What are the main factors that affect the BET specific surface area test results?

(1) It is related to the sample pretreatment time. Taking nickel hydroxide as an example, its processing time needs at least 8 hours. Since its drying process is easy to harden, the processing temperature should not be too high (generally 90OC). Since the processing temperature is not high enough, it needs to be extended to make up for it.

(2) It is related to the processing temperature of the sample. Taking alumina as an example, its processing temperature is generally 300OC. If the processing temperature is lowered, the measurement results will be low and the linearity of the BET measurement curve will be very poor.

(3) It is related to the vacuum degree during processing. The degree of vacuum is low, which causes the saturated vapor pressure of the vacuum chamber to be high, and the sample processing is not clean, which will result in low measurement results (except for individual samples).

(4) It is related to the weighing sample amount. The size of the sample is related to its specific surface area. Generally, the larger the specific surface area, the smaller the weighing sample size. However, when the volume of the sample tube is certain, too much volume can easily cause pipeline blockage, and too little volume can easily cause desorption peak tailing. Therefore, it is necessary to choose the appropriate weighing sample volume.

(5) It is related to the self-adsorption characteristics of the test sample. The specific surface area of most samples after treatment is greater than the specific surface area before treatment, but the specific surface area of some samples is very large when untreated, but becomes smaller after treatment.

(6) It is related to the type of instrument. Generally speaking, the results measured by static volumetric method are more accurate than those measured by flow chromatography. This is because the former measures adsorption data, while the latter measures desorption data. If there are irregular pores in the sample, after nitrogen molecules enter the pores and desorb, they may not come out due to the small outlet, causing distortion of the desorption data. In addition, due to the influence of thermal diffusion, the measurement error of flow chromatography will also be increased.