Loss on Ignition (LOI) in Perlite — Thermal Stability & Purity Indicators: Loss on Ignition (LOI) represents the percentage of mass lost when perlite is heated to high temperatures (typically 900–1,000°C). LOI reflects moisture, volatile compounds, and organic residues. In expanded perlite, LOI is a key indicator of purity, thermal stability, and expansion quality.
LOI measures the mass loss of perlite during controlled high temperature heating. It includes:
1.1 Free Moisture
• Evaporates at 100–200°C
• Does not affect expansion
• Indicates storage conditions
1.2 Chemically Bound Water
• Released at 850–1,100°C
• Drives expansion
• Critical for density and porosity
1.3 Volatile Impurities
• Organics
• Carbonates
• Hydroxyl groups
High LOI may indicate contamination or incomplete pre drying.
High quality perlite typically shows 2–4% LOI.
3.1 Standard Method: ASTM C114
1. Dry sample at 105°C
2. Heat to 900–1,000°C
3. Record mass loss
4. LOI (%) = (Mass loss / Initial mass) × 100
3.2 Importance of Controlled Heating
• Too fast → spattering
• Too slow → incomplete release
3.3 LOI vs. Bound Water
• LOI includes bound water but also other volatiles.
4.1 Geological Hydration
• Older deposits → higher bound water.
4.2 Weathering
• Increases hydroxyl content.
4.3 Organic Contamination
• Increases LOI beyond normal ranges.
4.4 Storage Conditions
• Humidity increases free moisture.
5.1 Expansion Quality
• Higher LOI → better expansion → lower density.
5.2 Thermal Stability
• Low LOI → stable performance in insulation.
5.3 Filtration
• High LOI may reduce purity.
5.4 Horticulture
• LOI affects pH and chemical stability.
• Hydration history
• Cooling rate
• Glass chemistry
• Deposit age
Deposits with optimal hydration show LOI values ideal for expansion.
Q: Does high LOI always mean better expansion?
Only if volatiles are structural water, not impurities.
Q: Can LOI be reduced artificially?
Yes, through pre drying, but bound water cannot be removed.
Q: Why does bulk density vary between producers?
Differences in hydration and weathering.
