BET Standard Operating Procedures

 

 

Index

Preparations for sample analysis

Diagram of BET

Degassing samples

Computer set up for degassing

Sample testing

Shutdown

 

Preparations for sample analysis:

 

·        Fill Liquid Nitrogen Dewar (note: do not tighten cap of dewar tight, this will prevent pressure build up)

·        Fill cold trap dewar with liquid nitrogen

o       Fill about 2 in from lip of container

·        Cold trap dewar is then mounted to autosorb-1. 

o       Lift and turn cold trap dewar so that bracket (A) is turned to the left and trap cell is inserted into dewar.

o       Rotate container clockwise until mounting bracket (A) is even with bracket (B) on sample preparation station.

o       Slide bracket (A) into (B).

 

 

 

·        Operator must sign in log book

·        Open He and N₂ cylinder valves and ball valves located after pressure regulators.  Confirm cylinder pressure regulators are set to 10 psi.

·        Insure the cold trap dewar is half full with liquid nitrogen if not fill according to above directions.

 

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Degassing samples prior to analysis purges impurities.

 

·        Choose appropriate cell size for sample (insert pgs. V-5,V-6 and V-7)

o       6, 9 or 12 mm.

o       insert clean fill rod into cell with sample.

·        Using a5-place analytical balance, weigh and record the weight of the empty sample cell with the cell holder (a plastic cup with bubble wrap).  Tare the weight and then fill the bulb with the recommended weight of the sample.  Record the weight of the sample as Initial weight.

·        Insert the proper rod into the cell and place cell into the heating mantle

·        Attach cell to sample preparation station (for outgas port 1 or 2).

o       Remove Knurled retainer ring from sample preparation station (insert pg III-2).

o       Assembly contains 3 parts: Knurled retainer ring, plunger and cell adapter (insert pg. VII-9).  Remove plunger and use only the retainer ring and cell adapter.

o       Choose appropriate size of cell adapter and assemble according to diagram (insert pg. V-8).

·        Set temperature (Insert pg. III-2) manually. 

o       Temperature should be set according to sample specifications. 

o       100C allows for water evaporation.

·        Pinch heating mantle to open the mouth.  Insert cell into mantle.  Pinch mantle to close and secure the mantle to cell (insert pg. III-2).

·        Turn heat on by lifting the toggle switch to the up position. 

·        Degassing may take more than 4 hrs.

 

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Computer set up for Degassing

 

 

·                    On Tool bar click <OPERATION>

·                    From the drop down menu click <OUTGASSER>

·                    From pop up menu click on Station 1 or station 2 for the station you are using.  If you are using both then click on both.

·                    Click <LOAD>

·                    Click OK

·                    This begins the sample outgas routine. 

·                    Record the start time.

 

Check sample for proper degassing.

·        On the Autosorb go to <OPERATIONS>

·        Click on <MENU>

·        Click on <OUTGASSER>

·        Select the station to test and press <TEST>

·        If the Outgasser test is passed in 1 min the sample is ready for analysis.  If the Outgas test continues to fail, continue Outgassing and click <OK>. Check the cell ports to make sure the sample is properly loaded.

·        When Outgassing is complete, remove sample by going to <OPERATIONS><MENU><OUTGASSER>. 

·        Select the sample you want to transfer and press <REMOVE>. 

·        When the LED indicator on the selected port turns orange, the sample is ready for transfer.

·        Remove heating mantle and allow sample cell to cool.  Once cool, quickly but carefully transfer the sample cell to the test port.

 

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Sample Testing

 

• Fill the sample cell Dewar half full with liquid Nitrogen and cool the sample cell. 
• On the computer, go to the <ANALYSIS><PHYSISORPTION ANALYSIS PARAMETERS> 
• Input the following
  • Sample ID
  • File ID: enter operators initials
  • Operator: Your name
  • Bath T: enter temp (77.35K)
  • Adsorbent: Nitrogen or Krypton
  • Leak Test: 3 min for Nitrogen or 1 min for Krypton
  • Maxi-dose: (ON) for Nitrogen and (OFF) for Krypton
  • Outgas time: Enter your recorded time
  • Outgas Temperature: enter outgas temp (100C)
  • Po Parameters: (Po Station) for Nitrogen and (User Entered Po) for Krypton
  • User Po /Ambient: (760mm Hg) for Nitrogen and (2.63mm Hg) for Krypton
  • Cell Type: Enter the bulb size used (6,9,12 mm) select with rod option.
  • Analysis Points:  11-point analysis for Nitrogen and 7 point analysis for Krypton
  • Sample weight: Enter 99g as a flag until the analysis is done
  • Evacuation: Select the Fine option
  • Temp Comp: Make sure this box is NOT checked

 

• After parameters are entered, press<START> to begin analysis. Click <OK> to remove the Physisorption screen.
• When the analysis is complete, remove the cell from the sample port and reweigh to obtain the degassed weight (Actual Weight)
• Enter correct weight into the software by going to the menu <DATA REDUCTION><EDIT ANALYSIS INFORMATION>.  The correct surface area will be automatically recalculated
• Check the analysis result by using the menu <DATA REDUCTION><SELECT MULTIPLE TABLES>. 
• Select the <MULTIPLE BET> option and press <OK>.  The data table with the analysis will appear
• The correlation coefficient should be greater than 0.999.  If the line is bending at the end, remove the first and last data points to correct the correlation.  This is done with the menu <DATA REDUCTION><EDIT RAW DATA AND TAGS>.  Select the first and last points listed and press <DELETE SELECTED POINTS>. Typically coefficients of 0.9997 + are obtained.
• After checking the correlation coefficient, examine the “C” value, which indicates whether the BET analysis is valid for this sample.  Ideally the number should be close to or greater than 100.  If it is less than 2, the BET theory is not valid for the sample. 
• If you not done, so, save the data to the hard drive or diskette.

 

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SHUT DOWN

 

• Empty powder from sample and save for other analysis or dispose of properly.
• Clean cell by sonication with DI water.  Dry with acetone or methanol.
• Make sure heater switch on degasser in sin the down position (OFF).
• Make sure that all of the ports are sealed with dowel plugs.

 

 

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