Glass specific heat capacity

A certain metal has a specific heat capacity of 0.500 J/g°C. A metal tray and a glass tray have the same mass. They are placed in an oven at 80°C. 

Mass of metal, g Temperature of metal, C Volume of water in calorimeter, litre Initial temperature in calorimeter, °C Maximum temperature of water in calorimeter, °C Increase in temperature of water in calorimeter, K Decrease in temperature of metal, K Specific heat capacity of water, cal/g K Ditto, of glass (from tabulated data), cal/g-K Amount of heat absorbed by glass of beaker and thermometer, cal... 

To determine the amount of heat absorbed by the glass of the calorimeter beaker, mark the level of the water in the beaker when running the experiment. Use the data obtained to approximately determine the mass of the glass heated by the water. Consider that the mass of the thermometer glass immersed in the liquid is about 2 g. Use the found specific heat capacity to calculate the atomic mass of lead by the Dulong and Petit law. 

The Nemst calorimeter is a calorimeter for the measurement of specific heat capacities at low temperatures. The sample to be measured is suspended in a glass or metal envelope that car be evacuated. The sample is heated by means of a platinum wire located in a bore inside the sample. The wire also serves as a resistance thermometer. The specific heat capacity is determined by recording the temperainre rise in the sample for a given delivery of energy. 

Figure 4.1. Schematic illustration of temperature dependences of specific heat capacities of amorphous polymers. The heat capacity jumps to a much higher value over a narrow temperature range as the polymer goes through the glass transition. It increases more slowly with increasing temperature above Tg than it did below Tg.

When discussing the sensitivity of heat flow calorimetry a representative example was chosen of a reaction releasing 27 W/batch on average when performed in a 2 liters glass vessel. A frequently found value for the coolant mass flow rate of a heat balance calorimeter amounts to 70 1/hour. Assuming a specific heat capacity of the coolant of 2600 J/kg K, this reaction power is transferred into a temperature difference between coolant inlet and outlet of 0,54 K. If the heat balance calorimeter and the heat flow calorimeter are to be of equal sensitivity, it follows that a resolution down to 1/100 K is required for the temperature difference. 

FIGURE 12.4 Specific heat capacity plotted against temperature for atactic polypropylene, showing the glass transition in the region of 260 K. (From O Reilly, J.M. and Karasz, F.E.,... 

As an independent experiment to verify the findings of the TDBS we also performed quasi adiabatic measurements of the specific heat capacity Cp (74) using modulated differential scanning calorimetry (N SC) (20-22). Usually the glass transition is characterized by a step like behavior of Cp(T). The thermal glass transition... 

Figure 10-3. Specific heat capacity Cp at constant pressure of partially crystalline (— — —) and amorphous (—0 — 0—) poly[oxy-(2,6-dimethyl)-l,4-phenylene]. Tcryst denotes the beginning of recrystallization, Tg is the glass transition temperature, and Tm is the melting temperature (after F. R. Karasz, H. E. Bair, and J. M. O. Reilly).

Table 10-1. Density p, Specific Heat Capacity at Constant Pressure Cp, Linear Coefficient of Expansion and Thermal Conductivity k of Polymers, Metals, and Glass at 25 C...

Experimental results for the effective specific heat capacity were obtained by DSC tests in [6]. MXB-360 (phenol-formaldehyde resin) with a 73.5% mass fraction of glass fibers was used in those tests. and were given in [6] as follows ... 

Most of the char material was composed of glass fiber and Cp was therefore considered as the specific heat capacity of the glass fibers. The results from Eq. 4.42 are compared with the results from the Einstein model (Eq. (4.33) in Figure 4.13 [12], as well as with the model used in previous studies [4, 5]. A linear function dependent on temperature for the specific heat capacity of fibers was used by Samanta et al. [4] and Looyeh et al. in 1997 [5], however, without direct experimental validation. As shown in Figure 4.13, the theoretical curve based on the Einstein model (Eq. (4.33) gives a reasonable estimation for the specific heat capacity of glass fibers. 

Figure 4.13 Comparison of temperature-dependent specific heat capacity models of E-glass fibers [12]. (With permission from Elsevier.)...

Polyterephthalates. The molecular motion and their connection to the thermal parameters for the three most common members of the homologous series of polyterephthalates is summarized in Fig. 6.40. The number of vibrations and the derived 0-temperatures allows the calculation of a vibrational heat capacity of the solid state, as outlined in Sect. 2.3.7. The changes within the 0-temperatures are practically within the error hmit. The specific heat capacities of the polyterephthalates are, as a result, also almost the same. The transition parameters are extrapolated to the equilibrium crystals and the fuUy amorphous glasses. Their values show regular changes with chemical stracture. All thermal properties are next related to the vibrational baselines computed from the parameters of Fig. 6.40. 

The reversing specific heat capacity in the glass transition region is illustrated in Fig. 6.52 [21 ]. The analysis in terms of the ATHAS Data Bank heat capacities shows that there is no low-temperature contribution due to conformational motion below the glass transition. The glass transition of the semicrystalline sample is broadened to higher temperature relative to the amorphous sample, as found in all polymers. Of... 

This large volume of data shows that the apparent reversing specific heat capacity increases with comonomer content. This is seen best immediately above the glass transition temperature, as displayed in the insert in Fig. 7.37. The amount of irreversible crystals, which are identified as the normally grown folded-chain crystals, decreases with increasing comonomer composition, as expected (see Figs. 7.37 and 7.38 and compare to Fig. 7.35). 

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