Alliage métallique amorphe | EPFL Graph Search

vignette|Alliage métallique amorphe. vignette|Pièces d'un alliage métallique amorphe de composition chimique . Le diamètre du cylindre est de . Un alliage métallique amorphe, ou métal amorphe, est un alliage métallique solide doté d'une structure amorphe plutôt que cristalline. Ces matériaux peuvent être obtenus par refroidissement très rapide depuis l'état fondu de l'alliage, ou par d'autres méthodes. Les alliages métalliques amorphes sont produits depuis 1960 sous forme de rubans d'environ d’épaisseur par trempe sur roue puis, depuis environ vingt ans, sous forme massive, c’est-à-dire dont la plus petite dimension est de l’ordre du centimètre. Ces matériaux présentent des caractéristiques uniques, liées à leur structure amorphe, et font l’objet d’intenses recherches, par des approches aussi bien théoriques qu’expérimentales. Par analogie avec le verre de silice, on parle de « verre métallique » pour un alliage métallique amorphe, sans que cela n'exclue les autres appellations lo

Interface Investigations on Titanium Nitride Bilayer Systems

Dominik Anwar Jaeger

Nanocomposite coatings composed of two phases with atomically sharp phase boundaries, show interesting mechanical properties. These properties are often originating from their high interface to volume ratio. Composites of nanocrystalline titanium nitride (TiN) grains surrounded by a one to two monolayer thick interlayer of silicon nitride (Si3N4) show an enhanced nanohardness. The central theme of this thesis is concernedwith the interfacial properties of two-dimensional bilayer systems, which are used as model systems to describe the interfaces occurring in nanocomposite coatings. The systems under investigation are TiN interfaces in contact with silicon (Si), silicon nitride (Si3N4) and aluminum nitride (AlN). The primary tool used to analyze the interfaces of bilayer systems is X-ray Photoelectron Spectroscopy (XPS) with emphasis put on the shake-up feature of the Ti 2p photoelectron line. Shake-ups in TiN are observed as an additional peak on the lower binding energy side of the energy lines of the Ti 2p orbitals. Shake-ups are strongly influenced by valence electrons and electron density distributions. This makes them a powerful tool to probe the chemical and electronic structure of TiN interfaces. The aim of this study is to utilize the shake-up energy and its intensity to gain insight into interfacial structures and correlate their changes to interfacial polarization and macroscopic mechanical properties. Single crystalline (sc-) and oxygen-free TiN as well as oxygen-free bilayer systems were deposited by unbalanced magnetron sputtering and analyzed by Angle Resolved (AR-)XPS. Bilayer samples were deposited and their quality was controlled using X-ray diffraction (crystallinity), Rutherford back scattering (elemental composition), and atomic force microscopy (roughness). All XPS samples were fabricated, transfered and analyzed whilst maintaining ultra high vacuum. A precise and self-consistent XPS data processing method was developed to evaluate Ti 2p spectra. This method accounts for the correct photoelectron line shape, background subtraction and photoelectron peak area intensity. Binding energy, shake-up energy and intensity ratios of shake-ups taken frompristine TiN surfaces are precisely determined, and the influence of oxygen on the information content in peak positions and intensities was investigated. The shake-up energy and intensity of bulk sc-TiN and its origin of the shake-up are discussed. An analytical description for the XPS signal ratio of bilayer systems is derived to separate the interfacial signals from the bulk information. The results obtained by this analytical description are strongly influenced by the interface thickness that has been found to be proportional to the overlayer thickness. The revealed interface properties show a correlation between the shake-up intensity and the interface morphology, oxygen content, overlayer material and overlayer thickness. AR-XPS and X-ray Photoelectron Diffraction (XPD) results were used to interpret the crystalline structure of the different TiN/AlN and TiN/Si3N4 bilayer systems. AlN shows XPD patterns indicating a crystalline growth of AlN on sc-TiN. The electrically insulating AlN overlayer creates a charge accumulation at the TiN interface, which results in an enhanced shake-up intensity. XPD patterns of Si3N4 systems revealed a crystalline growth of Si3N4 in the first 0.6nm. The intensity of the diffraction patterns reduces with increasing Si3N4 overlayer thickness due to a change in the growth behavior from crystalline to amorphous structures. Si3N4 films show, in comparison to AlN, reduced interface charging and hence a lower shakeup intensity. The crystalline growth of Si3N4 in the initial stages is hindered in systems where a bias voltage is applied to the substrate during the deposition process. In contrast to the unbiased systems, which have crystalline interfacial structures, the biased systems no longer show XPD patterns due to a loss of crystallinity. Additionally the shake-up intensity of biased systems is thickness-independent, which is in contrast to unbiased systems. The difference in the shake-up intensity of biased and unbiased Si3N4 is explained by a different band gap of the Si3N4 structure in the first two monolayers. This thesis shows that the increase in the shake-up intensity is correlated to intrinsic and extrinsic interface charging. The obtained results, in combination with theoretical structure models from literature, show that in one to two monolayer thick interlayers a build-up of interface polarization is unlikely. The observed nanohardness enhancement in TiN/Si3N4 systems is explained with already known hardness effects.

EPFL2012

Drops: Controlled crystallization of organic crystals and their use as matrix materials for encapsulation of volatiles

Aysu Ceren Okur

Encapsulation techniques open up new possibilities to control the kinetics and location of the release of active ingredients. Despite the progresses achieved to obtain a better control over the dimensions and composition of the capsules, the encapsulation of volatile substances is still challenging, even though it is of high relevance especially for the cosmetic industries. One way of encapsulating volatile substances is by kinetically arresting these molecules in a matrix which has a low permeability. A group of materials that likely is well-suited to generate such matrices is composed of small molecules capable of forming crystals.In this thesis, we will investigate the influence of the processing of composites containing small biocompatible organic molecules that serve as matrices with volatile active ingredients on the structure and permeability of the resulting particles. In particular, we will investigate the possibility to use organic salt crystals as matrix materials. Particles of well-defined sizes and compositions will be produced in double emulsions where the influence of the formation kinetics and confinements on the structure and permeability of the particles will be investigated. In addition, we will produce amorphous particles by kinetically suppressing the crystallization reaction using a microfluidic spray-drier. This will be achieved by co-spray-drying the active ingredient with the matrix material. We will investigate the effect of the drying speed and reactant composition on the structure and composition of the resulting particles and relate that to the release kinetics of the active ingredient. In addition, we will crystallize the amorphous composite particles and investigate the influence of the structure on the distribution of the actives within the matrix and its permeability. This project is done in collaboration with Firmenich who has all the infrastructure to quantify the release kinetics of volatile active ingredients.

EPFL2022

Effect of ZnO on the reactivity of cementitious systems

Andrea Eloisa Teixeira Pita

One of the biggest driving forces in cement research today is the mitigation of the CO2 emissions caused by its production. A potential solution to reduce the environmental impact is to replace cement with supplementary cementitious materials (SCMs). This replacement results in low strength at early ages because they are slow to react. The incorporation of minor elements has shown the potential to improve cement reactivity. A few percent of ZnO in C3S causes a signifi- cant increase in reactivity. This effect was related to the incorporation of zinc into the C-S-H struc- ture, which increases its needle length. This research investigates the effect of ZnO in more realis- tic systems such as alite, C3A-polyclinker, and C4AF-polyclinker. The positive effects observed in C3S are translated in the alite system, but differences were found in the polyclinkers, which have a prolonged induction period. This resulted due concentration of zinc in the interstitial phases and a small amount of zinc in alite phase. An amorphous phase was identified in the C3A polyclinker; it is believed to react rapidly with water, releasing Zn ions into the solution, which delays the reaction of alite. The addition of more gypsum controls the reaction of this phase, and thus the induction period is shortened.This work explores the possibilities of retaining Zn in alite to enhance the reactivity of more realis- tic cementitious systems. The cooling rate was critical, as a slow cooling rate promoted more Zn in the alite, less amorphous, and hence, an enhancement in the hydration of C3A-polyclinker doped with ZnO. The recalcination of this system did not affect the hydration of alite but increased the amount of crystalline C3A, which reacted faster. Thus, the amorphous phase was related to an aluminate phase. Moreover, a C4AF-polyclinker and a system with a lower amount of interstitial phase were investigated. The results showed a higher Zn concentration in alite but also extended induction periods. This was associated with the free ZnO and the amorphous content. Even when the hydration was delayed, the height of the alite peak increased with Zn doping, probably due to the incorporation of Zn into the C-S-H observed in pure C3S.In addition, the interaction between sulfates and zinc in the alite system doped with ZnO was in- vestigated. Severe retardation was observed, and the reason is proposed to be the formation of amorphous Zn compound. The presence of aluminum, ettringite formation, or an amorphous layer were discarded as the cause of the retardation.

EPFL2022

Effect of ZnO on the reactivity of cementitious systems

Andrea Eloisa Teixeira Pita

EPFL2022

Interface Investigations on Titanium Nitride Bilayer Systems

Dominik Anwar Jaeger

EPFL2012

Drops: Controlled crystallization of organic crystals and their use as matrix materials for encapsulation of volatiles

Aysu Ceren Okur

EPFL2022