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SF6 for dummies

by Yama Tomonaga

Extraction line

T1-T4: empty cold traps cooled to -196C using liquid nitrogen

V1, V2: separate extraction line from pumping lineV3-V6: divide extraction lineC: capillary prevents back-diffusion of the extracted gasesR: standard reservoir. Calibration: 0.1 ppm +/- 2% SF6 + 1.7 ppm +/- 1.1% CFC-12 dilluted in N299.9%, SF6 cc~20pptV, CFC-12 cc~30ppbVDR: drying column: AgNO3 powder, molecular sieve 3A (protects GC from H2O vapour and H2Sthat may interfere with SF6 peak)VAC: rotary vacuum pumpP: PiraniGC: gas chromatographECD: electron capture detector kept at 350C

FactsSF6 0.42 min retention time of peak.CFC-12 1.4 min retention time.Detection limit: 0.07 fmol/kg SF6, 2x10-15 mol/kg CFC-12.

Getting started

Check if the GC is more or less clean (overnight heating up to 300C). Set the GC to40C (holding the button SB & ISO1, type the temperature with the keypad andconfirm with enter).

Check if you have enough liquid N2 in the big container (the one you cannot holdover your head). If thats the case, then mount T4 and refill it with LN.

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Bring the rotary vacuum pump back to life (put the power cable in the appropriateplug).

Turn on the computer. Double click the Wccman link on the Desktop.

Pump the line: close (CL) V1 and V3, open (OP) V6, V5, V4 and V2. Check thepressure on channel B4: if it reaches the 5x10-2 mbar, then you are ready to attachyour sample to the line.

Connecting the sample to the line

Check that V1+V3 are closed. Connect the bottle to the line. If you think that thebottle is now air-tight sealed to the line, then close V2+V6 and open V1 to evacuatethe air contained in the extraction vessel. You will hear the pump working well. Whenthe noise from the pump decreases, open V6+V2 and check the pressure.

Standard

- CL V1, V2 (pumps), LN to T4 (if needed)- CL V3 (separate extraction vessel)- LN to T3 (liquid) (P ~ 5E-3?)- LN to T2 (liquid)- Check: GC to 40C and ~5-8 kHz?- Check: V7 & V8 closed? (with torque key)- OP V8 (standard bottle)- Wait 10 and update laboratory journal

- CL V8 (standard bottle)- OP V7 (standard in line!)- Wait 10- CL V7 (isolate bottle volume from extraction line)- VB1 from Open to Close (this closes trap T2)- H2O to T2 (get gases back to gaseous form)- Prepare computer program to measure: activate menu Run with mouse- VB2 from Load to Inject (gas injected to GC)- Start measurement: press S- Wait ~6 (until measurement done)- VB2 back to Load position

- VB1 back to Open position- Pump out extraction line- Evaluate measurement

Sample

- Check: OP V1, V2, V3, V4, V5, V6; CL V7, V8; VB1 = Open; VB2 = Load- Check: P ~4E-2 mbar (P

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- CL V3- Start countdown: 1000 refill LN to T1, T2, T3 close and remove bottle

sample pump head vessel with membrane pump and heat it with hair dryer- @ 0830: CL V4, H2O to T1 (P increases)- @ 0000: CL V5, remove H2O from T1

- VB1 to Close (close trap circulation), H2O to T2- GC to 40C?- Prepare computer program to measure (activate menu Run with mouse)- VB2 to Inject (gas injected to GC)- Start measurement: press S- Wait ~6 (until measurement done)- VB2 back to Load position- VB1 back to Open position (open trap circulation)- Start pumping line as follows:- T1: remove, dry and mount- CL V6; OP V2, V4

- Wait: until air is evacuated (hear the sound of the pump decreasing)- OP V6, V5- Remove LN from T3 and heat with hair dryer- Warm GC for 30 with 300C (holding SB & ISO1, type 300 and hit the

enter button)- Check: CL V1, V3- Change sample- CL V2, V6 (isolate purification line)- OP V1- OP V2, V3, V6- Dryer to DR (until P ok)- After 30 cool GC (SB &ISO1, 40, enter button), open GC door, frequency

down to ~5-8 kHz- Check: GC temperature, if OK close GC door- Restart

Connect membrane pump to SF6 line- MacGC in Mac at CFC line- All valves closed, online, OP 19- At the and of the day make the opposite

STOP- Vacuum in the system- CL all pumps and valves- Shut down oil pump and remove the trap from LN bottle and open and clean

the trap if necessary- Warm GC to 300 C