Thermal heating rate

FIG. 10 Weight loss curves for thermal (---------) (heating rate 1.7°C min, nitrogen) and thermo-oxidative (-) (heating... 

Optimum heat-transfer results when the thermal capacity rates of the two fluid streams are balanced, ie, where or = 1.0. 

The definition of polymer thermal stabiUty is not simple owing to the number of measurement techniques, desired properties, and factors that affect each (time, heating rate, atmosphere, etc). The easiest evaluation of thermal stabiUty is by the temperature at which a certain weight loss occurs as observed by thermogravimetric analysis (tga). Early work assigned a 7% loss as the point of stabiUty more recentiy a 10% value or the extrapolated break in the tga curve has been used. A more reaUstic view is to compare weight loss vs time at constant temperature, and better yet is to evaluate property retention time at temperature one set of criteria has been 177°C for 30,000 h, or 240°C for 1000 h, or 538°C for 1 h, or 816°C for 5 min (1). 

Kerogen Decomposition. The thermal decomposition of oil shale, ie, pyrolysis or retorting, yields Hquid, gaseous, and soHd products. The amounts of oil, gas, and coke which ultimately are formed depend on the heating rate of the oil shale and the temperature—time history of the Hberated oil. There is Htde effect of shale richness on these relative product yields under fixed pyrolysis conditions, as is shown in Table 5 (10). 

Fig. 13. Differential thermal analysis of wood and its components at a heating rate of 12°C pet minute and a gas flow rate of 30 cm pet minute. Sample...

Thin films of photochromic glass containing silver haUde have been produced by simultaneous vacuum deposition of siUcon monoxide, lead siUcate, aluminum chloride, copper (I) chloride, and silver haUdes (9). Again, heat treatment (120°C for several hours) after vacuum deposition results in the formation of photochromic silver haUde crystaUites. Photochemical darkening and thermal fade rates are much slower than those of the standard dispersed systems. 

What is the potential temperature rise by undesired reactions or thermal decomposi- tion, such as from contaminants, impurities, etc. What are the consequences What is the maximum pressure Enthalpy of undesired reaction Specific heat Rate of undesired reaction as a function of temperature DTA/DSC Dewar flask experiments APTAC /ARC /RSST/VSP... 

The as-spun acrylic fibers must be thermally stabilized in order to preserve the molecular structure generated as the fibers are drawn. This is typically performed in air at temperatures between 200 and 400°C [8]. Control of the heating rate is essential, since the stabilization reactions are highly exothermic. Therefore, the time required to adequately stabilize PAN fibers can be several hours, but will depend on the size of the fibers, as well as on the composition of the oxidizing atmosphere. Their are numerous reactions that occur during this stabilization process, including oxidation, nitrile cyclization, and saturated carbon bond dehydration [7]. A summary of several fimctional groups which appear in stabilized PAN fiber can be seen in Fig. 3. 

Thermal oxidation of graphite moderators is significant in several contexts. In the early air-cooled reactors the moderator temperature was low and hence the thermal oxidation rate was acceptable. However, the rate increased as the graphite became damaged by neutron irradiation. Moreover, the heat produced from the exothermic reaction... 

The thermal mass of parts and tools and the heating capacity of the autoclave naturally limit the maximum heating rate. Attempting to increase the heat-up rate by overheating the autoclave air can result in overheating of areas of the assembly with low thermal mass. 

As an alternative to the thermal or cycle efficiency of Eq. (1.1), the cyclic heat rate (the ratio of heat supply rate to power output) is sometimes used ... 

Ablative systems are not limited by the heating rate or environmental temperature, but rather by the total heat load. In spite of this limitation, however, the versatility of ablation has permitted it to be used on various hypervelocity atmospheric vehicles. No single, universally acceptable ablative material has been developed. Nevertheless, the interdisciplinary efforts of materials scientists and engineers have resulted in obtaining a wide variety of ablative compositions and constructions. These thermally protective materials have been arbitrarily categorized by their matrix composition, and typical materials are given in Table 2-9. 

The expln temp under confinement with a heating rate of 50/mii is 190°. The self-ignition temp of a vap/air riiixt is 193°. The principle prod of the thermal decompn of NPN is carbon monoxide. The combined molar vol from one mole of NPN of carbon monoxide and carbon dioxide is 1.84 moles (at 305psi and 200°)... 

The thermal reactions of CaC204 H20 have been very fully investigated and this substance has been used as a thermal analysis reference material [1058], Dehydration, decomposition to the carbonate, and dissociation to CaO are all well separated, though kinetic characteristics are influenced by the presence of C02, 02 and H20 as well as by the reaction conditions, including heating rate, sample size, and sample container. Kinetic parameters for the oxalate decomposition reaction have been summarized by Gurrieri et al. [1059]. Values of E are close to 314 8 kJ mole-1. Decompositions [1057,1060,1061] of Sr (643—743 K) and Ba (663—743 K) oxalates involves some disproportion of CO, yielding residual carbon. 

Figure 2.33. Thermal desorption spectra of oxygen from mixed oxygen-chlorine adlayers on Pt(100).9S The initial chlorine and oxygen concentrations as well as the dosing temperatures are indicated in the figure. Heating rate 20 K s 1.95 Reprinted with permission from Elsevier Science.

Figure 4.46. Thermal desorption spectra after electrochemical O2 supply to Ag/YSZ through the electrolyte for 10 min. Each curve corresponds to different adsorption temperature and current in order to achieve nearly constant initial coverage. Desorption was performed with linear heating rate, p=l K/s (Inset) Effect of potential on peak temperature.31 Reprinted with permission from Academic Press.

Figure 5.21. Experimental setup (inset) showing the location of the working (WE), counter (CE) and reference (RE) electrodes and of the heating element (HE) thermal desorption spectra after gaseous oxygen dosing at 673 K and an 02 pressure of 4x1 O 6 Torr on Pt deposited on YSZ for various exposure times. Oxygen exposure is expressed in kilo-langmuirs (1 kL=l0 3 Torrs). Desorption was performed with linear heating rate, ()=1 K/s.4 S Reprinted with permission from Academic Press.

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