Ovens for Oxidation

To facilitate cleaning, ovens must have ready access, such as a walkway, which would permit entry, but provided with adjustable lift-up flaps situated on the same levels as the dividing partitions of any horizontal sections. Air-flow should be turbulent to prevent local hot-spots. 

In general, rollers that are 1 m wide should be about 150 mm in diameter and if 2 m wide, 350 mm in diameter, in order to ensure sufficient rigidity to restrict bending, if any, to a permissible level. Excessive bow would allow the fiber band to move towards the center line, causing fiber-bunching and a build-up of heat in the thicker tow band, which could eventually result in a fire. Rollers can be fitted with wiper blades to remove stray filaments. Metal doctor blades, though efficient, tend to be noisy and therefore, felt is preferred. 

Free-running pass-back rollers permit the fiber to stretch or shrink without restriction. If any of the rollers are to be driven, they must be manufactured to a specific tolerance on the diameter, since different diameter rollers would give variable line speed. 

The uniformity of the air flow within the oven can be checked at room temperature using a hot wire anemometer, although frictional resistance on the recirculating air will add about 20° C to the ambient temperature, making it a rather uncomfortable commissioning procedure. Since oxidation is extremely temperature dependent, it is a wise precaution to use duplex thermocouples with the second arm acting as a check thermocouple, or as a possible replacement, In the event of a failure. Type K, Chromel vi Alumel (Ni-Cr/Ni-Al) thermocouples are preferred. 

The interior of the oven can be subjected to fairly corrosive conditions and should be fabricated from either zinc coated steel, or stainless steel which is a better option, to avoid expensive shut-downs due to corrosion damage in the future, especially where temperatures have dropped below the dew point. Exhaust vapors are kept hot to reduee eondensation of tars and aqueous hquors. The efficieney of the oven insulation and eheeking for heat losses by a eonduetive path ean be undertaken by surveying the oven surfaee with an infrared heat spy eamera. 

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Martin et al. [24] were the first to apply chemical amplification reactions in gas chromatography. They used Emich s system of reactions to increase the amount of carbon dioxide. The amplification system consisted of three stages, each involving a series arrangement including an oven for reduction of carbon dioxide with charcoal and an oven for oxidation of carbon monoxide to carbon dioxide with copper oxide. The experimental gain factor found for this system was 7,45 (theoretical value 8.0). Martin et al. [24] pointed out the promising nature of this method for GC. 

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