Modulus of rapture (MOR) of porcelain by substitution of quartz with rice husk ash (RHA) and palm oil fuel ash (POFA) at different temperatures

This paper investigates to effects RHA and POFA in porcelain body as substitute materials for quartz. In order to collect experimental data, the effects of ground RHA and POFA replacement rate from 0 wt% up to 25 wt% in porcelain body was studied. The RHA and POFA were grounded in a ball mill until the median particle size was reduced to about 50 μm. They were used to substitute quartz in porcelain body from 0 wt% to 25 wt%. The mixed powder was pressed into pellets at mould pressure of 91 MPa. All the pellets were sintered at a temperatures of 1000 ºC, 1100 ºC, 1200 ºC and 1300 ºC for the soaking times of 2 hours. It was found out among other things that the Modulus of Rapture (MOR) of the samples increases with increase in substitution and also with the increase in temperature. With a value of 35 MPa the MOR of the samples containing 20 wt% sintered at a soaking time of 2 hours were higher than the standard porcelain. This could be attributed to the formation of larger amount of SiO2 glass, in the presence of fluxing components such as MgO, CaO and Na2O), more abundant in samples containing RHA and POFA

Syrian Refugees and the Digital Passage to Europe: Smartphone Infrastructures and Affordances

This research examines the role of smartphones in refugees’ journeys. It traces the risks and possibilities afforded by smartphones for facilitating information, communication, and migration flows in the digital passage to Europe. For the Syrian and Iraqi refugee respondents in this France-based qualitative study, smartphones are lifelines, as important as water and food. They afford the planning, navigation, and documentation of journeys, enabling regular contact with family, friends, smugglers, and those who help them. However, refugees are simultaneously exposed to new forms of exploitation and surveillance with smartphones as migrations are financialised by smugglers and criminalized by European policies, and the digital passage is dependent on a contingent range of sociotechnical and material assemblages. Through an infrastructural lens, we capture the dialectical dynamics of opportunity and vulnerability, and the forms of resilience and solidarity, that arise as forced migration and digital connectivity coincide

S-Rich PbS Quantum Dots:A Promising p-Type Material for Optoelectronic Devices

PbS colloidal quantum dots (CQDs) are versatile building blocks for bottom-up fabrication of various optoelectronic devices. The transport properties of thin films of this class of materials depend on the size of the CQDs, their surface ligands, and stoichiometry. The most common synthetic methods yield PbS CQDs with an excess of Pb atoms, which induces n-type transport properties in CQD films. In this work, we developed a new synthesis, which offers S-rich PbS CQDs. Thanks to their sufficient colloidal stability in nonpolar solvents, we established a protocol for the integration of these CQDs into thin field-effect transistors and found strong hole-dominated transport with a hole mobility of about 1 × 10–2 cm2/Vs. Moreover, we were able to enhance the electron mobility for almost two orders of magnitude while keeping the hole mobility nearly the same. This approach allows us to obtain reliably p-doped PbS CQDs, which can be used for the fabrication of various electronic and optoelectronic devices.ISSN:0897-475

Influence of egg shell as heterogeneous catalyst in the production of biodiesel via transesterification of Jatropha oil

The increase in energy demand together with the negative global environmental impacts of using fossil fuel for energy generations brings a question on dependability on it for sustainable economic growth. The way out is the use of renewable sources of energy such as biodiesel which has significant advantages over its counterpart (fossil fuel). Biodiesel can be produced through various methods such as transesterification, micro emulsion and pyrolysis. The influence of egg shell as heterogeneous catalysts in the production of biodiesel via transesterification of Jatropha oil was investigated. The physical and chemical properties of the catalyst were studied using scanning electron microscopy (SEM) and Xray fluoroscopy (XRF) characterizations. The crude Jatropha oil was transesterified and 0.1 wt%, 0.2 wt%, 0.3wt%, 0.5wt% and 0.5wt% of egg shell were used as heterogeneous catalyst during transesterification process. Fourier Transform Infrared (FTIR) was used to determine the functional group of the samples. SEM and FTIR characterizations indicate the presence of dispersed particles on the catalyst and ester (biodiesel) on the samples respectively. The maximum percentage of biodiesel yield is 94.3% at the application of 0.2wt% egg shell as catalyst using 1:6 oil to methanol ratio in 1hr at 60-65℃. This indicated that the egg shell has high potential to be used as catalyst in the production of biodiesel via transesterification of Jatropha oil

Reversible amorphous-crystalline phase changes in a wide range of Se1-xTex alloys studied using ultrafast differential scanning calorimetry

The reversible amorphous-crystalline phase change in a chalcogenide material, specifically the Se1-xTex alloy, has been investigated for the first time using ultrafast differential scanning calorimetry. Heating rates and cooling rates up to 5000 K/s were used. Repeated reversible amorphous-crystalline phase switching was achieved by consecutively melting, melt-quenching, and recrystallizing upon heating. Using a well-conditioned method, the composition of a single sample was allowed to shift slowly from 15 at. % Te to 60 at. % Te, eliminating sample-to-sample variability from the measurements. Using Energy Dispersive X-ray Spectroscopy composition analysis, the onset of melting for different Te-concentrations was confirmed to coincide with the literature solidus line, validating the use of the onset of melting T-m as a composition indicator. The glass transition T-g and crystallization temperature T-c could be determined accurately, allowing the construction of extended phase diagrams. It was found that T-m and T-g increase (but T-g/T-m decrease slightly) with increasing Te-concentration. Contrarily, the T-c decreases substantially, indicating that the amorphous phase becomes progressively unfavorable. This coincides well with the observation that the critical quench rate to prevent crystallization increases about three orders of magnitude with increasing Te concentration. Due to the employment of a large range of heating rates, non-Arrhenius behavior was detected, indicating that the undercooled liquid SeTe is a fragile liquid. The activation energy of crystallization was found to increase 0.5-0.6 eV when the Te concentration increases from 15 to 30 at. % Te, but it ceases to increase when approaching 50 at. % Te. (C) 2014 AIP Publishing LLC

Interface formation of two- and three-dimensionally bonded materials in the case of GeTe-Sb2Te3 superlattices

GeTe–Sb2Te3 superlattices are nanostructured phase-change materials which are under intense investigation for non-volatile memory applications. They show superior properties compared to their bulk counterparts and significant efforts exist to explain the atomistic nature of their functionality. The present work sheds new light on the interface formation between GeTe and Sb2Te3, contradicting previously proposed models in the literature. For this purpose [GeTe(1 nm)–Sb2Te3(3 nm)]15 superlattices were grown on passivated Si(111) at 230 °C using molecular beam epitaxy and they have been characterized particularly with cross-sectional HAADF scanning transmission electron microscopy. Contrary to the previously proposed models, it is found that the ground state of the film actually consists of van der Waals bonded layers (i.e. a van der Waals heterostructure) of Sb2Te3 and rhombohedral GeSbTe. Moreover, it is shown by annealing the film at 400 °C, which reconfigures the superlattice into bulk rhombohedral GeSbTe, that this van der Waals layer is thermodynamically favored. These results are explained in terms of the bonding dimensionality of GeTe and Sb2Te3 and the strong tendency of these materials to intermix. The findings debate the previously proposed switching mechanisms of superlattice phase-change materials and give new insights in their possible memory application

Strain Relaxation in "2D/2D and 2D/3D Systems":Highly Textured Mica/Bi2Te3, Sb2Te3/Bi2Te3, and Bi2Te3/GeTe Heterostructures

Strain engineering as a method to control functional properties has seen in the last decades a surge of interest. Heterostructures comprising 2D-materials and containing van der Waals(-like) gaps were considered unsuitable for strain engineering. However, recent work on heterostructures based on Bi2Te3, Sb2Te3, and GeTe showed the potential of a different type of strain engineering due to long-range mutual straining. Still, a comprehensive understanding of the strain relaxation mechanism in these telluride heterostructures is lacking due to limitations of the earlier analyses performed. Here, we present a detailed study of strain in two-dimensional (2D/2D) and mixed dimensional (2D/3D) systems derived from mica/Bi2Te3, Sb2Te3/Bi2Te3, and Bi2Te3/GeTe heterostructures, respectively. We first clearly show the fast relaxation process in the mica/Bi2Te3 system where the strain was generally transferred and confined up to the second or third van der Waals block and then abruptly relaxed. Then we show, using three independent techniques, that the long-range exponentially decaying strain in GeTe and Sb2Te3 grown on the relaxed Bi2Te3 and Bi2Te3 on relaxed Sb2Te3 as directly observed at the growth surface is still present within these three different top layers a long time after growth. The observed behavior points at immediate strain relaxation by plastic deformation without any later relaxation and rules out an elastic (energy minimization) model as was proposed recently. Our work advances the understanding of strain tuning in textured heterostructures or superlattices governed by anisotropic bonding

Scalable PbS Quantum Dot Solar Cell Production by Blade Coating from Stable Inks

The recent development of phase transfer ligand exchange methods for PbS quantum dots (QD) has enhanced the performance of quantum dots solar cells and greatly simplified the complexity of film deposition. However, the dispersions of PbS QDs (inks) used for film fabrication often suffer from colloidal instability, which hinders large-scale solar cell production. In addition, the wasteful spin-coating method is still the main technique for the deposition of QD layer in solar cells. Here, we report a strategy for scalable solar cell fabrication from highly stable PbS QD inks. By dispersing PbS QDs capped with CH3NH3PbI3 in 2,6-difluoropyridine (DFP), we obtained inks that are colloidally stable for more than 3 months. Furthermore, we demonstrated that DFP yields stable dispersions even of large diameter PbS QDs, which are of great practical relevance owing to the extended coverage of the near-infrared region. The optimization of blade-coating deposition of DFP-based inks enabled the fabrication of PbS QD solar cells with power conversion efficiencies of up to 8.7%. It is important to underline that this performance is commensurate with the devices made by spin coating of inks with the same ligands. A good shelf life-time of these inks manifests itself in the comparatively high photovoltaic efficiency of 5.8% obtained with inks stored for more than 120 days

Phase Separation in Ge-Rich GeSbTe at Different Length Scales: Melt-Quenched Bulk versus Annealed Thin Films

Integration of the prototypical GeSbTe (GST) ternary alloys, especially on the GeTe-Sb2Te3 tie-line, into non-volatile memory and nanophotonic devices is a relatively mature field of study. Nevertheless, the search for the next best active material with outstanding properties is still ongoing. This search is relatively crucial for embedded memory applications where the crystallization temperature of the active material has to be higher to surpass the soldering threshold. Increasing the Ge content in the GST alloys seems promising due to the associated higher crystallization temperatures. However, homogeneous Ge-rich GST in the as-deposited condition is thermodynamically unstable, and phase separation upon annealing is unavoidable. This phase separation reduces endurance and is detrimental in fully integrating the alloys into active memory devices. This work investigated the phase separation of Ge-rich GST alloys, specifically Ge5Sb2Te3 or GST523, into multiple (meta)stable phases at different length scales in melt-quenched bulk and annealed thin film. Electron microscopy-based techniques were used in our work for chemical mapping and elemental composition analysis to show the formation of multiple phases. Our results show the formation of alloys such as GST213 and GST324 in all length scales. Furthermore, the alloy compositions and the observed phase separation pathways agree to a large extent with theoretical results from density functional theory calculations

Single-Source, Solvent-Free, Room Temperature Deposition of Black γ-CsSnI₃ Films

The presence of a non-optically active polymorph (yellow-phase) competing with the optically active polymorph (black $\gamma$-phase) at room temperature in CsSnI3 and the susceptibility of Sn to oxidation, represent two of the biggest obstacles for the exploitation of CsSnI3 in optoelectronic devices. Here room-temperature single-source in vacuum deposition of smooth black $\gamma$ - CsSnI3 thin films is reported. This has been done by fabricating a solid target by completely solvent-free mixing of CsI and SnI2 powders and isostatic pressing. By controlled laser ablation of the solid target on an arbitrary substrate at room temperature, the formation of CsSnI3 thin films with optimal optical properties is demonstrated. The films present a band gap of 1.32 eV, a sharp absorption edge and near-infrared photoluminescence emission. These properties and X-ray diffraction of the thin films confirmed the formation of the orthorhombic (B-$\gamma$) perovskite phase. The thermal stability of the phase was ensured by applying in situ an Al2O$_3$ capping layer. This work demonstrates the potential of pulsed laser deposition as a volatility-insensitive single-source growth technique of halide perovskites and represents a critical step forward in the development and future scalability of inorganic lead-free halide perovskites.Comment: Accepted by Advanced Materials Interfaces, 16 pages, 4 figures, and supplemen