 Good morning. In this particular video session, we are going to learn a topic, analytical chemistry and a subject from that topic that is thermal methods of analysis. This is the learning outcome for today's session. At the end of this session, students will be able to describe thermogravimetric analysis of the sample. This is the content that we are going to learn in this session. First, we will learn the two definitions. One is of thermal methods of analysis. And second definition is of thermogravimetric analysis. Then we will see the construction and working of thermogravimetric unit. And finally, we will learn what are the applications of thermogravimetric analysis. Now, we will learn the definition of thermal analysis. This is the technique in which changes in physical and chemical properties of a substance are measured as a function of temperature is called as thermal analysis. The technique in which changes in physical and chemical properties of substances are measured as a function of temperature is defined as thermal analysis. Then we will see the thermogravimetric analysis TZA. It is a technique in which a change in the weight of a substance is recorded as a function of temperature which is known as TZA. So, thermal analysis is a broad definition of all the methods that are coming under thermal analysis method. And thermogravimetric analysis is one of the sub-methods of the thermal analysis. What happens in thermal analysis? We are learning what kind of changes are there in physical and chemical properties of the substances with respect to the heating to that sample is there. And particularly in thermogravimetric analysis, it is a technique in which a change in the weight of a substance is recorded as a function of temperature. Now, this is the block diagram. If you see here, the first part is a sample holder where we are holding a very small quantity of the sample to be analyzed. The sample holder is covered with a proper insulating chamber and the sample holder is kept in a furnace. The furnace is then connected with microprocessor controlled power source which is capable to heat the sample at a controlled rate for a specific period of time. Which heats minimally 2 degree centigrade per minute to 250 degree centigrade per minute. That is the role of the microprocessor controlled power source. Now, the furnace is also connected with the thermocouple as the thermal balance. Thermocouple and thermo balance both are connected to the furnace. When the sample is being heated, some of the signals are received by thermocouple and some of the signals are received by the thermo balance. So, thermo balance receives the signal which gives us the knowledge about change in mass of a sample with respect to heating. And the thermocouple what are the signal it receives? It gives us the knowledge what kind of temperature values are there which is incorporated to the sample is there. Then both are received to the recorder where recorder plots a graph in between the values of temperature and change in mass and by reading that graph one can predict about the purity of the sample. Now, if you see here this is the environment control equipment. The role of the environment control equipment is to maintain the inert atmosphere across the sample while the sample is being heated. Because there is a possibility of reacting the sample with the atmospheric impurities and the possibilities that the sample may get converted to unwanted byproducts. To avoid the chemical reactivity of the sample to maintain the inert atmosphere around the sample it is connected with the environment control equipment which gives the flow of inert gases across the sample. Now, here I would like to ask you one question. The environment control unit is connected for the option A is for maintaining inert atmosphere inside the furnace. Second option for heating the sample. Third option for forming the byproducts and last option all of these. Think for a moment and the correct answer is the environment control equipment is provided for maintaining inert atmosphere inside the furnace to avoid the chemical reactivity of the sample with atmosphere. To order the components and how the TGA works. The main components of TGA apparatus are analytical thermo balance for measurement of mass of sample accurately at various temperatures. And the furnace linked with microprocessor controlled power source program to increase temperature linearly at the predetermined rate of 0.5 to 250 degree centigrade per minute up to 1200 degree centigrade. The third component is environment control equipment which is provided for maintaining inert atmosphere during the heating of the sample. Thermocouple is provided for recording temperature values during heating of sample. The recorder plots the graph between change in mass of a sample with respect to values of temperature. Now, if you see here the recorder gives the graph in between mass and the temperature. This is a particular example of calcium oxalate. Initially the temperature is very low so the mass is more but when the temperature goes on increasing the mass also comes down. Because with respect to temperature at the specific stages some of the molecule gets either evaporated, either degraded, either decomposed and that kind of pattern we are learning with respect to thermogram. So, this is the thermogram between mass of a sample with respect to the heating values. Now, there are two types of TGA curves. The qualitative and quantitative analysis recording the substance under study can be obtained from thermogram that is a plot of change in mass versus temperature. Or a plot of dm by dt versus temperature and the TGA curve consists of horizontal portions and downward portions. Not all horizontal portions? These portions represent no loss in weight with increase of temperature and the compound is thermally stable over that temperature range. This information is important because it reveals the temperature range in which substance like polymer, packing material, alloys may be safely used. So, I will show you the graph. So, this is called as the horizontal portion where the compound is thermally stable. So, in this particular temperature range there is no change in the mass of the sample that is known as the horizontal portions. The second type of curve is downward portions. The portions indicate the weight loss due to dehydration, decomposition, formation of volatile products at the temperature. TGA thermogram is characteristic for a given compound since unique sequence of physical or chemical changes in compound occurring over a definite temperature range which is a function of molecular structure. Now, we will learn applications of TGA that is qualitative analysis. The stability of a substance at the increased temperatures can be learned. Identification of compound, the curve being characteristic footprint for the compound, purity of compound and decomposition mechanism of polymer, salts, etc. This is the quantitative applications. The percentage of compound in a mixture can be calculated from TGA. Percentage of compound in a mixture can be calculated from TGA. TGA study can help to find the amount of filler in a polymer. Now, finally, what are the limitations? It is applicable for only those substances which undergo change in mass with temperature. The limitation is that it is applicable for only those substances which undergo this type of mechanism that is change in mass with temperature. It is not useful for pure fusion reactions, crystalline transitions and solid state reactions in which no volatile products are formed. All this I have referred by using a textbook of engineering chemistry written by Jain and Jain. Thank you.