Ultrasound-assisted fast encapsulation of metal microparticles in SiO2 via an interface-confined sol-gel method

Although the traditional Stoˇber process-based methods are widely used for encapsulation of metal nanoparticles in SiO₂, these time-consuming methods are not effective for coating metal microparticles with a uniform SiO₂ layer of desired thickness. Herein, an ultrasound-assisted, interface-confined sol–gel method is proposed for fast encapsulation of metal microparticles in SiO₂, and the encapsulation of Sn microparticles is chosen as an example to illustrate its feasibility. The proposed method involves covering metal microparticles with liquid films that contain water, alcohol, surfactant (Span-80) and catalyst (NH₄F) and then ultrasonically dispersing these particles into cyclohexane, where tetraethylorthosilicate (TEOS) is added. To ensure the hydrolysis-condensation reactions of TEOS occurring at the particle-cyclohexane interface so that the formed SiO₂ is coated on the particles, the microparticles should be well dispersed into cyclohexane with the liquid films being not broken away from their surfaces. It is found that the assistance of probe sonication and the addition of surfactant are crucial to achievement of a good dispersion of metal microparticles in cyclohexane. And using high-viscosity alcohol (namely glycerol), controlling the volume ratio of water to alcohol and the amount of water, and choosing a suitable ultrasonic power are essential for preventing the formation of free SiO₂ (namely SiO₂ that is not coated on the particles), which is a result that the liquid films escape from the particle surfaces under ultrasonic cavitation. Our results have also revealed that the thickness of SiO₂ layer can be adjusted by changing the reaction time or the total amount of water. In particular, the thickness of SiO₂ layer can be easily raised by simply repeating the encapsulation procedure. Compared with the traditional Stoˇber process-based methods, the proposed method is time-saving (reaction time: about 30 min vs. more than 12 h) and extremely effective for coating microparticles with a continuous, uniform SiO₂ layer of desired thickness.     

Two-stage optimization of lens grinding parameters for multi-quality target combining Taguchi method and neural network software

In this paper we present an efficient two-stage method combining the merits of the Taguchi method and neural network software to achieve nonlinear fine optimal lens grinding parameters for both the roughness and the curvature deviation robust over a wide range of lens refraction power. Discrete and rough optimal grinding parameters for roughness and for curvature deviation are first obtained respectively using the Taguchi method with an L₁₈ orthogonal array. Then all the experimental data of the 18 experiments are used as input training data for neural network software to obtain a set of compromised nonlinear accurate optimal parameters for the roughness and the curvature deviation. Results of confirmation experiments using these final parameters show that lens surfaces ground with polishers ranging in curvature from −7:00 to +7.00D are robust in desired quality targets.     

Water formation on oxygen exposure of some hydrides of intermetallic compounds

It is found that a large number of metal hydrides such as hydrides of materials in Ca−Mg−Ni can form water when exposed to O₂ largely without signs for concomitant substrate oxidation. One can speak of a catalytic reaction in this connection as the H-depleted metal matrix can in most cases be rehydrided and water synthesis repeated on exposure to O₂. In some cases a considerable portion of the H combustion reaction takes place in a matter of seconds. Some of the metal hydrides such as hydrides of CaNi₄B, CeNi₃, and YbNi₂, are relatively stable concerning decomposition of the alloy by the product water, while others, for example hydrides of CaNi₃, and CaNi₂, are rapidly decomposed by the product water forming the hydroxide of the electropositive metal. They also produce fine ferromagnetic Ni-particles which could be interesting for other catalytic purposes. Guest professor, work also performed at University of California at San Diego where support by a grant from DOE, Basic Energy Sciences, is acknowledged.     

Characterizing the dynamic behavior of nano-TiO<Subscript>2</Subscript> agglomerates in suspensions by photocorrelation spectroscopy

Metal oxide nanoparticles are small but easily form agglomerates in suspension, depending on the strength of particle–particle and particle–media interactions. To understand the agglomeration behavior of nanoparticles in media and relate to it to product performance testing, measurement methods are desired to characterize highly scattering metal oxide nanoparticle suspensions without dilution. In this article, we describe the advantages of using photocorrelation spectroscopy (PCS) in a backscattering detection configuration to carry out a realistic agglomerate size measurement in multiple scattering media found in most metal oxide nanoparticle suspensions. The dynamic behavior of nano-titanium dioxide (TiO₂) particles in buffer solutions of different chemical composition and pH values was investigated as a sample system using PCS. The resulting autocorrelation functions (AFs) at different time intervals, particle concentrations, and pH values were measured at several detection angles. The AF exhibits a multi-mode relaxation time feature and the calculated hydrodynamic diameters strongly depended on media composition and detection angle. This result indicates that the size and dispersion of nano-TiO₂ agglomerates are significantly affected by solution media. A measurement protocol for determining size and dispersion of metal oxide particles in media is proposed and related to a performance test found in industry.     

Laser shock forming of aluminum sheet: Finite element analysis and experimental study

Laser shock forming (LSF) is characterized in non-contact load, high pressure and high strain ratio. This new forming process using laser-induced shock pressure can shape sheet metal without complicated forming equipments. The know-how of the forming process is essential to efficiently and accurately control the deformation of sheet metal. Experiment and numerical simulation are the important approaches for forming analysis. Taken the aluminum sheets with different thickness as the specimen, the finite element (FE) analysis for LSF was performed. In the paper, Q-switch Nd:YAG Laser with a maximum power density of 4.5 GW/cm² was used. The simulation results were in good agreement with the experiment. It showed that the formed aluminum sheets were in the form of concavo-convex. Finally, the transient and static deformations of thin sheet metal under specific operation conditions were also studied.     

硬质合金Wc—TiC—Co的研制和机理初探

本文介绍了在45钢表面利用大功率CO_2激光束制取硬质合金WC-TiC-Co的方法,并对合金层的显微组织和性能进行了观察和测试,对形成硬质合金的机理作了初步讨论,结果表明;采用这种方法对提高金属材料表面性能是成功的。     

Structuring of aluminum films by laser-induced local oxidation in water

A simple method for patterning of thin (15–650 nm) aluminum films on glass substrates by direct, low-power, laser-thermal oxidation in water under common laboratory conditions is demonstrated. Local heating of the metal film enhances the formation of aluminum oxide (hydrargillite, Al₂O₃–3H₂O) and provokes breakdown of the passivation layer followed by local corrosion at temperatures close to the boiling point of water. Moving the focus of an Ar-ion laser (λ=488 nm) over the aluminum film with a speed of several μm/s yields grooves flanked by hydrargillite. Upon through oxidation of the metal these structures act as electrically insulating domains. Depending on the film thickness, the minimum width of the line structures measures between 266 nm and 600 nm. The required laser irradiation power ranges from 1.7 mW to 30 mW. It is found that the photo-thermal oxidation process allows for writing of two-dimensional electrode patterns. Received: 16 July 2001 / Accepted: 23 July 2001 / Published online: 2 October 2001     

3D laser-forming strategies for sheet metal by geometrical information

Forming sheet metal by laser-induced thermal stress (laser forming) is considered to offer great potential for rapid prototyping and flexible manufacturing. Accordingly, many studies have been carried out in different areas of laser forming. However, in order to apply the laser-forming process to real 3D products, a method that encompasses the whole process planning is required, including the laser irradiation patterns, laser power, and travel speed, when the target shape is given. In this work, a new method for 3D laser forming of sheet metal is proposed. This method uses geometrical information rather than a complicated stress–strain analysis. Using this new method the total calculation time is reduced considerably while affording strong potential for enhanced accuracy. Two different target shapes were formed by laser irradiation with the proposed procedure to validate the algorithm.     

Development of irradiation strategies for free curve laser forming

Although forming sheet metal by laser-induced thermal stresses (laser forming) has been extensively studied, the research has mainly focused on a single angle forming process. The task of free curve laser forming of sheet metal is to determine a set of process parameters such as laser scanning paths, laser power and scanning speed that will make a given shape. Two methods were used for generating the laser scanning paths and the bending angles of each path. Each method was analyzed by computer simulation and the two methods were compared. Experiments verified the applicability of the proposed methods.     

典型重金属污染水体光谱特征分析———以广东省大宝山尾矿水为例

目前水体重金属遥感反演相关研究仍比较薄弱。自然界中重金属污染水体的光谱特征研究是重要的基础性工作,是将来实现卫星遥感反演时波段选择的重要理论依据,也是遥感反演模型所必须的基础参数。首先利用Analytical Spectral Devices（ASD）光谱仪,测量获得以大宝山尾矿水为例的典型重金属污染水体在两种水深和两种光照条件下的离水反射率光谱曲线,发现在600~700 nm（红波段）均有稳定的反射峰,然后进一步与自然界常见的两类水体（浑浊水体和富营养化水体）的反射峰位置进行对比,发现：以长湖水库石英砂厂附近为例的浑浊水体反射峰在550~700 nm（绿、红波段）,以北江韶关冶炼厂附近为例的富营养化水体反射峰在550~600 nm（绿波段）,3种水体的反射峰位置各异,说明该重金属污染水体反射率光谱与这两类水体具有很好的可分性。然后在测量水体反射率基础上,结合水质遥感模型和进行室内消光系数测量,反演得到大宝山尾矿水体的总散射系数和总吸收系数光谱,并进一步分离水分子吸收作用,最终得到水中成分的综合吸收系数光谱曲线,结果表明：在紫光波段吸收最强,在红光波段吸收最弱;具体表现为：从400 nm开始,吸收系数快速递减,在蓝绿光波段递减速度变缓,从黄光波段又开始快速递减,到676 nm达到极小值,然后又快速增强至750 nm,随后变化减缓。最后结合水样的水质化验结果,对该重金属污染水体的光谱成因进行分析,发现现场水色和水中成分的综合吸收系数光谱特征皆与作者前期研究测量获得的硫酸铁溶液颜色及其吸收系数光谱特征吻合,因此认为水中成分的光谱特征是由硫酸铁及其水解产物所引起。以上说明该重金属污染水体的光谱特征明显,反射峰和强吸收波长位置明确,这是将来利用卫星遥感手段反演水中重金属浓度的重要特征波段。该研究获得了以大宝山尾矿水为例的典型重金属污染水体反射率、消光系数、散射系数和吸收系数的光谱结果,为日后推广至其他种类重金属矿的尾矿水体及水中成分光学参数反演提供方法依据,也为将来利用卫星遥感技术对水中重金属浓度进行定量提取打下良好的理论基础。     

Spray Forming: Controlling the Atomization Result with Regard to Particle Properties

Spray forming is a new production process for manufacturing semi‐finished metal products. The procedure combines the liquid metal atomization with the compaction event of the generated metal droplets on a substrate. During spray forming, the heat emission of the molten metal particles is one of the most important transfer operations defining the thermal conditions in the spray and deposit. Definite thermal conditions throughout the manufacturing process lead to fine equi‐axed grain structures and therewith to characteristic and desired material properties. Thus, in particular, the disintegration of the molten metal occurring during spray forming is an essential step.     

Optical Properties of Micro-patterned Silver Nanoparticle Substrates

In this paper, we describe a novel technique for depositing metal nanoparticles (NPs) on a planar substrate whereby the NPs are micro-patterned on the surface by a simple stamp-printing procedure. The method exploits the attractive force between negatively charged colloidal metal NPs and positively-charged polyelectrolyte layers which have been selectively deposited on the surface. Using this technique, large uniform areas of patterned metal NPs, with different plasmonic properties, were achieved by optimisation of the stamping process. We report the observation of unusual fluorescence emission from these structures. The emission was measured using epifluorescence microscopy. Fluorescence lifetime behaviour was also measured. Furthermore, the μ-patterned NPs exhibited blinking behaviour under 469 nm excitation and the fluorescence spectrum was multi-peaked. It has been established that the fluorescence is independent of the plasmon resonance properties of the NPs. As well as optimising the novel NP μ-patterning technique, this work discusses the origin and characteristics of the anomalous fluorescence behaviour in order to characterise and minimise this unwanted background contribution in the use of metal NPs for plasmonic enhancement of fluorescence for optical biochip applications.     

金属-光折变材料复合全息结构对表面等离激元的波前调控

表面等离激元(surface plasmon polaritons, SPPs)控制具有重要意义.表面电磁波全息法是在金属表面设计能有效控制SPP传输的凹槽阵列结构.本文提出一种新的SPP传输的控制方法,利用金属-光折变材料复合全息结构控制SPP传播.在金属表面覆盖一层光折变材料,两束SPP波在光折变材料内干涉生成全息结构,利用此全息结构能够控制SPP的传播.通过时域有限差分法模拟验证,结果显示,通过金属-光折变材料复合全息结构可以有效地控制SPP波束的传输,实现SPP平面波束的单点聚焦、两点聚焦,以及生成零阶和一阶高斯SPP波束.经过优化发现,光折变材料的最佳厚度为3.3μm,最佳折射率调制度为0.06.现有SPP控制器件主要是通过离子束刻蚀,而金属-光折变材料复合全息结构不需要刻蚀,从而扩展了SPP控制的器件的制作方法,为SPPs的全光控制提供了新的思路,使SPP全光控制成为可能,进一步实现了SPP全光开关等功能.     

An experimental investigation of underwater pulsed laser forming

Laser forming is a new forming technology, which deforms a metal sheet using laser-induced thermal stresses. This paper presents an experimental investigation of pulsed laser forming of stainless steel in water and air. The effects of cooling conditions on bending angle and morphology of the heat affected zone (HAZ) are studied. It is shown that the case of the top surface in air and the bottom surface immersed in water has the greatest bending angle based on the forming mechanism of TGM. The water layer above the sample decreases the coupling energy, leading to a small bending angle. For a thin water thickness (1 mm), the water effects on the HAZ are limited. As water layer thickness increases (5 mm), the concave shape of the HAZ is more remarkable and irregular because the shock waves by high laser energy heating water are fully developed. However, the area and the depth of the HAZ become less significant when water thickness is 10 mm due to the long pathway that laser undergoes.     

A study of longitudinal pulse-periodic discharges in high-pressure vapor-gas mixtures

A study is reported of high-power longitudinal pulse-periodic discharges at multiatmospheric pressures in mixtures of helium and metal vapor. It is shown that the metal vapor acting as the ionization controlling impurity (ICI material) will stabilize a homogenous discharge in a large-diameter tube (∼ 3 cm) up to at least 5 atm at excitation power levels of about 25 kW/m. Mechanisms responsible for the self-stabilization of this type of discharge are discussed. Zh. Tekh. Fiz. 67, 25–31 (April 1997)     

Patterning thin metallic film via laser structured weakly bound template

A weakly bound buffer material is structured on a surface by interfering low power laser beams, as a template for patterning metallic thin films deposited on top. The excess buffer material and metal layer are subsequently removed by a second uniform laser pulse. This laser pre-structured buffer layer assisted patterning procedure is demonstrated for gold layer forming a grating on a single crystal Ru(1 0 0) under UHV conditions, using Xe as the buffer material. Millimeters long, submicron (0.65 μm) wide wires can be obtained using laser wavelength of 1.064 μm with sharp edges of less than 30 nm, as determined by AFM. This method provides an all-in-vacuum metallic film patterning procedure at the submicron range, with the potential to be developed down to the nanometer scale upon decreasing the patterning laser wavelength down to the UV range.     

Side reaction in the hydrogen and carbothermal reductions of BaO and BaCO3: The role of an infinitesimal amount of water

Alkaline earth (AE) metals are irreplaceable ingredients in the synthesis of AE metal-based antiperovskite oxides, and it can be achieved by a chemical reduction of a stable AE metal compound. In this study, hydrogen and carbothermal reduction of BaO and BaCO₃ were attempted, and we here report an undesirable side reaction creating barium hydroxide (Ba(OH)₂) as the product of the reaction with the small amount of water in ultra-high purity inert gas used in the reduction processes. Such side reaction pathways and products are hardly identifiable in a high-temperature reaction; yet, systematic investigations on phase evolutions using X-ray diffraction, IR spectroscopy, and thermogravimetric analysis enabled the detection of Ba(OH)₂·xH₂O. Unintentional creation of alkaline earth metal oxides in intermediate and subsequent hydration even under a negligible amount of H₂O may lead to an unexpected loss of alkaline earth metal element and, consequently, its deficiency in a desired final product.     

Performance analysis of a new biolistic gun using high power laser irradiation

Impingement of a high power laser pulse (above 10⁹ W/cm²) on a metal foil causes ablation, which is characterized by a rapid expulsion of matter and initiation of a strong shock wave inside the solid metal. The shock propagates through the foil and reverberates on the rear side causing instant deformation of the foil, whose surface is treated with micro particles prior to ablation. Based on this principle of micro particle ejection, we develop a new biolistic gun with improved controllability, stability, efficiency of our previous system, and perform characterization of the penetration shapes at varying confinements and energy levels. The confinement media include BK7 glass, water, and succulent jelly (ultrasound gel). Biological tissue was replicated by a gelatin-water solution at a 3% weight ratio. Present data show that confinement effect results in a conspicuous enhancement of penetration reached by 5 μm cobalt micro particles. Also, there exists an optimal thickness at each energy level when using liquid confinement for enhanced particle delivery.     

Dissociative adsorption of H2: Time-dependent quantum studies

In this short review we consider some selected results for the dissociation of hydrogen on metal surfaces. In particular we focus our attention on the effects that surface corrugation have on the dissociation and also how rotations and vibrations couple in the interaction region. Results from time dependent quantum wavepacket calculations have been particularly helpful in forming our ideas of how diatomics dissociate. We describe this method along with two examples of propagation schemes. The power of limited dimensional models to rationalize experimental observations is clearly demonstrated.     

The use of vacuum arc discharge as a load for XPG-1 high-current generator

It was attempted to use the vacuum arc discharge as a load of a high-current generator. The idea is as follows: metal vapor is injected using the vacuum arc discharge into a microgap of a load unit of the current generator. When the generator current flows over metal vapor, such a load begins to compress as in the classical Z pinch. During compression, Rayleigh—Taylor instabilities develop, which results in the formation of waists and hot spots. The hot spot radiation power can exceed the radiation power in the case of the X pinch used as a load by a factor of 1.5–2. The signal amplitude spread is significantly smaller than that when using the X pinch. The spectrum and sizes of the hot spot can be varied by selecting the mass and type of metal injected into the discharge region.