Dilatometric behavior and microstructure of sintered Fe–NbC and Fe–TaC composites

Fe-reinforced composites were manufactured by the addition of 10–20 wt.% NbC or TaC particles aiming at improved mechanical and wear behavior. Two varieties of Fe powders from Hoeganaes Corp. were used, Ancorsteel 1000B and 45P. Composites produced using the former variety included a small amount of Fe₃P to induce liquid-phase sintering whereas 45P powder was pre-alloyed with P by the manufacturer. The hardness of the matrix was adjusted adding carbon to the composite mixture. The powders were milled for different times and annealed prior to pressing. A dilatometric study was carried out under hydrogen to establish optimum sintering profiles. Relative densities up to 97% TD were achieved. Both microstructure and density of the sintered pellets were evaluated in order to establish correlations involving composition, processing parameters and microstructure of the composite.     

Specific growth rate of sulfate reducing bacteria in the presence of manganese and cadmium

The development of technologies based on the use of sulfate-reducing bacteria (SRB) to treat sulfate contaminated wastewaters has produced a cost-effective route to precipitate metals. In this work the effects of cadmium and manganese in the SRB growth rates were assessed. It was observed that duplication time is 50h in the presence of cadmium and 6h in the presence of manganese, thus showing that the SRB growth rate was more affected by the presence of cadmium. A low sulfate reduction (maximum 25%) occurred which was sufficient for metal precipitation. The results are discussed considering their implications for metal precipitation in acid mining drainage.     

Application of liquid chromatography/quadrupole-linear Ion trap mass spectrometry and time-of-flight mass spectrometry to the determination of pharmaceuticals and related contaminants in wastewater

This paper describes an enhanced liquid chromatography-mass spectrometry (LC-MS) strategy for the analysis of a selected group of 56 organic pollutants in wastewater. This group comprises 38 pharmaceuticals and 10 of their most frequent metabolites, 6 pesticides, and 2 disinfectants. The LC-MS methodology applied is based in the use of a hybrid triple-quadrupole linear ion trap mass spectrometer (QTRAP) in combination with time-of-flight mass spectrometry (TOF-MS). The join application of both techniques provided very good results in terms of accurate quantification and unequivocal confirmation. Quantification was performed by LC-QTRAP-MS operating under selected reaction monitoring (SRM) mode in both positive and negative electrospray ionization. Unequivocal identification was provided by the acquisition of three SRM transitions per compound in most of the cases and by LC-TOF-MS analysis, which allows obtaining accurate mass measurements of the identified compounds with errors lower than 2 ppm. Additionally, the use of TOF-MS permits retrospective analysis, since the full spectrum is recorded at all times with a high sensitivity. Thus, review of recorded chromatograms looking for new compounds or transformation products suspected to be present in the samples is feasible allowing one to increase the scope of the method along the monitoring program. The analytical performance of the quantitative LC-QTRAP-MS method was evaluated in effluent wastewater samples. Linearity of response over 3 orders of magnitude was demonstrated for most compounds (R(2) > 0.99). Method limits of detection were between 0.04 and 50 ng L(-1). Finally, the methodology was successfully applied to a monitoring study intended to characterize wastewater effluents of six sewage treatment plants in Spain. The presence of most of compounds was detected at concentrations ranging from 9 ng L(-1) (atrazine) to 15 microg L(-1) (paraxanthine).     

Ultra-widely tunable long-period holey-fiber grating by the use of mechanical pressure

We report an ultra-widely tunable long-period holey-fiber grating, which combines the wide-range single-mode behavior and transverse strain sensitivity of the holey fibers with the advantages of mechanically induced long-period fiber gratings. We obtain a versatile widely tunable long-period holey-fiber grating with attractive transmission spectral characteristics for optical communications, fiber-based amplifiers, and lasers. The mechanically induced long-period holey-fiber grating shows a continuous tuning range over 500 nm, more than 12 dB depth notches with less than 0.75 dB out-of-band losses, and bandwidth control from 10 to 40 nm.     

Principal components analysis of the photoresponse nonuniformity of a matrix detector

The principal component analysis is used to identify and quantify spatial distributions of relative photoresponse as a function of the exposure time for a visible CCD array. The analysis shows a simple way to define an invariant photoresponse nonuniformity and compare it with the definition of this invariant pattern as the one obtained for long exposure times. Experimental data of radiant exposure from levels of irradiance obtained in a stable and well-controlled environment are used.     

Liquid side heat transfer and pressure drop in finned-tube cooling-coils operated with secondary refrigerants

In this study full-scale experiments with two different conventional cooling-coils aimed for display cabinets were performed. Heat transfer and pressure drop on the liquid side for three different single phase secondary refrigerants were studied and compared to predictions by existing correlations. Predominantly, the laminar flow regime was studied. The results show that when predicting the heat transfer performance on the liquid side of a cooling-coil the Gnielinski correlation for thermally developing flow and uniform wall temperature boundary conditions (T) leads to good agreement for 0.0014 < x^* < 0.017 if 50 < Re < 1700, assuming a new entrance length is formed after each U-bend. In addition, these entrance lengths must also be accounted for, when predicting the pressure drop on the liquid side of the cooling-coil. The uncertainty of measurement can be a problem in this type of investigations and this has been taken into consideration when analysing the results.     

Reversible toluene adsorption on monolithic carbon aerogels

Thirteen monolithic carbon aerogels with different pore textures were used as toluene adsorbents. Adsorption was carried out under both static and dynamic conditions. Under static conditions at 25 degrees C and at saturation, an adsorption capacity as high as 1.36 cm(3) g(-1) or 1180 mg g(-1) was obtained. Toluene adsorption was a reversible process in all carbon aerogels, and the adsorbed toluene was completely recovered by heating them at 400 degrees C. Regenerated adsorbents showed larger surface area and micropore width than the original samples, indicating that no pore blockage was produced. Adsorption under dynamic conditions at 100 degrees C was also completely reversible after at least three consecutive adsorption-desorption cycles. The ability of these carbon aerogels to reversibly adsorb toluene could be useful for their application in thermal swing adsorption or pressure swing adsorption equipment.     

Chemometric study of Maya Blue from the voltammetry of microparticles approach

The use of the voltammetry of microparticles at paraffin-impregnated graphite electrodes allows for the characterization of different types of Maya Blue (MB) used in wall paintings from different archaeological sites of Campeche and YucatAn (Mexico). Using voltammetric signals for electron-transfer processes involving palygorskite-associated indigo and quinone functionalities generated by scratching the graphite surface, voltammograms provide information on the composition and texture of MB samples. Application of hierarchical cluster analysis and other chemometric methods allows us to characterize samples from different archaeological sites and to distinguish between samples proceeding from different chronological periods. Comparison between microscopic, spectroscopic, and electrochemical examination of genuine MB samples and synthetic specimens indicated that the preparation procedure of the pigment evolved in time via successive steps anticipating modern synthetic procedures, namely, hybrid organic-inorganic synthesis, temperature control of chemical reactivity, and template-like synthesis.     

Coupling solar photo-Fenton and biotreatment at industrial scale: main results of a demonstration plant

This paper reports on the combined solar photo-Fenton/biological treatment of an industrial effluent (initial total organic carbon, TOC, around 500mgL(-1)) containing a non-biodegradable organic substance (alpha-methylphenylglycine at 500mgL(-1)), focusing on pilot plant tests performed for design of an industrial plant, the design itself and the plant layout. Pilot plant tests have demonstrated that biodegradability enhancement is closely related to disappearance of the parent compound, for which a certain illumination time and hydrogen peroxide consumption are required, working at pH 2.8 and adding Fe(2+)=20mgL(-1). Based on pilot plant results, an industrial plant with 100m(2) of CPC collectors for a 250L/h treatment capacity has been designed. The solar system discharges the wastewater (WW) pre-treated by photo-Fenton into a biotreatment based on an immobilized biomass reactor. First, results of the industrial plant are also presented, demonstrating that it is able to treat up to 500Lh(-1) at an average solar ultraviolet radiation of 22.9Wm(-2), under the same conditions (pH, hydrogen peroxide consumption) tested in the pilot plant.     

Study of mechanical degradation of UHMWPE acetabular components due to clinical X-ray procedures

The use of multi-component femoral implants to replace the femur head and re-establish bone motion has been widespread since the 70s. Frequently these implants have spherical metallic heads made of, for example, 316-L stainless steel or Cr–Co alloys, which allow rotational motion towards a polymeric component (UHMWPE). One of the major causes of implant rejection is the generation of UHMWPE debris on the surface between the implant head and the polymeric component. The gamma ray sterilization of implants and the periodical X-ray medical control could contribute to premature degradation of the polymeric surface, resulting in increased wear and shortened lifetime of the implant. In this work we study the degradation degree of the polymeric UHMWPE component as function of the X-ray dose. The elasto-plastic deformation and recovery were carried out by means of a nanohardness tester equipment and the polymer degradation was measured using a fast Fourier transform infra-red (FT-IR) equipment. The results show the compromise among the irradiation doses, the surface oxidation and the mechanical properties of the samples.