P. Quintana

Preparation and characterization of MgO powders obtained from different magnesium salts and the mineral dolomite

Abstract The characterisation of the physical properties of MgO powders, obtained from three commercial magnesium compounds, MgSO 4 ·7H 2 O, MgNO 3 ·6H 2 O and Mg(CH 3 CO 2 ) 2 ·4H 2 O and the mineral dolomite (natural source from Mexico), synthesised by chemical precipitation, is presented. The decomposition of the precipitated Mg(OH) 2 was analysed by DTA/TGA and the crystallisation process was observed by XRD. The variation of the properties with the nature of the precursors at 960°C was studied: as the crystallite size, density, specific surface area, degree of agglomeration, and the total porosity. The microstructural differences between the MgO agglomerates were examined by SEM, at different temperatures.

Corrosion resistance and microstructure of electrodeposited Zn and Zn alloy coatings

The nature of electrodeposited zinc coating corrosion inhibition by alloying with Fe group metals is not fully understood, because it depends on several factors including the microstructure. The crystallographic texture and lattice cell parameters were determined for nonchromated Zn, Zn-Co, Zn-Fe and Zn-Ni coatings, deposited from alkaline baths, and the results have been used to explain the observed differences in their corrosion behaviour in aerated chloride solutions and in neutral salt spray tests. The presence of Ni or Co in the zinc matrix increases the Zn coating corrosion resistance, while Fe has no effect. It has been suggested that the lower Zn-Ni alloy corrosion rate is due to the predominant presence in this layer of crystallographic planes with a higher packing density. The lower Zn-Co alloy corrosion rate compared with that of Zn and Zn-Fe has been associated with the lower values of its lattice cell parameter c/a (axial ratio).

Formation of the band gap energy on CdS thin films growth by two different techniques

Abstract The band gap formation during the first stages of growth of CdS thin films, deposited on glass substrates by chemical bath deposition (CBD) and close spaced sublimation (CSS) techniques was studied. To obtain the first stages of growth, we used deposition times between 5 and 40 min for CBD films, and 4–60 s for CSS films. CBD technique with two chemical bath agitation modalities — the traditional magnetic agitation and ultrasonic vibration — was used for film preparation. Morphological, structural, optical, and stoichiometrical results were obtained on each CdS films group. Higher values of the band gap energy (3.2 eV) were obtained for the thinnest films (2–3 nm) by CBD with ultrasonic vibration; others films, showed similar band gap energy values to those reported for polycrystalline CdS films (2.42 eV). Energy vs. α2 curves, presented strong differences between the two deposition techniques used. The behavior of the optical window effects, the surface roughness, the structural results, and the films thickness related to the deposition techniques are discussed. The CBD technique with ultrasonic vibration produces films with cleaner surfaces, controlled thickness and better optical properties.

Comparison of properties of CdS thin films grown by two techniques

Abstract Polycrystalline cadmium sulfide (CdS) thin films were deposited on glass substrates by chemical bath deposition (CBD) and close-spaced sublimation (CSS) techniques. The typical deposition temperatures between these techniques are quite different. The CdS thin films deposited by CBD were prepared using two methods of bath agitation: magnetic and ultrasonic agitation. We found that films deposited with ultrasonic agitation presented a cleaner surface with minor presence of contaminants, similar to the obtained for CSS films, as demonstrated by Auger analysis. Properties of the CdS films such as morphology, optical transmission, crystallinity and band gap energy, are discussed in order to compare them in both techniques. We obtain that crystallinity of CdS films depends strongly on the temperature used for deposition. In agreement with several works, films prepared by CBD technique presented a cubic structure, while films grown by CSS technique exhibited an hexagonal symmetry.

Equation of motion of domain walls and equivalent circuits in soft ferromagnetic materials

The equation of motion for ferromagnetic domain walls is compared with initial permeability measurements of Co‐based soft ferromagnetic amorphous ribbons at frequencies in the range 100 Hz–13 MHz. The analysis of these results by complex permeability methods leads to an equivalent circuit formed by a parallel RL arrangement in series with a small resistance RW due to resistance of the measurement coil. This equivalent circuit, however, cannot model the irreversible magnetization behavior for fields higher than the pinning (or propagation) field. It is shown that the equation of motion is also consistent only with the reversible magnetization mechanism, if the displacement term, x, represents instead the bulging of the pinned wall. The correlations between the terms in the equation of motion and the elements of the equivalent circuit are established.

Effects of nanocrystallization upon the soft magnetic properties of Co‐based amorphous alloys

Amorphous samples of Vitrovac(R) 6025 metallic alloys were nanocrystallized by thermal annealing at temperatures in the range 576–716 K, well below the crystallization temperature (831 K, as obtained by differential scanning calorimetry at 20 K/min) and times in the range 10–90 min. Initial magnetic permeability exhibited a maximum of ∼109 000 (from ∼20 000 for the as‐quenched state) for annealing times of ∼15 min, and then a decrease toward a plateau value (30 000–40 000) for longer times. Domain wall relaxation frequency showed the opposite behavior, a minimum of ∼9 kHz (from 40 kHz for the as‐quenched value) for the permeability maximum, and then a stabilization at ∼15 kHz. Transmission electron microscopy observations confirmed that for annealing times up to 60 min., crystallite size is smaller than 30 nm. Permeability and relaxation frequency results are interpreted in terms of the dependence of wall bulging on anisotropy and free‐wall surface area between pinning sites.

Mechanism of copper patina formation in marine environments

Data analysis of the initial superficial layers of copper patina formed in several marine environments, using X-ray diffraction and cathodic reduction techniques, are presented. It was observed that cuprite phase decreases and the paratacamite phase increases, as corrosion develops on the surface of copper. The data presented show good agreement with previously published eletrochemical reactions of copper corrosion in marine environments.

Cobalt oxide films grown by a dipping sol-gel process

Cobalt oxide thin films were prepared by the dipping sol-gel process, using two different inorganic precursors: cobalt chloride and cobalt nitrate salts. Also, samples with a different number of dipping-annealing cycles (3, 5, and 7) where prepared. Composition, structure, surface morphology and optical properties of such films have been characterised by means of X-ray diffraction, differential thermogravimetric analysis (DTA), transmittance spectra and atomic force microscopy (AFM). The results show that starting from distinct precursors leads to different properties: film water contents, surface roughness, crystallite size, total film transmittance, absorption coefficient and refractive index. Absorption coefficients higher than 104 cm−1 where found for all the samples. Refractive indices vary from n ~ 1.9–2.8 in the near infrared region. Our study shows that using a relatively simple preparation method like the sol-gel process, cobalt oxide films with specific properties, can be made.

Antifungal Coatings Based on Ca(OH)2 Mixed with ZnO/TiO2 Nanomaterials for Protection of Limestone Monuments

The presence and deteriorating action of microbial biofilms on historic stone buildings have received considerable attention in the past few years. Among microorganisms, fungi are one of the most damaging groups. In the present work, antimicrobial surfaces were prepared using suspensions of Ca(OH)2 particles, mixed with ZnO or TiO2 nanoparticles. The antimicrobial surfaces were evaluated for their antifungal activity both in the dark and under simulated natural photoperiod cycles, using Penicillium oxalicum and Aspergillus niger as model organisms, and two limestone lithotypes commonly used in construction and as materials for the restoration of historic buildings. Both Ca(OH)2-ZnO and Ca(OH)2-TiO2 materials displayed antifungal activity: ZnO-based systems had the best antifungal properties, being effective both in the dark and under illumination. In contrast, TiO2-based coatings showed antifungal activity only under photoperiod conditions. Controls with coatings consisting of only Ca(OH)2 were readily colonized by both fungi. The antifungal activity was monitored by direct observation with microscope, X-ray diffraction (XRD), and scanning electron microscopy (SEM), and was found to be different for the two lithotypes, suggesting that the mineral grain distribution and porosity played a role in the activity. XRD was used to investigate the formation of biominerals as indicator of the fungal attack of the limestone materials, while SEM illustrated the influence of porosity of both the limestone material and the coatings on the fungal penetration into the limestone. The coated nanosystems based on Ca(OH)2-50%ZnO and pure zincite nanoparticulate films have promising performance on low porosity limestone, showing good antifungal properties against P. oxalicum and A. niger under simulated photoperiod conditions.

Treatment of Parkinson's disease: nanostructured sol-gel silica-dopamine reservoirs for controlled drug release in the central nervous system

Introduction We have evaluated the use of silica–dopamine reservoirs synthesized by the sol–gel approach with the aim of using them in the treatment of Parkinson’s disease, specifically as a device for the controlled release of dopamine in the striatum. Theoretical calculations illustrate that dopamine is expected to assume a planar structure and exhibit weak interactions with the silica surface. Methods Several samples were prepared by varying the wt% of dopamine added during the hydrolysis of tetraethyl orthosilicate. The silica–dopamine reservoirs were characterized by N2 adsorption, scanning and transmission electron microscopy, and Fourier transform infrared spectroscopy. The in vitro release profiles were determined using ultraviolet visible absorbance spectroscopy. The textural analyses showed a maximum value for the surface area of 620 m2/g nanostructured silica materials. The stability of dopamine in the silica network was confirmed by infrared and 13C-nuclear magnetic resonance spectroscopy. The reservoirs were evaluated by means of apomorphine-induced rotation behavior in hemiparkisonian rats. Results The in vitro dopamine delivery profiles indicate two regimes of release, a fast and sustained dopamine delivery was observed up to 24 hours, and after this time the rate of delivery became constant. Histologic analysis of formalin-fixed brains performed 24–32 weeks after reservoir implantation revealed that silica–dopamine implants had a reddish-brown color, suggesting the presence of oxidized dopamine, likely caused by the fixation procedure, while implants without dopamine were always translucent. Conclusion The major finding of the study was that intrastriatal silica–dopamine implants reversed the rotational asymmetry induced by apomorphine, a dopamine agonist, in hemiparkinsonian rats. No dyskinesias or other motor abnormalities were observed in animals implanted with silica or silica–dopamine.