Silica Grades Research Articles

Research on resource comprehensive utilization of granite-type sulfide mine tailings

In order to recover and utilize mica and quartz from the tailings of a granite-type sulfide ore in Jiangxi Province, the technique of separating mica and quartz from the tailings by flotation without acid was investigated. Pyrite flotation was performed on a 500 g tailing sample to remove pyrite. And the middlings were acquired by desliming of the unfloated products. Finally mica and quartz was separated from the middlings in the mechanical flotation cell. Under conditions of pH=10.3 with a pulp concentration of 35% and a collector concentration of 180 g/t, a yield of 12.89% mica and 42.73% quartz was obtained, with silica grades as high as 71.50% in the quartz. The mica and quartz products can be used in construction ceramics and construction sand, respectively. It is believed that the outcomes of this work could provide ideas for comprehensive utilization of sulfide tailings.

Study of Disordered Mesoporous Silica Regarding Intrinsic Compound Affinity to the Carrier and Drug-Accessible Surface Area.

There is increasing research interest in using mesoporous silica for the delivery of poorly water-soluble drugs that are stabilized in a noncrystalline form. Most research has been done on ordered silica, whereas far fewer studies have been published on using nonordered mesoporous silica, and little is known about intrinsic drug affinity to the silica surface. The present mechanistic study uses inverse gas chromatography (IGC) to analyze the surface energies of three different commercially available disordered mesoporous silica grades in the gas phase. Using the more drug-like probe molecule octane instead of nitrogen, the concept of a "drug-accessible surface area" is hereby introduced, and the effect on drug monolayer capacity is addressed. In addition, enthalpic interactions of molecules with the silica surface were calculated based on molecular mechanics, and entropic energy contributions of volatiles were estimated considering molecular flexibility. These free energy contributions were used in a regression model, giving a successful comparison with experimental desorption energies from IGC. It is proposed that a simplified model for drugs based only on the enthalpic interactions can provide an affinity ranking to the silica surface. Following this preformulation research on mesoporous silica, future studies may harness the presented concepts to guide formulation scientists.

Stabilisation of acrylic latexes containing silica nanoparticles for dirt repellent coating applications

This study examines the feasibility of using colloidal silica nanoparticles as active agents in high concentration waterborne polymer latex formulations. We showed that distributing the silica throughout the waterborne emulsion formed a composite coating material with a hydrophilic surface that consequently reduced exterior dirt pickup. Two grades of silica nanoparticles were studied, one using sodium stabilisation and another using epoxysilane modification to introduce glycidoxypropyltrimethoxysilane surface functionality. Rheological study of the waterborne latex on mixing showed that there was an immediate pH responsive interaction between the silica sols and the polymer latex. Once loading of sodium charge stabilised silica NPs exceeded the volume required for heteroflocculation to occur the mixture demonstrated the potential to gel on standing – a process which took weeks, or months, to occur depending on the pH and relative concentrations used. At least fifty percent silane modification to the NP surface was found to be necessary to maintain a stable colloidal dispersion for long term storage of the waterborne latex. Despite this both grades of silica were found to imbue reductions in dirt pickup when applied to exterior masonry concrete studies over a 3-month weathering test.

Strength evaluation of soil stabilized with nano silica- cement mixes as road construction material

In pursuit of replacing the conventional GSB courses by stabilizing locally available soil and reconciling it for road constructions, an experimental investigation was undertaken by treating silty sand with colloidal nano silica in three different concentration grades of NS-20, NS-30 and NS-40. Each proportion was further treated with 2%, 4% and 6% of cement. Experiments were conducted to study the effect of nano silica on modified proctor compaction, CBR and UCS tests. XRD and SEM tests were conducted to discern the latent mechanisms to study the physico- chemical changes within the soil matrix. The results demonstrated that the increase in cement content with different grades of nano silica treated soil played an indispensable role in improving the mechanical properties of soil. Optimal results were obtained for soil treated with NS-40 and 6% cement. Soaked CBR values of soil mixes were substantially enhanced by 240.76%, 268.62% and 312.90% and 7-days UCS results were observed to be enhanced by 20.98%, 43.93% and 80.19% on addition of 2%, 4% and 6% cement in case of optimized soil mixes. XRD and SEM results postulated the evidences of the furtherance in cementitious activity within the soil matrix. The paper also discusses about Resilient Modulus parameters for optimized samples by cyclic triaxial tests under different cell pressures. Results demonstrated that nano silica-cement reinforced soil satisfied the criteria for chemically stabilized bound sub bases as per codal provisions.

Non-specific adsorption of protein to microfluidic materials

Non-specific adsorption of proteins to the surfaces of microfluidic channels poses a serious problem in lab-on-a-chip devices involving complex biological fluids. Materials commonly used in the formation of microfluidic channels include CYTOP, silica and SU-8. CYTOP is a transparent fluoropolymer (Poly[perfluoro(4-vinyloxy-1-butene)]) with a low refractive index that approximately matches the refractive index of biologically compatible fluids, and is useful in optical biosensors. Using a microfluidic and fluorescence microscopy set-up, the non-specific adsorption of bovine serum albumin (BSA) labeled with fluorescein isothiocyanate (FITC) to three grades of CYTOP (S, M and A), silica, and SU-8 is investigated. Surface properties such as roughness and wettability are also characterized via an atomic force microscope and a contact angle measurement system. The non-specific adsorption of protein occurs with a highly variable load across these materials. Surprisingly, significantly lower adsorption occurred on SU-8 compared to the other materials, likely due to its hydrophilicity (post-cleaning). Among the 3 grades of CYTOP considered, the lowest adsorption occurred on S-grade. BSA adsorption to silica was higher than on S-grade CYTOP and significantly higher than on SU-8 despite being hydrophilic, due to a fixed positive charge formed within the layer during fabrication, which attracts negatively-charged BSA in buffer.

Insights into the ameliorating ability of mesoporous silica in modulating drug release in ternary amorphous solid dispersion prepared by hot melt extrusion

In this work, the application of various mesoporous silica grades in the preparation of stabilized ternary amorphous solid dispersions of Felodipine using hot melt extrusion was explored. We have demonstrated the effectiveness of mesoporous silica in these dispersions without the need for any organic solvents i.e., no pre-loading or immersion steps required. The physical and chemical properties, release profiles of the prepared formulations and the surface concentrations of the various molecular species were investigated in detail. Formulations containing 25 wt% and 50 wt% of Felodipine demonstrated enhanced stability and solubility of the drug substance compared to its crystalline counterpart. Based on the Higuchi model, ternary formulations exhibited a 2-step or 3-step release pattern which can be ascribed to the release of drug molecules from the organic polymer matrix and the external silica surface, followed by a release from the silica pore structure. According to the Korsmeyer-Peppas model, the release rate and release mechanism are governed by a complex quasi-Fickian release mechanism, in which multiple release mechanisms are occurring concurrently and consequently. Stability studies indicated that after 6 months storage of all formulation at 30% RH and 20 °C, Felodipine in all formulations remained stable in its amorphous state except for the formulation comprised of 40 wt% Syloid AL-1FP with a 50 wt% drug load.

Multivariate geostatistical simulation with PPMT: an application for uncertainty measurement

ABSTRACT Grade models built by traditional estimation or simulation methods often fail to reproduce the complex relationships between the variables. This work investigates the use of the multivariate transformation called Projection Pursuit Multivariate Transform (PPMT), which fully decorrelates the multiple variables of interest, allowing the independent conditional simulation of each variable in the transformed space. Finally, the simulated variables are back-transformed, reproducing the initial correlations of the data. The PPMT workflow was applied to a nickel laterite deposit considering five variables: nickel, iron, silica, magnesium, and calcium grades. Conditional simulations of each variable were run and validated. The back-transformed realisations reproduced the multivariate relationships of the data. To calculate the uncertainties, mining panels equivalent to two and four weeks of production were generated using the k-means clustering technique. Uncertainties were summarised by the coefficient of variation (CV) and the results were used to define classes of mineral resources.

Combined effects of SiO2 ratio and purity on physical properties and microstructure of in situ alumina‐mullite ceramic

AbstractThe in situ formation of mullite (Al6Si4O13) is a complex process based on solid‐state reactions strongly affected by the characteristics of Al2O3 and SiO2 sources. This study investigated the combined effects of variable SiO2/Al2O3 ratios and the presence of low‐melting‐point impurities on the physical properties and microstructure of in situ alumina‐mullite ceramics. Two grades of synthetic amorphous silica, known as microsilica, of similar physical properties and significant differences in the content of alkali‐based impurities (0.8 and 3.6 wt%), were combined with thin calcined alumina particles in different proportions (from silica‐free up to stoichiometric mullite), pressed and sintered. The samples were tested for total porosity, flexural strength, and pore size distribution, and their crystalline phases and microstructures formed were investigated. Small amounts of both microsilica grades (up to 8.9 wt%) hindered the densification of the alumina‐mullite matrix and favored grain growth events, increasing porosity and reducing strength. For samples containing higher microsilica loads (16.4–28.2 wt%), the impurities content significantly affected the amount of liquid phases formed. Such impurities altered the ratio and shape of the pores and the total amount of mullite after sintering. Therefore, different microstructures and levels of flexural strength and total porosity were observed.

New Insights into the Morphology of Silica and Carbon Black Based on Their Different Dispersion Behavior.

Precipitated silica in combination with bifunctional organosilanes almost fully replaces currently the commonly used carbon black fillers in modern passenger car tire tread compounds to improve tire properties such as wet traction (safety) and rolling resistance (fuel consumption). However, it is still challenging to reach a sufficient level of abrasion resistance (service life). An optimum macrodispersion quality of the silica is a fundamental precondition for an optimum abrasion resistance. This goal can be reached by the development of new tailor-made highly dispersible silica grades. In order to achieve this, it is essential to be aware of the analytical silica parameters, which affect the dispersion process. One of these parameters known from carbon black is the structure of the filler. To gain deeper insights into the in-rubber dispersibility of the silica, the structure was investigated by two different methods, the DOA measurement and the void volume measurement. The results were correlated to the in-rubber macrodispersion. In contrast to carbon black filled compounds, no sufficient correlation of the structure with the macrodispersion could be found for the silica-filled compounds. Therefore, it was concluded that the morphology of silica differs from that one that is claimed for carbon black. Additional investigations like TEM, FT-IR and X-ray diffraction measurements were carried out. Carbon black shows a more elastic structure, which can withstand the external forces during the mixing process in a better way. Silica contains a much higher void volume in the structure even after exposed to high forces. These new findings will help to understand the macrodispersion process in rubber in a better way.

Effect of Strain Rates on Tensile Properties of Kenaf Fiber and Rice Husk Silica Reinforced Polypropylene Composites

The expanding interest for eco-accommodating materials, expanding exhaustion rate, and squeezing ecological controls have all set off a developing enthusiasm toward the field of composites. There is a demand for composites which not only possess good mechanical properties but also low cost, eco-friendly and lightweight. The objective of this study is to investigate the tensile behavior under elevated strain rates of kenaf fiber and rice husk silica reinforced polypropylene composites at different grades of rice husk silica (89.09% and 94.05%) content. The samples of composite materials were prepared by using injection molding at different composite percentage of kenaf fiber, rice husk silica and polypropylene composites. Tensile test was carried out to determine the tensile stresses of the composite at the best composition ratio of kenaf fiber and rice husk silica. Generally, the sample with 20 wt.% of kenaf fiber and 20 wt.% of rice husk silica which have high silica content exhibited the best yield stress, ultimate tensile strength and elongation which are 20.31MPa, 20.86MPa and 13.05% respectively. The result shows that 2nd grade with high silica content of rice husk silica has better behavior with increases the yield and ultimate tensile strength compared to results of 1st grade of rice husk silica.

Preparation and Characterization of Mullite-Alumina Structures Formed "In Situ" from Calcined Alumina and Different Grades of Synthetic Amorphous Silica

The reaction between alumina and silica to obtain mullite (Al6Si4O13) can be significantly affected by using synthetic amorphous silica (SAS) sources instead of crystalline ones (quartz and cristobalite). For instance, SASs promote early mullite formation (below 1300°C) and greater densification during sintering. This paper reports the in situ formation of mullite-alumina structures from fine calcined alumina (α-Al2O3) and four grades of SAS of different particles' morphology, specific surface area and internal porosity. After sintering assisted by dilatometry (up to 1500°C), the samples' total porosity, density and flexural strength were measured. The relative density and strength levels of some of these structures were greater than or comparable to other studies which similar compositions were sintered at higher temperatures (1600-1700°C). Their microstructure assessment indicated that the specific surface area and internal porosity of SAS particles showed a major influence the development of these physical properties.

INVESTIGATION OF CARBON BLACK AND SILICA SURFACE STRUCTURE BY STATIC GAS ADSORPTION WITH VARIOUS GASES

ABSTRACT The surface of various carbon black and silica grades is characterized via static gas adsorption using different gases. From decomposition of the adsorption isotherm into distinct energetic contributions, the adsorption energy distribution as well as the surface area are obtained. The decomposition is done by an iterative expectation maximization algorithm specifically designed for this problem. It is found that the adsorption isotherms of the various gases differ significantly in the low-pressure regime, leading to characteristic energy distributions with distinct maxima. As expected, the mean adsorption energy generally increases with the cross section of the gases, and systematic deviations are found reflecting the polar and dispersive interaction characteristics of silica and carbon black, respectively. The surface fractal dimension of two different carbon black grades is estimated using the yardstick method. The obtained values 2.6 and 2.7 agree with previous findings that the carbon black surface morphology is very rough. The adsorption of CO2 on both carbon blacks delivers unexpectedly low values of the monolayer coverage or specific surface area, indicating that mainly high energetic sites of the surface are covered. In consequence, compared with N2, a relatively high value of the mean adsorption energy is found. For both investigated silicas, the mean adsorption energy scales with the quadrupole moments of CO2 and N2, which is indicative of a large polar contribution to interaction energy.

Impact of processing methods on the dissolution of artemether from two non-ordered mesoporous silicas

Poor aqueous solubility is often linked with a poor dissolution rate and ultimately, limited bioavailability of pharmaceutical compounds. This study describes the application of mesoporous materials (Syloid 244 and Syloid AL1) in improving the dissolution rate of a drug with poor aqueous solubility, namely artemether, utilising different processing methods including physical mixing, co-grinding and solid dispersions prepared by solvent evaporation and the lyophilisation technique. The prepared formulations were extensively characterised for their solid-state properties and the drug release attributes were studied. Differential scanning calorimetry and X-ray diffraction confirmed conversion of crystalline artemether into a disordered and amorphous form, whilst no intermolecular interactions were detected between artemether and silica. Both silica grades enhanced the dissolution rate of artemether in comparison with drug alone, for example from 17.43% (±0.87%) to 71.55% (±3.57%) after 120mins with lyophilisation and Syloid 244 at a 1:3 ratio. This enhancement was also dependant on the choice of processing method, for example, co-ground and lyophilised formulations prepared with Syloid 244 at 1:3 ratio produced the most extensive dissolution, thus endorsing the importance of materials as well as choice of formulation method.

Processing Technology Development for Organic Clay Suspension System

Nail polish as a system used in cosmetics still faces stability issues. Pigment sedimentation and syneresis are the most common problems for solvent based systems. The scope of this research was to produce a working 'gel' dispersion for use as a suspension agent in nail polish systems. Various thixotropic agents (hectorite and bentonite clays and hydrophobic and hydrophilic silica grades) and methods (high shear homogenisation (HSH) and high pressure homogenisation (HPH)) were employed to affect this result. From the rheology results it is concluded, that the HPH ensures the development of the systems with the required viscosity recovery properties. It is also concluded that high shear developed systems with hydrophilic silica thixotropic agent are well suited for use as a suspension agent in nail polish formulations.

Simulation of the linear rheological behavior of silica-filled, star-shaped SBR compounds

The rheological behavior of star-shaped SSBR/silica 60 phr compounds with different filler surface areas was experimentally studied and simulated using constitutive modeling. Rheological behavior was characterized in small amplitude oscillatory shear (SAOS) and stress relaxation after a small step shear. Unfilled SBR and SBR filled with four different silica grades with BET surface areas of 55, 135, 160, and 195 m2/g were used. A clear trend in rheological behavior was observed with surface area. A frequency sweep in the SAOS regime indicated an increase in dynamic properties with surface area. Additionally, linear stress relaxation tests at a strain level of 0.05 showed an increase in relaxation modulus with surface area and the presence of a plateau in the relaxation modulus at large times in compounds containing silica with high surface areas. The Leonov and Simhambhatla-Leonov models, modified to incorporate multimode particle network relaxation, were successfully used to simulate the frequency dependence of the storage modulus and the time evolution of the linear relaxation modulus for all samples. However, simulations of the frequency dependence of the loss modulus showed poor results in comparison with experimental data for the filled compounds.

Preparation, characterization, and cytotoxicity studies of niclosamide loaded mesoporous drug delivery systems

Recent reports on the anticancer potential of niclosamide have opened new avenues for anticancer treatment. Niclosamide belongs to the BCS class II, which is indicative of poor solubility and dissolution rate limited absorption. The aim of this study was to improve the dissolution rate of the drug by mesoporous drug delivery system. Porous silica grades (ordered and nonordered) with different pore size, pore volume and surface area were used in the study. The drug was loaded on silica carriers by the solvent evaporation method and characterized by BET surface area analysis, SEM, P-XRD, DSC, and FTIR. A discriminatory dissolution medium was developed for performing the in vitro dissolution of niclosamide. In comparison to the plain drug, all silica based formulations showed improvement in the dissolution rate. Maximum enhancement in the dissolution rate was observed in 1:2 drug:carrier loading ratio when compared to 1:1 ratio. Different properties of mesoporous silica like structural geometry, pore size and microenvironment pH demonstrated a significant impact on drug release from the formulations. Cytotoxicity of the optimized mesoporous formulations of niclosamide was explored in HCT-116, HCT-15, NCI, MDA-MB-231 and A549 cancer cell lines. Nearly 3 fold and 2 fold increase in% cytotoxicity of drug loaded Syloid-244 and Sylysia 350 at 1:2 ratio respectively, were observed when compared to the plain drug.

Ionoluminescence of fused silica under swift ion irradiation

Ion beam induced luminescence spectra have been in-situ recorded during He+ (2.5MeV), O4+ (13.5MeV) and Si4+ (24.4MeV) irradiations for three vitreous silica grades with different OH content (KU1, KS-4V and Infrasil 301). Remarkable changes in the ionoluminescence spectra of the three silica grades were observed for low ion fluences. He+ irradiated samples exhibited higher luminescence than equivalent ones irradiated with heavier O4+ and Si4+ ions. KU1 samples with the highest OH content showed the lowest blue luminescence. Blue luminescence maximum during ion irradiations with O4+ and Si4+ ions is correlated with structural changes.

Design and characterization of anionic hydrogels confined in Daisogel silica composites microspheres and their application in sustained release of proteins

This paper presents the synthesis and characterization of some composite sorbents prepared by the impregnation and cross-linking copolymerization of acrylamide in the pores of two grades of Daisogel silica, followed by post-hydrolysis of amide groups with generation of COO− functional groups. Polymer content of the composites was determined from the thermally decomposed amount of organic part by thermogravimetric analysis. Fourier transform infrared spectroscopy was used to show the structure of polymers confined in the silica pores and potentiometric titration to determine the point of zero charge (pzc). The silica supported functional polymers were tested in the loading/release of lysozyme (LYS) as macromolecular drug. H type sorption isotherms of LYS onto the novel composites were found which support a very high affinity of the anionically charged composite for the positively charged protein. Release mechanism of LYS as a function of the environment was a Fickian diffusion irrespective of the medium and the morphology of Daisogel. This study demonstrates, for the first time, the feasibility of the anionically modified poly(acrylamide) hydrogel confined in the silica pores as very promising sustained release system.

Structural changes induced in silica by ion irradiation observed by IR reflectance spectroscopy

The structural changes produced by ion irradiation, He+ (2.5MeV), O4+ (13.5MeV), Si4+ (24.4MeV), and Cu7+ (32.6MeV), in different types of silica (KU1, KS-4V and Infrasil 301) were observed by IR reflection spectroscopy. The IR reflectance spectra were measured between 400 and 1400cm−1. Structural bands wavenumber of the three silica grades, irradiated with the same ion and fluence, is independent on OH or impurity content of silica. Modification in the surface structure of the irradiated face of a silica sample was studied monitoring the changes in the wavenumber of fundamental structural bands as function of the ion fluence. Samples irradiated at high ion fluence present a shift of known structural bands and new IR reflection bands around 608cm−1 and between 920 and 990cm−1, corresponding to a new structure. The spectra of neutron irradiated samples at fluences 1017 and 1018n/cm2 were also measured and compared with ion irradiated samples.

Morphology and Mechanical Properties of iPP/Silica Composites Modified with (Styrene-b-ethylene-co-butylene-b-styrene) Grafted with Maleic Anhydride

The effects of different silica grades and elastomer content on interfacial properties, morphology and mechanical properties of polypropylene/silica 96/4 composites modified with added 5, 10, 15, and 20% of poly(styrene-b-ethylene-co-butylene-b-styrene) grafted with maleic anhydride (SEBS-g-MA) were investigated. The iPP/silica/SEBS-g-MA composites were designed by adding four silica fillers differing in size (nano- vs. micro-) and in surface properties (hydrophilic vs. hydrophobic) and SEBS-g-MA that was used as a proven effective impact modifier and compatibilizer simultaneously. The morphology of every composite was a spectrum of several morphologies rather than one exclusive morphology. Good concordance between observed and predicted morphology indicated that the morphology of a particular composite was controlled primarily by interfacial properties. Tensile and impact properties were influenced primarily by competitive effects of a stiff filler and tough SEBS-g-MA elastomer. Increased impact strength and strain at break caused by adding SEBS-g-MA indicated a significant overcoming of the elastomeric toughening effect in relation to the filler’s stiffening effect.