New transesterification between ester and alkoxysilane groups: application to ethylene-co-vinyl acetate copolymer crosslinking

The transesterification between ester and alkoxysilane groups in the range of temperatures 100-250 °C takes place only in the presence of dibutyltin oxide (DBTO) as efficient catalyst. Without DBTO, no reaction is observed. This interchange reaction has been used to crosslink ethylene-co-vinylacetate copolymer. Kinetic and rheology data have shown that only two alkoxide groups from one tetrafunctional alkoxysilane molecule are involved in the crosslinking reaction.     

Imbalance diets in preschool children: study in a day-care center in the Province of Buenos Aires,Argentina

The purpose of this study was to investigate the impact of low fat diets in children aged 2 to 5. Eighty two children (40 females and 42 males) attending a school cafeteria (Province of Buenos Aires, Argentina), in a cross sectional study, were evaluated. Body weight (W), height (H) and body composition (BC) by bioimpedance were recorded. The anthropometric raw data were processed as Z-score of the weight-for-age (WEZ) and of the height-for-age (HAZ). Serum insulin-like growth factor 1 (IGF-1) and Zinc/haemoglobin ratio (Zn/Hb) were also measured. Results showed that 73.2% of the children were adequate (A) according WEZ, 13.4% were lean (L) and 13.4% overweight (O). 8.5% presented simultaneously impairment in WEZ and HAZ. Body fat percentage and energy metabolism were higher in O than in L and A (p < 0.05). Serum IGF-1's children--aged 4 to 5 years--with HAZ deficit were low than adequate HAZ ones. No statistical differences in Zn/Hb ratio between A, L and O were found. This cross sectional study suggests metabolic disorders in young children attending school cafeterias. These conclusions will allow to design balanced diets in order to optimize the resources, promote optimal growth and development and prevent adult diseases through dietary practices in childhood.     

The effect of grazing intensity and the presence of a forage legume on nitrogen dynamics in Brachiaria pastures in the Atlantic forest region of the south of Bahia, Brazil

It has been shown that with careful grazing management and addition of Pand K, but not N, fertilisers Brachiaria pastures are ableto maintain sustainable live weight gains over many years. However, standardon-farm practice, which generally involves high stocking rates, leads after afew years to pasture decline due mainly to N deficiency for grass regrowth. Togenerate an understanding of the mechanism of pasture decline and possiblemanagement options to mitigate this process, a study was performed in theAtlantic forest region of the south of Bahia state to study the N dynamics inpastures of Brachiaria humidicola subject to threedifferent stocking rates of beef cattle, with and without the presence of theforage legume Desmodium ovalifolium. Despite the fact thatthe C:N ratio of the deposited litter was high (60 to 70) the rate ofdecomposition was very rapid (k –0.07 gg^–1 day^–1) and annual rates of Nturnover through the litter pathway were between 105 and 170 kg Nha^–1 year^–1. In the grass-onlypasturesas stocking rate increased from 2 to 3 head ha^–1, N recycledinthe litter decreased by 11%, but a further increase to 4 headha^–1 decreased N recycling by 30% suggesting thatbeyonda certain critical level higher grazing stocking rates would lead to pasturedecline if there was no N addition. High stocking rates decreased theproportionof the legume in the sward, but at all rates the concentration of N in both thegreen and dead grass in the forage on offer and in the litter was higher in themixed sward. The presence of the legume caused a decrease in the C:N ratio ofthe microbial biomass while both soil N mineralisation and nitrificationincreased. This increased rate of turnover of the microbial biomass and thecontribution of N₂ fixation to the legume resulted in largeincreasesin the N recycled via litter deposition ranging from 42 to 155 kg Nha^–1 year^–1.     

Synthesis, Characterization, and Processing of Cordierite-Glass Particles Modified by Coating with an Alumina Precursor

The surfaces of cordierite and glass particles were modified by coating them with an alumina precursor using a precipitation process in the presence of urea. Scanning electron microscopy (SEM), high-resolution transmission electron microscopy, X-ray diffraction, electrophoresis, and rheological measurements were used to characterize the coated powders. SEM and transmission electron microscopy morphologies of the coated powders revealed that amorphous and homogeneous coatings have been formed around the particles. The morphology of the coated powders showed a coiled wormlike surface. The coating Al₂O₃ layer dominated the surface properties of the coated glass and cordierite powders. The influence of the coating layer on the processing ability of cordierite-based glass-ceramics substrates by tape casting was studied in aqueous media. It could be concluded that the coating of the powders facilitates the processing and yields green and sintered tapes with denser, more homogeneous microstructures compared with the uncoated powders.     

Hydroxyapatite coating on selectively passivated and sensitively polymer-protected surgical grade stainless steel

Surgical grade stainless steel (316L SS) is a widely used implant material in orthopedic surgeries. However, the release of metallic ions evidenced from the 316L SS implants in vivo conditions is a big challenge. In order to minimize the release of metallic ions, coating the 316L SS implant with a biocompatible material like hydroxyapatite [HAP, Ca₁₀(PO₄)₆(OH)₂] is one of the suitable methods. In this paper, the hydroxyapatite coating on borate passivated through poly-ortho-phenylenediamine (PoPD)-coated 316L SS by a dip coating method has been reported. The coatings were characterized by electrochemical techniques such as potentiodynamic polarization, electrochemical impedance spectroscopy, and cyclic voltammetry. Surface characterization studies of the coatings such as X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM) were also carried out. The leach out characteristics of the coatings was determined at the impressed potential. The mechanical property of the coatings was evaluated by Vicker’s microhardness test. The Cr-rich passive film formed underneath the PoPD layer showed a higher protective efficiency. The ability to form apatite on the post-passivated PoPD-coated 316L SS specimen was examined by immersing it in the simulated body fluid. The enhanced corrosion resistivity of the HAP coating on the post-passivated PoPD-coated 316L SS was due to an effective barrier of PoPD followed by the passive film underneath the PoPD.     

The effect of the nature of vanadium species on benzene total oxidation

The nature of the vanadium species present on V₂O₅/Al₂O₃ catalysts was investigated by using solid state ⁵¹V NMR, diffuse reflectance spectroscopy (DRS), X-ray diffraction (XRD) and temperature programmed reduction (TPR). ⁵¹V NMR and DRS analyses indicated the presence of V⁵⁺ in tetrahedral symmetry at low vanadium loading. A surface polymeric vanadium species and/or the bulk crystalline V₂O₅ were mainly observed at high vanadium loading as also detected by XRD. The positions of the absorption edges determined through the UV–VIS spectra allowed distinguishing between various tetrahedral symmetries. After TPR, the average oxidation state of vanadium depended on the vanadium content. The nature of vanadium species was related to the catalyst behavior on the benzene oxidation reaction. The catalysts containing high vanadium content were more active suggesting that a high amount of V⁴⁺ is responsible for the higher activity.     

Composition and behaviour of cerium films on galvanised steel

The composition and corrosion performance of galvanised steel treated by immersion in cerium nitrate solution was investigated by electrochemical techniques and surface analysis. The surface film consists of a mixture of Ce(III) and Ce(IV) compounds, being very rich in Ce(III) in the first instants of the deposition process and becoming gradually enriched in the more oxidised form, Ce(IV). The presence of this film on the surface hinders the corrosion reaction by reducing the rate of both the cathodic and the anodic reactions. The film becomes thicker but more uneven when the time of film growth increases, with the development of defects in the film, which in contact with electrolyte behaves anodic with respect to the covered areas of the surface. These thicker films have revealed lower resistance to corrosion initiation.     

Chitosan Microspheres as Carriers for pH‐Indicating Species in Corrosion Sensing

Chitosan microspheres containing bromocresol green, cresol red, and phenolphthalein for corrosion detection, through pH change, are synthesized in order to be used in protective coatings for aluminium alloys. Microspheres containing corrosion detection species are characterized morphologically (SEM) and physico‐chemically (FTIR, TGA). Release studies (UV–vis) are performed in corrosion‐promoting conditions (pH, NaCl), and detection studies by immersion in media associated with corrosion activity while microspheres' sensing activity is evaluated visually. Electrochemical characterization of AA2024 substrates in the presence of chitosan spheres is performed to understand material performance, and a color change is observed as a result of local pH increase in cathodic areas when corrosion takes place. These findings can be correlated with the results from release studies and seem a promising approach for corrosion sensing purposes, not only because pH increase is possible to detect due to corrosion, but also because chitosan is considered an environmentally friendly material.     

Design and synthesis of foam glasses from recycled materials

Recycling has emerged as an environmental key point due to the diminishing of natural resources and the generation of ever-increasing amounts of industrial solid wastes. Glass wastes are among the materials that attract great interest in the recycling concept. This work presents the results of foams production from four series of compositions. The first series comprises powders of a sodium-calcium-silicate sheet glass cullet as the main component, an alkali-earth aluminosilicate glass as an additive, and a reagent grade silicon carbide (SiC) powder as gassing agent. In the second series, the glass cullet was used in combination with fly ashes (FLA) as main components, while SiC waste from abrasive paper served as foaming agent. In the third and fourth series, carbonates (calcite and dolomite) were used for foaming powder mixtures composed of sheet glass cullet and FLA, and powdered cathode ray tube panel glasses, respectively. All the processing parameters, including the main components, the nature and content of foaming agents are shown to play a crucial role on the foaming ability and final properties of the glass foams.     

Microstructure and mechanical properties of Al2O3/ZrO2 composites by two-step sintering

Composites of Al₂O₃/ZrO₂ (containing 25, 50, and 75 vol% ZrO₂) were prepared by mixing Al₂O₃ and ZrO₂ suspensions. The microstructural control via two-step sintering (TSS) was the main objective of this work. For this purpose, different sintering curves were constructed, aiming to achieve the best temperature combination for the sintering steps that provides higher density and finer microstructure. The results were compared with single-step sintering (SSS). Furthermore, microhardness and fracture toughness were measured for the best TSS specimens under each composition. The results showed that the high densities were obtained, and the reduction of grain size was greater than 40% for two-step sintered specimens, compared to SSS ones. Consequently, microhardness values increased. However, fracture toughness values remained unchanged.