The Experts below are selected from a list of 2844 Experts worldwide ranked by ideXlab platform

Dimitrios Panias - One of the best experts on this subject based on the ideXlab platform.

  • thermal insulating foamy geopolymers from perlite
    Minerals Engineering, 2010
    Co-Authors: V Vaou, Dimitrios Panias
    Abstract:

    Geopolymerization is an emerging technology which utilizes solid aluminosilicate raw materials that are easily soluble in caustic solutions, in order to produce inorganic polymers with excellent physical, mechanical and thermal properties. In this paper is demonstrated the ability of Geopolymerization technology for production of thermal insulating foamy inorganic polymers utilizing as solid raw material ultrafine perlite which is a by-product from comminution and sizing operations of perlite exploitation. Hydrogen peroxide is used as a chemical blowing agent for the foaming of inorganic polymers. The effect of addition of the blowing agent on the thermophysical properties of thermal insulating materials is demonstrated and these properties are compared with the ones of the commercial thermal insulating materials indicating the high potentiality for the development of this new family of inorganic polymeric materials.

  • Hydrolytic stability of sodium silicate gels in the presence of aluminum
    Journal of Materials Science, 2010
    Co-Authors: Ifigenia Giannopoulou, Dimitrios Panias
    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.

  • utilization of alumina red mud for synthesis of inorganic polymeric materials
    Mineral Processing and Extractive Metallurgy Review, 2009
    Co-Authors: Dimitrios D Dimas, Ifigenia Giannopoulou, Dimitrios Panias
    Abstract:

    Red mud is a residue coming from the metallurgical treatment of bauxite with the Bayer process. Million of tons of red mud are produced annually worldwide and disposed of on land, degrading vast areas. Therefore, red mud utilization is a first-priority issue for any alumina plant. In the present work, the potential use of red mud for synthesis of inorganic polymeric materials through Geopolymerization process was studied. The main focus was the production of inorganic polymeric materials that could be used in the construction sector as artificial structural elements such as massive bricks. The Geopolymerization process involves a chemical reaction between red mud and alkali metal silicate solution under highly alkaline conditions. The product of this reaction is an amorphous to semi-crystalline polymeric structure, which binds the individual particles of red mud transforming the initial granular material to a compact and strong one. The effect of main synthesis parameters—like solid-to-liquid ratio, caust...

  • polymerization in sodium silicate solutions a fundamental process in Geopolymerization technology
    Journal of Materials Science, 2009
    Co-Authors: Dimitrios Dimas, Ifigenia Giannopoulou, Dimitrios Panias
    Abstract:

    Geopolymerization is an innovative technology that can transform several solid aluminosilicate materials into useful products called geopolymers or inorganic polymers. Although the Geopolymerization mechanism is not well understood, the most proposed mechanism includes four parallel stages: (a) dissolution of solid aluminosilicate materials in alkaline sodium silicate solution, (b) oligomerization of Si and/or Si–Al in aqueous phase, (c) polymerization of the oligomeric species, and (d) bonding of undissolved solid particles in the polymer. It is obvious that polymerization in sodium silicate solutions comprises a fundamental process in Geopolymerization technology. Therefore, this article aims at studying experimentally the polymerization stage in synthetic pure sodium silicate solutions. The structure of sodium silicate gels as a function of the SiO2/Na2O molar ratio is examined and their hardness as well as hydrolytic stability are determined. In addition, the effect of aluminum incorporation in the hydrolytic stability of these gels is also examined. Finally, the structure of sodium silicate and aluminosilicate gels is correlated to the measured properties drawing very useful conclusions that could be applied on Geopolymerization technology.

G C Lukey - One of the best experts on this subject based on the ideXlab platform.

  • reaction mechanisms in the geopolymeric conversion of inorganic waste to useful products
    Journal of Hazardous Materials, 2007
    Co-Authors: J S J Van Deventer, John L Provis, Peter Duxson, G C Lukey
    Abstract:

    Abstract High-performance materials for construction, waste immobilisation and an ever-growing range of niche applications are produced by the reaction sequence known as ‘geopolymerisation’. In this process, an alkaline activating solution reacts with a solid aluminosilicate source, with solidification possible within minutes and very rapid early strength development. Geopolymers have been observed to display remarkable chemical and thermal stability, but due to their largely X-ray amorphous nature have only recently been accurately characterised. It has previously been shown that both fly ash and ground granulated blast furnace slag are highly effective as solid constituents of geopolymer reaction slurries, providing readily soluble alumina and silica that undergo a dissolution–reorientation–solidification process to form a geopolymeric material. Here a conceptual model for geopolymerisation is presented, allowing elucidation of the individual mechanistic steps involved in this complex and rapid process. The model is based on the reactions known to occur in the weathering of aluminosilicate minerals under alkaline conditions, which occur in a highly accelerated manner under the conditions required for geopolymerisation. Transformation of the waste materials to the mixture of gel and nanocrystalline/semicrystalline phases comprising the geopolymeric product is described. Presence of calcium in the solid waste materials affects the process of geopolymerisation by providing extra nucleation sites for precipitation of dissolved species, which may be used to tailor setting times and material properties if desired. Application of geopolymer technology in remediation of toxic or radioactive contaminants will depend on the ability to analyse and predict long-term durability and stability based on initial mix formulation. The model presented here provides a framework by which this will be made possible.

  • effect of alkali metals on the preferential Geopolymerization of stilbite kaolinite mixtures
    Industrial & Engineering Chemistry Research, 2001
    Co-Authors: And J. S. J. Van Deventer, G C Lukey
    Abstract:

    Stilbite is used as the main aluminosilicate oxide source to determine the effect of various factors on the extent of Geopolymerization of stilbite/kaolinite mixtures. Increasing the M2O/H2O ratio (where M = Na and/or K) results in an increase in the dissolution of aluminum and silicate species from stilbite and kaolinite, which therefore leads to an improvement in the compressive strength of the geopolymer. The SiO2/M2O ratio affects significantly the degree to which polymerization between Al(OH)4- and Si complexes can occur. The results also show that Na+ compared with K+ enhances the dissolution of aluminum and silicate species. However, K+ improves the compressive strength of the geopolymer compared with Na+. It has been established for the first time that kaolinite and stilbite react differently with different alkali metals. The successful Geopolymerization of stilbite/kaolinite mixtures can occur only by homogeneously dispersing condensed Na2SiO3 in a MOH solution prior to adding solids.

  • Effect of Alkali Metals on the Preferential Geopolymerization of Stilbite/Kaolinite Mixtures
    Industrial & Engineering Chemistry Research, 2001
    Co-Authors: And J. S. J. Van Deventer, G C Lukey
    Abstract:

    Stilbite is used as the main aluminosilicate oxide source to determine the effect of various factors on the extent of Geopolymerization of stilbite/kaolinite mixtures. Increasing the M2O/H2O ratio (where M = Na and/or K) results in an increase in the dissolution of aluminum and silicate species from stilbite and kaolinite, which therefore leads to an improvement in the compressive strength of the geopolymer. The SiO2/M2O ratio affects significantly the degree to which polymerization between Al(OH)4- and Si complexes can occur. The results also show that Na+ compared with K+ enhances the dissolution of aluminum and silicate species. However, K+ improves the compressive strength of the geopolymer compared with Na+. It has been established for the first time that kaolinite and stilbite react differently with different alkali metals. The successful Geopolymerization of stilbite/kaolinite mixtures can occur only by homogeneously dispersing condensed Na2SiO3 in a MOH solution prior to adding solids.

Issara Sereewatthanawut - One of the best experts on this subject based on the ideXlab platform.

  • Effects of seeding nucleation agent on Geopolymerization process of fly-ash geopolymer
    Frontiers of Structural and Civil Engineering, 2018
    Co-Authors: Lapyote Prasittisopin, Issara Sereewatthanawut
    Abstract:

    Geopolymer, an inorganic aluminosilicate material activated by alkaline medium solution, can perform as an inorganic adhesive. The geopolymer technology has a viability to substitute traditional concrete made of portland cement (PC) because replacing PC with fly ash leads to reduced carbon dioxide emissions from cement productions and reduced materials cost. Although fly ash geopolymer stimulates sustainability, it is slow Geopolymerization reaction poses a challenge for construction technology in term of practicality. The development of increasing Geopolymerization reaction rate of the geopolymer is needed. The purpose of this study is to evaluate seeding nucleation agents (NA) of fly ash geopolymer that can accelerate polymerization reactions such that the geopolymer can be widely used in the construction industry. Results from the present study indicate that the use of NA (i.e., Ca(OH)_2) can be potentially used to increase Geopolymerization reaction rate and improve performance characteristics of the fly ash geopolymer product.

  • Effects of seeding nucleation agent on Geopolymerization process of fly-ash geopolymer
    Frontiers of Structural and Civil Engineering, 2017
    Co-Authors: Lapyote Prasittisopin, Issara Sereewatthanawut
    Abstract:

    Geopolymer, an inorganic aluminosilicate material activated by alkaline medium solution, can perform as an inorganic adhesive. The geopolymer technology has a viability to substitute traditional concrete made of portland cement (PC) because replacing PC with fly ash leads to reduced carbon dioxide emissions from cement productions and reduced materials cost. Although fly ash geopolymer stimulates sustainability, it is slow Geopolymerization reaction poses a challenge for construction technology in term of practicality. The development of increasing Geopolymerization reaction rate of the geopolymer is needed.

Guoping Zhang - One of the best experts on this subject based on the ideXlab platform.

  • the strength and microstructure of two geopolymers derived from metakaolin and red mud fly ash admixture a comparative study
    Construction and Building Materials, 2012
    Co-Authors: Jian He, Jianhong Zhang, Yuzhen Yu, Guoping Zhang
    Abstract:

    Abstract The effects of source materials on the microstructure and mechanical properties were studied by comparing two types of geopolymers synthesized from metakaolin, a non-waste material, and the admixture of two wastes, red mud and fly ash. Unconfined compression testing was conducted to assess their curing time and mechanical properties, while X-ray diffraction and scanning electron microscopy employed to examine Geopolymerization reactions and the composition and microstructure of the end products. For a given Si/Al ratio, the metakaolin-derived geopolymer exhibits higher compressive strength than the waste-based one. Both geopolymers contain a significant amount of voids and unreacted phases as inactive fillers within the geopolymer binder, resulting in complexity and variability in their mechanical behavior. The difference in strength and microstructure between the two geopolymers is attributed to the different reactivity of source materials, percentage of nonreactive fillers, and alkalinity for Geopolymerization reactions.

  • Geopolymerization of Red Mud and Fly Ash for Civil Infrastructure Applications
    Geo-Frontiers 2011, 2011
    Co-Authors: Jian He, Guoping Zhang
    Abstract:

    This paper presents a study that investigates the Geopolymerization of red mud, a major industrial waste from alumina refining, and fly ash, also an industrial waste from coal combustion, using very limited non-waste materials. Different synthesis parameters (e.g., red mud to fly ash ratio, sodium silicate solution to solid mixture (red mud and fly ash) ratio, and different types of sodium silicate solution) were varied to assess their influences on the mechanical properties of final geopolymer products. The results of unconfined compression testing show that these factors have significant influence on the mechanical properties of the synthesized geopolymers. Depending on the synthesis conditions, the unconfined compressive strength ranges from 3 to 13MPa, and the high values are comparable with certain types of Portland cement. The process of Geopolymerization was confirmed by the composition of the final products analyzed by X-ray diffraction. The findings suggest that the two major industrial wastes, red mud and fly ash, can be reused to produce geopolymers that may replace Portland cement and hence be applied in civil infrastructure construction.

  • synthesis characterization and mechanical properties of red mud based geopolymers
    Transportation Research Record, 2010
    Co-Authors: Guoping Zhang, Robert P Gambrell
    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...

Jinhong Zhang - One of the best experts on this subject based on the ideXlab platform.

  • The making of Class C fly ash as high-strength precast construction material through Geopolymerization
    Mining Metallurgy & Exploration, 2020
    Co-Authors: Jinhong Zhang, Qingming Feng
    Abstract:

    A study has been carried out to apply fly ash as a high strength, water-resistant precast construction material through Geopolymerization. Experiment results show that the working conditions such as water content, the concentration of NaOH, curing temperature, and curing time significantly affect the mechanical property of geopolymer matrix. Through optimization, an above-100 MPa compressive strength has been achieved with the Geopolymerization products. The optimum working conditions involves 10 M NaOH concentration, 14–15% water content, and curing at 90 °C in an oven for 1 day or at ambient condition for 3 weeks. Adding Ca(OH)_2 does not help to increase the compressive strength of the specimen. Water soaking tests show that the Geopolymerization product has a very high water resistance without losing noticeable compressive strength, even after a 1-month soaking time. To elucidate the Geopolymerization mechanism, microscopic techniques such as SEM/EDS (scanning electron microscopy and energy-dispersive X-ray spectroscopy), XRD (X-ray diffraction) and ATR-FTIR (attenuated total reflectance Fourier transform infrared) are also applied to investigate the microstructure, the elemental and phase composition of Geopolymerization products. The findings of the present work provide a novel method for applying fly ash as a high-strength water-resistant precast construction material.

  • The making of Class C fly ash as high-strength precast construction material through Geopolymerization
    Mining Metallurgy & Exploration, 2020
    Co-Authors: Jinhong Zhang, Qingming Feng
    Abstract:

    A study has been carried out to apply fly ash as a high strength, water-resistant precast construction material through Geopolymerization. Experiment results show that the working conditions such as water content, the concentration of NaOH, curing temperature, and curing time significantly affect the mechanical property of geopolymer matrix. Through optimization, an above-100 MPa compressive strength has been achieved with the Geopolymerization products. The optimum working conditions involves 10 M NaOH concentration, 14–15% water content, and curing at 90 °C in an oven for 1 day or at ambient condition for 3 weeks. Adding Ca(OH)_2 does not help to increase the compressive strength of the specimen. Water soaking tests show that the Geopolymerization product has a very high water resistance without losing noticeable compressive strength, even after a 1-month soaking time. To elucidate the Geopolymerization mechanism, microscopic techniques such as SEM/EDS (scanning electron microscopy and energy-dispersive X-ray spectroscopy), XRD (X-ray diffraction) and ATR-FTIR (attenuated total reflectance Fourier transform infrared) are also applied to investigate the microstructure, the elemental and phase composition of Geopolymerization products. The findings of the present work provide a novel method for applying fly ash as a high-strength water-resistant precast construction material.

  • Use of Mine Tailings as Precast Construction Materials through Alkali Activation
    Mining Metallurgy & Exploration, 2019
    Co-Authors: Bo Huang, Qingming Feng, Jinhong Zhang
    Abstract:

    A study of the application of mine tailings as precast construction materials through alkali activation has been carried out, focusing on efficiently activating mine tailings, reducing alkali consumption, decreasing curing time and improving compressive strength. Firstly, the effect of temperature on the alkali activation of mine tailings was studied. Secondly, the impact of additives, i.e., calcium hydroxide and aluminum oxide, on the compressive strength of samples was investigated. Thirdly, the impact of forming pressure on sample strength was studied. Test results showed that unconfined compressive strength (UCS) of 40 MPa was achieved with the Geopolymerization products through optimization. Finally, to elucidate the Geopolymerization mechanism of mine tailings, microscopic and spectroscopic techniques including SEM/EDX, XRD, and FTIR spectroscopy were used to investigate the microstructure and the elemental and phase composition of the Geopolymerization products. The findings of the present work provide a practical method for applying mine tailings as precast construction materials through alkali activation.

  • synthesis and characterization of fly ash modified mine tailings based geopolymers
    Construction and Building Materials, 2011
    Co-Authors: Lianyang Zhang, Saeed Ahmari, Jinhong Zhang
    Abstract:

    Abstract Each year, the mining industry generates a significant amount of mine tailings. Storage of these tailings occupies large areas of land and leads to high monetary, environmental and ecological costs. In this research, a feasibility study is performed on Geopolymerization of mine tailings so that they can be recycled and utilized as construction material. Considering the extremely high silicon to aluminum (Si/Al) ratio for the mine tailings, class F fly ash is used to adjust the Si/Al ratio. Sodium hydroxide (NaOH) solution is used as the alkaline reaction agent. The research consists of unconfined compression tests to evaluate the mechanical properties, scanning electron microscopy (SEM) imaging to investigate the microstructure, and the X-ray diffraction (XRD) analysis to study the phase compositions. The effects of fly ash content (which affects the Si/Al ratio), alkalinity (NaOH concentration), and curing time on the Geopolymerization of mine tailings are studied in a systematic way. The results show that the Si/Al ratio and the alkalinity have profound effects on the mechanical and micro-structural properties of the mine tailings-based geopolymers. The curing time affects the mechanical and micro-structural properties of the mine tailings-based geopolymers mainly during the first 7 days. Based on the research, it can be concluded that mine tailings are a viable and promising construction material if the Geopolymerization technology is utilized.