Influence of ultrasonic agitation on the abrasive wear characteristics of Al-Cu/ 2 vol.% Grp composite

In the present study, the abrasive wear behavior of Al-4.4 wt.% Cu composite reinforced with 2 vol.% graphite particle (Grp) has been investigated. In the preparation of composite, Ultrasonic Treatment (UT) is provided in the composite melt for the uniform distribution of reinforcement particles. Two bond abrasive wear tests are conducted for composites treated with ultrasound and without UT and base alloy. The results of abrasive wear studies indicate that at 5 and 10 Newton (N) loads, the composite with UT has a higher coefficient of friction (COF) and wear resistance than that of the base alloy (Al-4.4 wt.% Cu). Whereas, at 15 and 20 N load, the value of COF and wear resistance is lower for the composite. Two abrasive wear mechanisms micro-plowing and micro-cutting have been observed during the wear tests of base alloy and composites. The analysis of worn-out sample surfaces at higher load reveals that softened material layer due to localized elevation in temperature between two contact surfaces during wearing acts as a tribolayer in base alloy while in composites both softened material layer and graphite layer have worked together as tribolayer.

Nanometers-Thick Ferromagnetic Surface Produced by Laser Cutting of Diamond

In this work, we demonstrate that cutting diamond crystals with a laser (532 nm wavelength, 0.5 mJ energy, 200 ns pulse duration at 15 kHz) produces a ≲20nm thick surface layer with magnetic order at room temperature. We have measured the magnetic moment with a SQUID magnetometer of six natural and six CVD diamond crystals of different size, nitrogen content and surface orientations. A robust ferromagnetic response at 300 K is observed only for crystals that were cut with the laser along the (100) surface orientation. The magnetic signals are much weaker for the (110) and negligible for the (111) orientations. We attribute the magnetic order to the disordered graphite layer produced by the laser at the diamond surface. The ferromagnetic signal vanished after chemical etching or after moderate temperature annealing. The obtained results indicate that laser treatment of diamond may pave the way to create ferromagnetic spots at its surface.

Research Results of Discharge Products

Products from an arc discharge between various conducting materials (copper-copper, graphite-graphite, natural graphite and their combination) in water and air have been studied. The SEM and SEM-EDS analysis, and the BET analysis on products from discharges were done as well identifying their size distribution. There are two essential types of product taken in investigation as (i) pure metallic particulates, and (ii) specific structures of materials. The visual properties of nano-sized products formed in two media at different current are compared. In products obtained in air, tiny spherical particulates of size in nano-order are observed repeatedly, as well ordinary nano-sized particulates as ones in water. The main visual feature of the particulates formed in air is their existence in deposition in which they are separated by itself. Plenty of individual scrolling sheets of graphite layer of enormous size frequently encounter in soot on electrodes.

Peeling graphite layer by layer reveals the charge exchange dynamics of ions inside a solid

Over seventy years ago, Niels Bohr described how the charge state of an atomic ion moving through a solid changes dynamically as a result of electron capture and loss processes, eventually resulting in an equilibrium charge state. Although obvious, this process has so far eluded direct experimental observation. By peeling a solid, such as graphite, layer by layer, and studying the transmission of highly charged ions through single-, bi- and trilayer graphene, we can now observe dynamical changes in ion charge states with monolayer precision. In addition we present a first-principles approach based on the virtual photon model for interparticle energy transfer to corroborate our findings. Our model that uses a Gaussian shaped dynamic polarisability rather than a spatial delta function is a major step in providing a self-consistent description for interparticle de-excitation processes at the limit of small separations.

Influence of Graphite Layer on Electronic Properties of MgO/6H-SiC(0001) Interface

This paper concerns research on magnesium oxide layers in terms of their potential use as a gate material for SiC MOSFET structures. The two basic systems of MgO/SiC(0001) and MgO/graphite/SiC(0001) were deeply investigated in situ under ultrahigh vacuum (UHV). In both cases, the MgO layers were obtained by a reactive evaporation method. Graphite layers terminating the SiC(0001) surface were formed by thermal annealing in UHV. The physicochemical properties of the deposited MgO layers and the systems formed with their participation were determined using X-ray and UV photoelectron spectroscopy (XPS, UPS). The results confirmed the formation of MgO compounds. Energy level diagrams were constructed for both systems. The valence band maximum of MgO layers was embedded deeper on the graphitized surface than on the SiC(0001).

Realizing the large current field emission characteristics of single vertical few-layer graphene by constructing a lateral graphite heat dissipation interface

An in situ TEM result showed that a vertical few-layer graphene field emitter can carry large emission current at high temperature, benefiting from a graphite layer at the substrate interface which helps to efficiently dissipate heat during field emission.

Synthesis, Characterization and Wettability of Cu-Sn Alloy on the Si-Implanted 6H-SiC

The wettability of the metal/SiC system is not always excellent, resulting in the limitation of the widespread use of SiC ceramic. In this paper, three implantation doses of Si ions (5 × 1015, 1 × 1016, 5 × 1016 ions/cm2) were implanted into the 6H-SiC substrate. The wetting of Cu-(2.5, 5, 7.5, 10) Sn alloys on the pristine and Si-SiC were studied by the sessile drop technique, and the interfacial chemical reaction of Cu-Sn/SiC wetting couples was investigated and discussed. The Si ion can markedly enhance the wetting of Cu-Sn on 6H-SiC substrate, and those of the corresponding contact angles (θ) are raised partly, with the Si ion dose increasing due to the weakening interfacial chemical reactions among four Cu-Sn alloys and 6H-SiC ceramics. Moreover, the θ of Cu-Sn on (Si-)SiC substrate is first decreased and then increased from ~62° to ~39°, and ~70° and ~140°, with the Sn concentration increasing from 2.5%, 5% and 7.5% to 10%, which is linked to the reactivity of Cu-Sn alloys and SiC ceramic and the variation of liquid-vapor surface energy. Particularly, only a continuous graphite layer is formed at the interface of the Cu-10Sn/Si-SiC system, resulting in a higher contact angle (>40°).