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Thermo%208%202009

Thermo%208%202009 - Mat E 510 Thermodynamics of Solids Mat...

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Mat E 510 Thermodynamics of Solids Lecture #8 Yury Gogotsi A.J. Drexel Nanotechnology Institute and Department of Materials Science & Engineering, Drexel University, Philadelphia, Pennsylvania, USA Mat E 510 Thermodynamics of Solids

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Fe-C Phase Diagram (calculated)
Phase Stability Diagrams Consider equilibrium in the Si-C-O system at 1000ºC. Fixing activities of 2 components, fixes the activity of the 3 rd component. When C and O 2 activities are fixed, the activity of Si is fixed and a defined equilibrium exists. Following 2-D representations of the phase stability can be considered: T = const, a C vs p O2 a C = const, T vs p O2 p O2 = const, T vs a C Solid phases: Si, SiO 2 , SiC, C and gas (CO-CO 2 ). 5 phases – no degree of freedom. If gas phase is always present: 4 cond. Phases + gas in an invariant state 3 cond. Phases in equilibrium + gas at any T 2 cond. Phases in equilibrium + gas at arbitrary T and a C or p O2 1 cond. Phase + gas at arbitrary T, a C and p O2 4 possible equilibria with 3 cond. phases and gas 6 possible equilibria with 2 cond. phases and gas

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Phase Stability Diagrams Case 1: Si-SiO 2 -gas phase Si+O 2 =SiO 2 G°(1273K) = -63,300J = -RT ln (1/ p O2 ) = 8.3144 x 1273 x 2.303 log p O2 Thus, equilibrium between Si and SiO 2 requires log p O2 = -28.04 (AB line) Case 2: Si-SiC-gas phase Si + C = SiC G°(1273K) = -683,400J = -RT ln (1/ a C ) = 8.3144 x 1273 x 2.303 log a C Thus, equilibrium between Si and SiC requires log a C = -2.6 Case 3: SiC-SiO2-gas phase Case 4: SiC-C – gas phase Case 5: SiO2-C-gas phase Case 6: Si-C-gas phase
Si-C-O Phase Stability Diagram

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Si-C-O Phase Stability Diagram
Si-C-O Phase Stability Diagram

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Ulf Bossel - European Fuel Cell Forum - July 2008 0 2000 4000 6000 8000 10000 12000 1930 1970 2010 2050 2090 Mtoe Year Coal Gas Oil Data source: Oil, Gas, Colin Campbell/ASPO 2005 Coal-, Nuclear Scenario, LBST 2005 2008 Modified original from Werner Zittel. LBST SES-Presentation, Zurich, 2 June 2006 World Energy Situation Forecast No chance to substitute fossil fuels by conventional energy at present levels Only renewable energy is available for a gradual replacement of fossil fuels Rational use of energy (energy efficiency) is key to sustainble future ? All source are „below ground“ Nuclear Energy
Fundamental Laws of Thermodynamics 1st Law of Thermodynamics: “Energy cannot be created or destroyed” “It can only be converted from one form into another“ 2nd Law of Thermodynamics: „Some energy is always lost when energy is converted“ … neither by presidential initiatives, majority votes, decisions of committees, political parties, nor by power plants, utilities, oil companies etc. …

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Physical Consequences derived from these fundamental laws Sustainable energy solutions require: - better overall energy efficiency - energy from renewable sources Energy problem cannot be solved by: - change of energy carriers (e.g. hydrogen) - manipulation of fossil fuels (e.g. clean coal) - innovative conversion technologies (e.g. fuel cells) - energy storage There are no other options!!!!
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Thermo%208%202009 - Mat E 510 Thermodynamics of Solids Mat...

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