Bulk density of sulfur powder is divided into loose bulk density (freely poured, uncompacted) and tapped bulk density (after vibration/compaction). Values vary significantly with particle size (mesh fineness), particle size distribution, and compaction state.
Standard Values by Particle Size
1. Conventional industrial sulfur powder (100–200 mesh / 75–150 μm)
This is the most common grade from standard dry grinding:
- Loose bulk density: 0.9 – 1.1 g/cm³ (900 – 1100 kg/m³)
- Tapped bulk density: 1.2 – 1.4 g/cm³ (1200 – 1400 kg/m³)
This range aligns with Chinese national standard GB/T 2449.3-2021 for industrial sulfur powder testing, and matches typical bulk handling data for general-purpose ground sulfur.
2. Fine sulfur powder (325 mesh / ~45 μm)
Widely used in rubber compounding, agriculture and fine chemical applications:
- Loose bulk density: 0.6 – 0.8 g/cm³
- Typical commercial rubber-grade 325-mesh sulfur is specified at approximately 0.65 ± 0.1 g/cm³ in loose form.
3. Ultrafine / micronized sulfur powder (d₅₀ < 10 μm)
Produced by jet milling or deep ultrafine grinding:
- Loose bulk density: 0.3 – 0.6 g/cm³
The extremely high specific surface area and inter-particle voids result in very low bulk density, and the powder is highly prone to fluidization and dust formation during handling.
Key Reference: True Density
The true (solid) density of orthorhombic elemental sulfur (the stable form in standard ground powder) is a fixed physical property at 2.06 – 2.07 g/cm³, independent of particle size. Bulk density is always lower because it includes air gaps between powder particles.
Factors That Change Bulk Density
- Finer particle size → lower loose bulk density: More interstitial air is trapped between smaller particles.
- Wider particle size distribution → higher bulk density: Fine particles fill gaps between coarser particles.
- Compaction / vibration: Tapping or mechanical compaction can increase bulk density by 20–40%.
- Anti-caking or flow additives: Surface-treated sulfur grades may have slightly different bulk density due to coating agents.
