Material surface temperatures, infrared drying

This latter point was stressed by some of us in a recent report studying NO storage and reduction on commercial LSR (lean storage-reduction) catalysts, in order to catch valuable information about the behaviour of typical NO storage materials in real application conditions. Nature, thermal stability and relative amounts of the surface species formed on a commercial catalyst upon NO and 02 adsorption in the presence and in the absence of water were analysed using a novel system consisting of a quartz infrared reactor. Operando IR plus MS measurements showed that carbonates present in the fresh catalyst are removed by replacement with barium nitrate species after the first nitration of the material. Nitrate species coordinated to different barium sites are the predominant surface species under dry and wet conditions. The difference in the species stabilities suggested that barium sites possess different basicity and, therefore, that they are able to stabilize nitrates at different temperatures. At temperatures below 523 K, nitrite species were observed. The presence of water at mild temperatures in the reactant flow makes unavailable for NO adsorption the alumina sites [181]. 

Generally speaking, the methods used to characterize carbonaceous material surfaces are referred to as wet and dry techniques. The former include potentiometric titrations and zeta potential or electrochemical methods the latter include temperature-programmed desorption (TPD) and spectroscopic methods such as x-ray photoelectron spectroscopy (XPS) and diffuse reflectance infrared spectroscopy (DRIFT). 

Materials are heated directly by infrared irradiation. Infrared lamps as well as hot rods and plates with efficient emission performance can be used as infrared sources. When wet materials are heated in the constant drying rate period by infrared radiation, the surface temperature increases to a temperature higher than the wet bulb temperature and the drying rate is enhanced. However, the drying operation must be... 

Vacuum band dryers are suitable for all types of pastelike materials. Wet material is dried as it is transported on a moving band. Fleat is supplied by infrared low-temperature radiators or by contact with heated bands. A multiband vacuum dryer is shown in Figure 33.15. To allow continuous production, such dryers are equipped with an automatic discharge system that prevents dehermetization of the dryer chamber. Drying chambers that provide drying surface areas up to 120 m are available commercially. 

To accelerate the drying process, most modern laboratories make use of alternative drying techniques such as halogen lamps, microwaves and infrared radiators. Because of a possible thermal decomposition of the polymer or emulsifiers however the temperature of the sample must not be allowed to rise much above the temperature range specified above. Furthermore, the drying rate should not be too high since this may cause skin formation on the surface of the sample. If the skin bursts material can be lost from the sample tray. 

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