characterization by x-ray diffraction of polycrystalline diamond samples from different origins...
TRANSCRIPT
Characterization By X-ray Diffraction of Polycrystalline
Diamond Samples from Different Origins
Tshegofatso MoipolaiEnergy Postgraduate
Conference 2013
IntroductionDiamonds • Investigation of natural polycrystalline diamonds remains of
interest to both scientists and researchers as their mechanisms of formation are still under debate
• These mechanisms of formation depend on different pressures and temperatures:o HP and HT - 1 &2o LP and HT - 3o Ultra HT & HP - 4
• Allotrope of carbon • Tetrahedral network of
carbon atoms
Fig. 1. Mechanisms of formation of diamonds found at or near the earth’s surface
Fig.2.Cubic structure of Diamond
Introduction cont..
• Ballaso Occurs in Brazil and Africao Globular aggregates, grey in colour
with negligible poreso Single phase with very few inclusions
Fig.3 The South African Ballas 10 X 10 X 8 mm3
• Carbonadoo Occurs in Brazil ,Central Africa and Soviet Union o Pebble shaped, greyish –black in colour and
porouso Contains secondary phases
Fig 4. The Brazilian Carbonado 14 X 10 X 4 mm3
• Why study this type of diamondo Contribute to the debate around its formation
mechanisms Determination of the near surface
residual stress using x-ray diffraction technique
• Residual stress o Stress that remains in the material when
there is no externally applied force Tensile Compressive
• Residual stress in diamondo Bulk
Extended strain fields having defects dislocations ,bundles of
dislocations stacking faults inclusions plastic deformation surface defects where surface
strain extends to the bulk Inhomogeneous spatial distribution of
point defects concentration gradient of
impuritieso Surface
Termination species Surface processing
chemical and mechanical
Objectives• Characterization investigations:
o SEM: Imaging and EDS of the morphology and elemental composition
o XRD: Chemical phase studies Residual stress of near surface regions
• Motivationo This study presents the new work on near surface residual stress on
naturally occurring polycrystalline diamondo Due to scientific value of samples, no sample preparations could be
applied. Non-destructive investigations essential
o We have a batch of samples from different origins thus enabling comparative studies
• Methodology o SEM
30 kVo XRD
Cu 40kV,40mA
Phase ID
Angle range 15 °-150° Residual Stress
ɸ: 0°,180°,90°,270°,45°,225°Ψ range: 0°-70°
Peak chosen for measurement:311, 92.093°
Mag. 500X
X-Ray Diffraction
2
)(hklF -Structure Factor
-Multiplicity factorhklM
Fig.5 Geometrical illustration of the Bragg’s lawFig.6 A powder X-ray diffraction pattern
sin2
0
211
Y = 0ºY = 10º
Y = 20ºY = 30ºY = 40º
Y = 50ºY = 60ºY = 70ºY = 80ºY = 89.7º
Q211
2211
I
222 22 2222 2
d211
C
2
1 11 22
1s
2sC
Q211Q211
Q211Q211
Q211Q211
Q211Q211
Q211Q211
Q211Q211
Q211Q211
Q211Q211
Q211Q211
Q211Q211 Scattering plane
compressive stress
cot
0
0
d
dd
Results: SEM
Fig. 7 SE& EDS analysis of Carbonado
Fig. 8 SE & EDS analysis of Ballas
Results : XRD Phase ID
Fig.9 The Diffraction pattern of BallasFig.10 The diffraction pattern of Carbonado
Results: Residual Stress
Fig.11 Debye diffraction ring collected using an area detector
• Ballas
Investigations impossible due to:• Large grain size
Uneven intensity distribution around the Debye Scherer ring
Fig.12 Strain vs. sin2Ψ curve of Brazillian Carbonado sample
• Carbonado
Discussions & Results
• EDS: Chemical elements present identified• XRD: Cubic diamond with low content of minority phase . No presence of hexagonal phase• XRD stress: Large spread of values ascribed to:
Irregularities of sample Termination species
• Residual stress on Ballas was not possible due to the presence of large grainsProposed further work
o Detailed neutron diffractiono Detailed synchrotron-XRD
Measurement Position
Elemental composition
Major Minor
Chemical Phase Composition
Major Minor(98%) (< 2%)
Stress σ11
[MPaStress σ22
[MPa]
1 C (89%) O (5%) N (2%) Na (1%) Si (0.5%) Al (0.5%)
Diamond: Cubic Pyrite - FeS Silicon Oxide SiO2
-110 ± 77 -52 ± 84
2 C (84%) Ca (5%) O (6%) Si (2%) Al (1%) Ti (1%)
Diamond: Cubic -285 ± 71 -769 ± 70
3 C (94%) O (3%) Si (1%) Al (1%) N (1%)
Diamond: Cubic-252 ± 62 -90 ± 68
4 C(92%) O (4%) Al (1%) N (1%) Si (1%)
Diamond: Cubic-493 ± 82 218 ± 83
Conclusions
• These results represent amongst the first results of surface residual stress in naturally occurring polycrystalline diamonds
• Despite the irregular surface roughness of these samples, it was possible to get results by careful area selection
• Both tensile and compressive stress could be observed• Theoretical calculations indicate this as expected and can be
ascribed to surface defects and surface chemistry• Surface stress is an interesting new observable for the
characterization of natural diamond samples• The work opens the door for further work to understand the
diamond surface in greater detail in order to develop surface stress analysis as a tool for these studies
Acknowledgements
• Scientific collaborators• Dr. Marco Andreoli for samples• Dr. Remi Bucher (iThemba LABS South for
animations)
References
1. L.F Treub and W.C Butterman, The American Mineralogist 54 (1969) 413- 425
2. www.geology.com Accessed on 08 March 20133. S. De, P.J Hearney, E.P. Vicenzi, J. Wang, Earth and Planetary
Science Letters 185 (2001)4. J.E Butler, Y.A Mankelevich, A. Cheesman, J Ma and M.N.R Ashfold,
J. Phys.: Condens. Matter 21 (2009) 364201 205. Krawitz, A.D., “Introduction to Diffraction in Materials Science and
Engineering”, John Wiley and Sons Inc., (2001), ISBN 0-471-24724-3
6. Hauk, V., ed., “Structural and Residual Stress Analysis by Non-destructive Methods Evaluation, Application, Assessment”, Elsevier, Amsterdam (1997), ISBN 0-444-82476-6