4 - Corrosion of Metals and Alloys Flashcards
What are the types of non-metallic corrosion?
Chemical Reaction Corrosion
Physical Interaction Corrosion
In chemical reaction corrosion, what affects the corrosion of polymers?
Effect of Heat
Effect of UV Radiation
Effect of Water
Effect of Ozone
This occurs when polymers are exposed to heat above a specified temperature limit, which is unique for each type of polymer.
Chain scission
What are the types degradation in physical interaction corrosion?
Thermal degradation
Photodegradation
Oxidative degradation
Hydrolytic degradation
Biodegradation
Oxidative Photodegradation
Thermoxidative degradation
Photo hydrolytic degradation
There are materials made of long, repeating chains of molecules. These materials have unique properties, depending on the type of molecules being bonded and how they are bonded.
Polymers
These materials do not experience a specific corrosion rate. They are usually completely resistant to chemical attack or they deteriorate rapidly.
Plastic
Plastics are attacked by either _____ or ______.
Chemical reaction
Solvation
It is the penetration of the plastic by a corrodent, which causes softening, swelling, and ultimate failure.
Solvation
Classification of Corrosion of plastics:
Disintegration or degradation
Oxidation
Hydrolysis
Radiation
Thermal Degradation
Dehydration
Corrosion of plastics due to absorption, permeation, solvent action, or other factor.
Disintegration or degradation
Corrosion of plastics where chemical bonds are attacked.
Oxidation
Corrosion of plastics where ester linkages are attacked.
Hydrolysis
Causes of radiation in polymeric materials.
Embrittlement
Fading
Surface cracking
Chalking
It is a molecular migration through microvoids either in the polymer or between polymer molecules. This is detrimental when a polymer is used to line piping or equipment.
Permeation
Permeation is a function of these two variables:
- Relating to diffusion between molecular chains.
- Relating to solubility of the permeant in the polymer.
Factors affecting permeation:
Temperature
Pressure
Permeant concentration
Thickness of the polymer
What is the relationship of permeation rate, solubility, and temperature?
Directly proportional
Relationship of permeation rate of gases with partial pressure gradient, permeation rate, and corrosion rate?
Directly proportional
Permeation rate decreases with the ________ of thickness.
squared
Relationship of density and permeation rate.
Inversely proportional
This can cause softening of the polymer, introduce high stresses, and cause failure of the bond on lined components.
Swelling
These plastics reacts well to chemicals and other corrosive agents.
Polypropylene
High density polyethylene (HDPE)
Polyvinylidene fluoride (PVDF)
It is a material that is neither metallic nor organic. It may be crystalline, glassy, or both. It is typically hard and chemically non reactive and can be formed or densified with heat.
Ceramic
Ceramic materials with exceptional chemical resistance:
Alumina
Silicates
Silicon carbide
It takes place in a ceramic materials as a result of chemical dissolution. The corrosion product formed is non protective, being either poorly adherent, soluble, or a good transport medium for the corrodent to the ceramic face.
Uniform corrosion
Factors affecting ceramic degradation:
Frost
Mold growth
Impact and abrasion
Water
Soluble salts
Mold growth occurs in ceramic due to high _______:
Humidity
At what temperature water can dissolve or deform ceramics that have been low fired?
600 C
In _____ humidity, salts become ______. In _____ humidity, salts _______.
A. High, crystallize. Low, soluble
B. Low, crystallize, High, soluble
C. Low, soluble. High crystallize
D. High, soluble. Low, crystallize
D
Composites are also known as _______.
Fiber-reinforced polymer (FRP) Composites
These are mad of polymer matrix that is reinforced with an engineered, man-made or natural fiber (like glass, carbon or aramid), or other reinforcing material.
Composites
This is a vital procedure that includes the examination and measurement of the attributes of polymers, engineering plastics, composites, coatings, and paints to ascertain the reason for failure.
Failure Analysis of Polymeric Materials
Common modes of polymeric materials failures:
Plastic deformation
Crazing
Fatigue
Thermal and residual stress
Physical aging
Moisture effect
Photodegradation
Chemical attack
Two prominent mechanisms of plastic deformation:
Slip
Twinning
_____ and _____ are used to shape objects into desired form.
Pressure and heat
________ causes rapid material changes, and at times, unable to conform to the structural changes, the material may break.
Speed of stress
This occurs in high compact plastics due to the combined effect of stress and aggressive environment.
Crazing
This prolonged cyclical stresses cause undue or unexpected wear on a part until it ultimately fails.
Fatigue
In _______, repeated support of extreme weights can cause fibers to tear.
In _______, prolonged of cyclical exposure to weight or pressure can cause cracks that eventually leads to failure.
Composites, polymers.
Plastic deformation mechanism that occurs below glass transition temperature, and materials becomes brittle.
Physical aging
This is a common feature in failure of ceramic components. It occurs at a critical velocity, which is of the order of half the speed of sound in the specific glass under study.
Crack Branching
Material selection for non metallics:
Rubbers
Plastics
Ceramics
Carbon and graphite
Wood
This material possesses excellent corrosion and high temperature resistance, with the main disadvantages being brittle and low tensile strength.
Ceramics
This material shows good corrosion resistance, electric and heat conductivity, but are fragile.
Carbon
Changing mediums as prevention strategies in the corrosion of non metals:
- Lowering temperature
- Lowering pressure
- Changing permeant concentration
- Increasing permeant thickness and density
- Decreasing velocity
- Removing oxygen/oxidizers
This type of corrosion in non metals occurs at high velocities.
Erosion corrosion
True or False.
Non metals has a better resistance to stagnant solutions than flowing mediums.
True
This chemical reduces the amount of dissolved oxygen from feedwater.
Oxygen scavenger
Pairing oxygen scavenger with ______ greatly reduces the amount of chemical use.
Deaerator
