A non-destructive X-ray microtomography approach for measuring fibre length in short-fibre composites

An improved method based on X-ray microtomography is developed for estimating fibre length distribution of short-fibre composite materials. In particular, a new method is proposed for correcting the biasing effects caused by the finite sample size as defined by the limited field of view of the tomographic devices. The method is first tested for computer generated fibre data and then applied in analyzing the fibre length distribution in three different types of wood fibre reinforced composite materials. The results were compared with those obtained by an independent method based on manual registration of fibres in images from a light microscope. The method can be applied in quality control and in verifying the effects of processing parameters on the fibre length and on the relevant mechanical properties of short fibre composite materials, e.g. stiffness, strength and fracture toughness.     

Nanoscale strainability of graphene by laser shock-induced three-dimensional shaping

Graphene has many promising physical properties. It has been discovered that local strain in a graphene sheet can alter its conducting properties and transport gaps. It is of great importance to develop scalable strain engineering techniques to control the local strains in graphene and understand the limit of the strains. Here, we present a scalable manufacturing process to generate three-dimensional (3D) nanostructures and thus induce local strains in the graphene sheet. This process utilizes laser-induced shock pressure to generate 3D tunable straining in the graphene sheet. The size dependent straining limit of the graphene and the critical breaking pressure are both studied. It is found that the graphene film can be formed to a circular mold (～50 nm in diameter) with an aspect ratio of 0.25 and strain of 12%, and the critical breaking pressure is 1.77 GPa. These values were found to be decreasing with the increase of mold size. The local straining and breaking of graphene film are verified by Raman spectra. Large scale processing of the graphene sheet into nanoscale patterns is presented. The process could be scaled up to roll-to-roll process by changing laser beam size and scanning speed. The presented laser shock straining approach is a fast, tunable, and low-cost technique to realize strain engineering of graphene for its applications in nanoelectrical devices.     

Electrical and thermal conduction in atomic layer deposition nanobridges down to 7 nm thickness

While the literature is rich with data for the electrical behavior of nanotransistors based on semiconductor nanowires and carbon nanotubes, few data are available for ultrascaled metal interconnects that will be demanded by these devices. Atomic layer deposition (ALD), which uses a sequence of self-limiting surface reactions to achieve high-quality nanolayers, provides an unique opportunity to study the limits of electrical and thermal conduction in metal interconnects. This work measures and interprets the electrical and thermal conductivities of free-standing platinum films of thickness 7.3, 9.8, and 12.1 nm in the temperature range from 50 to 320 K. Conductivity data for the 7.3 nm bridge are reduced by 77.8% (electrical) and 66.3% (thermal) compared to bulk values due to electron scattering at material and grain boundaries. The measurement results indicate that the contribution of phonon conduction is significant in the total thermal conductivity of the ALD films.     

Combustion of polymer pellets in a bubbling fluidised bed

Single pellets (≈3 mm diameter) of high density polyethylene (HDPE) have been burned in an electrically heated bed of silica sand, fluidised by air or mixtures of N₂ and O₂ at atmospheric pressure. During the combustion of single pellets, measurements were made of the concentrations of CO and CO₂ in the off-gas, enabling burnout-times to be derived. This was done for different temperatures (400–900 °C) in a bubbling fluidised bed and a range of masses for the HDPE pellets. In addition, the size of the sand, the fluidising velocity and the concentration of O₂ in the fluidising gas were all varied. In a bed above 400 °C, a polymer pellet melted on entering the hot sand, which was wetted to form a small aggregate (or “blob” ∼5 mm in diameter) of sand particles held together by molten polymer. Next, the blob sank and volatilisation and thermal decomposition of the polymer produced hydrocarbon vapours, which burned mainly above the sand. It was deduced that there are actually three ranges of temperature, each with a different mechanism of combustion. With the bed in the high temperature regime at 640–900 °C, burnout was controlled by mass transfer of hydrocarbon vapour (deduced to have a mean composition of approximately (C₂H₄)₅) away from such a blob of sand and molten polymer. When the bed was between 485 and 640 °C (the medium temperature regime), radiative heat transfer to a blob of polymer controlled burnout. At 400–485 °C (the low temperature region) the burnout-time was controlled by the volatilisation (gasification) of a polymer pellet to produce a combustible hydrocarbon vapour. The activation energy for this gasification was ∼58 kJ/mol. This is the same as that characterising the ignition delay, which was also measured. The measured rates of burning indicate an enthalpy of gasification of ≈450 J/g. The total yield of CO and CO₂ was found to depend on the bed’s temperature and was low enough to indicate that soot, together with unburned hydrocarbons, can be important products from such a bed.     

Improving Interoperability by Incorporating UnitsML Into Markup Languages

Maintaining the integrity of analytical data over time is a challenge. Years ago, data were recorded on paper that was pasted directly into a laboratory notebook. The digital age has made maintaining the integrity of data harder. Nowadays, digitized analytical data are often separated from information about how the sample was collected and prepared for analysis and how the data were acquired. The data are stored on digital media, while the related information about the data may be written in a paper notebook or stored separately in other digital files. Sometimes the connection between this “scientific meta-data” and the analytical data is lost, rendering the spectrum or chromatogram useless. We have been working with ASTM Subcommittee E13.15 on Analytical Data to create the Analytical Information Markup Language or AnIML—a new way to interchange and store spectroscopy and chromatography data based on XML (Extensible Markup Language). XML is a language for describing what data are by enclosing them in computer-useable tags. Recording the units associated with the analytical data and metadata is an essential issue for any data representation scheme that must be addressed by all domain-specific markup languages. As scientific markup languages proliferate, it is very desirable to have a single scheme for handling units to facilitate moving information between different data domains.At NIST, we have been developing a general markup language just for units that we call UnitsML. This presentation will describe how UnitsML is used and how it is being incorporated into AnIML.     

Repair of composite structures on Formula 1 race cars

The chassis of a Formula 1 car is constructed for the most part from carbon fibre reinforced composite materials. Primary structures such as the monocoque/survival cell, suspension and gearboxes and the overwhelming majority of secondary (wings, bodywork, etc.) structures are routinely produced using such materials. During the operation of the vehicles it is fairly commonplace for composite components to sustain a degree of damage. The level of damage varies from being very minor (small holes and dents from stone strikes, etc.) to very serious structural damage to major components resulting from accidents. Although F1 Teams operate with large budgets, the funding available is finite and the logistics very tight such that there is a need, wherever possible, to repair and return to service damaged parts rather than scrap and replace them. This must of course be done in such a way that the safety and performance of the cars are in no way compromised. The repair of composite structures is far from a trivial exercise; the degree of damage must be assessed and a repair scheme “designed” and implemented in the shortest possible time. The degree of invasive “surgery” is kept to the minimum and all corrective work carried out must be fully documented and capable of future condition monitoring as part of the team’s total quality management (TQM) process. Additionally, repair techniques may be used to reverse progressive damage (analogous to metal fatigue) within composite structures thus preventing major failures and extending their service lives. Commonly used repair techniques and methodologies are discussed and illustrated with practical examples culminating with the repair of major structural damage to the monocoque.     

Dissolution and Interface Reactions between Palladium and Tin(Sn)-Based Solders: Part II. 63Sn-37Pb Alloy

The interface microstructures and dissolution behavior were studied, which occur between 99.9 pct Pd substrates and molten 95.5Sn-3.9Ag-0.6Cu (wt pct, Sn-Ag-Cu) solder. The solder bath temperatures were 513 K to 623 K (240 °C to 350 °C). The immersion times were 5 to 240 seconds. The IMC layer composition exhibited the (Pd, Cu)Sn₄ (Cu, 0 to 2 at. pct) and (Pd, Sn) solid-solution phases for all test conditions. The phases PdSn and PdSn₂ were observed only for the 623 K (350 °C), 60 seconds test conditions. The metastable phase, Pd₁₁Sn₉, occurred consistently for the 623 K (350 °C), 240 seconds conditions. Palladium-tin needles appeared in the Sn-Ag-Cu solder, but only at temperatures of 563 K (290 °C ) or higher, and had a (Pd, Cu)Sn₄ stoichiometry. Palladium dissolution increased monotonically with both solder bath temperature and exposure time. The rate kinetics of dissolution were represented by the expression At ⁿ exp(∆H/RT), where the time exponent (n) was 0.52 ± 0.10 and the apparent activation energy (∆H) was 44 ± 9 kJ/mol. The IMC layer thickness increased between 513 K and 563 K (240 °C and 290 °C) to approximately 3 to 5 μm, but then was less than 3 μm at 593 K and 623 K (320 °C and 350 °C). The thickness values exhibited no significant time dependence. As a protective finish in electronics assembly applications, Pd would be relatively slow to dissolve into molten Sn-Ag-Cu solder. The Pd-Sn IMC layer would remain sufficiently thin and adherent to a residual Pd layer so as to pose a minimal reliability concern for Sn-Ag-Cu solder interconnections.     

A scenario analysis of investment options for the Cuban power sector using the MARKAL model

The Cuban power sector faces a need for extensive investment in new generating capacity, under a large number of uncertainties regarding future conditions, including: rate of demand growth, fluctuations in fuel prices, access to imported fuel, and access to investment capital for construction of new power plants and development of fuel import infrastructure. To identify cost effective investment strategies under these uncertainties, a supply and power sector MARKAL model was assembled, following an extensive review of available data on the Cuban power system and resource potentials. Two scenarios were assessed, a business-as-usual (BAU) scenario assuming continued moderate electricity load growth and domestic fuel production growth, and a high growth (HI) scenario assuming rapid electricity demand growth, rapid increase in domestic fuel production, and a transition to market pricing of electricity. Within these two scenarios sets, sensitivity analyses were conducted on a number of variables. The implications of least-cost investment strategies for new capacity builds, investment spending requirements, electricity prices, fuel expenditures, and carbon dioxide emissions for each scenario were assessed. Natural gas was found to be the cost effective fuel for new generation across both scenarios and most sensitivity cases, suggesting that access to natural gas, through increased domestic production and LNG import, is a clear priority for further analysis in the Cuban context.     

Surface interfaces in low temperature water-gas shift: The metal oxide synergy,the assistance of co-adsorbed water,and alkali doping

With new developments in polymer electrolyte membrane fuel cells, interest is growing in fuel processor technology for converting feedstocks to hydrogen. One critical step in the process to convert CO and purify hydrogen is low temperature water-gas shift (LTS). Control of the LTS rate can be achieved by designing catalysts in a way that produces and rapidly decomposes the surface formate anion intermediate. In this account, examples are provided to demonstrate various interfacial phenomena important for achieving these goals. The interface between a metal and a partially reducible oxide promotes surface reduction of the oxide to the low temperature range, generating sites for the low temperature activation of H₂O on the oxide. Partial reduction of the oxide and surface activation of H₂O at low temperature provide a route for formate production at low temperature. Adjacent co-adsorbed water molecules participate in the transition state of formate decomposition, accelerating the formate turnover rate and altering the selectivity to favor dehydrogenation. The rate-limiting-step involves formate C–H bond scission, with the metal abstracting hydrogen at the interface between metal and oxide, serving as a conduit for hydrogen release. Catalysts may be improved by increasing formate mobility on the oxide; furthermore, the optimization of alkali doping levels can electronically promote formate C–H bond scission.