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MAT E 273 Final Exam

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True

(T/F) Polymers are often subject to embrittlement (glass transition) near and around 0 C, and the max temp is around 200 C because the hydrocarbons burn

Zinc-blende crystal structure coordination number, examples, and properties

- CN = 4 - Examples = SiC - Properties = Used in LEDs, lasers, etc as semi-conductors

Diamond cubic crystal structure coordination number, examples, and properties

- CN = 4 - Examples = C, Ge, Si - Properties = Used in microelectronics as semi-conductors

Rocksalt crystal structure coordination number, examples, and properties

- CN = 6 - Examples = NaCl - Properties = N/A

Cesium chloride crystal structure coordination number, examples, and properties

- CN = 8 - Examples = CsCl - Properties = N/A

Fluorite (CaF2) crystal structure coordination number, examples, and properties

- CN = 8 - Examples = PuO2, ThO2, ZrO2 - Properties = These compounds are radioactive, so they're used as a way to generate heat through applied voltage (or vice versa)

Perovskite crystal structure coordination number, examples, and properties

- CN = Ti ions touch 8 Ba ions and 6 O ions - Examples = BaTiO3 - Properties = Electrically polarized which leads to piezoelectricity (applied voltage -> strain and vice versa)

General ceramic categorization

- Generally poor conductors of electricity - Generally poor conductors of heat at room temperature - Generally high melting points - Generally covalent / ionic bonds - Generally high tensile strength and low density - Generally brittle at room temp

Thermosets

- Harden on first cooling or curing, burn on heating - Not easily recyclable - Heavily cross-linked and network polymers

Carbides HfC and TaC properties

- High electrical conductivity - The two highest melting point binary compounds - High hardness and melting points, so sintering is used to machine large parts

Titanium Nitride (TiN) properties

- High-hardness and wear-resistant coating for tool tips like drill bits and saws - Gold appearance

Partially Stabilized Zirconia (PSZ)

- Multi phase tetragonal and cubic - 4-8 mol% Y2O3 with 7-8 mol% being the most common - Produced via sintering at 1600-1800 C and then precipitating t-phase solutions down via annealing at around 1000-1500 C - Fracture toughness exists reliably until 900 C - Toughened by ferroelastic transformation at high temps (1200 C) - Used as coatings in high temperature applications such as gas turbine engines

Silicon Nitride (Si3N4) properties

- Often used in bearings (high hardness/low friction) - Low weight compared to metals

Zirconia (ZrO2)

- Phases in temperature ascending order -> Monoclinic, tetragonal, cubic - The volume expansion between the t-m phase causes high stress which provokes a brittle response thus making it infeasible to traditionally manufacture

Cubic Stabilized Zirconia (CSZ)

- Single phase cubic - >8 mol% Y2O3 with 8-10 mol% being the most common - No thermal phase changes are expected below melting temperature - Strength and toughness are inferior to TZP and PSZ because it doesn't undergo stress-induced phase changes, but it has no thermal cycling issues

Tetragonal Zirconia Polycrystal (TZP)

- Single phase tetragonal - 2-4 mol% Y2O3 with 3 mol% being the most common - Offers high bending strength and fracture toughness - Produced via sintering at 1300-1500 C - Exhibits the highest practical strength and fracture toughness values across all ceramics - Grinding the surface can invoke the t-m transformation near the surface which helps prevent crack propagation - Limited by low-temperature cycling (200-300 C) over hundreds of hours, especially in the presence of water: adding Aluminum Oxide prevents this - Upper temperature limit is 1100 C

Thermoplastics

- Soften/melt on heating, harden when cooled - Recyclable - Linear and branched polymers

Boron Carbide (B4C) properties

- Used for ceramic body armor - Machined through sintering

Silicon Carbide (SiC) properties

- Used for ignitors, abrasives, and crucibles/labware - Potential to be used in gas turbine engine blades (1/3 the weight of Nickel jet engine blades)

Alumina (Aluminum Oxide or Al2O3)

- Used for milling spheres (to flatten surfaces) and crucibles/labware - Used for hip replacements - Used for heat/electrical shielding in fiber form

Silica (SiO2)

- Used for technical glasses (touch screens) - Used as the main component of soda-lime glass - Used for heat shield tiles for spacecraft reentering the atmosphere

Tungsten Carbide (WC) properties

- Very hard, so it's resistant to abrasions, scratches, etc. - Shiny and not completely brittle - Used for high-hardness bearings as well as cutting tools

Silicone

A class of polymer that is commonly used for medical coatings, membranes, and tubing, because it is relatively inert and also anticoagulant in nature.

Silicon

A highly covalent elemental semiconductor that is hard, brittle, and crystallizes with the diamond cubic crystal structure under STP

Poly(cis-isoprene)

A natural polymer that is extremely elastomeric, exhibiting very high elastic strains for relatively low stresses

Polycarbonate (PC)

A very strong and very tough polymer that is transparent and therefore useful as a substitute for ceramic glass

Amorphous: - Not tightly packed - Weaker, but more ductile - Less dense Crystalline: - Tightly packed (normally linear or branched) - Stronger, but more brittle - More dense

Amorphous vs Crystalline Structure

Silica (Silicon Dioxide or SiO2)

Optically transparent ceramic compound with an amorphous, coordination-4 (tetrahedral) covalent network used in modern glass making

Poly(Acrylonitrile-Butadiene-Styrene) (ABS)

Plastic used in LEGOs

Viscoelastic creep

Polymer will permanently flow over time in response to a constant applied stress

Primary: - Covalent Secondary: - Van der Waal force - Interactions between dipoles that are temporarily induced - Interactions between temporarily induced and permanent dipoles

Primary/Secondary Bonding between Polymers

Viscoelastic stress relaxation

Stress applied to a polymer must decay over time in order to maintain a constant strain

Vulcanization

The introduction of sulfur crosslinks within poly(cis-isoprene) (also known as natural rubber)

Soda-lime glass

The majority of ceramic production today is for ___

- n = degree of polymerization (number of repeat units) - M = number average molecular weight (mass of the chain) - m = molecular weight of the repeat unit (mass of one repeat unit in the chain)

What do the terms of n = M/m mean?

Maxwell Viscoelastic model and it describes linear and branched polymers

What model is this and what does it describe?

Voight Viscoelastic model and it describes cross-linked polymers

What model is this and what does it describe?

Alternating Chemical Architecture

What type of chemical architecture is this?

Block Chemical Architecture

What type of chemical architecture is this?

Grafted Chemical Architecture

What type of chemical architecture is this?

Random Chemical Architecture

What type of chemical architecture is this?

Branched Polymer Structure

What type of polymer structure is this?

Crosslinked Polymer Structure

What type of polymer structure is this?

Linear Polymer Structure

What type of polymer structure is this?

Network Polymer Structure

What type of polymer structure is this?

Poly(vinyl-chloride) (PVC) and it's used for PVC pipes