Key indicators
Vacuum method
Dynamic method
Method introduction
The adsorbent sample is placed in a vacuum environment, and the adsorbate vapor is volatilized into the vacuum system and controlled at a specified partial pressure P/P0, and time-weight data is continuously obtained until the adsorption equilibrium is obtained;
In this process, the sample is first in a vacuum environment, and the adsorbed mass vapor is not flowing, and is “static†adsorbed, so it is also called “static method†or “vacuum method†steam adsorption.
The vacuum gravimetric method is an ideal physical adsorption analysis method with strong functions. No need for carrier gas, no factors affecting the adsorption process. The data has high reliability and is a research-level analytical instrument; this method appears later than the "dynamic method" and has high technical requirements.
The adsorbent sample is placed in an atmospheric environment with a balance of flowing carrier gas, and a mixed gas of carrier gas and adsorbate vapor is passed through the sample to continuously acquire time-weight data until the adsorption equilibrium is obtained;
In this process, the adsorbent vapor is “dynamically†flowing, so it is called “dynamic method†steam adsorption.
The dynamic gravimetric method, applied earlier, was developed by the early researcher's self-built “balance + constant temperature and humidity chamber†method. The gravimetric vapor adsorption data can be obtained in a simpler way. Since the instrument does not require a vacuum system, the instrument has a simple structure. It has become a common method in the early steam adsorption industry and has been used ever since.
Sample pretreatment
"Vacuum degassing" mode, high efficiency
The “impurity†gas such as moisture and air on the surface of the sample to be tested is removed by “heating and vacuumingâ€; this pretreatment method is called “degassingâ€;
Because it can heat vacuum degassing, for samples with strong adsorption capacity, such as microporous materials, molecular sieves, activated carbon and other large surface samples, the treatment effect is excellent, the pretreatment temperature can be as high as 400 ° C, and there is no secondary pollution in the processed samples. ;
Sample surface treatment "clean" is the basis for correct test data.
"Atmospheric purge" mode, low efficiency
The sample is pretreated by "heating and allowing the dry carrier gas to blow through the sample to be tested". This pretreatment method is called "purging";
The sample is pretreated by means of a carrier gas purge; the pretreatment temperature is up to 200 ° C, and it is difficult to remove gas impurities such as moisture in the micropores;
If the auxiliary method of vacuum oven drying is adopted, the sample is easy to fly because it does not have the anti-pumping mode; and when the sample is processed, the sample is again exposed to the air, and the treatment effect is lowered.
Sample pretreatment is not “clean†and correct test results are not guaranteed.
Steam inlet
After the sample is degassed by heating and vacuum, the sample chamber is in a vacuum environment. The vapor adsorbate is evaporated from the liquid in the reagent tube to the sample chamber and becomes vapor. The sample is adsorbed by the sample. The P/P0 partial pressure control is controlled by the steam pressure. achieve.
The method has high accuracy of partial pressure control (error less than 0.1%) and wide range of partial pressure control (0~99%);
The sample is in a normal pressure environment, and the carrier gas carries the vapor adsorbate dynamically flowing through the sample and is adsorbed by the sample; the P/P0 partial pressure control is achieved by controlling the ratio of the carrier gas and the vapor.
In this mode, the partial pressure control accuracy is relatively low (error 1%), and the partial pressure control range is narrow (2~90%);
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