Thermal exposure magnitude

Examples of their results [154] are shown in the set of curves in Fig. 13. At a given humidity, the Co concentration increases with T the thermal activation energy is about 0.4 eV. At a given temperature, the corrosion increases with an increase in humidity. As the humidity changes from 30 to 90%, the corrosion rate increases about an order of magnitude. The data allow a calculation of the acceleration factors for a variety of conditions. For example, the acceleration factor for 90°C/90% RH with respect to 30°C/40% RH is calculated to be 150. If the product passes a 2-week exposure to 90 °C/90% RH, the test indicates that it will survive in excess of 6 years at 30 °C/40% RH. The values of the acceleration factors, however, may vary from film to film. 

It must be pointed out that, at the laser power and scanning rates used, the surface temperature of the sample did not rise more than a few degrees above ambient, as shown recently by Tsao and Ehrlich (10). Since the laser exposure time was five orders of magnitude shorter in our experiments as in Tsao s work, thermal initiation can be neglected. Further support of an exclusive photoeflect in the laser curing of these resins came from the absence of any detectable polymerization when the photoinitiator was not introduced in the formulation. 

With fresh activated-clay catalyst, endothermic peaks are observed at temperatures of about 300, 1200, and 1600°F. These three peaks are attributed to loss of physically adsorbed water, loss of chemically bound (hydroxyl) water, and collapse of the montmorillonite structure, respectively. The hydroxyl water originally present amounts to 3 or 4%. The magnitude of the peak at 1200°F. decreases if the sample is heated above 800°F. prior to thermal analysis, and disappears completely if the sample is calcined at 1100°F. The thermal-analysis curve for the dehydrated catalyst is flat up to the point at which the montmorillonite structure begins to disappear. If the catalyst has not been heated above 1450°F., it becomes rehydrated upon exposure to moisture and a new endothermic peak appears in the curve between 800 and 1000°F. The size of the new peak increases as that of the original hydroxyl-water peak decreases it corresponds to 1.5 to 2.0% sorbed water with catalyst that has been rehydrated after calcination at 1100°F. The rehydration capacity of the catalyst decreases as the catalyst becomes partially deactivated with use. 

Exposure to low concentrations may not produce immediate effects. However, the severity of poisoning is not related to the presentation or magnitude of immediate symptoms. Symptoms may include eye and airway irritation, tearing, shortness of breath, coughing, wheezing, chest tightness, and delayed pulmonary edema. If halogens have been released, there may be redness of the skin, chemical bums or even thermal burns. 

The problems encountered with catalysts for auto emission purification are of the same type but of a totally different magnitude. Superior mechanical properties and, specifically, exceptional resistance to attrition are required. Furthermore, these properties should be unaffected by exposure to 1000°C and even 1100°C. Furthermore, a surface area of 50-80 m2/g and porosity of 0.6-0.8 cm3/g must remain after heating. Naturally the carrier must also withstand thermal shocks, offer the least possible diffusional limitation to reagents, and react as little as possible —or at least without unfavorable results—with the catalytically active oxides and metals deposited on its surface. 

For sports that have intermittent exposure to heat and cold, thermal buffers may be appropriate (Shim et ah, 2001). Some ski jackets are equipped with phase change materials that absorb body heat when liquidized and transfer heat to the body when the materials become solid. Although the effects are currently minimal in magnitude for a certain weight, new materials may have better cooling properties (Mondal, 2008). 

High Temperature Mechanical Properties in Short-Term Tests. In materials that are not thermally stable, there will be an effect due to irreversible changes in properties. Its magnitude depends on the temperature and duration of exposure. Figs. 3.1-40 and 3.1-41. 

---