Water irradiation by high-frequency ultrasonic wave: effects on properties of passive film formed on stainless steel

In this paper an aqueous solution was irradiated with a 1.63MHz ultrasonic wave. It is shown that if stainless steel can passivate under dynamic polarization in this medium, under static polarization, the latter does not show any repassivation behaviour with time. This is attributed to a diminution of the diffusion layer thickness that is developed at the electrode/electrolyte interface, which is associated with a production of H(2) species by sonolysis and which maintains reductive conditions at the interface. The oxide film formed under ultrasonic irradiation for 1h at a passive potential of+0.2V(SCE) shows an early stage of passivation and an increased disordered state, which implies a considerable decrease in the corrosion resistance behaviour of the sample. The polarization resistance of the stainless steel R(p) is divided by a value of 4.5 under ultrasonic conditions.     

Morphological and compositional analysis of passive film on austenitic stainless steel in nitric acid medium

Passive film properties of type 304L stainless steel in nitric acid medium are investigated in both ex situ and in situ conditions. Ex situ results revealed that variation in passive film morphology occurs depending upon the concentration and time of immersion. In situ surface morphological investigation showed formation of platelet like structures at lower concentrations (0.1 M, 0.5 M), and towards higher concentration (0.6 M, 1 M) the platelet like structures got agglomerated, homogenized and started depleting from the surface leading to opening up of oxide boundaries. Compositional analysis of the passive film revealed duplex nature at lower concentration consisting of hydroxide and oxide layer, and with increasing concentration oxide layer predominates over the surface.     

Low-nickel stainless steel passive film in simulated concrete pore solution: A SIMS study

Low-nickel and AISI 304 austenitic stainless steel (SS) passive films were studied using secondary ion mass spectrometry (SIMS). An alkaline Ca(OH)₂ saturated test solution containing different chloride additions was used at room temperature. The passive film formed consists mainly of an inner chromium-rich oxide layer and an outer iron-rich oxide layer. The chemistry of the passive film depends strongly on the chloride content in the alkaline solution. Under these exposure conditions nickel was detected in the outer part of the oxide, whereas chloride ions were not found in the passive film for either the low-nickel or AISI 304 SS alloys.     

Chemical activation of ultrasonic cavitation

A method for intensifying ultrasonic cavitation in water and aqueous solutions has been proposed, which consists of a chemical fixation of dissolved oxygen. The influence of selected reducing agents on the intensity of cavitation in water and alkaline solutions has been investigated.     

Nature of oxygen in the passive film on stainless steels in 0.1 M NaCl solution

Three different oxygen species, O^2–, OH^–, and H₂O, are introduced into the deconvolution of the oxygen peaks measured in the prior study and their true concentrations are investigated in the depth profile. It is found that H₂O exists mainly in the outermost part of the passive film at the interface of solution and the passive film. OH^– and O^2– are found throughout the passive film; they have a maximum concentration in the outer layer at around 10 to 20 Å depth, with a concentration of 40 at.% for the stainless steel 29-4-2 and 50 at.% for 18-12. After the maximum the concentrations are sharply reduced with increasing sputtering time and remain at a constant concentration of about 10 at.% at 35 Å depth. Both species still exist at this concentration even after long time sputtering.     

Influence of nitrogen on the mechanism of austenitic stainless steel hardening

On the example of a C18N12M2 austenitic stainless steel, the influence of nitrogen (whose content varied from 0 to 0.45 wt.%) on the grain boundary hardening coefficient k _h entering into the Hall-Patch equation is analyzed. High values of k _h in steels with and without nitrogen are found. The data of the Auger analysis show that the hardening coefficient in the steel without nitrogen is determined by the grain-boundary segregation of carbon and oxygen. The grain-boundary hardening in the steel with nitrogen is not connected with the predominant segregation of nitrogen at grain boundaries. It is completely governed by intragranular processes—interaction of nitrogen atoms with dislocations. Omsk State Pedagogical University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 47–52, July, 1999.     

Polymerization resulting from ultrasonic cavitation

Polymerization due to ultrasonically induced cavitation is reported for a number of compounds: bromobenzene, styrene, isoprene, and methyl methacrylate. The molecular weight of the polymethylmethacrylate produced through ultrasound is considerably lower than that due to normal aging. The bromobenzene and styrene products are dark friable solids. The isoprene product has an ultra-violet absorption suggesting a conjugated system of about ten carbon-carbon bonds in length.     

Influence of concentration of substances used in ultrasonic cleaning in alkaline solutions on cavitation intensity

Cavitation intensity vs. temperature of aqueous solutions of three substances most frequently used in ultrasonic cleaning: sodium carbonate, metasilicate and phosphate were measured. Shapes of cavitation - temperature curves for 0-10% solutions during heating and cooling in the 20-70 degrees C temperature range were compared. Maximal cavitation intensity curves for these solutions at 60 degrees C (most frequently used temperature of ultrasonic cleaning in aqueous solutions), in identical conditions and at various ultrasound frequencies are presented as diagrams.     

Influence of water cavitation peening with aeration on fatigue behaviour of SAE1045 steel

Water cavitation peening (WCP) with aeration is a recent potential method in the surface enhancement techniques. In this method, a ventilation nozzle is adopted to improve the process capability of WCP by increasing the impact pressure, which is induced by the bubble collapse on the surface of components in the similar way as conventional shot peening. In this paper, fatigue tests were conducted on the both-edge-notched flat tensile specimens to assess the influences of WCP on fatigue behaviour of SAE1045 steel. The notched specimens were treated by WCP, and the compressive residual stress distributions in the superficial layer were measured by X-ray diffraction method. The tension-tension (R = S_min/S_max = 0.1, f = 10 Hz) fatigue tests and the fracture surfaces observation by scan electron microscopy (SEM) were conducted. The experimental results show that WCP can improve the fatigue life by inducing the residual compressive stress in the superficial layer of mechanical components.     

Facile preparation of super-hydrophobic and super-oleophilic silica film on stainless steel mesh via sol-gel process

A super-hydrophobic and super-oleophilic silica film on stainless steel mesh was obtained by simple sol-gel method using tetraethoxysilane (TEOS) and methyltriethoxysilane (MTES) as precursors. The super-hydrophobic and super-oleophilic properties were achieved owing to the hierarchical structure of the silica film with methyl groups terminated domains constructed on the mesh. The effects of the particle size, molar ration of MTES/TEOS, molar concentration of TEOS and aging of the silica sol on the hydrophobicity of the silica film were discussed. With increasing the dimensional size of silica particle, molar ration of MTES/TEOS, molar concentration of TEOS and aging period, the hydrophobicity of the silica film can be enhanced due to the increase of the surface roughness or coverage of the methyl groups. Besides, diiodomethane droplet can spread out on the silica film within 6.71 s for the capillary force and intrinsic oleophilicity of the methyl groups.     

超声空化对丙酮激光喇曼光谱的影响

本研究设计了一种可吸入超声的喇曼光谱样品池,对丙酮的激光喇光曼谱的检测表明,超声空化降低了喇曼光谱的强度,我们认为,超声空化减少了激光光路上参与散射的丙酮分子数是光谱强度降低的主要原因。     

Dependence of the cavitation threshold on the ultrasonic frequency

A theoretical prediction of the dependence of the ultrasonic cavitation threshold for sonoluminescence on the acoustic frequency is presented. Data were obtained from the numerical solution of nonlinear oscillations of a single isolated gas-filled bubble in a viscous compressible liquid. Principal reasons for the increase of cavitation threshold with acoustic frequency and liquid viscosity are also briefly discussed.The author wishes to thank professor Ivo Hrazdira for permanent support of this work. All calculations were run on ICL 2950/10 computer of the Regional Computing Centre of the Czechoslovak Academy of Sciences, Brno.     

Electrical detection of the ultrasonic cavitation onset

We propose a new technique for the study of ultrasonic cavitation. This method is based on the quantification of the electrical admittance variations of the emitter in a range around the resonance frequency at different excitation levels. As the cavitation threshold is reached, the state of the fluid is changing; we evaluate these changes. The high-power piezoelectric transducer is modelled through an analytical model, which is used to relate the characteristics of the fluid domain (bubble density, extent) to the electrical admittance (peak value, resonance frequency, and bandwidth). Thus, the admittance we measure allows us to determine the characteristics of the bubbly liquid. The procedure is applied to the inertial cavitation field generated at 24kHz at very high amplitudes. The results obtained show that a very high bubble density layer is formed at the surface of the sonotrode.     

A dual passive cavitation detector for localized detection of lithotripsy-induced cavitation in vitro

A passive cavitation detector (PCD) identifies cavitation events by sensing acoustic emissions generated by the collapse of bubbles. In this work, a dual passive cavitation detector (dual PCD), consisting of a pair of orthogonal confocal receivers, is described for use in shock wave lithotripsy. Cavitation events are detected by both receivers and can be localized to within 5 mm by the nature of the small intersecting volume of the focal areas of the two receivers in association with a coincidence detection algorithm. A calibration technique, based on the impulse response of the transducer, was employed to estimate radiated pressures at collapse near the bubble. Results are presented for the in vitro cavitation fields of both a clinical and a research electrohydraulic lithotripter. The measured lifetime of the primary growth-and-collapse of the cavitation bubbles increased from 180 to 420 microseconds as the power setting was increased from 12 to 24 kV. The measured lifetime compared well with calculations based on the Gilmore-Akulichev formulation for bubble dynamics. The radiated acoustic pressure 10 mm from the collapsing cavitation bubble was measured to vary from 4 to 16 MPa with increasing power setting; although the trends agreed with calculations, the predicted values were four times larger than measured values. The axial length of the cavitation field correlated well with the 6-dB region of the acoustic field. However, the width of the cavitation field (10 mm) was significantly narrower than the acoustic field (25 mm) as bubbles appeared to be drawn to the acoustic axis during the collapse. The dual PCD also detected signals from "rebounds," secondary and tertiary growth-and-collapse cycles. The measured rebound time did not agree with calculations from the single-bubble model. The rebounds could be fitted to a Rayleigh collapse model by considering the entire bubble cloud as an effective single bubble. The results from the dual PCD agreed well with images from high-speed photography. The results indicate that single-bubble theory is sufficient to model lithotripsy cavitation dynamics up to time of the main collapse, but that upon collapse bubble cloud dynamics becomes important.     

Local electrical characteristics of passive films formed on stainless steel surfaces by current sensing atomic force microscopy

A current sensing atomic force microscope was used to study the topography and the local electronic properties of the passive film formed on a duplex ferrite-austenite stainless steel (Uranus 50). Comparison of current maps with topography AFM images reveals that the passive film covering austenite and ferrite phases exhibits different properties. On freshly formed passive film, a high and homogenous resistance (typically 10 GΩ for 1 V) characterises the film on austenite grains while current maps of the passive layer covering the ferrite grains show a high density of spots (few 100 MΩ for 1 V). Besides the current maps, local I-V curves acquired on austenite show wider band gap energy than the ones obtained on ferrite grains. Finally, the conductivity difference in passive films covering ferrite and austenite grains is discussed.     

强流脉冲离子束辐照对不锈钢耐腐蚀性能的影响

 利用强流脉冲离子束（HIPIB）对316L不锈钢进行了表面辐照处理,研究了HIPIB辐照对其在0.5mol/L H2SO4溶液中电化学腐蚀性能的影响。极化曲线测量结果表明,HIPIB辐照能够显著提高316L的抗腐蚀性能,自腐蚀电流对辐照次数的依赖性与自腐蚀电位相比明显较强。采用扫描电子显微镜（SEM）、X射线衍射（XRD）和电子探针（EPMA）分析辐照后试样表面形貌、表面层相结构和元素分布的变化。结果表明：HIPIB辐照使试样表面光滑化,表面层产生择优取向,且发生了杂质元素的选择性烧蚀,是316L不锈钢耐电化学腐蚀性能得以提高的主要原因。     

Spectroscopic analysis of CIGS2/CdS thin film solar cell heterojunctions on stainless steel foil

This paper presents a spectroscopic analysis of the interface between a CuIn_1−xGa_xS₂ (CIGS2) absorber and a CdS buffer layer on stainless steel foil by Auger electron spectroscopy (AES), inverse photoemission spectroscopy (IPES) and photoelectron spectroscopy (PES) such as X-ray photoelectron spectroscopy (XPS), and ultraviolet photoelectron spectroscopy (UPS). By combining these spectroscopic techniques, detailed information about the electronic and chemical properties of the CIGS2 surface and the CdS/CIGS2 interface can be obtained. The gallium concentration in CIGS2 films was found to increase continuously towards the Mo back contact. XPS analysis showed the presence of KCO₃ on the surface of CdS, deposited on etched and un-oxidized samples indicating diffusion of potassium. No potassium was observed on oxidized as well as samples having thicker CdS (50 nm) indicating the effectiveness of oxidation and chemical bath deposition (CBD) process in cleaning the sample surface effectively. In addition, investigation of the electronic level alignment at the interface has been carried out by combining PES and IPES. Conduction band offset of −0.45 (±0.15) eV and a valence band offset of −1.06 (±0.15) eV were measured. These unfavorable conditions limit efficiency of CIGS2 thin film solar cells.     

A comparison of ultrasonic cavitation intensity in liquids

Cavitation intensity in 37 organic liquids is compared with cavitation intensity in water under the same conditions. Temperature ranges are established over which cavitation intensities in these liquids are at their highest.     

Enhancement of ultrasonic cavitation yield by multi-frequency sonication

The paper reports the enhanced effect of multi-frequency ultrasonic irradiation on cavitation yield. The cavitation yield is characterized by electrical conductivity determination, fluorescence intensity determination and iodine release method. Two-frequency (28 kHz/0.87 MHz) orthogonal continuous ultrasound, two-frequency (28 kHz/0.87 MHz) orthogonal pulse ultrasound and three-frequency (28 kHz/1.0 MHz/1.87 MHz) orthogonal continuous ultrasound have been used. It has been found that the combined irradiation of two or more frequencies of ultrasound can produce a significant increase in cavitation yield compared with single frequency irradiation. The possible mechanisms of the enhanced effect are briefly discussed.     

Exploration of heterogeneous duplex grain structure in type 304 austenitic stainless steel using ultrasonic spectroscopy

Cyclic stress-strain tests at different temperatures for a given constant strain range on a single reference heat (9T2796) of Type 304 austenitic stainless steel showed many unexpected features. The metallographic investigations of the fatigued specimens showed existence of heterogeneous duplex grain structure of ASTM grain size numbers ranging from 1.6 to 3.2. Since it was not feasible economically to cut even a small portion, for the metallographic examination, of the machined and heat treated specimen ready for the test, a non-destructive technique was needed to sort out specimens according to their grain structures prior to testing. Results of using ultrasonic spectroscopy for this purpose are described in this work.