Raman spectroscopy is an industrial process widely utilized to determine the chemical composition and structural components found within various materials. This phenomenon was originally observed by C.V. Raman in 1928, marking a pivotal milestone in its experimental verification. It encompasses an inelastic light-scattering phenomenon where the frequency of the monochromatic light used for excitation undergoes variation upon interaction with the substance under examination. This article focuses on the Raman spectroscopic analysis of glass and ceramic materials.
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A Brief Overview of Raman Spectroscopy
Laser lights are usually employed for the Raman spectroscopic analysis. The photons emitted by the laser light are absorbed by the sample, temporarily entering a non-stationary, exceedingly brief state, lasting approximately 10 to 15 seconds. Subsequently, these photons are promptly re-emitted.
The frequency of these re-emitted photons experiences a shift, either upward (referred to as the anti-Stokes Raman effect) or downward (known as the Stokes effect), relative to the original single frequency. This shift is quantified as the Raman shift, providing valuable insights into the vibrational, rotational, and other low-frequency transitions occurring within the molecules or molecular groups within the analyzed sample. Raman spectroscopy is a versatile technique applicable to the examination of solid, liquid, and gaseous samples.
Use of Raman Spectroscopy for Glass and Ceramics
Raman spectroscopy is a non-destructive analysis technique, that offers qualitative insights. While Raman spectroscopy of glass generally does not yield precise local structural details, it often reveals the presence of terminal anions, such as non-bridging oxygen (NBO or ONB) ions in oxide glasses, through the observation of characteristic high-frequency peaks within the spectra.
It also finds application in the investigation of the impacts of incorporating alkali metals into glasses, particularly silicate glasses. The inclusion of alkali metals in glasses leads to structural modifications particularly responsible for changing their properties, including a significant transformation involving the disruption of the backbone structure.
In ceramic analysis, Raman spectroscopy finds its primary application in the examination of ceramic mineralogy and the investigation of the glassy components present in glazes. Raman spectroscopy offers direct insights into the structural attributes of mineral phases. While it may entail a considerable amount of time, it remains the sole analytical technique capable of identifying amorphous and glassy phases.
Researchers have effectively employed Raman spectra as distinctive markers of the molecular structure within ceramics, utilizing them in a chronological examination of pottery production within specific geographical regions. Moreover, in particular instances, a mineralogical Raman study can also serve as a valuable tool for relative dating purposes.
Experimental Procedure
Raman spectroscopy is performed via an experimental setup consisting of a light source such as a laser, a specimen compartment, a spectrometer, an efficient detector, and an optical microscope.
The glass/ceramics sample is typically prepared by either grinding it into a fine powder or by polishing it to achieve a flat, pristine surface suitable for analysis. Subsequently, a monochromatic laser is precisely directed onto the sample. The scattered light emanating from the sample is systematically collected and subjected to analysis through a spectrometer. The resultant Raman spectrum exhibits distinctive peaks at precise wavenumbers, each of which corresponds to specific vibrational modes within the sample.
For a comprehensive assessment, Raman spectra are either compared against reference spectra or processed through specialized software. This analytical approach serves to extract valuable information related to the sample's composition, structure, and various other inherent properties.
Which Instruments are Preferred for Accurate Raman Spectroscopy?
Raman spectroscopy can be performed with various light sources, including continuous-wave (CW) lasers spanning the ultraviolet (UV) to the near-infrared (NIR) spectrum. Laser sources are the most apparent selection, with argon ion laser, krypton ion laser, or the helium-neon (He-Ne) laser the most prominent choices.
Two primary types of spectrometers, the dispersive and the Fourier-transform spectrometers, are highly utilized. Among these, the dispersive spectrometer is the most prevalent, and within this category, a frequently employed system for the examination of glasses and ceramics incorporates a double monochromatic arrangement. This configuration combines high-resolution capabilities with effective stray light rejection.
Traditionally, the photomultiplier tube (PMT) operating in photon counting mode held the status of being the preferred choice for Raman signal detection over many years. However, PMTs have gradually given way to multi-channel detectors, such as charge-coupled devices (CCDs).
Industrial Utilization
As mentioned above, apart from compositional and structural analysis, the materials engineering industry uses this technique for quality control purposes. In the production of glass and ceramics, maintaining a consistent level of quality is of utmost importance. Raman spectroscopy is used to continually oversee the overall integrity of materials at every stage of the manufacturing process. This efficient monitoring process ensures that the final products adhere to the specified requirements and industrial standards.
In real-world applications, when glass or ceramic parts experience failures, Raman spectroscopy proves invaluable for investigating the underlying causes. It assists in identifying the structural deficiencies and impurities that could have caused the breakdown.
Latest Research
Researchers from the United States, in their latest article published in the Journal of Non-Crystalline Solids:X, studied the structure and tested the chemical stability of telluride glasses. Telluride glasses (Ge-As-Te, Ge-Te, and As-Te glasses) have gathered considerable attention due to their extensive infrared transparency.
In general, the mode assignment within Ge-As-Te Raman spectra proved to be relatively straightforward, revealing four primary peaks that align with earlier research findings. Nevertheless, two prevalent sources of error were recognized.
The first common source of error rose from laser-induced modifications or crystallization occurring during Raman data acquisition. The second common source of error was attributed to an uncommon yet notably rapid oxidation process that occurred on the surface of telluride glass. Studies should be performed to remove such unwanted errors.
Recently, the implementation of Artificial Intelligence has led to intelligent machine learning-based spectroscopy aiding in faster Raman spectra processing. Scientists are implementing this technique in the biomedical industry to find cures for terminal diseases. The applications of Raman spectroscopy are essential for the materials science industry and are constantly improving the characteristics of ceramics and glasses.
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References and Further Reading
WZR Ceramic Solutions, 2022. Raman-Spectroscopy – A key to ceramic investigation. [Online]
Available at: https://wzr.cc/en/raman-spectroscopy/
[Accessed 09 September 2023].
Bayko, D. P., & Lucas, P. (2023). Structural analysis and chemical stability of Ge and As telluride glasses by Raman spectroscopy. Journal of Non-Crystalline Solids: X, 18, 100186. Available at: https://doi.org/10.1016/j.nocx.2023.100186
Van Pevenage, J. et. al. (2017). Raman spectroscopy and the study of ceramic manufacture: possibilities, results and challenges. In The Oxford handbook of archaeological ceramic analysis (pp. 531-543). Oxford University Press. Available at: https://www.doi.org/10.1093/oxfordhb/9780199681532.013.29
Neuville, D. et. al. (2021). Applications of Raman spectroscopy, a tool to investigate glass structure and glass fiber. Available at: https://hal.science/hal-03408691/document
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