Corrosion process and control (TKK-2289) 15/16 Semester genap Corrosion process and control (TKK-2289) Instructor: Rama Oktavian; Vivi Nurhadianty. Email: rama.oktavian86@gmail.com Office Hr.: T. 13-15, W. 11-12, Th. 13-15

Tujuan Mengetahui proses korosi dan pencegahan serta pengendaliannya

Pokok bahasan Kuliah ke- Pokok bahasan Metode kuliah 1-4. Pendahuluan dan Pengenalan tentang korosi dan proses korosi: Proses elektrokimia korosi Kinetika korosi Tipe – tipe korosi Ceramah Tugas mandiri 5-8 Proses Korosi di industri kimia Presentasi Studi kasus 9-12 Pengendalian korosi: Cathodic protection Corrosion control by inhibition Coating Pemilihan material 13-16 Pengendalian korosi pada Proses Industri Kimia

Introduction Textbooks 1. Zaki Ahmad,” Principles of Corrosion Engineering and Corrosion Control, Butterworth-Heinemann (2006). Pierre R. Roberge, “Corrosion Engineering: Principles and Practice, Mc Graw-Hill (2008).

Introduction Grading system Grading criteria Percentage (%) Tugas 20 Quiz I / midterm 40 Final exam

Environmental Degradation of Materials Corrosion Environmental Degradation of Materials Materials are “attacked” by their operating environment

So, What exactly is corrosion? Corrosion is an irreversible interfacial reaction of a material (metal, ceramic, polymer) with its environment which results in consumption of the material or in dissolution into the material of a component of the environment. Chemistry is at work. We are talking about a certain class of chemical reactions between a metal and the environment.

Corrosion Example: metal corrosion caused by water results from chemical reaction where metal surface is oxidized to form iron oxide (rust).

Corrosion is an oxidation process occurred at low temperature Corrosion is an electrochemical process Anode, electrode which gives electron. Cathode, electrode which accepts electron

Corrosion

Corrosion • Two reactions are necessary: • Other reduction reactions: -- oxidation reaction: -- reduction reaction: • Other reduction reactions: Zn + 2HCl → ZnCl2 + H2 -- in an acid solution -- in a neutral or base solution

Corrosion • Two outcomes: --Metal sample mass --Metal sample mass --Metal is the anode (-) --Metal is the cathode (+) (relative to Pt) (relative to Pt) Standard Electrode Potential

Corrosion • EMF series • Metal with smaller EMF: Electromotive Force V (i.e., more active) corrodes.Ex: Cd-Ni cell V o o metal metal metal Au Cu Pb Sn Ni Co Cd Fe Cr Zn Al Mg Na K +1.420 V +0.340 - 0.126 - 0.136 - 0.250 - 0.277 - 0.403 - 0.440 - 0.744 - 0.763 - 1.662 - 2.262 - 2.714 - 2.924 o DV = 0.153V EMF: Electromotive Force

Corrosion The EMF of a standard Ni-Cd galvanic cell is -0.153 V. If the standard half-cell EMF for the oxidation of Ni is -0.250 V, what is the standard half-cell EMF of cadmium if cadmium is the anode? Solution: The standard half-cell EMF of the cadmium can be calculated by considering the half-cell reactions:

Corrosion Rusting of iron The oxidation reaction that will occur at the local anodes is Fe → Fe2+ + 2e- (anodic reaction) The reduction reaction that will occur at the local cathodes is O2 + 2H2O + 4e- → 4OH- (cathodic reaction) A piece of iron immersed in oxygenated water, ferric hyroxide [Fe(OH)3] will form on its surface

Corrosion • Ranks the reactivity of metals/alloys in seawater Platinum Gold Graphite Titanium Silver 316 Stainless Steel Nickel (passive) Copper Nickel (active) Tin Lead Iron/Steel Aluminum Alloys Cadmium Zinc Magnesium

Corrosion Consider a magnesium-iron galvanic cell consisting of a magnesium electrode in a solution of 1 M MgSO4 and an iron electrode in a solution of 1 M FeSO4. Each electrode and its electrolyte are separated by a porous wall, and the whole cell is at 25°C. Both electrodes are connected with a copper wire. Which electrode is the anode? Which electrode corrodes? In which direction will the electrons flow? In which direction will the anions in the solution move? In which direction will the cations in the solution move? Write an equation for the half-cell reaction at the anode. Write an equation for the half-cell reaction at the cathode. Mg 25°C Fe 1.0 M 1.0 M Mg + 2 solution Fe 2+ solution

Corrosion The magnesium electrode is the anode. The magnesium electrode corrodes since the anode in a galvanic cell corrodes (oxidizes). The electrons will flow from the anode, Mg, to the cathode, Fe. The SO42− anions will flow toward the magnesium anode. The cations will flow toward the iron cathode. The oxidation reaction that occurs at the magnesium anode is: Mg → Mg2++2e− The reduction reaction that occurs at the iron anode is: Fe2++2e−→ Fe .

Corrosion Types of corrosion: Uniform or general attack corrosion Galvanic or two-metal corrosion Pitting corrosion Crevice corrosion Intergranular corrosion Stress corrosion Erosion corrosion Selective leaching or dealloying

Corrosion 1. Uniform/general attack (korosi umum) This one is common in steel that is unprotected by any surface coating. Most noticeable. Surface effect, leaving rust on the surface. The good thing about this, if there is one, is that the corrosion is widely spread around.

Corrosion 1. Uniform/general attack (korosi umum)

2. Galvanic corrosion (korosi galvanis) Steel screw in Mg Steel screws and brass Dissimilar metals, the damage occurs at the anode.

3. Crevice corrosion (korosi celah)

4. Pitting corrosion (korosi sumur) This is similar to crevice corrosion. It is based on low oxygen concentration at the bottom of the pit. This is very common in materials that protect themselves with a passive layer, i.e. stainless. Also, aluminum.

5. Erosion corrosion (korosi erosi) This is caused by the impingement of a high velocity turbulent flow on a surface. The flow is often multi-phase. This means there can be entrained solid particles, or even gas bubbles, as in cavitation of a propeller. The flow will carry away any protective layer that was intended to protect the material, and even abrade the flow surface.

6. Stress corrosion (korosi tegangan) Sometimes called stress corrosion cracking. Ingredients: (1) tensile stress in the metal (2) corrosive (electrolyte) environment. Accelerators: presence of Chloride ion and high temp. Victims: Stainless steel is unsafe in water above 50C and over a few ppm of chloride, if any tension exists. Others: mild steel in alkaline environment, copper alloys in ammonia env. The anode is the stresses region.

6. Stress corrosion (korosi tegangan)

Kontrol terhadap korosi Corrosion PENCEGAHAN KOROSI Korosi dapat dikontrol dengan berbagai cara. Pertimbangan utama adalah masalah ekonomi, terutama akibat yang ditimbulkannya . Kontrol terhadap korosi Pemilihan material: Logam Non logam Coating (pelapisan): Organik Non organik Disain: menghindari konsentrasi tegangan menghindari kontak dengan logam tidak sejenis menghindari adanya jebakan air Proteksi katodik dan anodik Kontrol lingkungan. (temperatur, konsentrasi oksigen dll).

Corrosion Metallic Selection General rules for metallic selection For reducing or, nonoxidizing conditions such as air-free acids & aqueous solutions, Ni & Cu alloy are often used. For oxidizing conditons, Cr containing alloy are used. For extremely powerful oxidizing conditions, Ti & its alloy are commonly used.

Corrosion Coatings Metallic, inorganic, & organic coatings are applied to metals to prevent or reduce corrosion Metallic coating eg.; Zinc coating on steel (sacrificial anode) Inorganic coating (ceramics & glass) eg.; Glass-lined steel vessels Organic coating eg.; paints, varnishes & lacquers

Alteration of Environment 4 general methods of altering an environment to prevent or reduce corrosion are: Lower the system temperature to lower the reaction rates and thus reduce corrosion. Certain exceptions exist, such as seawater, for which the temperature should be raised rather than reduced. Decrease the velocity of corrosive fluids such that erosion corrosion is reduced while fluid stagnation is avoided. Remove oxygen from water solutions. Reduce the concentration of corrosive ions in a solution which is corroding a metal.

Cathodic protection The protection of a metal by connecting it to a sacrificial anode or by impressing a DC voltage to make it cathode Eg; sacrificial anode Impressed current Cathodic protection of an underground pipeline by using sacrificial Mg anode Cathodic protection of an underground tank by using impressed currents

Thank You !