Materials Science Exam 4

What type of structure/ state do glasses have?

Non-Crystalline (amorphous) silicates containing other oxides

What is a defining characteristic, an important characteristic and one application of glasses?

Defining characteristic - Non Crystalline (amorphous) silicate containing other oxides

Important characteristic - optically transparent

Application - window panes, containers

What type of structure/state do glass-ceramics have?

fine-grained polycrystalline material

What is a defining characteristic, an important characteristic and one application of glass ceramics?

Defining Characteristic - Fine grained polycrystalline material produced through controlled crystallization of base glass

Important characteristic - low coefficent of thermal expansion

Application - Ovenware (Corningware)

What are two reasons why clay products are so widely used

Found naturally in great abundance, ease of shaping and forming

what must be done to most clay products in order to improve material properties?

Dried to remove the moisture in them, and then fired at elevated temperatures to sinter (to heat up and solidify but not at liquification temperatures) particles

What is a defining characteristic, an important characteristic and one application of a clay product?

Defining Characteristic: Mixed with water, formed, dried and then fired at high temp to improve strength

Important characteristic: Found naturally in great abundance

Applications: Porcelain

What is a defining characteristic, an important characteristic and one application of a refractory ceramic?

Defining: Unreactive and inert when exposed to high temperatures or corrosive environments

Important: resistant to thermal shock

Application: cement kilns

What are two prime requisites for an abrasive ceramic?

high hardness, and excellent wear resistance

What is a defining characteristic, an important characteristic and one application of an abrasive ceramic?

Defining: Used to wear, grind, or cut away other materials by use of contact force

Important: high hardness, good wear resistance, naturally occuring

application: grinding wheels

What is a defining characteristic, an important characteristic and one application of a clay cement?

Defining: when mixed with water, interlocks and hardens

Important: curing requires appropriate moisture content and will become weaker if dried out

application : mortar for masonry work, form concrete

The setting/hardening of cement depends on what process?

the hydration - chemical reaction with water

What is a defining characteristic, an important characteristic and one application for a ceramic biomaterial?

Defining: relatively high fracture toughness

Important: can bond and interact with tissue

application : orthopedic applications/implants

waht is a prime liability of a ceramic biomaterial?

disposition to brittle fracture

What is a defining characteristic, an important characteristic and one application of diamond?

Defining: allotrope of carbon

Important: lowest sliding coefficient of friction of any solid, hardest of all bulk materials

Application: jewelry

What is a defining characteristic, an important characteristic and one application of graphite?

Defining: allotrope of carbon

Important: optically opaque with black-silver color

Application: lubricants, pencils

What is a defining characteristic, an important characteristic and one application of carbon fiber?

Defining: atoms bonded parallel to the fiber

Important: high strength

Application: aerospace (rocket nozzles)

Characteristics of carbon fibers is that they have _____ diameter, _____ strength, and ________ modulus.

Small; high; high

What is one application of carbon fiber?

Used as the reinforcing material in a fiber-reinforced composite

what are the characteristics of a glassy or non-crystalline material that is transforming from a liquid to a solid and what is the glass temperature?

Upon cooling, a glass in a liquid phase becomes more viscous continuously as temperature decreases. One of the distinctions between crystalline and noncrystalline materials lies in the dependence of specific volume on temperature.

Why is glass annealed?

To reduce the internal thermal stress

Why is glass tempered and how does the residual stress distribution vary over the cross section of a tempered glass plate?

To increase the strength, the heat gives the outer edge of the glass a high compressive stress, and the interior a slight tensile stress. Any cracks that form on the outside are now less likely to propagate

after a clay product has been formed by methods such as hydroplastic forming or slip casting, how is the material strengthened?

The object is dried, and then fired at high temperatures, where the particles undergo vitrification, flows around nonmelted particles and fills some of the pore volume. the fused phase forms a stronger glassy matrix. COMPLETE vitrification cannot occur or the object can collapse

Sintering

is a process where powdered materials are heated below their melting point to cause particles to bond together, reducing porosity and increasing strength.

Vitrification

is the transformation of a material into a glass-like, non-crystalline solid by heating, during which the particles partially melt and flow to fill spaces between them, enhancing density and strength.

Thermal Tempering

is a heat treatment process that increases the strength and durability of glass by inducing internal stresses through controlled heating and rapid cooling.

What type of intramolecular bonding occurs with hydrocarbon molecules?

covalent

what is the difference between saturated and unsaturated hydrocarbon molecules?

saturated = all single bonds, unsaturated = double or triple bonds

How does the size of a hydrocarbon affect its state/phase?

At room temperature, lowest size = gas. As size increases size = liquid, and largest size = solids. As the size goes up the boiling point increases and the state changes from gas to liquid to solid

If two hydrocarbon molecules have the same chemical formula, will they have the same physical properties

no, the termed isomerisms will have different properties.

What is the difference between a hydrocarbon and a polymer?

polymers are a much larger size

what is the difference between a monomer and a repeat unit?

Same chemical formula, but the bonding arrangement is difference, and the monomer is what is used to synthesize the polymer and the repeat unit is the smallest structural entitity

what is the basic process involved with addition polymerization?

start with monomer and free radical, free radical breaks the double bond, creating two active sites, then bonds with one of the carbon sites. The other site is open to bond with another monomer, which then creates another active site. How long the chain grows will affect its molecular weight.

what are 3 things that contribute to the random coils and molecular entanglements?

1.) single bonded atoms in the backbone of the polymer molecule make an approximate angle of 109 between each other

2.) single bonded atoms have rotational flexibility and end up with numerous kinks and coils

3.) double bonded atoms and bulky/large side groups don’t have much rotational flexibility.

what structures are the random kinks/coils/entanglements considered to be?

amorphous

Linear polymers

mass of spaghetti - van der waals and hydrogen bonding between the chains. Thermoplastic

Branched polymers

side branches attached to chain which results in a lowering of the polymer density, thermoplastic, less likely to be crystalline since branches impede crystallinity

crosslinked polymers

adjacent linear chains are joined one to another at various positions by covalent bonds. thermosetting. lower crosslinking increases elastic region and many of the rubber elastic materials have this structure

network polymers

adjacent linear chains are joined one to another at various positions by covalent bonds, tend to be thermosetting, typically high strength and brittle

Molecular configurations

polymers that have more than one side atom or group of atoms bonded, the regularity and symmetry of the side group arrangement can significantly influence the properties. This can lead to variations in physical properties such as viscosity, tensile strength, and melting temperature.

Thermosets:

significant crosslinking, hard and brittle, doesnt soften with heat, vulcanized rubber, epoxies

Thermoplastic

little crosslinking, ductile, soften w/ heating

what is a copolymer and why are they synthesized/used?

two repeat units, and often has a combination of the two polymer properties to improve mechanical properties to improve mechanical properties

what are 3 differences between metal/ceramic crystals and polymer crystals?

1.) packing of the chains rather than the location of the atoms produce an ordered atomic array is what is considered a crystalline structure in polymer

2.) polymer are often only partially crystalline with orderly pcked chains surrounded by amorphous regions

3.) unit cells are very complex

how does the degree of crystallinity affect the density strength, and how heat affects the material?

the density of a crystalline polymer is greater than an amorphous polymer of the same material and molecular weight. The crystallne packing is more efficient than amorphous packing. The degree of crystallinity of a polymer depends on the rate of cooling during solidification as well as on the chain configuration. Higher crystallinity increases density and strength, while heating can reduce crystallinity and affect overall mechanical properties.

what molecular sturcture tends to have high degree of crystallinity, and which are amorphous?

linear polymers have easy crystallation because there are fewer restrictions. side branches interfere with crystallization such as that branched polymers may be crystalline, but less so than linear. the larger/bulkier the side group of atoms, the less tendency to crystallize.

what shape do many semicrystalline bulk polymers grow into and what does it look like?

spherulite - nucleation site with aggregate of ribbonlike chain folded crystallites radiating outwardwith a spherical structure resembling a flower or a star.

what are three examples of defencts in a crystalline region of a polymer?

edge dislocations, impurities, and vacancies.

isomerism

Isomerism is the phenomenon where compounds with the same molecular formula exist in different structural forms or arrangements. These variations can lead to different physical and chemical properties.

functionality

Functionality refers to the number of reactive groups or sites in a molecule that can participate in chemical reactions, influencing the types of reactions and properties a polymer can undergo.

monomer

A small, repeating unit that can join together to form a polymer, often determining the polymer's properties and behavior.

Repeat unit

The specific arrangement of atoms in a monomer that contributes to the overall structure and characteristics of a polymer. Repeat units are the fundamental components that define the polymer's repetitive structure.

Saturated

A type of hydrocarbon in which all carbon-carbon bonds are single bonds, resulting in the maximum number of hydrogen atoms bonded to the carbon chain.

unsaturated

A type of hydrocarbon that contains one or more double or triple carbon-carbon bonds, resulting in fewer hydrogen atoms bonded to the carbon chain compared to saturated hydrocarbons.

what three things are the stress strain behavior sensitive to and how does each affect the mechanical properties

temperature - increasing the temperature results in a decreae in both tensile strength and modulus of elasticity and an increase in ductility

rate of deformation(strain rate) - increasing the rate of strain increases the strength and modulus decreases the ductility

chemical nature of the environment

what characteristic must a polymer display in order for it to be classified as an elatomer?

large recoverable strains produced at low stress levels

Viscoelastic Deformation

A property of materials that exhibit both viscous and elastic characteristics when undergoing deformation, allowing them to dissipate energy and return to their original shape over time.

viscoelastic creep

The gradual deformation of a material under a constant load over time, which includes both the time-dependent strain and recovery.

what types of polymers tend to have brittle fractures and how does their molecular structure contribute to this?

thermosetting polymers are more brittle due to the heavily crosslinked networks. cracks form at regions where there is localized stress concentration. The stress is amplified at the tips of these cracks, leading to crack propagation and fracture. Covalent bonds in the network or crosslinked structure are severed.

thermoplastic polymers are more ductile at normal operating temperatures

what type of polymers could possibly have both brittle and ductile fractures and how does their molecular structure contribute to this characteristic?

both ductile and brittle modes are possible and many of these materials are capable of experiencing ductile-to-brittle transition. Factors that favor brittle fracture are a reduction in temperature, an increase in strain rate, the presence of a sharp notch, an increase in thickness of specimen and the extent of crystallinity in the polymer that can lead to different failure mechanisms under varying conditions.

What are the two stages of elastic deformation in semicrystalline polymers?

stage 1.) elongation

stage 2.) increase in lamellar crystallite thickness due to bending and stretching of chains in region

3 stages of plastic deformation

stage 3.) after elastic deformation, the adjacent chains in the lamallae slide past one another and tilt so that the chain folds become more aligned with the tensile axis.

Stage 4.) crystalline block segments separate from the lamellae with the segments attached to one another by tie chains

stage 5.) the blocks and tie chains become oriented in the direction of the tensile axis

what material property changes happens during in the final stages of plastic deformation when the blocks and tie chains become oriented in the direction of the tensile axis?

tensile strength, toughness, and modulus of elasticity all improve

how does molecular weight affect material properties?

tensile strength increases with Molecular Weight

how does degree of crystallinity affect material properties?

tensile modulus increases slightly, tensile strength increases, and density increases with increasing degree of crystallinity

how does predeformation by drawing affect material properties?

increases tensile strength, modulus, and anisotropy of a semicrystalline material. For an amorphous material, the material must be cooled quickly for these material properties to be changed.

What material property changes happen during the final stage of plastic deformation (before fracture) when the blocks and tie chains become oriented int he direction of the tensile axis?

tensile strength, modulus of elasticity, and toughness all improve

what classifies a polymer as an elastomer?

has the ability to be deformed to large deformation and then elastically spring back to its original form

what type of structure (amorphous, semicrystalline, or crystalline) are elastomers?

amorphous

what type of molecular structure (linear, branched, crosslinked, networked) most often occurs in elastomers?

vulcanization is the crosslinking that is achieved by a nonreversible chemical reaction to enhance the strength and modulus of elasticity of an elastomer. Rubber is vulcanized by the addition of sulfur and other agents/activators

what is the crystallization process for polymers

upon cooling through the melting temperature, nuclei form, in which small regions of the tangled and random molecules become ordered and aligned in the manner of chain-folded layers

when a polymer is held at a specific temperature during crystallization, how does time affect the degree of crystallinity?

there is a higher percent of crystallizationa s time increases

what are two features distinctive to melting of polymers that are not seen in metals or ceramics?

1.) melting occurs over a range of temperatures

2.) melting behavior depends on the history of the specimen, in particular the temperature at which it crystallized. The thickness of chain-folded lamellae depends on crystallization temperature, the thicker the lamellae, the higher the melting temperature

what happens at the glass transition temperature?

the temperature at which the polymer experiences the transition from rubbery into rigid states

what are two major factors that affect the melting and glass transition temperatures?

1.) chain stiffness, caused by double bonds bulky side groups or polar groups which increases Tm and Tg

2.) increasing molecular weight increases Tm and Tg

What is the one general criteria for a material to be considered a plastic?

have some structural rigidity under load and are used in general-purpose application

polymers that are plastic:

1.) may have any degree of crystallinity and all molecular structures and configurations

2.) can be thermoplastic or thermosetting

3.) if linear or branched polymers must be used below their glass transition temperatures, they must be crosslinked enough to maintain their shape

fiber polymers that are drawn into long filaments having at least a 100:1 length to diameter ratio must have specific characteristics in order to be useful as a textile material? what are 3 characteristics?

highly crystalline material to have high tensile strength over temperature range, high modulus of elasticity, and abrasian resistance

do fibers typically have high or low molecular weights and why?

must be relatively high or the molten material will be too weak and can break during the drawing process.

polymerization

process by which monomers are linked together to generate long chains composed of repeat units

additional polymerization / chain reaction polymerization

process by which monomer units are attached one at a time in chainlike fashion to form a linear macromolecule. composition is an exact multiple of the OG reactant monomer

condensation polymerization

formation of polymers of stepwise intermolecular chemical reactions that may incolve more than one monomer species.

what is a composite?

a material that is multi-phased and artificially made

in a composite, what are the matrix and dispersed phases?

the matrix is continuous and surrounds the other phae. its purpose is to transfer stress to the dispersed phase and protect the dispersed phase from the environment. Only a small amount of the load is supported by the matrix, however the strength of the composite is dependent on the bonding force between the matrix and the dispersed phase.

the dispersed phase is discontinuous and surrounded by the matrix. it enhances mechanicla, thermal, and electrical properties of the composite

particle-reinforced composite

geometry of the dispersed phase is equilaxed

fiber-reinforced composite

dispersed phase has the geometry of a fiber

structural composite

multilayered and designed to have low densities and high degrees of structural integrity.

Polymer Matrix Composite

Matrix is a high molecular weight reinforcing plastic. easily fabricated, has a low cost, and can decrease the overall weight of the design components. low service temperature, and the matrix could be susceptible to degradation

Metal Matrix Composites (MMC)

matrix is a ductile metal, dispersed phase is often carbon and can improve the specific yield and tensile strengths, and creep resistance. Higher service temperatures than PMC, nonflammability, greater resistance to degradation by organic fluids. More difficult to manufacture, and more expensive than PMCs.

Ceramic Matrix Compound (CMC)

matrix is a ceramic, dispersed phase is often another ceramic such as zirconia and impedes the crack propagation through the matrix and improves fracture toughness as well as thermal shock resistance. use in high service temperatures, high stress and fracture toughness. Lower fracture toughness than MMC and most expensive

Concrete - matrix and dispersed phases and strengthening mechanism

silicate and oxide matrix. Dispersed phase-aggregate which includes sand, gravel, and crushed sand. strengthens through introduction of water where it then forms interlocking mineral hydrates. high durability and inexpensive, but has low tensile strength.