Chromic materials for responsive surface-enhanced resonance Raman scattering systems: a nanometric pH sensor

The use of chromic materials for responsive surface-enhanced resonance Raman scattering (SERRS) based nanosensors is reported. The potential of nano-chromic SERRS is demonstrated with the use of the halochrome methyl yellow to fabricate an ultrasensitive pH optical sensor. Some of the challenges of the incorporation of chromic materials with metal nanostructures are addressed through the use of computational calculations and a comparison to measured SERRS and surface-enhanced Raman scattering (SERS) spectra is presented. A strong correlation between the measured SERRS and the medium's proton concentration is demonstrated for the pH range 2-6. The high sensitivity achieved by the use of resonance Raman conditions is shown through responsive SERRS measurements from only femtolitres of volume and with the concentration of the reporting molecules approaching the single molecule regime.

Evaluation of Several Carbon-Supported Nanostructured Ni-Doped Manganese Oxide Materials for the Electrochemical Reduction of Oxygen

Physical and electrochemical properties of nanostructured Ni-doped manganese oxides (MnO(x)) catalysts supported on different carbon powder substrates were investigated so as to characterize any carbon substrate effect toward the oxygen reduction reaction (ORR) kinetics in alkaline medium. These NiMnO(x)/C materials were characterized using physicochemical analyses. Small insertion of Ni atoms in the MnO(x) lattice was observed, which consists of a true doping of the manganese oxide phase. The corresponding NiMnO(x) phase is present in the form of needles or agglomerates, with crystallite sizes in the order of 1.5-6.7 nm (from x-ray diffraction analyses). Layered manganite (MnOOH) phase has been detected for the Monarch 1000-supported NiMnO(x) material, while different species of MnO(x) phases are present at the E350G and MM225 carbons. Electrochemical studies in thin porous coating active layers in the rotating ring-disk electrode setup revealed that the MnO(x) catalysts present better ORR kinetics and electrochemical stability upon Ni doping. The ORR follows the so-called peroxide mechanism on MnO(x)/C catalysts, with the occurrence of minority HO(2)(-) disproportionation reaction. The HO(2)(-) disproportionation reaction progressively increases with the Ni content in NiMnO(x) materials. The catalysts supported on the MM225 and E350G carbons promote faster disproportionation reaction, thus leading to an overall four-electron ORR pathway. (C) 2011 The Electrochemical Society. [DOI: 10.1149/1.3528439] All rights reserved.

Evaluation of grinding methods for pellets preparation aiming at the analysis of plant materials by laser induced breakdown spectrometry

It has been demonstrated that laser induced breakdown spectrometry (LIBS) can be used as an alternative method for the determination of macro (P, K. Ca, Mg) and micronutrients (B, Fe, Cu, Mn, Zn) in pellets of plant materials. However, information is required regarding the sample preparation for plant analysis by LIBS. In this work, methods involving cryogenic grinding and planetary ball milling were evaluated for leaves comminution before pellets preparation. The particle sizes were associated to chemical sample properties such as fiber and cellulose contents, as well as to pellets porosity and density. The pellets were ablated at 30 different sites by applying 25 laser pulses per site (Nd:YAG@1064 nm, 5 ns, 10 Hz, 25J cm(-2)). The plasma emission collected by lenses was directed through an optical fiber towards a high resolution echelle spectrometer equipped with an ICCD. Delay time and integration time gate were fixed at 2.0 and 4.5 mu s, respectively. Experiments carried out with pellets of sugarcane, orange tree and soy leaves showed a significant effect of the plant species for choosing the most appropriate grinding conditions. By using ball milling with agate materials, 20 min grinding for orange tree and soy, and 60 min for sugarcane leaves led to particle size distributions generally lower than 75 mu m. Cryogenic grinding yielded similar particle size distributions after 10 min for orange tree, 20 min for soy and 30 min for sugarcane leaves. There was up to 50% emission signal enhancement on LIBS measurements for most elements by improving particle size distribution and consequently the pellet porosity. (C) 2011 Elsevier B.V. All rights reserved.

Comparison of univariate and multivariate calibration for the determination of micronutrients in pellets of plant materials by laser induced breakdown spectrometry

The application of laser induced breakdown spectrometry (LIBS) aiming the direct analysis of plant materials is a great challenge that still needs efforts for its development and validation. In this way, a series of experimental approaches has been carried out in order to show that LIBS can be used as an alternative method to wet acid digestions based methods for analysis of agricultural and environmental samples. The large amount of information provided by LIBS spectra for these complex samples increases the difficulties for selecting the most appropriated wavelengths for each analyte. Some applications have suggested that improvements in both accuracy and precision can be achieved by the application of multivariate calibration in LIBS data when compared to the univariate regression developed with line emission intensities. In the present work, the performance of univariate and multivariate calibration, based on partial least squares regression (PLSR), was compared for analysis of pellets of plant materials made from an appropriate mixture of cryogenically ground samples with cellulose as the binding agent. The development of a specific PLSR model for each analyte and the selection of spectral regions containing only lines of the analyte of interest were the best conditions for the analysis. In this particular application, these models showed a similar performance. but PLSR seemed to be more robust due to a lower occurrence of outliers in comparison to the univariate method. Data suggests that efforts dealing with sample presentation and fitness of standards for LIBS analysis must be done in order to fulfill the boundary conditions for matrix independent development and validation. (C) 2009 Elsevier B.V. All rights reserved.

Simultaneous optimization by neuro-genetic approach for analysis of plant materials by laser induced breakdown spectroscopy

A simultaneous optimization strategy based on a neuro-genetic approach is proposed for selection of laser induced breakdown spectroscopy operational conditions for the simultaneous determination of macronutrients (Ca, Mg and P), micro-nutrients (B, Cu, Fe, Mn and Zn), Al and Si in plant samples. A laser induced breakdown spectroscopy system equipped with a 10 Hz Q-switched Nd:YAG laser (12 ns, 532 nm, 140 mJ) and an Echelle spectrometer with intensified coupled-charge device was used. Integration time gate, delay time, amplification gain and number of pulses were optimized. Pellets of spinach leaves (NIST 1570a) were employed as laboratory samples. In order to find a model that could correlate laser induced breakdown spectroscopy operational conditions with compromised high peak areas of all elements simultaneously, a Bayesian Regularized Artificial Neural Network approach was employed. Subsequently, a genetic algorithm was applied to find optimal conditions for the neural network model, in an approach called neuro-genetic, A single laser induced breakdown spectroscopy working condition that maximizes peak areas of all elements simultaneously, was obtained with the following optimized parameters: 9.0 mu s integration time gate, 1.1 mu s delay time, 225 (a.u.) amplification gain and 30 accumulated laser pulses. The proposed approach is a useful and a suitable tool for the optimization process of such a complex analytical problem. (C) 2009 Elsevier B.V. All rights reserved.

Evaluation of laser induced breakdown spectroscopy for the determination of micronutrients in plant materials

Laser induced breakdown spectroscopy (LIBS) has been evaluated for the determination of micronutrients (B, Cu, Fe, Mn and Zn) in pellets of plant materials, using NIST, BCR and GBW biological certified reference materials for analytical calibration. Pellets of approximately 2 mm thick and 15 mm diameter were prepared by transferring 0.5 g of powdered material to a 15 mm die set and applying 8.0 tons cm(-2). An experimental setup was designed by using a Nd:YAG laser operating at 1064 nm (200 mJ per pulse, 10 Hz) and an Echelle spectrometer with ICCD detector. Repeatability precision varied from 4 to 30% from measurements obtained in 10 different positions (8 laser shots per test portion) in the same sample pellet. Limits of detection were appropriate for routine analysis of plant materials and were 2.2 mg kg(-1) B, 3.0 mg kg(-1) Cu, 3.6 mg kg(-1) Fe, 1.8 mg kg(-1) Mn and 1.2 mg kg(-1) Zn. Analysis of different plant samples were carried out by LIBS and results were compared with those obtained by ICP OES after wet acid decomposition. (C) 2009 Elsevier B.V. All rights reserved.

Evaluation of laser induced breakdown spectroscopy for the determination of macronutrients in plant materials

Laser induced breakdown spectroscopy (LIBS) has become an analytical tool for the direct analysis of a large variety of materials in order to provide qualitative and/or quantitative information. However, there is a lack of information for LIBS analysis of agricultural and environmental samples. In this work a LIBS system has been evaluated for the determination of macronutrients (P, K, Ca, Mg) in pellets of vegetal reference materials. An experimental setup was designed by using a Nd:YAG laser operating at 1064 nm and an Echelle spectrometer with ICCD detector. The plasma temperature was estimated by Boltzmann plots and instrumental paragmeters such as delay time, lens-to-sample distance and pulse energy were evaluated. Certified reference materials as well as reference materials were used for analytical calibrations of P, K, Ca, and Mg. Most results of the direct analysis of plant samples by LIBS were in reasonable agreement with those obtained by ICP OES after wet acid decomposition. (C) 2008 Elsevier B.V. All rights reserved.

Composite materials obtained from textile fiber residue

This article presents the use of fibers residue from textile industry to minimize environmental problems associated with material accumulation. Composite materials utilizing textile fiber residues and high density polyethylene were prepared. Effect of treatment with hot water on fibers to prepare composites was studied to provide an improvement in mechanical properties of these materials. This treatment on fibers was evaluated by X-ray diffraction and scanning electron microscopy techniques. Experimental results of mechanical properties indicated higher mechanical strength for treated fiber composites compared to the untreated fiber composites.

Magnetization studies of binary and ternary Co-rich phases of the Co-Si-B system

CoB, CO(2)B, CoSi, Co(2)Si and CO(5)Si(2)B phases can be formed during heat-treatment of amorphous co-Si-B soft magnetic materials. Thus, it is important to determine their magnetic behavior as a function of applied field and temperature. In this study, polycrystalline single-phase samples of the above phases were produced via arc melting and heat-treatment under argon. The single-phase nature of the samples was confirmed via X-ray diffraction experiments. AC and DC magnetization measurements showed that Co(2)Si and CO(5)Si(2)B phases are paramagnetic. Minor amounts of either Co(2)Si or CoSi(2) in the CoSi-phase sample suggested a paramagnetic behavior of the CoSi-phase, however, it should be diamagnetic as shown in the literature. The diamagnetic behavior of the CoB phase was also confirmed. The paramagnetic behavior of CO(5)Si(2)B is for the first time reported. The magnetization results of the phase CO(2)B have a ferromagnetic signature already verified on previous NMR studies. A detailed set of magnetization measurements of this phase showed a change of the easy magnetization axis starting at 70K, with a temperature interval of about 13K at a very small field of 1 mT. As the strength of the field is increased the temperature interval is enlarged. The strength of field at which the magnetization saturates increases almost linearly as the temperature is increased above 70K. The room temperature total magnetostriction of the CO(2)B phase was determined to be 8 ppm at a field of 1T. (C) 2010 Elsevier B.V. All rights reserved.

Magnetic characterization of Mn(5)SiB(2) and Mn(5)Si(3) phases

In this work the Mn(5)Si(3) and Mn(5)SiB(2) phases were produced via arc melting and heat treatment at 1000 degrees C for 50 h under argon. A detailed microstructure characterization indicated the formation of single-phase Mn(5)Si(3) and near single-phase Mn(5)SiB(2) microstructures. The magnetic behavior of the Mn(5)Si(3) phase was investigated and the results are in agreement with previous data from the literature, which indicates the existence of two anti-ferromagnetic structures for temperatures below 98 K. The Mn(5)SiB(2) phase shows a ferromagnetic behavior presenting a saturation magnetization M(s) of about 5.35 x 10(5) A/m (0.67 T) at room temperature and an estimated Curie temperature between 470 and 490 K. In addition, AC susceptibility data indicates no evidence of any other magnetic ordering in 4-300 K temperature range. The magnetization values are smaller than that calculated using the magnetic moment from previous literature NMR results. This result suggests a probable ferrimagnetic arrangement of the Mn moments. (C) 2009 Elsevier B. V. All rights reserved.

Magnetostriction of Fe-Sn polycrystalline alloys

In the present work we study the magnetostriction of Fe(91)Sn(9) and Fe(80)Sn(20) polycrystalline samples produced by arc melting and heat treated at temperatures of 1153 K for 6 h and 1023 K for 24 h, looking for high values of magnetostriction as in Fe-Ga alloys. Magnetostriction, as well as saturation magnetization measurements, was carried out at temperatures close to 203 K in the magnetic field interval 0 to 1.5 T. Results of magnetostriction on sample Fe(91)Sn(9), which has almost pure alpha-phase, show magnitude and behavior similar to pure Fe. The two additional Fe(80)Sn(20) samples have a combination of alpha-phase plus either Fe(5)Sn(3) or Fe(3)Sn(2) and show a peculiar behavior of the magnetostriction for mu(0)H < 0.3 T the magnetostriction grows from zero to saturation of the alpha-phase. Following, for mu(0)H > 0.3 T, the magnetostriction starts again to grow linearly with the field, but saturation was not observed up to 5 T. This behavior was attributed to the presence of Fe(5)Sn(3) or Fe(3)Sn(2) phases in these samples that are also ferromagnetic as the alpha-phase is. (c) 2008 Elsevier B.V. All rights reserved.

Experimental analysis of active-passive vibration control using viscoelastic materials and extension and shear piezoelectric actuators

Hybrid active-passive damping treatments combine the reliability, low cost and robustness of viscoelastic damping treatments and the high-performance, modal selective and adaptive piezoelectric active control. Numerous hybrid damping treatments have been reported in the literature. They differ mainly by the relative positions of viscoelastic treatments, sensors and piezoelectric actuators. In this work we present an experimental analysis of three active-passive damping design configurations applied to a cantilever beam. In particular, two design configurations based on the extension mode of piezoelectric actuators combined with viscoelastic constrained layer damping treatments and one design configuration with shear piezoelectric actuators embedded in a sandwich beam with viscoelastic core are analyzed. For comparison purposes, a purely active design configuration with an extension piezoelectric actuator bonded to an elastic beam is also analyzed. The active-passive damping performance of the four design configurations is compared. Results show that active-passive design configurations provide more reliable and wider-range damping performance than the purely active configuration.

Non-linear boundary element formulation with tangent operator to analyse crack propagation in quasi-brittle materials

This work deals with analysis of cracked structures using BEM. Two formulations to analyse the crack growth process in quasi-brittle materials are discussed. They are based on the dual formulation of BEM where two different integral equations are employed along the opposite sides of the crack surface. The first presented formulation uses the concept of constant operator, in which the corrections of the nonlinear process are made only by applying appropriate tractions along the crack surfaces. The second presented BEM formulation to analyse crack growth problems is an implicit technique based on the use of a consistent tangent operator. This formulation is accurate, stable and always requires much less iterations to reach the equilibrium within a given load increment in comparison with the classical approach. Comparison examples of classical problem of crack growth are shown to illustrate the performance of the two formulations. (C) 2009 Elsevier Ltd. All rights reserved.

Analytical formulae for electromechanical effective properties of 3-1 longitudinally porous piezoelectric materials

A unidirectional fiber composite is considered here, the fibers of which are empty cylindrical holes periodically distributed in a transversely isotropic piezoelectric matrix, The empty-fiber cross-section is circular and the periodicity is the same in two directions at an angle pi/2 or pi/3. Closed-form formulae for all electromechanical effective properties of these 3-1 longitudinally periodic porous piezoelectric materials are presented. The derivation of such expressions is based on the asymptotic homogenization method as a limit of the effective properties of two-phase transversely isotropic parallel fiber-reinforced composites when the fibers properties tend to zero. The plane effective coefficients satisfy the corresponding Schulgasser-Benveniste-Dvorak universal type of relations, A new relation among the antiplane effective constants from the solutions of two antiplane strains and potential local problems is found. This relation is valid for arbitrary shapes of the empty-fiber cross-sections. Based on such a relation, and using recent numerical results for isotropic conductive composites, the antiplane effective properties are computed for different geometrical shapes of the empty-fiber cross-section. Comparisons with other analytical and numerical theories are presented. (c) 2008 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Sorption aspects for unconsolidated materials of the Sao Carlos region (SP), Brazil

The transport of liquid and gaseous pollutants through porous geological media depends on the physical and chemical characteristics of the unconsolidated material, rocks and water associated with the characteristics of the pollutants. Of these characteristics, the sorption aspect is of fundamental importance and is a function of the mineral proportions, pH, Eh and void aspects encountered in the porous media. In the Sao Carlos region, located in the eastern-central part of the 9 ate of Sao Paulo, Brazil, there are basically two types of unconsolidated materials: the first is a residual from sandstones cemented with fines and the secondarily composed of claystones, siltstones and conglomerates from the Cretaceous Period that constitute the Itaqueri Formation; the second is a sandy sediment of the Tertiary Period. These geological conditions are found in areas where chemical products are disposed of characterized as either diffuse or point pollutions sources. Because of this situation, a study was developed to evaluate the sorption aspects of some inorganic cations that are frequently found in these sources, in varied concentrations. Taken into consideration were their physical/chemical properties, such as: specific weight, grain size, mineralogy, cationic exchange capacity, pH, hydraulic conductivity. Batch tests were run using solutions of KCl, ZnCl(2) and CuCl center dot H(2)O at three different pH values, and then with a combined solution (KCl + ZnCl(2) + CuCl center dot H(2)O), also at three different pH values.