Introduction
Metal surface cleanliness has traditionally been assessed by visual methods and tactile methods. Visual methods are limited by the resolution capabilities of the human eye, and tactile methods are time consuming and prone to human errors. In recent years, a wide variety of new methods have been developed to enable the rapid, accurate, and reliable assessment of metal surface cleanliness in industrial processing. This paper will briefly discuss the standard methods that are used to assess metal surface cleanliness, and then discuss the latest method—Raman spectroscopy—in more detail.
Standard Methods for Assessment of Metal Surface Cleanliness
The most widely used methods for assessing metal surface cleanliness include visual inspection, scanning electron microscopy (SEM), differential scanning calorimetry (DSC), grazing incidence X-ray diffraction (GIXRD), and energy dispersive X-ray spectroscopy (EDX).
- Visual inspection: Visual inspection of a metal part is the traditional, and most widely used, method of assessing surface cleanliness. This method is limited, however, by the resolution capabilities of the human eye and by subjective variables such as lighting and operator experience.
- Scanning electron microscopy (SEM): Scanning electron microscopy provides high resolution images of metal surfaces and is capable of identifying contaminants that may not be visible to the unaided eye. This method is limited, however, by its cost and time consuming nature.
- Differential scanning calorimetry (DSC): Differential scanning calorimetry can detect contaminants on the surface of metals through the measurement of heat changes that occur when the sample is subjected to a temperature gradient. This method is also limited, however, by its cost and time consuming nature.
- Grazing incidence X-ray diffraction (GIXRD): GIXRD can identify contaminants on a metal surface by measuring the intensity of the diffraction peaks generated when the sample is exposed to X-rays. This method is limited, however, by its cost and time consuming nature.
- Energy dispersive X-ray spectroscopy (EDX): Energy dispersive X-ray spectroscopy is capable of detecting both metal and non-metal contaminants on a metal surface through the analysis of the X-ray spectra generated by the sample. This method is also cost and time consuming, however.
Raman Spectroscopy: A New Method of Assessing Metal Surface Cleanliness
Raman spectroscopy is a newly developed method for assessing metal surface cleanliness that combines the best aspects of the traditional methods with the most advanced elements from modern analysis techniques. Raman spectroscopy is based on the phenomenon of inelastic scattering, in which a photon interacts with a molecule and is scattered at an energy different from the initial photon energy. When the incident light is in the visible or near infrared spectral range and is scattered from a material, the resulting inelastic light is known as Raman scattering, and the Raman spectrum of any given material is characteristic of its molecular structure.
Raman spectroscopy has several advantages over existing methods for assessing metal surface cleanliness. Firstly, Raman spectroscopy is non-destructive, and can be performed rapidly and without added sample preparation. Secondly, unlike SEM or EDX, Raman spectroscopy can identify both metal and non-metal contaminants on a metal surface with just one scan. Lastly, Raman spectroscopy is highly sensitive and can detect even trace amounts of contaminants on metallic surfaces.
Conclusion
Metal surface cleanliness is essential for the successful performance of many industrial processes. The traditional methods of assessment, such as visual inspection, SEM, and EDX, are limited by their cost and time consuming nature. Raman spectroscopy, however, combines the best aspects of the traditional methods with the most advanced elements from modern analysis techniques, making it an ideal choice for the rapid, accurate, and reliable assessment of metal surface cleanliness.
