Behaviour of fly ash geopolymer binders under exposure to alkaline media

Abstract: Alkaline agents are primary binder components of geopolymer systems. In the converse, however, the hardened geopolymer binders can be adversely affected under exposure to strong alkalis. This paper presents an investigation conducted to evaluate the effects of highly alkaline exposure environment on fly ash geopolymer binders. In the study, a combination of sodium silicate and 12M NaOH solution was used as the alkali activator to prepare a low calcium (Class F) fly ash - based geopolymer binder. Fly ash geopolymer pastes or mortars were cast into 50 mm cubes and 25 x 25 x 285 mm prisms, then immersed in different media consisting of water or 1M to 3M NaOH solutions maintained at varied temperatures of 23, 38 and 80⁰C. The tests done include compressive strength, expansion, weight changes. Analytical studies were done using X - ray diffraction, X - ray fluorescence, Fourier transform infrared spectroscopy, scanning electron microscopy. Leaching analysis of storage solutions was also conducted

Effect of mix parameters on strength of geopolymer mortars - experimental study

Abstract: In this article, an investigation is reported on development of strength in South African fly ash (FA) – based geopolymer mixtures. Locally available Class F, FA from one of the coal power stations was used in the investigation. The alkali-activator used consisted of sodium silicate (SS) and sodium hydroxide (SH) mixed in varied ratios of 1.0, 1.5, 2.0, 2.5 and 3.0 SS to SH. The SS of silicate modulus = 2.5 was used but the SH concentration in the activator was varied to 10, 12, 14M NaOH. Mortars of 2.25 aggregate/binder ratio were used to prepare 50 mm cubes. In preparing mortar mixtures, the liquid to solids (L/S) ratios were varied to L/S = 0.3, 0.4, 0.5 and 0.6. Mortar cubes were cast and cured at 80oC for 7 days then tested for compressive strength. It was found that all three parameters consisting of SS/SH ratio of the activator, concentration of NaOH used in the activator and the L/S ratio, showed significant influence upon compressive strength development. The optimum strength of the geopolymer mortar mixtures was obtained at SS/SH = 2.0, 12M NaOH concentration ad L/S = 0.5

The Nehari Manifold for p-Laplacian Equation with Dirichlet Boundary Condition

The Nehari manifold for the equation −∆pu(x) = λu(x)|u(x)|p−2 + b(x)|u(x)|γ−2u(x) for x ∈ Ω together with Dirichlet boundary condition is investigated in the case where 0 < γ < p. Exploiting the relationship between the Nehari manifold and fibrering maps (i.e., maps of the form of t → J(tu) where J is the Euler functional associated with the equation), we discuss how the Nehari manifold changes as λ changes, and show how existence results for positive solutions of the equation are linked to the properties of Nehari manifold

Pozzolanic materials and waste products for formulation of geopolymer cements in developing countries : a review

Abstract: Potential use of Geopolymers as binders in concrete instead of ordinary Portland cement (OPC) has attracted worldwide attention in recent years, due to its advantages such as environmental benefits, better durability and acceptable mechanical properties. In this paper, it is shown that the large resources of aluminosilicate waste materials in developing countries present a great opportunity for their use to make geopolymer concretes towards building of local physical infrastructure. This paper reviewed research on characteristics and properties of geopolymer binders and concretes. The effects of different raw materials, various activators, mixture formation and curing are discussed

Effect of peak power on microstructure, mechanical and tribological properties of W-Ti-C-N(O) ceramic films produced by hybrid sputtering

This research investigates the impact of peak power (from 44 to 105 kW) on the structural and tribological properties of W-Ti-C-N(O) films. Chemical analysis of the coatings, using energy-dispersive spectroscopy and Raman spectroscopy, indicates that increasing target power results in a rise in the oxygen (from 2.6 to 12.0 at%), carbon (from 19.7 to 32.4 at%), and sp3 (from 9.8% to 24.3%) content. Morphological and topographical analysis reveal that an increase in target power causes a transition from a columnar structure (with nodular grains) to a dense structure (with textured grains). The indentation and dry sliding tests demonstrate that the maximum level of H/E2 (0.00047 GPa-1) is achieved, along with a low wear rate of 8.1 × 10-7 mm3/N.m.info:eu-repo/semantics/publishedVersio

Effect of substrate bias voltage on structural and tribological properties of W-Ti-C-N thin films produced by combinational HiPIMS and DCMS co-sputtering

Protective multi-component thin films at the surface of cutting tools have been significantly developed to reduce wear and friction. The present work investigates the effect of substrate bias voltage on the structural-tribological relations of W-Ti-C-N thin films produced by HiPIMS and DCMS co-sputtering. Chemical analysis of the coatings is obtained and composite phase structure is revealed. Morphology of the coatings illustrates that defectless surfaces may be achieved. Topographical parameters are investigated by employing graphical software. Indentation, scratch and pin-on-disk tests (pin is AISI 52100 steel) are applied to study mechanical behaviors of the films. To produce a wear-resistant film, a median bias voltage ( 60 V) and as a result, optimum content of tungsten concentration (19.2 at. %), grain size (42.8 nm) and average peak interval (188 nm) is required. Finally, a model based on the representative volume element is developed to show crack propagation and delamination.info:eu-repo/semantics/publishedVersio

Superior UVC light-mediated catalytic activity of a novel NiFe₂O₄@ TiO₂ magnetic nanocomposite synthesized with green route using Pulicaria Gnaphalodes plant extract for enhanced photocatalytic degradation of an antibiotic in water solution

In this study, the NiFe₂O₄@TiO₂ magnetic nanocomposite was synthesized by the green synthesis method, which is an efficient and economical method. Pulicaria Gnaphalodes plant extract was used for nanocomposite synthesis because this method is suitable for the biosynthesis of nanocomposites on a large scale, and the nanocomposite produced by plants is more stable. The efficiency of the synthesized nanocomposite was investigated for the photocatalytic degradation of Penicillin G (PNG) under UVC light irradiation in aqueous solutions. The structural characteristics of this nanocomposite were determined by field emission scanning electron microscopy, transmission electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, vibrating sample magnetometer, and dynamic light scattering. The effect of different parameters including pH, nanocomposite dose, penicillin G concentration and time were studied to reach optimum conditions. About 71% of PNG in optimal conditions (pH = 9, nanocomposite dose = 0.6 g/L, and penicillin G concentration = 10 mg/L) was decomposed. Generally, the NiFe₂O₄@TiO₂ nanocomposite can be used as an efficient catalyst for the degradation of PNG in aqueous solutions

Phyto-assisted synthesis of magnetic NiFe₂O₄ nanocomposite using the Pulicaria gnaphalodes methanolic extract for the efficient removal of an antibiotic from the aqueous solution: a study of equilibrium, kinetics, isotherms, and thermodynamics

In this research, the magnetic NiFe₂O₄ nanocomposite was synthesized using Pulicaria gnaphalodes methanolic extract and applied to remove penicillin G from aqueous solutions. The results of field emission scanning electron microscopy, X-ray powder diffraction, Fourier transform infrared, Vibrating-Sample Magnetometer (VSM), and energy-dispersive spectroscopy-mapping analyses showed that this nanocomposite was well synthesized with a size of approximately 50–70 nm. The maximum adsorption capacity of the magnetic NiFe₂O₄ nanocomposite was 22.95 mg/g under optimal conditions. In addition, the experimental data of penicillin G adsorption by the magnetic NiFe₂O₄ nanocomposite showed that ΔH and ΔS values were positive and ΔG was negative and were following the Temkin isotherm model with R² ¼ 0.99 and follows the pseudo-second-order kinetic model

Pulicaria gnaphalodes-assisted green synthesis of NiFe₂O₄@ZnO nanocomposites for sustainable remediation of an antibiotic from aqueous solution

In this study, the NiFe₂O₄@ZnO nanocomposite was synthesized in a simple, accessible and affordable method using Pulicaria gnaphalodes plant extract as a reducing agent. The structural characteristics of this nanocomposite were determined by transmission electron microscopy (TEM), X-ray diffraction, Fourier transform infrared spectroscopy, vibrating sample magnetometer, X-ray energy diffraction spectroscopy and dynamic light scattering. TEM micrograph confirmed the formation of spherical and cubic spinel ferrite with average dimensions of 75–85 nm. Some parameters such as pH, dose of NiFe₂O₄@ZnO nanocomposite, concentration of penicillin G and reaction time to reach optimal conditions were investigated. According to the results of the present research, the photocatalyst process along with the use of NiFe₂O₄@ZnO nanocomposite as an oxidizing agent is an effective method in degradation of the penicillin G antibiotic from aqueous solutions

Polarization of Broad Absorption Line QSOs I. A Spectropolarimetric Atlas

We present a spectropolarimetric survey of 36 broad absorption line quasi-stellar objects (BAL QSOs). The continuum, absorption trough, and emission line polarization of BAL QSOs yield clues about their structure. We confirm that BAL QSOs are in general more highly polarized than non-BAL QSOs, consistent with a more equatorial viewing direction for the former than the latter. We have identified two new highly-polarized QSOs in our sample (1232+1325 and 1333+2840). The polarization rises weakly to the blue in most objects, perhaps due to scattering and absorption by dust particles. We find that a polarization increase in the BAL troughs is a general property of polarized BAL QSOs, indicating an excess of scattered light relative to direct light, and consistent with the unification of BAL QSOs and non-BAL QSOs. We have also discovered evidence of resonantly scattered photons in the red wing of the C IV broad emission lines of a few objects. In most cases, the broad emission lines have lower polarization and a different position angle than the continuum. The polarization characteristics of low-ionization BAL QSOs are similar to those of high-ionization BAL QSOs, suggesting a similar BAL wind geometry.Comment: 39 pages, 6 figures (20 .gif files), accepted for publication in The Astrophysical Journal Supplement