In situ time-resolved X-ray diffraction of tobermorite formation in autoclaved aerated concrete: Influence of silica source reactivity and Al addition

The hydrothermal formation of tobermorite during the processing of autoclaved aerated concrete was investigated by in situ X-ray diffraction (XRD) analysis. High-energy X-rays from a synchrotron radiation source in combination with a newly developed autoclave cell and a photon-counting pixel array detector were used.To investigate the effects of the silica source, reactive quartz from chert and less-reactive quartz from quartz sand were used as starting materials. The effect of Al addition on tobermorite formation was also studied. In all cases, C-S-H, hydroxylellestadite and katoite were clearly observed as intermediates.Acceleration of tobermorite formation by Al addition was clearly observed. However, Al addition did not affect the dissolution rate of quartz. Two pathways, via C-S-H and katoite, were also observed in the Al-containing system. These results suggest that the structure of initially formed C-S-H is important for the subsequent tobermorite formation reactions.     

Photocatalytic hydrogen production from water with nonfood hydrocarbons as oxidizing sacrifice agents

To enhance photocatalytic water splitting, various oxidizing sacrifice agents (OSA) have been added to the system in order to scavenge the coproduced O₂, and, thus, to hinder the reverse reactions. In the aim of achieving carbon‐neutral photocatalytic water splitting, nonfood hydrocarbons of castor‐ and jojoba‐oils were evaluated as OSA. Moreover, various surfactants were tested as emulsifiers for W/O binary solution for promoting photocatalytic water splitting rate. Among the OSA used, the castor‐oil was found to be more suitable candidate compared to jojoba‐oil, which was attributed to its smaller carbon chain numbers of mainly 18. Without surfactants, around 20 vol %‐castor‐oil aqueous binary solution with TiO₂/Pt(0.10 wt %) provided the highest water splitting rate of about 30 mL‐H₂/(m²·h). Among tested surfactants, liquid‐detergent was the best due to its optical transparency. 40 vol %‐ or 60 vol %‐castor‐oil emulsion with a drop of liquid‐detergent resulted in a water splitting rate of 125 mL‐H₂/(m²·h), which was four times greater that the aforementioned highest value. © 2010 American Institute of Chemical Engineers AIChE J, 2011     

Very slow formation of copper sulfide and cobalt sulfide nanoparticles in montmorillonite

Intercalation of semiconductor nanoparticles, copper sulfide or cobalt sulfide, into montmorillonite was carried out by solid–solid reactions of Cu(II)- or Co(II)-montmorillonite with sodium sulfide at room temperature. The intercalation compounds were characterized by X-ray diffraction, thermal analysis, transmission electron microscopy, Raman, UV–visible and photoluminescence spectroscopy. The photoluminescent copper sulfide and cobalt sulfide nanoparticles in the interlayer spaces formed after the sample storage at room temperature for several months.     

Combustion synthesis of LaSi3N5:Eu2+ phosphor powders

LaSi₃N₅:Eu²⁺ phosphor powders were prepared by a highly efficient combustion synthesis method. It was found that the compositions of the raw powder mixtures had great influences on the phase compositions and particle morphologies of the synthesized powders. By selecting appropriate starting compositions and combustion parameters, single phase LaSi₃N₅:Eu²⁺ phosphors could be synthesized. When excited by a UV light, the LaSi₃N₅:Eu²⁺ phosphors emitted green light. The wavelength and intensity of the emission spectra were affected by the amount of Eu²⁺ dopant. With increasing amount of Eu²⁺ dopant, concentration quenching could occur and emission spectra shifted to longer wavelengths.     

Measurements of fiber bundle interfacial properties of three-dimensionally reinforced carbon/carbon composites up to 2273 K

Experimental techniques for evaluating the interfacial properties between fiber bundles and the matrix of three-dimensionally reinforced carbon/carbon composites were examined. Specially arranged fiber bundle push-out and pull-out tests were conducted up to 2273 K in vacuum. In these tests, a fiber bundle in the specimens was extruded or pulled out by external compressive or tensile loads. Post-fracture observations revealed that a shear fracture was successfully induced within the carbon matrices at the loaded fiber bundle interface. The interfacial shear strength and initial sliding stress of the fiber bundle monotonically increased with the test temperature. The relief of residual thermal stress and increases in the frictional resistance and anchor effect at the fiber bundle interface were considered to be the major mechanisms that caused the enhancements. An increase in the heat treatment temperature during the processing of the composites resulted in a significant decrease in and .     

Flexible and Conductive 3D Printable Polyvinylidene Fluoride and Poly(N,N‐dimethylacrylamide) Based Gel Polymer Electrolytes

In this work, 3D printable gel polymer electrolytes (GPEs) based on N,N‐dimethylacrylamide (DMAAm) and polyvinylidene fluoride (PVDF) in lithium chloride containing ethylene glycol solution are synthesized and their physicochemical properties are investigated. 3D printing is carried out with a customized stereolithography type 3D gel printer named “Soft and Wet Intelligent Matter‐Easy Realizer” and free forming GPE samples having variable shapes and sizes are obtained. Printed PVDF/PDMAAm‐based GPEs exhibit tunable mechanical properties and favorable thermal stability. Electrochemical proprieties of the printed GPEs are carried out via impedance spectroscopy in the temperature range of 25–90 °C by varying PVDF content. Ionic conductivity as high as 6.5 × 10^?4 S cm^?1 is achieved at room temperature for GPE containing low PVDF content (5 wt%) and conductivity of the GPEs is increased as temperature rises.     

Fracture Resistance Behavior of High‐Thermal‐Conductivity Silicon Nitride Ceramics

Silicon nitride ceramics were prepared from a high‐purity silicon powder doped with 2 mol% Y₂O₃ and 5 mol% MgO as sintering additives via a route of sintering of reaction‐bonded silicon nitride (SRBSN). The materials sintered at 1900°C for 3, 6, 12, and 24 h had thermal conductivities of 109, 125, 146, and 154 W/m/K, and four‐point bending strengths of 786, 676, 608, and 505 MPa, respectively. The fracture toughness values, determined by the single‐edge‐precracked‐beam (SEPB) method, were 8.4, 8.6, 9.7, and 10.7 MPa m^1/2 for the materials sintered for 3, 6, 12, and 24 h, respectively, which were similar to the results measured by the chevron‐notched‐beam (CNB) test method. The materials sintered for longer times (12 and 24 h) showed stronger R‐curve behaviors over longer range of crack extension, in comparison with the materials sintered for shorter times (3 and 6 h).     

Optical Spectra of Synthetic Spinels in the System MgAl2O4–MgCr2O4

Unpolarized optical spectra were measured in the wavelength range 322–1666 nm by the diffuse reflection technique from spinel powders synthesized in the system MgAl₂O₄–MgCr₂O₄. The spectra were interpreted by the crystal-field theory on the basis of trigonally distorted spinel octahedra with D_3d symmetry. For chromium-rich solid solutions, including the MgCr₂O₄ end-member, results after peak fittings showed octahedral D_3d local symmetry around Cr³⁺ ions, identical to the crystallographic site symmetry. For chromium-poor solid solutions, however, octahedral C_3v local symmetry was suggested around Cr³⁺ ions, different from the D_3d crystallographically expected.     

Corrosion of MgO—MgAl2O4 Spinel Refractory Bricks by Calcium Aluminosilicate Slag

Microstructural analysis of MgO—MgAl₂O₄ refractory bricks corroded at 1400–1450°C by calcium aluminosilicate slag reveals secondary spinel, monticellite, merwinite, and MgO as microscopic corrosion products, generally forming in this sequence as the brick is penetrated. The secondary spinel forms an incomplete layer close to (but not at) the MgO grain. Thermodynamic calculations are used to support a detailed model of the corrosion mechanism.     

Influence of Cu metal on the domain structure and carrier mobility in single-layer graphene

We demonstrate that domain structure of single-layer graphene grown by ambient pressure chemical vapor deposition is strongly dependent on the crystallinity of the Cu catalyst. Low energy electron microscopy analysis reveals that graphene grown using a Cu foil gives small and mis-oriented graphene domains with a number of domain boundaries. On the other hand, no apparent domain boundaries are observed in graphene grown over a heteroepitaxial Cu(111) film deposited on sapphire due to unified orientation of graphene hexagons. The difference in the domain structures is correlated with the difference in the crystal plane and grain structure of the Cu metal. The graphene film grown on the heteroepitaxial Cu film exhibits much higher carrier mobility than that grown on the Cu foil.