Abstract
The fundamental characteristics of metal coatings that influence heat transfer are porosity and surface roughness. It is a challenge to analyze the porosity and surface roughness due to the inadequate amount of copper per coated area. In this study, a new approach to non-invasively determine the porosity of metal films utilizing a helium pycnometer and computed micro-tomography (CMT) is presented. Furthermore, a telescope-goniometer is used to measure the surface roughness. Experiments are conducted on four varieties of thin film samples coated with copper powder using wire flame and plasma thermal spray coating methods. The porosities of the thin films were determined to be between 39 and 43%. The thermal spray coating increased the hydrophobicity of the surface and the plasma coating created super-hydrophobic surfaces. The new approach establishes that the porosity of thin films can be non-invasively determined and may also be applied to a wide variety of coated surfaces.
Highlights
Gas adsorption measurements are often used to quantify open porosity[9,10]
Direct imaging methods can be used to analyze the porosity of thin films, including scanning electron microscopy (SEM) with energy dispersive X-ray spectroscopy (EDX), wavelength dispersive X-ray spectroscopy[11], focused ion beam SEM (FIB-SEM) and transmission electron microscopy (TEM)
The combination of pycnometry and computed micro-tomography was successfully demonstrated as a new tool to determine the porosity of thin films produced by thermal spray coating
Summary
Gas adsorption measurements are often used to quantify open porosity[9,10]. The material to access the closed pores and quantify the total porosity. Imaging methods allow for quantification of the porosity via visualization and reconstruction of the pore geometry from 2-D projections of thin films cross sections[12]. A direct imaging process that can visualize non-invasively and nondestructively is desirable. Gas expansion methods that employ Boyle’s law, most notably helium pycnometry, are among the most accurate techniques for measuring porosity[13,15]. The pycnometer can only measure the volume of pores accessible to the helium, it can only measure the open porosity of a sample. Pycnometry has to be combined with another non-invasive method for complete analysis of both open and closed pores
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