Direct determination of Al, B, Co, Cr, Mo, Ti, V and Zr in HF acid-digested nickel alloy using the Agilent 4210 Microwave Plasma-Atomic Emission Spectrometer

Significance of the topic

Nickel-based alloys combine high- and low-temperature strength with corrosion resistance, making them indispensable in petrochemical, gas turbine, aerospace and military industries. Accurate determination of alloying elements such as Al, B, Co, Cr, Mo, Ti, V and Zr is vital because small compositional deviations can impair mechanical performance and service life.

Objectives and overview

This study demonstrates a rapid, direct method for quantifying key elements in HF-acid digested nickel alloys using the Agilent 4210 Microwave Plasma-Atomic Emission Spectrometer (MP-AES). By employing an inert sample introduction system, the method avoids the conventional HF neutralization step, streamlining workflow and reducing contamination risks. A certified IN 100 nickel alloy reference material validates the approach.

Methodology and instrumentation

• Sample digestion: 0.15 g of alloy digested in HNO3–HCl–HF mixture using Milestone UltraWave microwave system (45 bar N2, no sealing required). Final volume: 40 mL.
• Calibration: Aqueous single-element CRMs in 20 % aqua regia/5 % HF matrix; ranges tailored to expected concentrations.
• Instrument: Agilent 4210 MP-AES with nitrogen plasma. Inert sample introduction: alumina-containing torch, OneNeb Series 2 nebulizer, and inert double-pass spray chamber. Nebulizer gas humidifier fitted for stability with high total dissolved solids.
• Software: MP Expert for wavelength selection and Fast Linear Interference Correction (FLIC).
• Analytical lines: Selected wavelengths (e.g., Al 394.401 nm, Cr 435.177 nm) to minimize interferences; FLIC used for overlapping signals (e.g., V interference on Cr).
• Internal standard: Lu (261.542 nm) at 50 mg/L, introduced online.

Main results and discussion

• Detection limits: mg/L levels in solution correspond to sub-ppm LOQs in solid sample (e.g., 6.2 mg/kg Al, 20 mg/kg Cr).
• Dynamic range: Elements quantified over three orders of magnitude (ppm to %), eliminating re-dilutions.
• Long-term stability: Eight-hour continuous run on IN 100 CRM showed < 5 % RSD and recoveries within ±10 % of certified values.
• Recovery: Triplicate digestions and duplicate analyses achieved recoveries of 93 %–107 % across all target elements.
• Role of HF: Digests without HF under-recover Mo, Ti and Zr; HF yields complete dissolution of refractory elements.

Benefits and practical applications

• Elimination of neutralization: Direct HF digest analysis reduces preparation time and contamination risk and preserves boron quantification.
• Safety and cost: Nitrogen plasma avoids flammable gases and supports unattended operation in remote laboratories.
• Throughput: Fast sequential measurement with minimal sample handling and wide dynamic range boosts laboratory productivity.

Future trends and opportunities

• Expansion to other refractory alloys and matrices requiring HF digestion (e.g., refractory metals, ceramics).
• Integration with automated digestion platforms and in situ sample introduction for online process monitoring.
• Advanced chemometric tools to resolve complex spectra and extend quantitative capabilities to trace impurities.
• Broader adoption of green plasma sources and miniaturized MP-AES systems for field and on-line quality control.

Conclusion

The Agilent 4210 MP-AES coupled with an inert sample introduction system provides a robust, efficient method for multielement analysis of HF-acid digested nickel alloys. High accuracy, low detection limits, wide linear range and excellent stability demonstrate its suitability for metallurgical QC, aerospace component testing and research applications.

References

1. Decker RF, Freeman JW. Mechanism of beneficial effects of boron and zirconium on creep-rupture properties of a complex heat resistant alloy. NACA TN 4286 (1958).
2. Kontis P et al. Effect of boron on grain boundary character in a new polycrystalline superalloy. Acta Mater. 2016;103:688–699.
3. McDonald D, Amorin A. Direct determination of Cu, Fe, Mn, P, Pb and Ti in HF acid-digested soils using Agilent 4200 MP-AES. Agilent, 2015.
4. Engineering Properties of IN-100 Alloy. Nickel Institute.
5. Agilent MP Expert Software. Agilent Publication 5990-8975EN (2011).