Experimental technology for physical adsorption measurement - Database & Sql Blog Articles

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The physical adsorption analysis mainly measures the relationship between the adsorption amount of the sample and the pressure at a certain temperature, that is, the adsorption isotherm curve. Adsorption

The amount as a function of pressure can be achieved by volumetric measurement (capacity method) and gravimetric analysis. ?

1)

Gravimetric analysis:

Gravimetric analysis consists of a sensitive microbalance and a pressure sensor that directly measures the amount of adsorption, but

Buoyancy correction is required (and buoyancy is not directly measurable). Gravimetric analysis at a temperature that is not centered at room temperature

When it is carried out within the scope, it is a very convenient research method. ?

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In the gravimetric method, the adsorbate cannot be directly connected to the temperature regulating device, so it is not acceptable at low temperature or high temperature.

Easy to control and measure the true temperature of the adsorbate. Therefore, at liquid nitrogen temperature (77.35K) or liquid argon temperature (87.27K)

The measurement of nitrogen, argon and helium adsorption mainly relies on volume measurement. ?

2)

The volumetric measurement method, that is, the vacuum volume method, is based on the calibrated volume and pressure, which is achieved by the conservation of total gas volume. use

The amount of adsorption is calculated by the difference between the total amount of gas entering the sample tube and the amount of gas in the free space. ?

Both volumetric and gravimetric methods require that the measured adsorption reaction occur under static and quasi-equilibrium conditions. In the quasi-equilibrium state,

The adsorbed gas continuously enters the sample tube at a low rate, and the desorption curve is obtained by continuous reduction of pressure. Relevant

The hardest part of the static balancing process is that we need to achieve a satisfactory balance every moment. In order to detect such an equilibrium state,

The slow gas release rate (gassing) should be used repeatedly for analysis. If the same number is obtained at two different gas rates

According to this, the correctness of the analysis results can be confirmed. The main advantage of this method is that it can achieve a true balance and can be obtained

Very high resolution adsorption isotherms. ?

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3)

Continuous flow method: In contrast to the quasi-static equilibrium method, this is a mixture of carrier gas (helium) and adsorbed gas (eg, nitrogen).

The gas stream is continuously passed through a method of placing a fluidized bed of the sample. The adsorption of nitrogen by the sample causes a change in the composition of the gas. Thermal conductivity detection

The device (TCD) can monitor this change and calculate the amount of adsorption. This method is still widely used for single point specific surfaces.

Rapid analysis of the product. ?