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Biomedical subjects

J Yvon

Publications and source records attributed to J Yvon.

7 recordsLinked to original sources
PubMed2005

Assessment of the surface areas of silica and clay in acid-leached clay materials using concepts of adsorption on heterogeneous surfaces.

Two clays of the areas of Kaélé and Kousseri (extreme North Cameroon) containing mainly smectites and minor amounts of kaolinite were activated with sulfuric acid (1 to 8 N). Crystal-chemical properties were studied using X-ray diffraction, Fourier transform infrared spectroscopy, and chemical analysis, while textural properties were analyzed by step-by-step nitrogen adsorption at 77 K and low-pressure quasi-equilibrium argon adsorption at 77 K. As is generally observed, smectite is more sensitive to acid leaching than kaolinite. As a result of smectite decomposition, amorphous Al-containing silica forms, leading to an increase in the specific surface area of the leached materials. The content of the clay minerals and amorphous silica can be estimated on the basis of changes in the chemical composition of the samples upon acid leaching. As far as adsorption energy distributions derived from low-pressure argon derivative adsorption isotherms are concerned, the main modifications occur when 1 N sulfuric acid is used, due to the replacement of calcium and sodium compensating cations by protons. When higher acid concentrations are used, variations in adsorption energy distribution can be assigned to the presence of amorphous silica. It was possible to model experimental adsorption energy distributions as weighted sums of argon adsorption energy distributions obtained on (i) 1 N samples representing protonated clays and (ii) a silica gel used as a reference aluminous silica. Using such an approach, increasing acid concentration results in an increase in the surface area of silica, whereas the surface area of the remaining clay minerals remains roughly constant.

Adsorption↗
PubMed2004

Trace element carriers in combined sewer during dry and wet weather: an electron microscope investigation.

The nature of trace element carriers contained in sewage and combined sewer overflow (CSO) was investigated by TEM-EDX-Electron diffraction and SEM-EDX. During dry weather, chalcophile elements were found to accumulate in sewer sediments as early diagenetic sulfide phases. The sulfurization of some metal alloys was also evidenced. Other heavy metal carriers detected in sewage include metal alloys, some iron oxihydroxide phases and neoformed phosphate minerals such as anapaite. During rain events, the detailed characterization of individual mineral species allowed to differentiate the contributions from various specific sources. Metal plating particles, barite from automobile brake, or rare earth oxides from catalytic exhaust pipes, originate from road runoff, whereas PbSn alloys and lead carbonates are attributed to zinc-works from roofs and paint from building siding. Soil contribution can be traced by the presence of clay minerals, iron oxihydroxides, zircons and rare earth phosphates. However, the most abundant heavy metal carriers in CSO samples were the sulfide particles eroded from sewer sediments. The evolution of relative abundances of trace element carriers during a single storm event, suggests that the pollution due to the "first flush" effect principally results from the sewer stock of sulfides and previously deposited metal alloys, rather than from urban surface runoff.

Aluminum Silicates↗
PubMed2001

Ferric chloride and lime conditioning of activated sludges: an electron microscopic study on resin-embedded samples.

Ferric chloride and lime conditioning of sewage sludge is usually interpreted in terms of enhanced aggregation of sludge components. In this study, transmission electron microscopy was used to investigate the conditioning mechanism at a submicronic scale. Samples were collected from two municipal wastewater treatment plants at different stages of the process, embedded in an epoxy resin, and sectioned with an ultramicrotome. Transmission electron microscopy examination of thin sections revealed that clumps of crystalloids develop on external surfaces of flocs after the application of both conditioners. This precipitate creates a rigid structure around the flocs which, upon mechanical dewatering, transmits the stresses applied to the inner parts of flocs. The porous structure of the precipitate may also participate to the withdrawal of water as a draining media. Energy dispersive X-ray spectroscopy revealed that Fe, P, and Ca are the dominant elements in the precipitate with Fe/P and Fe/Ca elemental ratios close to 2.8-3 and 1.1-3, respectively.

Calcium↗
PubMed1995

Dental abnormalities and early diagnosis of hyperphosphatasemia.

Dental hard tissue abnormalities have never been described as part of the symptoms associated with hyperphosphatasemia. Fourteen teeth obtained from a young man, who had a mild form of hyperphosphatasemia, were analyzed using scanning electron microscopy (SEM), secondary ion mass spectroscopy (SIMS), X-ray diffraction (XRD), and infrared (IR) spectroscopy. SEM revealed a thin enamel, presenting a prismatic structure with many pits, and atypical cementum and dentin showing numerous resorption areas. The X-ray diffractograms revealed poorly crystalline hydroxyapatite associated with alpha-tricalcium phosphate and magnesium hydroxide phases. SIMS data showed high Ca concentrations: 40.5 weight % ¿wt%; standard deviation (SD = 0.13) and 42.5 wt% (SD = 1.03) in enamel and dentin respectively, and high Ca/P weight ratios: 2.28 in the enamel, 2.65 in the dentin. The lack of crystallinity may be linked to the high content of proteins and magnesium adsorbed onto apatite. This study demonstrates the need for thorough radiographical and biological investigations for skeletal abnormalities, even in the absence of systemic symptoms, when generalized dental abnormalities of both enamel and dentin are observed.

Adult↗
PubMed1994

Shear bond strength of a light-cured resin composite vs. dentin characteristics.

OBJECTIVES: The aim of this work was to determine if any significant correlation can be found between dentin characteristics and the shear bond strength of a bonded resin composite. METHODS: The number of tubules, the diameter of tubules, the real dentin surface (RDS), the Vickers hardness (VHN), and the Ca and P concentrations ([Ca] and [P]) were measured. Two commercial bonding systems, the All-Bond 2 (Bisco) and Scotchbond 2 (3M Dental Products), were tested on 70 extracted human molars purposely abraded and polished. Experimental results were statistically analyzed. RESULTS: The average bond strength ranged from 9.1 +/- 5.3 MPa (All-Bond 2) to 3.2 +/- 1.9 MPa (Scotchbond 2). Only the Bisco adhesive gave rise to cohesive dentin fractures. The Vickers hardness depended on both the real dentin surface and the calcium concentration according to the empirical law: VHN = 0.753 RDS + 0.320 [Ca] - 16.330. The shear bond strength does not depend on the measured dentin characteristics. SIGNIFICANCE: Under these testing conditions, the nature of the surface composite determined the adhesion; the properties of the dentin substrate were of minor importance.

Adhesiveness↗