Formation Of Colloidal Silica Research Articles

Three Tribolayers Self-Generated from SiC Individually Work for Reducing Friction in Different Contact Pressures

The low friction of silicon carbide (SiC)/water systems is understood to be the result of a self-forming silica-based tribolayer that is produced by tribochemical reactions. Although several experimental studies have revealed that this silica-based tribolayer contains a considerable amount of carbon, the detailed structure of the tribolayer and its role in providing low friction remain unclear. Here, we conducted a reactive molecular dynamics sliding simulation of an amorphous SiC (a-SiC)/water system to elucidate the atomic-scale structure of the self-forming tribolayer and the mechanism underlying its formation. We found that the water selectively oxidized Si atoms at the surface of the a-SiC, resulting in their removal as SiO2 wear particles. Some of these wear particles dissolved in the water, resulting in the formation of colloidal silica, whereas others were deposited on the a-SiC surface, where they formed a layer of silica hydrate. Meanwhile, carbon atoms remained at the a-SiC surface and formed a C-rich layer, which corresponds to the initial process of an amorphous carbon layer formation. Based on our findings, we propose that colloidal silica, silica hydrate, and amorphous carbon act as individual tribolayers to reduce friction in the low-, intermediate-, and high-contact-pressure areas, respectively. In the low-contact-pressure area, water mainly separates the surfaces, and the silica hydrate holds the water at the sliding interface because of its high hydrophilicity, increasing the load-carrying capacity of the water. In the intermediate-contact-pressure area, the water cannot separate the surfaces, but the colloidal silica layer can because of its high viscosity. In the high-contact-pressure area, where the water and silica-based layers are broken, the amorphous carbon layer works as a solid lubricant. Thus, the three self-forming tribolayers together produce the low friction that characterizes SiC/water systems.

The Potential Role of Colloidal Silica as a Depressant in Scheelite Flotation

The main challenge in scheelite flotation lies in the contamination of the concentrate by other calcium-bearing minerals, mainly calcite. To remedy this problem, sodium silicate is frequently used as a depressant. According to the literature, one hypothesis for the mechanism of water glass consists in its absorption onto calcite through colloidal silica formation, preventing hydrophobization by the collector. This short communication presents research conducted on the direct use of colloidal silica as a depressant in scheelite flotation. Colloidal silica is shown to have an impact on scheelite flotation, especially by depressing silicates.

Processing Pathway Dependence of Amorphous Silica Nanoparticle Toxicity: Colloidal vs Pyrolytic

We have developed structure/toxicity relationships for amorphous silica nanoparticles (NPs) synthesized through low-temperature colloidal (e.g., Stöber silica) or high-temperature pyrolysis (e.g., fumed silica) routes. Through combined spectroscopic and physical analyses, we have determined the state of aggregation, hydroxyl concentration, relative proportion of strained and unstrained siloxane rings, and potential to generate hydroxyl radicals for Stöber and fumed silica NPs with comparable primary particle sizes (16 nm in diameter). On the basis of erythrocyte hemolytic assays and assessment of the viability and ATP levels in epithelial and macrophage cells, we discovered for fumed silica an important toxicity relationship to postsynthesis thermal annealing or environmental exposure, whereas colloidal silicas were essentially nontoxic under identical treatment conditions. Specifically, we find for fumed silica a positive correlation of toxicity with hydroxyl concentration and its potential to generate reactive oxygen species (ROS) and cause red blood cell hemolysis. We propose fumed silica toxicity stems from its intrinsic population of strained three-membered rings (3MRs) along with its chainlike aggregation and hydroxyl content. Hydrogen-bonding and electrostatic interactions of the silanol surfaces of fumed silica aggregates with the extracellular plasma membrane cause membrane perturbations sensed by the Nalp3 inflammasome, whose subsequent activation leads to secretion of the cytokine IL-1β. Hydroxyl radicals generated by the strained 3MRs in fumed silica, but largely absent in colloidal silicas, may contribute to the inflammasome activation. Formation of colloidal silica into aggregates mimicking those of fumed silica had no effect on cell viability or hemolysis. This study emphasizes that not all amorphous silicas are created equal and that the unusual toxicity of fumed silica compared to that of colloidal silica derives from its framework and surface chemistry along with its fused chainlike morphology established by high-temperature synthesis (>1300 °C) and rapid thermal quenching.

Inhibitory effects of poly(adipic acid/amine-terminated polyether D230/diethylenetriamine) on colloidal silica formation

Colloidal silica (SiO 2) scale is considered to be the most undesirable inorganic deposit formed in industrial water. It is formed either in bulk or on surfaces such as membrane, heat exchangers and pipelines. Conventional mineral scale inhibitors do not inhibit its formation. Chemical cleaning is difficult and not free from hazards. Ongoing research on silica scale prevention has led to experiments using various chemical approaches, such as ion exchange, coagulation, and softening. This paper focuses on a scale inhibition approach using a novel chemical additive, adipic acid/amine-terminated polyether D230/diethylenetriamine copolymer (AA/AT/DE). The influence of various concentrations of AA/AT/DE on colloid silica formation are tested and compared to traditional mineral inhibitors, such as phosphonates and anionic polymers. Phosphonates include ATMP, HEDP, EDTMP, DTPMP, HTDMP, and PBTCA, while anionic polymers include PAA, PMA, PESA, PASP, and AA/AM. Among these, only AA/AT/DE showed significant inhibitory activity in contrast to mineral inhibitors, which showed virtually no inhibition. Based on the zeta potential of colloid silica aqueous solutions in the presence of AA/AT/DE, an attractive interaction between AA/AT/DE and silica particles may be present. AFM images of silica also confirm that AA/AT/DE can interfere with the silica polymerization reaction.

Effect of the average particle size and the surface oxidation layer of silicon on the colloidal silica particle through direct oxidation

Colloidal silica was prepared using a direct oxidation process of silicon powders with different purities, average particle sizes, and surface oxidation layer thicknesses in a water solvent with the base catalysts. Purities of 97.00–99.96% and average particle sizes of 200 and 500 mesh of silicon starting materials were evaluated. The materials were thermally oxidized for 3, 16, and 30 h to observe the effect of the surface oxidation layer on the formation of colloidal silica. The longer the thermal oxidation time, the higher the oxide layer thickness on the silicon, and the larger the average size of silica particle observed in the product of colloidal silica when silicon particles had the oxide layer up to approximately 50 nm. When the oxide film was higher than 50 nm, the silica particle size did not increase with an increase in the oxide layer of silicon. The dependence of the average particle silica size on the oxide layer thickness of silicon was observed to be smaller in the colloidal silica from the 200 mesh size of silicon than from the 500 mesh size. The average particle size of silicon was found to affect the average particle size of silica in the direct oxidation, however the correlation between the purity of silicon and the average particle size of silica was not determined as it fell outside the range of this experiment.

Effect of cerium modification on the formation of colloidal silica

Colloidal silica was modified by cerium ion to improve its polishing performance. The active silicic acid was mixed with cerium ion and was then titrated into the seed solution for surface modification via surface growth process. According to the experimental results, we found that the additional cerium ion can improve the surface growing ability on the seed (colloidal silica) surface. The particles size of cerium modified colloidal silica is larger than that without cerium modification. The mean particle size of the modified colloidal silica is decreased by increasing the seed concentration. The removal rate of SiO 2 of the modified colloidal silica is higher than that of without cerium modification colloidal silica.

Industrial water systems: problems, challenges and solutions for the process industries

Mineral scale deposits such as calcium carbonate and phosphate, calcium oxalate, barium and strontium sulfate, magnesium silicate and others and colloidal inorganic species such as silica present important challenges for process water applications. When silica is left uncontrolled it forms hard and tenacious deposits that are difficult and hazardous to remove. Conventional phosphonate mineral scale inhibitors do not inhibit silica formation and deposition. Chemical cleaning is not free from hazards and requires operational shut-downs. Another challenge is corrosion of critical metal surfaces of industrial equipment. Last but not least, biofouling due to the development of microorganisms. This paper is focused on the presentation of the general scope of these problems and their solutions. More specifically, it concentrates on (a) inhibition of colloidal silica formation, (b) colloidal silica dissolution, and (c) metallic corrosion, in water applications by use of designed chemical approaches. The additives used for silica inhibition were polyaminoamide dendrimers, polyethyloxazoline and polyethyleneimine polymers. For silica dissolution the dissolvers tested were carboxymethyl inulin (CMI), Genesol 40 (a proprietary blend of additives), polyacrylic acid. In principle, silica inhibition is a function of time and inhibitor dosage. Silica dissolution is dependent in a rather unpredictable fashion on the structure of the dissolver, time and dosage. Mild steel corrosion inhibition has been achieved by synergistic use of zinc ions and polyphosphonate anions that create protective films.

Environmentally benign chemical additives in the treatment and chemical cleaning of process water systems: Implications for green chemical technology

Supersaturated process waters high in silicates frequently result in deposition of colloidal silica or metal silicate salts. Silica cannot be inhibited by conventional phosphonate mineral scale inhibitors. Chemical cleaning poses hazards and requires operational shut-downs. This paper is focused on a dual approach for silica scale control, inhibition of colloidal silica formation and colloidal silica dissolution in water technology applications by use of designed chemical approaches. The additives used for silica inhibition were polyaminoamide dendrimers (PAMAM) and polyethyleneimine (PEI), in combination with carboxymethyl inulin (CMI) and polyacrylate (PAA) polymers. In principle, silica inhibition is a function of time and inhibitor dosage. Amine-terminated PAMAM-1 and 2 dendrimers as well as PEI combined with anionic polymers, such as CMI and PAA, seem to have a significant inhibitory effect on silica formation, most likely at its earlier stages where the reaction products are oligomeric silicates. CMI and PAA assist the inhibitory action of PAMAM-1 and 2 and PEI by alleviating formation of insoluble SiO 2-PAMAM precipitates. This most likely occurs by partial neutralization of the positive charge that exists in –NH + 3 surface groups. Increase of anionic polymer dosage above a certain threshold has a detrimental effect on the activity of the cationic inhibitors. In that case the polymer’s negative charge “overwhelms” the cationic charge of the inhibitor and poisons its inhibition ability. For silica dissolution, acetic, oxalic, citric acids, histidine and phenylalanine were used as potential replacements of ammonium bifluoride (NH 4F·HF). Silica dissolution is dependent in a rather unpredictable fashion on the structure of the dissolver, time and dosage. This paper continues our research efforts in the discovery, design and application of antiscalant additives that have mild environmental impact. These chemicals are also known as “green additives”.

Formation mechanisms of colloidal silica via sodium silicate

Colloidal silica is formed by titrating active silicic acid into a heated KOH with seed solution. The colloidal silica formation mechanisms are investigated by sampling the heated solution during titration. In the initial stage, the added seeds were dissolved. This might due to the dilution of seed concentration, the addition of potassium hydroxide (KOH) and the heating at 100°C. Homogenous nucleation and surface growth occur simultaneously in the second stage of colloidal silica formation. Homogenous nucleation is more important when the seed concentration is relatively low. On the other hand, surface growth plays an important role when the seed concentration is increased. In the middle seed concentration, the seed particles grow up and some new small particles are born by the homogenous nucleation process to form a bimodal size distribution product. As the titrating volume of active silicic acid exceeds a specific value in the last stage the particle size increases rapidly and the particle number decreases, which may be caused by the aggregation of particles. The intervals between each stage were varied with the seed concentration. Increasing the seed concentration led to the formation of uniform particle size colloidal silica.

Effects of seeds concentration on the formation of colloidal silica

The effects of seed concentration on the mechanism of colloidal silica formation via sodium silicate were studied in this article. When the seed concentration is less than 0.62 wt%, the mechanism of particle formation is dominated by the homogenous nucleation of the active silicate acid. Increasing the seed concentration increases the importance of heterogeneous nucleation via surface growth on seeds. In the seed concentration range of 0.62–1.36 wt%, the formation mechanism is homogenous nucleation parallel to surface growth. Two kinds of particles, one has a small particle size and the other has a large particle size, were observed by transmission electron microscope pictures. A maximum mean particle size of the final product is observed at 0.74 wt% seed concentration. When the seed concentration is in the range of 1.36–2.48 wt%, the mechanism of particle formation is surface growth. The final particles are uniform in diameter. The particles are aggregated and gelled when the seed concentration is greater than 2.48 wt%. The particle size of the final colloidal silica was estimated by the assumption that the additional silica of added as active silicic acid grows on the seeds. The results are compared with the particle size measurement from dynamic light scattering (DLS).

Formation of Colloidal Silica and Alumina During Experimental Granodiorite Weathering

The role of aluminum and silica in the formation of colloids during granodiorite weathering was studied on the basis of long-term experiments in batch reactors. Rock samples were dissolved in un-buffered solutions of initial pH ∼ 3.2, 5.4, and 9.9 at ambient conditions for 500 days. During weathering, extremely high supersaturation with respect to various secondary solids was attained in the solutions. Consequently, new solids, part of which was conserved in solutions as colloids, condensed. The mean concentrations of colloidal Si reached values of 70, 50, and 48 μmol 1−1 in the alkaline, neutral, and acid solutions, respectively. The mean concentrations of colloidal Al, reached values of 34, 22, and 12 μmol 1−1 in the alkaline, neutral, and acid solutions, respectively. The concentration of colloids gradually decreased after 200-400 days of experiment. This phenomenon was interpreted as being due to the competition between homogeneous nucleation and crystal growth. At the initial stages of the experiments, the colloidal species (predominantly colloidal Al) comprised a large proportion of the total amounts of aqueous species. Their share, however, decreased with time. The molar Al/Si-ratios of colloids were as high as 2–2.5 at the early stages of the experiment. After 250–300 days of experiments, on the other hand, these ratios decreased to values of about 0.5 in both the neutral and alkaline solutions and to a value of 0.15 in the acid solution. The evolution of colloids was consistent with the evolution of secondary solids in the sequence Al-hydroxides – clay minerals (illite, chlorite), in both the neutral and alkaline solutions. In acid solutions, the evolution of Al/Si-colloids was influenced by the presence of sulfate ion and Al-sulfate precipitation. Besides Al and Si, other elements, in particular Ca or Mg as a major component and Na, K, P, S, and Cl as minor components, readily participated in the formation of colloids.

Microgravity effects on thermodynamic and kinetic properties of colloidal dispersions.

Microgravity experiments on the physicochemical properties of colloidal dispersions reported hitherto have been reviewed. In microgravity, reliability and reproducibility of experimental data have been improved significantly by the elimination of convection in the suspension. Vanishment of the excess downward diffusion in microgravity has also produced a significant effect on properties of colloidal suspensions. For example, colloidal crystallization rates decreased in microgravity, whereas colloidal alloy crystallization rates increased. These results demonstrate the important role of the segregation effect in normal gravity. Colloidal silica formation reactions are retarded in microgravity, a phenomenon that is correlated deeply with disappearance of the downward diffusion of heavy products.

Silicon induced cadmium tolerance of rice seedlings

Cadmium (Cd2+) toxicity and effects of silicon (Si) applications on the cellular and intracellular accumulations and distributions of Cd were investigated by conventional electron microscopy and EDX analysis. The Si‐deprived rice (Oryza sativa L.) plants (‐Si) differ greatly from Si‐replete ones in cell walls and vacuoles distributions of Ca in their leaves and roots. Energy dispersive x‐ray microanalysis revealed that considerable amounts of Cd could be detected in the cytoplasm, vacuole or cellular organelles in ‐Si rice plants, while very little to be found in +Si ones. From the nanochemical and nanobiological points of views, cell wall templates mediated the formation of colloidal silica with the high specific adsorption property to prevent the uptake of Cd into the cell.

Formation of tribochemical layer of ceramics sliding in water and its role for low friction

The formation of a tribochemical layer on silicon nitride sliding in water is studied. The wear mode changes from mechanically dominated wear to tribochemically dominated wear as sliding distance increases. The silica tribochemical layer is formed on the friction surface and reduces the friction. Introducing an additive that accelerates the formation of colloidal silica makes the running-in distance shorter. The activation energy for tribochemical reaction is estimated to be as small as 1/6–1/8 of that for static reaction.

Chemical Aspects of Iron Colloid Plugging in Quartz Sands and Implications for Formation Damage

Chemical Aspects of Iron Colloid Plugging in Quartz Sands and Plugging in Quartz Sands and Implications for Formation Damage Summary A research direction having great potential for better understanding of formation damage is the influence of colloid plugging on fluid flow behavior in porous media. Using flow through experimental equipment, we have explored the dependence of the degree of ferric oxyhydroxide colloid plugging of quartz sand packs on the solution pH and anion type at a constant temperature of 208-F [97.7 deg C). At a pH of 5, permeability reductions were greatest in the order PO 3/4-, SO 2/4-, and C1 This order was reversed at a pH of 9. The results suggest that plugging occurs by two fundamentally different plugging occurs by two fundamentally different mechanisms. First, flocculation/coagulation of the ferric hydroxide leads to formation of filter cake in the low-ph case. Second, colloid/quartz surface interaction produces a more uniform accumulation of colloid produces a more uniform accumulation of colloid throughout the core at higher pH's. Introduction Recently the phenomenon of colloid fouling or colloid plugging has become more widely recognized as a plugging has become more widely recognized as a potential problem for oilfield production, especially in potential problem for oilfield production, especially in waterflooding and in enhanced oil recovery (EOR). Colloids are defined as particles in the 0.1 - to 200-Am size range. Concern about this problem has led to strict control over injection fluid chemistry, particularly in regard to hydrolyzable metal ions such as Fe3+, Al3+, and Mn2+5+4+. A similar concern exists about controlling the fluid chemistry of reinjection fluids from geothermal wells. Even if the fluid chemistry is well controlled, the corrosion of casing or the existence and formation of colloidal material within the reservoir from the dissolution/oxidation of minerals, such as siderite, pyrite, and chlorite, are potential problems. In addition, pyrite, and chlorite, are potential problems. In addition, EOR operations, such as alkaline flooding and steam-flooding, can lead to a strong increase in dissolved silica concentrations and the formation of colloidal silica. Also, the very fine-grained nature of many clays makes their surface chemical behavior identical to amorphous colloids. Clay migration is a well-known but not well-understood phenomenon, although considerable progress has been made by several groups in modeling progress has been made by several groups in modeling the clay release and plugging process. If the interaction of colloids with reservoir rock is understood, the occurrence of plugging problems may be predicted and a more quantitative model for clay predicted and a more quantitative model for clay migration and plugging can be developed. In addition to preventing plugging, selective colloid fouling might be preventing plugging, selective colloid fouling might be used as a mobility buffer in reservoirs with a heterogeneous permeability distribution. The purpose of this paper is to discuss some of the chemical aspects of colloid plugging, particularly ferric iron colloids, and to discuss some experimental studies of Fe 3 + colloid plugging behavior in quartz sands. Furthermore, application plugging behavior in quartz sands. Furthermore, application of these results to reservoir systems is discussed. Review Three major processes are involved in colloid plugging:(1)generation of colloids,(2)transport of suspended particles, and(3)attachment of particles. Generation of particles, and(3)attachment of particles. Generation of colloids, particularly those of interest in formation damage, such as ferric iron and aluminum hydroxide and silica colloids, can result from a number of processes. Corrosion and/or oxidation of steel casing and pumps are responsible for much of the iron colloids. Silica and aluminum colloids typically result from high levels of supersaturation in the solution phase produced during perturbations of the reservoir through injection of caustic perturbations of the reservoir through injection of caustic or steam. This paper, however, will deal primarily with the transport and attachment of ferric colloids. Transport is a physical hydraulic process that is dependent on parameters such as flow rate, grain size and shape, and viscosity. Attachment is a chemical process and is dependent on both chemical and physical parameters of the system. Fortunately, a great deal of parameters of the system. Fortunately, a great deal of work has been done in the area of particle migration because of the importance of colloid filtration in water quality engineering. The majority of this research has been conducted on particle filtration at room temperature in aqueous fluids. We present a short summary of the previous research on transport and attachment processes. previous research on transport and attachment processes. Transport/Collection. During the last 10 years, a number of transport models have been proposed to explain the behavior of suspended particles during filtration using porous media. These models are based on theories developed for aerosol filtration. JPT P. 1682

Sol-gel transition in simple silicates II

Silica gels were presented from alcoholic solutions of tetraethylorthosilicate (TEOS) using a two-step hydrolysis process; small angle X-ray scattering (SAXS), gas-liquid chromatography, and 1H NMR spectroscopy were employed to study their formation. The first step (1 mol. H 2O/mol. TEOS with HCl catalyst) resulted in a rather wide species distribution comprised of hydrolyzed and unhydrolyzed monomers, dimers, and chains. The second step (additional water plus acid or base) resulted in completely hydrolyzed polymers in the acid system which apparently were highly overlapped prior to gelation. In the base system, hydrolysis was incomplete due to unhydrolyzed monomer and the resulting polymers were more highly condensed (or collapsed) and discrete compared to the acid system. The formation of colloidal silica was not obseerved in either case.

Effects of Sample Size and Concentration of Leaching Acid on Formation of Colloidal Silica in Porous Glass

Effects of Sample Size and Concentration of Leaching Acid on Formation of Colloidal Silica in Porous Glass