Courbe de refroidissement | EPFL Graph Search

thumb|Courbe de refroidissement du naphtalène de l'état liquide à l'état solide. Une courbe de refroidissement est une courbe qui représente le changement de l'état de la matière, généralement d'un gaz à un solide ou d'un liquide à un solide. La variable indépendante (axe des abscisses) est le temps et la variable dépendante (axe des ordonnées) est la température. Le point initial de la courbe est la température de départ de la matière. Lorsqu'un changement de phase se produit, la température reste constante. Le taux de refroidissement est la pente de la courbe de refroidissement en tout point. Les courbes de refroidissent sont utilisées entre autres pour déterminer le point de fusion des cires de pétrole. Notes et références Catégorie:Thermique Catégorie:Cire

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

Firing, quenching and annealing studies on thick-film resistors

Thomas Maeder, Peter Ryser, Sonia Vionnet Menot

In this work, we aim to understand the firing behaviour of three representative thick-film resistor compositions used in force and pressure sensors. The dependence of the materials' microstructure and properties (sheet resistance and its temperature coefficient, gauge factor) is studied as a function of firing temperature and time, and cooling rate (furnace or quench). The stability of the properties is assessed by annealing at intermediate temperatures (100 and 250 °C). Microscopic and structural analysis is also carried out. The results are discussed in the light of the possible evolution mechanisms of the resistor materials: diffusion, dissolution, precipitation and stress relaxation.

2004

Influence of thermo-mechanical history on the ordering kinetics in 18 carat Au alloys

Nadine Baluc, Marina Garcia Gonzalez, Steven Van Petegem, Helena Van Swygenhoven

Precious alloys are subjected to a series of mechanical and thermal operations during manufacturing. For 18 carat gold alloys the processing operations can induce L1(0) ordered nanodomains, known to lead to the buildup of residual stresses, which are the prime cause for shape distortion. Here, in situ high-energy synchrotron X-ray diffraction experiments in combination with electron microscopy observations reveal the influence of the thermo-mechanical history and chemical composition on the ordering kinetics during isochronal heating. Initially, during heating, the elastic lattice strain in the ordered nanodomains increases. The ordering rate and accumulation of lattice strain depend on the cooling rate, predeformation and chemical composition. Above a given temperature, which depends on the deformation state and chemical composition, the lattice strain in the ordered domains relaxes which is ascribed to the formation of a tweed structure. (C) 2020 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

PERGAMON-ELSEVIER SCIENCE LTD2020

Effect of ZnO on the reactivity of cementitious systems

Andrea Eloisa Teixeira Pita

EPFL2022