(Tamil)THERMAL Analysis ThermoGravimetric TGA Differential Scanning Calorimetry DSC DTA Differential

Tamil THERMAL ANALYSIS Classification of thermal techniques TGA – Mass change on heating or cooling. . DTA - Temperature difference between the sample and reference. DSC – Heat absorbed or liberated during heating or cooling Thermal Gravimetric Analysis(TGA) Measures temperature difference between the sample and reference during heating or cooling. 3. Differential Scanning Calorimetry (DSC) Measures heat absorbed by the sample or liberated during heating or cooling Heat absorbed means endothermic Heat released means exothermic Measures temperature difference between the sample and reference during heating or cooling. TGA – INSTRUMENTATION 1. Detection Unit: Furnace, sample and reference holder, and sensor, heat and cool the sample in the furnace, and detects the sample temperature and property. 2. Temperature Control Unit: Controls the furnace temperature. 3. Data Recording Unit: R ecords the signals of sensor and sample temperature, and software analyzes them. PRINCIPLE The substance under study is either heated or cooled at a controlled rate and the weight of the substance is recorded as a function of time and temperature. If the temperature varies during the study, then the weight is plotted as function of temperature. If the temperature is kept constant , the weight is plotted as a function of time. The change in weight is used for quantitative analysis and the temperature at which the change in weight takes place can be used for qualitative analysis 2 Factors affecting Thermogravimetry I - Instrumental factors Heating rate Furnace atmosphere – static air, dynamic air, inert atmosphere Sample holder II- Characteristics of the sample Weight of the sample Particle size of the sample Heat of reaction Compactness of the sample Source of the sample Applications The determination of purity and thermal stability of both primary and secondary standards used in volumetric analysis Determination of correct drying temperatures and the suitability of various weighing forms for gravimetric analysis Determination of composition of complex mixtures Determination of suitable ignition temperature Direct application to analytical problems Classification of TGA Curves Atmospheric Reaction, Increase in mass, reactions like surface oxidation. Single Stage Decomposition Multistage Decomposition CALCIUM OXALATE DECOMPOSITION TGA of Calcium Oxalate Monohydrate Thermogram Differential Thermogram Reasons and Mechanisms of Weight Change in TGA WEIGHT LOSS Decomposition: The breaking apart of chemical bonds. Evaporation: The loss of volatiles with elevated temperature. Reduction: Interaction of sample with a reducing atmosphere (hydrogen, ammonia, etc). Desorption. WEIGHT GAIN: Oxidation: Interaction of the sample with an oxidizing atmosphere. Absorption or Adsorption.