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Differential scanning calorimetry or DSC is a thermoanalytical technique in which the difference in the amount of heat required to increase the temperature of a sample and reference are measured as a function of temperature. Both the sample and reference are maintained at very 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 basic principle underlying this technique is that, when the sample undergoes a physical transformation such as phase transitions, more (or less) heat will need to flow to it than the reference to maintain both at the same temperature. Whether more or less heat must flow to the sample depends on whether the process is exothermic or endothermic. For example, as a solid sample melts to a liquid it will require more heat flowing to the sample to increase its temperature at the same rate as the reference. This is due to the absorption of heat by the sample as it undergoes the endothermic phase transition from solid to liquid. Likewise, as the sample undergoes exothermic processes (such as crystallization) less heat is required to raise the sample temperature. By observing the difference in heat flow between the sample and reference, differential scanning calorimeters are able to measure the amount of heat absorbed or released during such transitions. DSC may also be used to observe more subtle phase changes, such as glass transitions. DSC is widely used in industrial settings as a quality control instrument due to its applicability in evaluating sample purity and for studying polymer curing.[1][2][3] Thermal analysis is a branch of materials science where the properties of materials are studied as they change with temperature. ...
For other uses, see Heat (disambiguation) In physics, heat, symbolized by Q, is energy transferred from one body or system to another as a result of a difference in temperature. ...
This article includes a list of works cited or a list of external links, but its sources remain unclear because it lacks in-text citations. ...
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In physics, a phase transition, (or phase change) is the transformation of a thermodynamic system from one phase to another. ...
In chemistry, an exothermic reaction is one that releases heat . ...
In Chemistry an endothermic reaction is one in which the reactants have less energy than the products, and thus a net input of energy, usually in the form of heat, is required. ...
In physics, melting is the process of heating a solid substance to a point (called the melting point) where it turns into a liquid. ...
In physics, a phase transition, (or phase change) is the transformation of a thermodynamic system from one phase to another. ...
Frost crystallization on a shrub. ...
A calorimeter is a device used for calorimetry, the science of measuring the heat of chemical reactions or physical changes as well as heat capacity. ...
A simplistic view of a materials glass transition temperature (Tg) is the temperature below which molecules have very little mobility. ...
An alternative technique, which shares much in common with DSC, is differential thermal analysis (DTA). In this technique it is the heat flow to the sample and reference that remains the same rather than the temperature. When the sample and reference are heated identically phase changes and other thermal processes cause a difference in temperature between the sample and reference. Both DSC and DTA provide similar information; DSC is the more widely used of the two techniques.[1][2][3] This article does not cite any references or sources. ...
== DSC curves ==LEo was here
The result of a DSC experiment is a heating or cooling curve. This curve can be used to calculate enthalpies of transitions. This is done by integrating the peak corresponding to a given transition. It can be shown that the enthalpy of transition can be expressed using the following equation: t In thermodynamics and molecular chemistry, the enthalpy or heat content (denoted as H or ΔH, or rarely as χ) is a quotient or description of thermodynamic potential of a system, which can be used to calculate the useful work obtainable from a closed thermodynamic system under constant pressure. ...
ΔH = KA
where ΔH is the enthalpy of transition, K is the calorimetric constant, and A is the area under the curve. The calometric constant will vary from instrument to instrument, and can be determined by analyzing a well-characterized sample with known enthalpies of transition.[2]
Applications
Figure 3. A schematic DSC curve demonstrating the appearance of several common features Differential scanning calorimetry can be used to measure a number of characteristic properties of a sample. Using this technique it is possible to observe fusion and crystallization events as well as glass transition temperatures (Tg). DSC can also be used to study oxidation, as well as other chemical reactions.[1][2][3] This image has been released into the public domain by the copyright holder, its copyright has expired, or it is ineligible for copyright. ...
The melting point of a crystalline solid is the temperature at which it changes state from solid to liquid. ...
Quartz crystal Synthetic bismuth hopper crystal Insulin crystals Gallium, a metal that easily forms large single crystals A huge monocrystal of potassium dihydrogen phosphate grown from solution by Saint-Gobain for the megajoule laser of CEA. In chemistry and mineralogy, a crystal is a solid in which the constituent atoms...
The most fundamental reactions in chemistry are the redox processes. ...
Glass transitions may occur as the temperature of an amorphous solid is increased. These transitions appear as a step in the baseline of the recorded DSC signal. This is due to the sample undergoing a change in heat capacity; no formal phase change occurs.[1][3] An amorphous solid is a solid in which there is no long-range order of the positions of the atoms. ...
In thermodynamics, the Kauzmann Paradox is the apparent result that it is possible to obtain a supercooled liquid with an entropy lower than that of its corresponding crystal. ...
As the temperature increases, an amorphous solid will become less viscous. At some point the molecules may obtain enough freedom of motion to spontaneously arrange themselves into a crystalline form. This is known as the crystallization temperature (Tc). This transition from amorphous solid to crystalline solid is an exothermic process, and results in a peak in the DSC signal. As the temperature increases the sample eventually reaches its melting temperature (Tm). The melting process results in an endothermic peak in the DSC curve. The ability to determine transition temperatures and enthalpies makes DSC an invaluable tool in producing phase diagrams for various chemical systems.[1] Viscosity is a measure of the resistance of a fluid to deform under shear stress. ...
Frost crystallization on a shrub. ...
t In thermodynamics and molecular chemistry, the enthalpy or heat content (denoted as H or ΔH, or rarely as χ) is a quotient or description of thermodynamic potential of a system, which can be used to calculate the useful work obtainable from a closed thermodynamic system under constant pressure. ...
In physical chemistry, mineralogy, and materials science, a phase diagram is a type of graph used to show the equilibrium conditions between the thermodynamically-distinct phases. ...
DSC may also be used in the study of liquid crystals. As matter transitions between solid and liquid it often goes through a third state, which displays properties of both phases. This anisotropic liquid is known as a liquid crystalline or mesomorphous state. Using DSC, it is possible to observe the small energy changes that occur as matter transitions from a solid to a liquid crystal and from a liquid crystal to an isotropic liquid.[2] Schlieren texture of Liquid Crystal nematic phase Liquid crystals are substances that exhibit a phase of matter that has properties between those of a conventional liquid, and those of a solid crystal. ...
This article is being considered for deletion in accordance with Wikipedias deletion policy. ...
Isotropic means independent of direction. Isotropic radiation has the same intensity regardless of the direction of measurement, and an isotropic field exerts the same action regardless of how the test particle is oriented. ...
Using differential scanning calorimetry to study the oxidative stability of samples generally requires an airtight sample chamber. Usually, such tests are done isothermally (at constant temperature) by changing the atmosphere of the sample. First, the sample is brought to the desired test temperature under an inert atmosphere, usually nitrogen. Then, oxygen is added to the system. Any oxidation that occurs is observed as a deviation in the baseline. Such analyses can be used to determine the stability and optimum storage conditions for a compound.[1] General Name, Symbol, Number nitrogen, N, 7 Chemical series nonmetals Group, Period, Block 15, 2, p Appearance colorless gas Standard atomic weight 14. ...
DSC is widely used in the pharmaceutical and polymer industries. For the polymer chemist, DSC is a handy tool for studying curing processes, which allows the fine tuning of polymer properties. The cross-linking of polymer molecules that occurs in the curing process is exothermic, resulting in a positive peak in the DSC curve that usually appears soon after the glass transition.[1][2][3] Pharmacology (in Greek: pharmacon is drug, and logos is science) is the study of how chemical substances interfere with living systems. ...
A polymer is a substance composed of molecules with large molecular mass composed of repeating structural units, or monomers, connected by covalent chemical bonds. ...
In polymer chemistry and Process Engineering, curing refers to the toughening or hardening of a polymer material by cross-linking of polymer chains, brought about by chemical additives, ultraviolet radiation or heat. ...
Vulcanization is an example of cross-linking. ...
In the pharmaceutical industry it is necessary to have well-characterized drug compounds in order to define processing parameters. For instance, if it is necessary to deliver a drug in the amorphous form, it is desirable to process the drug at temperatures below those at which crystallization can occur.[2] It has been suggested that Blockbuster drug be merged into this article or section. ...
In food science research, DSC is used in conjunction with other thermal analytical techniques to determine water dynamics. Changes in water distribution may be correlated with changes in texture. Similar to material science studies, the effects of curing on confectionery products can also be analyzed. Food science is a discipline concerned with all technical aspects of food, beginning with harvesting or slaughtering, and ending with its cooking and consumption. ...
An analytical technique is a method that is used to determine the concentration of a chemical compound or element. ...
DSC curves may also be used to evaluate drug and polymer purities. This is possible because the temperature range over which a mixture of compounds melts is dependent on their relative amounts. This effect is due to a phenomenon known as freezing point depression, which occurs when a foreign solute is added to a solution. (Freezing point depression is what allows salt to de-ice sidewalks and antifreeze to keep your car running in the winter.) Consequently, less pure compounds will exhibit a broadened melting peak that begins at lower temperature than a pure compound.[2][3] Freezing-point depression is the difference between the freezing points of a pure solvent and a solution of a nonelectrolyte in that solvent. ...
A substance is soluble in a fluid if it dissolves in the fluid. ...
Making a saline water solution by dissolving table salt (NaCl) in water This article is about chemical solutions. ...
See Also Isothermal Titration Calorimetry (ITC) is a biophysical technique used to determine the thermodynamic parameters of (biochemical) interactions. ...
Dynamic mechanical analysis (DMA) or dynamic mechanical thermal analysis (DMTA) is a technique used to study and characterize materials. ...
This article does not cite any references or sources. ...
Thermogravimetric Analysis or TGA is a type of testing that is performed on samples to determine changes in weight in relation to change in temperature. ...
This article does not cite any references or sources. ...
Dielectric Analysis (DEA) or Dielectric Thermal Analysis (DETA) is a materials science technique similar to dynamic mechanical analysis except that an oscillating electrical field is used instead of a mechanical force. ...
Thermal analysis is a branch of materials science where the properties of materials are studied as they change with temperature. ...
References - ^ a b c d e f g Dean, John A. The Analytical Chemistry Handbook. New York. McGraw Hill, Inc. 1995. pp. 15.1–15.5
- ^ a b c d e f g h Pungor, Erno. A Practical Guide to Instrumental Analysis. Boca Raton, Florida. 1995. pp. 181–191.
- ^ a b c d e f Skoog, Douglas A., F. James Holler and Timothy Nieman. Principles of Instrumental Analysis. Fifth Edition. New York. 1998. pp. 905–908.
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