmite depends on the crystallite size and determines the temperature where transformation into transitional alumina takes place. The boehmite crystallite size also defined pore size and distribution in transitional aluminas as well as their grain and crystallite size. Since the transformation of the transitional alumina into 4x-A1203 depends on hydroxyls diffusion, the corresponding temperature is higher for the transitional alumina with a larger grain size. Steaming promoted crystal growth, because water molecules favored migration of aluminum atoms. Nitrogen adsorption—desorption isotherms of transitional aluminas derived from pseudoboehmite exhibited hysteresis loops corresponding to less ordered structures associated with swelling of platelets-during desorption of nitrogen molecules. Consequences on the properties of transitional aluminas used as cracking catalysts were inferred. As texture and acidity evolve in opposite directions, there is a need for controlling them independently.
机译：为了发现勃姆石和假勃姆石的各自性能对过渡氧化铝及其生产的a.-A1203性能的影响，对勃姆石和假勃姆石进行了研究。还考虑了蒸煮对这些性能的影响。通过X射线粉末衍射，晶体结构细化，扫描电子显微镜，热分析和氮吸附对样品进行表征。勃姆石和假勃姆石具有相同的晶体结构，但晶粒尺寸不同。晶格参数之间的差异（沿b轴仅为0.0052 nm）是如此之小，以至于许多作者都认为假勃姆石在其晶体结构中嵌入了水，这一假设无法得到支持。垂直于（020）平面的晶面增加了具有较大活性区域的小型微晶，这说明假勃姆石与干燥时的勃姆石相比，脱附的水量更大。勃姆石中氢键的长度取决于微晶尺寸，并决定了转变成过渡氧化铝的温度。勃姆石微晶尺寸还限定了过渡氧化铝中的孔尺寸和分布以及它们的晶粒和微晶尺寸。由于过渡氧化铝向4x-Al2O3的转化取决于羟基的扩散，因此具有较大晶粒尺寸的过渡氧化铝的相应温度更高。蒸汽促进了晶体的生长，因为水分子有利于铝原子的迁移。源自假勃姆石的过渡型氧化铝的氮吸附-解吸等温线表现出磁滞回线，对应于在氮分子解吸期间与血小板膨胀相关的结构较不规则。推断了用作裂解催化剂的过渡氧化铝性能的后果。随着质地和酸度沿相反的方向发展，需要独立地控制它们。

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