DIFFERENTIAL THERMAL ANALYSIS (DTA)

DIFFERENTIAL THERMAL ANALYSIS (DTA)

1. DIFFERENTIAL THERMAL ANALYSIS [DTA]

2. Definition of Thermal Analysis (TA): Thermal Analysis (TA)is a group of techniques that study the properties of materials as they change with temperature. TYPES : • TG ( Thermogravimetric ) analysis: weight • DTA (Differential Thermal Analysis): temperature • DSC (Differential Scanning Calourimetry ):temperature WHAT IS THERMAL ANALYSIS ?

3. Differential Thermal Analysis (DTA) :- A technique in which the difference in tempreture between the sample and referance material is monitored against time or tempreture while the tempreture of the sample, in a specified atmosphere, is programmed. WHAT IS DIFFERENTIALTHERMAL ANALYSIS ?

4. INTRODUCTION : • This is a comparison method When a material is heated its structural and chemical composition can undergo changes such as fusion, melting, crystallization, oxidation, transition, decomposition, expansion and sintering. Using Thermal Analysis such changes can be monitored in every atmosphere of interest. The obtained information is very useful in both quality control and problem solving. In DTA ,the material under study and an inert reference are made to undergo identical thermal cycles ,while recording any temperature difference between sample and reference. This differential temperature is then plotted again time or, or against temperature.

5. The curve plotted is called as DTA curve or thermo gram. Changes in the sample either endothermic or exothermic,can be detected relative to the inert reference.

6. PRINCIPAL : A technique in which the temperature difference between a substance and reference material is measured as function of temperature, while the substance and reference are subjected to controlled temperature programmed. The difference in the temp is called as differential temperature and is plotted against temp or function of time. Physical changes usually result in endothermic peaks, whereas chemical reaction those of an oxidative nature show exothermic peak. • Endothermic reaction(absorption of heat) includes sublimation and gives downward peak. • Exothermic reaction(liberation of heat) includes oxidation, polymerization and gives upward.

7. INSTRUMENTATON : A DTA consists of a – 1. Sample holder 2. Thermocouples 3. A furnace; 4. A temperature programmer 5. A recording system. The key feature is the existence of two thermocouples connected to a voltmeter. One thermo couple is placed in an inert material such as aluminum oxide, while the other is placed in a sample of the material under study.

8. 2.Sensors/thermocouples: Platinum or chromyl thermocouples one for sample and one for reference material is joined to differentialtemperaturecontroller . 3. Furnace: alumina block containing sample and reference cells. 4.Temperature controller: controls temperature program and furnace atmosphere. 5.Recordingsystem: It is a system where the change in the temperature i.e. differential temperature is recorded and the enthalpy is recorded 1.Sampleholder: The sample holder and reference cells are made up of aluminum.

9. WORKING : We need to take two aluminum containers for keeping the sample as well as reference in them. Thermocouples are connected to each of the material for measuring their temperature, and heat is applied to them under cautiously regulated conditions. Now, if it is seen that the sample material has gone through certain chemical reaction or physical transformation, its temperature will change significantly due to the change in its ‘enthalpy' or heat content. However, the temperature of the reference material will remain unchanged.

10. FACTORS AFFECTING RESULT IN DTA : There are so many factors that affects the DTA curve.They are divided into two types as follows ;

11. INSTRUMENTAL FACTORS :

12. Sample characteristics factors :

13. Factors Effect Suggestion 1.Heating factor Change in the peak size and position Use allow heating rate 2.Location of thermocouple Irreproducible curve Standardize thermocouple location 3.Atmosphere around the sample Change in the curve Inert gas should be allowed to flow 4.Amount of sample Change in the peak size and position Standardize sample mass 5.Particle size of sample Irreproducible curve Use small uniform particle 6.Packing density Irreproducible curve Standardize packing techniques 7.Sample container Change in peak Standardize container Lets see how these factors affect the curve :

14. 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%.

15. Applications of differential thermal analysis : Qualitative and Quantitative identification of Minerals : Detection of any minerals in sample. Polymeric materials : DTA is useful for characterization of polymeric materials in the light of identification of thermophysical , thermo-chemical ,thermo-mechanical, and thermo-elastic changes or transition. Measurement of crystalline : Measurement of the mass fraction of crystalline material in semi-crystalline polymer. Impurities may be detected by depression of the M.P. DTA is widely used in the pharmaceutical] and food industries. DTA may be used in cement chemistrymineralogical researchand in environmental studies.