Amorphous Aluminosilicate Gel Research Articles

Comparative investigation of reactivity of different kinds of fly ash in alkaline media

Comparison of the influence of temperature and different alkali activators on the reactivity of two types of fly ash (conventional, fluidized) was presented. The main emphasis was put on fluidized fly ash as potential component of binding mixtures containing low amount of cement. Conventional fly ash was used as a reference. It was found that for these materials the key differences affecting products of activation are: availability of calcium and sulfate ions as well as structure of fly ash grains influencing dissolution of aluminate and silicate species. Fluidized fly ash, contrary to conventional fly ash, undergoes reaction in 0.1 M solutions of hydroxides forming mainly ettringite. In the case of 4 M hydroxides, both fly ashes undergo hydration processes. Conventional fly ash formed mainly amorphous aluminosilicate gel, while fluidized fly ash may create zeolitic products especially in the case of elevated temperature of early hydration. Sulfate and alkali ions can be incorporated into aluminosilicate structure of new formed products; however, this process depends strictly on the type of used hydroxide and its concentration. The presence of Ca(OH)2, carbonates and alkali sulfates was also registered in the case of hydrated fluidized fly ash.

Synthesis of SSZ-13 zeolite with zeolite L-added synthesis gel absent from additional aluminum source

SSZ-13 zeolite with a SiO2/Al2O3 ratio in the range of 26–183 was synthesized by adding zeolite L in the synthesis gel absent from additional aluminum source, and the effects of SiO2/Al2O3 and N,N,N-trimethyladamantammonium hydroxide (TMAdaOH)/SiO2 ratios on the crystallization were investigated. The crystallization mechanism was studied with X-ray diffraction, Scanning electron microscopy, Fourier transform infrared spectroscopy and 29Si and 27Al MAS NMR spectroscopy techniques. It is shown that the SiO2/Al2O3 and TMAdaOH/SiO2 ratios have a significant effect on the acidity, and thus, the methanol-to-olefins (MTO) performance of SSZ-13. The co-presence of TMAdaOH, NaOH and extra silica source (SiO2) is necessary for formation of SSZ-13. The crystallization of SSZ-13 occurs by decomposing structure of zeolite L into double six- and four-membered rings that subsequently restructure into CHA topology under the direction of TMAdaOH, and further induce the nucleation and crystal growth. It is noteworthy that the Al species in zeolite L directly transform into those of SSZ-13 without forming monomeric species. The prepared SSZ-13 shows higher catalytic stability and selectivity to ethylene and proplyene than the conventionally synthesized sample from amorphous aluminosilicate gel in MTO reaction.

Development of low cost supplementary cementitious materials utilizing thermally activated Pisha sandstone

Pisha sandstone was the main resource of Yellow river sediment mineral with a low pozzolanic activity. This paper reports an investigation of the possibility of development of low cost supplementary cementitious materials using Pisha sandstone via thermally activated. The decomposition of Pisha sandstone when thermally treated at 600 °C and 800 °C and the effect of this treatment on its physicochemical properties, pozzolanic reactivity in cementitious materials were studied. The hydration of the mineral component, reaction products and micromorphology were studied by TG-DTG, XRD and SEM-EDS technique, respectively. Compressive strength test was conducted to assess the mechanical property of modified pastes, and Mercury intrusion porosimetry (MIP) was employed to investigate the pore structure and pore size distribution. This work confirmed that Pisha sandstone could be acted as a kind of low cost supplementary cementitious materials via thermally activated, and the optimal calcination temperature was 600 °C. It was shown that the decomposition of clay mineral of Pisha sandstone via thermal treatment result in an enhance of hydration reaction and mechanical strength, and the sample (calcined at 600 °C) exhibited the highest compressive strength (21.9 MPa). The results of the investigation show that the amorphous aluminosilicate gels (C-A-S-H) were the main hydration products.

Understanding the seeding mechanism of hierarchically porous zeolite/carbon composites

Recent research has demonstrated a new synthesis route for hierarchically porous zeolite composites by mechanical modification of the support surface using ultrasonication in a nanoparticle suspension. It was believed that target zeolites should be added as seeds for the sonication. In this study, the effect of nanoparticles was investigated with ultrasonication to understand the crystallization mechanism of zeolites obtained by the nanoparticles–assisted synthesis. It has been found that the nanoparticles under the influence of ultrasonication generate fissures or cracks as nucleation sites on the carbon surface. These nanoparticles such as zeolite A, γ-Al2O3, quartz and sand are different from the target zeolite X. Therefore, an amorphous aluminosilicate gel nucleates at those cracks during the hydrothermal treatment. Thus, the mechanical activation of the support surface is the process to induce the formation of strongly attached zeolite X over the template, not a seeding step. This is confirmed as an attachment due to the weak bond between the support and the zeolite for ‘non-seeded’ composites whereas the ‘seeded’ composites have a robust structure which maintains a zeolite coating upon mechanical agitation.

29Si{27Al}, 27Al{29Si} and 27Al{1H} double-resonance NMR spectroscopy study of cementitious sodium aluminosilicate gels (geopolymers) and gel-zeolite composites.

The influence of starting materials and synthesis route on the properties and the structure of cementitious sodium aluminosilicate gels is not fully understood, partly due their amorphous nature and the fact that they often contain residual reactants, which can make the results of single-pulse NMR spectroscopy applied to these materials difficult to interpret or ambiguous. To overcome some of these limitations, 29Si{27Al} TRAPDOR NMR as well as 27Al{29Si} and 27Al{1H} REDOR NMR spectroscopy were applied to materials synthesized by the one-part alkali-activation route from three different amorphous silica starting materials, including rice husk ash. The latter led to formation of a fully amorphous sodium aluminosilicate gel (geopolymer), while the materials produced from the other silicas contained amorphous phase and crystalline zeolites. Application of the double-resonance NMR methods allowed to identify hydrous alumina gel domains in the rice husk ash-based material as well as significantly differing amounts of residual silica in the three cured materials. Four-coordinated Al existed not only in the aluminosilicate gel framework but also in a water-rich chemical environment with only a small amount of Si in proximity, likely in the alumina gel or possibly present as extra-framework Al in the aluminosilicate gel. The results demonstrate how the employment of different silica starting materials determines the phase assemblage of one-part alkali-activated materials, which in turn influences their engineering properties such as the resistance against chemically/biologically aggressive media.

Study on Development of GeopolymerBinder from Terracotta Roof Tile Waste by Experimental and Statistical Method

Alkali activation of aluminosilicate materials produces geopolymers at ambient or slightly elevated temperatures by geopolymerization process. The reaction product is an amorphous aluminosilicate gel having a structure similar to that of zeolitic precursors. In this paper study on development of geopolymer binder from terracotta tile waste was carried out through experimental and statistical analysis. Compressive strength test was conducted with sixteen combinations of specimens by varying four identified parameters. A 24 full factorial design was adopted for the experimental study with each parameter having two levels. The significance of parameter effect on geopolymerization has been investigated using full factorial design. The influence of the parameters such as molarity of sodium hydroxide, alkali activator to binder ratio and elevated curing temperature on geopolymerization are found significant where as influence of sodium silicate to sodium hydroxide solution ratio was insignificant at 5% level of significance. The interaction effect among the parameters are studied and found to be negligible.

The use of different by-products in the production of lightweight alkali activated building materials

This paper investigates the value of different industrial by-products and residues in the production of lightweight alkali activated materials (AAM). Waste metakaolin, recycled waste glass, aluminium scrap recycling waste, and steel-plant waste (SPW) were considered as secondary raw materials. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Energy-dispersive X-ray spectroscopy (EDX), scanning electron microscopy (SEM), and X-ray micro-tomography examinations were performed in order to analyse the reaction products, to identify their phase composition, and to observe the micro-morphology.The results showed that highly porous lightweight building materials could be obtained, with densities ranging from 380 to 470kg/m3, heat conductivities ranging between 0.14 and 0.15W/m·K, and compressive strengths ranging between 1.1 and 2.0MPa. It was also shown that the main hydration products were amorphous aluminosilicate gels, whereas the crystalline compounds from the SPW remained in the structure of the AAM. The results of X-ray micro-tomography showed that lightweight AAM contained 72.0–89.0vol% of pores, with sizes ranging between 1 and 5mm. In the paper a brief description is given of the waste management method which can be applied to obtain materials that can be used in the building industry as lightweight load-bearing insulation materials.

Modeling the Formation of Alkali Aluminosilicate Gels at the Mesoscale Using Coarse-Grained Monte Carlo.

Alkali-activated materials (AAMs) are currently being pursued as viable alternatives to conventional ordinary Portland cement because of their lower carbon footprint and established mechanical performance. However, our understanding of the mesoscale morphology (∼1 to 100 nm) of AAMs and related amorphous aluminosilicate gels, including the development of the three-dimensional aluminosilicate network and nanoscale porosity, is severely limited. This study investigates the structural changes that occur during the formation of AAM gels at the mesoscale by utilizing a coarse-grained Monte Carlo (CGMC) modeling technique that exploits density functional theory calculations. The model is capable of simulating the reaction of an aluminosilicate particle in a highly alkaline solution (sodium hydroxide or sodium silicate). Two precursor morphologies have been investigated (layered alumina and silica sheets mimicking metakaolin and spherical aluminosilicate particles reminiscent of coal-derived fly ash) to determine if the precursor morphology has an impact on the structural evolution of the resulting alkali-activated aluminosilicate gel. The CGMC model can capture the three major stages of the alkali-activation process-dissolution, polycondensation, and reorganization-revealing that the dissolved silicate and aluminate species, ranging from monomers to nanoprecipitates (100s of monomers in size), exist in the pore solution of the hardened gel. The model also reveals that the silica concentration of the activating solution controls the extent of dissolution of the precursor particle. From the analysis of the aluminosilicate cluster size distributions, the mechanisms of AAM gel growth have been elucidated, revealing that Ostwald ripening occurs in systems containing free silica at the start of the reaction. On the other hand, growth of the hydroxide-activated systems (metakaolin and fly ash) occurs via the formation of intermediate-sized clusters in addition to continual growth of the largest particle. The simulation results indicate that the nature of the gel growth is not influenced by the precursor particle morphology.

The influence of alkali activator type, curing temperature and gibbsite on the geopolymerization of an interstratified illite-smectite rich clay from Friedland

Illitic clays, such as the interstratified illite-smectite clays, are one of the most abundant aluminosilicates on Earth's surface and are widely available for geopolymer production. Geopolymers are a group of alkali-activated materials, which are gaining increasing attention as low-CO2 binders with some advantageous properties compared to ordinary Portland cement. In this study, high strength geopolymers were formed from a calcined and ground interstratified illite-smectite clay, which was mixed with 6M NaOH or KOH and cured at 25, 50 and 75°C. We furthermore tested the effect of increasing Al content of the precursor by adding gibbsite to the metaclay. The temperature dependent reactivity of the precursor, i.e. the Si and Al solubility of the metaclay and gibbsite is shown. It is revealed that the geopolymerization of the meta-illite-smectite clay was favored by KOH-activation at 50°C. Adding 10wt% gibbsite by solid mass increased the strength of the geopolymers by ~20% from 38 to 45N/mm2, which is partly attributed to increased formation of an amorphous aluminosilicate gel. NaOH-activation was not affected by gibbsite addition and increased strength only at 75°C, which was related to phillipsite (zeolite) crystallization. Na-geopolymers showed lower strength of ~30N/mm2 and abundant capillary pores.

MECHNICAL STRENGTH AND DURABILITY OF ALKALI-ACTIVATED FLY ASH/SLAG CONCRETE

This study investigated the mechanical strength and durability of alkali-activated binders composed of blends of fly ash (FA) and ground granulated blast furnace slag. Five samples with FA/slag ratios of 100/0, 75/25, 50/50, 25/75, and 0/100 by mass were employed to prepare alkali-activated FA/slag (AAFS) concrete. Sodium oxide (Na_2O) concentrations of 6% and 8% of binder weight and activator modulus ratios (mass ratio of SiO_2 to Na_2O) of 0.8, 1.0, and 1.23 were used to prepare alkaline activators. Test results revealed that higher slag contents, Na_2O concentrations, and activator modulus ratios increased the compressive strength and splitting tensile strength of AAFS concrete. The total charge passed through AAFS concrete was between 2500 and 4000 C, higher than that passed through reference ordinary Portland cement (OPC) concrete. However, AAFS concrete demonstrated higher performance than that of OPC concrete when exposed to sulfate. According to scanning electron microscopy observations, the main hydration products of AAFS concrete were amorphous alkaline aluminosilicate and low-crystalline calcium silicate hydrate gel. As the slag content increased, the amount of C-S-H gel increased and that of A-S-H gel decreased. According to the results, 100% slag-based AAFS concrete with a Na_2O concentration of 8% and activator modulus ratio of 1.23 offers superior performance.

Effect of Alkaline Activation on Low Grade Natural Kaolin for Synthesis of Zeolite A

The conventional technique to synthesizes zeolite A from kaolin is calcination. However, this technique has one drawback since, the impurities in kaolin, such as muscovite and quartz, remain. Therefore, the hydrothermal process without calcination is used to synthesize high purity zeolite A. Hydrothermal synthesis without calcination can be separated into two steps, namely first and second hydrothermal steps. Alkaline activation reaction in the first hydrothermal step was used to study the effect of NaOH concentration ranging from 4M, 6M, 8M, 10M to 12M at 200°C for 3 hours. In this step, sodium aluminosilicate (cancrinite and nepheline hydrate) was produced and then dissolved in HCl. After filtration, the impurity was removed, and adjusted for neutral pH of 7 to form amorphous aluminosilicate gel. For the second hydrothermal step, amorphous gel was mixed with NaOH (1-4M) to form zeolite A at 90°C for 3 days. The x-ray diffraction (XRD) and Scanning Electron Microscope (SEM) were used for characterization.

Development of building material utilizing a low pozzolanic activity mineral

In this work, the effects of different activators, particle size and curing conditions on the mechanical properties and hydration progress of alkali activated Pisha mortars were studied. Four different activators (NaOH, Na2CO3, Na2SO4 and water glass) based on two different fineness Pisha were used, two kinds of curing temperature, 25 and 80°C were considerate. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TG) and scanning electron microscopy (SEM) were conducted to analyze the reaction products, indentify the phase composition and observe the micro-morphology, respectively. It was found that the modulus of water glass and fineness of Pisha have significant influence on the compressive strength and hydration process of alkali activated Pisha mortars. The optimum activators were water glass, the sample (Ms=1.5, curing at 80°C) exhibited the highest compressive strength (14.4MPa) at 28days. The results of the investigation also show that the amorphous aluminosilicate gels were the main hydration products.

Effects of the alkaline solution/binder ratio and curing condition on the mechanical properties of alkali-activated fly ash mortars

Abstract The study investigates the effects of the alkaline solution/binder ratio and the curing condition on the mechanical properties of alkali-activated fly ash (AAFA) mortars. Class F fly ash was used as the raw material, and sodium hydroxide and liquid sodium silicate were used for the preparation of alkaline activators. Three alkaline solution-to-binder ratios (0.35, 0.5, and 0.65) and four different initial curing conditions (curing in air at ambient temperature for 24 h, 30°C for 24 h, 65°C for 12 h, and 85°C for 6 h) were considered. Test results show that AAFA mortars with alkaline solution-to-binder ratio of 0.35 had higher compressive strength, lower drying shrinkage, lower water absorption, and lower initial surface absorption rate than the other mortars. Furthermore, the curing condition influenced the compressive strength development and drying shrinkage of AAFA mortars at early ages. AAFA mortars cured at 65°C for 12 h appeared to have superior mechanical properties. XRD demonstrates that the hydration products of AAFA mortars are mainly amorphous alkaline aluminosilicate gel, which attributed to the compressive strength. Consequently, the alkaline solution-to-binder ratio significantly affects more the mechanical properties than the curing condition based on the presented results.

Effects of modulus ratio and dosage of alkali-activated solution on the properties and micro-structural characteristics of alkali-activated fly ash mortars

This study investigates the properties and micro-structural characteristics of alkali-activated fly ash (AAFA) mortars. Sodium oxide (Na2O) dosages of 121 and 150kg/m3 and liquid sodium silicate with alkaline modulus ratios (mass ratio of SiO2 to Na2O) of 1.23 and 0.8 were prepared as activators. Three alkaline solution to binder ratios of 0.35, 0.5, and 0.65 were selected to cast AAFA mortars. Compressive strength test, drying shrinkage test, water absorption test, initial surface absorption test, mercury intrusion porosimetry test (MIP), scanning electron microscopy (SEM) and X-ray diffraction analysis were conducted and their performance was discussed and compared with reference mortars produced with ordinary Portland cement (OPC). Test results show that both alkaline modulus ratio and the dosage of Na2O are two significant factors influencing the characteristics of AAFA mortars. The higher alkaline modulus ratio and dosage of Na2O are, the superior properties of AAFA mortars achieved. SEM and XRD demonstrate that the activation products of AAFA mortars are mainly amorphous alkaline aluminosilicate gels, which are attributed to the compressive strength. Under the alkaline modulus ratio of 1.23 and liquid/binder ratio of 0.5, AAFA mortars with Na2O dosage of 150kg/m3 may be considered as the optimum mix design based on the results.

Mechanical and Microstructural Characterization of Alkali-Activated Materials Based on Fly Ash and Slag

This study investigates the mechanical and microstructural characterization of alkali-activated fly ash/slag (AAFS) mortars with various ratios of fly ash to slag. The liquid/binder ratios of 0.35, 0.5 and 0.65 are considered for the AAFS mortars. 4% Sodium oxide (Na 2 O) concentration of cementitious material weight in mixture and liquid sodium silicate with modulus ratio (mass ratio of SiO 2 to Na 2 O) of 1 were used as alkaline activators to alkali-activate various fly ash/slag ratios. Compressive strength test, water absorption test, drying shrinkage test, scanning electron microscopy (SEM) and X-ray diffraction (XRD) analysis were conducted. Test results reveal that both fly ash/slag ratio and the liquid/binder ratio are two significant factors influencing the mechanical and microstructural characterization of AAFS mortars. The hydration products of AAFS mortars are mainly amorphous alkaline aluminosilicate and low-crystalline calcium silicate hydrate gel.

Direct crystallization of CHA-type zeolite from amorphous aluminosilicate gel by seed-assisted method in the absence of organic-structure-directing agents

Highly crystalline CHA-type aluminosilicate zeolites with the Si/Al ratio of around 4–5 were successfully synthesized by a seed-assisted method in the absence of organic-structure-directing agents (OSDAs); a method for so-called “OSDA-free synthesis” of the CHA zeolite has been newly developed. In this OSDA-free system, in addition to the seeds with the CHA topology, a judicious use of potassium or cesium cations together with sodium cations is a crucial key to the crystallization of the amorphous aluminosilicate gel into the CHA structure. The Si/Al ratio of the CHA zeolite was increased by decreasing the total amount of alkali cations added and/or the use of cesium cations in place of potassium ones. Furthermore, the employment of the amorphous aluminosilicate gel containing boron species led to the formation of the CHA zeolite with a high Si/Al ratio of 6.1 compared with the synthetic chabazite crystallized through the interzeolite conversion of the FAU zeolite (Si/Al: 2.0). The catalytic performance of the prepared CHA zeolites was also evaluated. In the methanol-to-olefins reaction, the catalyst life was improved by increasing the Si/Al ratio of the CHA zeolite.

Binding mechanism and properties of alkali-activated fly ash/slag mortars

Binding mechanism and properties of alkali-activated fly ash/slag (AAFS) mortars with various ratios of fly ash to slag were investigated by compressive strength test, flexural strength test, water absorption test, drying shrinkage test, scanning electron microscopy (SEM) and X-ray diffraction (XRD) analysis. Sodium oxide (Na2O) concentrations of 4% and 6% by cementitious material weight and liquid sodium silicate with modulus ratio (mass ratio of SiO2 to Na2O) of 1 were prepared as activators. The liquid/binder ratio was kept at a constant of 0.5. Test results show that both fly ash/slag ratio and the dosage of Na2O are two significant factors influencing the binding mechanism and properties of AAFS mortars. The hydration products of AAFS mortars investigated by SEM and XRD are mainly amorphous alkaline aluminosilicate and low-crystalline calcium silicate hydrate gel. With the exception of drying shrinkage, better properties, such as compressive strength, flexural strength and water absorption, have been obtained in AAFS mortars than comparable OPC mortars. Meanwhile, the binding mechanism and properties of AAFS mortars improved with an increase dosage of Na2O. AAFS mortars with a fly ash/slag ratio of 50/50 alkali-activated by Na2O concentrations of 6% may be considered as the optimum mix design based on the results.

Feasibility of manufacturing geopolymer bricks using circulating fluidized bed combustion bottom ash

This paper presents a study on geopolymer bricks manufactured using bottom ash from circulating fluidized bed combustion (CFBC). The alkali activators used for synthesis were sodium silicate, sodium hydroxide, and potassium hydroxide and lithium hydroxide solutions. The study included the impact of alkali activator on compressive strength. The reaction products were analysed by XRD, FT-IR and SEM/EDS. The compressive strength of bricks was dependent on the modulus of the sodium silicate activator and the type and concentration of alkali activator. The highest compressive strength could be gained when the modulus was 1.5, and the value could reach 16.1 MPa (7 d after manufacture) and 21.9 MPa (28 d after manufacture). Under pure alkaline systems, the compressive strength was in the order of 10 M KOH>10 M NaOH>5 M LiOH>5 M KOH>5 M NaOH. Quartz was the only crystalline phase in the original bottom ash, and no new crystalline phase was found after the reaction. The main product of reaction was amorphous alkali aluminosilicate gel and a small amount of crystalline phase was also found by SEM.

Preparation and Characterization of the Mine Residue-based Geopolymeric Ceramics

The goal of the present work was to investigate the development of a geopolymeric ceramic material from a mixture of mine residue, coal fly ash, blast furnace slag, and alkali activator solution by the geopolymer technique. The results showed that the higher compressive strength of geopolymeric ceramic material increased with an increase in active filler (blast furnace slag + coal fly ash) contents and with a reduction of mine residue contents. The geopolymeric ceramic had very high early age strength. The compressive strength of the geopolymeric ceramic depended on the added active filler content. The maximum compressive strength of the geopolymeric ceramic containing 20 wt.% mine residue was 141.2 MPa. The compressive strength of geopolymeric ceramic manufactured by adding mine residue was higher than that of portland cement mortar, which is 60 MPa, when cured for 28 days. SEM observation showed the possibility of having amorphous aluminosilicate gel within geopolymeric ceramic. XRD patterns indicate that the geopolymeric ceramic was composed of amorphous aluminosilicate, calcite, quartz, and muscovite. The Korea Standard Leaching Test (KSLT) was used to determine the leaching potential of the geopolymeric ceramic. The amounts of heavy metals were noticeably reduced after the solidification of mine residue with active filler.

A novel synthesis of nano-sized mullite from aluminosilicate precursors

A novel method was proposed for the preparation of aluminosilicate-based ceramic materials by temperature induced transformation of amorphous aluminosilicates (zeolite precursors) as an alternative to conventional methods based on the thermal treatment of kaolin, feldspar and other silicate, aluminosilicate and/or oxide mixtures, or by sol–gel method. Amorphous aluminosilicate gels that are usually used as precursors for the crystallization of zeolites after exchanging their host's cations (sodium) with ammonium cations from solution were thermally treated (at 1263 K for 3 h) and yielded a mixture of mullite and amorphous silica. Further chemical treatment of the mixture with sodium hydroxide solution yielded a pure mullite phase having particle size below 100 nm.