Amherst Process Instruments

Time-of-flight aerosol beam spectrometry was first described by Dahneke in 1973 [139]. A commercial instrument, the Aerosizer, [140] was developed by Amherst Process Instruments Inc. which is now a division of Thermo Systems Inc.The TSI Model 3603 replaces the Aerosizer. 

Fig. 11.8 are photographs of two instruments offered by Amherst Process Instruments (API). Fig. 11.8a is the API aerosizer, a high resolution particle size analyzer for fine powders (range 0.2 - 700 pm), which is based on aerodynamics. A gas containing the entrained particles expands through a nozzle at supersonic velocities into a partial vacuum which is contained within a barrel shock envelope. The exit velocity of a particle depends on its density and size. Two laser beams, separated by a defined distance, and two photomultipliers form the measurement zone. From the velocity and the known density of the particulate solid, the aerosizer determines size, one by one, with a speed of up to 100,000 particles per second and an accuracy of better than 1 % which make this instrument rather unique. The system uses interchangeable dispersers for different types of particles and, in total (refer to Fig. 11.8a), consists of particle dispersers (A), sensor unit (B), vacuum system (not shown), and computer (C). 

Amherst Process Instruments (Europe) Ltd, Mill Street, Tewkesbury GL20 5SB, UK tel +44-1684-291966 fax +44-1684-293567 Amoco Chemical (Europe) SA, 15 Rue Rothschild, CH-1211 Geneva 21, Switzerland tel +41-22-715-0701 fax +41-22-738-8037 Amoco Chemical Belgium NV, Amocolaan 2, B-2440 Geel, Belgium tel +32-14-86-43-45 fax +32-14-86-73-72,... 

Amherst Process Instruments Inc., The Pomeroy Building, 7 Pomeroy Lane, Amherst, MA, USA, 01002-2942... 

Fig ure 6.16. Schematic diagram of the inspection zone of the Amherst Process Instruments Inc. Aerosizer dme-of-flight particle sizer. 

Figure 6.17. Typical data generated by the Amherst Process Instruments Inc. Aerosizer for aerosol systems, and powders aerosolized prior to characterization smdies. a) Calibration using aerosols of standard latex spheres of known size, b) Characterization of a mixture standard of polystyrene latex spheres, c) Characterization of a sample of 5 micron silica microspheres mixed with a small number of 10 micron microspheres. D) Glass spheres used in reflective paint (ballotini). E) Two oil mists diatacterized by direct injection into the Aerosizer .

Figure 6.18. Data generated by the Amherst Process Instruments Inc. Aerosizer for an irregular iron powder clearly demonstrates the effect of interpreting the data as a number size distribution as compared to a volume size distribution, a) Micrograph of the irregular iron powder. (Micrograph courtesy of D. Alliet, Xerox Corp.) b) Number size distribution of the iron powder of (a), c) Volume size distribution of the iron powder.

Amherst Process Instruments Inc., Mountain Farms Technology Park, Hadley, MA 1035-9547. USA, (413) 586 2744... 

The AeroSizer, manufactured by Amherst Process Instmments Inc. (Hadley, Massachusetts), is equipped with a special device called the AeroDisperser for ensuring efficient dispersal of the powders to be inspected. The disperser and the measurement instrument are shown schematically in Figure 13. The aerosol particles to be characterized are sucked into the inspection zone which operates at a partial vacuum. As the air leaves the nozzle at near sonic velocities, the particles in the stream are accelerated across an inspection zone where they cross two laser beams. The time of flight between the two laser beams is used to deduce the size of the particles. The instrument is calibrated with latex particles of known size. A stream of clean air confines the aerosol stream to the measurement zone. This technique is known as hydrodynamic focusing. A computer correlation establishes which peak in the second laser inspection matches the initiation of action from the first laser beam. The equipment can measure particles at a rate of 10,000/s. The output from the AeroSizer can either be displayed as a number count or a volume percentage count. 

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