Franco Padella

Mechanical alloying of the Ti-Al system

Ti-AI alloys have been prepared by mechanical alloying (MA) of pure titanium and aluminium powders for four compositions: Ti80AI20, Ti75AI25, Ti50AI50, and Ti40AI60. The 50 < Ti(at%) < 80 compositions could be fully amorphized with a milling time strongly dependent on the starting chemical composition. For the Ti40AI60 composition only partial amorphization was observed. The investigation on the early stage of MA shows that the different systems amorphized through two different paths. On the titanium rich side (Ti=75,80 at%) the MA first leads to the formation of an h.c.p. αTi(AI) solid solution with an aluminium content of 14–16% which subsequently collapses into the amorphous state. For the aluminium rich side (Al=50,60 at%), MA sooner promotes the nucleations of disordered forms of Ti3AI and TiAl intermetallic compounds respectively. The inhibition of the ordering transition of the observed intermetallic phases is ascribed to the low temperature at which the SSR takes place. The complete (Ti50AI50) or partial (Ti40AI60) amorphization of the powder is then attained through a destabilization of the disordered Ti3AI and TiAl phases. The present results confirm the existence of a metastable f.c.c. phase as final alloying stage for the Ti75AI25 and Ti40AI60 compositions.

Synthesis of amorphous and metastable Ti40Al60 alloys by mechanical alloying of elemental powders

Ti40Al60 amorphous and metastable alloys have been prepared by mechanical alloying (MA), under controlled milling conditions in a planetary mill. Three different quantities of kinetic energy at the collision instant have been achieved by using balls of different size, φb = 5, 8 and 12 mm, keeping constant all other device parameters. Assuming the collision between the balls and the vial walls to be inelastic, during the early stage of alloying, the amount of energy transferred to the trapped powder could be estimated. The experimental results show that the milling with balls of diameter φb = 5 or 8 mm leads to a solid-state amorphization of the Ti40Al60 mixture, through the attainment of a supersaturated solid solution of aluminium into α-titanium. Otherwise, the milling causes the nucleation of the A1-fcc disordered form of the TiAl intermetallic compound. The end products of MA-induced solid-state reaction (SSR) have been ascribed to the different temperature reached by the powder during each collision and to the reaction time scale for the formation of the amorphous phase, δta, and for the nucleation of the non-equilibrium intermetallic compound, δtd. Differential scanning calorimetry has indicated that the crystallization of amorphous samples follows a two-step reaction. At a temperature Tc≈400 °C, the amorphous phase crystallizes into the A1 -fcc. TiAl phase having a measured heat of crystallization of 6.2 kJ(g at)−1. Upon further heating, the system undergoes A1 → L1o reordering transition with an enthalpy release of about 3.2 kJ (g at)−1.

Biodistribution and acute toxicity of a nanofluid containing manganese iron oxide nanoparticles produced by a mechanochemical process

Superparamagnetic iron oxide nanoparticles are candidate contrast agents for magnetic resonance imaging and targeted drug delivery. Biodistribution and toxicity assessment are critical for the development of nanoparticle-based drugs, because of nanoparticle-enhanced biological reactivity. Here, we investigated the uptake, in vivo biodistribution, and in vitro and in vivo potential toxicity of manganese ferrite (MnFe2O4) nanoparticles, synthesized by an original high-yield, low-cost mechanochemical process. Cultures of murine Balb/3T3 fibroblasts were exposed for 24, 48, or 72 hours to increasing ferrofluid concentrations. Nanoparticle cellular uptake was assessed by flow-cytometry scatter-light measurements and microscopy imaging after Prussian blue staining; cytotoxicity was evaluated by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) and colony-forming assays. After a single intravenous injection, in vivo nanoparticle biodistribution and clearance were evaluated in mice by Mn spectrophotometric determination and Prussian blue staining in the liver, kidneys, spleen, and brain at different posttreatment times up to 21 days. The same organs were analyzed for any possible histopathological change. The in vitro study demonstrated dose-dependent nanoparticle uptake and statistically significant cytotoxic effects from a concentration of 50 μg/mL for the MTT assay and 20 μg/mL for the colony-forming assay. Significant increases in Mn concentrations were detected in all analyzed organs, peaking at 6 hours after injection and then gradually declining. Clearance appeared complete at 7 days in the kidneys, spleen, and brain, whereas in the liver Mn levels remained statistically higher than in vehicle-treated mice up to 3 weeks postinjection. No evidence of irreversible histopathological damage to any of the tested organs was observed. A comparison of the lowest in vitro toxic concentration with the intravenously injected dose and the administered dose of other ferrofluid drugs currently in clinical practice suggests that there might be sufficient safety margins for further development of our formulation.

Design and characterization of antimicrobial usnic acid loaded-core/shell magnetic nanoparticles

The application of magnetic nanoparticles (MNPs) in medicine is considered much promising especially because they can be handled and directed to specific body sites by external magnetic fields. MNPs have been investigated in magnetic resonance imaging, hyperthermia and drug targeting. In this study, properly functionalized core/shell MNPs with antimicrobial properties were developed to be used for the prevention and treatment of medical device-related infections. Particularly, surface-engineered manganese iron oxide MNPs, produced by a micro-emulsion method, were coated with two different polymers and loaded with usnic acid (UA), a dibenzofuran natural extract possessing antimicrobial activity. Between the two polymer coatings, the one based on an intrinsically antimicrobial cationic polyacrylamide (pAcDED) resulted to be able to provide MNPs with proper magnetic properties and basic groups for UA loading. Thanks to the establishment of acid-base interactions, pAcDED-coated MNPs were able to load and release significant drug amounts resulting in good antimicrobial properties versus Staphylococcus epidermidis (MIC = 0.1 mg/mL). The use of pAcDED having intrinsic antimicrobial activity as MNP coating in combination with UA likely contributed to obtain an enhanced antimicrobial effect. The developed drug-loaded MNPs could be injected in the patient soon after device implantation to prevent biofilm formation, or, later, in presence of signs of infection to treat the biofilm grown on the device surfaces.

Early and Late Mechanical Alloying Stages of the Pd-Si System

Four Pd-Si compositions (Pd/Si=2.5/1; 3/1; 4/1 and 5/1) were mechanically alloyed by a ball-milling technique. X-ray diffraction and fluorescence analysis were used to monitor the mechanical alloying (MA) process which was carried out in planetary and vibratory ball mills. The first step of the milling process consists in a very fine fragmentation of the silicon particles into the palladium matrix. After this early stage of milling, formation of the intermetallic line compound Pd3Si can occur for the 2.5/1, 3/1 and 4/1 composition depending on the milling conditions and/or milling apparatus adopted: i.e. on the conditions of energy transfer experimentally realized. Subsequent milling indicates that amorphization probably occurs starting from the previously formed Pd3Si compound. Long milling times, up to 56 h, promote a demixing process towards the parent elements for the 2.5/1 and 4/1 compositions. Thermal treatments of the long-term milled samples confirm the final products obtained from the near room-temperature solid state reaction induced by MA. For the Pd5Si composition the conditions for Pd3Si formation and subsequent amorphization were never reached.

Evidences of Rubber Grafting on Activated Carbon Surfaces Containing Fullerene‐like Structures

Abstract It is shown that graphite is converted into an high disordered carbon black by prolonged ball milling. The kinetics of this transformation has been followed by powder x‐ray diffraction, measurements of the crystallinity and of the surface area. Ball milling is able to introduce an high concentration of defective sites in the pristine graphite including the fullerene‐like structures. By mixing with natural rubber both the pristine and the ball‐milled graphite, it is shown by bound rubber measurements that the amount of rubber grafted (chemically linked) on the pristine graphite surface is negligible but reaches a very high level in the ball‐milled graphite. Similarly, ball‐milling of N660 carbon black causes a deep activation of its surface activity which can be measured by a significant increase in the bound rubber level and in the amount of grafted rubber in comparison to the pristine N660 sample. The bound rubber measurement has been performed also on a natural rubber masterbatch with extracted fullerene carbon black (EFCB). Also in this case extremely high levels of rubber grafting have been achieved in comparison to graphite. It is discussed and demonstrated that the fullerene‐like nanostructures in carbon blacks play a key role in the formation of bound rubber phenomenon and in grafting natural rubber on carbon black surface. #Dedicated to Prof. J. B. Donnet on the occasion of his 80th birthday.

Reactive Pellets for Improved Solar Hydrogen Production Based on Sodium Manganese Ferrite Thermochemical Cycle

Hydrogen production by water-splitting thermochemical cycle based on manganese ferrite/sodium carbonate reactive system is reported. Two different preparation procedures for manganese ferrite/sodium carbonate mixture were adopted and compared in terms of material capability to cyclical hydrogen production. According to the first procedure, conventionally synthesized manganese ferrite, i.e., high temperature (1250°C) heating in Ar of carbonate/oxide precursors, was mixed with sodium carbonate. The blend was tested inside a temperature programed desorption reactor using a cyclical hydrogen production/material regeneration scheme. After a few cycles, the mixture resulted rapidly passivated and unable to further produce hydrogen. An innovative method that avoids the high temperature synthesis of manganese ferrite is presented. This procedure consists in a set of consecutive thermal treatments of a manganese carbonatel sodium carbonateliron oxide mixture in different environments (inert, oxidative, and reducing) at temperatures not exceeding 750°C. Such material, whose observed chemical composition consists of manganese ferrite and sodium carbonate in stoichiometric amounts, is able to evolve hydrogen during 25 consecutive water-splitting cycles, with a small decrease in cyclical production efficiency.

On the formation of Pd3Si by mechanical alloying solid-state reaction

Abstract Pure palladium and silicon powders have been mechanically alloyed by ball milling technique. Two compositions were investigated, namely Pd 75 Si 25 , corresponding to the stable intermetallic compound Pd 3 Si, and Pd 80 Si 20 . It has been found that the amorphization process, monitored by X-ray diffraction, proceeds via the formation of the intermetallic Pd 3 Si for both compositions examined. Complete amorphization is never reached in these samples but a higher amorphous fraction is always present in the Pd 80 Si 20 sample. The experimental results have been interpreted in the light of a schematic free-energy diagram for the binary system.

Mechanical alloying of the PdSi system. Investigation of the early and late milling stages

Abstract Four PdSi compositions (Pd 2.5 Si, Pd 3 Si, Pd 4 Si and Pd 5 Si) have been processed by mechanical alloying. After the early milling stages, consisting of very fine fragmentation of the silicon particles into a palladium matrix, the compositions Pd 2.5 Si, Pd 3 Si, and Pd 4 Si can nucleate intermetallic Pd 3 Si depending on the milling conditions and/or milling apparatus. Subsequent milling seems to promote amorphization, probably starting from the previously formed Pd 3 Si compound. A demixing process, for the Pd 2.5 Si and Pd 4 Si compositions, is observed after long milling times and is explained by oxygen pickup during milling.

Metal Hydride-Based Composite Materials with Improved Thermal Conductivity and Dimensional Stability Properties

To address the issues of poor thermal conductivity and fragmentation of metal hydride particles undergoing hydriding/dehydriding reactions, a metal hydride-based composite material was developed. The active metal phase was embedded in a silica matrix and a graphite filler was incorporated by ball milling. A set of compact pellet samples at different composition were prepared and tested. Experimental data obtained from the thermal conductivity measurements shown that using powder graphite produced a quite linear increase in the thermal conductivity of the metal hydride – silica composite. Ongoing studies include composition optimization as well as long-term testing upon cycling of such metal hydride composites to evaluate their potentiality in technological hydrogen storage applications.