Understanding the negative thermal expansion in planar graphite–metal composites

The addition of graphitic fibers and flakes as fillers is commonly used to control the thermal expansion of metals. Sintered metal matrix composites with a planar distribution of graphite flakes show a low or negative thermal expansion coefficient perpendicular to the orientation plane of the graphite (z-CTE). Since the metal matrix has a positive isotropic expansion and graphite has a high z-CTE, this effect cannot be explained by a simple model of stapled metal–graphite layers. Instead, a mechanical interaction between graphite and matrix must be considered. With neutron scattering measurements, we show that there is little or no strain of the graphite flakes caused by the matrix, which can be explained by the high modulus of graphite. Instead, we suggest that a macroscopic crumpling of the flakes is responsible for the low z-CTE of the composite. The crumpled flakes are thicker at low temperature and get stretched and flattened by the expanding matrix at high temperature, explaining the reduction in the thermal expansion across the orientation plane

Surface integrity study for FC300 cast iron using TiAIN ball end mill

Finishing of FC300 gray cast iron predominantly done by manual polishing. Study the surface integrity of FC300 after machining is crucial to investigate the surface characteristics before polishing. This work aims to investigate the surface profiles and subsurface alterations induced by milling of FC300 gray cast iron using TiAlN Ball end mill. Machining trials were performed using CNC variaxis machine in dry condition at the cutting speeds of 66-99 m/min, feed rates of 0.27-0.42 mm/tooth and constant depth of cut of 0.1 mm. The results shows that the surface roughness decreased as the cutting speed increased from 66 m/min to 88 m/min. Smooth and shiny surface profiles appeared at the lower cutting speed of 66 m/min due to effect of lubrication layer that formed from the small fragmented graphite flakes. When the cutting speed increased to 99 m/min, surface profiles appeared with smeared and large graphite flakes probably due to higher rotational impact from the cutting tool. Analysis of subsurface microstructure observed bending effects at the region where worn cutting tool applied. Severe crack nucleation’s were evidence to reflect severe rubbing action from worn cutting tool

Preliminary science report on the directional solidification of hypereutectic cast iron during KC-135 low-G maneuvers

An ADSS-P directional solidification furnace was reconfigured for operation on the KC-135 low-g aircraft. The system offers many advantages over quench ingot methods for study of the effects of sedimentation and convection on alloy formation. The directional sodification furnace system was first flown during the September 1982 series of flights. The microstructure of the hypereutectic cast iron sample solidified on one of these flights suggests a low-g effect on graphite morphology. Further experiments are needed to ascertain that this effect is due to low-gravity and to deduce which of the possible mechanisms is responsible for it

Adsorption of Bovine Serum Albumin on Carbon-Based Materials

The protein adsorption plays a very important role in biotechnology, biomolecular engineering and it is one of the main factors determining bio- and hemocompatibility of biomedical materials in medical applications, such as blood purification and wound healing. Here we report adsorption properties of two carbon-based materials, thermally expanded graphite (EGr) and graphene nanoplatelets (GnP), for bovine serum albumin (BSA), the most abundant blood plasma protein. The influence of the surface chemistry of expanded graphite on the mechanism of BSA adsorption was studied by using EGr modified with oxygen or nitrogen functionalities. Having low microporosity and the specific surface area in the range of 5 to 50 m2/g, the expanded graphite exhibits high protein adsorption capacity at high equilibrium concentrations, which makes this material a potential candidate for biomedical applications as a carrier for high molecular weight (HMW) drug delivery or adsorption of HMW metabolites. At low equilibrium concentrations, the effect of specific protein-surface functional groups interaction reveals the differences between the adsorption affinity of different surface modified EGr materials to BSA. The adsorption of BSA on GnP with a specific surface area of 286 m2/g and a developed micro-/mesoporous structure did not follow the same mechanism as seen with EGr materials. At low equilibrium concentration of BSA, GnP exhibits high adsorption efficiency. An important finding is that no release of nanoparticles from expanded graphite adsorbents was observed, which makes them potentially suitable for direct contact with blood and other tissues while very small nanoparticles were noticed in the case of graphene nanoplatelets

Formulation of a Graphene Based Ink for Inkjet Printing Wearable Electronics

The field of printable electronics and sensors has been experiencing increased interest and growth to meet the demands of low-cost, flexible, and lightweight devices. From this subset of devices, graphene-based printable electronics and sensors are of specific interest due to their transparency, flexibility, biocompatibility, and high conductivity. Among all modern ink printing technology, screen printing, spray coating, 3D printing, and inkjet printing are often utilized to fabricate flexible electronic applications from conductive ink. Compared with the other three, inkjet printing has received the most attention due to the simple printing process, high repeatability, economy, and time-savings compared to other printing techniques. However, inkjet printing often suffers from nozzle clogging due to aggregation of the particles in the conductive inks. In this research, a conductive graphene-based ink is developed to be used in a regular inkjet printer. A formulation process based on bath sonication and solvent exchange allows a graphene rich ink to be created with advantageous fluid properties that allow it to be printed easily.Small flake size of the graphene will allow us to avoid the issue of clogging the nozzle with flake aggregation and eventually aflexible hydration sensor will beprinted out with this graphene-based conductive ink

On the mechanisms of precipitation of graphene on nickel thin films

Growth on transition metal substrates is becoming a method of choice to prepare large-area graphene foils. In the case of nickel, where carbon has a significant solubility, such a growth process includes at least two elementary steps: (1) carbon dissolution into the metal, and (2) graphene precipitation at the surface. Here, we dissolve calibrated amounts of carbon in nickel films, using carbon ion implantation, and annealing at 725 \circ or 900 \circ. We then use transmission electron microscopy to analyse the precipitation process in detail: the latter appears to imply carbon diffusion over large distances and at least two distinct microscopic mechanisms

Wear model for reciprocating ball-on-flat wear tests

During the design phase of components is very difficult to obtain a reliable extrapolation for the outcome of a wear process and its implications. Regarding this situation, a wear model suitable for sliding wear was designed, allowing to estimate the volume loss on the both sliding surfaces. The current model was created specifically to ball on flat contact applications. A Hertzian normal contact pressure and a friction stress field are used to determine the resulting contact stresses leading to local analysis of the wear process. The quantification and matching wear amount can be established using a model based on the energy dissipated by friction or alternatively a model based on the normal pressure. An experimental validation study was produced for a pair of materials commonly used in mechanical applications, regarding a steel sphere (AISI 52100) against a grey cast iron flat specimen (GJL 200) for a normal load of 10N, 1 Hz frequency and a duration range between 5000 and 10000 cycles. Initial results present a very good correlation between experimental data and predicted values from the wear model, in spite of a high dependency on experimental wear rate values used in the model. The resulting wear is compared considering both the local wear depth and the wear volume of experimental tests with the forecasted values. The referred dependency of wear rates was expected since the process is dependent on the energy dissipated by friction. The scar morphology should be improved with a more continuous contact geometry iteration.This research was co-sponsored by Portuguese Foundation to Science and Technology and Huf - Portuguesa, Grant SFRH / BDE / 52102 / 2013 which is cofunded by the program COMPETE from QREN with co-participation from the European Community and by FEDER funds through the program COMPETE – Programa Operacional Factores de Competitividade, under the project CENTRO -07- 0224 -FEDER -002001 (MT4MOBI)

Simple room-temperature preparation of high-yield large-area graphene oxide

Graphene has attracted much attention from researchers due to its interesting mechanical, electrochemical, and electronic properties. It has many potential applications such as polymer filler, sensor, energy conversion, and energy storage devices. Graphene-based nanocomposites are under an intense spotlight amongst researchers. A large amount of graphene is required for preparation of such samples. Lately, graphene-based materials have been the target for fundamental life science investigations. Despite graphene being a much sought-after raw material, the drawbacks in the preparation of graphene are that it is a challenge amongst researchers to produce this material in a scalable quantity and that there is a concern about its safety. Thus, a simple and efficient method for the preparation of graphene oxide (GO) is greatly desired to address these problems. In this work, one-pot chemical oxidation of graphite was carried out at room temperature for the preparation of large-area GO with ~100% conversion. This high-conversion preparation of large-area GO was achieved using a simplified Hummer’s method from large graphite flakes (an average flake size of 500 μm). It was found that a high degree of oxidation of graphite could be realized by stirring graphite in a mixture of acids and potassium permanganate, resulting in GO with large lateral dimension and area, which could reach up to 120 μm and ~8000 μm2, respectively. The simplified Hummer’s method provides a facile approach for the preparation of large-area GO

Al/Gf composite foams with SiC-engineered interfaces for the next generation of active heat dissipation materials

Interfacial engineering has been investigated as a method of increasing thermal conductivity in a variety of aluminium/graphite composites but remains unexplored in the few graphite-containing aluminium foams developed to date. In this study, the replication method was used to fabricate aluminium/graphite composite foams by infiltrating with liquid aluminium packed preforms containing SiC-coated oriented graphite flakes and NaCl particles, the latter acting as a templating agent. The effects of interfacial modification caused by the SiC presence were investigated alongside those of NaCl and graphite flake particle sizes. Materials benefit from low pressure drops when large NaCl particles are used. Furthermore, large graphite flakes coated with SiC provide thermal conductivities up to 232 Wm-1K-1, improved mechanical properties and power dissipation capacities up to 2-fold and 6-fold higher than aluminium/graphite composite foams with unmodified interfaces and standard aluminium foams, respectively, making them ideal candidates for active heat sinks in next-generation electronic devices.This work was made possible by funding from the Spanish Agencia Estatal de Investigación (AEI), the Spanish Ministry of Science and Innovation, and the European Union under grant PDC2021-121617-C21 for the development of foams with novel phases that can be integrated into new systems for upcoming filtration applications. The authors would also like to acknowledge the financial support received for the same purpose from the Conselleria d'Innovació, Universitats, Ciència, i Societat Digital of the Generalitat Valenciana through grant GVA-COVID19/2021/097. L.P. Maiorano also acknowledges the financial support from the University of Alicante through grant UAFPU2019-33 “Programa Propio para el fomento de la I+D+i del Vicerrectorado de Investigación y Transferencia de Conocimiento”