FUNDAMENTALS AND APPLICATIONS OF THERMAL ANALYSIS.

transcript

FUNDAMENTALS AND APPLICATIONS

OF THERMAL ANALYSIS

Objectives:

To explain principle of different types of thermal

techniques.

To describe instrumentation of different types of

thermal techniques

To distinguish between DSC,DTA & TGA

To explain application of thermal method

Introduction:

Thermal analysis is a branch of material science where the properties of

materials are studied as they change with temperature.

When matter is heated it undergoes certain physical and chemical changes.

These physical and chemical take place over a wide temperature range.

Physical changes such as melting or boiling may occur at widely varying

temperature, depending on material involve.

Chemical changes such as decomposition or reaction may also take place at very

different temperatures.

Ref-Instrumental methods of chemical analysis by Gurdeep Chatwal and shyam anand, himalaya publication thermal method,p no-2-701

Definition of Thermal Analysis

A branch of materials science where the properties of materials are studied as they change with temperature.

Ref-Skoog, Douglas A., F. James Holler and Timothy Nieman (1998). Principles of Instrumental Analysis (5 ed.). New York. pp. 805.

Technique Name

Abbreviation

Instrument Apply

Parameter Measure

1 Thermogravimetry

TG Thermobalance

Mass mass vs temp

2 Derivative Thermogravimetry

DTG Thermobalance

dm/dt dm/dt vs temp

3 Diff.Thermal Analysis

DTA DTA Appts ∆T ∆T vs temp

4 Diff.Scanning Calorimetry

DSC Calorimeter dH.dt dH/dt vs temp

5 Thermometric Titrimetry

…….. Calorimeter Temp. Temp vs titrant volume

6 Dynamic Reflectance Spectroscopy

DRS Spectrophotometer

Reflectance

%refle.and temp.

7 Evolved gas detection

EGD Thermal conductivity cell

T.C. T.C. vs temp

8 Dialotometry TMA Dialatometer

Vol.of Length

Vol or length vs temp

9 Electrical conductivity

EC Electrometer or Bridget

Current or resistance

I or R vs temp

10 Emanation Thermal Analysis

ETA ETA appts. Radioactivity

E vs temp

Ref-Instrumental methods of chemical analysis by Gurdeep Chatwal and shyam anand, himalaya publication thermal method,p no 2.701-2.702

Thermal Analysis Instrument Manufacturers Perkin Elmer Thermal Analysis Systems

http://www.perkin-elmer.com/thermal/index.html TA Instruments

http://www.tainst.com/ Mettler Toledo Thermal Analysis Systems

http://www.mt.com/ Rheometric Scientific

http://www.rheosci.com/ Haake

http://polysort.com/haake/ NETZSCH Instruments

http://www.netzsch.com/ta/ SETARAM Instruments

http://setaram.com/ Instrument Specialists, Inc.

http://www.instrument-specialists.com/

Ref-by google search thermal method instrument

Thermogravimetry:

It is a technique whereby the weight of the

substance, in an environment heated or cooled at a

controlled rate, is recorded as a function of time or

temperature.

Ref-Skoog, Douglas A., F. James Holler and Timothy Nieman (1998). Principles of Instrumental Analysis (5 ed.). New York. pp. 805-806

Types of thermogravimetry:

1. Static thermogravimetry

2. Quasistatic thermogravimetry

3.Dynamic thermogravimetry

Instrumentation: TGA

TEMPERATURE PROGRAMMER

BALANCE

CONTROLLER

POWER FURNACE TEMP.

SAMPLE TEMP.

WEIGHT INLET

10 Ref-Google image search

1.Balance: 1.Balance:

Requirements:

1. Accurate, sensitive, reproducible

2. Adequate range of automatic weight adjustment.

3. High degree of mechanical & electronic stability.

4. Rapid response to weight changes.

5. Should be unaffected by vibrations, simple to operate

& versatile.

Ref-Instrumental methods of chemical analysis by Gurdeep Chatwal and shyam anand, himalaya publication thermal method,p no 2.705

Types of balances:

1.Deflection balance

2.Null point balance

Types of deflection balance:

1.Beam type

2.Helical or spring type

3.Cantilever type

4.Torsion type

Types of Deflection Balance:

Fig: Deflection balance

Null-Point Balance:

Fig: Null-Point Balance

2. Sample Holders:

Types:

1.Shallow Pans

2.Deep Crucibles

3.Loosely Covered Crucibles

4.Retort Cups

Ref-Instrumental methods of chemical analysis by Gurdeep Chatwal and shyam anand, himalaya publication thermal method,p no 2.703-706

3.The Furnace:

For 1100ºC – Nichrome is used

1100 to 1500ºC. – Platinum or an alloy of

platinum and rhodium

Above 1750ºC – tungsten or molybdenum

Nitrogen or argon are usually used to purge the

furnace & prevent oxidation of sample.

4. Temperature measurement:

Fig: Position of a Thermocouple in a Thermobalance

5. Recorder:

Time base potentiometric strip chart recorder

X Y recorder

6.Thermobalance:

1)Continuously the weight changes of the sample as a function of temperature & time.

2) The temperature recorded to an accuracy of better than

3) Temperature should, ideally, be the sample Temperature.

4) No chemical attack of volatile products on the apparatus.

5) The balance is protected from furnace.

6) The weight loss should be recorded to an accuracy of ±1%.

TGA Applications: Inorganics

Hydrates decomposition, drying phenomena Carbonates and other salts decomposition Kinetics and mechanisms of oxidation, and other solid-gas

reactions Analysis of magnetic materials Automatic TG analysis Evaluation of TG pptet. Test purity Curie point determination

Ref-M C Ramos-Sanchez, F J Rey, M L Rodríguez, F J Martin-Gil, J Martin-Gil, "DTG and DTA studies on typical sugars", , 134: 55-60

TGA Applications: Organics

Identification of polymers and pharmaceutical agents Thermal stability of synthetic and natural polymers and other

organics Analysis of polymer-matrix composites Kinetics and mechanism of solid organics – gas reactions Residual solvent determinations Building material Glass technology

DTA measures temperature difference between a sample and an inert reference (usually Al2O3) while heat flow to the reference and the sample remains the same

Differential Thermal Analysis (DTA)

Ref-Mansfield, E.; Kar, A.; Quinn, T. P.; Hooker, S. A. (2010). ". Analytical Chemistry 82

Principle:

The principle of method consists of measuring the change in

temperature associated with physical or chemical changes during the

gradual heating of the substance.

Differential Thermal Analysis

Advantages:

• Instruments can be used at very high temperatures

• Instruments are highly sensitive

• Characteristic transition or reaction temperatures can be accurately determined

Disadvantages:

• Uncertainty of heats of fusion, transition, or reaction estimations is 20-50%.

Applications –

Physical chemistry Analytical chemistry Quality control Inorganic chemistry Organic chemistry

Differential Scanning Calorimetry (DSC)

Differential Scanning Calorimetry technique is a thermal

technique in which the difference in the amount of heat required to

increase the temperature of a sample & reference is measured as a

function of temperature.

Differential Scanning Calorimetry (DSC)29

DSC measures differences in the amount of heat required to increase the temperature of a sample and a reference as a function of temperature

Differential Scanning Calorimeter

Differential Scanning CalorimeterPerkin Elmer DSC 731

Platinum sensors

Sample heater Reference heater

Temperature range 110 – 1000 K Heating rate 0.1 – 500 K/min

(normally 0.5 – 50 K/min) Noise ± 4 W Sample volume up to 75 mm3

Applications-

Physical chemistry Analytical chemistry Quality control Inorganic chemistry Organic chemistry

DSC in Polymer Analysis

Main transitions which can be studied by DSC:

Melting Freezing Glass transition

Difference Between:

TGA DTA DSC

Measures thermo-chemical effect.

Measures thermo-physical, thermo-chemical effect.

Measures thermo-physical, chemical effect with more sensitivity.

Provide range: Thermal Chemical stability of materials.

Provide range: Thermal, Physical and Chemical stability of materials.

Provide range: Thermal, Physical and Chemical stability and also transition time. E.g. Curie Temperature

Contains: Thermobalance.

Contains: Thermocouple for measuring ∆T.

Contains: Secondary heater for measure ∆H.

Thermo mechanical analysis:

Thermo mechanical analysis (TMA) is the technique in

which a physical dimensions of a material is monitored

as a function of temperature. With the other methods a

thermocouple is used to monitor the temperature of the

sample in an oven through which a purge gas flow.

Ref- introduction to thermal method by brown m.e. p.no-149

Thermo mechanical Analysis: Instrumentation

Consist of Transducer(Linear Variable Displacement Transducer) Probe (made up of quartz glass) Thermocouple Furnace

Ref-www.google.com

Principle-

Measurement of effect of heat on mechanical property of sample eg. Expansion,Compression,Penetration and Extension.

Applications-

Polymer study Quality control

Dielectric thermal analysis:

Dielectric thermal analysis (DETA) or Dielectric

Analysis (DEA), is a material science technique similar

to dynamic mechanical analysis except that an oscillating

electrical field is used instead of a mechanical force.

Ref- vogel textbook of chemical analysis p.no.-474-576

Dielectric thermal analysis: Principle

In a typical test, the sample is placed in contact with two electrodes(the

dielectric sensor) and a sinusoidal voltage (the excitation) is applied to one

electrode. The resulting sinusoidal current (the response) is measured at the

second electrode. The response signal is attenuated in amplitude and shifted

in phase in relation to the mobility of the ions and the alignment of the

dipoles.

Ref- vogel textbook of chemical analysis p.no.-474-576

Evolved gas analysis:

Evolved gas analysis (EGA) is a method used to study

the gas evolved from a heated sample that undergoes

decomposition or desorption.

It is possible to detect which gas is evolved using

(EGD) Evolved gas detection..

Thermometric titrations:

Definition:

A Titration in which the temperature of the titrant is

monitored as a function of added titrant volume is a

thermometric titration.

Principle:

Thermometric Titrations is based on the change in temperature

with theaddition of titrant & determine the end point from a

plot of temperature vs. volume of titrant. In thermometric

titration change in temperature occurs only when titration is in

progress & sample reactant is present.

Theory-

A titration reaction follow chemical equation

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In this method there should be change in free energy at end point.

A(sample)+B(titrant)C(product)+heat

∆H=∆G+T∆S

Instrumentation:

It consist of Delivery pump fig: thermometric titration assembly

Adiabatic cell (Dewar cell) Calibration unit Temperature sensing system Amplification & Recording

Enthalpimetry:Enthalpimetry:

Quantitative analysis of a sample can be sometimes be performed by measurement of the change in enthalpy that is associated with the addition of excess of a chemical reactant to the sample.

When a chemical reaction takes place heat is liberated or absorbed. This is known as heat of reaction or enthalpy.

Methods:

1.Direct injection enthalpimetric titration (DIE): In this technique in which a single portion of an excess of one

chemical reactant is added to a fixed volume of a sample that contains other reactant.

2. Continuous flow enthalpimetry: Similar to DIE except that an excess of one reactant is

continuously to flowing stream of sample added.

FUNDAMENTALS AND APPLICATIONS OF THERMAL ANALYSIS.

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