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80 Cards in this Set
- Front
- Back
What are the two most important factors in preventing corrosion? |
1. Removal of the electrolyte 2. Application of protective coating |
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What is the electrochemical deterioration of a material or its properties due to its chemical reaction with the surrounding environment? |
Corrosion |
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What is the smallest unit made up of an element, made up of a positively charged nucleus surrounded by a system of negatively charged electrons? |
Atom |
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What is a negatively charged subatomic particle? |
Electron |
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What is an atom or group of atoms or molecules which has acquired a net electric charge by gaining or losing electrons? |
Ion |
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What is a liquid containing ions? |
Electrolyte |
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All metals will corrode to some extent in a natural environment. |
Theory of Corrosion |
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What four conditions must exist before metal corrosion can occur? |
1. Anode (metal with tendency to corrode) 2. Cathode (dissimilar conductive material) 3. Electrolyte (conductive liquid) 4. Electrical contact |
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Where do all corrosive attacks begin? |
On the surface of the metal |
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When is the best time to prevent corrosion? |
Design stage |
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Most alloys are made up entirely of small crystalline regions called _____. |
Grains |
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The _____ the difference in dissimilar metals, the _____ corrosion occurs. |
Greater, difference |
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If the surface area of the _____ (corroding metal) is smaller than the surface area of the _____ (less active metal), corrosion will be rapid and severe. |
Anode, cathode |
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What occurs when the concentration of the electrolyte on the surface varies from one location to another? |
Concentration Cell |
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What occurs when some of the electrolyte on a metal surface is partially confined, metal in the confined area corrodes more rapidly than other metal surface areas? |
Oxygen Concentration Cell |
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What environments tend to produce more rapid corrosion due to accelerated chemical reactions? |
Higher temperature |
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What is the most common type of corrosion that results from a direct chemical attack on a metal surface that proceeds over the entire exposed surface? |
Uniform Surface Corrosion |
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What two appearances does uniform surface corrosion have? |
1. Dulling or etching of surface. 2. Rough and possibly frosted. |
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What two ways can you treat uniform surface corrosion? |
1. Coating/sealing 2. Air movement and drain holes |
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What corrosion occurs when different metals are in contact with each other and an electrolyte, such as seat water? |
Galvanic Corrosion |
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What appearance does galvanic corrosion have? |
Corrosion at the joint between metals |
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When is the potential for galvanic corrosion the greatest? |
When two metals are well separated from each other on the galvanic series. |
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What corrosion occurs when the form of extremely localized attacks results in holes in the metal? |
Pitting Corrosion |
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What appearance does pitting corrosion have? |
White or gray powdery deposits, similar to dust. |
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What metal is most susceptible to pitting? |
Stainless steel |
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What corrosion is the attack on the grain boundaries of the metal? |
Intergranular Corrosion |
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What type of corrosion are aluminum alloys highly susceptible to? |
Intergranular Corrosion |
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What is the advanced form of intergranular corrosion where the surface grains of a metal are lifted up by the force of expanding corrosion products occurring at the grain boundaries? |
Exfoliation Corrosion |
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What appearance does exfoliation corrosion have? |
Lifting up or swelling |
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How do you prevent exfoliation corrosion in aluminum sheet around steel fasteners? |
Separate the aluminum and steel by a barrier |
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What corrosion occurs when in any crevice where a stagnant solution has pooled? |
Crevice Corrosion |
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What three methods are used to close crevices in order to prevent crevice corrosion? |
1. Welding 2. Soldering 3. Nonabsorbent gaskets |
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What is a form of crevice corrosion which occurs on metal surfaces having a thin organic protective coating? |
Filiform Corrosion |
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What corrosion is recognized by its characteristic worm-like trace of corrosion products beneath the coating? |
Filiform Corrosion |
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What four ways can filiform corrosion be prevented? |
1. Keep humidity below 65% 2. Using coating with low rate of diffusion of oxygen and water vapors 3. Maintaining coatings 4. Applying CPC (corrosion preventive compounds) |
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What is the increase in the rate of attack on a metal due to the action of a corrosive fluid against the metal surface? |
Erosion Corrosion |
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What is erosion corrosion characterized by? |
Grooves, gullies, waves, rounded holes and/or valleys in the metal surface |
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What is the intergranular or transgranular cracking of a metal caused by the combined effects of constant tensile stress and corrosion? |
Stress Corrosion (also called Stress Corrosion Cracking SCC) |
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What type of corrosion is an extremely dangerous type of failure because it can occur without warning? |
Stress Corrosion (also called Stress Corrosion Cracking SCC) |
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What three specific environmental effects have been identified which cause stress corrosion cracking? |
1. Salt solutions 2. Sea water 3. Moist salt laden air |
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What three ways can stress corrosion be prevented? |
1. Insulating barrier 2. Protective coatings 3. Water dispalcing corrosion preventive compunds |
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What is the cracking of metals caused by the combined effects of cyclic stress and corrosion? |
Corrosion Fatigue |
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What three measures are used to prevent corrosion fatigue? |
1. Reduce stress 2. Use corrosion inhibitors 3. Apply metallic coating |
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What corrosion occurs at the contact areas between materials under load subject to repeated vibration? |
Fretting Corrosion |
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What general appearance does fretting corrosion have? |
Galling |
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What corrosion occurs at high temperatures, such as those found in turbine engine combustors, turbine sections, and afterburners? |
Hot Corrosion |
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What can reduce hot corrosion? |
High temperature ceramic coatings |
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What are the most widely used materials for aircraft construction? |
Aluminum and aluminum alloys |
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What is the corrosion product of aluminum? |
White to gray powdery material |
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What two ways can corrosion of aluminum be removed? |
1. Mechanical polishing 2. Abrasive brushing |
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What are the three main methods of protection of aluminum? |
1. Chemical coating 2. Paints 3. CPC (corrosion preventive compounds) |
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What is an electrochemically applied oxide coating used for protecting of metals? |
Anodize |
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What are the lightest structural metals used for aircraft and missile airframes? |
Magnesium alloys |
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What are the corrosion products of magnesium alloys? |
White powdery snow-like mounds |
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How can the corrosion of magnesium alloys be diminished? |
Use of proper protective finish |
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What six types of corrosion is aluminum alloy susceptible to? |
1. Pitting 2. Intergranular 3. Exfoliation 4. Stress 5. Fatigue 6. Fretting
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What is the corrosion appearance of aluminum alloy? |
White to gray powder |
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What type of corrosion is magnesium alloy susceptible to? |
Pitting |
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What are three corrosion appearances of magnesium alloy? |
1. White powdery 2. Snow-like mounds 3. White spots |
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What two types of corrosion is carbon and low alloy steel susceptible to? |
1. Pitting 2. Intergranular |
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What is the corrosion appearance of carbon and low alloy steel? |
Reddish-brown oxide (rust) |
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What five types of corrosion is stainless steels susceptible to? |
1. Crevice corrosion 2. Pitting 3. Stress 4. Intergranular 5. Uniform surface |
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What is the corrosion appearance of stainless steels? |
Rough surface |
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What type of corrosion is titanium alloy susceptible to? |
Highly corrosive resitant |
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What is the corrosion appearance of titanium alloy? |
Colored surface oxides develop above 700 F. |
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What type of corrosion is cadmium susceptible to? |
Uniform Surface Corrosion |
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What are the two corrosion appearances of cadmium? |
1. White powdery deposit 2. Black/brown molting of surface |
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What type of corrosion is chromium susceptible to? |
Pitting |
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What type of corrosion is nickel-base alloy susceptible to? |
Pitting |
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What is the corrosion appearance of nickel-base alloy? |
Green powdery deposit |
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What two types of corrosion is electroless nickel susceptible to? |
1. Pitting 2. Uniform surface |
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What two types of corrosion is copper-base alloy, brass, and bronze susceptible to? |
1. Surface 2. Intergranular |
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What are the two corrosion appearances of copper-base alloy, brass, and bronze? |
1. Blue powdery deposit 2. Green powdery deposit |
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What type of corrosion is silver susceptible to? |
Will tarnish in the presence of sulfur |
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What is the corrosion appearance in silver? |
Brown to black film |
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T/F. Gold is highly corrosion resistant. |
True |
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What is the corrosion appearance in gold? |
Deposits cause darkening of reflective surfaces |
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What is the corrosion appearance in tin? |
Whisker-like deposits |
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What is used as a coating to protect steel hardware, such as bolts, washers, and screws? |
Cadmium |
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What is used as a protective plating? |
Chromium |