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Low Temperature Ageing Of Silicas Gasil-i And Tk800

机译：二氧化硅Gasil-i和Tk800的低温老化

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Gasil-I (a mesoporous silica) and TK800 (a non-porous pyrogenic silica) were investigated in the early 1970s as standard reference materials. Since then the specific surface areas of both silicas have decreased to ～85% of their initial values, suggesting that the surface character and the ageing mechanism may be the same for both. Comparisons of the shapes of nitrogen-adsorption isotherms, confirmed by comparisons of the shape ratios for Gasil-I and TK800, indicate that Gasil-I has greater microbore character and a higher absorption at p/p_0 > 0.5 than TK800 and that the isotherm shapes have changed little since 1974. The specific volume of Gasil-I has remained nearly constant during the ageing period but the pore size distribution (PSD) has shifted markedly to higher values. Electron micrographs show that low (room) temperature gas-solid ageing results in similar enlargement at the point of contact between attached secondary particles as that which occurs in hydrothermal ageing. In the gas-solid case, this change, which accounts for the decrease in overall surface area, is attributed to the surface transport of silica material in the presence of near monolayer quantities of adsorbed water. Ageing in this manner is geometry-limited so that the rate of ageing is expected to approach zero, resulting in time-stable silicas.
机译：在1970年代初，研究了Gasil-I（中孔二氧化硅）和TK800（无孔热​​解二氧化硅）作为标准参考材料。从那以后，这两种二氧化硅的比表面积已降至其初始值的〜85％，这表明这两种二氧化硅的表面特性和老化机理可能相同。氮吸附等温线形状的比较，通过对Gasil-1和TK800的形状比的比较证实，表明，Gasil-1与TK800相比，具有更大的微孔特征，在p / p_0> 0.5时具有更高的吸收率，并且等温线形状自1974年以来变化不大。在老化期间，Gasil-I的比容几乎保持不变，但孔径分布（PSD）已明显移至更高的值。电子显微照片显示，低温（室温）气固老化导致附着的次级粒子之间的接触点处的膨胀与水热老化中发生的膨胀类似。在气固情况下，这种变化（占总表面积的减少）归因于存在近单层吸附水的情况下二氧化硅材料的表面迁移。这种方式的时效受到几何形状的限制，因此时效率有望接近零，从而形成了时间稳定的二氧化硅。

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