Processing temperature Terms Links

If the activity of the catalyst is slowly modified by chemisorption of materials that are not easily removed, the deactivation process is termed poisoning. It is usually caused by preferential adsorption of small quantities of impurities (poisons) present in the feedstream. Adsorption of extremely small amounts of the poison (a small fraction of a monolayer) is often sufficient to cause very large losses in catalytic activity. The bonds linking the catalyst and poison are often abnormally strong and highly specific. Consequently, the process is often irreversible. If the process is reversible, a change in the temperature or the composition of the gas to which it is exposed may be sufficient to restore catalyst... 

For primary cable insulation. Cable jackets and pipes manufactured from LDPE, medium to high-molecular-weight grades are used and are frequently cross-linked after processing. Long-term heat stabilizer is of primary importance in these applications, since lifetimes of up to 50 years are required (usually at elevated temperatures with short-time peaks up to 100°C for cables). The antioxidants have to be extremely compatible and resistant to extraction. Some typical antioxidants customary for insulation are as follows ... 

The first and most important thermodynamic potential we need is entropy. One way to define entropy would be to simply say that the Z-term in Equation (3.14) does indeed exist, where entropy is called S, and Z = —S. This provides a useful analogy between pressure-volume and temperature-entropy, and we will see these terms linked together in many equations. They represent work and heat energy in many processes we will be considering. 

In principle MID manufacture is not restricted to any given base material. In fact, very different polymers can be used. The choice of material and production process is primarily linked to the mechanical, thermal, and electrical requirements of the end purpose of the finished MID. The materials group of thermoplastics is normally subdivided on the basis of heat distortion resistance or long-term service temperature on the one hand, and the price of the raw materials on the other [93]. 

In the rubbery region, which is just above (in terms of temperature) the leathery region, polymer chains have high mobility and may assume many different conformations, such as compact coils, by bond rotation and without much disentanglement. When these rubbery polymers are elongated rapidly, they snap back in a reversible process when the tension is removed. This elasticity can be preserved over long periods of time if occasional cross-links are present, as in vulcanized soft rubber, but the process is not reversible for linear polymers when the stress is applied over long periods of time. 

Equations (10) are generally valid for both liquid and gas phases if reactions take place there. They represent nothing but a differential mass balance for the film region with the account of the source term due to the reaction. To link this balance to the process variables like component concentrations, some additional relationships - often called constitutive relations (see Ref. [16]) - are necessary. For the component fluxes Ni, these constitutive relations result from the multicomponent diffusion description (Eqs. (1), (2)) for the source terms, from the reaction kinetics description. The latter strongly depends on the specific reaction mechanism [27]. The reaction rate expressions lli usually represent nonlinear dependencies on the mixture composition and temperature of the corresponding phase. 

---