Silica Suspensions Research Articles

Effect of Liquid Properties on the Non-Newtonian Rheology of Concentrated Silica Suspensions: Discontinuous Shear Thickening, Shear Jamming, and Shock Absorbance.

Concentrated particle suspensions exhibit rheological behavior, such as discontinuous shear thickening (DST) and dynamic shear jamming (SJ), which affect applications such as soft armors. Although the origin of this behavior in shear-activated particle-particle interactions has been identified, the effect of chemical factors, especially the role of liquids, on this behavior remains unexplored. Hydrogen bonding in suspensions has been proposed to be essential for frictional contacts between particles, and therefore, most studies on DST and SJ have focused on aqueous and protic organic media with a definite hydrogen bonding ability. To identify an alternative molecular mechanism, this study explored the effects of liquid polarity and an aprotic nature on the rheological behavior of concentrated suspensions of silica microparticles. Owing to their excellent particle dispersion, the DST behavior of polar liquids was observed, independent of protic and aprotic liquids. In contrast, nonpolar liquids formed particle agglomerates because of the particle-particle attraction and became a paste at a high particle fraction. The SJ behavior was confirmed for three aprotic organic liquids (propylene carbonate, 1,3-dimethyl-2-imidazolidinone, and 1,3-dimethylpropyleneurea), suggesting the hydrogen bonding ability of these aprotic liquids. The diverse mechanisms of shear-activated interactions between particles present material design possibilities for the non-Newtonian rheology of concentrated particle suspensions.

Novel pilot study on plasma metabolites and biomarkers in a rat model of silica-induced lung inflammation and fibrosis

Silica-induced lung damage may be associated with changes in distinct metabolites potentially serving as biomarkers. Due to the lack of metabolomic data from animal models, this pilot study aimed to evaluate changes in markers of inflammation and fibrosis, as well as plasma metabolites in rats at 14 and 28 days after silica instillation.Adult male Wistar rats were administered a single oropharyngeal intratracheal dose of silica suspension or sterile saline in controls. Selected markers of inflammation, oxidative stress, fibrosis, and cell counts in blood and bronchoalveolar lavage fluid have been evaluated. Finally, plasma metabolites were detected using a targeted metabolomics approach with an MxP® Quant 500 kit.Silica instillation induced noticeable inflammatory, oxidative, and fibrotic changes in lung tissue within the first 14 days. During the next two weeks, the shifts in some markers were further accentuated. After exposure to silica, the metabolomic analysis identified significant changes in metabolites associated with lipid metabolism, biogenic amines, amino acid derivatives, carboxylic acids, bile acids, putrescine, glycosylceramides, and acylcarnitines.This pilot study provides initial evidence that significant alterations in plasma metabolite profiles accompany silica-induced lung injury in rats. These findings suggest a possible systemic impact, particularly on lipid metabolism, and indicate the urgent need for a deeper understanding of the metabolic reprogramming associated with silica-induced lung injury to pave the way for the discovery of novel biomarkers.

Dual admixtures for cement-based composites comprising steel slag powder and residual lignin-based liquor

Steel slag is a by-product of the steel industry that can be used as an aggregate and/or mineral admixture, conferring physical and mechanical benefits to cement-based composites. In parallel, sugarcane bagasse is a by-product of the sugar/alcohol industry used in biorefineries to produce bioethanol. The delignification processes, employed as a pretreatment in biorefineries, generate residual liquors that contain lignin. Lignin is a natural polymer with plasticizing properties when incorporated into cement mixtures. Given this scenario, this work sought to produce and evaluate dual admixtures containing a residual lignin-based liquor and a steel slag powder. The proposed dual admixtures were prepared from two strategies and incorporated in cement pastes and mortars at different dosages. Mixtures containing a commercial silica suspension and a reference mixture (without admixtures) were also evaluated. The flow test showed that the dual admixtures promoted higher spreading than the silica suspension in all the proposed dosages. Also, the mortars containing the dual admixtures had significantly higher compressive strengths and more refined pore structures than the reference mortar. The residual lignin-based liquor enhanced the workability of the composites and favored the dispersion of the steel slag powder into the matrix. The liquor's plasticizing and set-retarding capacities were attributed to its anionic functional groups and sugar content, respectively. Additionally, the high-efficiency grinding of the steel slag powder contributed to improving its specific surface area and fineness parameters, justifying its performance as a filler and a supplementary cementitious material. This study presents a new route for developing more eco-efficient cement-based composites. It also complies with the principles of circular economy by offering a feasible strategy for valorizing large-scale industrial wastes in civil construction.

Integrated multi-omics analyses reveal the pro-inflammatory and pro-fibrotic pulmonary macrophage subcluster in silicosis

BackgroundSilicosis is a lethal occupational disease caused by long-term exposure to respirable silica dust. Pulmonary macrophages play a crucial role in mediating the initiation of silicosis. However, the phenotypic and functional heterogeneities of pulmonary macrophages in silicosis have not been well-studied. MethodsThe silicosis mouse model was established by intratracheal administration of silica suspension. Bronchoalveolar lavage fluids (BALFs) of mice were collected for the multiplex cytokine analysis. Single-cell RNA sequencing (scRNA-seq) and spatial transcriptomics were performed to reveal the heterogeneity and spatial localization of macrophages in the lung tissues. The formation of the fibrotic nodules was characterized by histology, hydroxyproline assay, and immunohistochemical staining, respectively. The expression of the pro-inflammatory or pro-fibrotic genes was investigated by quantitative polymerase chain reaction (qPCR). ResultsWe found that the level of pro-inflammatory cytokines and chemokines is significantly increased in the BALFs of silicosis mice. Apparent collagen deposition can also be observed in the silicotic lung tissues. By scRNA-seq, we have identified a subpopulation of Mmp12hi macrophages significantly expanding in the lung tissues of mice with silicosis. Spatial transcriptomics analysis further confirmed that the Mmp12hi macrophages are mainly enriched in silicosis nodules. Pseudotime trajectory showed that these Mmp12hi macrophages, highly expressing both pro-inflammatory and pro-fibrotic genes, are derived from Ly6c+ monocytes. Additionally, 4-octyl itaconate (4-OI) treatment, which can alleviate pulmonary fibrosis in silicosis mice, also reduces the enrichment of the Mmp12hi macrophages. Moreover, we found a subset of macrophages in BALFs derived from patients with silicosis exhibited similar characteristics of Mmp12hi macrophages in silicosis mice models. ConclusionsOur study suggested that a group of Mmp12hi macrophages highly express both pro-inflammatory and pro-fibrotic factors in silicosis mice, and thus may contribute to the progression of fibrosis. The findings have proposed new insights for understanding the heterogeneity of lung macrophages in silicosis, suggesting that the subset of Mmp12hi macrophages may be a potential therapy target to further halt the progression of silicosis.

Rheological Behavior of an Aqueous Suspension of Oxidized Carbon Nanohorn (CNHox).

Oxidized carbon nanohorn (CNHox) a carbon nanomaterial that has attracted attention due to its unique material properties. It is expected to be applied in various areas like cancer treatment, gene-expression technology, fluids with high thermal conductivity, lubricants, and so on. While the rheological measurements of suspensions provide information on the effective size and interactions of suspended particles, the rheological behaviors of aqueous suspensions of CNHox have never been systematically investigated. To clarify the rheological behaviors of aqueous suspensions of CNHox, their viscosity and dynamic viscoelasticity were measured with changing particle concentration and salt concentration. The viscosity of a CNHox suspension showed yield stress at low shear rates and showed shear-thinning behavior with increasing shear rates. The viscosity of 5 weight % CNHox suspensions was comparable to that of 60 weight % silica suspensions. This high viscosity at a low CNHox concentration is probably due to the porous structure and large effective volume of the CNHox particle. The estimated effective volume of CNHox calculated by the Krieger-Dougherty equation was 18.9 times larger than the actual volume calculated by the mass concentration and density. The dependence of rheological behavior of the CNHox suspension on salt concentration was weak compared to that of the colloidal silica suspension. This weak dependence on salt concentration may be due to the roughness of the particle surface, which would weaken the effect of electric double-layer interactions and/or van der Waals interactions between particles. These rheological behaviors of the aqueous suspension of CNHox shown in this research will be useful in efforts to improve the efficiency of its utilization for the various applications.

Research on the mechanism of shengxian and jinshuiliujun decoction in treating silicosis based on network pharmacology

Objective: To explore the active ingredients of shengxian and jinshuiliujun decoction with the method of network pharmacology, and to verify the experimental mechanism of its treatment of silicosis. Methods: In May 2023, the active ingredients and targets of drugs in shengxian and jinshuiliujun decoction were obtained through the Traditional Chinese Medicine Systems Pharmacology Database and Analysis Platform (TCMSP) database. The target of silicosis disease was screened by databases such as Genecards, Disease Gene Network (DisGeNET), Comparative Toxicogenomics Database (CTD), etc. The screened drug targets and disease targets were intersected to obtain the target set of shengxian and jinshuiliujun decoction for the treatment of silicosis. Protein-protein interaction (PPI) network analysis was performed on the target set through STRING database, and core target genes were screened. GO enrichment analysis and KEGG pathway analysis of intersection genes were performed based on Metascape database, and molecular docking verification of key components and targets of shengxian and jinshuiliujun decoction was carried out. Twenty-four adult male SD rats with SPF grade were randomly divided into control group, model group and TCM intervention group, with 8 rats in each group. The dust-stained rat model was prepared by non-tracheal exposure of 1 ml silica suspension (50 mg/ml) in one go, and TCM intervention group was given shengxian and jinshuiliujun decoction[6 g/ (kg·d) ] on the second day. The CT of the lungs of each group was observed 28 days after the dust-stained rat model. Paraffin sections of rat lung tissues were prepared and stained with Hematoxylin-Eosin (HE) and Masson. Western blot was used to verify the expression of core target-related proteins in rat lung tissues after the intervention of shengxian and jinshuiliujun decoction for 28 days, and the differences in protein expression between groups were compared by one-way analysis of variance. Results: A total of 205 active ingredients and 3345 active compounds were selected from shengxian and jinshuiliujun decoction, corresponding to 281 targets, among which 240 targets were related to silicosis. Serine/threonine kinase 1 (AKT1), tumor protein p53 (TP53), tumor necrosis factor (TNF) and interleukin (IL) 6 may be the key targets of shengxian and jinshuiliujun decoction in the treatment of silicosis. Through enrichment analysis, 30 GO entries and 20 potential signaling pathways were screened according to P-value, including nuclear factor κB (NF-κB), mitogen-activated protein kinase (MAPK) and cancer signaling pathways. Molecular docking showed that the active compounds of shengxian and jinshuiliujun decoction had good binding with the core target proteins, and the strongest binding properties were beta-sitosterol and TNF-α (-10.45 kcal/mol). In animal experiments, the inflammatory infiltration and fibrosis of lung tissue of rats in TCM intervention group were significantly improved. Compared with control group, the levels of TNF-α, IL-1β, IL-6 and NF-κB in lung tissue of model group were significantly increased (P<0.05). Compared with model group, the lung injury of rats in TCM intervention group was significantly improved, and the expressions of TNF-α, IL-1β, IL-6 and NF-κB were significantly decreased (P<0.05) . Conclusion: Shengxian and jinshuiliujun decoction in the treatment of silicosis may play an anti-fibrosis role by inhibiting the NF-κB signal transduction pathway mediated by inflammatory factors such as TNF-α and IL-1β, which provides a reference for further exploring the material basis and mechanism of its action.

Repeated Silica exposures lead to Silicosis severity via PINK1/PARKIN mediated mitochondrial dysfunction in mice model

Background and objectivesSilicosis, one of the occupational health illnesses is caused by inhalation of crystalline silica. Deposition of extracellular matrix and fibroblast proliferation in lungs are linked to silicosis development. Mitochondrial dysfunction plays critical role in some diseases, but how these processes progress and regulated in silicosis, remains limited. Detailed study of silica induced pulmonary fibrosis in mouse model, its progression and severity may be helpful in designing future therapeutic strategies. MethodsIn present study, mice model of silicosis has been developed after repeated silica exposures which may closely resemble clinical symptoms of silicosis in human. In addition to efficiently mimicking the acute/chronic transformation processes of silicosis, this is practical and efficient in terms of time and output, which avoids mechanical injury to the upper respiratory tract due to surgical interventions. Sonicated sterile silica suspension (120 mg/kg) was administered through intranasal route thrice a week at regular intervals (21, 28 and 35 days). ResultsPresence of minute to larger silicotic nodules in H&E-stained lung sections were observed in all silica induced model groups. Enhanced ECM deposition was noted in MT stained lung sections of silica exposure groups as compared to control which were confirmed by significantly higher MMP9 expression levels and hydroxyproline content in silica 35 days group. Increase in Reactive oxygen species (ROS), inflammatory cell recruitment mainly, neutrophils and macrophage were observed in all three silica exposure groups. Transmission electron microscopic analysis has confirmed presence of many aberrant shaped mitochondria (swollen, round shape) in 35 days model where autophagosomes were minimum. Western blot analysis of mitophagy and autophagy markers such as Pink1, Parkin, Cytochrome c, SQSTM1/p62, the ratio of light chain LC3B II/LC3B I was found higher in 21 and 28 days which were significantly reduced in 35 days silica model. ConclusionsHigher MMP9 activity and MMP9 /TIMP1 ratio demonstrate excessive extracellular matrix damage and deposition in 35 days model. Significantly reduced expressions of autophagy and mitophagy markers have also confirmed progression in fibrosis severity and its association with repeated silica exposures in 35 days model group.

A novel interpretation of pH-dependent microstructure and rheology evolution in silica suspension based on interparticle interactions

A novel interpretation of pH-dependent microstructure and rheology evolution in silica suspension based on interparticle interactions

Temperature Dependence of the Mechanical Dissipation of Gallium Bonds for Use in Gravitational Wave Detectors.

The mirror suspensions in gravitational wave detectors demand low mechanical loss jointing to ensure good enough detector performance and to enable the detection of gravitational waves. Hydroxide catalysis bonds have been used in the fused silica suspensions of the GEO600, Advanced LIGO, and Advanced Virgo detectors. Future detectors may use cryogenic cooling of the mirror suspensions and this leads to a potential change of mirror material and suspension design. Other bonding techniques that could replace or be used alongside hydroxide catalysis bonding are of interest. A design that incorporates repair scenarios is highly desirable. Indeed, the mirror suspensions in KAGRA, which is made from sapphire and operated at cryogenic temperatures, have used a combination of hydroxide catalysis bonding and gallium bonding. This Letter presents the first measurements of the mechanical loss of a gallium bond measured between 10K and 295K. It is shown that the loss, which decreases with temperature down to the level of (1.8±0.3)×10^{-4} at 10K, is comparable to that of a hydroxide catalysis bond.

Applying colloidal silica suspensions injection and sequential gelation to block vertical water flow in well annulus: laboratory testing on rheology, gelation, and injection

We evaluated the application of silica suspension injection and sequential gelation to block vertical water flow in the annuli of long-screened wells. First, we studied the viscosity, rheological behavior, and gelation performance of colloidal silica suspensions in batch tests. Then, we tested the injection of silica suspensions and the water flow blocking efficiency of the later formed silica gel in column and bench-scale sandbox experiments. Micron-sized fumed powder silica suspensions and nanosized silica suspensions recovered from geothermal fluids were tested in this work. Fumed silica suspensions showed shear thinning, while nanosized silica suspensions exhibited Newtonian flow behavior. During the gelation process, the nanosized silica suspension changed from a Newtonian fluid to a shear thinning fluid while increasing its overall viscosity. At comparable concentrations, the nanosized silica suspensions have much lower viscosity than that of the fumed silica suspensions. Increases in the Na+ concentration and silica particle concentration in these suspensions shortened the gelation time. Silica suspension gelation in sand columns completely blocked the water flow and sustained the injection pressure up to 50 psig (344.7 kPa). A silica suspension was successfully injected into the target zone in the annulus of a bench-scale sandbox mimicking long-screened wells in the field. The silica gel formed in the annulus effectively blocked chemical transport through the gelled zone. Our research reveals that a process using silica suspension injection and sequential gelation technology is promising for blocking the vertical water flow and chemical transport through the filter pack in targeted zones within the annulus of long-screened well systems.

Wavenumber-dependent dynamic light scattering optical coherence tomography measurements of collective and self-diffusion

We demonstrate wavenumber-dependent DLS-OCT measurements of collective and self-diffusion coefficients in concentrated silica suspensions across a broad q-range, utilizing a custom home-built OCT system. Depending on the sample polydispersity, either the collective or self-diffusion is measured. The measured collective-diffusion coefficient shows excellent agreement with hard-sphere theory and serves as an effective tool for accurately determining particle sizes. We employ the decoupling approximation for simultaneously measuring collective and self-diffusion coefficients, even in sufficiently monodisperse suspensions, using a high-speed Thorlabs OCT system. This enables particle size and volume fraction determination without the necessity of wavenumber-dependent measurements. We derive a relationship between the particle number-based polydispersity index and the ratio of self and collective mode amplitudes in the autocorrelation function and utilize it to measure the particle number-based polydispersity index. Notably, the polydispersity determined in this manner demonstrates improved sensitivity to smaller particle sizes compared to the standard intensity-based DLS cumulant analysis performed on dilute samples.

NLRP3 inflammasome mediates abnormal epithelial regeneration and distal lung remodeling in silica‑induced lung fibrosis.

NOD-like receptor protein 3 (NLRP3) inflammasome is closely related to silica particle‑induced chronic lung inflammation but its role in epithelial remodeling, repair and regeneration in the distal lung during development of silicosis remains to be elucidated. The present study aimed to determine the effects of the NLRP3 inflammasome on epithelial remodeling and cellular regeneration and potential mechanisms in the distal lung of silica‑treated mice at three time points. Pulmonary function assessment, inflammatory cell counting, enzyme‑linked immunosorbent assay, histological and immunological analyses, hydroxyproline assay and western blotting were used in the study. Single intratracheal instillation of a silica suspension caused sustained NLRP3 inflammasome activation in the distal lung. Moreover, a time‑dependent increase in airway resistance and a decrease in lung compliance accompanied progression of pulmonary fibrosis. In the terminal bronchiole, lung remodeling including pyroptosis (membrane‑distributed GSDMD+), excessive proliferation (Ki67+), mucus overproduction (mucin 5 subtype AC and B) and epithelial‑mesenchymal transition (decreased E‑Cadherin+ and increased Vimentin+), was observed by immunofluorescence analysis. Notably, aberrant spatiotemporal expression of the embryonic lung stem/progenitor cell markers SOX2 and SOX9 and ectopic distribution of bronchioalveolar stem cells were observed in the distal lung only on the 7th day after silica instillation (the early inflammatory phase of silicosis). Western blotting revealed that the Sonic hedgehog/Glioma‑associated oncogene (Shh/Gli) and Wnt/β‑catenin pathways were involved in NLRP3 inflammasome activation‑mediated epithelial remodeling and dysregulated regeneration during the inflammatory and fibrotic phases. Overall, sustained NLRP3 inflammasome activation led to epithelial remodeling in the distal lung of mice. Moreover, understanding the spatiotemporal profile of dysregulated epithelial repair and regeneration may provide a novel therapeutic strategy for inhalable particle‑related chronic inflammatory and fibrotic lung disease.

Characterizing stress development and cracking of ceramic particulate coatings during drying

AbstractDuring drying, liquid‐applied particulate coatings develop stress and are consequently prone to stress‐induced defects, such as cracking, curling, and delamination. In this work, the stress development and cracking of coatings, prepared from aqueous silica and zinc oxide particle suspensions, were characterized using cantilever beam deflection with simultaneous imaging of the coating surface. Drying uniformity was improved and lateral or edge‐in drying was discouraged by using thin silicone walls around the perimeter of the cantilever. Coatings prepared from larger monodisperse silica particles (D50 ∼ 0.9 µm) dried uniformly but had a high critical cracking thickness (&gt;150 µm) that prevented simultaneous study of stress development and cracking. Coatings prepared from smaller silica particles (D50 ∼ 0.3 µm) cracked readily at low thicknesses but exhibited edge‐in drying that complicated the stress measurement data. This drying nonuniformity was connected to the potential for these small particles to accumulate at the coating surface during drying. Hence, the selection of particle size and density was critical to drying uniformity when characterizing stress development and cracking. Coatings prepared from suspensions of zinc oxide particles (D50 ∼ 0.4 µm) were well‐suited for these studies, with uniform drying stress peaking at ∼1 MPa. Characteristic features in the stress development data above and below the critical cracking thickness (53 µm) were identified, demonstrating that cantilever beam deflection is a useful tool for studying the effectiveness of crack mitigation methods and the fundamentals of coating fracture during drying.

Simulation of bidisperse colloidal centrifugal sedimentation using a mixture viscosity model

Understanding the sedimentation behavior of bidisperse colloidal suspensions is critical in determining their stability and separation. While centrifugation is often used to accelerate separation, the settling of bidisperse colloids and their phase separation under these conditions is complex and difficult to predict explicitly. As an alternative, this work proposes a one-dimensional advection-diffusion model that uses an effective maximum volume fraction with a bidisperse viscosity scheme, which reflects important characteristics of bidisperse sedimentation while remaining computationally efficient. The influence of Derjaguin–Landau–Verwey–Overbeek interactions on packing fraction and dispersion viscosity is also considered. A numerical implementation is described using an adaptive finite-difference solver, which can be used for concentration profile and settling rate prediction of both species under variable acceleration. Validation experiments with silica suspensions in two size ratios (500:800 and 100:500 nm) and various total concentrations are performed using an analytical centrifuge, with results also being compared to Richardson–Zaki empirical predictions. The model is shown to be a very good fit to the data for both size ratio dispersions at three mixing ratios, with differences &amp;lt;10%. Slightly higher levels of variation were detected for the 500:800 nm system, owing to the smaller size ratio and resulting greater effect of uncounted secondary hydrodynamic factors, which enables the limits of the mixture viscosity model to be established. Nevertheless, this work highlights that mixture viscosity modeling combined with effective maximum volume fraction modifications can provide critical insights into the effect of bidisperse suspension dynamics on separation efficiencies.

Sol-Gel-Derived Functional Coatings for Pre-Sowing Seed Treatment

The superatomic structure of film-forming sols obtained by the acid hydrolysis of tetraethoxysilane (TEOS) in an aqueous medium (free of organic solvents) was studied using the SAXS method. The formation of nanoparticles (NPs) was confirmed in alcohol-free silica sols with both a low (1 vol. %) content of TEOS and a high (10 vol. %) content of TEOS, hydrolyzed in an aqueous-alcoholic medium. A trimodal size distribution was revealed for the resulting NPs, with radii ranging from less than 1 nm to ~11 nm. The volume fraction of NPs tends to grow with increases in TEOS concentration, as well as with the introduction of magnetic NPs of iron oxides into silica sols. The synthesized silica sols and suspensions based on silica sols with FexOy NPs were used for the pre-sowing treatment of white and cauliflower cabbage seeds in order to provide a functional coating on their surfaces, thereby improving seed germination, stimulating their growth in the early stages of development, and suppressing the effect of phytopathogens. The effect of the pre-sowing seed treatment in sol-gel compositions on seed germination and the growth characteristics of plant seedlings is analyzed, including the influence of iron-oxide magnetic NPs’ compositions and concentrations in silica sols.

Light-Scattering Analysis of Drying Behavior in Suspension Droplets with Silica and Polystyrene Particles and a Hydrosoluble Polymer.

The coffee-ring structure, which is the final drying pattern of a sessile suspension droplet, is a key factor in controlling the uniformity of the particulate deposits in various coatings. Two light-scattering methods, diffusing wave spectroscopy (DWS) and multispeckle DWS (MSDWS), were used to quantitatively distinguish temporal changes in particle mobility in evaporating suspension droplets containing micrometer-sized silica and polystyrene (PS) particles. The characteristic particle mobility was measured in terms of the mean square displacement in the early stage of drying, and the local particle dynamics around the edge and center regimes of the droplets during drying were analyzed using MSDWS. Hydroxyethyl cellulose (HEC), a hydrosoluble polymer, was added to the silica and PS suspensions to further investigate its role in suppressing or enhancing coffee-ring patterns based on particle-polymer interactions. Consequently, dried microstructures can be directly correlated with real-time drying dynamics, as well as the interactions between solutes by comprehensive light-scattering methods.

Novel silanized colloidal silica-MgO self-flowing dispersions with improved hydroxylation resistance

MgO-containing and colloidal silica-bonded are important classes of refractory castables of, respectively, high refractoriness and straightforward processing. On the other hand, their combination is not synergetic. Although 0.1–1 wt% additions of MgO set and harden typical colloidal silica-bonded castables in a 1-hour time frame, greater amounts gel the system instantaneously. This paper addresses the combination of fine MgO sinter with a novel aqueous dispersion of colloidal silica whose particles’ surfaces were modified with an epoxysilane-based coupling agent. Their low reactivity produced self-flowing MgO-colloidal silica suspensions of excellent workability and, after curing, generated a packed magnesium silicate hydroxide hydrate (Mg5Si8O20(OH)2.8H2O) protective coating over MgO particles, hindering their hydroxylation and preventing volumetric expansion. The cast structures attained displayed safer drying and suitable strength. During thermal treatment, silica particles softened and promoted viscous flow, favoring grains densification. Therefore, after sintering, the microstructure comprised dense MgO grains surrounded by thin layers of forsterite (Mg2SiO4).

Understanding the Behavior of Sodium Polyacrylate in Suspensions of Silica and Monovalent Salts.

This study investigated the interaction of monovalent cations with different sizes on quartz surfaces and the rheological impact that this causes in concentrated suspensions when subjected to the action of a rheological modifier, in this case, sodium polyacrylate (NaPA). Yield stress was determined using a rheometer with a vane-in-cup configuration to establish the relationship between shear stress and strain. Experiments were carried out in LiCl, NaCl, KCl, and CsCl solutions. The results show that the yield stress increases following the order Li < Na < K < Cs in the absence of PAA. However, the addition of NaPA significantly reduced the yield stress in all cases. This reduction was more noticeable in the LiCl and NaCl solutions than in the KCl and CsCl solutions, suggesting a more pronounced effect of PA in maker salts. We conducted molecular dynamics simulations to understand how PA interacts with dissolved salts on the quartz surface. Our results showed that Li had the highest adsorption, followed by Na, K, and Cs. As the salt concentration increased, so did the adsorption. We validated these simulation results with rheological experiments, which helped us understand the observed differences. The molecular interactions indicate that, in the lithium system, cationic bridges and the synergy between hydrogen bridges and hydrophobic bridges predominate mainly. This tendency decreases as the type of cation is changed due to the decrease in the electrical density of the cation in the following order: Li < Na < K < Cs. This reduces bridging with the quartz surface and, therefore, directly impacts the system's rheological properties.

Biomediated control of colloidal silica grouting using microbial fermentation

Colloidal silica grouting is a ground improvement technique capable of stabilizing weak problematic soils and achieving large reductions in soil hydraulic conductivities for applications including earthquake-induced liquefaction mitigation and groundwater flow control. In the conventional approach, chemical accelerants are added to colloidal silica suspensions that are introduced into soils targeted for improvement and the formation of a semi-solid silica gel occurs over time at a rate controlled by suspension chemistry and in situ geochemical conditions. Although the process has been extensively investigated, controlling the rate of gel formation in the presence of varying subsurface conditions and the limited ability of conventional methods to effectively monitor the gel formation process has posed practical challenges. In this study, a biomediated soil improvement process is proposed which utilizes enriched fermentative microorganisms to control the gelation of colloidal silica grouts through solution pH reductions and ionic strength increases. Four series of batch experiments were performed to investigate the ability of glucose fermenting microorganisms to be enriched in natural sands to induce geochemical changes capable of mediating silica gel formation and assess the effect of treatment solution composition on pH reduction behaviors. Complementary batch and soil column experiments were subsequently performed to upscale the process and explore the effectiveness of chemical, hydraulic, and geophysical methods to monitor microbial activity, gel formation, and engineering improvements. Results demonstrate that fermentative microorganisms can be successfully enriched and mediate gel formation in suspensions that would otherwise remain highly stable, thereby forgoing the need for chemical accelerants, increasing the reliability and control of colloidal silica grouting, enabling new monitoring approaches, and affording engineering enhancements comparable to conventional colloidal silica grouts.

Physico-mechanical properties of metakaolin and diatomite-based geopolymers

Geopolymers (inorganic polymers) are sustainable materials obtained from the dissolution of an aluminosilicate precursor by a high-alkaline liquid medium. Many studies point out that the properties of such materials depend on essential parameters, such as precursor, activating solution, SiO2 source, curing temperature, and others. This work evaluated the combination of two aluminosilicates (metakaolin and calcined diatomite) with Na-based alkaline liquid reagents (containing sodium silicate or colloidal silica) and how they affected the physico-mechanical properties of the prepared geopolymers after curing at 40 °C for 24 h. The following tests were carried out to characterize the compositions: in situ Young’s modulus evolution as a function of time; cold crushing strength; apparent porosity; and structural analyses via XRD and FTIR measurements. The synthesized geopolymers showed amorphous inorganic structure containing residual crystalline phases (quartz and illite), which are in tune with the Si-O-Si and Si-O-Al bonds identified in the ATR-FTIR spectra. The samples presented cold crushing strength and Young’s modulus up to 39.4 MPa and 13.4 GPa, respectively. The geopolymerization reactions were favored when using colloidal silica suspension, which led to the development of silicate-free geopolymers with enhanced performance at low temperature.