Gloria Ischia

Miniemulsions as chemical nanoreactors for the room temperature synthesis of inorganic crystalline nanostructures: ZnO colloids

We successfully explored, for the first time, the use of the w/o inverse miniemulsion route to prepare surfactant-functionalised nanocrystalline ZnO colloids. The adopted route exploits the micelles as nanoreactors for the precipitation of the desired oxide in a confined space. Triton X-100 (TritX-), sodium dodecyl sulfate (SDS-) and polyvinylpyrrolidone (PVP-) coated ZnO crystalline nanoparticles (NPs) have been obtained at room temperature (RT) with no need for post-treatment, by precipitation of zinc chloride with ammonium or sodium hydroxide into w/o inverse micelles. Their hydrodynamic diameter, evaluated by Dynamic Light Scattering (DLS), is about 35 nm. X-Ray Photoelectron Spectroscopy (XPS), X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), Inductively Coupled Plasma Atomic Emission Spectrometry (ICP-AES), Fourier Transform Infrared (FT-IR) spectroscopy and Thermogravimetric Analysis (TGA) have been used to characterize powders separated by miniemulsions. The NP inorganic core is constituted of wurtzite ZnO, with a high degree of crystallinity, as determined by XRD. XRD data and TEM images revealed the formation, in the case of ZnOTritX, of anisotropic plate-like crystallites, with an average diameter of 72 nm and a thickness of 15–20 nm. The RT photo-luminescent (PL) spectrum of ZnOPVP NPs shows a strong UV emission band, attributed to the free exciton recombination, with a relevant tail in the Vis region due to the presence of structural defects. The morphology of these systems, investigated by SEM, corresponds to a homogeneous dispersion of globular sponge structures in a compact and fibrous matrix.

Spark plasma sintering of cryomilled copper powder

Abstract The densification and sintering behaviour of a cryomilled copper powder (grain size of 17±2 nm and dislocation density of 6·26±0·04×1016 m−2) were investigated and compared to those of an atomised copper powder with the same mean particle size in order to highlight the effect of the nanostructure on spark plasma sintering (SPS). Oxygen and nitrogen contamination of the cryomilled powder gives rise to extensive degassing during SPS up to 400°C. The cryomilled powder is more resistant to plastic deformation than the atomised one, but the huge density of dislocations and grain boundary activates sintering at low temperature. Densification is therefore promoted by deformation in the atomised powder and by sintering shrinkage in the cryomilled one. As a consequence, in the SPS conditions investigated, the atomised specimen is densified but not sintered, while the cryomilled one is effectively sintered and consequently densified.

Differences of the microstructural evolution of Cu powder during continuous and interrupted mechanical milling

ABSTRACT Water atomised copper powders (AT-Cu) have been processed by continuous and interrupted mechanical milling (MM) for different milling times. For continuous cycle the powders are subjected first to a severe flattening process and then to an intense welding phenomenon. In the case of interrupted cycle MM behaviour proceeds with an intense fracturing process. By quantitative X-ray-diffraction analysis the interrupted cycle shows constantly a delay of the microstructure evolution with all the phenomena shifted at longer milling time. For both types of cycle crystalline size decreases down to 20 nm. After 6000 min of interrupted MM the formation of Cu2O has been revealed and a strong dependency between oxygen content and microstructural parameter has been attested analysing the variations of lattice parameter and lattice strain. When the interstitial oxygen atoms lose their Cottrell locking action dislocation annihilation occurs leading to a reduction of dislocation density and lattice strain.

Robust and Biocompatible Functionalization of ZnS Nanoparticles by Catechol-Bearing Poly(2-Methyl-2-Oxazoline)s

Zinc sulfide (ZnS) nanoparticles (NPs) are particularly interesting materials for their electronic and luminescent properties. Unfortunately, their robust and stable functionalization and stabilization, especially in aqueous media, has represented a challenging and not yet completely accomplished task. In this work, we report the synthesis of colloidally stable, photoluminescent and biocompatible core-polymer shell ZnS and ZnS:Tb NPs by employing a water-in-oil miniemulsion (ME) process combined with surface functionalization via catechol-bearing poly-2-methyl-2-oxazoline (PMOXA) of various molar masses. The strong binding of catechol anchors to the metal cations of the ZnS surface, coupled with the high stability of PMOXA against chemical degradation, enable the formation of suspensions presenting excellent colloidal stability. This feature, combined with the assessed photoluminescence and biocompatibility, make these hybrid NPs suitable for optical bioimaging.

Effect of austenitisation temperature on austenite transformations in 0·7%C Cr–Mo PM steel

Abstract The effect of austenitisation temperature on austenite transformations on 0·7%C Astaloy CrL steel was studied by dilatometry. The steel has a good hardenability, forming martensite at most of the austenitisation temperatures and cooling rates investigated. Only on cooling from 1073 K, austenite transforms into bainite completely at 3 K s−1 and partially at 12·5 K s−1. The effect of austenitisation temperature on the prior austenitic grain size is quite poor because of the pinning effect of pores. The martensite start temperature Ms increases slightly with the austenitisation temperature up to 1173 K and decreases at 1523 K. This trend is due to the presence of nanometric carbides (Cr23C6), which were detected at TEM. They dissolve almost completely in austenite at 1523 K only, increasing the stability of austenite against the martensitic transformation. The effect of temperature in the range from 1073 K up to 1523 K is poor. As a consequence, the microstructural characteristics of hardened steels are very similar.