In situ analysis of mechanical stress in Al 2 O 3 :Cr (Ruby) and MgO - - PowerPoint PPT Presentation

In situ analysis of mechanical stress in Al2O3:Cr (Ruby) and MgO induced by swift heavy ion irradiation K Bonokwane & N Mayedwa Supervisors: T Strukova, N.S.Kirilkin, V.A.Skuratov

Brief project overview

The irradiation testing of nuclear ceramics and oxides with heavy ions

• f fission fragment energy
• The radioactive waste is one problem which the nuclear power stations

come up against, so the inert matrices fuels were introduced as one of the concepts in reducing the waste.

• The material to be used as inert matrices for transmutation of minor

actinides should be resistant to radiation damage caused by fission fragment The aim of this study is to investigate radiation damage induced by swift heavy ions (E= 1-3 MeV/amu) in several ceramics and single crystals (MgO, Al2O3, ZrO) in order to quantify them as candidates for inert matrices fuel

• One useful method to study the radiation damage is the optical

spectroscopy known as photoluminescence

The experimental work

• Ruby is crystalline alumina (Al2O3) in which a small fraction of the Al3+ ions

have been replaced by chromium ions, Cr3+.

• It is the chromium ions that give rise to the characteristic pink or red color of

ruby and it is in these ions that a population inversion is set up in a ruby laser .

Basis of the piezospectroscopic effect – the applied stress strains the lattice and alters the energy of transitions between electronic states ∆ν = Πij×σij

Πij – piezospectroscopic coefficients

Typical piezospectroscopic probes: Cr3+ in Al2O3

GPa cm

ij

/ 53 . 1 50 . 3 56 . 2

1 −

          = Π

R1-line

GPa cm

ij

/ 16 . 2 80 . 2 65 . 2

1 −

          = Π

R2-line

• D. Clarke et. al. Non-Contact Methods of Measuring

Stresses in High Temperature Materials Hydrostatic stress level σh (GPa) ≈ ∆ν2(cm-1)/7.61

14340 14360 14380 14400 14420 2000 4000 6000 8000 IL signal, a.u

wavenumber, cm

• 1

10

10 cm

• 2

9x0

12 cm

• 2

1.8x0

13 cm

• 2

Xe(167 MeV), 80K

wavenumber, cm-1 Ion fluence, cm-2

! No stress relaxation occurs if Se less than threshold value of damage formation via electronic excitation

Xe

The threshold of damage formation through dense ionization is about 20 keV/nm. B. Canut et al. PRB 51

(1995) 12194. Se=25 keV/nm

Ion fluence, cm-2 wavenumber, cm-1

Kr Xe Bi

Se=41 keV/nm

Se=25 keV/nm Se=16 keV/nm The stresses are compressive in basal plane of the sample and tensile in perpendicular direction

each Cr3+ ion acts as an independent strain sensor The splitting of the R-lines directly indicates on the presence

• f differently stressed regions in the irradiating ruby

specimen

Step heights formed on the surfaces of MgAl2O4 and Al2O3 along a border of masked and 85 MeV I+7 ion irradiated area. Ion fluence 1.2× 1019 m-2.

Examination of the dense ionization effect in ceramics and oxides with heavy ions of fission fragments energy Examination of the dense ionization effect in ceramics and oxides with heavy ions of fission fragments energy

The swelling due to amorphization is estimated to be around 15–20%

• T. Aruga et al. / NIM B 197 (2002) 94–

100

Examination of the dense ionization effect in ceramics and oxides with heavy ions of fission fragments energy Examination of the dense ionization effect in ceramics and oxides with heavy ions of fission fragments energy

No amorphization

• ccurs for MgO

samples even at the fluence of 1.2× 1019 m-2 XTEM image of polycrystalline MgAl2O4 sample irradiated with 85 MeV I+7 ions to 0.28× 1019 m-2 (a) and 1.2× 1019 m-2 (b)

• T. Aruga et al. / NIM B 197 (2002) 94–

100

Summary

Piezospectroscopic method was explored for monitoring of the build up and accumulation of mechanical stresses in alumina irradiated with high energy heavy ions. in situ ionoluminescence reveals high level compressive stresses in Al2O3:Cr crystals. Stress accumulation proceeds in several stages if the electron stopping power exceeds the threshold of radiation damage formation via electronic excitations. It is suggested that ion track region overlapping may stimulate the stress relaxation processes.

Acknowledgements

• National Research Fund (NRF)
• Joint Institute for Nuclear Research (JINR)
• Prof M L Lekala
• Dr N M Jacobs
• M r. N. S. Kirilkin
• M r Vusi M alaza

Thank You