Stefano Gialanella

Effect of deep cryogenic treatment on the mechanical properties of tool steels

Abstract The effect of deep cryogenic treatment (−196°C) on the properties of some tool steels was studied by means of both field tests on real tools and laboratory tests. The execution of the deep cryogenic treatment on quenched and tempered high speed steel tools increases hardness, reduces tool consumption and down time for the equipment set up, thus leading to cost reductions of about 50%. A laboratory investigation on an AISI M2 and an AISI H13 steel confirms the possibility of increasing the wear resistance and toughness by carrying out the treatment after the usual heat treatment.

X-ray diffraction characterization of heavily deformed metallic specimens

Ordered intermetallic compound powders can be heavily deformed and disordered by ball-milling. This highly energetic deformation process introduces several kinds of defects into the powder and changes the aspect of the grains. By a novel analysis of the diffraction spectra we can analyse most of such defects and characterize the correlation between the shape of the powder and its crystallographic orientation. In this way we can also recognize how deformation may occur along specific crystallographic planes. The quantitative evaluation of dislocations, twins, stacking and deformation faultings allows us to correlate the disordering process to the introduction and development of defects under the effect of milling. It is shown how a full pattern fitting of diffraction spectra can be successfully applied to a comprehensive investigation of a material modification process, if appropriate physical models are used to describe the scattering event instead of semiempirical functions.

Sol–gel synthesis and characterisation of ZnO-based nanosystems

Semiconductor nanoclusters embedded in thin coatings of transparent and homogeneous silica glasses are suitable materials for the development of optical devices. The optical properties of such systems are strongly dependent on the elemental composition and the morphology of the coatings as well as on the nanocluster size distribution, their mutual interactions and the interactions with the host matrix. To achieve a good control over film composition and morphology the sol–gel route was used. The sol–gel synthesis of ZnO nanocrystals embedded in silica has been faced by the study of the gel-derived binary system ZnO–SiO2. The dip-coating procedure from alcoholic solutions containing tetraethoxysilane [Si(OC2H5)4, TEOS] and zinc acetate [Zn(CH3COO)2] was adopted. Zinc oxide nanograins have been generated in silica by hydrolysis of TEOS and the zinc salt and subsequent thermal annealing of the coatings. The system evolution under thermal treatment was studied by X-ray photoelectron spectroscopy, X-ray diffraction, transmission electron microscopy, UV-Vis absorption spectroscopy and secondary-ion mass spectrometry.

Photodegradation of Pollutants in Air: Enhanced Properties of Nano-TiO2Prepared by Ultrasound

Nanocrystalline TiO2samples were prepared by promoting the growth of a sol–gel precursor, in the presence of water, under continuous (CW), or pulsed (PW) ultrasound. All the samples turned out to be made of both anatase and brookite polymorphs. Pulsed US treatments determine an increase in the sample surface area and a decrease of the crystallite size, that is also accompanied by a more ordered crystalline structure and the samples appear to be more regular and can be considered to contain a relatively low concentration of lattice defects. These features result in a lower recombination rate between electrons and holes and, therefore, in a good photocatalytic performance toward the degradation of NOxin air. The continuous mode induces, instead, the formation of surface defects (two components are present in XPS Ti 2p3/2region) and consequently yields the best photocatalyst. The analysis of all the characterization data seems to suggest that the relevant parameter imposing the final features of the oxides is the ultrasound total energyper volume (Etot/V) and not the acoustic intensity or the pulsed/continuous mode.

MICROSTRUCTURAL AND KINETIC ASPECTS OF THE TRANSFORMATIONS INDUCED IN A FeAl ALLOY BY BALL-MILLING AND THERMAL TREATMENTS

Abstract A Fe–40Al (at.%) alloy powder having a B2 ordered structure was milled in a high energy planetary ball-mill. The microstructural evolution of the alloy was followed by analysing powder specimens milled for different times by X-ray diffraction, Mossbauer spectroscopy and magnetisation measurements. Grain refinement and chemical disordering were the main transformations resulting from milling. A complete destruction of the long-range order under the adopted conditions of milling was not achieved. From diffraction analyses it was possible to see how the concentrations of such defects as dislocations, planar faults, antiphase domain boundaries, etc., were modified by the heavy deformations involved with milling. Starting from the specimens milled for the longest time, considered in this study, isothermal annealing experiments were carried out to monitor the reverse transformations. The annealing temperatures were selected on the basis of differential scanning calorimetric and thermogravimetric magnetic measurements, which revealed that several transformations occur when treating the deformed powders. Recovery and reordering take place at temperatures ranging from 100 up to 250°C. A complete reordering is possible only at higher temperatures, i.e. 700°C, when recrystallisation is fully accomplished.

Effect of Mgo content changes (8 to 15%) on the devitrification of glasses obtained from porphiric sands, Mgo and Tio(in2) (4%)

Glasses have been prepared from porphiric sands, TiO2 and MgCO3 and the effect of changing the MgO content on the isothermal devitrification has been studied.The experimental data suggest that an increase in MgO content increases the devitrification rate owing to a greater aptitude to form nuclei, so that a fine grained microstructure can be obtained more easily.

Green and low temperature synthesis of nanocrystalline transition metal ferrites by simple wet chemistry routes

Crystalline and nanostructured cobalt (CoFe2O4), nickel (NiFe2O4), zinc (ZnFe2O4) and manganese (MnFe2O4) spinel ferrites are synthesized with high yields, crystallinity and purity through an easy, quick, reproducible and low-temperature hydrothermal assisted route starting from an aqueous suspension of coprecipitated metal oxalates. The use of water as a reaction medium is a further advantage of the chosen protocol. Additionally, the zinc spinel is also prepared through an alternative route combining coprecipitation of oxalates from an aqueous solution with thermal decomposition under reflux conditions. The nanocrystalline powders are obtained as a pure crystalline phase already at the extremely low temperature of 75 °C and no further thermal treatment is needed. The structure and microstructure of the prepared materials is investigated by means of X-ray powder diffraction (XRPD), while X-ray photoelectron spectroscopy (XPS) and inductively coupled plasma-atomic emission spectroscopy (ICP-AES) analyses are used to gain information about the surface and bulk composition of the samples, respectively, confirming the expected stoichiometry. To investigate the effect of the synthesis protocol on the morphology of the obtained ferrites, transmission electron microscopy (TEM) observations are performed on selected samples. The magnetic properties of the cobalt and manganese spinels are also investigated using a superconducting quantum device magnetometer (SQUID) revealing hard and soft ferrimagnetic behavior, respectively.

Sol-Gel Synthesis and Characterisation of TiO2-Anatase Powders Containing Nanometric Platinum Particles Employed as Catalysts for 4-Nitrophenol Photodegradation

A set of TiO2 and Pt-TiO2 polycrystalline samples were prepared by sol-gel method hydrolysing a modified alkoxide titanium precursors under acidic conditions. The Pt-TiO2 samples gave an homogeneous nanometric metal dispersion after drying heat treatment forming platinum particles in the range 2–4 nm. All the samples have been characterised using several techniques, namely thermogravimetric analysis, gas-chromatography, mass spectrometry, thermogravimetric analysis combined with mass spectrometry or with gas chromatography/mass spectrometry, X-ray diffraction coupled with a Rietveld refinement procedure, X-ray photoelectron spectroscopy and determination of specific surface area. Moreover, the samples have been employed as catalysts for 4-nitrophenol photodegradation in aqueous suspension used as a “probe” reaction. Characterisation results indicate that the thermal and chemical treatments of the catalysts influenced the photocatalytic activity. In the Pt-TiO2 samples both Pt(0) and Pt(II) species are present in the catalyst particles and the most abundant phase is anatase for all of the samples. Doping with Pt beneficially influences the photo-oxidant properties of TiO2 while the presence of organic residual species on the surface, deriving from the preparation procedure of the catalyst particles interferes negatively in the kinetics of the photocatalytic process.

FeAl alloy disordered by ball-milling

Abstract Fe-40 at% Al powder was ball-milled in a planetary mill, and it was found that 8 h milling sufficed to remove all long-range order. The lattice parameter increased by 0.8%, the increase continued somewhat after all X-ray evidence of long-range order had disappeared. The findings are discussed in relation to other methods which have been used to induce disordering.

Chemical and physical routes for composite materials synthesis: Ag and Ag2S nanoparticles in silica glass by sol–gel and ion implantation techniques

Two composite systems, “Ag” and “Ag–S” nanoparticles in silica films, were approached by using two different synthesis routes, namely sol–gel and ion implantation. Silica composites containing embedded nanosized silver- and silver sulfide-crystallites were obtained by the sol–gel process. The formation of silver nanograins was also observed in Ag-implanted silica samples, while sequential implantation (first Ag then S) led to the formation of core–shell Ag–Ag2S nanoclusters. The systems were then characterised using different analytical tools, i.e. X-ray photoelectron spectroscopy (XPS), X-ray-excited Auger electron spectroscopy (XE-AES), X-ray diffraction (XRD), secondary-ion mass spectrometry (SIMS), Rutherford backscattering spectrometry (RBS) and transmission electron microscopy (TEM). These advanced microscopic and X-ray analytical methods were combined to gain complementary information concerning the composition and microstructure of the investigated composite systems. In addition, the characterisation of both systems by means of several investigation techniques provided a valuable insight into the potential features offered by sol–gel and ion implantation and enabled a fruitful comparison between these preparative routes. The influence of the different synthesis parameters on the final features of the composites is analysed and discussed.