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Hubert Rahier - One of the best experts on this subject based on the ideXlab platform.

  • the influence of air and temperature on the reaction mechanism and molecular structure of fe silicate Inorganic Polymers
    Journal of Non-crystalline Solids, 2019
    Co-Authors: Arne Peys, Hubert Rahier, Bart Blanpain, Alexios P Douvalis, Christina Siakati, Yiannis Pontikes
    Abstract:

    Abstract Fe-rich Inorganic Polymers are rising in importance because of their low CO2 emissions during production and their potential in upcycling metallurgical residues. Here, the oxidation of Fe during formation of the binder from 0.4CaO-1.2FeOx-SiO2 slag is investigated in more detail using 57Fe Mossbauer spectroscopy. It was shown that the oxidation at early stages is not influenced by (O2 in the) air. Later, the quadrupole split Fe2+ state in the binder transforms to Fe3+ when the samples are crushed and exposed to air as powder for 28 days at room temperature or 1 h at ≥200 °C. This transformation does not affect the connectivity of the silicate network according to infrared spectroscopy. During heating of the Inorganic Polymer powder, the Mossbauer spectra remain stable until 400–500 °C. At 400 °C the Fe2+ in the slag starts to be oxidized, showing the formation of new Fe3+ components.

  • metakaolinite phosphate cementitious matrix Inorganic Polymer obtained by acidic activation
    Materials, 2019
    Co-Authors: Antigoni Katsiki, Tobias Hertel, Tine Tysmans, Yiannis Pontikes, Hubert Rahier
    Abstract:

    This work aims to study an aluminosilicate phosphate cementitious matrix. The cementitious matrix was studied on paste samples. The synthesis of metakaolinite phosphate cement (MKPC) was investigated using calorimetric techniques. A systematic study was performed by emphasizing a broad range of Al/P molar ratios, covering the different behavior of the material to the extremes, as well as the optimum composition. X-ray diffraction and scanning electron microscopy revealed that the final structure was mainly an amorphous network, albeit with some non-reacted phases. The compressive strength was studied on mortars using a cement/sand ratio of 1:3. MKPC specimens with Al/P ratios close to 1/1 showed optimal behavior. MKPCs with Al/P ratios above 1/1 were characterized by high porosity and low strength, whereas MKPCs with Al/P < 1 contained an excess of phosphates. The influence of the Al/P molar ratio on compressive strength was also studied, reaching a maximum of 68 MPa for the optimum composition. Based on the results, MKPC may be a promising candidate for construction purposes.

  • metakaolin based Inorganic Polymer synthesis using cotton shell ash as sole alkaline activator
    Construction and Building Materials, 2018
    Co-Authors: Madi A Balo, Hubert Rahier, Alessandra Mobili, Antigoni Katsiki, Nathalie Fagel, Melo U Chinje, D Njopwouo
    Abstract:

    Abstract Inorganic Polymers were synthesised using metakaolin and cotton shell ash as activator. In this way, the negative environmental impact of sodium or potassium silicate solutions as alkaline activators can be eliminated. Phase transformations investigated using FTIR suggested the formation of Inorganic Polymers through the shift of the most intense band from 1031 cm−1 in metakaolin to around 973 cm−1 in the final product and the absence of the band at 789 cm−1 in the latter. XRD results revealed the presence of kalsilite and zeolite K-F, which appear as hexagonal and elongated crystals in SEM. A maximum compressive strength of 36.7 MPa was obtained. Compressive strength values increased with increasing K/Al ratios and with the reduction of pore densities due to the formation of the amorphous Inorganic Polymer matrix as observed on the SEM micrographs. Cotton shell ash can thus be used as an alternative activator.

  • development of Inorganic Polymer by alkali activation of untreated kaolinitic clay reaction stoichiometry strength and dimensional stability
    Construction and Building Materials, 2015
    Co-Authors: Muayad Esaifan, Hubert Rahier, Ahmed Barhoum, Hani Khoury, M Hourani, Jan Wastiels
    Abstract:

    Abstract An environmental friendly building material was developed by alkali-activation of untreated kaolinitic clay using sodium hydroxide. The reaction was studied using differential scanning calorimetry. The chemical structure of the produced Inorganic Polymer was deduced from infrared spectroscopy, X-ray powder diffraction, thermogravimetric analysis, and scanning electron microscopy to be the tetrahydrate phase of hydroxysodalite with a Na/Al ratio of 4/3. Its strength and stability were evaluated in terms of compressive strength under dry and saturated conditions using different ratios of mixing water and NaOH. The compressive strength of dry samples ranges between 45 and 50 MPa. The wet samples after soaking in water show a strength between 20 and 25 MPa, and the wet samples after alternating cycles of drying and wetting also show a strength of 20–25 MPa.

  • low temperature synthesized aluminosilicate glasses part iv modulated dsc study on the effect of particle size of metakaolinite on the production of Inorganic Polymer glasses
    Journal of Materials Science, 2003
    Co-Authors: Hubert Rahier, Joeri F M Denayer, B Van Mele
    Abstract:

    The effect of the particle size of metakaolinite on the reaction kinetics of low-temperature synthesized Inorganic Polymer glasses is studied. The heat capacity of the material during isothermal cure is measured by Modulated DSC (MDSC). This signal can be followed quantitatively during the complete course of the reaction, whereas the heat flow signal is sometimes too small for quantitative interpretations. A characteristic time for the reaction, defined as onset of vitrification, is also measured with Dynamic Mechanical Analysis (DMA). The DMA and MDSC results show that the reaction rate increases with decreasing particle size of metakaolinite, at least till a particle size of about 2 μm. It can be concluded that the first step of the reaction, breaking down the metakaolinite grains, occurs at the surface of the particles. The second step is the building of a network starting from the reaction products of the former reaction.

Jan Wastiels - One of the best experts on this subject based on the ideXlab platform.

  • development of Inorganic Polymer by alkali activation of untreated kaolinitic clay reaction stoichiometry strength and dimensional stability
    Construction and Building Materials, 2015
    Co-Authors: Muayad Esaifan, Hubert Rahier, Ahmed Barhoum, Hani Khoury, M Hourani, Jan Wastiels
    Abstract:

    Abstract An environmental friendly building material was developed by alkali-activation of untreated kaolinitic clay using sodium hydroxide. The reaction was studied using differential scanning calorimetry. The chemical structure of the produced Inorganic Polymer was deduced from infrared spectroscopy, X-ray powder diffraction, thermogravimetric analysis, and scanning electron microscopy to be the tetrahydrate phase of hydroxysodalite with a Na/Al ratio of 4/3. Its strength and stability were evaluated in terms of compressive strength under dry and saturated conditions using different ratios of mixing water and NaOH. The compressive strength of dry samples ranges between 45 and 50 MPa. The wet samples after soaking in water show a strength between 20 and 25 MPa, and the wet samples after alternating cycles of drying and wetting also show a strength of 20–25 MPa.

  • low temperature synthesized aluminosilicate glasses part ii rheological transformations during low temperature cure and high temperature properties of a model compound
    Journal of Materials Science, 1996
    Co-Authors: H Rahier, B Van Mele, Jan Wastiels
    Abstract:

    The reaction below 100 °C of a dehydroxylated clay (metakaolinite) suspended in an alkaline sodium silicate solution leads to an amorphous aluminosilicate, called low-temperature Inorganic Polymer glass (LTIPG or IPG). Some rheological transformations during the isothermal hardening process are followed with dynamic mechanical analysis (DMA) and compared with differential scanning calorimetry (DSC) and modulated differential scanning calorimetry (MDSC). It can be concluded that the change in storage modulus (DMA) during the formation of the Inorganic network can be characterized quantitatively with the evolution of the heat capacity (MDSC), and that the reaction rate is not decreased by the vitrification process. During the first heating after Polymerization up to 1000°C, the material shrinks due to the evaporation of residual water from the reaction mixture as illustrated by thermogravimetric analysis (TGA) and thermomechanical analysis (TMA). The low-temperature synthesized Inorganic Polymer glass is thermomechanically stable up to a temperature of at least 650°C. In that temperature zone, the glass transition can be detected with TMA and DMA.

  • low temperature synthesized aluminosilicate glasses
    Journal of Materials Science, 1996
    Co-Authors: Hubert Rahier, Jan Wastiels, B Van Mele, Monique Biesemans, Xiaodan Wu
    Abstract:

    The reaction below 100 °C of a dehydroxylated clay (metakaolinite: (Al2O3)(SiO2)2(H2O)0.05) suspended in an alkaline sodium silicate solution ((Na2O)(SiO2)1.4(H2O)x) leads to an amorphous glassy aluminosilicate, called in this work “low-temperature Inorganic Polymer glass” (LTIPG or IPG).

Dongsheng Wang - One of the best experts on this subject based on the ideXlab platform.

  • flocculation dewatering behavior of waste activated sludge particles under chemical conditioning with Inorganic Polymer flocculant effects of typical sludge properties
    Chemosphere, 2019
    Co-Authors: Peng Yang, Weijun Zhang, Ning Wang, Zhaoyi Yang, Dongsheng Wang
    Abstract:

    The effects of typical sludge properties (solids concentration, soluble extracellular Polymeric substances (SEPS) and alkalinity) on waste activated sludge flocculation-dewatering behavior and mechanisms under chemical conditioning with Inorganic Polymer flocculant-polyaluminum chloride (PACl) were systematically examined in this study. The results indicated that increasing the solids concentration was conductive to sludge dewatering and could greatly decrease the PACl demand in chemical conditioning. Solids concentration had important effects on properties of sludge floc flocculated with PACl, floc structure was more compact and of low EPS concentration at high solids concentrations. High levels of SEPS were adverse to sludge dewaterability after flocculation with PACl, since the SEPS could interact with hydroxy-aluminium through complexation and increase the demand of coagulants. In addition, advantageous speciations of hydroxy-aluminium were rapidly converted into amorphous hydroxides with low flocculation activity at high alkalinity, so the sludge conditioning efficiency was greatly declined. At the same time, the dominant mechanism of chemical conditioning was changed from charge neutralization to sweep coagulation. Finally, this study provides control strategies at complex sludge properties for improving the effectiveness of PACl as a chemical conditioner.

  • Journal of Environmental Sciences 2011, 23(5) 705–710 Hydrolyzed Al(III) clusters: Speciation stability of nano-Al13
    2016
    Co-Authors: Dongsheng Wang, Shuifeng Wang, Chihpin Huang, Christopher W K. Chow
    Abstract:

    Pure nano-Al13 and aggregates at various concentrations were prepared to examine the particle size effect of coagulation with Inorganic Polymer flocculant. The property and stability of various species formed were characterized using Infrared, 27Al-NMR, photo correlation spectroscopy (PCS), and Ferron assay. Results showed that concentration and temperature exhibited different roles on the stability of Al13. The quantity of Alb species analyzed by ferron assay in the initial aging period corresponded well with that of Al13, which has been confirmed in a dimension range of 1–2 nm by PCS. Al13 solutions at high concentrations (0.5–2.11 mol/L) were observed to undergo further aggregation with aging. The aggregates with a wide particle size distribution would contribute to the disappeared/decreased Al13 basis on the 27Al-NMR spectrum, whereas a part of Al13 would still remain as Alb. At low concentrations, Al13 solution was quite stable at normal temperature, but lost its stability quickly when heating to 90°C. Key words: nano-Al13; clusters; Inorganic Polymer flocculant; speciation stabilit

  • understanding the impact of chemical conditioning with Inorganic Polymer flocculants on soluble extracellular Polymeric substances in relation to the sludge dewaterability
    Separation and Purification Technology, 2014
    Co-Authors: Weijun Zhang, Dongsheng Wang, Ping Xiao, Shiwei Xu, Feng Xiao, Christopher W K. Chow
    Abstract:

    Generally, sludge conditioned with Inorganic coagulants exhibits rigid structure and is suitable for high pressure dewatering process. Sludge flocs possess multilayered structure, and the sludge dewaterability is mainly dependent on the properties of soluble extracellular Polymeric substances (SEPS). However, few studies have focused on influence of chemical conditioning on the characteristics of SEPS. In this study, the surplus sludge obtained from wastewater treatment plant (WWTP) was conditioned with two Inorganic Polymer flocculants (IPFs), PACl and HPAC, for improving the sludge dewaterability which was measured using specific resistance to filtration (SRF). Meanwhile, the variation in SEPS properties was investigated with combined high performance size-exclusion chromatography (HPESC) and fluorescence excitation-emission matrix (EEM). According to the experimental results, HPAC showed better performance in improving sludge dewaterability due to higher charge density and better bridging properties. EEM coupled to fluorescence region integration (FRI) demonstrated that protein-like substances were dominant fraction of soluble EPS. HPSEC analysis indicated that most of the SEPS with high molecular weight (>2000 Da) were effectively removed from aqueous phase after conditioning, they might play more important roles in sludge dewatering. SRF correlated well with zeta potential, dissolved organic carbon (DOC) and EPS content located in all four EEM regions under chemical conditioning. This result revealed that EEM in conjunction with FRI was an attractive way to evaluate the sludge conditioning efficiency of IPFs. (C) 2014 Elsevier B.V. All rights reserved.

  • interaction of ozone and organic matter in coagulation with Inorganic Polymer flocculant pacl role of organic components
    Desalination, 2009
    Co-Authors: Fangqin Cheng, Hailong Liu, Dongsheng Wang
    Abstract:

    In this study, two model waters were used to evaluate the ozone effect on aquatic organic matter (AOM) removal by coagulation with Inorganic Polymer flocculant (IPF)-polyaluminum chloride (PACl). Flocs formation during coagulation processes were detected by using PDA (Photometric Dispersion Analyzer). Apparent molecular weight distribution (AMWD) and resin fractionation (RF) were also performed to characterize the change of AOM as a result of pre-ozonation. The experimental results show that the dosage Of O(3), characteristics and composition of AOM are the most important factors on the behavior of coagulation. Great differences have been found between the two model waters. Coagulation in model water 1 (MW1) (composed of humic acids) is impaired markedly by pre-ozonation, as more DOC (Dissolved Organic Carbon) is produced with increasing O(3) dosage. Floc formation, as exhibited from decreasing of the slopes of A (Flocculation Index), is retarded gradually during coagulation process. Although residual turbidity is reduced with 1.15 mg/L O(3), removals of DOC and UV(254) all decreased. As for model water 2 (MW2) (composed of salicylic acid), A is retarded also, but turbidity and DOC removals of coagulation after pre-ozonation are improved to a certain extent. Coagulation performance judged from removal of DOC is improved distinctly by pre-ozonation. Fractionation results show that molecular weight of organic matter (OM) of MW1 is converted from higher to lower: and OM becomes from more hydrophobic to more hydrophilic, which might be one of the mechanisms involved in the impairment of ozonation on coagulation effect. OM in MW2 is oxidized and mineralized to a greater extent, thus its impairment on coagulation is released. Finally, according to water properties, some proposed applications were provided for application of ozone in water treatment process. (C) 2009 Elsevier B.V. All rights reserved.

  • speciation stability of Inorganic Polymer flocculant pacl
    Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2004
    Co-Authors: Dongsheng Wang, Wei Sun, Hongxiao Tang, John Gregory
    Abstract:

    The speciation distribution, physico-chemical properties of coagulants, and principles for their further species transformation under various water and wastewater treatment conditions are of paramount importance in coagulation processes. In this paper, the effect of various factors on the speciation transformation of typical Inorganic Polymer flocculants (IPFs)–polyaluminum chloride (PACl) was investigated by ferron assay. Dilution and co-existing electrolyte exhibit little effect on the speciation distribution of PACl after dosing. Solution pH has significant effect on the species transformation, depending mainly on OH/Al ratio (denoted as B value). The lower the B value, the more significant the effect pH exhibits. A large amount of Alb, i.e. rapid reactive species by ferron assay, could form for alum and PACl0 in the weak acidic pH range, which transforms quickly into Alc after aging. PACl, at high B values, maintains high speciation stability under the various conditions investigated. The ferron method provides a measure to explain the reactivity of different species with ferron. The classification of three kinds of aluminum hydrolysis species based on kinetic differences needs further modification.

Yiannis Pontikes - One of the best experts on this subject based on the ideXlab platform.

  • the influence of air and temperature on the reaction mechanism and molecular structure of fe silicate Inorganic Polymers
    Journal of Non-crystalline Solids, 2019
    Co-Authors: Arne Peys, Hubert Rahier, Bart Blanpain, Alexios P Douvalis, Christina Siakati, Yiannis Pontikes
    Abstract:

    Abstract Fe-rich Inorganic Polymers are rising in importance because of their low CO2 emissions during production and their potential in upcycling metallurgical residues. Here, the oxidation of Fe during formation of the binder from 0.4CaO-1.2FeOx-SiO2 slag is investigated in more detail using 57Fe Mossbauer spectroscopy. It was shown that the oxidation at early stages is not influenced by (O2 in the) air. Later, the quadrupole split Fe2+ state in the binder transforms to Fe3+ when the samples are crushed and exposed to air as powder for 28 days at room temperature or 1 h at ≥200 °C. This transformation does not affect the connectivity of the silicate network according to infrared spectroscopy. During heating of the Inorganic Polymer powder, the Mossbauer spectra remain stable until 400–500 °C. At 400 °C the Fe2+ in the slag starts to be oxidized, showing the formation of new Fe3+ components.

  • use of modified bauxite residue based porous Inorganic Polymer monoliths as adsorbents of methylene blue
    Journal of Cleaner Production, 2019
    Co-Authors: Tobias Hertel, Rui M Novais, Roberto Murillo Alarcon, J A Labrincha, Yiannis Pontikes
    Abstract:

    Abstract Porous Inorganic Polymer (IP) monoliths were synthesised using a modified bauxite residue (BR) as the reactive fraction with the objective of using them as adsorbents for methylene blue (MB) from synthetic wastewater. First, unreactive, as-produced BR was transformed into a suitable glassy precursor material for IPs by blending BR with minor quantities of C and CaSiO3, thermally treating it at 1200 °C for 2 h, and quenching in water. The alkaline activation of this slag in combination with a pore foaming agent led to the formation of a highly porous microstructure with up to 85% in total porosity. The synthesised porous monoliths demonstrated high MB uptake (up to 17 mg of MB/g of IP with an initial MB concentration of 75 mg/L). A higher porosity of the monoliths, a higher pH, an increasing initial MB concentration as well as stirring of the testing solution have a positive effect on the adsorption capacity, while an optimum solution volume for adsorption was identified. Furthermore, the reuse of these novel monolithic adsorbents was demonstrated by repeating adsorption tests up to five cycles (adsorption-desorption), with a decrease in adsorption capacity of approximately 30%, but a promising cumulative uptake of about 40 mg of MB per g IP.

  • metakaolinite phosphate cementitious matrix Inorganic Polymer obtained by acidic activation
    Materials, 2019
    Co-Authors: Antigoni Katsiki, Tobias Hertel, Tine Tysmans, Yiannis Pontikes, Hubert Rahier
    Abstract:

    This work aims to study an aluminosilicate phosphate cementitious matrix. The cementitious matrix was studied on paste samples. The synthesis of metakaolinite phosphate cement (MKPC) was investigated using calorimetric techniques. A systematic study was performed by emphasizing a broad range of Al/P molar ratios, covering the different behavior of the material to the extremes, as well as the optimum composition. X-ray diffraction and scanning electron microscopy revealed that the final structure was mainly an amorphous network, albeit with some non-reacted phases. The compressive strength was studied on mortars using a cement/sand ratio of 1:3. MKPC specimens with Al/P ratios close to 1/1 showed optimal behavior. MKPCs with Al/P ratios above 1/1 were characterized by high porosity and low strength, whereas MKPCs with Al/P < 1 contained an excess of phosphates. The influence of the Al/P molar ratio on compressive strength was also studied, reaching a maximum of 68 MPa for the optimum composition. Based on the results, MKPC may be a promising candidate for construction purposes.

  • identifying hotspots of environmental impact in the development of novel Inorganic Polymer paving blocks from bauxite residue
    Resources Conservation and Recycling, 2018
    Co-Authors: James P Joyce, Tobias Hertel, Yiannis Pontikes, Andrei Goronovski, Alan H Tkaczyk, Anna Bjorklund
    Abstract:

    High bauxite residue content Inorganic Polymer paving blocks have the potential not only to provide a solution to the ongoing waste management issues faced by the alumina sector, but to simultaneou ...

  • transforming enhanced landfill mining derived gasification vitrification glass into low carbon Inorganic Polymer binders and building products
    Journal of Sustainable Metallurgy, 2017
    Co-Authors: Lieven Machiels, Lukas Arnout, Pengcheng Yan, Peter Tom Jones, Bart Blanpain, Yiannis Pontikes
    Abstract:

    The current paper reviews the concept of the production of high-added value construction materials produced as part of a zero waste enhanced landfill mining process. The calorific fraction of the excavated waste is concentrated to produce a solid recovered fuel, which is introduced to a gasification/vitrification process to be converted to a synthetic gas, a slag and a metal alloy. The slag is subsequently cooled to produce a glass. The glass is milled and blended with an alkaline silicate solution to produce an Inorganic Polymer binder. The binder can be used as an alternative for ordinary Portland cement (OPC) in concrete to produce precast construction materials, such as pavers, tiles and wall elements. Pilot industrial production and testing of the durability, environmental footprint and economic feasibility of the process are currently being performed. Traditional OPC based production lines can be used, and when comparing with OPC based concrete, materials with similar to improved properties (e.g. higher hardening rate and higher final strength) can be produced.

Jannie S. J. Deventer - One of the best experts on this subject based on the ideXlab platform.

  • Acid resistance of Inorganic Polymer binders. 1. Corrosion rate
    Materials and Structures, 2012
    Co-Authors: Redmond R. Lloyd, John L Provis, Jannie S. J. Deventer
    Abstract:

    The resistance to acid-induced corrosion of Inorganic Polymer (including “fly ash geoPolymer”) binders is examined, by exposing specimens to nitric and sulphuric acids at pH values between 1 and 3, and measuring the corroded depth as a function of exposure time. The Inorganic Polymer binders are shown to be affected by acid attack by surface corrosion, which contradicts some previous claims of extremely high acid resistance in such binders. Corroded depth is shown to be a more sensitive measure of the performance of Inorganic Polymer binders than change in mass, because acid attack on the highly-connected aluminosilicate network of an Inorganic Polymer binder leads to the formation of an apparently intact, but physically weak and porous, reaction product layer on the sample surface, rather than complete disappearance of the binder as is often the case for other binder types. A strong correlation between permeability and resistance to acid attack is noted across a wide range of Inorganic Polymer formulations, including samples based on fly ash, ground granulated blast furnace slag, and mixtures of the two. The presence of calcium (supplied either by a Class C fly ash or by slag) and of high alkali concentrations each show a positive influence on acid resistance, which is attributed to the reduction in mass transport rates through the finer and more tortuous pore networks of such binders.

  • pore solution composition and alkali diffusion in Inorganic Polymer cement
    Cement and Concrete Research, 2010
    Co-Authors: Redmond R. Lloyd, John L Provis, Jannie S. J. Deventer
    Abstract:

    Abstract Extraction of pore solutions from hardened Inorganic Polymer cement (“geoPolymer”) paste samples shows that the pore network of these materials is rich in alkali cations and has pH > 13, with a relatively low dissolved Si concentration. However, there is little soluble Ca available in these materials to play a buffering role similar to Ca(OH) 2 or high-Ca C–S–H in hydrated Portland cements, meaning that preventing alkali loss is essential in ensuring the protection of reinforcing steel. It has been seen previously that calcium in an Inorganic Polymer cement binder is important in the formation of a low-permeability pore system; alkali diffusion measurements confirm these observations and highlight the role of Ca in reducing effective alkali diffusion coefficients by up to an order of magnitude. This is crucial for the durability of Inorganic Polymer concretes containing steel reinforcement, as it appears that the use of calcium-containing raw materials will be highly preferable.

  • spatial distribution of pores in fly ash based Inorganic Polymer gels visualised by wood s metal intrusion
    Microporous and Mesoporous Materials, 2009
    Co-Authors: Redmond R. Lloyd, John L Provis, Kevin J Smeaton, Jannie S. J. Deventer
    Abstract:

    Abstract Inorganic Polymer cements, or ‘geoPolymers’, are now finding use as a replacement for Portland cement in concrete production, and have a complex pore structure which has proven difficult to measure accurately by gas or mercury porosimetry. These materials consist of an alkali aluminosilicate-based gel binder phase, within which are embedded unreacted precursor (usually coal fly ash and/or blast furnace slag) particles. Impregnation of the Inorganic Polymer samples with Wood’s metal, a low-melting-point alloy which solidifies at room temperature, and examination by scanning electron microscopy, allows both the size of pores and their physical distribution within the gel to be determined. Pore sizes as small as 10 nm are directly observable in high-resolution imaging. Much of the difficulty in applying standard porosimetry techniques to Inorganic Polymers may be identified as being related to the presence of numerous ‘ink-bottle’ pores, as well as the very wide distribution of pore diameters (spanning several orders of magnitude). The effect of gel chemistry on pore structure, and in particular the presence of calcium in the Inorganic Polymer formulation, is also considered.

  • Microscopy and microanalysis of Inorganic Polymer cements. 1: remnant fly ash particles
    Journal of Materials Science, 2009
    Co-Authors: Redmond R. Lloyd, John L Provis, Jannie S. J. Deventer
    Abstract:

    Accurate and precise electron microscopic analysis of the remnant solid precursor (fly ash and blast furnace slag) particles embedded in an Inorganic Polymer cement (or “fly ash geoPolymer”) provides critical information regarding the process of gel binder formation. Differential solubility of phases in the fly ash is seen to be important, with insoluble mullite crystals becoming exposed by the retreat of the surrounding glassy phases. High-iron particles appear to remain largely unreacted, and the use of sectioned and polished specimens provides a view of the inside of these particles, which can show a wide variety of phase separation morphologies and degrees of intermixing of high iron and other phases. Calcium appears to be active in the process of alkali activation of ash/slag blends, although the competitive and/or synergistic effects of ash and slag particles during the reaction process remain to be understood in detail.

  • microscopy and microanalysis of Inorganic Polymer cements 2 the gel binder
    Journal of Materials Science, 2009
    Co-Authors: Redmond R. Lloyd, John L Provis, Jannie S. J. Deventer
    Abstract:

    By scanning electron microscopy and microanalysis of fly ash-based and mixed fly ash-slag Inorganic Polymer cement (i.e., “fly ash geoPolymer”) binders, a more detailed understanding of the gel structure and its formation mechanism have been developed. The binder is predominantly an aluminosilicate gel charge balanced by alkali metal cations, although it appears that calcium supplied by slag particles becomes relatively well dispersed throughout the gel. The gel itself is comprised of colloidal-sized, globular units closely bonded together at their surfaces. The microstructure of the binder resulting from hydroxide activation of fly ash is much less uniform than that which forms in a corresponding silicate-activated system; this can be rationalized in terms of a newly developed explanation for the differences in reaction mechanisms between these two systems. In hydroxide activation, the newly formed gel phase nucleates and grows outwards from the ash particle surfaces, whereas the high silica concentration in a silicate-activated system enables a more homogeneous gelation process to take place throughout the inter-particle volume.