Nanosecond laser texturing of aluminium for control of wettability

There is increasing interest in the use of lasers to modify the wettability of surfaces. Here we report on the use of a 20W nS pulsed IR fibre laser to create strong ydrophobicity on the surface of aluminium sheets. This is unexpected, hydrophobicity is usually associated solely with femto- or pico- second laser processing. At a 20W average power level the area coverage rate is too small for many industrial applications. Further trials using a 800W DPSS laser are described and the ability of this system to change surface wettability at a much higher production rate are indicated. There is little reported literature on surface texturing at higher average power levels. Indications of the productivity, or surface coverage rate, are given. Keywords: Fibre lasers, DPSS lasers, Surface Engineering, texturing, wettability, aluminiu

Oxygen Exchange on Vanadium Pentoxide

The isotopic exchange of 18O2 on polycrystalline V216O5 was studied by Raman spectroscopy at different temperatures between 300 and 580 °C and in the presence of different mixtures of oxygen with ethane, propane, or n-butane in the gas phase. Supported by DFT calculations, a method was developed to determine which of the three differently coordinated oxygen atoms in the crystal structure of V2O5 (vanadyl oxygen O1, 2-fold-coordinated oxygen O2, and three-coordinated oxygen O3) are involved in the exchange with 18O2 from the gas phase. Thus, it was found that the band at 994 cm–1, which is commonly exclusively assigned to a V═16O1 stretching (Ag) vibration, also contains contributions of an 16O1–V–16O2 stretching vibration (B2g). If only the O1 position is exchanged, the B2g component shifts to 964.2 cm–1, while if both O1 and O2 are exchanged, a shift to 953.4 cm–1 is expected. In contrast, the Ag component shifts only to 955 cm–1, regardless of whether only the O1 position or all three oxygen atoms are exchanged. On this basis, it was found that oxygen exchange at 573 °C in absence of an alkane involves O1 and O3 atoms, whereas in the presence of propane all three oxygen atoms are exchanged. In the latter case, the overall exchange rate appears to be limited by bulk diffusion. At typical reaction temperatures for the oxidative dehydrogenation of propane between 320 and 430 °C, no exchange occurs in pure oxygen. In presence of ethane or propane, only O1 is partly exchanged possibly at the surface and/or in a near-surface region. Under the typical reaction conditions of oxidative dehydrogenation of propane at 400 °C, there is hardly any variation in the spectra, and the small changes observed after long times on stream only affect O1, which, considering the sensitivity of the measurement method, leaves open whether the Mars–van Krevelen mechanism is indeed the predominant reaction mechanism under the conditions of oxidative dehydrogenation of alkanes on V2O5

The Brine Shrimp \u3ci\u3eArtemia franciscana\u3c/i\u3e in Closed Microalgal-Based Microcosms (Biospheres)

The purpose of this study was to examine the effects of three experimental variables on the stability and fecundity of a brine-shrimp community in a closed, micro algal-based microcosm. Xenic microalgal cultures and brine shrimp (Artemia franciscana Kellogg) in 300-cc acrylic spheres (referred to as biospheres or microcosms) were subjected to three experimental variables: (1) the culture volume (150 ml or 250 ml), (2) presence or absence of daily culture mixing (sphere rotation), and (3) a microcosm atmosphere that was either closed or open to the surrounding atmosphere. Each sphere started with 200 brine shrimp cysts and the microalga Nannochloris at a density of 5-7 x 107 cells/ml in a culture medium of 35 ppt total salts. The biospheres were monitored twice a week with closeup color photography, noting culture color and transparency, oxygen bubble accumulation, settling of planktonic algae, and the density, size, and maturity of the brine shrimp over time. The brine shrimp copulated by 21/2 weeks; a second generation of nauplii appeared in ca 30 days, temporarily increasing the density. These observations constitute the first report of brine shrimp sexual reproduction (ovoviviparity) in closed microcosms. The density of the brine shrimp appeared to stabilize during days 50-82, at an approximated 0.08 individuals/ml. Because all biospheres were yellow in the final weeks, i.e. showed no signs of Nannochloris, the brine shrimp were likely sustained by bacteria generated from the brine-shrimp feces. Blue-green algal filaments, a culture contaminant, at the air-water interface, out of the reach of brine shrimp, appeared to have provided oxygen in the absence of Nannochloris

Laser Induced Micro Plasma Processing of Polymer Substrates for Biomedical Implant Applications

This paper reports the experimental results of a new hybrid laser processing technique; Laser Induced Micro Plasma Processing (LIMP2). A transparent substrate is placed on top of a medium that will interact with the laser beam and create a plasma. The plasma and laser beam act in unison to ablate material and create micro-structuring on the “backside” of the substrate. We report the results of a series of experiments on a new laser processing technique that will use the same laser-plasma interaction to micromachining structures into glass and polymer substrates on the “topside” of the substrate and hence machine non-transparent material. This new laser processing technique is called Laser Induced Micro Plasma Processing (LIMP2). Micromachining of biomedical implants is proving an important enabling technology in controlling cell growth on a macro-scale. This paper discusses LIMP2 structuring of transparent substrate such as glasses and polymers for this application. Direct machining of these materials by lasers in the near infrared is at present impossible. Laser Induced Micro Plasma Processing (LIMP2) is a technique that allows laser operating at 1064 nm to machine microstructures directly these transparent substrates. © (2015) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only

The integration of optical interconnections on ceramic substrates

High heat conductivity and high heat capacity make ceramic substrates indispensable to the manufacture of Multi-Chip Modules (MCM) and power electronics. In this paper a detailed description of the integration process of optical lines on to ceramic substrates is presented. The manufacturing of microgrooves in ceramic substrates and the process of integration of optical fibres and active elements is described. Coupling active elements to optical fibre is also presented. Through such an integrated optical line a 4 Gbps signal was transmitted. © 2016 Elsevier B.V. All rights reserved

The microwave cavity perturbation technique for contact-free and in situ electrical conductivity measurements in catalysis and materials science

We have developed a noncontact method to probe the electrical conductivity and complex permittivity of single and polycrystalline samples in a flow-through reactor in the temperature range of 20–500 °C and in various gas atmospheres. The method is based on the microwave cavity perturbation technique and allows the simultaneous measurement of microwave conductivity, permittivity and of the catalytic performance of heterogeneous catalysts without any need for contacting the sample with electrodes. The sensitivity of the method towards changes in bulk properties was proven by the investigation of characteristic first-order phase transitions of the ionic conductor rubidium nitrate in the temperature range between 20 and 320 °C, and by studying the temperature dependence of the complex permittivity and conductivity of a niobium(V)-doped vanadium-phosphorous-oxide catalyst for the selective oxidation of n-butane to maleic anhydride. Simultaneously, the catalytic performance was probed by on line GC analysis of evolving product gases making the technique a real in situ method enabling the noninvasive investigation of electronic structure–function relationships

Acoustic Mechanisms that Determine the Ear-Canal Sound Pressures Generated by Earphones

In clinical measurements of hearing sensitivity, a given earphone is assumed to produce essentially the same sound-pressure level in all ears. However, recent measurements [Voss et al., Ear and Hearing (in press)] show that with some middle-ear pathologies, ear-canal sound pressures can deviate by as much as 35 dB from the normal-ear value; the deviations depend on the earphone, the middle-ear pathology, and frequency. These pressure variations cause errors in the results of hearing tests. Models developed here identify acoustic mechanisms that cause pressure variations in certain pathological conditions. The models combine measurement-based Thevenin equivalents for insert and supra-aural earphones with lumped-element models for both the normal ear and ears with pathologies that alter the ear\u27s impedance (mastoid bowl, tympanostomy tube, tympanic-membrane perforation, and a \u27high- impedance\u27 ear). Comparison of the earphones\u27 Thevenin impedances to the ear\u27s input impedance with these middle-ear conditions shows that neither class of earphone acts as an ideal pressure source; with some middle-ear pathologies, the ear\u27s input impedance deviates substantially from normal and thereby causes abnormal ear-canal pressure levels. In general, for the three conditions that make the ear\u27s impedance magnitude lower than normal, the model predicts a reduced ear-canal pressure (as much as 35 dB), with a greater pressure reduction with an insert earphone than with a supra-aural earphone. In contrast, the model predicts that ear-canal pressure levels increase only a few dB when the ear has an increased impedance magnitude; the compliance of the air-space between the tympanic membrane and the earphone determines an upper limit on the effect of the middle-ear\u27s impedance increase. Acoustic leaks at the earphone-to-ear connection can also cause uncontrolled pressure variations during hearing tests. From measurements at the supra-aural earphone-to-ear connection, we conclude that it is unusual for the connection between the earphone cushion and the pinna to seal effectively for frequencies below 250 Hz. The models developed here explain the measured pressure variations with several pathologic ears. Understanding these mechanisms should inform the design of more accurate audiometric systems which might include a microphone that monitors the ear-canal pressure and corrects deviations from normal

Microstructures Manufactured in Diamond by Use of Laser Micromachining.

Different microstructures were created on the surface of a polycrystalline diamond plate (obtained by microwave plasma-enhanced chemical vapor deposition-MW PECVD process) by use of a nanosecond pulsed DPSS (diode pumped solid state) laser with a 355 nm wavelength and a galvanometer scanning system. Different average powers (5 to 11 W), scanning speeds (50 to 400 mm/s) and scan line spacings ("hatch spacing") (5 to 20 µm) were applied. The microstructures were then examined using scanning electron microscopy, confocal microscopy and Raman spectroscopy techniques. Microstructures exhibiting excellent geometry were obtained. The precise geometries of the microstructures, exhibiting good perpendicularity, deep channels and smooth surfaces show that the laser microprocessing can be applied in manufacturing diamond microfluidic devices. Raman spectra show small differences depending on the process parameters used. In some cases, the diamond band (at 1332 cm-1) after laser modification of material is only slightly wider and shifted, but with no additional peaks, indicating that the diamond is almost not changed after laser interaction. Some parameters did show that the modification of material had occurred and additional peaks in Raman spectra (typical for low-quality chemical vapor deposition CVD diamond) appeared, indicating the growing disorder of material or manufacturing of the new carbon phase

Enhanced catalytic performance of MnxOy-Na2WO4/SiO2 for the oxidative coupling of methane using an ordered mesoporous silica support

The oxidative coupling of methane is a highly promising reaction for its direct conversion. Silica supported MnxOy–Na2WO4 is a suitable catalyst for this reaction. In this study, a variety of different SiO2 materials have been tested as supports. Surprisingly, the application of ordered mesoporous silicas, here exemplarily shown for SBA-15 as support materials, greatly enhances the catalytic performance. The CH4 conversion increased two fold and also the C2 selectivity is strongly increased