Decomposition Zone

After the decomposition zone, that is, at the location with axial temperature greater than 900° C, it can be assumed that the dissociation of calcium carbonate, Equation (10.10), an endothermic reaction with AH = -1660kJ/kg CaC03, is essentially complete. 

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Furthermore, for A = l/2-Amin, the term in brackets in Eqn. (12.30) has a maximum. Therefore, after a sufficient time of continuous spinodal decomposition, zones with the Amax periodicity will predominate. With other words, the decomposed solid solution exhibits periodicity in the direction, and the period length is Amax- min and max increase with strain, as can be seen from Eqns. (12.29) and (12.31). If the strain energy is high enough, Amax may become sufficiently large so that spinodal decomposition does not take place any more. 

Figure 15.5 Variation of grain size of deposits as a function of the vaporization temperature of Cp2V. Substrate temperature = 973 K. S, T, and D denote Sublimation, Transition domain, and Decomposition zones, respectively.

High temperature - fuel rich devolatilization zone Production of reducing species NOx decomposition zone Char oxidizing zone... 

The decomposition of AB material in solution could be attractive for many reasons. From a chemical engineering point of view, the use of a liquid fuel is generally preferred because of the simplifled transport compared to solid materials. Liquid AB hydrogen sources can be used to improve the controllability of the AB decomposition by separating the decomposition zone (reactor) from the storage tank. This measure would be an important improvement with respect to safety, since the dehydrogenation reaction potentially bears the risk of a thermal run-away due to its exothermic nature. 

In the method of Belscher [1], a nitrogen stream saturated with Fe(CO)5 at some temperature is combined in the bulb-shaped reactor of the apparatus hown in Fig. 338 with a stream of very hot nitrogen. The hot-gas quantity is always several times that of the cold one. Thus, for example, if the carbonyl-saturated Ng flows at a rate of 2 liters/hour, the flow rate of the hot N g must be 40-100 liters/hour. If the reaction temperature is maintained between 200 and 700°C and the Fe concentration in the decomposition zone does not exceed 10 mg./liter, a uniform, fibrous product collects in the settling chamber. 

In the method of Belscher [1] iron globules are formed at the maximum possible Fe(CO)5 concentration in the decomposition zone. The apparatus of Fig. 339 is used. The air is flushed out with a moderately fast stream of N g introduced via the inlet tube to a. Then the liquid carbonyl compound is vaporized at a rate of 30 ml./hr. and the vapor fed into the decomposition chamber, which is heated to 200-600°C (depending on the reaction conditions). At this point the Ng flow is either reduced or shut off completely. The tubing from the distillation flask to the decomposition tube (which is surrounded by a vertical heater) must be well insulated or maintained at about 110°C by means of a small electric coil or tape in order to avoid decomposition of the iron carbonyl. The first crop of product does not have the desired properties. A uniform powder consisting of microscopic globules is obtained only after a certain induction period. 

For all substances which melt without decomposition, zone refining is indeed the most effective method of purification. Following the development of the method in 1952 by Pfann for inorganic semiconductors, it was rapidly extended to organic materials [2]. Many sequential repetitions of the purification procedure can be carried out quite readily in the zone-refining process. 

The H2 production rate depends directiy on the rate of O2 removal from the H2O decomposition zone. This also depends on the O2 permeability of the membrane, which is a function of the electron and 02-ion conductivities, surface O2 exchange kinetics of the membrane, and oxygen partial pressure (PO2) gradient across the membrane (Balachandran et al., 2004 Ma, Balachandran, Chao, Park, Segre, 1997 Maiya et al., 1997). 

The unirradiated polypropylene sample remains stable from 30°C to 253 C, where there is no weight loss of the sample. This stable zone is followed by a slow rate of decomposition from 253°C to 400°C. A faster rate of decomposition starts between 400°C and 470°C, followed by a slower rate of decomposition between and 590°C, at which the sample is completely decomposed. A weight loss of about 94% has been recorded in this zone. The irradiated polymer remains stable up to a comparatively higher temperature, that is, from 30°C to 276°C for gamma irradiation at the 20 to 120 kGy level. It also follows the same trend of double-step decomposition as that of the unirradiated polypropylene. A slower rate of decomposition takes place from 270°C to 420°C where the sample loses about 10% of its initial weight. This is followed by a fast decomposition zone from 420°C to 460°C, with a weight loss of about 90%. The irradiated sample is completely decomposed at 570°C. 

In this Chapter, thermal analysis of the decomposition process has been performed -hence, the flame retardancy and thermal stabihzation of halogenated and non-halogenated polyester resins by ZHS may be explained by the formation of smface-localized spherical barriers which are growing according to the nucleation growth mechanism and which attenuate the transfer of heat from the decomposition zone to the substrate. This effect was foimd as dominating in the flame-retardancy mode of action. 

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