Initiators high temperature

Direct or American Process. The direct process is noted for its simplicity, low cost, and excellent thermal efficiency. It consists of an initial high-temperature reduction (1000-1200 °C) of a zinc-containing material (as oxide), the reducing agent being coal. Reduction takes place according to Boudouard s equations ... 

LD in which relaxation occurs after an initial high temperature... 

Finally, Chiefari et al. [315-317] suggested another technique leading to the synthesis of addition-fragmentation-type macromonomers but without the use of any CTA. This method, clean, easy, and economical, involves heating a mixture of acrylate or styrene monomer in an appropriate solvent with an azo or peroxy initiator. High temperatures (typically up to 150 °C) are required. To prove the expected mechanism, the authors studied the poly(alkyl acrylate) reactions in the presence (or not) of monomers and by using different conditions. They showed the reaction does not occur without the monomer. Moreover, an increase of the temperature leads to a better yield and a decrease of the molar mass. Macromonomers have been synthesized by this technique withMn between 103 and 104 gmol... 

These findings support the idea that the observed growth is in a transitory regime between the initial high temperature sintering and the more stable reaction induced sintering at low temperature. 

In all these cases it appears that the exothermic process must be initiated by heating the preformed pellets, etc. in a furnace. This is again the above-described high-temperature process in which the need for promoting reactivity by an initial high temperature derives either from the dilution of the reactants with oxides, the low heat output of the main reaction, or both. 

The original methods for PE synthesis, from the 1930s, used free radical initiators, high temperatures (>170°C), high pressures ( 200 MPa) and produced highly branched polymer with low percent crystallinity. Densities were 915 kg/m to 925 kg/mL The densities of amorphous and crystalline PE are 880 kg/m and 1000 kg/m respectively [17], Improved versions of the high temperature and pressure fi-ee-radical polymerization process are still used in... 

Validated models for creep damage assessment are available and these can produce estimates of time to crack initiation. High-temperature crack growth models can then be used to predict both time to failure and the nature of that event. 

In contrast with nuclear fission where a large nucleus is split into two more stable nuclei, fusion relies on the formation of larger stable nuclei from small nuclei. The main difference is that fusion requires an initial high temperature of millions of degrees to overcome the energy repulsion barrier of the nuclei. In the fusion H-bomb, the high temperature (10 K) is achieved by a fission bomb. 

At low elevated temperature cures, the ether and ester reactions take place at about the same frequency. At higher temperatures, the ester linkage occurs more frequently and this probably accounts for the reduced elevated temperature performance of systems gelled at initially high temperatures. Because reaction 3 can take place independently in the acid medium, the ratio of anyhydride to epoxy is less critical than with an amine. It can vary from 0.5 to 0.9 equivalents of epoxy and is determined experimentally to achieve desired properties. 

In order to augment the quantity and quality of final synthesis yield as obtained from conventional hydrothermal activation, another modified method has been introduced which utihzes two different steps, an initial high temperature fusion of fly ash-alkah mixture, prior to employing the final stage of hydrothermal activation of the fused product. The main variables have been fusion temperature and time, alkali type and its concentration and crystallization time in hydrothermal synthesis process, which can affect the quahty and yield of final product. As such, it has been confirmed that the final yield can be quantified to exhibit zeolitic conversion up to 62 % together with by production of alkaline waste solution which can become a threat to the environment after disposal. A flowchart of the synthesis process is depicted in Fig. 3.3 [1, 2, 9, 10, 12, 43, 44]. 

In autoclave processes, a mixture of fast initiator (low-temperature initiator) and slow initiator (high-temperature initiator) is used. Some examples of the commercial initiators used in high-pressure polyethylene processes are shown in Table 2. 

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