Effect Of Ultrasonic Frequency Research Articles

Effect of Ultrasonic Frequency on Thickener Performance

Gravity thickening is an important aspect to solve numerous environmental and safety problems that were created by tailings discharging at low solid concentrations. Furthermore, in order to efficiently facilitate the separation of released water and solid sediments, a continuous thickening system with ultrasonic equipment has been used to investigate the thickening performance of copper‐mine tailings under different ultrasonic frequencies (16 kHz, 20 kHz, 22 kHz, 25 kHz, and 28 kHz). After freeze‐drying treatment, the underflow samples are imaged using the scanning electron microscope (SEM); then, the structure of floc or aggregates in the SEM images is quantifiably analyzed using the software of Image J. Results show that the underflow concentration increases as the ultrasonic frequency increases and decreases afterwards. A linear logarithmic function can explain the relationship between underflow concentration and run time at a certain ultrasonic. The underflow concentration is maximized at 64.47 wt. % when the ultrasonic frequency is 22 kHz. Based on the analysis on the microstructure of underflow samples, the minimum pore average size and pore average fraction are obtained when the ultrasonic frequency is 22 kHz, implying that 22 kHz is the optimum ultrasonic frequency combining the results of the underflow concentration.

Ultrasonic Frequency Effects on the Melt Pool Formation, Porosity, and Thermal-Dependent Property of Inconel 718 Fabricated by Ultrasonic Vibration-Assisted Directed Energy Deposition

Abstract Ultrasonic vibration-assisted (UV-A) directed energy deposition (DED) has become a promising technology to improve the as-built quality and mechanical performance of metal parts. Ultrasonic frequency, a critical parameter of the ultrasonic vibration, can remarkably affect the ultrasonic vibration behaviors in assisting DED processes. However, leveraging varied ultrasonic frequencies in UV-A DED attracts little attention, and the effects of ultrasonic frequency have been thus overlooked. Linking ultrasonic frequency and part performance emphasizes the need for an understanding of the underlying thermodynamics in the melt pool due to the key role of thermal history in the DED process. In this work, we fabricated Inconel 718 (IN718) parts using the UV-A DED process under different levels of ultrasonic vibration frequency (including 0, 25 kHz, 33 kHz, and 41 kHz). For the first time, melt pool size, temperature distribution, and peak temperature within the melt pool, as well as the peak temperature fluctuation within a layer deposition, were studied. Porosity and thermal-dependent properties including grain size and microhardness were also investigated. The results indicated that the increase in ultrasonic frequency led to an increase in both melt pool size and peak temperature. Moreover, the lowest porosity was obtained at an ultrasonic frequency of 25 kHz, while grain refinement and microhardness enhancement were achieved at the highest frequency of 41 kHz. This investigation provides great insights into the link among ultrasonic frequency, melt pool formation, temperature field, porosity, and thermal-dependent properties in the UV-A DED-built IN718 parts.

Effect of ultrasonic frequency on the bacterial community structure during biofouling formation in microfiltration membrane bioreactors for wastewater treatment

Biofouling significantly reduces the performance efficiency of membrane bioreactors due to the colonization and accumulation of a matrix of microorganisms. In order to investigate the effect of ultrasonic frequency on biofilm formation and bacterial ecology at different frequencies, four microfiltration membrane modules were subjected at 0, 20, 30 and 40 kHz in pilot-scales. The results of massive parallel sequencing showed that the application of ultrasonic frequency significantly affected the bacterial population in biofouling and modifies the species richness even at low frequency. This research reveals that the application of ultrasonic frequencies avoids the colonization of Acinetobacter genus, which is considered an initial colonizer of biofouling and clogging in the submerged membrane reactor, fact that caused problems in full-scale wastewater treatment plant. The promotion of Gordonia genus was observed during the application of any ultrasounds frequencies (20,30 and 40 Hz). The compositional statistics data exposed the similarity of bacterial communities under medium-high ultrasonic frequency, while those great distances were found in both low and no-ultrasounds frequencies apply. These results suggest that the application of ultrasounds in membrane bioreactor for treating wastewater could be effective in the potential reduction of biofouling formation in order to improve the to improve the useful life of this system with short periods of application of ultrasound.

Effect of ultrasonic frequency and surfactant addition on microcapsule destruction

In a previous study, we found that cavitation bubbles cause the ultrasonic destruction of microcapsules containing oil in a shell made of melamine resin. The cavitation bubbles can be smaller or larger than the resonance size; smaller bubbles cause Rayleigh contraction, whereas larger bubbles are not involved in the sonochemical reaction. The activity in and around the bubble (e.g., shear stress, shock wave, microjet, sonochemical reaction, and sonoluminescence) varies substantially depending on the bubble size. In this study, we investigated the mechanism of the ultrasonic destruction of microcapsules by examining the correlations between frequency and microcapsule destruction rate and between microcapsule size and cavitation bubble size. We evaluated the bubbles using multibubble sonoluminescence and the bubble size was changed by adding a surfactant to the microcapsule suspension. The microcapsule destruction was frequency dependent. The main cause of microcapsule destruction was identified as mechanical resonance, although the relationship between bubble size and microcapsule size suggested that bubbles smaller than or equal to the microcapsule size may also destroy microcapsules by applying shear stress locally.

Effects of multi-frequency ultrasound on physicochemical properties, structural characteristics of gluten protein and the quality of noodle.

In this study, the influence of multi-frequency ultrasound irradiation on the functional properties and structural characteristics of gluten, as well as the textural and cooking characteristics of the noodles were investigated. Results showed that the textural and cooking characteristics of noodles that contain less gluten pretreated by multi-frequency ultrasonic were ultrasonic frequency dependent. Moreover, the noodles that contain a smaller amount of sonicated gluten could achieve the textural and cooking quality of commercial noodles. There was no significant difference in the cooking and texture characteristics between commercial noodles and noodles with 12%, 11%, and 10% gluten pretreated by single-frequency (40kHz), dual-frequency (28/40kHz), and triple-frequency sonication (28/40/80kHz), respectively. Furthermore, the cavitation efficiency of triple-frequency ultrasound was greater than that of dual-frequency and single-frequency. As the number of ultrasonic frequencies increased, the solubility, water holding capacity and oil holding capacity of gluten increased significantly (p<0.05), and the particle size was reduced from 197.93±5.28nm to 110.15±2.61nm. Furthermore, compared to the control group (untreated), the UV absorption and fluorescence intensity of the gluten treated by multi-frequency ultrasonication increased. The surface hydrophobicity of gluten increased from 8159.1±195.87 (untreated) to 11621.5±379.72 (28/40/80kHz). Raman spectroscopy showed that the α-helix content of all sonicated gluten protein samples decreased after sonication, while the β-sheet and β-turn content increased, and tryptophan and tyrosine residues were exposed. Through scanning electron microscope (SEM) analysis, the gluten protein network structure after ultrasonic treatment was loose, and the pore size of the gluten protein network increased from about 10μm (untreated) to about 26μm (28/40/80kHz). This work elucidated the effect of ultrasonic frequency on the performance of gluten, indicating that with increasing frequency combination increases, the ultrasound effect became more pronounced and protein unfolding increased, thereby impacting the functional properties and the quality of the final product. This study provided a theoretical basis for the application of multi-frequency ultrasound technology in the modification of gluten protein and noodle processing.

Ultrasound-assisted electrochemical treatment for phenolic wastewater.

With the rapid development of industry, especially the rapid rise of the chemical industry, the problem of water pollution is becoming more and more serious. Among them, the discharge of organic pollutants represented by phenolic substances has always been at the forefront. In this paper, ultrasound-assisted electrochemical treatment for phenolic wastewater is investigated. The effects of ultrasonic frequency, current, pH value and the amount of fly ash-loaded titanium TiO2-Fe3+ particles on phenol removal from phenol-containing wastewater are investigated. The experimental results demonstrate that the removal rate of phenol in phenol-containing wastewater is the best when ultrasonic frequency is 45kHz, power is 200W, the current is 1.2 A, pH is 5 and the dosage of fly ash-loaded titanium TiO2-Fe3+ particles is 3g. In addition, microwave-assisted-Fenton reagent treatment for phenol wastewater is investigated. The effects of Fenton reagent dosage, initial pH value, microwave power density and radiation time on phenol degradation rate are investigated. The results show that microwave can accelerate the reaction rate, reduce the number of metal ions, save the process cost and reduce the difficulty of post-treatment. Finally, the research status of phenol wastewater treatment technology at the present stage is reviewed, and the future development direction is discussed.

Ultrasound-assisted regeneration of zeolite/water adsorption pair.

The use of ultrasound to enhance the regeneration of zeolite 13X for efficient utilization of thermal energy was investigated as a substitute to conventional heating methods. The effects of ultrasonic power and frequency on the desorption of water from zeolite 13X were analyzed to optimize the desorption efficiency. To determine and justify the effectiveness of incorporating ultrasound from an energy-savings point of view, an approach of constant overall input power of 20 or 25W was adopted. To measure the extent of the effectiveness of using ultrasound, the ultrasonic-power-to-total power ratios of 0.2, 0.25, 0.4 and 0.5 were investigated and the results compared with those of no-ultrasound (heat only) at the same total power. To analyze the effect of ultrasonic frequency, identical experiments were performed at three nominal ultrasonic frequencies of ~28, 40 and 80kHz. The experimental results showed that using ultrasound enhances the regeneration of zeolite 13X at all the aforementioned power ratios and frequencies without increasing the total input power. With regard to energy consumption, the highest energy-savings power ratio (0.25) resulted in a 24% reduction in required input energy and with an increase in ultrasonic power, i.e. an increase in acoustic-to-total power ratio, the effectiveness of applying ultrasound decreased drastically. At a power ratio of 0.2, the time required for regeneration was reduced by 23.8% compared to the heat-only process under the same experimental conditions. In terms of ultrasonic frequency, lower frequencies resulted in higher efficiency and energy savings, and it was concluded that the effect of ultrasonic radiation becomes more significant at lower ultrasonic frequencies. The observed inverse proportionality between the frequency and ultrasound-assisted desorption enhancement suggests that acoustic dissipation is not a significant mechanism to enhance mass transfer, but rather other mechanisms must be considered.

Size selection of levitated aerosol particulate in an ultrasonic field.

The ability to characterize and manipulate micron-size aerosols and particulate is useful for applications in medicine, environmental monitoring, and chemical-biological defense. An experiment was conducted to determine the effects of ultrasonic frequency on the size-selectivity of concentration of polyglycol aerosols that are entrained in air within an ultrasonic resonator. Measurements of aerosol concentration at 4, 25, and 40 kHz were compared with theoretical predictions based on one-dimensional models for radiation pressure and asymmetric Stokes drag effects. The experimental results are shown to be consistent with theory.

Ultrasound-Ionic Liquid Pretreatment Enhanced Conversion of the Sugary Food Waste to 5-Hydroxymethylfurfural in Ionic Liquid/Solid Acid Catalyst System

The purpose of this study was to efficiently convert the sugary food waste (SFW) to 5-hydroxymethylfurfural (5-HMF) by ultrasound-[Bmim]Cl pretreatment in ionic liquids (ILs)-ion exchange resin system. The effect of ultrasonic pretreatment on SFW and the effect of ultrasonic frequency, ILs, acid resin and catalyst load on SFW conversion were studied. The kinetic curve and the relationship between products and intermediates were studied. In addition, the structure of SFW was also studied by FT-IR and SEM. The results indicated ultrasound-[Bmim]Cl pretreatment can significantly promote the dissolution of cellulose in SFW, and the optimal ultrasonic frequency, solvent and catalyst were 20 + 40 + 60 kHz, [Bmim]Cl and D001-cc resin, respectively; under the best reaction conditions, the maximum 5-HMF yields from the orange and apple wastes were 42.15 and 44.66 mol%, respectively. The kinetic studies showed that the early stage of 100 and 120 °C was mainly the hydrolysis reaction, and late stage was mainly isomerization and dehydration reaction; the early stage of 140 and 160 °C was a rapid hydrolysis and dehydration reaction, and the late stage was mainly the rehydration reaction of 5-HMF. The relationship between the intermediate precursors and 5-HMF showed that the rates of formation and rehydration of 5-HMF increased with the increase in temperature, and the formation reaction was mainly concentrated in zone II. The FT-IR and SEM results of degradation products showed that cellulose in SFW was more easily hydrolyzed at high temperature and long time.

Ultrasound enhanced solid-phase extraction of ultra-trace arsenic on Fe3O4@AuNPs magnetic particles

Using ultrasound (US) to reduce the agglomeration of magnetic materials has attracted many researchers’ attention in the field of magnetic solid phase extraction (MSPE). This paper showed that even the simple magnetic material (Fe3O4@AuNPs) can stimulate excellent arsenic (As) enrichment performance with the assistance of US. Compared with stirring dispersion, the extraction efficiencies of Fe3O4@AuNPs for 0.2 μg L−1 As(III) and As(V) improved by a factor of about 6.2- and 5.7-times with ultrasonic agitation, respectively. Importantly, when the ultrasonic frequency and power are varied within a certain range, the extraction efficiency was increased by about 50% and 130%, respectively. This effect of ultrasonic frequency and power on the enrichment of arsenic by magnetic materials has never been reported. The number, dispersion uniformity and energy released by the bursting of cavitation bubbles under different conditions are considered to be the main reasons for the above phenomena. Additionally, the As(III) or As(V) can be converted into a gaseous product by in-situ slurry chemical hydride generation (SCHG) technology, and the material adsorbed by the material can be effectively removed, thereby ensuring that the complex is repeated at least 5 times or more. Under the optimized conditions, the whole enrichment process can be shortened from ~1 h to several minutes in the presence of US. At the same time, the linear calibration range was 0.01–3.0 μg L−1 documenting that this US-assisted dispersive MSPE method coupled with a sensitive spectral detector (e.g. atomic fluorescence spectrometer, AFS) is suitable for analysis of inorganic As in natural water samples. The content of arsenic in five kinds of natural water samples ranged from 34 ng L−1 to 2.3 μg L−1.

Ultrasound-Assisted Marination: Role of Frequencies and Treatment Time on the Quality of Sodium-Reduced Poultry Meat.

The objective of this study was to evaluate the influence of high-power ultrasound (US) to accelerate marination of chicken breast; the effect of ultrasonic frequencies and marination times were investigated on samples containing full sodium levels (FS) or 25% sodium reduction, either by reducing NaCl (R50) or by its partial substitution with KCl (SR). Chicken breasts were marinated in plastic bags immersed in an ultrasonic bath operating with a frequency of 25, 45 or 130 kHz for 1, 3 or 6 h at a temperature of 2.5 ± 0.5 °C. Chicken marinated using US had a significantly higher uptake (p < 0.05) of sodium compared to control samples (no US) marinated for the same amount of time. No significant changes were observed in the quality parameters of sonicated chicken samples compared to controls. However, significant decreases (p < 0.05) in lipid oxidation were observed in SR samples when treated by US. These results suggest the use of ultrasound in the meat processing industry as a novel technology for enhancing marination processes and formulation of reduced sodium meat products.

Ultrasonic vibration-assisted laser engineered net shaping of Inconel 718 parts: Effects of ultrasonic frequency on microstructural and mechanical properties

Abstract Laser additive manufacturing (LAM) becomes a competitive method in fabricating Inconel 718 (IN718) parts in recent years. Among different LAM processes, laser engineered net shaping (LENS) has small substrate deformation, unique advantages of part remanufacturing capability, high part building efficiency, and high efficiency of powder utilization. LENS of IN718 is receiving extensive research and industrial applications. However, several problems (e.g. heterogeneous microstructures, internal cavities, and large porosity) still exist in LENS-fabricated IN718 parts. To reduce these problems, ultrasonic vibration-assisted (UV-A) LENS has been developed based on ultrasonic vibration’s actions in materials melting and solidification processes. This process has been proven to be an effective manufacturing method in fabrication of IN718 parts. As one of the basic parameters of ultrasonic vibration, ultrasonic frequency will greatly influence the UV-A LENS processes, since it significantly affects ultrasonic vibration-induced two nonlinear effects (including cavitation and acoustic streaming) in materials melting and solidification processes. The influences of ultrasonic frequency in UV-A LENS processes are still unknown. The effects of ultrasonic frequency on microstructural properties (such as grain sizes, phase composition, precipitated phase morphology, bonding interface, and porosity) and mechanical properties (including microhardness, wear rate, and elastic modulus) of UV-A LENS fabricated IN718 parts are studied in this investigation. With the ultrasonic frequency increasing in UV-A LENS, the grain size is decreased, Laves phase is changed from long-bar columnar shape to particle shape, the bonding interface becomes smoother, the porosity is increased, the microhardness is increased, and the elastic modulus is decreased.

Rotary ultrasonic machining of carbon fiber–reinforced plastic composites: effects of ultrasonic frequency

Rotary ultrasonic machining (RUM) is effective and efficient in cutting carbon fiber–reinforced plastic (CFRP) composites. With ultrasonic vibration assistance, both machining efficiency and machining effectiveness can be improved. Ultrasonic vibration has two major variables (including ultrasonic amplitude and ultrasonic frequency), which play important roles in RUM processes. Other intermediate variables, such as ultrasonic power and indentation depth, are directly related to these two variables. Effects of ultrasonic vibration amplitude have been extensively investigated in RUM hole making and surface machining processes. However, the effects of ultrasonic frequency in RUM have not been reported. The effects of ultrasonic frequency under different combinations of tool rotation speed, feed rate, and depth of cut on output variables, including cutting forces, surface roughness, and machined surface characteristics, are investigated, for the first time, in this study. The critical frequency is analyzed for the RUM process. Three different levels of ultrasonic frequencies are generated and applied to the RUM process. The kinematic motions of abrasive grains in RUM with different frequencies are analyzed and discussed. The results show that RUM with higher frequency of ultrasonic vibration is a more effective machining process, leading to cutting force reduction and the machined surface quality improvement.

Fracture test of nanocomposite ceramics under ultrasonic vibration based on nonlocal theory

Based on the non-local theory, the dispersion characteristics of ultrasonic vibration in three-point bending are analyzed, and the effects of ultrasonic frequency and amplitude on the dispersion characteristics are obtained through theoretical analysis. Three-point bending tests were carried out using an ultrasonic vibration system and specimens, and the test process as well as the workpiece after the test were observed and analyzed. The effects of ultrasonic vibration on fracture properties and crack growth mechanism of ceramics under different loading conditions were verified by experiments. The introduction of ultrasonic vibration changes the internal stresses of the ceramic fracture, affects the hardness of the workpiece, and also causes the scattering of particles, which leads to the intensification of ultrasonic attenuation and phase velocity dispersion. SEM and XRD analysis showed that with the increase in ultrasonic frequency and amplitude, the transgranular fracture was more obvious, tearing edges and dimples increased, and microvoids increased in size and number. Ultrasonic vibration can cause ZrO2 to undergo t-m phase transformation under stress induction and absorb the strain, thus greatly improving the mechanical properties of nanocomposite ceramics. Due to the toughening mechanism of the inherent phase transformation, the material has improved plastic mechanical properties, and it is easier to achieve ductile domain processing.

Effect of ultrasonic frequency on cavitation behavior, microstructure and mechanical properties of AZ80 magnesium alloy

In this paper, the effects of single-frequency ultrasonic treatment (SUT) and dual-frequency ultrasonic treatment (DUT) on the microstructure and mechanical properties of AZ80 magnesium alloy were investigated by numerical simulation and experimental research. Numerical simulation shows that the effective cavitation area of 15 kHz SUT is about twice that of 20 kHz, while the cavitation area of the 15 + 20 kHz DUT is larger than the sum of two SUT. The experimental results find that grains are refined after ultrasonic treatment, while the refinement effects of SUT and DUT are different. Under the same power condition, the refinement effect of 15 kHz is better than 20 kHz, but the DUT has higher efficiency than both SUT. The average grain size of untreated ingot is 174 μm, which is reduced to 123 μm, 99 μm and 80 μm after 20 kHz SUT, 15 kHz SUT and 15 + 20 kHz DUT, respectively. Therefore, applying DUT is more efficient in refining the grain size of the AZ80 magnesium alloy.

Does power ultrasound affect heterogeneous electron transfer kinetics?

Most of the observations seen in the application of power ultrasound in electrochemistry or also known as sonoelectrochemistry are due to enhanced mass-transport of electroactive species from the bulk solution to the electrode surface caused by efficient stirring, acoustic streaming and cavitation. However, fundamental studies on the effect of ultrasound on electrode kinetics i.e. on the electron-transfer are scarce. The main question still remains to be answered:Does power ultrasound affect heterogeneous electron transfer kinetics?This opinion paper discusses the effect of ultrasonic frequency and intensity upon the electrode kinetic parameters such as the half-wave potential (E1/2) and the apparent heterogeneous rate constant (ko). A few sonoelectrochemical studies have highlighted changes in half-wave potential and in apparent heterogeneous rate constant for both quasi-reversible and irreversible systems when the data were compared to silent conditions. These observations are thought to be due to the contribution of mass-transport and macroscopic temperature effects, as well as the continuous cleaning of the electrode surface caused by the collapse of high-energy cavitation bubbles and the production of high velocity jets of liquid. However, there still remains mechanistic controversy in assigning whether these findings could also be due to localised temperature increases, the contribution of sonolysis products or solely due to enhanced mass-transport at the electrode surface. Thus, the effect of stirring, macroscopic temperature and sonication time upon these electrode kinetic parameters is also shown to be important factors in comparing the validity of any sonoelectrochemical effects.

Tailoring Characteristics of PEDOT:PSS Coated on Glass and Plastics by Ultrasonic Substrate Vibration Post Treatment

In this work, we excited as-spun wet films of PEDOT:PSS by ultrasonic vibration with varying frequency and power. This is a low-cost and facile technique for tailoring the structural and surface characteristics of solution-processed thin films and coatings. We deposited the coatings on both rigid and flexible substrates and performed various characterization techniques, such as atomic force microscopy (AFM), scanning electronic microscopy (SEM), X-ray photoelectron spectroscopy (XPS), attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR), transmittance, electrical conductivity, and contact angle measurements, to understand how the ultrasonic vibration affects the coating properties. We found that as a result of ultrasonic vibration, PEDOT:PSS sheet conductivity increases up to five-fold, contact angle of water on PEDOT:PSS increases up to three-fold, and PEDOT:PSS roughness on glass substrates substantially decreases. Our results affirm that ultrasonic vibration can favor phase separation of PEDOT and PSS and rearrangement of PEDOT-rich charge transferring grains. In addition to providing a systematic study on the effect of ultrasonic frequency and power on the film properties, this work also proves that the ultrasonic vibration is a novel method to manipulate and tailor a wide range of properties of solution-processed thin films, such as compactness, chain length and arrangement of polymer molecules, conductivity, and surface wettability. This ultrasonication method can serve organic, printed and flexible electronics.

Cavitation Bubble Dynamics Induced by Hydrodynamic Pressure Oil Film in Ultrasonic Vibration Honing

During ultrasonic vibration honing (UVH), a thin hydrodynamic oil film formed can seriously affect the cavitation effect in the grinding fluid, but the mechanism is still unclear now. Based on the hydrodynamics theory, a revised cavitation bubble model with oil film pressure is developed, and it has been calculated by the four-order Runge–Kutta method. The calculation results show that the oil film pressure under UVH is a positive–negative alternant pulse pressure, and it can induce the secondary expansion of the bubble, leading to double microjets during the process of the bubble collapsing. The effects of ultrasonic amplitude, ultrasonic frequency, oil film height, and reciprocation speed of the honing stone on the bubble dynamics are discussed. With the increase of ultrasonic amplitude, the amplitude of the bubble expansion is increased, and the oscillation interval is extended. As increasing normalized oil film height, the variation of the bubble first expansion is slight, while the amplitude of the bubble secondary expansion is reduced and the oscillation interval is also shortened. The main effect of ultrasonic frequency and reciprocation speed of the honing stone on the bubble dynamics is connected with the secondary bubble expansion. The bubble secondary expansion is decreased with the increasing reciprocation speed of the honing stone, ultrasonic frequency, and oil film height. The results of the simulations are consistent with the surface roughness measurements well, which provides a theoretical prediction method of cavitation bubbles control.

Formation of inorganic nitrogenous byproducts in aqueous solution under ultrasound irradiation

The effects of ultrasonic frequency, power intensity, temperature and sparged gas on the generation of nitrogenous by-products NO2− and NO3− have been investigated, and the new kinetics model of NO2− and NO3− generation was also explored. The results show that the highest primary generation rate of NO2− and NO3− by direct sonolysis in the cavitation bubbles (represented by k1′ and k2′, respectively) was obtained at 600 kHz and 200 kHz, respectively, in the applied ultrasonic frequency range of 200 to 800 kHz. The primary generation rate of NO2− (represented by k1′) increased with the increasing ultrasonic intensity while the primary generation rate of NO3− (represented by k2′) decreased. The lower temperature is beneficial to the primary generation of both NO2− and NO3− in the cavitation bubbles. The optimal overall yields of both NO2− and NO3− were obtained at the N2/O2 volume (in the sparged gas) ratio of 3:1 which is near to the ratio of N2/O2 in air. The dissolved O2 is the dominant oxygen element source for both NO and NO2, compared with water vapor. Ultrasonic irradiation can significant enhance the recovery rates of dissolved N2 and O2 and thus keep the N2 fixation reaction going even without aeration.

Chemical coloring on stainless steel by ultrasonic irradiation

To solve the problems of high temperature and non-uniformity of coloring on stainless steel, a new chemical coloring process, applying ultrasonic irradiation to the traditional chemical coloring process, was developed in this paper. The effects of ultrasonic frequency and power density (sound intensity) on chemical coloring on stainless steel were studied. The uniformity of morphology and colors was observed with the help of polarizing microscope and scanning electron microscopy (SEM), and the surface compositions were characterized by X-ray photoelectric spectroscopy (XPS), meanwhile, the wear resistance and the corrosion resistance were investigated, and the effect mechanism of ultrasonic irradiation on chemical coloring was discussed. These results show that in the process of chemical coloring on stainless steel by ultrasonic irradiation, the film composition is the same as the traditional chemical coloring, and this method can significantly enhance the uniformity, the wear and corrosion resistances of the color film and accelerate the coloring rate which makes the coloring temperature reduced to 40°C. The effects of ultrasonic irradiation on the chemical coloring can be attributed to the coloring rate accelerated and the coloring temperature reduced by thermal-effect, the uniformity of coloring film improved by dispersion-effect, and the wear and corrosion resistances of coloring film enhanced by cavitation-effect. Ultrasonic irradiation not only has an extensive application prospect for chemical coloring on stainless steel but also provides an valuable reference for other chemical coloring.