Etude de l'action des agents de mouture sur le broyage du clinker

National audienceDans cette étude, du clinker a été broyé dans un broyeur planétaire, en présence de deux types d'agents de mouture, A et B. L'évolution de la surface spécifique mesurée par la méthode de Blaine (finesse) en fonction de la durée de broyage dépend de la nature de l'agent de mouture utilisé. L'agent de mouture B agit plutôt au début du broyage et pour des vitesses faibles alors que l'agent de mouture A permet d'obtenir de grandes finesses même pour des durées de broyage élevées. Ce dernier, cependant, entraîne une adhésion plus importante de la poudre sur les bols de broyage que l'agent de mouture B. Ces deux produits agissent donc différemment pendant le broyage du clinker. Cette étude donne des indications sur les modes d'action possibles de ces deux agents de mouture

Influence of finely ground limestone on cement hydration

International audienceSome work has been carried out on the effect of calcium carbonate on cement paste, but there is no general agreement on the relative effects of different amounts of calcium carbonate on cement paste properties. The objective of the present work is to assess the effect of various amounts of calcium carbonate on the hydration of tricalcium silicate in order to explain the physico-chemical changes occurring during Portland cement hydration. It is shown that calcium carbonate has an accelerating effect on C3S and cement hydration and leads to the precipitation of some calcium carbosilicate hydrate

Curie temperature measurement by thermomagnetic analysis (TMA) and differential scanning calorimetry (DSC)

National audienceThermomagnetic analysis and differential scanning calorimetry are two experimental techniques commonly used for physical chemical analysis. However, they could be useful in the determination of the Curie temperature which is an important characteristic of magnetic materials. This work is related to a large study into the preparation of yttrium iron garnets (YIG) by coprecipitation. Its aim is to study the effect of Fe3+ substitution by nonmagnetic Al3+ ion s for Y3Fe5-xAlxO12 garnets. The variation of the Curie temperature (Tc) as a function of the degree X of substitution are compared with the results already obtained by other authors

Effect of synthesis parameters on the thermal behaviour of yttrium and iron amorphous oxides prepared by coprecipitation.

National audienceAs part as of an overall research subject to control the densification of yttrium iron garnets prepared by coprecipitation, we have studied the thermal behaviour of the hydroxide obtained at the end of the synthesis. The use of thermal analysis methods such as differential thermal stability (DTA) and high temperature X-Rays diffractometry (HTXRD) allows us to show the effect of some synthesis parameters on the crystallization of the yttrium iron garnet. The observed phenomena can be related to the presence of the anions which stay in the solid

Study of efflorescence forming process on cementitious materials // Etude du processus de formation des efflorescences sur des matériaux cimentaires

International audienceEfflorescence is a white deposit of calcium carbonate on the surface of cementitious materials. It appears under specific climatic conditions. Besides the aesthetic problems, an important economical problem also exists, especially for colored materials. Indeed, this phenomenon is a cause for rejection of products by customers. The aims of the study presented herein are to understand the mechanisms involved and identify the main parameters which control efflorescence formation. A procedure was previously performed to produce primary efflorescence in a climatic chamber. As pozzolans are frequently used in order to decrease the intensity of efflorescence, substitution of cement by different pozzolans was studied. This latest research allowed the Authors to underline which parameters were modified by the substitutions and to link decreases in the intensity of efflorescence with those modifications. // Les efflorescences forment un dépôt blanc de carbonate de calcium à la surface de matériaux cimentaires. Elles apparaissent pour des conditions climatiques spécifiques. Au delà du problème esthétique, un important problème économique intervient car ce phénomène peut être la cause du rejet d'un produit par les clients. Les objectifs de l'étude sont la compréhension des mécanismes et l'identification des paramètres principaux qui contrôlent la formation d'efflorescences. Au préalable, un test a été mis au point dans une chambre climatique pour reproduire des efflorescences. Comme les pouzzolanes sont souvent utilisées pour atténuer les efflorescences, la substitution du ciment par différentes pouzzolanes a été étudiée. Cette étude a permis d'identifier les paramètres affectés par ces substitutions et de relier ces modifications à l'atténuation des efflorescences

Effect of different fluxes on the morphology of the LaPO4 : Ce, Tb phosphor

LaPO4:Ce, Tb (LaCeT) is a green phosphor used in fluorescent lamps and plasma display panels. In order to improve the fabrication process of this phosphor, different fluxes have been used. Their influence on the particles size and shape is described thanks to SEM analyses. Fluxes were found to control the morphology of particles : LaCeT particles, from spherical to parallelepiped-like shape, with suitable sizes, from 0.1 to 10 µm, have been synthesized. Furthermore the photoluminescence emission of the obtained powders has been checked, and it has been proved that the effect of the fluxes studied is not harmful to the LaCeT final optical properties

Thermoluminescence of a mixed rare earth phosphate powder La1−x−yCexTbyPO4

International audienceThe properties of thermoluminescence (TL) observed from various mixed rare earth (RE) phosphate powders La1−x−yCexTbyPO4 are reported. TL peaks appear around −175°C, −135°C, −80°C, −35°C and +25°C and the TL emission spectra of La1−x−yCexTbyPO4 are mainly composed of characteristic line transitions of Tb3+ ions. The results show that the co-doping with Ce3+ is not required to observe the TL emission of Tb3+. A model for the recombination mechanisms of the various TL peaks is discussed

Etude physico-chimique d'un composite ciment-bois durant les premières heures d'hydratation.

3 pagesDans le domaine des nouveaux matériaux de construction, l'utilisation de composites à base ciment et de matériaux organiques devient essentiel. Elle permet d'améliorer ou de modifier les propriétés d'un ciment. Dans ce contexte, le matériau composite ciment-fibre de bois est extrêmement intéressant de par ses propriétés d'isolation phonique et acoustique ainsi que par sa faible masse spécifique. Le but de ce travail est de mieux comprendre les interactions chimiques entre le bois et le ciment ainsi que ces conséquences sur l'hydratation du ciment

The influence of wood aqueous extractives on the hydration kinetics of plaster

International audienceThe influence of wood aqueous extractives on the hydration of plaster is discussed in this paper. Two species were chosen: poplar and forest pine, and the effect of a thermal treatment, which acts as a dimensional stabiliser for wood, was considered. Calorimetric measurements prove that delays of the setting must be expected, especially for the retified poplar. Conductimetric experiments show that wood extractives seem to act as a retardant of the nucleation phase of the hydration reaction. The chemical analysis of the extracts reveals the presence of acetic acid and phenolic molecules, but other experiments prove that their action is not sufficient to explain the retarding effect. Special attention should be given to the influence of polyphenolic substances known as tannins

Effect of swift heavy ion irradiations in polycrystalline aluminum nitride

13International audienceThanks to its high thermal conductivity, aluminum nitride may be a serious candidate as fuel coating for the Gas Fast Reactor. However, its behavior under irradiation is not entirely well understood. In order to catch a glimpse of this behavior, specimens were irradiated with swift heavy ions of different energies then characterised by both thermally stimulated luminescence and optical absorption spectrophotometry. With these techniques, the native defects, as well as those affected by irradiation, were identified: thus, by comparison to the virgin sample, no new defect detectable by these techniques is created by irradiations. Eventually, the fact that these techniques complement each other allowed to understand the effect of irradiation parameters on the defect concentration