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Corrosion of Mg

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by

Rowida Tarek

on 30 June 2013

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Transcript of Corrosion of Mg

Corrosion of Mg Alloys
Introduction
Magnesium is the third most abundant structural metal in the earth’s crust,only exceeded by aluminum and iron. The relative density of magnesium is 1.74 g/cm3, which is two-thirds the density of aluminum, and typical magnesium alloys weigh 35% less than their aluminum counterparts at equal stiffness. Their high strength-to-weight ratio makes magnesium alloys extremely promising for applications
requiring light weight, such as aerospace and transports.


Experimental Work
First Tafel Test

Results
Immersion
Thank You
Using Tafel & Immersion Tests
Presented to:
Dr.Nahed El-Mahallawy

Interestingly, magnesium ions are present in large amounts in the human body and involved in many metabolic reactions and biological mechanisms. This means that magnesium can serve as a metallic biodegradable material in the human body in which magnesium can be gradually dissolved, consumed or absorbed
As a potential biodegradable material, magnesium shows many advantages over current metallic materials and biodegradable plastics and ceramics. These advantages include its greater fracture toughness over ceramic bio-materials, higher strength than biodegradable plastics, and more favorable elastic modulus than commonly used biomedical metals.
Advantages
Disadvantages
Nevertheless, several problems such as inadequate strength when used at load-bearing sites, rapid corrosion which causes subcutaneous gas bubbles must be solved before this unique metal can be widely used in biomedical fields. To improve its strength and corrosion resistance, alloying is the most widely used strategy. However, a drawback of Mg as a potential bone implant material is its fast degradation rate in human body fluid. The physical and mechanical properties of Mg also decrease along with the corrosion progression. An implant that degrades too fast could fail under loading.
Measures Ecorr and Icorr.
Range of Voltage was took from -1700 till 1700; since open
circuit potential of Mg and it’s alloys was always at -1500 to
-1600 and starting voltage was equal: OCP – 200, the ending
voltage was predicted , which means we can stop the
operation when we see that the curve is completed and the rate
was 1mV/sec. The area exposed to the SBF was 0.122567989 mm².
The samples were grinded and polished before testing, washed
with distilled water then alcohol.
was used in the present work and weight loss method took place in representing the results.
Two types of samples were used in this study (extruded and rolled samples). The samples were grinded and polished before testing, washed with distilled water then alcohol. The surface areas were measured as well as the weight of the samples. The beakers were covered by watch glasses in order to avoid any contaminations from the surroundings.
Simulated body fluid is used as the corrosive medium. The temperature of the test was controlled at 37 degrees and pH was controlled at 7.5
A simulated body fluid (SBF) is a solution with an ion concentration close to that of human blood plasma, kept under mild conditions of pH and identical physiological temperature. SBF was first introduced by Kokubo in order to evaluate the changes on a surface of a bioactive glass ceramic.

Second Immersion test
And the washing solution used to remove the corroded Mg particles consisted or 150 gm/liter CrO3 and 10 gm/liter AgNO3.
For every reading, the samples were washed in the cleaning solution to remove the corroded parts then washed in distilled water after that washed and rinsed in alcohol before drying using hot air. The samples were weighted after that using a scale of 0.1 mg accuracy.
The samples were subjected to the weight loss corrosion test by immersing in simulated body fluid with a controlled pH value of 7.5 and the readings took place over 1,2,3,4 till 10 days.
Each beaker contained two samples of the same chemical composition (one extruded and the other rolled) and the weight loss was calculated for each of them separately. The number of samples were 14.

Immersion Test
Ecorr =1500 volt
Icorr = 0.0125 ampere

Ecorr = -1425 volts
Icorr = 0.00794 ampere

Ecorr = -1500 volts
Icorr = 0.001258 ampere
Ecorr = -1500 volts
Icorr = 0.01412 ampere
Ecorr = -1550 volts
Icorr = 0.002511 ampere


Ecorr = -1525 volts
Icorr = 0.0446 ampere

Ecorr = -1600 volts
Icorr = 0.006309 ampere

Ecorr = -1575 volts
Icorr = 0.0000316 ampere

Ecorr = -1500 volts
Icorr = 0.006309 ampere

Ecorr = -1600 volts
Icorr = -0.00794 ampere
Ecorr = -1550 volts
Icorr = 0.01995 ampere
Ecorr = 200 volts
Icorr = 0.00158 ampere

Ecorr = -1250 volts
Icorr = 6.3095 nanoampere
Ecorr = -1300 volts
Icorr = 5.0118 nanoampere
Ecorr = -1250 volts
Icorr = 0.1995 nanoampere
Presented By:
Yasmin Tawfik Halim
Full transcript