Heat flow calorimetry measuring curve

In the various sections of this article, it has been attempted to show that heat-flow calorimetry does not present some of the theoretical or practical limitations which restrain the use of other calorimetric techniques in adsorption or heterogeneous catalysis studies. Provided that some relatively simple calibration tests and preliminary experiments, which have been described, are carefully made, the heat evolved during fast or slow adsorptions or surface interactions may be measured with precision in heat-flow calorimeters which are, moreover, particularly suitable for investigating surface phenomena on solids with a poor heat conductivity, as most industrial catalysts indeed are. The excellent stability of the zero reading, the high sensitivity level, and the remarkable fidelity which characterize many heat-flow microcalorimeters, and especially the Calvet microcalorimeters, permit, in most cases, the correct determination of the Q-0 curve—the energy spectrum of the adsorbent surface with respect to... 

Figure 11.5 Typical curve for a continuous titration calorimetry study of an exothermic reaction, using the calorimeter of Figure 11.1 in the heat flow isothermal mode of measurement./ is the frequency of the constant energy pulses supplied to the heater C in Figure 11.1 b. Adapted from [196,197],...

Many different test methods can be used to study polymers and their physical changes with temperature. These studies are called thermal analysis. Two important types of thermal analysis are called differential scanning calorimetry (DSC) and differential thermal analysis (DTA). DSC is a technique in which heat flow away from a polymer is measured as a function of temperature or time. In DTA the temperature difference between a reference and a sample is measured as a function of temperature or time. A typical DTA curve easily shows both Tg and T . 

Differential Scanning Calorimetry (DSC) This is by far the widest utilized technique to obtain the degree and reaction rate of cure as well as the specific heat of thermosetting resins. It is based on the measurement of the differential voltage (converted into heat flow) necessary to obtain the thermal equilibrium between a sample (resin) and an inert reference, both placed into a calorimeter [143,144], As a result, a thermogram, as shown in Figure 2.7, is obtained [145]. In this curve, the area under the whole curve represents the total heat of reaction, AHR, and the shadowed area represents the enthalpy at a specific time. From Equations 2.5 and 2.6, the degree and rate of cure can be calculated. The DSC can operate under isothermal or non-isothermal conditions [146]. In the former mode, two different methods can be used [1] ... 

It appears, therefore, that the measurement of heat flow using direct calorimetry, is a suitable technique for biogeochemical studies in aquatic systems since under carefully controlled conditions a reproducible "fingerprint" (or power-time curve) is obtained. 

Fig. 2.19. (upper figure) Differential scanning calorimetry scans of various Nr/Zr multilayer diffusion couples heated at a constant rate of 20 C/s. The heat flow rate, k, has been normalized by the total Ni/Zr interfacial area in the diffusion couple. The dotted line corresponds to an individual Ni layer thickness of 30 nm and an individual Zr layer thickness of 45 nm, the dashed line to 50nm/8nm, and the solid line to lOOnm/lOOnm, respectively. (lower figure) a plot of In (X%) (note that H is proportional to A"-the proportionality constant is determined by direct measurement of Hm and I, the final thickness of the amorphous layers) vs. (1/7 ) for the third sample in the upper figure. See text for further explanation. The slope of the curve gives the activation energy for interdiffusion of Ni and Zr in the amorphous layer [2.69]... 

Differential scanning calorimetry (DSC) Uses a similar type of instrument as DTA, but measures directly the heat flow of the exothermic and endothermic reactions occurring. The data obtained that are of interest are shape of the curve, temperatures of the onset and the top of an exothermic or an endothermic peak, slope of the upcurve, width of the peak. 15,36(U363... 

A quantitative, isothermal measurement of the crystallization kinetics, usable for analysis by the Avrami method, is illustrated in Fig. 3.98 by the upper left curve. Similar curves can be generated by dilatometry or adiabatic calorimetry as described in Sects. 4.1 and 4.2. At time zero, one assumes that the isothermal condition has been reached. The dotted segments of the heat-flow response are then proportional to the heat of crystallization evolved in the given time intervals and can be converted directly into the changes of the mass fraction of crystallinity after calibration or normalization to the total heat evolved. An independent crystallinity determination... 

Differential scanning calorimetry, DSC, is a technique which combines the ease of measurement of heating and cooling curves as displayed in Fig. 4.9 with the quantitative features of calorimetry (see Sect. 4.2). Temperature is measured continuously, and a differential technique is used to assess the heat flow into the sample and to equalize incidental heat gains and losses between reference and sample. Calorimetry is never a direct determination of the heat content. Measuring heat is different from volume or mass determinations, for example. In the latter cases the total amount can be established with a single measurement. The heat content, in contrast, must be measured by beginning at zero kelvin where the heat content is zero, and add all heat increments up to the temperature of interest. 

Using differential scanning calorimetry (DSC), one can measure the heat flow rate curve of polymer solid changing with the temperatures, as demonstrated in Fig. 6.15a. Heating (cooling) rates are constant. 

Differential scanning calorimetry (DSC) A technique in which the difference in energy inputs into a substance and a reference material is measured as a function of temperature whilst the substance and reference material are subjected to a controlled temperature program. Two modes, power-compensation DSC and heat-flux DSC, can be distinguished, depending on the method of measurement used. Usually, for the power-compensation DSC curve, heat flow rate should be plotted on the ordinate with endothermic reactions upwards, and for the heat-flux DSC curve with endothermic reactions downwards. 

Figure 4.3 shows a sample temperature-heat flow differential scanning calorimetry (DSC) curve obtained for high-density polyethylene using a PerkinEImer DSC-7 instrument. It illustrates the measurement of the T and heat of melting in a single run. 

The calorimetric curve upon cement hydration, which is generally continuously monitored, provides valuable kinetic information. Thus, the hydration times can be identified when further discontinuous hydration experiments, e.g. using XRD or TGA, can be carried out. There have also been interesting combinations of isothermal calorimetry and other measurement techniques published (mainly in fields other than cement science), such as the measurement of pressure, ion concentration, pH, relative humidity, rheology and chemical shrinkage (Champenois et al. 2013 Johansson and Wadso 1999 Lura et al. 2010 Minard et al. 2007 Wadso and Anderberg 2002). Recent work focused also on the calculation of heat flow curves from in situ hydration experiments done by quantitative XRD analysis (Bizzozero 2014 Hesse et al. 2011 Jansen et al. 2012a,b). 

In principle, differential thermal analysis, DTA is a technique which combines the ease of measurement of the cooling and heating curves discussed in Chapter 3 with the quantitative features of calorimetry which are treated in Chapter 5. Temperature is measured continuously and a differential technique is used in an effort to compensate for heat gains and losses. In the case of DTA as also in calorimetry, the actual heat measurement does not rely on a direct measurement of the heat content. A heat meter, as such, does not exist. In volume or mass determinations (see Chapters 6 and 7, respectively), the total quantity of interest can be established with one simple measurement. In the determination of heat content, in contrast, one must start at zero kelvin and measure all heat increments and add them up to the temperature of interest. In DTA one derives the flow of heat, AQ/dt, from a measurement of the temperature difference between a reference material and the sample. ... 

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