Dynamic differential calorimetry

Differential thermal analysis DTA Dynamic differential calorimetry... 

Palenzola and Cirafici [1975PAL/CIR] have measured the enthalpies of formation of ThSn3(cr) by dynamic differential calorimetry (integration of DTA curves) from an appropriate mixture of the elements, held in a molybdennm container. As discussed in Appendix A, the DTA peak reached its maximnm at 793 K. Palenzola and Cirafici [1975PAL/CIR] report the valne of Af//° (ThSns, cr) = -(162 + 16) kJ-mof to be that at 298.15 K, but make no mention of any corrections applied to the experimental valne. We have therefore assumed the value to be that at the maximum in the DTA peak, 793 K and have doubled the uncertainty stated by the anthors. However, in view of the nncertainties in the processing of the data from both these studies, these values are quoted for information only. 

These authors report the enthalpies of formation of RX3 compounds (R = Y, Th or U X = Ga, In, n, Sn or Pb) as determined by dynamic differential calorimetry (integration of DTA peaks, with a calibration from elements and compounds of known heats of fusion). These studies follow previous studies by the same group on rare earth intermetal-lic compounds having the same general formula. The calorimetric method used is described in one of these earher publications [1973PAL]. 

PAL] Palenzona, A., Dynamic differential calorimetry of intermetallic... 

Methods for the study of changes of state in systems under dynamic thermal conditions are examined. The effects of heat transfer rate on thermal analysis are discussed, and both exothermic and endothermic reactions are considered. The theoretical basis for the measurement of heating and reaction rates using dynamic differential calorimetry is discussed. 

Differential thermal analysis (DTA), thermogravimetric analysis (TGA), and dynamic differential calorimetry (DDC) are major techniques for the identification and investigation of rapid changes of state under dynamic thermal conditions. The difference between DTA and TGA is well delineated in technique and analysis however, the distinction between DDC and DTA remains poorly established in the experimental literature. It must be noted that DTA and DDC differ in their use of a homogeneous sample block and separated sample cups, respectively. These arrangements produce isolated thermal peaks by the former method and quantitative reaction heat determinations by the latter. In each analytical method, atmospheric effects must be considered in as much detail as are heat transfer conditions, specimen characteristics, and other physical parameters. 

MODULATED TEMPERATURE DIFFERENTIAL SCANNING CALORIMETRY/DYNAMIC DIFFERENTIAL SCANNING CALORIMETRY... 

The curing behavior of an epoxy system was investigated by dynamic differential scanning calorimetry (DSC). The epoxy resin (R) was a blend of bisphenol-A-diglycidylether (90%) and a monoepoxide (10%). The hardener (H) was a triethylene-tetramine-phenol-formaldehyde adduct containing 2% free phenol. 

The kinetics of copolymerization or curing of epoxy resins with cyclic anhydrides initiated by tertiary amines was investigated by chemical analysis 52,65,73,74,90) differential scanning calorimetry isothermal methods electric methods , dynamic differential thermal analysis , IR spectroscopy dilatometry or viscometry Results of kinetic measurements and their interpretation differ most authors agree, however, that the copolymerization is of first order with respect to the tertiary amine. 

While the first paper on liquid crystalline elastomers [30] already reports the detection of a cholesteric-isotropic transition using differential calorimetry and polarizing microscopy, comparatively little work has been done to characterize thy physical properties in the vicinity of this phase transition (compare, however, also the discussion of electromechanical effects in the next section) [9, 30, 31]. Combined liquid crystalline elastomers have been synthesized and various of these materials show a cholesteric-isotropic transition using X-ray scattering, polarizing microscopy and differential scanning calorimetry [31]. Dynamic mechanical investigations have been carried... 

A two-pack PU coating was analysed using thermoanalytical techniques. The curing reaction was monitored using pressure differential calorimetry, rheometry and dynamic mechanical analysis. The decomposition behaviour was examined using TGA. 13 refs. 

The crystal stmcture of glycerides may be unambiguously determined by x-ray diffraction of powdered samples. However, the dynamic crystallization may also be readily studied by differential scanning calorimetry (dsc). Crystallization, remelting, and recrystallization to a more stable form may be observed when Hquid fat is solidified at a carefully controlled rate ia the iastmment. Enthalpy values and melting poiats for the various crystal forms are shown ia Table 3 (52). 

Other PDMS—sihca-based hybrids have been reported (16,17) and related to the ceramer hybrids (10—12,17). Using differential scanning calorimetry, dynamic mechanical analysis, and saxs, the microstmcture of these PDMS hybrids was determined to be microphase-separated, in that the polysiUcate domains (of ca 3 nm in diameter) behave as network cross-link junctions dispersed within the PDMS oligomer-rich phase. The distance between these... 

Glass-transition temperatures are commonly determined by differential scanning calorimetry or dynamic mechanical analysis. Many reported values have been measured by dilatometric methods however, methods based on the torsional pendulum, strain gauge, and refractivity also give results which are ia good agreement. Vicat temperature and britde poiat yield only approximate transition temperature values but are useful because of the simplicity of measurement. The reported T values for a large number of polymers may be found ia References 5, 6, 12, and 13. 

Thermal analysis iavolves techniques ia which a physical property of a material is measured agaiast temperature at the same time the material is exposed to a coatroUed temperature program. A wide range of thermal analysis techniques have been developed siace the commercial development of automated thermal equipment as Hsted ia Table 1. Of these the best known and most often used for polymers are thermogravimetry (tg), differential thermal analysis (dta), differential scanning calorimetry (dsc), and dynamic mechanical analysis (dma). 

The thermal glass-transition temperatures of poly(vinyl acetal)s can be determined by dynamic mechanical analysis, differential scanning calorimetry, and nmr techniques (31). The thermal glass-transition temperature of poly(vinyl acetal) resins prepared from aliphatic aldehydes can be estimated from empirical relationships such as equation 1 where OH and OAc are the weight percent of vinyl alcohol and vinyl acetate units and C is the number of carbons in the chain derived from the aldehyde. The symbols with subscripts are the corresponding values for a standard (s) resin with known parameters (32). The formula accurately predicts that resin T increases as vinyl alcohol content increases, and decreases as vinyl acetate content and aldehyde carbon chain length increases. 

A number of analytical techniques such as FTIR spectroscopy,65-66 13C NMR,67,68 solid-state 13 C NMR,69 GPC or size exclusion chromatography (SEC),67-72 HPLC,73 mass spectrometric analysis,74 differential scanning calorimetry (DSC),67 75 76 and dynamic mechanical analysis (DMA)77 78 have been utilized to characterize resole syntheses and crosslinking reactions. Packed-column supercritical fluid chromatography with a negative-ion atmospheric pressure chemical ionization mass spectrometric detector has also been used to separate and characterize resoles resins.79 This section provides some examples of how these techniques are used in practical applications. 

Dynamic DSC, 409. See also Differential scanning calorimetry (DSC) Dynamic mechanical analysis (DMA), 138, 163, 241-242, 407, 409... 

A3 AIBN c Cp DLS DLVO DSC EO GMA HS-DSC KPS LCST Osmotic third virial coefficient 2,2 -Azobis(isobutyronitrile) Polymer concentration Partial heat capacity Dynamic light scattering Derjaguin-Landau-Verwey-Overbeek Differential scanning calorimetry Ethylene oxide Glycidylmethacrylate High-sensitivity differential scanning calorimetry Potassium persulphate Lower critical solution temperature... 

Teoh, H.M., Schmidt, SJ., Day, G.A., and Faller, J.F. 2001. Investigation of commeal components using dynamic vapor sorption and differential scanning calorimetry. J. Food Sci. 66, 434-440. Tromp, R.H., Parker, R., and Ring, S.G. 1997. Water diffusion in glasses of carbohydrates. Carbo-hydr. Res. 303, 199-205. 

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