Dynamic method to test specific surface area - Database & Sql Blog Articles

(1) The dynamic method, also known as continuous flow chromatography, involves performing nitrogen adsorption in a flowing nitrogen-containing atmosphere at liquid nitrogen temperature. This allows the system to reach a dynamic equilibrium under varying 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 released. To measure each pressure point, the sample tube must be inserted into and removed from the liquid nitrogen cup repeatedly during the process. (2) This technique relies on helium as the carrier gas since it is not adsorbed at liquid nitrogen temperatures. By adjusting the ratio of nitrogen to helium or controlling their flow rates while keeping the total gas pressure constant, different partial pressures of nitrogen can be achieved. The pressure of the mixed gas remains approximately at atmospheric level. The partial pressure of nitrogen is calculated as the nitrogen flow rate divided by the sum of the helium and nitrogen flow rates. This allows the nitrogen partial pressure to range from 0 to atmospheric levels without requiring vacuum conditions. (3) Continuous flow chromatography gets its name from the use of a thermal conductivity detector (TCD) to measure the amount of nitrogen adsorbed. The sample tube is placed in series between the reference arm and the measuring arm of the TCD. When the sample adsorbs or desorbs nitrogen, the nitrogen concentration in the two arms becomes unbalanced, causing an electrical signal to be generated. This results in an adsorption or desorption peak, with the area under the peak directly proportional to the amount of nitrogen involved. A standard sample is used to determine the exact quantity of nitrogen adsorbed or desorbed. Due to the significant difference in thermal conductivity between helium and nitrogen, even small changes in the nitrogen concentration within the gas mixture greatly affect the balance of the TCD, thereby increasing its sensitivity. (4) One of the main advantages of the dynamic surface area meter is the direct comparison method. This involves using a standard sample with a known specific surface area. Under a fixed nitrogen partial pressure (typically a nitrogen/helium ratio of 0.2), the specific surface area of the unknown sample can be calculated by comparing the desorption peak area of the sample with that of the standard. This method is fast and suitable for real-time monitoring on production lines. However, it does not account for differences in adsorption characteristics between materials, which can lead to significant errors when the sample has very different adsorption behavior compared to the standard. (5) The BET (Brunauer–Emmett–Teller) method addresses these limitations by allowing the adjustment of nitrogen partial pressure and reaching a steady state. The dynamic BET specific surface measurement instrument can also perform the direct comparison method by setting the nitrogen partial pressure to 0.2 or 0.3 and using a standard sample with a known surface area. This approach ensures more accurate and reliable results, especially for samples with complex or variable adsorption properties.

Passenger Elevator

Passenger Elevator,Mrl Passenge Elevator,Passenger Lifts,Passenger Lifts For Homes

ZHONG HAN INTERNATIONAL TRADE CO., LTD , https://www.cck-ht.com