TitleMeasurement of Corrosion Rate in Acid Media AbstractThe importance of corrosion can be seen in daily life. Corrosion causes accidents in industry, on highways, and in homes. It is wasteful financially, costing industrialized nations 4-5% of their gross domestic products annually. This report disclose the importance of corrosion and to measure the corrosion rate in the acid media.

IntroductionThere are many type of corrosion happen in everyday life. Pitting corrosion, or pitting, is a form of extremely localized corrosion that leads to the creation of small holes in the metal. The driving power for pitting corrosion is the depassivation of a small area, which becomes anodic while an unknown but potentially vast area becomes cathodic, leading to very localized galvanic corrosion. The corrosion penetrates the mass of the metal, with limited diffusion of ions.Galvanic corrosion, resulting from a metal contacting another conducting material in a corrosive medium, is one of the most common types of corrosion. It may be found at the junction of a water main, where a copper pipe meets a steel pipe, or in a microelectronic device, where different metals and semiconductors are placed together, or in a metal matrix composite material in which reinforcing materials, such as graphite, are dispersed in a metal, or on a ship, where the various components immersed in water are made of different metal alloys. In many cases, galvanic corrosion may result in quick deterioration of the metals but, in other cases, the galvanic corrosion of one metal may result in the corrosion protection of an attached metal, which is the basis of cathodic protection by sacrificial anodes. Galvanic corrosion is an extensively investigated subject, and is qualitatively well understood but due to its highly complex nature, it has been difficult to deal with in a quantitative way until recently. The widespread use of computers and the development of software have made great advances in understanding and predicting galvanic corrosion. When two dissimilar conducting materials in electrical contact with each other are exposed to an electrolyte, a current, called the galvanic current, flows from one to the other. Galvanic corrosion is that part of the corrosion that occurs at the anodic member of such a couple and is directly related to the galvanic current by Faradays law. Under a coupling condition, the simultaneous additional corrosion taking place on the anode of the couple is called the local corrosion. The local corrosion may or may not equal the corrosion, called the normal corrosion, taking place when the two metals are not electrically connected. The difference between the local and the normal corrosion is called the difference effect, which may be positive or negative. A galvanic current generally causes a reduction in the total corrosion rate of the cathodic member of the couple. In this case, the cathodic member is cathodically protected.

Objective To measure the corrosion rate of iron and copper To study the effect of corrosion media to steel To learn about the galvanic and pitting corrosion Materials and Equipment Corrosion medium (water), Beaker,Iron and copperGrit, silicon paper, Optical microscope, Metal cutting equipment

ProcedurePart 1: Galvanic corrosion 1. 200 cm3 of corrosion medium (water) is measured into a 250 cm3 beaker. 2. The sample (iron and copper) are cut into 3 cm x 3 cm dimension. 3. The sample surfaces are ground with 120 grit silicon paper and their respective weight is measured. 4. Both sample together are then clamped. 5. The sample are immersed into the corrosion medium.6. Subsequently, the sample surface are observed under optical microscopeafter one week.

Part 2: Pitting corrosion 1. A plate of mild steel is cut into 3cm x 3 cm. 2. The plate is grounded with 120 grit silicon paper. 3. KCL solution are prepared and poured into separate beaker. 4. The mild steel plate is immersed completely into KCl solution.5. Subsequently, the plate are cleaned and dried.6. The surface exposed to the corrosion medium are then observed under optical microscope after one week.

Part 3 : Rate of Corrossion1. A plate of mild steel and a plate of copper are cut into 3cm x 3 cm. 2. The plates are grounded with 120 grit silicon paper. 3. After that, the plates initial weight, length, width and thickness are measured and recorded.4. KCL solution are prepared and poured into separate beaker. 5. The mild steel plate and copper plate are immersed completely into separate KCl solution.6. The samples are weighed in every 24 hours for the calculation of corrosion rate.

ResultPart A

Mild Steel (galvanic corrossion) (x20) Mild Steel (galvanic corrossion) (x50)

Copper (galvanic corrossion) (x20) Copper (galvanic corrossion) (x50)

Part B

Mild Steel (pitting corrossion) (x20) Mild Steel (pitting corrossion) (x50)

Part CSampleWeight Length Width ThicknessArea Volume

Mild steel19.0313g30.00mm13.90mm5.81mm4.17cm22422.77mm2

Copper 19.9528g31.86mm12.98mm5.91mm4.1354cm22444.04mm2

SampleWeight (g)

Initial22 hours 40min47 hours 20min70 hours

Mild steel19.031319.029719.027619.0249

Copper 19.952819.952319.952219.9307

SampleWeight Loss (g)

Initial22 hours 40min47 hours 20min70 hours

Mild steel00.00160.00370.0064

Copper 00.00050.00060.0221

SampleCorossion Rate (cm2/hour)

Initial22 hours 40min47 hours 20min70 hours

Mild steel01.1513 x 10-31.2753 x 10-31.4915 x 10-3

Copper 03.1786 x 10-41.8269 x 10-44.5500 x 10-3

Corossion Rate are calculated using formula,

Corossion Rate = (534w)/(DAT)Where w = Weight loss (g),D = Density (g/cm3),A = Area (cm2),T = Hours Immersed (h).Density copper 8.96 g/cm3Density mild steel 7.85 g/cm3

Discussion In this experiment, the experiment are divided into three parts. In the first part, we run the experiment to see the effect of galvanic corrosion on mild steel and copper. Galvanic corrosion or "Bimetallic Corrosion" or "Dissimilar Metal Corrosion", as sometimes called, is defined as the acceleratedcorrosionof a metal because of an electrical contact (including physical contact) with a more noble metal or nonmetallic conductor (the cathode) in a corrosive electrolyte. The potential difference (i.e., the voltage) between two dissimilar metals is the driving force for the destructive attack on the active metal (anode). Current flows through the electrolyte to the more noble metal (cathode) and the less noble (anode) metal will corrode.

Anode and cathode junction in this galvanic corrosion is determined based on the galvanic series of metal. The galvanic or electrochemical series ranks metals according to their potential, generally measured with respect to the Standard Calomel Electrode (S.C.E.). Copper is more noble than steel thus copper will be the cathode and less noble metal which is steel will corrode. This can be seen clearly on our observation.The less corrosion resistant or the "active" member of the couple experiences accelerated corrosion while the more corrosion resistant or the "noble" member of the couple experiences reduced corrosion due to the "cathodic protection" effect.The conductivity of electrolyte will also affect the degree of attack. Also, the cathode to anode area ratio is directly proportional to the acceleration factor.

In the second part of our experiment, mild steel plate is immersed in the KCL in a beaker. We can see from the microscope image, the microstructure of the corroded steel which appear having small hole. This type of corossion is called pitting corrosion. The pits often appear to be rather small at the surface, but may have larger cross section areas deeper inside the metal. Since the attack is small at the surface and may be covered by corrosion products, a pitting attack often remains undiscovered until it causes perforation and leakage. Pitting corrosion, or pitting, is a form of extremely localized corrosion that leads to the creation of small holes in the metal. The driving power for pitting corrosion is the depassivation of a small area, which becomes anodic while an unknown but potentially vast area becomes cathodic, leading to very localized galvanic corrosion. The corrosion penetrates the mass of the metal, with limited diffusion of ions. The more conventional explanation for pitting corrosion is that it is an autocatalytic process. Metal oxidation results in localized acidity that is maintained by the spatial separation of the cathodic and anodic half-reactions, which creates a potential gradient and electromigration of aggressive anions into the pit.

Anodic reactions inside the pit:

Fe = Fe2+ + 2e- (dissolution of iron)

The electrons given up by the anode flow to the cathode where they are discharged in the cathodic reaction:

1/2O2 + H2O + 2e- = 2(OH-)

As a result of these reactions the electrolyte enclosed in the pit gains positive electricalThe positively charged pit attracts negative ions of chlorine Cl- increasing acidity of theelectrolyte according to the reaction:

FeCl2 + 2H2O = Fe(OH)2 + 2HCl

This kind of corrosion is extremely insidious, as it causes little loss of material with small effect on its surface, while it damages the deep structures of the metal. The pits on the surface are often obscured by corrosion products.

In the third part of our experiment, we run experiment to measure the corrosion rate between mild steel and copper. We can determine the corrosion rate by using the formula of corrosion rate. From the result, the corrosion rates of steel is greater compared to the copper which indicates the steel corrodes in KCL solution faster than the copper. It is because copper is more noble compared to steel which oxidize easily.Corrosion rates of metal also appear to be accelerated as longer the time immersed.

There are precaution that should be taken during conducting the experiment and there are few problems and errors that we encounter during the experiment. The metal plates should be grind carefully so that no oxide layer are present that will effect the corrosion process. There are large different in corrosion rates of copper probably due to inconsistance reading of the weight balance as the weight change is very small and need carefull reading.

ConclusionIn this experiment, we have learned about galvanic and pitting corrosion and also the way to measure the rates of corrosion. Steel and Copper have different corrosion rates.Alhamdulillah with the help of our demonstrator bro Firdaus, we managed to complete the experiment succesfully.

RecommendationUniversity should buy new weighing machine as it is insufficient so that student could done the experiment easily in the future.

References1. M. Houser, Corrosion Control Services, Inc., introduction handbook (2011)2. Mars Guy Fontana, McGraw-Hill, Corrosion engineering 19863. Corrosion Engineering: Principles and Practice, Pierre Roberge, McGraw-Hill Professional; 1 edition (2008)4. Schtze, M. (2002), Corrosion Books: Handbook of Corrosion Engineering. Pierre R. Roberge