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THERMAL ANALYSIS 1  THERMAL ANALYSIS Thermal analysis includes a group of techniques which Winners & Tech hub classes monitors the change in physical properties such as weight,...

THERMAL ANALYSIS 1  THERMAL ANALYSIS Thermal analysis includes a group of techniques which Winners & Tech hub classes monitors the change in physical properties such as weight, temperature or enthalpy of a sample material as a function of temperature. The sample is subjected to a programmed heating from an initial lower temperature to a final higher temperature at a specified heating rate during the analysis. The most commonly used techniques include thermogravimetry (TG), differential thermal analysis (DTA) and differential scanning calorimetry (DSC). 2  Thermal analysis has been used to determine the Winners & Tech hub classes physical and chemical properties of polymers, electronic circuit boards, geological materials, etc. Thermal events that may occur in the sample as it is undergoing a change in temperature include phase transitions, melting, sublimation/volatilization, decomposition, glass transition in polymers, oxidation/reduction, etc. 3  The summary of thermal analysis techniques Technique Quantity measured Typical applications Thermogravimetric Change in weight of the sample is Thermal stability of a analysis (TGA) recorded as a function of substance and temperature. compositional analysis of Winners & Tech hub classes alloys and mixtures and corrosion studies Differential thermal Temperature difference between Generation of phase analysis (DTA) a sample substance and the diagrams and study of reference material is measured as phase transitions of a solid a function of temperature when sample, thermal stability subjected to a controlled and characterization of temperature programme. polymers Differential scanning Difference in energy inputs into a Reaction kinetics, purity calorimetry (DSC) sample substance and a analysis of drugs reference material is measured as a function of temperature when subjected. to a controlled temperature programme. 4  The thermal analysis instrumentation consists of four components Winners & Tech hub classes (i) The furnace which is controlled by the computer and a temperature sensor and has a controlled atmosphere such as air or inert gases (N2, He, Ar). (ii) The sample and its container (iii) The sensors for measuring temperature and sample properties (iv) The computer, data collection and processing equipment and a display device for the results 5  THERMOGRAVIMETRY (TG) Definition: Thermogravimetry is a technique in which a change in weight of the sample is recorded as a function of temperature. Winners & Tech hub classes Principle: The weight of the sample is continuously monitored as a function of temperature when the sample is heated at a controlled heating rate of 10-200C/minute. When the temperature is increased from ambient to 1200 0C, the sample may undergo dehydration, decomposition or volatilization which results in direct weight loss. The online plot of sample weight versus temperature is called a TG thermogram. 6  Instrumentation The major component of TG is the thermobalance or Winners & Tech hub classes thermogravimetric analyzer for measuring the mass. It includes a thermobalance and a microprocessor controlled tubular furnace. Fig shows the instrumentation of TG Block diagram of TG apparatus 7  1. Sample: A solid sample of 5-50 mg is placed in a platinum Winners & Tech hub classes crucible (sample container) and connected to a sensitive microbalance. The sensitive microbalance can detect a weight change of 1µg of the sample. 2. Thermobalance: The balance is placed inside the tubular furnace. A thermocouple, located immediately below the crucible, monitors the furnace temperature. The temperature of the furnace is accurately controlled and programmed for any change by the microprocessor 8  3. The null point balance is used in TG. Winners & Tech hub classes When there is a change in the weight of the sample, the balance beam will deviate from its usual position. A sensor detects the deviation and initiates a force that will restore the balance to the null position. The restoring force is proportional to the change in weight. The atmosphere inside the furnace can be controlled by using inert gases such as nitrogen, helium or argon or reactive gases such as oxygen, hydrogen, etc. 9 Winners & Tech hub classes 4. Data processor and recorder: The balance assembly measures the initial weight of the sample and continuously monitors changes in sample weight as heat is applied to the sample inside the furnace. The furnace data and balance data are collected during the experiment and sent to the computer for manipulation. The computer records the TG curve. 10  The thermogram obtained for calcium oxalate monohydrate is Winners & Tech hub classes shown in Fig ▪ The horizontal portions or plateaus indicate regions where there is no weight loss and the curved portion or downward steps indicate regions of weight loss. TG curve for decomposition of CaC2O4.H2O 11  Summary of thermal reactions in the decomposition of calcium oxalate monohydrate Temperature Thermal reaction Change in mass Winners & Tech hub classes range inoC 30 – 130 1st plateau region. No change in mass CaC2O4.H2O is thermally stable 130 - 190 1st downward step. Loss of water of CaC2O4.H2O ⟶CaC2O4 + H2O crystallization and there is decrease in mass 190 – 400 2nd plateau region. No change in mass Anhydrous CaC2O4.is thermally stable 12  Summary of thermal reactions in the decomposition of calcium oxalate monohydrate Winners & Tech hub classes 400 - 470 2nd downward step. Decrease in mass due CaC2O4. ⟶ CaCO3 + CO to loss of CO. 470 - 700 3rd plateau CaCO3 is thermally No change in mas stable. 700 - 840 3rd downward step Decrease in mass due CaCO3 ⟶CaO + CO2 to loss of CO2 840 - 1000 4th plateau CaO is thermally The residue obtained stable No change in mass. is CaO. 13  The thermogram obtained for CuSO4.5H2O Winners & Tech hub classes TG curve for CuSO4.5H2O 14  Summary of thermal reactions in the decomposition of CuSO4.5H2O Winners & Tech hub classes Temperature Thermal reaction Change in mass range in oC 30 - 90 1st plateau region. CuSO4.5H2O is No change in mass thermally stable 90 - 150 1st downward step. Loss of water of CuSO4.5H2O ⟶CuSO4. H2O+3 H2O crystallization and there is decrease in mass 150 – 200 2nd plateau region. CuSO4. H2O is No change in mass thermally stable 15  200 – 275 2nd downward step. Decrease in mass Winners & Tech hub classes CuSO4. H2O ⟶CuSO4+ H2O due to loss of H2O 275 – 700 3rd plateau anhydrous CuSO4 is No change in mass thermally stable. 700 - 900 3rd downward step. Decrease in mass CuSO4⟶CuO+SO2+ ½ O2 due to decomposition 900 – 1000 4th plateau CuO is thermally stable No change in mass. 1000 - 1100 4th downward step Reduction of CuO to 2CuO⟶ Cu2O+ ½ O2. Cu2O and there is decrease in mass 16  Applications of TGA 1. In the analysis of thermal decomposition of inorganic salts Winners & Tech hub classes and complexes which are used as catalysts, semiconductors and fine chemicals. 2. The decomposition temperature of commodity plastics and rubber are investigated by TGA. Each kind of polymer has a characteristic thermogram and can be used for identification purposes. 17 Winners & Tech hub classes TG curve for the determination of thermal stability of polymers Fig shows the thermogram of some common polymers. The thermal stability of polymers deceases in the order PTFE < LDPE < PMMA < PVC. PVC shows two-stage decomposition 18  Applications of TGA 3. TGA of pharmaceuticals, coal and minerals is useful in the study of complex thermal reactions. Winners & Tech hub classes 4. In the determination of composition of alloys and mixtures. E.g. determination of a mixture of calcium and strontium as their carbonates. Both undergo decomposition with evolution of CO2. But the decomposition of CaCO3 occurs in the temperature range 650- 850oC whereas SrCO3 decomposes in the higher range 950-1150oC. 5. In qualitative analysis of compounds. 6. In studying the oxidation of alloys. 19  DIFFERENTIAL THERMAL ANALYSIS (DTA) Definition: Differential thermal analysis is a technique in which the temperature difference (ΔT) between the Winners & Tech hub classes sample and an inert reference material is measured as a function of sample temperature when both are heated uniformly 20  Principle: When the sample undergoes any transition like melting, dehydration, decomposition etc., there is liberation or absorption of energy by the sample with the Winners & Tech hub classes corresponding deviation of its temperature from that of the reference. When the sample does not undergo any physical or chemical change, both the sample and the inert reference material are at the same temperature and ΔT is zero. If any endothermic or exothermic reaction occurs in the sample, the temperature of the sample decreases or increases and causes a difference in temperature (ΔT) between the sample and reference. A plot of ΔT vs. T gives the DTA thermogram. 21  Instrumentation: The instrument consists of a microprocessor controlled furnace, data processor and recorder and a facility to control the atmosphere. Winners & Tech hub classes A block diagram of the DTA instrument is shown in Fig Block diagram of the DTA instrument 22  1. Sample holder assembly: The solid sample and the reference material (usually an inert substance) like alumina of 10 mg is Winners & Tech hub classes placed in a platinum crucible (sample container) and connected to a sensitive microbalance. The temperature of the sample and reference is measured by an individual thermocouple. 2. Microprocessor controlled furnace: The whole sample holder assembly is placed inside the furnace. The sample and the reference are heated at the same heating rate from ambient to 1500oC. A temperature programmer or furnace control maintains a constant heating rate of 1 0C /min -100 0C /min. 23  3. Facility to control atmosphere: Sample and reference chamber are designed to permit the circulation of inert gases such as nitrogen or reactive gases such as oxygen or air. Winners & Tech hub classes 4. Data processor and recorder: The difference in temperature (ΔT) between the sample and the reference (S and R) thermocouples is continuously measured. After amplification, the difference in signal is recorded on the y-axis. The temperature of the furnace is measured by an independent thermocouple and recorded on the x axis. The balance and furnace data collected is sent to the PC for manipulation and a DTA plot of (ΔT) vs. T is obtained. 24  Peak 1 is an exothermic peak and peak 2 is an endothermic peak. Endothermic peaks signify changes in crystallinity or dehydration reactions while exothermic curves results due to Winners & Tech hub classes chemical reactions such as oxidation. Idealized DTA curve 25  Applications of DTA 1. Qualitative analysis of materials: DTA measurements provide a rapid method for the finger printing of minerals, clays and polymeric materials. Fig shows the DTA thermogram of calcium oxalate monohydrate in Winners & Tech hub classes flowing air (O2) obtained by increasing the temperature at a rate of 8oC/min. It contains two endothermic peaks and one exothermic peak. 26  2. DTA provides information regarding processes like fusion, dehydration, oxidation, reduction, adsorption and solid state Winners & Tech hub classes reactions and in generation of phase diagram and the study of phase transitions. 3. It provides an accurate way of determining the melting and boiling points for organic compounds. 4. It has been widely used to study and characterization of polymers and qualitative analysis of polymer mixture. 27 Winners & Tech hub classes DTA thermogram of polymer The DTA curve which illustrates the various types of transitions that occurs during heating of a polymer 28  Winners & Tech hub classes THANK YOU 29