Corrosion and Erosion-Corrosion Processes of Metal-Matrix Composites in Slurry Conditions

The corrosion and erosion-corrosion (EC) processes of four metal-matrix composites (MMCs) in a simulated cooling water environment have been assessed in this article. The MMCs consisted of two Ni-base and two Fe-base matrices alloyed with different concentrations of chromium, molybdenum, boron, silicon, and carbon; the matrices were reinforced with tungsten carbide (WC) particles. The corrosion behavior has been investigated using a combination of potentiostatic polarization and post-tests surface analysis. The EC processes were studied by in situ electrochemical techniques measuring the current density and corrosion potential response at different slurry temperatures and sand content. At static conditions it was found that as the temperature increased, there was a transition from a homogeneous corrosion of the matrix to an interfacial corrosion mechanism. The Ni-base MMCs showed a better corrosion resistance and interestingly a highly alloyed matrix did not significantly improved MMC’s corrosion resistance. In the in situ EC tests, the Fe-base MMCs showed a constant increase in the current density at all sand contents. Whereas, significant changes were not observed in the Ni-base MMCs below 0.5 g/L. Although sand content had an effect on the monitored current density (the current increased as the sand content increased) this effect was less pronounced above 3 g/L.     

Mechanical properties and biomass carbon ratios of poly(butylene succinate) composites filled with starch and cellulose filler using furfural as plasticizer

Polymer composites consisting of poly(butylene succinate) (PBS) as matrix and corn starch (CS) or cellulose filler (CF) with a small amount of furfural (FR) from biomass were prepared by a hot‐pressing method at 120°C from a powder mixture. Mechanical properties of the composites' films were investigated using tensile test methods. The strain of these films was found to be developed by adding CS or CF and further improved by adding FR. The strain at break PBS with 15 wt % FR was improved by more than 16 times of that of PBS without FR. The biomass carbon ratios of polymer composites with oil‐based PBS (major component) and with biobased CS, CF, and FR were evaluated by ¹⁴C concentration ratio measured by accelerator mass spectrometry (AMS) based on ASTM D6866. PBS with 40 wt % CS or CF had a biomass carbon ratio of 31 and 36%, respectively. PBS with 15 wt % FR had a biomass carbon ratio of 3.4%. This deviation was confirmed by FR content calculated from the peak area of the ¹H‐NMR spectrum of PBS with FR which was 3.4%, almost the same as the biomass carbon ratio measured by AMS. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Study of the performance of Mo2C for iso-octane steam reforming

In the present work, the performance of commercial molybdenum carbide (Mo₂C) for isooctane steam reforming has been investigated in order to determine the effects of major operating parameters (temperature, space velocity, and steam to carbon ratio) on the catalytic activity. While the results obtained indicate an onset reforming temperature of 850 °C, high concentrations of H₂ in the reforming environment were found to reduce the onset temperature to 750 °C. The catalytic activity at 850 °C was sufficient to produce hydrogen yields greater than 90% and carbon conversions close to 100%, with a low selectivity to CH₄ and CO₂. In addition, and consistent with thermodynamic predictions, a steam to carbon ratio of 1 appeared to optimize the reforming rates. Finally, based on experimental observations, a reaction mechanism was formulated and used to interpret the results obtained during catalytic activity measurements. This mechanism involves continuous oxidation and reduction of Mo metal, which can provide activity and stability to the catalyst when occurring at similar rates.     

Recrystallization studies on isotropic cold-crystallized PET: Influence of heating rate

The nanostructural changes associated to the multiple melting behaviour of isotropic cold-crystallized poly(ethylene terephthalate) (PET) have been investigated by means of simultaneous wide- and small-angle X-ray scattering, using a synchrotron radiation source. Variations in the degree of crystallinity, coherent lateral crystal size and long period values, as a function of temperature, for two different heating rates are reported for cold-crystallized samples in the 100-190 °C range. The Interface Distribution Function analysis is also employed to provide the crystalline and amorphous layer thickness values at various temperatures of interest. Results suggest that samples crystallized at both low (T_a = 100-120 °C) and high (T_a = 160-190 °C) temperatures are subjected to a nearly continuous nanostructural reorganization process upon heating, starting immediately above T_g (≈80 °C) and giving rise to complete melting at ≈260 °C. For all the T_a investigated, a melting-recrystallization mechanism seems to take place once T_a is exceeded, concurrently to the low-temperature endotherm observed in the DSC scans. For low-T_a and slow heating rates (2 °C/min), a conspicuous recrystallization process is predominant within T_a + 30 °C ≤ T ≤ 200 °C. In contrast, for high-T_a, an increasingly strong melting process is observed. For both, high- and low-T_a, an extensive structural reorganization takes place above 200 °C, involving the appearance of new lamellar stacks simultaneously to the final melting process. The two mechanisms should contribute to the high-temperature endotherm in the DSC scan. Finally, the use of a high heating rate is found to hinder the material's overall recrystallization process during the heating run and suggests that the high-temperature endotherm is ascribed to the melting of lamellae generated or thickened during the heating run.     

Hot corrosion behaviour of 7YSZ + Gd2O3 nano-composites in molten salts prepared by spark plasma sintering

This study compares the hot corrosion performance of yttria-stabilised zirconia (7YSZ), and 7YSZ?+?Gd₂O₃ composite samples in the presence of molten mixture of Na₂SO₄?+?V₂O₅ at 1150°C. For 7YSZ, the reaction between NaVO₃ and Y₂O₃ produces YVO₄ and leads the transformation of tetragonal ZrO₂ to monoclinic ZrO₂. A high-density in sintered 7YSZ?+?Gd₂O₃ samples, led minor amounts of monoclinic ZrO₂ and tetragonal GdVO₄ as the hot corrosion products with only traceable amounts of YVO₄, and a stable corroded layer was formed. Due to the synergic effect of doping of zirconia with Gd₂O₃, the 7YSZ?+?Gd₂O₃ sample has a much better hot corrosion crack resistance than 7YSZ.     

Preparation and electrical characterization of poly(vinyl amine) hydrogels,crosslinked with Cu(II) ions,and evaluation of their potentiality as water sensor material

A method to prepare water sensitive composites employing crosslinked poly(vinyl amine) (PVAm) and Cu(II) ions as reticulation agent is disclosed in this work. This article presents in detail, the reticulation reaction and its pH dependence, as well as its electrical, rheological, and thermal properties of the PVAm‐Cu(II) composites obtained. The complex bonds formed between the Cu(II) ions and the amine groups of PVAm produce an interesting network of crosslinked structures that generate a microporous morphology when the material is extruded. This characteristic favors fast absorption of water when it is wetted, and a concomitant decrease in its apparent resistivity in a very short period of time. Furthermore, they present an excellent thermal stability and suitable processability. These characteristics make them interesting candidates to design ultra fast water sensors. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Finite size effects in multilayered polymer systems: Development of PET lamellae under physical confinement

The glass transition temperature and the crystallization behaviour of poly(ethylene terephthalate) PET ultra-thin layers (a few tens of nm) within multilayered PET/polycarbonate (PC) coextruded films are investigated as a function of layer thickness by means of calorimetric measurements. Results are discussed in terms of reduced thickness and interface effects. The appearance and evolution of lamellar orientation upon isothermal crystallization of ultra-thin PET layers from the glassy state are explored based on real time small-angle X-ray scattering (SAXS) studies. Analysis of the SAXS measurements reveals that finite size effects hamper the crystallization process. However, the final lamellar structure is similar in both, the nanolayered PET and the bulk material. Results suggest that not only lamellar insertion but also some lamellar thickening contribute to the development of the final lamellar structure. Room temperature SAXS and wide-angle X-ray diffraction (WAXS) measurements indicate that two lamellar populations develop: edge-on lamellae are proposed to appear close to the interphases while flat-on lamellae, arising as a consequence of confinement, should be preferentially located in the layers core.     

Monitoring access to water in rural areas based on the human right to water framework: a local level case study in Nicaragua

Much effort has gone into the recognition of the human right to water. Without doubt, this milestone influences governance and decision making processes at many scales so it is essential now to shift the discussion from the legal and conceptual framework to practice. Along this line, the article proposes a methodology for monitoring access to water in rural areas using the framework of this human right. The practicality of the approach is demonstrated by a case study carried out in Nicaragua. Different criteria of the right to water were included in surveys and structured interviews that were conducted in rural households and water committees, respectively. A discussion analyzes the advantages and challenges of using this framework. Finally, the approach provides elements for policy making that can be used by different stakeholders in the development and human rights sectors.