Temperature consumer preference studies

Routine measurements of d-d spectra are performed on solutions. If a suitable solvent cannot be found for a solid sample, a diffuse reflectance spectrum of a powdered sample can be taken. This is actually an absorption spectrum of the surface layers of the sample and is subject to a number of anomalies and artefacts. It is much better to study microscopic single crystals, preferably at low temperatures. Large crystals (if they can be grown) tend to absorb too strongly around band maxima small, thin (c. 0.01mm) plates are best. It is usually necessary to condense the incident beam by means of a lens in order to obtain detectable intensities of transmitted radiation. Thus the technique is more difficult and time-consuming than the familiar, routine solution measurement but it can provide much more information. 

In order to study pure rates of desorption, temperature scanning rates in a TS-PF-SSR should be coordinated with flow rates so that a predetermined maximum change in concentration in the fluid phase is not exceeded. This is necessary to limit the extent of back-reaction and thereby determine the rate of the desorption reaction in isolation. The preferred procedure to do this is to vary flow rate during a constant-rate temperature ramping so that the sweeping stream does not exceed a preset concentration. Interpretation of data is based on the amount of material released/consumed by the solid per unit of time during the ramp (see Chapter 5). 

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