Ultrasonic Measurement of Sub-Micron Particles

Based on technology described in a Du Pont patent for an offline system, we have developed a prototype in-line ultrasonic cell for measuring particle size distribution. We have used this cell to verify the Allegra-Hawley model of ultrasonic attenuation in dilute (< 5 % vol) slurries of sub-micron ceramic particles, and we are developing a model that can cope with the multiple scattering effects occuring at higher concentrations. In this paper we present the results of attenuation measurements for ultrasound (2–50 MHz) in slurries with concentrations ranging from 0.5 010 to 38 010 (vol). The attenuation is proportional to slurry concentration up to 5 010 (vol) and is predicted by single scattering models. Above approximately 100% concentration, the attenuation is actually lower than expected. For the dilute slurries we find excellent agreement between our measurements and the Allegra-Hawley calculations, and the effects of the particle size distribution are evident in the ultrasonic attenuation spectrum. These ultrasonic data can be inverted to determine the particle size and concentration in aqueous slurries of sub-micron particles.     

Information Content of Acoustic Attenuation Spectra

In recent years ultrasonic attenuation spectroscopy has gained much attention as a method for the characterisation of concentrated dispersions. Several publications have shown, that this method allows the accurate determination of particle size. In particular for submicron dispersions there is, however, some uncertainty to which degree the details of a size distribution can be resolved by acoustic attenuation measurements. Ideally the inversion of an attenuation spectrum into a size distribution would yield as much distribution parameters as sound frequencies. In practice, however, the measurement errors affect the inversion very strongly and may result in multiple solutions for the size distribution. The maximum number of distribution parameters, for which a unique solution exists, can be therefore regarded as the information content. For a given ultrasonic spectrometer and material system it is possible to quantify the information content. Such an information analysis has been conducted with selected material systems in the submicron range. The investigation shows that the information content of acoustic attenuation spectra with regard to particle size analysis in the submicron range is relatively low. On the other hand, the results imply that the number of frequencies can be reduced significantly without loss of information content or stability of inversion algorithms.     

Particle Size Distribution Analysis of Industrial Colloidal Slurries using ultrasonic spectroscopy

Several solid-liquid suspensions containing submicron particles at moderate to high concentrations (5 to 50 volume percent) are encountered in industrial slurry processing. Measurements of ultrasonic attenuation spectra are used in a newly developed AcoustoPhor particle analysis system to get particle size distributions of such colloidal suspensions. This paper deals with the performance evaluation of the AcoustoPhor system. The automated ultrasonic spectrometer component of the AcoustoPhor system was tested using a reference silicone liquid for its accuracy and precision. The particle size distribution (PSD) estimation capabilities were evaluated using a set of well-dispersed slurries covering a wide range of particle concentrations. Sensitivity to process variations was evaluated in field tests at a pigment manufacturing plant. The AcoustoPhor system appears to be capable of providing reliable PSD data for inorganic pigment slurries with particle diameters ranging from 0.01 to 100 micrometers at particle concentrations as high as 50 volume percent.     

超声衰减和速度谱测量亚微米乳液的粒径

研究了超声衰减谱法和相速度测量高浓度多分散脂肪两相乳浊液的粒径分布问题.在理论分析基础上,实验测量了多个浓度(2%～20%)脂肪乳试样在2～13 MHz频带下超声衰减和相速度谱,结合反演算法由实验数据计算出乳浊液颗粒的粒径分布,并讨论了相速度法的意义和特点.将原始浓度(20%)下测得粒径分布与消光法在稀释条件下相同试样测量结果作对比,二者比较吻合,表明超声谱法可在无稀释的高浓度条件下作乳浊液粒径分布的表征.     

非侵入式超声波浆料浓度测量技术研究*

设计了一种基于非侵入式超声波透射衰减法的浆料浓度测量系统,根据超声传播衰减原理,建立超声衰减值与浆料浓度之间的关系。实验中采用生物显微镜和激光粒度仪对颗粒标称粒径进行验证,采用中心频率为200 kHz的超声波换能器,利用一发一收模式对超声波在有机玻璃管内的浆料进行非侵入式测量并分析透射波信号,对体积百分浓度小于25%、不同粒径的石英砂浆料进行测量,通过拟合方法获得浆料温度、体积百分浓度与声衰减对应的关系,并据此构造浓度求解方程,通过现场实时在线测量并与取样结果进行对比验证方程的准确性,结果显示,本方法可有效测量浆料浓度。     

表征超声衰减谱粒度的改进和声搜索算法

针对超声衰减谱法颗粒粒径测量,提出一种改进和声搜索算法,在和声搜索算法迭代达到200次时,加入拟牛顿算法,调节和声搜索算法全局和局部搜索能力,提高算法的收敛精度.对服从3种典型粒径分布函数颗粒系进行数值模拟,改进算法反演得出罗辛-拉姆勒(Rosin-Rammler)分布参数值相对误差小于8％,正态分布参数值相对误差小于...     

Calculation of Particle Size Distributions from Ultrasonic Measurements: A Mineral Slurry Case Study

Ultrasonic transmission measurements have been used extensively to determine the particle size of solids in slurries. This case study examines the application of mathematical inversion techniques to the determination of the particle size distribution of a mineral slurry from data collected at a minerals processing plant. A new mathematical inversion technique, based on an extension of modified Chahine iteration combined with the principle of maximum entropy has been developed. Four algorithms were constructed and used to calculate particle size distributions from synthetic and raw plant data. These incorporated modified Chahine iteration and its extension, together with two different approaches to applying a density measurement constraint on the particle size distribution. In general the algorithms performed well with regression errors below 3 %. The correlation coefficients and slopes for this technique were 0.86 and 1.35 for the weight fraction of particles less than 75 microns when compared with the laser diffraction analysis. A better match was obtained for the plant data by using the new inversion technique, into which the principle of maximum entropy has been incorporated whereas this was not the case with the synthetic data, illustrating the need to match the inversion technique to the problem.     

Acoustic wave in a suspension of magnetic nanoparticle with sodium oleate coating

The ultrasonic propagation in the water-based magnetic fluid with doubled layered surfactant shell was studied. The measurements were carried out both in the presence as well as in the absence of the external magnetic field. The thickness of the surfactant shell was evaluated by comparing the mean size of magnetic grain extracted from magnetization curve with the mean hydrodynamic diameter obtained from differential centrifugal sedimentation method. The thickness of surfactant shell was used to estimate volume fraction of the particle aggregates consisted of magnetite grain and surfactant layer. From the ultrasonic velocity measurements in the absence of the applied magnetic field, the adiabatic compressibility of the particle aggregates was determined. In the external magnetic field, the magnetic fluid studied in this article becomes acoustically anisotropic, i.e., velocity and attenuation of the ultrasonic wave depend on the angle between the wave vector and the direction of the magnetic field. The results of the ultrasonic measurements in the external magnetic field were compared with the hydrodynamic theory of Ovchinnikov and Sokolov (velocity) and with the internal chain dynamics model of Shliomis, Mond and Morozov (attenuation).     

Study of low concentrated ionic ferrrofluid stability in magnetic field by ultrasound spectroscopy

Ultrasound spectroscopy has been used to investigate the effect of magnetic field on particle (cluster) size distribution in ionic ferrofluid. The method applied is non-destructive, fast and sensitive to structural changes of a suspension as it is based on measurements of ultrasonic attenuation. Changes in the ultrasound attenuation induced by an external magnetic field have been measured for different frequencies of the acoustic wave. According to the Harker-Temple theory, the aggregation process has been analysed on the basis of the cluster size distribution determined for different magnetic field intensities.     

Intercomparison of Inversion Algorithms for Particle‐Sizing Using Mie Scattering

The applicability of different inversion algorithms to retrieve a size distribution of particles in air from light scattering is examined. The investigation is focused on an optical measurement setup with an elliptical mirror as the main optical element. In order to evaluate the capabilities of the individual inversion methods, light scattering by spherical particles is simulated in the size ranges of 0.1 – 10 μm and 0.05 – 1 μm. The distribution of the particle diameters is modeled with three different parametric functions, i.e., RRSB, logarithmic‐normal and a more specific distribution from an ultrasonic nebulizer. Different kinds of noise, e.g., additive and/or multiplicative, are applied in different levels to the simulated scattering measurement to include real physical measurement conditions. The convergence properties of the scattering simulation are investigated with respect to the number of size classes, and thus, information concerning the size resolution required to simulate a measurement for a given particle size distribution is obtained. Further parameters of interest are the minimum angular resolution of the measurements, the number of size classes of the retrieved particle size distribution and the measured polarization of the scattered light.     

Using ultrasonic attenuation to monitor slurry mixing in real time

Staff at Pacific Northwest National Laboratory have developed and applied a simple ultrasonic attenuation measurement to measure slurry concentration in real time during suspension of solids settled in a large tank. This paper presents a simple single frequency ultrasonic measurement technique that demonstrates the ability of ultrasonic sensors to measure slurry concentration. Sensor calibration data show that in this attenuation regime ultrasonic signal attenuation is proportional to the applied frequency and to the slurry volume fraction. Real-time measurements of ultrasonic signal attenuation were used to track the process of slurry mixing using single sensors and sensor arrays. Results from two experiments show the use of real-time measurements of ultrasonic signal attenuation to track the process of slurry mixing in situ and to track the ability to maintain a well-mixed steady state condition. Comparison of concentration means of the ultrasonic measurements with concentration means obtained from discrete extractive measurements show that the distributions overlap and cannot be statistically distinguished. The real-time ultrasonic sensor can be used as a primary measurement method or to reduce reliance upon extractive methods to measure slurry density and solids concentration.     

Ultrasonic pretreatment of corn slurry for saccharification: A comparison of batch and continuous systems

The effects of ultrasound on corn slurry saccharification yield and particle size distribution was studied in both batch and continuous-flow ultrasonic systems operating at a frequency of 20 kHz. Ground corn slurry (28% w/v) was prepared and sonicated in batches at various amplitudes (192–320 μm_{peak-to-peak (p–p)}) for 20 or 40 s using a catenoidal horn. Continuous flow experiments were conducted by pumping corn slurry at various flow rates (10–28 l/min) through an ultrasonic reactor at constant amplitude of 12 μm_p–p. The reactor was equipped with a donut shaped horn. After ultrasonic treatment, commercial alpha- and gluco-amylases (STARGEN^TM 001) were added to the samples, and liquefaction and saccharification proceeded for 3 h. The sonicated samples were found to yield 2–3 times more reducing sugars than unsonicated controls. Although the continuous flow treatments released less reducing sugar compared to the batch systems, the continuous flow process was more energy efficient. The reduction of particle size due to sonication was approximately proportional to the dissipated ultrasonic energy regardless of the type of system used. Scanning electron microscopy (SEM) images were also used to observe the disruption of corn particles after sonication. Overall, the study suggests that both batch and continuous ultrasonication enhanced saccharification yields and reduced the particle size of corn slurry. However, due to the large volume involve in full scale processes, an ultrasonic continuous system is recommended.     

Titania Gold Composite: Effect of Illumination on Size of Gold Nanoparticles with Consequent Implication on Photocatalytic Water Splitting

This work deals with the study of photodeposition (PD) of gold nanoparticles (AuNPs) on TiO₂ by using different illumination sources, Medium pressure Mercury lamp (ML), Solar Simulator equipped with AM 1.5 (SL) and Tungsten lamp (WL). Different particle size of AuNPs on TiO₂ were obtained by photodeposition method under different illumination sources, which clearly proves the influence of light source on the synthesis of Au–TiO₂. The plasmonic activity of Au–TiO₂ photocatalyst for water splitting reaction was observed to be strongly influenced by the particle size of Au as well as illumination source. Amongst the three different illumination sources used, smallest particle size for AuNP–TiO₂ were observed under ML followed by SL and WL, as revealed by TEM analysis. Different illumination sources were also investigated to evaluate the activity of Au–TiO₂ samples thus prepared under different illumination conditions. The order of hydrogen evolution rate (HER) observed for Au–TiO₂ with different source of illuminations is ML > SL > WL. The highest HER of 1709 μmol/h was observed for Au–TiO₂, which was synthesized and evaluated under ML irradiation. This may be explained on the basis of reduced catalytic activity and photothermal effect of Au nanoparticles with increasing particle size.     

Estimation of surface area concentration of workplace incidental nanoparticles based on number and mass concentrations

Surface area was estimated by three different methods using number and/or mass concentrations obtained from either two or three instruments that are commonly used in the field. The estimated surface area concentrations were compared with reference surface area concentrations (SA_REF) calculated from the particle size distributions obtained from a scanning mobility particle sizer and an optical particle counter (OPC). The first estimation method (SA_PSD) used particle size distribution measured by a condensation particle counter (CPC) and an OPC. The second method (SA_INV1) used an inversion routine based on PM1.0, PM2.5, and number concentrations to reconstruct assumed lognormal size distributions by minimizing the difference between measurements and calculated values. The third method (SA_INV2) utilized a simpler inversion method that used PM1.0 and number concentrations to construct a lognormal size distribution with an assumed value of geometric standard deviation. All estimated surface area concentrations were calculated from the reconstructed size distributions. These methods were evaluated using particle measurements obtained in a restaurant, an aluminum die-casting factory, and a diesel engine laboratory. SA_PSD was 0.7–1.8 times higher and SA_INV1 and SA_INV2 were 2.2–8 times higher than SA_REF in the restaurant and diesel engine laboratory. In the die casting facility, all estimated surface area concentrations were lower than SA_REF. However, the estimated surface area concentration using all three methods had qualitatively similar exposure trends and rankings to those using SA_REF within a workplace. This study suggests that surface area concentration estimation based on particle size distribution (SA_PSD) is a more accurate and convenient method to estimate surface area concentrations than estimation methods using inversion routines and may be feasible to use for classifying exposure groups and identifying exposure trends.     

Ultrasonic diffraction grating spectroscopy and the measurement of particle size

The results of measurements using ultrasonic diffraction grating spectroscopy (UDGS) are found to be dependent upon the particle size of the slurry. This illustrates the emergence of a new technique for measuring particle size. Theoretical calculations are underway to describe and predict them as well. The ultrasonic grating surface is in contact with the slurry. The diffraction grating was formed by machining triangular grooves with a periodicity of 483 microm on the flat surface of an aluminum unit with send and receive transducers fastened to it. For this experimental configuration, the ultrasonic beam strikes the back of the grating at an incident angle of 30 degrees and produces a transmitted beam of spectral order m=1 in the slurry. The angle of this transmitted beam changes with frequency and, at the critical frequency of 3.47 MHz, it is located at an angle of 90 degrees. The receive transducer measures the reflected m=0 beam at an angle of 30 degrees. At a frequency slightly less than the critical frequency, the m=1 transmitted beam no longer exists and its energy is shared with all other beams. Therefore, due to energy conservation, the signal in the receive transducer exhibits a peak at the critical frequency. During the transition, the wave interacts with the particles of the slurry and ultrasound amplitude is reduced. Therefore, the peak observed by the receive transducer is reduced, compared to that for water. Data have been obtained for slurries of polystyrene spheres, ranging in size from 215 microm to 463 microm, and for weight percentages of 1-12%. Polystyrene spheres of different diameter show differing amounts of energy loss and thus, particle size identification is possible.     

基于超声衰减谱的纳米颗粒粒度分布测量研究

利用变声程方式测量纳米颗粒悬浮液的超声衰减谱,以McClements模型和BLBL模型为理论基础,采用最优正则化(ORT)算法,反演得到纳米颗粒的粒度分布。运用该方法,对体积浓度1%的纳米二氧化钛-水悬浊液进行测量,与透射电镜(TEM)图像以及离心沉降纳米粒度分析仪检测结果对比,测量结果吻合较好,表明了利用超声衰减谱方法测量纳米颗粒粒度分布的可行性与可靠性。      

Fabrication and characterization of silver/titanium dioxide composite nanoparticles in ethylene glycol with alkaline solution through sonochemical process

This paper aims to study fabrication and characterization of silver/titanium oxide composite nanoparticle through sonochemical process in the presence of ethylene glycol with alkaline solution. By using ultrasonic irradiation of a mixture of silver nitrate, the dispersed TiO₂ nanoparticle in ethylene glycol associated with aqueous solution of sodium oxide yields Ag/TiO₂ composite nanoparticle with shell/core-type geometry. The powder X-ray diffraction (XRD) of the Ag/TiO₂ composites showed additional diffraction peaks corresponding to the face-centered cubic (fcc) structure of silver crystallization phase, apart from the signals from the cores of TiO₂. Transmission electron microscopy (TEM) images of Ag/TiO₂ composites, which average particle size is roughly 80 nm, reveal that the titanium oxide coated by Ag nanoparticle with a grain size of about 2–5 nm. Additionally, the formation of silver nanoparticles on TiO₂ was monitored by ultraviolet visible light spectrophotometer (UV–Vis). As measured the optical absorption spectra of as-synthesized Ag nanoparticle varying with time, the mechanism of surface formatting silver shell on the cores of TiO₂ could be explored by autocatalytic reaction; the conversion of Ag particle from silver ion is 98% for the reaction time of 1000 s; and the activity energy of synthesizing Ag nanoparticles on TiO₂ is 40 kJ/mol at temperature ranging from 5 to 25 °C. Hopefully, this preliminary investigation could be used for mass production of composite nanoparticles assisted by ultrasonic chemistry in the future.     

非晶态快离子导体(AgI)x(Ag4P2O7)1-x的声学性质

用液氮骤冷方法制备了(AgI)_x(Ag₄P₂O₇)_1-x系列非晶态快离子导体。对AgI摩尔浓度x=0.50,0.60,0.67,0.75,0.80的样品,在77—300K温度范围及2,5,10,15MHz的频率上测量了纵波和横波的超声衰减和声速。发现在200—240K附近存在一个异常强的弛豫型超声吸收峰,随AgI含量的增加,该峰的位置向低温方向移动,且峰的高度增大。在实验的温度范围内,观察到纵波和 关键词：     

Ultrasonic properties of nanoparticles-liquid suspensions

A polymer colloidal solution having dispersed nanoparticles of Cu and Au metals have been developed using a novel chemical method. Average size of the nanoparticles could be varied in the 4-10 nm range by conducting the reaction at an elevated temperature of 50-70 degrees C. Colloidal solutions of representative concentrations of 0.1-2.0 wt% Cu/Au contents in the primary solutions are used to study the modified ultrasonic attenuation and ultrasonic velocity in PVA polymer molecules on incorporating the Cu/Au particles. A characteristic behaviour of the ultrasonic velocity and the attenuation are observed at the particular temperature/particle concentration. The results demonstrate that the primary reaction during the nanoparticles-PVA colloidal formation occurs in divided groups in small micelles. The results are analyzed predicting the enhanced thermal conductivity of the samples.     

On Measuring and Modeling Local Average Particle Velocities for particle ensembles in classifying systems

In most multi-phase flow problems, the particulate phase is exposed to an external field which causes dispersion. Therefore, local velocity measurements of the disperse phase are no longer equivalent with respect to averaging in time and averaging in volume. While the local time-averaged velocity still characterizes the transport of the ensemble in the Eulerian sense, one has to be be careful in modeling this velocity average by considering the ensemble's composition. It is shown for different particle ensembles that the conventional particle velocity average M_1,0 calculated with respect to the dispersion relationship and a particle size number density distribution is far below the measured ensemble average; the deviation depends on the width of the particle size distribution. It is deduced that Eulerian particle velocity values referring to a certain time interval can be modeled by a ratio of velocity moments M_2,0/M_1,0 calculated with particle size number distributions referring to a certain probe volume. This relationship was confirmed by measurements.