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Title: Porous copper by the lost carbonate sintering-powder metallurgy process applied to tape casting
Author: Mosalagae, Mosalagae
ISNI:       0000 0004 7964 4932
Awarding Body: University of Sheffield
Current Institution: University of Sheffield
Date of Award: 2018
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The use of porous metals for heat sinks and heat exchangers is becoming more and more wide-spread in engineering and technological applications. As a result, researchers and engineers continue with the purpose of determining effective ways of producing this type of porous metal at a lower manufacturing cost. Apart from aluminium, copper is mostly used as a base metal for making heat sinks, because the properties of copper make it suitable for the purpose. Over the years several methods have been explored to improve the properties of porous metals as heat sinks. The Lost Carbonate Sintering (LCS) method offers a simple and efficient way of producing porous metals with a wider range of porosities. On the other hand, tape casting is also an efficient and low-cost method for processing powders into thin sheets. This PhD thesis investigates the production and characterisation of porous copper heat sinks fabricated by the LCS powder metallurgy process applied to tape casting. LCS was employed to provide flexibility to control the pore parameters such as porosity and pore distribution within the component being tape cast. The effectiveness of the process was examined throughout, as well as the resulting structure. Potassium carbonate (K2CO3) was introduced into the matrix as a space holder. Additives such as plasticizers, binders, dispersant and solvents were added to control the properties of the green body and ease fabrication. The component was successfully debound and sintered at 450 °C and 890 °C respectively under vacuum. The potassium carbonate was removed from the sintered component via dissolution in water. A simple assessment of porous structure was carried out by employing various techniques such Scanning Electron Microscopy (SEM), micro-CT scanning, X-ray diffraction, Raman spectrometry, energy dispersive X-ray Spectrometry (EDS) techniques. The effectiveness of the dissolution route at removing the space holder was investigated. The mechanical properties were also assessed. To verify the porous copper samples produced in this study, their suitability for heat sink applications was investigated with simple assessments of the thermal properties under forced convection using air as a coolant. An open circuit heat transfer rig developed and designed in-house was used. In the results, a thin double-layered sheet of thin porous copper integrated with a dense copper layer was successfully produced. The sheets had volumetric or bulk porosity ranging from 50 - 82 % within the porous layer, which increased with the addition of K2CO3 space holder during processing, and pore size within the sheets ranged from 30 - 790 µm. By tape casting, thicknesses ranging from 900 -1800 µm were achieved. The heat transfer performance of the porous sheets improved with increasing porosity. The sheets with the highest porosity achieved a thermal transmittance of 5.0 W/K when tested on a cylindrical heating system (CHS) under a higher Reynolds number regime (Re = 486). Similar sheets achieved thermal transmittance (Tr) of 1.6 W/K on a flat heating system (FHS) at Re = 1,069.
Supervisor: Goodall, Russell ; Woolley, Robert Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available