Low temperature furnaces

Chrome—nickel alloy heating elements that commonly ate used in low temperature furnaces are not suitable above the very low end of the range. Elements commonly used as resistors are either silicon carbide, carbon, or high temperature metals, eg, molybdenum and tungsten. The latter impose stringent limitations on the atmosphere that must be maintained around the heating elements to prevent rapid element failure (3), or the furnace should be designed to allow easy, periodic replacement. 

Van Hall et al. [100] inject a 20 litre sample into a high-temperature furnace at 950 °C containing catalyst to promote oxidation of carbon compounds to carbon dioxide, which is then passed into a non-dispersive infrared analyser. The carbonate interference can be determined by passing an acidified portion of the sample through a low-temperature furnace [101-103]. 

Another type of Micro TG/DTA sample holder is shown in (Fig. 13 e). It can be equipped with Al, Ni, or Pt crucibles with a miximum volume of 0.15 cm3. For use with the low-temperature furnace, or for sensitive DTA in the middle-range temperature furnace up to a maximum of 600 °C. 

In experiments which are carried out under normal pressure, the gaseous products are taken from a modified, commercially available low temperature furnace. The gas flows viscously in the specially designed capillary through an intermediate volume to the peristaltic pump. Hereby the gas pressure in the intermediate volume is reduced to approx. 1 mm Hg. By means of a variable... 

B implants and low-temperature furnace annealing with transient diffusion that is associated with the activated removal of implant damage in the tail region of the implant. The magnitude of the enhanced, transient diffusivity increases with implant dose and energy but reaches saturation at 2 x 10 13 cm2/s. 

For example, these comments have considerable negative impact on the desirability of high-Btu coal gasification and of the "Hydrogen Economy" for the purpose of distributing these synthetic fuels about for combustion in low-temperature furnaces and boilers. 

For medium or low temperature furnaces/ovens/dryers operating below about 1400 F (760 C), a forced recirculation furnace or recirculating oven delivers better temperature uniformity and better fuel economy. The recirculation can be by a fan and duct arrangement, by ceiling plug fans, or by the jet momentum of burners (especially type H high-velocity burners—fig. 6.2). 

Table 7.2 is based on aheating rate of 1(X) lb of steel per hour for each square foot of hearth whereas 40 Ib/ft hr is more reasonable for low-temperature furnaces. However, sometimes a furnace that was designed for low temperature is pushed into service at a higher temperature, in which case a damper or large piece of hard refractory can be used to partially block off an oversize flue. In smaller furnaces, the ratio of flue port area to hearth area must be larger. 

Mechanical circulation can be accomplished internally by plug fans (usually in the roof) with the driving motor outside the furnace and a drive shaft extending through the roof to an axial set of blades within the furnace. Materials limitations restrict this method to rather low temperature furnaces. 

Refractory materials can be melted, spun, and blown into fiber strands similar to wool or blanket insulations. They are used in many medium- and low-temperature furnaces and ovens furnaces, and for outer layers in multilayered refractory walls. Because of all their small air spaces, they are much better insulators than solid refractories, but they are more fragile, less durable, and more difficult to install so that they do not settle, shrink, or otherwise lose their good insulating property. Many of the suggestions in a later section on insulation installation can apply to fiber refractory installation. 

Pigment content By weight difference after extraction of all the vehicle using a suitable solvent mixture and centrifugation By low-temperature furnace ashing (some organic pigments may be lost by this method)... 

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