G. Poli

Studies on the antioxidant and free radical scavenging properties of IdB 1016 a new flavanolignan complex.

Silybin has been complexed in 1:1 ratio with phosphatidyl choline to give IdB 1016 in order to increase its bioavailability. The antioxidant and free radical scavenger action of this new form of silybin has been evaluated. One hour after the intragastric administration to rats of IdB 1016 (1.5 g/kg b.wt.) the concentration of silybin in the liver microsomes was estimated to be around 2.5 micrograms/mg protein corresponding to a final concentration in the microsomal suspension used of about 10 microM. At these levels IdB decreased by about 40% the lipid peroxidation induced in microsomes by NADPH, CCl4 and cumene hydroperoxide, probably by acting on lipid derived radicals. Spin trapping experiments showed, in fact, that the complexed form of silybin was able to scavenge lipid dienyl radicals generated in the microsomal membranes. In addition, IdB 1016 was also found to interact with free radical intermediates produced during the metabolic activation of carbon tetrachloride and methylhydrazine. These effects indicate IdB 1016 as a potentially protective agent against free radical-mediated toxic damage.

“Tribological behaviour of multi-layered PVD nitride coatings”

Abstract Multi-layers resulting from the combination of layers of different PVD nitrides (TiN, Ti 2 N, Ti(C,N), (Ti,Al)N) were deposited by arc evaporation on AISI M2 tool steel and their tribological behaviour has been investigated. The effect of a MoS 2 layer deposited on top of the PVD nitride multi-layers was also studied. Dry sliding and abrasive wear behaviour have been studied by a slider-on-cylinder tribometer and a micro-scale abrasion tester, respectively. The main sliding wear mechanism was abrasion from hard particles formed at the contact interface as a consequence of extensive oxidation of the counter-material (hard chromium). The prevalence of abrasion damage in the sliding tests explains the good correlation between the results given by sliding tests at low applied loads and the micro-abrasion tests, and shows that hardness plays a key role in influencing the behaviour of the multi-layers. Milling tests, carried out in order to evaluate the cutting performance of coated tools, showed that end mills coated with the TiN-based multi-layers live longer than the others. The difference of performance was much less marked at the highest cutting speed.

The Chemistry of Catalysts Based on Vanadium-Phosphorous Oxides. Note II. The Role of the Method of Preparation

Abstract Vanadium-phosphorous mixed oxides, specific catalysts for C 4 . oxidation to maleic anhydride, were prepared using two methods as follows; i) method A, by reduction of V 2 O 5 with HCl after addition of H 3 PO 4 and ii) method B, by addition of NH 4 VO 3 to a solution containing H 3 PO 4 and oxalic acid as reducing agents. It was observed that, with both procedures, H 3 PO 4 in excess to that for a ratio of P/V = 1.1 serves to stabilize the tetravalent form of vanadium in calcination at high temperatures. The nature of the compounds formed was different for the two methods. For P/V less than 1.1, βVOPO 4 was formed with method A and amorphous αVOPO 4 was formed with method B. For P/V greater than 1.1, method A gave the β-phase, described in the literature as the active phase, while method B gave other crystalline and amorphous compounds. It is suggested that the β-phase formed as a polyphosphate of V(IV) containing excess phosphorous. The differences observed with the two preparation procedures are related to the different precursors which formed after the drying stage at 125°C. Method A gave (VO) 2 P 2 O 7 ,2H 2 O and method B VO(NH 4 )P0 4 ,4H 2 O.

Preliminary study of micro-scale abrasive wear of a NiTi shape memory alloy

Abstract Nitinol (NiTi), a nearly equiatomic nickel–titanium alloy is known for its unique shape memory and superelastic properties, which result from martensitic transformations. It is the material of choice for numerous biomedical applications such as endovascular stents, vena cava filters, dental files and guidewires for non-invasive surgery, etc. Micro-scale abrasion tests (MSATs) have been performed on the NiTi shape memory alloy, so as to evaluate the influence of different commercial abrasives such as silicon carbide, alumina and glass on the wear behaviour. The aim of the work was the selection of the most effective abrasive for cleaning the inner surface of laser-cut cardiovascular stents. Abrasive particles have been characterised by X-ray diffraction, SEM and EDS before and after MSATs. Worn surfaces have been studied by stylus profilometry, SEM and atomic force microscopy. The effect of abrasive particle hardness, size and angularity on the wear behaviour has been evaluated and discussed.

Enhanced reactive NiAl coatings by microwave‐assisted SHS

Purpose – The paper aims to focus on microwave (2.45 GHz) assisted SHS (MA‐SHS) preparation of NiAl intermetallic coatings on titanium substrates conducted in single mode applicator in order to promote the formation of a complex Ni‐Al‐Ti interface. This enhances the NiAl coating adhesion to the Ti substrate and presents high hardness, high toughness and the capability of stopping the fracture propagation.Design/methodology/approach – Numerical modelling, coupling electromagnetic and heat transfer, allowed to demonstrate that the interface cooling rate can be controlled immediately after SHS using microwave heating, benefiting from the possibility of conveying energy to the newly formed intermetallic compounds, despite an adverse temperature gradient which would negatively affect conventional heating techniques, based exclusively on heat transfer. Experimental validation of the modelling results confirmed that by altering the synthesis conditions (load geometry, microwave power, auxiliary microwave absorbe...

Unalloyed copper inclusions in ancient bronze artefacts

Ancient bronze artifacts, that represent a considerable part of the archeological finds, have been largely studied because of their complex degradation phenomena taking place in the long time span that have not been fully understood. One of the peculiar features of ancient bronzes is the presence of inclusions of copper unalloyed with tin. Unalloyed Copper Inclusions (UCI) have been observed in buried archaeological bronze artefacts by several authors, but each paper reports only on a limited number of cases. In our extensive studies on bronze artefacts, UCI have been observed in many bronze artefacts with very different features and purposes. Both as-cast and wrought artefacts were studied, so that the influence of the manufacturing process and the composition of the artefacts on the formation of UCI might be evaluated. The microstructure and composition of these artefacts were studied and the features of UCI have been related with those of the surrounding phases. The results have been discussed and compared with those obtained by other authors. The presence of UCI in buried archaeological bronze artefacts could indicate some unusual corrosion processes that might need to be accounted for when designing conservation treatments.

Microwave Assisted Combustion Synthesis of Non-equilibrium Intermetallic Compounds

Abstract A simplified model of the microwave-assisted combustion synthesis of Ni and Al metal powders to form the NiAl intermetallic on titanium and steel substrates is presented. The simulation couples an electro-thermal model with a chemical model, accounting for local heat generation due to the highly exothermic nature of the reactions between the powders. Numerical results, validated by experimental values, show that the capability of microwaves to convey energy, and not heat, can be used to alter the temperature profiles during and after the combustion synthesis, leading to unique intermetallic microstructures. This phenomenon is ascribed to the extended existence of high temperature liquid intermetallic phases, which react with the metallic substrates at the interface. Moreover, microwave heating selectivity allows to maintain the bulk of the substrate metallic materials to a much lower temperature, compared to combustion synthesis in conventionally heated furnaces, thus reducing possible unwanted transformations like phase change or oxidation.

Structure and reactivity of vanadium-phosphorus oxides

The contribution of thermal methods of analysis to the study of the structure and reactivity of vanadium-phosphorus oxides is examined. In particular, data are reported on the solid-state reaction VOHPO4·1/2H2O→(VO)2P2O7+2 H2O for VOHPO4·1/2H2O prepared in different ways, on the redox properties of oxidation and reduction of vanadium for catalysts prepared with different P∶V atomic ratios in the range 0.9–1.3, and on the surface properties determined by TPD of catalysts with different P∶V ratios. The relationship between these properties and the catalytic properties in the selective oxidation ofn-butane and but-1-ene is discussed.ZusammenfassungDer Beitrag thermischer Analysenmethoden zur Untersuchung der Struktur und Reaktivität von Vanadin-Phosphor-Oxiden wird erörtert. Insbesondere werden sich auf die Festkörperreaktion 2VOHPO4.1/2H2O→(VO)2P2O7+2H2O für auf verschiedene Weise dargestelltes VOHPO4.1/2H2O, auf die Redox-Eigenschaften von Vanadin in Katalysatoren mit P/V-Atomverhältnissen im Bereich 0.9–1.3 und auf durch TPD bestimmte Oberflächeneigenschaften von Katalysatoren mit unterschiedlichen P/V-Verhältnissen beziehende Angaben gemacht. Zusammenhänge zwischen diesen Eigenschaften und den katalytischen Eigenschaften bei der selektiven Oxydation von n-Butan und N-Buten werden diskutiert.РезюмеИсследован вклад тер мических методов ана лиза в изучение структуры и реакционной способности системы окислов ванадий-фосф ор. Приведены, в зависимо сти от метода получен ия VOHPO4 · 1/2H2O, данные для тверд отельной реакции VOHPO4 · 1/2H2O→(VO)2P2O7 + 2H2O, оказывающей влияние на окислительно-восста новительные и поверх ностные свойства свойства ванадиевых катализа торов с атомным соотн ошением P∶V в области 0,9∶1,3. Обсуждена зависимость между эт ими свойствами катал изаторов и их каталитической ак тивностью при селективном окислен ии н-бутана и 1-бутена.

On the chemistry of vanadium-phosphorus oxides. note v: crystallogenesis of vanadyl hydrogen phosphate

Abstract The chemistry of the preparation of VOHPO 4 .case12H 2 O, precursor in the formation of (VO) 2 P 2 0 7 , the active phase in n-butane selective oxidation, was investigated. The VOHPO 4 .12H 2 0 was prepared from an acid aqueous solution of VO 2+ and ortho- or pyro-phosphoric acid. The results indicate that the precipitation of the insoluble VOHPO 4 .case12H 2 0 occurs only in highly concentrated solutions, where it is proposed that a sol of VOHPO 4 or (VO) 2 P 2 0 7 form which constitute the precursor phase of the crystalline VOHPO 4 .case12H 2 O. The necessity of the formation of this precursor phase is related to the difficulty of the precipitation/crystallization process, as compared with other Me 4+ hydrogen phosphate preparations. Different methods of preparation, which do not lead to the formation of this intermediate, did not lead to the formation of VOHPO 4 .case12H 2 0. The role of the method of preparation in obtaining pure VOHPO 4 .case12H 2 O is also discussed.

Microwave Ignited Combustion Synthesis as a Joining Technique for Dissimilar Materials

Microwave energy has been exploited to ignite combustion synthesis (CS) reactions of properly designed powders mixtures, in order to rapidly reach the joining between different kinds of materials, including metals (Titanium and Inconel) and ceramics (SiC). Beside the great advantage offered by CS itself, i.e., rapid and highly localized heat generation, the microwaves selectivity in being absorbed by micrometric metallic powders and not by bulk metallic components represents a further intriguing aspect in advanced materials joining applications, namely the possibility to avoid the exposition to high temperatures of the entire substrates to be joined. Moreover, in case of microwaves absorbing substrates, the competitive microwaves absorption by both substrates and powdered joining material, leads to the possibility of adhesion, interdiffusion and chemical bonding enhancements. In this study, both experimental and numerical simulation results are used to highlight the great potentialities of microwave ignited CS in the joining of advanced materials.