Thermal characterization

Thermal characteristics of cells and batteries are one of the most important aspects of safe cell and battery design. Individual materials and complete battery modules should be characterized. 

Differential scanning calorimetry (DSC) is being applied to understand the effects of thermal abuse on battery materials. This technique enables the thermal response of individual and selected combinations of cell components to be measured over a broad temperature range. In favorable cases, this information allows identification of the components participating in thermal activity. The DSC technique also allows 

A Perkin Elmer Pyris 1 Thermal Gravimetric Analyzer (TGA) was used to determine the weight percent concentration of nanotubes in the composite samples. Approximately 20 mg of each sample was heated from 25 to 950 °C at a rate of 20°C/min in a nitrogen environment. As the sample is heated, the mass is measured as function of temperature. The mass retained is calculated by dividing the mass at the temperature of interest by the initial mass. Once the polymer has degraded, the remaining mass is assumed to be the mass of the MWNTs since the MWNTs are thermally stable in nitrogen to temperatures above 1000°C (from discussion with David Carnahan, President of Nano-Lab). 

Aerogels are probably the best known superinsulation materials with thermal conductivity values as low as half of the value of standing air (0.025 W m  

Like in any porous insulation material, the total heat losses are the sum of the skeletal conduction (phonons), gas conduction (collisions between gas molecules), and radiation contributions. The particular mesoscopic structure of aerogels leads to a considerable reduction of the gas-phase conduction contribution due to a trapping effect of the pore gas. For most terrestrial applications, the thermal conductivity at ambient temperature and pressure is relevant, which although well studied, is still a challenge to determine accurately [203], primarily due to the lack of large-area homogeneous aerogel specimens. 

The measurement of very low thermal conductivities is done directly by equilibrium methods, where typically a constant heat flux is measured to maintain a given temperature difference between a hot and a cold side. Dynamic methods rely on a transient heat pulse or wave that is sent from a material interface and travels over a known distance to reach a detector. Indirect methods then rely on physical models to calculate the thermal conductivity based on heat diffusion equations. A detailed review on the physics of heat transport in aerogels was given by Ebert [203] in the aerogels handbook. Various theoretical models exist, which allow one to determine the effective thermal conductivity of superinsulation materials based on dynamic measurement methods. 

The most efficient and sensitive tool to characterize a glass that can give rise to a glass-ceramic is differential thermal analysis (DTA). It allows the different characteristic temperatures of the material that permit prediction of the glass behaviour under thermal treatments to be determined. To ensure the reproducibility of the characteristic temperatures and to compare various samples or experiments, the thermal analysis has to be carried out carefully at a same heating rate, often 10°C/min. In some cases, a series of DTA 

The key to obtaining a partial and controlled crystallization is generally to observe two or more crystallization peaks that are sufficiently separated so that the precipitation of one phase only can be obtained. In the case of oxyfluoride systems, the oxide matrix must offer 

In oxyfluoride systems, too, it is possible to modify the composition of the fluoride phase in order to lower its crystallization temperature. For instance, the phase diagram PbF2-CdF2 has been explored by several authors [29, 30, 31]. The existence of a solid solution permits to lower the precipitation temperamre without external nucleating agent or excessive content of the phase itself inducing homogeneous nucleation. 

LaFa containing glass-ceramic systems have been shown to incorporate a limited part of the rare-earth ions into the crystal phase [38]. 

The induction time can be conveniently determined on a TGA, but other instruments can be used as well, for instance a DSC. Thermal characterization will be discussed in the next section. 

In thermal characterization, a controlled amount of heat is applied to a sample and its effect measured and recorded. In isothermal operations, the effect is recorded as a function of time at constant temperature. In a programmed temperature operation, the temperature is changed in a predetermined fashion, e.g., at a certain rate, and the effect is recorded as a function of temperature. General texts on thermal characterization inciude Wendlandt [85], Daniels [86], and Turi [87]. 

Differential thermal analysis (DTA) and differential scanning calorimetry (DSC) are similar techniques. They measure change in the heat capacity of a sample. These techniques can be used to determine various transition temperatures (T , Tg, T , Tp, etc.), specific heat, heat of fusion, percent crystallinity, onset of degradation temperature, induction time, reaction rate, crystallization rate, etc. A DSC instrument operates by compensating electrically for a change in sample heat. The power for heating is controlled in such a way that the temperature of the sample and the reference is the same. The vertical axis of a DSC temperature scan shows the heat flow in cal/s. 

A DTA instrument operates by measuring the change in sample temperature with respect to an inert reference. Newer DTA instruments with externally mounted thermocouple and reproducible heat path have a precision comparable to the DSC. Older DTA instruments with the thermocouple placed in the sample were less accurate and reproducible. 

A thermogravimetric analyzer measures the change in weight of a sample due to volatilization, reaction, or absorption from the gas phase. With polymers, the TGA is used to measure the amount and loss of moisture or diluent, and rates and tempera- 

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E. A. Turi, Thermal Characterization of Polymeric Materials, Academic, New York, 1997, Chapter 5,... 

Thermal Characterization of PPO Modified by Friedel-Crafts Reactions... 

Table V. Thermal Characterization of PPO Containing Biphenyl Groups...

Table VI. Thermal Characterization of PECH Containing Methoxybiphenyl Groups...

Ladesma, R., Compo, P., and Isaacs, L. L., Thermal Characterization of Coal... 

A Perkin-Elmer DSC-7 was used for thermal characterization of the starting phenolic resins and copolymers prepared. Scans were run at 10"C/min using sample weights of 15-25 mg. In all cases the amorphous, powdered polymers were used for the evaluation. 

THERMAL CHARACTERIZATION OF O-CRESOL NOVOLAC-DIMETHYL SILOXANE COPOLYMERS... 

THERMAL CHARACTERIZATION OF POLY (DIMETHYL SILOXANE) COPOLYMERS WITH POLY (HYDROXY STYRENE) AND 2-METHYL... 

Feliu, J. A., C. Sottile, C. Bassani, J. Ligthart, and G. Maschio (1996). "Thermal Characterization of the Polymerization of Methyl Methacrylate." Chemical Engineering Science 51, 11,2793-98. 

In general, the miscibility between two polymers can be predicted by thermal characterization of the blends [36], One of the most simple and effective ways to predict miscibility between two polymers is to consider the behavior of the glass transition temperature in the blend systems, which is known as the Tg method. In miscible blend systems, only a single 7 g intermediate between two components appears in the amorphous state. Therefore, we studied the change of... 

Here we will concentrate on the modification of cotton through reaction with tin-containing reactants and thermal characterization of the products. 

Table II. Thermal Characterization by DSC of PSU and PPO with Pendant Vinyl Groups...

Biliaderis, C. G., Page, C. M., Maurice, T. J., and Juliano, B. O. (1986). Thermal characterization of rice starches A polymeric approach to phase transition of granular starch. /. Agric. Food Chem. 34, 6-14. 

Zhong, Z. and Sun, X. S. (2005). Thermal characterization and phase behavior of cornstarch studied by differential scanning calorimetry. /. Food Eng. 69, 453-459. 

For thermal characterization and temperature sensor calibration a microhotplate was fabricated, which is identical to that on the monoHthic sensor chips, but does not include any electronics. The functional elements of this microhotplate are connected to bonding pads and not wired up to any circuitry, so that the direct access to the hotplate components without electronics interference is ensured. The assessment of characteristic microhotplate properties, such as the thermal resistance of the microhotplate and its thermal time constant, were carried out with these discrete microhotplates. 

The circular microhotplate was thermally characterized, and the results were compared with simulations carried out according to the approach discussed in Chap. 3. Applying FEM simulations as described in Sect. 3.3 generate a temperature field, and the temperature in the membrane center represents the overall membrane temperature according to Eq. (3.21). The values that have been used for the simulation are summarized in Table 4.2. 

The microhotplate with the transistor heater was electrothermally characterized similarly to the procedures presented in Sect. 4.1.3. Special care was taken to exclude wiring series resistances by integration of on-chip pads that allow for accurate determination of Fsg and sd- With the two on-chip temperature sensors in the center (Tm) and close to the transistor (Tt) the temperature homogeneity across the heated area was assessed as well. Both sensors were calibrated prior to thermal characterization. The relative temperature difference (Tj - Tm)/Tm was taken as a measure for the temperature homogeneity of the membrane. The measured thermal characteristics of a coated and an uncoated membrane are summarized in Table 4.6. The experimental values have been used for simulations according to Eq. (4.10). 

Arana et al. have performed extensive modeling and thermal characterization experiments on their reactor design. They modeled their design consisting of two suspended SiN - tubes linked with slabs of silicon using two-dimensional computation fluid dynamics and a heat transfer model (Femlab, Comsol Inc.). The heat of reaction of the steam reforming or... 

Solymar, L. and Walsh, D. 1998. Electrical Properties of Materials. Oxford University Press, New York. Turi, E. 1997. Thermal Characterization of Polymeric Materials, 2nd ed. Academic Press, Orlando, PL. Urban, M. 1996. Attenuated Total Reflectance Spectroscopy of Polymers. Oxford University Press, New York. 

Wiesbrock F, Hoogenboom R, Leenen M et al. (2005) Microwave-assisted synthesis of a 4 X 2-membered library of diblock copoly(2-oxazoline)s and chain-extended homo poly(2-oxazoline)s and their thermal characterization. Macromolecules 38 7957-7966... 

Electrical and Thermal Characterization of MESFETs, HEMTs, and HBTs, Robert Anholt... 

R. B. Seymour, Modern Plastics Technology, Chapter 15, Reston Publishing, Reston, Va. (1975). C. E. Carraher, Thermal characterizations of inorganic and organometallic polymers, J. Macromol Sci, Chem. A17(8), 1293-1356 (1982). 

Polyphosphazenes are the most important and the most thermally characterized of the phosphorus-containing inorganic polymers. Linear, cycloli-near, and cross-linked cyclomatic polymers based on phosphazene structures have been produced. The repeating units of some polyphosphazenes are as follows ... 

Thermal Characterization of Polymer Materials (E. A. Turi, ed.), Academic Press, New York, 1981. 

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