BET中比表面积检测方案(蒸汽吸附仪)

Calculating BET surface area using isothermal datameasured using the lGAsorp. The IGAsorp was used to measure a water sorption isotherm at 25℃ on thestandard sample CRM-BAM-PM-103. The data was used to calculate a BET surfacearea. The standard has a known surface area previously determined by BET in N2 at-196°C. The surface area calculated from the water sorption data measured using theIGAsorp is compared to the quoted BET surface area for the standard. Experimental Details： Experiment： Isothermal adsorption Vapour： Water Sample： CRM-BAM-PM-103， Aluminium Oxide Type 60 Temperature： 25°C Dry Mass： 45.4845 mg (after 250°C drying stage) The sample was loaded into the IGAsorp in a stainless steel mesh bucket.It wasthen dried at 25°C for 4.5 hours. A 40 step isotherm from 0-94 %RH was performed with RH steps of 2% from 0-56%RH， 3% from 56-83 %RH and two final steps of 4% and 7 % to 87 %RH and 94%RH. The adsorption scan was performed， after which a drying stage at 250°℃ forapproximately 5 hours was performed so that the dry mass could be determined. (The BET measurement made in N2 at-196°C had been dried at 250°C for 5 hours). Figure 1 shows the recorded %RH versus %weight data and Figure 2 shows the BETfit of the data measured between 0.19 and 0.3 P/Po. IGAsorp data analysis： First， the measured uptake is converted into grams of water per gram of dry sample.This was done using the total weight of the sample at each %RH point measuredusing the IGAsorp and the dry mass determined after heating to 250°C. Next， %RH was converted into P/Po by division of %RH by 100%.A graph of (P/Po) versus P/Po/(Uptake x (1-P/Po)) was then plotted between P/Po =0.019 and P/Po = 0.3 (See Figure 2).).TThe monolayer uptake was then calculatedusing the equation below： Note， the P/P。range used to calculate the gradient and intercept was chosen to bethe same as that used to determine the standard's referenced surface area. BET surface area can then be calculated as： Where： Um 三 Mono-layer uptake 0.04446 (gg) from the graph M Molecular mass of the adsorbate 18.01 (gmol) for water 23N Avagadro's number A 一 Molecular area adsorbate 10.5(A) for water For this experiment the BET surface area calculated from the lGAsorp data was156.05mg. The referenced surface area for this standard measured by a nitrogen isothermbetween 0.05 and 0.3 P/P。 at-196°℃ is 156 +/-1.3 m²g". The IGAsorp data gives asurface area， which is within the quoted error of the standard sample.. Thereforewater sorption isotherms measured using the IGAsorp give good and comparablesurface area results. Figure 1， Water Sorption Isotherm measured on BAM -PM-103 at 25C %RH Figure 2， BET plot for the water sorption isotherm shown in figure 1， measuredbetween P/P0=0.019-0.3. 8 0.25 0.3 P/PO