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Carbon nanotubes (CNTs) can improve the fracture toughness of ceramic composites. It is widely believed that defects in the CNTs will alter key properties that ultimately dictate composite toughening. However, to date there have been no studies that directly correlate these specific properties to controlled defect levels in CNTs. This type of investigation is presented here, using ceramic nanocomposites with a polymer derived ceramic (PDC) matrix, reinforced with multiwalled CNTs. This work includes basic fracture measurements on full composite films, combined with careful testing of individual CNTs embedded in the same PDC matrix. The defect levels in these CNTs were controlled with high energy carbon ions. By using this approach, it was possible to directly correlate defect levels with the interfacial shear strength (IFSS) of the CNT/PDC interface, the CNT fracture strengths, and the pull-out lengths observed after fracture of the full composites. The radiation induced defects led to substantial increases in the IFSS, and only a marginal decrease is observed in the measured fracture strength. Based on this, the shorter pull-out lengths that occurred with higher defect levels were primarily attributed to stronger bonding at the CNT/PDC interface. [ABSTRACT FROM AUTHOR]

Carbon nanotubes (CNTs) have been considered an ideal reinforcement for light-weight and high-strength ceramic matrix composites. Understanding the interfacial properties between CNTs and the matrix is crucial for engineering the desired properties in such composites. Here in-situ pull-out experiments with a polymer derived ceramic (PDC) matrix are carried out with both pristine CNTs and CNTs coated with Al 2 O 3 (CNT/Al 2 O 3 ) produced by Atomic Layer Deposition (ALD), using micro-fabricated devices in a scanning electron microscope. This carefully designed comparative study makes it possible to better understand the interfacial interactions between CNTs and PDC matrices. The interfacial shear strength (IFSS) of CNT-PDC is 9.99 ± 2.84 MPa, while the IFSS of (CNT/Al 2 O 3 )/PDC with ∼3 nm Al 2 O 3 coating thickness is 14.52 ± 2.66 MPa, demonstrating a 45.3% improvement. The non-linear failure observed with the coated CNTs is also indicative of energy dissipation mechanisms that promote toughening in ceramic matrix composites. The improved properties in (CNT/Al 2 O 3 )/PDC are believed to originate from increased surface roughness, which leads to mechanical interlocking at the interface during the pull-out process. The combination of special interlayer structures such as ALD Al 2 O 3 and strong CNTs opens up interesting opportunities for improving the mechanical properties of ceramic nanocomposites reinforced by CNTs. [ABSTRACT FROM AUTHOR]

Abstract: A chemical vapor infiltration (CVI) technique was used to overcome most of the challenges involved in fabricating exceptionally-tough CNT/SiC composites. Nanotube pullout and sequential breaking and slippage of the walls of the CNTs during failure were consistently observed for all fractured CNT/SiC samples. These energy absorbing mechanisms result in the fracture strength of the CNT/SiC composites about an order of magnitude higher than the bulk SiC. The CVI-fabricated CNT/SiC composites have an strongly-bonded tube/matrix interface and an amorphous, crack-free SiC matrix, enabling the composites to withstand oxidization at 700–1600°C in air. [Copyright &y& Elsevier]

Ideal hydrophobic-hydrophilic composite cavities are highly desired to enhance nucleate boiling. However, it is challenging and costly to fabricate these types of cavities by conventional micro/nano fabrication techniques. In this study, a type of hydrophobic-hydrophilic composite interfaces were synthesized from functionalized multiwall carbon nanotubes by introducing hydrophilic functional groups on the pristine multiwall carbon nanotubes. This type of carbon nanotube enabled hydrophobic-hydrophilic composite interfaces were systematically characterized. Ideal cavities created by the interfaces were experimentally demonstrated to be the primary reason to substantially enhance nucleate boiling. [ABSTRACT FROM AUTHOR]

Protonic ceramic electrochemical cells (PCECs) have the potential in reducing the energy input and carbon emissions in ethylene production from ethane dehydrogenation. The performance of conventional perovskite-based anode materials for ethane conversion in PCECs is limited by their low active surface area and proneness to coke deposition. In this work, for the first time, we demonstrate the use of aligned carbon nanotube forests (CNTFs) as a novel anode material for an ethane fueled PCEC to co-produce ethylene and electricity. The CNTF electrode was grown on the electrolyte by the chemical vapor deposition (CVD) method. Highly dispersed iron carbide nanoparticles are formed in situ on the CNTFs during the CVD process, acting as highly active catalysts for ethane dehydrogenation. The novel PCECs show superior catalytic and electrochemical performances to that using conventional perovskite-based anodes. The cell also exhibits excellent durability and anti-coking abilities within 100 h test. This work showcases the promising application of nanostructured carbon, a new class of non-perovskite materials, as the multifunctional electrode materials for PCECs. [Display omitted] • CNTF can be integrated into PCEC as electrode and catalyst support by CVD method. • CNTF is a promising non-perovskite candidate electrode material for PCEC. • CNTF shows superior electrochemical and catalytic performance than SFM. • Carburized Fe species on CNTF are the active species for EDH reaction. [ABSTRACT FROM AUTHOR]