Fundamental%20Concepts%20of%20Thermodynamics

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Fundamental Concepts of Thermodynamics

• First, second, and third law
• Entropy
• Heat capacity, enthalpy
• Reaction enthalpies and thermochemical cycles
• Phase transitions
• Calorimetry

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Why I Count Calories for a Living

• They are fascinating
• Energetics whisper secrets of the strength of
  chemical bonds
• Entropies sing of vibrating atoms, moving
  electrons, and structural disorder
• Systematics have predictive power
• They pay
• thermodynamic data are essential to good
  materials processing
• Environmental science needs thermodynamics, both
  for issues of stability and as a starting point
  for kinetics
• Mineralogy, petrology, and deep Earth geophysics
  need thermodynamic data.

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Calorimetry Measures

• Heat capacities
• Heats of phase transitions
• Heats of formation

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From these data one calculates

• Entropies and free energies
• Solubililities
• Phase diagrams
• Petrologic and geochemical processes
• Materials synthesis and compatibility

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Phase Transitions
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Low temperature heat capacity and standard
entropy, Fe2SiO4 olivine and spinel,
calorimetry on a chip
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Thermal Analysis and Scanning Calorimetry

• Measure a signal (mass, heat, evolved gas,
  lemgth, X-ray pattern) at a variable heating
  (cooing) rate
• Systems
• Room temp to 600 oC, common
• 600-1500 oC, less common but we have
• 1500-2400 oC, uncommon but we have

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Example HfO2
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TMA on HfO2
TMA traces of HfO2 (1.5 Zr) in Ar flow. (HfO2
pellet L 2.5 mm Ø 5 mm sintered at 1700 C for 2
hours). Heating rate 10 C/min. 5 gram load. \
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High Temperature Oxide Melt Solution Calorimetry

• Dissolve oxide samples (5-15 mg) in a molten
  oxide solvent (20 g) at to form a dilute
  solution
• Difference in heat of solution of reactants and
  products gives heat of reaction
• Oxidative reactions for nitrides, sulfides,
  selenides, carbides
• Needed for ceramic materials which do not
  dissolve in aqueous solvents

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Solvents and Systems

• Lead borate (2PbO-4B2O3, sodium molybdate
  (3Na2O-4MoO3), alkali borate
• Oxides dissolve
• H2O and CO2 evolve as gases
• Nitride oxidized to evolved N2
• Sulfide oxidized to dissolved sulfate

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High-Temperature Calorimetry
DS
TTD
SOL
25oC
25oC
25oC
700oC
700oC
700oC
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Thermochemical Cycles - Perovskites

• 1. AO(xl, 298K) AO(dissolved, 973K)
• 2. BO2(xl, 298K) BO2(dissolved, 973K)
• 3. ABO3(xl, 298K)
• ABO3(dissolved, 973K)
• ______________________________
• 4. AO(xl, 298K) BO2(xl, 298K) ABO3(xl,
  298K) , H4 H1 H2 H3
• Tolerance factor t dAO/1.414dBO

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Gas Adsorption Calorimetry

• Combine sensitive microcalorimeter with automated
  gas dosing system
• Measure heat of adsorption and adsorption
  isotherm simultaneously
• Apply to high surface area and microporous
  materials

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Differential (a) and integral (b) heats of H2O
adsorption for anatase with surface area of 90,
200 and 240 m2/g and rutile of 61 and 103 m2/g
(Levchenko et al. 2006).
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The Peter A. Rock Thermochemistry Laboratory

• A unique suite of equipment and expertise
• Can design a calorimetric experiment to suit
  almost any material and problem