Printing and characterization of 3D high-loaded nanocomposites structures

Additive Manufacturing (AM) technologies are spreading rapidly both in academic research and industrial environments [1]. Nanomaterials have proven to provide new size-dependent properties compared to traditional bulk materials [2]. The integration of nanotechnology into AM opens new and interesting challenges in manufacturing advanced nanocomposite materials with custom-made properties and geometries [3]. Synergy between nanomaterials, such as metal and oxide nanoparticles, and AM can in fact result in improved functional and structural performance of manufactured devices, filling the gap between design and production of a specific tool. For instance, silica nanoparticles (SiO2 NPs) are increasingly used as nanofillers, thanks to their excellent mechanical properties, to fabricate nanocomposites used in a wide range of applications [4]. Stereolithography (SLA) represents one of the most widespread AM technologies used to fabricate 3D engineered structures. The general procedure for building objects with SLA involves photo-polymerization of liquid monomer into solid resin by means of an ultraviolet (UV) laser, which creates targeted cross-linked regions where the light irradiates the matrix [5]. SLA AM of nanocomposites usually involves mixing of ex situ synthesized nanoparticles with commercially available acrylic monomers, followed by an optimized printing process. Stable dispersion of colloidal SiO2 NPs in acrylate monomers or oligomers are commercially available, such as Nanocryl product family commercialized by Evonik. These products are traditionally used in adhesive and electronic applications, such as highly scratchresistant coatings for fiber optic cables, conformal coatings, UV curing adhesives for printed circuit boards and can be successfully employed in AM of high-loaded nanocomposites. The produced 3Dprinted specimens were employed to characterize the nanocomposites microstructure and thermomechanical properties respectively by means of scanning electron microscopy (SEM) and dynamicmechanical analyses (DMA)

High concentration Yb-Er co-doped multi-component phosphate glasses for compact eye-safe optical amplifiers

In recent years, the increasing need of airborne LIght Detection And Ranging (LIDAR) systems for environmental monitoring and surveillance has noticeably boosted the development of compact eye-safe optical amplifiers. In this scenario, multi-component phosphate glasses can be regarded as ideal candidate materials as they can be doped with a large amount of rare-earth (RE) ions without clustering, thus enabling the realization of few-cm long optical amplifier sections featured by high optical gain per unit length. In this work we will report the ongoing activities and the recent results obtained by our research group on the design, processing and characterization of a series of Yb-Er co-doped phosphate glasses to be used as active materials for the core of a waveguide amplifier. The physical, thermo-mechanical, optical and spectroscopic properties of the prepared glasses have been thoroughly investigated

Energy level decay processes in Ho3+-doped tellurite glass relevant to the 3-µm transition

The primary excited state decay processes relating to the 5I6 --> 5I7 at 2.9 um laser transition in singly Ho3+-doped tellurite (TZBG) glass have been investigated in detail using time-resolved fluorescence spectroscopy. Selective laser excitation of the 5I6 energy level at 1151 nm and 5I7 energy level at 1958 nm has established that the rate of energy transfer up-conversion between holmium ions excited to the 5I7 level is negligible for Ho3+ concentrations up to 4 mol. %. Excited state absorption was not observed from either the 5I7 or 5I6 levels and the luminescence from the 5I7 and 5I6 energy levels was measured to peak at 2050 nm and 2930 nm, respectively. The 5I6 level has a low luminescence efficiency of 8.9% due to strong nonradiative multiphonon relaxation. In contrast, decay from the 5I7 level is essentially fully radiative. A linear decrease in the decay time of the 5I6 level with Ho3+ concentration augmentation results from energy transfer to OH ions in the glass (with NOH=8.2x10^17 ions cm^-3) and reduces the luminescence efficiency of the 5I6 level to 8% for [Ho3+]=4 mol. %. Numerical simulation of a fiber laser incorporating 4 mol. % Ho3þ showed that a population inversion of 7.8% is reached for square pulses of 100 us duration and a repetition frequency of 20 Hz at a moderate pump intensity of 418 kW cm^-2 if energy transfer to OH- radicals is neglected

TeO2-ZnO-La2O3 glass composition for mid infrared wavelengths generation and transmission in optical fibers

Numerous applications in the Mid InfraRed (Mid IR) wavelength region still require basic optical components such as sources and optical fibers as transmission medium. Thanks to its mid IR transparency and nonlinearity, tellurite glass allows for developing both these types of components. However, practical applications require materials able to handle high optical intensity through enhanced material damage threshold. We report on the synthesis of a tellurite glass in the TeO2-ZnO-La2O3 (TZL) system which presents enhanced thermo mechanical properties with respect to typical tellurite glass compositions. We measured for the TZL composition a glass transition of 626 K, hence 70 K higher than the glass transition temperature of “standard” TZN compositions. The coefficient of thermal expansion was measured to be 138.10-6/K as compared to typical value of 180.10-6/K for TZN glass. We manufactured two types of fibers to assess the prospect for achieving high average power SC sources and Mid IR transmission in TZL glass fibers. First, a high Numerical Aperture (NA) aperture fiber was developed through standard rod in tube technique, where the cladding glass tube was manufactured by extrusion. The 50 μm core fiber presents an optical attenuation value of 0.26 dB/m at 1.55 μm. As an intermediate step towards the fabrication of an antiresonant hollow core fiber for high power transmission, we manufactured a preform and drew it into a cane. A TZL glass tube, 120 mm long and 9 mm/12 mm of inner/outer diameters (ID/OD) was manufactured via rotational casting technique. This latter tube was drawn into a tube of 2 mm in diameter which was cut into sections 130 mm long. Seven of those were stacked in another tellurite glass tube 6.5 mm/12 mm of ID/OD diameters, respectively. This preform was then drawn into a microstructured cane 1.6 mm in diameter which features tubular structures periodically arranged and of uniform thickness

Novel PBAT‐Based Biocomposites Reinforced with Bioresorbable Phosphate Glass Microparticles

Biocomposites based on poly(butylene adipate terephthalate) (PBAT) and reinforced with micro-particles of inorganic biodegradable phosphate glass (PG) at 2, 10, and 40 wt% are prepared and characterized from a mechanical and morphological point of view. Scanning electron microscope (SEM) images show a good dispersion of the PG micro-grains, even at high concentrations, in the PBAT matrix, resulting in homogeneous composites. Tensile and dynamic-mechanical tests, respectively, indicate that Young’s and storage moduli increase with PG concentration. The reinforcement of PBAT aims at modifying and tailoring the mechanical and viscoelastic properties of the material to expand its application field especially in the food and agricultural packaging sector, thanks to the similarity of PBAT performance with polyethylene

Fracture behavior of concretes containing MSWI vitrified bottom ash

The incorporation of waste materials into concrete allows responding to some of the most significant issues of our society: waste management and climate change. Experimental studies carried out in last decades have shown that municipal solid waste incineration (MSWI) ash, and particularly bottom ash, which constitutes the major solid by-product of incineration process, can be adopted to produce building materials. However, several issues are related to the safety and the environmental impact of MSWI ash utilization for concrete production, mainly linked with the leaching of heavy metals and toxic organic components. To solve these problems, several treatments for MSWI ash can be adopted and, among them, in this work the attention was focused on vitrification technology, which enables to convert the ash in a glassy inert solid material. The aim of the present paper is to study the feasibility of developing a “green concrete” that incorporates vitrified MSWI bottom ash as partial cement replacement, so reducing the cement content and consequently the carbon dioxide emissions as well as the raw materials consumption related to its production. The vitrified MSWI bottom ash, ground at micrometer size, was inserted into the admixtures by considering two percentages of cement substitution (10% and 20% by weight of cement). The flexural behavior of concrete containing vitrified MSWI ash was investigated through three-point bending tests under crack mouth opening displacement control. The crack path evolution was further explored by adopting the Digital Image Correlation technique. By analyzing the obtained results, it can be concluded that the use into concrete of vitrified MSWI bottom ash as cement replacement up to a percentage of 20% by weight of cement, allows reaching comparable flexural resistances with respect to the reference concrete. So, the proposed approach can represent a viable solution for the development of environmental-friendly concretes able to reduce the environmental impact of the concrete industry, which is mostly related to cement production, as known

Design and Manufacturing of a Nd-Doped Phosphate Glass-Based Jewel

This paper reports the results of the designing, manufacturing and characterization of a jewel obtained by means of coupling the dogmas of industrial design to the analytical engineering approach. The key role in the design of the jewel was played by an in-house synthesized Neodymium (Nd)-doped phosphate glass, selected due to its easy handling and capability to change color according to the incident light wavelength. The glass core was covered by a metal alloy to mitigate its relatively high fragility and sensitivity to thermal shock and, at the same time, to highlight and preserve its beauty. The selection of the proper metal alloy, having thermo-mechanical properties compatible with those exhibited by the glass, was carried out by means of Ashby’s maps, a powerful tool commonly adopted in the field of industrial design

Multifunctional bioresorbable phosphate glass optical fibers for theranostics

We report on the design and development of microstructured phosphate glass optical fibers for minimally invasive diagnosis and therapy. We discuss preliminary results of fiber drawing and characterization

Toward the fabrication of directly extruded microstructured bioresorbable phosphate glass optical fibre preforms

The steps toward the fabrication of directly-extruded microstructured fibre preforms made of a bioresorbable phosphate glass are herein presented. Microstructured fibres show a wide range of applications, i.e. photonic crystal fibres, large mode area fibres, hollow gas/liquid sensors, etc. Nevertheless, the fabrication of bioresorbable microstructured fibres has not been feasible so far due to a lack of bioresorbable transparent glass and more flexible fibre preform fabrication techniques. A custom developed calcium-phosphate glass has been designed and carefully prepared in our laboratory to be dissolvable in a biological fluid while being optically transparent and suitable for both preform extrusion and fibre drawing. This glass has been characterised both in terms of mechanical and optical properties as well as for dissolution in aqueous medium. Furthermore, the proposed glass is thermally stable, i.e. can be processed both in the extruder and in the drawing tower. Several extrusion experiments have been carried out with different glass preforms’ shapes. Analyses of these preforms by means of Optical Profilometry and Atomic Force Microscopy have been carried out to assess the roughness of the surface of the extrudate. To support the production of an optimized die for the preform extrusion, a simplified laminar flow model simulation has been employed. This model is intended as a tool for a fast and reliable way to catch the complex behaviour of glass flow during each extrusion and can be regarded as an effective design guide for the dies to fulfil specific needs for preform fabrication. After die optimisation, extrusion of a capillary was realised, and a stacking of extruded tubes was drawn to produce a microstructured optical fibre made of bioresorbable phosphate glass. The combination of bioresorbability and fibre microstructure, show a promising pathway toward a new generation of implantable biomedical devices