05 Corrosion of Non-Metals Flashcards
Chain scission
______________ will occur when polymers are exposed to heat above a specified temperature limit, which is unique for each type of polymer
oxygen
In the presence of _____________, UV-radiation can cause a breakdown of the polymer chains.
hydrolysis
Absorption of water at elevated temperatures causes ______________ of certain groups in a polymer chain (e.g. urethane and ester groups).
ozone
Attacks from ___________ on unsaturated polymers (e.g. natural rubber) under stress, causes characteristic cracks.
Photohydrolytic Degradation
Light + Humidity
Thermooxidative Degradation
Heat + Oxygen
Oxidative Photodegradation
Light + Oxygen
Photodegradation
Sunlight
Polymers
These 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.
Plastic materials
These do not experience a specific corrosion rate. They are usually completely resistant to chemical attack, or they deteriorate rapidly. They are attacked either by chemical reaction or by solvation
Solvation
____________ is the penetration of the plastic by a corrodent, which causes softening, swelling, and ultimate failure.
- Hydrolysis
- ______________ of a physical nature due to absorption, permeation, solvent action, or other factors.
ultraviolet (UV) radiation
Polymeric materials in outdoor applications are exposed to weather extremes that can be extremely deleterious to the material, the most harmful of which is exposure to ________________, which can cause embrittlement, fading, surface cracking, and chalking.
UV-A
This type of UV radiation causes polymer damage.
UV-B
This type of UV radiation includes the shortest wavelengths at the Earth’s surface.
UV-C
This type of UV radiation if found only in outer space.
UV-B
UV type with range of 315-280 mm wavelength.
UV-C
UV type with range of 280-100 mm wavelength.
UV-A
UV type with range of 400-315 mm wavelength.
Permeation
It is a molecular migration through microvoids either in the polymer (if the polymer is more or less porous) or between polymer molecules. In neither case is there any attack on the polymer. This action is strictly a physical phenomenon.
lined equipment
In _______________, permeation can result in:
partial pressure; concentration gradient
Driving force of diffusion is the ____________ of gases and the ____________ of liquids.
Solubility
_____________ is a function of the affinity of the permeant for the polymer
increases; increases
As the temperature ______________, permeation rate ______________.
linearly
The permeation rate of many gases increases _____________ with the partial pressure gradient.
square of the thickness
The thickness will generally decrease permeation by the _________________.
Absorption
Polymers have the potential to absorb varying amounts of corrodents with which they come into contact, particularly organic liquids.
Swelling
_____________ can cause softening of the polymer, introduce high stresses, and cause failure of the bond on lined components.
ceramic
A __________________ is a material that is neither metallic nor organic. It may be crystalline, glassy or both crystalline and glassy.
technical ceramic
When compared to steel and plastic polymers, ______________ offer superior corrosion resistance.
Uniform corrosion
_________________ in a ceramic takes place as a result of chemical dissolution.
molds
When the humidity is high, __________ can begin to form on ceramic, particularly ones in which there is no glaze.
frost
Damage can occur when ceramics are exposed to ________________.
Impact and abrasion
With its delicate nature, ceramics that have been used over a period of time will sustain cracks, nicks, and blemishes.
high; low
In __________ humidity, salts become soluble, and in __________ humidity, they crystallize.
Soluble salts
_______________ respond to changes in humidity both high and low.
Composites
________________ are made from a polymer matrix that is reinforced with an engineered, man-made or natural fiber (like glass, carbon or aramid) or other reinforcing material.
Fiber-Reinforced Polymer (FRP)
Other name for composites.
Composites
These do not rust or corrode, which are especially important characteristics in harsh operating environments. The corrosionresistant composite solutions perform within many industries that rely on nondeterioration for safety and endproduct delivery.
Failure Analysis of Polymeric Materials
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 the failure
slip and twinning
Two prominent mechanisms of plastic deformation in metals: ______________ and ______________
irreversible
The plastic deformation is _______________ and it stays even after the removal of the applied forces.
speed of stress
The _______________ causes rapid material changes, and at times, unable to conform to the structural changes the material may break.
heat and pressure
Plastic deformation employed in the production of goods involves subjecting the material to controlled ___________ and ___________. This enables the material to undergo structural adjustments and incrementally bending until achieving the desired shape.
Slip
Occurs in discrete multiples of atomic spacing.
Twinning
The movement of atoms is lesser in atomic spacing.
Slip; Twinning
Occurs over a wide plane: __________
Crazing
This occurs in high-impact plastics due to the combined effect of stress and aggressive environment.
Crazing
Since ___________ is a series of cracks in your glaze, they are the perfect hideaways for food particles, bacteria, and fungi like mold to grow.
stress-strain diagram
Schematic __________________ for compressive loading of a polymer that develops extensive shear banding beyond the elastic limit and undergoes considerable permanent strain before fracture.
Fatigue
______________ is simply one failure mechanism, in which prolonged cyclical stresses cause undue or unexpected wear on a part until it ultimately fails.
composites; polymers
In ______________, repeated support of extreme weights can cause fibers to tear.
localized stress variations
These temperature variations lead to ___________________ within the material, causing compressive stresses on the outer portion and tensile stresses on the inner portion of a component.
Physical aging
Occurs below glass transition temperature (Tg) and material becomes brittle. It is a significant phenomenon characterized by changes in material properties over time due to molecular relaxations.
ductility; creep resistance
Lowering of Tg, increase in ____________, loss of ____________.
humidity
In non-metal materials, ____________ can cause swelling and shrinking.
Crack branching
It is a common feature in failure of ceramic components. Cracks branch at a critical velocity, which is of the order of half the speed of sound in the specific glass under study.
critical velocity
The acceleration of crack initiation to the ______________ depends on the energy dissipation available from the release of stored energy. The energy source can be applied stress, prestressing or residual stress.
Ceramics
These possess excellent corrosion and high-temperature resistance, with the main disadvantages being brittleness and lower tensile strength.
Carbons
These show good corrosion resistance, electric and heat conductivity, but they are fragile.
Wood
This is attacked by aggressive environments.
Lowering temperature
This usually causes a pronounced decrease in corrosion rate. In other cases, increasing temperature decreases attack.
inversely
The square of thickness is _____________ proportional to permeation.
inversely
Density is _____________ proportional to permeation.
velocity
Very high _____________ should be always avoided where possible, because of erosion-corrosion effects
deaerator
Pairing a _____________ with an oxygen scavenger will greatly reduce the amount of chemical used.
chemical oxygen scavenger
A ________________ such as sulfite is still required to completely remove dissolved oxygen from the feedwater.
bond failure
As thickness increases, the thermal stresses on the boundary increase, which can result in ________________.
coefficients of thermal expansion
Temperature changes and large differences in _____________________ are the most common causes of bond failure.
Thickness and modulus of elasticity
________________ and ________________ are two of the factors that influence these stresses.
Thermal insulation
______________ of the substrate will reduce the temperature gradient across the vessel. This also reduces the rate and magnitude of temperature changes, keeping blisters to a minimum.
Useofoperatingprocedures/devices on Thermoset
It will limit the ratio of process pressure reductions or temperature increases will provide added protection.
thermoplasts
A general rule as to the differences in the corrosion resistance of the ______________ can be derived from the periodic table.
Curing the resin
______________ plays an important part in the chemical resistance of the thermoset.
accelerator
The presence of contaminants in the fluid may act as an _______________.
inhibitors
It is important to remember that ____________ are specific in terms of metal, environment, temperature, and concentration range.
entropy
Because of their large molecular weight, very little ___________ can be gained by mixing a given mass of polymer with another substance, making them generally quite difficult to dissolve.
swelling
A more common and related problem is ____________, where small molecules infiltrate the structure, reducing strength and stiffness and causing a volume change.
chain length
The most common form of degradation, however, is a decrease in polymer _______________.
Radiation
Most plastics, after being exposed to direct sunlight for a period of years, exhibit reduced impact resistance, lower overall mechanical performance, and a change in appearance.
shorter; longer
Photochemical degradation is caused by photons or light-breaking chemical bonds. Light of any wavelength ____________ than the threshold will break a bond, while ____________ wavelengths cannot fracture it.
weatherability
However, the higher grades of a resin usually exhibit higher ______________ than the lower molecular weight grades with comparable additives.
Permeation
Plastic materials tend to be an order of magnitude larger in their porosity than metals in which gases, liquids or vapors can permeate polymers.
Indirect Dissolution
The corrosion process of a solid material by a liquid can involve the formation of an interface or reaction product between the solid and the solvent. This reaction product mayor may not create an attached surface layer.
vapor pressure
The ____________ of covalent materials is generally greater than that of ionic materials and therefore tend to vaporize or sublime more quickly.
polar; nonpolar
Ionic materials tend to be soluble in ____________ solvents (e.g., salt in water) and covalent materials tend to be soluble in ____________ solvents (e.g., SiC in hexane).
true composite
As defined by Holmes and Just, a ______________ involves combining distinct materials in a deliberate manner to create structural characteristics superior to those of the individual components.
Boron fibers
These exhibit good heat resistance up to around 500°C but experience significant strength reduction at higher temperatures due to increased oxidation rates.
Boron carbide; boron nitride
___________ is highly stable in oxidizing atmospheres up to 1090°C, while ___________ is stable only up to 850°C.
Carbon or graphite fibers
_____________, introduced in the 1970s, experience strength loss above 500°C due to oxidation and possess a notable negative axial thermal expansion coefficient.
Glass fibers
_______________ are commonly used in composites for low-temperature applications, particularly in polymer matrices for marine or moist environments.
borosilicate glass fibers
However, exposure to moisture can lead to surface tensile stresses in ______________, resulting in potential failure due to alkali-hydrogen exchange.
Ceramic Matrix Composites (CMCs)
These exhibit a high modulus of elasticity and excellent resistance to high temperatures and corrosion, although they typically have poor crack propagation resistance.
slip planes
A slip involves the sliding of blocks of crystal over one another along different crystallographic planes known as ____________.
Crazing
___________ is the development of a network of fine random cracks or fissures on the surface of concrete or mortar caused by shrinkage of the surface layer.
Crazing
____________ cracks are sometimes referred to as shallow map or pattern cracking. They do not affect the structural integrity of concrete and rarely do they affect durability or wear resistance.
Fatigue
________________ is a failure mechanism that involves the cracking of materials and structural components due to cyclic (or fluctuating) stress. While applied stresses may be tensile, compressive or torsional, crack initiation and propagation are due to the tensile component.
Crack initiation
Fatigue cracks almost always initiate at a free surface and near a stress riser (e.g. the toe of a weld). The initial development of a fatigue crack occurs at localized discontinuities in the materials crystal structure. The generation and movement of discontinuities actually strengthens the metal through plastic deformation.
Crack propagation
Once a crack is initiated, continued cyclical stresses repeat the process, slowly growing the micro-crack, which becomes a threat to structural integrity.
Failure
The final failure event (i.e. catastrophic fracture) can be ductile or brittle, depending on the material, thickness, temperature and the applied stress. Fatigue failures typically occur suddenly. The fatigue-induced fracture surfaces of a broken component are typically smooth and show no evidence of plastic deformation.
glass transition temperature
The ______________ is the temperature at which an amorphous polymer transitions from hard/glassy to soft/leathery, or vice versa.
Wood
____________ is a hygroscopic material, meaning that it will continually trying to achieve an equilibrium condition with its environment.
Checking
_____________, or cracking, is one symptom of non-uniform drying, and it is common and typically not structurally significant.
Photodegradation
______________ is the process by which a substance is altered via photons, especially those found in the wavelengths of the sun’s rays.
photodissociation
Photodegradation includes _______________, the breakup of molecules into smaller pieces by photons.
Thermoplastics
These melt when heated up and solidify when cooled down.
