Ultrasonic Attenuation Spectra Research Articles

Particle size distribution of two-phase medium measured by ultrasonic wave

Abstract Measurement of ultrasonic attenuation spectra of particle suspensions using a variable acoustic range approach is introduced. This study is based on the improved ECAH model. In this paper, an experimental test was performed on an emulsion with a concentration of 15%. Then, the NNLS algorithm is used for inversion calculations. Compared with laser particle size meter results, the measurement results are in good agreement.

Characterization of kaolinite aqueous suspensions by acoustophoresis: Influence of crystallinity and of the ratio between basal and lateral surface of grains

The electrokinetic properties of aqueous suspensions of two kaolins were studied using the acoustophoretic method by measuring the ultrasonic attenuation spectrum in a wide frequency range (1–20 MHz). Then, the zeta potential is calculated according to the size distribution of grains. A high state of crystallinity of the kaolinite platelets strongly influences the amplitude and the variation of zeta potential versus the pH due to a high density of hydroxyl surface groups. It was also shown that specific adsorption occurs mainly with the hydroxyl surface groups of the platelet edges by using strong electrolytes (NaOH and HCl) and also organic molecules (Tiron and sodium salt of citrate). The variation of the surface chemical properties of platelets during the amorphous phase formation after temperature treatment of kaolin powder is also studied. The electrokinetic properties of kaolin suspensions treated between 200 and 800 °C successively show an increase in the positive contribution to the zeta potential up to 400 °C for the best-crystallized kaolinite and a decrease in the density of surface hydroxyl groups when the sheets delaminate from 400 °C for the less-crystallized kaolinite. This study shows that the characterization in aqueous suspension of surface properties of kaolinite complements other studies carried out on powder and therefore it makes it possible to choose kaolin as a raw material according to the intended application.

Ultrasonic attenuation model of mixed particle three-phase system based on Monte Carlo method

From the perspective of calculating ultrasonic absorption and scattering properties of individual solid particle and droplet, the ultrasonic wave is treated as discrete phonons. And by tracking their motion process and event statistics, a new prediction model of ultrasonic attenuation of spherical mixed particles in gaseous medium is established with Monte Carlo method. Considering the difference in physical properties between solid particles and liquid particles, the ultrasonic absorption characteristics of the two kinds of particles are obviously different, and when dimensionless particle size <i>kR</i> ≤ 1, the backscattering of particles is uniform and dominant, then the ultrasonic scattering pressures gradually transit from the dominant position of backscattering to the trend of forward enhancement with the increase of dimensionless particle size. The numerical simulation results for the system with a single particle type are compared with those from various standard models such as classical ECAH model and McC model, showing that they are in good agreement. Similarly, the results are then compared with experimental results, which accord with each other in general. After calculating and verifying the ultrasonic attenuation of aluminum particles and submicron droplets respectively in air, the method is extended to the three-phase monodisperse and polydisperse mixed particle system composed of aluminum particles and liquid droplets. In the three-phase system of gas-liquid-solid mixed particles, the particle type has a significant influence on ultrasonic attenuation, and the attenuation contribution of different particles against mixing ratio does not follow the linear gradient with the increase of volume concentration. For a polydisperse system, the ultrasonic attenuation spectrum is greatly affected by the average particle size, but it is insensitive to the width of particle size distribution. The numerical results also show that both the particle type and particle distribution size should be carefully take into account in the polydisperse system. Moreover, the MCM model can be further extended to non-spherical particles and combined with mathematical inversion to form the theoretical basis for the measurement of mixed particle system.

Non-negative differential evolution for particle sizing from ultrasonic attenuation spectroscopy

Ultrasonic attenuation spectroscopy (UAS) is a potentially characterising technique for nano-meter size materials. It is the inversion of the ultrasonic attenuation spectrum to particle size distribution (PSD) by using an optimisation technique. Because the particle size is non-negative number, the inversion has to be optimised in the non-negative real number domain. However, many optimisation techniques have traditionally added the non-negative constrain into a cost function as a result the function becoming complex. In this article, the modification of the differential evolution (DE) technique has been proposed to narrow the searching solution domain bounded in the non-negative real number domain. An absolute function has been added to a mutant vector of the DE technique to guarantee the solution is non-negative real number. This technique is called DE-Nonneg technique. The technique has been demonstrated by characterising size of silica suspension. The optimisation results show that the PSD predictions are comparatively to simulated annealing (SA) technique. Moreover, the performance of DE-Nonneg could be improved via adjusting the parameters (expanding factor, cross over, number of parameters and mutation type) following the guideline addressed here. In addition, it is also possible to predict the PSD without using the structural PSD model. With this advantage, DE-Nonneg could possibly be applied for other non-negative optimisation problems.

Synchronous Acquisition and Analysis of Ultrasonic Spectral Information for the Characterization of Particle Size Distribution

Particle sizing methods have gained considerable attention in the past few decades, but there is still a big challenge in high concentration situations (i.e., volume fraction>10%). However, the ultrasonic spectroscopy technique is a common tool for the noninvasive determination of essential parameters for high concentration systems by analyzing ultrasonic spectra with inversion algorithms, including the particle size distribution (PSD), volume fraction of each phase, and physicochemical properties. For the ultrasonic measurements, proper acquisition and analysis of ultrasonic spectra are becoming significant in order to understand the relationship between the unknown parameters and the ultrasonic spectra. In the work, an experimental setup was provided to synchronously acquire ultrasonic reflection and transmission signals. A series of experiments were performed on silicon-water solutions at volume fractions 8%, 10%, and 12% to obtain the ultrasonic attenuation spectra and ultrasonic phase velocity spectra based on different measurement methods, i.e., the pulse-echo method, reference reflection method, and through-transmission method, respectively. Based on the Epstein-Carhart-Allegra-Hawley (ECAH) forward model, genetic algorithm (GA) and optimum regularization technique (ORT) algorithms were implemented to determine PSD with the measured spectra; the obtained PSD was then compared with the optical microscope method. It revealed that the spectra obtained by different measurement methods showed individual features while the obtained PSD was consistent and the volume median diameters were within a deviation of 10% with GA and ORT algorithms. The differences and characteristics of these three measurement methods for signal acquisition and interpretation were discussed and presented to provide an evaluation and recommendation for ultrasonic particle sizing.

Particle size distribution measurement based on ultrasonic attenuation spectra using burst superposed wave

Abstract In the characterization of particle size distribution (PSD) using ultrasonic attenuation method, the spectrum characteristics such as bandwidth or the number of frequencies is of great significance. To obtain desired attenuation spectra consisting of sufficient information, a direct digital synthesis (DDS) based excitation method has been proposed as burst superposed wave (BSW) featuring in ultrasonic frequencies to be freely defined and component waves’ energy to be artificially controlled. Corresponding experimental systems are designed, in which the traditional pulse wave (PW) and burst single frequency wave (BSFW) are implemented. A pair of broadband ultrasonic transducers with center frequency of 15 MHz is performed to obtain the attenuation spectra of three polystyrene material aqueous suspension (volume fraction 10%). The experimental results show that the traditional methods are unsatisfactory for the relatively large particles. Conversely, BSW can effectively broaden the scope of attenuation spectra and increase the number of frequencies. Afterwards, optimum regularization technique algorithm was used for inversion. The resultant comparisons suggest that the scope and the ultrasonic frequency number of measured attenuation spectra have exerted an obvious impact on the inversion and the BSW technology manifests obvious improvements from the accuracy and reliability of the inversion.

Evolution of spall-damage in iron caused by repeated plate impacts: Ultrasonic evaluation

This paper focuses on the developed of spall-damage that occurs in pure iron as a result of repeated impact. The employed low-frequency scanning acoustic microscopy (LF-SAM) observations combined with the measurements of ultrasonic wave velocity, attenuation, backscattering intensity and amplitude spectrum of the reflected wave, enabled us to provide a nondestructive evaluation. The spall-damage distribution was analyzed in the C-scan images, and we found the spall-damage increase with impact stress when the latter exceeds the characteristic spall-threshold stress. Moreover, we recorded the decreased sound velocity, amplitude ratio, and the increase of backscattering intensity, significant attenuation (the high frequency component of the reflected wave) for enhanced impact stress. It was also demonstrated that the tiny cracks generated in iron develop significantly during subsequent impacts either with lower or higher impact stress. Since the presented results concern for the first time the multiple-impact experiments, we contend that the applied ultrasonic investigations constitute the effective method of nondestructive spall-damage evaluation.

Determination of particle size of heavy oil in water dispersion system by ultrasonic attenuation method

The ultrasonic attenuation measurement was used to analyze the particle size of heavy oil in water dispersion system for the first time. The particle size and particle size distribution of the 70% dispersion system (Venezuela heavy oil/water) under different conditions were determined. The results show that the ultrasonic attenuation spectrum of the crude heavy oil and water at different frequencies is obviously different. The ultrasonic attenuation method was able to characterize the particle size and particle size distributions of heavy oil/water dispersion. The particle size distribution of the Venezuela heavy oil/water dispersion is uniform and the average particle size is about 100µm. Whereby 80% particle size of the system is between 60µm–178µm and only less than 10% of the particle size is more than 180µm or less than 55µm. Moreover, the measurement tendencies of ultrasonic attenuation method are consistent with the results of apparent viscosity. It indicates that the ultrasonic attenuation method can be regarded as an effective approach to determine particle size of heavy oil/water dispersion, which should have high value of application in the online detection in petroleum industry.

Chain dynamics of ethylene oxide oligomer melts. An ultrasonic spectroscopy study.

Between 0.2 and 2000 MHz, the ultrasonic attenuation spectra of oligomer melts have been measured at 25 °C. The oligomers comprise ethylene glycols with eight different mean degrees [Formula: see text]of polymerization (1 ≤ [Formula: see text] ≤ 13.2), a poly(propylene glycol) ([Formula: see text] = 16.9) and three poly(ethylene glycol) dimethyl ethers (3 ≤ [Formula: see text] ≤ 10.3). The complexity of the ultrasonic spectra increases with [Formula: see text]. The spectra have been analyzed assuming up to four discrete relaxation terms. The relaxation times of these terms are assigned to the first odd modes in the oligomer conformational dynamics and are discussed in the light of the Rouse spring-and-dashpot and the Tobolsky torsional oscillator models of chain variations. The relaxation amplitudes indicate that not only the shear viscosity but also the volume viscosity is involved in ultrasonic relaxation processes. Comparison of relaxation times and shear viscosities for the ethylene glycols with the corresponding data for dimethyl ethers and also n-alkanes reveals significant effects of association.

Broadband ultrasonic spectrometry of polystyrene-cyclohexane critical mixtures

Mutual diffusion coefficients, shear viscosities, and broadband ultrasonic attenuation spectra in the frequency range 100 kHz to 300 MHz have been measured for solutions of polystyrene in cyclohexane at two degrees of polymerization N and various temperatures near the critical. The exponent y(η) in the power law representation of the critical part in the viscosity deviates substantially from the universal value y(η) = 0.0435: y(η) = 0.028 (N = 288) and y(η) = 0.014 (N = 6242). Also, the adiabatic coupling constant g and the amplitudes ξ(0) and Γ(0) in the power laws of the correlation length and the relaxation rate of fluctuations, respectively, depend on N. This is especially obvious with the relaxation rates, for which Γ(0) = 5.8×10(9) at N = 288 and Γ(0) = 6.1×10(7) with the larger polymer results. A noteworthy feature is the difference between the relaxation rates from the diffusion coefficients and shear viscosities on the one hand and from the ultrasonic spectra on the other. Near the critical temperatures the latter Γ values deviate from power law behavior, indicating a coupling between the concentration fluctuations and structural isomerizations of the polymers.

Fluctuations Near the Critical Micelle Concentration. II. Ultrasonic Attenuation Spectra and Scaling

Based on a thermodynamic model of amphiphile solutions derived in the first part of the paper, the ultrasonic attenuation of such systems has been considered theoretically, including fluctuations of local concentrations and micelle sizes. At amphiphile concentrations smaller than the critical micelle concentration (cmc), scaling behavior in terms of the concentration distance to the cmc is predicted by theory, in fair agreement with experimental evidence. The scaling function in the sound attenuation below the cmc reveals the unsymmetric broadening in the spectra that clearly emerges from measurements when approaching the cmc. The shape of the scaling function corresponds to the experimental spectra of solutions with comparatively large cmc as well as with the relaxation spectral function of the unifying model of non-critical concentration fluctuations. Above the cmc, an additional relaxation term is predicted in correspondence with the Landau-Khalatnikov term in the sound attenuation of superfluid helium. This term is difficult to verify by measurements because, in the relevant frequency range, other processes may also contribute the ultrasonic attenuation spectra.

Measurement of SiC Particle Size Based on Ultrasonic Attenuation Spectrum

To compare the different effects under different excitation methods during the measurement on the particle size of silicon carbide (SiC), an experimental system has been established to get different signal excitations of burst wave, continuous wave and pulsed wave. Variable sound path method is adopted during the measurement to obtain the ultrasonic attenuation spectrum of SiC suspensions with two immersion transducers at four different mass concentrations under the same experimental condition. It is found that the ultrasonic attenuation coefficients excited by three different waves increase with increasing frequency and the tendency is approaching the same. The result calculated by a normalized spectrum of the optimal regularization methods shows that SiC particle size distribution under the three excitation methods is similar, which indicate that the different excitation methods on particle size characterization have almost no influence to result.

Does the Viscosity Exponent Derive from Ultrasonic Attenuation Spectra?

Based on a representation of the sound velocity of critical liquids in terms of a frequency-dependent complex specific heat at constant pressure, a simple relation between the low-frequency normalized sonic attenuation coefficient and the correlation length of fluctuations is derived. This relation provides a promising alternative for the determination of the dynamics exponent and thus the critical exponent of the shear viscosity. Sonic attenuation data from the literature, measured at frequencies down to 50 kHz, are re-evaluated with a view of the viscosity exponent determination. It is found that only in a small temperature range, the major requirement of the approach is fulfilled with the available data. Close to the critical temperature, the frequencies of measurement are still insufficiently small as compared to the inverse relaxation time of order parameter fluctuations. Criteria for future experiments are discussed briefly.

Cholesterol-Induced Variations in the Domain Structure Fluctuations and Microdynamics of Lipid Membranes

Broadband ultrasonic attenuation spectra (100 kHz to 2 GHz) of aqueous solutions of vesicles from 1,2-dimyristoyl-l-3-phosphatidylcholine, with different amounts of cholesterol admixed, have been measured at temperatures between 20 and 28 °C. The spectra have been evaluated in terms of suitable relaxation functions. They are discussed in view of the effect of cholesterol on the membrane behavior around the gel-fluid phase transition temperature T(m). In addition to a frequency-independent asymptotic high-frequency term, all spectra reveal a critical term and a Debye-type relaxation term with relaxation time around 0.5 ns. The former is evaluated in the light of the Bhattacharjee-Ferrell dynamic scaling theory. It is assigned to the critical domain structure fluctuations of the membranes. Critical slowing of fluctuations is demonstrated. Also shown are relations of the critical amplitudes to thermodynamic parameters. The Debye term reflects the rotational isomerization of the phospholipid alkyl chains. The relaxation time of isomerization reveals a significant steplike change at T(m). At moderate cholesterol content an additional Debye relaxation term exists. It is assigned to the axial diffusion of the membrane molecules. Because it likewise shows effects of slowing near T(m), the diffusion appears to be coupled to the domain structure fluctuations. A further relaxation term at small cholesterol concentration is assumed to be due to small-range shape fluctuations of vesicles near the phase transition temperature.

Scaling function of critical binary mixtures: Nitrobenzene– n-hexane data revisited

Ultrasonic attenuation spectra of the nitrobenzene– n-hexane mixture of critical composition have been analysed. Data between 50 kHz and 1 GHz from different sources have been included to show that at a given temperature the spectra, in addition to the critical contribution, reveal a non-critical relaxation term. Taking this additional term into account inconsistencies in the scaling function reported in the literature are avoided. In the final analysis the scaling function of the nitrobenzene– n-hexane system follows the predictions of the Bhattacharjee–Ferrell theory with critical amplitude and relaxation rate of concentration fluctuations in nice agreement with determinations from independent methods. The low-frequency attenuation data are briefly discussed with a view to a bulk viscosity approach which yields a slightly different proportionality constant in the linear regime of the scaling function than the Bhattacharjee–Ferrell theory. Evidence in favour of the latter is obtained.

Hydrogen Network Fluctuations of Alcohols. Evidence from Ultrasonic, Dielectric, and Shear Impedance Spectrometry

Broadband dielectric spectra (1 MHz to 40 GHz) and ultrasonic attenuation spectra (300 kHz to 3 GHz) as well as frequency-dependent complex shear viscosities (6 MHz to 120 MHz) are reported for alcohols and for their mixtures with other alcohols, with alkanes, and with water. The spectra are discussed with a view to features controlling the molecular dynamics of associating liquids. Special attention is given to (i) the rotation of terminal single-hydrogen-bonded hydroxy groups of associated structures, (ii) the dominating relaxation process of the structures, involving multiply-hydrogen-bonded hydroxy groups, (iii) the alkyl chain rotational isomerization, (iv) effects of clustering in alcohol–alkane mixtures, and (v) indications of non-critical concentration fluctuations of alcohol–water mixtures. The hydrogen network fluctuations of the alcohol systems can be consistently described in terms of a wait-and-switch model of relaxation. The concentration fluctuations are well represented by a recent “unifying” theoretical model, indicating a predominant impact of hydrophobic groups in the promotion of a micro-heterogeneous structure of mixtures with water.

Anomalous Dynamics of Solutions of Nonionic Micelles in Water

In addition to a previous theory on the coupling between noncritical concentration fluctuations and elementary chemical processes, an alternative treatment is presented which allows for a closed-form solution of ultrasonic attenuation spectra. This analytical form is first compared to a previous model and also to experimental spectra of binary liquid mixtures. The broadening of the spectra is briefly discussed in terms of molecular interactions and of the ratio of the relaxation times of the chemical equilibrium and of the diffusion of fluctuations. Extension of the theoretical model to apply to nonionic micelle solutions reveals that a flat contribution in the experimental spectra of such quasi-ternary systems may be simply due to different structure factors of the monomers and the micelles. Some exceptional findings for polyethylene glycol monoalkyl ether/water mixtures are discussed in light of the theory.

Ultrasonic Spectrometry of Aqueous Solutions of Alkyl Maltosides: Kinetics of Micelle Formation and Head‐Group Isomerization

At frequencies between 100 kHz and 400 MHz, ultrasonic attenuation spectra are measured at 25 degrees C for aqueous solutions of hexyl-, heptyl-, octyl-, nonyl-, and decyl-beta-D-maltopyranoside as well as of decyl-alpha-D-maltopyranoside. The spectra with surfactant concentration c above the relevant critical micelle concentration (cmc) display three relaxation terms with discrete relaxation times. That with a relaxation time between 0.1 and 1.2 micros is due to exchange of monomers between micelles and the suspending phase. It is discussed in the light of the Teubner-Kahlweit-Aniansson-Wall model of the formation/decay kinetics of systems with Gaussian size distribution of micelles. The relaxation parameters are compared to those for solutions of other non-ionic surfactants, such as alkyl monoglycosides and poly(ethylene glycol) monoalkyl ethers. At c < cmc this low-frequency relaxation term is missing and at c approximately = cmc it is broadened, as is characteristic of solutions of oligomeric molecular structures rather than proper micelles. The relaxation terms with relaxation times between 6 and 15 ns and 0.7 and 2.3 ns reveal head-group rotations around glycosidic angles and isomerization of the exocyclic hydroxymethyl group, respectively. These unimolecular reactions are also examined with a view to solutions of alkyl monoglycosides as well as of glucose and maltose.

Monomer Exchange and Rotational Isomerization of Alkyl Monoglycosides in Water

Ultrasonic attenuation spectra between 100 kHz and 400 MHz are reported for solutions of hexyl-, heptyl, octyl-, and nonyl-beta-d-glucopyranoside in water. Results for a mixture of an octyl glucopyranoside with an octyl galactopyranoside are also presented. The analytical descriptions of the spectra in terms of relaxation spectral functions feature up to four relaxation regions. The high-frequency relaxation processes, with relaxation times at around 2 and 10 ns, respectively, correspond with molecular processes also existing in saccharide solutions. They are assigned to the exocyclic hydroxymethyl group isomerization as well as to the rotation around glycosidic bond angles. The low frequency terms, with relaxation times in the range from 30 ns to 3 mus, are characteristic of micelle solutions. They are discussed in terms of two modes of monomer exchange. One mode reflects the well-known exchange kinetics of systems with Gaussian size distribution of globular micelles. The other mode is considered to be due to the monomer exchange at micelle sites with closer packing of surfactants, as is characteristic of large micelles with nonglobular shape.

New ultrasonic probes for in-line monitoring of polymer melts

In this paper, new in-line ultrasonic probes for monitoring of polymer melts in polymer processing are described. The probes are designed to half inch thread as industry standard with high temperature and pressure stability. The application of a buffer rod system with a glassy carbon core material provides high signal intensity and a high signal-to-noise ratio. With these probes, we are able to measure ultrasonic attenuation spectra. First results for in-line monitoring of the content of fillers in polymers in the melt under processing conditions are presented.