ES 08: Maintaining Cleanliness of QCM Crystals
QCM Research Engineering Spec. ES 08
Procedure for Maintaining the Cleanliness of QCM Crystals
1.0 Equipment Required
1.1.4 Trichloroethane 1,1,1 (Methychloroform)
1.2.1 Polyurethane Foam Swabs #1
1.2.3 Hand Blower
1.2.4 Frequency Counter
2.0 Application of the Various Tools
2.1 Polyurethane Swabs.
Disassemble the lab-quality urethane-covered pad from the applicator, leaving a circle (approximately 1" [2.54cm] in dia.) of Urethane. Cut the circle of Urethane with scissors to approximately 3/16" [0.50cm] in dia.
The tweezers are used to pick-up the 3/16" Urethane, submerge in the cleaning solution and then very carefully wipe the contaminant off the crystal.
2.3 Hand Blower.
The hand blower is used to help evaporate the solution from the crystal after the Urethane pad has very gently wiped the film off the crystal and, as a consequence, left some solution.
2.4 Frequency Counter.
Use of a frequency counter to monitor the degree of contaminant on the crystal is a great help. Not only can you see, by the frequency, the degree of cleanliness that you are getting, it also tells you with repeated applications if you should change the Urethane pad and tells you when you have approached the cleanliness you require.
3.1 This is a manual operation.
3.2 Take one of the Urethane-covered swabs from stock.
3.3 Disassemble and remove the Urethane pad that comes with the swab.
3.4 Cut the Urethane pad into 3/16"dia pieces.
3.5 Take one of these pieces with a tweezer and soak it with one of the cleaning solvents listed in Sec. 1.1.
3.6 Wipe it gently across the crystal noticing the frequency change. The wiping action may cause the crystal to stop oscillating but soon it will return to normal oscillation. Use the hand blower to evaporate the solvent if you have trouble restarting the oscillation. The softness of the Urethane pad along with the gentle manual wiping action should prevent any destructive action on the surface of the crystal. Any scratch that occurs on the electrode during this process will increase the frequency of the crystal (decreasing the beat frequency), and several such scratches could render it useless.
3.7 Change Urethane pads and try it a second time. Watch the frequency counter to see if you have removed additional film contaminating the crystal.
3.8 When you have finally achieved a crystal that is acceptably clean, rinse the crystal with a new pad of Urethane and blow the crystal dry with a hand held blower, always watching the frequency counter.
1. Baxter Scientific Products, High Sorbency Swabs, Cat. No. A5008-1A.