Working Principle of Oxygen Nitrogen Hydrogen Analyzer

Oxygen, nitrogen, and hydrogen serve as critical micro/trace elements in metallic and non-metallic materials, whose concentrations directly influence mechanical properties (such as strength, toughness, and fatigue life), processing characteristics, and chemical stability. The Oxygen Nitrogen Hydrogen Analyzer (ONH Analyzer) is a specialized instrument designed for precise determination of these three elements in various materials. Widely used in metallurgy, materials science, aerospace, automotive manufacturing, and other fields, it serves as a core piece of equipment for material quality control and research and development.

Currently, mainstream Oxygen Nitrogen and Hydrogen Analyzers are based on the combined technology of “inert gas fusion - infrared detection (IR) + thermal conductivity detection (TCD)”. The core principle involves converting oxygen, nitrogen, and hydrogen in the sample into gaseous forms that can be precisely detected, by quantitative analysis using corresponding detectors. The specific process can be divided into four key steps:

1. Sample Preparation

To eliminate interference from surface oils, oxide layers, or adsorbed moisture/impurities on test results, it is necessary to prepare samples: Metal Samples: Normally using sandpaper grinding, alcohol wiping, or ultrasonic cleaning to ensure surface cleanliness and absence of contaminants.

Powdered/Brittle Samples: Must be compacted into blocks (to prevent spattering during melting) or enclosed in specialized crucibles (to prevent sample dispersion).

2. Inert Gas Melting (Core Step)

Place the prepared sample into a crucible (typically high-purity graphite) within a high-frequency induction furnace (for metallic samples, utilizing electromagnetic induction to generate high temperatures) or a graphite resistance furnace (for non-metallic/refractory metals such as ceramics, tungsten, molybdenum, etc.);

Introduce high-purity inert gas (e.g., argon, ≥99.9999% purity) into the furnace to displace air (preventing interference from atmospheric O2, N2, and H2O);

Heat to 1800-3000°C (temperature adjustable based on sample melting point). At high temperatures, the sample melts, and its oxygen, nitrogen, and hydrogen undergo the following reactions:

Oxygen: Reacts with the graphite crucible to form carbon monoxide (CO) or carbon dioxide (CO2). Some instruments convert CO to CO2 via a catalyst for easier infrared detection;

Nitrogen: Released as free nitrogen gas (N2). (Nitrogen in some metals exists as nitrides, which decompose into N₂ at high temperatures.)

Hydrogen: Released as hydrogen gas (H2). (Primarily from hydrogenate or adsorbed hydrogen within the sample.)

3. Gas Separation and Purification

The mixed gases produced during melting (CO/CO2, N2, H2, unreacted argon) pass through a purification system:

Dust removal (small amounts of oxide/carbide powder generated from sample melting);

Removes moisture (via desiccants such as magnesium perchlorate);

Some instruments utilize “selective adsorption columns” to separate different gases (e.g., first separating CO2, then separating N2 and H2), ensuring no cross-interference in subsequent detection.

4. Gas Testing and Quantification

Oxygen Testing: Utilizes an infrared detector (IR) — CO2 (or CO) strongly absorbs infrared radiation at specific wavelengths, with absorption intensity proportional to gas concentration (Lambert-Beer Law). By measuring the attenuation of infrared light, oxygen content can be calculated. Nitrogen and Hydrogen Testing: Utilizing a Thermal Conductivity Detector (TCD) — Significant differences exist in the thermal conductivity coefficients of various gases (e.g., H2 exhibits a thermal conductivity coefficient far exceeding that of argon, while N2 has a coefficient slightly higher than argon). When a mixed gas stream passes through thermo sensitive element of TCD, it causes changes in the element's temperature and electrical resistance. By measuring the resistance difference, the respective nitrogen and hydrogen contents can be calculated.