Silicate Polymerization Research Articles

Mechanism of recalcification and its effects on the microstructure and transport properties of cement paste

Calcium leaching involves the removal of calcium ions from the pore solution and hydration products, leading to a decrease in pH, coarsening of pore structure, and, in severe cases, loss of cohesion, shrinkage, and cracking. Recalcification is a restoration process aiming at repairing degraded C-S-H structures by externally supplying calcium ions. However, our understanding of recalcification mechanism, its potential to reverse calcium leaching, and its effects on deteriorated cementitious matrices remains limited. This study aims at enhancing the understanding of the impact of recalcification on calcium leached cement pastes. Our findings demonstrate that calcium leaching can be partially reversed by immersion in a saturated calcium hydroxide solution. Recalcification functions by introducing calcium ions to the degraded matrix, triggering a reaction with the degraded C-S-H. This process reverses silicate polymerization, increases the Ca/Si ratio in the degraded zone’s, and densifies the pore structure. After only 14 days of recalcification, the degraded portion experienced a 50 % reduction in porosity, an increase in pH. By day 28, recalcification halved the permeability of the treated sample and completely consumed all silica gel. Additionally, our findings reveal that higher temperatures adversely affect the structure of C-S-H, hindering the beneficial structural modifications facilitated by recalcification.

The Structural Phase Transition, Degree of Polymerization and Dynamics Characteristics of Liquid Magnesium Silicate: A Molecular Dynamics Simulation

The Structural Phase Transition, Degree of Polymerization and Dynamics Characteristics of Liquid Magnesium Silicate: A Molecular Dynamics Simulation

A case study of depolymerization in silicates: Melting of quartz and zircon crystallization at high pressure

The experimental study of depolymerization reaction SiO2 + ZrO2 → ZrSiO4 reveals that melting of quartz and crystallization of zircon in the presence of water increases at high pressure. The melting rate of quartz is identified as the rate-determining step of the reaction. In highly polymerized silicates, Si-O-Si bond angles are subject to alteration under the influence of pressure. This phenomenon is particularly noticeable within the three-dimensional lattice structure of quartz, where each corner of the tetrahedra is shared. Theoretical analysis of the Si-O-Si bond angle bending demonstrates a change in oxygen hybridization from sp to sp2, favoring larger Si-O distances. The sp2 hybridization in bridging oxygen promotes acid attack by hydrogen ions of water, resulting in SiO bond heterolysis in quartz. The depolymerization from tectosilicates to nesosilicates leads to an increase in oxygen “size” and polarizability, as well of closer packing of oxygen atoms. This change in behavior and packing of oxygens is further illustrated by the high-pressure-driven transition from tridymite to stishovite. Additionally, the impact of network-modifying elements on the structure of polymerized silicates is investigated; particularly those acting as electron donors, which lengthen Si-O distances in quartz. The findings are discussed in relation to key topics in Earth Sciences, including the crystal chemical basis of the Bowen's reaction series, the “metallization” in rocky planets and the structural controls of hydrous and dry melting in silicates.

Preparation and application of polymeric silicate coagulant: a short review

Coagulation, a fundamental and crucial operation in water treatment, has a long history of application in water/wastewater treatment processes. The efficiency of coagulation depends primarily on the quality, type, and quantity of coagulants used. Although aluminum or iron-based coagulants are the most commonly employed, polymeric silicate coagulants (PSCs) are less frequently utilized. However, the PSCs are promising candidates that deserve further exploration and examination of their potential applications. This review presents an examination of the advantages, synthesis theory, coagulation mechanism, and structure of PSCs. It also delves into the current limitations of these coagulants in research and the challenges that lie ahead for future studies. Finally, it offers some suggestions for future research directions. These discussions are intended to aid readers in comprehending the fundamental characteristics of these coagulants, enabling them to grasp their design methodologies and application area. This understanding can contribute to overcoming the limitations of this type of flocculants, further enhancing their effectiveness.

Understanding the setting behaviours of alkali-activated slag from the dissolution-precipitation point of view

Ground granulated blast-furnace slag (GGBS) is widely used as supplementary cementitious material of interest for adjusting the performance of concrete. Unlike standard commercial products, characteristics of GGBS from different iron manufacturers vary significantly and assessment of its reactivity, especially at an early age, is not well-established despite numerous parameters specified in current standard systems. Three GGBSs with different setting features during the alkali-activated process were dissolved in either deionised (DI) water or NaOH solution in this study. To illustrate the fundamental processes of reaction kinetic, the dissolved ion concentrations, glassy structural changes, and chemically bound water were measured using ICP-OES, FTIR, and TG respectively. Meanwhile, thermodynamic calculations were carried out to estimate the precipitation of C–S–H gels, which is directly linked with setting behaviours. The results clearly show the differences in the dissolution of the three GGBSs, which could be used to indicate the activity of GGBS. The GGBS with higher activity (i.e. faster setting during alkali activation) tends to dissolve evenly in DI water, whilst those with lower activity show that the silicate groups with lower polymerisation dissolved faster. The chemically bound water determined by TG analysis and the effective saturation index (ESI) are promising parameters for reflecting the activity of GGBS during dissolution in the alkali media. Although this study demonstrated the dissolution rate of higher polymerised silicate groups in GGBS should be the root for the differences in its activity, more structural information on the glassy phase and the interactions of alkali with the surface of GGBS still require further understanding. It is speculated that the ratio of Al[IV]/Al[V] plays an important role in the activity of GGBS. This finding may shape a certain basic understanding of how GGBSs dissolve in neutral and high pH solutions and highlight a re-evaluation of assumptions in thermodynamic simulation under different conditions.

Design and characterization of iron–calcium–aluminium–silicate–hydrate as low-temperature binder

This work aims to synthesize new cementitious materials (binders) using marble powder, rice husk ash, activated laterite and NaOH solution by applying low energy process. The binder was used to stabilize solid precursors (laterite and pozzolan). To achieve this objective, calcium–silicate–hydrate (CSH) was first synthesized at different temperatures (26, 50, 80 and 100 °C). The best physical–mechanical properties were chosen to produce iron–calcium–aluminium–silicate–hydrate [Fe–C(A)SH] at different concentrations of sodium hydroxide solution: 4, 5, 6 M. Finally, the formulated binder at 6 M of NaOH solution was used to stabilize laterite and pozzolans at the following proportions 20%, 30%, 40% and 50%. The samples were characterized after 28 days of curing at room temperature. FT-infrared spectroscopy, X-ray diffraction, and environmental scanning electron microscope ESEM-EDS permitted to confirm the formation of CSH, and Fe–C(A)SH. The mechanical test used to evaluate the performance showed that the incorporation of 10% iron-rich laterite into CSH increased the strength up to 42.93 MPa and the addition of Fe–C(A)SH in the laterite/pozzolans increased the compressive strength of the final product (15.34 and 15.8 MPa for laterite and pozzolan, respectively). The highest concentration (6 M) increases the alkalinity and reduces the efficiency of silicate polymerization affecting the final structural compound. From the results, low-energy Fe–C(A)SH-based cement and stabilized compounds appeared promising for the development of sustainable infrastructures.

Synthesis of porous gas materials for a semiconductor carbon(ii) oxide sensor and their investigation

In this article, the process and conditions for the synthesis of porous silica materials based on alkoxysilanes and metal oxides are studied. the main stages are discussed. A change in the pH value of a solution affects the relative rate of hydrolysis and condensation reactions of the solution, which makes it possible to obtain various structures from weakly branched silicate polymers to ordered, densely packed particles. The H2O/TEOS molar ratio (R) also has a significant effect on the structure of the synthesized silica materials. By changing R, silica materials can be obtained in the form of solid gels and colloidal particles. The composition and properties of the developed gas sensitive materials were studied by SEM, XRD and thermal analysis.

System "dispersed polyvinyl acetate-calcium silicate" in furnishing materials

This article focuses on the processes of interaction between calcium silicate hydrates and dispersed polyvinyl acetate in tight films with the aim of developing compounds meant for restoration and finishing works. The basis of this development relies on the concept concerning the determining role of the crystal-chemical factor of the silicate phase in the formation of organic-mineral compounds of increased durability. The characteristics of dispersed calcium silicate hydrates are portrayed. The preparation conditions, accounting for the synthesis of the product of submicrocrystalline structure, conforming with the stoichiometry CaO:SiO2=0.8-2.0 have been determined. The interaction has been studied for compounds achieved by mixing ingredients in a rapid whirling mixer, and subjected to hardening at T=20+2 °C. With the aid of XRD, DTA and Infra-Red Spectrometry methods the formation process of the sophisticated polymer silicate phase in the material was observed for a period of 90 days. The properties of the film were investigated and its high resistance against the influence of external factors was established. On this basis a conclusion concerning the quite high effectiveness of substituting portland cement with dispersed calcium silicate hydrate in polymer cement compounds has been made White colour and other various special properties determine the suitability for repair and finishing works on facades of buildings.

Effective treatment of leachate concentrate from waste incineration plant by combination of coagulation and direct contact evaporation

In order to verify that coagulation as pre-treatment can reduce the temperature of the hot air used for direct contact evaporating the leachate concentrate (LC) and low-grade waste heat such as exhaust steam in the waste incineration plant can be used to evaporate the LC. The supernatants after coagulation using polymerized ferrous sulfate (PFS), polymeric-aluminum (PAC), polymeric silicate aluminum ferric (PSAF) and poly-aluminum ferric chloride (PAFC) as coagulants were further treated in a lab-scale direct contact evaporation system. The results showed that the best performance with removal efficiencies of COD and NH3–N of 58.70% and 29.09% was achieved after coagulation when PAFC dosage = 15 g/L, PAM dosage = 30 mg/L and initial pH of supernatant = 6. After coagulation, a large amount of the fulvic-like acid and aromatic heterocyclic compounds were removed and the degree of complexity and aromaticity of organics decreased. After direct contact evaporation, using PAFC as coagulant still was the best selection due to its lowest concentrations of COD and NH3–N (22 mg/L and 1.02 mg/L) in the condensate produced by this two-stage treatment when initial pH of supernatant was 6 during evaporation and the condensate produced by this two-stage treatment met the water quality standard for using as supplying water for circulating cooling water system when temperature of hot air used for heating LC was at low temperature (250 °C). The fulvic-like acid and aromatic heterocyclic compounds in the condensate continuously reduced. Phenol, adamantane, 1-isocyanato, phthalic anhydrid, tri(2-chloroethyl) phosphat, Heptadecane, 2-methyl, ginsenol and Octadecane, 2-methyl- in the condensate obviously decreased. The effect of four coagulants as pretreatment on reducing the temperature of hot air used for evaporating LC was ranked as PAFC > PFS > PAC > PSAF. PSAF was not recommended due to the large amount of NH3–N produced when using PSAF to treat the LC.

Structure and Properties of Polyester Composites with Polymer Silicate Modifier

Structure and Properties of Polyester Composites with Polymer Silicate Modifier

Effect of Composition on the Physicochemical Properties of Cross-Linked Poly(sodium acrylate)/Sodium Silicate Hydrogels

The paper presents the results of research on the influence of the components of composition on the physicochemical properties of cross-linked poly(sodium acrylate)/sodium silicate hydrogels. The results of the rheological measurements showed that an increasing share of polyacrylate in the sample causes a shift of the cross-over point towards longer times and improves mechanical properties. In turn, increasing the share of sodium silicate has a positive effect on extending the fire insulation time (I). TG/DSC analysis indicated that if the sample contained more than 50 wt.% of polymer, the thermal decomposition was a three-stage process, while if the sample contained more water glass, the decomposition was two stage. UV-Vis measurements and SEM analysis confirmed, inter alia, that increasing the share of polyacrylate causes improvement of the optical parameters and homogeneity of the tested hydrogels. The presented results suggest that by controlling the share of the main components of the silicate–polymer hydrogels, it is possible to control their mechanical, optical and thermal properties. Multiplication of the layers or increasing their thickness improves their fire-retardant properties.

Chemical structure and complex growth modes of magnesium silicate hydrate: Nanoparticle orientation, aggregation, and fusion

The extent of utilization of magnesium silicate hydrate (MSH) in construction is limited partly because of insufficient data ascertaining the kinetics of its precipitation. Here, MSH grown homogeneously or heterogeneously in the range of magnesium to silicon solution molar concentration ratios, [Mg]/[Si] = 0.5–1.5, and temperature = 25–80 °C was analyzed for its chemical structure and morphology. Infrared spectroscopy and geochemical modeling show that increasing the [Mg]/[Si] ratio results in less silicate polymerization in MSH. Atomic force microscopy reveals the presence of nanoparticles that aggregate and fuse to form films. Oriented attachment of nanoparticles and features indicative of enhanced crystallinity were observed at higher temperatures and longer reaction times. These data provide direct evidence for the persistence of hierarchical structures (i.e., nanoparticles forming 3D microparticles and 2D film layers) at the nanoscale to mesoscale. These findings offer insights into the precise chemical synthesis of MSH and its widespread use as a binder for construction purposes.

Synthesis of iron oxide nanocubes and their incorporation with luminescent lanthanide (Ln = Tb/ Eu)-Terephthalate complex in silica nanospheres using a reverse microemulsion method

Luminescent magnetic nanocomposites are of interest because of their promising applications in the biomedical field. This article reports the preparation of silica-coated lanthanide terephthalate complexes, Ln-TA (Ln = Tb and Eu) containing luminescent magnetic nanocomposites. Cubic-shaped iron oxide nanoparticles were synthesized through the thermal decomposition of the iron-oleate complex. Then, polymerization of tetraethyl ortho silicate in a water-in-oil reverse microemulsion in the presence of previously prepared iron oxide nanocubes and a terbium (Tb3+)/europium (Eu3+)-terephthalate (TA) complex was performed to obtain luminescent magnetic Fe3O4@Ln-TA (Ln = Tb, Eu)/SiO2 nanocomposites. The size (8.9 nm) and cubic shape of magnetic core were determined via transmission electron microscopy and the superparamagnetic behavior using a vibrating sample magnetometer. Energy dispersive X-ray analysis and inductively coupled plasma optical emission spectroscopy found that the luminescent Tb-TA and Eu-TA complexes were incorporated in the magnetic silica nanocomposites. The nanocomposites, Fe3O4@Ln-TA/SiO2, exhibited distinct luminescent green and red emission peaks and showed promise as a T1 contrast agent for magnetic resonance imaging.

Enhancing the treatment efficiency of recycled concrete fines with aqueous carbonation

Recycled concrete fines (RCFs, 0.3 mm ≪ 2.36 mm) are the fine fractions of waste concrete generated during the recycling process. RCFs contain less natural aggregate and more residual cement paste than their coarser counterparts, thus more prone to carbonation. Although carbonation is beneficial for the microstructure and reactivity of RCFs by refining the pores and changing the phase compositions of the residual cement paste, carbonation rate is usually too slow for practical applications. In this study, two critical modifications (i.e., manipulating the initial carbonate concentrations and using elevating temperatures) were applied to aqueous carbonation of RCFs, aiming to improve the carbonation efficiency. Particularly, the rate of calcium carbonate (Cc) precipitation, the advance of Cc deposition front, the mineralogy, the development of microstructure, and the aqueous chemistry during carbonation were investigated using techniques of multiple scales. Based on the results, the rate of Cc precipitation and advancement of the Cc deposition front was significantly improved. The pore structure was drastically refined. Using elevated temperatures not only activated carbonate transport but also enhanced silicate polymerization, leading to the formation of a larger amount of silica gel as well as the increase in Q4/Q3 ratio, thus improving the reactivity of RCFs. A lab-scale production of carbonated RCFs was conducted, and the carbonation products were used for preparing cement mortars. Based on the compressive strength results, the carbonation treatment duration for RCFs could be reasonably reduced to hours and even minutes.

Alite hydration at the single grain level

Understanding cement hydration processes is crucial for achieving the desired properties in concrete. However, the nanoscale mechanism whereby calcium silicate hydrate (C–S–H) transforms, particularly regarding morphology, structure, and composition evolution, remains unclear. Here, we employed multimodal transmission electron microscopy (TEM) to investigate the hydration kinetics of alite at the single grain level, extracting comprehensive chemical and structural information. Our findings reveal that rapid nucleation of C–S–H occurs at the boundaries within minutes, followed by subsequent C–S–H growth. The development of C–S–H fibrils can be categorized into two distinct stages: needle elongation and texture densification. Through quantitative analysis, we estimated the growth rate of C–S–H needles to be 7 nm/min, while observing a decrease in the intrinsic porosity of C–S–H from 7.9% to 3.1% concurrent with the thickening of C–S–H lamella. Electron diffraction analysis further demonstrates the homogenization of C–S–H throughout hydration, involving structural compaction and silicate polymerization. Our work provides valuable insights into the origins of C–S–H nucleation and growth, thereby enhancing our understanding of hydration mechanisms at a fundamental level.

Effect of superheat degree and MnO on structural characteristics of CaO-SiO2-TiO2-based blast furnace slags

High-temperature equilibration experiments were carried out to investigate the liquidus temperature of CaO-SiO2-TiO2-MnO slags, and the addition of MnO into the slag could decrease the liquidus temperature. Furthermore, Raman spectra of CaO-SiO2-TiO2–1wt%MnO quenched slags under various superheat degrees and slags with different MnO content were also studied to uncover the slag structure characteristics. Higher superheat degree mainly simplified the complicated structural units of CaO-SiO2-TiO2–1wt%MnO slags by promoting to form simpler silicate units. Increasing the MnO content in the slag could provide more free oxygen ions to break the Si-O bond of polymerized silicate units and weaken the silicate network stability. The relationship between slag viscosity and nBO was fitted, and the viscosity (lnη) linearly increased with increasing the nBO. To some extent, the fitted expression could reflect the relationships of the slag viscosity and structure.

Mitigating drying shrinkage and enhancing mechanical strength of fly ash-based geopolymer paste with functionalized MWCNTs grafted with silane coupling agent

In this study, the functionalized MWCNTs grafted with silane coupling agent are obtained by means of successive chemical modification methods. The structure and dispersity of the functionalized MWCNTs are characterized using the FT-IR, XPS and HR-TEM, respectively. Then the reaction kinetics, mineralogical phases, morphology and elemental components of modified geopolymer incorporated with the functionalized MWCNTs are evaluated by means of the XRD, TAM, FT-IR and SEM-EDS analysis. In addition, the influences of functionalized MWCNTs on the mechanical strength and drying shrinkage behaviors are investigated. The MIP and 29Si NMR are employed to investigate the pore size distribution and microstructural rearrangement of gel products. The results show that the functionalized MWCNTs can be dispersed uniformly in aqueous solution without any dispersant. Importantly, the modified geopolymer incorporated with 0.2% functionalized MWCNTs-KH550 exhibits a lower drying shrinkage(0.098%) and higher mechanical strength compared with that of all geopolymer pastes. The hydrophobic modification of functionalized MWCNTs reduces significantly the mass loss of the geopolymer. The MIP results indicate that a critical pore size(ds)computed from both the pore size distributions and water loss is related with drying shrinkage, and the drying shrinkage of geopolymer pastes decreases with the increment of the ds value. A strong interaction between adjacent C(N)-A-S-H particles occurs in microstructure rearrangement period by means of the silicate polymerization and micropore closure. Moreover, the new dual interaction mechanism decreasing drying shrinkage and increasing mechanical strength of geopolymer pastes are proposed.

Detection of polymeric silicate in the pore water of freshwater lakes

Detection of polymeric silicate in the pore water of freshwater lakes

Investigation of the Porous Structure of Concretes Treated with Polymer Silicate Compositions with Nanoadditives

Investigation of the Porous Structure of Concretes Treated with Polymer Silicate Compositions with Nanoadditives

Insight on the mechanical properties of hierarchical porous calcium-silicate-hydrate pastes according to the Ca/Si molar ratio using in-situ synchrotron X-ray scattering and nanoindentation test

Nanocrystalline calcium–silicate–hydrate (C-S-H) is a typical heterogeneous material with a multiscale structure spanning a wide length scale from angstrom to micrometer, and whose structure is determined by the Ca/Si ratio. In this study, we directly applied compressive loads on synthetic C-S-H pastes with Ca/Si ratios of 0.6–1.2 and investigated their mechanical properties using the elastic modulus calculated at three length scale levels (i.e., angstrom to nanometer, micrometer, and millimeter) via in-situ synchrotron X-ray scattering, nanoindentation tests, and strain gauges, respectively. Further, 29Si nuclear magnetic resonance spectroscopy was conducted on the C-S-H pastes to elucidate the alterations in the silicate polymerization. The experimental results confirmed the deformation behavior of the C-S-H paste with different Ca/Si ratios under external loading, which was demonstrated to be transferred from the surface of the pastes to particles owing to the presence of multiscale pores.