Spectroscopy acoustic

On-line particle sizing by ultrasonic (acoustic attenuation) spectroscopy was developed for use during batch crystallization processes.14 Crystallization of the alpha polymorph of (l) -glutamic acid from aqueous solution was monitored by continuously pumping the crystallizing solution through an on-line ultrasonic spectrometer. The method enabled measurement of the crystal size distribution and solid concentration throughout the 

Ultrasonic spectroscopy has been utilized for real-time measurements of polymerization reactions and polymer melt extrusion.15,16 In these applications the time required for the ultrasonic waves to propagate through the sample to a transducer was measured. The velocity of the sound wave in the medium is related to the modulus and density of the sample matrix. 

The ring-opening metathesis polymerization of dicyclopentadiene was monitored by ultrasonic spectroscopy.16 The thermoset poly(dicyclopentadiene) is formed by ringopening and cross-linking in a reaction injection molding system. A reaction cell with a plastic window was constructed for use with pulse echo ultrasonic spectroscopy. Realtime measurements of density, longitudinal velocity, acoustic modulus and attenuation were monitored. Reaction kinetics were successfully determined and monitored using this technique. 

Besides measuring the attenuation of acoustic waves, another type of acoustic spectroscopy has been demonstrated to be able to size particles in the rang from 0.1 to 30 pm. In this technique, the transit time (hence, the velocity) of pulsed multiple frequency ultrasonic waves passing through a concentrated suspension (up to 10 v%) is measured. The frequencies applied (50 kHz- 50 MHz) in this technique are lower than those in the attenuation measurement so that a longer operational distance between the ultrasonic source and detector can be used [37]. The zeta potential of the particles in suspension can also be determined using an acoustic instrument if additional devices are used to measure the colloid vibration potential in the acoustic field. 

Electroacousitc Spectral Analysis - Zeta Potential Determination and Sizing (0.1-100 pm) 

Piezoelectric and magnetostrictive transducers have been the conventional method of generating and detecting ultrasonic waves. However, it is also possible to generate sound by nonlinear electro-strictive coupling via the intense electromagnetic excitation of a laser beam, an effect known as stimulated Brillouin scattering. 

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Acoustic emission tests Acoustic insulation Acoustic measurements Acoustic microscopy Acoustic spectroscopy Acoustic waves... 

The attenuation of ultrasound (acoustic spectroscopy) or high frequency electrical current (dielectric spectroscopy) as it passes through a suspension is different for weU-dispersed individual particles than for floes of those particles because the floes adsorb energy by breakup and reformation as pressure or electrical waves josde them. The degree of attenuation varies with frequency in a manner related to floe breakup and reformation rate constants, which depend on the strength of the interparticle attraction, size, and density (inertia) of the particles, and viscosity of the Hquid. 

Opto-Acoustic Spectroscopy Applied to the Detection of Gaseous Pollutants... 

POLLUTION DETECTION WITH OPTO-ACOUSTIC SPECTROSCOPY... 

Conventional analytical techniques generally operate at the part per million or higher levels. Some techniques such as laser photo acoustic spectroscopy are capable of measuring phenomena at the 10-8-10-6 mol/L level. The most sensitive conventional analytical techniques, time-resolved laser-induced fluorescence, and ICP-MS are capable of measuring concentrations at the part per trillion level, that is, 1 part in 1012, but rarely does one see detection sensitivities at the single atom level as routinely found in some radioanalytical techniques. While techniques such as ICP-MS are replacing the use of neutron activation analysis in the routine measurement of part per billion concentrations, there can be no doubt about the unique sensitivity associated with radioanalytical methods. 

Additional processes that can be monitored using spectroscopic tools of PAC are crystallization and distillation. Crystallization is an important step in manufacture of many products including APIs. Tracking the process and production of material is more valuable than testing a final product to verify that the correct crystal structure has been attained. The use of acoustic spectroscopy 4 and NIR spectroscopy48 in industrial crystallization processes has been demonstrated and will be implemented more widely. Monitoring distillation processes, such as for solvent recovery, is another growing area of use of PAC. 

Alba, F. Crawley, G.M. Fatkin, J. Higgs, D.M.J. Kippax, P.G., Acoustic spectroscopy as a technique for the particle sizing of high concentration colloids, emulsions and suspensions Colloids and Surfaces A Physiochem. Eng. Asp. 1999, 15, 495-502. 

Photo-acoustic spectroscopy (PAS) is a kind of infrared (IR) spectroscopy which is a popular choice for real-time monitoring of VOCs at ppbv levels. Recently there has been a great revival of interest in PAS because it offers much greater sensitivity than conventional spectroscopic techniques. All spectroscopic methods yield quantitative and qualitative information by measuring the amount of light a substance absorbs PAS simply measures this in a more sensitive way. 

INNOVA Air Tech. (1997) Photo-acoustic Spectroscopy Booklet, INNOVA Air Tech., Denmark. 

IR Infra-Red Spectroscopy, including FTIR Fourier Transform IR PAS-IR IR Photo Acoustic Spectroscopy RS Raman Spectroscopy... 

A.S. Dukhin, P.J. Goetz, Acoustic spectroscopy for concentrated polydisperse colloids with high density contrast, Langmuir 12 (1996) 4987-4998. 

The introduction of Fourier Transform Infrared Spectroscopy (FTIR) brought along a number of typical solid sample techniques. DRIFTS (Diffuse Reflectance Fourier Transform Infrared Spectroscopy) is probably most commonly known. Another technique, developed specifically for measuring solid, opaque samples is PAS (Photo Acoustic Spectroscopy). This accessory is less known, probably due to its high cost and its rather difficult modus operandi. 

Dispersion technologies, USA (http //www. dispersion, com/) Felix Alba Associates (Scatterer.com) Scatterer Electro-acoustic spectroscopy Data interpretation software Particle sizing, zeta potential Particle size analysis No Yes... 

Matec (www.matec.com) Acoustisizer Electro-acoustic spectroscopy Particle sizing and zeta potential No Yes... 

Acoustic spectroscopy measures the speed and attenuation of sound waves interacting with a colloidal suspension. When a sound wave in the range of 1 to 100 MHz interacts with a colloidal suspension, the measured acoustic attenuation and... 

Acoustic spectroscopy has several characteristics that make it useful. One clear advantage over light-scattering techniques is the ability to stir, pump, or otherwise physically agitate the sample during analysis, making the technique well suited to potentiometric titration and analysis of unstable suspensions. When the acoustic signal is measured as a function of the transmitter-receiver gap, it requires no... 

There are several shortfalls in acoustic spectroscopy. Information about particle shape is lacking in the spectrum, and a substantial amount of physical and thermodynamic information may be needed to interpret acoustic spectra, including particle density, liquid density and viscosity, and the weight or volume fraction of the suspension.73 Such information may not always be available for complex environmental suspensions. Also, relatively large sample requirements may restrict the use of acoustics to idealized laboratory systems. 

Dukhin, A.S. and Goetz, P.J., Characterization of concentrated dispersions with several dispersed phases by means of acoustic spectroscopy, Langmuir, 16, 7597, 2000. 

The attenuation and velocity of acoustic energy in polymers are very different from those in other materials due to their unique viscoelastic properties. The use of ultrasonic techniques, such as acoustic spectroscopy, for the characterization of polymers has been demonstrated [47,48]. For AW devices, the propagation of an acoustic wave in a substrate causes an oscillating displacement of particles on the substrate surface. For a medium in intimate contact with the substrate, the horizontal component of this motion produces a shearing force. In such cases, there can be sufficient interaction between the acoustic wave and the adjacent medium to perturb the properties of the wave. For polymeric materials, attenuation and velocity of the acoustic wave will be affected by changes in the viscoelastic behavior of the polymer. 

The modified log-normal equation has been applied to particle size determination in acoustic spectroscopy using the Pen Kem 8000 Acoustophor [103]. The authors state that the unmodified equation overestimates the fraction of large particles and under-estimates the median size. They also state that the median size generated using the truncated log-normal distribution for fitting the acoustic spectrum is not the 50% size. 

Monitoring methods may be classified as direct scanning without subsequent spectral conversion or as additional methcxls such as measutements based upon fluorescence, photo-acoustic spectroscopy, spin resonance, and radioactivity measurements. 

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