Colloidal Silica Suspensions Research Articles

Conversion Of Cellulosic Waste Materials Into Nanostructured Ceramics And Nanocomposites

Cellulosic waste materials which include sawdust, wastepaper, corncob and sugarcane bagasse were converted into nanostructured ceramics and nanocomposites by submersion in silica colloidal suspension (sol) and subsequently by calcination of the cellulosic/SiO2 nanocomposites under controlled conditions. Depending on the calcination conditions used, nanostructured SiO2 ceramics and carbon/SiO2 nanocomposites were obtained. The morphology of resulting nanostructured ceramics and nanocomposites obtained from four types of cellulosic waste materials were characterized by Scanning Electron Microscopy (SEM), Fourier transformed infrared spectroscopy (FTIR), and CHN elemental analyzer. The effect of cellulosic materials on the properties of nanostructured ceramics and nanocomposites formed were investigated. Copyright © 2011 VBRI press.

Multi-phase biocomposite material in-situ fabricated by using hydroxyapatite and amorphous nanosilica

Abstract In the present study hydroxyapatite (HA) and HA/nanosilica (NS) slurries were separately prepared by adding precipitated HA to distilled water and to colloidal silica suspension, respectively and their rheological properties were compared to each other. Both slurries where then dried, powdered, compacted as disks and sintered at 1 100–1 300°C to evaluate and compare their physical, mechanical and some biological properties. The results showed that the HA/NS slurry was more stable and thixotropic than the pure HA slurry. X-ray diffraction analysis showed that the sintered HA/NS was a multi-phase material composed of apatite, tricalcium phosphate, cristobalite and amorphous glass, depending on sintering temperature. Both mechanical and biological properties of the composite were considerably better than those of sintered HA. Bioactivity of the composite was confirmed by precipitation of apatite nanocrystals onto the surfaces of the sample after soaking in simulated body fluid. The results of cell culture tests showed the same proliferation rate of rat calvaria osteoblasts on both sintered HA and composite with higher alkaline phosphatase activity for the latter. The results indicated that the composite with improved mechanical and biological properties may act more successfully than HA as a bone scaffold material.

The minimum transport velocity of colloidal silica suspensions

A 26 mm N.B. horizontal pipe loop has been used to study the transport velocity of aqueous dispersions of colloidal silica. At low electrolyte concentrations the silica spheres form a stable dispersion, while at high electrolyte concentration particle aggregates are readily formed. Two measurement techniques have been used to study the critical transport velocity; (i) flow visualisation, and (ii) ultrasonic Doppler velocity profiling. Both measurement techniques show agreement in identifying the critical transport velocity. The study has shown that the critical transport velocity can be reduced when the suspension is transformed from a dispersed ( d 50=0.8 μm) to an aggregated ( d 50=4.6 μm) state. Such behaviour is related to the introduction of inter-floc flow through aggregates, enhancing the turbulence intensity of the fluid.

Characteristics of filter cake exfoliation in upward ultrafiltration of nanoparticle suspensions.

Downward and upward ultrafiltration (UF) was performed using the suspensions of nanosized colloidal silica with different particle diameters and their filtration rates were compared. In downward UF, the filtration rate decreases as the particle diameter decreases because the specific filtration resistance of the filter cake becomes significantly higher. In contrast, the filtration rate in upward UF increases with the decrease in the particle diameter because the filter cake consisting of small particles is exfoliated much more easily under the influence of gravity than that of large ones. In order to evaluate the characteristics of the filter cake exfoliation, the steady filtration rate in the upward mode was measured. The steady filtration rate has a tendency to decrease with particle concentration as well as mean particle diameter. Therefore, when the small particles are added into a given concentration of large particle suspension, the mean particle diameter decreases and the total particle concentration increases due to the dosage of small particles. This results in a maximum of the steady filtration rate at a certain dosage of small particles. Moreover, an estimation equation was proposed for predicting the steady filtration rate in upward UF of colloidal silica suspensions with various mean particle diameters and total particle concentrations.

Impact of Ultra-Low-Voltage, Ultra-High Resolution Scanning Electron Microscopy for Nano-Surface Analysis: Examination and Analysis of Nano-inclusions in a Type 304 Stainless Steel

For successful application of low-voltage, ultra-high resolution scanning electron microscopy for nano-surface analysis, sample surface preparation is of key importance. Here, this is demonstrated through the examination of fine inclusions in a type 304 stainless steel. Inclusions are mostly MnS, TiO2, Al2O3 and TiN; they are present either in isolation or forming clusters of two, three, or four features. With the use of mirror-finished surfaces, prepared by mechanical polishing using a suspension of colloidal silica, these inclusions were not revealed clearly due to the presence, at the surface, of thin contaminant layers. After removal of such contaminant layers by radio-frequency-powered glow discharge sputtering, however, inclusions were revealed at the clarity never seen before. By sputtering, thin contaminant layers are removed successfully, without formation of new altered surface layers. Simultaneously, sputtering generates fine textures over the surface of inclusions that are directly related to their compositions. Through the use of such sputter-induced textures, compositional variations in mixed inclusions of sizes even below 50 nm can be revealed clearly and at a high lateral resolution of ∼1 nm.

Hierarchically porous silica monoliths with tuneable morphology, porosity, and mechanical stability

Colloids have been used as sacrificial templates to produce porous materials with controllable morphology and pore sizes. Ceramic particles were employed to prepare porous ceramics and strong composite materials by freeze-casting. However, highly porous monodisperse microspheres have been rarely used as building blocks to obtain hierarchically porous structures. In the present study, porous monodisperse silica microspheres were prepared by a modified Stober method and then used as building blocks to produce porous silica with meso-/micro-pores and macropores by a controlled freezing approach. The macropore morphologies could be tuned with the addition of surfactants in the silica colloidal suspensions during the freezing process. The engineering of porosity and improvement on mechanical stability of the silica materials were achieved via a further soaking and sol–gel process. It was also possible to enhance the mechanical stability through the thermal treatment of the materials.

Effects of pH and Ionic Strength on Colloidal Fouling of Charged Nanofiltration Membranes

The fouling potential of a colloidal silica suspension as the feed phase at varied solution chemistry has been investigated using negatively charged polyamide thin-film-composite nanofiltration (NF) membranes. Specifically, the effects of solution chemistry, feed pH and ionic strength, and colloidal particle size on the fouling potential measurement have been investigated. The effect of pH on the measurement of the fouling potential is different for different membranes. An alkaline feed solution pH is preferred because of its minimal tendency to foul the membranes. Colloidal size does not have a remarkable effect on the fouling potential measurement for the size range studied herein (about 10 nm), but larger particles result in less fouling, as observed normally. Ionic strength also plays an important role in the fouling of silica colloid suspensions, with lower ionic strength resulting less fouling.

Evaluation of colloidal silica suspension as efficient additive for improving physicochemical and in vitro biological properties of calcium sulfate-based nanocomposite bone cement

In the present study new calcium sulfate-based nanocomposite bone cement with improved physicochemical and biological properties was developed. The powder component of the cement consists of 60wt% α-calcium sulfate hemihydrate and 40wt% biomimetically synthesized apatite, while the liquid component consists of an aqueous colloidal silica suspension (20wt%). In this study, the above mentioned powder phase was mixed with distilled water to prepare a calcium sulfate/nanoapatite composite without any additive. Structural properties, setting time, compressive strength, in vitro bioactivity and cellular properties of the cements were investigated by appropriate techniques. From X-ray diffractometer analysis, except gypsum and apatite, no further phases were found in both silica-containing and silica-free cements. The results showed that both setting time and compressive strength of the calcium sulfate/nanoapatite cement improved by using colloidal silica suspension as cement liquid. Meanwhile, the condensed phase produced from the polymerization process of colloidal silica filled the micropores of the microstructure and covered rodlike gypsum crystals and thus controlled cement disintegration in simulated body fluid. Additionally, formation of apatite layer was favored on the surfaces of the new cement while no apatite precipitation was observed for the cement prepared by distilled water. In this study, it was also revealed that the number of viable osteosarcoma cells cultured with extracts of both cements were comparable, while silica-containing cement increased alkaline phosphatase activity of the cells. These results suggest that the developed cement may be a suitable bone filling material after well passing of the corresponding in vivo tests.

Stick−Slip Patterning at Low Capillary Numbers for an Evaporating Colloidal Suspension

Pattern formation from a silica colloidal suspension that is evaporating has been studied when a movement is imposed to the contact line. This article focuses on the stick-slip regime observed for very low contact line velocities. A capillary rise experiment has been specially designed for the observation and allows us to measure the pinning force that increases during the pinning of the contact line on the growing deposit. We report systematic measurements of this pinning force and derive scaling laws when the velocity of the contact line, the colloid concentration, and the evaporation rate are varied. Our analysis supports the idea that the pinning of the contact line results from a competition between the geometry of the growing deposit and the force due to gravity.

Cationic acrylamide copolymers and terpolymers as flocculants for model aqueous suspensions

Summary — Cationic acrylamide copolymers with diallyldimethylammonium chloride and terpolymers of the both monomers with N-vinylformamide were synthesized, characterized by capillary viscometry and their flocculation efficiency evaluated by extinction, sludge volume and solid matter recovery measurements. The polymerization reactions were carried out either as thin-layer processes in aqueous solutions or as microsuspension polymerization. The results from the numerous flocculation tests performed on model aqueous suspensions of fine coal, colloidal silica and talc have been presented and discussed. Flocculation efficiency was determined taking into account the type and dose of the used copolymer.

Synthesis of Y 2O 3:(Li,Eu) films using phosphor powders coated with SiO 2 nano particles

Y 1.9− x Li 0.1Eu x O 3 ( x=0.02, 0.05, 0.08, and 0.12) films were fabricated by spin-coating method. A colloidal silica suspension with Y 1.9− x Li 0.1Eu x O 3 phosphor powder was exploited to obtain the highly stable and effective luminescent films onto the glass substrate. After heating as-prepared Y 1.9− x Li 0.1Eu x O 3 films at 700 °C for 1 h, the phosphor films exhibit a high luminescent brightness as well as a strong adhesiveness on the glass substrate. The emission spectra of spin-coated and pulse-laser deposited Y 1.82Li 0.1Eu 0.08O 3 films were compared. The cathodoluminescence of the phosphor films was carried out at the anode voltage 1 kV.

Photon Trapping and the Enhancement of Electronic Excitation Energy Transfer Efficiency Caused by Colloidal Crystals

AbstractSummary: The efficiency of electronic excitation energy transfer from photoexcited fluorescein to rhodamine 6G is enhanced by 2.26 times in an exhaustively deionized colloidal silica suspension. This enhancement is caused by the photon trapping effects due to the Bragg reflection of colloidal crystals formed in the suspension. The lower enhancement efficiency of 1.41 times observed for rhodamine B as an acceptor is attributed to the inefficient spectral overlap between donor fluorescence and acceptor absorption bands.

Slurry Particle Agglomeration Model for Chemical Mechanical Planarization (CMP)

AbstractIn this work we propose a particle agglomeration model for chemical mechanical planarization (CMP) under the primary motivation of understanding the creation and behavior of the agglomerated slurry abrasive particles during the CMP process, which are a major cause of defectivity and poor consumable utility due to sedimentation.The proposed model considers the slurry composition as a colloidal suspension of charged colloidal silica in an electrically neutral aqueous electrolyte. First, a theoretical relationship between the measurable chemical parameters of the slurry's aqueous electrolyte, the surface potential of the abrasive particles, and corresponding zeta potential between the agglomerated abrasive particles is presented. Secondly, this zeta potential is used in a modified DVLO interaction potential model to determine the particle interaction potentials due to both the attractive van Der Waals forces and repulsive electrostatic interactions. Finally, the total interaction potential created is then used to define a stability ratio for slow versus fast agglomeration and corresponding agglomeration rate equations between particles; these are used in a discrete population balance framework to describe the final particle size distribution with respect to time and agglomerate composition.The proposed model will provide both a qualitative and quantitative description of agglomeration of abrasive slurry particles during CMP that can be extended to account for slurry composition or abrasive particle type, enabling more accurate process control, increased consumable utility, and possible defectivity reduction.

Drying of Colloidal Suspensions and Polymer Solutions near the Contact Line: Deposit Thickness at Low Capillary Number

Drying experiments with a receding contact line have been performed with silica colloidal suspensions and polyacrylamide (PAAm) polymer solutions. The experimental setup allows to control the receding movement of the contact line and the evaporation flux separately. Deposit thickness as a function of these two control parameters has been investigated. The different systems exhibit a similar behavior: in the regime of very low capillary numbers the deposit thickness scaled by the solute volume concentration and the evaporation rate is proportional to the inverse of the contact line velocity. Both the scaling exponent and the constant (which has the dimension of a length) do not depend on the system under study. The observation of this evaporative regime confirms some recent results obtained by Le Berre et al. on a very different system (phospholipidic molecules) and fully supports their interpretation. Following their approach, a simple model based on mass balance accounts for these results. This implies that this regime is dominated by the evaporation and that the deformation of the meniscus induced by viscous forces does not play any significant role. When increasing the velocity, another regime is observed where the thickness does not depend significantly on the velocity.

The Influence of the Particle Size of Silica on the Ballistic Performance of Fabrics Impregnated with Silica Colloidal Suspension

This study investigated the effect of the particle size of silica colloidal suspension (SCS) in SCS-impregnated plain woven fabrics on the ballistic performance of those fabrics. In order to examine the particle size effect, spherical silica particles with average diameters of 100 nm, 300 nm, and 500 nm were used to fabricate SCS. The SCS-impregnated fabrics were subjected to ballistic tests under various boundary conditions. The fabric impregnated with SCS produced using silica particles with an average particle diameter of 100 nm showed better impact performance than those of the SCS-impregnated fabrics containing larger particles and untreated fabrics in terms of impact energy absorption and resistance to blunt trauma, while earlier failure of their primary yarns in the impacted zone under fully clamped conditions was also observed. The results of the drop impact test and yarn pull-out tests indicated that SCS-impregnated fabric with smaller particles exhibits the largest increment of inter-yarn friction at the onset shear strain for shear thickening. It was found that impregnation with SCS affected the interfacial friction of filaments and yarns, which contributes to a larger transfer of the impact energy to interaction of individual yarns in the fabric, resulting in significantly higher energy dissipation with less transverse deformation. Further, the influence of impregnation with SCS on ballistic performance was found to be closely associated with boundary conditions. Thus, the particle size of the SCS and the boundary conditions are the dominant factors that can be manipulated to fully utilize the benefits of SCS impregnated fabrics for flexible body armor.

An investigation of the flocculation characteristics of polyacrylamide‐grafted chitosan

AbstractTo investigate the flocculation characteristics of polyacrylamide (PAM)‐grafted chitosan, a series of PAM‐grafted chitosan copolymer (Chito‐g‐PAM1 to Chito‐g‐PAM4) have been synthesized by ceric ammonium nitrate‐induced solution polymerization technique in nitrogen atmosphere. The flocculation characteristics of the polymer samples (PAM, grafted and ungrafted chitosan) were studied by settling test and jar test methods in the colloidal suspensions of kaolin, iron ore, silica, and bentonite powder. It was found that the settling performance of Chito‐g‐PAM3 is best among the polymer samples. The jar test results indicate that the ungrafted chitosan has better water clarifying performance than both the PAM and grafted chitosan. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

Interconnected porous epoxy monoliths prepared by concentrated emulsion templating

Porous epoxy monoliths were prepared via a step polymerization in a concentrated emulsion stabilized by non-ionic emulsifiers and colloidal silica. A solution in 4-methyl-2-pentanon was used as the continuous phase, which contained glycidyl amino epoxy monomer (GAE), curing agent, and an emulsifier. An aqueous suspension of colloidal silica was used as the dispersed phase of the concentrated emulsion. After the continuous phase was completely polymerized, the dispersed phase was removed and a porous epoxy was obtained. An optimal HLB value of emulsifier for the GAE concentrated emulsion was determined. In addition, the morphology of the porous epoxy was observed by SEM. The effect of the colloidal silica, the emulsifier, the curing of the epoxy, and the volume fraction of the dispersed phase on the morphology of porous epoxy are systematically discussed.

Convectional, sedimentation, and drying dissipative patterns of colloidal silica (183 nm in diameter) suspensions in a glass dish and a watch glass

Convectional, sedimentation, and drying dissipative structural patterns formed during the course of drying aqueous colloidal crystals of silica spheres (183 nm in diameter) have been studied in a glass dish and a watch glass. Spoke-like convectional patterns were observed in a watch glass. The broad ring sedimentation patterns formed especially in a glass dish within 30–40 min in suspension state by the convectional flow of water and colloidal spheres. The macroscopic broad ring drying patterns formed both in a glass dish and a watch glass. The ratio of the broad ring size in a glass dish against the initial size of suspension, i.e., inner diameter of the glass dish, d f/d i, in this work, were compared with previous work of other silica spheres having sizes of 305 and 560 nm and 1.2 μm in diameter. The d f/d i values in a glass dish increased as sphere concentration increased, but were rather insensitive to colloidal size. The d f/d i values on a watch glass also increased as sphere concentration increased, and further increased as sphere size decreased. Segregation effect by sphere size in a watch glass takes place by the balancing between the upward convectional flow of spheres in the lower layers of the liquid and the downward sedimentation of spheres. Colorful microscopic drying patterns formed both in a glass dish and a watch glass.

Experimental characterization and population balance modelling of the dense silica suspensions aggregation process

Concentrated suspensions of nanoparticles subjected to transport or shear forces are commonly encountered in many processes where particles are likely to undergo processes of aggregation and fragmentation under physico-chemical interactions and hydrodynamic forces. This study is focused on the analysis of the behavior of colloidal silica in dense suspensions subjected to hydrodynamic forces in conditions of destabilization. A colloidal silica suspension of particles with an initial size of about 80 nm was used. The silica suspension concentration was varied between 3% and 20% of weight. The phenomenon of aggregation was observed in the absence of any other process such as precipitation and the destabilization of the colloidal suspensions was obtained by adding sodium chloride salt. The experiments were performed in a batch agitated vessel. The evolution of the particle size distributions versus time during the process of aggregation was particularly followed on-line by acoustic spectroscopy in dense conditions. Samples were also analyzed after an appropriate dilution by laser diffraction. The results show the different stages of the silica aggregation process whose kinetic rates depend either on physico-chemical parameters or on hydrodynamic conditions. Then, the study is completed by a numerical study based on the population balance approach. By the fixed pivot technique of Kumar and Ramkrishna [1996. On the solution of population balance equations by discretization—I. A fixed pivot technique. Chemical Engineering Science 51 (8), 1311–1332], the hypothesis on the mechanisms of the aggregation and breakage processes were justified. Finally, it allows a better understanding of the mechanisms of the aggregation process under flowing conditions.

Formation of porous epoxy monolith via concentrated emulsion polymerization

Step polymerization was introduced into the concentrated emulsion templating method and was illustrated with the preparation of porous epoxy monolith. A solution of diglycidyl ether of bisphenol-A (DGEBA), its curing agent low molecular weight polyamide resin, and surfactant nonyl phenol polyoxyethylene ether in 4-methyl-2-pentanon as a solvent was used as the continuous phase, an aqueous suspension of colloidal silica as the dispersed phase of the concentrated emulsion. After the continuous phase polymerized and the dispersed phase removed, a porous material is obtained. The key point in this work is to find a compromise between the rates of curing and phase separating and thus achieve a kinetic stability of the concentrated emulsion. The effects of loading of colloidal silica, the pre-curing of the epoxy precursors, and the volume fraction of the dispersed phase were systematically investigated.