1 Guard your heart above all else, for it determines the course of your life.

Alexandra Khvan, Andy Watson Some like it hot ! Or Calorimetry

What is calorimetry? How old is calorimetry? Very old but gold! First calorimeters appeared before Thomas Johann Seebeck invented the thermocouple What do we want to find out? What do we measure? How can we measure? (different types of calorimeters) Is it easy? Yes and NO at the same time How long do calorimeters live? They live and produce good results much longer than the people who created them 3

What do we count calories for? 4 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 Answer taken from presentation of Prof Alex Navrtosky US Davis 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, metallurgy and deep Earth geophysics need thermodynamic data.

What do we want to find out? Enthalpies of formation (reaction)Δ f H, Δ r H Heat capacities Cp Enthalpies of mixing (solution phases)ΔHmix Enthalpies of transformation ΔHtr 5

But what do we actually measure? 6 Calorimeter is an instrument for the measurement of released or absorbed heat during some physical, chemical or biological process Pierre-Simon Laplace Antoine Laurent de Lavoisier 1780

Calorimetry Measure the amount of heat change Cannot measure enthalpy directly. »Isoperibol calorimetry Measure the temperature change (Tc), Ts = constant »Isothermal calorimetry Ice calorimeter (Bunsen) Ts = Tc = constant »Adiabatic calorimetry Variation in heat input (to the calorimeter) Ts = Tc ≠ constant »Heat flowTian-Calvet, Ts - Tc = constant 7

Isothermal calorimeter 8 Ts=Tc=constant No temperature rise, temperature not measured Heat evolved melts solid Measure amount of liquid produced Calculated heat evolved from Heat of fusion In Lavoisier and the young mathematician Pierre Simon de Laplace developed the device to measure the content of the "element" caloric in a sample of combustible oil.

Isoperibol calorimeter 9 Surroundings are held at constant temperature Ts=const Tc is changing as a function of time There is a heat exchange between surroundings and calorimetric vessel during the experiment Witting &Huber (1956)

10 O Kubaschewski, 1955 (NPL, Teddington UK) Samples are heated up to the T r. Start of the reaction is indicated by a change in electrical resistance. Reaction increases the temperature.=> raise of alumina block temperature For calibration electrical energy was out into the furnace. H=H start react +H r

Adiabatic calorimeter Ts=Tc≠const No heat losses to the surrounding Measure the heat input to raise sample over a prescribed temperature range 11

Determination of enthalpies of formation Sample heated from “safe” temperature to “final” temperature Safe= Tmax, where no alloying take place Final=Tmin where complete alloying take place within 30 min 12 Adiabatic calorimeter (Direct reaction calorimetry)

13 University of Provence in Marseille Prof. Albert Tian Invented the heat flux microcalorimeter: isoperibol with a thrmopile of 42 junctions Prof Edouard Calvet Introduced the differential setup (1948) and a rational construction of the two twinned calorimetric elements, transforming Tian's appliance into a true laboratory instrument Heat-flow calorimeters

Reaction vessel connected to surroundings by a series of thermocouple junctions Thermopile Heat flow between reaction vessel and surroundings realised as an emf Seebeck effect Tian-Calvet calorimeters ε=dE/dT ε=thermoelectric power E=emf For n thermocouples E=nε(T A -T C ) Proportion of the flux conducted by a single thermocouple wire Total emf in relation to the heat flux

Twin microcalorimeter 15 Prof. Kleppa calorimeter Micro refers to small heat effects, not small instruments! 3D thermopile detector surrounding sample, with thermocouples providing main path of heat transfer from calorimeter chamber to block Usually twinned construction, but not necessary (though improves baseline stability) and not an issue of sample and reference chambers, both used for experiments Measure heat flow from sample chamber to constant T heat sink, integrate to get heat effect, use an experimental calibration

16 Metal 1 Metal 2 Inner temperature Outer temperature

17 Assembling thermopiles

Thermopiles Manual: A/Alexsys1000UCDAVIS-1A.pdf, p. 12 Brochure: ALEXSYS-Calorimeter.pdf, p.2

High temperature Heat-Flow calorimeters 19 Setaram HT 1500 Kleppa calorimeter Taken from presentation of Prof. P.Nash, Illinois Institute of Technology Cacciamani - Genova

Drop calorimetry Sample is dropped into the calorimeter From T 1 (Typically room temperature) To T 2 (The calorimeter temperature) Electrical output from thermopile H(T 2 )-H(T 1 ) H(T 2 )-H(T 1 )+Δ r H 20

Enthalpy of formation by direct Reaction Drop Calorimetry First drop (reaction drop) 21 Second drop (reference drop)

Solution and drop solution calorimetry Near room temperature –Water, aqueous acid of base –Hydrofluoric acid –Organic solvents At high temperature –Molten metals, e.g. Sn –Molten salts, e.g. nitrate or chloride eutectics –Molten oxides 22

Enthalpy of Formation by metal dissolution Drop Calorimetry 23 Samples are dissolved in an appropriate solvent Moles solvent >>moles solute Samples of the component elements Samples of the compound interest Convert material chemically to a state with known enthalpy or to common state for reactants and products, usually a solution

Enthalpy of Formation by oxide melt drop solution calorimetry A => solution ΔH 1 B => same solution Δ H 2 A => B Δ H 3 = Δ H 1 - Δ H 2 The task is to find a reaction scheme and solvent that lets you do this accurately A can be elements, B compound A can be binary oxides, B ternary compound A can be end-members, B solid solution or alloy A,B can be different polymorphs 24

Enthalpy of mixing by Metal Dissolution Drop Calorimetry 25 Small solute samples are added incrementally to liquid solvent

Looks simple but why is it so hard? Factors effecting the baseline Electrical and electronic stability Constancy of surroundings Mechanical stability of setups Chemical issues –Corrosion –Vaporization –Side reactions 26 Good calorimetry needs good samples Single phase or pure elements Homogeneous Chemically analyzed Oxidation state known for initial samples and after dissolution No parasitic side reactions

28 Calorimetry In the laboratory………and beyond!

Speaker is very grateful to following people for providing materials for this presentation Prof. Alexandra Navrotsky Dr. Kristina Lilova Prof. Philip Nash Gary Etherington and Pierre Leparlouer 29

TASK Provided: Room temperature during calibration and experiment Temperature of the Calorimeter during calibration and experiment Ma for Pt, Al,O Heat capacity equation for Al 2 O 3 Task: Enthalpy increment of Pt