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Most materials experience some type of interaction with a large number of diverse environments. Often, such interactions impair a material's usefulness as a result of the deterioration of its physic-mechanical properties (e.g., ductility, strength, appearance and shape etc). In metals, material loss is either by dissolution (corrosion) or by the formation of nonmetallic scale or film (oxidation). There are different ways to prevent corrosion which includes electroplating, coating and painting, use of inhibitors, cathodic protection and anodic protection.
One of the most effective means of corrosion prevention is cathodic protection; in some situations, completely stops corrosion. Cathodic protection simply involves supplying electrons from an external source to the metal to be protected, making it a cathode; the reaction above is thus forced in the reverse direction (or reduction). Basically two types of cathodic protection systems are available, impressed current and sacrificial anode.
In Impressed current system an external DC source is used to provide the required amount of current. The current is provided by suitable rectifier through inert type of anode (ground bed). Because of supply of current; anodes are consumed (at lower rate) by corrosion. It is therefore desirable to use materials for cathode that should consume anode at a much lower rate than usual pipeline metals. This will ensure reasonable long life for anodes.
Sacrificial anode system; employs a galvanic couple, in which protective current is generated by galvanic action. The metal to be protected is electrically connected to another metal that is more reactive in the particular environment. The latter experiences oxidation upon giving up electrons, and protects the first metal from corrosion. The oxidized metal is often called a sacrificial anode. Magnesium, zinc, aluminum, and their alloys are commonly used as anode because their electromotive force (emf) is least positive in the galvanic series.
Literature review indicates that aluminum can be used as an anode in cathodic protection but it is restricted because a passive layer is formed on its surface. This passive layer is acting as a barrier for the current hence the cathodic process stops. To overcome this problem cerium oxide (ceria) particles are added in it.
Ceria is basically an oxide of the rare earth metal cerium which is also known as ceric oxide, Cerium (IV) oxide, or cerium dioxide. Powdered ceria is slightly hygroscopic and also absorb a small amount of carbon dioxide from the atmosphere. When ceria particles are present into aluminum; minimize the side effect of passive layer by providing a passage to environment to react with it. Concomitantly cathodic protection reaction continues without any hindrance. It is observed that rate of cathodic reaction increases with increasing surface area of the ceria particles. Therefore nano ceria particles have been alloyed in aluminum in order to improve its cathodic protection efficiency.
Keeping in view the recent development in the manufacturing of aluminum anode the present study is aimed to manufacture ceria aluminum-zinc composite anode. Cheaper cathodic protection for metallic structures can be anticipated. In present study effect of micro and nano size ceria particles on cathodic protection of Al-Zn will be evaluated.
JUSTIFICATION AND SCOPE OF THE STUDY
Aluminum anodes can be used in catholically protects steel in seawater and other saline electrolyte. But the uses of aluminum anodes are very restricted because, the surface film that forms on anode tend to reduce the current output. Therefore sacrificial anode system does not work efficiently in saline or sea water environment. To protect the metallic structure like ships, boats, pipelines etc, magnesium and zinc anodes are normally used which are very costly as compared to aluminum. Literature pertaining to sacrificial anode system reveals that ceria particles added to aluminum will increase its efficiency within seawater and saline electrolyte environments. As such in Pakistan no work is done yet to develop a cheapest sacrificial aluminum anode. Therefore it would be appreciating to manufacture such cost effective anode as compared to magnesium and zinc.
AIMS AND OBJECTIVES
Following are the main objectives of the proposed project.
Development of Nano and micro ceria particles.
Manufacturing of Al-Zn alloy composites with nano and micro ceria by casting method.
Determination of corrosion protection efficiency of the composite anode.
To manufacture Nano-Ceria Al-Zn based sacrificial anode, and to evaluate corrosion efficiency the methodology is briefly described as under.
Aluminum, Zinc, Mild steel rod, Cerium Nitrate and Cerium Oxide will be purchased from the market.
Preparation of Nano-Ceria
Nano-ceria will be prepared by precipitation method. In this method the cerium nitrate is added with ammonia solution at pH 8 and heated up to 80oC for particular time interval. Time of precipitation is one of the major factors that will be manipulated in present study.
Characterization Of Nano Ceria
Composition and particle size of nano ceria will be determined by using SEM and XRD.
Grinding And Sizing
Cerium oxide (Ceria) particles are available in the market (1-3mm size). These will be grinded in a ball mill. After grinding the -500+300µm, -300+200 µm and -200+100 µm size fractions will be collected by using sieving method.
Anode of 95wt% Al and 5wt%Zn will be casted using muffle furnace.
Composite Anode Manufacturing
Composite anode will be made by adding different wt% of nano ceria particles and micro ceria particles of -500+300µm, -300+200 µm and -200+100 µm size fractions.
For hardness testing Micro-Vicker hardness tester will be used.
Wear Resistance Test
For determination of wear resistance weight loss method will be used at room temperature.
Micro-structural analysis such as grain size and grain boundary of the anode will be done by using SEM. Samples will be polished by using metallographic technique.
Anodes will be evaluated for biological corrosion by immersing the anodes in marine water for 3 days. Thereafter species concentration will be determined by MTN method.
Potential energy of the anodes will be determined with the help of copper/copper sulfate reference electrode in 3.5% NaCl solution.
Galvanic Efficiency of the anodes will be determined by coupling test anode and a steel cathode in 3.5% NaCl solution for a period of 30 days. Surface area ratio of anode to cathode will be maintained at 1:10.
Self-corrosion of the anodes will be determined by immersing the anode in 3.5% NaCl solution for a period of 30 days.
PRACTICAL USE OF PROBABLE RESULTS
The research results will be a source of reference for the researchers and scholars in the field of nano-science, composite manufacturing and cathodic protection.
The research results will be helpful in protecting the marine structures etc.
Aluminum can be used as a sacrificial anode commercially by casting it with ceria. This can save the cost on protection of the gas pipe line as the magnesium and zinc anodes are costly.