Amount Of SiO2 Research Articles

Effects of SiO2 and CaO on Distributions of Platinum Group Metals Between Cu–CuO0.5 and Pb–PbO-Based Slags at 1523 K

Platinum group metals (PGMs) are recovered using molten Cu or Pb as collector metals during pyrometallurgical recycling processes. The collector metal containing PGMs is oxidized to produce a PGM-enriched alloy and slag, primarily containing Cu or Pb oxide. Additionally, the slag comprises a considerable amount of PGMs. Therefore, it is returned to the upstream processes to be used as a secondary raw material, and some of PGMs remain in the recycling processes. Herein, the distributions of Rh, Pd, and Pt between molten metals (Cu, Pb) and corresponding metal oxide-based (CuO0.5, PbO) slags were investigated at 1523 K. SiO2 or CaO was added to the slag to a maximum concentration of 20 mass pct, thereby reducing the oxygen partial pressure in the system. Furthermore, the addition of an optimum amount of SiO2 or CaO into various combinations of slags and collector metals reduced the concentrations of PGMs in the slags to less than approximately 1/10 of those without adding SiO2 or CaO. Therefore, the addition of SiO2 or CaO during the oxidation smelting process effectively reduced the dissolution of PGMs in the slag, resulting in a less amount of PGMs circulating in the recycling processes.

Assessment of Fly Ash-Rice Straw Ash-Laterite Soil Based Geopolymer Mortar Durability

Geopolymer is an inorganic form of alumina-silica that is synthesized through materials containing lots of silica (Si) and alumina (Al) originating from nature or from industrial by-products. The geopolymer binder is a two-component inorganic system consisting of solid components that have sufficient amounts of SiO2 and Al2O3 to form compounds such as fly ash, rice straw ash, pozzolan, laterite soil, slag, etc. This study aims to analyze the compressive strength, chemical compositions, and geopolymerization process of geopolymers produced from fly ash, rice straw ash, and lateritic soil bound with an alkaline activator, sodium hydroxide (NaOH), with a concentration of 12 M. The durability of the geopolymer mortar was determined by soaking for 3, 7, and 28 days using water curing and sulphate curing (Sodium Sulphate, Na2SO4, and Sulfuric Acid, H2SO4). The results showed that sodium hydroxide (NaOH) can release silica and alumina in the amorphous phase and can be used as a binder for geopolymer mortar made from straw ash, fly ash, and laterite soil without using oven heat, according to compressive strength, chemical compositions, and the geopolymerization process. The results of this study can be used to support the use of waste materials (fly ash and laterite soil) and local materials (straw ash) as geopolymer mortar-forming materials. Furthermore, it can aid in the development of eco-friendly (environmentally friendly) national infrastructure by eliminating the need for oven heat to initiate the polymerization reaction. However, this research can also be developed to increase the compressive strength of geopolymer mortar, which resembles that of conventional concrete in general. Doi: 10.28991/CEJ-2023-09-06-012 Full Text: PDF

Use of coal-fired slag in filling bodies with early strength for mining applications

The global output of coal-fired slag (CS) has far exceeded 300 million tons, and the annual output in China is 4.5 billion tons, which seriously affects the ecological security. Additionally, with the continuous increases in mine production capacities, the filling cost continues to rise, which seriously affects the normal production levels of the mines. To reduce the filling cost and make full use of the CS, this study was designed to realize diversified application of coal-fired slag (CS) as a backfill with early strength. First, physical and chemical analyses were conducted for coal-fired slag powder (CSP), fly ash (FA), flue gas desulfurization gypsum (FGDG) and mine waste rock (MWR). Based on the alkali excitation theory, mixture design, response surface theory and early strength testing of the backfill, the optimal ratio for the solid waste cementitious material and the backfill with early strength was determined. The primary and interaction effects of the backfill were analysed. Finally, the hydration mechanism for the CS-based cementing materials was revealed by monitoring the resistivity and water content and with scanning election microscopy (SEM), X-ray diffraction (XRD) and thermogravimetry/differential scanning calorimetry (TG-DSC) analyses of the hydration products. The results showed that (1) the total amount of SiO2 and Al2O3 in the CS was 61.08%, and the content of CaO was 17.3%, which indicated potential gelling activity. (2) The backfill with early strength was prepared by mixing CSP, FGDG and FA at 70%, 3% and 27%, with MWR and CS exhibiting a specific mass fraction (81%), binder-sand ratio (4:6) and CS-MWR ratio (5:5). The 3 d and 7 d uniaxial compressive strengths of the backfill were 1.7 MPa and 3 MPa. (3) The CS-MWR ratio of the backfill and the interaction between the CS-MWR ratio and binder-sand ratio significantly influenced on the early uniaxial compressive strength. (4) The early hydration process for the CS-based cementitious materials included the dissolution period, the induced formation and induction period and the condensation and hardening period. At 3 d, the hydration products were mainly generated by the CSP (the total amount of hydration products produced was 7.01%), while at 4 d–7 d, the FA was involved (the total amount of hydration products produced was 7.37%. The results of this research provide theoretical guidance for using CS to develop low-cost backfills with early strengths for application in mines.

Modified SiO2 microspheres/polyacrylate resin composites for the enhancement of oil-absorbing performance

Inserting inorganic materials into the skeleton of oil-absorbing resin (OAR) would weaken the interchain winding of polymer, regulate the pore channel structure, and thus enhance the oil-absorbing performance. However, the effects of surface modifiers on the oil-absorbing ability have been rarely explored. Herein, SiO2 microspheres coated with three kinds of silane coupling agents (3-aminopropyltriethoxysilane (APTES), γ-(methacryloxypropyl) trimethoxy silane (MEMO) and chlorotrimethylsilane (TMCS)) were composited with P(SMA-co-BA-co-ST) (octadecyl methacrylate (SMA), butyl acrylate (BA) and styrene (ST)). The as-prepared composite resin microspheres (OAR-APTES-SiO2, OAR-MEMO-SiO2 and OAR-TMCS-SiO2) were fully characterized by Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), optical microscopy (OM) and thermal gravimetric analysis (TGA). The results showed that the average particle sizes of the as-prepared SiO2 microspheres were nearly 300 nm and the silane coupling agent of APTES exhibited the best surface modification for SiO2 microspheres (grafting rate reached 16.78%). While, the average particle sizes of composite resins (OAR-APTES-SiO2, OAR-MEMO-SiO2 and OAR-TMCS-SiO2) were nearly 1.5 mm, 2 mm and 2.5 mm, respectively. Meanwhile, composite resin OAR-APTES-SiO2 showed the highest saturated oil-absorbing capacities, which were calculated to be 44.97, 38.12, 27.29 and 22.86 g/g for CCl4, CHCl3, CH2Cl2 and gasoline, respectively, under the optimal adding amount of SiO2 (ω(SiO2) = 0.8%), reaching more than 90% of the saturated oil-absorbing capacity in 30 min. Meanwhile, the oil-absorbing capacity of composite resin is 1.34 times higher than that of bare acrylic resin. It can be recycled 7 times without the obvious decrease in oil absorption ability. This study provides a novel method for the preparation of composite materials with high stability, high oil-absorbing capacity and low-saturation oil-absorbing time by regulating the resin pore structure.

Study on Growth Mechanism and Characteristics of Zirconium Alloy Micro-Arc Oxidation Film

Ceramic coatings on R60705 zirconium alloy were prepared on the surface by the micro-arc oxidation (MAO) technique in electrolytes containing Na2SiO3, NaOH, and Na2EDTA. The growth behavior of the MAO ceramic coatings at different stages, including growth rate, microstructure, and phase composition, was investigated using the method of direct observation of the boundary area. The results showed that the growth of the MAO coatings on R60705 zirconium alloy occurred in both inward and outward directions. At an oxidation time of 5 min, the thickness of the oxidation layer increased fastest, reaching 103.43 μm, with a growth rate of 0.345 μm/s. After 5 min, the growth rate decreased and tended to level off around 15 min, with a thickness and growth rate of 162.7 μm and 0.181 μm/s, respectively. The total thickness of the coatings continuously increased throughout the process, with the outward growth thickness always higher than the inward growth thickness. The composition of the zirconium alloy micro-arc oxidation coatings mainly consisted of monoclinic zirconia (m-ZrO2), tetragonal zirconia (t-ZrO2), and a small amount of SiO2. The main elements in the coatings were Zr, O, and Si. The corrosion resistance of the zirconium alloy micro-arc oxidation coatings increased first and then decreased with increasing oxidation time, with a corrosion current density of 8.876 × 10−9 A·cm−2 at 15 min, indicating the best corrosion resistance.

Mineral Assemblage of Olivine-Hosted Melt Inclusions in a Mantle Xenolith from the V. Grib Kimberlite Pipe: Direct Evidence for the Presence of an Alkali-Rich Carbonate Melt in the Mantle Beneath the Baltic Super-Craton

This report deals with the first mineralogical examination of secondary crystallized melt inclusions (CMIs) in healed cracks within olivine in a mantle peridotite xenolith from the V. Grib kimberlite pipe (Arkhangelsk diamondiferous province). In contrast to micro/nano-inclusions in diamonds, the studied CMIs are quite large (up to 50 µm), so that the mineral composition of the CMIs can be determined via conventional analytical approaches, e.g., Raman spectroscopy and scanning electron microscopy. Garnet peridotite is a coarse-grained mantle rock that equilibrates at 3.3 GPa and 750 °C (corresponding to a depth of ~100 km). The CMIs are therefore tiny snapshots of melt that existed in the shallow lithospheric mantle and were entrapped in olivine. In total, nineteen mineral species were identified among the daughter magmatic minerals of the CMIs. Various Na-K-Ca-, Na-Ca-, Na-Mg-, Ca-Mg-, Mg- and Ca-carbonates; Na-Mg-carbonates with the additional anions Cl−, SO42− and PO43−; alkali sulfates; chlorides; phosphates; sulfides; oxides; and silicates were established. Within the mineral assemblage, carbonates were predominant, with their abundance being more than 62 vol.%. The CMIs contained twelve alkali-rich minerals; nine of them were Na-bearing and showed bulk molar (Na + K)/Ca ≥ 1. The CMIs’ parental melt was an alkali-rich carbonate liquid that contained low amounts of SiO2 (≤9.6 wt%) and H2O (≤2.6 wt%). According to our estimates, the time of complete equilibration between olivine within the healed cracks and host olivine in the mantle at the calculated P-T parameters for the studied xenolith should be no more than several years. Based on this geologically short time span, a genetic link between the studied CMIs and the magmatism that formed the V. Grib kimberlite pipe is suggested.

Chromatographic separation performance of silica microspheres surface-modified with triazine-containing imine-linked covalent organic frameworks

In this work, 2,4,6-tris(4-aminophenyl)-1,3,5-triazine (TAPT) and 1,3,5-tris(4-formylphenyl)benzene (TFPB) were used as monomers to construct a triazine-containing imine-linked covalent organic framework (COF), which was then bonded onto the surface of aldehydized silica (SiO2–CHO), and finally a COF@silica composite material (TAPT-TFPB COF@SiO2) was successfully prepared. The chromatographic separation performance of SiO2–CHO, TAPT-TFPB COF@SiO2 and TAPT-TFPB COF@SiO2/SiO2–CHO (80/20, mass ratio) was evaluated and compared. It was found that separation efficiency was obviously enhanced by adding an appropriate amount of SiO2–CHO into TAPT-TFPB COF@SiO2. The obtained TAPT-TFPB COF@SiO2/SiO2–CHO showed more favorable separation ability than SiO2–CHO and TAPT-TFPB COF@SiO2. Various aromatic compounds including alkylbenzenes, polycyclic aromatic hydrocarbons, environmental endocrine disruptors, foodborne stimulants and phenyl ketones were effectively separated on the TAPT-TFPB COF@SiO2/SiO2–CHO column in reversed phase chromatography mode. The silica microspheres surface-modified with triazine-containing imine-linked COFs proved to be a new type of promising chromatographic packing materials.

Concretes on a composite gypsum binder using limestone stone crushing waste

The article discusses the possibility of obtaining Composite Gypsum Binders (CGB) and heavy concretes based on them using local raw materials from Palestine. As an active mineral additive in the composition of the composite gypsum binder, it is proposed to use finely dispersed quartz sand with a specific surface area of ​​500 m2/kg, on the surface of which, during grinding, a disturbed microlayer is formed containing a limited amount of amorphous SiO2, which is capable of binding Ca(OH)2 at ordinary temperatures with the formation of insoluble compounds, that is, it has pozzolanic activity, and as a result provides a significant increase in the strength of composites, increases their water resistance. Based on the developed composite gypsum binder with sufficiently high strength (24.8 MPa) and water resistance (K = 0.73), heavy concretes were obtained with a class of compressive strength B7.5 - B15, for use in residential, public, and industrial buildings in the form of load-bearing, self-supporting and enclosing structures.

Effect of SiO2 Coating on Microstructure and Electrochemical Properties of LiNi0.5Mn1.5O4 Cathode Material

Abstract We present a simple method for producing SiO2-modified LiNi0.5Mn1.5O4 (LNMO) cathode materials. Manganese carbonate was directly mixed with nickel nitrate and lithium hydroxide, and a spherical structure LNMO cathode material was prepared by two-step calcination, then ethyl orthosilicate and LNMO powder were simply mixed in solid and liquid phases to prepare SiO2-coated LNMO material. The effect of SiO2 coating on the structure of LNMO was studied by diffraction of X-rays, scanning electron microscope (SEM), transmission electron microscope (TEM), and thermogravimetric analysis and differential scanning calorimetry. An amorphous SiO2 coating layer developed on the surface of the LNMO particles in the modification and this could alleviate the strike of hydrogen fluoride (HF) caused by electrolyte decomposition as well as the development of a solid electrolyte interphase. The electrochemical performance of the coated material was as follows: when the amount of SiO2 was 0 wt%, 1 wt%, 2 wt%, and 3 wt%, the initial discharge capacity of the sample was 98.2, 84.1, 101.3, and 89.8mAh/g, respectively. After 50 charge−discharge cycles, the capacity retention rates are 92.7%, 66.8%, 97.9%, and 93.8%, respectively. The cyclic stability of the samples can be significantly improved when the SiO2 coating amount is 2 wt% and 3 wt%, indicating that SiO2 coating can not only improve the discharge-specific capacity of the material but also improve its cyclic stability.

Preparation of mullite whiskers from high alumina fly ash and its reinforced porous structure

Porous has been formed in samples when mullite whiskers are prepared by firing compacts of high-aluminum fly ash and ammonium aluminum sulfate hydrate with a small amount of sodium dihydrogen phosphate and SiO2 at high temperature for 4 h. The effects of the particle size of fly ash, the firing temperature, and the content of sodium dihydrogen phosphate on the porous structure and the formation of whiskers are discussed. The results show that the smaller the particle size of fly ash, the more uniform porous in sample after fired, which is more conducive to the nucleation of mullite whiskers. Additionally, the amount of whiskers formation increased significantly with the firing temperature increasing, nonetheless, the pore size of porous reduced and the aspect ratio of whiskers gradually increased by reducing the content of sodium dihydrogen phosphate; owing to the reduction of glass melt in the matrix, the Al2O3/SiO2 ratio of the formed mullite whiskers gradually decreased. Thus, in order to obtain mullite whiskers self-reinforcement porous ceramics with the relatively low cost and no pollution to the environment, through the above preparation process, the addition amount of sodium dihydrogen phosphate and calcination temperature should be properly controlled.

Xanthium strumarium seed as a potential source of heterogeneous catalyst and non-edible oil for biodiesel production

A sustainable process has been developed for synthesis of biodiesel by utilizing seed shell ash and non-edible seed oil from Xanthium strumarium seeds. The catalyst prepared by open air burning (UC), calcinations at 550 °C (C550) and 700 °C (C700) was characterized by powder X-ray diffraction (XRD), fourier transform infrared (FT-IR), field emission scaning electron microscope (FESEM), energy dispersive X-ray (EDX), field emission transmission electron microscope (FETEM), X-ray photoelectron spectrometer (XPS), thermogravimetric (TG) and brunauer-emmett-teller (BET) analysis. Elemental analysis by XPS and EDX displayed the presence of potassium (34 wt%) in high concentrations that can contribute effectively to the transesterification process. The derived catalyst provides a high biodiesel yield (98.3%) at optimum operating conditions viz. 6 wt% catalyst concentrations, 9:1 methanol to oil ratio at 60 °C within 70 min. FFA content reduced from 5.63 mg in the oil to 0.28 mg in the biodiesel due to presence of considerable amount of amphoteric SiO2 and acidic P2O5 in the catalyst. The catalyst prepared at 550 °C showed the highest pH value of 11.78. The Hammett indicator test provides higher basicity for C550 (0.513 mmol/g) than that of C700 and uncalcined catalyst. The reaction follows pseudo-first-order kinetics and the activation energy was found to be 37.413 kJ mol−1. The reusability study also showed satisfactory biodiesel yield (82.3%) at 3rd round of transesterification reaction. The prepared biodiesel was characterized by 1H and 13C NMR, GC-MS analysis and the fuel parameters are evaluated by the standard protocols.

Preparation of Sulfonated Poly(arylene ether)/SiO2 Composite Membranes with Enhanced Proton Selectivity for Vanadium Redox Flow Batteries

Proton exchange membranes (PEMs) are an important type of vanadium redox flow battery (VRFB) separator that play the key role of separating positive and negative electrolytes while transporting protons. In order to lower the vanadium ion permeability and improve the proton selectivity of PEMs for enhancing the Coulombic efficiency of VRFBs, herein, various amounts of nano-sized SiO2 particles were introduced into a previously optimized sulfonated poly(arylene ether) (SPAE) PEMs through the acid-catalyzed sol-gel reaction of tetraethyl orthosilicate (TEOS). The successful incorporation of SiO2 was confirmed by FT-IR spectra. The scanning electron microscopy (SEM) images revealed that the SiO2 particles were well distributed in the SPAE membrane. The ion exchange capacity, water uptake, and swelling ratio of the PEMs were decreased with the increasing amount of SiO2, while the mechanical properties and thermal stability were improved significantly. The proton conductivity was reduced gradually from 93.4 to 76.9 mS cm-1 at room temperature as the loading amount of SiO2 was increased from 0 to 16 wt.%; however, the VO2+ permeability was decreased dramatically after the incorporation of SiO2 and reached a minimum value of 2.57 × 10-12 m2 s-1 at 12 wt.% of SiO2. As a result, the H+/VO2+ selectivity achieved a maximum value of 51.82 S min cm-3 for the composite PEM containing 12 wt.% of SiO2. This study demonstrates that the properties of PEMs can be largely tuned by the introduction of SiO2 with low cost for VRFB applications.

Effect of SiO2-doped on microstructural evolution and hydrogen storage performances of AB2 type alloy

The influence of impurities (such as Si, O) on the properties of hydrogen storage alloys in industrial processes received extensive attention, yet the role of Si and O coexisting on the hydrogen absorption and desorption properties of AB2-type hydrogen storage alloys remains to be clarified. We investigated the doping of SiO2 on the microstructure and hydrogen storage properties of Ti-Mn based AB2-type hydrogen storage alloy. When a small amount of SiO2 (<1.0 wt%) was added, the hydrogen storage properties of the alloy did not change much and still maintained excellent cyclic stability, and the only difference was the plateau pressure of the alloys doped with SiO2 decreased. However, when excessive SiO2 (∼2.0 wt%) was added, the hydrogen storage plateau slope of the alloy increased sharply, and the hydrogen storage capacity decreased. It is ascribed that the formation of ZrO2 phase and the doping of Si with the SiO2 content increase, resulting in the lattice constant of the alloy increasing and the plateau pressure decreasing. These findings hold promising reference prospects for practical production.

Evaluation of Corrosion Resistance and Surface Film Analysis after Corrosion Testing of Materials Coated by Chemical Densified Coating Method under Boiling Sulfuric Acid Environment

For the purpose of developing metallic materials with excellent corrosion resistance under boiling sulfuric acid environment, the coated materials were evaluated for their corrosion resistance and the differences in surface morphology were investigated. As a result, the corrosion resistance of SUS304 coated and sintered eight times by chemical densified coating method (S-ZAC) was maintained at the point after 12h corrosion test, but the corrosion rate rapidly increased after 100h corrosion test. The cross-sectional microstructural analysis of the specimens showed that only a small amount of SiO2 remained on the surface, while Cr2O3 completely disappeared. The mechanism of film delamination in S-ZAC is assumed to be due to the thermal expansion caused by heating, which resulted in curvature of the thick film and cracks at the Cr2O3 and SiO2 interfaces. On the other hand, SUS304 coated with higher density of Cr2O3 by repeating the coating and sintering eleven times (MS-ZAC) showed excellent corrosion resistance as well as SiC even after 100h corrosion test. The results of cross-sectional microstructural analysis showed that MS-ZAC had higher Cr2O3 concentration, finer SiO2 grain size, and fewer porosity than S-ZAC. In particular, the mechanism of film maintenance in MS-ZAC is assumed to be the formation of a stacked structure in Cr2O3 particle layer, in addition to the thinning of the entire film.

Palaeoenvironment of the Albian‐Cenomanian Mundeck Formation in the Douala Basin (SW, Cameroon): Evidence from facies analysis and geochemistry

The Lower Cretaceous syn‐rift deposits of the Douala Basin (Mundeck Formation), located in the equatorial West African margin were investigated in order to determine the palaeoenvironment and organic matter source, redox conditions, palaeoclimate, and tectonic settings, based on facies, organic and inorganic geochemical analyses. The sediments consist of pebble, coarse, medium‐ to fine‐grained sandstone, siltstone, and grey to black fossiliferous shales. The shales are characterized by an average total organic carbon (TOC) of 1.02%, fair to poor source generative potential with present‐day hydrogen index values, which range from 31 to 350 mg HC/g TOC suggesting that the shale contains Type III kerogens with mainly gas generative potential. The organic particles are dominated by phytoclasts (40% on average) and non‐fluorescent amorphous organic matter (34% on average). The palynomorphs represent about 26% on average with a large amount of pollen grain and a minor amount of dinoflagellate cysts and microforaminifera test linings. The inferred depositional environment of the studied sediments is an alluvial fan to fluvio‐lacustrine with shallow marine incursion. This depositional environment received the contribution of aquatic algae and microorganisms with a large amount of terrestrial organic matter, evidenced by the presence of some dinoflagellate cysts and microforaminifera test linings, and relatively higher amounts of SiO2, Al2O3, and phytoclasts. The presence of trace elements such as Ba, Sr, V, Ni, Co and Cr in the analysed samples and their ratio, suggest suboxic to anoxic conditions of deposition with low salinity. The warm to cold and dry climatic conditions prevailed during the deposition of the Mundeck deposits and sediments from active continental margin setting during the lower Cretaceous periods in the Douala Basin as confirmed by inorganic geochemical data. This study sheds light on the early stage of the evolution of the Douala Basin which could be integrated into the context of a mid‐Jurassic to lower Cretaceous regional evolution of the opening of a passive margin. This evolution is characterized by an alluvial fan, fluviatile, lacustrine, lagoon and marine depositional system. This depositional system is recognized as part of the petroleum system recognized within the syn‐rift deposits in the others basins along the West African margin, where giant hydrocarbons have been discovered.

Mechanisms of SiO oxidation: Implications for dust formation

Reactions of SiO molecules have been postulated to initiate efficient formation of silicate dust particles in outflows around dying (AGB) stars. Both OH radicals and H2O molecules can be present in these environments and their reactions with SiO and the smallest SiO cluster, Si2O2, affect the efficiency of eventual dust formation. Rate coefficients of gas-phase oxidation and clustering reactions of SiO, Si2O2 and Si2O3 have been calculated using master equation calculations based on density functional theory calculations. The calculations show that the reactions involving OH are fast. Reactions involving H2O are not efficient routes to oxidation but may under the right conditions lead to hydroxylated species. The reaction of Si2O2 with H2O, which has been suggested as efficient producing Si2O3, is therefore not as efficient as previously thought. If H2O molecules dissociate to form OH radicals, oxidation of SiO and dust formation could be accelerated. Kinetics simulations of oxygen-rich circumstellar environments using our proposed reaction scheme suggest that under typical conditions only small amounts of SiO2 and Si2O2 are formed and that most of the silicon remains as molecular SiO.

Evolution Mechanism of MgO–Al2O3–SiO2–CaO Inclusions During Continuous Casting of Si‐Killed Spring Steel

In article number 2200475, Qing Liu and co-workers show the inclusion evolution during the continuous casting process of the 55SiCrA spring steel. The primary inclusions are CaO-Al2O3-SiO2-MgO inclusions. The [Si], [Al], and [Mg] reacted with [O] because of the secondary oxidation and the temperature decline, increasing the amount of SiO2, Al2O3, and MgO in oxide inclusions. The melting point of inclusions increased.

Valorisation of Water Potabilization Sludges as Precursors for Alkali-Activated Binders: Characterization and Feasibility Study.

Water potabilization sludges (WPS) are a heterogeneous waste generated from the coagulation-flocculation process of drinking water production, whose composition is highly dependent on the geological context of reservoirs, the composition and volume of treated water, and the types of coagulants used. For this reason, any feasible approach for reusing and valorising of such waste cannot be disregarded from the detailed investigation of its chemical and physical characteristics and they have to be evaluated at a local scale. In this study, WPS samples from two plants serving the Apulian territory (Southern Italy) were subjected for the first time to a detailed characterization with a view to evaluating their recovery and reuse at a local scale as a raw material for producing alkali activated binders. WPS samples were investigated by X-ray fluorescence (XRF), X-ray powder diffraction (XRPD) including phase quantification by the combined Rietveld and reference intensity ratio (RIR) methods, thermogravimetric and differential thermal analysis (TG-DTA), Fourier-transform infrared spectroscopy (FTIR) and scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX). Samples showed aluminium-silicate compositions with up to 37 wt% of Al2O3 and up to 28 wt% of SiO2. Small amounts of CaO were also found (6.8 and 4 wt%, respectively). The mineralogical investigation indicates the presence of illite and kaolinite as clayey crystalline phases (up to 18 wt% and 4 wt%, respectively), in addition to quartz (up to 4 wt%) and calcite (up to 6wt%) and a large amorphous fraction (63 wt% and 76 wt%, respectively). WPS were subjected to heating from 400 °C to 900 °C and mechanical treatment by high energy vibro-milling in order to determine the best pre-treatment condition in view of their use as solid precursors to prepare alkali-activated binders. Alkali activation (8M NaOH solution; room temperature curing) was attempted on untreated WPS, on 700 °C heated and on 10-minute high-energy milled samples, which were considered the most suitable based on the preliminary characterization. Investigations of alkali-activated binders confirmed the geopolymerisation reaction occurrence. Variations in gel features and compositions depended on the amount of reactive SiO2, Al2O3 and CaO available in the precursors. WPS heated at 700 °C led to the most dense and homogeneous microstructures, due to a greater availability of reactive phases. The results of this preliminary study demonstrate the technical feasibility of preparing alternative binders from the investigated Apulian WPS, paving the way for a local reuse of these waste products, leading to economic and environmental benefits.

Evaluation the mechanical and electrochemical anti-corrosion properties of polydimethylsiloxane/SiO2 gel coated carbon steel rebar in concrete pore solution

The aim of the current study was to evaluate the mechanical and electrochemical anti-corrosion properties of carbon steel rebar in concrete pore solution after the steel was coated with polydimethylsiloxane/SiO2 (PDMS/SiO2) hybrid material as an organic–inorganic hybrid coating. PDMS/SiO2 hybrid material was prepared using a base-catalyzed sol-gel process with different SiO2 contents (0 wt%, 5 wt%, 10 wt%, 15 wt% and 20 wt%). Mechanical studies showed that the synergetic effect of PDMS and SiO2 increased the values of yield stress and Young's modulus and decreased the elongation at break. Electrochemical studies using EIS and polarization tests showed that the coated steel rebar samples had higher corrosion resistance than the uncoated steel sample, illustrating that the PDMS/SiO2 coating exhibits great barrier properties in corrosion reactions and indicates more corrosion resistance in the CPS corrosive media, and increasing the SiO2 content in the hybrid coating from 5 to 15 wt% promotes corrosion inhibition effectiveness. The steel rebar sample coated with the PDMS/SiO2 hybrid sample with 15 wt% SiO2 content as the optimal amount of SiO2 showed the highest corrosion resistance and inhibition efficiency (95.81%) values. SEM micrographs of the surface morphology of uncoated and PDMS/15SiO2 coated steel rebar surface samples immersed in CCP solutions for 24 h revealed that the PDMS/15SiO2 coating effectively inhibits steel corrosion in CCP solution due to less corrosive ion penetration to the steel surface.

Thermal and dielectric properties of PVDF/PEO/SiO2 nanodielectrics for flexible radioelectronic device technologies

Hybrid polymer nanocomposites (HPNCs) are innovative multifunctional materials, which are developed and intensively studied for their uses in the rapid evolution of flexible and lightweight device technologies. Accordingly, to contribute in this area, thermal properties of the crystal phases and the broadband radio frequencies dielectric dispersion and relaxation behaviour of the HPNC films based on poly(vinylidene fluoride) (PVDF)/poly(ethylene oxide) (PEO)/silica (SiO2) are formulated and studied by employing differential scanning calorimeter (DSC) and impedance/material analyzer (IMA). DSC thermograms of these semicrystalline HPNCs explained the wide range alteration in the crystals melting temperature of PVDF (153–167 ​°C) and PEO (59–72 ​°C) and the total degree of crystallinity (4–87%) with varying compositional ratio over the entire range of the PVDF/PEO blend host matrix and the dispersed amount of amorphous SiO2 nanomaterial up to 15 ​wt%. The dielectric dispersion behaviour of these HPNCs, at 20 ​°C, confirmed a non-linear decrease in permittivity with the increase of applied radio wave electric field frequency from 1 ​MHz to 1 ​GHz, which lies in the range of 6 to 2. At a fixed frequency, dielectric permittivity values exhibited an uneven variation with the increase of SiO2 amount and also the modification in the composition of polymer blend matrix in these composites. The analysis of dielectric loss spectra and relaxation processes revealed that these are low loss dielectrics and the presence of SiO2 nanoparticles in the polymer blend matrix impedes the chain segmental dynamics and the dipole reorientation. The electrical conductivity of these HPNCs enhanced in the range of 10−8 to 10−4 ​S/cm with the increase in frequency but it changed anomalously when the constituent amounts of the formulated composites are varied. The polymer crystals thermal properties and the dielectric and electrical conductivity dispersion behaviour of these materials are demonstrated with the consideration of polymer-polymer and polymer-nanoparticle hybrid interfaces and interactions. The experimental results evidenced the behaviour of PVDF/PEO/SiO2 films as tunable nanodielectrics with their compositions and could be used as insulator and dielectric substrate materials in the advances of flexible radioelectronics and energy storage devices.