Wire and Rod Analysis by Glow Discharge

Importance of the Topic

Glow discharge enables direct, rapid, and solvent-free elemental analysis of solid samples, crucial for quality control and materials research in metallurgy and manufacturing. Its adaptability to small wires and rods reduces analysis time and environmental impact compared to wet chemical digestion.

Objectives and Study Overview

This study outlines procedures to analyze fine wires and rods using a LECO GDS500A spectrometer equipped with standard and small-anode lamp options and two specialized sample holders. It covers sample mounting strategies, preparation workflows, and performance evaluation across diverse sample diameters and alloy types.

Used Instrumentation

• LECO GDS500A Glow Discharge Spectrometer
• Standard lamp with interchangeable 4 mm and optional 2 mm anodes
• Small 2 mm lamp assembly
• Sample Holder Assembly 612-708 (3 mm pilot hole, drillable to 12 mm)
• Wire Holder 833-101-139 for forging wires ≤3 mm
• LECO MSX-205-M2 water-cooled cut-off saw
• Belt grinders and polishers (zirconium oxide 120-grit, SiC 320-grit disks)

Methodology

Glow discharge analysis is conducted under argon at a constant electric field, causing cathodic sputtering of surface atoms that emit element-specific photons. Samples must be flat and conductive to seal against an o-ring and complete the circuit. Lamp options include a 4 mm anode for diameters ≥3 mm and a 2 mm anode or dedicated small lamp for wires down to <3 mm. Wires <3 mm are bundled and forged in Holder 833-101-139; larger wires and rods are mounted in Holder 612-708 and secured with a set screw. Sample preparation involves annealing (if needed), sectioning, surface grinding with appropriate abrasives, and cleaning with solvent.

Main Results and Discussion

Precision testing on low-alloy steel (Holder 612-708, 6.5 mm hole) demonstrated RSDs below 1% for major elements (C, Mn, Si) and acceptable repeatability for trace elements. Forged 0.9 mm steel wire (Holder 833-101-139) achieved RSDs under 3% for most constituents. Aluminum alloy wire and stainless steel ribbon analyses also yielded consistent average concentrations (RSDs <6%). Proper centering and crater inspection ensure minimal holder contamination.

Benefits and Practical Applications

• Direct solid analysis eliminates wet digestion, reducing hazardous waste and sample preparation time
• Adaptable to a wide range of wire and rod diameters using interchangeable lamp and holder configurations
• Sufficient precision and accuracy for quality control in steel, aluminum, and stainless alloys
• Rapid turnaround (analysis and preparation under 15 minutes per sample)

Future Trends and Potential Applications

Advancements may include automated sample handling and holder alignment, miniaturized lamps for even smaller samples, and expanded applications to coated or composite wires. Integration with in-line process monitoring and development of improved holder materials could further enhance versatility.

Conclusion

The adapted glow discharge methodology on the GDS500A effectively extends direct elemental analysis to wires and rods of small diameters with high precision and minimal preparation. Specialized holders and lamp options ensure reliable mounting, and the technique supports fast, eco-friendly quality control in industrial and research laboratories.