15 - Surfaces and Interfaces Surfaces and Interfaces...

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urfaces and Interfaces Surfaces and Interfaces
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Surface tension γ γ = = U G A A S,V,n P,T,n ii most important thermodynamic parameter for characterizing an interface. nit is energy/area [J/m Unit is energy/area [J/m 2 ]
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Interfacial tensions of solid materials ystem emperature terface tension System Temperature (°C) Interface tension (m J/m²) Al 2 O 3 (s) - Silicate - Glass (l) 1000 < 700 2 O 3 (s) - Pb (l) 400 1440 2 O 3 (s) - Ag (l) 1770 2 O 3 (s) - Fe (l) 1570 2300 SiO 2 (Glass) - Na - Silicate (l) < 25 iO Glass) - Cu (l) 1120 1370 SO 2 (G ass) Cu ( ) 0 370 Ag (s) - Na 2 3 (l) 900 1040 Cu (s) - Na 2 3 1500 Cu (s) - Cu 2 S (l) 1131 90 TiC (s) - Cu (l) 1200 1225 gO(s)-Ag( l) 300 50 MgO (s) - Ag (l) 1300 850 MgO (s) - Fe (l) 1725 1600
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General trend: Interfacial tension in between similar compounds are small compared to the sum of surface tensions. etal oxide melts on oxides and metal oxide melts on oxides and metal melts on metals have low terface tensions ie excellent wetting interface tensions , i.e. excellent wetting.
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terfacial Energies Interfacial Energies 5
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Grain-Boundary Configuration 6
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Ideal Surfaces • No change happens – unit cell is ut cut
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eal surfaces Real surfaces elaxation Relaxation
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Reconstruction
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Mechanical properties of ceramics
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lasticity Elasticity oad on material (stress = leads to deformation Load on material (stress σ ) leads to deformation (strain = ε ) σ ε /2 Elastic deformation: σ = E ε here E = Young’s modulus where E Young s modulus hear loading = Shear loading = τ = G γ where G = shear modulus
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lastic oduli Pa Elastic Moduli in GPa Rubber 0.0035 Concrete 13.8 aCl 4 2 NaCl 44.2 Glass 69 ZrO2 138 O2 73 UO2 173 Spinel 284 Al2O3 380 SiC 414 TiC 462 iamond 035 Diamond 1035
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Effects of Porosity on Elastic Properties Pores concentrate stress •so less stress is necessary to achieve the same strain • therefore E decreases and mechanical strength decreases; • at the same time, increased porosity decreases uctility overall and brittle fracture is more likely ductility overall and brittle fracture is more likely • also causes the mechanical strength of the material to decrease
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ore on Porosity and Elastic Modulus More on Porosity and Elastic Modulus =E - 9P+09P 2 E = E 0 (1 1.9P + 0.9P ) where E 0 = E of nonporous material P = volume fraction of pores valid for up to 50% porosity and Poisson’s ratio of 0.3
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ffect of Temperature on Elastic Modulus Effect of Temperature on Elastic Modulus • E decreases slightly as T increases – because of the increase in interatomic spacing om thermal expansion from thermal expansion (as the interatomic spacing increases, less force is needed to increase interatomic separation)
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oisson’s Ratio Poisson s Ratio - /d) / ( l) = Poisson’s Ratio ν = ( Δ d/d) / ( Δ l/l) = Poisson s Ratio Δ d/d Δ d/d sually 0 1- 5for Δ l/l Usually 0.1 0.5 for ceramics ceramic is: If ceramic is: • isotropic Δ l/l • polycrystalline =2G(1+ Tensile load E = 2G (1 + ν ) Theory limits E = 3G and -1< ν < 0.5
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easuring Elastic Modulus Measuring Elastic Modulus train gauges which measure strain Strain gauges , which measure strain versus stress oad deflection curves from nsile
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15 - Surfaces and Interfaces Surfaces and Interfaces...

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