Chapter10 - Chapter 10 Electrical Properties Electrical...

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Chapter 10 Electrical Properties Electrical Conduction Charge per carrier Mobility Energy bands and number of charge carriers Conductors, semiconductors and insulators Ionic conduction Conducting polymers Superconductivity
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Chapter 10 Definitions at the end of the chapter Conductors Concept of band gaps Insulators Semiconductors Intrinsic Extrinsic Superconductors Ionic Conductors
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Electrical Conduction V = IR Ohm’s Law Positive potential Negative potential A R L ρ = 1 σ =
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Electrical conductivities for a variety of materials at room temperature Metals and alloys σ [( -cm) -1 ] Al 3.8 x 10 5 Ag 6.3 x 10 5 Au 4.3 x 10 5 Co 1.6 x 10 5 Cr 7.8 x 10 4 Cu 6.0 x 10 5 Fe 1.0 x 10 5 Mg 2.2 x 10 5 Ni 1.5 x 10 5 Pd 9.2 x 10 4 Pb 4.8 x 10 4 Pt 9.4 x 10 4 Sn 9.1 x 10 4 Ta 8.0 x 10 4 Zn 1.7 x 10 5 Zr 2.5 x 10 4 Plain carbon steel (1020) 1.0 x 10 5 Stainless steel (304) 1.4 x 10 4 Gray cast iron 1.5 x 10 4
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Electrical conductivities for a variety of materials at room temperature Ceramics σ [( -cm) -1 ] ReO 3 5.0 x 10 5 CrO 2 3.3 x 10 4 SiC 1.0 x 10 -1 Fe 3 O 4 1.0 x 10 2 SiO 2 <10 -14 A1 2 O 3 <10 -14 Si 3 N 4 <10 -14 MgO <10 -14 Si 1.0 x 10 -4 Ge 2.3 x 10 -2
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Electrical conductivities for a variety of materials at room temperature Polymer σ [( -cm) -1 ] Nylon 10 -12 -10 -15 Polycarbonate 5 x 10 -17 Polyethylene < 10 -16 Polypropylene <10 -15 Polystyrene <10 -16 Polytetrafluoroethylene 10 -18 Polyvinylchloride 10 -12 -10 -16 Phenolformaldehyde 10 -13 Polyesters 10 -11 Silicones <10 -12 Aetal 10 -15 Range 6X10 5 to 10 -15 ( -cm) -1
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The Magnitude of Electrical Conductivity The number of mobile charge carriers/unit volume, N, with units m -3 . Charge per carrier, q, with units of Coulombs. The mobility of the charge carriers, μ , with units m 2 /(V-s). Nq σ μ =
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Number of Mobile Carriers in a Metal The resistance of an aluminum (L= 1 m and A = 1 mm 2 ) wire is 0.0283 . Calculate the number of mobile electrons contributed by each Al atom. Assume the current is carried exclusively by electrons which have a mobility of 1.22X10 -3 m 2 /(V-s)
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( 29 7 1 29 3 3 3 28 3 3 3 1 3.5 10 ( ) 1.81 10 / ( ) 2 4 4 2 16 2 4 1 6.05 10 / 16 2 4 2 2.99 V o o o V V L m RA N mobile electrons m q atoms atomic density unit cell volume a r r a a r atoms m r r N mobile electrons per atom σ ρ μ - = = = × Ω - = = × = = = = = = = × =
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Metallic Bond Ion cores of 2+ charge Delocalized cloud of valence electrons Schematic of metallic bonds in solid magnesium
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Reference Conductor Temperature ( ° C) ρ o( -cm) α e ( ° C -1 ) Al 20 2.65 x 10 -6 0.0043 Ag 20 1.59 x 10 -6 0.0041 Au 20 2.35 x 10 -6 0.0040 Co 20 6.24 x 10 -6 0.0060 Cr 0 1.29 x 10 -5 0.0030 Cu 20 1.67 x 10 -6 0.0068 Fe 20 9.71 x 10 -6 0.0065 Mg 20 4.45 x 10 -6 0.0065 Ni 20 6.84 x 10 -6 0.0069 Pd 20 1.08 x 10 -5 0.0038 Pb 20 2.06 x 10 -5 0.0034 Pt 20 1.06 x 10 -5 0.0039 Sn 0 1.10 x 10 -5 0.0047 Ta 25 1.25 x 10 -5 0.0038 Zn 20 5.92 x 10 -6 0.0042 Zr 20 4.00 x 10 -5 0.0044 Electrical resistivities, ρ o, and temperature coefficients of resistivity, α e , for selected conductors
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The Influence of Alloying on Conductivity ( 29 ( ) d i i T ρ = + [ ] (1 ) d AB B B AB BA b x x b b ρ= - In the dilute solution range
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Charge Mobility Collisions v at v E v E μ = =
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Charge Mobility 0 T μ < Thermal vibrations Foreign atoms Vacancies 0 D N <
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The Influence of Cold Work Alloy Content on Conductivity
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Chapter10 - Chapter 10 Electrical Properties Electrical...

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