Journal articles: 'Amorphous Silica Surface'

1

Zhuravlev, L. T. "Characterization of amorphous silica surface." Reaction Kinetics & Catalysis Letters 50, no. 1-2 (September 1993): 15–25. http://dx.doi.org/10.1007/bf02062184.

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Stievano, Lorenzo, Ling Yu Piao, Irène Lopes, Ming Meng, Dominique Costa, and Jean-François Lambert. "Glycine and lysine adsorption and reactivity on the surface of amorphous silica." European Journal of Mineralogy 19, no. 3 (July 2, 2007): 321–31. http://dx.doi.org/10.1127/0935-1221/2007/0019-1731.

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Taj, S., A. Rosu-Finsen, and M. R. S. McCoustra. "Impact of surface heterogeneity on IR line profiles of adsorbed carbon monoxide on models of interstellar grain surfaces." Monthly Notices of the Royal Astronomical Society 504, no. 4 (May 22, 2021): 5806–12. http://dx.doi.org/10.1093/mnras/stab1174.

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ABSTRACT Surface heterogeneity of model amorphous silica films used as a model for interstellar grain surfaces is revealed through the application of the pre-exponential optimized inversion method to previously reported sub-monolayer thermal desorption studies of carbon monoxide (CO) desorption. The impact of that surface heterogeneity, as represented by the coverage dependence of the CO activation energy for desorption from the amorphous silica surface, on the IR spectroscopy of the CO stretching vibration is explored through vibrational line profile synthesis. Comparison is then made to previous investigations of CO line profiles on this surface and on amorphous solid water as reported in Taj et al. (2017, 2019a). A tentative conclusion is drawn that CO vibrationally promoted desorption from, and diffusion on, the amorphous silica surface may be responsible for the correspondingly short vibrational excited state lifetime of CO on that surface. The contrast with CO on amorphous solid water, where direct and rapid vibrational relaxation into the solid water phonon bath occurs, is highlighted. The consequences of this from the standpoint of CO deposition on grain surfaces are discussed.

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Liu, Quan Xiao, and Wen Cai Xu. "Study on Amorphous Silica Powder Properties." Advanced Materials Research 512-515 (May 2012): 2428–33. http://dx.doi.org/10.4028/www.scientific.net/amr.512-515.2428.

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In this paper amorphous silica powder properties are analyzed and studied. It shows that precipitated silica has larger specific surface area, higher absorption value, higher whiteness and lower bulk density. Different usage of amorphous silica has different properties and different particle size. The order of particle size is that precipitation silica for rubber is bigger than precipitated silica for filler, and the smallest is precipitated silica for coating. XRD, FTIR, SEM and TEM show that precipitated silica is amorphous silica which has wealthy hydroxyl and porous properties and chain branched structure.

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Tosheva, Lubomira, Valentin Valtchev, and Johan Sterte. "Amorphous very high surface area silica macrostructures." Journal of Materials Chemistry 10, no. 10 (2000): 2330–37. http://dx.doi.org/10.1039/b001096k.

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Wang, Bai Kun, Hao Ding, Yun Xing Zheng, and Ning Liang. "Preparation and Characterisation of Amorphous Silica from Alkali Wastewater Produced in Manufacturing Process of ZrOCl₂." Advanced Materials Research 194-196 (February 2011): 2164–68. http://dx.doi.org/10.4028/www.scientific.net/amr.194-196.2164.

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The amorphous silica was prepared from the alkali wastewater rich in Na2O•nSiO2 produced in manufacturing process of zirconium oxychloride (ZrOCl2). The composition and microstructure of amorphous silica were studied by X-ray diffraction, X-ray fluorescence and scanning electron microscope, respectively. The results showed that the amorphous silica was mainly composed of uncrystallized substance, and the silica content was 96.4%. Its whiteness was 97.5% and the particle size was between 100nm and 200nm without agglomeration. The specific surface area of the amorphous silica was 531.9 m2/g, and its pore volume and diameter were 0.945 cm3/g and 4.94 nm, respectively.

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Hefland, R. B., P. E. Schwarzel, B. V. Johansen, T. Myran, N. Uthus, and M. Refsnes. "Silica-induced cytokine release from A549 cells: importance of surface area versus size." Human & Experimental Toxicology 20, no. 1 (January 2001): 46–55. http://dx.doi.org/10.1191/096032701676225130.

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Physical and chemical properties such as structure, composition and surface reactivity determine the biological activity of mineral particles. Long-term exposureto crystalline silica is known to cause persistent pulmonary inflammation leading to adverse health effects. There is less information about the potential health effects of amorphous (noncrystal-line) silica. In this study, the inflammatory and cytotoxic potency of crystalline and amorphous silica in relation to particle size and surface area was assessed. Human epithelial lung cells (A549) were exposed to different size fractions of quartz (aerodynamic diameter 0.5,2 and 10 sm) and amorphous silica (diameter 0.3 pm). All particles induced increased release ofthe proinflammatory cytokines interleukin (IL)-6 and IL-8. When cells were exposed to equal masses of quartz, the smallest size fraction was the most potent. These differences, however, disappeared when cytokine release was related to equal surface areas. When amorphous silica and quartz were compared, the amorphoussilicawas mostpotentto induce IL-6 regardless of how exposure was expressed, whereas the smallest size fraction of quartz was the most potent inducer of IL-8. Thus, the surface area seems to be the critical determinant when potency of different sizes of quartz is compared.

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Yong, R. N., A. M. O. Mohamed, and B. W. Wang. "Influence of amorphous silica and iron hydroxide on interparticle action and soil surface properties." Canadian Geotechnical Journal 29, no. 5 (October 1, 1992): 803–18. http://dx.doi.org/10.1139/t92-088.

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The study of the physicochemical properties of pure amorphous materials (complexes) consisting of Fe2O3 and SiO2 in various proportions indicates that the amorphous complexes will exhibit different properties and characteristics depending on the proportions of Fe2O3 and SiO2. Addition of the amorphous complexes with illitic clay studied shows that the properties of the clay admixture will also vary according to the properties of the amorphous complex, albeit to a lesser degree. The properties and behaviour observed for the amorphous complexes and the clay admixtures can be linked directly to the large specific surface area and high surface charge of the amorphous complexes. The contribution of amorphous complexes to the clay – amorphous complex mixtures (clay admixtures) is twofold: firstly, by the amount of amorphous complex in the clay admixture, and secondly by the composition of the amorphous complex used. The contribution from the amorphous complex is in two forms: water-holding capacity and bonding action. The presence of pH-dependent surface charges associated with the amorphous complexes makes the physicochemical properties and behaviour of the clay admixtures (e.g., liquid limits and zeta potential) sensitive to the pH environment. Coating of amorphous colloids onto clay particle surfaces, shown by scanning electron microscopy, appears to, be enhanced by a decrease in pH of the system, indicating that the enhancement is likely due to the increased electrostatic attraction resulting from the increased amounts of positive charges on the amorphous colloids. Key words : amorphous materials, mass ratio, zeta potential, Bingham yield stress, clay admixtures, hydrogen bonding, specific surface area, cation exchange capacity, anion exchange capacity, fabric and soil structure.

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9

Schrader, Alex M., Jacob I. Monroe, Ryan Sheil, Howard A. Dobbs, Timothy J. Keller, Yuanxin Li, Sheetal Jain, M. Scott Shell, Jacob N. Israelachvili, and Songi Han. "Surface chemical heterogeneity modulates silica surface hydration." Proceedings of the National Academy of Sciences 115, no. 12 (March 5, 2018): 2890–95. http://dx.doi.org/10.1073/pnas.1722263115.

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An in-depth knowledge of the interaction of water with amorphous silica is critical to fundamental studies of interfacial hydration water, as well as to industrial processes such as catalysis, nanofabrication, and chromatography. Silica has a tunable surface comprising hydrophilic silanol groups and moderately hydrophobic siloxane groups that can be interchanged through thermal and chemical treatments. Despite extensive studies of silica surfaces, the influence of surface hydrophilicity and chemical topology on the molecular properties of interfacial water is not well understood. In this work, we controllably altered the surface silanol density, and measured surface water diffusivity using Overhauser dynamic nuclear polarization (ODNP) and complementary silica–silica interaction forces across water using a surface forces apparatus (SFA). The results show that increased silanol density generally leads to slower water diffusivity and stronger silica–silica repulsion at short aqueous separations (less than ∼4 nm). Both techniques show sharp changes in hydration properties at intermediate silanol densities (2.0–2.9 nm−2). Molecular dynamics simulations of model silica–water interfaces corroborate the increase in water diffusivity with silanol density, and furthermore show that even on a smooth and crystalline surface at a fixed silanol density, adjusting the spatial distribution of silanols results in a range of surface water diffusivities spanning ∼10%. We speculate that a critical silanol cluster size or connectivity parameter could explain the sharp transition in our results, and can modulate wettability, colloidal interactions, and surface reactions, and thus is a phenomenon worth further investigation on silica and chemically heterogeneous surfaces.

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10

Zhang, Xiao Jing, Hao Ding, and Bai Kun Wang. "Recycling and Characterisation of Amorphous Silica from Zr-Containing Silica Residue." Advanced Materials Research 194-196 (February 2011): 2109–14. http://dx.doi.org/10.4028/www.scientific.net/amr.194-196.2109.

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Preparation of amorphous silica using Zr-containing silica residue and the properties of the product have been studied. The results show that the separation of amorphous silica from Zr component can be realized using a process flow that pulping, grinding, washing and solid-liquid separation. The main constituent of the product is amorphous state, the content of SiO2 in the product comes up to 94.3%, the content of ZrO2 comes up to 7.48%, the grain size is 2-3 μm, the surface area is 494.3 m2/g. The quality of the recovery can meet the requirement of white carbon black standards ISO 5794-1 and HG/T 3061.

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Greathouse, Jeffery A., Tyler J. Duncan, Anastasia G. Ilgen, Jacob A. Harvey, Louise J. Criscenti, and Andrew W. Knight. "Effects of nanoconfinement and surface charge on iron adsorption on mesoporous silica." Environmental Science: Nano 8, no. 7 (2021): 1992–2005. http://dx.doi.org/10.1039/d1en00066g.

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A combination of molecular simulation and X-ray adsorption spectroscopy reveal the effects of pore size and nanoconfinement on the adsorption and surface complexation of aqueous iron at amorphous silica surfaces.

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12

Zhuravlev, L. T. "The surface chemistry of amorphous silica. Zhuravlev model." Colloids and Surfaces A: Physicochemical and Engineering Aspects 173, no. 1-3 (November 2000): 1–38. http://dx.doi.org/10.1016/s0927-7757(00)00556-2.

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13

Manaila, R., and M. Zaharescu. "Local Order in High Surface Area Amorphous Silica." physica status solidi (a) 98, no. 2 (December 16, 1986): 377–82. http://dx.doi.org/10.1002/pssa.2210980207.

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14

Delle Piane, Massimo, and Marta Corno. "Can Mesoporous Silica Speed Up Degradation of Benzodiazepines? Hints from Quantum Mechanical Investigations." Materials 15, no. 4 (February 12, 2022): 1357. http://dx.doi.org/10.3390/ma15041357.

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This work reports for the first time a quantum mechanical study of the interactions of a model benzodiazepine drug, i.e., nitrazepam, with various models of amorphous silica surfaces, differing in structural and interface properties. The interest in these systems is related to the use of mesoporous silica as carrier in drug delivery. The adopted computational procedure has been chosen to investigate whether silica–drug interactions favor the drug degradation mechanism or not, hindering the beneficial pharmaceutical effect. Computed structural, energetics, and vibrational properties represent a relevant comparison for future experiments. Our simulations demonstrate that adsorption of nitrazepam on amorphous silica is a strongly exothermic process in which a partial proton transfer from the surface to the drug is observed, highlighting a possible catalytic role of silica in the degradation reaction of benzodiazepines.

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15

Jensen, Martin, Ralf Keding, Thomas Höche, and Yuanzheng Yue. "Biologically Formed Mesoporous Amorphous Silica." Journal of the American Chemical Society 131, no. 7 (February 25, 2009): 2717–21. http://dx.doi.org/10.1021/ja808847y.

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16

Tosoni, S., B. Civalleri, F. Pascale, and P. Ugliengo. "Hydroxylated crystalline edingtonite silica faces as models for the amorphous silica surface." Journal of Physics: Conference Series 117 (June 1, 2008): 012026. http://dx.doi.org/10.1088/1742-6596/117/1/012026.

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17

Du, Mao-Hua, Andrew Kolchin, and Hai-Ping Cheng. "Hydrolysis of a two-membered silica ring on the amorphous silica surface." Journal of Chemical Physics 120, no. 2 (January 8, 2004): 1044–54. http://dx.doi.org/10.1063/1.1630026.

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18

Chartres, CJ. "A preliminary investigation of hardpan horizons in north-west New South Wales." Soil Research 23, no. 3 (1985): 325. http://dx.doi.org/10.1071/sr9850325.

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Micromorphological, scanning electron microscope, electron microprobe, X-ray diffraction and chemical analyses of morphologically differing hardpan horizons show a wide range of constituent materials and interparticle cements. A number of different fabric elements occur within the hardpans. These include porphyroskelic zones with amorphous silica in the s-matrix, zones composed almost entirely of amorphous silica, chlamydic zones with clay coatings on skeleton grains, and zones of calcareous material filling fissures. A further porphyroskelic fabric type, in which the plasma consists of strongly oriented clay intimately mixed with isotropic material containing amorphous silica, was also recognized in one type of hardpan. Amorphous silica is the cementing agent within some of the fabric zones identified, but in the chlamydic zones, at least, clay minerals enriched in silica, iron and titanium, and depleted in aluminium, appear to be the cementing medium. Micromorphological evidence indicates a complex development of the hardpans with alternating phases of silica, clay and carbonate deposition.

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19

Halbert, Stéphanie, Simona Ispas, Christophe Raynaud, and Odile Eisenstein. "Modelling the surface of amorphous dehydroxylated silica: the influence of the potential on the nature and density of defects." New Journal of Chemistry 42, no. 2 (2018): 1356–67. http://dx.doi.org/10.1039/c7nj03922k.

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20

Becker, Lillian C., Wilma F. Bergfeld, Donald V. Belsito, Ronald A. Hill, Curtis D. Klaassen, Daniel Liebler, James G. Marks, et al. "Safety Assessment of Silylates and Surface-Modified Siloxysilicates." International Journal of Toxicology 32, no. 3_suppl (May 2013): 5S—24S. http://dx.doi.org/10.1177/1091581813486299.

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The Cosmetic Ingredient Review (CIR) Expert Panel assessed the safety of silica silylate, silica dimethyl silylate, trimethylsiloxysilicate, and trifluoropropyldimethyl/trimethylsiloxysilicate as used in cosmetics. These silylates and surface-modified siloxysilicates function in cosmetics as antifoaming agents, anticaking agents, bulking agents, binders, skin-conditioning agents—emollient, skin-conditioning agents—occlusive, slip modifiers, suspension agents—nonsurfactant, and viscosity increasing agents—nonaqueous. The Expert Panel reviewed the available animal and clinical data as well as information from a previous CIR safety assessment of amorphous silica. The CIR Expert Panel concluded that silica silylate, silica dimethyl silylate, trimethylsiloxysilicate, and trifluoropropyldimethyl/trimethylsiloxysilicate are safe as used when formulated and delivered in the final product not to be irritating or sensitizing to the respiratory tract.

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21

Hassanali, Ali A., Hui Zhang, Chris Knight, Yun Kyung Shin, and Sherwin J. Singer. "The Dissociated Amorphous Silica Surface: Model Development and Evaluation." Journal of Chemical Theory and Computation 6, no. 11 (October 11, 2010): 3456–71. http://dx.doi.org/10.1021/ct100260z.

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22

Snel, Ruud. "Surface concentration of aluminum in amorphous silica-alumina catalysts." Industrial & Engineering Chemistry Product Research and Development 24, no. 2 (June 1985): 219–21. http://dx.doi.org/10.1021/i300018a009.

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23

Zhuravlev, L. T. "Structurally bound water and surface characterization of amorphous silica." Pure and Applied Chemistry 61, no. 11 (January 1, 1989): 1969–76. http://dx.doi.org/10.1351/pac198961111969.

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Mellowes, J. W., C. M. Chun, and I. A. Aksay. "Amorphous silica coating on α-alumina particles." Proceedings, annual meeting, Electron Microscopy Society of America 53 (August 13, 1995): 210–11. http://dx.doi.org/10.1017/s0424820100137422.

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Mullite (3Al2O32SiO2) can be fabricated by transient viscous sintering using composite particles which consist of inner cores of a-alumina and outer coatings of amorphous silica. Powder compacts prepared with these particles are sintered to almost full density at relatively low temperatures (~1300°C) and converted to dense, fine-grained mullite at higher temperatures (>1500°C) by reaction between the alumina core and the silica coating. In order to achieve complete mullitization, optimal conditions for coating alumina particles with amorphous silica must be achieved. Formation of amorphous silica can occur in solution (homogeneous nucleation) or on the surface of alumina (heterogeneous nucleation) depending on the degree of supersaturation of the solvent in which the particles are immersed. Successful coating of silica on alumina occurs when heterogeneous nucleation is promoted and homogeneous nucleation is suppressed. Therefore, one key to successful coating is an understanding of the factors such as pH and concentration that control silica nucleation in aqueous solutions. In the current work, we use TEM to determine the optimal conditions of this processing.

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Williams, Christopher D., Karl P. Travis, John H. Harding, and Neil A. Burton. "Selective Ordering of Pertechnetate at the Interface between Amorphous Silica and Water: a Poisson Boltzmann Treatment." MRS Proceedings 1744 (2015): 53–58. http://dx.doi.org/10.1557/opl.2015.298.

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ABSTRACTCalculations based on Poisson-Boltzmann theory are used to investigate the equilibrium properties of an electrolyte containing TcO4− and SO42− ions near the surface of amorphous silica. The calculations show that the concentration of TcO4− is greater than SO42− at distances less than 1 nm from the surface due to the negative charge density caused by deprotonation of the amorphous silica silanol groups. At lower pH, the surface becomes protonated and the magnitude of this effect is reduced. These results have implications for the potential use of oxyanion-SAMMS for the environmental remediation of water contaminated with 99Tc.

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Jirátová, Květa, Hana Šnajdaufová, Lenka Morávková, and Ludmila Kubelková. "Reductive Amination of Diethylene Glycol to Morpholine over Supported Nickel Catalysts: Zeolites as Catalyst Admixtures." Collection of Czechoslovak Chemical Communications 57, no. 4 (1992): 901–8. http://dx.doi.org/10.1135/cccc19920901.

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The effect of HZSM-5, H-silicalite and amorphous silica admixtures on the surface properties of nickel catalysts as well as on their activities, selectivities and stabilities in the reductive amination of diethylene glycol was studied. It was found that, in comparison with amorphous silica, zeolites do not positively affect the catalytic properties of nickel catalysts. In addition, the acidity of the zeolites, the dispersity of the nickel phase, changes in the chemical composition during the reaction and adsorption of the reaction components or intermediates on the surface and consequent blocking of the zeolite surface played a role.

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Pitukhin, Aleksandr Vasilyevich, Gennady Nikolaevich Kolesnikov, Nikolai Gennadievich Panov, and Sergey Borisovich Vasilyev. "Amorphous Silica Micro Powder Additive Influence on Bending Strength of One-Ply Particle Board." Key Engineering Materials 706 (August 2016): 82–85. http://dx.doi.org/10.4028/www.scientific.net/kem.706.82.

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The methods and results of experimental investigation on the additive influence of amorphous silica micro powder when mixed in the glue for one-ply particle board are presented in the article. Wooden particles of coniferous and hardwood species as well as glue solution based on carbamide-formaldehyde resin were used for boards manufacturing. The amorphous silica micro powder contained particles 8 μm by the size and specific surface 120...400 m2/g was used in the experiment. The samples were tested to determine their physical-mechanical properties. It was found that 1 % amorphous silica micro powder additive increases the breaking point of one-ply particle board under bending strength by 43%.

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Ramesh, Sivarajan, Yuri Koltypin, and Aharon Gedanken. "Ultrasound driven aggregation and surface silanol modification in amorphous silica microspheres." Journal of Materials Research 12, no. 12 (December 1997): 3271–77. http://dx.doi.org/10.1557/jmr.1997.0430.

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Post formed, silica submicrospheres synthesized by Stober's method have been subjected to a high intensity ultrasound radiation (20 kHz, 100 W/cm2) and their size, morphology, and surface silanol structure modified in situ. The processed silica powders have been characterized by a variety of techniques, such as powder x-ray diffraction (XRD), transmission electron microscopy (TEM), dynamic light scattering (DLS), BET nitrogen adsorption, and FT-IR spectroscopy. The silica microspheres formed through an irreversible sol-gel transition have been shown to aggregate by the condensation of interparticle silanols to larger particles under the influence of the shock waves emanating from an imploding cavity. The particle size as a function of sonication time passes through a maximum, suggesting the disintegration of the aggregates on longer exposure to ultrasound radiation. The sonication of dried silica microspheres in an inert dispersant decalin also led to the aggregation of microspheres to a lesser degree, suggesting the deactivation of surface silanols. Infrared spectroscopic investigations suggest a disruption of the hydrogen bonded network of surface silanols. The observed morphological changes have been discussed in terms of direct effect of cavitation on well-formed spheres rather than changes in growth mechanism and capture of primary particles.

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Salim, Musdalilah Ahmad, Halina Misran, S. Z. Othman, N. N. H. Shah, N. A. A. Razak, and K. M. Mahbor. "Nonsurfactant Surface Modifications of Monodispersed Si-Cu Core-Shell Nanocomposite." Advanced Materials Research 895 (February 2014): 571–74. http://dx.doi.org/10.4028/www.scientific.net/amr.895.571.

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Monodispersed silica spheres with particles size of ca. 450 nm were successfully synthesized using modified Stöber method. The synthesized monodispersed silica spheres were successfully coated with copper through modified sol-gel method employing nonsurfactant template and catalyst. A renewable nonsurfactant template, decyl-alcohol (C10) and catalyst were used to modify the silica surfaces prior to coating with copper. In order to study the effect of catalyst on copper deposition onto silica surfaces, ammonia was used as catalyst in various amounts. The X-ray diffraction patterns of Si-Cu core-shell exhibited a broad peak corresponding to amorphous silica networks and exhibited monoclinic CuO phase. It was found that samples modified in the presence of 1 ml catalyst exhibited relatively homogeneous deposition. The surface area of uncoated core (SiO2) was at ca. 7.04 m2/g and coated samples 1 ml catalyst was at ca. 8.21m2/g.

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Nasir, Izzati, Nadiah Ameram, Arlina ALI, Siti Roshayu HASSAN, Nurul Akmar Che ZAUDIN, and Jamil MOHAMED SAPARI. "review of rice husk silica as a heterogeneous catalyst support." Journal of Metals, Materials and Minerals 31, no. 4 (December 16, 2021): 1–12. http://dx.doi.org/10.55713/jmmm.v31i4.1176.

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The yield of amorphous silica has less residue of mineral content in rice husk (RH) and a high specific surface area through the simple alkaline extraction process at first, then acid precipitation of RH. At this time, the leaching process using alkali and calcination of RH is the best method to acquire amorphous silica with a high surface area. The different temperatures were used for the calcination of RH and continue with sodium hydroxide (NaOH) treatment by using different concentration. The sample titrated using hydrochloric acid (HCl) to extract silica. Pretreatment with acid leaching for the RH was also conducted before the calcination of the RH. Results acquired were analysed and compared.

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Breznan, Dalibor, Nazila Nazemof, Filip Kunc, Myriam Hill, Djordje Vladisavljevic, James Gomes, Linda J. Johnston, Renaud Vincent, and Prem Kumarathasan. "Acellular oxidative potential assay for screening of amorphous silica nanoparticles." Analyst 145, no. 14 (2020): 4867–79. http://dx.doi.org/10.1039/d0an00380h.

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Abu Bakar, Noor Hana Hanif, Mohammed M. Bettahar, and Mohamad Abu Bakar. "The Influence of Supports on the Surface Properties of PtNi Bimetallic Catalysts." Advanced Materials Research 602-604 (December 2012): 1716–24. http://dx.doi.org/10.4028/www.scientific.net/amr.602-604.1716.

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A series of Pt100and bimetallic PtNi catalysts were prepared on various supports namely amorphous silica (Degussa), crystalline silica (Chempure) and cerium oxide (CeO2). The samples were prepared via precipitation method using NaBH4as a reducing agent. H2-TPR analysis revealed that total reduction of the metal salts to metal particles occurred during this stage. All catalysts were tested for the hydrogenation of benzene to cyclohexane. It was found that the catalysts exhibited a decrease in the catalytic reactivity in the order of amorphous silica, crystalline silica and CeO2. This is mainly due to the surface area and acidity of the support. Comparison of the PtNi catalysts with their respective monometallic catalyst showed that only the PtNi prepared on Chempure exhibited an enhanced reactivity. This is due to alloying of PtNi. For catalysts prepared on Degussa, the low H2-chemisorption properties as well as lack in Pt peak shift in the XRD profiles leads to the believe that Ni and Pt may exist separately. H2-TPD analysis supports these findings.

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Ewing, Christopher S., Saurabh Bhavsar, Götz Veser, Joseph J. McCarthy, and J. Karl Johnson. "Accurate Amorphous Silica Surface Models from First-Principles Thermodynamics of Surface Dehydroxylation." Langmuir 30, no. 18 (May 2, 2014): 5133–41. http://dx.doi.org/10.1021/la500422p.

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Liu, Hong Xia, Song Chen, Rong Shao, Rui Dong, and Ming Lin Jia. "Preparation and Characterization of Hydrophobic Mesoporous SiO₂ Aerogel." Advanced Materials Research 306-307 (August 2011): 1393–97. http://dx.doi.org/10.4028/www.scientific.net/amr.306-307.1393.

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Hydrophobic mesoporous silica aerogels were synthesized using cheap industrial grade tetraethyl orthosilicate (TEOS) as precursor by ambient pressure drying.The silica alcogels were prepared by acid-base sol-gel polymerization of the TEOS, the surfaces of silica alcogels were modified using trimethylchlorosilane/ hexamethyldisiloxane via simultaneous solvent exchange and surface modification. The attachment of trymethylsilyl (-Si(CH3)3) groups to the silica surface was confirmed by the presence of Si-CH3 peaks at 2963, 1256 and 845 cm−1 in the IR spectra. Properties of the aerogels were examined by SEM, TEM, XRD, BET and DTA-TG analyses. The results indicate that the aerogels in a typical amorphous state have a highly porous network with an average pore diameter in the range of 5–10 nm, have high specific surface area (931 m2/g) and are thermally stable up to 322 °C.

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35

Vaikuntam, Sankar Raman, Eshwaran Subramani Bhagavatheswaran, Fei Xiang, Sven Wießner, Gert Heinrich, Amit Das, and Klaus Werner Stöckelhuber. "Friction, Abrasion and Crack Growth Behavior of In-Situ and Ex-Situ Silica Filled Rubber Composites." Materials 13, no. 2 (January 7, 2020): 270. http://dx.doi.org/10.3390/ma13020270.

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The article focuses on comparing the friction, abrasion, and crack growth behavior of two different kinds of silica-filled tire tread compounds loaded with (a) in-situ generated alkoxide silica and (b) commercial precipitated silica-filled compounds. The rubber matrix consists of solution styrene butadiene rubber polymers (SSBR). The in-situ generated particles are entirely different in filler morphology, i.e., in terms of size and physical structure, when compared to the precipitated silica. However, both types of the silicas were identified as amorphous in nature. Influence of filler morphology and surface modification of silica on the end performances of the rubbers like dynamic friction, abrasion index, and fatigue crack propagation were investigated. Compared to precipitated silica composites, in-situ derived silica composites offer better abrasion behavior and improved crack propagation with and without admixture of silane coupling agents. Silane modification, particle morphology, and crosslink density were identified as further vital parameters influencing the investigated rubber properties.

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Ramesh, Sivarajan, Israel Felner, Yuri Koltypin, and Aharon Gedanken. "Reaction Pathways at the Iron–microspherical Silica Interface: Mechanistic Aspects of the Formation of Target Iron Oxide Phases." Journal of Materials Research 15, no. 4 (April 2000): 944–50. http://dx.doi.org/10.1557/jmr.2000.0135.

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Oxidative hydrolysis of elemental iron nanoclusters on hydroxylated surfaces such as silica or alumina is known to be influenced by the degree of hydration of the surface. The understanding and control of this process is crucial in the synthesis of iron oxide coated silica microspheres with a desired magnetic property. The hydrolysis of iron nanoparticles followed by heat treatment in the case of a hydrated microspherical silica surface results in the formation of maghemite (γ–Fe2O3), whereas a dehydrated surface yielded hematite (α–Fe2O3) nanoparticles. The influence of adsorbed water on the formation of intermediate iron oxides/oxidehydroxides and the mechanistic aspects of their subsequent thermal dehydration iron oxide phases were investigated by thermogravimetric analysis, Fourier transform infrared, and Mössbauer spectroscopies. The reactions on both the hydrated and the dehydrated surfaces were found to proceed through the formation of an x-ray amorphous lepidocrocite [γ–FeO(OH)] intermediate and its subsequent dehydration to maghemite (γ–Fe2O3). Maghemite to hematite transformation was readily facilitated only on a dry silica surface. The retardation of the lepidocrocite →maghemite →hematite transformation in the case of a hydrated silica surface is suggested to arise from strong hydrogen-bonded interactions between the substrate silica and the adsorbed nanoparticles.

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Bolis, Vera, Claudia Busco, Valentina Aina, Claudio Morterra, and Piero Ugliengo. "Surface Properties of Silica-Based Biomaterials: Ca Species at the Surface of Amorphous Silica As Model Sites." Journal of Physical Chemistry C 112, no. 43 (October 3, 2008): 16879–92. http://dx.doi.org/10.1021/jp805206z.

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Jin, Yaming, Huifang Xu, and Abhaya K. Datye. "Electron Energy Loss Spectroscopy (EELS) of Iron Fischer–Tropsch Catalysts." Microscopy and Microanalysis 12, no. 2 (March 10, 2006): 124–34. http://dx.doi.org/10.1017/s1431927606060144.

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Electron energy loss spectroscopy (EELS), X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy have been used to study iron catalysts for Fischer–Tropsch synthesis. When silica-containing iron oxide precursors are activated in flowing CO, the iron phase segregates into iron carbide crystallites, leaving behind some unreduced iron oxide in an amorphous state coexisting with the silica binder. The iron carbide crystallites are found covered by characteristic amorphous carbonaceous surface layers. These amorphous species are difficult to analyze by traditional catalyst characterization techniques, which lack spatial resolution. Even a surface-sensitive technique such as XPS shows only broad carbon or iron peaks in these catalysts. As we show in this work, EELS allows us to distinguish three different carbonaceous species: reactive amorphous carbon, graphitic carbon, and carbidic carbon in the bulk of the iron carbide particles. The carbidic carbon K edge shows an intense “π*” peak with an edge shift of about 1 eV to higher energy loss compared to that of the π* of amorphous carbon film or graphitic carbon. EELS analysis of the oxygen K edge allows us to distinguish the amorphous unreduced iron phase from the silica binder, indicating these are two separate phases. These results shed light onto the complex phase transformations that accompany the activation of iron catalysts for Fischer–Tropsch synthesis.

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Guesmi, Hazar, Robert Gryboś, Jarosław Handzlik, and Frederik Tielens. "Characterization of molybdenum monomeric oxide species supported on hydroxylated silica: a DFT study." Phys. Chem. Chem. Phys. 16, no. 34 (2014): 18253–60. http://dx.doi.org/10.1039/c4cp02296c.

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Chayasombat, Bralee, N. Tarumi, T. Kato, Tsukasa Hirayama, Katsuhiro Sasaki, and Kotaro Kuroda. "Transmission Electron Microscopy Studies of Oxidation of Single Crystal Silicon Carbide at High Temperature." Materials Science Forum 561-565 (October 2007): 2135–38. http://dx.doi.org/10.4028/www.scientific.net/msf.561-565.2135.

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The microstructures of high-temperature oxide scales on the Si-terminated surface and C-terminated surface of 6H-SiC were investigated by transmission electron microscopy (TEM). We found that mechanical polishing caused surface strains, about 100 nm in depth, on both sides of specimens. Mechanically polished specimens were oxidized at 1473 K for 20 h in air. Oxide scales of about 250 nm in thickness were formed on the Si-terminated surface and of about 400 nm on the C-terminated surface. Since the strain regions caused by mechanical polishing were oxidized, strains were no longer observed. As a result, this oxidation condition effectively removed the strains. The oxide scales were identified as amorphous silica on the Si-terminated face, while crystalline oxides and amorphous silica were observed on the C-terminated face.

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Manurung, Posman, Erika Sempana Ginting, Ediman Ginting, and Suprihatin -. "Synthesis and Characterisation of Nano-silica Based on Pumice Using NaOH." Journal of Physical Science 33, no. 1 (April 25, 2022): 17–28. http://dx.doi.org/10.21315/jps2021.33.1.2.

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Nano-silica was synthesised from pumice by extraction method using sodium hydroxide (NaOH), sulphuric acid (H2SO4) and hydrochloric acid (HCl). The raw material of pumice was collected from local area, Tanggamus-Lampung Indonesia. After grinding, the pumice powder was activated at 450°C for 2 h before mixing with NaOH for extraction. After extraction, the powder was heated at 800°C for 4 h, to maintain the silica is in amorphous phase. Physical characteristics were analysed using transmission electron microscopy (TEM) for measuring particle size, Brunauer-Emmett-Teller (BET) technique for surface area measurement, x-ray diffraction (XRD) for structure and x-ray fluorescence (XRF) for determination of oxides. XRD analysis proved that besides amorphous nano-silica, there are peaks of sodium sulfate (Na2SO4) as representation of crystalline structure. The maximum silicon dioxide (SiO2) content was found on 3.0 molar (M) NaOH. The highest surface area of 165 m2 /g was obtained in sample of 3.5 M NaOH. The truly amorphous nano-silica content was found in NaOH of 3.0 M. The formation temperature may occur between 1100°C–1200°C. The particle size is in the range of 9 nm–17 nm.

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Xia, Xinxing, Fang Wang, Xiaojing Qin, Tingting Tang, and Tianwen Zhou. "Low-temperature precausticizing — a hopeful approach for green liquor desilication." February 2017 16, no. 02 (2017): 57–61. http://dx.doi.org/10.32964/tj16.2.57.

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We investigated silica removal by low-temperature precausticizing and the properties of second causticizing calcium carbonate (CCC). The results showed that about 89.3% of silica removal was achieved when 20% (the stoichiometric ratio) of causticizing quicklime was added for precausticizing at 20ºC for 60 min. After that, silica removal became slow. When no precausticizing quicklime was used to remove silica, the CCC particles had a rhombohedral crystal structure covered with amorphous material. As precausticizing quicklime was increased to 30%, the amorphous material and the crack disappeared, and the specific surface area decreased significantly. When CCC was used as filler, the Cobb value decreased significantly, and the sizing effect improved as precausticizing quicklime increased.

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Ward, Antony J., Rebecca A. Lesic, Nicholas Proschogo, Anthony F. Masters, and Thomas Maschmeyer. "Strained surface siloxanes as a source of synthetically important radicals." RSC Advances 5, no. 122 (2015): 100618–24. http://dx.doi.org/10.1039/c5ra20399f.

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The calcination of pure amorphous silica at temperatures up to 850 °C results in the formation of strained siloxane rings which are capable of undergoing homolytic cleavage to generate radicals when in the presence of an appropriate substrate.

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Hassanali, Ali A., and Sherwin J. Singer. "Model for the Water−Amorphous Silica Interface: The Undissociated Surface." Journal of Physical Chemistry B 111, no. 38 (September 2007): 11181–93. http://dx.doi.org/10.1021/jp062971s.

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Gierada, Maciej, Frank De Proft, Marialore Sulpizi, and Frederik Tielens. "Understanding the Acidic Properties of the Amorphous Hydroxylated Silica Surface." Journal of Physical Chemistry C 123, no. 28 (June 25, 2019): 17343–52. http://dx.doi.org/10.1021/acs.jpcc.9b04137.

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Yusupova, Alsu, Alexey Khatsrinov, and Lenar Shafigullin. "Chemisorption of aluminum chloride on the surface of amorphous silica." Materials Today: Proceedings 19 (2019): 1932–36. http://dx.doi.org/10.1016/j.matpr.2019.07.044.

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Chai, Jingchun, Shuyan Liu, and Xiaoning Yang. "Molecular dynamics simulation of wetting on modified amorphous silica surface." Applied Surface Science 255, no. 22 (August 2009): 9078–84. http://dx.doi.org/10.1016/j.apsusc.2009.06.109.

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Meier, A., and H. Gamsjäger. "Characterisation of the surface of a new amorphous microporous silica." Reactive Polymers 11 (January 1989): 155–63. http://dx.doi.org/10.1016/0923-1137(89)90098-5.

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Wang, Ming, Fangli Duan, and Xiaojing Mu. "Effect of Surface Silanol Groups on Friction and Wear between Amorphous Silica Surfaces." Langmuir 35, no. 16 (March 29, 2019): 5463–70. http://dx.doi.org/10.1021/acs.langmuir.8b04291.

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Jenie, Aisyiyah S. N., Fransiska S. H. Krismastuti, Yudia P. Ningrum, Anis Kristiani, Mutia D. Yuniati, Widi Astuti, and Himawan T. B. M. Petrus. "Geothermal silica-based fluorescent nanoparticles for the visualization of latent fingerprints." Materials Express 10, no. 2 (February 1, 2020): 258–66. http://dx.doi.org/10.1166/mex.2020.1551.

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The development of silica nanoparticles from the waste of geothermal power plants and their subsequent modification using a fluorescent dye, rhodamine 6G (R-6G), has been reported. The optimum specific surface area of the silica nanoparticles before modification was 289.2 m2 g–1. After modification, the intrinsic properties of the fluorescent silica nanoparticles were studied, and the results showed that they were in their amorphous phase, with a particle size of 5–10 nm. We proposed that the interaction between R-6G and the silica nanoparticle surface was due to the hydrogen bonding, using the results from the Fourier transform infrared spectroscopy. The obtained fluorescent silica nanoparticles had excellent fluorescence enhancement of 2-fold compared to R-6G in its original state. This study reports, for the first time, the synthesis of fluorescent nanoparticles from geothermal silica and its ability to visualize latent fingerprints on different smooth dry surfaces, making it an excellent candidate for fluorescent powders in forensic applications.

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Journal articles on the topic 'Amorphous Silica Surface'

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