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Photoacoustic powder

Porous materials, such as silica and alumina, have thermal diffusion lengths of approximately 10 m, which is much less than the typical thickness of pressed discs. The small thermal diffusion length gives photoacoustic spectroscopy a larger dynamic range than transmission methods when applied to powdered samples. An additional advantage is the ease of sample preparation, since photoacoustic spectroscopy uses powdered samples with no special preparation required. [Pg.450]

Transmission spectroscopy offers two significant advantages over photoacoustic spectroscopy of powders. First, transmission spectroscopy is not susceotible to external acoustic disturbances. Commercial spectrometers must be modified for vibrational isolation in order to obtain good photoacoustic spectra. Secondly, transmission spectroscopy can use solid state detectors with very fast response times, whereas photoacoustic spectroscopy is much slower, with spectra taking a few minutes to collect as compared to a few seconds for transmission spectra when both are taken with an FTIR. [Pg.450]

Figure 4. Photoacoustic signal measured in a sample liquid with an attached piezoelectric transducer having a resonant frequency of several tens of thousands of kilohertz. Note the change in scale of the amplitude and thus the much greater sensitivity of the detector at low light chopping frequencies. Argon ion laser light source, 400 mW, x = 488 nm sample 25 pg/mL BaSO powder suspended in aqueous glycerine. Reproduced with permission from Ref. 21 copyright 1980, American Chemical Society. Figure 4. Photoacoustic signal measured in a sample liquid with an attached piezoelectric transducer having a resonant frequency of several tens of thousands of kilohertz. Note the change in scale of the amplitude and thus the much greater sensitivity of the detector at low light chopping frequencies. Argon ion laser light source, 400 mW, x = 488 nm sample 25 pg/mL BaSO powder suspended in aqueous glycerine. Reproduced with permission from Ref. 21 copyright 1980, American Chemical Society.
Special attention should be given to the photoacoustic signal generation in powders. Due to interstitial gas flow in and out of powders, an important increase of the signal is seen when going from a homogeneous bulk form to that of a crushed powder. [Pg.498]

Although this artefact is extremely welcome to scientists, working on powdered substrates, it inevitably has its effects on the quantitative aspect of photoacoustic measurements. This is probably the main disadvantage of photoacoustic spectroscopy of powders. [Pg.498]

Therefore, we would suggest that photoacoustic spectroscopy on powders should only be used quantitatively, if materials of the same chemical composition and the same physical characteristics are compared. [Pg.498]

Iwasaki, T. Oda, S. Kamada, H. Honda, K. Study of photochemical reaction of sensitizing dyes adsorbed on semiconductor powder by means of photoacoustic spectroscopy, J. Phys. Chem. 1980, 84, 1060. [Pg.346]

Near-IR spectroscopy proved valuable for the analysis of pharmaceutical powders in a 1981 paper by Becconsall et al. [73]. Near-IR and UV photoacoustic spectroscopy were used for determination of propranolol (PR)/magnesium carbonate mixtures. Spectra were collected from 1300 to 2600 nm with carbon black as the reference. An aromatic C-H combination band at 2200 nm and an overtone band at 1720 nm were used to quantify PR. In this case, the UV data were nonlinear, while the NIR method provided a linear calibration. [Pg.93]

Near-IR photoacoustic spectra have been reported for talc and other minerals [38]. Samples were passed through a 240-mesh (64jim) sieve, and were ground first if necessary. The powder was oven-dried overnight at 105°C prior to analysis. Bands were observed at 1.4S (O-H band), 2.14, 2.18, 2.27, 2.36, 2.43, and 2.S0 /tm. The UV-visible photoacoustic spectrum was featureless. [Pg.539]

The measurement of very small absorption coefficients (down to lO-5 cm-1) of optical materials has been carried out by laser calorimetry. In this method, the temperature difference between a sample illuminated with a laser beam and a reference sample is measured and converted into an absorption coefficient at the laser energy by calibration [13]. Photoacoustic spectroscopy, where the thermal elastic waves generated in a gas-filled cell by the radiation absorbed by the sample are detected by a microphone, has also been performed at LHeT [34]. Photoacoustic detection using a laser source allows the detection of very small absorption coefficients [14]. Photoacoustic spectroscopy is also used at smaller absorption sensitivity with commercial FTSs for the study of powdered or opaque samples. Calorimetric absorption spectroscopy (CAS) has also been used at LHeT and at mK temperatures in measurement using a tunable monochromatic source. In this method, the temperature rise of the sample due to the non-radiative relaxation of the excited state after photon absorption by a specific transition is measured by a thermometer in good thermal contact with the sample [34,36]. [Pg.103]

Certain aspects of the photoacoustic effect suggest that this technique might be generally applicable to all chiral solids regardless of crystal class, size or perfection, or strength of absorption. Although subsequent theoretical developments and experimental results have caused us to limit considerably the predicted scope of this method, nevertheless, it is possible now to say clearly that the experiment does work and offers prospects for unique results. In this paper we review briefly the nature of the theory and practice of condensed phase photoacoustic spectroscopy and its extension to the measurement of natural circular dichroism, and present initial results for single crystals and powders. [Pg.376]

The photoacoustic detection of natural circular dichroism has been demonstrated successfully. Preliminary results at several fixed wavelengths on a limited number of samples show qualitative agreement with corresponding transmission data. In spite of the small signal levels involved, reproducibility is good. It appears that powders suffer scattering depolarization effects, which also occur with diffuse transmission measurements. [Pg.394]

PAS has been found to be an ideal technique for the study of surfaces and adsorbed species. In studies of optically thin samples, pulsed laser excitation has been shown to enable sensitivities of 10 to be obtained. The degree of chemical modiflcation of silica gel surfaces has been monitored by PAS. A linear relationship between the photoacoustic signal and the amount of carbon or nitrogen adsorbed on the surface was found. PAS has also been used to study the photoinduced transient formed when eosine Y was adsorbed onto ZnO powder, and the thin oxide layers (<4nm thick) on a copper electrode. An investigation of layered samples has shown that PAS may be capable of depth discrimination. ... [Pg.22]

Surface moisture is a problem of concern in ceramic powders, and IR has been used to characterize the surface groups of -OH and -H [58,63,64]. IR was also applied to characterize chemically bound hydrogen in chemical vapor-deposited silicon nitride at various ammonia-silane ratios [65]. Surface silicon dioxide on SiC powders was determined by photoacoustic IR and diffuse reflectance IR spectroscopy [66,67]. IR spectroscopy was also used to study the surface oxidation of SiC and SisN4 [68,69]. [Pg.144]

Figure 4. The photoacoustic infrared spectra of (A) a cotton yarn (B) a cotton yarn sized with a polyurethane (C) the corresponding powder from the sized yarn. Figure 4. The photoacoustic infrared spectra of (A) a cotton yarn (B) a cotton yarn sized with a polyurethane (C) the corresponding powder from the sized yarn.
For the investigation of the kinetics and thermodynamics of intermediate phases of rare earth oxides and photochemical reactions of the surface of rare earth oxides [52], it is reported that photoacoustic spectroscopy (PAS) technique is effective enough. Some information on the lattice structure of powder grains can be attained from the spectra. Raman and resonance Raman spectroscopy were also investigated on rare earth oxides of EU2O3, Dy203, and Tm203 [53]. [Pg.271]

The basics of photoacoustic spectroscopy (PAS) are described in Chapter 5. PAS is useful for examining highly absorbing samples that are difficult to analyze by other IR techniques. Minor or even no sample preparation is required here. The size and shape of the sample are not critical. PA spectra can be obtained from a wide variety of samples such as powders, polymer pellets, viscous glues, single crystals, and single fibres. [Pg.97]

Rettelbach T, Sauberlich J, Korder S, Fricke J (1995) Thermal conductivity of silica aerogel powders at temperatures from 10 to 275K. J Non-Cryst Solids 186 278-284 Shen Q, Toyoda T (2003) Dependence of thermal conductivity of porous silicon on porosity characterized by photoacoustic technique. Rev Sci Instr 74 601-603 Shinoda H, Nakajima T, Ueno K, Koshida N (1999) Thermally induced ultrasonic emission from porous silicon. Nature 400 853-855... [Pg.862]

J. K. BecconsaU, J. Percy, and R. E Reid, Quantitative Photoacoustic Spectroscopy of Propranolol/Magnesium Carbonate Powder Mixtures in the Ultraviolet and the Near-Infrared Regions, Anal. Chem., 53, 2037 (1981). [Pg.95]

The attenuated reflectance technique presents an excellent example of how radiation at sample surface can enhance signal-to-noise ratio. Details of general optics and reflectance techniques can be found in the classic text (10). This technique is used extensively to determine differences between the structure of polymers in surface and bulk phases. Commercial accessories make these spectroscopic experiments easy to perform, although quantitative analysis of the data remains difficult. Examples of ATR applications include chemical composition analysis of polymers, surface orientation resulting from various processing methods, and chemical or thermal degradation of polymers. For samples such as powders or poorly defined surfaces, the diffuse reflectance technique can be used (11). In addition, the photoacoustic technique has been used to probe surface structure and multilayer structure commonly found in polymer laminates (17). In all these cases, optical effects can complicate analysis of infrared spectra. Nevertheless, these data have proven very useful in analytical applications. [Pg.8813]


See other pages where Photoacoustic powder is mentioned: [Pg.198]    [Pg.115]    [Pg.13]    [Pg.264]    [Pg.240]    [Pg.198]    [Pg.78]    [Pg.53]    [Pg.54]    [Pg.55]    [Pg.81]    [Pg.313]    [Pg.113]    [Pg.6047]    [Pg.135]    [Pg.219]    [Pg.223]    [Pg.226]    [Pg.553]    [Pg.179]    [Pg.3719]    [Pg.4446]    [Pg.4701]    [Pg.4702]    [Pg.128]   


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