Commercial bentonites as detoxifier of broiler feed contaminated with aflatoxin

Some bentonites have been probed to be efficient as sequestering agents for aflatoxins; they decreased the bioavailability of the toxin in the gastrointestinal tracts of birds when they are incorporated in the diets. The binding capacity of these adsorbents varied with the rheological source and even among batches of a given source. Three bentonites from different sources in Argentina, which have very different aflatoxins (AFs) adsorption capacity, were studied. The characterization comprises chemical analysis, scanning electron microscopy (SEM), X-ray power diffraction (XRD), Hg intrusion porosimetry, swelling capacity, etc. The main factors affecting the adsorption of AFs seem to be related to the isomorphic substitution of the montmorillonite and to electrostatic interactions generated by the surface charge of the samples. Neither the mean pore size nor the percentage of quartz has any effect upon the AFs adsorption.     

Compressive behaviors and energy-absorption properties of an open-celled porous Cu fabricated by replication of NaCl space-holders

An open-celled porous Cu has been successfully fabricated by replication of NaCl space-holders. Detailed investigations on the quasi-static uniaxial compressive behaviors indicate that compressive stress-strain curves of the present porous Cu are directly related to the porosity, but less dependent on the strain rate. It has also been found that layer-by-layer collapse is the predominant compressive deformation mechanism of the present porous Cu. Studies on energy-absorption properties indicate that the porous Cu specimens with different porosities show different variation tendencies with the change of strain.     

Rates of alkoxylation and hydrolysis of alkoxyl groups on silica surfaces

The rate of reactions on silica surfaces was investigatedfor the alkoxylation and hydrolysis of alkoxyl groups. Silica gel particles were contacted with vapors of several alcohols and water in a flow-type reactor at various temperatures. The surface concentrations of alkoxyl groups were measured by thermogravimetric analyses to determine the rates of reactions. The apparent rate constants could be calculated by applying the progressivereaction model. The apparent rates based on the total number of surface groups were determined for alkoxylation reactions. Among the alcohols investigated, alkoxylation with methanol showed the smallest activation energy and the largest rate constant. The rates of hydrolysis of alkoxyl groups were also measured on samples which had been alkoxylatedto about 10% of the initial surface groups. The activation energy of hydrolysis was almost constant for all alkoxyl groups. However, the hydrolysis of methoxy groups showed the largest rate constant. The influence of preheating treatment on the rate of alkoxylation was examined for the reaction with 1-butanol. Even when the reaction temperature was the same, the rate constant increased with increasing preheating temperature. The increase in the rate constant could be attributed to the increase in the frequency factor, since the preheating treatment increased the activation energy.     

A superhard diamond-like carbon film

A superhard hydrogen-free amorphous diamond-like carbon (DLC) film was deposited by pulsed arc discharge using a carbon source accelerator in a vacuum of 2×10⁻⁴ Pa. The growth rate was about 15 nm/min and the optimum ion-plasma energy was about 70 eV. The impact of doping elements (Cu, Zr, Ti, Al, F(Cl), N) on the characteristics of DLC films deposited on metal and silicon substrates was studied aiming at the choice of the optimum coating for low friction couples. The microhardness of thick (≥20 μm) DLC films was studied by Knoop and Vickers indentations, medium thick DLC films (1–3 μm) were investigated using a ‘Fischerscope’, and Young's module of thin films (20–70 nm) was studied by laser induced surface acoustic waves. The bonds in DLC films were investigated by electron energy loss spectroscopy (EELS), X-ray excited Auger electron spectroscopy (XAES), and X-ray photoelectron spectroscopy (XPS). The adhesion of DLC films was defined by the scratch test and Rockwell indentation. The coefficient of friction of the Patinor DLC film was measured by a rubbing cylinders test and by a pin-on-disk test in laboratory air at about 20% humidity and room temperature. The microhardness of the Patinor DLC film was up to 100 GPa and the density of the film was 3.43–3.65 g/cm³. The specific wear rate of the Patinor DLC film is comparable to that of other carbon films.     

The effect of acids and bases on the dispersion and stabilization of ceramic particles in ethanol

The dispersion and stability of alumina, titania, and silicon carbide powders in ethanolic medium have been investigated. An operational pH-scale, pH*, based on an ethanol-based reference electrode, was used to systematize the suspension properties. The electrokinetic behavior was determined as a function of pH*. The isoelectric points in ethanol — pH¹_iep(SiC)=7.5; pH¹_iep(Al₂O₃)=4.4 and pH¹_iep(TiO₂)=4.2 — were discussed in relation to the dissociation constants of the charge determining reactions at the powder surfaces. We have evaluated the long-term stability of the ethanolic dispersions through settling studies which showed that the primary particle size could be retained for extended times providing that the surface potential and ionic strength were optimized.     

Enhanced visible light photocatalytic activity of Zn2SnO4 via sulfur anion-doping

Sulfur anion doped Zn₂SnO₄ was prepared by calcining the mixture of thiourea and spinel Zn₂SnO₄ at 300 °C under argon atmosphere and characterized by XRD, XPS and DRS. It was found that S^2? was incorporated interstitially into the bulk phase of Zn₂SnO₄. After the doping of S^2?, the band gap of Zn₂SnO₄ was sharply decreased to 2.7 eV compared with that of undoped Zn₂SnO₄ (~ 3.6 eV). The photocatalytic activity of S-doped Zn₂SnO₄ was enhanced for photodegradation of Rhodamine B (RhB) in aqueous solution under visible light irradiation.     

Changes in appearance and natural microflora on iceberg lettuce treated in warm,chlorinated water and then stored at refrigeration temperature

The objective of this study was to determine the effect of warm, chlorinated water on the survival and subsequent growth of naturally occurring microorganisms and visual quality of fresh-cut iceberg lettuce. After dipping cut lettuce leaves in water containing 20 mg l⁻¹free chlorine for 90 s at 50°C, samples were stored at 5 or 15°C for up to 18 or 7 days, respectively. Populations of aerobic mesophiles, psychrotrophs, Enterobacteriaceae, lactic acid bacteria, and yeasts and molds were determined. The visual appearance and development of brown discoloration were monitored. Treatment of lettuce in warm (50°C) chlorinated water delayed browning of lettuce. Shelf life of lettuce stored at 5°C, as determined by subjective evaluation of color and general appearance, was about 5 days longer than that of lettuce stored at 15°C. Treatment in warm (50°) water, with or without 20 mg l⁻¹chlorine, and in chlorinated water at 20°C significantly (α= 0·05) reduced the initial population of mesophilic aerobic microflora by 1·73–1·96 log₁₀cfu g⁻¹. Populations increased, regardless of treatment, as storage time at 5°C and 15°C increased. The same trends were observed in populations of psychrotrophs and Enterobacteriaceae. Yeast populations increased slightly in lettuce stored at 5°C but were consistently about 3 logs lower than mesophilic aerobes. Populations of molds and lactic acid bacteria were less than 2 log₁₀cfu g⁻¹throughout storage at 5 or 15°C. Results suggest that heat (50°C) treatment may have delayed browning and reduced initial populations of some groups of micro-organisms naturally occurring on iceberg lettuce, but enhanced microbial growth during subsequent storage.