Physical bases of dental material science

Transcription

1 Physical bases of detal aterial sciece The ioizatio eergy of the sodiu ato is 496 kj/ol. How large eergy is ecessary i ev to ioize oe ato? The ioizatio eergy of a sigle ato: E i ,7 10 ε i 8,7 10 ( J / ato) 5,15eV / ato 3 19 NA ,6 10 Iré Bárdos-Nagy where E i is the olar ioizatio eergy, NA is the Avogadro uber. There is CO gas i a 0 l tak. At 5 C o teperature the pressure i the tak is *10 5 Pa. How ay oles of CO gas are i the tak. How large is the total ass ad the desity of the gas? pv ν RT ν p V R T ν 8, ,6( ol) ν M 1, ,07( g) V, ,0035( g / c 3 ) 0000 V specificvo lue ,4( c 3 / g) 71,07 ε Calculate the velocity of the olecules i the itroge gas at roo teperature (0 C o )! Suppose the sae velocities! The olar ass of the itroge (cosiderig that the particles are N olecules) is 8 g/ol (0.08 kg/ol). How large is the kietic eergy of oe olecule? ki k T 1 v v 3 1, v 3 v 3 k T 3 31, , ,8( ) s ,08 509, ,04 10 ( J / olecule) 0,038( ev )

2 Gas phase (ideal gas) i a force field gravitatio Exaple: desity () of air chages i fuctio of the potetial eergy? h p p e. 0 e p cost 0 theral equilibriu! air - Baroetric Forula The Baroetric forula is a special case of a geeral law Boltza distributio Distributio of particles o the levels of potetial eergy ε i i ε i 0 ε 0 Δε ε i Δε i 0 e 0 e 0 e i RT 0 e ε ε i 0 Δε R k N A N A less ad less particles are foud (i the sae volue) at the levels of higher potetial eergy ( at higher altitudes ) h - the uber of particles is saller at the levels of higher eergy - o the sae level, the uber is saller at higher teperatures - the lowest eergy level has the highest uber of populatio ε barrier Wide rage of applicatios baroetric forula theral eissio of etals Nerst equatio equilibriu ad rate of cheical reactios cocetratio of theral defects i ordered, structured systes coductivity of seicoductors... Exaple: reactio coordiate k AB cost. e K A B ε barrier ε A e ε A ε B Arrheius plot eergy of activatio At which altitude decreases the oxyge cocetratio by half of the sea level if the teperature is 0 C? Suppose that the atosphere is i rest! p p 0 e 0 e 0 0 / e Mgh RT 1 RT l 8,31 73 ( 0,693) h 5010( ) M g 0,03 9,81

3 Stregth of bod eergy Effect of teperature T ( ~ E ki ) Fluids structure of liquid water solid fluid gas volue shape crystallie aorphous Teporary regios of short rage order withi a few olecules ~10 doai size High cocetratio of structural defects Costat volue No fir shape - liquid High otioal freedo of particles Isotropy teporary regios of short rage order log rage order crystal lattice short rage order desity (, kg/ 3 ) disorder Phase diagra of water Liquid water has outstadig properties critical poit -- large dipole + strog H-bodig high specific heat high surface tesio efficiet solvet

4 Iportat properties of fluids 1. Viscosity (η) a itrisic echaical property costat Resistace to shearig otio: frictioal force betwee adjacet layers as they slide past oe aother laiar flow Newto s law viscosity is a costat η depeds o - the teperature - the agitude of F/A (η is a costat oly up to a certai agitude of the shear stress) fluidity ~ 1/η F η A Δ v Δh [ η] Pa s F A Shear stress F s η Δ v η g [Pa] h v A Δ viscosity of soe aterial as the fuctio of teperature expoetioal decrease (Boltza distributio) No-Newtoia fluids: the viscosity depeds o the velocity gradiet (ot costat) Tie depedece of viscosity (cheical ad/or physical chage i the structure) thixotropic (η decreases i tie) To ove a 0 c glass plate i a fluid with 100 1/s velocity gradiet 1 N force is required. How large is the viscosity of the fluid? rheopectic (η icreases i tie) F η A Δ v Δh Viscosity of fluids/aterials of detal applicatios aterial liquid water glycerol ethylethacrylate ooer ethylee glycol diethacrylate ooer Z-phosphate Zic oxide eugeol detal ceet silico 1 (0 C) 60 (0 C) 0,5 (5 C) 3,4 (5 C) η (Pas) (5 C) (37 C) (37 C) η F A g v 0, ( Pas)

5 . Properties of fluid iterfaces.1. Fluid-air (gas) iterfaces surface tesio (surface eergy) cohesive forces i the liquid eergy is required to icrease the surface by a area ΔA ΔA surface tesio J N Teperature depedece of water surface tesio Surface tesio of aterials i air ΔA J N aterial (J/ ) liquid water 0,073 blood 0,06 saliva 0,05 paraffi 0,05 alcohol 0,03 detie 0,09 eael 0,087 Hg PMMA 0,484 0,037 The spherical shape of a liquid drop is due to the surface tesio

6 .. Liquid-solid iterfaces Adhesio velcro Iterfacial eergy of the boudary betwee two aterials the eergy chages whe the area of the boudary chages iterfacial eergy < surface eergy of the two aterial attractio betwee the two aterials aggregatio adhesio Classificatio of adhesio forces: echaical cheical electrostatic dispersive diffusive adhesio forces ~ area cheically purified surface of eael wetted surface of eael gecko s foot Wettig Water drops o differet aterials (etal, glass, wax) θ : Cotact agle (wettig agle) What the shape of the drop depeds o? How ca we characterise the shape of the drop? Basic issue: what is eergetically ore favorable? To for a solid-liquid or a solid-air iterface?

7 θ α!! sair s air sliquid sl ΔA sl Youg-equatio Cases of wettig ΔA sair sair + ΔAcos θ 0 sl lair for the case of eergy-iiu cosθ solid-air θ cosθ if θ 180 liquid air o solid-liquid e.g. liquid water : 73 J/ solid glass: 130 J/ θ 16,5 glass - water: 60 J/ e.g. Liquid Hg: 500 J/ solid glass: 130 J/ θ 17 glass Hg: 430 J/ Cotact agle of a ercury drop is 140 o glass. How large is the iterfacial tesio of the glass-ercury boudary? Other surface tesio values: ercury air 480 J/, glass air 90 J/. cosθ solid-air liquid air solid-liquid solid air liquid air cosθ solid liquid cos140 solid liquid 458( J / ) solid liquid