三元共晶成分Al2O3/YAG/ZrO2粉体及陶瓷的制备与组织性能研究

本文采用醇水共沉淀法制备了三元共晶成分Al₂O₃/YAG/ZrO₂粉体,在600-1350_oC温度范围煅烧后研究其物相转变过程。经1300_oC煅烧后Al₂O₃/YAG/ZrO₂共晶成分粉体的物相由α-Al₂O₃、c-ZrO₂和YAG构成,且具有α-Al₂O₃相包裹c-ZrO₂相的特殊结构。将煅烧粉体在1550_oC下热压烧结,制备具有内晶型结构的共晶成分Al₂O₃/YAG/ZrO₂复相陶瓷,其致密度、室温抗弯强度、断裂韧性和高温(1000_oC)抗弯强度分别为98.8%、420 MPa、3.69 MPa.m_1/2和464 MPa,并对复相陶瓷组织结构的形成机理进行了探讨。     

Classification of moroccan olive cultivars by linear discriminant analysis applied to ATR–FTIR spectra of endocarps

The potential of FTIR combined with chemometrics was studied to classify five Moroccan varieties of olives by analysis on the endocarps. Attenuated total reflectance (ATR) enabled the samples to be examined directly in the solid state. The spectral data were subjected to a preliminary derivative elaboration based on the Norris gap algorithm to reduce the noise and extract larger analytical information. Linear discriminant analysis (LDA) was adopted as classification method, and Principle component analysis (PCA) was employed to compress the original data set into a reduced new set of variables before LDA. The calibration set was built by using the IR data from seventy‐five samples scanned in reflectance mode, and the ranges 3000–2400 and 2300–600 cm^?1 were selected because furnishing the most useful analytical information. PCA allowed clustering the samples in five classes by using the first two principal components with an explained variance of 98.16%. Application of LDA on an external test set of twenty‐five samples enabled to classify them into five variety groups with a correct classification of 92.0%.     

Electrical Resistivity Behavior and VRH Transport Mechanism in Semiconducting La0.6Sr0.4Mn1−2x Fe x Cr x O3 (0.10≤x≤0.25) Manganites

The transport properties and conduction mechanism in La_0.6Sr_0.4Mn_1?2x Fe _x Cr _x O₃ (0≤x≤0.3) have been investigated. The undoped samples show metal–semiconductor transition with a peak of resistivity at a temperature T _P , whereas for all doped compounds the semiconducting behavior persists in the whole temperature range. The insertion of Cr³⁺ and Fe³⁺ ions leads to the increase of resistivity because the simultaneous substitution of Fe³⁺ and Cr³⁺ for Mn³⁺ reduces the number of available hopping sites for the Mn e _g↑ electron and suppresses the double-exchange mechanism. It was found that the transport mechanism for substituted samples is dominated by the variable range hopping of small polarons between localized states in a model where the various parameters estimated from Mott’s relation obey the variable range hopping (VRH) mechanism.     

New oligomeric containing aliphatic moiety phthalonitrile resins: their mechanical and thermal properties in presence of silane surface-modified zirconia nanoparticles

This study deals with the influences of both the length of the aliphatic spacer within the phthalonitrile monomers backbones, and the amount of the silane surface modified zirconia nanoparticles on the mechanical and thermal properties of the so-called second generation phthalonitrile resins. Investigation on the curing behavior under differential scanning calorimeter outlined an important gain in the processability as the aliphatic spacer became longer. Results from the mechanical tests revealed that changing the length of the aliphatic spacer affects the mechanical properties in different ways. For instance, as the aliphatic spacer became longer, the toughness state was enhanced. At the same time, the tensile modulus and stress as well as the microhardness values were slightly reduced. It was also noticed that the introduction of the reinforcing phase caused an increase in all the tested mechanical properties. Furthermore, results from the thermogravimetric analysis and dynamic mechanical analysis revealed that reducing the length of the aliphatic spacer and adding nanofillers caused an increase in the thermal stability, storage modulus, and glass transition temperature. Moreover, a morphological study has been conducted under scanning electron microscope and transmission electron microscope to put in light the mechanisms of enhancements. Finally, this study demonstrated that the excellent properties of the phthalonitrile resins can be tailored by two ways either by monomers design or by inorganic nanoparticles reinforcement.     

Hydromagnetic stagnation point flow by a perturbation technique

An analysis is performed to study the momentum, heat and mass transfer characteristics of MHD natural convection flow and heat generating/absorbing fluid at the stagnation point of an isothermal two-dimensional porous body immersed in a fluid saturated porous medium. The results are obtained by solving the coupled non-linear partial differential equations describing the conservation of mass, momentum and energy by a perturbation technique [A. Aziz, T.Y. Na, Perturbation Methods in Heat Transfer, Springer-Verlag, Berlin, 1984 (pp. 1–184), R. Kenneth Cramer, Shih-I Pai, Magnetofluid Dynamics for Engineers and Applied Physicists, McGraw-Hill Book Company, New York, 1973 (pp. 164–171).]. These results are presented to illustrate the influence of the Hartmann number, Prandtl number, and dimensionless heat generation/absorption coefficient and suction injection parameter. Numerical results for the dimensionless velocity profiles, the temperature profiles, the local friction coefficient and the local Nusselt number are presented for various parameters. These effects of the different parameters on the velocity and temperature as well as the skin friction and wall heat transfer are presented graphically.     

Bioactive injectable triple acting thermosensitive hydrogel enriched with nano-hydroxyapatite for bone regeneration: in-vitro characterization,Saos-2 cell line cell viability and osteogenic markers evaluation

Hydrogels forming in-situ have gained great attention in the area of bone tissue engineering recently, they were also showed to be a good and less invasive alternative to surgically applied ones. The primal focus of this study was to prepare chitosan-glycerol phosphate thermosensitive hydrogel formed in-situ and loaded with risedronate (bone resorption inhibitor) in an easy way with no requirement of complicated processes or large number of equipment. Then we investigated its effectiveness for bone regeneration. In-situ forming hydrogels were prepared using chitosan cross-linked with glycerol phosphate and loaded with risedronate and nano-hydroxyapatite as bone cement. The prepared hydrogels were characterized by analyzing their gelation time at 37?°C, % porosity, swelling index, in-vitro degradation, rheological properties, and in-vitro drug release. Results showed that the in-situ hydrogels prepared using 2.5% (w/v) chitosan cross-linked with 50% (w/v) glycerol phosphate in the ratio (9:1, v/v) reinforced with 20?mg/mL and nano-hydroxyapatite possessed the most sustained drug release profile. This optimized formulation was further evaluated using DSC and FTIR studies, in addition to their morphological properties using scanning electron microscopy. The effect on Saos-2 cell line viability was evaluated also using MTT assay on the optimized hydrogel formulation in addition to their action on cell proliferation using fluorescence microscope. Moreover, calcium deposition on the hydrogel and alkaline phosphatase activity were evaluated. Risedronate-nano-hydroxyapatite loaded hydrogels significantly enhanced the Saos-2 cell proliferation in addition to enhanced alkaline phosphatase activity and calcium deposition. Such results suggest that risedronate-nano-hydroxyapatite loaded hydrogels present great biocompatibility for bone regeneration. Proliferation of cells, as well as deposition of mineral on the hydrogel, was an evidence of the biocompatible nature of the hydrogel. This hydrogel formed in-situ present a good less invasive alternative for bone tissue engineering.     

Coupled approach for flatness prediction in cold rolling of thin strip

The paper presents a predictive model of the flatness defects, which appear during rolling of thin plates, the origin of which is the roll stack thermo-elastic deformation. The combination of the elastic deflection, the thermal crown and the roll grinding crown results in a non-parallel bite, and if the deformed roll transverse profile is not an affinity of the incoming strip profile, differential elongation results and induces high stresses in the outgoing strip. The latter, combined with the imposed strip tension force, result in a net post-bite stress field which may be sufficiently compressive locally to promote buckling. A variety of non-developable shapes may result, generally occurring as waviness (centre waves, wavy edges, quarter-buckles, etc.). This problem is most of the time addressed in a decoupled way, i.e. as a post-processing of the residual stresses computed by a strip rolling model; the present paper on the contrary describes a fully coupled approach of in-bite plastic deformation and post-bite buckling. For this purpose, a simple buckling criterion has been introduced in a FEM model of strip and roll deformation, Lam3/Tec3; its implementation is documented in details. The capabilities and limits of the present approach are described and discussed. Characterised by its coupled approach, it is primarily devoted to cases where on-line (under tension) manifested defects occur. It is shown that the impact of the post-bite, post-buckled stress field on the in-bite stress and strain fields is quite small in the cases investigated; however, subtle changes appear in the velocity field at bite exit, and this is sufficient to transform completely the post-bite stress field, which is found in much better agreement with measurements if such a coupled treatment is used.     

Effect of Nanoparticles on the Hysteresis Loop in Mixed Convection within a Two-Sided Lid-Driven Inclined Cavity Filled with a Nanofluid

The present work deals with numerical modeling of mixed convection flow in a two-sided lid driven inclined square enclosure filled with water-Al₂O₃ nanofluid. The limiting cases of a cavity heated from below and cooled from above and the one differentially heated are recovered respectively for inclination angles 0° and 90°. The moving walls of the cavity are pulled in opposite directions with the same velocity and maintained at constant but different temperatures while the remaining walls are kept insulated. The numerical resolution of the studied problem is based on the lattice Boltzmann method. A parametric study is conducted and a set of graphical results is presented and discussed to illustrate the effects of the presence of nanoparticles and enclosure inclination angle on fluid flow and heat transfer characteristics. The governing parameters of this problem are the Richardson number (varied from 0.1 to 10⁶), the nanoparticles volume fraction (varied from 0 to 0.04) and the inclination angle (varied from 0° to 180°). The critical conditions leading to the transition from monocellular flow to multicellular flow and vice versa are determined. In the common ranges of Richardson number and inclination angle where both monocellular and tri-cellular patterns coexist, the heat transfer is seen to be strongly reduced by the latter.     

Detection of Olive Oil Adulteration Using FT-IR Spectroscopy and PLS with Variable Importance of Projection (VIP) Scores

Determination of adulteration and authenticity of extra virgin olive oil (EVOO) was investigated by means of infrared spectroscopy and chemometric methods. The study was focused on the detection and quantification of extra virgin olive oil adulteration by soybean (SB) and sunflower (SF) oils using FT-IR spectroscopy based on the use of PLS modeling and variable importance of projection (VIP) scores. A PLS model, using orthogonal signal correction and mean centering data pretreatments, and VIP scores variable preselection, was able to predict the concentration of sunflower and soybean oil adulterants in the 1–24 % weight ratio range with relative prediction errors lower than 3 % (w/w), for external validation samples. Moreover, the PLS-DA (discriminant analysis) model using the same preselected wavelengths was able to explain 99.9 % of variance and to predict with 100 % accuracy both classes of adulteration (EVOO–SB and EVOO–SF) in the external validation.     

Assessment of Trace Elements in Soils and Mine Water Surrounding a Closed Manganese Mine (Anti Atlas,Morocco)

Five mine water samples, 23 topsoil samples, and four mine waste (tailings) samples were collected to assess the effects of a closed Moroccan Mn mine. Based on the pH, electrical conductivity, and concentrations of sulphate, Cu, Zn, As, Cd, Pb, and Mn, mining has not adversely influenced mine water quality. Soil samples were analyzed for 23 chemical elements and the results were interpreted by univariate and multivariate statistical techniques. Based on an enrichment factor (EF) calculation, only Cd, As, V, and Mn were selected for further study. Geochemical background (GB) and geoaccumulation index (I_geo) were determined for these elements to differentiate between geogenic and anthropogenic enrichment. The GB values showed that the Tiwiyyine soils contained a high geogenic content of Cd, As, V, and Mn that reflected the geochemistry of the parental rocks in this mineralized region. The I_geo calculation revealed that these soils were moderately influenced by anthropogenic activity, which had increased the concentrations of those elements. Finally, geochemical maps revealed that mining was likely responsible for the anthropogenic soil pollution.