Thermal Analysis Techniques Presented By MOHSIN KHAN Thermal

Thermal Analysis Techniques Presented By MOHSIN KHAN

Thermal Analysis Techniques • When a material is heated its structural and chemical composition can undergo changes such as fusion, melting, crystallization, oxidation, decomposition, transition, expansion etc. • Using Thermal Analysis such changes can be monitored in every atmosphere of interest. The obtained in formation is very useful in both quality control and problem solving.

Types of thermal analysis • TG (Thermo gravimetric analysis): Weight • DTA (Differential Thermal Analysis): Temperature • DSC (Differential Scanning Calorimetry): temperature

DTA (Differential Thermal Analysis) n n In Differential Thermal Analysis, the temperature difference that develops between a sample and an in reference material is measured, when both are subjected to identical heat treatments. • The related technique of Differential Scanning Calorimetry relies on differences in energy required to maintain the sample and reference at an identical temperature

INTRODUCTION n n n This is a comparison method Analytical method for recording the difference in temperature (∆T) b/w a substance and an in reference material as a function of temperature or time Any transformation–change in specific heat or an enthalpy of transition can be detected by DTA

n n n In DTA both test sample & an in reference material (alumina)–controlled heating or cooling programming If zero temperature difference b/w sample & reference material–sample does not undergo any chemical or physical change. If any reaction takes place temperature difference (∆T) will occur b/w sample & reference material

n n A DTA curve can be used as a fingerprint for identification purposes, for example, in the study of clays where the structural similarity of different forms renders diffraction experiments difficult to interpret

Apparatus The key features of a differential thermal analysis are as follows 1. Sample holder comprising thermocouples, sample containers and a ceramic or metallic block. 2. Furnace. 3. Temperature programmer 4. Recording system n

DTA Instrumentation

n n ∆T VS Temp. Sharp Endothermic–changes in crystallinity or fusion Broad endotherms-dehydration reaction Physical changes usually result in endothermic curves Chemical reactions are exothermic

Key points in thermogram n n Sharp endotherm: crystalline rearrangemets, fusion, solid state transition Broader endotherm: dehydration, melting of polymers, slow reactions Narrow exotherm: crystallization Sharp exotherm: phase change

n n Q. Discuss the principle and working of DTA. What useful result can you get by this technique. Q. Draw and discuss DTA grams of the maganese phosphinate monohydrate[Mn(PH 2 O 2)2. H 2 O (S)

DTA curve for Mn(PH 2 O 2)2. H 2 O (S)

Advantages Instruments can be used at very high temperatures • instruments are highly sensitive • characteristic transition or reaction temperatures can be accurately determined. n

Factors affect results in DTA n n n Sample weight Particle size Heating rate Atmospheric conditions Conditions of sample packing into dishes.

Applications n n Quantitative identification and purity assessment of materials are accomplished by comparing the DTA curve of sample to that to reference curve Impurities may be detected by depression of the M. P.

Differential Scanning Calorimeter

Exothermal d. Q/d. T Differential Scanning Calorimetry (DSC) Temperature n DSC measures differences in the amount of heat required to increase the temperature of a sample and a reference as a function of temperature

Typical DSC Curve of a Thermoplastic. DSCPolymer Sample: PET 80 PC 20_MM 1 1 min Size: 23. 4300 mg Method: standard dsc heat -cool-heat Comment: 5/4/06 File: C: . . . DSCMelt Mixed 1PET 80 PC 20_MM 1. 001 Operator: SAC Run Date: 05 -Apr-2006 15: 34 Instrument: DSC Q 1000 V 9. 4 Build 287 Tm 1. 5 245. 24°C Heat Flow(W/g) 1. 0 Tc Tg 137. 58°C 20. 30 J/g 79. 70°C(I) 0. 5 75. 41°C 228. 80°C 22. 48 J/g 81. 80°C Cycle 1 144. 72°C 0. 0 -0. 5 Exo Down 0 50 100 150 Temperature (°C) 200 250 300 Universal V 4. 2 E TA Instruments

DSC: Applications n n Polymer characterization (PET) Gas adsorption/desorption

Thermo gravimetry (TG) n n n Thermo gravimetry is the measurement of the mass of a sample as a function of temperature or time. This method is useful for determining the weight loss due to dehydration and decomposition reactions. This changes in weight are a result of rupture or formation of various physical and chemical bonds.

n n The graph plotted b/w weight loss vs temperature is called “Thermogram”. Thermogram gives the information about-thermodynamics and kinetics of various chemical reactions, -the reaction mechanism, -the reaction intermediate, -and the final products.

Fig-thermogram of calcium oxalate monohydrate(Ca. C 2 O 4. H 2 o)

TG Curve of Mn(PH 2 O 2)2. H 2 O

TGA: Instrumentation n n Sample and reference pans – Pt, Al, alumina, quartz, ceramic Microbalance (a thermobalance) Furnace high temperatures

n n n n Thermocouple – Acts as a thermometer Purge‐gas system – Used for atmosphere control – Inert (N 2, Ar) or reactive gas (O 2, H 2, etc. ) Computer system – Temperature program, data collection, etc.

TGA: Thermo balance (simplified)

TGA: Applications • Thermogravimetric techniques have a very wide field of application. • Thermogravimetric analysis has also been involved in determining the age of art treasures, particularly paintings and in determining the stability of explosives.

n n The technique is commonly used to control the dehydration procedures for crops. This is also used extensively in the pharmaceutical industry in the examination of drug stability and the rate of degradation of certain drugs when expose to air.

n n The most important application of TGA methods are in the study of polymers. It provides different decomposition pattern for different polymers. And from this pattern we can identify the polymers.

n n Q. Discuss the principle and working of TGA. What useful result can you get by this technique. Q. Draw and discuss TGA grams of the maganese phosphinate monohydrate[Mn(PH 2 O 2)2. H 2 O (S)