Transmissivity, infrared drying

Transmission infrared spectroscopy is an important tool in catalyst preparation to study the decomposition of infrared-active catalyst precursors as a result of drying, calcination or reduction procedures. In particular, if catalysts are prepared from organometallic precursors, infrared spectroscopy is the indicated technique for investigation [26]. 

The first application of transmission infrared spectroscopy to the study of adsorbed species appears to be the work of Buswell et at in 1938 (5). Those authors pressed a montmorillonite clay into a disc which was then "dried" at various temperatures. The spectra they obtained bear a remarkable similarity to many others that have been produced in the literature over the next forty years the authors were clearly able to resolve bands due to hydroxyl groups associated with the clay lattice and to adsorbed water which was slowly removed as a function of drying. 

There are three general methods used for examining solid samples in transmission infrared spectroscopy i.e. alkali halide discs, mulls and films. The choice of method depends very much on the nature of the sample to be examined. The use of alkali halide discs involves mixing a solid sample with a dry alkali halide powder. The mixture is usually ground with an agate mortar and pestle and... 

Transmission infrared (isotropic) spectra were recorded for both the AnC6SH and AnC7SH molecules both produced equivalent spectra. Monolayer modified gold slide electrodes were removed from solution, rinsed with ethanol, and dried with N2 gas before RAIR spectra were recorded. RAIR spectra were collected for AnC6SH/Au and AnC7SH/Au and compared to the AnC6SH isotropic spectrum. Figure 1. Virtually all vibrations present in the RAIR spectra are observed in the... 

If more traditional spectra are required, the usual approach is to press a thin film of the samples using a temperature which is above the Tg or T j and to record a transmission spectrum. A transmission infrared spectrum of polypropylene produced from a film pressed at 170 °C is shown in Figure 7. Another technique that can be used to obtain transmission spectra is to dissolve the sample up using a suitable solvent and to cast a film. Care has to be taken to remove all of the solvent by drying in an oven otherwise it can influence the data obtained. A transmission infrared spectrum of PVC produced from a film cast from a solution in THF is shown in Figure 8. 

Water Transport. Two methods of measuring water-vapor transmission rates (WVTR) ate commonly used. The newer method uses a Permatran-W (Modem Controls, Inc.). In this method a film sample is clamped over a saturated salt solution, which generates the desired humidity. Dry air sweeps past the other side of the film and past an infrared detector, which measures the water concentration in the gas. For a caUbrated flow rate of air, the rate of water addition can be calculated from the observed concentration in the sweep gas. From the steady-state rate, the WVTR can be calculated. In principle, the diffusion coefficient could be deterrnined by the method outlined in the previous section. However, only the steady-state region of the response is serviceable. Many different salt solutions can be used to make measurements at selected humidity differences however, in practice,... 

Figure 20-29 Fourier transform infrared spectrum of polystyrene film. The Fourier transform of the background interferogram gives a spectrum determined by the source intensity, beamsplitter efficiency, detector response, and absorption by traces of H20 and C02 in the atmosphere. The sample compartment is purged with dry N2 to reduce the levels of H20 and C02. The transform of the sample interferogram is a measure of all the instrumental factors, plus absorption by the sample. The transmission spectrum is obtained by dividing the sample transform by the background transform.

The STG was cast from alx 10 3 M solution into which the mirror had been immersed for from 10 to 20 min (see Appendix 1). The presence of a monolayer was confirmed by ellipsometry (18 A). The spectral data agreed with data gathered on a similar system in a powder form. In this case, CuzO powder was immersed in a 0.01 M solution of isooctyl thioglycolate (OTG) in isopropanol for from 1 to 10 min, washed with pure isopropanol, dried in air, and analyzed via infrared transmission in a KBr dispersion pellet (see Appendix 2). A similar spectral shift of approximately 15 cm 1 (1739— 1724 cm-1) was observed and the lack of two distinct carbonyl absorbances suggested the formation of a monolayer. In both cases, the formation of a copper-mercaptoester salt may be responsible... 

Each oxide powder was washed copiously with pure isopropanol, dispersed in a KBr pellet, and analyzed via infrared transmission for organic contaminants and to obtain reference spectra of the blank oxides. The washed powders were then air-dried and placed aside in a desiccator. Next, 500 ml of 0.01 M solution of isooctyl thioglycolate (OTG) in isopropanol was prepared and 15 ml glass vials were then filled with approximately 0.50 g of each powder. This was followed by the addition of about 10 ml of the OTG solution to each vial. The vials were then seated and agitated for about 10 min. This... 

Crystalline Phosphate Studies. On the basis of the results with triethyl phosphate, a series of calcium phosphates was examined by infrared spectrophotometry. Pertinent properties of these materials are summarized in Table II, and their spectral characteristics are shown in Table III. None of the synthetic hydroxyapatites [Caio(P04)e(OH)2] had the stoichiometric Ca/P ratio of 1.667, although they showed the apatite lattice structure. A typical infrared transmission spectrum (between 1500 and 700 cm.-1) of a dry powder synthetic hydroxyapatite is shown in Figure 1. 

Vibrational spectroscopy is the method of choice for the characterizing functional groups in complex organic molecules. Infrared transmission spectroscopy has been used on dried humics pressed into KBr pellets to determine the relative carboxylate content of humic materials (14-16). However, interferences arise from the presence of water bands and possible alterations of the samples under the high pressures used to form the pellets. Diffuse-reflectance techniques can avoid some of the difficulties associated with the KBr pressed-pellet method (9,17-18). To obtain a spectrum analogous to an absorption spectrum, the data are transformed from reflectance units to Kebulka-Munk (K-M) units. However, K-M units are related to... 

Detailed experimental procedures for obtaining infrared spectra on humic and fulvic acids have been reported previously 9,22,25-26) and will be briefly described here. Infrared spectra were taken on the size-fractionated samples by using a Fourier transform infrared spectrometer (Mattson, Polaris) with a cooled Hg/Cd/Te detector. Dried humic and fulvic materials were studied by diffuse reflectance infrared spectroscopy (Spectra Tech DRIFT accessory) and reported in K-M units, as well as by transmission absorbance in a KBr pellet. Infrared absorption spectra were obtained directly on the aqueous size-fractioned concentrates with CIR (Spectra Tech CIRCLE accessory). Raman spectra were taken by using an argon ion laser (Spectra-Physics Model 2025-05), a triple-grating monochromator (Spex Triplemate Model 1877), and a photodiode array detector system (Princeton Applied Research Model 1420). All Raman and infrared spectra were taken at 2 cm resolution. 

Acid Form of Nafion. The infrared spectrum of the acid form of Nafion is distinct from the spectra of its salts. Figure 3 shows the transmission spectrum of Nafion 142 in the acid form at three water contents. It has been noted by Lopez et al. (1) and by Heitner-Wirguin (2) that Nafion membranes in the acid form absorb almost completely below 3700 cm"1. As Figure 3 shows, this is true only at high water contents. Dry or nearly dry membranes yield spectra characteristic of the acid group -SO3H. 

Plasticizers are attached to the polymer by weak physical bonds rather than chemical ones, so can be separated readily by solvent extraction. A suitable solvent should selectively dissolve the plasticizer from the polymer. Methanol is frequently employed. Excess methanol should be dried off at 105°C. Infrared spectroscopy can be used to identify plasticizers by smearing the sample on one side of a KBr tablet and running a transmission spectrum or by examining the neat extract by ATR-FTIR spectroscopy. The resulting spectra can be compared with those in a specialized database of additives (Scholl, 1981). 

A Fourier-transform infrared (FT-IR) spectrometer in transmission mode under dry nitrogen flow (10 cubic centimeters per minute, cepm) was used to test the physicochemical interactions between PPy and Fc203 nanoparticles. The dried PPy powder was mixed with powdered KBr, ground and compressed into a pellet. Its spectrum was recorded as a reference for comparison with that of the Fe203/PPy nanocomposites. 

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