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(1) The dynamic method, also known as continuous flow chromatography, involves performing nitrogen adsorption in a flowing nitrogen-rich atmosphere at liquid nitrogen temperature. This technique allows the system to reach a dynamic equilibrium of adsorption under various nitrogen partial pressures. If the sample tube is removed from the liquid nitrogen and allowed to warm up to room temperature, all the adsorbed nitrogen will be completely desorbed. In this method, the sample tube must be inserted into and removed from the liquid nitrogen cup for each pressure measurement.
(2) Unlike traditional methods, the dynamic approach uses helium as a carrier gas, since helium is not adsorbed at liquid nitrogen temperatures. By adjusting the ratio of nitrogen to helium or controlling their flow rates, different nitrogen partial pressures can be achieved without altering the overall pressure of the gas mixture. The total pressure remains close to atmospheric, and the nitrogen partial pressure can be varied between 0 and atmospheric levels. This eliminates the need for vacuum conditions, making the process more efficient and user-friendly.
(3) Continuous flow chromatography employs a thermal conductivity detector to measure the amount of nitrogen adsorption. The sample tube is placed in series between the reference and measuring arms of the thermal conductivity cell. When the sample adsorbs (or desorbs) nitrogen, it disrupts the thermal equilibrium, causing a detectable electrical signal. This results in an adsorption or desorption peak, whose area corresponds to the amount of nitrogen involved. Since helium and nitrogen have significantly different thermal conductivities, even small changes in nitrogen concentration lead to noticeable shifts in the detector's output, enhancing sensitivity.
(4) One of the key advantages of the dynamic surface area meter is its ability to directly compare specific surface areas using a standard sample with a known surface area. By comparing the desorption peak area of the sample with that of the standard at a fixed nitrogen/He ratio (typically 0.2), the surface area can be calculated quickly. This method is fast and ideal for real-time monitoring on production lines. However, it does not account for differences in adsorption behavior between materials, which may result in significant errors when comparing samples with distinct adsorption characteristics.
(5) The BET method overcomes these limitations by allowing precise control of nitrogen partial pressure and achieving a steady state. A dynamic BET surface area instrument can also perform direct comparison measurements by setting the nitrogen partial pressure to 0.2 or 0.3 and using a standard sample. This provides more accurate and reliable results, especially for materials with complex or variable adsorption properties. Test - lowercase jpg Kaixin micro test Test probe P100-M3 0805 side white