bet analysis (Bet analysis)

getbet analysisThere are three possible reasons for the negative BET value of. First, the sample itself. If the sample has no adsorption on the adsorbate, the isothermal adsorption and desorption curve should be close to zero. Coupled with instrument errors, the curve may show a negative value. Secondly, too little sample amount during the test leads to a very low adsorption value, resulting in a negative value. Finally, the degassing conditions are unreasonable. Too high degassing temperature will change the pore structure, or insufficient degassing time will lead to incomplete degassingbet analysis; Secondly, the overall analysis report BET analysis includes key data such as BET surface area pore volume and average pore diameter. BET surface area is calculated using the BET model. The pore volume is calculated using the pressure pump method, and the average pore diameter is calculated using the BJH method to calculate the desorption branch curve. Further, understand the adsorption and desorption curve chart displaybet analysisDifferent adsorption isotherms types Type I Type II Type III Type IV Type VI Type I isotherms reflect the microporous filling phenomenon of microporous adsorbent; In order to deeply understand the principle of BET, this post will introduce in detail the advanced knowledge of BET testing and analysis. Starting from the adsorption theory, we will gradually introduce the necessary conditions before the BET equation test, weighing sample mass and pore size analysis and other core aspects. First, the basic assumptions of BET adsorption theory include the uniformity of four-point adsorption sites, the possibility of multi-layer adsorption without interaction between molecules and the difference in adsorption heat. The BET equation is used to describe the relationship between the equilibrium pressure of gas adsorption and the adsorption volume; When conducting BET tests, it is often necessary to consider whether to use adsorption data or desorption data to build a pore distribution pattern. The general view prefers to use desorption data because it is considered to be closer to a pure physical process. However, there is no consensus in the academic community. In order to obtain more accurate results, it is recommended to use adsorption and desorption data simultaneously and combine thembet analysisHe calculated a model for comparative analysis. If the BJH pore distribution is mentioned, then BET is a specific surface area analysis model.

In addition,"bet" can also be extended to a solemn promise of what to do or not to do, etc. Therefore, it has many meanings in various occasions. No matter what the situation is,"bet" has its own specific usages and meanings. If you need to understand it in depth, you can consult the dictionary for more detailed explanations and example sentences. In addition, please note that in different contexts, there may also be some unique understandings and applications unique to cultural factors, which can be divided into actual situations; There may be three reasons for the negative value. The sample itself. For example, the isothermal adsorption and desorption curve shows no adsorption, and the adsorption value is close to 0. In addition, instrument errors may cause the negative value to be added too little sample, resulting in a very low total adsorption value. The degassing temperature and time are unreasonable. High temperature degassing leads to changes or collapses of pore structure. Low temperature or short time degassing leads to incomplete degassing. Why is the isothermal adsorption and desorption curve not closed? BET test, that is, specific surface area test, is based on the adsorption theory proposed by Hillonor Emmet and Taylor. By measuring the adsorption capacity of multiple layers of samples under different nitrogen partial pressures, the relationship between the adsorption capacity of single layers and the adsorption capacity of multiple layers is deduced. Based on this, the specific surface area of the sample is calculated. BET analysis is mainly used to process adsorption data with relative pressures between 005 and 035. Outside this range may affect the accuracy of the model. The adsorption is on the surface of gas and solid; The BET test actually analyzes the isothermal adsorption and desorption curve of nitrogen, rather than directly measuring the BET parameters. The method uses a specific algorithm to process the data in the range of pp0 =005 to 035, thereby estimating the adsorption volume Vm of the monolayer, and then calculating the specific surface area. In the actual measurement results, the adsorption and desorption curve exists objectively, and the specific surface area pore size distribution, etc. are subjective calculations based on these data, which involve the adsorption phenomena of the material molecules and the solid surface.

During BET testing, the pore distribution is usually between 354nm, and in most cases, the desorption process is considered to be closer to a pure physical process, so desorption data is usually used for analysis. However, the academic community has not yet decided whether to choose adsorption data or desorption data to make a BET pore distribution graph. In order to obtain more realistic results, it is recommended to use adsorption data and desorption data at the same time for comparison, and combine other calculation models for comprehensive analysis; Common problems in BET testing include instrument reasons, sample reasons, and insufficient helium degassing before testing. Test requirements involve sample processing conditions, adsorbate gas characteristics and test method factors, common problems and reasons analysis, instrument reasons, instrument reasons, such as solid particles on the valve core of the solenoid valve hinder the pressure balance during gas desorption, which may lead to incomplete curve closure. Sample reasons: Improper sample pretreatment or sample with a specific pore structure may; Common questions related to BET pore size analysis mainly include the following key assumptions. When the BJH method is used to calculate the mesoporous pore size distribution, it is assumed that the pore size is rigid and regular in shape, no micropores, and the pore size distribution does not exceed the maximum pore limit. Data requirements require reliable pore size distribution calculation requires pore size rigidity and narrow and clear pore size distribution, and at the same time, no micropores or macropores influence the analysis. H1-type hysteresis loop indicates uniformly; In order to ensure measurement accuracy, the mass of the sample should be reweighed after analysis. If the mass after analysis is not equal to the initial mass before analysis after degassing, the mass after analysis should be used for recalculation. 3 Aperture analysis 4 influencing factor BET specific surface area is The most easily obtained parameter that can be calculated by the physical adsorption analyzer, because its basic calculation data is taken from the saturation stage of the adsorption isotherm, which is also the most gentle section of the isotherm. However, The final result is influenced by many factors;BET surface analysis is an important method to measure the specific surface area of materials based on adsorption theory. The following is a detailed explanation of the basic principles of BET surface analysis. BET testing is based on the adsorption theory proposed by Hilanore Emmet and Taylor. It measures the multilayer adsorption amount of a sample under different nitrogen partial pressures, deduces the relationship between the monolayer adsorption amount and the multilayer adsorption amount, and thus calculates the specific surface area of the sample. The application range of BET analysis is mainly used for processing.

The pore size distribution BET test method can not only measure the total volume of pores, but also deduce the distribution of different pore sizes in solid materials by analyzing parameters such as adsorption isotherms. This is crucial for understanding the microstructure and performance of materials. Surface quality BET test can also provide information about the surface properties of solid materials, such as the distribution of chemical composition and functional groups on the surface, which plays a key role in understanding the adsorption mechanism and catalytic performance of materials; For specific materials, the adsorption behaviors of Ar and N2 are different. Ar fills the micropores at higher relative pressures, while N2 fills the micropores at lower relative pressures. The capillary condensation process of CO2 in the mesopores does not occur, making it impossible to calculate the pore size distribution of the mesopores. However, for micropores smaller than 1nm, it is a very useful analytical probe. Pay attention to the Shuobo testing circle, and you can get a variety of dry goods gift packages by replying to specific keywords, including basic knowledge of common instruments, BET dry goods infrared; Based on classic statistical theory, the three scientists proposed a multi-molecular layer adsorption model, and derived the famous BET equation. This equation describes the relationship between the adsorption capacity of a single layer Vm and the adsorption capacity of multiple layers Vm. It is more close to the actual adsorption process, so it has a high degree of accuracy in the study of particle surface adsorption properties and the analysis of related instrument data. Through the BET test, experimenters usually measure the multi-layers under different nitrogen partial pressures on 35 groups of samples.