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Title: Fluid flow and particle size in gas atomization for fine powders
Author: Naylor, Michael J.
Awarding Body: University of London
Current Institution: Imperial College London
Date of Award: 1987
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The production of rapidly solidified fine metal powders has become of increasing interest in recent years as the microstructural benefits such as refined grain size, increased solid solubility and elimination of segregated phases has become apparent. The cooling rate associated with solidification is the single most important process variable affecting the microstructure and therefore the properties of the product. Gas atomization can produce average cooling rates of up to 10° K/sec and is the only currently available mass production method for fine metal powders. However the effect of process variables on particle size are badly documented and confusing. In order to investigate the effect of the nozzle size, geometry, and process variables, on particle size an experimental apparatus was constructed to carry out low temperature modelling of the atomization process using wax. A prefilming type nozzle design was selected for study and air was used as the atomizing gas. The experimental apparatus permitted independent control of the gas and liquid flowrates. Gas flow outside the nozzle was characterized by measuring the suction created at the tip of the nozzle, by using Schlieren photography to visualize the gas flow, and pitot tubes to measure the Mach number. Investigations carried out included changes in the nozzle size and geometry, gas flow, liquid flowrate and liquid properties. High speed photography was used to observe the process of atomization. Detailed size analysis of the powder size produced was carried out using a Malvern Particle Size Analyser. The particle sizes measured were fitted to known size distributions using a computer program, which also calculated mean diameters and the dispersion of the particles about the mean. S.E.M. work was also been carried out to look into the shape of the wax particles produced to see whether they are similar to those of metals.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available