Showing papers on "Sodium silicate published in 2010"
TL;DR: In this article, the compressive strength of C fly ash (CFA) and a mixed alkali activator of sodium hydroxide and sodium silicate solution was investigated, where the modulus of the activator viz., molar ratio of SiO 2 /Na 2 O was 1.5, and proper content of this activator as evaluated by the mass proportion of Na 2 O to CFA was 10%.
Abstract: Geopolymers prepared from a class C fly ash (CFA) and a mixed alkali activator of sodium hydroxide and sodium silicate solution were investigated. A high compressive strength was obtained when the modulus of the activator viz., molar ratio of SiO 2 /Na 2 O was 1.5, and the proper content of this activator as evaluated by the mass proportion of Na 2 O to CFA was 10%. The compressive strength of these samples was 63.4 MPa when they were cured at 75 °C for 8 h followed by curing at 23 °C for 28 d. In FTIR spectroscopy, the main peaks at 1036 and 1400 cm −1 have been attributed to asymmetric stretching of Al–O/Si–O bonds, while those at 747 cm −1 are due to the Si–O–Si/Si–O–Al bending band. The main geopolymeric gel and calcium silicate hydrate (C–S–H) gel co-exist and bond some remaining unreacted CFA spheres as observed in XRD and SEM–EXDA. The presence of gismondine (zeolite) was also observed in the XRD pattern.
621 citations
TL;DR: In this article, the properties of two N-A-S-H gels (with Si/Al = 1 and 2) synthesized in highly alkaline media, in the presence of calcium are reported.
Abstract: This paper reports a research on the properties of synthetic sodium aluminosilicate hydrate gels as models for the gels arising in alkali-activated aluminosilicate systems. The interaction between these N-A-S-H gels and aqueous calcium was studied to explore a potential consequence of mixing conventional Portland cements and alkali-activated systems. The properties of two N-A-S-H gels (with Si/Al = 1 and 2) synthesized in highly alkaline media, in the presence of calcium are reported. N-A-S-H gels were synthesized using aluminum nitrate, sodium hydroxide, and a sodium silicate. FTIR, NMR, and TEM/EDX techniques were used to characterize N-A-S-H gels before and after adding calcium. The results obtained show that calcium is uptaken in N-A-S-H gels resulting in a modification of the chemical composition due to the substitution of sodium per calcium.
212 citations
TL;DR: In this paper, an analysis of coal fly ash and lignite coal fly ashes was carried out by means of conduction calorimetry, X-ray diffraction, thermogravimetric analysis and scanning electron microscopy to assess their potential for mortar and concrete production.
191 citations
TL;DR: In this article, the use of calcined sodium silicate as a novel solid base catalyst in the transesterification of soybean oil with methanol was examined, and the results showed that the catalyst can be reused for at least five cycles without loss of activity.
144 citations
TL;DR: It is demonstrated that simple two- and three-carbon molecules spontaneously form silicate complexes of four- and six-carbon sugars, respectively, which suggest that formose-like reactions may provide a feasible pathway for the abiotic formation of biologically important sugars, such as ribose.
Abstract: Understanding the mechanism of sugar formation and stabilization is important for constraining theories on the abiotic origin of complex biomolecules. Although previous studies have produced sugars from small molecules through the formose and related reactions, the product mixtures are complex and unstable. We have demonstrated that simple two- and three-carbon molecules (glycolaldehyde and glyceraldehyde), in the presence of aqueous sodium silicate, spontaneously form silicate complexes of four- and six-carbon sugars, respectively. Silicate selects for sugars with a specific stereochemistry and sequesters them from rapid decomposition. Given the abundance of silicate minerals, these observations suggest that formose-like reactions may provide a feasible pathway for the abiotic formation of biologically important sugars, such as ribose.
140 citations
TL;DR: Utilization of CFA and Ca-containing admixtures in AACB is feasible and these binders may be widely utilized in various applications such as in building materials and for solidification/stabilization of other wastes, thus making the wastes more environmentally benign.
136 citations
TL;DR: In this article, the potential of reusing red mud, an abundant industrial waste produced from alumina refining by the Bayer process, by geopolymerization reactions with another solid waste, fly ash, and sodium silicate was investigated.
Abstract: A pilot study investigates the potential of reusing red mud, an abundant industrial waste produced from alumina refining by the Bayer process, by geopolymerization reactions with another solid waste, fly ash, and sodium silicate. Parameters involved in the synthesis, including red mud to fly ash ratio (values of 80/20, 50/50, and 20/80), presence of sand filler, curing duration (up to 28 days), and sodium silicate solution to solid mixture (consisting of red mud and fly ash) ratio, were examined to understand the extent and degree of geopolymerization. Unconfined compression testing was employed to assess the influence of these synthesis parameters on the mechanical properties of the end products, red mud-based geopolymers. The composition and microstructure were characterized by X-ray diffraction and scanning electron microscopy, respectively, which confirm the geopolymerization reactions. The mechanical properties, including strength, stiffness, and failure strain, were analyzed against the chemical com...
130 citations
TL;DR: It is shown that the temporal stability of ACC can be influenced in a deliberate manner also in much simpler purely abiotic systems and to illustrate this, the progress of calcium carbonate precipitation at high pH from solutions containing different amounts of sodium silicate is monitored.
Abstract: In biomineralization, living organisms carefully control the crystallization of calcium carbonate to create functional materials and thereby often take advantage of polymorphism by stabilizing a specific phase that is most suitable for a given demand. In particular, the lifetime of usually transient amorphous calcium carbonate (ACC) seems to be thoroughly regulated by the organic matrix, so as to use it either as an intermediate storage depot or directly as a structural element in a permanently stable state. In the present study, we show that the temporal stability of ACC can be influenced in a deliberate manner also in much simpler purely abiotic systems. To illustrate this, we have monitored the progress of calcium carbonate precipitation at high pH from solutions containing different amounts of sodium silicate. It was found that growing ACC particles provoke spontaneous polymerization of silica in their vicinity, which is proposed to result from a local decrease of pH nearby the surface. This leads to ...
122 citations
TL;DR: In this article, a method to synthesize low-density transparent mesoporous silica aerogel beads by ambient pressure drying (APD) was reported, where the beads were prepared by acid-base sol-gel polymerization of sodium silicate in aqueous ammonia solution via the ball dropping method (BDM).
116 citations
TL;DR: In this paper, a microarc oxidation (MAO) technique was used to produce hard oxide coatings resistant to wear on 2017A-T6 Al alloy by using an alkali electrolyte consisting of different sodium silicate concentrations.
86 citations
TL;DR: In this article, the results of tests conducted to ascertain at high temperatures the mechanical behavior of cements whose most prominent characteristic is the absence or near absence of Portland cement in their composition are discussed.
Abstract: This paper discusses the results of tests conducted to ascertain at high temperatures the mechanical behavior of cements whose most prominent characteristic is the absence or near absence of Portland cement in their composition. More specifically, it reports on the study of three binders: (a) Portland cement (control); (b) 100% sodium silicate-activated fly ash; and (c) a blend of 70% ash+30% clinker activated with solid-state activators (solid sodium silicate+Na2CO3). Two types of tests were conducted: (i) tests to determine the mechanical strength and fracture toughness of the three materials between 25° and 600°C and (ii) postthermal treatment tests to evaluate the residual strength after 1 h of exposure to temperatures ranging from 200° to 1000°C. XRD and SEM techniques were also deployed to track the mineralogical and microstructural variations in the materials as a result of such an exposure. The findings showed that a pseudo-viscous phase is generated in alkaline cements at around 600°C that would explain the decline in strength observed when specimens were loaded at increasing temperatures. This phase and its subsequent recrystallization into new phases (nepheline, albite, and gehlenite) were also responsible for the high-residual mechanical strength values observed in these materials after exposure to high temperatures and subsequent cooling but absent in OPC.
TL;DR: In this paper, a chemical method was used to activate the ordinary Portland cement-slag mortars (OSM) and the results showed that the effects of the combined activators are better than that of an individual one.
TL;DR: In this article, the synthesis adopted for the preparation of silica and silica based mixed oxide/composite aerogels through ambient pressure drying is discussed in detail and the properties of the prepared aerogel are also discussed.
Abstract: Silica aerogels have received much attention in recent years as it has got a wide range of properties like high surface area, low density, high porosity, low dielectric constant, low thermal conductivity. Recently to make aerogels for commercial application ambient pressure drying has been preferred and also a cheap precursor like sodium silicate has been employed as the starting material instead of the alkoxides. In this review, attention will be given to the synthesis adopted for the preparation of silica and silica based mixed oxide/composite aerogels through ambient pressure drying. The properties of the prepared aerogels are also discussed in detail.
TL;DR: In this paper, an ambient pressure drying method was used to synthesize silica aerogels from industrial fly ash by using trimethylchlorosilane(TMCS)/ethanol(EtOH)/hexane mixed solution.
Abstract: Silica aerogels were synthesized from the industrial fly ash by ambient pressure drying method. The process consists of two stages, preparation of sodium silicate solution from fly ash by hydrothermal reaction with sodium hydroxide, and synthesis of porous silica aerogels from the obtained sodium silicate solution. Silica wet gels were formed by vitriol-catalysis or resin-exchange-alkali-catalysis of the obtained sodium silicate solution. The trimethylchlorosilane(TMCS)/ethanol(EtOH)/hexane mixed solution was used for solvent exchange/surface modification of the wet gel so as to obtain porous silica aerogels via ambient pressure drying. The results indicated that the synthesized silica aerogels were lightweight and hydrophobic. The BET specific surface area, pore volume and average pore diameter were 362.2–907.9 m 2 g − 1 , 0.738–4.875 cm 3 g − 1 , and 7.69–24.09 nm respectively. Particularly, the synthesized silica aerogels by resin-exchange-alkali-catalysis method showed uniform mesoporous structure, and had much higher specific surface area (907.9 m 2 g − 1 ) and pore volume (4.875 cm 3 g − 1 ) than that of by vitriol-catalysis process.
TL;DR: In this paper, a transparent silicate coating was formed on the surface of hot-dip galvanized (HDG) steels by immersing in sodium silicate solution with SiO 2 :Na 2 O molar ratio in the range from 1.00 to 4.00.
Abstract: Passivation treatment by sodium silicate solution is considered as an alternative to chromium chemical conversion treatment to improve the corrosion resistance of hot-dip galvanized (HDG) steels. In this paper, a transparent silicate coating was formed on the surface of HDG steel by immersing in sodium silicate solution with SiO 2 :Na 2 O molar ratio in the range from 1.00 to 4.00. The parameter about the SiO 2 :Na 2 O molar ratio of silicate solution has been discussed using corrosion resistance and surface morphology. Tafel polarization, electrochemical impedance spectroscopy (EIS) measurements and neutral salt spray (NSS) test show that silicate coatings increase the corrosion resistance of HDG steels. From the results obtained, it is deduced that the optimum SiO 2 :Na 2 O molar ratio is 3.50. Scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction analysis (XRD), and reflectance absorption infrared spectroscopy (RA-IR) show that there are no obvious differences of the chemical composition and structure in various silicate coatings. The silicate coatings mainly consist of zinc oxides/hydroxides, zinc silicate and SiO 2 . However, atomic force microscopy (AFM) images reveal that the surface of silicate coatings with a molar ratio of 3.50 is more compact and uniform than other silicate coatings.
TL;DR: In this paper, a hydrophobic mesoporous silica powder was prepared by surface modification of a sodium silicate-based wet-gel slurry using trimethylchlorosilane (TMCS).
TL;DR: Both concentrated and diluted sodium silicate solutions have been investigated by combining (29)Si NMR spectroscopy and SAXS experiments and the results evidence the preponderant presence of neutral Si(7)O(18)H(4)Na( 4) complexes, which behave like colloid complexes.
TL;DR: In this article, the effects of surface modifications with silane coupling agents from the group of alkoxysilanes with different functional groups have been determined, and both unmodified and modified silicas have been thoroughly characterised by scanning electron microscopy (SEM) and dynamic light scattering (DLS) and other methods.
TL;DR: In this article, the authors analyzed the application of nanotechnology for manufacturing refractory concretes and examined the influence of nanostructure formation in the binding material on the properties of the concrete.
Abstract: This article reviews the manufacturing nanotechnologies of modern refractory concretes and some other cementitious materials. The main part of the article focuses on the results obtained by the authors who analyzed the application of nanotechnology for manufacturing refractory concretes and examined the influence of nanostructure formation in the binding material on the properties of refractory concretes. In one case, investigations were carried out using two‐component (sodium silicate solution mixed with dicalcium silicate) and three‐component (sodium silicate solution mixed with dicalcium silicate plus calcium aluminate cement) binding materials, whereas in other case, multi‐component material, middle cement refractory concrete with mullite aggregates, microsilica and additives of single and hybrid deflocculant (polycarboxylate ether Castament FS20 and sodium tripolyphosphate) were researched. Preliminary investigations showed that the three‐component binding material under development hardens ...
01 Jan 2010
TL;DR: In this article, the effect of incorporating silica fume in the fly ash geopolymer on its porosity and compressive strength was investigated, and the results of an experimental study performed to investigate effect of integrating silica Fume in fly ash was presented.
Abstract: This paper presents the results of an experimental study performed to investigate effect of incorporating silica fume in the fly ash geopolymer on its porosity and compressive strength. Geopolymer specimens were prepared by activating fly ash incorporated with additional silica fume in the range of 2.5% to 5% with a mixture of sodium hydroxide and sodium silicate having Na2O content of 8%. The characterization of the geopolymer specimens was done with ESEM/EDAX and MIP tests. Addition of silica fume up to 5% enhanced compressive strength of geopolymer mortars. However, further increase of silica fume caused a decrease in compressive strength. SEM micrographs for specimens incorporated with silica fume showed better microstructure and exhibited lesser porosity. MIP results of paste specimens indicate higher pore volume in the specimen prepared with additional silica fume while for mortar specimens; the pore volume was seen lesser in specimens with additional silica fume. Silica fume may be used as an additional material to improve or modify some properties of the resulting geopolymer.
TL;DR: In this article, the authors explore the ability of FTIR and Raman spectroscopy for obtaining structural information of aqueous solutions of various sodium silicates and show that both the average molweight and the dissociation level are functions of both the Na/Si ratios and the concentration of dissolved silicates.
TL;DR: In this paper, pure chemosynthetic Al2O3-2SiO2 geoploymers displaying positive alkali-activated polymerization properties and high compressive strength at room temperature were effectively fabricated utilizing a sol-gel method.
Abstract: Pure chemosynthetic Al2O3–2SiO2 geoploymers displaying positive alkali-activated polymerization properties and high compressive strength at room temperature were effectively fabricated utilizing a sol–gel method. The molecular structure of the precursor powder and resulting geopolymers were investigated by X-ray diffraction (XRD) and nuclear magnetic resonance (NMR) analysis. In addition, the mechanical and alkali-activated polymerization properties of these materials were also studied. NMR data revealed that the chemosynthetic powders began to contain 5-coordinated Al atoms when the calcination temperatures exceeded 200 °C. These calcined powders were capable of reacting with sodium silicate solutions at calcination temperatures exceeding 300 °C, which is, however, much lower than the temperature required to convert kaolin to Metakaolin.
TL;DR: In this article, micro arc oxidation (MAO) coatings were synthesized on magnesium substrate employing 11 different electrolyte compositions containing systematically varied concentrations of sodium silicate (Na2SiO3), potassium hydroxide (KOH), and sodium aluminate (NaAlO2).
Abstract: In the present work, micro arc oxidation (MAO) coatings were synthesized on magnesium substrate employing 11 different electrolyte compositions containing systematically varied concentrations of sodium silicate (Na2SiO3), potassium hydroxide (KOH), and sodium aluminate (NaAlO2). The resultant coatings were subjected to coating thickness measurement, energy dispersive spectroscopy (EDS), scanning electron microscopy (SEM), image analysis, and three-dimensional (3-D) optical profilometry. The corrosion performance of the coatings was evaluated by conducting potentiodynamic polarization tests in 3.5 wt pct NaCl solution. The inter-relationships between the electrolyte chemistry and the resulting chemistry and porosity of the coating, on one hand, and with the aqueous corrosion behavior of the coating, on the other, were studied. The changes in pore morphology and pore distribution in the coatings were found to be significantly influenced by the electrolyte composition. The coatings can have either through-thickness pores or pores in the near surface region alone depending on the electrolyte composition. The deleterious role of KOH especially when its concentration is >20 pct of total electrolyte constituents promoting the formation of large and deep pores in the coating was demonstrated. A reasonable correlation indicating the increasing pore volume implying the increased corrosion was noticed.
TL;DR: According to the diffuse reflection spectra of the silica hollow particles in powder form, these particles showed the high reflection of UV and visible light, which increased with added NaCl in the preparation process of the interfacial reaction method.
Abstract: Silica microcapsules (silica hollow particles) are readily prepared by a single step of the interfacial reaction method, where a W/O/W emulsion is employed effectively. This is a simple (one-step process), inexpensive approach (silica source is sodium silicate) to producing hollow silicas. The addition of NaCl to the sodium silicate solution as the inner water phase of the W/O/W emulsion plainly influenced the shell structure of the silica hollow particles. The increase of the addition of NaCl expanded the size of the mesopores in their silica shell, which reached to macropores (>50 nm). The nanoparticles in the shells of some silica hollow particles attained approximately 200−400 nm in size, which is comparable to the wavelengths of UV and visible light. According to the diffuse reflection spectra of the silica hollow particles in powder form, these particles showed the high reflection of UV and visible light, which increased with added NaCl in the preparation process of the interfacial reaction method. ...
TL;DR: In this paper, a novel adsorbent design technique based on the concept of Kelvin equation was proposed to develop hydrophilic adsorbents applicable to water vapor adsorption heat pump (AHP) for high performance.
TL;DR: In this paper, a silica aerogel with high specific surface area and large pore volume was successfully synthesized using oil shale ash (OSA) via ambient pressure drying.
TL;DR: In this paper, the effect of tetra-coordinated aluminum addition on the hydrolytic stability of sodium silicate gels was elucidated and the structure of prepared sodium hydroaluminosilicates was analyzed.
Abstract: Polycondensation in alkali silicate solutions comprises a fundamental process of the geopolymerization technology. Previous works had shown that the hydrolytic stability of sodium silicate gels depends on the SiO2/Na2O ratio. Sodium silicate gels totally insoluble in water can be produced at SiO2/Na2O molar ratios higher than 4.4. This article aims at elucidating the effect of tetra-coordinated aluminum addition on the hydrolytic stability of sodium silicate gels. According to the results, the aluminum addition stabilizes the sodium silicate gels in an aqueous environment. A sodium silicate gel with SiO2/Na2O molar ratio 3.48, which is totally soluble in deionized water at ambient temperature, can be transformed to insoluble sodium hydroaluminosilicates with the addition of tetrahedral aluminum at Al/Si molar ratios higher than 0.08. In addition, this article studies the structure of prepared sodium hydroaluminosilicates and draws very useful conclusions for the geopolymerization technology.
TL;DR: In this paper, the process of alkali fusion activation and optimization of the composition were studied by TG-DTA, XRD, and calcium ion exchange capacity for the synthesis of zeolite A using alkali-activated bentonite as raw material.
Abstract: Optimization studies were carried out for the synthesis of zeolite A by a hydrothermal method using alkali-activated bentonite as raw material. The process of alkali fusion activation and optimization of the composition were studied by TG-DTA, XRD, and calcium ion exchange capacity. It was found that a mixture of additional alumina (aluminum hydroxide) and bentonite was converted to highly reactive sodium silicate, sodium aluminate, and aluminosilicate by alkali fusion activation using Na2CO3 at high temperature. Zeolite A with a maximum crystallinity of 82.7% and calcium ion exchange capacity of 302 mg of CaCO3/g was obtained at optimized conditions.
TL;DR: In this paper, a novel process was developed to fractionate the coal fly ash into high purity nano silicon particles and aluminum enriched residual ash, which has major steps as sodium silicate dissolution with sodium hydroxide, first carbonation to remove impurities, second carbonation, precipitate silicon, and silicon precipitate recovery as a mesospheric nano particles product.