ISSN ONLINE(2319-8753)PRINT(2347-6710)
R.Nagalakshmi1, S.Rajendran2 J.Sathiyabama3 Assistant Professor, Department of Chemistry, Aarupadai Veedu Institute of Technology, Chennai-603104, Tamilnadu, India1 Professor, PG and Research Department of Chemistry, GTN Arts College, Dindigul-624 005, Tamilnadu, India. Research Centre RVS School of Engineering and Technology, Dindigul -624 005, Tamilnadu, India2 Associate Professor, PG and Research Department of Chemistry, GTN Arts College, Dindigul-624 005, Tamilnadu, India3 |
Related article at Pubmed, Scholar Google |
Visit for more related articles at International Journal of Innovative Research in Science, Engineering and Technology
Corrosion resistance of two metals namely mild steel (MS), Nickel Titanium super elastic alloy has been evaluated in artificial urine in the absence and presence of sodium chloride. AC impedance spectra have been used to investigate the corrosion behaviour of these metals. The order of corrosion resistance of metals in artificial urine, in the absence and also in the presence of sodium chloride was Ni-Ti super elastic alloy> mild steel.
Keywords |
||||||||||||||||||
Mild steel (MS), Nickel Titanium super elastic alloy, artificial urine, sodium chloride | ||||||||||||||||||
INTRODUCTION |
||||||||||||||||||
Metallic biomaterials are commonly used in reconstruction in the orthopedic and dental surgery, operative cardiology and urology. Implant alloys exhibit attractive properties such as mechanical strength and biocompatibility, corrosion resistance, safety, ductility, and wear resistance. Stainless steels, titanium alloys and cobalt alloys are commonly used as biomaterials [1]-[7] Biocompatibility of implants in tissue environment is determined by inseparable biochemical, biomechanical and bioeletronic factors. Biological reactions are analyzed with respect to metabolic, bacteriological, immunological and oncological processes [8], [10]-[13], [15]-[17], [19]-[25], [28].Current chemical compositions of the stainless steel (Cr-Ni-Mo) should ensure good pitting corrosion resistance and monophase austenitic structure. The austenite grain size (less than 4 acc. to ISO) and non-metallic inclusions (max. 1.5 acc. to ISO) are limited. Fine grain and low level of non-metallic inclusions ensure good mechanical properties and reduce crackability, specially in implants with small cross-sections. They also increase corrosion resistance of implants [16], [17], [23].Great number of publications is austenitic focused on generalization of corrosion failure of implants. These analyses are focused on implants commonly used in reconstruction in the orthopedic, dental surgery, operative cardiology and urology .These implants are mainly made of stainless steel [8], [9], [12], [14], [18], [26]-[28]. Long-term research on corrosion of implants made of the mentioned steel show the complexity of corrosion processes depending on the implant form, its chemical and phase composition, surface condition, surgical procedure and implantation period [16], [17], and [23]. Corrosion products infiltrate tissues. This process is called metalosis [10]. Phatomorphological changes, dependent on the type and concentration of elements, occur in tissues close to implant. Histopathological changes are observed in the detoxication organs (liver, kidneys, spleen) [16]. Therefore, corrosion tests in simulated body fluids are the basis for searching optimal fields of usage and improvement of existing solutions. In general the human urine contains sodium chloride and also excreted by the human body. In this research paper, if the person undergone implantation in the urinary tract how the metal undergoes corrosion in the presence of excess amount of sodium chloride. The present work was undertaken to study the corrosion behavior of two metals namely mild steel (MS),Nickel Titanium super elastic alloy in artificial urine, in the absence and presence of 50ppm and 100ppm of sodium chloride by AC impedance spectra. Corrosion parameters such as charge transfer resistance, double layer capacitance and impedance value have been derived from these studies. | ||||||||||||||||||
II.EXPERIMENTAL |
||||||||||||||||||
A.Materials and Methods | ||||||||||||||||||
Two metals namely mild steel (MS), Nickel Titanium super elastic alloy were chosen for the present study. The composition of mild steel was (wt %):0.026S, 0.06P, 0.4 Mn, 0.1 C and balance iron (ArockiaSelvi et.al. 2009) [29]. The composition of Ni-Ti super elastic alloy was (wt %) Ni 55.5, and balance Ti [30]. The metal specimens were encapsulated in Teflon. The surface area of the exposed metal surface was 0.0785 cm2.The metal specimens were polished to mirror finish and degreased with trichloroethylene. The metal specimens were immersed in artificial urine (AU) (J. Przondziono et al, 2009) [31], whose composition was: Solution A: CaCl2.H2O-1.765g/l,Na2SO4 - 4.862g/l, MgSO4.7H2O - 1.462g/l, NH4Cl - 4.643g/l, KCl – 12.130g/l. Solution B: NaH2PO4.2H2O - 2.660g/l, Na2HPO4 - 0.869 g/l, C6H5Na3O7.2H2O - 1.168 g/l, NaCl - 13.545 g/l. The pH of the solution was 6.5 (W.Kajzer et al, 2006) [5]. | ||||||||||||||||||
In electrochemical studies the metal specimens were used as working electrodes. Artificial urine (AU) was used as the electrolyte (10 ml). The temperature was maintained at 37±0.10C.Commercially available sodium chloride was used in this study. 50ppm and 100ppm of sodium chloride was used in artificial urine. | ||||||||||||||||||
B.AC Impedance Spectra | ||||||||||||||||||
The instruments used for polarization study was used to record AC impedance spectra also. The cell set up was the same. The real part (Z’) and imaginary part (Z”) of the cell impedance were measured in ohms at various frequencies. Values of the charge transfer resistance (Rt) and the double layer capacitance (Cdl) were calculated from Nyquist plots. Impedance log (Z/ohms) value was calculated from Bode plots | ||||||||||||||||||
III. RESULTS AND DISCUSSION |
||||||||||||||||||
AC Impedance Spectra | ||||||||||||||||||
1. Corrosion resistance of Mild steel in AU in presence of NaCl: AC impedance parameters such as charge transfer resistance (Rt), double layer capacitance (Cdl) (derived from Nyquist plots) and impedance value logz/ohm (derived from Bode plots) of MS immersed in AU and AU containing sodium chloride are given in Table.1. The AC impedance spectra are shown in Fig.1a, 1b, 1c (Nyquist plots) 2, 3, 4 (Bode plots). | ||||||||||||||||||
It is observed from the table that when sodium chloride is added to AU the Rt value decreases, the Cdl value increases (Nyquist plot). This indicates that in presence of sodium chloride, the corrosion resistance of MS decreases. This is further supported that in presence of sodium chloride the impedance value (Logz/ohm) decreases. Further the phase angle value decreases (Bode plots). The AC impedance spectra leads to the conclusion that in the presence of sodium chloride the corrosion resistance of MS in AU decreases. So the use of MS in presence of sodium chloride in urology should be avoided. Otherwise MS will undergo corrosion and it will leads to many problem | ||||||||||||||||||
The equivalent circuit diagram for the above three system is shown in scheme 1. | ||||||||||||||||||
Cdl – Double layer capacitance | ||||||||||||||||||
Rs – Solution resistance | ||||||||||||||||||
Rct– Charge transfer resistance | ||||||||||||||||||
2. Corrosion resistance of Ni-Ti Superelastic in AU in presence of NaCl : AC impedance parameters such as charge transfer resistance (Rt), double layer capacitance (Cdl) (derived from Nyquist plots) and impedance value logz/ohm (derived from Bode plots) of Ni-Ti superelastic alloy immersed in AU and AU containing sodium chloride are given in Table.2. The AC impedance spectra are shown in Fig.5a, 5b, 5c (Nyquist plots) 6, 7, 8 (Bode plots). | ||||||||||||||||||
It is observed from the table that when sodium chloride is added to AU the Rt value decreases, the Cdl value increases (Nyquist plot). This indicates that in presence of sodium chloride, the corrosion resistance of Ni-Ti superelastic alloy decreases. This is further supported that in presence of sodium chloride the impedance value (Logz/ohm) decreases. Further the phase angle value decreases (Bode plots) [32], [33].The AC impedance spectra lead to the conclusion that in the presence of sodium chloride the corrosion resistance of Ni-Ti superelastic alloy in AU decreases. | ||||||||||||||||||
The enlarged graph in the high frequency region of Figures 5a, 5b, 5c are shown in Figures 5a.1, 5b.1, 5c.1 respectively. It is observed from these graphs that the reactions are diffusion controlled processes that is diffusion of ions from the bulk of the solution towards the metal surface. The equivalent circuit diagram for such system is shown in scheme.2. | ||||||||||||||||||
It is observed that the graphs seen in Fig.5a, 5b, 5c are very close to that of very corrosive protective system (insulator). That is electron transfer from metal to system is very difficult. Since the protective film formed on the metal surface is very stable and compact. | ||||||||||||||||||
It is observed from the impedance Bode plots (Fig.6, 7, 8) that the value of impedance decreases sharply as the log z value increases. The slope of the line in the middle frequency region is 0.5. This is characteristic of very protective film [34]. | ||||||||||||||||||
The equivalent circuit diagram for such system is shown in scheme.2 | ||||||||||||||||||
Rs – Solution resistance | ||||||||||||||||||
IV.CONCLUSION |
||||||||||||||||||
AC impedance spectra have led to the following conclusions: In the absence of sodium chloride the order of corrosion resistance was: Ni -Ti super elastic>Mild steel. In the presence of 50ppm and 100ppm of sodium chloride, the order of corrosion resistance was: Ni-Ti super elastic >Mild steel. Ni-Ti super elastic was more corrosion resistant in the absence of sodium chloride than in the presence of sodium chloride. Mild steel was less corrosion resistant in the presence of sodium chloride and in the absence of sodium chloride | ||||||||||||||||||
ACKNOWLEDGEMENT |
||||||||||||||||||
The authors are thankful to their Managements and St. Joseph’s Research and Community Development Trust, Dindigul, India for their help and encouragement | ||||||||||||||||||
Tables at a glance |
||||||||||||||||||
|
||||||||||||||||||
Figures at a glance |
||||||||||||||||||
|
||||||||||||||||||
References |
||||||||||||||||||
|