Infiltration of Al2O3/Y2O3 mix into SiC ceramic preforms

Silicon carbide ceramics are very interesting materials to engineering applications because of their properties. These ceramics are produced by liquid phase sintering (LPS), where elevated temperature and time are necessary, and generally form volatile products that promote defects and damage their mechanical properties. In this work was studied the infiltration process to produce SiC ceramics, using shorter time and temperature than LPS, thereby reducing the undesirable chemical reactions. SiC powder was pressed at 300 MPa and pre-sintered at 1550 degrees C for 30 min. Unidirectional and spontaneous infiltration of this preform by Al2O3/Y2O3 liquid was done at 1850 degrees C for 5, 10, 30 and 60 min. The kinetics of infiltration was studied, and the infiltration equilibrium happened when the liquid infiltrated 12 mm into perform. The microstructures show grains of the SiC surrounded by infiltrated additives. The hardness and fracture toughness are similar to conventional SiC ceramics obtained by LPS. (c) 2007 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

Manufacture of ceramic membranes for application in demulsification process for cross-flow microfiltration

This paper describes the manufacture of tubular ceramic membranes and the study of their performance in the demulsification of soybean oil/water emulsions. The membranes were made by iso-static pressing method and micro and macro structurally characterized by SEM, porosimetry by mercury intrusion and determination of apparent density and porosity. The microfiltration tests were realized on an experimental workbench, and fluid dynamic parameters, such as transmembrane flux and pressure were used to evaluate the process relative to the oil phase concentration (analysed by TOC measurements) in the permeate. The results showed that the membrane with pores` average diameter of 1.36 mu m achieved higher transmembrane flux than the membrane with pores` average diameter of 0.8 mu m. The volume of open pores (responsible for the permeation) was predominant in the total porosity, which was higher than 50% for all tested membranes. Concerning demulsification, the monolayer membranes were efficacious, as the rejection coefficient was higher than 99%.

Manufacture and characterization of ultra and microfiltration ceramic membranes by isostatic pressing

This paper describes the manufacture of tubular UF and MF porous and supported ceramic membranes to oil/water emulsions demulsification. For such a purpose, a rigorous control was realized over the distribution and size of pores. Suspensions at 30 vol.% of solids (zirconia or alumina powder and sucrose) and 70 vol.% of liquids (isopropyl alcohol and PVB) were prepared in a jar mill varying the milling time of the sucrose particles, according to the pores size expected. The membranes were prepared by isostatic pressing method and structurally characterized by SEM, porosimetry by mercury intrusion and measurements of weight by immersion. The morphological characterization of the membranes identified the formation of porous zirconia and alumina membranes and supported membranes. The results of porosimetry analysis by mercury intrusion presented an average pore size of 1.8 mu m for the microfiltration porous membranes and for the ultrafiltration supported membranes, pores with average size of 0.01-0.03 mu m in the top-layer and 1.8 mu m in the support. By means of the manufacture method applied, it was possible to produce ultra and microfiltration membranes with high potential to be applied to the separation of oil/water emulsions. (C) 2011 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

Mechanical and tribological properties of a sintered glass-ceramic compared to granite and porcelainized stoneware

Mechanical and tribological properties of a partially crystallized sintered glass-ceramic were compared to two commercial floor tiles: black granite and porcelainized stoneware. Mechanical properties, hardness and elastic modulus were evaluated by instrumented indentation. Friction coefficient and wear characterization were evaluated using a reciprocating ball-on-flat tribometer in two controlled environments: air with relative humidity of 53% and under running water at 23 degrees C. The sintered glass-ceramic and porcelainized stoneware presented similar mechanical and tribological properties. Regarding the mechanical and tribological properties, the results suggest that this glass-ceramic is suitable to be used as industrial tile. (C) 2011 Elsevier B.V. All rights reserved.

Residual stresses in titanium nitride thin films obtained with step variation of substrate bias voltage during deposition

In this work, a series of depositions of titanium nitride (TiN) films on M2 and D2 steel substrates were conducted in a Triode Magnetron Sputtering chamber. The temperature; gas flow and pressure were kept constant during each run. The substrate bias was either decreased or increased in a sequence of steps. Residual stress measurements were later conducted through the grazing X-ray diffraction method. Different incident angles were used in order to change the penetration depth and to obtain values of residual stress at different film depths. A model described by Dolle was adapted as an attempt to calculate the values of residual stress at each incident angle as a function of the value from each individual layer. Stress results indicated that the decrease in bias voltage during the deposition has produced compressive residual stress gradients through the film thickness. On the other hand, much less pronounced gradients were found in one of the films deposited with increasing bias voltage. (C) 2010 Elsevier B.V. All rights reserved.

Residual stresses in TiN, DLC and MoS(2) coated surfaces with regard to their tribological fracture behaviour

Thin hard coatings on components and tools are used increasingly due to the rapid development in deposition techniques, tribological performance and application skills. The residual stresses in a coated surface are crucial for its tribological performance. Compressive residual stresses in PVD deposited TiN and DLC coatings were measured to be in the range of 0.03-4 GPa on steel substrate and 0.1-1.3 GPa on silicon. MoS(2) coatings had tensional stresses in the range of 0.8-1.3 on steel and 0.16 GPa compressive stresses on silicon. The fracture pattern of coatings deposited on steel substrate were analysed both in bend testing and scratch testing. A micro-scale finite element method (FEM) modelling and stress simulation of a 2 mu m TiN-coated steel surface was carried out and showed a reduction of the generated tensile buckling stresses in front of the sliding tip when compressive residual stresses of 1 GPa were included in the model. However, this reduction is not similarly observed in the scratch groove behind the tip, possibly due to sliding contact-induced stress relaxation. Scratch and bending tests allowed calculation of the fracture toughness of the three coated surfaces, based on both empirical crack pattern observations and FEM stress calculation, which resulted in highest values for TiN coating followed by MoS(2) and DLC coatings, being K(C) = 4-11, about 2, and 1-2 MPa M(1/2), respectively. Higher compressive residual stresses in the coating and higher elastic modulus of the coating correlated to increased fracture toughness of the coated surface. (C) 2009 Elsevier B.V. All rights reserved.

High temperature flexural strength and fracture toughness of AlN with Y(2)O(3) ceramic

The effects of temperature on the fast fracture behavior of aluminum nitride with 5 wt% Y(2)O(3) ceramic were investigated. Four-point flexural strength and fracture toughness were measured in air at several temperatures (30-1,300 A degrees C). The flexural strength gradually decreased with the increase of temperature up to 1,000 A degrees C due to the change in the fracture mode from transgranular to intergranular, and then became almost constant up to 1,300 A degrees C. Two main flaw types as fracture origin were identified: small surface flaw and large pores. The volume fraction of the large pores was only 0.01%; however, they limited the strength on about 50% of the specimens. The fracture toughness decreased slightly up to 800 A degrees C controlled by the elastic modulus change, and then decreased significantly at 1,000 A degrees C due to the decrease in the grain-boundary toughness. Above 1,000 A degrees C, the fracture toughness increased significantly, and at 1,300 A degrees C, its value was close to that measured at room temperature.

The Penicillium chrysogenum aclA gene encodes a broad-substrate-specificity acyl-coenzyme A ligase involved in activation of adipic acid, a side-chain precursor for cephem antibiotics

Activation of the cephalosporin side-chain precursor to the corresponding CoA-thioester is an essential step for its incorporation into the P-lactam backbone. To identify an acyl-CoA ligase involved in activation of adipate, we searched in the genome database of Penicillium chrysogenum for putative structural genes encoding acyl-CoA ligases. Chemostat-based transcriptome analysis was used to identify the one presenting the highest expression level when cells were grown in the presence of adipate. Deletion of the gene renamed aclA, led to a 32% decreased specific rate of adipate consumption and a threefold reduction of adipoyl-6-aminopenicillanic acid levels, but did not affect penicillin V production. After overexpression in Escherichia coli, the purified protein was shown to have a broad substrate range including adipate. Finally, protein-fusion with cyan-fluorescent protein showed co-localization with microbody-borne acyl-transferase. Identification and functional characterization of aclA may aid in developing future metabolic engineering strategies for improving the production of different cephalosporins. (C) 2009 Elsevier Inc. All rights reserved.

Influence of substrate surface topography in the deposition of nanostructured diamond-like carbon films by high density plasma chemical vapor deposition

In this work, we have studied the influence of the substrate surface condition on the roughness and the structure of the nanostructured DLC films deposited by High Density Plasma Chemical Vapor Deposition. Four methods were used to modify the silicon wafers surface before starting the deposition processes of the nanostructured DLC films: micro-diamond powder dispersion, micro-graphite powder dispersion, and roughness generation by wet chemical etching and roughness generation by plasma etching. The reference wafer was only submitted to a chemical cleaning. It was possible to see that the final roughness and the sp(3) hybridization degree strongly depend on the substrate surface conditions. The surface roughness was observed by AFM and SEM and the hybridization degree of the DLC films was analyzed by Raman Spectroscopy. In these samples, the final roughness and the sp(3) hybridization quantity depend strongly on the substrate surface condition. Thus, the effects of the substrate surface on the DLC film structure were confirmed. These phenomena can be explained by the fact that the locally higher surface energy and the sharp edges may induce local defects promoting the nanostructured characteristics in the DLC films. (C) 2008 Elsevier B.V. All rights reserved.

Effects of mechanical properties, residual stress and indenter tip geometry on instrumented indentation data in thin films

In this work, an axisymmetric two-dimensional finite element model was developed to simulate instrumented indentation testing of thin ceramic films deposited onto hard steel substrates. The level of film residual stress (sigma(r)), the film elastic modulus (E) and the film work hardening exponent (n) were varied to analyze their effects on indentation data. These numerical results were used to analyze experimental data that were obtained with titanium nitride coated specimens, in which the substrate bias applied during deposition was modified to obtain films with different levels of sigma(r). Good qualitative correlation was obtained when numerical and experimental results were compared, as long as all film properties are considered in the analyses, and not only sigma(r). The numerical analyses were also used to further understand the effect of sigma(r) on the mechanical properties calculated based on instrumented indentation data. In this case, the hardness values obtained based on real or calculated contact areas are similar only when sink-in occurs, i.e. with high n or high ratio VIE, where Y is the yield strength of the film. In an additional analysis, four ratios (R/h(max)) between indenter tip radius and maximum penetration depth were simulated to analyze the combined effects of R and sigma(r) on the indentation load-displacement curves. In this case, or did not significantly affect the load curve exponent, which was affected only by the indenter tip radius. On the other hand, the proportional curvature coefficient was significantly affected by sigma(r) and n. (C) 2010 Elsevier B.V. All rights reserved.

Transport Barkhausen-like noise in uniaxially pressed Bi(1.65)Pb(0.35)Sr(2)Ca(2)Cu(3)O(10+delta) ceramic samples

We report on the detection of the transport Barkhausen-like noise (TBN) in polycrystalline samples of Bi(1.65)Pb(0.35)Sr(2)Ca(2) Cu(3)O(10+delta) (Bi-2223) which were subjected to different uniaxial compacting pressures. The transport Barkhausen-like noise was measured when the sample was subjected to an ac triangular-shape magnetic field (f similar to 1 Hz) with maximum amplitude B(max) approximate to 5.5 mT, in order to avoid the flux penetration within the superconducting grains. Analysis of the TBN signal, measured for several values of excitation current density, indicated that the applied magnetic field in which the noise signal first appears, B(a)(t(i)), is closely related to the magnetic-flux pinning capability of the material. The combined results are consistent with the existence of three different superconducting levels within the samples: (i) the superconducting grains; (ii) the superconducting clusters; and (iii) the weak-links. We finally argue that TBN measurements constitute a powerful tool for probing features of the intergranular transport properties in polycrystalline samples of high-T(c) superconductors. (C) 2010 Elsevier B.V. All rights reserved.

Experimental and theoretical study of transport properties in uniaxially pressed (Bi, Pb)(2)Sr(2)Ca(2)Cu(3)O(10+delta) ceramic samples

Experimental and theoretical studies on the magnetic field dependence of the electrical resistance R(B(a)) and the transport noise (TN) in polycrystalline high-T(c) superconductors subjected to different uniaxial compacting pressures were conducted. X-ray diffraction rocking curves were performed in different surfaces of the samples in order to investigated the degree of texture The results indicated an improvement of the degree of texture with increasing the uniaxial compacting pressure In theoretical simulations of the data, the polycrystalline superconductors were described as a series-parallel array of Josephson devices The intergranular magnetic field is described within the framework of the intragranular flux-trapping model and the distribution of the grain-boundary angles is assumed to follow the Rayleigh statistical function The proposed model describes well the experimental magnetoresistance R(B(a)) data We have found that the behavior of the R(B(a)) curves changes appreciably when different uniaxially compacting pressures are applied to the sample and such a changes are reproduced by the model when different grain-boundary angles distributions are used In addition, changes in the R(B(a)) dependence have their counterparts in the experimental transport noise signals (C) 2009 Elsevier B.V. All rights reserved

Pheromone paths attached to the substrate in meliponine bees: helpful but not obligatory for recruitment success

In contrast to marking of the location of resources or sexual partners using single-spot pheromone sources, pheromone paths attached to the substrate and assisting orientation are rarely found among flying organisms. However, they do exist in meliponine bees (Apidae, Apinae, Meliponini), commonly known as stingless bees, which represent a group of important pollinators in tropical forests. Worker bees of several Neotropical meliponine species, especially in the genus Scaptotrigona Moure 1942, deposit pheromone paths on substrates between highly profitable resources and their nest. In contrast to past results and claims, we find that these pheromone paths are not an indispensable condition for successful recruitment but rather a means to increase the success of recruiters in persuading their nestmates to forage food at a particular location. Our results are relevant to a speciation theory in scent path-laying meliponine bees, such as Scaptotrigona. In addition, the finding that pheromone path-laying bees are able to recruit to food locations even across barriers such as large bodies of water affects tropical pollination ecology and theories on the evolution of resource communication in insect societies with a flying worker caste.

The effect of a novel crystallised bioactive glass-ceramic powder on dentine hypersensitivity: a long-term clinical study

P>The aim of this comparative clinical study was to evaluate a novel bioactive glass-ceramic (Biosilicate (R) 1-20 mu m particles) to treat dentine hypersensitivity (DH). Volunteers (n = 120 patients/ 230 teeth) received the following treatments: G1-Sensodyne (R), G2-SensiKill (R), G3-Biosilicate (R) incorporated in a 1% water-free-gel and G4-Biosilicate (R) mixed with distilled water at 1:10 ratio. G1 and G3 were applied at home, daily for 30 days; G2 and G4 were applied once a week by a dentist (four applications). A visual analogue scale (VAS) was employed to evaluate pain for each quadrant in one sensitive tooth at baseline, weekly during treatment and during a 6-month follow-up period. Dentine hypersensitivity values (G1/n = 52), (G2/n = 62), (G3/n = 59) and (G4/n = 59) were analysed with Kruskal-Wallis/Dunn tests. All the products were efficient in reducing DH after 4 weeks. Among the four materials tested, G4 demonstrated the best clinical performance and provided the fastest treatment to reduce DH pain. Distilled water proved to be an adequate vehicle to disperse Biosilicate (R). Low DH scores were maintained during the 6-month follow-up period. The hypothesis that the novel bioactive glass-ceramic may be an efficient treatment for DH was confirmed.

Substrate-inhibited kinetics with catalyst deactivation in an isothermal CSTR

Analytical expressions are developed for the time-dependent reactant concentration and catalyst activity in an isothermal CSTR with Langmuir-Hinshelwood kinetics of deactivation and reaction. Several parallel and series posioning mechanisms are considered for a reactor which, without poisoning, would operate at a unique steady state. The use of matched asymptotic expansions and abandonment of the usual initial-steady-state assumption give results, valid from startup to final loss of activity, whose accuracy can be improved systematically.