Ultrasonic effects on electroorganic processes. Part 17. Product selectivity control in cathodic reduction of acrylonitrile

Product selectivity for adiponitrile, which was formed as the corresponding hydrodimeric product along with propionitrile as the hydromonomeric product in the cathodic reduction of acrylonitrile, was significantly increased under ultrasonic irradiation with an intensity above the ultrasonic cavitation threshold. This ultrasonic effect is rationalized as due to mass transport promotion of acrylonitrile molecules to the cathode surface from the bulk electrolytic solution by high speed jet streams caused by the cavitation. A mechanism for the ultrasonic effect is discussed in detail on the basis of the reaction pathway of the hydrodimerization of acrylonitrile.     

Ultrasonic effects on electroorganic processes. Part 27. Electroreduction of acrylonitrile at suspended lead particle-electrode

Ultrasonic effect on the electroreduction of acrylonitrile at suspended lead particle-electrode was examined. The product selectivity for adiponitrile, which was formed as the corresponding hydrodimeric product along with propionitrile as the hydromonomeric one in the cathodic reduction of acrylonitrile, was increased by addition of lead particles as a particle-electrode, and moreover the selectivity was further increased under ultrasonication. This ultrasonic effect is rationalized as due to not only mass transport of lead particles to the feeder cathode but also an increase in the effective surface area of particle-electrode by ultrasonic dispersion. A mechanism for the ultrasonic effect is discussed in detail on the basis of the reaction system.     

不同表面状态镀锡钢板铬酸盐钝化膜中铬元素的XPS分析

用X射线光电子能谱(X-ray photoelectron spectroscopy, XPS)分析的方法,对铬酸盐钝化镀锡钢板的正常表面及缺陷点处铬元素的含量、价态以及由铬元素组成的化合物进行了研究。用超声波的方法对铬酸盐钝化镀锡钢板进行处理后,研究了超声波处理对缺陷处的铬元素的含量、价态的影响。结果表明,钝化膜中主要含有Cr,O, Sn元素。镀锡铬酸盐钝化膜中正常表面的铬元素主要是以Cr(OH)₃,Cr单质以及Cr₂O₃的形态存在。在对镀锡板表面进行阴极电解钝化的过程中,Cr(Ⅵ)发生了转化,价态降低。在缺陷处,除了有Cr(OH)₃和Cr₂O₃以外,还有微量的Cr(Ⅵ)存在。在缺陷处铬元素的含量低于正常表面,在超声波清洗处理后,缺陷处铬元素的含量明显低于不经超声波清洗的含量。施加的超声波因产生强烈的洗脱作用,使吸附在缺陷处的微量的Cr(Ⅵ)消失。     

Decomposition of nitrotoluenes in wastewater by sonoelectrochemical and sonoelectro-Fenton oxidation

Oxidative degradation of dinitrotoluene (DNT) and 2,4,6-trinitrotoluene (TNT) in wastewater was conducted using electrochemical and electro-Fenton processes respectively, combined with ultrasonic irradiation, wherein a synergistic effect is observed. Experiments were carried out to elucidate the influence of various operating variables on the sonoelectrolytic behavior, such as electrode potential, sonoelectrolytic temperature, acidity of wastewater, oxygen dosage, and dosage of ferrous ions. It deserves to note that the nitrotoluene contaminants could be completely decomposed by sonoelectro-Fenton method, wherein hydrogen peroxide was in situ generated from cathodic reduction of oxygen, supplied partially by anodic oxidation of water. During the sonoelectrolytic process, in spite of existence of degassing phenomenon, the high yield of hydrogen peroxide was produced due to the significantly enhanced mass transfer rate of oxygen toward the cathode, caused by ultrasonic irradiation. Because higher removal efficiency of DNTs and TNT obtained at ambient conditions, it is believed that the sonoelectrolytic method is potentially applied to dispose wastewater from toluene nitration processes.     

Sonoelectrochemical recovery of silver from photographic processing solutions

This paper describes the effect of ultrasound upon the electrochemical recovery of silver from photographic processing solutions using a newly designed electrochemical cell--SonoEcoCell. Rates of deposition of silver (obtained potentiostatically) were studied in the model 'fix' solutions (dilute aqueous Na2S2O3/NaHSO3 at a stainless steel cylinder electrode in both the absence and the presence of ultrasound. Under silent conditions, the magnitude of the cathodic potential is a major factor in the removal of silver. Under 20 kHz sonication, the rate of deposition of silver increases with increasing ultrasonic intensity. The cathode efficiency is also enhanced under insonation. The position of the ultrasonic probe with respect to the rotating cylinder electrode (RCE) was studied. It was found that for a 'face-on' geometry (probe parallel to the electrode) led to higher rate constants compared with a 'side-on' geometry (probe perpendicular to the electrode). The effect of coupling an RCE with ultrasound upon these rate constants employing the two geometry was also investigated. It was found that, employing either the face-on or the side-on geometry alone, improved rate constants were obtained below approximately 1500 and 2000 rpm, respectively.     

Ultrasonic irradiation and its application for improving the corrosion resistance of phosphate coatings on aluminum alloys

In this paper, ultrasonic irradiation was utilized for improving the corrosion resistance of phosphate coatings on aluminum alloys. The chemical composition and morphology of the coatings were analyzed by X-ray diffraction analysis (XRD) and scanning electron microscopy (SEM). The effect of ultrasonic irradiation on the corrosion resistance of phosphate coatings was investigated by polarization curves and electrochemical impedance spectroscopy (EIS). Various effects of the addition of Nd₂O₃ in phosphating bath on the performance of the coatings were also investigated. Results show that the composition of phosphate coating were Zn₃(PO₄)₂ · 4H₂O(hopeite) and Zn crystals. The phosphate coatings became denser with fewer microscopic holes by utilizing ultrasonic irradiation treatment. The addition of Nd₂O₃ reduced the crystallinity of the coatings, with the additional result that the crystallites were increasingly nubby and spherical. The corrosion resistance of the coatings was also significantly improved by ultrasonic irradiation treatment; both the anodic and cathodic processes of corrosion taking place on the aluminum alloy substrate were suppressed consequently. In addition, the electrochemical impedance of the coatings was also increased by utilizing ultrasonic irradiation treatment compared with traditional treatment.     

Phase-transfer catalysis and ultrasonic waves. I. Cannizzaro reaction

The aim of this work is to study the effect of an ultrasonic wave on the Cannizzaro reaction catalyzed by a phase-transfer catalyst. The reaction of benzaldehyde with potassium hydroxide was chosen as the reference reaction. The kinetics of the reaction was followed by the amount of benzoic acid which is well characterized and easily isolatable. Investigations were made on variables such as the kind of aldehyde, the phase-transfer catalyst, the temperature and the frequency of ultrasonic wave. As the phase-transfer catalyst depends strongly on mass transfer between two phases, it is well understood that ultrasonic waves have a greater efficiency of interface mixing than conventional agitation. The results showed that an ultrasonic wave of 20 kHz dramatically accelerates on the reaction.     

Crystallization of potash alum: effect of power ultrasound.

The influence of power ultrasound on the crystallization of potash alum was investigated. Experiments have been carried out in a batch stirred vessel. It was found that ultrasonic waves decrease the supersaturation limits and modify the morphology of the crystals produced. The average crystal size decreases with an increase of ultrasonic power. To investigate also the action of ultrasound on already existing crystals, crystals produced in silent conditions were suspended in saturated potash alum solution at various ultrasonic powers. The results show that ultrasound has also an abrasive effect on potash alum crystals for high power inputs.     

Enantioselective decomposition of chiral alkyl bromides on Cu(6 4 3): Effects of moving the chiral center

The enantioselective surface chemistry of two chiral alkyl halides, S-1-bromo-2-methylbutane and R-2-bromobutane, have been compared on the naturally chiral Cu(6 4 3)^R&S surfaces. Temperature programmed reaction spectroscopy was used to quantify the yields of the various decomposition products during heating. A fraction of the adsorbed alkyl bromides desorb intact while the remainder decomposes by debromination to form either S-2-methyl-1-butyl or R-2-butyl groups on the surfaces. The S-2-methyl-1-butyl group then reacts by β-hydride elimination to form 2-methyl-1-butene or by hydrogenation to form 2-methylbutane. The R-2-butyl group reacts by β-hydride elimination to form butene or by hydrogenation to form butane. This surface chemistry on Cu(6 4 3)^R&S is not enantioselective at low coverages but is enantioselective at high coverages. In R-2-bromobutane the chiral carbon atom coincides with the debromination reaction center while the β-hydride elimination centers are achiral. In S-1-bromo-2-methylbutane the chiral carbon atom coincides with the β-hydride elimination reaction center while the center for debromination is achiral. Results show that the enantioselectivities are influenced by the surface structure to a greater extent than they are by the adsorbate structure.     

超声滚压中的空化现象*

在超声滚压加工中引入切削液后可能会产生空化现象,由此产生的微射流和冲击波对超声表面强化将有积极作用。为研究超声滚压加工中空化现象是否存在及空化效应在超声滚压中的作用,本文首先分析了超声滚压中的空化阈值,然后进行了染色法试验和超声滚压后试样氧元素能谱分析,最后通过超声滚压加工对比试验研究了空化效应对加工后材料表面粗糙度和显微硬度的影响。研究发现,超声滚压加工中的声压幅值远大于空化阈值,满足空化存在的必要条件;超声滚压中发生了明显的卡纸染色现象,引入切削液后工件超声滚压加工表面氧元素含量显著提高,表明超声滚压中发生了空化现象。超声滚压加工中的空化效应能进一步降低工件表面粗糙度和提高表面显微硬度,有利于提高工件表面强化质量。本研究为空化效应在超声滚压中的积极利用提供了依据。     

Load characteristics of high power sandwich piezoelectric ultrasonic transducers

Based on the equivalent circuit theory, the load characteristics of high power piezoelectric ultrasonic sandwich transducers are studied. Two types of loads are studied. One is liquid load as in ultrasonic cleaning, and the other is solid load as in ultrasonic drilling and machining. The effect of load and structure of the transducer on the resonance frequency of the transducer is analyzed. It is shown that the effect of load on the resonance frequency of sandwich transducers with different structures is different. For liquid load as in ultrasonic cleaning, the effect of the load on the resonance frequency of the sandwich transducer with symmetrical structure is the largest. It is the smallest for the transducer with its displacement node in the back metal cylinder. For solid load as in ultrasonic drilling and machining, the effect of the load on the resonance frequency of the sandwich transducer with its displacement node in the front metal cylinder is the largest. It is also the smallest for the transducer with its displacement node in the back metal cylinder. On the other hand, for some applications, such as ultrasonic drilling, when the lateral dimension of the tool is much less than that of the transducer, its effect on the resonance frequency of the transducer is small. The conclusions are useful in designing vibrating systems for different ultrasonic applications.     

Study on removing calcium carbonate plug from near wellbore by high-power ultrasonic treatment

In this paper, the effects of ultrasonic wave on the removal of inorganic scaling and plugging in cores and the influence of the key wave field parameters, process parameters and core physical parameters on the plugging removal efficiency are systematically studied. The main dynamic mechanism of ultrasonic plugging removal is also systematically analyzed. Results show that the transducer frequency, transducer power, ultrasonic treatment time and initial permeability of core have great influence on the effect of ultrasonic scale removal. When the cumulative treatment time of ultrasonic wave exceeds 60 min, the recovery rate of core permeability tends to be stable. Best effect can be achieved when processing for 80–120 min cumulatively; the plugging removal effect is improved with the increase of ultrasonic transducer power and ultrasonic frequency, but the effect of plugging removal is not obvious with the further increasing of them. In addition, it is proved that the effect of removing calcium carbonate plug from near wellbore by hydrochloric acid solution is slightly better than that by ultrasonic treatment alone. Finally, the micro dynamic mechanism of removing inorganic scale plug by high-power ultrasonic treatment is discussed in view of ultrasonic inorganic scale body crushing, ultrasonic cavitation, ultrasonic friction, ultrasonic peristaltic transport operation and ultrasonic fracture-making and permeability-increasing effect.     

超声振动珩磨作用下空化泡动力学及影响参数

为了合理利用超声振动珩磨作用下的空化效应,以磨削区单个空化泡为研究对象,考虑珩磨头合成扰动速度和珩磨压力的作用建立了磨削区空化泡的动力学模型。数值模拟了空化泡初始半径,珩磨压力,液体静压力和超声声压幅值对磨削区空化效应的影响。研究表明考虑超声振动珩磨作用时,空化泡膨胀的幅值会受到抑制,其溃灭时间也会缩短,而且较容易出现稳态空化。珩磨压力和液体静压力对磨削区空化主要起抑制作用,超声波声压幅值在一定范围内能够促进磨削区空化效果的提升。本文的研究为进一步理解超声振动珩磨的空化机理提供了理论支持。     

Effect of irradiation distance on degradation of phenol using indirect ultrasonic irradiation method

Ultrasound is used as degradation of hazardous organic compounds. In this study, indirect ultrasonic irradiation method was applied to the degradation process of phenol, the model hazardous organic compound, and the effects of irradiation distance on radical generation and ultrasonic power were investigated. The chemical effect estimated by KI oxidation dosimetry and ultrasonic power measured by calorimetry fluctuated for the irradiation distance, and there was a relationship between the period of the fluctuation of ultrasonic effect and the wavelength of ultrasound. The degradation of phenol was considered to progress in the zero-order kinetics, before the decomposition conversion was less than 25%. Therefore, the simple kinetic model on degradation of phenol was proposed, and there was a linear relation in the degradation rate constant of phenol and the ultrasonic power inside the reactor. In addition, the kinetic model proposed in this study was applied to the former study. There was a linear relation in the degradation rate constant of phenol and ultrasonic energy in the range of frequency of 20-30 kHz in spite of the difference of equipment and sample volume. On the other hand, the degradation rate constant in the range of frequency of 200-800 kHz was much larger than that of 20-30 kHz in the same ultrasonic energy, and this behaviour was agreed with the former investigation about the dependence of ultrasonic frequency on chemical effect.     

Ultrasonic assisted dyeing: Dyeing of acrylic fabrics C.I. Astrazon Basic Red 5BL 200%

The dyeing of acrylic fabrics using C.I. Astrazon Basic Red 5BL 200% has been studied with both conventional and ultrasonic techniques. The effect of dye concentration, dye bath pH, ultrasonic power, dyeing time and temperature were studied and the resulting shades obtained by dyeing with both techniques were compared. Colour strength values obtained were found to be higher with ultrasonic than with conventional heating. The results of fastness properties of the dyed fabrics were studied. X-ray and Scanning Electron Microscope SEM were carried out on dyed samples using both methods of dyeing to find out an explanation for the better dyeability of acrylic fabrics with (US) method. Dyeing kinetics of acrylic fabrics using C.I. Astrazon Basic Red 5BL 200% using conventional and ultrasonic conditions were compared. The time/dye-uptake isotherms are revealing the enhanced dye-uptake in the second phase of dyeing. The values of dyeing rate constant, half-time of dyeing and standard affinity and ultrasonic efficiency have been calculated and discussed.     

A novel angular geometry for the sonochemical silver recovery process at cylinder electrodes

In order to obtain maximum ultrasonic effect upon electrochemical silver recovery, mass transfer measurements were investigated. The effect on limiting current of changing the position of an ultrasonic horn tip (i.e. vertical and horizontal) and using a cylinder electrode (CE), was studied in an attempt to find the optimum position required for maximum sonoelectrochemical effect. The importance of the ultrasonic intensity, the electrode-horn distance and positioning (angle) in assigning limiting currents was also investigated. For the CE placed at an angle of 45 degrees with respect to the ultrasonic horn, it was suggested that the 50% increase in limiting current for the 'face-on' geometry is caused by an approximately 50% decrease in diffusion layer thickness for the 'face-on' geometry compared to the 'angular' geometry due to the difference in the sonicated areas for both geometries.     

光电效应实验中阳极光电流的测量

分析了光电效应实验中阳极光电流和阴极光电流的形成机理.探索了二者之间的关系.阳极光电流值的K倍与阴极光电流值关于原点对称,因此当K足够大时,用电压大于0时的实测电流值代替阴极光电流值,可以求得电压小于0时的阳极光电流值.     

Absorption kinetics of ozone in water with ultrasonic radiation

A mathematical model was proposed to depict classical unsteady state method that was used to determine volumetric mass transfer coefficient of ozone from gaseous phase to aqueous phase during sonolysis. The rate constant of ozone self-decomposition with ultrasonic radiation, which was one of the parameters in the model, was determined with separate experiments. The results showed that self-decomposition rate constants of ozone were enhanced by ultrasound. The self-decomposition rate constant of ozone is linearly dependent on ultrasonic power, but the increase of the decomposition rate could not enhance ozone mass transfer coefficient. The volumetric mass transfer coefficients of ozone were also enhanced by ultrasonic radiation, while ultrasonic power had little effect on volumetric mass transfer coefficient of ozone. The degassing effect of ozone due to ultrasonic radiation was insignificant in the sparged system when ozone was bubbled during sonolysis.     

Investigation on ultrasonic volume effects: Stress superposition,acoustic softening and dynamic impact

Conventional high power ultrasonic vibration has been widely used to improve manufacturing processes like surface treatment and metal forming. Ultrasonic vibration affects material properties, leading to a flow stress reduction, which is called ultrasonic volume effect. The volume effect contains multi-mechanisms such as stress superposition due to oscillatory stress, acoustic softening by easier dislocation motion and dynamic impact leading to extra surface plastic deformation. However, most researches ignored the stress superposition for the convenience of measurement, and few studies considered ultrasonic dynamic impact since the relatively low ultrasonic energy in macro scale. The purpose of this study is to investigate the characteristics and mechanisms of different ultrasonic volume effects in micro-forming. A 60 kHz longitudinal ultrasonic-assisted compression test system was developed and a series of ultrasonic-assisted compression tests at different amplitudes on commercially pure aluminum A1100 in micro-scale were carried out combining the surface analysis by SEM, EDX and micro-hardness test. Three different ultrasonic volume effects, stress superposition, acoustic softening and dynamic impact, were confirmed in the ultrasonic-assisted compression tests. In order to quantitatively predict stress superposition, a hybrid model for stress superposition is developed considering the elastic deformation of experimental apparatus in practice, the evolution of the modeling results fitted well with the experimental results. With low ultrasonic amplitude, stress superposition and acoustic softening occurred because vibrated punch contacted with the specimen all the time during compression. However, with higher amplitude, due to the extra surface plastic deformation by larger ultrasonic energy, forming stress was further reduced by the ultrasonic dynamic impact. A possible method to distinguish the effects of dynamic impact and acoustic softening is to analyze the waveform of the oscillatory stress in the process. In the case of ultrasonic dynamic impact effect, a higher amount of oxidation was observed on the specimen surface, which could be the result of local heating by surface plastic deformation and surface friction when the vibrated punch detached from the specimen. The findings of this study provide an instructive understanding of the underlying mechanisms of volume effects in ultrasonic-assisted micro-forming.     

A phenomenological investigation into the opposing effects of fluid flow on sonochemical activity at different frequency and power settings. 1. Overhead stirring

The effect of flow in an ultrasonic reactor is an important consideration for practical applications and for the scale-up of ultrasonic processing. Previous literature on the influence of flow on sonochemical activity has reported conflicting results. Therefore, this work examined the effect of overhead stirring at four different frequencies, 40, 376, 995 and 1179 kHz, in two different reactor configurations. Comparable power settings were utilised to elucidate the underlying mechanisms of interactions between the flow and sonochemical activity. The sonochemical activity was determined by the yield of hydrogen peroxide, measured by iodide dosimetry, and the active region was visualised with sonochemiluminescence imaging. The overhead stirring in the low frequency reactor altered the yield of hydrogen peroxide so it produced the maximum yield out of the four frequencies. The increase in hydrogen peroxide yield was attributed to a reduction in coalescence at 40 kHz. However at the higher frequencies, coalescence was not found to be the main reason behind the observed reductions in sonochemical yield. Rather the prevention of wave propagation and the reduction of the standing wave portion of the field were considered.