Semi-conductive properties of passive films formed on copper in chromate solutions

doi:10.1016/j.tsf.2008.10.045

Thin Solid Films

Volume 517, Issue 6, 30 January 2009, Pages 1995-1999

https://doi.org/10.1016/j.tsf.2008.10.045 Get rights and content

Abstract

The semi-conductive properties of passive films formed on copper in chromate solutions were investigated by means of capacitance measurements. The effects of the formation potential and temperature, chloride and chromate concentration in electrolyte solution, as well as measured frequency on the semi-conductive properties of passive films were studied. The results show that the passive films formed on copper display n-type semi-conductive characteristics. The slopes of the straight lines in Mott-Schottky plots decrease with moving the formation potential toward positive, increasing the chloride ion concentration, decreasing the formation temperature and the chromate solutions concentration. Moreover, the initial grain size of copper surface impacts remarkably on the semi-conductive properties. The donor density of the passive films formed on ultra-fine grained (UFG) copper is higher than that of the passive films on coarse-grained (CG) copper.

Introduction

Copper is a key material in microelectronics because of its superior electronic conductivity and low electro-migration resistance. Superior corrosion resistance results from thin passive films formed on copper, which can prevent the further occurrence of corrosion process on its surface [1], [2], [3]. Generally, passive films formed on metals or alloys exhibit semi-conductive properties. Investigations on the semi-conductive properties of the passive films can provide some insights into the electronic properties of the passive films, which can be related to the mechanisms of the films formation, breakdown and dissolution. Since the films formation, breakdown and dissolution are tightly related to the corrosion process, many researches have been investigated on the semi-conductive properties of passive films to acquire more corrosion information [4], [5], [6], [7], [8], [9], [10]. Hence, it is necessary to understand the semi-conductive properties of passive films formed on these metals or alloys (including copper) in order to improve the corrosion resistance of metals or alloys.

Previous studies have been performed at oxide films formed on copper under anodic conditions. It shows that the reaction of the copper with its aqueous environment is very complex, and both soluble and insoluble products consist of two different oxidation states, Cu (I) and Cu (II) depending upon the applied potential. Millet B and his co-workers [11] have reported a duplex Cu₂O films formed on copper after a long period of time in aerated and in the NaCl solutions, which are made of two semi-conductive components of different stoichiometries, p-type and n-type semiconductors. Arivial et al. [12] demonstrated the detailed mechanism for the electrochemical reactions of copper in alkaline solutions, and modifications of the reduction potential of cuprous oxide have been related to the conditions of the anodic potential sweep. However, only few papers available in the literature concerning the semi-conductive properties of passive films formed on copper in chromate solutions. In the present work, the semi-conductive properties of passive films formed on copper in chromate solutions were studied by using capacitance measurement. The effects of film formation potential and temperature, chloride and chromate concentration in electrolyte solution, as well as measured frequency on the semi-conductive properties of the films were examined.

Section snippets

Sample preparations

The samples were prepared by melting weighed mixtures of pure copper (99.95 wt.%) in an electric furnace, nitrogen gas was pulled on the molten surface to protect the oxidation. The molten copper was poured into a copper mould of 500 K in the atmosphere to form the rod (Φ 20 × 200 mm). Then the ultra-fine grained (UFG) coppers were processed by equal channel angular pressing (ECAP) with up to 4 passes at room temperature using route C with a rotation of 180° between passes [13]. A transmission

Mott-Schottky analysis

In general, oxide films formed on metals or alloys display n-type or p-type semi-conductive characters, the oxide films have a forbidden band of 1∼4 eV [14]. The Mott-Schottky analysis is often used to illustrate the semi-conductive properties of passive films by measuring the electrode capacitance as a function of the potential (E). Assuming that the capacitance of the space charge layer (C) is much less than that of the Helmholtz layer, then, the charge distribution at the

Polarization curves

Fig. 2 shows the polarization curve of UFG copper in 0.001 M chromate solutions. It can be seen that copper is in a stable passive state in the potential region from − 0.50 V to 0.48 V and exhibits good corrosion resistance property in 0.001 M chromate solutions. In addition, a peak appears when the potential reached to about 0.05 V. It may be related to the oxidation of Cu (I) to Cu (II) under this potential. The passive current change can affect the Mott-Schottky plots of passive films at peak

Conclusions

The results obtained in this study indicate that copper is in a stable passive state over the potential range from − 0.50 to 0.48 V in 0.001 M chromate solutions. From capacitance measurements (Mott-Schottky plots), the anodic passive films formed on copper in chromate solutions appear to have n-type semi-conductive properties and copper exist in two different oxidation states, Cu (I) and Cu (II). The Mott-Schottky plots of the films are frequency dependent and C^− 2 increased with increasing

Acknowledgements

This work was financially supported by National high technology research and development program of China (863 plan) (Grant No. 2002AA331110) and by the doctorial foundation of Xi'an Jiaotong University (Grant No. DFXJTU 2003-4).

References (25)

M.J. Carmezim et al.
Corros. Sci.
(2005)
M.Z. Yang et al.
Thin Solid Films
(1999)
A.D. Rata et al.
Surf. Sci.
(2003)
S. Maximovitch
Electrochim. Acta,
(1996)
P. Knauth et al.
J. Electroanal. Chem.
(1998)
Elzbieta Sikora et al.
Electrochim. Acta
(2002)
B. Millet et al.
Corros. Sci.
(1995)
J.F. Dewald
J. Phys. Chem. Solids
(1960)
A.D. Paola
Electrochim. Acta
(1989)
B. Yu et al.
Scripta Mater.
(2007)

D. Starosvetsky et al.

Electrochim. Acta.

(2006)

J.A. Switzer et al.

J. Mater. Res.

(1998)

Cited by (22)

The effect of applied stress on the crevice corrosion of 304 stainless steel in 3.5 wt% NaCl solution
2022, Corrosion Science
Citation Excerpt :
This result is consistent with Feng’s study [35]. Thus, according to this result and previous reports [35,36], capacitance measurements were conducted at a frequency of 1 kHz. Fig. 4(a) shows the cyclic potentiodynamic polarization curves of 304 stainless steel inside crevice under various applied stresses in 3.5 wt% NaCl solution.
The effect of applied stress on the crevice corrosion of 304 stainless steel in 3.5 wt% solution is investigated. The delayed and immediate crevice corrosion of 304 stainless steel could occur under various applied stresses and different polarized potential. Both these two types of crevice corrosion are developed from the evolution of metastable pits. The lifetime of metastable pits is prolonged with the increased stress and the secondary metastable pit is observed under 400 MPa applied stress. This contributes to increased probability of metastable pits transiting to stable pits and then promotes crevice corrosion development with the increased stress.
A comprehensive investigation of the electrochemical behavior of nickel-aluminum bronze alloy in alkaline solution: The effect of film formation potential
2021, Colloids and Surfaces A: Physicochemical and Engineering Aspects
Citation Excerpt :
The analysis showed that all curves give straight lines having a positive slope, which indicates that the passive film on Nickel-Aluminium-Bronze alloy exhibits an n-type semiconductor. Previous works in alkaline solutions have revealed the same behavior for the passive film formed on copper and its alloys [46–48]. The donor density is inversely proportional to the slope.
Nickel- aluminium bronze (NAB) is one of the well-known copper-based alloys; it is a well-recognized material in the marine environment thanks to its good corrosion and wear resistance along with its high strength. In this paper, the effect of film-forming potential on the electrochemical behavior of NAB alloy in 0.1 M Na₂SO₄ solution was evaluated. The study of the stability of passive films formed on NAB alloy was investigated using potentiodynamic and potentiostatic polarizations, Mott–Schottky (MS) and electrochemical impedance spectroscopy (EIS) analysis. The compositions of the passive films were determined by scanning electron microscope (SEM), UV–vis–NIR spectroscopy, and X-ray diffraction (XRD). All electrochemical tests revealed that the anodic potentials had a strong influence on passive films formed on NAB alloy. At intermediate frequencies above 450 mV_SCE, the corrosion process is controlled by the adsorption/desorption process along with charge transfer and diffusion processes. Mott–Schottky analysis indicated that the donor density is in the range of 10²¹ cm⁻³ and increased with an increase in the film-forming potential. Moreover, the SEM analysis showed that the NAB alloy suffered a severe corrosion attack of the copper-rich α phase leading to the retention of the κ phases of the as-cast NAB in the passive films. The passive films were grown on the NAB alloy and displayed n-type semi-conductor behavior, which is entirely predictable from the main Cu and Al oxide in the film.
Biological, antibacterial activities and electrochemical behavior of borided commercially pure titanium in BSA-containing PBS
2020, Transactions of Nonferrous Metals Society of China (English Edition)
The effects of boride coating on the bioactivity, antibacterial activity, and electrochemical behavior of commercially pure titanium (CP-Ti) in phosphate buffer solution (PBS) with bovine serum albumin (BSA) were studied. The grazing incidence X-ray diffraction (GIXRD) pattern confirmed the formation of a TiB/TiB₂ coating via boriding process. Scanning electron microscopy (SEM) observation indicated that the TiB₂ cross-linked particles covered the TiB whiskers. Water contact angle measurements revealed that boriding led to the formation of a surface with intermediate water affinity. Potentiodynamic polarization (PDP) assays demonstrated that the TiB/TiB₂ coating had acceptable passivation behavior in BSA-containing PBS. Electrochemical impedance spectroscopy (EIS) measurements revealed that the passivation behavior of the CP-Ti and the borided samples was improved by increasing exposure time. Based on the Mott-Schottky (M-S) tests, it was realized that the charge carriers of passive films of both samples decreased with increasing exposure time in BSA-containing PBS. The bioactivity test results in a simulated body fluid showed that the TiB/TiB₂ coating switched the CP-Ti from bioinert to bioactive material. Finally, the antibacterial activity test of the TiB/TiB₂ coating against Escherichia coli and Staphylococcus aureus indicated 99% antibacterial activity.
Enhanced corrosion resistance of a Cu–10Ni alloy in a 3.5 wt% NaCl solution by means of ultrasonic surface rolling treatment
2019, Surface and Coatings Technology
Cu10Ni alloy with a gradient nano-structured surface layer was synthesized by ultrasonic surface rolling process (USRP). The microstructure and mechanical properties of the nanosurface layer were characterized by X-ray diffractometry (XRD), microhardness testing, scanning electron microscope (SEM) and transmission electron microscope (TEM). The corrosion behavior of the USRPed and coarse-grained (CG) Cu10Ni alloy in a 3.5 wt% NaCl solution was investigated. The results showed that the topmost surface possessed an average grain size of 70 nm, and the corresponding surface hardness increased by 80% after USRP treatment. Additionally, the electrochemical test results showed that the USRPed Cu10Ni alloy exhibits enhanced corrosion resistance relative to that of the CG sample in a 3.5 wt% NaCl solution. The higher corrosion resistance of the nanograined Cu10Ni alloy was attributed to the nanograined surface promoting the formation of a passivation film on the surface during the corrosion process, which can effectively prevent further corrosion. This study demonstrates that the hardness properties and corrosion resistance of Cu10Ni alloys can be improved simultaneously by means of surface nanocrystallization.
In-vitro electrochemical study of TiB/TiB<inf>2</inf> composite coating on titanium in Ringer's solution
2018, Journal of Alloys and Compounds
In this work, different electrochemical analyses in Ringer's solution at 37 °C were implemented to understand the electrochemical response of diversity of titanium boride coatings developed on the commercially pure titanium (CP–Ti) via pack cementation method. X-ray diffraction (XRD) patterns and scanning electron microscopy (SEM) images indicated that the boriding creates the TiB whiskers and TiB whiskers/TiB₂ dense layer on the top of the surface of CP–Ti in respect to the heat-treatment at 900 and 1000 °C for 3 h. Potentiodynamic polarization curves cleared the passive behavior of the borided samples. Electrochemical impedance spectroscopy (EIS) assays revealed the satisfactory corrosion resistance of the borided samples in Ringer's solution. Mott–Schottky (M–S) assessments represented that the passive films formed on CP–Ti and the borided samples behaved as doped n-type semiconductor properties. Furthermore, M–S assessments indicated that the donor concentration of the passive films decreased with increasing the time. Finally, the borided sample at 900 °C in comparison with the borided sample at 1000 °C illustrated to be the more suitable selection for bioimplant applications, mainly due to better surface conditions to form a less defective and more protective passive film.
Assessment of microstructural and electrochemical behavior of severely deformed pure copper through equal channel angular pressing
2017, Journal of Alloys and Compounds
In the present research, the passive and electrochemical responses of pure copper, heavily deformed by equal channel angular pressing (ECAP), in a phosphate buffer solution (pH = 10.69) were investigated. For this purpose, various electrochemical tests such as potentiodynamic polarization (PDP), electrochemical impedance spectroscopy (EIS), and Mott–Schottky (M–S) analysis were carried out. Also, the influences of ECAP on distribution of the plastic strain and maximum principal stress were analyzed using a three-dimensional (3D) simulation by finite element methods (FEM). According to the field emission scanning electron microscope (FESEM) micrograph, by increasing the ECAP passes, finer microstructure was obtained. Considering all the electrochemical tests results, it can be concluded that the passive and electrochemical responses of pure copper are improved under influence of ECAP process, mainly due to the formation of thicker and less defective passive film.

View all citing articles on Scopus

View full text

Semi-conductive properties of passive films formed on copper in chromate solutions

Abstract

Introduction

Section snippets

Sample preparations

Mott-Schottky analysis

Polarization curves

Conclusions

Acknowledgements

Corros. Sci.

Thin Solid Films

Surf. Sci.

Electrochim. Acta,

J. Electroanal. Chem.

Electrochim. Acta

Corros. Sci.

J. Phys. Chem. Solids

Electrochim. Acta

Scripta Mater.

Electrochim. Acta.

J. Mater. Res.