Thermogravimetric Analysis Medical Presentation

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Published on : Jan 13, 2018 | Views : 5696 | Downloads : 54

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Welcome you all TO THE WORLD OF TGA
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PRESENTED BY S.MATHIVANAN. M.PHARM-1st YEAR DEPARTMENT OF PHARMACEUTICS
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Outline of this seminar Definition of thermal analysis What is thermal analysis and its types Thermogravimetric analysis TGA Theory and their types Instrumentation of TGA Methodology Factors affecting thermogravimetry results TGA applications.
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Thermal analysis DEFINITION: TA is a group of techniques that study the properties of materials as they change with temperature. In practice TA gives properties like enthalpy, thermal capacity, mass changes and the coefficient of heat expansion. Solid state chemistry uses TA for studying reactions in the solid state, thermal degradation reaction, phase transitions and phase diagrams.
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Introduction Thermal analysis is defined as “series of techniques for measuring the temperature dependency of a physical property of a certain substance while varying the temperature of the substance according to a specific program.” Physical properties include mass, temperature, enthalpy, dimension, dynamic characteristics, and others, and depending on the physical properties to be measured, the techniques of thermal analysis.
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Cont… Conventionally thermal analysis has been mainly employed in measurements for research and development, but in recent times it is used in many practical applications, as the testing standards on the basis of thermal analysis have been established, for example, in quality control in the production field, process control, and material acceptance inspection. It is also applied in wide fields, including polymer, glass, ceramics, metal, explosives, semiconductors, medicines, and foods.
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Basic principles of Thermal analysis
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THERMOGRAVIMETRIC ANALYSIS (TGA) Often Different properties are measured at the same time TGA-DTA, TGA-DSC, TGA-EGA (TGA-MS, TGA-FTIR)
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TGA Measurement changes in weight in relation to changes in temperature. THEORY: A large number of chemical substance invariably decompose upon heating, and this of heating a sample to observe weight changes is the underlying principle of thermo gravimetric analysis(TGA).
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Cont… The measured weight loss curve gives information on: Change in sample composition Thermal stability Kinetic parameters for chemical reaction in the sample A derivation weight loss curve can be used to tell the point at which weight loss is most apparent.
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Phenomenon causing mass change
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Types of TGA DYNAMIC TGA Sample is subjected to condition of continuous increase in temperature that is invariably found to be linear with time. STATIC TGA (Iso thermal) Sample is maintained at a constant temperature for a period of time during which any changes in weight observed carefully
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Types of TGA based on loading sample
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Instrumentation
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Instrumentation A high precision balance Sample holder A furnace Furnace programmer(controller) A recording device
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Balance
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Null point type It makes use of an appropriate sensing- element which aptly detects any slightest deviation of the balance beam. It provides the application of a restoring forces, directly proportional to the change in weight, thereby returning the beam to its original null-point. The restoring force is subsequently recorded either directly or with the aid of a transducer.
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Deflection type It is essentially based on either a conventional analytical balanced consisting of: Beam type: Conversion of beam deflection Helical spring type: Elongation or contraction of the spring with weight changes. Cantilever beam type: One end of the beam is fixed and the other end, on which the sample is placed, is free to undergo deflection. Torsion wire type: The wire is firmly fixed at either or both ends so that the deflection of the beam are proportional to weight changes.
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Ideal properties of balance Its accuracy, sensitivity, reproducibility and capacity should be similar to analytical balance It should have a high degree of mechanical and electrical stability It should have a rapid response to weight changes.
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Sample holder This is most important in accurate TGA Depending upon the nature of sample, its weight and quantity to be handled, different size and shapes of sample holders known as crucibles are employed These are constructed from various materials like glass, quartz, aluminum, stainless steels, platinum etc; These generally are of 2 types, Shallow pan for holding samples which eliminates gas, vapours of volatile matter by diffusion during heating Deep crucible for general purpose.
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Furnace Must be designed in such a fashion so as to incorporate an appropriate smooth input there by maintaining either a fixed temperature (or) predetermined linear heating program (e.g.., 100c-6000c per hour (6c/min) Temperature control is achieved via a thermocouple mounted very close to the furnace –winding
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Maximum operational temperature may be obtained using different thermocouple as indicated below
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Furnace temperature programmer (controller) These are the controller which can provide gradual rise of temperature at a fixed rate. This device has a course and fine control knob through which desired temperature with respect to rate or time can be obtained. This controlling is done by increasing voltage through the heated element by motor driven variable transformer or by different thermocouples.
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Recorder The recording device must be such so as to Record both temperature and weight continuously and Make a definite periodic records of the time. One main advantage of these recorder is that can check the heating rate of the furnace for linearity.
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Measurement possibilities
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TGA Methodology Ex. Decomposition of calcium oxalate monohydrate Calcium oxalate monohydrate, a standard material often used to demonstrate TGA performance. Exhibits three weight losses with temperature in an inert atmosphere (e.g. N2). -H2O -CO -CO2 CaC2O4 • H2O CaC2O4 CaCO3 CaO
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STAGE 1: The water of hydration (or crystallization) from calcium oxalate monohydrate is lost which corresponds to 2.46 mg (12.3%) equivalent to 1 mole of H2O in temperature ranges 100-250 C. STAGE 2 : One mole of calcium mono oxide is evolved subsequently from calcium oxalate, corresponding to 3.84 mg (19.2%) in the temperature ranges 400-500 C. STAGE 3 : Finally, a mole of CO2 is evolved from calcium carbonate that corresponds to 6.02mg (30.1%) in temperature ranges 700-800 C.
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Factors affecting results Instrumental factor: These include various aspects of instrument like, Furnace heating (its temperature and rate) Recording of changes on charts (its speed) Furnace atmosphere (its rate of cooling and maintaining temperature), Sample holder and its geometry (decomposition of calcium carbonate carried out in inert nitrogen) Sensitivity of balance.
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Cont… Characteristics of sample: The important factors about the sample are Weight of sample (E.g. decomposition of calcium oxalate.) Particle size of sample (decomposition proceeds at higher temperature) Nature of evolved gas or volatile matter Thermal conductivity of sample. The heat of decomposition of the reaction. Compactness of the Sample (decomposes higher than the loose samples)
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Why TGA??
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TGA-DSC for Pseudo-polymorphism
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THANK YOU…!!!