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Electrochemical behaviour of boron-implanted nickel surfaces
Surface and Coatings Technology, 46 (1991) 103—109
103
Electrochemical behaviour of boron-implanted nickel surfaces J. Takadoum Laboratoire de Microanalyse des Surfaces, ENSMM 25030 Besancon Cédex (Prance)
(Received June 20, 1990)
Abstract The influence ofthe addition of boron on the corrosion of nickel in sulphuric acid medium has been studied in pure binary alloys obtained by ion implantation. No beneficial effect of the structure was observed when the implanted dose of boron was high enough to produce an amorphous state. The passive current density i~,increased with the implanted boron concentration. A.c. impedance measurements were performed through which it was possible to show that boron impedes nickel passivation by preventing the formation of the intermediate species (NiOH),~which precedes the growth of an oxide film.
1. Introduction
Ion implantation as a surface alloying technique offers the possibility of obtaining coatings with excellent mechanical and physical properties [1—41. By doping metallic surfaces with suitable elements the corrosion rates may be significantly reduced [5, 6]. In addition, when the implanted doses are high enough amorphous phases may be produced [7—9]. Amorphous alloys in general have excellent corrosion resistance because of the rapid formation of a homogeneous protective passive ifim [10—12]. The chemically homogeneous single-phase nature of amorphous alloys is an important factor in their electrochemical behaviour, but it is not the only decisive one. Several authors have shown that the protective quality of the surface film depends on the chemical composition of the alloy [13—15]. Corrosion studies have been focused on amorphous alloys obtained by rapid quenching. These materials are often of complex composition and contain inclusions and impurities. Their surfaces are rough, but cannot be polished mechanically since the outermost layers crystaffize during such treatment [16]. In contrast, amorphous films obtained by ion implantation are pure and have simple compositions. This makes it possible to study the chemical effect of the added element and of the structure. In the present paper we attempt to study the influence of the respective effects of radiation damage to nickel surfaces implanted with low boron concentrations, of amorphous clusters formed at intermediate fluences, and of complete amorphization at high fluences, on the anodic behaviour of Ni—B 0257-8972/91/$3.50
© Elsevier Sequoia/Printed in The Netherlands
104
“multi-energy” implanted layers with relatively uniform concentration over a depth of 250 urn, using polarization curves and impedance diagrams. 2. Experimental details The surface of pure (99.999%) polycrystalline nickel, previously polished, first with diamond pastes down to 1 j.tm and then electrolytically, was implanted with increasing doses of ‘1B~ions. Implantation was performed using an Orsay machine, designed to implant well-resolved mass-filtered beams under a vacuum of 10-8 Torr [17]. In order to obtain a uniform concentration of boron over a larger depth (250 urn), boron implantation was carried out at three different energies (180, 70 and 20 keY) with increasing doses. Implantation parameters are given in Table 1, where R 0 is the mean projected range of the implanted ion and C(RP) the maximum boron concentration at a depth R~. The purity and depth composition of the implanted layers were analysed by glow discharge optical spectrometry (GDOS), secondary ion mass spec. trometry (SIMS) and Rutherford backscattering spectrometry (RBS) (Fig. 1). The proffles for implantations at single energies are discussed in ref. 18. The experimental values of R~are in good agreement with the calculated ones, but the distributions are significantly wider than the theory predicts, and thus the concentrations G(R~)are lower than their calculated values (Table 1). The theoretical concentrations of implanted boron given in colunrn 5 of Table 1 are cumulative concentrations, and the experimental concentrations in colunm 6 are average values. The proffle in Fig. 1 for the highest boron concentration shows that the concentration fluctuates by only 10% around this average value within the whole implanted thickness. The kinetics and mechanism of amorphization of nickel surfaces caused by boron implantation are discussed in refs. 19—2 1. TABLE 1
Implantation parameters Ion
B
Energy (keV) 70 180 20
Dose (cm 2) 7 2.4x10’7 5.6x10’ 8.5x10’6 SameX2/3 Samexl/3 SameXi/lO Samex2/100
R~
C(R~)
Amorphous
(urn) 240 110 30
fraction at R~ Theoretical 2.5x10’ 3.1x10’ ~ 2.9x10’
Experimental 2.5x10’
1
Samex2/3 SaineXl/3 SameXi/lO SameX2/100
1.6x101 8.0x10’ 2.5x102 5.0X103
8.0X101 2.0x10’ 0 0
105 36
10
I I
110
240
I
I
Reflected light
I
Calculated ranges Rp(flm)
I”/1’
,~
~
0
~~~\\~__
6 Fig.0 1. Depth profile obtained bySputtering GDOS of time(s) the composition of a nickel surface implanted with 2 respectively. boron ions of 180, 70 and 20 keV at doses of 5.6, 2.4 and 0.8X l0’~ions cm
The electrolyte used was a 0.5 N H 2S04 solution deaerated by bubbling with high purity argon. All potentials were sheet measured with respect to an 2 platinum constituted the counterHg2SO4 electrode (ESS). A 3 cm electrode. Electrochemical measurements were performed with a PAR potentiostat 173 and a Solartron 1186 transfer function analyser. The impedance data were stored on tape and analysed using an Apple II Computer. 3. Results Anodic polarization curves for all the specimens studied are given in Fig. 2. Data from these curves are given in Table 2. They show the dependence of the critical current density required to initiate passivity i~,the minimum passive current density i~.and the corrosion potential, on the boron concentration and amorphous fraction. The effect of increasing the boron dose was to increase the passive current density, indicating a decrease in the protective quality of the passive film. Moreover, the addition of boron led to an ennoblement of the corrosion potential. The impedance diagrams from measurements in the passive range consist of two loops for pure nickel and nickel implanted with low boron doses (Figs. 3(a) and 3(b)). The high frequency half-circle corresponds to an R—C circuit. It is displaced from the origin owing to the finite electrolyte resistance. The inductive ioop observed at low frequencies is related to the relaxation of the adsorbed intermediate species (N~OH)a~ fraction on the electrode area [22, 23]. For nickel implanted with high doses (Figs. 3(c) and 3(d))the experimental data may be fitted at low frequencies to a straight line with a slope of 450 which is characteristic of mass diffusion-controlled kinetics [22].
106 2I
IIPA,cm
00
-600
-300
0
.300
EImv/Ess)
Fig. 2. Current—potential curves recorded in deaerated 0.5 N H 2S04: 7-4—44—, ions cm2 nickel respectively; implanted with—,boron same ions as above of 180, but70doses and 20 arekeV X 2/3; at doses of, 5.6, same2.4asand above 0.8 but X iO’doses are X 1/3; —0—0—, same as above but doses are X 1/10; —, same as above but doses are X2/100. —.
TABLE 2 Principal electrochernical parameters of nickel after B Ion B
Energy (keV)
Dose (cm2)
180 70 20
Ecor
Amorphous
(~.Acm2)
(pA crn2)
(rnV/ESS)
fraction at R~
5.6X10’7 2.4X 10’~ 8.5x i0’~
35X102
470
—725
1
Samex2/3 SameXl/3 SameXi/lO
14X102 7X102 33x102
450 30 15
—570 —570 —568
8.0X10’ 2.0x10~’ 0
15X102
11
—563
0
30x102
8
Samex2/100 Nickel
implantation
4. Discussion and conclusion Jouanneau et al. studied the anodic behaviour of nickel in acidic media and proposed a general model of the electrode reaction path [24]: both dissolution and passivation are preceded by the formation of the intermediate species (NIOH)ads or (NiA)~~ where A may be HSO 4 when the electrolyte is H2S04. The formation of these intermediate species may be inhibited when —
107 N
E
N
E ---~.~
.
~ e
—
—-
—
N _-__0 .0
N
/
2
N°
~
‘—~
•1 -
.
U
N
d
N N
0
1
0 ‘0
.EOQE
0 N
0 0 0
N
—
N ~0
—
0 In ~In
N
— N
—
— N
N
~
ocli
8•-
‘~‘c4 I
0 0
0 0
2
~.O
Q’~~’:~ c~ NW
zc”
________________
E
—
0
N
0
&LC
0
N
E
— ——
0
-~
d N
/
N
/ 10
7
d
~LI
/
0
d~ .-
0
8
//
~
0
0 N ‘I
Co
0 0
0 10
0
N C
0
0 N —
~
2
-. N
NO’
9
0 0
I
0
~ .~
~ __0 N
0
.~ ~
0
0
N
0
0
0 ~.,
L
0
~
N
108
the nickel contains impurities such as phosphorus, boron or sulphur [25, 26]. OH anions are easily adsorbed on transition metals such as nickel and iron because of the vacancies in the d-band orbitals [271. Adding boron, phosphorus or sulphur to iron or nickel alloys leads to the formation of bonded states, between the 2p states of the metalloid and the 3d states of the metal. One result of this is that the adsorption of a hydroxyl ion on the surface could be obstructed and consequently the passivation impeded. The reduction of the inductive loop with low doses of boron and its disappearance at high doses (Fig. 3) indicate that the formation of the (N~OH)a~adsorbed layers is obstructed by boron. Marcus [26] has examined in detail the effect of sulphur on nickel corrosion, showing that nickel dissolves selectively leading to surface enrichment with sulphur until a superficial compound Ni3S2 forms, which gives -
only poor protection. In contrast with sulphur, boron dissolves easily [281. At potentials corresponding to active dissolution, boron is expected to dissolve selectively. The reduction in i~with the boron dose confirms this hypothesis (Table 2). The increase in i,, at low boron doses (Table 2) is probably due to the increasing strain in the nickel lattice caused by the insertion of boron atoms and by the formation of numerous dislocations during implantation [20, 21, 29]. This effect disappears with intermediate doses when amorphous clusters are formed leading to a decrease in the lattice strain. Diffusion of boron towards the surface and its dissolution have been shown in Fe40Ni40B20 and Fe80B20 glasses [281. However, X-ray photoelectron spectrometry of passive films formed on amorphous alloys containing chromium has shown that boron is included as borate in the passive films [15, 30, 31]. The intrusion of borate is detrimental rather than beneficial for the surface owing to its lowering of the passivating ability [32]. Thus it seems that the formation of a corrosion product containing boron impedes passivation even when the alloy contains passivating species such as chromium. In the range of potentials corresponding to passivation, i~,increases monotomcally with the boron content. No beneficial effect attributable to the amorphous state has been observed. An amorphous state alone does not improve the corrosion resistance or passivating ability of NiXB, -x alloys. The chemical composition seems to be the preponderant factor. References 1 J. Takadoum, J. C. Pivin, H. M. Pollock, J. D. J. Ross and H. Bernas, Nuci. Instrum. Methods Phys. Res. B, 18 (1987) 153. 2 J. Takadoum, J. C. Pivin, J. Chaumont and C. Roques-Carmes, J. Mater. Sci., 20 (1985) 1480. 3 J. C. Pivin, F. Pons, J. Takadoum, H. M. Pollock and G. Farges, J. Mater. Sci., 22 (1987) 1087.
:
109
4 I. L. Singer, Mater. Res. Soc. Symp. Proc., 27 (1984) 585. 5 P. L. Bonora, M. Bassoli, G. Cerisola, P. L. De Anna, S. Lo Russo, P. Mazzoldi, B. Tiveron, I. Scoton, C. Tosello and A. Bernard, Nuct. Instrum. Methods, 182/183 (1981) 1001. 6 C. R. Clayton, Nuct. Instrum. Methods, 182 /183 (1981) 865. 7 J. A. Borders, Annu. Rev. Mater. Sci., 9 (1979) 313. 8 L. Thome, J. C. Pivin, A. Benyagoub, H. Bernas and R. W. Calm, Ann. Chim. Fr., 9 (1984) 287. 9 C. Cohen, A. V. Drigo, H. Bemas, J. Chaumont, K. Krolas and L. Thome, Phys. Rev. Lett., 48 (1982) 1193. 10 K. Hashimoto and T. Masumoto, in H. Herman (ed.), Treatise on Materials Science and Technokx.jy, Vol. 20, Academic Press, New York, 1981, p. 291. 11 K. Hashimoto, K. Osada, T. Masumoto and S. Shimodaira, Corros. Sd., 16 (1976) 71. 12 M. Naka, K. Hashimoto and T. Masunioto, J. N. Cris. Sot., 34 (1979) 257. 13 M. Naka, K. Hashimoto and T. Masumoto, J. N. Cris. Sot., 30 (1978) 29. 14 M. Naka, K. Hashimoto and T. Masumoto, J. N. Cris. Sot., 28 (1978) 403. 15 K. Asarni, M. Naka, K. Hashimoto and T. Masumoto, J. Electrochem. Soc., 127 (1980)
2130. 16 J. Takadoum, M. A. Clerc, J. C. Pivin, C. Roques-Carmes and H. M. Pollock, in 4thEUROTPJB Conf Proc., Vol. 1, Elsevier, Amsterdam, SV~edn., 1985, p. 1—4—9. 17 J. Chaumont, F. Lalu, M. Salome, A. M. Lahoise and H. Bernas, Nuct. Instrum. Methods, 189 (1981) 193. 18 J. Talcadoum, J. C. Pivin, J. Pons-Corbeau, R. Berneron and J. C. Charbonnier, Surf Interf Artat., 6 (4) (1984) 174. 19 L. Thome and H. Bernas, Ann. C/tim. Fr., 9 (1984) 279. 20 C. Cohen, A. Benyagoub, H. Bernas, J. Chaumont, L. Thome, H. Berti and A. V. Drigo, Phys. Rev. B, 31 (1985) 5. 21 M. Schack, Thesis, Orsay, France (1984). 22 R. D. Armstrong, R. E. Firman and H. R. Thirsk, Faraday Discuss. Chem. Soc., 56 (1973) 23 24 25 26 27
244. I. Epelboin, M. Keddam and J. C. Lestrad, Faraday Discuss. Chem. Soc., 56 (1973) 264. A. Jouanneau, M. Kedamm and J. C. Petit, Electrochem. Acta, 21 (1976) 287. P. Marcus and 0. Oda, Mem. Sd. Rev. Met. (November 1979) 715. P. Marcus, Thesis, University of Paris, 1979. J. C. Scully, in D. W. Hopkins (ed.), The Fundamentals of Corrosion, Pergamon, New
York, 1975, p. 119. 28 K. E. Heusler and D. Huerta, in Proc. 29 30 31 32
mt. Congr. on Metal Corrosion, Vol. 1, National
Research Council of Canada, 1984, p. 222. R. Moreton and J. K. Lancaster, J. Mater. Sci. Lett., 4 (1985) 133. K. Hashiinoto, M. Naka, K. Asarni and T. Masumoto, Corros. Eng., 27 (1978) 271. K. Hashimoto, K. Asami, M. Naka and T. Masumoto, Corros. Eng., 28 (1979) 271. K. Hashimoto, in M. Froment (ed.), Passivity of Metals and Semiconductors, Elsevier, Amsterdam, 1983, p. 247.
103
Electrochemical behaviour of boron-implanted nickel surfaces J. Takadoum Laboratoire de Microanalyse des Surfaces, ENSMM 25030 Besancon Cédex (Prance)
(Received June 20, 1990)
Abstract The influence ofthe addition of boron on the corrosion of nickel in sulphuric acid medium has been studied in pure binary alloys obtained by ion implantation. No beneficial effect of the structure was observed when the implanted dose of boron was high enough to produce an amorphous state. The passive current density i~,increased with the implanted boron concentration. A.c. impedance measurements were performed through which it was possible to show that boron impedes nickel passivation by preventing the formation of the intermediate species (NiOH),~which precedes the growth of an oxide film.
1. Introduction
Ion implantation as a surface alloying technique offers the possibility of obtaining coatings with excellent mechanical and physical properties [1—41. By doping metallic surfaces with suitable elements the corrosion rates may be significantly reduced [5, 6]. In addition, when the implanted doses are high enough amorphous phases may be produced [7—9]. Amorphous alloys in general have excellent corrosion resistance because of the rapid formation of a homogeneous protective passive ifim [10—12]. The chemically homogeneous single-phase nature of amorphous alloys is an important factor in their electrochemical behaviour, but it is not the only decisive one. Several authors have shown that the protective quality of the surface film depends on the chemical composition of the alloy [13—15]. Corrosion studies have been focused on amorphous alloys obtained by rapid quenching. These materials are often of complex composition and contain inclusions and impurities. Their surfaces are rough, but cannot be polished mechanically since the outermost layers crystaffize during such treatment [16]. In contrast, amorphous films obtained by ion implantation are pure and have simple compositions. This makes it possible to study the chemical effect of the added element and of the structure. In the present paper we attempt to study the influence of the respective effects of radiation damage to nickel surfaces implanted with low boron concentrations, of amorphous clusters formed at intermediate fluences, and of complete amorphization at high fluences, on the anodic behaviour of Ni—B 0257-8972/91/$3.50
© Elsevier Sequoia/Printed in The Netherlands
104
“multi-energy” implanted layers with relatively uniform concentration over a depth of 250 urn, using polarization curves and impedance diagrams. 2. Experimental details The surface of pure (99.999%) polycrystalline nickel, previously polished, first with diamond pastes down to 1 j.tm and then electrolytically, was implanted with increasing doses of ‘1B~ions. Implantation was performed using an Orsay machine, designed to implant well-resolved mass-filtered beams under a vacuum of 10-8 Torr [17]. In order to obtain a uniform concentration of boron over a larger depth (250 urn), boron implantation was carried out at three different energies (180, 70 and 20 keY) with increasing doses. Implantation parameters are given in Table 1, where R 0 is the mean projected range of the implanted ion and C(RP) the maximum boron concentration at a depth R~. The purity and depth composition of the implanted layers were analysed by glow discharge optical spectrometry (GDOS), secondary ion mass spec. trometry (SIMS) and Rutherford backscattering spectrometry (RBS) (Fig. 1). The proffles for implantations at single energies are discussed in ref. 18. The experimental values of R~are in good agreement with the calculated ones, but the distributions are significantly wider than the theory predicts, and thus the concentrations G(R~)are lower than their calculated values (Table 1). The theoretical concentrations of implanted boron given in colunrn 5 of Table 1 are cumulative concentrations, and the experimental concentrations in colunm 6 are average values. The proffle in Fig. 1 for the highest boron concentration shows that the concentration fluctuates by only 10% around this average value within the whole implanted thickness. The kinetics and mechanism of amorphization of nickel surfaces caused by boron implantation are discussed in refs. 19—2 1. TABLE 1
Implantation parameters Ion
B
Energy (keV) 70 180 20
Dose (cm 2) 7 2.4x10’7 5.6x10’ 8.5x10’6 SameX2/3 Samexl/3 SameXi/lO Samex2/100
R~
C(R~)
Amorphous
(urn) 240 110 30
fraction at R~ Theoretical 2.5x10’ 3.1x10’ ~ 2.9x10’
Experimental 2.5x10’
1
Samex2/3 SaineXl/3 SameXi/lO SameX2/100
1.6x101 8.0x10’ 2.5x102 5.0X103
8.0X101 2.0x10’ 0 0
105 36
10
I I
110
240
I
I
Reflected light
I
Calculated ranges Rp(flm)
I”/1’
,~
~
0
~~~\\~__
6 Fig.0 1. Depth profile obtained bySputtering GDOS of time(s) the composition of a nickel surface implanted with 2 respectively. boron ions of 180, 70 and 20 keV at doses of 5.6, 2.4 and 0.8X l0’~ions cm
The electrolyte used was a 0.5 N H 2S04 solution deaerated by bubbling with high purity argon. All potentials were sheet measured with respect to an 2 platinum constituted the counterHg2SO4 electrode (ESS). A 3 cm electrode. Electrochemical measurements were performed with a PAR potentiostat 173 and a Solartron 1186 transfer function analyser. The impedance data were stored on tape and analysed using an Apple II Computer. 3. Results Anodic polarization curves for all the specimens studied are given in Fig. 2. Data from these curves are given in Table 2. They show the dependence of the critical current density required to initiate passivity i~,the minimum passive current density i~.and the corrosion potential, on the boron concentration and amorphous fraction. The effect of increasing the boron dose was to increase the passive current density, indicating a decrease in the protective quality of the passive film. Moreover, the addition of boron led to an ennoblement of the corrosion potential. The impedance diagrams from measurements in the passive range consist of two loops for pure nickel and nickel implanted with low boron doses (Figs. 3(a) and 3(b)). The high frequency half-circle corresponds to an R—C circuit. It is displaced from the origin owing to the finite electrolyte resistance. The inductive ioop observed at low frequencies is related to the relaxation of the adsorbed intermediate species (N~OH)a~ fraction on the electrode area [22, 23]. For nickel implanted with high doses (Figs. 3(c) and 3(d))the experimental data may be fitted at low frequencies to a straight line with a slope of 450 which is characteristic of mass diffusion-controlled kinetics [22].
106 2I
IIPA,cm
00
-600
-300
0
.300
EImv/Ess)
Fig. 2. Current—potential curves recorded in deaerated 0.5 N H 2S04: 7-4—44—, ions cm2 nickel respectively; implanted with—,boron same ions as above of 180, but70doses and 20 arekeV X 2/3; at doses of, 5.6, same2.4asand above 0.8 but X iO’doses are X 1/3; —0—0—, same as above but doses are X 1/10; —, same as above but doses are X2/100. —.
TABLE 2 Principal electrochernical parameters of nickel after B Ion B
Energy (keV)
Dose (cm2)
180 70 20
Ecor
Amorphous
(~.Acm2)
(pA crn2)
(rnV/ESS)
fraction at R~
5.6X10’7 2.4X 10’~ 8.5x i0’~
35X102
470
—725
1
Samex2/3 SameXl/3 SameXi/lO
14X102 7X102 33x102
450 30 15
—570 —570 —568
8.0X10’ 2.0x10~’ 0
15X102
11
—563
0
30x102
8
Samex2/100 Nickel
implantation
4. Discussion and conclusion Jouanneau et al. studied the anodic behaviour of nickel in acidic media and proposed a general model of the electrode reaction path [24]: both dissolution and passivation are preceded by the formation of the intermediate species (NIOH)ads or (NiA)~~ where A may be HSO 4 when the electrolyte is H2S04. The formation of these intermediate species may be inhibited when —
107 N
E
N
E ---~.~
.
~ e
—
—-
—
N _-__0 .0
N
/
2
N°
~
‘—~
•1 -
.
U
N
d
N N
0
1
0 ‘0
.EOQE
0 N
0 0 0
N
—
N ~0
—
0 In ~In
N
— N
—
— N
N
~
ocli
8•-
‘~‘c4 I
0 0
0 0
2
~.O
Q’~~’:~ c~ NW
zc”
________________
E
—
0
N
0
&LC
0
N
E
— ——
0
-~
d N
/
N
/ 10
7
d
~LI
/
0
d~ .-
0
8
//
~
0
0 N ‘I
Co
0 0
0 10
0
N C
0
0 N —
~
2
-. N
NO’
9
0 0
I
0
~ .~
~ __0 N
0
.~ ~
0
0
N
0
0
0 ~.,
L
0
~
N
108
the nickel contains impurities such as phosphorus, boron or sulphur [25, 26]. OH anions are easily adsorbed on transition metals such as nickel and iron because of the vacancies in the d-band orbitals [271. Adding boron, phosphorus or sulphur to iron or nickel alloys leads to the formation of bonded states, between the 2p states of the metalloid and the 3d states of the metal. One result of this is that the adsorption of a hydroxyl ion on the surface could be obstructed and consequently the passivation impeded. The reduction of the inductive loop with low doses of boron and its disappearance at high doses (Fig. 3) indicate that the formation of the (N~OH)a~adsorbed layers is obstructed by boron. Marcus [26] has examined in detail the effect of sulphur on nickel corrosion, showing that nickel dissolves selectively leading to surface enrichment with sulphur until a superficial compound Ni3S2 forms, which gives -
only poor protection. In contrast with sulphur, boron dissolves easily [281. At potentials corresponding to active dissolution, boron is expected to dissolve selectively. The reduction in i~with the boron dose confirms this hypothesis (Table 2). The increase in i,, at low boron doses (Table 2) is probably due to the increasing strain in the nickel lattice caused by the insertion of boron atoms and by the formation of numerous dislocations during implantation [20, 21, 29]. This effect disappears with intermediate doses when amorphous clusters are formed leading to a decrease in the lattice strain. Diffusion of boron towards the surface and its dissolution have been shown in Fe40Ni40B20 and Fe80B20 glasses [281. However, X-ray photoelectron spectrometry of passive films formed on amorphous alloys containing chromium has shown that boron is included as borate in the passive films [15, 30, 31]. The intrusion of borate is detrimental rather than beneficial for the surface owing to its lowering of the passivating ability [32]. Thus it seems that the formation of a corrosion product containing boron impedes passivation even when the alloy contains passivating species such as chromium. In the range of potentials corresponding to passivation, i~,increases monotomcally with the boron content. No beneficial effect attributable to the amorphous state has been observed. An amorphous state alone does not improve the corrosion resistance or passivating ability of NiXB, -x alloys. The chemical composition seems to be the preponderant factor. References 1 J. Takadoum, J. C. Pivin, H. M. Pollock, J. D. J. Ross and H. Bernas, Nuci. Instrum. Methods Phys. Res. B, 18 (1987) 153. 2 J. Takadoum, J. C. Pivin, J. Chaumont and C. Roques-Carmes, J. Mater. Sci., 20 (1985) 1480. 3 J. C. Pivin, F. Pons, J. Takadoum, H. M. Pollock and G. Farges, J. Mater. Sci., 22 (1987) 1087.
:
109
4 I. L. Singer, Mater. Res. Soc. Symp. Proc., 27 (1984) 585. 5 P. L. Bonora, M. Bassoli, G. Cerisola, P. L. De Anna, S. Lo Russo, P. Mazzoldi, B. Tiveron, I. Scoton, C. Tosello and A. Bernard, Nuct. Instrum. Methods, 182/183 (1981) 1001. 6 C. R. Clayton, Nuct. Instrum. Methods, 182 /183 (1981) 865. 7 J. A. Borders, Annu. Rev. Mater. Sci., 9 (1979) 313. 8 L. Thome, J. C. Pivin, A. Benyagoub, H. Bernas and R. W. Calm, Ann. Chim. Fr., 9 (1984) 287. 9 C. Cohen, A. V. Drigo, H. Bemas, J. Chaumont, K. Krolas and L. Thome, Phys. Rev. Lett., 48 (1982) 1193. 10 K. Hashimoto and T. Masumoto, in H. Herman (ed.), Treatise on Materials Science and Technokx.jy, Vol. 20, Academic Press, New York, 1981, p. 291. 11 K. Hashimoto, K. Osada, T. Masumoto and S. Shimodaira, Corros. Sd., 16 (1976) 71. 12 M. Naka, K. Hashimoto and T. Masunioto, J. N. Cris. Sot., 34 (1979) 257. 13 M. Naka, K. Hashimoto and T. Masumoto, J. N. Cris. Sot., 30 (1978) 29. 14 M. Naka, K. Hashimoto and T. Masumoto, J. N. Cris. Sot., 28 (1978) 403. 15 K. Asarni, M. Naka, K. Hashimoto and T. Masumoto, J. Electrochem. Soc., 127 (1980)
2130. 16 J. Takadoum, M. A. Clerc, J. C. Pivin, C. Roques-Carmes and H. M. Pollock, in 4thEUROTPJB Conf Proc., Vol. 1, Elsevier, Amsterdam, SV~edn., 1985, p. 1—4—9. 17 J. Chaumont, F. Lalu, M. Salome, A. M. Lahoise and H. Bernas, Nuct. Instrum. Methods, 189 (1981) 193. 18 J. Talcadoum, J. C. Pivin, J. Pons-Corbeau, R. Berneron and J. C. Charbonnier, Surf Interf Artat., 6 (4) (1984) 174. 19 L. Thome and H. Bernas, Ann. C/tim. Fr., 9 (1984) 279. 20 C. Cohen, A. Benyagoub, H. Bernas, J. Chaumont, L. Thome, H. Berti and A. V. Drigo, Phys. Rev. B, 31 (1985) 5. 21 M. Schack, Thesis, Orsay, France (1984). 22 R. D. Armstrong, R. E. Firman and H. R. Thirsk, Faraday Discuss. Chem. Soc., 56 (1973) 23 24 25 26 27
244. I. Epelboin, M. Keddam and J. C. Lestrad, Faraday Discuss. Chem. Soc., 56 (1973) 264. A. Jouanneau, M. Kedamm and J. C. Petit, Electrochem. Acta, 21 (1976) 287. P. Marcus and 0. Oda, Mem. Sd. Rev. Met. (November 1979) 715. P. Marcus, Thesis, University of Paris, 1979. J. C. Scully, in D. W. Hopkins (ed.), The Fundamentals of Corrosion, Pergamon, New
York, 1975, p. 119. 28 K. E. Heusler and D. Huerta, in Proc. 29 30 31 32
mt. Congr. on Metal Corrosion, Vol. 1, National
Research Council of Canada, 1984, p. 222. R. Moreton and J. K. Lancaster, J. Mater. Sci. Lett., 4 (1985) 133. K. Hashiinoto, M. Naka, K. Asarni and T. Masumoto, Corros. Eng., 27 (1978) 271. K. Hashimoto, K. Asami, M. Naka and T. Masumoto, Corros. Eng., 28 (1979) 271. K. Hashimoto, in M. Froment (ed.), Passivity of Metals and Semiconductors, Elsevier, Amsterdam, 1983, p. 247.