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. Isoperibol No heat flow vs. corrected for heat flow...

CHM 342 Heat to constant mass Loss of waters of hydration CuSO 4  5H 2 O (s)  CuSO 4(s) + 5 H 2 O (g) Decomposition of  Oxalates CaC 2 O 4(s) + ½ O 2(g)  CaCO 3(s) + CO 2(g)  Carbonates CaCO 3(s)  CaO (s) + CO 2(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 O 2 CuO oxidizes traces of C and CO into CO 2. It also ensures that all of the H 2 is oxidized completely to H 2 O H 2 O is collected in an absorber filled Mg(ClO 4 ) 2 CO 2 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 – mass loss as a function of temperature or time Sometimes derivative plot 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 info on activation energy barriers

CHM 342 DSC Data

CHM 342 DSC with TGA Combine the thermo/kinetic data of DSC with the stoichiometric data from TGA Increases complexity, cost, and information obtained PrecursorBi(tmhd)3 Molecular formula(C 11 H 19 O 2 ) 3 Bi Vapor pressure0.1 Torr at 160°C Phase & ColorColorless crystalline Melting point °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

CHM 342 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 NH 3 chemisorption (allows determination of the heat of reaction per mole of adsorbed NH 3 ).  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 CaCO 3, two pulses of the reaction product CO 2 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 CaCO 3 is 2.03 mg, the amount of evolved CO 2 measured by the TG curve was 2.02 mg. The CO 2 calculated from thecalibrated MS data corresponds to 2.01 mg.