(2)-Ceramics(1 Main characteristics Fragile and difficult to be machined Very hard Electric and thermal insulator Refractory and high temperature resistant Chemically inert also in aggressive
(2)- Ceramics(Ⅰ) Main characteristics • Fragile and difficult to be machined • Very hard • Electric and thermal insulator • Refractory and high temperature resistant • Chemically inert also in aggressive medias
(2)-Ceramics(I) Atoms behave as negative or positive ions,at least partially bonded by coulombic forces O Combination of metals or semiconductors and oxygen,nitrogen or carbon:oxide(Al2O3), carbides(SiC),nitrides(SigN4) ●High T melting ● Manufactured by sintering,never by melting (except glasses) Examples:bricks,concrete
(2)- Ceramics(Ⅱ) Atoms behave as negative or positive ions, at least partially bonded by coulombic forces Combination of metals or semiconductors and oxygen, nitrogen or carbon: oxide(Al2O3 ), carbides(SiC), nitrides(Si3N4 ) High T melting Manufactured by sintering, never by melting (except glasses) Examples: bricks, concrete, tiles, china, glasses
(3)-Glasses They may be classified as ceramics,but in the amorphous state(non ordered) Made by melting of oxydes (Si02,Na20,Ca0,Al203,K20…) Hard and fragile,machinable only at high T Do not conduct heat and electricity Examples:glass walls,windscreen,safety glasses,optical fibers
(3)- Glasses They may be classified as ceramics, but in the amorphous state (non ordered) Made by melting of oxydes (SiO2 , Na2O, CaO, Al2O3 , K2O…) Hard and fragile, machinable only at high T Do not conduct heat and electricity Examples:: glass walls, windscreen, safety glasses, optical fibers, …
(4)-polymers(I The features of polymers: OVery light(low density,also lower than 1g/cm3) ● Cannot face high T ● Insulator O Low mechanical properties O Plastically deformable O Some have elastic propertie
(4)- polymers(Ⅰ) The features of polymers: Very light(low density, also lower than 1g/cm3 ) Cannot face high T Insulator Low mechanical properties Plastically deformable Some have elastic properties
(4)-polymers(II) Covalent and also secondary bonds (Van der Waals and hydrogen) Are made by macromolecular organic compounds, natural or as synthesis Are made by organic synthesis Can be machined Low mechanical properties and low resistance to T BUT THERE ARE A LOT OF COUNTEREXAMPLES Examples:tyres,adhesives,paintings,bitumen
(4)- polymers(Ⅱ) Covalent and also secondary bonds (Van der Waals and hydrogen) Are made by macromolecular organic compounds, natural or as synthesis Are made by organic synthesis Can be machined Low mechanical properties and low resistance to T BUT THERE ARE A LOT OF COUNTEREXAMPLES Examples: tyres, adhesives, paintings, bitumen, …