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Determination of valence electronic structure of Ni in Ni-B alloy coatings using Kβ-to-Kα X-ray intensity ratios
Applied Radiation and Isotopes 144 (2019) 24–28
Contents lists available at ScienceDirect
Applied Radiation and Isotopes journal homepage: www.elsevier.com/locate/apradiso
Determination of valence electronic structure of Ni in Ni-B alloy coatings using Kβ-to-Kα X-ray intensity ratios
T
⁎
Erhan Cengiza, , Oğuz Kağan Köksalb, Gökhan Apaydınb, İsmail Hakkı Karahanc, Ersin Ünald a
Alanya Alaaddin Keykubat University, Faculty of Engineering, Department of Fundamental Sciences, Antalya, Turkey Karadeniz Technical University, Faculty of Science, Department of Physics, Trabzon, Turkey c Mustafa Kemal University, Faculty of Arts and Sciences, Department of Physics, Hatay, Turkey d Department of Mechanical Engineering, Osmaniye Korkut Ata University, Osmaniye, Turkey b
H I GH L IG H T S
work is about the valance electronic structure of Ni in Ni-B alloys. • This changes in the crystal structure due to TMAB were observed by XRD. • The • Valance electronic structures were commented by the changes in 3d electron population from Kβ-to-Kα X-ray intensity ratios.
A R T I C LE I N FO
A B S T R A C T
Keywords: K X-ray intensity ratios Ni-B alloy Valence electronic structure 241 Am source
In this study, Kβ-to-Kα X-ray intensity ratios of Ni in Ni-B alloy coatings were investigated. These samples were excited by 59.5 keV gamma-rays from a 241Am annular radioactive source. K X-rays emitted by the samples were counted using an Ultra-LEGe detector with a resolution of 150 eV at 5.9 keV. The Kβ-to-Kα X-ray intensity ratios of Ni-B alloys are compared with pure Ni and each other. Deviations between the results were explained by the change in valence electronic structures of Ni in Ni-B alloy coatings.
1. Introduction In recent years, nickel-boron alloy coatings, which stand out due to their excellent properties, have high hardness, high abrasion resistance (better than hard chrome coatings) and good anti-corrosion properties. Ni-B coatings are also known for their lubricity, excellent solderability, good electrical properties, antibacterial properties, extraordinary electromagnetic properties, and low porosity. However, Ni-B coatings when heat-treated are known to be more resistant to corrosion than Ni-P coatings and harder than commercial hard chrome coatings. Ni-B coatings have high thermal stability due to their high melting point (1350–1360 °C). In addition, Ni-B coatings have a low electrical resistance (89 × 10−6 Ω cm) and are therefore suitable for the electronics industry. Ni-B coatings are used in the automotive, space, nuclear, petrochemical, computer, electronics, plastics, optics, textile, paper, food and printing industries (Shakoor et al., 2014; Waware et al., 2018). X-ray fluorescence parameters such as fluorescence cross-section, intensity ratio, etc. are the basic magnitude that explain the interaction of X-rays with matter. These parameters are significant due to their extensive use in many fields such as physics, chemistry, biomedicine, ⁎
and others. It is also well known that X-ray emission spectra are affected by the chemical combination of X-ray emitting atoms with different ligands. Since 3d transition metals have different physical properties and are used in many applications, they have caused the need to examine their valence electron structures. The ED-XRF method and Kβ-toKα intensity ratio parameter is used to provide information about the valence electronic structures of the 3d transition metal. The Kβ-to-Kα intensity ratios of 3d transition metals depends on the chemical and physical properties of these metals in the sample. This dependence can be explained by the change in the 3d electron population of the transition metal (Pawlowski et al., 2002). Therefore, the Kβ-to-Kα intensity ratios of 3d transition metals have been studied by a number of researchers (Rebohle et al., 1996; Polasik, 1998; Raj et al., 2001; Kalaycı et al., 2007; Han and Demir, 2010; Cengiz et al., 2014; Perişanoğlu and Demir, 2015; Kaçal et al., 2015; Akman, 2016; Alım et al., 2016; Uğurlu et al., 2017; Menesguen et al., 2018; Cengiz et al., 2017; Söğüt et al., 2018). The purpose of present study is to determine the valence electronic structure of Ni in Ni-B alloy coatings using the Kβ-to-Kα intensity ratio and to interpret the lack of consistency between pure Ni and alloys with
Corresponding author. E-mail address: [email protected] (E. Cengiz).
https://doi.org/10.1016/j.apradiso.2018.11.009 Received 19 September 2018; Received in revised form 6 November 2018; Accepted 20 November 2018 Available online 23 November 2018 0969-8043/ © 2018 Elsevier Ltd. All rights reserved.
Applied Radiation and Isotopes 144 (2019) 24–28
E. Cengiz et al.
The experimental K-shell X-ray intensity ratios Kβ/Kα were evaluated using the following equation:
the changes in 3d electron population. 2. Experimental procedure
IK β IK α
2.1. Sample preparation
=
NK β β K α ε K α NK α β K β ε K β
(1)
where NKβ and NK α are the ratios of the counting rates under the Kβ and Kα peaks; β K α and β Kβ are the ratios of self-absorption correction factors of the target that accounts for the absorption of incident photons and emitted K X-ray photons; and ε K α and ε Kβ represent the ratios of the detector efficiency values for Kα and Kβ X-rays, respectively. The self-absorption correction was calculated as below:
Ni-B alloy and pure nickel (for comparison) coatings were deposited on a St-37 steel substrate in a Watts-type nickel bath with direct current (by Parst at 2273 A model electrochemical analyzer). In the electrochemical coating bath, the cathode and the anode were placed parallel to each other. Saturated calomel electrode (SCE) was used as the reference electrode. The deposition time was limited to 60 min and the deposition current density was set at 50 mA/cm2. The bath pH value was adjusted to 4 using HCl and NaOH. Bath temperature during deposition was fixed at 43 ± 1 °C. St-37 steel substrates were sanded with 600, 1200, and 2400 s and paper, respectively, to clean the oil and dirt layers before the coating process. The substrate was then washed with acetone and rinsed with distilled water. Lastly, it was etched in the acid solution of 20% HCl for 1–2 min and then rinsed with distilled water and then ready for coating. In the electrochemical plating bath, nickel sulfate (NiSO4·6H2O) and nickel chloride (NiCl2·6H2O) were used as nickel source and trimethylamine borane complex (TMAB) was used as the boron source. TMAB was used at different concentrations in the bath to analyze the effects on Ni-B coating. After deposition, the coating was rinsed with distilled water and dried at room temperature. Table 1 shows the process conditions, and the elemental compositions of the samples determined by Energy Dispersive X-ray Spectrometry (ZEISS, SUPRA-55).
β KX =
1 − exp{[−(μinc cscθ1 + μemt cscθ2) t ]} (μinc cscθ1 + μemt cscθ2) t
(2)
where μinc and μemt are the mass attenuation of incident photons and emitted characteristic X-rays, respectively (Berger et al., 2005); the angles of incident photons and emitted X-rays with respect to the sample surface, θ1 and θ2, were equal to 45° and 90°, respectively. t is the target thickness in g/cm2. The product I0 G ε that contains the incident photon flux, a geometrical factor and absolute efficiency of the X-ray detector, was determined for this study by collecting Kα and Kβ X-ray spectra of samples of K, Ca, Ti, Cr, Mn, Co, Ni, Zn, Ga, As, Se, Br, Y, Mo, Sn and Te in the same geometry using the equation:
I0 Gε KX =
NKX σKX β KX mi
(x = α and β) (3)
where the terms NKx and β Kx are the same meaning in Eq. (1). mi is the elemental concentration (g/cm2). σKx X-ray production cross-section was calculated using the following equation:
2.2. XRD measurements
σKx = σK (E ) ωK FKx
The crystallographic orientations of Ni-B alloy coatings were determined by Rigaku X-ray diffractometer operated at 40 kV potential and 30 mA current values with Cu Kα radiation.
(4)
where σK (E ) is the K-shell photoionization cross-section of the given element for the excitation energy E (Scofield, 1973), ωK is the K-shell fluorescence yield (Krause, 1979), and FKx is the emission rate of the fractional X-ray for Kα and Kβ X-rays (Scofield, 1974). The factor I0 Gε Kx was fitted as a function of energy using the polynomials:
2.3. ED-XRF measurements The measurement geometry between detector, radioactive source and sample are shown in Fig. 1. This geometry was prepared so that the angle of the excitation radiation with the sample surface was 45° and the X-ray fluorescence radiation emitted from the sample was 90° with the sample surface. The live time was selected as 10,000 s to obtain statistical sensitivity. The alloy coatings having thicknesses between 0.0209 and 0.0405 g/cm2 were exposed to 59.5 keV photons emitted by an annular 50 mCi 241Am radioactive source. The fluorescence K X-rays from each alloy were detected by an Ultra-LEGe detector having a thickness of 5 mm and energy resolution 150 eV at 5.96 keV. The output from the preamplifier, with a pulse pile-up rejection capability, was fed to a multi-channel analyzer interfaced with a personal computer provided with suitable software for data acquisition and peak analysis. For determining peak intensity, the X-ray spectra were analyzed with the use of QXAS package (Vekemans et al., 1994). The Ni Kα and Kβ energies are 7.472 keV and 8.265 keV, respectively. The K X-ray spectra of Ni for sample 2 are shown in Fig. 2.
I0 Gε Kx = A0 + A1 Ei + A2 Ei2 + A3 Ei3 (1st part)
(5)
I0 Gε Kx = B0 + B1 Ei + B2 Ei2 (2nd part)
(6)
where Ei is the Kα or Kβ X-ray energy. The variation I0 Gε Kx as a function of the K X-ray energy is shown in Fig. 3. The Eqs. (5) and (6) correspond to the left-hand side and right-hand side of Fig. 3, respectively. 3. Results and discussion The experimental results for the Kβ-to-Kα X-ray intensity ratios of Ni in pure Ni and Ni-B alloy coatings and the normalized Kβ-to-Kα X-ray intensity ratios in the alloy coatings with respect to pure Ni are presented in Table 2. The overall error in the present measurement is estimated to be̴ 6%. This error is the quadrature sum of the uncertainties in the different parameters used to evaluate the K-shell fluorescence
Table 1 Process conditions and elemental compositions. Sample
NiSO4.6H2O (g/l)
NiCl2.6H2O(g/ l)
TMAB (g/ l)
Temperature (◦C)
pH
Deposition time (min)
Agitation speed (rpm)
Current density (mA/ cm2)
% Ni
%B
Pure Ni 1 2 3 4 5
240 240 240 240 240 240
45 45 45 45 45 45
– 3 6 9 12 15
43 43 43 43 43 43
4 4 4 4 4 4
60 60 60 60 60 60
500–600 500–600 500–600 500–600 500–600 500–600
50 50 50 50 50 50
100 88.15 87.98 87.30 86.10 84.00
– 11.85 12.02 12.70 13.90 16.00
± ± ± ± ± ±
1 1 1 1 1 1
25
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E. Cengiz et al.
Fig. 1. The measurement geometry.
concentration (decreasing Ni concentration) except for sample 2. The inconsistency between the intensity ratios of Ni in the Ni-B alloy coatings and pure Ni can be explained by changes in 3d electron population due to delocalization and/or charge transfer resulting from alloying effect. The structural changes were observed with the XRD measurements when the Ni concentration in the alloying coatings was decreased. As seen from Fig. 4, the crystal structure of the pure nickel has the facecentered cubic (fcc), and the nickel-specific diffraction peaks are (111), (200), (220), (311) and (222). With the influence of the boron source TMAB added to the electrochemical coating bath, the diffraction peaks (200), (220), (311) and (222) completely disappeared except for the bath with 6 g/l TMAB bath concentration. With the inclusion of boron atoms in the structure, the average crystal grain size reduced and it was seen in XRD patterns that the crystal structure exhibits amorphous or nanocrystalline properties. The main diffraction peak (200) was observed in pure nickel, while the (111) diffraction peak was observed as the main peak and single peak in the Ni-B alloy coating due to the influence of TMAB. In the XRD pattern of the coating with 6 g/l TMAB bath concentration, other peaks appear to be weak except for (111). The intensity of (111) peaks in Ni-B alloy coatings increased with increasing TMAB concentration in the bath, up to 12 g/l TMAB bath concentration, then decreased again in the 15 g/l TMAB bath concentration. Besides; when the amount of TMAB in the electrolyte reached 6 g/l, the grain size increased from 12.6 nm to 19.4 nm and the lattice parameter increased as seen from Table 3. The Kβ-to-Kα X-ray intensity ratios, which were inversely proportional to the grain size, decreased with increasing grain size and then increased due to increasing TMAB. The changes in the grain sizes and the lattice parameters of the alloy coatings have also affected the 3d electron population of the nickel as determined from the Kβ-to-Kα X-ray intensity ratios of Ni in the Ni-B alloy coatings. The decreasing in the present results for Ni-B alloy coatings for the first four alloy coatings with respect to pure Ni can be attributed to rearrangement of electrons between 3d and (4 s, 4p) states. Normally, it is expected that B will attract to Ni valence electrons because B has higher electronegativity value than Ni. Actually, this attracting has shown from the intensity results but the rearrangement process is more dominant than the charge transfer. However; in the sample 5, B concentration is the highest and the intensity ratio of the Ni is bigger than pure Ni. It is shown that the more dominant process is the charge transfer from Ni to B.
Fig. 2. The K X-ray spectra of Ni in sample 2.
Fig. 3. The variation of I0Gε as a function of K X-ray energy.
parameters, i.e. target thickness (2%), the evaluation of the peak area (3%), the detector efficiency I0GεKx (3%) and the absorption correction factor (3%). As seen from Table 2, the experimental result for the Kβ-to-Kα X-ray intensity ratio of pure Ni is in good agreement with the theoretical value of Scofield (1974); however, it is smaller than values of Coulomb gauge and Babuskin gauge (Polasik, 1998) for all cases. Unlike the sample 5, the Kβ-to-Kα X-ray intensity ratios of Ni in the Ni-B alloy coatings are lower than the pure nickel value. Besides, the intensity values of Ni in the Ni-B alloy coatings increase with the increasing B
4. Conclusion In this study, the Kβ/Kα X-ray intensity ratios of nickel in pure Ni and Ni-B alloy coatings have been determined. The experimental 26
Applied Radiation and Isotopes 144 (2019) 24–28
E. Cengiz et al.
Table 2 Kβ/Kα X-ray intensity ratios of Ni in NiB alloy coatings (⎛⎜IKβ /IK α ⎞⎟ :experimental Kβ-to-Kα X-ray intensity ratios and ⎛⎜IKβ /IK α ⎞⎟ :relative Kβ-to-Kα X-ray intensity ratios ⎝ ⎠A ⎝ ⎠B with respect to pure Ni). Sample
Experimental
Theoretical
⎛⎜I /I ⎞⎟ Kβ Kα ⎝ ⎠A
⎛⎜I /I ⎞⎟ Kβ Kα ⎝ ⎠B
Pure Ni
0.1238 ± 0.0069
1
1 2 3 4 5
0.1171 0.1139 0.1192 0.1204 0.1392
0.9460 0.9203 0.9635 0.9730 1.1252
± ± ± ± ±
0.0066 0.0064 0.0067 0.0067 0.0078
Scofield (1974)
3d84s2 3d94s1 3d10
0.1227
Coulomb gauge (Polasik, 1998)
Babushin gauge
0.1361 0.1333 0.1313
0.1374 0.1346 0.1325
Fig. 4. The effect of TMAB bath concentration on the crystal structure of Ni-B alloy coatings. Table 3 The grain size and lattice parameters of the alloy coatings. Sample
2θ(degree)
d(Å)
FWHM (degree)
Grain size(nm)
(hkl)
Lattice(a)
Pure Ni 3 g/l TMAB 6 g/l TMAB 9 g/l TMAB 12 g/l TMAB 15 g/l TMAB
51.91 44.53 44.50 44.68 44.46 44.49
1.76 2.03 2.03 2.02 2.03 2.03
0.194 0.71 0.46 1.04 1.008 1.00
47.6 12.6 19.4 8.6 8.8 8.9
(200) (111) (111) (111) (111) (111)
3.520(a) 3.521(a) 3.523(a) 3.510(a) 3.526(a) 3.523(a)
phthalocyanines. Can. J. Phys. 95, 125–129. Cengiz, E., Özkendir, O.M., Kaya, M., Tıraşoğlu, E., Karahan, İ.H., Kimura, S., Hajiri, T., 2014. Alloying effect on K-shell fluorescence parameters of porous NiTİ shape memory alloys. J. Electron. Spectrosc. Relat. Phenom. 192, 55. Han, I., Demir, L., 2010. Valence-electron configuration of Ti and Ni in TixNi1-x alloys from Kβ-to-Kα X-ray intensity ratio studies. Appl. Radiat. Isot. 68, 1035. Kaçal, M.R., Han, İ., Akman, F., 2015. Determination of K shell absorption jump factors and jump ratios of 3d transition metals by measuring K shell fluorescence parameters. Appl. Radiat. Isot. 95, 193–199. Kalaycı, Y., Aydinraz, A., Tugluoglu, B., Mutlu, R.H., 2007. Valence electronic structure of Ni in Ni-Si alloys from relative K X-ray intensity studies. Nucl. Instrum. Methods B 255, 438–440. Krause, M.O., 1979. Atomic radiative and radiationless yield for K and L shells. J. Phys. Chem. Ref. Data 8, 307. Menesguen, Y., Lepy, M.-C., Hönicke, P., Müller, M., Uterumsberger, R., Beckhoff, B., Hoszowska, J., Dousse, J.-C.I., Blachucki, W., Ito, Y., Yamashita, M., Fukushima, S., 2018. Experimental determination of the X-ray atmic fundemental parameters of nickel. Metrologia 55, 56–66. Pawlowski, F., Polasik, M., Raj, S., Padhi, H.C., Basa, D.K., 2002. Valence electronic structure of Ti, Cr, Fe, and Co in some alloys from Kβ-to-Kα X-ray intensity ratio studies. Nucl. Instrum. Methods B 195, 367–373. Perişanoğlu, U., Demir, L., 2015. A study of K shell X-ray intensity ratios of NixCr1-x alloys in external magnetic field and determination of effective atomic numbers of these alloys. Rad. Phys. Chem. 110, 119–125. Polasik, M., 1998. Influence of changes in the valence electronic configuration on the Kβto-Kα X-ray intensity ratios of the 3d transition metals. Phys. Rev. A 58, 1840–1845. Raj, S., Padhi, H.C., Polasik, M., Pawlowski, F., Basa, D.K., 2001. Kβ-to-Kα X-ray intensity ratio studies of the valence electronic structure of Fe and Ni in FexNi1-x alloys. Phys. Rev. B 63, 073109. Rebohle, L., Lehnert, U., Zschornack, G., 1996. Kβ/Kα intensity ratios and chemical effects of some 3d elements. X-ray Spectrom. 25, 295. Scofield, H., 1973. Theoretical Photoionization Cross Sections From 1 to 1500 keV. 51326 Lawrence Livermore Laboratory (UCRL). Scofield, J.H., 1974. Relativistic hartree-slater values for K and L emission rates. At. Data Nucl. Data Tables 14, 121. Shakoor, R.A., Kahraman, R., Waware, U.S., Gao, W., 2014. Synthesis and properties of electrodeposited Ni-B-Zn ternary alloy coatings. Int. J. Electrochem. Sci. 9, 5520–5536. Söğüt, Ö., Kerli, S., Cengiz, E., Apaydın, G., 2018. Examination of the change of the
intensity ratio of pure nickel agrees with Scofield's theoretical value and is smaller than the values of Coulomb gauge and Babuskin gauge. It was determined that when the boron concentration was increased in the NiB alloy coatings, the crystal structure and grain size were changed. These changes have also affected the valence electronic configuration of Ni due to the charge transfer and rearrangement processes as can be seen from the Kβ/Kα X-ray intensity ratios. References Akman, F., 2016. K to L shell vacancy transfer probabilities and Auger electron emission ratios for elements in the atomic range 30 < = Z < = 58. Can. J. Phys. 94, 679–686. Alım, B., Han, İ., Demir, L., 2016. Effect of external magntic field on valence-electron structures of Fe and Ni in Invar, Permalloy, and the other Fe-Ni alloys by using Kβ/Kα X-ray intensity ratios. Appl. Radiat. Isot. 112, 5–12. Berger, M.J., Hubbell, J.H., Seltzer, S.M., Chang, J., Coursey, J.S., Sukumar, R., Zucker, D. S., 2005. XCOM: Photon Cross SectionDatabase (version 1.3) [Online] (Gaithersburg, MD: National Institute of Standards and Technology). Available at 〈http://physics. nist.gov/xcom〉. Cengiz, E., Doğan, M., Bıyıklıoğlu, Z., Çakır, D., Tıraşoğlu, E., Apaydın, G., 2017. K X-ray fluorescence parameters peripherally and non-peripherally tetra-substituted zinc (II)
27
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E. Cengiz et al. characteristic X-rays of the zinc in fluorine- and boron-doped ZnO thin films. Acta Phys. Pol. A 133. Uğurlu, M., Alım, B., Han, İ., Demir, L., 2017. Delocalization and charge transfer studies of PERMENDUR48, KOVAR and Ti50Co50 alloys from relative K X-ray intensity ratios. J. Alloy. Compd. 695, 2619–2627. Vekemans, B., Janssens, K., Vincze, L., Adams, F., Van Espen, P., 1994. Analysis of X-ray
spectra by iterative least squares (AXIL): new developments. X-ray Spectrom. 23, 278–285. Wawarea, U.S., Hamoudaa, A.M.S., Wasekar, N.P., 2018. Mechanical properties, thermal stability and corrosion behavior of electrodeposited Ni-B/AlN nanocomposite coating. Surf. Coat. Technol. 337, 335–341.
28
Contents lists available at ScienceDirect
Applied Radiation and Isotopes journal homepage: www.elsevier.com/locate/apradiso
Determination of valence electronic structure of Ni in Ni-B alloy coatings using Kβ-to-Kα X-ray intensity ratios
T
⁎
Erhan Cengiza, , Oğuz Kağan Köksalb, Gökhan Apaydınb, İsmail Hakkı Karahanc, Ersin Ünald a
Alanya Alaaddin Keykubat University, Faculty of Engineering, Department of Fundamental Sciences, Antalya, Turkey Karadeniz Technical University, Faculty of Science, Department of Physics, Trabzon, Turkey c Mustafa Kemal University, Faculty of Arts and Sciences, Department of Physics, Hatay, Turkey d Department of Mechanical Engineering, Osmaniye Korkut Ata University, Osmaniye, Turkey b
H I GH L IG H T S
work is about the valance electronic structure of Ni in Ni-B alloys. • This changes in the crystal structure due to TMAB were observed by XRD. • The • Valance electronic structures were commented by the changes in 3d electron population from Kβ-to-Kα X-ray intensity ratios.
A R T I C LE I N FO
A B S T R A C T
Keywords: K X-ray intensity ratios Ni-B alloy Valence electronic structure 241 Am source
In this study, Kβ-to-Kα X-ray intensity ratios of Ni in Ni-B alloy coatings were investigated. These samples were excited by 59.5 keV gamma-rays from a 241Am annular radioactive source. K X-rays emitted by the samples were counted using an Ultra-LEGe detector with a resolution of 150 eV at 5.9 keV. The Kβ-to-Kα X-ray intensity ratios of Ni-B alloys are compared with pure Ni and each other. Deviations between the results were explained by the change in valence electronic structures of Ni in Ni-B alloy coatings.
1. Introduction In recent years, nickel-boron alloy coatings, which stand out due to their excellent properties, have high hardness, high abrasion resistance (better than hard chrome coatings) and good anti-corrosion properties. Ni-B coatings are also known for their lubricity, excellent solderability, good electrical properties, antibacterial properties, extraordinary electromagnetic properties, and low porosity. However, Ni-B coatings when heat-treated are known to be more resistant to corrosion than Ni-P coatings and harder than commercial hard chrome coatings. Ni-B coatings have high thermal stability due to their high melting point (1350–1360 °C). In addition, Ni-B coatings have a low electrical resistance (89 × 10−6 Ω cm) and are therefore suitable for the electronics industry. Ni-B coatings are used in the automotive, space, nuclear, petrochemical, computer, electronics, plastics, optics, textile, paper, food and printing industries (Shakoor et al., 2014; Waware et al., 2018). X-ray fluorescence parameters such as fluorescence cross-section, intensity ratio, etc. are the basic magnitude that explain the interaction of X-rays with matter. These parameters are significant due to their extensive use in many fields such as physics, chemistry, biomedicine, ⁎
and others. It is also well known that X-ray emission spectra are affected by the chemical combination of X-ray emitting atoms with different ligands. Since 3d transition metals have different physical properties and are used in many applications, they have caused the need to examine their valence electron structures. The ED-XRF method and Kβ-toKα intensity ratio parameter is used to provide information about the valence electronic structures of the 3d transition metal. The Kβ-to-Kα intensity ratios of 3d transition metals depends on the chemical and physical properties of these metals in the sample. This dependence can be explained by the change in the 3d electron population of the transition metal (Pawlowski et al., 2002). Therefore, the Kβ-to-Kα intensity ratios of 3d transition metals have been studied by a number of researchers (Rebohle et al., 1996; Polasik, 1998; Raj et al., 2001; Kalaycı et al., 2007; Han and Demir, 2010; Cengiz et al., 2014; Perişanoğlu and Demir, 2015; Kaçal et al., 2015; Akman, 2016; Alım et al., 2016; Uğurlu et al., 2017; Menesguen et al., 2018; Cengiz et al., 2017; Söğüt et al., 2018). The purpose of present study is to determine the valence electronic structure of Ni in Ni-B alloy coatings using the Kβ-to-Kα intensity ratio and to interpret the lack of consistency between pure Ni and alloys with
Corresponding author. E-mail address: [email protected] (E. Cengiz).
https://doi.org/10.1016/j.apradiso.2018.11.009 Received 19 September 2018; Received in revised form 6 November 2018; Accepted 20 November 2018 Available online 23 November 2018 0969-8043/ © 2018 Elsevier Ltd. All rights reserved.
Applied Radiation and Isotopes 144 (2019) 24–28
E. Cengiz et al.
The experimental K-shell X-ray intensity ratios Kβ/Kα were evaluated using the following equation:
the changes in 3d electron population. 2. Experimental procedure
IK β IK α
2.1. Sample preparation
=
NK β β K α ε K α NK α β K β ε K β
(1)
where NKβ and NK α are the ratios of the counting rates under the Kβ and Kα peaks; β K α and β Kβ are the ratios of self-absorption correction factors of the target that accounts for the absorption of incident photons and emitted K X-ray photons; and ε K α and ε Kβ represent the ratios of the detector efficiency values for Kα and Kβ X-rays, respectively. The self-absorption correction was calculated as below:
Ni-B alloy and pure nickel (for comparison) coatings were deposited on a St-37 steel substrate in a Watts-type nickel bath with direct current (by Parst at 2273 A model electrochemical analyzer). In the electrochemical coating bath, the cathode and the anode were placed parallel to each other. Saturated calomel electrode (SCE) was used as the reference electrode. The deposition time was limited to 60 min and the deposition current density was set at 50 mA/cm2. The bath pH value was adjusted to 4 using HCl and NaOH. Bath temperature during deposition was fixed at 43 ± 1 °C. St-37 steel substrates were sanded with 600, 1200, and 2400 s and paper, respectively, to clean the oil and dirt layers before the coating process. The substrate was then washed with acetone and rinsed with distilled water. Lastly, it was etched in the acid solution of 20% HCl for 1–2 min and then rinsed with distilled water and then ready for coating. In the electrochemical plating bath, nickel sulfate (NiSO4·6H2O) and nickel chloride (NiCl2·6H2O) were used as nickel source and trimethylamine borane complex (TMAB) was used as the boron source. TMAB was used at different concentrations in the bath to analyze the effects on Ni-B coating. After deposition, the coating was rinsed with distilled water and dried at room temperature. Table 1 shows the process conditions, and the elemental compositions of the samples determined by Energy Dispersive X-ray Spectrometry (ZEISS, SUPRA-55).
β KX =
1 − exp{[−(μinc cscθ1 + μemt cscθ2) t ]} (μinc cscθ1 + μemt cscθ2) t
(2)
where μinc and μemt are the mass attenuation of incident photons and emitted characteristic X-rays, respectively (Berger et al., 2005); the angles of incident photons and emitted X-rays with respect to the sample surface, θ1 and θ2, were equal to 45° and 90°, respectively. t is the target thickness in g/cm2. The product I0 G ε that contains the incident photon flux, a geometrical factor and absolute efficiency of the X-ray detector, was determined for this study by collecting Kα and Kβ X-ray spectra of samples of K, Ca, Ti, Cr, Mn, Co, Ni, Zn, Ga, As, Se, Br, Y, Mo, Sn and Te in the same geometry using the equation:
I0 Gε KX =
NKX σKX β KX mi
(x = α and β) (3)
where the terms NKx and β Kx are the same meaning in Eq. (1). mi is the elemental concentration (g/cm2). σKx X-ray production cross-section was calculated using the following equation:
2.2. XRD measurements
σKx = σK (E ) ωK FKx
The crystallographic orientations of Ni-B alloy coatings were determined by Rigaku X-ray diffractometer operated at 40 kV potential and 30 mA current values with Cu Kα radiation.
(4)
where σK (E ) is the K-shell photoionization cross-section of the given element for the excitation energy E (Scofield, 1973), ωK is the K-shell fluorescence yield (Krause, 1979), and FKx is the emission rate of the fractional X-ray for Kα and Kβ X-rays (Scofield, 1974). The factor I0 Gε Kx was fitted as a function of energy using the polynomials:
2.3. ED-XRF measurements The measurement geometry between detector, radioactive source and sample are shown in Fig. 1. This geometry was prepared so that the angle of the excitation radiation with the sample surface was 45° and the X-ray fluorescence radiation emitted from the sample was 90° with the sample surface. The live time was selected as 10,000 s to obtain statistical sensitivity. The alloy coatings having thicknesses between 0.0209 and 0.0405 g/cm2 were exposed to 59.5 keV photons emitted by an annular 50 mCi 241Am radioactive source. The fluorescence K X-rays from each alloy were detected by an Ultra-LEGe detector having a thickness of 5 mm and energy resolution 150 eV at 5.96 keV. The output from the preamplifier, with a pulse pile-up rejection capability, was fed to a multi-channel analyzer interfaced with a personal computer provided with suitable software for data acquisition and peak analysis. For determining peak intensity, the X-ray spectra were analyzed with the use of QXAS package (Vekemans et al., 1994). The Ni Kα and Kβ energies are 7.472 keV and 8.265 keV, respectively. The K X-ray spectra of Ni for sample 2 are shown in Fig. 2.
I0 Gε Kx = A0 + A1 Ei + A2 Ei2 + A3 Ei3 (1st part)
(5)
I0 Gε Kx = B0 + B1 Ei + B2 Ei2 (2nd part)
(6)
where Ei is the Kα or Kβ X-ray energy. The variation I0 Gε Kx as a function of the K X-ray energy is shown in Fig. 3. The Eqs. (5) and (6) correspond to the left-hand side and right-hand side of Fig. 3, respectively. 3. Results and discussion The experimental results for the Kβ-to-Kα X-ray intensity ratios of Ni in pure Ni and Ni-B alloy coatings and the normalized Kβ-to-Kα X-ray intensity ratios in the alloy coatings with respect to pure Ni are presented in Table 2. The overall error in the present measurement is estimated to be̴ 6%. This error is the quadrature sum of the uncertainties in the different parameters used to evaluate the K-shell fluorescence
Table 1 Process conditions and elemental compositions. Sample
NiSO4.6H2O (g/l)
NiCl2.6H2O(g/ l)
TMAB (g/ l)
Temperature (◦C)
pH
Deposition time (min)
Agitation speed (rpm)
Current density (mA/ cm2)
% Ni
%B
Pure Ni 1 2 3 4 5
240 240 240 240 240 240
45 45 45 45 45 45
– 3 6 9 12 15
43 43 43 43 43 43
4 4 4 4 4 4
60 60 60 60 60 60
500–600 500–600 500–600 500–600 500–600 500–600
50 50 50 50 50 50
100 88.15 87.98 87.30 86.10 84.00
– 11.85 12.02 12.70 13.90 16.00
± ± ± ± ± ±
1 1 1 1 1 1
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Fig. 1. The measurement geometry.
concentration (decreasing Ni concentration) except for sample 2. The inconsistency between the intensity ratios of Ni in the Ni-B alloy coatings and pure Ni can be explained by changes in 3d electron population due to delocalization and/or charge transfer resulting from alloying effect. The structural changes were observed with the XRD measurements when the Ni concentration in the alloying coatings was decreased. As seen from Fig. 4, the crystal structure of the pure nickel has the facecentered cubic (fcc), and the nickel-specific diffraction peaks are (111), (200), (220), (311) and (222). With the influence of the boron source TMAB added to the electrochemical coating bath, the diffraction peaks (200), (220), (311) and (222) completely disappeared except for the bath with 6 g/l TMAB bath concentration. With the inclusion of boron atoms in the structure, the average crystal grain size reduced and it was seen in XRD patterns that the crystal structure exhibits amorphous or nanocrystalline properties. The main diffraction peak (200) was observed in pure nickel, while the (111) diffraction peak was observed as the main peak and single peak in the Ni-B alloy coating due to the influence of TMAB. In the XRD pattern of the coating with 6 g/l TMAB bath concentration, other peaks appear to be weak except for (111). The intensity of (111) peaks in Ni-B alloy coatings increased with increasing TMAB concentration in the bath, up to 12 g/l TMAB bath concentration, then decreased again in the 15 g/l TMAB bath concentration. Besides; when the amount of TMAB in the electrolyte reached 6 g/l, the grain size increased from 12.6 nm to 19.4 nm and the lattice parameter increased as seen from Table 3. The Kβ-to-Kα X-ray intensity ratios, which were inversely proportional to the grain size, decreased with increasing grain size and then increased due to increasing TMAB. The changes in the grain sizes and the lattice parameters of the alloy coatings have also affected the 3d electron population of the nickel as determined from the Kβ-to-Kα X-ray intensity ratios of Ni in the Ni-B alloy coatings. The decreasing in the present results for Ni-B alloy coatings for the first four alloy coatings with respect to pure Ni can be attributed to rearrangement of electrons between 3d and (4 s, 4p) states. Normally, it is expected that B will attract to Ni valence electrons because B has higher electronegativity value than Ni. Actually, this attracting has shown from the intensity results but the rearrangement process is more dominant than the charge transfer. However; in the sample 5, B concentration is the highest and the intensity ratio of the Ni is bigger than pure Ni. It is shown that the more dominant process is the charge transfer from Ni to B.
Fig. 2. The K X-ray spectra of Ni in sample 2.
Fig. 3. The variation of I0Gε as a function of K X-ray energy.
parameters, i.e. target thickness (2%), the evaluation of the peak area (3%), the detector efficiency I0GεKx (3%) and the absorption correction factor (3%). As seen from Table 2, the experimental result for the Kβ-to-Kα X-ray intensity ratio of pure Ni is in good agreement with the theoretical value of Scofield (1974); however, it is smaller than values of Coulomb gauge and Babuskin gauge (Polasik, 1998) for all cases. Unlike the sample 5, the Kβ-to-Kα X-ray intensity ratios of Ni in the Ni-B alloy coatings are lower than the pure nickel value. Besides, the intensity values of Ni in the Ni-B alloy coatings increase with the increasing B
4. Conclusion In this study, the Kβ/Kα X-ray intensity ratios of nickel in pure Ni and Ni-B alloy coatings have been determined. The experimental 26
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Table 2 Kβ/Kα X-ray intensity ratios of Ni in NiB alloy coatings (⎛⎜IKβ /IK α ⎞⎟ :experimental Kβ-to-Kα X-ray intensity ratios and ⎛⎜IKβ /IK α ⎞⎟ :relative Kβ-to-Kα X-ray intensity ratios ⎝ ⎠A ⎝ ⎠B with respect to pure Ni). Sample
Experimental
Theoretical
⎛⎜I /I ⎞⎟ Kβ Kα ⎝ ⎠A
⎛⎜I /I ⎞⎟ Kβ Kα ⎝ ⎠B
Pure Ni
0.1238 ± 0.0069
1
1 2 3 4 5
0.1171 0.1139 0.1192 0.1204 0.1392
0.9460 0.9203 0.9635 0.9730 1.1252
± ± ± ± ±
0.0066 0.0064 0.0067 0.0067 0.0078
Scofield (1974)
3d84s2 3d94s1 3d10
0.1227
Coulomb gauge (Polasik, 1998)
Babushin gauge
0.1361 0.1333 0.1313
0.1374 0.1346 0.1325
Fig. 4. The effect of TMAB bath concentration on the crystal structure of Ni-B alloy coatings. Table 3 The grain size and lattice parameters of the alloy coatings. Sample
2θ(degree)
d(Å)
FWHM (degree)
Grain size(nm)
(hkl)
Lattice(a)
Pure Ni 3 g/l TMAB 6 g/l TMAB 9 g/l TMAB 12 g/l TMAB 15 g/l TMAB
51.91 44.53 44.50 44.68 44.46 44.49
1.76 2.03 2.03 2.02 2.03 2.03
0.194 0.71 0.46 1.04 1.008 1.00
47.6 12.6 19.4 8.6 8.8 8.9
(200) (111) (111) (111) (111) (111)
3.520(a) 3.521(a) 3.523(a) 3.510(a) 3.526(a) 3.523(a)
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