Characterization of polyisoprene-clay nanocomposites prepared by solution blending

The effects of clay dispersion and the interactions between clays and polymer chains on the viscoelastic properties of polymer/clay nanocomposites are investigated using oscillatory shear rheology, X-ray diffraction (XRD), small-angle X-ray scattering (SAXS), and transmission electron microscopy (TEM). Four different montmorillonite silicates of natural clays, plasma-treated clays, and organically modified clays (OCs) have been used in this study. For the polyisoprene (PI)/clay nanocomposites, the exfoliation of the OC dispersed in the PI matrix is confirmed with XRD and SAXS although TEM images show both exfoliated and non-exfoliated nanoclay sheets. In contrast aggregation or intercalation is obtained for the other PI/clay composites studied here. Additionally, the effective maximum volume packing fraction of OC for the exfoliated nanocomposites is determined from the overlapping of dynamic viscosity at low frequency regime, in which the effective maximum volume packing fraction is larger than the percolation threshold determined from the storage modulus of the nanocomposites.     

Use of acoustic emission technique for the early detection of aluminum alloys exfoliation corrosion

Exfoliation corrosion of aluminum alloys is a form of localized corrosion which affects many industries, specially aeronautics. The study of this corrosion mode using only electrochemical techniques is not fully efficient for the detection and control on line of this phenomenon. Therefore, we developed a non-destructive testing technique based on the acoustic emission recordings in order to follow-up this form of corrosion on aluminum alloys. Indeed, recent works have shown the interest of the acoustic emission for the detection, the monitoring and the localization of pitting corrosion on aluminum alloys. This pitting corrosion phenomenon is currently well understood and the experimental methodology acquired during that study is transposed to the study of exfoliation corrosion of aluminum alloys.The present study is conducted on two aluminum alloys: (Al 2024 T3, and Al 7449 T6 and T7). Samples are immersed 4 days in the modified ASTM STP 1134 saline solution. Observations of the structures after tests show that the exfoliation corrosion sensitivity of alloy 7449 T6 is more important than for alloy 7449 T7 which exhibits only the presence of small and non-occluded pits. Very severe exfoliation corrosion was also observed on Al 2024 T3, but after a longer immersion time or in a more acid solution.The recording of the acoustic emission activity shows evident links between this activity and the exfoliation corrosion rate. The analysis of the signal's characteristics reveals a population corresponding to the release of hydrogen bubbles. A few more energetic signals have also been observed. Their source can be either, the cracking resulting from the separation of sheets of metal, or the development and evolution of hydrogen bubbles formed inside blisters during exfoliation corrosion.     

Appropriate conditions for preparing few-layered graphene oxide and reduced graphene oxide

Oxidation time and exfoliated conditions of graphite oxides (GOs) were investigated to prepare few–layer graphene oxide and reduced graphene oxide via a modified Hummers approach. Different oxidative degree of GOs was prepared by changing oxidation time, and the effects of oxidative degree of GOs in different oxidation time were studied by XRD, FT-IR. Afterwards, highly oxidized GOs were used as precursor to prepare graphene oxide and reduced graphene oxide by ultrasonic dispersion method and thermal expansion method. The exfoliated conditions (ultrasonic power and ultrasonic time, thermal exfoliated temperature) were investigated to prepare few-layered graphene oxide and reduced graphene oxide.     

Preparation and characterization of polymer/layered silicate pharmaceutical nanobiomaterials using high clay load exfoliation processes

The purpose of this study was to prepare and characterize lamellar silicate nanocomposites using exfoliation processes, high clay load and polyvinylpyrrolidone (PVP), ethylcellulose (EC) and polyquaternium-H (PQH). The clays (sodium montmorillonite, Viscogel S4™, S7™ and B8™) were pre-treated with ultrasonic energy in order to increase clay exfoliation yields. Polymeric nanocomposites were characterized by XRPD, DSC, TGA, DLS and NMR. The results revealed a new exfoliation method and new intercalated nanocomposites. High clay load was used to obtain the nanocomposites, which enables its application at an industrial scale. These nanocomposites could be broadly applied across the pharmaceutical, medical and food industries.     

Graphitic platelets prepared by electrochemical exfoliation of graphite and their application for Li energy storage

Electrochemical exfoliation of graphite in the flame-retarded electrolyte is used for the preparation of novel carbon materials for the first time. Graphitic platelets with submicron thickness are prepared by an electrochemical graphite exfoliation route in the trimethyl phosphate (TMP) based electrolyte. The morphology and size of the graphitic platelets can be controlled by adjusting the reaction temperature and current density. A possible mechanism is proposed for the interesting graphite exfoliation in the TMP-based electrolyte. Compared with common micrometer-scale graphite and graphene nanosheets, this novel graphitic material exhibits different voltage profiles but good rate capability as anode in the Li-ion batteries.     

超临界锅炉高再管氧化皮脱落分析与解决措施

根据现场检修情况及日常超温统计，提出超临界锅炉高再管氧化皮脱落的原因。从检修及运行两方面采取措施，防止高再管的超温，及因氧化皮脱落引起的爆管。     

Thermal Annealing and Graphene Modification of Exfoliated Hydrogen Titanate Nanosheets for Enhanced Lithium-ion Intercalation Properties

Hydrogen titanate has been considered as a promising lithium intercalation material due to its unique layered structure. In the present work, we fabricate 2D graphene/hydrogen titanate hybrid nanosheets for application as anode materials in lithium-ion batteries. H2Ti307 nanosheets are synthesized by exfoliation of a layered precursor via interacting bulky tetrabutylammonium （TBA＋） cations, followed by ion exchange with Na＋ ions and washing with water. The as-prepared hydrogen titanate nanosheets are well-dispersed exhibiting ultra-thin thickness with a lateral size up to a few micrometers. The sample is then annealed at 450, 650 Rnd 850 ℃, to optimize its Li＋-intercalation property. Heating at 450 ℃ leads to well-crystallized hydrogen titanate with a trace amount of TiO2. Heating at 650 and 850 ℃ results in mixed sodium titanates, since some sodium ions in the interlayer structure cannot be washed away and become chemically bonded to [TiO6] octahedra at high temperatures. Electrochemical properties of all the four samples are then evaluated by charged/discharged for 100 electrochemical cycles at 0.01-2.5 V vs. Li＋/Li at a specific current of 170 mA g-1. The unannealed hydrogen titanate delivers the highest initial discharge capacity of 130.5 mA h g-l, higher than 124.6 mA h g-1 from hydrogen titanate annealed at 450 ℃, as well as 101.3 and 63.8 mA h g-1 from hydrogen titanate annealed at 650 and 850℃, respectively, due to the high surface area from well-dispersed unannealed nanosheets. However, after 100 electrochemical cycles, well-crystallized hydrogen titanate annealed at 450 ℃ retain the highest charge capacity of 115.2 mA h g-1, corresponding to a capacity retention of 92.5%, while unannealed hydrogen titanate exhibits a final capacity of 72.1 mA h g-1 and a capacity retention of only 55.2%. To further improve energy density of lithium-ion battery, graphene/hydrogen titanate hybrid nanosheets are fabricated by adding graphene nanosheets into hydrogen titanates. The initial charge cap     

Aniline- and N,N-dimethylformamide-assisted processing route for graphite nanoplates: intercalation and exfoliation pathway

Aniline-intercalated graphite nanoplates (AGNPs) were synthesized directly from graphite via an intercalation and exfoliation pathway using aniline as the intercalating agent and N,N-dimethylformamide (DMF) as the exfoliating agent. Thus, the obtained AGNPs were dispersible in various organic solvents like ethanol, isopropanol, chloroform, and benzene. This process is convenient, readily scalable and eco-friendly. We found that π-π interactions and the charge transfer complex formation between aniline and graphite nanoplates (GNPs) are responsible for the dispersion of AGNPs in organic solvents. The formation of AGNPs was confirmed by transmission electron microscopy (TEM), high-resolution TEM (HRTEM), selected area electron diffraction (SAED), X-ray diffraction (XRD), X-ray photoelectron (XPS), Raman and UV-Visible spectroscopic measurements.     

Quantitative study of exfoliation corrosion: Exfoliation of slices in humidity technique

A new technique, exfoliation of slices in humidity (ESH), was developed for the determination of exfoliation corrosion (EFC) susceptibility and quantification of EFC kinetics. Two AA7178 plates taken from the wingskin of a retired KC135 airplane were used as test samples. Slices of the plate were pretreated by potentiostatic polarization in chloride solution to develop localized corrosion sites. Subsequent exposure to high humidity after pretreatment of properly oriented and unconstrained samples resulted in the development of EFC at the edges of the slices. The EFC kinetics were determined by measuring the width of the central unattacked region of the samples. The ESH results were representative of the different EFC behavior of the two plates during outdoor exposure. These results show the capability of the ESH test to discriminate between plates of varying susceptibility and to determine EFC rates quantitatively. The different susceptibility of the two plates to EFC was attributed to differences in microstructure and grain boundary chemistry.