Download x-ray powder diffraction

X-RAY POWDER DIFFRACTION
Author: Dr LE SAOUT Gwenn
Contact: [email protected], +41(0) 44 823 44 17
Introduction
Measurement Principle
Experiments
Output for powder
Bragg law
2dhklsinθ = nλ
X-ray
λCuKα = 1.54 A
X- ray diffraction (XRD) is one of the most important
techniques for characterizing cementitious materials.
detector
d-spacing [Å]
5
n=1
4
2
[011]
From the XRD pattern, it is generally possible to
identify and quantify crystalline components
which have over 1%wt in a sample.
[001]
θ
(001)
For quantification, the measured pattern can be fitted
to a theoretical pattern generated from data files on
the crystal structures of the phases (Rietveld
analysis).
[012]
[102]
θ
[010]
[100]
[110]
[111]
d001
20
Quantification of amorphous phase may be also
possible by adding an internal standard in the
powder sample or using an external standard.
30
40
50
Angles 2θ (degrees), CuKα
Relevance for Our Field
● comparison with the Powder Diffraction
File (PDF) database
Ca
O
H
Portlandite
Ca(OH)2
● identification of the crystalline phases in
the powder sample
Example
Mineralogical quantification of cement is necessary to
predict the performances of the resulting concrete.
Hydration of an Ordinary Portland Cement without (PC) and with 4%wt of calcite (PC4) [1]
PC PC4
60
Weight %
Kinetics of hydration of the cement phases can be
followed as well as the kinetics of formation of the
hydrated products. However quantification of the
amorphous content is needed.
40
40
Amorphous
0
12
Weight %
main crystalline hydrated products
- portlandite
Ca(OH)2
- ettringite
Ca6[Al(OH)6]2(SO4)3 26H2O
ill crystallized hydrated products
- monocarbonate [Ca2Al(OH)6] (CO3)0.5 2.5H2O
- C-S-H
Cax Siy zH2O
Amorphous+AFm
60
XRD
Modelling
Alite
20
main crystalline phases in anhydrous Portland cement:
- alite
Ca3SiO5
- belite
Ca2SiO4
- aluminate
Ca3Al2O6
- ferrite
Ca2AlxFe(1-x)O5
8
20
0
Monocarbonate
Monosulfate
Belite
12
Ferrite
Ettringite
8
Aluminate
4
0
Portlandite
4
0
0 0.01
0.1
1
10
100
1000
0.01
0.1
Hydration time (days)
1
10
100
1000
Hydration time (days)
Limitations
Applications & Potentials
• Identification of crystalline components
• No information on the nature of amorphous phase(s)
Alite
6000
Portlandite
• Quantification of the crystalline phases
in anhydrous cement
• Problem of solid solution
Ettringite
Intensity
• Quantification of the crystalline phases
3
as a function of hydration time
• Quantification of the amorphous content
in hydrated cement paste
• In situ experiments using the Thermal Humidity Chamber
4000
Gypsum
• Difficult to assess an error bar
2000
0
400
Ti
m 800
e
(m
in) 1200
10
20
2θ a
(de
ngles
30
40
), Cu
g re e s
Kα
[1] B. Lothenbach, G. Le Saout, E. Gallucci, K. Scrivener, Influence of limestone on the hydration of Portland cements, Cement and Concrete Research 38 (2008) 848-860.
EMPA Concrete / Construction Chemistry Laboratory