Thesis (M.Sc.)-Cairo University, 2022.

Bibliography: pages 111-132.

The present work is devoted to systematic and detailed investigation concerning
the electrochemical and corrosion behavior of the dental, non-precious Ni-Cr
based alloy in artificial saliva solution which permits the estimation of the
behavior of the material in the oral cavity. A modification of the dental alloy
properties could be performed by coating the alloy surface using two ecofriendly
coatings, including, polyvinyl silsesquioxane (pvs) and nanohydroxyapatite
(nHAp) separately in artificial saliva solution. The aim is to
develop protection systems with improved corrosion protection properties and a
low environmental impact.
Accordingly, this thesis is organized into four chapters.
Chapter 1: Introduction:
This chapter presents a review of established literature, relevant to the main
themes of this thesis. It provides a general introduction to the biomaterials and
the dental Ni-Cr alloys and their applications history. Silane coupling agent used
in dentistry and trialkoxysilane in addition to the hydroxyapatite used in the
form of coatings on metal implants.
Chapter 2: Experimental:
describes the methods for preparing the different coating materials and their
composition also the techniques employed include measurements of the opencircuit
potential (OCP), potentiodynamic polarization, electrochemical
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impedance spectroscopy (EIS as well as surface characterization studies of the
coatings such as SEM and EDX.
Chapter 3: Results and discussion:
The electrochemical corrosion behavior of dental Ni-Cr (Wirolloy) was studied
in absence and presence of two types of environmentally friendly coating
materials PVS or HAp and nHAp in artificial saliva solution at 37 °C for 14
days of immersion using chemical dip-coating method or electrochemical
coating technique.
the following are the main points found in this study :
The corrosion behavior for uncoated and coated samples in artificial saliva
solution was achieved by using OCP, EIS and polarization techniques to
investigate the effectiveness of the coating films in improving the corrosion
resistance of the Ni-Cr alloy. The results support that electrochemically coated
sample with nHAp is favored and has the highest positive potential values over
all time intervals.
EIS results showed that the total resistance (RT) of the surface film on the tested
electrode is found to decrease with time of immersion, and that the total
impedance values for the non-coated alloy is much lower than those of
chemically or electrochemically coated alloy with PVS or HAp and nHAp
which assumes a great influence of the coatings on increasing the Wirolloy
impedance. In this work we are focused to model the response function of this
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biomaterial using an Electrical Equivalent Circuit (EEC) to analyze data
obtained by the Electrochemical Impedance Spectroscopy (EIS). The
experimental results showed that the Ni-Cr alloy is a passive biomaterial which
presents a quiet good resistance to corrosion when coated with PVS or nHAp. A
model of electric circuit was proposed to describe the electrochemical behavior
of the uncoated and coated biomaterial on the frequency range (0,100 KHz). The
equivqlent circuit proposed the presence of 2 Constant Phase Elements (CPE)
which explain the heterogeneity on the Metal/Electrolyte interface. Theoretical
model results were in good agreement with the experimental data with a best-fit
corresponding to a minimum standard deviation.
The polarization results showed that the lower (icorr) and the corresponding
higher (RP) for Both electrochemically nHAp & PVS coatings after 14 days
immersion in saliva solution indicate stable and higher corrosion prevention
rather than the chemically dip-coated alloy, although the impedance of the later
was greatly enhanced along the first three days of immersion but it consequently
started to drop rapidly and the film loses its protective properties.
The stability of the tested alloy coats increases in the order: EC coated nHAp >
EC coated PVS > C coated HAp > C coated PVS > non-coated alloy, as
obtained from EIS measurements. The results of OCP, EIS and polarization are
concurrent with each other that the electrochemically nHAp and PVS coatings
are the most corrosion prevention.
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The good corrosion protection of the nHAp coated alloy surpassing those for
the PVS coated ones can be attributed to the adsorption of HA nanoparticles on
the alloy surface, hindering the transfer of electrons and ions between the alloy
and the artificial saliva, which seemed to provide some corrosion protection.
SEM and EDX analyses proved the formation of the examined coating films on
the electrode surface, the electrochemically deposited nHAp and PVS have
excellent corrosion resistance, stability and more uniform surface coverage.
The chemical analysis of the corrosion products showed that all the formed
coatings are efficient in suppression of leaching of Ni ions into the solution with
some advantage to the electrochemical method over the chemical/dip-coating
method

العمل الحالي مخصص لتحقيق منهجي ومفصل بشأن
السلوك الكهروكيميائي والتآكل للأسنان Ni-Cr غير الثمينة
سبيكة أساسها في محلول اللعاب الاصطناعي مما يسمح بتقدير
سلوك المواد في تجويف الفم. تعديل سبيكة الأسنان
يمكن تنفيذ الخصائص عن طريق طلاء سطح السبائك باستخدام اثنين صديقين للبيئة
الطلاءات، بما في ذلك البولي فينيل سيلسكويوكسان (pvs) ونانوهيدروكسيباتيت
(nHAp) بشكل منفصل في محلول اللعاب الاصطناعي. والهدف هو
تطوير أنظمة الحماية مع تحسين خصائص الحماية من التآكل و أ
تأثير بيئي منخفض.
وبناء على ذلك فقد تم تنظيم هذه الرسالة في أربعة فصول.

Issues also as CD.

Text in English and abstract in Arabic & English.