Static Characterisation Techniques

A variety of other static characterisation methods have been described in this chapter which are not listed in Table 4.2. Many of these are new and in a state of rapid evolution, as for example those involving NMR and radiation scattering. Whilst appropriate for research investigations they do not seem yet to be appropriate as a means of general characterisation. However with the rapid progress under way in these areas, some of these techniques we feel may in the future be ideally suited to membrane characterisation. 

Characterisation of Pyrogenic Aggregates with Static Scattering Techniques... 

Static secondary ion mass spectroscopy (SSIMS) is another surface selective technique for surface characterisation [262, 263, 264]. The information obtained from SSIMS is complementary to XPS because SSIMS can differentiate those polymers that give very similar XPS spectra. Moreover, it offers more surface selectivity than XPS. The typical sampling depth of SSIMS is approximately 1 nm. This method has sensitivity, sufficient to detect amounts less than a monomolecular layer, particularly when a high resolution time-of-flight (ToF) mass analyser is used [265]. 

The problem with sulfide catalysts (hydrotreatment) is to determine the active centres, which represent only part of their total surface area. Chemisorption of O2, CO and NO is used, and some attempts concern NIL, pyridine and thiophene. Static volumetric methods or dynamic methods (pulse or frontal mode) may be used, but the techniques do not seem yet reliable, due to the possible modification (oxidation) of the surface or subsurface regions by O2 or NO probe molecules or the kinetics of adsorption. CO might be more promising. Infrared spectroscopy, especially FTIR seems necessary to characterise co-ordinativcly unsaturated sites, which are essential for catalytic activity. CO and NO can also be used to identify the chemical nature of sites (sulfided, partially reduced or reduced sites). For such... 

The local structure around zinc and manganese atoms in as-synthesised sample of MnZnAPO-34 was also characterised by means of EXAFS. This technique provides a description of the short-range order of selected atomic species in terms of the number of neighbours, distances, and thermal and static disorder within a range of those distances. 

The techniques given in Table 4.2 are well established and have been sub-divided into those which are described as either static or dynamic. We feel this distinction is of particular importance in the characterisation of the porous structure of membranes. Here the performance is determined by the complex link between the structural texture and transport behaviour. An insight into this complexity is frequently provided by dynamic techniques, which are not restricted by the limited quantity of membrane material and are sensitive to the active pathways through the porous structure. Further developments are required in this area both in the improvement of existing techniques and introduction of new techniques. Progress will also come from advances in the theory and modelling of flow behaviour in such porous media, which involve percolation theory and fractal geometry for example. With the refinement of such... 

Berry, G. C. Cotts, P. M. (1999) Static and dynamic light scattering, in Pethrick, R. A. Dawkins, J. V. (Eds.) Modem Techniques for Polymer Characterisation, Chichester John Wiley and Sons. 

Characterisation of foams employs one of two techniques, either static or dynamic. In the static method, a foam is generated by sparging a gas into a liquid under controlled conditions and then stopped. The decay of the foam level is then monitored against time. The half-life of the foam is termed the foam lifetime. The dynamic method generates the foam continuously under standard conditions and the equilibrium volume measured. With care, a linear relationship between foam volume and gas velocity can be determined. The gradient of this linear response is the foam lifetime. It is not surprising that foam lifetime and viscosity show an identical dependence on temperature. 

Because these samplers physically disturb the natural state of the marine microlayer, in vitro results obtained from collected samples could not be proven to represent films in their natural state. Despite this limitation, these studies resulted in characterisation of quasi-static film elasticities and led to parameterisations that adequately define bounds within which the marine microlayer typically ranges. By setting such bounds, these works provided constraints for laboratory experiments (e.g., Hirsa et al. 1995, McKenna 1997, Saylor 1997). At the same time, techniques for making short wave measurements in situ were developed by independent researchers (Hwang 1989, Bock and Hara 1995), and others have followed (Zhang 1995, Suoja2000). 

Two different types of guest-induced flexibilities exist in MOF host lattices. The first can be considered as essentially static in nature, involving bulk framework deformations that may be readily characterised using diffraction-based techniques and which are frequently observable at the macroscale through changes in crystal dimensions. The second are dynamic and arise due to molecular vibrations or local guest-induced framework deformations away from the parent structure. The latter are not so readily detectable by diffraction methods and... 

An additional more complex type of static magnetic interaction is experienced by nuclei which have a spin quantum number greater than one half. Far from ruling out the studies of such species, application of quadrupolar techniques has added a new dimension to the characterisation of polymers. This is because the quadrupolar interaction is remarkably sensitive to order, orientation and local motion. With the necessary synthetic skills quadrupolar atoms such as deuterium can be inserted into a polymer at a chosen segmental site and can then be persuaded to report on their surroundings. The spectrometer is tuned to the specific nuclear frequency and the data are collected without unwanted responses from the rest of the sample. It is only the need for labelling that has restricted the more routine use of deuterium NMR for the study of polymers. Despite this, it has developed into an uniquely powerful research tool. 

The particle concentration of the eluent is normally measured by means of infrared or ultraviolet photometers. Additionally, fluorescence photometer, interferometric measurements (for the refractive index), or mass-spectroscopic methods (e.g. induced coupled plasma mass spectroscopy—ICP-MS, Plathe et al. 2010) are employed. The combination of different detection systems offers an opportunity for a detailed characterisation of multi-component particle systems. Note that the classification by FFF is not ideal and the relevant material properties are not always known moreover, the calibration of FFF is rather difficult. The attribution of particle size to residence time, thus, bears some degree of uncertainty. Recent developments of FFF instrumentation, therefore, include a particle-sizing technique additional to the flow channel and the quantity measurement (usually static and dynamic light scattering, Wyatt 1998 Cho and Hackley 2010). 

Static and dynamic scattering techniques are spectroscopic characterisation methods in the sense of Sect. 2.2. These techniques evaluate the functional dependency of measurement signals on a spectral parameter, i.e. on time, space, or classically on wavelength or frequency. The major advantage of spectroscopic methods is the reduced sample preparation (no fractionation), but they involve the inversion problem. That is, the spectrum is a—most frequently incomplete and discrete— nonlinear projection of the size distribution. Beside the scattering techniques, there are further spectroscopic methods which are based on the extinction of radiation or on any other response of the particle system to an external field. This section describes optical, acoustic, and electroacoustic methods that have gained relevance for the characterisation of colloidal suspensions. 

Some aspects related to catalysts characteristic and behaviour will be treated such as determination of metal surface area and dispersion, spillover effect and synterisation. A detailed description of the available techniques will follow, taking in consideration some aspects of the gas-solid interactions mechanisms (associative/dissociative adsorption, acid-base interactions, etc.). Every technique will be treated starting from a general description of the related sample pretreatment, due to the fundamental importance of this step prior to catalysts characterisation. The analytical theories will be described in relation to static and dynamic chemisorption, thermal programmed desorption and reduction/oxidation reactions. Part of the paper will be dedicated to the presentation of the experimental aspects of chemisorption, desorption and surface reaction techniques, and the relevant calculation models to evaluate metal surface area and dispersion, energy distribution of active sites, activation energy and heat of adsorption. 

The combination of the described techniques and the integration of the experimental results produce a detailed picture of the investigated catalyst, allowing a better comprehension of the reaction mechanisms in complicated processes and a detailed characterisation of catalyst activity and selectivity. Most of the experimental results shown in the present paper have been obtained in the application lab of CE Instruments (ThermoQuest S.p.A.), Milan - Italy. All the graphs related to static volumetric chemisorption have been obtained by the adsorption apparatus Sorptomatic 1990, while the graphs related to TPD, TPR/0 and pulse chemisorption analyses with the dynamic apparatus TPDRO 1100. 

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