PARTICLE INSTRUMENTS

CATALOGS

Particle Instruments Catalog

SPEC SHEETS

	Model 3400A and 3433
	Model 3450
	Model 3475
	Model 3480
	Model 8108

SERVICE INFORMATION

APPLICATION NOTES

	Electrostatic Classifier Model 3080 Optional Positive High Voltage Power Supply (3080-001)
	Electrostatic Classifier Model 3080 Optional Positive High Voltage Power Supply (3080-001)

MANUALS

NRC Supplementary Information

STANDARD REPLACEMENT PARTS

	Model 3080/3936 Standard Replacement Parts
	Model 3400A Standard Replacement Parts
	Model 3433 Standard Replacement Parts
	Model 3450 Standard Replacement Parts
	Model 3475 Standard Replacement Parts
	Model 3480 Standard Replacement Parts
	Model 8108 Standard Replacement Parts

FREQUENTLY ASKED QUESTIONS

1. Are the particles coming out of the SSPD charged?
   Yes. Turbulence in the venturi builds up charges on the particles. The direct straight-line transport to the APS minimizes transport loss however.
2. Can I use _______ in the VOAG?
   I don’t know. Try it and let me know how it works. Seriously, this is an answer that we must give out often. There are people putting dilute sulfuric acid, liquid nitrogen, and just about anything else you can think of through the VOAG. The main requirement is that the substance can be dissolved into a solution that has a low enough viscosity. Because the generator head is made of stainless steel and the tubing is Teflon®, most substances should not be harmful to the VOAG. Parts that could be a cause of concern are the plastic syringe, seals on the drain, and the pressure gauge.
3. Can I use a suspension in the VOAG rather than a solution?
   Sure, as long as you do not expect a monodisperse aerosol, and the suspended matter is not so large it plugs either the orifice or the filter attached to the end of the syringe. While the droplets coming out of the VOAG will be monodisperse, what is left after drying will not be monodisperse because a suspension is not uniform. In general, the VOAG is not recommended for use with a suspension.
4. Do I need to change the bronze beads every time I change powders (Model 3400A)?
   Yes. Once the bronze beads are used they are contaminated by the powder. Used beads should be saved for reuse when the same powder will be aerosolized again.
5. How do you get aerosol from the outlet on top of the SSPD to the inlet on top of the APS™ spectrometer?
   The APS™ spectrometer can be inverted and set upside down on top of the SSPD. It is recommended that you use a foam pad of about 4 cm thick to raise the APS up so that it will be level. The APS runs perfectly fine upside down. Alternatively a conductive tube can be used to transmit particles from the outlet of the SSPD into the inlet the APS. Some losses of larger particles may occur due to settling and impaction in the bend of a tube.
6. How long does it take for the output concentration to stabilize (Model 3400A)?
   With fresh bronze beads it may take seven or eight hours for the output concentration to fully stabilize. Until this time the concentration will constantly increase. If the beads have been previously allowed to stabilize with the same powder then a constant output will occur within a couple of minutes. Also, if the feed rate of the powder is changed it will take several hours for the generator to restabilize.
7. My orifice is plugged, how do I clean it?
   The first cleaning attempt should be a “backflush” of the orifice. Put the stainless dispersion cap over the piezoelectric quartz, turn on the dispersion air, and open the drain. Now, by plugging the opening in the top of the dispersion cap with your thumb, pressure will build up inside the cap and force air back through the drain. The cap will eventually pop off its O-rings when pressure builds too high inside. This process should be repeated 2 to 3 times, and then an attempt should be made to start the jet with pure propanal. If the backflush does not work, the orifice should be removed and soaked in filtered detergent solution. Ordinary lab or household detergent is fine and the solution should be about 10% detergent and 90% distilled water. After soaking the orifice, it should be rinsed in distilled water followed by alcohol. If this process does not work the first time, it should be repeated, increasing the soaking time to overnight. If soaking the orifice does not work, try an ultrasonic bath with the detergent solution as a last resort. This process may damage the orifice, however.
8. What is the maximum viscosity solution that can be generated?
   The maximum viscosity is 5 centipoise. If a more viscous liquid needs to be used, the operator can dilute it down into a solution. The more dilute the solution, the larger the initial droplet size must be to obtain the same final particle size.
9. What size range does the VOAG generate?
   The VOAG generates droplets from about 20 to 400 µm, which will dry to a final particle size of about 0.5 to 50 µm. The final size figures given are more of a practical limit than an absolute limit. Going below 0.5 µm requires extremely pure solvents that will not leave residue after the evaporation. Larger particles are difficult to transport and would require very high concentration solutions that may not work due to viscosity or other problems.
10. Why am I not getting any particles larger than 3 or 4 µm coming out of the Fluidized Bed (Model 3400A)?
    There is a cyclone at the outlet of the Fluidized Bed the cuts out all particles larger than 3.5 µm. The cyclone comes installed from the factory, but may be easily removed.
11. Why are my particles larger than they should be?
    This is normally caused by incomplete drying of the droplets. Drying time should be increased or heat added. It is also possible that residue is being left from the solvent. Finally, many solids will dry into hollow spheres or crystal type structures if they are dried too fast. Drying can be slowed by using a less volatile solvent, for instance, water rather than alcohol. Solvents may also be mixed to obtain the proper drying speed.
12. Why can't you use the SSPD for very fine powders smaller than 1 µm?
    Powders that are smaller than 1 µm will not deagglomerate efficiently in the SSPD.
13. Why is the VOAG not producing a monodisperse aerosol?

    There are three main reasons why the VOAG may not be producing a monodisperse aerosol.

    1. The instrument is not being operated within the correct pump speed and frequency parameters. Check the tables in the instruction manual.
    2. The dispersion air is off or on too low. This results in the droplets coagulating into doublets, triplets, etc.
    3. Satellite particles are being formed. At certain frequencies, one of these small satellite particles will be formed for every normal particle being formed. Most of the time satellites can be eliminated by adjusting the amplitude of the signal (amplitude control is on front of VOAG).

    If the amplitude adjustment does not help, then the frequency must be adjusted slightly.