Lecture 5 Chemical Causes PDF

Chemical causes of Materials Degradation Eden May Dela Peña, PhD Department of Mining, Metallurgical and Materials Engineering College of Engineering, UP Diliman DEPARTMENT OF MINING, METALLURGICAL AND MATERIALS ENGINEERING  Copyright not...

Chemical causes of Materials Degradation Eden May Dela Peña, PhD Department of Mining, Metallurgical and Materials Engineering College of Engineering, UP Diliman DEPARTMENT OF MINING, METALLURGICAL AND MATERIALS ENGINEERING  Copyright notice This material has been reproduced and communicated to you by or on behalf of University of the Philippines pursuant to PART IV: The Law on Copyright of Republic Act (RA) 8293 or the “Intellectual Property Code of the Philippines”. The University does not authorize you to reproduce or communicate this material. The Material may contain works that are subject to copyright protection under RA 8293. Any reproduction and/or communication of the material by you may be subject to copyright infringement and the copyright owners have the right to take legal action against such infringement. Do not remove this notice. DEPARTMENT OF MINING, METALLURGICAL AND MATERIALS ENGINEERING  “Most materials experience some type of interaction with a large number of diverse environments. Interactions may result in the deterioration of mechanical properties of the material, other physical properties, or appearance.” DEPARTMENT OF MINING, METALLURGICAL AND MATERIALS ENGINEERING  Chemically mediated degradation DEPARTMENT OF MINING, METALLURGICAL AND MATERIALS ENGINEERING  Chemically mediated degradation Involves damage by water, salt water or acids to metals, which either rust or dissolve DEPARTMENT OF MINING, METALLURGICAL AND MATERIALS ENGINEERING  Chemically mediated degradation DEPARTMENT OF MINING, METALLURGICAL AND MATERIALS ENGINEERING  Chemically mediated degradation Biological organisms can treat solid materials as a food source, or else, the material is degraded by corrosive excretions from organisms. DEPARTMENT OF MINING, METALLURGICAL AND MATERIALS ENGINEERING  Chemically mediated degradation MOST SIGNIFICANT MODE: METALS: Aqueous oxidation at ambient or moderately elevated temperatures and dry oxidation at high temperatures POLYMERS AND CERAMICS: Damage by water and solvents DEPARTMENT OF MINING, METALLURGICAL AND MATERIALS ENGINEERING  Corrosion of Metal in Aqueous Media Rusting: can lead to complete destruction of a steel component. DEPARTMENT OF MINING, METALLURGICAL AND MATERIALS ENGINEERING  Corrosion DEPARTMENT OF MINING, METALLURGICAL AND MATERIALS ENGINEERING  Corrosion in Metals Corrosion Øthe chemical or electrochemical reaction between a material, usually a metal, and its environment that produces a deterioration of the material and its properties Oxidation Ømaterial loss in metals by the formation of a nonmetallic scale or film DEPARTMENT OF MINING, METALLURGICAL AND MATERIALS ENGINEERING  Corrosion in Metals Rusting Ø the aqueous or atmospheric corrosion of iron, zinc, copper, aluminum and other metals Ø corrosion products are oxides and hydroxides Ø activated by – Oxygen (O2) – Water (H2O) – Atmospheric pollutants such as sulfur compounds (SO2) and carbon dioxide (CO2) DEPARTMENT OF MINING, METALLURGICAL AND MATERIALS ENGINEERING  Variety of Corrosion Products: Iron Fe2O3.H2O Fe3O4.H2O (also written as Fe(OH)3) Fe3O4 (or ferrous ferrite, Fe2O3.FeO) DEPARTMENT OF MINING, METALLURGICAL AND MATERIALS ENGINEERING  Corrosion in Ceramics Øusually occurs at elevated temperatures or in extreme environments ØDegradation of ceramics is frequently also called corrosion. Chun, et. Al (2012) DEPARTMENT OF MINING, METALLURGICAL AND MATERIALS ENGINEERING  Corrosion in Ceramics Ø CERAMIC DUSTING occurs in systems involving combustion and pyrolysis reactions DEPARTMENT OF MINING, METALLURGICAL AND MATERIALS ENGINEERING  Corrosion in Ceramics Ø CERAMIC DUSTING occurs in systems involving combustion and pyrolysis reactions; Ø as the carbon and reaction products build up, they push the grains apart, eventually loosening them enough so that they shed as DUST DEPARTMENT OF MINING, METALLURGICAL AND MATERIALS ENGINEERING  Corrosion in Polymers Ø mechanism and consequences of interaction with the environment differ from those for metals and ceramics DEPARTMENT OF MINING, METALLURGICAL AND MATERIALS ENGINEERING  Corrosion in Polymers: Mechanism Ø SWELLING: small molecules infiltrate the structure, reducing strength and stiffness and causing a volume change DEPARTMENT OF MINING, METALLURGICAL AND MATERIALS ENGINEERING  Corrosion in Polymers: Mechanism Ø SWELLING: small molecules infiltrate the structure, reducing strength and stiffness and causing a volume change Ø LEACHING: plasticizers which can be leached out of the structure, causing brittleness or other undesirable changes DEPARTMENT OF MINING, METALLURGICAL AND MATERIALS ENGINEERING  Corrosion in Polymers Ø POLYMER CHAIN SCISSION: caused by free radicals and oxidizers such as oxygen, ozone, and chlorine Rubber products Plastic shopping bags DEPARTMENT OF MINING, METALLURGICAL AND MATERIALS ENGINEERING  Threats of Corrosion Ø ordinarily begins at the surface Ø destructive and unintentional attack of a metal Ø approximately 5% of an industrialized nation’s income is spent on corrosion prevention and the maintenance or replacement of products lost or contaminated as a result of corrosion DEPARTMENT OF MINING, METALLURGICAL AND MATERIALS ENGINEERING  Fundamentals of Electrochemistry DEPARTMENT OF MINING, METALLURGICAL AND MATERIALS ENGINEERING  Two bars of dissimilar metals DEPARTMENT OF MINING, METALLURGICAL AND MATERIALS ENGINEERING  Electrochemical cell Elements of an electrochemical cell: 1. Electrode 2. Electrolyte 3. Electrical Connection Reactions at the electrodes: – Anodic: 𝑍𝑛 → 𝑍𝑛!" + 2𝑒̅ – Cathodic: 2𝑒̅ + 2𝐻#𝑂" → 𝐻! + 2𝐻!𝑂 DEPARTMENT OF MINING, METALLURGICAL AND MATERIALS ENGINEERING  Electrochemical cell DEPARTMENT OF MINING, METALLURGICAL AND MATERIALS ENGINEERING  Electrochemical cell DEPARTMENT OF MINING, METALLURGICAL AND MATERIALS ENGINEERING  Electrochemical cell Metallic Zinc: ü converted into zinc ions ü forms a coordination complex with water ü donates electrons and loses metal to the electrolyte ü anode DEPARTMENT OF MINING, METALLURGICAL AND MATERIALS ENGINEERING  Electrochemical cell Copper electrode: ü Electrons are consumed ü does not suffer chemical changes ü Site where reaction occurs ü cathode DEPARTMENT OF MINING, METALLURGICAL AND MATERIALS ENGINEERING  Electrode Potential the magnitude of the potential difference may be thought of as representing the driving force for the electrochemical oxidation–reduction reaction DEPARTMENT OF MINING, METALLURGICAL AND MATERIALS ENGINEERING  Standard Electromotive Force (EMF) Series consecutively lists the electrode potentials of various metals relative to the hydrogen electrode (taken as the standard reference) Standard half cell - a pure metal electrode immersed in a 1M solution of its ions and at 25°C DEPARTMENT OF MINING, METALLURGICAL AND MATERIALS ENGINEERING  The rapidity of reaction is a critical feature of electrochemistry Ø Rate of reaction of the more chemically active metal (zinc) is increased by sharing some of the stages in chemical reaction with a less active metal (copper). DEPARTMENT OF MINING, METALLURGICAL AND MATERIALS ENGINEERING  Two outcomes: Standard Hydrogen Electrode -- Corrosion -- Electrodeposition e- e- e- e- H2(gas) H+ 2e - ne - 2e - ne - H+ Mn+ H+ Platinum Mn+ Platinum metal, M metal, M ions ions H+ 25°C 25°C 1M Mn+ sol’n 1M H + sol’n 1M Mn+ sol’n 1M H+ sol’n -- Metal is the anode (-) -- Metal is the cathode (+) o Vmetal 0 (relative to Pt) Standard Electrode Potential DEPARTMENT OF MINING, METALLURGICAL AND MATERIALS ENGINEERING 32  Ranking the reactivity of metals/alloys in seawater Platinum more cathodic Gold Graphite (inert) Titanium Silver 316 Stainless Steel (passive) Nickel (passive) Copper Nickel (active) Tin more anodic Lead 316 Stainless Steel (active) (active) Iron/Steel Aluminum Alloys Cadmium Zinc Magnesium DEPARTMENT OF MINING, METALLURGICAL AND MATERIALS ENGINEERING  Polymers DEPARTMENT OF MINING, METALLURGICAL AND MATERIALS ENGINEERING  Two basic forms of degradation Ø solvation and partial solvation of the polymer by a solvent which is usually organic Ø chemical reaction leading to fracture of the polymer or in extreme cases conversion to a powder. DEPARTMENT OF MINING, METALLURGICAL AND MATERIALS ENGINEERING  Solvation or partial solvation Swelling: first stage of solvation. Solvent molecules diffuse into spaces between chains DEPARTMENT OF MINING, METALLURGICAL AND MATERIALS ENGINEERING  Dissolution by solvent and gum formation @ elevated T, rubber is converted into a slimey product DEPARTMENT OF MINING, METALLURGICAL AND MATERIALS ENGINEERING  Chain scission Ø polymer chains are split Ø Effect: increase in brittleness of the polymer DEPARTMENT OF MINING, METALLURGICAL AND MATERIALS ENGINEERING  Crazing Ø formation of a network of cracks over the surface of the polymer DEPARTMENT OF MINING, METALLURGICAL AND MATERIALS ENGINEERING  Effect of molecular weight End of polymer chains – preferred reaction sites for degradation reaction Resistance to degradation increases with molecular weight DEPARTMENT OF MINING, METALLURGICAL AND MATERIALS ENGINEERING  Polymer oxidation Inevitable process since it is used in open air DEPARTMENT OF MINING, METALLURGICAL AND MATERIALS ENGINEERING  Polymer degradation is not always destructive… BIODEGRADABLE PLASTIC BAG DEPARTMENT OF MINING, METALLURGICAL AND MATERIALS ENGINEERING  Technique of introducing biodegradability Introduction of amino acid sub groups DEPARTMENT OF MINING, METALLURGICAL AND MATERIALS ENGINEERING  Degradable polymers are extremely useful… Degradable polymer mesh DEPARTMENT OF MINING, METALLURGICAL AND MATERIALS ENGINEERING  Polymer composites Both matrix and reinforcement phase maybe at risk DEPARTMENT OF MINING, METALLURGICAL AND MATERIALS ENGINEERING  Biocorrosion Bacteria preferentially attack the fiber-matrix interface DEPARTMENT OF MINING, METALLURGICAL AND MATERIALS ENGINEERING  Degradation during processing Excessively vigorous mixing of fibers and matrix DEPARTMENT OF MINING, METALLURGICAL AND MATERIALS ENGINEERING  Cement, concrete, and glass DEPARTMENT OF MINING, METALLURGICAL AND MATERIALS ENGINEERING  Cement and its derivative material Concrete DEPARTMENT OF MINING, METALLURGICAL AND MATERIALS ENGINEERING  Cement ØConsists of hydrated calcium silicate and calcium aluminate DEPARTMENT OF MINING, METALLURGICAL AND MATERIALS ENGINEERING  Cement swelling Ø caused by raising the water content DEPARTMENT OF MINING, METALLURGICAL AND MATERIALS ENGINEERING  Glass DEPARTMENT OF MINING, METALLURGICAL AND MATERIALS ENGINEERING  Corrosion in glasses DEPARTMENT OF MINING, METALLURGICAL AND MATERIALS ENGINEERING  Organic compounds and strong acids @ ambient temperature do not cause severe corrosion Glass is resistant to most acids except hydrofluoric acid DEPARTMENT OF MINING, METALLURGICAL AND MATERIALS ENGINEERING  Corrosion damage to ceramics LEACHING: process of pore and pit formation in ceramics by corrosion. DEPARTMENT OF MINING, METALLURGICAL AND MATERIALS ENGINEERING  Thank you for listening J That’s it for today! Thank you for coming to class! J DEPARTMENT OF MINING, METALLURGICAL AND MATERIALS ENGINEERING  Feedback Top 3 things you learned today Muddy points. You may ask questions here. Comments and/or suggestions on how the class was handled. You may raise any concern/s you have in class. D E P A R T M E N T O F M I N I N G, M E T A L L U R G I C A L A N D M A T E R I A L S E N G I N E E R I N G  References Dennis Yu. Corrosion and Degradation of Materials. IMEMATS 3rd Term, 2011-2012. Chun et. al. “Ceramic dusting corrosion of yttria-stabilized zirconia in ultra high temperature reverse-flow pyrolysis reactors.” Journal of the American Ceramic Soceity, Vol 95 (12), Dec 2012, pp. 3962-3970. J.R. Davis. Corrosion – Understanding the Basics. ASM International. 2000. Callister. Introduction to Materials Science and Engineering. DEPARTMENT OF MINING, METALLURGICAL AND MATERIALS ENGINEERING