External Thermal Oven

The most common source materials used in external thermal ovens are elemental solids and metal chlorides such as AICI3, BeCl2, SnCl2 and MnCl2. Other compounds include GaAs, CdS, GaN, CdSe, ZnSe, and CdTeT With elemental Al, Zn, In, Mn, etc., care must be taken to avoid metallization of insulators in the source. Care must also be taken with BeClj because of the formation of toxic BeO. ... 

Figure 4.3 Schematic diagram of a thermal sweeper system located between two columns in the gas cliromatograph Cl, C2 and C3 are column connections, with C2 being small enough to allow the slotted heater S to pass over the connection. The accumulator column A retards the travel of solutes tlnough this section until the sweeper expels them out to the uncoated column (called a pigtail (P)), wliich then delivers them as a naixow band to the second column. The modulation drive, M, is external to the GC oven.

In short, the microwave energy was successfully applied for the first time for the rapid synthesis of condensation polymers such as polyimides and polyamides from the salt monomers (and co-amino acids) by using a simple domestic microwave oven. The rapid polymer formation is caused by the efficient internal heating of the reactants. This compares favorably with the long reaction time required for the conventional thermal polycondensation with external heating. 

Stresses caused by steady-state thermal gradients may or may not cause failure, depending on the degree of constraint imposed by some parts of the item upon others or by external mounting. Thermal stress resistance (face-to-face temperature differentials) that causes tensile stress is observed in some types of glasses. When glass is suddenly cooled, as by the removal from a hot oven, tensile stresses are introduced in the surfaces and... 

Catalytic runs were carried out at atmospheric pressure in a quartz-made fixed-bed flow microreactor (10 mm i d.). All the stainless-steel equipment devices had been passivated by hot HNO3 treatment before the assembly. The catalyst was activated in situ (6 h at 773 K under COj-free air flow). 4-Methylpentan-2-ol was fed in with an N2 stream (partial pressure, Po.aicohoi = 19.3 kPa time factor, W/F = 0.54 gcat-h/gakohoi)- On-line capillary GC analysis conditions were Petrocol DH 50.2 column, oven temperature between 313 and 473 K, heating rate 5 K/min. Products identification was confirmed by GC-MS. For each catalyst a run in which several reactor temperatures were checked was carried out, in order to study the influence of the thermal history of the sample on its catalytic behaviour and to reach an appropriate conversion level (ca. 50%) at which the selectivities values of the different catalysts can be compared. Then, a new run with a fresh portion of the same sample was started at the desired temperature and carried out isothermally for 80 h. Further runs, where both the flow rate and the catalyst amount were considerably changed, while keeping the same W/F value, were also carried out no significant differences in conversion were observed, which rules out the occurrence of external diffusion limitations. 

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