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CHM 342 Thermal Methods of Analysis Background and Continued Evolution into Hyphenated Methods of Chemical Analysis

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CHM 342

Thermal Methods of Analysis

Background and Continued Evolution into Hyphenated Methods of Chemical Analysis

CHM 342

Thermal Methods of Analysis

Properties are measured as a function of temperature, time, or both Heat flow – direction and magnitude Mass change – loss / gain Mechanical properties

Sheer Strain Dynamic loading

Gas evolution

CHM 342

Traditional Thermal Analysis Calorimetric Methods of Analysis

Coffee cup calorimetry (constant P) Bomb calorimetry (constant V)

Gravimetric Methods of Analysis Heating until constant weight loss Traditional C / H analysis

Differential Thermal Analysis (DTA) Analysis of heat flow direction (endo vs. exo)

as a function of temperature as a function of time at a given temperature

CHM 342

Coffee Cup Calorimetry

CHM 342

Bomb Calorimetry

Adiabatic vs. IsoperibolNo heat flow vs. corrected for heat flow . . .

CHM 342

Heat to constant mass Loss of waters of hydrationCuSO45H2O(s) CuSO4(s) + 5 H2O(g)

Decomposition of Oxalates

CaC2O4(s) + ½ O2(g) CaCO3(s) + CO2(g)

Carbonates

CaCO3(s) CaO(s) + CO2(g)

CHM 342

Combustion Analysis a known mass of a compound (with an unknown formula but

known elemental makeup) is burned in an excess of O2 CuO oxidizes traces of Cand CO into CO2. It also ensures that all of the H2 is oxidized completely to H2O H2O is collected in an absorber filled Mg(ClO4)2 CO2 is collected in a separate absorber filled with NaOH The change in mass of the absorbers is used to determine the

amount of CO2 and H2O produced and thus the initial amount of C and H in the compound

CHM 342

Differential thermal analysis (DTA) DTA involves heating or

cooling a test sample and an inert reference under identical conditions, while recording any temperature difference between the sample and reference.

This differential temperature is then plotted against time, or against temperature.

Changes in the sample which lead to the absorption or evolution of heat can be detected relative to the inert reference.

CHM 342

Evolution of Thermal Analysis ThermoGravimetric Analysis (TGA)

Analysis of mass change as a function of temperature as a function of time at a given temperature

Differential Scanning Calorimetry (DSC) Quantification of heat flow

as a function of temperature as a function of time at a given temperature

Dynamic Mechanical Analysis (DMA) ThermoMechanical Analysis (TMA) and more . . .

CHM 342

TGA – Principle of Operation

Thermogravimetry (TG) determines the mass change of a sample as a function of temperature or time.

A good tool for: quality control and assurance failure analysis of complex polymer mixtures and

blends study of a variety of chemical processes accompanied

by mass changes

CHM 342

TGA – Equipment The heart of the instrument

is the balance . . . . Rigorous demands for

microbalance in variable

temperature environ.

Data – massloss as a functionof temperatureor timeSometimes derivativeplot used to find pts. of inflection

CHM 342

Differential Scanning Calorimetry  Differential Scanning Calorimetry (DSC) is one of the

most frequently used techniques in the field of thermal characterization of solids and liquids

melting/crystallization behavior solid-solid reactions polymorphism degree of crystallinity glass transitions cross-linking reactions oxidative stability decomposition behavior purity determination specific heat

CHM 342

Differential Scanning Calorimetry  – Principle of Operation a sample is placed inside a crucible which is then

placed inside the measurement cell (furnace) of the DSC system along with a reference pan which is normally empty (inert gas may be used).

By applying a controlled temperature program (isothermal, heating or cooling at constant rates), phase changes can be characterized and/or the specific heat of a material can be determined.

Heat flow quantities are calculated based on calibrated heat flow characteristics of the cell.

CHM 342

Differential Scanning Calorimetry  – Equipment Two pans Heat transfer disk (almost always made of

Constantan – an alloy of 60% Cu and 40% Ni) Data on endo or exo transitions at constant

temperature or during a temperature ramp

•Kinetic and thermodynamic information •Vary ramp rate to extract infoon activation energy barriers

CHM 342

DSC Data

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DSC with TGA

Combine the thermo/kinetic data of DSC with the stoichiometric data from TGA

Increases complexity, cost, and information obtained

Precursor Bi(tmhd)3Molecular formula (C11H19O2)3BiVapor pressure 0.1 Torr at 160°CPhase & Color Colorless crystallineMelting point 112-116°C

CHM 342

Evolved Gas Analysis (EGA) using TGA and MS Attach a reasonably priced

(Quadrupole?) MS to a TGA While monitoring mass loss

with the TGA also examine

the gases present in the inert

background gas stream Allows the chemistry proposed based on mass

loss data to be confirmed via gas analyses

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A fluorinated ethylene-propylene copolymer (7.9 mg) was heated at 10 K/min in He atmosphere. Decomposition occurs in two steps. Tetrafluor-ethylene (100 amu) and hexafluor-propylene (150 amu) were detected.

TGA-QMS measurement on FEP

Evolved Gas Analysis (EGA) using TGA and Mass Spectrometry

CHM 342

Evolved Gas Analysis with FT-IR

Attach a reasonably priced FT-IR to a TGA While monitoring mass loss with the TGA also examine the gases present in the inert background gas stream w/FT-IR Allows the chemistry proposed based on mass loss

data to be confirmed via gas analyses

CHM 342

Evolved Gas Analysis with FT-IR

CHM 342

Pulse Thermal Analysis

Developed within the last decade to allow analysis of reaction products in various gases

Pulse gases in . . . Monitor products at

various temperatures

Depending on the type of gas injected, the method offers three primary options for the investigation of gas-solid reactions:

CHM 342

Pulse Thermal Analysis

Injection of gas which reacts chemically w/solids: Investigation of changes in the

solid phase & gas composition resulting from the injected gas pulse.

Chemical reactions such as reduction, oxidation, or catalytic processes between solid catalyst and gaseous reactant(s) can be investigated at desired temperatures.

See Figure for redox sequence in the zirconia-supported PdO catalyst: reduction of PdO by methane and subsequent reoxidation of Pd by oxygen at 500°C

CHM 342

Pulse Thermal Analysis

Injection of gas which adsorbs on the solid: Investigation of adsorption

phenomena occurring under atmospheric pressure at required temperatures.

Figure depicts the adsorption of ammonia at 200°C on ZSM-5 zeolite.

Exothermal effect (section A) is related to weight gain resulting from NH3 chemisorption (allows determination of the heat of reaction per mole of adsorbed NH3).

Section B presents the reversible physisorption process.

CHM 342

Pulse Thermal Analysis

Injection of inert gas for calibration of the MS - direct calibration for MS quantitation introduce a known amount of the analyzed gas

into the carrier gas determine the relationship between the amount

of the gas and the intensity of the MS signal.

Ex. During the calcination of CaCO3, two pulses of the reaction product CO2 were injected before and after the MS signal (m/z = 44) resulting from the decomposition.

The stoichiometric weight loss for the 4.62 mg of CaCO3 is 2.03 mg, the amount of evolved CO2 measured by the TG curve was 2.02 mg.

The CO2 calculated from thecalibrated MS data corresponds to 2.01 mg.