INVESTIGATIONS OF A NEW AEROSOL GENERATOR FOR THE PRODUCTION OF CARBON AGGREGATE PARTICLES

The operating characteristics of a new aerosol generator for the production of ''soot-like'' particles have been investigated. The aerosol is produced by a spark discharge between two graphite electrodes in argon as carrier gas. The particle mass flow rate can be varied between 20 mug h-1 and 7 mg h-1 by simply changing the spark frequency. The discharge voltage is kept constant by a control mechanism that adjusts the distance between the electrodes. This results in a very constant operation of the generator over time periods of several hours. The mass production rate of the instrument has been determined gravimetrically and a well reproducible linear relation with the spark frequency was found. The shape of the particles was determined by scanning electron microscopy as well as by transmission electron microscopy. The size of the primary particles is in the range of 5 nm forming agglomerates between 50 and 200 nm. The size distibution of the aerosol was measured for different operating parameters using a differential mobility analyser and an aerosol electrometer. The size distibution turned out to be mainly influenced by the coagulation process that forms the agglomerates. The final mean size of the particles can be controlled by the amount of dilution air that the aerosol is mixed with directly at the generator outlet.