Eight influencing factors for errors in BET test data

BET, as a readily available parameter in the SSA4000/SSA7000 physical adsorption analyzer, is a widely used method for calculating the specific surface area of microporous/mesoporous materials. The BET calculation is based on the saturation stage of the adsorption isotherm, which is the flatter part of the isotherm, i.e. P/Po<0.35. However, due to various factors, there are differences in data between different instruments and laboratories. The sources of error include several aspects:

1. The pore structure of the sample affects the experimental results: the simpler the pore structure, the easier it is to reproduce the results.

2. The type of testing instrument affects the experimental results: In most cases, dynamic chromatography results are not as accurate as static volumetric methods because adsorption data is more accurate than desorption data.

3. The type of adsorbed gas affects the experimental results: Different gases have different diffusion rates in the pores of microporous samples, which affects the accuracy of the final results.

4. The sample pretreatment time affects the experimental results: the drying process of nickel hydroxide is prone to agglomeration, and the treatment temperature should not exceed 90 ℃, so the degassing time needs to be extended.

5. The effect of pre-treatment on degassing vacuum degree on experimental results: Vacuum degree is positively correlated with degassing degree, and surface impurities on the sample will affect the test results to a lesser extent.

6. The amount of sample to be weighed affects the experimental results: The amount of sample is negatively correlated with its specific surface area, meaning that the larger the specific surface area, the less sample to be weighed.

7. The effect of sample processing temperature on experimental results: Taking alumina as an example, reducing its processing temperature to below 300 ℃ can easily result in smaller results and poor linearity of the BET curve.

8. The range of sampling points on the adsorption curve affects the experimental results: it is necessary to follow the BET sampling principle.