Comprehensive Understanding of Hillocks and Ion Tracks in Ceramics Irradiated with Swift Heavy Ions

Amorphizable ceramics (LiNbO3, ZrSiO4, and Gd3Ga5O12) were irradiated with 200 MeV Au ions at an oblique incidence angle, and the as-irradiated samples were observed by transmission electron microscopy (TEM). Ion tracks in amorphizable ceramics are confirmed to be homogenous along the ion paths. Magnified TEM images show the formation of bell-shaped hillocks. The ion track diameter and hillock diameter are similar for all the amorphizable ceramics, while there is a tendency for the hillocks to be slightly bigger than the ion tracks. For SrTiO3 (STO) and 0.5 wt% niobium-doped STO (Nb-STO), whose hillock formation has not been fully explored, 200 MeV Au ion irradiation and TEM observation were also performed. The ion track diameters in these materials are found to be markedly smaller than the hillock diameters. The ion tracks in these materials exhibit inhomogeneity, which is similar to that reported for non-amorphizable ceramics. On the other hand, the hillocks appear to be amorphous, and the amorphous feature is in contrast to the crystalline feature of hillocks observed in non-amorphizable ceramics. No marked difference is recognized between the nanostructures in STO and those in Nb-STO. The material dependence of the nanostructure formation is explained in terms of the intricate recrystallization process.

PADC response to 0.3 - 3 MeV protons

Two types of Poly-Allyl-Diglycol Carbonate, the Neutrak and PN3 were investigated using track diameter distribution induced by the monoenergetic protons with energies in the range of 0.3 to 3 MeV. The energies and intensities were controlled by a silicon surface barrier detector and a nickel scattered foil placed in a 4 MV Van der Graaf accelerator. After different etching times, the etch track-sizes were scanned and measured with the optical microscope. PN3 and Neutrak track diameter responses to protons were measured, plotted, and discussed as a function of energy.

Antiwear Performance Evaluation of Halloysite Nanotube (HNT) Filled Polymer Nanocomposites

Polymer nanocomposites containing various types of reinforcements and fillers are oftenly used in applications such as sliding elements in the machine and automotive parts, gear assemblies etc., in which tribological performance parameters viz. friction and wear are the major issues. In this work, the specific wear rate of HNT filler loading (0-4wt %) in Glass-Epoxy nanocomposites fabricated by vacuum bagging technique are evaluated experimentally. For this purpose, the specimens are prepared and tests are conducted as per the ASTM G-99 standard for a number of trials with the assistance of a pin-on-disc machine by varying load and speed values, keeping time and track diameter constant. The results obtained from experiments reveals that reduction in specific wear rate and the amount of material loss is quite significant for HNT loaded specimens when compared with neat sample even at higher operating conditions. This indicates that HNT comprises of hard ceramic elements viz. SiO2 and Al2O3 which eventually enhances the antiwear behaviour of prepared nanocomposites. Finally, a study on wear mechanisms and morphologies are carried out by analyzing the worn surfaces through SEM micrographs.

C60 ions of 1 MeV are slow but elongate nanoparticles like swift heavy ions of hundreds MeV

This study reports that high fluence fullerene ion (C60+) irradiation of 1–6 MeV, which was made possible by a new-type of high-flux ion source, elongates metal nanoparticles (NPs) in amorphous SiO2 as efficiently as swift heavy ions (SHIs) of 200 MeV Xe14+, i.e., two orders of the magnitude higher energy ions. Comparing the irradiation effects induced by both the beams, the stopping processes of C60 ions in SiO2 are discussed in this paper. Despite of having almost the same elongation efficiency, the C60+ irradiation induced ~10 times more efficient sputtering due to the clustering enhancement and/or the synergy effect. Ion tracks of ~10.4 nm in diameter and 60–80 nm in length were observed in crystalline SiO2 under 4 MeV C60 irradiation. While the track diameter was comparable to those by SHIs of the same electronic stopping, much shorter track lengths than those predicted by a rigid C60 molecule model indicates that the fragmentation occurred due to nuclear collisions. The elongation of the metal NPs was induced only down to the depth where the tracks were observed but not beyond.

Advances in Spectral Distribution Assessment of Laser Accelerated Protons using Multilayer CR-39 Detectors

We show that a spectral distribution of laser-accelerated protons can be extracted by analyzing the proton track diameters observed on the front side of a second CR-39 detector arranged in a stack. The correspondence between the proton track diameter and the incident energy on the second detector is established by knowing that protons with energies only higher than 10.5 MeV can fully deposit their energy in the second CR-39 detector. The correlation between the laser-accelerated proton track diameters observed on the front side of the second CR-39 detector and the proton incident energy on the detector stack is also presented. By calculating the proton number stopped in the CR-39 stack, we find out that its dependence on the proton energy in the 1–15 MeV range presents some discontinuities at energies higher than 9 MeV. Thus, we build a calibration curve of the track diameter as a function of the proton incident energy within the 1–9 MeV range, and we infer the associated analytical function as the calculations performed indicate best results for proton spectra within the 1–9 MeV range. The calibration curve is used as a tool to ascertain the pits identified on the surfaces of both CR-39 detectors to proton tracks. The proton tracks spatial distribution analyzed by optical and atomic force microscopy is correlated with the peculiarity of the used targets.

Multi-response optimization of dry sliding wear parameters of AA6026 using hybrid gray relational analysis coupled with response surface method

Experimental study on dry sliding wear properties of aluminum alloy 6026 were performed utilizing pin-on-disk wear testing machine, considering the wear parameters like the applied load on the pin and the rotational and track diameter of disk. Wear of the pin, coefficient of friction and frictional force were observed during the test procedure for analysis. The experimental trials were designed by L16 Orthogonal Array based on Taguchi’s design of experiments and a hybrid approach of gray relational analysis combined with response surface methodology was applied for optimizing the output responses. The optimum conditions obtained for lower wear, coefficient of friction and frictional force were 35.21 N load, 376 r/min speed of disk and 111.53 mm disk track diameter, respectively. Scanning electron microscopy image of specimens taken after testing shows that abrasive wear mechanism is the predominant mechanism of wear. Experiment of confirmation with optimum conditions shows that the result was nearer to the predicted results.

Effect of Alpha Energy on Track Characteristics

Radiation imaging using solid state nuclear track detectors is an important non destructive technique for estimation of radioactive species like plutonium, thorium etc. In this study, two alpha sources were used for imaging of alpha tracks. From the image analysis of the tracks, different track characteristics were analysed. The frequency distribution of track parameters is Gaussian in nature and is found to be affected by the energy of alphas. It was seen that the maximum of the frequency distribution was located at higher values of track diameter (or area) for the tracks registered with alphas of higher energy. This could be attributed to greater extents of structural changes within the polymer upon impingement of alphas with higher energy. The studies could prove to be a marker for the identification of alpha sources of different nuclides.

Effect of Contact Area on the Wear and Friction of UHMWPE in Circular Translation Pin-on-Disk Tests

Circular translation pin-on-disk (CTPOD) tests were performed for ultrahigh molecular weight polyethylene (UHMWPE) with a view to reproducing wear mechanisms that prevail in total hip prostheses. The contact surface diameter varied from 3.0 mm to 30 mm, while the slide track diameter was fixed, 10 mm. The counterface was polished CoCr, and the lubricant was diluted alpha calf serum. Either the nominal contact pressure (1.1 MPa) or the load (126 N) was kept constant. With a constant contact pressure, the wear factor decreased steeply when the contact diameter exceeded the slide track diameter, apparently because the wear debris was not readily conveyed away from the contact. With constant load, both the wear factor and the coefficient of friction increased linearly with increasing contact area. This trend was in agreement with clinical observations that the wear rate of UHMWPE acetabular cups increased with increasing femoral head size. With nominal contact pressures approaching 10 MPa however, the bearing surface topography markedly differed from clinical observations. This was probably due to overheating of the contact and plastic deformation that resulted in the formation of protuberances not seen clinically. The present study emphasized the importance of test parameters in the pin-on-disk wear screening of prosthetic joint materials. It appeared that the contact surface diameter of the flat-on-flat test should be below the slide track diameter, and that the nominal contact pressure should be of the order of 1 MPa.