Elemental analysis of glass helps us to uncover chemical compositions, therefore its applications are vast. These include quality control, production diagnosis, material verification, and more. This article discusses the elemental analysis of glass using scanning electron microscopy (SEM).
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There are countless ways to construct glass through different chemical compositions. The composition of glass can affect its optical, physical, chemical, thermal and mechanical properties.
Several investigative tools are used for the elemental analysis of different materials. SEM analysis is a powerful investigative tools which produce high magnification images of the surface of a sample by using a focused beam of electrons. Additionally, it is also used to characterize particles. For example, during mechanical wear testing, SEM can characterize debris. It also helps to determine the size, number and morphology of small particles to understand different properties of the material.
How Does SEM Analysis Work?
Scanning electron microscopy (SEM) is one of the standard methods for imaging the microstructure and morphology of materials. In SEM analysis, a low energy electron beam is radiated to the sample’s surface for scanning. Due to the interactions between the sample’s surface and electron beam, electrons and photons start emitting from or near the surface, which produces receiving signals. Different types of detectors then sense these signals to form an image. The type of detector depends upon the mode of SEM that is being used in the analysis.
Different modes, such as secondary electron imaging, electron channeling, X-ray mapping, backscattered electrons imaging and Auger electron microscopy, are used to characterize materials.
Components of SEM
A scanning electron microscope consists of components that include an electron gun emitting electrons that are then raised to 0.1-30keV energy levels, a Tungsten gun which helps to make high-resolution images by making high diameter beams, electromagnetic lenses that help to form concentrated spots of the electron beam on the sample, and a high-vacuumed chamber that helps electrons not to get absorbed or scattered by air molecules.
Components of Glass
Glass is an amorphous translucent or transparent material that is made up of a mixture of silicates. It is made by fusion of molten silicate and then solidification without crystallization. Most commercially produced glasses utilize sand (SiO2), and normally other oxides like CaO, Na2O, and K2O are added, which help reduce the viscosity and melting point of SiO2.
Other materials are also added depending upon the required properties of the glass; for example, PbO increases refractivity, B2O3 reduce thermal expansion, Al2O3 increase durability etc. Therefore, there are various elemental components in glass that help determine properties.
Different Methods Used for Elemental Analysis of Glass
Different analytical methods exist to determine the elemental composition of glass. These include but are not limited to laser ablation-inductively coupled plasma mass spectrometry (LA-ICP-MS), scanning electron microscopy (SEM) and X-ray fluorescence (XRF) etc., with each method having its advantages and limitations.
Elemental Analysis of Glass using SEM
The manufacturers control the concentration of different elements to obtain specific glass products depending on the required properties, and sometimes SEM is used to identify glass fragments.
Procedure
Elementary analysis of glass using SEM determines the ratio of concentrations of Na/Mg, Ca/K, Mg/Al, Ca/Na, and Na/Al. Through these ratios, the glass is categorized, and properties are determined.
The glass sample to be examined for elementary analysis using SEM is firstly cleaned and dried. Small irregular samples can be used for this purpose, but flat and regular shaped samples are preferred for precise and accurate quantitative results. Flat surfaces can be obtained by putting the sample in resin and then polishing it.
After that, SEM-ED X-ray spectrometry measurements are taken for the sample. For this purpose, the magnification and beam current used depends on the size of the sample and the capabilities of the instrument. For example, for most of the samples, 1000X magnification is used, but up to 10,000X can be used depending upon the sample size and other requirements. 10 to 20 kVolts is normally used as the acceleration voltage.
To obtain a representative spectrum from the sample, the scan area should be as large as possible. There should also be consistency between operating parameters with that of the specimen to which the sample is compared. Current should be set for count rates in a way that analytical time is not excessive. Sodium migration occurs at high operating currents, and it can be noted by a drop in the intensity of NaK with time; detector-to-specimen distance should also be optimum. For complete quantitative analysis, calibration with matrix-matched standards embedded in each stub along with the analytical samples under identical operating conditions is required.
Advantages of SEM
One of the biggest advantages of SEM is its non-destructive nature. Concentrations of different elements can be observed using only small samples. Moreover, when SEM-ED is joined with energy dispersive X-ray fluorescence spectrometry, it allows product-use classification of the sample. Overall, SEM has many advantages over traditional tools used for the same purpose, such as having high resolution and the ability to focus on multiple glass specimens at one time.
References and Further Reading
Kuisma‐Kursula, P. (2000). Accuracy, precision and detection limits of SEM–WDS, SEM-EDS and PIXE in the multi‐elemental analysis of medieval glass. X‐Ray Spectrometry: An International Journal, 29(1), 111-118. https://citeseerx.ist.psu.edu/
Montero, S., Hobbs, A., French, T. and Almirall, J., 2003. Elemental Analysis of Glass Fragments by ICP-MS as Evidence of Association: Analysis of a Case. Journal of Forensic Sciences, 48(5), p.2001413. https://www.researchgate.net/publication/9057604_Elemental_Analysis_of_Glass_Fragments_by_ICP-MS_as_Evidence_of_Association_Analysis_of_a_Case
Moore, Sarah. (2021, May 06). A Look at Elemental Analysis of Glass in Research Applications. AZoM. Retrieved on March 10, 2022, from https://www.azom.com/article.aspx?ArticleID=20398.
Omidi, M., Fatehinya, A., Farahani, M., Akbari, Z., Shahmoradi, S., Yazdian, F., ... & Vashaee, D. (2017). Characterisation of biomaterials. In Biomaterials for oral and dental tissue engineering (pp. 97-115). Woodhead Publishing. https://doi.org/10.1016/B978-0-08-100961-1.00007-4
Scientific Working Group for Materials Analysis (SWGMAT) 2004, Elemental analysis of glass, Retrieved fromhttps://www.asteetrace.org/static/images/pdf/05%20Elemental%20Analysis%20of%20Glass.pdf
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