Synthesis of Novel Superhard Phases in the B-C-N System

Novel ternary diamond-like phases of the B-C-N system were synthesized at pressures up to 30 GPa and temperatures up to 3500 K by static and dynamic compression of graphite-like BN-C solid solutions. Structure and properties of these new phases were studied using X-ray diffraction with synchrotron radiation, analytical transmission electron microscopy (ATEM), electron energy loss spectroscopy (EELS), microhardness measurements and nanoindentation.     

Economic feasibility study of polyelectrolyte-enhanced ultrafiltration (PEUF) for water softening

In polyelectrolyte-enhanced ultrafiltration (PEUF), a water-soluble anionic polyelectrolyte (in this study sodium polystyrene sulfonate or PSS) is added to hard water. The calcium and magnesium bind to the polymer which has a high enough molecular weight to be rejected by an ultrafiltration membrane. The permeate is softened water. Economically, the PSS needs to be recovered from the retentate for reuse. Three methods of recovery developed in this study were addition of NaCl, Na₂CO₃ or HCl to PEUF to regenerate PSS. Of the three PEUF processes considered, NaCl/PEUF as compared to Na₂CO₃/PEUF and HCl/PEUF provided the best scheme for the water softening process. PEUF is shown in this study to be competitive with lime softening at low flow rates. The PEUF process is more expensive than ion exchange for a stream containing only hardness ions. However, PEUF becomes nearly comparable with ion exchange for a stream containing hardness ions as well as bacteria, viruses and pyrogen. The cost comparisons are based on fully continuous operations and include treatment of waste streams from each process.     

Corrosion and oxidation properties of NiCr coatings sprayed in presence of gas shroud system

The oxidation of a NiCr bond coat during air plasma spraying was controlled by designing a gas shroud system attached to the plasma torch nozzle. Two nozzles, termed as “normal” and “high-speed” nozzles examined the effect of nozzle internal design on the microstructure and phase structure of coatings. X-ray diffraction and SEM morphologies showed that the shroud system reduced the oxidation of NiCr particles during the spray process. Compared with conventional air plasma spraying, the argon gas shroud reduced the coating hardness because the volume fraction of partially melted particles increased. The high-speed nozzle reduced the oxidation and hardness of NiCr coatings due to the increase of partially melted particles in the coatings.     

Effect of annealing on the nanoscratch behavior of multilayer Si0.8Ge0.2/Si films

In this study, we examined the nanoscratch behavior of annealed multilayered silicon-germanium (SiGe) films comprising alternating sublayers (Si) deposited using an ultrahigh-vacuum chemical vapor deposition (UHV/CVD) system. Annealing consisted of ex situ thermal treatment in a furnace system. We used a nanoscratch technique to investigate the nanotribological behavior of the SiGe films and atomic force microscopy (AFM) to observe deformation phenomena. Our AFM morphological studies of the SiGe films revealed that pile-up phenomena occurred on both sides of each scratch. The scratched surfaces of the SiGe films that had been subjected to various annealing conditions exhibited significantly different features, it is conjectured that cracking dominates in the case of SiGe films while ploughing dominates during the scratching process. We obtained higher coefficients of friction (μ) when the ramped force was set at 6000 μN, rather than 2000 μN, suggesting that annealing of SiGe films leads to higher shear resistance; annealing treatment not only produced misfit dislocations in the form of a significantly wavy sliding surface but also promoted scratching resistance.     

Void formation in zirconium under irradiation in the high-voltage electron microscope

NUCLEAR TRACKS IN SOLIDS PRINCIPLES AND APPLICATIONS, by Robert L Fleischer, P. Buford Price and Robert M. Walker. University of California Press 1975. 605 pages, £20.50.

NEW USES OF ION ACCELERATORS, J. F. Ziegler, ed. Plenum Publishing Corporation, $33.60.

ATOMIC COLLISIONS IN SOUDS, Volumes 1 and 2, Edited by S. Datz, B. R. Appleton and C. D. Moak. Plenum Publishing Corporation, New York, $90.00.

HYPERFINE INTERACTIONS, Journal devoted to research in the border region of solid state, atomic and nuclear physics. Editors: B. I. Deutch and H. de Waard. North-Holland, Amsterdam, $46.95 per year.

ATOMIC ENERGY LEVELS AND GROTRIAN DIAGRAMS, VOL. 1, HYDROGEN I-PHOSPHORUS XV, by S. Bashkin and J. 0. Stoner, Jr., North-Holland Publishing Co., Amsterdam 1975. 615 pp., $59.95, Dfl. 150.00.

THE DYNAMICS OF SPECTROSCOPIC TRANSITIONS, by James D. Macomber. John Wiley and Sons, New York, 1976, $23.00, £1.50. 332 pages, 93 figures, 67 bibliographical references, 37 problems, a general index and a key to symbols.     

o-C8 Carbon: a New Allotrope of Superhard Carbon

An orthonormal crystal of carbon with PMMA space group (o-C₈) was found to be a stable superhard carbon allotrope by particle swarm optimization algorithm and density functional calculations. The phonon spectrum calculations demonstrate that the o-C₈ carbon phase is dynamically stable. The volume compression calculations show that it is highly incompressible, with bulk modulus of 298.6 GPa. The calculations demonstrate that it is a low-density superhard material with density of 2.993 g/cm³ and Vickers hardness of 82.4 GPa.     

Structure and micro-mechanical properties of helium-implanted layer on Ti by plasma-based ion implantation

The present paper concentrates on structure and micro-mechanical properties of the helium-implanted layer on titanium treated by plasma-based ion implantation with a pulsed voltage of −30 kV and doses of 3, 6, 9 and 12 × 10¹⁷ ions/cm², respectively. X-ray photoelectron spectroscopy and transmission electron microscopy are employed to characterize the structure of the implanted layer. The hardnesses at different depths of the layer were measured by nano-indentation. We found that helium ion implantation into titanium leads to the formation of bubbles with a diameter from a few to more than 10 nm and the bubble size increases with the increase of dose. The primary existing form of Ti is amorphous in the implanted layer. Helium implantation also enhances the ingress of O, C and N and stimulates the formations of TiO₂, Ti₂O₃, TiO, TiC and TiN in the near surface layer. And the amount of the ingressed oxygen is obviously higher than those of nitrogen and carbon due to its higher activity. At the near surface layer, the hardnesses of all implanted samples increases remarkably comparing with untreated one and the maximum hardness has an increase by a factor of up to 3.7. For the samples implanted with higher doses of 6, 9 and 12 × 10¹⁷ He/cm², the local displacement bursts are clearly found in the load-displacement curves. For the samples implanted with a lower dose of 3 × 10¹⁷ He/cm², there is no obvious displacement burst found. Furthermore, the burst width increases with the increase of the dose.     

Fabrication of high-performance nickel/graphene oxide composite coatings using ultrasonic-assisted electrodeposition

Ultrasonic-assisted electrodeposition was used to fabricate the nickel/graphene oxide composite coatings with high hardness, low friction coefficient, and high wear resistance. In the present study, the effects of ultrasonic power and concentration of graphene oxide on the mechanical and tribological properties of the electrodeposited nickel/graphene oxide composite coatings were systematically studied. X-ray diffraction (XRD) analyses showed that the crystallite size of the nickel decreased with an increase of ultrasonic power (0–50 W, 40 KHz, square wave) and concentration of graphene oxide (0.1–0.4 g/L). Morphologies of the surface and cross-section of the composite coatings observed by Scanning Electron Microscopy (SEM) confirmed the existence of graphene oxide particles in the nickel matrix. The results from microhardness measurement demonstrated that the hardness was increased by 1.8 times using 50 W ultrasonic-assisted electrodeposition with the fixed concentration of graphene oxide (0.1 g/L), compared to the pure nickel coating. The hardness was increased by 4.4 times for the 0.4 g/L graphene oxide with the optimized ultrasonic power of 50 W in comparison to the pure nickel coating. Meanwhile, the friction coefficient decreased gradually with an increase in ultrasonic power and concentration of graphene oxide, respectively, where the effect of the concentration of graphene oxide played a more important role.     

Internal and external eigenvalue problems of Hermitian operators and their use in electronic structure theory

Within the fragment resolution of molecular systems the conceptual and interpretative advantages of using the separate eigenvalue problems for the internal and external part of the Hermitian matrix representing a physical quantity in quantum mechanics are examined. By definition, these two parts accordingly combine only the diagonal and off-diagonal subsystem-resolved blocks of matrix elements. These two partial eigenvalue problems bring about the matrix internal or external decouplings, respectively, which have recently been used in several interpretations of the molecular electronic structure. A character and structure of the external eigensolutions is examined in some detail and their recent applications in the Charge Sensitivity Analysis—to extract the most important electron-transfer effects between constituent atoms of model chemisorption systems, and in the Molecular-Orbital theory—to precisely identify the inter-orbital flows of electrons, are summarized and commented upon. The grouping relation, for combining the external/internal eigensolutions into those for the whole matrix, is derived in the context of the complementary “rotations” of the basis set vectors.     

The effects of organoclay on the morphology and mechanical properties of PAI/clay nanocomposites coatings prepared by the ultrasonication assisted process

In this research, solvent based polyamide – imide (PAI)/clay nanocomposites were prepared successfully using the solution dispersion technique. With the assistance of the ultrasonic wave, the effect of the ultrasonic wave time on the microstructure of 3 wt% PAI/C20A nanocomposite (NC) was investigated. Then, the best ultrasonic parameters were selected and the effects of the concentration of Cloisite 20A (C20A) (1, 3 and 5 wt% C20A) on the microstructure and mechanical properties (adhesion, hardness, flexibility, wear and impact) of NCs were investigated. The PAI, C20A and nanocomposites (NC)s were characterized by Fourier transform infrared spectroscopy (FTIR), field emission scanning electron microscopy (FE-SEM), energy dispersive X-ray analysis (EDX), and Wide-angle X-ray diffraction (WAXD). The results showed that the sample with 1 and 3 wt% C20A had better mechanical properties, as compared to the pure PAI and the 5 wt% NC.