CHEMMAT 121

Isotatic form

Side groups are all arranged on the same side of the polymer chain. Forms crystalline structure.

dispersion strengthening

A fine dispersion of a second phase within the parent phase. Most effective when there are lots of small precipitates of a hard phase in a softer parent phase. (age hardening)

Martensite

A metastable phase formed by shear transformation through rapid quenching (FCC to BCT). It is hard, brittle and strong.

Age Hardening

A special dispersion-strengthening heat treatment. By solution treatment, quenching (to form a super saturated solid), and aging (allows atoms to diffuse), a coherent precipitate forms that provides a substantial strengthening effect. (also known as precipitation hardening)

glass

A type of ceramic (normally based on silica) that has no long range order. They are amorphous.

network modifiers

Additives used to reduce the viscosity of loose networks in glasses e.g. Na2O and CaO.

Multiphase Strengthening

By having multiple phases present there are more barriers to dislocation movement. Generally done with a small amount of brittle phase in a more ductile one.

Transformation toughening

Crash temperature without allowing expansion so that tetragonal phase is not able to expand into monoclinic phase unless space becomes available.

Solid Solution Strengthening

Hardening and strengthening of metals that result from alloying in which a solid solution is formed. The presence of impurity atoms restricts dislocation mobility by distorting the lattice.

thermal tempering

Increasing the strength of a glass piece by the introduction of residual compressive stresses within the outer surface using an appropriate heat treatment.

Silicate composition and structures

SiO4- tetrahedra. In the form of chains, rings or sheets.

Spheroidising of steels

Pearlite is heated for several hours resulting in the formation of spheres (from layers) to reduce the surface area.

Elastomers

Polymeric materials that return to their original shapes after stretching. Have a few cross links.

atactic form

Random arrangement of side groups on either side of the chain. Forms amorphous structure.

around Tg polymers are ...

Rubbery

Vitrification

Some of the components melt and flow around the ceramic particles and solidify as glass.

Degree of Polymerization (DP)

The average number of repeat units per polymer chain molecule.

Powder pressing

The formation of a solid material by the compacting of fine particles under pressure. This green compact is then densified through heating.

hydroplastic forming

The molding or shaping of clay-based ceramics that have been made plastic and pliable by adding water.

Co-ordination number

The number of atoms the central one is in contact with.

Piezoelectric Materials

a material that generates electricity when pressure is applied to it, and one that changes shape when electricity is applied to it.

Thermoplastic

a material that softens when heated and hardens again when cooled

Co-polymer

a polymer consisting of two or more different monomers. Can be in the form of alternating, block random or graft.

Homopolymer

a polymer made up of one type of repeating unit. It is made from one monomer only.

Sintering

a process whereby particles are heated to the point that they fuse together at their borders in order to reduce the surface area. The rate increases with decreased particle size and/or increased temperature.

The theoretical strength of ceramics is never reached due to...

cracks, pores and holes.

below Tg, polymers are ______

glassy, amorphous solids that are brittle or elastic.

Annealing

heat (metal or glass) and allow it to cool slowly, in order to remove internal stresses and toughen it.

Polymer

large compound formed from combinations of many monomers

BCT materials have .... slip systems

no

cross-linked polymer

polymer in which long-chain molecules are attached to each other. Can be covalent or ionic.Results in hard, stiff and strong materials.

slip casting

process whereby ceramic powder is mixed with a water-based liquid to form a mass or slip. the slip is pressed into a mould and baked at high temperature by drying and firing.

Ceramic toughening mechanisms include...

reducing porosity and reinforcing with other materials such as fibers.

Porosity effects strength by....

reducing the cross-sectional area and concentrating stress.

amorphous

shapeless (tangle of polymer chains)

The alloying ingredients in low alloy steels.....

slow the diffusion of carbon

crystaline structure

the regular pattern of atoms, molecules, or ions in a crystal

Ceramics are typically brittle and stiff because...

there are no slip systems due to the opposite charges repelling each other. This also results in a high young's modulus due to stiffness.

above Tg, polymers are ____

viscous liquids as thermal vibrations have overcome secondary bonds.

Thermoset

when exposed to high temperatures, bonds are set, can't be unlocked due to cross links.