IntroductionCategoryDetailsPhysical Properties– Molecular Weight: 4.003 g/mol– Density (Gas): 0
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| Category | Details |
|---|---|
| Physical Properties | – Molecular Weight: 4.003 g/mol |
| – Density (Gas): 0.1785 kg/m³ (0°C, 1 atm); (Liquid): 125 kg/m³ (-269°C) | |
| – Boiling Point: -268.93°C (4.2 K) | |
| – Critical Temperature: -267.96°C (5.19 K) | |
| – Thermal Conductivity: 0.1513 W/m·K (2.7× air) | |
| Technical Specifications | – Purity: 99.995% (4.6 grade, industrial); 99.9995% (5.0 grade, research) |
| – Impurity Limits: O₂ ≤ 0.5 ppm, N₂ ≤ 1 ppm, H₂O ≤ 0.2 ppm (5.0 grade) | |
| – Pressure: 137 bar (20°C, liquid in cylinders); 1 bar (vapor at 25°C) | |
| – Cylinder Sizes: 10L, 50L, 100L (compressed gas); 50L–10.000L (liquid) | |
| – Valve Types: CGA 580 (US), DIN 477 (EU), and JIS B 8241 (Japan) | |
| – Flow Rate: 0.1–50 SLPM (standard liters per minute) | |
| – Purity Analysis: GC-TCD (Gas Chromatography with Thermal Conductivity Detector) | |
| Key Applications | – Cryogenics: Cooling superconducting magnets (MRI, NMR) |
| – Welding: Shielding gas for aluminum/stainless steel (He/Ar mixtures) | |
| – Leak Detection: Pressurized systems (helium mass spectrometry) | |
| – Aerospace: Pressurizing rocket fuel tanks | |
| – Breathing Mixtures: Deep-sea diving (He/O₂ blends) | |
| Safety Data | – CAS No.: 7440-59-7 |
| – UN Number: 1046 (compressed); 1963 (liquid) | |
| – NFPA 704: Health 0. Flammability 0. Reactivity 0 (inert) | |
| – Asphyxiation Risk: Displaces oxygen in confined spaces; monitor O₂ levels (≥19.5%) | |
| – Cryogenic Hazard: Liquid He causes severe frostbite (use PPE: gloves, face shield) | |
| Storage & Handling | – Compressed Gas: Store upright in cool, well-ventilated areas (≤50°C); secure cylinders to prevent falls |
| – Liquid Helium: Use vacuum-insulated dewars; avoid spills (rapid vaporization) | |
| – Ventilation: Ensure airflow in enclosed spaces to prevent CO₂/He buildup | |
| Certifications | – ISO 7291: Gaseous purity standards |
| – ASTM D7673: Cryogenic liquid testing | |
| – OSHA 29 CFR 1910: Cryogenic liquids regulations | |
| Environmental Impact | – Non-Toxic & Inert: Minimal direct environmental impact |
| – Resource Scarcity: Non-renewable (extracted from natural gas); global shortage concerns | |
| – Recycling: Encouraged in MRI/NMR systems to mitigate supply risks | |
| Controllo qualità | – Traceability: Lot-specific certificates of analysis (COA) |
| – Leak Testing: Helium mass spectrometry (≤1×10⁻⁹ atm·cm³/s) | |
| – Shelf Life: 24–36 months (certified stability when stored properly) |
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