Electrochemical Cells & Batteries PDF

## Electrochemical Cells & Batteries ### Electrochemical Cells - **Electrochemical:** examining the phenomena resulting from combined chemical and electrical effects. - **Or:** the area of chemistry concerned with the interconversion of chemical and electrical. - **Electrochemical cells are two ba...

## Electrochemical Cells & Batteries ### Electrochemical Cells - **Electrochemical:** examining the phenomena resulting from combined chemical and electrical effects. - **Or:** the area of chemistry concerned with the interconversion of chemical and electrical. - **Electrochemical cells are two basic types:** - **Galvanic cells:** A spontaneous chemical reaction generates an electric current. - **Electrolytic cells:** An electric current drives a nonspontaneous reaction. - **An electrochemical cell consists of:** two electronic conductors and an ionic conductor. - **Or:** an electrochemical cell, a device for interconverting chemical and electrical energy. ### Batteries - **Battery:** is galvanic cells, or electrochemical cell or voltaic cells that can be used as a self-contained source of direct electric current. - **Dry Cell and Alkaline Batteries:** - **Consists of:** - Zinc (anode) - Graphite (cathode) - Solid manganese dioxide and carbon black - A moist paste of ammonium chloride and zinc chloride - Instarch (an electrolyte) - **Characterized by:** - Provides a potential of about 1.5V - The electrolyte is a viscous aqueous paste rather than a liquid solution. - **Lead Acid Battery:** - **Consists of:** - Lead Pb (anode) - Lead dioxide (cathode) - $H_2SO_4$(Solution) - **Characterized by:** - Made of six identical cells connected in series (each delivers 2V) - The lead storage is 12V - Used as a reliable source of power for starting automobiles. - Rechargeable - Discharge uses $H_2SO_4$ and the solution density. - The solution can be measured with a hydrometer. - **The Nickel Cadmium Battery** - **Consists of:** - Nickel (cathode) - Cadmium (anode) - Potassium hydroxide (solution) - **Characterized by:** use in calculators and portable power, because they are rechargeable. - **Lithim Batteries:** - **Consists of:** - Lithim or lithim atoms (anode) inserted into a graphite electrode. - Lit or $MnO_2$ and electrolyte (cathode) that contains a lithim salt suchas $LiClO_4$ in a organic solvent. - **Characterized by:** - Used in cell phone, laptops, cameras - Recharged can be recharged hundreds of times. - Light weight and high voltage about (3.0V) ### Fuel Cells - **Characterized by:** - Direct production of electricity. - Requires a continuous supply. - High efficiency. - The only waste product is water. - The overall cell reaction is the conversion of hydrogen and oxygen to water. ### Corrosion - **Corrosion:** is the deterioration of a metal by electrochemical process. - **Rusting:** This is the name given to the corrosion of iron. Iron corrodes when it's in the presence of water and oxygen. - **Different Manifestations of Corrosion** - **Uniform corrosion:** Occurs over the entire exposed surface of a metal. - **Galvanic corrosion:** Occurs near the junction between two dissimilar metals “in conducting medium” electrolyte. - **Crevice corrosion:** Occurs in crevices between components under polymer coatings and adhesives. - **Pitting corrosion:** Occurs in metals that normally passive. - **Intergranular corrosion:** Involves corrosion along the grain boundaries of the affected metals. - **Dealloying corrosion:** Dealloying is the selective leaching of one element from alloy. - **Stress corrosion:** Stress corrosion cracking involves the combination of stress and exposure to a corrosive environment. - **Concentration cell corrosion:** Same as galvanic corrosion. Occurs when two different metals are exposed to different air concentrations. - **Classification of Corrosion** - **Dry or chemical corrosion:** Occurs due to chemical attack by the environment suchas gas or due to high temperature. Is two types oxidation corrosion and corrosion by gases. - **Wet or electrochemical corrosion:** Occurs when aqueous solutions and electrolytes are present, or the relative humidity exceeds 60%. - **Factors Affecting Corrosion** - **Nature of the metal:** Position in galvanic series, over voltage, relative area of anodic/cathodic parts, purity of metal and surface film, passive character, solubility and volatility. - **Nature of environment:** Temperature and humidity, impurities and suspended particles, PH, formation of concentration cells and polarization of electrodes. - **Corrosion Control** - **Physical protection:** Provide a barrier against the oxygen and water: Paint, grease, oil, coat with plastic, coat with zinc (galvanize). - **Chemical protection:** Cathodic and sacrificial protection, galvanize, tin plating, electroplating and anodizing. - **The Ways to Prevent Corrosion** - Passivation - Formation of an alloy - Coating with a layer of less active metal. - Cathodic protection - **Prevention of Corrosion include** - Proper designing - Using pure metals - Using metal alloys - Use of inhibitors - Cathodic protection - Modifying the environment - Protective coating - **The specific type of corrosion that occurs depends on:** - Metal composition - Metal microstructure - Stress on the component - Component geometry - Environment - Contact between metals - Manner in which components are joined together.