Intelligent Sensors for Atomization Processing of Molten Metals and Alloys
ABSTRACT We briefly introduce the principles of atomization processing of molten metals and alloys, discuss potentially applicable instrumentation, and propose opportunities for developing intelligent sensors for monitoring and control of the process. Particle size and velocity are considered the two most important variables to monitor and control the atomization process. Several on-line sensors suitable for atomization of molten metals and alloys are compared: laser light scattering methods using small angle scattering analysis, moderate angle scattering analysis, and doppler analysis, electrical methods using surface ionization and triboelectric charging, and image analysis. The isokinetic sampling probe is introduced as a direct method to sample powders at the desired point in the atomized spray. Prospects and problems of integrating instruments based on these principles into intelligent processing of materials (IPM) scenarios are discussed.
Electrical detection of airborne particulates using surface ionization techniques
A variety of individual aerosol particles can be detected by causing them to impinge onto a heated metal surface where they pyrolyze and transfer surface-ionizable constituents to the surface within times of 10/sup -6/--10/sup -2/ sec, depending on the filament temperature. These surface-ionizable constituents then become ionized and are released from the surface as a burst of ions. For particles of similar composition, the number of ions per pulse is related to the particle size. This technique has been studied and has been applied to the continuous monitoring of submicron urban particulate matter.
Formation and Strength of Magnesia Whiskers
The formation of single-crystal magnesia whiskers during the compressive deformation of single crystals at room temperatures is described. These whiskers can have strengths of the order of millions of pounds per square inch. They are formed during fracture as a result of the discontinuous propagation of cracks which are mechanically relieving internal stresses resulting from plastic flow