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Characterization and stability studies of titanium beryllides
Fusion Engineering and Design 75–79 (2005) 759–763
Characterization and stability studies of titanium beryllides E. Alves a,b,∗ , L.C. Alves a,b , N. Franco a , M.R. da Silva b , A. Pa´ul c , J.B. Hegeman d , F. Druyts e a
Instituto Tecnol´ogico e Nuclear, Departamento de F´ısica, EN 10, 2686-953 Sacav´em, Portugal b CFNUL, University of Lisbon, Av. Prof. Gama Pinto 2, 1699 Lisbon, Portugal c Instituto de Ciencia de Materiales, Av. Americo Vespucio s/n, 41092 Sevilla, Portugal d NRG, P.O. Box 25, 1755 ZG, Petten, The Netherlands e SCK·CEN, The Belgian Nuclear Research Center, Boeretang 200, B-2400 Mol, Belgium Available online 3 August 2005
Abstract Beryllides appear as potential candidates to replace Be in future fusion power plants due to their improved properties. However, while the fabrication and properties of beryllium are well established a lack of knowledge still exists for beryllides. In this work, we present a detailed characterization of titanium beryllides, provided by JAERI in the frame of the IEA agreement, using a large number of techniques. Compositions of Be–5 at% Ti and Be–7 at% Ti were used to produce the samples. High resolution X-ray diffraction clearly shows the formation of Be10 Ti phase for the Be–7 at% Ti composition. For the Be–5 at% Ti, the major phase is Be12 Ti with traces of a Be-rich phase. In both cases, no evidence was found for the presence of pure Be phase in the samples. Ti elemental maps obtained with a scanning nuclear microprobe reveals the presence of regions containing large amounts of Cr, Mn, Fe, Ni, Cu and in some cases U. These impurities are common in Be and this behaviour suggests that a segregation process occurs during the beryllide formation. Moreover, the RBS spectra also show the presence of oxygen in this region while it seems to be depleted from the beryllide bulk. The oxidation seems to occur preferentially along the beryllide boundaries and Ti depleted region. © 2005 Published by Elsevier B.V. Keywords: Beryllides; Nuclear microprobe; X-ray diffraction; Scanning electron microscopy
1. Introduction Beryllium is among the best choices as neutron multiplier to increase the tritium breeding ratio (TBR) in the next generation of fusion reactors based on solid ∗ Corresponding author. Tel.: +351 219946086; fax: +351 219941525. E-mail address: [email protected] (E. Alves).
0920-3796/$ – see front matter © 2005 Published by Elsevier B.V. doi:10.1016/j.fusengdes.2005.06.145
lithium breeder ceramics. The next step towards fusion power plants is the construction of the International Thermonuclear Experimental Reactor (ITER) where the reference breeding blanket design foresees the use of beryllium as a plasma-facing component and as a neutron multiplier in the form of a pebble bed [1]. In fact, the design of such breeder blanket using lithium ceramics pebbles and RAFM steel as structural material foresees the use of Be pebble beds. Since pure
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E. Alves et al. / Fusion Engineering and Design 75–79 (2005) 759–763
beryllium becomes brittle and swells under neutron irradiation, its use in the form of beryllides offers various advantages [1–3]. Moreover in the water cooled design there are safety concerns in the case of a loss-of-coolant accident (LOCA). The exothermal reaction between hot beryllium and steam, producing hydrogen gas (Be + H2 O → BeO + H2 + heat) must be prevented [4]. At low temperatures (up to approximately 600 ◦ C) the oxidation of beryllium forms a protective oxide layer on the surface of the metallic beryllium and the oxidation rate decreases with time. When the temperature exceeds a critical value (typically around 700 ◦ C) oxidation becomes non-protective and proceeds until the beryllium is depleted [5]. In view of the intrinsic safety of ITER and DEMO whose blanket will withstand temperatures in the 600–900◦ C range, beryllides will appear as a viable alternative to metallic beryllium. In this work, we present a detailed study of structural stability of titanium beryllides and the oxidation behaviour under air annealing. Both high resolution Xray diffraction and microbeam techniques were used to follow the evolution of the composition and phases. The microstructure was studied with scanning electron microscopy.
2. Experimental details The material used in this study consisted of two beryllium alloys provided by JAERI in the frame of the IEA agreement. Compositions of Be–5 at% Ti and Be–7 at% Ti were used to produce the samples. The alloys were prepared by arc-melting under an inert atmosphere (argon). Small pieces were cut from the as-cast material and studied before and after annealing at 600 and 800 ◦ C in dry air. The impurity content and oxide layer were monitored with Rutherford backscattering spectrometry (RBS) and particle induce X-ray emission (PIXE) techniques. H+ and He+ microbeams (∼3 m) were used to scan the samples surface and the backscattered particles and X-rays were collected with a surface barrier and Si(Li) detectors, respectively. The major impurities are indicated in Table 1. High resolution X-ray diffraction studies were done using a 18 kW rotating Cu anode X-ray generator, with a flat Ge(4 4 4) monochromator in an achromatic
Table 1 Average impurity content of the Be–5 at% Ti sample Element
Concentration
Cr Mn Fe Ni Cu Zn Zr U
115 165 740 170 80 10 120 200
The results are expressed in g/g and were obtained from a scan spectrum of 530 m × 530 m.
geometry. All measurements were performed in a Theta–2Theta geometry with a Phi sample rotation (0–360◦ ), allowing a better crystals homogeneity. It was used 8 kW (40 kV, 200 mA) X-ray power with a spot size of 0.1 mm × 2 mm, the radiation was detected by the position sensitive detector (PSD) covering a 7◦ range with an ADC of 512 channels for 3600 s per step, from 30◦ to 84◦ . Scanning electron microscopy was used to study the microstructure.
3. Results and discussion The as-cast samples indicate the presence of several impurities as revealed by PIXE and indicated in Table 1. The major impurities found using this technique are Fe and U, whereas RBS spectra also reveal the presence of O. The elemental maps for the Be–5 at% Ti alloy clearly show the existence of a regular distribution of Ti-rich regions surrounded by Be-rich islands (see Fig. 1). The boundaries of these Ti regions are enriched in Be as well as in Fe and O (cf. Fig. 4b) while U seems to be homogeneously distributed all over the entire sample. It was also visible the presence of several Fe-rich precipitates embedded in the Be-rich regions. This type of microstructure was not so evident for the Be–7 at% Ti alloy. Despite the presence of the same impurities in the analyzed samples the Ti map (not shown) indicates a homogeneous distribution. The presence of uranium in such concentrations in the as-cast samples, although not mentioned in previous reports [6], must be taken into account when applications are foreseen. According to our results, there is no evidence for uranium segregation to the grain boundaries during phase precipitation. On the contrary both
E. Alves et al. / Fusion Engineering and Design 75–79 (2005) 759–763
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The elemental distribution measured with the microprobe follows the microstructure revelled by the SEM images (Fig. 2). The Be–5 at% Ti photograph reveal the presence of a two-phase structure consisting mainly on
Fig. 1. 530 m × 530 m Ti, Fe and U elemental maps obtained from an as-cast Be–5 at% Ti compound. The concentration of Fe in the Ti depleted regions is evident. Uranium is homogeneously distributed over the entire analyzed region. The lines are to guide the eye.
Fe and O are concentrated mainly in the Ti depleted regions. Taking into account these results it seems that the formation of one-phase system is favoured for the Be–7 at% Ti mixture while for the Be–5 at% Ti two phases are clearly visible in the near surface region of the samples.
Fig. 2. SEM plan view images, showing the microstructure of: (a) Be–7% Ti, (b) Be–5% Ti and (c) Be–5% Ti after annealing at 800 ◦ C 1 h.
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Fig. 3. As-cast XRD patterns of: (a) Be–7% Ti alloy, (b) Be–5% Ti alloy and (c) Be–5% Ti after annealing at 800 ◦ C 1 h. Phase identification was performed appealing to International Centre for Diffraction Data (ICDD) database and all spectra were normalized and vertical shifted for better visualization.
Be12 Ti and a Be-rich zone as indicate by EDS and in agreement with the microbeam results. The image from the Be–7 at% Ti alloy shows a homogeneous structure with a granular shaped surface, which was also observed in the microprobe. X-ray diffraction analysis was performed in order to identify the phases present in the samples for both alloys (Fig. 3). While in the Be–5 at% Ti mixture we detected the formation of Be12 Ti for the Be–7 at% Ti alloy only the phase Be10 Ti was clearly identified. The formation of these phases was also observed by other authors in Be–Ti binary systems [7]. To get information on phase stability and oxidation behaviour we annealed the Be–5 at% Ti up to 800 ◦ C under a dry air atmosphere. The RBS spectra obtained before and after the annealing are shown in Fig. 4. Fig. 4a shows the spectra obtained in the Ti-rich region. The presence of an Oxygen peak is visible immediately after 1 h annealing at 600 ◦ C. Further annealing at 800 ◦ C almost double the peak intensity and a small carbon signal is observed. The analysis in the Ti depleted region indicates higher oxygen content after the 600 ◦ C annealing (Fig. 4b). This results point out for an enhancement of the oxidation rate in the Be-rich region together with some impurity redistribution. Despite the growth of the oxide layer no evidence was found of cracks in the surface. The SEM micrograph indicates a smooth surface without any trace of morphology changes during the annealing. Moreover,
Fig. 4. RBS spectra obtained from: (a) Be12 Ti region and (b) Ti depleted region for the Be–5% Ti alloy before and after annealing. The increase of the oxygen signal is evident and more pronounced on the region with low Ti content.
during the annealing we did not observe any noticeable change on the beryllide phases. This is in agreement with the proposed equilibrium phase diagram [7] where, although the narrow concentration range, the Be12 Ti phase is expected to exist up to 1500 ◦ C. A detailed analysis (Fig. 3) of the XRD spectrum seems to indicate the presence of small peaks, which could be related with the presence of the BeO phase after the annealing. The RBS clearly shows the increase of the oxygen signal during the thermal treatments. Comparing the spectra from the beryllide and intergranular regions we can conclude that the amount of oxygen is higher outside the beryllide grains suggesting a faster oxidation rate in the region. Sato et al. claim that a protective layer of BeO grows on the top of the beryllide layer [8]. This layer prevents further grow of the oxide scale even after
E. Alves et al. / Fusion Engineering and Design 75–79 (2005) 759–763
25 h at 1000 ◦ C in dry air. However, our results indicate a continuous increase of oxygen during the different annealing stages. These results put in evidence the need for further studies to clarify the oxidation behaviour of these alloys and the role of the microstructure in this process.
4. Conclusions Beryllium–titanium intermetallic compounds were produced using a nominal composition of Be–5 at% Ti and Be–7 at% Ti. In the as-cast samples, Be10 Ti was the major phase formed in the Be–7 at% Ti sample and Be12 Ti for the Be–5 at% Ti sample. The Be–5 at% Ti alloy reveals intra-grain regions with high concentration of impurities (O, Fe and Ni) and Ti depletion. During thermal treatments up to 800 ◦ C for 1 h the phase stability was confirmed. Oxidation occurs preferentially at the beryllide grain boundaries, but a continuous increase of oxygen was found in the beryllide grains.
Acknowledgments This study was done in the framework of the fusion programme of IST/ITN and was supported by the
763
European Union within European Fusion Technology Programme. We also acknowledge JAERI for providing the samples in the frame of the IEA agreement.
References [1] M. Dalle Donne, G.R. Longhurst, H. Kawamura, F. ScaffidiArgentina, Beryllium R&D for blanket application, in: Proceedings of the 8th International Conference on Fusion Reactor Materials, Sendai, October 26–31, 1997. [2] E. Alves, A.A. Melo, L.C. Alves, J.C. Soares, M.F. da Silva, Final Report, ITER Task No.: BL16.5-3, Association EURATON/IST, December 1999. [3] E. Alves, A.A. Melo, L.C. Alves, J.C. Soares, M.F. da Silva, F. Scaffidi-Argentina, Fusion Technol. 38 (2000) 320. [4] F. Dryts, E. Alves, C.H. Wu, Proceedings of the 6th IEA International Workshop on Beryllium Technology for Fusion, Miyazaki, 2004, p. 103. [5] S. Zalkind, M. Polak, N. Shamir, Surf. Sci. 513 (2002) 501. [6] Y. Mishima, K. Yamamoto, Y. Kimura, M. Uchida, H. Kawamura, Proceedings of the 6th IEA International Workshop on Beryllium Technology for Fusion, Miyazaki, 2004, p. 203. [7] I. Ohnuma, R. Kainuma, M. Uda, T. Iwadachi, M. Uchida, H. Kawamura, K. Ishida, Proceedings of the 6th IEA International Workshop on Beryllium Technology for Fusion, Miyazaki, 2004, p. 172. [8] Y. Sato, M. Uchida, H. Kawamura, Proceedings of the 6th IEA International Workshop on Beryllium Technology for Fusion, Miyazaki, 2004, p. 203.
Characterization and stability studies of titanium beryllides E. Alves a,b,∗ , L.C. Alves a,b , N. Franco a , M.R. da Silva b , A. Pa´ul c , J.B. Hegeman d , F. Druyts e a
Instituto Tecnol´ogico e Nuclear, Departamento de F´ısica, EN 10, 2686-953 Sacav´em, Portugal b CFNUL, University of Lisbon, Av. Prof. Gama Pinto 2, 1699 Lisbon, Portugal c Instituto de Ciencia de Materiales, Av. Americo Vespucio s/n, 41092 Sevilla, Portugal d NRG, P.O. Box 25, 1755 ZG, Petten, The Netherlands e SCK·CEN, The Belgian Nuclear Research Center, Boeretang 200, B-2400 Mol, Belgium Available online 3 August 2005
Abstract Beryllides appear as potential candidates to replace Be in future fusion power plants due to their improved properties. However, while the fabrication and properties of beryllium are well established a lack of knowledge still exists for beryllides. In this work, we present a detailed characterization of titanium beryllides, provided by JAERI in the frame of the IEA agreement, using a large number of techniques. Compositions of Be–5 at% Ti and Be–7 at% Ti were used to produce the samples. High resolution X-ray diffraction clearly shows the formation of Be10 Ti phase for the Be–7 at% Ti composition. For the Be–5 at% Ti, the major phase is Be12 Ti with traces of a Be-rich phase. In both cases, no evidence was found for the presence of pure Be phase in the samples. Ti elemental maps obtained with a scanning nuclear microprobe reveals the presence of regions containing large amounts of Cr, Mn, Fe, Ni, Cu and in some cases U. These impurities are common in Be and this behaviour suggests that a segregation process occurs during the beryllide formation. Moreover, the RBS spectra also show the presence of oxygen in this region while it seems to be depleted from the beryllide bulk. The oxidation seems to occur preferentially along the beryllide boundaries and Ti depleted region. © 2005 Published by Elsevier B.V. Keywords: Beryllides; Nuclear microprobe; X-ray diffraction; Scanning electron microscopy
1. Introduction Beryllium is among the best choices as neutron multiplier to increase the tritium breeding ratio (TBR) in the next generation of fusion reactors based on solid ∗ Corresponding author. Tel.: +351 219946086; fax: +351 219941525. E-mail address: [email protected] (E. Alves).
0920-3796/$ – see front matter © 2005 Published by Elsevier B.V. doi:10.1016/j.fusengdes.2005.06.145
lithium breeder ceramics. The next step towards fusion power plants is the construction of the International Thermonuclear Experimental Reactor (ITER) where the reference breeding blanket design foresees the use of beryllium as a plasma-facing component and as a neutron multiplier in the form of a pebble bed [1]. In fact, the design of such breeder blanket using lithium ceramics pebbles and RAFM steel as structural material foresees the use of Be pebble beds. Since pure
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E. Alves et al. / Fusion Engineering and Design 75–79 (2005) 759–763
beryllium becomes brittle and swells under neutron irradiation, its use in the form of beryllides offers various advantages [1–3]. Moreover in the water cooled design there are safety concerns in the case of a loss-of-coolant accident (LOCA). The exothermal reaction between hot beryllium and steam, producing hydrogen gas (Be + H2 O → BeO + H2 + heat) must be prevented [4]. At low temperatures (up to approximately 600 ◦ C) the oxidation of beryllium forms a protective oxide layer on the surface of the metallic beryllium and the oxidation rate decreases with time. When the temperature exceeds a critical value (typically around 700 ◦ C) oxidation becomes non-protective and proceeds until the beryllium is depleted [5]. In view of the intrinsic safety of ITER and DEMO whose blanket will withstand temperatures in the 600–900◦ C range, beryllides will appear as a viable alternative to metallic beryllium. In this work, we present a detailed study of structural stability of titanium beryllides and the oxidation behaviour under air annealing. Both high resolution Xray diffraction and microbeam techniques were used to follow the evolution of the composition and phases. The microstructure was studied with scanning electron microscopy.
2. Experimental details The material used in this study consisted of two beryllium alloys provided by JAERI in the frame of the IEA agreement. Compositions of Be–5 at% Ti and Be–7 at% Ti were used to produce the samples. The alloys were prepared by arc-melting under an inert atmosphere (argon). Small pieces were cut from the as-cast material and studied before and after annealing at 600 and 800 ◦ C in dry air. The impurity content and oxide layer were monitored with Rutherford backscattering spectrometry (RBS) and particle induce X-ray emission (PIXE) techniques. H+ and He+ microbeams (∼3 m) were used to scan the samples surface and the backscattered particles and X-rays were collected with a surface barrier and Si(Li) detectors, respectively. The major impurities are indicated in Table 1. High resolution X-ray diffraction studies were done using a 18 kW rotating Cu anode X-ray generator, with a flat Ge(4 4 4) monochromator in an achromatic
Table 1 Average impurity content of the Be–5 at% Ti sample Element
Concentration
Cr Mn Fe Ni Cu Zn Zr U
115 165 740 170 80 10 120 200
The results are expressed in g/g and were obtained from a scan spectrum of 530 m × 530 m.
geometry. All measurements were performed in a Theta–2Theta geometry with a Phi sample rotation (0–360◦ ), allowing a better crystals homogeneity. It was used 8 kW (40 kV, 200 mA) X-ray power with a spot size of 0.1 mm × 2 mm, the radiation was detected by the position sensitive detector (PSD) covering a 7◦ range with an ADC of 512 channels for 3600 s per step, from 30◦ to 84◦ . Scanning electron microscopy was used to study the microstructure.
3. Results and discussion The as-cast samples indicate the presence of several impurities as revealed by PIXE and indicated in Table 1. The major impurities found using this technique are Fe and U, whereas RBS spectra also reveal the presence of O. The elemental maps for the Be–5 at% Ti alloy clearly show the existence of a regular distribution of Ti-rich regions surrounded by Be-rich islands (see Fig. 1). The boundaries of these Ti regions are enriched in Be as well as in Fe and O (cf. Fig. 4b) while U seems to be homogeneously distributed all over the entire sample. It was also visible the presence of several Fe-rich precipitates embedded in the Be-rich regions. This type of microstructure was not so evident for the Be–7 at% Ti alloy. Despite the presence of the same impurities in the analyzed samples the Ti map (not shown) indicates a homogeneous distribution. The presence of uranium in such concentrations in the as-cast samples, although not mentioned in previous reports [6], must be taken into account when applications are foreseen. According to our results, there is no evidence for uranium segregation to the grain boundaries during phase precipitation. On the contrary both
E. Alves et al. / Fusion Engineering and Design 75–79 (2005) 759–763
761
The elemental distribution measured with the microprobe follows the microstructure revelled by the SEM images (Fig. 2). The Be–5 at% Ti photograph reveal the presence of a two-phase structure consisting mainly on
Fig. 1. 530 m × 530 m Ti, Fe and U elemental maps obtained from an as-cast Be–5 at% Ti compound. The concentration of Fe in the Ti depleted regions is evident. Uranium is homogeneously distributed over the entire analyzed region. The lines are to guide the eye.
Fe and O are concentrated mainly in the Ti depleted regions. Taking into account these results it seems that the formation of one-phase system is favoured for the Be–7 at% Ti mixture while for the Be–5 at% Ti two phases are clearly visible in the near surface region of the samples.
Fig. 2. SEM plan view images, showing the microstructure of: (a) Be–7% Ti, (b) Be–5% Ti and (c) Be–5% Ti after annealing at 800 ◦ C 1 h.
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Fig. 3. As-cast XRD patterns of: (a) Be–7% Ti alloy, (b) Be–5% Ti alloy and (c) Be–5% Ti after annealing at 800 ◦ C 1 h. Phase identification was performed appealing to International Centre for Diffraction Data (ICDD) database and all spectra were normalized and vertical shifted for better visualization.
Be12 Ti and a Be-rich zone as indicate by EDS and in agreement with the microbeam results. The image from the Be–7 at% Ti alloy shows a homogeneous structure with a granular shaped surface, which was also observed in the microprobe. X-ray diffraction analysis was performed in order to identify the phases present in the samples for both alloys (Fig. 3). While in the Be–5 at% Ti mixture we detected the formation of Be12 Ti for the Be–7 at% Ti alloy only the phase Be10 Ti was clearly identified. The formation of these phases was also observed by other authors in Be–Ti binary systems [7]. To get information on phase stability and oxidation behaviour we annealed the Be–5 at% Ti up to 800 ◦ C under a dry air atmosphere. The RBS spectra obtained before and after the annealing are shown in Fig. 4. Fig. 4a shows the spectra obtained in the Ti-rich region. The presence of an Oxygen peak is visible immediately after 1 h annealing at 600 ◦ C. Further annealing at 800 ◦ C almost double the peak intensity and a small carbon signal is observed. The analysis in the Ti depleted region indicates higher oxygen content after the 600 ◦ C annealing (Fig. 4b). This results point out for an enhancement of the oxidation rate in the Be-rich region together with some impurity redistribution. Despite the growth of the oxide layer no evidence was found of cracks in the surface. The SEM micrograph indicates a smooth surface without any trace of morphology changes during the annealing. Moreover,
Fig. 4. RBS spectra obtained from: (a) Be12 Ti region and (b) Ti depleted region for the Be–5% Ti alloy before and after annealing. The increase of the oxygen signal is evident and more pronounced on the region with low Ti content.
during the annealing we did not observe any noticeable change on the beryllide phases. This is in agreement with the proposed equilibrium phase diagram [7] where, although the narrow concentration range, the Be12 Ti phase is expected to exist up to 1500 ◦ C. A detailed analysis (Fig. 3) of the XRD spectrum seems to indicate the presence of small peaks, which could be related with the presence of the BeO phase after the annealing. The RBS clearly shows the increase of the oxygen signal during the thermal treatments. Comparing the spectra from the beryllide and intergranular regions we can conclude that the amount of oxygen is higher outside the beryllide grains suggesting a faster oxidation rate in the region. Sato et al. claim that a protective layer of BeO grows on the top of the beryllide layer [8]. This layer prevents further grow of the oxide scale even after
E. Alves et al. / Fusion Engineering and Design 75–79 (2005) 759–763
25 h at 1000 ◦ C in dry air. However, our results indicate a continuous increase of oxygen during the different annealing stages. These results put in evidence the need for further studies to clarify the oxidation behaviour of these alloys and the role of the microstructure in this process.
4. Conclusions Beryllium–titanium intermetallic compounds were produced using a nominal composition of Be–5 at% Ti and Be–7 at% Ti. In the as-cast samples, Be10 Ti was the major phase formed in the Be–7 at% Ti sample and Be12 Ti for the Be–5 at% Ti sample. The Be–5 at% Ti alloy reveals intra-grain regions with high concentration of impurities (O, Fe and Ni) and Ti depletion. During thermal treatments up to 800 ◦ C for 1 h the phase stability was confirmed. Oxidation occurs preferentially at the beryllide grain boundaries, but a continuous increase of oxygen was found in the beryllide grains.
Acknowledgments This study was done in the framework of the fusion programme of IST/ITN and was supported by the
763
European Union within European Fusion Technology Programme. We also acknowledge JAERI for providing the samples in the frame of the IEA agreement.
References [1] M. Dalle Donne, G.R. Longhurst, H. Kawamura, F. ScaffidiArgentina, Beryllium R&D for blanket application, in: Proceedings of the 8th International Conference on Fusion Reactor Materials, Sendai, October 26–31, 1997. [2] E. Alves, A.A. Melo, L.C. Alves, J.C. Soares, M.F. da Silva, Final Report, ITER Task No.: BL16.5-3, Association EURATON/IST, December 1999. [3] E. Alves, A.A. Melo, L.C. Alves, J.C. Soares, M.F. da Silva, F. Scaffidi-Argentina, Fusion Technol. 38 (2000) 320. [4] F. Dryts, E. Alves, C.H. Wu, Proceedings of the 6th IEA International Workshop on Beryllium Technology for Fusion, Miyazaki, 2004, p. 103. [5] S. Zalkind, M. Polak, N. Shamir, Surf. Sci. 513 (2002) 501. [6] Y. Mishima, K. Yamamoto, Y. Kimura, M. Uchida, H. Kawamura, Proceedings of the 6th IEA International Workshop on Beryllium Technology for Fusion, Miyazaki, 2004, p. 203. [7] I. Ohnuma, R. Kainuma, M. Uda, T. Iwadachi, M. Uchida, H. Kawamura, K. Ishida, Proceedings of the 6th IEA International Workshop on Beryllium Technology for Fusion, Miyazaki, 2004, p. 172. [8] Y. Sato, M. Uchida, H. Kawamura, Proceedings of the 6th IEA International Workshop on Beryllium Technology for Fusion, Miyazaki, 2004, p. 203.