Toughening and hardening in double-walled carbon nanotube/nanostructured magnesia composites

Dense double-walled carbon nanotube (DWCNT)/nanostructured MgO composites were prepared using an in situ route obviating any milling step for the synthesis of powders and consolidation by spark-plasma-sintering. An unambiguous increase in both toughness and microhardness is reported. The mechanisms of crack-bridging on an unprecedented scale, crack-deflection and DWCNT pullout have been evidenced. The very long DWCNTs, which appear to be mostly undamaged, are very homogeneously dispersed at the grain boundaries of the matrix, greatly inhibiting the grain growth during sintering. These results arise because the unique microstructure (low content of long DWCNTs, nanometric matrix grains and grain boundary cohesion) provides the appropriate scale of the reinforcement to make the material tough

Tetragonal-(Zr,Co)O2 solid solution: Combustion synthesis, thermal stability in air and reduction in H2, H2–CH4 and H2–C2H4 atmospheres

The synthesis of Co2+-stabilized zirconia by the nitrate/urea combustion route is investigated. Using seven times the so-called stoichiometric urea proportion allows to obtain for the first time the Zr0.9Co0.1O1.9 solid solution fully stabilized in tetragonal form. The thermal stability in air and the reduction in H2, H2–CH4 and H2–C2H4 atmospheres are studied. The carbon forms obtained upon reduction are investigated. Reduction in H2–CH4 produces many carbon species including short carbon nanofibers, nanoribbons, hollow particles often forming bamboo structures, carbon-encapsulated Co particles and carbon nanotubes. Reduction in H2–C2H4 produces 15–30 nm nanofibers

Spark-plasma-sintering of double-walled carbon nanotube–magnesia nanocomposites

A double-walled carbon nanotube–MgO powder is prepared without any mixing. The applied pressure is the main parameter acting on densification. Increasing the maximum temperature and holding time is marginally beneficial. The nanotubes are blocking the matrix grain growth. The nanocomposite prepared using the most severe spark plasma sintering conditions (1700 °C, 150 MPa) shows mostly undamaged nanotubes and a higher microhardness than the other materials, reflecting a better bonding between nanotubes and matrix. The electrical conductivity of all nanocomposites is over 12 S/cm

Synthesis of Fe-ZrO2 nanocomposite powders by reduction in H2 of a nanocrystalline (Zr, Fe)O2 solid solution

The formation of Fe-ZrO2 nanocomposite powders by reduction in hydrogen of a nanocrystalline totally stabilized Zr0.9Fe0.1O1.95 solid solution was investigated by X-ray diffraction (XRD), field-emission-gun scanning electron microscopy (FEG-SEM) and Mössbauer spectroscopy. The reduction of the stabilized Zr0.9Fe0.1O1.95 solid solution and the formation of metallic particles precedes the transformation of zirconia into the monoclinic phase, which becomes the major zirconia phase upon reduction at 950 °C. α-Fe particles with a size distribution slightly increasing from 10–50 to 20–70 nm upon the increase in reduction temperature are observed and a second population of smaller (<5 nm) γ-Fe nanoparticles is also noticed when the reduction is performed at 1000 °C. Another metallic phase with a hyperfine field of not, vert, similar200 kOe at RT (not, vert, similar250 kOe at 80 K) is detected, which could account for an Fe/Zr phase. It could be formed by the reduction on an Fe2+-rich transient phase incorporating a small fraction of the Zr4+ ions, formed by a phase partitioning process superimposed to the reduciton processes

Iron-stabilized nanocrystalline ZrO2 solid solutions: Synthesis by combustion and thermal stability

The synthesis of Fe3+-stabilized zirconia by the nitrate/urea combustion route was investigated. Using several characterization techniques, including X-ray diffraction, field-emission-gun scanning electron microscopy and notably Mo¨ ssbauer spectroscopy, it was possible to determine the appropriate amount of urea that allows to obtain a totally stabilized Zr0.9Fe0.1O1.95 solid solution. The nanocrystalline zirconia solid solution is mostly tetragonal, but the presence of the cubic phase could not be ruled out. An indepth study of the thermal stability in air showed that the Fe3+ solubility in the stabilized solid solution starts to decrease at about 875 8C which results in the formation of hematite (possibly containing some Zr4+) at the surface of the zirconia grains and further provokes the progressive transformation into the monoclinic zirconia phase

Nanocomposites nanotubes de carbone-métal-oxyde (synthèse par CCVD et frittage par SPS)

TOULOUSE3-BU Sciences (315552104) / SudocLIMOGES-ENSCI (870852305) / SudocSudocFranceF

Household costs of dengue illness: secondary outcomes from a randomised controlled trial of dengue prevention in Guerrero state, Mexico

Abstract Background Dengue is a serious public health problem with an important economic impact. This study used data from a cluster randomised controlled trial of community mobilisation for dengue prevention to estimate the household costs of treatment of dengue illness. It examined the economic impact of the trial intervention in the three coastal regions of Mexico’s Guerrero State. Methods The 2010 baseline survey covered households in a random sample of 90 clusters in the coastal regions; the clusters were randomly allocated to intervention or control and re-surveyed in 2012. The surveys asked about dengue cases in the last 12 months, expenditures on their treatment, and work or school days lost by patients and care givers. We did not assign monetary value to days lost, since a lost day to a person of low earning power is of equal or higher value to that person than to one who earns more. Results The 12,312 households in 2010 reported 1020 dengue cases in the last 12 months (1.9% of the sample population). Most (78%) were ambulatory cases, with a mean cost of USD 51 and 10.8 work/school days, rising to USD 96 and 11.4 work/school days if treated by a private physician. Hospitalised cases cost USD 28–94 in government institutions and USD 392 in private hospitals (excluding additional inpatient charges), as well as 9.6–17.3 work/school days. Dengue cases cost households an estimated 412,825 work/school days throughout the three coastal regions. In the follow up survey, 6.1% (326/5349) of households in intervention clusters and 7.9% (405/5139) in control clusters reported at least one dengue case. The mean of days lost per case was similar in intervention and control clusters, but the number of days lost from dengue and all elements of costs for dengue cases per 1000 population were lower in intervention clusters. If the total population of the three coastal regions had received the intervention, some 149,401 work or school days lost per year could have been prevented. Conclusion The economic effect of dengue on households, including lost work days, is substantial. The Camino Verde trial intervention reduced household costs for treatment of dengue cases. Trial registration The trial was registered as ISRCTN:27,581,154