Method Comparison Guide

MIP vs Gas Adsorption

Mercury Intrusion Porosimetry and Gas Adsorption (BET/BJH) are complementary techniques with overlapping capabilities in the mesopore range (2-50 nm). Understanding their strengths, limitations, and optimal applications ensures accurate pore characterization across the full micro-to-macro spectrum.

Mercury Intrusion (MIP)

  • • Range: 3 nm – 1,100 μm
  • • Best for: Macropores > 50 nm
  • • Pressure: Up to 414 MPa
  • • Sample state: Destructive (Hg)

Gas Adsorption (BET/BJH)

  • • Range: 0.35 – 300 nm
  • • Best for: Micropores < 2 nm
  • • Temperature: 77 K (N₂)
  • • Sample state: Non-destructive

Detailed Analysis

Side-by-Side Technical Comparison

Parameter Mercury Intrusion Gas Adsorption
Physical Principle Non-wetting liquid forced into pores under pressure Physisorption of gas molecules on surface
Pore Size Range 3 nm – 1,100 μm (macro & meso) 0.35 – 300 nm (micro & meso)
Optimal Range 50 nm – 100 μm (macropores) 0.35 – 50 nm (micro/mesopores)
Surface Area Estimated (geometric assumption) Direct measurement (BET)
Sample Requirements 0.5-5 g solid, must withstand 414 MPa 0.05-2 g powder/solid, degassing needed
Analysis Time 2-4 hours typical 4-8 hours (including degassing)
Destructive? Yes - Mercury contamination No - Sample recoverable
Key Artifacts Ink-bottle effect, compression Micropore filling, tensile strength
Standards ISO 15901-1, ASTM D4284 ISO 9277, ISO 15901-2/3
Typical Cost/Test $200-500 $100-300

Critical Zone

The Mesopore Overlap Region (2-300 nm)

Both techniques can measure mesopores, but with different accuracies and artifacts. Understanding this overlap is crucial for method selection and data validation.

2-10 nm Range

Gas Adsorption Superior

  • • MIP: High pressure artifacts
  • • MIP: Possible pore collapse
  • • GA: DFT provides accuracy
  • • GA: Better for micropores

10-50 nm Range

Both Methods Viable

  • • Compare results for validation
  • • GA: BJH underestimates
  • • MIP: Ink-bottle effects
  • • Use both for complete picture

50-300 nm Range

MIP Preferred

  • • GA: Near upper limit
  • • GA: Long equilibration
  • • MIP: Good accuracy
  • • MIP: Faster analysis

📊 Data Correlation in Overlap Region

When both methods measure the same mesopore range, expect:

  • • Pore volume: MIP typically 10-20% higher due to compression corrections
  • • Mean pore size: BJH underestimates by 20-30% vs. MIP for 10-30 nm pores
  • • Surface area: BET more accurate; MIP assumes smooth cylindrical pores
  • • Distribution width: Similar trends but different absolute values

Selection Guide

Decision Flowchart

START: What do you need to measure?
Surface Area Priority?
↓
Use Gas Adsorption (BET)
Direct, accurate measurement
0.01 - 3000+ m²/g range
Macropores > 50 nm?
↓
Use MIP
Best for 50 nm - 100 μm
Total pore volume focus
Micropores < 2 nm?
↓
Use Gas Adsorption
DFT/NLDFT analysis
Consider Ar at 87 K

Material-Specific Recommendations

Use MIP for:

  • ✓ Cement and concrete
  • ✓ Geological samples
  • ✓ Ceramics and refractories
  • ✓ Paper and textiles
  • ✓ Large-pore membranes
  • ✓ Building materials

Use Gas Adsorption for:

  • ✓ Catalysts
  • ✓ Activated carbons
  • ✓ Zeolites and MOFs
  • ✓ Nanoparticles
  • ✓ Pharmaceutical powders
  • ✓ Battery materials

Best Practices

Using MIP & Gas Adsorption Together

Combining both techniques provides the most complete pore structure characterization, covering 0.35 nm to 1.1 mm — over 6 orders of magnitude.

Complementary Analysis Protocol

  1. Start with Gas Adsorption (non-destructive):
    • Measure BET surface area
    • Determine micropore volume (t-plot/DFT)
    • Analyze mesopore distribution (BJH/DFT)
    • Save sample for other tests
  2. Follow with MIP (destructive):
    • Measure macropore distribution
    • Determine total pore volume
    • Calculate bulk/skeletal density
    • Assess pore connectivity
  3. Data Integration:
    • Use GA for pores < 50 nm
    • Use MIP for pores > 50 nm
    • Compare overlap region for validation
    • Combine for full PSD curve

Real-World Case Studies

Case 1: Catalyst Pellet

Challenge: Bimodal pore structure with micropores for activity and macropores for transport

Solution:
• BET: 250 m²/g surface area
• GA: 0.5-2 nm active sites
• MIP: 100-1000 nm transport pores
• Combined: Complete picture of hierarchical structure

Case 2: Concrete Durability

Challenge: Assess both gel pores and capillary pores for freeze-thaw resistance

Solution:
• GA: 3-10 nm gel pores (C-S-H)
• MIP: 10-100 nm capillary pores
• MIP: Total porosity 12.5%
• Prediction: Good durability based on pore structure

Summary

Key Takeaways

  • 1 No single technique covers all pore sizes — MIP excels at macropores, gas adsorption at micropores
  • 2 The 2-50 nm mesopore range can be measured by both — use both for validation when accuracy is critical
  • 3 For surface area, always use BET — MIP surface area is estimated and less accurate
  • 4 Consider sample recovery needs — gas adsorption is non-destructive, MIP contaminates with mercury
  • 5 Combine techniques for complete characterization — especially for hierarchical or bimodal pore structures

Next Steps

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