Process microanalysis

The powders of zeolites of various trademarks are used to produce petroleum-refining catalysts. In this connection, it is very important to have complete information concerning not only chemical composition and distribution of impurity elements, but also shape, surface, stmcture and sizes of particles. It allows a more detailed analysis of the physical-chemical characteristics of catalysts, affecting their activity at different stages of technological process. One prospective for solving these tasks is X-ray microanalysis with an electron probe (EPMA). 

The development of X-ray microanalysis in the TEM has been driven by the improvement in spatial resolution in comparison with EPMA. This arises because thin specimens are used, so less electron scatter occurs as the beam traverses the specimen, and also because of the higher electron energy in the TEM also reduces scatter. The disadvantage is that the specimen has to be prepared in the form of a thin foil, and the problems involved in this process have already been discussed. 

Microanalysis of the three PET-4,4 -SD copolymer yarns for sulfur yielded concentrations in agreement with the theoretical values. Since the 4,4 -SD comonomer was definitely incorporated into the three copolymer yarns, the absorption and luminescence characteristics of the copolymers point towards a co-absorption process between 4,4 -SD and PET rather than an electronic energy transfer process. 

In a combined elemental microanalysis (to determine the C, H, N and Cl contents of char), TGA, DSC, mid-infrared and NMR study of the char forming process in polychloroprene, CPMAS solid-state 13C NMR was used to probe for structural changes that occurred during the degradation steps [88]. The NMR study supplied both valuable extra detail and confirmatory and complementary information. It was observed that while the dehydrochlorination of polychlo-prene proceeded, there was loss of sp3-hybridised carbon and commensurate... 

Like polarography, voltammetry is a microanalysis technique, so only a small proportion of the solution is ever modified by the processes occurring at the electrode. 

Aurbach and co-workers performed a series of ex situ as well as in situ spectroscopic analyses on the surface of the working electrode upon which the cyclic voltammetry of electrolytes was carried out. On the basis of the functionalities detected in FT-IR, X-ray microanalysis, and nuclear magnetic resonance (NMR) studies, they were able to investigate the mechanisms involved in the reduction process of carbonate solvents and proposed that, upon reduction, these solvents mainly form lithium alkyl carbonates (RCOsLi), which are sensitive to various contaminants in the electrolyte system. For example, the presence of CO2 or trace moisture would cause the formation of Li2COs. This peculiar reduction product has been observed on all occasions when cyclic carbonates are present, and it seems to be independent of the nature of the working electrodes. A single electron mechanism has been shown for PC reduction in Scheme 1, while those of EC and linear carbonates are shown in Scheme 7. ... 

Sometimes elemental microanalysis results are given as percentages by mass. The process used to calculate the empirical formula from the percentage by mass is similar to that just shown, assuming the total mass of the sample to be 100 g. 

In this book, we have highlighted the unique contributions of electron microscopy, microanalysis and ED to our understanding of catalysis and the rational design of advanced catalysts at the nano-scale and processes. EM methods, including in... 

It is therefore frequently difficult to find punctual areas in the sample having a sufficient concentration of the desired analyte to be detected by the x-ray microanalysis system. Thus, identification and eventually quantitation of metals in dec-orative/protective layers of pictorial samples by SEM/EDX frequently require an accurate and often time-consuming scanning process. 

Infrared analyses are conducted on dispersive (scanning) and Fourier transform spectrometers. Non-dispersive industrial infrared analysers are also available. These are used to conduct specialised analyses on predetermined compounds (e.g. gases) and also for process control allowing continuous analysis on production lines. The use of Fourier transform has significantly enhanced the possibilities of conventional infrared by allowing spectral treatment and analysis of microsamples (infrared microanalysis). Although the near infrared does not contain any specific absorption that yields structural information on the compound studied, it is an important method for quantitative applications. One of the key factors in its present use is the sensitivity of the detectors. Use of the far infrared is still confined to the research laboratory. 

Some catalyst activation processes are extremely important this is the case for oxides used as catalysts and supports (AI2O3, SiC>2, TiC>2, ZrC>2, silica-aluminas), and zeolites. Extremely elaborate procedures are used. This concerns bulk, not supported systems, and is dealt with in Section A.2.1. The case ofSiC>2 mixed with active phases (e.g. in oxidation) has little relevance to the subject of the present section, as it seems that SiOj does not play the role of a real support, but rather that of a diluent or spacer. An electron microscopy study coupled with microanalysis on a typical oxidation catalyst (propene to acrolein) shows that only a small fraction of the active phases is attached to silica or is situated in its immediate proximity [69]. There are not many cases... 

Energy-dispersive analysis of X-rays was the chosen analytical method because of its sensitivity to elements heavier than sodium, its capability of mapping elemental distribution, and its capacity for combination with a scanning electron microscope. EDS microanalysis has been reported to be suitable for the determination of mordant treatments on historical fibers (8-10) and has been used to characterize metal wrappings of combination yarns (11-13). EDS microanalysis has also been used to determine the composition of pseudomorphs and fibers in the process of mineral replacement (13, 14, 15). 

The Brownian motion of microdroplets is vigorous in solution. The volume of a micrometre-sized droplet is 10 - 10 dm. Therefore, a manipulation technique is indispensable for single microdroplet measurements. For the microanalysis of a single microdroplet, size of the probe should be smaller than that of the microdroplet. A light beam and a microelectrode are frequently used as a probe, and the analyses of small domains are performed by absorption/fluorescence microspectroscopy [24—29] and mi-croelectrochemical methods [17,30-32], In this section, single microdroplet techniques for the kinetic analysis of physical and chemical processes across a microdroplet/solution interface are described. 

K. Nakatani, T. Sekine and T. Negishi, Microanalysis of Mass Transfer Processes on a Single Particle in Encyclopedia of Surface and Colloid Science, Vol. 3, Ed. A. Hubbard, Marcel Dekker, New York, 2002, p. 3391. 

Environmental monitoring has also taken advantage of acoustic levitation for the investigation of physico-chemical processes relevant to the troposphere — mainly at temperatures below 0°C. Gas-liquid transfer of H2O2 from the gas phase to the levitated droplet was studied from in situ chemiluminescence measurements. Also, freezing of stably positioned droplets was observed by means of a microscope and a video camera, and the usefulness of this technique for simulation and investigation of cloud processes thus demonstrated. Ex situ microanalysis of sub-microlitre droplets by the use of an optical fibre luminometer also proved an effective means for investigating important physicochemical processes at the micro scale [100]. 

---