Geopolymers, possessing a semi-crystalline three-dimensional inorganic network generated by the dissolution and reaction of a solid alumino-silicate source with an activating solution, have attracted ...increasing attention from both academia and industry because of their unique and favorable characteristics. This review deals with the synthesis, characterization and potential applications of porous geopolymers, realized through different processing routes. Firstly, the processing approaches are divided into five categories: (i) Direct foaming, (ii) Replica method, (iii) Sacrificial filler method, (iv) Additive manufacturing, and (v) Other methods. Their microstructure, porosity and properties are compared and discussed in relation also to the different processing routes. This review highlights the fact that porous geopolymers are promising low-cost candidates for technologically significant applications such as catalyst supports or membranes, filtration of liquid or gases, adsorption and insulation. This review aims at summarizing the main published results and fostering further investigations into developing innovative ways to generate components with improved properties.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Geopolymer foams, as a new type of potential eco-friendly building material, are increasingly being discussed in the literature. This study reports the synthesis and characterization of geopolymer ...foams using hydrogen peroxide (H2O2) solution as pore-forming agent and oil as the stabilizing agent. The geopolymer foams with low bulk densities (0.37<ρb<0.74g/cm3), low thermal conductivities (0.11<λ<0.17W/(m.K)), high porosity (66<p<83 vol%), and acceptable compressive strength (0.3<σ<11.6MPa) were successfully fabricated at appropriate conditions. Factors that influence the insulating, mechanical, porous, and microstructural properties were investigated. It was found that the content of the stabilizing agent and the blowing agent had a significant influence on the porous structure and associated foam performance.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
Fire is one of the most unfavorable conditions that cement-based composites can face during their service lives. The uniaxial tensile and flexural tensile properties of the steel-polyvinyl alcohol ...fiber-calcium carbonate whisker (CW) multi-scale fiber reinforced cement matrix composites (MSFRCs) under high temperatures are studied, including strength, deformation capacity, energy dissipation capacity, and its ability to be assessed through the empirical calculation method. The study showed that with the increase of the treatment temperature, the MSFRC residual bending strength, bending toughness, and tensile strength decreased overall, but the decline was slow at 600 °C. The peak flexural deflection and peak tensile strain of MSFRC first reduced and then increased with the increase of the temperature. As the temperature increased, the nominal stiffness of MSFRC bending and straight gradually reduced, and the rate of decline was faster than that of its strength. However, the uniaxial tensile properties were more sensitive to the temperature and degraded more rapidly. A quantitative relationship was established between MSFRC residual bending, tensile strength, and temperature. A comparison with existing research results shows that MSFRC has achieved an ideal effect of high temperature resistance. The multi-scale hybrid fiber system significantly alleviates the deterioration of cement-based composite's mechanical properties under high temperatures. With the help of an optical microscope and scanning electron microscope (SEM), the high temperature influence mechanism on the uniaxial tensile and flexural properties of MSFRC was revealed.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
Geopolymers have been recently explored as sorbents for wastewater treatment, thanks to their mechanical and chemical stability and to their low-energy manufacturing process. One specific application ...could be the removal of ammonium (NH4+) through exchange with Na+ ions. Additive manufacturing (AM) represents an especially interesting option for fabrication, as it allows to tailor the size, distribution, shape, and interconnectivity of pores, and therefore the access to charge-bearing sites. The present study provides a proof of concept for NH4+ removal from wastewater using porous geopolymer components fabricated via direct ink writing (DIW) AM approach. A metakaolin-based ink was employed for the fabrication of a log-pile structure with 45° rotation between layers, producing continuous yet tortuous macropores which are responsible for the high permeability of the sorbents. The ink consolidates in an amorphous, mesoporous network, with the mesopores acting as preferential sites for ion exchange. The printed sorbents were characterized for their physicochemical and mechanical properties and the NH4+ removal capacity in continuous-flow column experiments by using a model effluent. The lattices present high permeability and high cation exchange capacity and maintained a high amount of active ions after four cycles, allowing to reuse them multiple times.
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•Geopolymer sorbents were prepared via Direct Ink Writing (DIW).•The synergy between material and fabrication provides optimal porosity.•Proof-of-concept study of aqueous NH4+ removal with 3D-printed geopolymers.•High permeability, high cation exchange capacity, and reusable for multiple times.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
A facile and effective route for the fabrication of porous geopolymers through the addition of a water-soluble pore forming agent (NaCl) is proposed in this study. NaCl/geopolymer samples were ...firstly obtained using metakaolin and slag as raw mineral materials combined with sodium-based alkali activator and NaCl as a sacrificial (soluble) template. After a simple extraction step by water, porous geopolymer were obtained. The effect of NaCl content on the pore morphology, porosity, density, boiling water absorption, and mechanical and structural characteristics of the synthesized porous geopolymers was investigated. High porosity (67.4–80.4 vol%) metakaolin/slag-based geopolymers, possessing also a high ratio of open porosity to total porosity (77.4–84.0%) and a good compression strength (2.4–7.0 MPa), were produced. The adsorption properties for methylene blue removal were investigated as well. The high strength bulk-type waste-based geopolymer adsorbents by this water-soluble templating method is suitable for applications in wastewater treatment systems.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
In this paper, synthetic metakaolin with fixed composition (Al2O3·2SiO2) was produced by a simple chemosynthetic route. The chemosynthetic metakaolin can eliminate the influence of impurities in ...metakaolin from natural kaolin minerals. The synthetic metakaolin together with NaOH and SiO2-sol were used to prepare Na-based geopolymer precursors with various molar ratios of Si/Al. The molar ratios of Si/Al from 1 to 2 were tailored by adding different contents of SiO2-sol. Zeolite/geopolymer composites or monolith-type zeolite were successfully fabricated from synthetic metakaolin-based geopolymer through a hydrothermal process. The effects of Si/Al ratios on the phase composition and microstructure of the produced zeolite/geopolymer composites or zeolites were studied. The results proved that the composition of synthetic metakaolin and geopolymer precursors can be facilely tuned, and the monolithic geopolymer precursors can be mostly, or even totally, transformed into zeolite after hydrothermal treatment.
Lightweight absorption materials with superior mechanical properties have received significant attention owing to their potential for use in military stealth and electromagnetic protection ...applications. Herein, a novel electromagnetic (EM) wave absorbing lattice structured composite material containing a hollow short carbon fiber (SCF)/Fe3O4/epoxy sphere filler, and an epoxy resin matrix, is described. The morphology, density, and isostatic compression strength of the hollow SCF/Fe3O4/epoxy spheres were measured, and the mechanical and electromagnetic wave absorption properties of the epoxy resin composite embedded with the hollow SCF/Fe3O4/epoxy spheres were studied. The results indicate that the composite possessed a high compression strength of ~57.3 MPa with a density of only ~0.92 g/cm3. Furthermore, the effective absorption bandwidth within the range of 2–18 GHz of the composite was 1.8 GHz, with an ultra-thin equivalent thickness of only ~0.48 mm. The macro-sized hollow structure spheres were effective EM wave absorption enhancements, and the lattice composite embedded with these hollow spheres presented a unique structure and excellent absorption performance.
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•Hollow macro-sized SCF/Fe3O4/epoxy spheres with high strength and microwave absorption properties were designed.•An epoxy resin matrix composite embedded with hollow SCF/Fe3O4/epoxy spheres was demonstrated to form a lattice structure.•The effective absorption bandwidth of this composites is 1.8 GHz, with an ultra-thin equivalent thickness of only ~0.48 mm.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Porous geopolymer precursors were firstly prepared by the direct foaming method using bauxite, fly ash (FA), and metakaolin (MK) as raw materials, and porous mullite ceramics were prepared after ...ammonium ion exchange and then high-temperature sintering. The effects of chemical foaming agent concentration, ion-exchange time, and sintering temperature on porous geopolymer-derived mullite ceramics were studied, and the optimal preparation parameters were found. Studies have shown that the concentration of blowing agent had great influence on open porosity (q) and porosity and cell size distributions of geopolymer samples, which in turn affected their compressive strength (σ). Duration of the ion exchange had no obvious effect on the sintered samples, and the amount of mullite phase increased with the increase in the sintering temperature. Mullite foams, possessing an open-celled porous structure, closely resembling that of the starting porous geopolymers produced by directly foaming, were obtained by firing at high temperatures. Stable mullite (3Al2O3·2SiO2) ceramic foams with total porosity (ε) of 83.52 vol%, high open porosity of 83.23 vol%, and compressive strength of 1.72 MPa were produced after sintering at 1400 ℃ for 2 h in air without adding any sintering additives using commercial MK, bauxite, and FA as raw materials.
MAX phases have exhibited diverse physical properties, inspiring their promising applications in several important research fields. The introduction of a chalcogen atom into a phase of MAX has ...further facilitated the modulation of their physical properties and the extension of MAX family diversity. The physical characteristics of the novel chalcogen-containing MAX 211 phase Zr2SeB and Zr2SeN have been systematically investigated. The present investigation is conducted from a multi-faceted perspective that encompasses the stability, electronic structure, and mechanical properties of the system, via the employment of the first-principles density functional theory methodology. By replacing C with B/N in the chalcogen-containing MAX phase, it has been shown that their corresponding mechanical properties are appropriately tuned, which may offer a way to design novel MAX phase materials with enriched properties. In order to assess the dynamical and mechanical stability of the systems under investigation, a thorough evaluation has been carried out based on the analysis of phonon dispersions and elastic constants conditions. The predicted results reveal a strong interaction between zirconium and boron or nitrogen within the structures of Zr2SeB and Zr2SeN. The calculated band structures and electronic density of states for Zr2SeB and Zr2SeN demonstrate their metallic nature and anisotropic conductivity. The theoretically estimated Pugh and Poisson ratios imply that these phases are characterized by brittleness.
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SiC/mullite composite porous ceramics were prepared from a mixture of calcined kaolin, aluminum hydroxide, silicon carbide, and graphite. The above mixture was heated in air at 1250–1450°C to produce ...pores by burning graphite and bond the SiC particles by reaction-derived mullite. The reaction bonding behavior, open porosity, firing shrinkage, and mechanical strength of the composites were investigated as a function of the mass ratio of calcined kaolin and Al(OH)3, sintering temperature, holding time, and graphite content. In addition, the phase composition and microstructure of the composites were also studied. The results show that when the mass ratio of calcined kaolin:Al(OH)3 is 1:1.5, in the absence of graphite, the flexural strength and the open porosity of the composites were 48.14MPa and 33.97%, respectively. However, when 15% graphite was added to the above composition, a flexural strength of 27.26MPa was achieved at an open porosity of 48.80%.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
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