Optical Spectroscopy for Characterizing Alloy Powder

In a recent study published in Powder Technology, researchers proposed an innovative spectroscopic method to evaluate metal powder oxidation. They employed Raman and ultraviolet-visible (UV-Vis) spectroscopy to analyze the composition and thickness of oxide layers, providing a more accessible and cost-effective alternative to traditional techniques.

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Background

Copper and silver (Cu-Ag) alloys offer exceptional strength and conductivity, making them ideal for electronics, power systems, materials engineering, machinery, and high-field magnets.

However, when exposed to ambient air, they are prone to oxidation, forming thin oxide layers that are challenging to measure due to their small size (typically a few nanometers thick) and uneven distribution. The properties of the Cu-Ag alloy can also further complicate measurement.

About the Research

This study introduced a novel technique for assessing the oxidation status of Cu with 3.4 % Ag by weight (CuAg3.4) alloy powder, a material valued for its high strength and conductivity. Raman spectroscopy identified the oxide layer composition, while a machine learning-based approach with UV-Vis spectroscopy determined the oxide layer thickness.

Two batches of CuAg3.4 powder were produced using a vacuum induction inert gas atomizer (VIGA) system: one stored under standard conditions (oxidized) and the other under an inert argon atmosphere (inert).

X-Ray diffraction (XRD), Raman spectroscopy, field emission scanning electron microscopy (FESEM), and energy-dispersive spectroscopy (EDS) were employed to characterize the powders. XRD identified the crystalline phases, FESEM visualized the surface morphology and microstructure, and EDS analyzed the elemental composition.

They employed Mie scattering theory within the scattnlay Python library to simulate the optical response of spherical particles with varying oxide layer thicknesses. This simulated data was then used to train a K-nearest neighbor regression model, enabling the prediction of oxide layer thickness from experimental UV-Vis spectra.

Research Findings

The analysis revealed distinct characteristics between the inert and oxidized CuAg3.4 alloy powder samples.

In both samples, Raman spectroscopy identified bands corresponding to cupric oxide (CuO) and cuprous oxide (Cu2O). However, the oxidized sample exhibited a significantly higher intensity of CuO bands than the inert sample, indicating a greater presence of CuO. These results aligned with the observation of silver oxide (Ag2O) bands only in the oxidized sample, further suggesting a more advanced oxidation state.

Microscopic analysis supported these observations, highlighting differences in surface morphology. The oxidized layer displayed distinctive holes and a wrapping-like feature, potentially indicative of outward diffusion processes during oxidation.

EDS confirmed the expected elemental composition of the alloy. The oxidized sample exhibited a higher Ag and oxygen (O) content than the inert sample. This increase in Ag content could be due to the preferential segregation of Ag to the surface during oxidation or a loss of Cu from the oxide layer.

The K-nearest neighbor regression model, trained on simulated data, provided quantitative data on the oxide layer thickness. The inert sample exhibited similar thicknesses of CuO and Cu2O, while the oxidized sample had a predominantly CuO oxide layer with a thickness of approximately 13.9 nm.

These outcomes provided valuable insights into the oxidation behavior of CuAg3.4 powder, highlighting the formation of CuO and the potential for Ag enrichment at the surface during oxidation.

Applications

The proposed spectroscopy-based method is a significant advancement in powder oxidation characterization, offering simplicity and ease of use for various fields:

  • Additive manufacturing: Understanding powder oxidation is crucial for maintaining flowability, laser absorption, and preventing defects in printed products.
  • Powder metallurgy: Evaluating the oxidation state enhances control over the sintering process and the properties of sintered products.
  • Material science: The technique aids in examining the oxidation behavior of various metal powders.

This method can also benefit industries like catalysis and electronics, where knowing the oxidation state is essential for material performance.

Conclusion

The comprehensive characterization of the CuAg3.4 alloy powder using Raman and UV-Vis spectroscopy effectively quantified the thickness and composition of the surface oxide layer.

This method offers a simple, effective alternative to complex techniques, providing valuable insights for optimizing powder storage, controlling sintering processes, and understanding oxidation behavior.

Journal Reference

Giardino, M., et al. (2024). Study of surface oxidation in metal powders by means of optical spectroscopy. Powder Technology. doi.org/10.1016/j.powtec.2024.119883

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Muhammad Osama

Written by

Muhammad Osama

Muhammad Osama is a full-time data analytics consultant and freelance technical writer based in Delhi, India. He specializes in transforming complex technical concepts into accessible content. He has a Bachelor of Technology in Mechanical Engineering with specialization in AI & Robotics from Galgotias University, India, and he has extensive experience in technical content writing, data science and analytics, and artificial intelligence.

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