|
Differential Thermal Analysis
Differential thermal analysis (DTA) is a thermoanalytic technique that is similar to differential scanning calorimetry. In DTA, the material under study and an inert reference are made to undergo identical thermal cycles, (i.e., same cooling or heating programme) while recording any temperature difference between sample and reference. This differential temperature is then plotted against time, or against temperature (DTA curve, or thermogram). Changes in the sample, either exothermic or endothermic, can be detected relative to the inert reference. Thus, a DTA curve provides data on the transformations that have occurred, such as glass transitions, crystallization, melting and sublimation. The area under a DTA peak is the enthalpy change and is not affected by the heat capacity of the sample. Apparatus A DTA consists of a sample holder, thermocouples, sample containers and a ceramic or metallic block; a furnace; a temperature programmer; and a recording system. The key feature is ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Thermal Analysis
Thermal analysis is a branch of materials science where the properties of materials are studied as they change with temperature. Several methods are commonly used – these are distinguished from one another by the property which is measured: * Dielectric thermal analysis: dielectric permittivity and loss factor * Differential thermal analysis: temperature difference versus temperature or time * Differential scanning calorimetry: heat flow changes versus temperature or time * Dilatometry: volume changes with temperature change * Dynamic mechanical analysis: measures storage modulus (stiffness) and loss modulus (damping) versus temperature, time and frequency * Evolved gas analysis: analysis of gases evolved during heating of a material, usually decomposition products * Isothermal titration calorimetry * Isothermal microcalorimetry * Laser flash analysis: thermal diffusivity and thermal conductivity * Thermogravimetric analysis: mass change versus temperature or time * Th ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Differential Scanning Calorimetry
Differential scanning calorimetry (DSC) is a thermoanalytical technique in which the difference in the amount of heat required to increase the temperature of a sample and reference is measured as a function of temperature. Both the sample and reference are maintained at nearly the same temperature throughout the experiment. Generally, the temperature program for a DSC analysis is designed such that the sample holder temperature increases linearly as a function of time. The reference sample should have a well-defined heat capacity over the range of temperatures to be scanned. The technique was developed by E. S. Watson and M. J. O'Neill in 1962, and introduced commercially at the 1963 Pittsburgh Conference on Analytical Chemistry and Applied Spectroscopy. The first adiabatic differential scanning calorimeter that could be used in biochemistry was developed by P. L. Privalov and D. R. Monaselidze in 1964 at Institute of Physics in Tbilisi, Georgia. The term DSC was coined to descr ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Isothermal Microcalorimetry
Isothermal microcalorimetry (IMC) is a laboratory method for real-time monitoring and dynamic analysis of chemical, physical and biological processes. Over a period of hours or days, IMC determines the onset, rate, extent and energetics of such processes for specimens in small ampoules (e.g. 3–20 ml) at a constant set temperature (c. 15 °C–150 °C). IMC accomplishes this dynamic analysis by measuring and recording vs. elapsed time the net rate of heat flow (μJ/s = μW) to or from the specimen ampoule, and the cumulative amount of heat (J) consumed or produced. IMC is a powerful and versatile analytical tool for four closely related reasons: # All chemical and physical processes are either exothermic or endothermic—produce or consume heat. # The rate of heat flow is proportional to the rate of the process taking place. # IMC is sensitive enough to detect and follow either slow processes (reactions proceeding at a few % per year) in a few grams of material, or ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Dynamic Mechanical Analysis
Dynamic mechanical analysis (abbreviated DMA) is a technique used to study and characterize materials. It is most useful for studying the viscoelastic behavior of polymers. A sinusoidal stress is applied and the strain in the material is measured, allowing one to determine the complex modulus. The temperature of the sample or the frequency of the stress are often varied, leading to variations in the complex modulus; this approach can be used to locate the glass transition temperature of the material, as well as to identify transitions corresponding to other molecular motions. Theory Viscoelastic properties of materials Polymers composed of long molecular chains have unique viscoelastic properties, which combine the characteristics of elastic solids and Newtonian fluids. The classical theory of elasticity describes the mechanical properties of elastic solid where stress is proportional to strain in small deformations. Such response of stress is independent of strain rate. Th ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Thermomechanical Analysis
Thermomechanical analysis (TMA) is a technique used in thermal analysis, a branch of materials science which studies the properties of materials as they change with temperature. Thermomechanical analysis is a subdiscipline of the thermomechanometry (TM) technique. Related techniques and terminology Thermomechanometry is the measurement of a change of a dimension or a mechanical property of the sample while it is subjected to a temperature regime. An associated thermoanalytical method is thermomechanical analysis. A special related technique is thermodilatometry (TD), the measurement of a change of a dimension of the sample with a negligible force acting on the sample while it is subjected to a temperature regime. The associated thermoanalytical method is thermodilatometric analysis (TDA). TDA is often referred to as zero force TMA. The temperature regime may be heating, cooling at a rate of temperature change that can include stepwise temperature changes, linear rate of change ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Thermogravimetric Analysis
Thermogravimetric analysis or thermal gravimetric analysis (TGA) is a method of thermal analysis in which the mass of a sample is measured over time as the temperature changes. This measurement provides information about physical phenomena, such as phase transitions, absorption, adsorption and desorption; as well as chemical phenomena including chemisorptions, thermal decomposition, and solid-gas reactions (e.g., oxidation or reduction). Thermogravimetric analyzer Thermogravimetric analysis (TGA) is conducted on an instrument referred to as a thermogravimetric analyzer. A thermogravimetric analyzer continuously measures mass while the temperature of a sample is changed over time. Mass, temperature, and time are considered base measurements in thermogravimetric analysis while many additional measures may be derived from these three base measurements. A typical thermogravimetric analyzer consists of a precision balance with a sample pan located inside a furnace with a programmab ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Dielectric Thermal Analysis
Dielectric thermal analysis (DETA), or dielectric analysis (DEA), is a materials science technique similar to dynamic mechanical analysis except that an oscillating electrical field is used instead of a mechanical force. For investigation of the curing behavior of thermosetting resin systems, composite materials, adhesives and paints, Dielectric Analysis (DEA) can be used in accordance with ASTM E 2038 or E 2039. The great advantage of DEA is that it can be employed not only on a laboratory scale, but also in process. Measuring principle In a typical test, the sample is placed in contact with two electrodes (the dielectric sensor) and a sinusoidal voltage (the excitation) is applied to one electrode. The resulting sinusoidal current (the response) is measured at the second electrode. The response signal is attenuated in amplitude and shifted in phase in relation to the mobility of the ions and alignment of the dipoles. Dipoles in the material will attempt to align with the elec ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Thermal Analysis
Thermal analysis is a branch of materials science where the properties of materials are studied as they change with temperature. Several methods are commonly used – these are distinguished from one another by the property which is measured: * Dielectric thermal analysis: dielectric permittivity and loss factor * Differential thermal analysis: temperature difference versus temperature or time * Differential scanning calorimetry: heat flow changes versus temperature or time * Dilatometry: volume changes with temperature change * Dynamic mechanical analysis: measures storage modulus (stiffness) and loss modulus (damping) versus temperature, time and frequency * Evolved gas analysis: analysis of gases evolved during heating of a material, usually decomposition products * Isothermal titration calorimetry * Isothermal microcalorimetry * Laser flash analysis: thermal diffusivity and thermal conductivity * Thermogravimetric analysis: mass change versus temperature or time * Th ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Differential Scanning Calorimetry
Differential scanning calorimetry (DSC) is a thermoanalytical technique in which the difference in the amount of heat required to increase the temperature of a sample and reference is measured as a function of temperature. Both the sample and reference are maintained at nearly the same temperature throughout the experiment. Generally, the temperature program for a DSC analysis is designed such that the sample holder temperature increases linearly as a function of time. The reference sample should have a well-defined heat capacity over the range of temperatures to be scanned. The technique was developed by E. S. Watson and M. J. O'Neill in 1962, and introduced commercially at the 1963 Pittsburgh Conference on Analytical Chemistry and Applied Spectroscopy. The first adiabatic differential scanning calorimeter that could be used in biochemistry was developed by P. L. Privalov and D. R. Monaselidze in 1964 at Institute of Physics in Tbilisi, Georgia. The term DSC was coined to descr ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Thermogravimetric Analysis
Thermogravimetric analysis or thermal gravimetric analysis (TGA) is a method of thermal analysis in which the mass of a sample is measured over time as the temperature changes. This measurement provides information about physical phenomena, such as phase transitions, absorption, adsorption and desorption; as well as chemical phenomena including chemisorptions, thermal decomposition, and solid-gas reactions (e.g., oxidation or reduction). Thermogravimetric analyzer Thermogravimetric analysis (TGA) is conducted on an instrument referred to as a thermogravimetric analyzer. A thermogravimetric analyzer continuously measures mass while the temperature of a sample is changed over time. Mass, temperature, and time are considered base measurements in thermogravimetric analysis while many additional measures may be derived from these three base measurements. A typical thermogravimetric analyzer consists of a precision balance with a sample pan located inside a furnace with a programmab ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Scientific Techniques
A scientific technique is any systematic way of obtaining information about a scientific nature or to obtain a desired material or product. Scientific techniques can be divided in many different groups, e.g.: # Preparative techniques ## Synthesis techniques, e.g. the use of Grignard reagents in organic chemistry ## Growth techniques, e.g. crystal growth or cell cultures in biology ## Purification techniques e.g. those in chemistry # Measurement techniques ## Analysis techniques, e.g. ones that reveal atomic or molecular composition. ## Characterization techniques, e.g. ones that measure a certain property of a material. ## Imaging techniques, e.g. microscopy In some cases these methods have evolved into instrumental techniques that require expensive equipment. This is particularly true in sciences like physics, chemistry, and astronomy. It is customary to abbreviate the names of techniques into acronyms, although this does not hold for all of them. Particularly the advent of ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
