estudos- quiz 3

Bonding Ionic bonding - just one of the atoms gives electrons to another of different type. In this kind of bond anions and cations are formed, so anions are attract to cations. Another characteristic is the ionic bonds have good strength and are very common in ceramic structure. Covalent Bonding- the valence electrons shared to form stable shells, it is a directionality bond. In this kind of bond the strength is high but the electrical conductivity is poor. It is common in polymer structure. Metallic Bonding- there is a valence electrons shared in a sea of electrons (electron cloud) and the positive cores attracted to negative sea. This kind of bond is relatively strong and has good electrical conductivity.

Metals can be characterized by its metallic bonds, electron cloud and crystalline structure. The most common crystalline structure in metals is FCC, BCC and HCP. The imperfections that can be occur is vacancy, interstitutal (point), dislocation (line), grain boundaries (planar) and porosity (volumetric). metals can be reinforced by particles that improve strength and stops dislocation movement or by fibers that improve modulus and decrease density. Ceramics are hard and brittle and the common bond is the ionic. Crystalline structures usually close packed cubic and HCP systems. Ceramics are reformed because Ionic bond makes material strong but brittle, Low ductility due to bond type and Fibers improve fracture toughness. Polymers are cheap and easily processed, have lower strength and modulus, low melting point. It is important to say that polymerization is the combining of many monomers. Polymer can be classify in two types: thermoset and thermoplastic. Thermoset has cross-linkingof chains (harder material), it harden upon curing and do not soften or flow when heated but decompose. Thermoplastic flows when exposed to heat and pressure, harden upon cooling, can be amorphous or semicrystalline. The molecular chain can be configured in linear, branched, cross-linked and ladder.