State-of-the-Art BET Surface Area Analysis

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

Mike Pohl
mike.pohl@horiba.com
www.horiba.com/us/particle

© 2010 HORIBA, Ltd. All rights reserved.

Outline

Surface Area Basics

The BET Technique

Measurement Workflow

Recent Advancements


Surface Area Basics


Why Surface Area?

Rates of…
Dissolution
Reaction
Absorption/adsorption
Combustion
Hydration


Porosity

Non-porous solid Porous solid
Low specific surface area High specific surface area
Low specific pore volume High 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
There are three parameters used to measure porosity; specific
surface area, specific pore volume or porosity, and pore size and its
distribution. Total surface area, m2
Specific Surface Area, m 2/g =
Mass of the solid, g

Porosity, % =
Volume of pores
X 100
Porosity Volume of solid (including pores)

Pore size and
its distribution Specific Pore volume, cm3/g
Total pore volume, cm3
=
Mass of the solid, g


Pore Size

Micropores Mesopores Macropores

Zeolite, Mesoporous silica, Sintered metals
Activated Activated carbon and ceramics
carbon,
Metal organic
framework
2 nm 50 nm


Definitions
ABsorption
Gas molecules penetrate mass of a solid

ADsorption
ABsorption
Gas molecules condense on free surfaces

Physisorption
Physical adsorption - van der Waals forces
ADsorption
Chemisorption
Chemical adsorption – chemical bonding

Note: Flowing-gas method uses physisorption


Comparison
Physisorption Chemisorption
Weak, long-range Strong, short-range
Not surface specific Surface specific
Lower energy of Ads. Higher energy of Ads.
Desorption increases Adsorption can
with increasing temp. increase with temp.
Non-reactive at Potentially reactive at
surface surface
Multilayer adsorption Monolayer adsorption
(BET used to model) (Langmuir model)


Physisorption Behavior


Isotherm Types

Type 1 Type 2 Type 3

W t W t W t
Non-porous
Chemisorption or macropore
powders
P / P0 P / P0 P / P0

Type 4 Type 5

W t
W t
Porous
Powders

P / P0 P / P0


Type IV Isotherm


The BET Technique


BET Calculation


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

V = V 1− P P
m a
o
(m ) i.e. V = 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 Multi-point Uncorrected Uncorrected Corrected Corrected
No. BET single-point difference single – difference
(m2/g) (m2/g) (%) point (%)
(m2/g)
1 4.923 4.241 -13.9 4.948 0.51
2 4.286 3.664 -14.5 4.275 -0.26
3 8.056 6.867 -14.8 8.011 -0.56
4 5.957 5.194 -12.8 6.060 +1.73


Method Comparison
Dynamic Static-Volumetric
(Flowing-Gas)
Faster Slower
Easy to use Easy to use
Increased sensitivity Low SSA longer
to low SSA materials measurement times
Higher throughput Lower throughput
Lower operating costs Higher operating costs
Lower service costs Higher service costs


Measurement Workflow


The SA-9600 Surface Area Analyzer

Outgassing station

Analysis stations

Liquid
nitrogen
bath


What You’ll Need
Gases
99.999% pure Helium
99.999% pure Nitrogen
Dry gas

Liquid Nitrogen
Cools material surface for adsorption

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


Workflow
Preparation
Check gas flow
Confirm temperature and pressure
Weigh sample (know how much)
Degas sample (prepare clean surfaces)

Measurement
Automatic calibration
Automatic adsorption and desorption
Automatic calculation of specific surface area
Save, Export, Print report


Recent Advancements


SA-9600 Software

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


SA-9600 Software
5 Measurement Types
3 Gas Mixture Points
6 Gas Mixture Points
13 point Pore Size Dist.
Pore Volume – Multiple
Runs
Single Point – Multiple Runs

Data Graphed on Screen
and Reports


Real-time Measurement

Adsorption

Desorption
Calibration


SA-9600 Security Module

User Name and Password
to Login to Software
Built-in Security with Users
and Groups
Setup Security Settings
Horiba Provides Master
System Administration Key
to Unlock System


21 CFR Part 11 Compliance

Audit Trail capability
Electronic Signature on reports
Analyzer must be controlled from
computer
Certain events require a User name
and Password


Electronic Signature

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.


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.


For More Details

Visit www.horiba.com/us/particle

Contact us directly at labinfo@horiba.com

Visit the Download Center to find this recorded
presentation and many more on other topics


State-of-the-Art BET Surface Area Analysis

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State-of-the-Art BET Surface Area Analysis