X-ray fluorescence (XRF)

Report
Total Carbon (TC) =
Total Organic Carbon (TOC) + Total Inorganic Carbon (TIC)
Calcite
TOC preparation:
• ~0.25 g dry, powdered sample
• acidified in baked glass beaker with 1N HCl, @ 60 oC for 12-14 hours
• filtered with de-ionized water to flush out Cl- onto a baked glass fiber filter
• transferred to a crucible boat for drying and elemental analysis
Trace elements coprecipitated
with secondary soil
minerals and soil organic matter (SOM)
Solid
Fe and Al oxides
Mn oxides
Ca carbonates
Illites
Smectites
Vermiculites
Organic matter
Coprecipitated trace elements
B, P, V, Mn, Ni, Cu, Zn, Mo, As, Se
P, Fe, Co, Ni, Zn, Mo, As, Se, Pb
P, V, Mn, Fe, Co, Cd
B, V, Ni, Co, Cr, Cu, Zn, Mo, As, Se, Pb
B, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Pb
Ti, Mn, Fe
Al, V, Cr, Mn, Fe, Ni, Cu, Zn, Cd, Pb, P, N
Carmichael Creek, MT
P2O5 (wt. %)
0.3
CCN
south-facing
0.25
0.2
4A
0.15
3A
4A
1A
CCS
north-facing
1A
2A
3A
2A
0.1
0.05
0
0
1
2
3
4
Total Organic Carbon (wt%)
5
X-ray fluorescence
(XRF)
The technology was
developed in the 1950’s.
X-ray fluorescence (XRF):
The emission of characteristic "secondary", or fluorescent, X-rays
from a material that has been excited by bombarding with highenergy X-rays or gamma rays.
www.niton.com/.../primary-x-ray-radiation.jpg
Irradiating an atom with high-energy primary X-ray
photons delivers sufficient energy for an electron to
be ejected completely out of the atom.
An outer shell L electron falls inward to fill the
void created in the inner shell, and an X-ray
characteristic of the atom's elements is
emitted.
X-ray fluorescence (XRF) spectrometers
Bragg’s Law
nλ= 2d * sinΘ
Schematic arrangement of wavelength dispersive spectrometer.
Schematic arrangement of energy dispersive
spectrometer
The dispersion and detection are a single operation. Proportional
counters or various types of solid state detectors (PIN diode, Si(Li),
Ge(Li), Silicon Drift Detector SDD) are used.
http://en.wikipedia.org/wiki/X-ray_fluorescence
Schematic arrangement of a wavelength-dispersive (WD)
X-ray fluorescence (XRF) spectrometer
A.
B.
Various types of detectors most commonly gas flow
proportional and scintillation are used to measure the
intensity of the emitted beam on bench top models.
A.
Gas flow proportional counters are used mainly for detection of longer
wavelengths (lighter elements). The gas is usually 90% argon, 10% methane
("P10"). The argon is ionized by incoming X-ray photons, and the electric field
multiplies this charge into a measurable pulse. The methane suppresses the
formation of fluorescent photons caused by recombination of the argon ions
with stray electrons.
B.
Scintillation counters consist of a scintillating crystal (typically of sodium
iodide doped with thallium) attached to a photomultiplier. The crystal must
be protected with a relatively thick aluminum/beryllium foil window, which
limits the use of the detector to wavelengths below 0.25 nm. Typically used
for heavier elements.
Scintillation - a flash of light produced in certain materials when
they absorb ionizing radiation.
Pressed Powder Disks/Pellets
To obtain good XRF results using the pressed
powder technique, control of particle size is
absolutely critical.
Used primarily for trace
elements and uniform
samples compositions.
Fused Glass Disk
For Major Oxide Analysis
Lithium metaborate flux +
sample in a 7:1 proportion
Fusion in Pt crucible
> 750 oC
Fused glass disk from
gold or brass mould
Sample Preparation
Typical Composition of Grinding Units
Material
Hardened
Steel
Stainless
Steel
Cr-free
Steel
Tungsten
Carbide
Alumina
Ceramic
Major
Elements
Minor
Elements
Hardness Resistance to
(Mohs)
Abrasion
Fe
Cr, Si, Mn, C
5.5-6
Moderate
High
Fe, Cr
Ni, Mn, S, Si
5-5.5
Moderate
High
Fe
C, Mn, Si, Mo
5-5.5
Moderate
High
W, C, Co
Ta, Ti, Nb
8.5 +
High
Long-wearing, but brittle
Al
9
Long-wearing, but brittle
8.5
Agate
Si
Si, Ca, Mg
Al, Na, Fe, K,
Ca, Mg
Zirconia
Silicon
Nitride
Zr
Hf, Mg
8.5
Si
Y, Al, Fe, Ca
8.5 +
Very High
Extremely
High
Extremely
High
Extremely
High
Plastic
C
--
1.5
Low
Available in the Department
Durability
Very long-wearing, but brittle
Very long-wearing
Very long-wearing
Low, but disposable
Trace Elements
Detection limit 2 ppm:
Zr
Pb
Sr
Ni
Rb
Y
Cr
Zn
Nb
Co
Detection limit 5 ppm:
Cu
W
Mo
Th
Detection limit 10 ppm:
U
V
Detection limit 50 ppm:
Ba
Major Oxides
Detection limit 0.02 %:
Al2O3
Fe2O3
P2O5
MnO
TiO2
Loss On Ignition (LOI) is carried out at 1000oC.
Removes
volatiles including carbon, sulfur and nitrogen compounds, and
structural and adsorbed water (H2O).
Detection limit 0.02 %:
LOI wt.% = (sample weight - residue weight) * 100
sample weight
CaO
K2O
Na2O
MgO
SiO2
Laboratory Bench-top Models
Field Hand-held Models
Linear Regressions for Select Trace Elements
using Standard Reference Materials (SRMs)
160
140
120
100
80
60
40
20
0
Nb Regression
300
250
Nb (ppm)
Mo (ppm)
Mo Regression
y = 28.399x
R2 = 0.9894
200
150
y = 17.083x
R2 = 0.9959
100
50
0
0
1
2
3
4
5
0
5
intensity Mo
200
400
intensity Sr
Zr (ppm)
Sr (ppm)
20
Zr Regression
y = 0.0399x
R2 = 0.9348
0
15
intensity Nb
Sr Regression
35
30
25
20
15
10
5
0
10
600
800
1400
1200
1000
800
600
400
200
0
y = 16.189x
R2 = 0.9875
0
20
40
intensity Zr
60
80
PD Soil Profile
Major Oxide
Concentrations (wt.%)
Core #1
Trace Elements
Concentrations (ppm)
Profile Horizons
Al2O3
A
Fe2O3
AB
Na2O
MgO
Bt
Bxta
Bxtb
II Bt
Zr
II Bx
Sr
II Bx2
V
0
5
10
15
20
0 100 200 300 400 500
PD Soil Profile
Major Oxide
Concentrations (wt.%)
Core #1
Trace Elements
Concentrations (ppm)
Profile Horizons
Al2O3
A
Fe2O3
AB
Na2O
MgO
Bt
Bxta
Bxtb
II Bt
Zr
II Bx
Sr
II Bx2
V
0
5
10
15
20
0 100 200 300 400 500

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