Mercury Porosimetry Advantages and Limitations

transcript

Porotec Workshop 15 & 16th Nov. 2004NYSCC Alfred University

Mercury PorosimetryAdvantages and Limitations

Herbert Giesche

New York State College of Ceramics

at Alfred University

Outline:

• Introduction / Theory

• The Measurement Technique– Tips and Tricks – Precision and Accuracy

• What Information do we get?

• Hysteresis

• Pore-Network Models

• Alternative Techniques

But first, “Where on earth is Alfred ?”

What type or size of pore is measured ?Closed Pores Blind Pores Cross-linked Pores Through Pores

In all cases, Hg-Porosimetry measures the largest available access to a pore,the size of the “entrance” towards a pore.

Most times this is substantially smaller than the inner pore diameter!

Theory

=P :equation - Washburnand -Laplace Young21

Essentially all calculations are based on the assumption of cylinder pores.

This is a major assumption !!!

What are the basic parameters to be measured ?

• Pressure

• Intruded volume

• Contact angle, θ

• Surface tension, γ

Pressure

• Pressure transducer have to cover the entire measurement range. (> 5 orders of magnitude !)

• Use several transducer with overlapping ranges.

• Avoid temperature drifts.

• Avoid accidental over-range exposure.

• Calibrate and check with “Standards”

Volume Measurement

• The “antique” techniques: Optically Contact wire Resistance wire

• Nowadays used in essentially all instruments:Precision capacitance bridge

Contact angle (which one ?)

Contact angle (cont.)

• Bashforth-Adams tables

• Max. Height

• Anglometer

cos = 1- g h

Contact angle (cont.)• Adjust θ in order to get close to N2-surface area

Hg-Porosimetry N2-Adsorption

Tungsten powder 0.11 0.10Iron powder 0.20 0.30Zinc dust 0.34 0.32Copper powder 0.34 0.49Silver iodide 0.48 0.53Aluminum dust 1.35 1.14Fluorspar 2.48 2.12Iron oxide 14.3 13.3Anatase 15.1 10.3Graphitized carbon black 15.7 12.3Boron nitride 19.6 20.0Hydroxyapatite 55.2 55.0Carbon black, Spheron-6 107.8 110.0

P V(P) cos

1 darea

This assumes a reversible process !

It is strongly effected by small pores, even in minor quantities !

The Instrument

Sample Cell and Calibration-kit

Tips and Tricks: Sample Preparation• Sample weight ???

• Heat treatment (?)

• Evacuation (final vacuum & time)

• Clean surfaces !

• Choice of ‘best’ penetrometer

• Filling with mercury (head-pressure)

• Use optimum switch-over between‘low’ and ‘high’ pressure port

Tips and Tricks (cont.)

• Artificial pores due to sample positioningstainless steel wire as sample holder and as ‘separator’

• Space filler to reduce compressibility effects and amount of ‘wasted’ mercury.

• Reactive metals (e.g. Zn, Ag, Pb) coated with stearic acidwith Cu a light oxidation might be sufficient

• Watch out for compressibility of the sample:especially with highly porous sol-gel or polymer samples.

Removing Mercury• Repeat measurements on same sample after

removing Hg at > 360°C under vacuum

• Collect spilled Hg with Cu-wire brush (activated with HNO3 and dipping in mercury)“Quecksilber Teufel”

• Or vacuum suction

Precision and Accuracy• < 1 – 2% for “data” in repeat tests• Contact angle uncertainty:

• Surface tension value:Impurities can reduce γHg up to 20%

Temperature has only a minor effect: 2.1 10-4 N/m °C

Pressure: γ (N/m) – 2.66 104 ΔP (MPa) e.g. up to 12% at 200 MPa

• ! Temperature changes by up to 15°C during compression and expansion; volume changes

%28100 153 cos

130 cos - 153 cosor %52 100

115 cos

115 cos - 130 cos

Kinetic Effects• Time for mercury to

move through pores

• Over-pressure is needed• Smaller pore take longer

Example: 110% injection pressure

Pore radius 0.5 to 50 μm

Equilibration rate - example

Pore Volume (cm3/g) Pore diameter (m)

• 0 seconds 0.5823 0.0081

• 2 seconds 0.5938 0.0089

• 10 seconds 0.5939 0.0095

• 30 seconds 0.6161 0.0098

• 0.001 l/g-sec 0.6210 0.0102

Equilibration Kinetics of FCC-catalyst

Equilibration Kinetics of FCC-catalyst (Intrusion)

Equilibration Kinetics of FCC-catalyst (Extrusion)

What Information do we get?• Pore Size (which size ??)

• Pore Volume• Density (bulk, skeletal, or at various stages)

• Compressibility

• Surface Area

• Particle Size

• Pore Shape (?)

• Pore Connectivity (?)

Compressibility

Compressibility (cont.)

• Compressibility

• Surface Area

• Particle Size

• Pore Shape (?)

Particle Size (?)• We use the inter-particle pore size as an estimation of

the particle size (Mayer & Stove)

Particle Size (cont.)

• Pore size particle size (as shown)

This is highly dependent on the particle packing characteristics (particle shape, stickiness, compaction pressure, etc.)

Approximation: pore = 20% of particle size

• Alternatively we use the calculated surface area to convert this into an equivalent particle size

• Compressibility

• Surface Area

• Particle Size

• Pore Shape (?)

Pore Shape and Pore Networks

• Intrusion describes primarily the pore opening or entrance

• Hysteresis is caused by:– Network effects– Pore shape (or pore connections)– Surface properties (contact angle effects)

• Permeability (flow through) provides additional information (check for simulations)

Hysteresis and Pore-Shape

Hysteresis due to Surface ChemistryAlumina sample coated with Cu-sulfate

Intrusion: a) for all samples

Extrusion: b) untreated

c) 0.5% d) 2% e) 40% CuSO4

Network modelsMercury intrusion in model porous media. By C. Tsakiroglou and A. Payatakes; Adv. Colloid Interface Sci; 75, 215-53 (1998)

Network modelsMercury retraction in model porous media.

By C. Tsakiroglou and A. Payatakes; Adv. Colloid Interface Sci; 75, 215-53 (1998)

“Snap-off in ‘lenticular’ Throats”By C. Tsakiroglou and A. Payatakes; Adv. Colloid Interface Sci; 75, 215-53 (1998)

Pore-Connectivity / Network - EffectBy C. Tsakiroglou and A. Payatakes; Adv. Colloid Interface Sci; 75, 215-53 (1998)

Initial stage

↓Final stage

“Energy Barrier Model”

Length Intrusion Extrusion PI/PE

μm MPa MPa

100 0.735 0.726 1.01

10 0.735 0.650 1.13

5 0.735 0.566 1.31

2 0.735 0.309 2.78

1.5 0.735 0.166 7.58

1.4 0.735 0.050 14.66

Conical-Cylinder PoreCylindrical Pore1 μm diameter; Θ = 140°; γ = 0.48 N/m

Pore-Cor Simulation Model

sandstone sample: showing mercury intrusion (grey), after injection by polymer (blue). Yellow volumes are empty.

Generates a 3-D representation of the pore space using information derived directly from mercury intrusion data.

PoreCor data reduction shows:

• porosity • pore connectivity • pore throat correlation • pore tortuosity • absolute gas permeability (gas diffusion through a dry sample) • trapping of non-wetting fluids

Complimentary Porosity Characterization Techniques• Microscopy

• Permeability measurements

• Infiltration tests:– Wood’s metal– Water or other liquids

• CT (computer tomography)

• NMR studies of relaxation times

• Light Scattering, SAXS (and SANS)

Conclusions

• Hg-Porosimetry uniqueness; it covers 5 orders of magnitude; from mm to nm.

• Safety and Environmental concerns; manageable.• Remember: Intrusion = Pore Entrance• Hysteresis may lead to understanding of pore shape

and connectivity.• Work on model pore structures is needed to gain

more understanding.• New simulation software offers great possibilities;

but use with caution !!

Thanks for your interest and

thanks to the organizer for the opportunity to be here!

Literature• H. Giesche; Chapter 2.7 in ‘Handbook of Porous Solids’,

Wiley (2002) Overview article

• H. Giesche, et.al.; Colloid & Surfaces, 37, 93-113 (1989) Ordered silica sphere structures

• C. Tsakiroglou et.al.; Adv. Colloid Interface Sci; 75 215-53 (1998) 2-D model pore structures; experiments & simulations

Others not specifically referenced in this presentation:

• Sean Rigby; numerous publications over the last 5 yearsNetwork models for hysteresis effects; experiments and interpretation

• Peter Matthew; numerous publications over the last 10 years‘Pore Core’ simulation model

• Geoffrey Mason; numerous publications over the last 20 yearsSurface curvature; intrusion and extrusion in simple rod-plate structures

• Powder Technology, Vol. 29 (1981), special issue Hg-porosimetry

Literature• H. Giesche; Chapter 2.7 in ‘Handbook of Porous Solids’,

Wiley (2002) Overview article

• H. Giesche, et.al.; Colloid & Surfaces, 37, 93-113 (1989) Ordered silica sphere structures

• C. Tsakiroglou et.al.; Adv. Colloid Interface Sci; 75 215-53 (1998) 2-D model pore structures; experiments & simulations

Others not specifically referenced in this presentation:

• Sean Rigby; numerous publications over the last 5 yearsNetwork models for hysteresis effects; experiments and interpretation

• Peter Matthew; numerous publications over the last 10 years‘Pore Core’ simulation model

• Geoffrey Mason; numerous publications over the last 20 yearsSurface curvature; intrusion and extrusion in simple rod-plate structures

• Powder Technology, Vol. 29 (1981), special issue Hg-porosimetry

Literature

Thanks for your interest and

thanks to the organizer for the opportunity to be here!

http://people.alfred.edu/~giesche/Publications.htm

Mercury Porosimetry Advantages and Limitations

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