BET
instrument |
|
type |
QUANTACHROME
Quantasorb
|
short
description of method |
Detection
of specific grain surface by nitrogen adsorption at liquid
nitrogen temperature in a flow-through cell. Heat
conductivity detector detects heat conductivity change in
He/N gas mixture after nitrogen adsorption to sample
surfaces at liquid nitrogen temp followed by desorption at
room temperature. |
sample
cells |
Flow-through
cells, quartz glass, access tube diameter 2 mm, cell
volumes 2.5 cm³ / 10 cm³ |
Gas
supply |
10L
cylinder with Gas mixture 30% N in 70 % He
Nitrogen 4.6 for sample preparation and calibration |
sample
preparation |
heating
under Nitrogen flow min. 1 h at 60°C (depends on
sample)
|
sample
size |
Physically
to fit into the sample cell: grains < 2mm,
The small cell has a volume of 2 cm3, the
large one in picture above has 10 cm3.
Assuming a powder sample takes about 50% of the volume:
max. about 2.5 grams (of sediment, density 2.7g/m3)
in normal cell / max. 12.5 grams in large cell.
cube-shaped grains without any porosity or surface
structure should be less than 25µm of sediment if
you use the normal cell and less than 125µm when
you use the big cell. Realistically grain size might be
about a factor 2 larger (thus 50 / 250 µm) due to
irregular shapes, surface structure and/or porosity.
see quick specific area estimate below: small cell: 2.5
*6 / (2.7*25) or large cell: 12.5 * 6 / (2.7 * 125) =
0.22 m2 absolute surface area in cell
|
calibration |
simulation
of desorption peak by injection of appropiate amount of
nitrogen into N/He gas stream
|
detection
limit |
0.2
m² absolute surface ( i.e. 5 grams of sediment
material with a specific surface of 0.04 m²/g or
0.1 gram of a material with a specific surface of 2
m²/g)
|
analysis
time |
1
sample
|
10
similar samples |
6
hours
|
2
days |
quick
estimate |
simple
grain size to specific surface conversion for
cube-shaped particles
A = m * 6/(d*rho)
A - specific surface in m²/g
m - sample mass in g
d - grain size in µm
rho - density in g/cm3
Amount of powder that fits into cell assuming powder
occupies half the volume
m = 0.5 * V * rho
V - sample cell volume in cm3: 2 cm3
for small cell, 10 cm3
for large cell
|
tips
+ tricks |
|
page
updated on |
07Mar23,.
|