J.P. Lecompte

Effect of oxygen on the thermal conductivity of aluminium nitride ceramics

Sintered aluminium nitride is a good thermal conductor which is one of the principal properties of this ceramic. Previous studies have shown that the thermal flux transfer depends strongly on the oxygen contained in the crystal lattice, and on the powder surface. An AlN ceramic containing YF3 as additive has been fabricated by tape-casting and sintering. This study shows that binder burnout must be carried out in air at 550 °C or in nitrogen at 650 °C. Sublimation of YF3 to YOF, and formation of yttrium aluminate occurred during calcination. The amount of YF3 present, thermal treatment duration and the rate of temperature increase and decrease affected oxygen diffusion in the nitride lattice. However, there is no correlation between thermal conductivity and oxygen content and microstructural characteristics are more influential than total oxygen content up to a thermal conductivity value of 220 W/m K.

Lithium metazirconate for nuclear application: physical and mechanical properties

Lithium metazirconate is a candidate in fusion reactor designs as a tritium-breeding material. An amorphous powder was synthesized by gelling zirconium propylate and lithium acetate: after heat treatment at 900 °C, pure Li2ZrO3-l was obtained. Preliminary tests made on sintered pellets, obtained from this powder, demonstrated an appropriate tritium release at low temperature, when the sample porosity was about 20% and the mean pore radius 3 μm. The subject of this paper was to realize a good compromise between mechanical properties and the spread porosity, necessary for tritium diffusion. Dilatometric investigations were performed on compacts of powders treated at 800, 900 and 1000 °C to identify the best temperature and time of sintering. The calcined powders were also uniaxially pressed at 200, 300 and 500 MPa: the green bodies were sintered at 1200, 1250 and 1300 °C for 2 or 4 h, in order to produce ceramics having different porosity. On the sintered bodies, the pore size distribution, the mean pore radius and mechanical properties were evaluated.

In vitro toxicity of carbon nanotubes, nano-graphite and carbon black, similar impacts of acid functionalization.

Carbon nanotubes (CNT) and nano-graphite (NG) are graphene-based nanomaterials which share exceptional physicochemical properties, but whose health impacts are unfortunately still not well understood. On the other hand, carbon black (CB) is a conventional and widely studied material. The comparison of these three carbon-based nanomaterials is thus of great interest to improve our understanding of their toxicity. An acid functionalization was carried out on CNT, NG and CB so that, after a thorough characterization, their impacts on RAW 264.7 macrophages could be compared for a similar surface chemistry (15 to 120 μg·mL(-1) nanomaterials, 90-min to 24-h contact). Functionalized nanomaterials triggered a weak cytotoxicity similar to the pristine nanomaterials. Acid functionalization increased the pro-inflammatory response except for CB which did not trigger any TNF-α production before or after functionalization, and seemed to strongly decrease the oxidative stress. The toxicological impact of acid functionalization appeared thus to follow a similar trend whatever the carbon-based nanomaterial. At equivalent dose expressed in surface and equivalent surface chemistry, the toxicological responses from murine macrophages to NG were higher than for CNT and CB. It seemed to correspond to the hypothesis of a platelet and fiber paradigm.

Thermoluminescence of aluminium nitride : Influence of the thermal treatment

Aluminium nitride powders are very sensitive to oxidation: nitrogen atoms are easily substituted by oxygen atoms in the hexagonal structure. Thermoluminescence (TL), in detecting defects in the matter can be used to study oxygen impurities in the AlN lattice. So we tested two powders with different synthesis processes and thermal treatments in order to observe the influence of the oxygen content on the TL curves. First aluminium nitride synthesised with amines and aluminium halides revealed the relation between the TL signal and crystallite size: the TL intensity increased despite the removal of oxide phases and the decrease of oxygen content. Second, Pyrofine R AlN was treated under oxygen flow for 3 h between 200 ° and 1100 °C. The TL spectrum showed the presence of γ-AlON at low temperature and the area of the TL peak (80 °C) increased with the weight ratio of AlN.

Influence of powder drying route on the mechanical properties of alumina-zirconia composites

Abstract This paper compares Al 2 O 3 -ZrO 2 composites obtained from the same powder precursors dried by two different methods: spray drying and alcohol extraction via sol-gel route. The composite with 15% ZrO 2 obtained by sintering microsphere powders produced via a sol-gel method exhibited better mechanical properties.

Reaction study of aluminium chloride with ammonia and mechanisms leading to aluminium nitride

Abstract The compound formed between AlCl 3 and NH 3 at room temperature and low temperature, characterized by different analysis methods, corresponds to the formula AlCl 3 · 6NH 3 . This intermediate was heated to 900 °C under an ammonia stream to obtain aluminium nitride in low yield; as by-product NH 4 Cl was formed during the thermolysis. In order to explain the decomposition mechanisms, two new pyrolysis were realized, under nitrogen and under reduced pressure. These showed formation of Al(NH 2 )NH in addition to NH 4 Cl during the thermal decomposition. Al(NH 2 )NH can react with HCl, which results from the dissociation of NH 4 Cl, to form AlClNH volatile combination. This is carried out by the gaseous stream during the thermolysis, thereby accounting for the low synthesis yield.

Treatment of fly Ashes Model by PTA : Modeling and Experimental Results on Pollutants Evaporation

A plasma transferred arc reactor was designed to follow on-line by ICP the evaporation of zinc chlorides and sulfates impregnated in a zeolite matrix (fly ash model). The zeolite granules were injected in a graphite crucible on which the transferred arc, in argon atmosphere, was transferred. The modeling of the zinc evaporation by using a first order law, allowed to determine the evaporation constant k of the law and provided a good agreement with the experiment