tailieunhanh - Handbook of Analytical Methods for Materials Part 5

Tham khảo tài liệu 'handbook of analytical methods for materials part 5', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | THERMAL ANALYSIS DESCRIPTION OF TECHNIQUES Thermal analysis measures physical or chemical changes in a material as a function of temperature. Two common complimentary techniques in this category are differential scanning calorimetry DSC and thermogravimetric analysis TGA . These methods are typically used to determine the material properties of organic polymers as the sample is heated or cooled in a controlled manner or held isothermally for a specified time. Differential thermal analysis DTA is a method similar to DSC but performed at higher temperatures for metals minerals ceramics and glasses. DSC - Differential scanning calorimetry measures heat flow to or from a sample as a function of temperature and time. A small portion of a sample is placed in an aluminum pan and heated and or cooled in a controlled manner. A reference material usually an empty aluminum pan simultaneously undergoes the same programmed time temperature routine. Calorimetric measurements are made during the heating cooling cycle. Two methods can be used for the calorimetric measurements. Differences in temperature between the sample and reference material can be measured as the same amount of heat energy calories is added to both. Or differences in the amount of heat energy added to both are measured as the temperature for both the sample and reference are kept constant. In both cases the heat flow and temperature of the sample are monitored in comparison to the reference material. The analysis is usually performed in an inert gas atmosphere such as nitrogen. The amount of energy absorbed endotherm or evolved exotherm as the sample undergoes physical or chemical changes . melting crystallization curing is measured in calories as a function of the temperature change. Any material reactions involving changes in heat capacity . glass transition are also detected. The thermal cycle for DSC typically can range from less than -50 C to 300 C or greater. The principals for differential thermal