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State-of-the-Art BET Surface AreaAn Introduction to the SA-9600 Technology

Mike Pohlmike.pohl@horiba.com

www.horiba.com/us/particle

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Surface Area Basics

The BET Technique

Measurement Workflow

Recent Advancements

Outline

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Surface Area Basics

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Why Surface Area?

Rates of…

DissolutionReactionAbsorption/adsorptionCombustionHydration

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Non-porous solidLow specific surface areaLow specific pore volume

Porous solidHigh specific surface areaHigh specific pore volume

Porous materials have highly developed internal surface area that can be used to perform a specific function. Almost all solids have some amount of porosity.

Porosity

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Pore size and its distribution

Specific Surface Area, m2/g =

Porosity

There are three parameters used to measure porosity; specific surface area, specific pore volume or porosity, and pore size and its distribution.

Mass of the solid, g

Total surface area, m2

Specific Pore volume, cm3/g

Mass of the solid, g

Total pore volume, cm3

=

Porosity, % =

Volume of solid (including pores)

Volume of poresX 100

Porosity

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2 nm 50 nm

Micropores Mesopores Macropores

Zeolite,Activated carbon,Metal organicframework

Mesoporous silica, Activated carbon

Sintered metals and ceramics

Pore Size

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ABsorptionGas molecules penetrate mass of a solid

ADsorptionGas molecules condense on free surfaces

PhysisorptionPhysical adsorption - van der Waals forces

ChemisorptionChemical adsorption – chemical bonding

ABsorption

ADsorption

Definitions

Note: Flowing-gas method uses physisorption

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Physisorption

Weak, long-rangeNot surface specificLower energy of Ads.Desorption increases with increasing temp.Non-reactive at surfaceMultilayer adsorption (BET used to model)

Chemisorption

Strong, short-rangeSurface specificHigher energy of Ads.Adsorption can increase with temp.Potentially reactive at surfaceMonolayer adsorption (Langmuir model)

Comparison

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Physisorption Behavior

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W t

P / P0

Type 1

Chemisorption

W t

P / P0

Type 2

Non-porous or macropore

powders

W t

P / P0

Type 3

W t

P / P0

Type 4

Porous Powders

W t

P / P0

Type 5

Isotherm Types

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Type IV Isotherm

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The BET Technique

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BET Calculation

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BET Calculation

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Single-point method offers the advantage of simplicity and speed, with acceptable accuracy.

( )oam PPVV −= 1 i.e. Vm = 1/slope

A relative pressure of 0.3 gives good general agreement with the multi-point method.

Correction of single point “error” at P/P0 = 0.3 by multiplying the single point BET value by C/C-2 decreases the difference.

Sample No.

Multi-point BET

(m2/g)

Uncorrected single-point

(m2/g)

Uncorrecteddifference

(%)

Corrected single –

point(m2/g)

Correcteddifference

(%)

1 4.923 4.241 -13.9 4.948 0.51

2 4.286 3.664 -14.5 4.275 -0.263 8.056 6.867 -14.8 8.011 -0.564 5.957 5.194 -12.8 6.060 +1.73

Effect of Multipoint

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Method Comparison

Dynamic (Flowing-Gas)

FasterEasy to useIncreased sensitivity to low SSA materialsHigher throughputLower operating costsLower service costs

Static-Volumetric

SlowerEasy to useLow SSA longer measurement timesLower throughputHigher operating costsHigher service costs

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Measurement Workflow

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Outgassing station

Analysis stations

Liquid nitrogen bath

The SA-9600 Surface Area Analyzer

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What You’ll Need

Gases99.999% pure Helium99.999% pure NitrogenDry gas

Liquid NitrogenCools material surface for adsorption

Mass BalanceInstrument measures total surface area, sample mass is used to convert to SSA

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Workflow

PreparationCheck gas flowConfirm temperature and pressureWeigh sample (know how much)Degas sample (prepare clean surfaces)

MeasurementAutomatic calibrationAutomatic adsorption and desorptionAutomatic calculation of specific surface areaSave, Export, Print report

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Recent Advancements

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Easy to Use SoftwareMulti-tasking – View, Edit and Print Data while Measuring.Measure and Display Window – Similar to LA Products

SA-9600 Software

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5 Measurement Types 3 Gas Mixture Points6 Gas Mixture Points13 point Pore Size Dist.Pore Volume – Multiple RunsSingle Point – Multiple Runs

Data Graphed on Screen and Reports

SA-9600 Software

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Real-time Measurement

Calibration

Adsorption

Desorption

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User Name and Password to Login to SoftwareBuilt-in Security with Users and GroupsSetup Security SettingsHoriba Provides Master System Administration Key to Unlock System

SA-9600 Security Module

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Audit Trail capabilityElectronic Signature on reportsAnalyzer must be controlled from computerCertain events require a User name and Password

21 CFR Part 11 Compliance

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Electronic Signature is the information printed at the Bottom of the report that is automatically generated based on information stored in the file and the current user.

Electronic Signature

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Audit Trail

Audit Trail contains all events related to the creation of data files, editing conditions, printing, etc. It also logs system access information such as login name, login time, and bad passwords.

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