Influence enhancement effect of bi-frequency ultrasonic irradiation by TA fluorescence method

Based on a previous research of cavitation effect under bi-frequency ultrasound irradiation, this paper studies bi-frequency irradiations with similar experimental settings. The additional irradiation sources with frequencies of 1.04MHz, 0.8MHz and 1.7MHz are individually combined with the main ultrasonic irradiation source with frequency of 28kHz to form bi-frequency ultrasonic irradiation. The intensity of 28kHz irradiation was fixed at 12.5W/cm2, while the intensity of the ultrasound at the other three frequencies is varied from1 W/cm2 to 18 W/cm2. It turns out that under the influence of the bi-frequency irradiation, the fluorescence intensity is obviously greater than the sum of those at individual frequencies. So the frequency of the additional sonication strikingly influences the fluorescence enhancement effect. For example, the fluorescence enhancement effect of 1.04MHz is stronger than that of 1.7MHz, and the enhancement effect of 0.8MHz is further stronger than that of 1.04MHz. Under the sonic intensity of 7.9W/cm2, the fluorescence intensity of 1.04MHz is approximately twice that of 1.7MHz while the fluorescence intensity of 0.8MHz is approximately 1.5 times that of 1.04MHz.     

Silicon nanocrystallites produced via a chemical etching method and photoluminescence properties

Silicon nanocrystallites (NCs) were fabricated via a simple and inexpensive method. The Si powders were chemically etched in the mixture of hydrofluoric and nitric acid, followed by the ultrasonic vibration in benzene, de-ionized water, or ethanol. The as-prepared Si particles feature two different sizes of ~2 and ~10 nm, respectively. The smaller particles are Si NCs suspended in the solvent, and the larger ones are several small Si NCs wrapped in amorphous shell. As excited with line of 340–420 nm, the suspensions display violet-blue emissions, which relate to the quantum confinement effect. The photoluminescence intensity of benzene suspension is the strongest and that of ethanol is the weakest.     

An easier method of preparation of mesoporous anatase TiO2 nanoparticles via ultrasonic irradiation

Mesoporous anatase TiO₂ nanopowder was synthesised by the sol–gel method using ultrasonic irradiation. This method is simple and faster for the synthesis of phase pure mesoporous anatase TiO₂ nanopowder. The product is characterised by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron spectroscopy (TEM), thermo gravimetric analysis, Brunauer–Emmett–Teller (BET) surface area, UV–visible diffuse reflectance spectroscopy and Fourier transform infrared spectroscopy. Analysis of XRD patterns, SEM and TEM image shows that the average particles size is of 19.9 nm and has an anatase structure. The mesoporous nature was determined by the BET method using the Barrett–Joyner–Halenda (BJH) model.     

Annealing effect on the photoluminescence properties of ZnO nanorod array prepared by a PLD-assistant wet chemical method

Well-aligned ZnO nanorod arrays were synthesized by a wet chemical method on the glass substrate with ZnO thin film as seed layer prepared by pulsed laser deposition. The effect of annealing temperature on the luminescence characteristics was investigated. As the annealing temperature increased, the photoluminescence properties show a general enhancing tendency. The nanorod array with high ultraviolet emission and negligible visible light emission (designated by the photoluminescence intensity ratio of ultraviolet to visible emission of 66.4) is obtained by annealing the sample at 700 °C for 1 h. Based on the results of X-ray photoelectron spectroscopy and photoluminescence spectra, the mechanisms of visible emission were discussed.     

Preparation of ZnO nanorods through wet chemical method

The different morphologies of nanorods have been obtained via a simple wet chemical method in the present of polyethylene glycol (PEG, M_w = 4000) by using zinc nitrate hexahydrate (Zn(NO₃)₂·6H₂O) and ammonium hydroxide (NH₃·H₂O) as the starting materials. Samples were characterized by XRD, EDS, TEM, SEM, ED and PL. XRD results prove the formation of ZnO with wurtzite structure. The ED and HRTEM reveal that single ZnO nanorod is single crystal and preferentially grows up along the [001] direction. The PL spectra showed that the ZnO nanorods have blue emission at 466 nm and green-yellow emission at 542 nm. The influence of reaction temperature, pH in system and evaporation of ammonia on the morphology has been investigated. A possible growth mechanism of ZnO with various morphologies is discussed.     

退火对氧化锌薄膜结晶性能的影响

采用射频磁控溅射法在(001)硅片上制备了ZnO薄膜,利用X射线衍射对薄膜的制备工艺进行了研究,结果表明,基板温度、溅射功率、氩氧比、总气压在一个较大的范围内变化时都可实现薄膜的c轴择优取向生长.随后对薄膜进行了空气退火并利用摇摆曲线表征薄膜的结晶质量,摇摆曲线的半高宽随退火温度的提高而减小,700℃退火后FWHM为2.5°.     

超声辅助湿法合成纳米HA及MWNT/HA复合材料

以Ca(NO3)2·4H2O、(NH4)2HPO4和NH3·H2O为原料,在超声波辅助下,湿法合成了羟基磷灰石,用FTIR、XRD和TEM对产物进行了分析,结果表明:合成的羟基磷灰石为纳米级纺缍状晶体,不用烧结即具有较高晶化度,且为单一的羟基磷灰石晶相。以此制备条件为基础,采用原位合成的方法制备了多壁碳纳米管/羟基磷灰石复合材料,FTIR、XRD和TEM的分析结果表明:碳纳米管能较好的分散于羟基磷灰石基体中,部分碳纳米管表面可被反应生成的羟基磷灰石所包覆,二者之间有着较好的相容性,可作为一种新型的生物复合材料应用。     

湿化学法合成纳米AlN粉末

采用醇盐水解工艺结合碳热氮化还原法进行纳米Al N粉末的制备。以异丙醇铝、果糖、无水乙醇为原料,制备出透明的凝胶,干燥后得到分子水平混合的前驱体,在1 450℃经碳热氮化还原法制备出单相Al N纳米粉末。系统研究了前躯体形成机制,以及碳热氮化还原的温度和时间、C/Al摩尔比、凝胶温度等因素对合成粉体的影响。采用XRD、TG-DSC和SEM对合成产物的特性进行了分析和表征。通过优化工艺,制得类球形的Al N粉末颗粒,其颗粒大小为30~90 nm。     

Morphological investigation on cobalt oxide powder prepared by wet chemical method

In this paper cobalt oxide has been prepared by wet chemical method using Co(NO₃)₂ sol (Co: 80 g/L) and NaHCO₃ sol (100 g/L) as starting materials. When organic reagent: ethanol, acetone, and Polyethylene glycol-400 (PEG-400) (all are 2 mL) or three sodium salts: sodium chloride, sodium sulfate and sodium acetate (all are 1 g) had been introduced into reaction as inert additives once every time, and the measurement of PH value, zeta potential and viscosity in all solutions retains on the same level of magnitude, but the SEM shows that specific shapes of cobalt oxide particle is obtained after firing of CoCO₃ at 300 °C for 2 h in air. The DLVO theory discloses effect of dielectric constant of organic reagent and steric hindrance effect is the main factor for big molecular PEG-400. By replacing partly Co(NO₃)₂ with CoCl₂, the behavior of Cl⁻ is studied in the process of nucleus growth, the results show that Cl⁻ existed in the structure of nucleus with the content from 1300 to 2400 ppm, the structure, which can stand several time washing in an ultrasonic bath after reaction, but collapse as soon as it is fired at 300 °C for 2 h in air. It is reasonable to conclude that there may be directed anion chemical adsorption existed in cobaltous carbonate structure, which results in corresponding cobalt oxide particle morphology via anisotropic growth of nucleus.     

The numerical research on the effect of ultrasonic field on metallic powders produced by the ultrasonic-assisted electrical discharge process

Journal of Materials Science - The ultrasonic-assisted electric discharge is a green, environment-friendly and easy-to-control method for preparation metallic powders. Previous experiments have...     

Low-temperature synthesis of CuS nanorods by simple wet chemical method

CuS nanorods of length 60–100 nm and 15 nm in diameter have been synthesized by simple wet chemical method at 105 °C using CuCl₂·2H₂O as Cu-precursor, CS₂ as S-source and ethylenediamine as the attacking reagent. The plausible reaction mechanism has been proposed and the effect of reaction temperature on morphology has been discussed. X-ray diffraction (XRD) pattern suggests the formation of hexagonal phase CuS. The morphology of the products has been studied by transmission electron microscope (TEM) analysis. A detailed optical study has also been done.     

The effect of crystallinity on the fracture of polytetrafluoroethylene (PTFE)

The extremely low coefficient of friction and biocompatibility provided by the inert nature of polytetrafluoroethylene (PTFE) have lead to its application in a wide range of biological implants ranging from single component PTFE structures to sliding contact pads in complex joints. In vivo fracture has been identified as a major cause of failure in these implants. It has recently been shown that the fracture behavior of PTFE undergoes transitions from brittle-fracture below 19 °C to ductile-fracture with fibril formation and large-scale plasticity over 30 °C associated with crystalline phase transformations. In this paper the formation of fibrils and an associated increase in J_IC fracture toughness are revealed to be restricted by an increase in crystalline content in PTFE. [LAUR 05-2223]     

Synthesis of organic ligand passivated zinc selenide nanorods via wet chemical route

Zinc selenide (ZnSe) nanorods have been synthesized by simple and inexpensive wet chemical method using N-Methylaniline as a capping agent. The morphologies and structure of ZnSe nanorods have been characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD). The SEM and TEM reveal the formation of nanorods. XRD shows the cubic structure with the lattice constant of 5.633 Å. Strong “blue shift” absorption is observed from UV-visible spectrophotometry. The enhanced luminescence property is measured from photoluminescence spectrophotometry. The presence of N-Methylaniline in the ZnSe nanorods is confirmed by the Fourier transformed infrared spectrum.     

多频超声辐照的声化学产额研究进展

声化学是一门新兴的交叉学科，具有很多用途，广泛地应用于医药，生物，海洋，航空，轻工，食品，化学，化工等诸多领域，打基础这年来对声化学的研究十分活跃，多频超声对声化学产额的影响是其中研究的热点之一。声化学反应的主动力是声空化，声化学产额与超声辐照频率有一定的关系。双频，三频正交超声辐照能显著地提高声化学产额，具有明显的增强效应。文章综述了这方面的研究进展情况，阐述了声化学产额的影响因素。提出了目前所存在的问题并进行展望。     

超声化学沉淀法制备纳米NiO

以Ni(NO3)2·6H2O和(NH4)2C2O4·H2O为原料,采用超声沉淀法制备了纳米NiO,并利用XRD、FT-IR和TEM等分析方法对前驱体及产品组成和形貌进行了表征.结果表明,超声沉淀法制备的纳米NiO前驱体是二水合草酸镍.和实验制备的大颗粒Nio相比,纳米氧化镍Ni-O伸缩振动吸收峰及肩峰均发生了红移.纳米...     

The effect of extrusion parameters on the fretting wear resistance of Al-based composites produced via powder metallurgy

The work reported in this paper is aimed at establishing the relationship between processing and the wear resistance of the metal matrix composites (MMCs) based on a novel alloy, Al-20Si-5Fe-3Cu-1Mg. The MMCs were processed via a commercially viable powder metallurgy (PM) route, i.e. through mixing the atomized matrix alloy powder with 10 vol% SiC or Al₂O₃ particles, cold isostatic pressing, degassing and hot extrusion. It has been found that the extrusion window of the MMCs is greatly narrowed due to their increased deformation resistance on one hand and incipient melting of their matrix on the other. For a sound MMC extrudate, a reduction ratio over a critical value must be applied. However, a further rise of this ratio leads to deterioration of local interfacial cohesion between the ceramic phase and the matrix dispersed with a high volume fraction of silicon crystals and intermetallic dispersoids, thus degrading the MMCs in tensile properties. Furthermore, fretting wear tests at room and elevated temperatures and with dry and wet contacts show that the MMCs extruded at a higher reduction ratio has a higher mass loss and an increased friction coefficient. The work points to the direction of further research, i.e. on MMCs containing spherical reinforcement instead of commonly used angular particles.     

Investigation on synthesis of tetragonal BaTiO3 nanopowders by a new wet chemical method

Journal of Materials Science: Materials in Electronics - In this paper, tetragonal barium titanate (BaTiO3) nanopowders were synthesized by a new wet chemical route named sol-hydrothermal method....     

Controlled growth of well-aligned hierarchical ZnO arrays by a wet chemical method

A simple synthesis route to hierarchical ZnO arrays on zinc substrate in aqueous solution containing zinc nitrate and ammonia water was reported, without the assistance of any seeds, catalysts and surfactants. The as-prepared product consisted of very thin nanosheets attached onto the top of well-aligned nanorod arrays. A possible growth mechanism was proposed. The room-temperature photoluminescence spectrum showed UV emission around 398 nm and diverse visible emission peaks, indicating there might be a large concentration of oxygen defects in the sample. This method is both controllable and reproducible.     

Selective synthesis of metallic nickel particles with control of shape via wet chemical process

Metallic nickel particles with shapes varying from sea urchin-like to spherical have been selectively synthesized via aqueous chemical reduction. The phase structure and morphology of particles have been investigated by means of X-ray diffraction and scanning electron microscopy. It was found that sodium carbonate greatly accelerated the reduction process to form needle-like dendrites under atmospheric pressure. The probable formation mechanism of the sea urchin-like particles is also discussed. In the mild reduction process, the particle size of nickel nanospheres could be easily controlled by adjusting the experimental parameters.