Fabrication and thermal conductivity of copper matrix composites reinforced with Mo2C or TiC coated graphite fibers

Graphite fiber reinforced Cu-based composites have good thermal conductivity, low coefficient of thermal expansion for heat sink applications. In these composites, the quality of interfacial bonding between the copper matrix and the graphite fibers has significant influence on the thermal properties of composites. In this study, two different carbide coatings (Mo₂C or TiC) were synthesized on graphite fiber to promote the interfacial bonding in composites. Fibers/Cu composites had been produced by spark plasma sintering process. The results showed that the densification, interfacial bonding and thermal conductivity of coated composites were improved distinctly compared to that of uncoated ones. The enhanced composites present 16–44% increase of thermal conductivity in X–Y plane. An original theoretical model was proposed to estimate the interface thermal resistance. The result showed that the interfacial thermal resistance was largely reduced by one order of magnitude with the introduction of carbide interlayer.     

Hydrogen content variation for enhancing the lubricated tribological performance of DLC coatings with ester

There are many types of DLC (diamond-like carbon) coatings, which mainly differ from each other according to their hydrogen content, sp² and sp³-bonded carbon atoms and alloying elements (such as Ti, Cr, W or Zr). The lubricated tribological performance of these coatings depends on the lubricant. Controversially, the same lubricant delivers different tribological performances with differently produced DLC coatings. It has been observed that the presence of hydrogen has a remarkable effect on the tribological performance of DLC coatings in inert and vacuum environments. In this paper, the hydrogen content of two different types of DLC coatings, a-C:H:Me (metal containing hydrogenated amorphous carbon) and a-C:H, was varied, in order to obtain an optimized tribological behavior with a synthetic ester (TMP ester). The tribological performance of the coatings with TMP ester is examined in a pin-on-disk tribometer. It could be shown that increasing the hydrogen content in a DLC coating improves their tribological performance with TMP ester. Besides, a-C:H type of coatings is found to be more suitable for TMP ester regarding low friction coefficients.     

Radiation-induced branching and crosslinking of poly(tetrafluoroethylene) (PTFE)

The effect of electron beams on poly(tetrafluoroethylene) (PTFE) at elevated temperatures above the melting point on oxygen-free conditions has been studied using differential scanning calorimetry (DSC), wide-angle X-ray scattering (WAXS), Fourier-transform infrared (FTIR) spectroscopy, thermo-gravimetric analysis (TGA) and tensile test. The investigations have shown that the chemical structure and several properties of PTFE are greatly altered by the irradiation. DSC and WAXS indicate that the crystallinity of the PTFE irradiated with high doses is reduced. CF₃ side groups and branched structures are assumed to hinder the crystallization. TGA has shown that the thermal stability of the radiation-modified PTFE is considerably lower than that of unirradiated PTFE.     

Capillary-based droplet cells: limits and new aspects

The Scanning Droplet Cell can be used on wetting and non-wetting samples. It uses the common three-electrode configuration together with all the potentiostatic or galvanostatic techniques like impedance spectroscopy and cyclic voltammetry. The resolution is extended to <10 μm and complete computer control of surface scans (and, therefore, electrochemical surface imaging) becomes possible by the addition of a mechanical force sensor.     

Relationship between impact energy and compression toughness energy of high-strength fiber-reinforced concrete

A simple, economical, and practical drop-weight impact testing machine was developed to determine the impact resistance for high-strength fiber-reinforced concrete (HSFRC) composite. Impact and compression tests were carried out on concrete cylinders reinforced with three different aspect ratios of hooked-end steel fibers l/d (length/diameter): 60, 75, and 83 (30/0.50, 60/0.80, and 50/0.60 mm/mm), and four different percentages of steel fibers 0.5%, 1.0%, 1.5% and 2.0% by volume of concrete. For each aspect ratio and volume of fibers, complete stress–strain curves of HSFRC were generated in order to determine the total energy absorbed for each cylindrical specimen in compression. The addition of steel fibres to concrete has improved impact resistance and also the compression toughness. The test results showed that a logarithmic relation exists between compression toughness energy (E_Ct) by means of the generated stress–stress curves from the compressive tests and the impact energy (E_I) by means of the modified impact machine for HSFRC at different l/d ratio of 60, 75, and 83.     

Multilayer architecture design to enhance load-bearing capacity and tribological behavior of CrAlN coatings in seawater

Steel materials employed in severe conditions including strong corrosion, high load and multi-factor coupling damages can easily cause incredible degradation until failure, and the protective CrN-based coatings should be one of promising candidates to relieve those damages for the steel equipment or components. In present paper, the monolayer CrAlN and multilayer Cr/CrAlN coatings were successfully deposited on steel substrates by multi-arc ion technology, and their microstructure, mechanical, tribological and corrosion performances were systematically investigated. The results show that the special multilayer Cr/CrAlN coating could possess much better load-bearing capacity and wear resistance than that of monolayer CrAlN coating, which was due to the facts that the multilayer architecture can effectively release the internal stress and inhibit the expansion of defects. Particularly, the multilayer interfaces could effectively prevent the aggressive medium in seawater infiltrating into the inside of coating, and thus the multilayer Cr/CrAlN coating could have higher corrosion resistance compared to monolayer CrAlN coating. As a result, this multilayer Cr/CrAlN coating could achieve excellent combined performances, indicating that it has greatly potential application as protective coating in seawater.     

Soft and Self-Adhesive Thermal Interface Materials Based on Vertically Aligned,Covalently Bonded Graphene Nanowalls for Efficient Microelectronic Cooling

Urged by the increasing power and packing densities of integrated circuits and electronic devices, efficient dissipation of excess heat from hot spot to heat sink through thermal interface materials (TIMs) is a growing demand to maintain system reliability and performance. In recent years, graphene-based TIMs received considerable interest due to the ultrahigh intrinsic thermal conductivity of graphene. However, the cooling efficiency of such TIMs is still limited by some technical difficulties, such as production-induced defects of graphene, poor alignment of graphene in the matrix, and strong phonon scattering at graphene/graphene or graphene/matrix interfaces. In this study, a 120  µ m-thick freestanding film composed of vertically aligned, covalently bonded graphene nanowalls (GNWs) is grown by mesoplasma chemical vapor deposition. After filling GNWs with silicone, the fabricated adhesive TIMs exhibit a high through-plane thermal conductivity of 20.4 W m⁻¹ K⁻¹ at a low graphene loading of 5.6 wt%. In the TIM performance test, the cooling efficiency of GNW-based TIMs is ≈ 1.5 times higher than that of state-of-the-art commercial TIMs. The TIMs achieve the desired balance between high through-plane thermal conductivity and small bond line thickness, providing superior cooling performance for suppressing the degradation of luminous properties of high-power light-emitting diode chips.     

Heterogeneous Fluorescent Organohydrogel Enables Dynamic Anti-Counterfeiting

Fluorescent patterns showing the unique color change in response to external stimuli are of considerable interest for their applications in anti-counterfeiting. However, there is still a lack of intelligent fluorescent patterns with high-security levels, presenting a dynamic display of encrypted information. In this study, a fluorescent organohydrogel is fabricated through a two-step interpenetrating technique, leading to the co-existence of naphthalimide moieties (DEAN, green-yellow fluorescent monomer) contained Poly(N,N-dimethylacrylamide) (PDMA) hydrogel network and Polyoctadecyl methacrylate (PSMA) organogel network bearing spiropyran moieties (SPMA, photochromic monomer). Due to the unique heterogeneous networks, the fluorescence color goes through a continuous change from green to yellow to red via the fluorescence resonance energy transfer (FRET) process with the extension of irradiation time. In addition, when H⁺ is introduced into the system, SP units exhibit transformation into the protonated merocyanine (MCH⁺) rather than merocyanine (MC) under UV light, which inhibits the FRET process. By selectively being treated with H⁺, the fluorescent organohydrogel can act as an effective platform for encrypting secret information, making them more difficult to forge.