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Thermal Methods
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It’s Hot in Here … Let’s talk
ThermalBy: Naaimat Muhammed
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Introduction
• A general accepted definition of thermal analysis is a group of techniques in which a physical property of a substance and/or its reaction products is measured as a function of temperature while the substance is subjected to a controlled temperature program.
• We will confine to three of the methods, which provide primarily chemical rather than physical information about samples of matter.
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Three Methods
1. Thermogravimetry (TG)
2. Differential thermal analysis (DTA)
3. Differential scanning calorimetry (DSC)
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Thermogravimetric Methods
• In thermo gravimetric analysis, the mass of a sample in a controlled atmosphere is recorded continuously as a function of temperature or time as the temperature of the sample is increased (usually linear with time). Thermogravimetry is the measurement of the mass of a sample as the temperature increases.
• This method is useful for determining sample purity and water, carbonate, and organic content; and for studying decomposition reactions.
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Differential Thermal Analysis (DTA)
Differential thermal analysis is the measurement of the difference in temperature between a sample and a reference as heat is applied to the system.
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This method is sensitive to endothermic and exothermic processes including:
1. phase transitions2. Dehydration3. decomposition4. Redox5. solid-state reactions
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Differential Scanning Calorimetry (DSC)
• Differential scanning calorimetry independently measures the rate of heat flow to a sample and a standard that are at the same temperature. Data is taken by monitoring the differential heat flow as a function of temperature.
• DSC is useful to make the same measurements as DTA and has the added capability to measure heat capacities.
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Instrumentation
• Sensitive analytical balance• Furnace• Purge gas system (for providing an
inert atmosphere)• Microcomputer/microprocessor (for
instrument control and data acquisition and display).
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Thermal gravimetric Furnace
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Example of TGA using Weightloss vs. Time
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Power vs. Temperature
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Heat content vs. Temperature
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References
1. http://www.chem.vt.edu/chem-ed/crossref/ac-thermal.html
2. Principles of Instrumental Analysis, Skoog, Holler, Nieman; Saunders College Pub. 5th Edition (1998)
3. http://www.ptli.com/testlopedia/subs/TGA-result.htm