高等学校化学学报 ›› 1981, Vol. 2 ›› Issue (4): 495.

• 论文 • 上一篇    下一篇

硅胶表面结构的热稳定性研究

戴闽光, 高月英, 赵振国, 顾惕人   

  1. 北京大学化学系胶体化学教研室
  • 收稿日期:1980-08-14 出版日期:1981-12-24 发布日期:1981-12-24

STUDY ON HEAT STABILITY OF THE SURFACE STRUCTURE OF SILICA GELS

Dai Minguang, Gao Yueying, Zhao Zhenguo, Gu Tiren   

  1. Department of Chemistry, Peking University, Beijing
  • Received:1980-08-14 Online:1981-12-24 Published:1981-12-24

摘要: 本文研究了热处理(200—1100℃)对自制的一种硅胶的表面结构的影响;测定了BET比表面(低温氮气吸附法)、孔体积、乙醇的吸附-脱附等温线,计算了孔径分布,求得了最可几Kelvin半径。结果表明,杂质的存在明显地降低硅胶的热稳定性。在发生熔结以前,孔径分布基本不变,当发生熔结时,孔半径显著减小。红外光谱的测定表明,随着热处理温度的升高,硅胶表面缔合羟基(~3500cm-1)迅速减少,在~800°时已去除殆尽,而自由羟基(~3720cm-1)减少缓慢,在1100℃时才迅速消失。X-射线衍射图表明,发生熔结后的硅胶显示有β-鳞石英的衍射峰,说明出现了有序晶相。对上述实验结果,文中作了初步的解释。

Abstract: The effects of heat-treatment on the surface and pore structure of silica gels heated in the range of 200-1100°C have been studied. We have measured the specific surface area by means of B. E. T. nitrogen adsorption method, and the adsorption-desorption isotherms of ethyl alcohol at 25°C by gravimetric method. Moreover, we have calculated the pore volume and the pore-size distributions of silica gels. After heat-treated at 950°C, the specific surface area and pore volume of the purified silica gels are decreased only 25% and 21% respectively, while those of unpurified gels are decreased more than 95%. From these results, it is concluded that the effect of impu-rity is to decrease the thermal stability of silica gel. After heat-treated at various temperatures (200-1100°C), the purified silica gels are studied by infrared spectroscopy in the 2350-4000cm-1 region (paraffin oil is used as mulling agent). The results show that the absorption bands at 3720cm-1 (isolated single hydroxyls) are decreased slightly when the temperature is raised from 200 to 950°C, and disappear completely when the temperature is raised to 1100°C. However, the absorption bands in 3300-3600cm-1 (associated hydroxyls) are decreased much more rapidly than band at 3720cm-1. The x-ray diffraction shows that only the purified silica gel heated at 1100°C shows the diffraction lines of β-tridymite. When the heating temperature is lower than 950°C,the sintering and thus the decreasing of free hydroxyls are only gentle. However, as the heating temperature is reached to 1100°C,the surface area and pore volume of silica gel decrease markedly, This shows the sintering has occured vigorously, and thus the free hydroxyls may be eliminated almost completely. It is interested to note that after heated at 1100°C the purified silica gel still has quite large surface area of 95m2/g and pore volume of 0.15cm3/g.

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