Aluminum oxide heat capacity

Reaction calorimeters are frequently calibrated using a known heat of a chemical reaction. No standard reaction is internationally accepted. For the measurement of heat capacities, drop calorimeters are frequently used and the calibration is made using a substance, the temperature dependence of which on heat capacity is known. As substances, metals like Cu, Ag, Au, and aluminum oxide in the form of sapphire are used. Calorimeters... 

The heat capacity constant (KCp) is determined by first subtracting or adding the baseline (empty pan) values as appropriate from the sample and calibration reversing heat capacity data. The baseline-corrected measured reversing heat capacity for the aluminum oxide is compared to the expected heat capacity, determined from the literature heat capacity data as follows ... 

It is also possible, if desired, to use the same data set to calibrate the underlying signal in terms of heat capacity. To do this, the baseline (empty pan) underlying heat flow is subtracted from this signal for the aluminum oxide and the sample experiments. The underlying heat flow is then converted to a heat capacity by dividing it by the linear component of the heat rate, and this value is compared to the known values to calculate an underlying heat capacity calibration constant KCpU, viz ... 

The next calibration concerns the area of the DSC trace or the amplitude at any one temperature. The peak area below the baseline in Fig. 4.62 can be compared with the melting peaks of standard materials such as the benzoic acid, urea, indium, or anthracene, listed at the bottom of the figure. The amplitudes measured from the baseline established in the heat-capacity mode of measurement are usually compared with the heat capacity of standard aluminum oxide in the form of sapphire. The heat capacity of sapphire is free of transitions over a wide temperature range and has been... 

In Fig. 1 there are three example applications from a Mettler DSC Application Description (DSC of the type illustrated in Fig. 4.4, left center). Calculate the crystallinity of the polyethylene sample (for the heat of fusion, look in the Appendbc) and the calibration constant for heat capacity measurement in J/(s V) [the aluminum oxide specific heat capacity is 1.005 J/(K g)j. Furthermore, estimate the heat of fusion of phenacetin [use Eq. (1), of Fig. 5.28 the equilibrium melting temperature of pure phenacetin is 407.6 K]. 

In addition to providing information regarding the capacity of the solid surface for the liquid phase adsorbate, the adsorption isotherm can also provide valuable conformational and thermodynamic information. The data of O Fig. 10.14 presents the adsorption isotherms for poly(methylmethacrylate) (PMMA) on oxidized aluminum and silicon surfaces (Watts et al. 2000). O Figure 10.14a shows the behavior at low and medium concentrations, and this follows the expected form for chemisorption. The data at higher concentration, O Tig 10.14b, shows a sharp rise in adsorption that is consistent with multilayer rather than monolayer adsorption. The answer, however, lies in the conformation of the molecules at low concentrations they are in an extended form (illustrated by the schematic inset of Fig. 10.14a), while at higher concentrations they are in a more compact form and pack more efficiently on the surface (shown in the schematic of O Fig. 10.14b). Another usefiil feature that can be established qualitatively from inspection of the isotherms of O Fig. 10.14a is the heat of adsorption. The sharpness of the knee at low concentration provides an indication of this value, thus for the data of PMMA on aluminum and silicon the heat of adsorption for PMMA on aluminum is more exothermic than on silicon. This is as one would expect as the silicon surface will be rich in acidic silanol groups very receptive to the basic PMMA, whilst the aluminum oxide surface is amphoteric and will not react so readily with PMMA. 

Polymer films coated with a thin layer of alnminnm or alnminnm oxide are extensively used in food packing as heat shields. The infiared rays were not transmitted through the films and were reflected protecting the contents from the harmful effects of infrared light. The quantitative measurement of the film thickness and infrared light reflection and absorption capacities of aluminum coated films used as packing materials were possible using infrared spectroscopy. 

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