DEPOSIZIONE AUTOCATALITICA DI COMPOSITI A MATRICE NI-P

Nel presente lavoro è stata studiata la deposizione autocatalitica di compositi Ni-P-B4C, Ni-P-CNT e Ni-PAl2O3 attraverso l’impiego di un elettrolita a base di sodio ipofosfito in cui sono state disperse particelle nanometriche di B4C, CNT e Al2O3. La dimensione delle particelle di Al2O3 e B4C è compresa rispettivamente tra 50-70 nm e 25-30 nm. I nanotubi di carbonio presentano un diametro compreso tra 10-30 nm. Per ciascun tipo di composito, sono state effettuate prove con concentrazioni comprese tra 0 e 4 g/l. Sono stati studiati gli effetti della concentrazione di particelle all’interno del bagno sulla velocità di deposizione, sulle caratteristiche meccaniche e sulle proprietà tribologiche dei depositi

RECYCLING OF LF-WHITE SLAG

Over the last few years technologies of the plants dedicated to recycle of ladle slag have been improved. The type of recycling evaluated in the present study mainly consists in the reuse of the ladle slag and refractory, injecting them into the Electric Arc Furnace. The recycling of ladle slag can permit to achieve interesting advantageous results: decreasing the amount of dumped material, the cost of EAF fluxes and improve the slag foaminess

Effect of electrolyte composition on micro-arc anodization of AM60B magnesium alloy

Anodic oxidation in micro-arc regime is one of the most investigated techniques used to coat magnesium alloys with ceramic coatings for protection from corrosion and wear. The anodization electrolyte composition affects the current/voltage characteristic of the cell, the anodic oxide layer morphology and its behaviour in aggressive environment. In this paper the influence of the electrolyte composition on the anodic oxidation process and oxide properties is discussed. Scanning electron microscopy, x- ray diffraction, and x- ray photoelectron spectroscopy were employed to assess morphology, crystallographic structure and composition of the anodic oxide. Electrochemical polarization tests were performed to evaluate the corrosion resistance behaviour of the coated magnesium alloys

Influence of added elements on autocatalytic chemical deposition electroless NiP

tThe mechanisms proposed to explain ACD electroless Ni–P deposition are re-examined and the mostimportant features underlined. Oxidation of hypophosphite on the Ni–P surface is recognized as therate determining step of the process. The possibility of a bridged intermediate with hypophosphite andhydrolyzed nickel adsorbed at the surface is examined and proved feasible by quantum mechanical calcu-lations. A comparison of electrodeposition and ACD electroless deposition shows that the two processesare anti-correlated, ACD being directly related to the electrolytic hydrogen discharge. Addition of otherelements can greatly influence ACD electroless NiP plating process. Metals giving anomalous alloy elec-trodeposition, such as Zn, Co and Fe behave normally in electroless baths. Elements electrodeposited byinduction, such as W and Mo, decrease the P content and the deposition rate. A similar effect occurs forRe, Ce and Cu. Some of the metal stabilizers have also a brightening effect on NiP deposits. This is the caseof Cd, Bi, Te and Cu and brightening is related to their interaction with adsorbed hydrogen, stabilized bythese additives

Influence of Added Elements on ACD Electroless NiP

Addition of other metals can greatly influence the Autocatalytic Chemical Deposition ACD NiP plating process. The most important effects are related to possible codeposition, obtaining ternary or quaternary alloys, or stabilization of the bath. Minor, but not less important, effects regard deposit aspect and structure, phosphorus content, corrosion and wear resistance, stability of the deposits with respect to thermal treatments. A general interpretation of the influence of the added elements on the process and the deposit properties is proposed. The behaviour of the added elements is generally anti-correlated with their behaviour in electrodeposition. Elements giving anomalous alloy electrodeposition, such as Zn, Co and Fe behave normally in electroless baths; elements electrodeposited by induction, such as W and Mo, have important effects on the electroless process: they decrease the P content and the deposition rate, while increasing the corrosion resistance. Some of the metal stabilizers, such as Pb, Tl, Hg, Cd, Sb, Bi and Te, can have also a brightening effect on NiP deposits. This is the case of Cd, Sb, Bi and Te and this effect can be related to their interaction with adsorbed hydrogen, which is stabilized by these additives

Cooperative phenomena and influence of strain energy in alloys

Thermodynamic approximations for cooperative phenomena in solids are reviewed and a new approximation is proposed and developed. The method calculates the configurational free energy for Ising and Heisenberg model systems, from a series of quasi-chemical reactions, adopting a system renormalization solution strategy.Magnetic and suitable order-disorder transformations are properly represented as higher order transitions. An elastic energy term is introduced to take into account the atomic size and shape change effects in metallic alloys. With this method we can distinguish when an ordering transition becomes first order. The method is also suitable for a theoretical calculation of the magnetic free energy contribution to ferromagnetic alloys