A computational simulation study on the acoustic pressure generated by a dental endosonic file: Effects of intensity,file shape and volume

One of the uses of ultrasound in dentistry is in the field of endodontics (i.e. root canal treatment) in order to enhance cleaning efficiency during the treatment. The acoustic pressures generated by the oscillation of files in narrow channels has been calculated using the COMSOL simulation package. Acoustic pressures in excess of the cavitation threshold can be generated and higher values were found in narrower channels. This parallels experimental observations of sonochemiluminescence. The effect of varying the channel width and length and the dimensions and shape of the file are reported. As well as explaining experimental observations, the work provides a basis for the further development and optimisation of the design of endosonic files.     

An activated fluid stream – New techniques for cold water cleaning

Electrochemical, acoustic and imaging techniques are used to characterise surface cleaning with particular emphasis on the understanding of the key phenomena relevant to surface cleaning. A range of novel techniques designed to enhance and monitor the effective cleaning of a solid/liquid interface is presented. Among the techniques presented, mass transfer of material to a sensor embedded in a surface is demonstrated to be useful in the further exploration of ultrasonic cleaning of high aspect ratio micropores. In addition the effect of micropore size on the cleaning efficacy is demonstrated. The design and performance of a new cleaning system reliant on the activation of bubbles within a free flowing stream is presented. This device utilised acoustic activation of bubbles within the stream and at a variety of substrates. Finally, a controlled bubble swarm is generated in the stream using electrolysis, and its effect on both acoustic output and cleaning performance are compared to the case when no bubbles are added. This will demonstrate the active role that the electrochemically generated bubble swarm can have in extending the spatial zone over which cleaning is achieved.     

Industrial Applications of Dimeric Surfactants: A Review

Dimeric surfactants also known as gemini surfactants have received lots of attention for high performance formulations in the various scientific and commercial products. Due to the greater amount of hydrocarbon per molecule, the critical micelle concentrations (CMC) of dimeric are typically one order of magnitude lower than the corresponding monomeric surfactant. They are ten to hundred times more efficient at reducing the surface tension of water and the interfacial tension of the oil-water interface than conventional surfactants. Besides, the Krafft temperatures of gemini surfactants with hydrophilic spacers are generally very low giving these surfactants the capacity to be used in cold water. These surfactants display a range of interesting properties, including elevated surface activity, extremely low CMC and extraordinary rheology and self-assimilation aspect. As a consequence of these properties, they have many potential applications include detergents and cleaning agents, cosmetics, textile, and dyeing, dispersion stabilization and emulsion polymerization, genetics science, pharmaceutical, and biological applications.      

浅谈印制电路板的一种清洗工艺

焊接是电子设备的生产中的重要步骤,焊接后必须进行清洗才能保证电子设备的可靠性、电气指标和工作寿命。鉴于军工产品必须要清洗,所以清洗工艺对于军工产品尤为重要。文中介绍了清洗的重要性,讨论了印制电路板污染物的种类和来源分析,提出了一种可靠的清洗工艺——溶剂气相清洗。气相清洗通常被认为是去除零件上有机污垢的一种最有效的清洁方法,这种方法甚至能去除工业中遇到的最为顽固的污垢。在溶剂蒸气清洗机中清洁后的零件从机器中出来时是干燥的,而且表面无任何残留物。     

Ultraviolet laser removal of small metallic particles from silicon wafers

Laser removal of small 1 μm sized copper, gold and tungsten particles from silicon wafer surfaces was carried out using ultraviolet radiation at 266 nm generated by Nd:YAG harmonic generation. Successful removal of both copper and gold particles from the surface was achieved whereas tungsten particles proved to be difficult to remove. The cleaning efficiency was increased with an increase of laser fluence. The optimum processing window for safe cleaning of the surface without any substrate damage was determined by measuring the damage threshold laser fluence on the silicon substrate and the required fluence for complete removal of the particles. The different cleaning efficiencies with particle type are discussed by considering the adhesion force of the particle on the surface and the laser-induced cleaning force for the three different particles.     

An erosion sensor based on a quartz crystal microbalance for quantitative determination of the cleaning efficiency in an ultrasonic vessel

The efficiency of ultrasonic cleaning vessels cannot be measured directly in an easy way. In the presented work, a sensor is developed which quantitatively measures the ablation of a test layer. The sensor element is a quartz crystal which is coated with a sacrificial layer. Small changes in mass of this layer can be measured by a frequency shift of the crystal oscillation. For measurements, a 10 MHz AT-cut quartz crystal was used in a cleaning vessel working at 44.9 kHz. To determine the frequency shift by the ablation of the test layer, the quartz crystal was driven by a frequency generator sweeping the frequency in the range of the resonance frequency and a characteristic frequency was determined. The test layer which was applied to the quartz crystal consisted of silica microparticles suspended in varnish. In a preliminary experiment using a commercial cleaner it could be shown that significant changes in resonance frequency by cavitation effect could be detected. The initial frequency shift of the sacrificial layer is reproducible within 10%. The test layer can be adapted to the conditions of the cleaning vessel. By changing the electrical input power of the vessel, a threshold in the cavitation erosion was found.     

Ultrasonic cleaning: An historical perspective

The development of ultrasonic cleaning dates from the middle of the 20th century and has become a method of choice for a range of surface cleaning operations. The reasons why this has happened and the methods of assessing the efficiency of ultrasonic cleaning baths are reviewed.     

Surface refinement and electronic properties of graphene layers grown on copper substrate: An XPS, UPS and EELS study

The present work focuses on the assessment of two surface treatment procedures employed under ultra high vacuum conditions in order to obtain atomically clean graphene layers without disrupting the morphology and the two dimensional character of the films. Graphene layers grown by chemical vapor deposition on polycrystalline Cu were stepwise annealed up to 750 °C or treated by mild Ar⁺ sputtering. The effectiveness of both methods and the changes that they induce on the surface morphology and electronic structure of the films were systematically studied by X-ray photoelectron spectroscopy, and electron energy loss spectroscopy. Ultraviolet photoelectron spectroscopy was employed for the study of the electronic properties of the as received sample and in combination with the work function measurements, indicated the hybridization of the C-π network with Cu d-orbitals. Mild Ar⁺ sputtering sessions were found to disrupt the sp2 network and cause amorphisation of the graphitic carbon. Annealing between 300 °C and 450 °C under ultra high vacuum proved to be an effective and lenient way for achieving an atomically clean graphene surface. At higher temperatures the rigid structure of graphene does not follow the expansion of the copper substrate leading to the graphene/Cu interface breakdown and possibly to further rippling of the graphene layers leaving bare areas of cooper substrate.     

Transient removal of a contaminated fluid from a cavity

A numerical and experimental study of the time-dependent hydrodynamic removal of a contaminated fluid from a cavity on the floor of a duct is presented. The duct flow has a parabolic inlet velocity profile and laminar flows are considered in a Reynolds number range between 50 and 1600 based on the duct height. The properties of the contaminated cavity fluid are assumed to be the same as for the fluid flowing in the duct. Attention is focussed on the convective transport of contaminated fluid out from the cavity and the effect of duct flow acceleration on the cleaning process. Passive markers which are convected with the flow are used in the numerical simulation for the purpose of identifying the contaminated cavity fluid. It is shown that the cleansing of the cavity is more pronounced during the unsteady start-up of the duct flow and the rate of cleaning decreases as the flow reaches a steady state. The cleaning process is enhanced as the cavity aspect ratio is increased and as the duct Reynolds number increases. A ‘volumetric’ approach based on the spread of markers is shown to be useful in determining the fraction of the cavity that remains contaminated after steady conditions have been reached. The distribution of the contaminant in a cavity during the unsteady stage and after steady conditions are reached are identified using passive markers.