Helium Characteristics and Purity Classification

Helium Characteristics and Purity Classification

Anhui NOY Technology Co., Ltd.

Helium is a colorless, odorless inert gas. Its relative molecular mass is 4.003, molecular diameter is 2.18×10⁻¹⁰ m, and molecular mass is 3.65×10⁻²⁷ kg. At standard conditions, its density is 0.1769 kg/m³, critical temperature is 5.25 K, critical pressure is 2.26×10⁵ Pa, boiling point at 1 atm is 4.214 K, melting point is 0.9 K, triple point temperature is 2.186 K, triple point pressure is 51.1×10⁻² Pa. Its thermal conductivity at standard conditions is 510.79 J/(m·h·K), specific heat at constant pressure is 5233 J/(kg·K), and dynamic viscosity coefficient is 1.86×10⁻⁵ Pa·s. One liter of liquid helium vaporizes to 700 liters of helium gas at standard conditions.

According to national standards, bottled helium is classified into three grades based on purity: industrial helium, pure helium, and high-purity helium.

1. Industrial helium: helium content ≥99%, dew point ≤43°C.

2. Pure helium is divided into three grades:

   - Premium grade: helium content ≥99.995%

   - First grade: helium content ≥99.993%

   - Qualified grade: helium content ≥99.99%

3. High-purity helium is divided into three grades:

   - Premium grade: helium content ≥99.9996%

   - First grade: helium content ≥99.9993%

   - Qualified grade: helium content ≥99.999%

Helium is used as a tracer gas in leak detection. Purity requirements are not critical, and industrial helium is generally selected.

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