Fast and Reliable Oxygen and Hydrogen Determination in Copper

Oxygen is typically employed in smelting processes as a means of eliminating unwanted elements such as iron or sulfur from copper ore, allowing pure copper to be retrieved.

Image Credit: Bruker AXS Inc.

The determination of oxygen is an essential quality control criterion in this wide-ranging demand for ‘oxygen-free copper’ (OFC) with oxygen content ≤10 ppm.

Cu-ETP (Electrolytic Tough Pitch Copper) is the most widely used copper type due to its highly conductive nature.

Cu-ETP is known to feature comparatively high oxygen concentrations of up to ~600 ppm – as well as hydrogen – making this much more prone to the condition known as copper ‘hydrogen sickness’ or ‘hydrogen disease.’

Hydrogen remains the leading reason for void and ‘bubble’ formation in solid metals, often resulting in lattice defects that change the material’s mechanical properties.

These factors highlight the importance of accurately determining oxygen and hydrogen contents in process and quality control throughout copper production and refining.

The G6 LEONARDO is an affordable, efficient and dependable tool for determining oxygen and hydrogen in copper.

Measuring Principle

Determination of hydrogen and oxygen in solids is performed via inert gas fusion (IGF) – the fusing of a sample in a graphite crucible under a flow of inert gas.

The G6 LEONARDO is fitted with a high-power electrode furnace, enabling temperatures of up to 3000 °C to decompose a wide range of samples - even robust samples like refractories.

When exposed to these conditions, oxygen present in the sample will react with the graphite crucible’s carbon to quantitatively form carbon monoxide (CO). While this is occurring, hydrogen present in the sample will also be released as H₂ during melting.

CO is assessed via advanced, non-dispersive infrared detectors, while hydrogen is evaluated via a thermal-conductivity detector.

Both CO and H₂ are determined directly during this process. They remain absolutely unchanged in a 1:1 ratio thanks to the detection techniques provided by the Smart Molecule Sequence™.

The crucible is outgassed during a standard analytical cycle to remove contaminants. This is done by heating the crucible to a temperature ~200 °C higher than the analysis temperature - an outgassing step performed prior to analysis to ensure negligible blank values.

Sample masses for the determination of oxygen and hydrogen are generally within the region of 0.3 g to 1.0 g. These masses can be analyzed without the need for additional fluxes.

The G6 LEONARDO’s shielded, rotating sample port enables the transfer of different shaped samples – for example, pieces, granules and chips – into the crucible without the use of extra capsules and with no risk of jamming.

Tin or nickel capsules are used where there is a need to determine a blank for powdered samples. Tin can also be employed as a flux to help support melt homogeneity and ensure the release of oxygen and hydrogen present in the material.

Figure 1. Electrode furnace programming for OH in copper in FUSION.ELEMENTS. Red: outgassing and delay; blue: analysis time. Image Credit: Bruker AXS Inc.

FusionControl – Temperature Matters

Temperature applied to the sample can be monitored via an integrated pyrometer (FusionControl) to prevent overheating and the formation of unwanted by-products. Virtual modes ensure stable conditions throughout the entire analysis, for example, the “power by temperature” mode.

Sample Preparation

If not present in an appropriate form, samples can be produced in pin or piece form by punching or cutting. This is particularly important for oxygen determination, where any existing surface alteration should be removed via etching.

The etching process begins with the application of concentrated HCl for 3 minutes and then with an acid mixture for 1 minute. This acid mixture is comprised of equal parts acetic acid (99%), nitric acid (65%) and phosphoric acid (85%). Finally, the sample is rinsed with distilled water and acetone three times each.

Freshly produced samples can be prepared by rinsing in acetone and drying with warm air. ASTM E 2575 provides a complete description of the standard practice for sampling and preparing copper and copper alloy samples.

Method Parameters

The FUSION.ELEMENTS software features virtual control modes for the electrode furnace, facilitating direct temperature input, though the control mode is current or power.

Method parameters are as follows:

• Furnace Control: Power (virtual by temperature)
• Outgassing: 45 seconds (1800 °C)
• Analysis Delay: 10 seconds (1600 °C)
• Analysis: isothermal (1600 °C)
• Analysis Time: 100-120 seconds (N₂ carrier gas)

The FUSION.ELEMENTS software is able to graphically visualize the resulting temperature versus time curve.

Calibration

The analyzer’s calibration can be undertaken via NIST, EZRM or another appropriate reference material.

The potential presence of oxygen surface alteration requires that calibration standards for oxygen are available in pin or ball form. These are typically coated with gold (balls) or tin (pins).

No certified reference materials (CRM) are available for hydrogen in copper, but steel standards can be used for this purpose.

Procedure

Determination of the Blank Value

Using the Calibration Wizard, a minimum of 3 replicates of the blank value should be run by placing a graphite crucible on the lower electrode tip before analyzing this.

When looking to establish a blank for the analysis of powdered samples using capsules, it is necessary to place an open capsule into the analyzer’s sample port prior to analysis. It is also important to clean both the upper and lower electrode between replicates.

Figure 2. Peak example OFC. Image Credit: Bruker AXS Inc.

Measuring Reference Materials

1. Using the calibration wizard, it is possible to select the most appropriate method and select CRMs for calibration from the list of available standards. If not present, these can be added by defining a designation, certified concentration and certified error.
2. Next, ~1.0 g of reference material should be weighed and its exact mass transferred to the software before the sample is placed into the sample funnel.
3. The upper and lower electrode should be cleaned before a graphite crucible is placed on the tip of the lower electrode and analysis commences.
4. Steps 2-3 should be repeated a minimum of three times for each reference material utilized.
5. The method should be calibrated with the blank values recorded earlier and the results acquired using suitable reference materials. The device’s user manual can provide further details on this step.

Sample Measurement

1. In the Measurement Center, an appropriate amount of the prepared sample should be weighed and its exact mass transferred to the software. The sample should then be placed into the sample funnel.
2. A graphite crucible should be placed on the tip of the lower electrode and analyzed.
3. Steps 1-2 should be repeated for sample analysis, with both the upper and lower electrode cleaned at regular intervals and glass wool exchanged in the dust trap as required.

Typical Results

A series of repetitive measurements of both standards and production samples demonstrate the G6 LEONARDO’s reproducibility and the reproducibility of the method.

Table 1. Source: Bruker AXS Inc.

Table 2. Source: Bruker AXS Inc.

Table 3. Source: Bruker AXS Inc.

¹⁾ Mean = arithmetic average; STD = absolute standard deviation (1σ)

Summary

The G6 LEONARDO offers the necessary precision for the determination of hydrogen and oxygen in copper in a compact form requiring minimal maintenance.

The instrument’s innovative SampleCare™ mechanism and its powerful, user-friendly software combine to ensure robust and cost-effective operation.

The G6 LEONARDO represents an ideal choice for quality control in virtually any metal production industry.

This information has been sourced, reviewed and adapted from materials provided by Bruker AXS Inc.

For more information on this source, please visit Bruker AXS Inc.