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A facile and novel surface activation approach using a strong-base solution enables the synthesis of carbon nanomaterials (CNMs) directly from bulk copper substrates via chemical vapor deposition. Amorphous carbon nanofibers (CNFs) were grown at temperatures as low as 250 °C, whereas at 600 °C the nanofibers were observed to be turbostratic, and at 700 °C turbostratic CNFs were synthesized together with a new aerogel-like 3D porous turbostratic CNM. A mechanistic model for the observed growth of CNMs from surface activated bulk copper is proposed. Our process is shown to yield conformal CNF growth on various complex-shaped copper substrates, such as meshes and wires, as well as copper-coated materials including carbon fibers and polymer films. [Display omitted] • Synthesis of carbon nanomaterials directly from the surface of a metallic substrate. • Catalytically active surface of bulk copper via basic aqueous solution treatment. • Catalyst nanoparticle formation via oxidation/roughening plus reduction steps. • Amorphous or turbostratic carbon nanofibers growth tunable by synthesis temperature. • Novel 3D "aerogel-like" turbostratic carbon by CVD, with sub-micron porosity. [ABSTRACT FROM AUTHOR]

Forsterite is a magnesium silicon oxide mineral with an olivine structure and a diverse spectrum of applications, ranging from biomedical to optical devices. Controlled purity and crystalline phases are key requirements for such applications, but the literature shows a limited understanding of the synthetic routes that would enable such control, in particular at the nanoscale. In this work, single-phase forsterite nanopowder with a crystallite size of 15.3 nm was synthesized by reverse strike co-precipitation. A reaction mechanism for the synthesis was proposed based on DSC/TGA analysis and intermediate products. Forsterite pellets using the nanopowder were produced by low-cost cold-pressing and showed high transparency and densities above 93%. The nanosized crystals allowed for lower sintering temperatures and enhanced hardness. [ABSTRACT FROM AUTHOR]

Polymer-derived pyrolytic carbons (PyCs) are often desirable for low density high-temperature structural applications when they can be reinforced with high stiffness and strength fibers to address brittleness. Nanofibers, such as aligned carbon nanotubes (A-CNTs), can be an ideal reinforcement owing to their high mass-specific properties, and while modeling suggests that properties of A-CNTs at high volume fractions (i.e., 10–30 vol%) could yield significant enhancements, it is unknown how CNT confinement influences processing, as such materials have never been synthesized. Here, we report process development demonstrating the first successful fabrication of fully infused, void-free A-CNT carbon matrix nanocomposites (A/C-NCs) via polymer infiltration pyrolysis (PIP) that establishes a platform to study nanofiber-reinforced polymer-derived ceramics. The size of the average A/C-NC graphitic crystallites increases as CNT vol% increases up to 30 vol%, and the inter-layer separation of the PyC graphitic crystallites decreases, evidencing a nanoscale confinement effect observed in concert with increased mechanical performance. Vickers microhardness testing in the axial CNT direction of A/C-NCs shows agreement with prior data for low vol% CNTs in PyC and mechanical modeling, where specific hardness increases from ∼ 3.3 GPa/(g/cm3) for PyC to ∼ 6.7 GPa/(g/cm3) for 30 vol% A/C-NCs, demonstrating A/C-NCs as an advantaged superhard lightweight material. [Display omitted] • Fabrication of pyrolytic carbon composites with 1-30 vol% aligned carbon nanotubes. • Vacuum- and capillary-assisted infiltration of phenolic resin enable full infusion. • Four polymer infiltration pyrolysis cycles decrease porosity and increases density. • Graphitic crystallites in matrix are longer and denser with nanotube reinforcement. • Specific microhardness increases up to 30 vol% carbon nanotubes, rivaling diamond. [ABSTRACT FROM AUTHOR]

Abstract Although many routes for the production of magnesium borates (Mg 2 B 2 O 5 , Mg 3 B 2 O 6 and MgB 4 O 7) are well known, the synthesis of single phases is still a challenge. Secondary phases such as other magnesium borates and MgO are commonly observed in the final product. In order to produce high quality Mg 2 B 2 O 5 nanorods, we developed a study analyzing the influence of different reaction atmospheres on the synthesis of magnesium borate in a tubular furnace. Through this investigation, a strong correlation between the produced borate phases and the composition of the atmospheres was verified. The sample produced under Ar presented Mg 2 B 2 O 5 , Mg 3 B 2 O 6 and MgO in molar percentages of 36.82%, 35.34% and 27.84% respectively, while the sample synthesized under H 2 is composed of 18.9 mol% of Mg 3 B 2 O 6 and 81.1 mol% of MgO. Mg 2 B 2 O 5 nanorods with elevated structural homogeneity were successfully produced under hydrogen and acetonitrile. Under this atmosphere only Mg 2 B 2 O 5 and Mg 3 B 2 O 6 were produced, with the formation of Mg 2 B 2 O 5 nanorods representing 87.5 mol% of the sample. The nanorods growth followed a solution-solid-solid (SSS) self-catalyzed mechanism. This synthesis was performed without the assistance of external agents such as catalysts or surfactants, guaranteeing elevated chemical purity for applications in the optical and electronic field. Reflectance and impedance analyses presented a wide range of light absorption and a dielectric character for the nanorods. The produced structure would be very interesting for theranostic applications. [ABSTRACT FROM AUTHOR]

Efficiency of solar devices is affected by several factors such as, devices surface reflection and the energy emitted in the ultraviolet and infrared regions, which are not harnessed by the cell, are among the main causes. To reduce these losses, we propose the use of rare-earth doped anti-reflection coatings. Erbium doped forsterite (Mg 2 SiO 4 :Er 3+ ) thin films were synthesized in order to bind the anti-reflective property of forsterite films with the upconversion property of erbium ion. For the first time in literature, Mg 2 SiO 4 :Er 3+ optical activity in the visible range with excitation at 1470 nm is presented. Single and double layers anti-reflective coating models, with forsterite as coating material, were simulated. The single layer model was compared to experimental data presenting elevated accordance. The coating application on silicon wafer leaded to a light absorption enhancement over 80% in the visible spectrum. The dopant influence on the films optical behavior was also studied indicating that despite the presence of erbium, the fosterite films preserved their anti-reflectivity. Moreover, the coatings were analyzed through chemical and mechanical resistance tests, indicating elevated scratch resistance (over 500 mN) and chemical stability at high humidity and corrosive environments. Mg 2 SiO 4 :Er 3+ films revealed to be a promising anti-reflection coating for increasing commercial silicon-based solar cells efficiency. [ABSTRACT FROM AUTHOR]