High Aspect Ration Research Articles

Investigating the effect of different tool electrodes in electric discharge drilling of Waspaloy on process responses

Despite the wide application of electric discharge machining in the fabrication of holes in difficult-to-cut materials, the process's performance and accuracy are governed by the choice of an appropriate tool material and process parameters. Moreover, the process becomes less productive due to unstable machining and inadequate debris flushing while drilling high aspect ration holes, resulting in a low material removal rate (MRR) and high average surface roughness (Ra). Further, the holes' accuracy deteriorates due to a high tool wear rate (TWR). To overcome these issues, a rotary tool electrode setup is proposed for the drilling of Waspaloy. The influence of three different tool materials, viz. copper, brass, and graphite, along with various process parameters, was studied on the process performance. The electrical discharge drilling (EDD) operation was performed by varying the input process parameters, viz. current (I), pulse-on-time (TON), pulse-off-time (TOFF), tool electrode speed (TES), and voltage (V), using copper, brass, and graphite tool electrodes. The influence of machining conditions was investigated on response variables, namely, Ra, TWR, and MRR. Taguchi-based L16 orthogonal array was used to design the experiments, and results were analysed using Analysis of Variance (ANOVA). An improvement in the performance of rotary EDD was observed due to proper flushing, efficient debris evacuation, and steady machining condition. The current was found to be the most significant electrical parameter. The graphite tool electrode had shown the highest MRR of 32.056 mm3/min at 25 A current which was 13.09% and 131.32% higher than that of the copper and brass tool electrodes, respectively. However, the graphite tool resulted in a poor surface quality, and a high energy transfer coefficient, indicating the highest Ra value of 8.385 μm. The brass tool electrode, owing to a lower thermal conductivity and melting point, caused a higher TWR than the copper and graphite tools. Finally, the microscopic images for drilled holes with different electrodes at various energy settings were captured using field emission scanning electron microscopy (FESEM) and compared for surface quality. In addition, the surface elemental analysis was performed using Energy Dispersive X-Ray Analysis (EDX) to investigate material migration from the tool electrodes to hole's side walls.

Collapse of conical granular columns

This paper experimentally analyzes the collapse of conical granular columns made out of non-cohesive granular materials. Dimensionless run-out lengths were found, as a function of the aspect ratio a, similar to those occurring in the collapse of cylindrical columns, although in the case of conical columns of high aspect ration, at the end of the collapse, a layer of grains that rotates around the cone axis appears and it affects the final profiles of the mounds.

Causes and Pathophysiology of Malignant Pleural Mesothelioma

Malignant pleural mesothelioma (MPM) results from the neoplastic transformation of pleural mesothelial cells. Asbestos exposure is a major risk factor for MPM, but epidemiologic studies demonstrated the occurrence of MPM in populations exposed to other fibers, and an excess of MPM in populations occupationally exposed to man-made vitreous fibers and previously to asbestos. The development of nanotechnologies also raises some concern about the potential health effects of new particles of high aspect ration, such as carbon nanotubes. Toxicological studies investigated the mechanism of asbestos-induced transformation of mesothelial cells, and molecular analyses defined the genomic and physiopathological changes in MPM. These findings allowed identifying some key events accounting for the neoplastic process. This article summarizes the known and suspected causes of MPM, the cellular events and responses of mesothelial cells to asbestos fibers and the alterations of key genes and regulatory pathways involved in the pathological mechanism.

In situ synthesis of VO2for tunable mid-infrared photonic devices

Tunable PhCs were fabricated by inclusion of VO2particles in high aspect ration MIR microtube arrays.

Polymer Nanocomposite Films with Functionalized MWCNTs

Polymer nanocomposites with carbon nanotubes (CNTs) have become very attractive class of materials for numerous engineering applications since carbon nanotubes exhibit a high aspect ration, unique electrical, mechanical and structural properties. Functionalization of CNTs offer new potentials for other technical challenges of the polymer based nanocomposites associated with their specific interactions. A biocompatible polymer matrices PMMA and PCL were used to provide good interfacial bonding between carbon nanotubes. MWCNT (d=30-50 nm, purity>95%) were used for preparation of polymer based nanocomposites with 0.2, 0.5 and 1.0 % w/w MWCNTs content. PMMA-based nanocomposites were prepared via the mixing of the MWCNT and polymer in a dichloromethane solution for 24 h, while for the PCL-based nanocomposites as a solvent tetrahyrofurane was used. Functionalization of the CNTs was performed in acid (HNO3) and alkali (NH4OH+H2O2) medium as well as by additional thermal oxidation at 490°C. Characterization of the nanocomposite films was performed by DSC, TGA, WAX, FTIR and SEM. The obtained results have shown that introducing MWCNT into polymer matrix significantly changes have been found in the properties of the obtained nanocomposites.

Synchrotron Micro Tomography Reveals 3D Shape of Precipitates in Cast Magnesium Alloy

Aim of the study is to compare the morphology of inclusions in magnesium alloy, investigated by both computed micro-tomography and light microscopy. Precipitates of denser material are found. The information of the light microscopic studies alone is by far insufficient to conclude on their three-dimensional shape. In contrast, the tomography reveals the full topology in all dimensions. The described inclusions are flake-like and can extend with high aspect ration into one, two or three dimensions.

Microelectrode Fabrication by Electrochemical Turning

In this paper micro-electrochemical turning for fabricating microelectrode is presented. A stainless steel film with 50 μm thickness as turning tool is the cathode and a rotary tungsten rod for the proposed microelectrode fabrication is the anode. By applying ultra short pulses in micro seconds, dissolution of the anode can be restricted to the small region very close to the cathode. Due to rotation of the anode and movement of the cathode along the rotary axis direction, the anode uniformity corrosion was improved and its rotating concentricity was ensured simultaneously. A micro-electrode with a high aspect ration, namely 20 μm in diameter and 2500 μm in length has been fabricated in the low concentration electrolyte, 4%NaOH.

Experimental Study of Micro-Electrode Array by Micro-WEDM

This paper discusses a processing preparation for micro-electrode array fabrication by micro wire electrical discharge machining. Based on a self-developed micro-WEDM machine tool and adopted thin tungsten wire electrode of 30μm in diameter, a series of experiments on micro-electrode array machining are introduced. The relationship between the discharge gap and working area of wire discharge under given voltage is investigated. The examination for micro-girder structure forming process has gone along and the axle journal's minimized width of least micro girder which could not bring on machining flexural thermal deformation has been obtained. The clamping method of work-piece intended for electrode array fabrication is analyzed and a special fixture is designed. The factors affecting forming accuracy are summarized. An amounted 5×5 squared-disk-type micro-electrode array structure with a high aspect ration, namely 20μm in axle journal width and 500μm in length of a single electrode, has been machined successfully.

ZnO Nanorods Synthesized in Large-Scale via Sonochemical Method and its Sensing Potential towards Methyl Mercaptan

A novel and simple approach has been developed for a large-scale synthesis of ZnO nanorods using ultrasound radiation. Double-pod-like ZnO nanorods were directly grown from the starting precursors of zinc nitrate hydrate [Zn(NO3)26H2O] and hexamethylene tetramine (HMT) in deionized water without any templates or seeds. The obtained double-pod-like product had a diameter ranging from 80 to 150 nm and length ranging from 1 to 5 um. Scanning electron microscope (SEM), X-ray diffraction (XRD) and transmission electron microscope (TEM) revealed that these products are of high purity, hexagonal and of single-crystalline structure. The ZnO nanorods synthesized were utilized for gas sensing application. Alumina plate consists of Pt interdigitated electrode was used as sensor substrate. The as-prepared products were transferred to the surface of substrate by screen printing method to fabricate the gas sensor. The sensing properties of the sensor were investigated toward methyl mercaptan (CH3SH). The sensor shows good and fast response towards methyl mercaptan at a fixed operating temperature. The high sensitivity may be ascribed to the high surface area and aspect ration of the double-pod-like nanomaterial.

Pulsed electrodeposition of monocrystalline Ni nanowire array by intermittent symmetric square wave

By means of a porous template without removing the aluminium substrate, a technique of pulsed electrodeposition with an intermittent symmetric square wave has successfully been applied to fabricate Ni nanowire array. The as-obtained nanowires have a diameter of about 60nm and exhibit high aspect ration of more than 50. The electron diffraction pattern investigation demonstrates that the nanowires are single crystal. Also, a preferred orientation [220] of the as-obtained Ni nanowires with high purity decided by XRD has been obtained.

Features of self-supporting tungsten nanowire deposited with high-energy electrons

The features of self-supporting tungsten nanowire fabricated by electron-beam-induced deposition using 200 keV electrons were investigated. The width of wire first decreases with the increase of the scan speed, then saturates at about 7–10 nm when the scan speed is higher than 10 nm/s. The wire has belt-shipped morphology elongated along the incident beam. The wire parallel to the substrate surface was fabricated at the beam scan speed of 4.0 nm/s, while those with upward and downward features were obtained by changing the scan speed. Nanobelt, nanorod, and nanotip with high aspect ration and small lateral size were fabricated with this method. Considering the forward scattering of electrons and the beam Gaussian profile, a model was developed for the growth of wire using high-energy electrons.

Microlayer coextrusion as a route to innovative blend structures

AbstractNanolayer and microlayer coextrusion is a method for combining two or three polymers as hundreds or thousands of alternating layers with individual layers as thin as tens of nanometers. The possibility for utilizing microlayer coextrusion as a tool for creating microplatelets of high aspect ration was explored. Polypropylene (PP) was combined with polyamide‐66 (PA66) in microlayers. A high volume fraction of PA66 microplatelets dispersed in PP was achieved by injection molding the microlayered materials at a temperature intermediate between the melting points of the two constituents. The difference in melting temperatures provided a broad processing window of about 60°C in which the PP layers melted to form the matrix whereas the PA66 layers remained in the solid state as dispersed microplatelets of high aspect ration. The resulting material had significantly improved oxygen barrier properties. An enhancement of 4–5 times over the barrier of the conventional melt blend resulted from increased tortuosity of the diffusion pathway.

Dispersion of graphite nanosheets in a polymer matrix and the conducting property of the nanocomposites

AbstractPoly(methyl methacrylate)(PMMA)/expanded graphite composite has been made via an in situ polymerization of methyl methacrylate(MMA) in the presence of expanded graphite obtained by rapid heating of the graphite intercalation compound (GIC). The composite was then blended with poly(vinyl chloride) (PVC) to form an electrically conducting composite. SEM, TEM and XRD showed that the graphite had been dispersed throughout the polymer matrix in the form of nanosheets with thicknesses of about 20 nm. The resulting composite showed excellent electrical conductivity despite a low concentration of graphite. The transition from an electrical insulator to an electrical semiconductor for the composite occurred when the graphite content was 3.5 wt%, much lower than that of conventional conducting polymer composites. Conductivity reached a maximum of 10−4 s/cm at a graphite concentration of 5.0 wt%. This improvement of conductivity could be attributed to the high aspect ration (width‐to‐thickness) of the graphite nanosheets dispersed in the polymer matrix.

Al planarization processes for multilayer metallization of quarter micrometer devices

Al planarization technology for application in quarter micrometer devices was explored. High temperature flow process as well as two-step cold/hot sputtering processes were investigated. Quarter micrometer contacts of dept. 1.2 μm were successfully filled by two-step cold/hot sputtering. Multilayer structures were planarized, yielding via resistance (<0.6Ω) lower than those of metallization based on tungsten-plugs. The key factors for reliable filing of contacts are a low base pressure, adequate coverage of the wetting layer (titanium) and continuous coverage of the first nucleation layer in the contacts. A low temperature (450 °C) process was demontrated. Aluminum deposited onto titanium results in a high surface reflectivity (210%, normalized to bare Si at 436 nm). In comparison with the flow process, the two-step cold/hot sputtering proces showed a unique advantage in that it was able to fill high aspect ration contacts at low temperature.

New high resolution and high sensitivity deep UV, x-ray, and electron beam resists

A new family of highly sensitive negative resists for Deep UV, X-ray and electron beam exposure capable of better than 100 nm resolution and very high pattern aspect ration has been investigated. The resists are based epoxidized novolac resins sensitized with acid generating compounds.

Self-aligning resist techniques for shadow evaporation of a superconducting three-terminal device

Multiple films deposited at oblique angles through a single high aspect ration evaporation mask can produce intricate structures with well-defined interfaces. The fabrication of an experimental tunnel junction geometry in which a number of shadow evaporation steps are used will be discussed.