Alkaline Attack Research Articles

Valorization of Aluminum Chips into γ-Al2O3 and η-Al2O3 with High Surface Areas via the Precipitation Route

In this study, pseudo-boehmite and bayerite precursors have been prepared from aluminum chips collected from metal manufacturing industry in the region of Sfax, Tunisia for the production of γ-Al2O3 and η-Al2O3, respectively. The alkaline attack of the scraps with 2 M NaOH solution provides the sodium aluminate solution which was neutralize with 2 M HNO3 acid solution at room temperature to different pH values of 6–10. The neutralization pH is an important parameter that controls the nature of the precipitated phase. At pH 6, the XRD pattern of the as-dried sample showed the characteristic peaks of well crystallized bayerite. The increase of the neutralization pH to 7–9, there is precipitation of pseudo-boehmite. At pH 10, we obtained a mixture of bayerite and pseudo-boehmite. Through the calcination of bayerite at 400 °C, η-Al2O3 was obtained with specific surface area of 455 m2/g, whereas the calcination of pseudo-boehmite leads to globular aggregate made by fibrous crystals of γ-Al2O3. During the structural transformation of pseudo-boehmite into γ-Al2O3 and bayerite into η-Al2O3 a portion of the aluminum atoms migrate from octahedral sites to tetrahedral sites in the alumina lattice. The tetrahedral to octahedral Al ratios are about 1–3 and 1–4 for γ-Al2O3 and η-Al2O3, respectively.

Durability of Hybrid Composite Beam Bridges Subjected to Various Environmental Conditioning

AbstractThe hybrid composite beam (HCB) is a novel idea that combines conventional construction materials (i.e., steel and concrete) with fiber-reinforced polymer (FRP) composites in a new configuration. This hybridization aims to optimize the beam’s structural performance and produce a structural element that is more durable than conventional members. This study examined the durability of a commercial glass FRP (GFRP) laminate that was used to encase the HCB elements in a recently constructed HCB bridge. The E-glass/vinyl ester laminate was subjected to five aging regimes. These conditioning regimes simulated an alkaline attack, a salt attack, a salt attack that was preceded by ultraviolet (UV) irradiation exposure, and sustained stresses that were accompanied by controlled thermal cycles and natural weathering. The durability of the E-glass/vinyl ester laminate was examined in terms of changes that occurred in the ultimate tensile strength. A microstructural analysis was performed on both unconditioned ...

English

Now-a-days, the rising cost of building materials for construction purposes is a factor of great concern. The price of building materials is rising day by day. Now, most of the researchers are paying much attention on the suitable materials which can reduce the cost of construction as well as increase the strength properties of concrete. Mainly gravel and sand are used in the preparation of conventional concrete. While the use of an agricultural by-product i.e. coconut shell as a partial replacement with conventional coarse aggregates is expected to serve the purpose of encouraging housing developers in building construction. Environmental impact can also be reduced by making sustainable use of this waste. The coconut shell aims to prepare light weight concrete which may reduce considerably the self-load of a structure and permits large precast units to be handled. The coconut shell is more resistant to acidic, salty and alkaline attack. The characteristic properties of concrete such as compressive strength, split tensile strength, flexural strength, impact resistance, bond strength using the mix made by replacing coarse aggregates with coconut shell were reviewed in this paper.

Wood waste as coarse aggregate in the production of concrete

An attempt was made in this experimental investigation to recycle wood waste. Concrete-containing wood aggregate in percentages of 0, 15, 20 and 25 in place of crushed stone was developed with a characteristic compressive strength of 25 MPa, with a mix proportion of 1:1.26:2.76 and with water/cement ratio of .45. One hundred and twenty specimens were cast and tested to evaluate the strength and durability properties of concrete. The performance of wood aggregate concrete was compared with control concrete that contained only crushed stone aggregate. The compressive strength of control concrete was 31.40 MPa and that of wood aggregate concrete with 15% replacement level was 32.36 MPa which is 3.06% above the control concrete. Split tensile strength of 15% replaced wood aggregate concrete was 2.25 MPa as against a value of 2.05 MPa for control concrete registering an increase of 9.75%. The flexural strength of control concrete was 2.49 MPa and that of concrete containing 15% wood aggregate was 2.51 MPa which was .80% higher than the control concrete. The weight loss of wood aggregate concrete with 15% replacement level under acid attack was 30.38% greater than the control concrete. Under alkaline attack, the weight loss of wood aggregate concrete with 15% replacement level registered an increase of 9.72% over control concrete. Therefore, wood aggregate can be used in the production of concrete, and the optimum replacement was found to be 15% from all considerations.

Ageing Problems of GFRP Grids Used for Masonry Reinforcement

In this study, an effort was made to develop an experimental protocol to study the effects of accelerated ageing on GFRP (Glass Fiber-Reinforced Polymer) grids. The physic-mechanical properties of different types of glass FRP grids were investigated. GFRP specimens were subjected to environmental agents including freeze-thaw, high relative humidity, high temperature. Mechanical and physical tests were used to measure the retained properties and to observe the causes of damage and strength reduction. The experimental data showed that resin properties may strongly influence the durability of FRP reinforcement, environmental combined cycles did not take to significant damage of conditioned specimens; GFRP grids are sensitive to alkaline attack when resin does not provide adequate protection to fibers.

Durability Analysis for FRP and SRG Composites in Civil Applications

In this study, an effort was made to develop an experimental protocol to study the effects of accelerated ageing on composite materials based on bamboo and steel fibers. The physic-mechanical properties of different types of steel and bamboo fibers were investigated. Specimens were subjected to environmental agents. Mechanical and physical tests were used to measure the retained properties and to observe the causes of damage and strength reduction. The experimental data showed that resin properties may strongly influence the durability of FRP reinforcement, environmental combined cycles did not take to significant damage of conditioned specimens; steel fibers are sensitive to alkaline attack when resin does not provide adequate protection to fibers.

Effect of Particle Size and Unburned Carbon Content of Fly Ash from Hadong Power Plant on Compressive Strength of Geopolymers

Fly ash is one of the aluminosilicate sources used for the synthesis of geopolymers. The particle size distribution of fly ash and the content of unburned carbon residue are known to affect the compressive strength of geopolymers. In this study, the effects of particle size and unburned carbon content of fly ash on the compressive strength of geopolymers have been studied over a compositional range in geopolymer gels. Unburned carbon was effectively separated in the <TEX>$-46{\mu}m$</TEX> fraction using an air classifier and the fixed carbon content declined from 3.04 wt% to 0.06 wt%. The mean particle size (<TEX>$d_{50}$</TEX>) decreased from <TEX>$22.17{\mu}m$</TEX> to <TEX>$10.79{\mu}m$</TEX>. Size separation of fly ash by air classification resulted in reduced particle size and carbon residue content with a collateral increase in reactivity with alkali activators. Geopolymers produced from carbon-free ash, which was separated by air classification, developed up to 50 % higher compressive strength compared to geopolymers synthesized from raw ash. It was presumed that porous carbon particles hinder geopolymerization by trapping vitreous spheres in the pores of carbon particles and allowing them to remain intact in spite of alkaline attack. The microstructure of the geopolymers did not vary considerably with compressive strength, but the highest connectivity of the geopolymer gel network was achieved when the Si/Al ratio of the geopolymer gel was 5.0.

Tensile behaviors of ECR-glass and high strength glass fibers after NaOH treatment

ECR-glass and high strength glass (S-glass) fibers were treated in 2 mol/l NaOH solution up to 5 h. The strength maintenance ratio and mass loss ratio of the fibers after treatment were investigated. The surface morphologies were characterized using scanning electron microscopy, and changes of chemical composition were analyzed by energy dispersive X-ray spectroscopy and Fourier transform infrared spectrometry. The alkali resistance and tensile strength of the S-glass fibers are higher compared to those of the ECR-glass fibers as they received less alkaline attack because of the more compact SiO2 network and the formation of a protective layer on the S-glass fiber surface. The S-glass fibers have a higher mass loss due to the smaller diameter and thinner corrosion layer.

Effect of Composition on Structure and Mechanical Properties of Metakaolin Based PSS-Geopolymer

Geopolymer is a type of cross linked long-chain inorganic compound, built in three-dimensional structures and has different attractive properties (thermal, mechanical, chemical, etc). This study elucidated the structure and mechanical properties of PSS type geopolymer obtained by alkaline attack of metakaolin. A systematic investigation was conducted to comprehend the effect of molar ratios Si/Al and Na/Al on the properties of this geopolymer by using 29Si and 27Al magnetic angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy, X-Ray diffraction and mechanical measurements. The results indicate that an increase of Si/Al ratio improves the geopolymer mechanical properties due probably to the formation of Si-O-Si bond in the geopolymer at the expense of Si-O-Al one. It was also shown that an introduction of NaOH in the geopolymer composition enhances the mechanical properties until a molar ratio Na/Al=1. Beyond this value, the excess of Na+ cation causes fragility of the geopolymer structure confirmed by a decrease of the mechanical strength.

Removal of heavy metal ions from aqueous solutions using low-cost sorbents obtained from ash

AbstractThis study’s main objective was the development of effective low-cost sorbents for the removal of heavy metal ions from aqueous solutions. The influence of different factors on the sorption capacity of ash and modified ash as low-cost sorbents obtained by different methods was investigated. The synthesis of new ash-based materials was carried out at ambient temperature (20°C), 70°C, and 90°C, respectively, in an alkaline medium with NaOH concentrations of 2 M and 5 M, respectively, corresponding to a mixture with solid/liquid ratios of 1: 3 and 1: 5, respectively. The prepared materials (sorbents) were characterised by scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDAX), X-ray diffraction, and BET surface measurement. Adsorption isotherms were determined using the batch equilibrium method. The results showed that these types of new materials displayed a good capacity to remove copper, nickel, and lead ions (29.97 mg of Cu2+ per g of sorbent, 303 mg of Ni2+ per g of sorbent, and 1111 mg of Pb2+ per g of sorbent) from aqueous solutions. The modified materials were prepared using an alkaline attack (a recognised method used in previous studies), but Romanian ash from a thermal power plant was studied for the above purpose for the first time. Hence, the factors which affect the sorption capacity of the prepared low-cost sorbents were determined and their behaviour was explained, taking into account the composition and structure of the new materials.

Compressive strength and durability properties of Rice Husk Ash concrete

The paper presents the experimental investigation conducted on Rice Husk Ash (RHA) concrete to evaluate the compressive strength and to study its durability properties. In the preparation of rice husk concrete, cement was replaced at various percentage levels such as 5%, 10%, 15% and 20%. Besides control concrete was also prepared for comparison purpose. Two grades of concrete, namely M30 and M60, were prepared. The strength of the concrete increased with the levels of percentage of replacement of 10% at which the increase in strength was 7.07% at 90 days compared to normal concrete. In the case of M60 grade concrete the compressive strength increases with the addition of super plasticizer. In general, Saturated Water Absorption (SWA) increased in the case of RHA Concrete up to 10% replacement level, but the same diminished with addition of super plasticizer. The porosity of RHA Concrete decreased from 4.70% to 3.45% when the replacement level increased from 5% to 20%. There is a further decrease with the addition of super plasticizer. The chloride ion permeability value of RHA Concrete was very low between 100–1000 coulomles, as compared to normal concrete. It was observed from tests that RHA concrete was more resistant to HCl solution than that of control concrete. The percentage of resistance against alkaline attack of M30 grade RHA concrete varied from 25 to 67 and the corresponding value for M60 grade was from 35 to 70 for replacement levels varying from 5% to 20%. Addition of 20% RHA showed higher resistance against sulphate attack for both continuous soaking and cyclic conditions. On the whole addition of RHA as CRM improves the strength and durability properties of concrete to considerable extent.

Nano-indentation on nickel aluminate spinel and the influence of acid and alkaline attacks on the spinel surface

Nickel aluminate spinel phase was successfully sintered from the thermal reactions between nickel oxide and kaolinite or γ-alumina precursor, to simulate the stabilization mechanism of hazardous metal-bearing waste by ceramic matrix. The product phases were then tested using nano-indentation to obtain their nanohardness and Young's modulus, as a means to evaluate the properties of the product after incorporating the waste material. The results indicate the beneficial effect of forming aluminate spinel phase in the system due to its superior mechanical properties. A higher sintering temperature was found to enhance crystal growth in the spinel phase, together with its nanohardness and modulus. The minimum temperature for fabricating nickel aluminate spinel with a surface property comparable to ceramic materials was found to be 1200°C, although the initiation of the spinel phase can be achieved at a lower temperature. Nano-indentation experiments performed on the spinel-containing samples leached by strong acid and alkaline solutions reveal the superiority of nickel aluminate spinel in resisting acid and alkaline attack and also suggest a reliable mechanism for hosting hazardous nickel in the crystal structure.

Preparation and characterization of glazes from combinations of different industrial wastes

The work reported here involves the preparation and characterization of ceramic glazes made from combinations of different industrial wastes. The wastes were float glass, granite and lime shale (a raw material waste from the oil shale industry in São Mateus do Sul, state of Paraná, Brazil), which were used to replace natural raw materials in a proportion of up to 50% in weight. The compositions were formulated using the Seger method and prepared by conventional ceramic processing. The stabilized suspensions were applied in commercial wall tile and porcelain stoneware tile, which were sintered at temperatures of 1080°C and 1150°C, respectively, using two different heating cycle. Three compositions were developed, two of which yielded opaque glazes and one a transparent glaze. Linear thermal expansion coefficients (α) of 80.10−7°C−1 to 100.10−7°C−1, and glaze softening temperatures of 600–700°C were characterized by dilatometric analysis. The glaze compositions showed chemical resistance against acid and alkaline attack after 96h, showing a mass loss of less than 0.1% in weight. The surface hardness of the glazes determined by the Mohs scale, Vickers microhardness and abrasion resistance (PEI indices) were between 6–7, 3–3.7GPa and 3–4, respectively. These properties are compatible with those of commercial glazes for wall tiles and porcelain stoneware ceramics.

Degradation of rubber to metals bonds during its cathodic delamination, validation of an artificial ageing test

Rubber-metal assemblies used for submarine applications are often associated to cathodic protection which can lead to cathodic disbonding of the polymer/metal interface. The degradation mechanisms of polychloroprene/epoxy adhesive/copper–aluminium substrate systems associated to an accelerated ageing test are compared to the degradations resulting from natural ageing conditions in the Mediterranean sea. From destructives tests, a kinetic in four steps is identified for both ageing conditions. This kinetic is confirmed by Electrochemical Impedance Spectroscopy data during ageing. In order to further identify the failure mode, the disbonded surfaces on polymer and steel sides are analyzed using SEM and FTIR. Both ageing conditions present the same type of degradation which validates the fact that the accelerated ageing protocol reproduces the natural conditions. The chemical transformations in delaminated epoxy are very similar to the chemical transformation in epoxy coatings under high energy electron-beam irradiation. However, bidendate metal carboxylates rather than carboxylic acid chain ends are the main oxidation products due to the alkaline environment at the coating-metal interface. It was shown that the metal/polymer interface is not destroyed by an alkaline attack but by a strongly oxidative attack caused by the intermediates of the oxygen reduction.

Delignification of switchgrass cultivars for bioethanol production

Three switchgrass cultivars (‘Performer’, ‘BoMaster’, and ‘Colony’ switchgrass) were delignified using NaOH at varying concentrations and residence times at 121 oC for improved sugar production in enzymatic hydrolysis. Because of its greater carbohydrate/lignin ratio and the more substantial lignin reduction upon alkaline attack, ‘Performer’ switchgrass gave greater sugar productions under all the pretreatment conditions investigated. Maximum sugar production from ‘Performer’ was 425 mg/g raw biomass, which was achieved at 1% NaOH and 0.5 h. Sugar production increased with the improvement of delignification until the lignin reduction reached 30%. The more severe pretreatment conditions, which led to greater lignin reductions, did not favor the increase of sugar production because of greater solid losses. Linear models were proven effective in correlating a modified severity parameter log(Mo) to lignin reduction and sugar production of ‘Performer’ switchgrass.

A miniemulsion polymerization technique for encapsulation of silicon quantum dots in polymer nanoparticles

Miniemulsion polymerization techniques were used to encapsulate luminescent alkylated silicon quantum dots (Si-QDs) within polymer nanoparticles composed of styrene and 4-vinylbenzaldehyde monomers. The polymer nanoparticles had mean diameters in the range 90-150 nm depending on the reaction conditions, however all samples showed narrow particle size distributions, as determined by dynamic light scattering and atomic force microscopy. The Si-QDs were found to have a small, but beneficial effect on the polymerization process by reducing the polydispersity of the final polymer particles, which we attribute to co-surfactant action of the undecene used to form the alkyl capping layer on the Si-QDs. Confocal microspectroscopy was used to confirm that the luminescent alkylated Si-QDs were encapsulated within the polymer nanoparticles and also provided luminescence and Raman spectra which show peaks corresponding to both alkylated Si-QDs and the polymer nanoparticles. Treatment of the polymer nanoparticles with dilute aqueous sodium hydroxide solution, which is known to corrode Si and extinguish the luminescence of alkylated Si-QDs, results in only a partial reduction in luminescence suggesting that the majority of the alkylated Si-QDs are encapsulated sufficiently deep within the polymer matrix to protect them from alkaline attack. Miniemulsion polymerization of the monomers styrene and 4-vinylbenzaldehyde affords polymer nanoparticles displaying reactive aldehyde groups upon their surfaces, which could then be decorated with a selection of molecules through imine, oxime or hydrazone condensation reactions. We speculate that polymer-SiQD composite nanoparticles whose surfaces can be further decorated will increase the utility of luminescent Si-QDs in applications such as anti-counterfeiting and as probes of biological processes.

Properties and Functions of Hierarchical Ferrierite Zeolites Obtained by Sequential Post-Synthesis Treatments

A post-synthesis route involving a sequence of up to three treatments in aqueous NaAlO2, HCl, and NaOH solutions, was designed to prepare a variety of complex hierarchical ferrierite zeolites, that is, microporous materials with auxiliary mesoporosity. The precise effect of each step on the composition, structure, morphology, porosity, and acidity of the samples was assessed by means of a multitechnique approach, including inductively coupled plasma-optical emissions spectrometry (ICP-OES), N2 sorption at 77 K, Ar sorption at 87 K, transmission electron microscopy (TEM), energy dispersive X-ray (EDX) analysis, X-ray diffraction (XRD), liquid and solid-state nuclear magnetic resonance (NMR), Fourier transform infrared spectroscopy (FTIR), and temperature-programmed desorption of ammonia (NH3-TPD). NaAlO2 desilicates a portion of the zeolite crystal by alkaline attack, although most of the extracted silicon is retained in the solid forming nanocrystals because of Al(OH)3 precipitation on the zeolite surface. A subsequent HCl washing removes the aluminum-containing deposit from the composite, uncovering a dual network of mesopores associated with the desilicated ferrierite platelets and the Si-rich nanocrystals. The latter species were selectively dissolved by mild NaOH washing. The impact of the relative amount of micro- and mesoporosity in the zeolites on the transport properties was studied by elution of butane isomers, and the pyrolysis of low-density polyethylene was selected as a model reaction to assess differences in catalytic performance. In addition, spray deposition was applied to support palladium nanoparticles onto selected ferrierite samples. The hierarchical zeolite yielded higher metal dispersion and size uniformity of Pd nanoparticles in comparison with the parent zeolite. Our study shows that an appropriate sequence of post-synthesis treatments comprises a powerful approach to tune the properties and functions of hierarchical zeolites.

The effect of high pH alkaline solutions on the mineral stability of the Boom Clay – Batch experiments at 60°C

Boom Clay is currently viewed as a reference host formation for studies on deep geological disposal of radioactive waste in Belgium. The interactions between bulk rock Boom Clay and 0.1 M KOH, 0.1 M NaOH, 0.1 M Ca(OH)2, young cement water and evolved cement water solutions, ranging in pH from 12.5 to 13.2, were examined as static batch experiments at 60 °C to simulate alkaline plume perturbations, which are expected to occur in the repository due to the presence of concrete. Both liquids and solids were investigated at specific times between 90 and 510 days in order to control the elemental budget and to search for potential mineralogical alterations. Also, the clay fraction was separated from the whole-rock Boom Clay at the end of each run and characterized for its mineralogical composition. Thereby, the importance of the mineral matrix to buffer the alkaline attack and the role of organic matter to protect clay minerals were also addressed. The results indicate that the degree of geochemical perturbation in Boom Clay is dependent on the initial pH of the applied solution together with the nature of the major cation in the reactant fluids. The higher the initial pH of the media, the stronger its interaction with Boom Clay. No major non-clay mineralogical alteration of the Boom Clay was detected, but dissolution of kaolinite, smectite and illite occurred within the studied experimental conditions. The dissolution of clays is accompanied by the decrease in the layer charge, followed by a decrease in the cation-exchange capacity. The highest TOC values coincide with the highest total elemental concentrations in the leachates, and correspondingly, the highest dissolution degree. However, no quantitative link could be established between the degree of organic matter decomposition and clay dissolution.

Hydrothermal Synthesis of Na-LTA, Na-X and HS Zeolites from Tunisian Sand and Aluminum Scraps

Na-LTA, Na-X and HS zeolites have been prepared from Tunisian sand and aluminum scraps. The alkaline attack of the sand leads to the metasilicate sol used as a source of silica. The aluminum source was prepared by dissolving aluminum in NaOH solution. The influence of several physicochemical parameters such as temperature, crystallization time and the alkalinity of the reaction mixture on the nature and the purity of the obtained products have been investigated.

Physico-chemical characterisation of the Douiret sand (Southern Tunisia): Valorisation for the production of Silica Gel

In order to widen the industrial uses of Douiret sand belonging to the Chenini formation (Southern Tunisia) experimental investigations have been performed to synthesized the silica gel from the natural raw material using alkaline attack, which correspond to the fusion of silica and sodium carbonate together at high temperature (1060∘C). Mineralogical and physicochemical characterisation of the natural raw material and synthetic silica gel indicate that pure and very fine sized Douiret sand can be yield a very interesting silica gel product characterised by high specific surface which can reach 720m2/g and a great capacity of adsorption.