Elemental Oxygen Sampling and Preparation

Uniform samples are a prerequisite for obtaining accurate data, so a thorough understanding of sampling techniques is necessary.GB/T20066 and/or ISO 14284 specify the corresponding sampling parts for finished steel products of various shapes to ensure the representativeness of the samples taken.

The form of the sample is very important, oxygen analysis is usually taken in the form of columnar, block or spherical samples. The specific surface area of the sample should be small so as to reduce the analytical bias introduced by surface contamination of the sample. Powdered and flaked samples can also be analysed, but surface oxides can affect the total oxygen content.

Oxygen analysis samples have strict surface requirements. The samples to be processed are made into cylindrical rods of about Φ5mm on the lathe, and are polished on the instrument lathe with silicon carbide emery cloth (sandpaper) and buckskin before the measurement; or the oxidised layer on the surface is filed off with a file, and a new surface layer appears. The processed cylindrical rods were cut off the ends with wire cutters, cut to the desired length (3-6 mm), and cleaned in an ultrasonic cleaner with carbon tetrachloride or acetone for 3-7 min to remove other contaminants. In some cases, processed samples can be treated with a chemical cleaning solution, washed in water, then washed with anhydrous ethanol (or acetone) and stored in an organic solvent, and blown dry with cold air before analysis. Commonly used cleaning solutions are phosphoric acid + hydrogen peroxide (1 + 3), phosphoric acid + nitric acid + glacial acetic acid (28 + 10 + 62) and so on. Select appropriate pre-treatment methods for samples of different materials, and pay special attention to the processing and pre-treatment of low-oxygen samples (such as GCr15 bearing steel, etc.) in the analysis.

Non-ferrous metal samples after processing should not be mechanically polished to eliminate the surface, available chemical corrosion method for processing. Copper and copper alloy analysis method standard, the requirements of copper metal samples after processing, with phosphoric acid + nitric acid + glacial acetic acid (28 + 10 + 62) of the mixed acid immersion for 10min, quickly cleaned with water, washed with anhydrous ethanol, cold air drying; titanium and titanium alloy analysis method standard with nitric acid (1 + 8) and hydrofluoric acid (1 + 23) and so on volume of the mixture of immersion for 5min; nickel with nitric acid + glacial acetic acid + hydrochloric acid ( 2.5 + 7.5 + 0.1) immersed in 30 ~ 60s; metal tin with 5% NaOH solution boiled for 5s, rinsed with running water, and then cleaned with anhydrous ethanol.

Blow-dried and cleaned specimens should be handled with clean tweezers to prevent contamination. As many materials will quickly re-oxidise, after preparation and analysis as soon as possible, or immersed in carbon tetrachloride and other organic solvents, such as analysis before blow-drying and use.