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Main factors affecting BET specific surface area test results

Release date:2018-04-10  source:粉体网  Browse times:820
     First, it is related to the sample pretreatment time. Taking nickel hydroxide as an example, its treatment time needs at least 8 hours. Because the drying process is easy to be knotted, the treatment temperature should not be too high (generally 90 ° C). Because the treatment temperature is not high enough, it needs to be compensated by adding a long time.

Second, it is related to the processing temperature of the sample. Taking alumina as an example, its processing temperature is generally 300 °C. If the processing temperature is lowered, the measurement result is likely to be low, and the linearity of the BET measurement curve is poor.

Third, it is related to the degree of vacuum during processing. The low degree of vacuum makes the saturated vapor pressure of the vacuum chamber too high, and the surface of the sample is not cleaned, which results in low measurement results (except for individual samples).

Fourth, it is related to the amount of sample. The amount of the sample is related to its own specific surface size, generally the larger the surface, the less the sample weight. However, in the case where the sample tube volume is constant, too much amount is likely to cause blockage of the tube, and too little desorption peak tailing is likely to occur. So it is necessary to choose the right amount of sample.

Fifth, it is related to the self-adsorption characteristics of the test sample. Most of the sample treated surface ratio is larger than the specific surface before treatment, but some samples are larger than the surface when untreated, but become smaller after treatment.

Sixth, related to the type of instrument, in general, the results measured by the static volume method are more accurate than those measured by flow chromatography. This is because the former measures the adsorption data and the latter measures the desorption data. If irregular pores are present in the sample, the nitrogen molecules enter the pores, and when they are desorbed, they may not come out because the outlet is small. Distorted data caused by desorption. In addition, flow chromatography measurement errors are also increased due to the effects of thermal diffusion.

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