Hot-zone design

Fig. 2.1. A typical hot-zone design approach the preparation of hot-zone parts could take several months...

Fig. 2.4. Power (top) and pulling speed (bottom) histones for different hot-zone designs the standard design (STD) and high-performance design (HPD) refer to the original default design and the computer-added one...

Some system designs have a double port feeding mechanism that is charged with inert gas to prevent air venting into the hot zone. 

A major goal in wall cooling is to spread out the hot zone and prevent very high peak temperatures. High peak temperatures cause poor reaction selectivity, cause carbon formation, deactivate catalysts, and cause corrosion problems in the reactor walls. CocuJTent flows spread out the hot zone and cause lower peak temperatures, but many additional design features must be considered in designing jacketed reactors. 

Offset design gives ready access along the axis of the hot zone. This design permits routine operation and cycling of the furnace without sacrificing control of contamination, access, and speed for condensables or noncondensables. 

A typical TG design is shown in Figure 5.1. Specimen powder is placed on a refractory pan (often porcelain or platinum). The pan, in the hot zone of the furnace, is suspended from a high precision balance. A thermocouple is in close proximity to the specimen but not in contact, so as not to interfere with the free float of the balance. The balances are electronically compensated so that the specimen pan does not move when the specimen gains or loses weight. 

Substrate heating is required in CVD reactors. Since the films are grown under isothermal conditions, the substrate must be held at a constant growth temperature for an extended period of time. The achievement of this requirement is facilitated in two ways, and reactors are classified into two groups depending on how the substrate is heated. In a hot-wall design, the entire reactor is placed in a tube furnace and the substrate, the region of forced gas convention, and the walls of the reactor are maintained at the same temperature. Of course the ends of the reactor are cooler than the middle because of heat loss from the ends and the introduction of cold gas at the entrance of the reactor. To remedy this imbalance, a three-zone furnace, with independent feedback control for each zone, is usually employed. Substrates are loaded only in the portion of the reactor where the temperature can be accurately maintained. 

Designed to meet the requirements of NFPA473, Professional Competencies of EMS Personnel Responding to Hazardous Materials Incidents. Protection from exposure, getting information on chemical toxicity, entry team medical monitoring, medical care in the hot zone, and contaminated patients. 

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