Fullerenes as precursors for nanocapsule formation

We have shown that Ni metal particles when melted in the presence of C₆₀ form graphitic layers around themselves with the Ni remaining as pure metal and without any evidence of carbide formation. We have successfully encapsulated particles over several orders of magnitude of size from ∼10 nm to several microns. The process has been observed taking place in real time using transmission electron microscopy (TEM). The process was not observed when graphite powder was used instead of C₆₀ powder and the Ni similarly heated to melting point, using the electron beam. Heating a mixture of Ni and C₆₀ powders together in a conventional manner also produced encapsulated Ni particles. This suggests that the encapsulation method is thermal in nature although the electron beam does offer the ability to control the process for individual particles. Further research has shown that the encapsulation process can also occur at temperatures as low as 800° C by a catalytic route. We have extended the work of heating a metal in the presence of fullerenes and have effectively encapsulated other metals such as Fe, Co, Ho, Cu and Au.     

Structural Characterization of the New Fullerene-Rare Gas Compound Ar1C60

Abstract

We communicate how C₆₀ Hot Isostatically Pressed (HIPed) at 200° or 400°C with a pressure of 1.7 kbar of Ar produces the new fullerene-rare gas compound Ar₁C₆₀. We have shown, using Xray powder diffraction and subsequent Rietveld analysis, that this solid can be characterised stoichiometrically as Ar₁C_60- The stoichiometry has also been confirmed by thermal gravimetric analysis (TGA) showing 5% by weight to be Ar (expected=5.25%). The presence of Ar is confirmed by transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDS). This material is found to be remarkably stable to loss of Ar over several weeks at room temperature. This represents the first full characterisation of an interstitial rare gas fullerene compound.

     

A computational characterization of CO@C60

The carbon monoxide encapsulation into C₆₀ is evaluated using the DFT and MP2 calculations. The CO encapsulation is attractive, yielding an energy gain of more than 12 kcal/mol. This substantial encapsulation energy should produce at the conditions used in the high-temperature and high-pressure synthesis (originally used for encapsulation of rare gases in fullerenes) an equilibrium CO@C₆₀ fraction of about 3.5% compared to the empty C₆₀. The computed IR and NMR spectra agree with the available observations for CO encapsulated into open-cage C₆₀ derivatives.     

Physical vapour deposition coating processes for encapsulation of powder metal components before hot isostatic pressing

Abstract

Application of coatings by plasma vapour deposition involving electron beam evaporation and ion plating onto green powder metal compacts has been studied as a potential method for encapsulating powder metal products before hot isostatic pressing. The deposition of defect free coatings is essential if this concept is to provide a reliable encapsulation technique. Coating structures are therefore discussed in terms of the plasma processing conditions and surface roughness of the powder substrate. It is shown that the most promising approach is a combined coating and sinter–hot isostatic pressing cycle, which enables defects within the coating to be removed by the formation of a transient liquid phase.

MST/1455     

Magnetic properties and transmission electron microscopy studies of Ni nanoparticles encapsulated in carbon nanocages and carbon nanotubes

Three types of carbon nanomaterials, including bamboo-shaped carbon nanotubes with Ni encapsulated and hollow and Ni catalytic particles filled carbon nanocages, have been prepared by methane catalytic decomposition at a relatively low temperature. Transmission electron microscopy observations showed that fascinating fullerene-like Ni–C (graphitic) core–shell nanostructures predominated. Detailed examination of high-resolution transmission electron microscopy showed that the walls of bamboo-shaped carbon nanotubes with quasi-cone catalytic particles encapsulated consisted of oblique graphene planes with respect to the tube axis. The Ni particles encapsulated in the carbon nanocages were larger than that encapsulated in carbon nanotubes, but the diameters of the cores of hollow carbon nanocages were less than that of Ni particles encapsulated in carbon nanotubes, suggesting that the sizes of catalyst particles played an important role during carbon nanomaterial growth. The magnetic properties of the carbon nanomaterials were measured, which showed relatively large coercive force (H_c = 138.4 O_e) and good ferromagnetism (M_r/M_s = 0.325).     

Size control for fullerene C60 nanocrystals during the high temperature and high pressure fluid crystallization process

The preparation and size control for mono-dispersed fullerene C₆₀ fine particles was successfully achieved during the high temperature and high pressure fluid (HTPL) crystallization process, in which acetone was used as the HTPL solvent and pure water or the mixture of acetone and water as the cooling solvent. The prepared fullerene C₆₀ particles had spherical shape and narrow size distribution with the average size ranging from 44 nm to 110 nm depending on the various experimental conditions, such as fluid temperature, solvent flow rate, system pressure and the ratio of acetone and water in cooling solvent. The products were characterized by using X-ray powder diffraction (XRD), scan electron microscopy (SEM), dynamic light scattering technique (DLS) and UV–VIS spectrum, respectively. And the size effect of such fullerene C₆₀ nanocrystals was confirmed.     

Cr3C2 incorporation into an Inconel 625 laser cladded coating: Effects on matrix microstructure,mechanical properties and local scratch resistance

There is an increasing industrial demand for metal alloys with high wear resistance under severe operating conditions. Ni-based alloys, such as Inconel superalloys, are an excellent option for these applications; however, their use is limited by their high cost. Ni-based coatings deposited onto carbon steel substrates are being developed to achieve desired surface properties with reduced cost. Laser cladding deposition has emerged as an excellent method for processing Ni based coatings. In this work, microstructure, mechanical properties and local wear behaviour have been investigated in response to the addition of Cr₃C₂ ceramic particles into an Inconel 625 alloy deposited onto a ferritic steel substrate by laser cladding. Using this deposition technique, a homogeneous distribution of Cr₃C₂ particles was observed in the coating microstructure. The addition of ceramic particles to the starting powder resulted in the formation of hard precipitates in the coating microstructure. The partial dissolution of Cr₃C₂ particles during the laser cladding process increased the hardness of the Inconel 625 matrix. Depth sensing indentation and scratch tests were performed to study the local wear behaviour and scratch resistance of the cermet matrix compared with the conventional Inconel 625 alloy. Finally, the effect of Cr₃C₂ on mechanical properties was correlated with the observed microstructure modifications.     

Two Alternative Ways for Formation of Mono‐atomic Carbon Layer on Ni(1 1 1): Organic‐Gas Cracking and Thermal Decomposition of Fullerenes in Thin Film

Abstract

Formation of graphite mono‐atomic layers (monolayer of graphite, MG) on Ni(1 1 1) single‐crystal surface by cracking of propylene C₃H₆ as well as by decomposition of fullerene molecules C₆₀ was investigated. Comparative analysis of carbon films was made in both cases by means of auger electron spectroscopy (AES), low energy electron diffraction (LEED), and scanning tunneling microscopy (STM) techniques. It was shown with the LEED measurements, that quality of graphite mono‐atomic layer obtained in the two different ways is similar and high enough. For the system prepared by fullerene fragmentation some fullerene‐similar topography features were found in STM images. These observations are explained as a result of arrangement of single C₆₀ molecules underneath the MG on Ni(1 1 1).     

Microstructure and property of Ni60A/WC composite coating fabricated by fiber laser cladding

Laser clad Ni60A/WC composite coating was fabricated on the surface of Q235 steel by using 6 kW fiber laser. The morphology, composition, and microhardness of composite coating were studied by using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X‐ray diffraction (XRD), and micro‐hardness tester. The results show that in the process of fiber laser cladding Ni60A/WC composite coating, residual WC particles partially dissolve and react with other elements to form eutectics, which exists in the shape of lumpy, strip and spherical. The main structures of laser cladding are γ‐Ni, WC, W₂C, M₇C₃, M₂₃C₆ etc. From the hardness analysis, the average hardness of the composite coating is four times of the substrate.     

Microstructural characterisation of high velocity oxyfuel thermally sprayed Stellite 6

Abstract

High velocity oxyfuel (HVOF) thermal spraying with an oxygen-propylene combustion flame was used to deposit coatings of a Co–Cr–W–C alloy (similar in composition to Stellite 6) from gas atomised feedstock powder. The microstructural characteristics of the deposits were investigated using the combined techniques of X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). In particular, the tripod polishing technique was used to prepare large areas of electron transparent membrane for TEM analysis; these areas were typically of the order of several hundred square micrometres. Accordingly, SEM and TEM analysis could be directly correlated, providing a clear understanding of the overall nature of the coatings. The coatings exhibited characteristic splatlike, layered morphologies due to the deposition and resolidification ofmolten or semimolten powder particles. The as sprayed microstructure consisted of a face centred cubic Co rich metallic matrix with a small fraction of CoCr₂O₄ spinel oxide. The latter formed either as intersplat lamellae or intrasplat globules. Under the HVOF spray conditions employed, a high proportion of the feedstock powder appeared to have been fully melted prior to impact on the substrate, with partially or unmelted powder accounting for < 20% of the microstructure. Formation of the M₇C₃ phase, normally present in Stellite 6, appeared to have been suppressed by the high cooling rate during spray deposition.     

Endohedral metallo [80] fullerene interactions with small polar molecules

The interaction of M@C₈₀ (M = Li, K and Na) with small polar molecules (H₂O, CH₃OH, HF and NH₃) is described by density functional theory (DFT) calculations. Our theoretical studies show that in several computed cases the binding energies of M@C₈₀ complexes with small polar molecules increases upon encapsulation. The observed behavior can be accounted for by charge transfer effects between the encapsulated metal and the surface of the C₈₀ cage. These assertions have been solidified by a corresponding analysis of the thermochemistry, vibrational frequencies and HOMO molecular orbital plots of the optimized species.     

Dry sliding wear behaviour at ambient and elevated temperatures of plasma transferred arc deposited aluminium composite coatings

Abstract

Plasma transferred arc (PTA) surfacing is a surface engineering process in which a coating is deposited on the substrate by the injection of metal powders and/or ceramic particles into the weld pool created by the formation of a plasma plume. The present work involved the tribological evaluation of metal matrix composite (MMC) coatings deposited onto an aluminium alloy using the PTA technique. Coatings were fabricated by the deposition of an Al–Ni powder containing either Al₂O₃ or SiC particles. Dry sliding wear behaviour of the coatings was evaluated at ambient and elevated temperatures. Under sliding conditions of low applied stress and ambient temperature, reinforcement properties such as interfacial structure and fracture toughness have a significant influence on wear resistance. The SiC particles, which exhibit high interfacial bonding and toughness, support the matrix by acting as load bearing elements, thereby delaying the transition in wear mechanism as applied stress increases. As applied stresses exceed the fracture strength of the SiC and Al₂O₃ particles, these particles suffer fragmentation and/or debonding and no longer support the matrix. At higher stresses and elevated temperature, matrix properties such as flow stress and the tribolayer formation play more important roles in determining wear resistance.     

Effect of texture evolution on tensile properties of Al–Ni eutectic alloy fabricated by equal channel angular pressing

Abstract

The present study investigated in detail the effect of texture evolution on the mechanical properties of an Al–5·7 wt-%Ni eutectic alloy, which was subjected to severe plastic deformation by the equal channel angular pressing (ECAP) technique. The ECAP procedure was carried out using two strain introduction methods, route B_C and route A, at a temperature of 298 K and a pressing rate of 0·33 mm s^?1. The as pressed microstructures were observed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Results indicated that the Al–Ni eutectic alloy specimens after ECAP processing by route B_C and route A methods had very different microstructures, which strongly affected the tensile properties of the specimens. It was demonstrated that after ECAP processing by route B_C, fine Al₃Ni particles of ～300 nm were homogeneously dispersed in the aluminium matrix, and the specimens showed no clear anisotropy in tensile properties. After ECAP processing by route A, however, eutectic textures containing α-Al and Al₃Ni fibrous dispersoids had a highly anisotropic distribution and were demonstrated to have significantly anisotropic tensile properties. Based on the experimental results, the fracture mechanism during tensile testing of the Al–Ni eutectic alloy using different strain induction methods is discussed.     

Metal-C60 Interface Interaction: Effects on Metal Dispersion in Co-Deposited Films

Abstract

In case of a metal finely dispersed in a C₆₀ matrix, the metal-to-C₆₀ charge transfer lowers the interface energy. The total cohesive energy per metal atom E_tot was estimated for Au clusters in fullerite. The results show that, for a charge Q_f ≥ 1 electron (e) transferred from the metal clusters to each C₆₀ cage, a minimum appears in E_tot, defining a most stable cluster size. Thereby, the equilibrium dispersion state of the metal in the fullerite matrix depends on Q_f.     

Pulsed Laser Processing of Carbon and Silicon Clusters and Thin Films

Abstract

Several new processes have been developed for the preparation of fullerenes and thin films by using a pulsed excimer laser. The irradiation of a pulsed KrF excimer laser beam onto a C₆₀ powder target produced single phase C₆₀ thin films when the laser energy fluence was in the range between 40 and 50mJ/cm². By atomic force microscopy, the laser-deposited C₆₀ thin film was verified to have a surface far smoother that the surfaces of films produced by the conventional evaporation method. The stainless steel rods coated with this film exhibited an excellent tribological property. Cluster formation from SiC and other carbides MC_n(M=Ti,W,B) was investigated by laser desorption time-of-flight mass spectrometry. No clear indication was observed for the production of such clusters as (SiC)₆₀ and (M_xC_60-x) from the sintered targets directly as well as from the films laser deposited from the targets. However, C₆₀ and C₇₀ were found to exists in the laser-deposited films, indicating a new applicability of pulsed laser processing for segregative cluster synthesis from solid solution. Preliminiary results on thin film deposition via pulsed ablation of (Ba,Na)_xSi₄₆ clathrate were also presented.     

The effect of recycling on the oxygen distribution in Ti-6Al-4V powder for additive manufacturing

Abstract

Ti-6Al-4V powder has been recycled 30 times in an electron beam melting system. A combination of electron microscopy techniques has been used to show that the recycled powder has a 35% higher oxygen content, and that the particles have a more irregular morphology, a narrower particle size distribution, and a much more variable microstructure than the virgin powder. The microstructures in the recycled powder particles vary from a martensitic α′ structure, which is identical to that in the virgin powder, to a two-phase α + β structure. This variability is related to the complex thermal history of the unmelted metal powder in the system. Despite these differences, all of the particles exhibit essentially the same surface oxide thickness; the excess oxygen in the recycled powders is instead located in the β phase. The possible consequences for the structure and properties of the resultant additively manufactured parts are discussed.     

Fullerene films deposited by evaporation in vacuum using spot-focused annular electron beam

A rapidly focused annular electron beam can provide for the effective evaporation of a fullerene mixture in a vacuum of ～10^?2 Pa. A 1-kW beam focused into a spot within 0.1–1 s produces explosive evaporation of a fullerene target at an extremely high efficiency of heating. A comparison of the Raman and electronic absorption spectra of the initial fullerene powder and a film deposited upon its evaporation shows that C₆₀ and C₇₀ fullerenes are evaporated without rupture of C-C covalent bonds. The electron beam evaporation in vacuum has been successfully used to obtain fullerene films on substrates with an area of ～0.1 m².     

Interfacial characteristics of electron beam welding joints of SiCp/Al composites

Abstract

The electron beam welding of SiCp/101Al composites has been carried out. The influence of welding parameters on weldability and mechanical properties of the welded joints was discussed. The welding parameters were therefore optimised under the current experimental circumstance. Results show that only weak interfacial reaction between SiC particle and liquid aluminium occurred. Minute quantity brittle Al₄C₃ compounds and single phase Si were generated in the welded joint. The interfacial reaction between SiC particles and Al matrix could be greatly suppressed by adopting appropriate technique measures such as high welding speed and low heat input. The content of Al₄C₃ can be therefore greatly decreased in the welded joint. Moreover, modification welding and electron beam scanning could further improve the appearance of weld, and the welded joint with better quality could be obtained.     

Ductile Fe-based bulk metallic glasses at room temperature

In this work, Fe₇₀Ni₁₀P₁₃C₇ and Fe₆₀Ni₂₀P₁₃C₇ bulk metallic glasses (BMGs) with high ductility are synthesised through the appropriate adjustment of flux conditions. Microstructure analyses indicate that the ductility of these two Fe-based BMGs is primarily determined by Fe–Ni and Ni–Ni metal–metal bonds, which enable the glasses to undergo a strain of more than 50% in the absence of fracture, as well as extensive bending ductility, similar to metals such as Fe and Ni. This study aims to find a solution to the brittleness problem in Fe-based BMGs, and the results have implications for understanding the deformation mechanism in Fe-based BMGs.     

C60 − Mean Lifetime as a Function of Electron Energy and Molecular Temperature

Abstract

The electron autodetachment rate constant of the negative ion C₆₀ ^? has been determined as a function of both electron energy and molecular temperature. The experimental findings provide proof of the statistical nature of the electron auto‐emission from C₆₀ ^?. The experimental data have been rationalized within the framework of statistical transition state theory.