页岩氮气吸附 BET比表面积测定误差校正方法

摘要

The theory of BET model which based on multi-molecular layer adsorption is the most commonly and mature method used for specific surface testing .For the nitrogen adsorption data of shale samples which at liquid nitrogen testing temperature , slectting the relative pressure from 0.05 to 0.30 between ( indicated for mesoporous materials) the BET specific surface of the sample can be calculated , but it will appear the problem of poor correla-tion coefficient and negative constant C which is not allowed to happen , the problem is often subject to ignore .The micropore pore size distribution calculated by carbon dioxide adsorption data using the DFT model shows shales con -tain a mount of microporous which aperture between 0.5 ~1.0 nm.The characteristics of shales nanometer pore distribution is the fundamental reason for the emergence of above problems .In other words , shale is not the meso-porous materials and narrower pore size distribution .On the contrary , by selecting the relative pressure which from 0.05 to 0.20 calculating the specific surface , the correlation coefficient reached more than 0.999 9, and emerged positive intercept on the Y axis, the relative pressure range is more reasonable , and the calculated BET specific sur-face is more reliable .%基于多分子层吸附理论的BET模型是最成熟、最常用于比表面测试的计算方法，然而，针对页岩样品在液氮温度下的氮气吸附数据，选取0．05～0．30间的相对压力点（适用于中孔材料）进行BET比表面计算时，将出现回归曲线相关系数较差、常数C为负值（无物理意义）情况，这一问题往往被测试者忽视。通过页岩的二氧化碳吸附数据运用DFT模型，计算出页岩的微孔分布可知，页岩含有大量0．5～1．0 nm之间的微孔，页岩纳米级孔隙分布范围广的特点是出现上述问题的根本原因，即页岩并非孔径分布较窄的介孔材料。通过调整相对压力点的选取范围，在相对压力0．05～0．20下计算页岩比表面其相关系数能达到0．9999以上，且在Y轴上产生正截距，该相对压力范围更为合理，计算出的BET比表面更为可靠。