Fundamental Concepts of
Thermodynamics
•
•
•
•
First, second, and third law
Entropy
Heat capacity, enthalpy
Reaction enthalpies and thermochemical
cycles
• Phase transitions
• Calorimetry
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.
Calorimetry Measures
• Heat capacities
• Heats of phase transitions’
• Heats of formation
From these data one calculates
• Entropies and free energies
• Solubililities
• Phase diagrams
• Petrologic and geochemical
processes
• Materials synthesis and
compatibility
Phase Transitions
Low temperature heat capacity
and standard entropy,
Fe2SiO4 olivine and spinel,
calorimetry on a chip
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
Example: HfO2
Unit cell volume, Å
3
Mon (P21/c)
144
Cub (Fm3m)
Tetr (P42/nmc)
ZrO2
HfO2
140
J. Wang et al. J. Mat. Sci. 92, 27(20) 5397
400
800
1200
1600
2000
Temperature, °C
Experiment: HfO2_calibr_probe_3rd_heating
Displacement/µm
SETSYS Evolution - 2400
Probe:
Graphite
Carrier gas:
Length (mm): 2.502 mm
Procedure: 1500>2300 (Zone 1)
0.0
TMA on HfO2
Heating
-5.0
-10.0
Delta : -0.71 %
Delta : 1.01 %
-15.0
-20.0
Cooling
-25.0
1800
1850
1900
Furnace temperature /°C
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. \
SETSYS Evolution - 2400
Experiment: 3rd_HfO2_W_10_1950
Crucible:W 85 µl
Carrier gas:
Procedure: 20>2000 (Zone 3)
Molar mass: 210.49
Mass (mg): 205.71
DTA signal, µV
-bl_cooling - 4 - 3r d_HfO2_W_10_1950/µV
-bl 2/µV
Exo
2
2.5
Exo
1
1.5
Peak :1762.13 °C
Onset Point :1771.45 °C
Enthalpy /µV.s : -126.0198 (Exothermic effect)
Cooling
0
-1
0.5
Heating
-0.5
Peak :1813.08 °C
Onset Point :1802.64 °C
Enthalpy /µV.s : 127.6076 (Endothermic effect)
1700
1750
1800
Sample temperature/°C
DTA traces of HfO2 (99.95% Aldrich) in Ar flow.
Heating rate 10 °/min, cooling rate 20 °/min.
Baseline correction applied.
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
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
High-Temperature Calorimetry
TTD
SOL
DS
25oC
25oC
25oC
HSOL
HTTD
700oC
HTTD  
700 C
25C
HDS
700oC
CP dT
700oC
HDS  HTTD  HSOL
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
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
Volumetric dosing system
Calvet-type twin
microcalorimeter
Micromeritics ASAP2020
Setaram DSC 111
sample
thermopiles
reference
H2O
to voltmeter
and amplifier
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).
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