Effect of alternative fuels on the microstructure and strength development of cement paste

The object of this study was to investigate the effect of using alternative fuels in the cement production process on the microstructure and strength development of the output cement. Five different samples were produced using different alternative fuels in a cement kiln. The samples were prepared respectively with all kinds of alternative fuels (in the dirty kiln), petrocoke (in the clean kiln), waste plastics, a mixture of waste plastics and sewage sludge and lastly sewage sludge. The microstructure of the cement clinkers was studied with scanning electron microscopy (SEM). The results showed that the distribution of main phases of alite, belite, aluminate and ferrite varies in the samples prepared with different fuels. The alite/belite ratio varied between 5.2 and 1.5 among the samples. The phase distribution measurements using x-ray diffractometry (XRD) showed good agreement with the SEM results. Chemical composition of the clinkers was analyzed using energy dispersive x-ray spectroscopy (EDS) and x-ray fluorescence (XRF) methods. The sulfur and phosphorous amounts were higher in the samples with higher belite content. Hydrated cement paste samples were prepared with water to cement ratio of 0.3 and 0.5 by mass. The strength of the hydrated cement samples was measured in the compression tests for several curing ages up to 28 days. Results showed that alternative fuel usage affected the compressive strength values of hydrated cement samples, particularly the sample produced with all alternative fuels. The reactivity of hydrated phases was investigated using SEM and XRD analyses

Fluorination of vanadium oxy-phosphates for high-energy cathode materials of li-ion batteries

The requirement for sustainable high energy density materials for next generations of Li-ion batteries is driving the research to develop new materials with enhanced properties. The thesis work was focused on fluorination of vanadium oxy-phosphate cathode materials with an aim of increasing their energy density. The synthesis, structural and chemical characteristics including electrochemical properties of the vanadium oxy-phosphates and their fluorinated counterparts were investigated. β-VPO4O, ε-LiVPO4O and β-LiVPO4O phases were synthesized by solid state synthesis method. The fluorination process was carried out under argon atmosphere at high temperatures (<600 °C) using a sealed stainless-steel reactor. Lithium fluoride (LiF) and Polytetrafluoroethylene (PTFE) compounds were used as the fluorine resources. The heat-treatment of the powder mixes of vanadium oxy-phosphate and F-containing compounds resulted in incorporation of F into the structure of materials. The ε-LiVPO4O phase preserved the main framework structure after the fluorination by LiF, but it changed to LiVPO4F-type framework by the use of PTFE as the F source. The β-VPO4O phase formed a LiVPO4F-type structure after the incorporation of LiF. All of the fluorinated materials had a Tavorite-type crystal structure, composed of VO6 octahedra interconnected through corners to PO4 tetrahedra. The operating potential of all the precursor vanadium oxy-phosphates increased after the fluorination, due to the higher ionicity of the V-O/F ligands brought by the inductive effect of F in the structure. Those conclusions were based on a systematic characterization at both micro- and nano-scale using XRD, NMR, SEM, STEM-EDS and STEM-EELS, in addition to the electrochemical characterizatio

Characterization of the corallina elongata alga and study of its biosorption properties for methylene blue

Biosorbents can be an alternative to activated carbon. They are derived from agricultural by-products or aquatic biomass. They are low cost and they may have comparable performances to those of activated carbon. The present study focuses on the characterization of the Corallina Elongata (CE) alga and its adsorption performance for Methylene Blue (MB), this alga is found in abundance at the Mediterranean coast of the city of Jijel in eastern Algeria. The dried alga was characterized using various characterization techniques such as DTA, TG, FTIR, XRD, SEM and EDX, which showed that the material consists essentially of a calcite containing magnesium. Batch adsorption studies were carried out and the effect of experimental parameters Such as pH, initial dye concentration, temperature, adsorbent dose and contact time, on the adsorption of MB was studied. The kinetic experimental data were found to conform to the pseudo-second-order model with good correlation and equilibrium data were best fitted to The Langmuir model, with a maximum adsorption capacity of 34.4 mg/g. The adsorption isotherms at various temperatures allowed the determination of certain thermodynamic parameters (Delta G, Delta H and Delta S). Finally, the adsorption results showed a good affinity between CE and MB with a high adsorption capacity

Calcined schist as promising ordinary Portland cement substitution: C3

Abstract An effective method to make cement and concrete more sustainable is to blend them with the proper supplementary cementitious materials (SCMs). This study evaluates a pair of schist‐type materials with slightly different phase compositions, as a partial replacement for ordinary Portland cement (OPC). Materials received from several mines in ground powder form were studied by X‐ray diffraction, thermogravimetric analysis (TGA), and scanning electron microscopy. According to the TGA results, the activation procedures for the candidate SCMs were determined. The as‐received powders were heat treated in three different decomposition regimes (30%, 50%, and 80% of the total weight losses during thermal decomposition). These regimes corresponded to the activation level of the potential SCMs due to the de‐hydroxylation of the clay‐type minerals within them. Pozzolanic reactivity (pozzolanicity) of untreated as well as treated powders were estimated via electrical conductivity measurements in saturated calcium hydroxide solution. Blended cement pastes with 30 wt.% of OPC substituted with calcined clay‐type materials have developed mechanical properties equal to those of pure cement (100 wt.% OPC) paste after 28 days of hydration time. Two blended cement pastes prepared with candidate SCMs were compared to 100% OPC and OPC composite paste with metakaolin, which is regarded in the literature as a standard

Boiling heat transfer performance enhancement using micro and nano structured surfaces for high heat flux electronics cooling systems

Flow boiling enhancement using structured surfaces in microchannels is a promising method to achieve high heat removal rates. In this study, it is aimed to study the effect of surface structure size (size scale i.e. micro and nano size) on boiling heat transfer characteristics of samples with different surface morphology. High speed and thermal cameras were employed for analyzing the obtained results. A channel with dimensions of 14×15×0.5 mm3 was utilized in the experiments. Distilled water was used as the working fluid, and the experiments were conducted at mass fluxes of 50, 75, 100 and 125 kg/m2.s. Heat transfer coefficients were obtained along with associated boiling images. Based on the visualization study results, two flow maps were constructed for a rectangular microchannel with micro and nano scale structures on copper surfaces. It was observed that the surface morphology remarkably changed boiling heat transfer mechanisms. According to the obtained thermal images, bubble departure frequency increased with surface structures, and the surface temperature distribution was more uniform for surfaces with nano scale structures (nano-structured and micro-nano-structured) compared to other surfaces (untreated, micro-structured). The promising results reveal the potential of micro and nano scale structured surfaces for achieving improved energy efficiency for electronics cooling systems

Effects of a mixed O/F ligand in the Tavorite-type LiVPO[sub]4O structure

We report the synthesis and detailed structuraland chemical characterization including electrochemicalproperties of a lithium vanadium oxy/fluoro-phosphatematerial. To the best of our knowledge, we have for the firsttime synthesized a LiVPO4O-type phase with a mixed O/Fligand. In the synthesis procedure, the LiVPO4O precursorcompound was fluorinated via LiF incorporation, withpreservation of the LiVPO4O framework structure. Theoperating potential of the synthesized material is increasedcompared to that of the LiVPO4O precursor (4.12 V vs 3.95 Vversus metallic lithium, respectively). The related increase inoperating potential was assigned to the effect of theintermixing O/F ligand, which is attained via the successfulfluorine incorporation into the LiVPO4O structure. A characterization of the investigated materials was performed usingmicroscale-covering XRD, XANES, and NMR techniques as well as nanoscale spatially resolved imaging and analytical STEMtechniques. The obtained oxy/fluoro-phosphate phase is isostructural to LiVPO4O; however, the presence of the mixed O/Fligand promoted a higher symmetry of vanadium octahedra. These variations of the vanadium local environment along with theobserved inhomogeneous distribution of the incorporated fluorine gave rise to the minor local deviations in vanadium valence.Our results clearly emphasize the connection among the fluorine ligand incorporation, its local distribution, and theelectrochemical properties of the material

Influence of sodium hydroxide on phase transformation of gamma alumina to alpha alumina

Corundum and transition alumina powders are commonly produced through the Bayer process—that is, by digestion of bauxite in a sodium hydroxide solution, followed by gibbsite precipitation, which contains significant amounts of Na+ ions. During the de-hydroxylation of gibbsite, Na+ is associated with retardation of the structural phase transformations between transition alumina and corundum (α-Al2O3) phases, although the exact role of Na is unclear. The influence of Na+ ions on the phase transformation of γ-Al2O3 to α-alumina was investigated by varying the concentration of NaOH in aqueous γ-Al2O3 suspensions. The phase transformation behavior of γ-Al2O3 was monitored through thermal analysis, X-ray diffraction, scanning electron microscope, X-ray photoelectron spectrometer (XPS), and transmission electron microscope. As the Na concentration in γ-alumina suspensions increased, the amount of α-Al2O3 decreased in samples that were heat treated at 1200°C for 2 h. XPS analysis indicated that washing transition alumina powders with NH4OH solutions had decreased the surface concentration of Na+ and facilitated the phase transformation to α-Al2O3

A microscopic view on the electrochemical deposition and dissolution of Au with scanning electrochemical cell microscopy – Part I

info:eu-repo/semantics/publishe

Impact of Tuned Oxidation on the Surface Energy of Sintered Samples Produced from Atomised B-Doped Al-Cu-Fe Quasicrystalline Powders

Super-hydrophobic surfaces and coatings have stimulated a great deal of research, with the aim being to achieve better wetting properties. Factors such as surface chemistry and roughness play an important role in changing the surface energy, which in turn leads to changes in the wettability. Here, we have analysed the time dependence of the oxide layer and possible surface adsorbates on the surface topography of an Al59Cu25Fe13B3 quasicrystalline material in relation to changes in the wettability. The quasicrystalline matrix phase was 94% of the sample volume, and it was covered by a very smooth, amorphous oxide layer. The AlB12 and AlFe2B2 boron-rich phases were embedded in the quasicrystalline material as a result of the 3 at.% boron addition, which made atomisation of the material a simpler process. Under ambient conditions, the sample was naturally covered by an oxide layer; therefore, it is referred to as “surfenergy” to distinguish it from the conventional surface energy of a bare quasicrystal surface. The growth of the oxide layer with atmospheric ageing and annealing at 500 °C in air for various times was investigated for both cases. The phase most prone to oxidation was the boron-rich AlFe2B2, which influenced the topography of the surface and accordingly the wetting behaviour of the specimen. We demonstrated that the surfenergy depends on the polar component, which is the most sensitive to the operating conditions. A correlation between the surfenergy components and the surface roughness was found. In addition, theoretical models to determine the wettability were included

Experimental studies on ferrofluid pool boiling in the presence of external magnetic force

The past decade has witnessed rapid advances in thermal-fluid applications involving nanoparticles due to existing heat transfer enhancements. The main challenges in working with nanoparticles are clustering, sedimentation and instability encountered in many studies. In this study, magnetically actuated Fe3O4 nanoparticles were coated with a fatty acid and dispersed inside a base fluid (water) in order to avoid clustering, sedimentation and instability as well as to improve the thermal performance. Boiling heat transfer characteristics of the ferrofluids were experimentally investigated with magnetic actuation and compared to the results without magnetic actuation. Nanoparticle mass fraction was the major parameter. Boiling heat transfer coefficient of the magnetically actuated system was found to be significantly higher compared to the case without magnetic actuation. The results showed that boiling heat transfer coefficient was not sensitive to the nanoparticle mass fraction