共查询到19条相似文献,搜索用时 78 毫秒
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《低温与超导》2021,49(2):55-60,104
水合物在相变蓄冷等领域具有广泛的应用前景,而降低水合物成核诱导期、提升水合物生长速率是影响水合物蓄冷技术发展的关键因素。开发了一套可视化水合物原位生成实验系统,通过反应釜底部气泡板持续产生气泡强化水合物成核生长,重点对鼓泡法下水合物诱导期和生长速率进行了研究。实验结果表明,气泡表面形成壳状水合物并不断堆积。鼓泡法显著地降低了甲烷水合物诱导期,在SDS体系下,鼓泡法对诱导期的缩减最高达到93.6%。同时,鼓泡法对后续水合物的生长也具有显著促进效果,使水合物生长速率提高15.1~37.5%。在纯水体系中,鼓泡法提高了甲烷气体的转化率,最高提高了14.57倍。同时实验呈现温度越低,气体转化率和水合物生长速率越大的规律。 相似文献
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采用分子动力学对CO2水合物生长进行模拟并分析其变化规律,探究了CO2水合物晶体生长的微观过程以及不同温度、压力条件对水合物生长特性的影响机理. CO2水合物的生长是从已有晶胞附近向外扩散并逐具有序性的过程,水分子间逐渐形成四面体氢键与CO2共同形成完整的水合物笼. 另外, CO2水合物生长需要合适的过冷度,在压力为30MPa、温度范围265K至275K,水合物笼型晶胞可正常生成,并且温度越低,生成速率越快;在高温290K和300K时,体系分子运动加剧,水合物笼直接散开. 此外,在温度为270K、不同压力条件下,发现相较温度而言,由于CO2溶解度随压力变化的不明显性,导致CO2水合物增长速度伴随压力的变化相对不敏感. 相似文献
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The electrochemical mechanism of Fe-Ni electrodeposition under ultrasonic was investigated by electrochemistry methods. Linear scanning voltammetry and cyclic voltammetry were used to show that the deposition process changed from the diffusion control under static conditions to an electrochemical control under ultrasonic conditions. Chronoamperometry curves showed that the Fe-Ni deposit occurred by a mechanism that instantaneous nucleation is followed by three-dimensional growth under charge transfer control. Chronopotentiogram indicated that because of the intensity of the ultrasound stripping effect, high ultrasonic power is unsuitable for electroforming Fe-Ni alloy, and a high current density is also not appropriate. Thus, the optimum parameters for Fe-Ni electrodeposition under ultrasonic conditions are ultrasonic power between 80 and 100 W (power density 0.28–0.35 W/cm2), and a current density lower than 10 mA/cm2 with temperature 323 K and pH 3. Experiments were performed to verify that the Fe-Ni masks prepared by ultrasonic-assisted electroforming had a good surface quality. The increase in ultrasonic power can obtain a larger grain size, thus got a low thermal expansion coefficient and a high hardness. Therefore, ultrasonic-assisted electrodeposition technology provides an effective and practically feasible manufacturing method for OLED Fe-Ni mask preparation. 相似文献
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V. N. Skokov V. P. Koverda A. V. Reshetnikov A. V. Vinogradov 《Thermophysics and Aeromechanics》2007,14(1):47-51
Experiments were carried out on ultrasonic cavitation in glycerin. The zone near the emitter has a structure from interacting
gas-vapor bubbles; this structure takes the form of fractal clusters. The photometry of passed laser emission was the tool
for studying dynamics of fluctuations. In transitive mode, the power spectrum of fluctuation varies by the law inversely proportional
to frequency. Distributions of local fluctuations are different from Gaussian and exhibit the property of scale invariance.
The qualitative behavior of the frequency dependence of the spectral fluctuation density was tested while varying the power
of the ultrasonic emitter. It was demonstrated that the growth of the high-frequency margin of flicker-type behavior evidences
for growing instability and can be considered as a forerunner of possible large-scale outbursts.
The work was financially supported by the Russian Foundation for Basic Research (Grant No. 05-08-01320a). 相似文献
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In this paper, the crystallization of L-glutamic acid with application of ultrasound was explored in detail, including the process of nucleation, polymorphic control and polymorphic transformation. The induction time and metastable zone widths (MSZWs) were measured with and without ultrasound during the nucleation process. The induction time and MSZWs were decreased by ultrasound and the induction time was further decreased by higher ultrasonic power. The calculated nucleation parameters (such as interfacial energy, critical nucleus size and critical Gibbs energy) showed an obvious decrease in the presence of ultrasound, indicating that the nucleation was enhanced with application of ultrasound. By adjusting the ultrasonic power in the quench cooling process, the difference in nucleation temperatures would determine the distribution of polymorphs. In further, the polymorphic transformation was investigated quantitatively, and to the best of our knowledge, it was the first time to study the transformation kinetics with ultrasound using Avrami-Erofeev model. In the transformation process, the crystallization mechanism of the stable form was modified by ultrasound. The ultrasound eliminated the nucleation element in the rate-limiting step and facilitated the crystal growth of stable form. Thus, the ultrasound has a profound influence on L-glutamic acid crystallization. 相似文献
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The effect of ultrasonic irradiation (42,150 Hz, 17 W dm(-3)/7.1 W cm(-2)) on the growth of calcite in the presence of the inhibitor nitrilotris(methylene phosphonic acid) (NTMP) was investigated at constant composition conditions. In seeded growth experiments, it was found that the inhibiting effect of NTMP on crystal growth could be seriously mitigated under influence of ultrasonic irradiation. An approximately twofold increase in volumetric growth rate was achieved during ultrasonic irradiation, and recovery of the growth rate following inhibition was strongly enhanced compared to growth experiments without ultrasonic irradiation. The results could be explained in part by the physical effect of ultrasound that causes breakage and attrition of poisoned crystals, which resulted in an increase in fresh surface area. Mass spectroscopy analysis of sonicated NTMP solutions revealed that there is also a chemical effect of ultrasound that plays an important role. Several breakdown products were identified, which showed that ultrasound caused the progressive loss of phosphonate groups from NTMP, probably by means of physicochemically generated free radicals and/or pyrolysis in the hot bubble-bulk interface. 相似文献
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The combination of ultrasound and photochemistry have been used to degrade an aqueous solution of 2,4,6-trichlorophenol. An ultrasonic probe of 22 kHz frequency and a UV tube of 15 W have been used. Anatase grade TiO2 was used as the semiconductor catalyst. The effect of parameters such as ultrasonic intensity, operating conditions, type of ultrasonic equipment, and mode of UV transmission have been studied. The sonophotochemical degradation has been found to be dependent on the intensity of sonication, temperature of the reaction, and the type of ultrasonic equipment used, but was independent of the mode of UV transmission. Enhancement in the degradation rate has been observed at a higher sonication intensity and temperature of the solution. 相似文献
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Ultrasonication is an emerging and evergreen technique for the efficient synthesis of the catalytically active heterostructured materials. In-situ one-pot ultrasonic-assisted synthesis method was demonstrated in this work for the fabrication of silver tungstate encrusted polypyrrole nanocomposite using semi-automatic ultrasonic probe maintained at 34°C/50 kHz ultrasonic frequency and at 150 W ultrasonic power. This material retains enhanced optical, electrical, morphological properties, photocatalytic behavior in photodegradation of congo red dye, tetracycline drug and its electrochemical sensing potential for the effective determination of a broad spectrum of antibacterial drug, nitrofurazone. Optical properties were investigated using UltraViolet–Visible diffuse reflectance spectral (UV–VIS DRS) data along with Tauc’s bandgap energy calculations. The morphological properties were examined using FESEM and TEM micrographs. All the PXRD and XPS details prove the effective distribution of PPy on the surface of Ag2WO4 rods with the help of powerful ultrasonic assistance. PPy acted as a support for nucleation and growth of Ag2WO4 and an inhibitor of phase transformations. Ag2WO4/PPy exhibits great photocatalytic behavior while comparing with pure PPy and Ag2WO4 in the degradation of carcinogenic dye congo red and antibiotic drug tetracycline. In addition to that, Ag2WO4/PPy modified GCE exposed a widespread linear range from 0.1 to 107 µM along with a very low detection limit of 12 nM and huge sensitivity of 1.74 µA µM−1cm−2 in the electrochemical determination of nitrofurazone. 相似文献
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Ovchinnikova OS Kertesz V Van Berkel GJ 《Rapid communications in mass spectrometry : RCM》2011,25(24):3735-3740
This paper describes the coupling of ambient pressure transmission geometry laser ablation with a liquid-phase sample collection into a continuous flow surface sampling probe/electrospray emitter for mass spectrometry based chemical imaging. The flow probe/emitter device was placed in close proximity to the surface to collect the sample plume produced by laser ablation. The sample collected was immediately aspirated into the probe and onto the electrospray emitter, ionized and detected with the mass spectrometer. Freehand drawn ink lines and letters and an inked fingerprint on microscope slides were analyzed. The circular laser ablation area was about 210 μm in diameter and under the conditions used in these experiments the spatial resolution, as determined by the size of the surface features distinguished in the chemical images, was about 100 μm. 相似文献
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Mahdi Chiha Oualid Hamdaoui Fatiha Ahmedchekkat Christian Pétrier 《Ultrasonics sonochemistry》2010,17(2):318-325
The aim of this work was to study the emulsification assisted by ultrasonic probe (22.5 kHz) and investigate the removal of copper(II) ions from aqueous solution using water-in-oil-in-water (W/O/W) emulsion liquid membrane process (ELM). The membrane was prepared by dissolving the extractant bis(2-ethylhexyl)phosphoric acid (D2EHPA) and the hydrophobic surfactant sorbitan monooleate (Span 80) in hexane (diluent). The internal phase consisted of an aqueous solution of sulfuric acid. Effects of operating parameters such as emulsification time, ultrasonic power, probe position, stirring speed, carrier (D2EHPA) and surfactant (Span 80) concentrations volume ratios of organic phase to internal striping phase and of external aqueous phase to membrane (W/O) phase, internal phase concentration and choice of diluent on the membrane stability were studied. With ultrasound, the W/O emulsion lifetime were much higher than those reported previously by mechanical agitation. The effect of carrier and Cu(II) initial concentration on the extraction kinetics was also investigated. Nearly all of the Cu(II) ions present in the continuous phase was extracted within a few minutes. Additionally, the influence of H2SO4 concentration on the stripping efficiency was examined. 相似文献
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The objective of this research was to modify the crystal shape and size of poorly water-soluble drug ropivacaine, and to reveal the effects of polymeric additive and ultrasound on crystal nucleation and growth. Ropivacaine often grow as needle-like crystals extended along the a-axis and the shape was hardly controllable by altering solvent types and operating conditions for the crystallization process. We found that ropivacaine crystallized as block-like crystals when polyvinylpyrrolidone (PVP) was used. The control over crystal morphology by the additive was related to crystallization temperature, solute concentration, additive concentration, and molecular weight. SEM and AFM analyses were performed providing insights into crystal growth pattern and cavities on the surface induced by the polymeric additive. In ultrasound-assisted crystallization, the impacts of ultrasonic time, ultrasonic power, and additive concentration were investigated. The particles precipitated at extended ultrasonic time exhibited plate-like crystals with shorter aspect ratio. Combined use of polymeric additive and ultrasound led to rice-shaped crystals, which the average particle size was further decreased. The induction time measurement and single crystal growth experiments were carried out. The results suggested that PVP worked as strong nucleation and growth inhibitor. Molecular dynamics simulation was performed to explore the action mechanism of the polymer. The interaction energies between PVP and crystal faces were calculated, and mobility of the additive with different chain length in crystal-solution system was evaluated by mean square displacement. Based on the study, a possible mechanism for the morphological evolution of ropivacaine crystals assisted by PVP and ultrasound was proposed. 相似文献