Routine Analysis of "Difficult" Alloys Using LECO Glow Discharge

Significance of the Topic

Glow discharge atomic emission spectroscopy (GDS) offers a powerful solution for routine chemical analysis of alloys with challenging matrices. In industrial quality control and research laboratories, accurate determination of elements in materials such as cast irons, leaded bronzes, and hypereutectic aluminum alloys is critical. GDS overcomes limitations of spark and X-ray methods by providing linear calibration over a wide dynamic range, minimal surface preparation requirements, and reliable analysis of volatile and low-mass elements.

Objectives and Study Overview

This study evaluates the performance of the LECO GDS500A spectrometer for routine analysis of “difficult” alloys. Key goals include:

• Assessing analytical precision and accuracy across a variety of sample types.
• Demonstrating linearity of calibration curves for major and trace elements.
• Validating rapid multi-burn analysis modes for increased throughput.

Methodology and Instrumentation

The LECO GDS500A uses a perpendicular glow discharge lamp to uniformly sputter material from the sample surface, producing a cylindrical crater with a flat bottom. Unlike spark sources, the relatively cool plasma minimizes melting and volatility losses. Surface contaminants are removed during a pre-burn cycle, revealing fresh material for analysis. Sample preparation follows a standardized guide: ferrous alloys are ground with 120-grit zirconia belts or wet disks, nonferrous with 320-grit silicon carbide, and as-cast materials finish-polished to 600-grit. The system supports “analyze all in one spot” mode, enabling three sequential analyses in 90 seconds without reclamping.

Instrumentation Used:

• LECO GDS500A atomic emission spectrometer
• Sample preparation accessories: LECO BG belt grinder, LECO VP polisher

Main Results and Discussion

Certified reference materials including grey cast iron, chilled ductile iron, 12L14 steel, 303 and 416 stainless steels, leaded bronze, and hypereutectic Al/Si alloys were analyzed. Key findings:

• Average recoveries matched certified values within 1–5% relative error for most elements.
• Relative standard deviations (RSD) typically ranged from 0.2% to 4%, demonstrating high precision.
• Calibration curves for elements such as Pb (up to 10%), Si (1–23%), and C in iron were linear across the tested ranges.

These results confirm that GDS provides accurate quantification of both major constituents and trace elements, including sulfur, phosphorus, boron, and magnesium, without special matrix-dependent methods.

Benefits and Practical Applications

The glow discharge approach delivers several advantages:

• Minimal surface preparation and immunity to surface contamination.
• Linear calibration over wide concentration ranges for metals and metalloids.
• Capability to analyze small components (fasteners, wires, springs) and malleable powders pressed into pellets.
• Rapid analysis cycles supporting higher sample throughput in QA/QC environments.

Future Trends and Applications

Emerging directions include integration of automated sample handling, expansion of calibration libraries with customer-specific reference materials, and coupling GDS with multivariate data analysis for complex alloy systems. Inline or near-line monitoring in production environments may further enhance process control. Advances in plasma modeling and detector sensitivity could extend analysis to ultra-trace elements and non-metallic inclusions.

Conclusion

The LECO GDS500A glow discharge spectrometer demonstrates robust performance for routine analysis of alloys with challenging matrices. Its precise sputtering mechanism, linear calibration, and fast multi-burn capabilities make it an ideal tool for industrial and research laboratories seeking reliable elemental data across a broad range of materials.

Reference

• LECO Corporation. Spectroscopy Performance Note: Routine Analysis of “Difficult” Alloys Using LECO Glow Discharge. Form No. 209-076-033, 2007.