Adsorption Test

Adsorption Test

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Brand

Micromeritics Instrument Corporation (ASAP2020), Micromeritics Instrument Corporation (Autosorb IQ)

 

Introduction 

The BET test method is the abbreviation of the BET specific surface area test method , which is named because it is based on the famous BET theory. BET is an acronym for three scientists (Brunauer, Emmett, and Teller). Based on the multi-layer molecular adsorption formula deduced from the classic statistical theory, the famous BET equation has become the theoretical basis of particle surface adsorption science. And it is widely used in the research of particle surface adsorption performance and data processing of related detection instruments.


Test items:

It is suitable for the research and product testing of various materials, including the measurement of various materials such as zeolite, carbon materials, molecular sieves, silica, alumina, soil, clay, organometallic compound skeleton structure and so on.

 

Services

  1. Specific surface area test, the main data is the specific surface area value, the test adsorption pressure can only achieve about 0.4, without a complete adsorption and desorption curve.
  2. Full mesopore analysis, including specific surface area, mesopore (2-50nm) pore size distribution data.
  3. Micro-pore analysis, including specific surface area, micro pore (0.5-2nm) pore size distribution data.
  4. Pore analysis, including specific surface area, full pore (0.5-50nm) pore size distribution data.
  5. Adsorption capacity test, you can choose carbon dioxide adsorption and nitrogen adsorption, the test temperature range is 0 to 60℃, 0℃ carbon dioxide adsorption can characterize the pore size distribution of micro pores. 
  6. High-pressure methane adsorption, the test pressure range is 0-18 atmospheres, and the test temperature range is 0-100℃. The pore size distribution can be used for BJH, T-Plot, DFT, HK and other pore size distribution models.

 

Requirement on Sample

  1. The sample is required to be solid (either powder, film, block), the sample needs to be dry without water
  2. For samples with known specific surface area value, you can roughly determine the amount of sample provided based on the formula: specific surface area*sample amount (g) = 15, providing the sample mass exceeds 20% of the calculated value.
  3. The specific surface area of the unknown sample, typically whole test pores and micro-pores to 100mg mass or more, need at least 200mg for mesopores test, the estimated value of the specific surface area of less than 10㎡/g need about 2g of sample.
  4. Block samples should be processed into particles with a particle size of about 0.2 mm for the convenient of the test.
  5. The film sample needs to be cut to a size of 0.5 x 0.5 cm or less for the convenient of the test.
  6. In order to facilitate the test, please do not use zip lock bags, especially when the sample volume is relatively small, please use a small centrifuge tube to send samples.
  7. The carbon dioxide adsorption test sample requires 3 times the quality required by the normal nitrogen BET test sample, and the methane adsorption sample amount requires the sample amount to be 1-3g.

 

FAQ

What are the main reasons why the curve is not closed?
a. One is an equipment problem, which may be a leak. The vacuum system of the instrument does not hold pressure. This can easily cause the adsorption to be negative and the subsequent adsorption and desorption curve will not close.

b. One is the sample weighing problem. Too little sample weighing can easily cause inaccurate measurement and unclosed curve.

c. The sample preparation problem may be that the impurities in the material were not sufficiently removed during the degassing process.

d. The specific surface area of ​​the sample itself is small.

Which models are used for different pore structures to represent pore size distribution?
- For micro pore pore size distribution, please refer to the pore size distribution data in HK; For the mesopore pore size distribution, please refer to the pore size distribution data in BJH; For the pore size distribution, please refer to the pore size distribution data in NLDFT or DFT; ​

How to choose the degassing time?
- The degassing time is determined by the degassing temperature and the complexity of the sample pores. The more complex the pores, the more difficult it is for the impurities in the pores to come out, and the longer the degassing time will be; the lower the degassing temperature, the slower the molecular diffusion speed, and the longer the degassing time; the degassing time of general samples can be set to no less than 6hour, For some samples with complex micro pores, it takes longer to degas. However, there are special cases. The United States Pharmacopeia stipulates that the degassing time of magnesium stearate is only 2hour. Note: Since the degassing temperature, degassing time and degassing vacuum degree are all related to the specific surface area value, the error of the BET result is inevitable, so the sample needs to be compared with fixed processing conditions.

Which models are used for different pore structures to represent pore size distribution?
- For micro pore pore size distribution, please refer to the pore size distribution data in HK; For the mesopore pore size distribution, please refer to the pore size distribution data in BJH; For the total pore pore size distribution, please refer to the pore size distribution data in NLDFT or DFT; ​

How to choose the sample pre-treatment temperature?
- The purpose of degassing is to remove impurities (such as water, organic matter, etc.) adsorbed on the surface of the sample under vacuum without damaging the properties of the sample. Generally, the sample is heated under vacuum. The general pre-treatment temperature is selected as follows: in a nitrogen atmosphere, half of the sample thermogravimetric decomposition temperature, and the highest pre-treatment temperature is 300°C.