الفهرس 
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Abstract
The work presented in this thesis deals with the study of the electrochemical corrosion behaviour of the biomedical Ti70Zr20Nb7.5Ta2.5 alloy in different physiological media such as Ringler’s solution, Hanke’s solution, saline, and saliva solution. Titanium and its alloys Ti-6Al-4V, which makes them have many medical uses and applications, whether in bones or dental implants. These materials are characterized by the presence of a layer of oxide once exposed to oxygen, which protects them from corrosion.
The thesis is divided into three main chapters, including the introduction, the experimental part, the results, and the discussion. The following is a summary of each chapter.
Chapter 1: Introduction
The introduction includes an overview of the types of titanium alloys and ther uses in medical applications, the specification of these alloys and their electrochemical behaviour in different media. The following is a list of some detailed points.
Biomaterials - Titanium and titanium alloys as biomedical implants - β-and α phases of titanium alloys - Mechanical properties of the titanium alloys - Physiological solutions - Effect of F- ions - Effect of inflammatory conditions - Effect of hydrogen peroxide (H2O2) - Effect of albumin - Corrosion behaviour of biomaterials Ti and Ti-alloys - Potentiodynamic polarization technique - Open circuit potential (OCP) - Electrochemical impedance spectroscopy (EIS).
Chapter 2: Materials and Methods
This chapter includes information about the chemicals used in this study, the preparation methods for each solution, the chemical composition of the used alloys, the measuring devices, and the conditions applied to each experiment during this study:
Chapter 3: Results and Discussion
In this chapter, the obtained results are presented and discussed. This chapter consists of four parts as follow:
Part 1
Electrochemical corrosion behaviour of a biomedical Ti70Zr20Nb7.5Ta2.5 alloy in an artificial saliva solution (ASS)
This part includes the results and discussion of the corrosion behaviour of a biomedical Ti70Zr20Nb7.5Ta2.5 alloy in an artificial saliva solution (ASS) at a temperature of 37 and compared with commercial titanium and conventional Ti-6Al-4V alloy.
The corrosion behavior of a biomedical Ti70Zr20Nb7.5Ta2.5 alloy was examined and matched with that of commercial titanium and the traditional biomaterial Ti-6Al-4V alloy in an ASS. Moreover, the impact of different concentrations of F- ions and pH on the corrosion behavior of Ti70Zr20Nb7.5Ta2.5 was also investigated. The corrosion potential decreases in the following order: Ti70Zr20Nb7.5Ta2.5 > Ti-6Al-4V > Ti. The steady state potential of the OCP, which agrees with the result of the PPC curves, indicates that the corrosion resistance decreases in the same order: Ti70Zr20Nb7.5Ta2.5 > Ti-6Al-4V > Ti. It was observed that the Ti70Zr20Nb7.5Ta2.5 alloy immersed in ASS at a high concentration of fluoride ions (2000 ppm) and low pH (pH 2.0) suffers from cracking and exhibits the lowest corrosion resistance compared to the sample immersed in the saliva solution without and with low concentrations of fluoride ions (0-1000 ppm) and at high pH values (5.0 and 7.0). These data reveal that if the fluoride ion concentrations enhance or the pH falls, corrosion resistance of the alloy reduces. The EIS data shows that the passive layer is made up of a duplex outer and inner oxide layer, and that the alloy’s resistance to corrosion in fluoride-containing solutions has been significantly reduced. Additionally, the data demonstrates that a Ti70Zr20Nb7.5Ta2.5 alloy’s corrosion resistance rises with increasing immersion time in both the presence and absence of F- ions. The protective passive oxides, according to XPS (X-ray photoelectron spectroscopy) investigation, include TiO2, ZrO2, Nb2O5, and TaO. Based on the conclusions, the alloy Ti70Zr20Nb7.5Ta2.5 can be regarded as the best suitable for usage as a biomaterial in ASS among all the materials tested in this work.
Part ІΙ:
Electrochemical corrosion behaviour of biomedical Ti70Zr20Nb7.5Ta2.5 alloy in Ringer’s solution
In this part of study, the in vitro corrosion resistance of the Ti70Zr20Nb7.5Ta2.5 alloy has been evaluated and contrasted with Ti-6Al-4V, and Ti in RS. Electrochemical studies were used to examine the corrosion behaviour of the Ti70Zr20Nb7.5Ta2.5 alloy when it was annealed at 600, 800, and 1000 °C and immersed for various immersion times. The data in this work led to the following conclusions:
1) The Zmod and Rb values of T70Z20N7.5T2.5 alloy are greater than those of Ti-6Al-4V alloy and Ti indicating that the spontaneous oxide coating for T70Z20N7.5T2.5 alloy has improved its ability to resist corrosion. According to PPC’s results, the Icorr value of the T70Z20N7.5T2.5 alloy (Icorr) is also smaller compared to Ti-6Al-4V and Ti. Both EIS and PPCs data show that T70Z20N7.5T2.5 has the highest level of corrosion resistance comparable to that of the Ti-6Al-4V alloy and Ti.
2) In contrast to the Ti-6Al-4V (OCP), and Ti (OCP) samples, the values of OCP for the T70Z20N7.5T2.5 sample in RS became more positive with time indicating that the T70Z20N7.5T2.5 is in a state of greatly stable passivation and is highly resistant to corrosion.
3) In comparison to the other samples, including annealed and unannealed ones, the T70Z20N7.5T2.5 alloy showed the best corrosion resistance when it was annealed at a temperature of 800 °C. The T70Z20N7.5T2.5 alloy annealed at 1000 °C had the greatest Ipass, whereas the alloy annealed at 800 °C had the lowest Ipass.
4) The EIS results display that the passive film is composed of a dual outer and inner oxide layer and that at a critical high temperature (up to 800 °C). The resistance of corrosion of the T70Z20N7.5T2.5 sample increases, but above this critical temperature (at 1000 °C) and without annealing, the resistance of corrosion decreases due to the dissolution process of the passive film on the T70Z20N7.5T2.5 sample surface.
5) The OCP data show that the resistance to corrosion of the T70Z20N7.5T2.5 sample treated at 800 °C, was the best in comparison to the untreated and annealed samples at 600 °C and the resistance to corrosion was the least when the alloy was treated at 1000 °C.
6) The PPCs data show that without immersion, the alloy corrosion resistance is higher than its value both with immersion and with decreasing the immersion time. These results agree with the EIS and OCP data of the alloy at the same immersion times.
7) The T70Z20N7.5T2.5 system was discovered to have a structure made up of alpha and beta-phases. An examination of the X-ray structure found a combination of hexagonal close-packed α-Ti (main phase, with 5.35 nm grain size) and body-centred -Ti. Of all the materials investigated in this work, the alloy T70Z20N7.5T2.5 can be regarded as a promising material appropriate for use as a biomaterial.
Part ΙІΙ:
Electrochemical corrosion behavior of Ti70Zr20Nb7.5Ta2.5 alloy in a physiological saline solution and the impact of inflammatory conditions
This part includes the results and discussion of the corrosion behaviour of a biomedical Ti70Zr20Nb7.5Ta2.5 alloy in a physiological saline solution (PSS) at a temperature of 37 and compared with commercial titanium and conventional Ti-6Al-4V alloy. Moreover, the effect of inflammatory conditions (H2O2 and BSA) on the corrosion behaviour of Ti70Zr20Nb7.5Ta2.5 alloy was also examined.
The corrosion potential decreases in the following order: Ti70Zr20Nb7.5Ta2.5 > Ti-6Al-4V > Ti. The steady state potential of the OCP, which agrees with the result of the PPC curves, indicates that the corrosion resistance decreases in the same order: Ti70Zr20Nb7.5Ta2.5 > Ti-6Al-4V > Ti. It was observed that the Ti70Zr20Nb7.5Ta2.5 alloy immersed in PSS and 1% H2O2 has the lowest corrosion resistance compared to the sample immersed in other solutions and thus higher rate of corrosion compared to samples immersed in other solutions at immersion times of 120 hours. The surface of alloy after immersion in each of (1% BSA and 1% H2O2) and (1%BSA) is less corrosion resistance than (1% H2O2) alone, which indicates that the presence of BSA protects the passive oxide layer formed on the surface of the alloy from corrosion and improves the corrosion rate. (EIS) data show that the passive layer consists of double outer and inner oxide layer. In addition, the data shows that the resistance of Ti70Zr20Nb7.5Ta2.5 alloy increases with increasing immersion time in the presence of (1%BSA and 1% H2O2) and (1%BSA) and (1% H2O2) and in their absence.
Based on the conclusions, the alloy Ti70Zr20Nb7.5Ta2.5 can be regarded as the best suitable for usage as a biomaterial in ASS among all the materials tested in this work.
Part ΙV:
The electrochemical corrosion behavior of Ti70Zr20Nb7.5Ta2.5 alloy in Hank’s physiological solution (HPS) and the impact of immersion time and H2O2
In this part of study, the in vitro corrosion resistance of the Ti70Zr20Nb7.5Ta2.5 alloy has been evaluated and contrasted with that of Ti-6Al-4V, and Ti in HPS. Electrochemical studies were used to examine the corrosion behaviour of the Ti70Zr20Nb7.5Ta2.5 alloy when it was immersed for different immersion times in the presence and absence of (H2O2). The data present in this work led to the following conclusions:
1- The Zmod and Rb values of T70Z20N7.5T2.5 alloy are greater than those of Ti-6Al-4V alloy and Ti indicating that the spontaneous oxide coating for T70Z20N7.5T2.5 alloy has improved its ability to resist corrosion. According to PPC’s results, the icorr value of the T70Z20N7.5T2.5 alloy (icorr) is also smaller compared to Ti-6Al-4V and Ti. Both EIS and PPCs data show that T70Z20N7.5T2.5 has the highest level of corrosion resistance comparable to that of the Ti-6Al-4V alloy and Ti.
2- In contrast to the Ti-6Al-4V (OCP), and Ti (OCP) samples, the values of OCP for the T70Z20N7.5T2.5 sample in HPS became more positive with time indicating that the T70Z20N7.5T2.5 is in a state of greatly stable passivation and is highly resistant to corrosion.
3- PPCS data show that after immersion the polarization curves were shifted towards a less noble potential from 5 days to 25 days, which indicates that the corrosion resistance of T70Z20N7.5T2.5 alloy decreases, but it shifted to a more noble potential from 45 to 60 days, which indicates showed that the corrosion resistance of the T70Z20N7.5T2.5 alloy increased. These results are consistent with the EIS and OCP data of the alloy at the same immersion times. Of all the materials investigated in this work, the alloy T70Z20N7.5T2.5 can be regarded as a promising material appropriate for use as a biomaterial.