Pierre Quintard

An FT–IR Study of the Chlorination of γ-Alumina Surfaces

Abstract Surface chlorination of two aluminas (Degussa and Condea; S BET =100xa0 m 2 g −1 ) has been realized either by reaction of CHCl 3 on an alumina pellet inside the IR cell or by flowing HCl (g) on alumina powder for one hour outside the IR cell. The FT–IR analysis of the chlorinated samples showed that the bands assigned to OH groups, specially in the range of higher wavenumbers (3800–3700xa0 cm −1 ), are sensitive to the presence of chlorine on the surface taking the place of the more basic surface OH groups by substitution reaction. The nature of the additive products influenced the bands in the 1600–1200xa0 cm −1 region. The evolution of surfaces rehydratation showed that the chlorinated aluminas are more stable than the raw ones with respect to the presence of H 2 O on the surface. The hydrolysis modified the surfaces of both raw Al 2 O 3 , whereas the surfaces of the chlorinated aluminas were restored after thermal treatment at 870xa0K. La chloration de surface de deux alumines (Degussa et Condea) de surface specifique de 100xa0 m 2 g −1 a ete realisee soit par reaction de CHCl 3 avec la surface a l’interieur de la cellule infrarouge soit par passage de HCl (g) sur la poudre d’alumine durant une heure a l’exterieur de celle-ci. L’etude infrarouge des surfaces chlorees montre la presence de reactions de substitution entre les groupes OH de la surface et le chlore des deux agents chlorants. Ce sont les groupes OH les plus basiques qui reagissent. La nature des additifs modifie aussi le spectre dans la region 1600–1200xa0 cm −1 . Une rehydratation a revele que les alumines ainsi chlorees sont plus stables que celles non traitees en ce qui concerne l’action de la molecule H 2 O sur la surface. En effet l’hydrolyse affecte la surface des deux alumines brutes, alors que celle des alumines chlorees est restauree apres chauffage a 870xa0K.

Wettability and corrosion of TiN, TiN–BN and TiN-AlN by liquid steel

The wettability and corrosion behaviour of titanium nitride by liquid steel has been studied. Due to its thermodynamic stability and low solubility in liquid iron, TiN has a good resistance to corrosion by liquid steel. However, its good wettability promotes adhesion to steel. Also, the effects of BN and AlN addition to TiN on the wetting parameters and the mechanisms of the ceramic corrosion by liquid steel have been investigated.

FT-IR Characterization of High Surface Area Silicon Nitride and Carbide

The surface chemistry of SiC and Si3N4 prepared by laser-driven gas-phase reactions has been characterized by transmission/absorption FT-IR spectroscopy. Different surface sites, such as surface silanols, silyl amino- and imido- groups, alkyl groups, silane bonds, surface carbonyls and siloxanes bridges have been evidenced. Their amounts depend on surface treatments: evacuation, oxidation, surface nitridation.

Influence of boron nitride and carbon additives on the behaviour of sintered AlN in a steel-making environment

In an earlier work we showed that the corrosion of pure aluminium nitride by steels takes place via an attack on the grain boundary Al/O/N phases and through AlN decomposition, with oxidation of aluminium by the dissolved oxygen. To reduce this type of corrosion, we tried to remove alumina and Al/O/N phases from the grain boundary by adding to the initial powders a small quantity of BN or carbon. The quantity of added BN must be in strict accordance with the quantity necessary to clean the grain boundaries. Best results were obtained with 10 wt% of BN. Carbon addition, which helps to improve the thermal shock resistance as well, produces the same result, but through a different mechanism. Best results were obtained with quantities between 5 and 10 wt% of carbon.

Fourier-transform infrared characterization of an aluminium nitride surface

In order to identify the structure of the surface of AIN, an infrared study was conducted. AIN powder was thermally treated either under vacuum or under controlled atmospheres using probe molecules at different temperatures. The surface presented OH and NH groups originating from the hydrolysis of Al—N bonds as well as Al3+ Lewis-acid sites (Al3+ ions in both tetrahedral and octahedral coordination). Some Al—H bonds were also present.

FT-IR study of CH3OH adsorption on chlorinated γ-aluminas

Abstract In a previous paper, the surfaces of as-received or Cl—treated aluminas were studied. In this work, the action of CH3OH molecules on pure or Cl- treated alumina was analyzed using FT-IR spectrometry. The methoxylation of all surfaces was observed through the presence of OCH3 linked to AlVI or AlIV. Above 470 K, the methoxy group tended to disappear and a new species, formate, was found. The positions of v(CH3) frequencies depended on the production process of alumina powders as well as on their treatment. The modification of the evolution into formate at the different surfaces was discussed.

Lattice vibrations and bulk properties of ceramics-forming materials: Piezoeffect in SiC and elasticity of ZrO2

The role of lattice vibrations in the crystal properties related to the homogeneous strains is discussed. Such properties depend on the individual phonon characteristics measurable by vibrational spectroscopy. So, being applicable to powderlike samples, it can provide an indirect information on those bulk characteristics which cannot be directly measured for such samples. The piezoelectricity of cubic SiC, and the elasticity of tetragonal ZrO2 are considered along with the phonon spectra. Thus the mechanism of the polarization of sphalerite-like materials is elucidated; a contradiction between the elastic properties of the t-ZrO2 lattice and the conventional interpretation of its Raman spectra is revealed.

Surface oxidation of high-surface-area silicon carbide: FT-IR studies

The surface of ultrafine silicon carbide powders, prepared by a laser-driven gas-phase reaction was studied as a self-supporting disk by FT infrared spectrometry. After evacuation silicon and carbon atoms located at the surface give rise tovSiH andvCH bands. When heating in oxygen, subtraction spectra showed features which could be strictly correlated with a progressive growth of a silica layer: SiH and CH bands were replaced by new bands characteristic of amorphous silica and the typical band of surface silanol groups on silica (3745 cm−1) simultaneously increased.