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Journal articles on the topic 'Amorphous silica-alumina'

Author: Grafiati

Published: 4 June 2021

Last updated: 25 May 2024

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1

Sri Rahayu, Endang, Gatot Subiyanto, Arief Imanuddin, Wiranto, Sabrina Nadina, Rista Ristiani, Suhermina, and Endang Yuniarti. "Kaolin as a Source of Silica and Alumina For Synthesis of Zeolite Y and Amorphous Silica Alumina." MATEC Web of Conferences 156 (2018): 05002. http://dx.doi.org/10.1051/matecconf/201815605002.

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Kaolin is the clay mineral which containing silica (SiO2) and alumina (Al2O3) in a high percentage, that can be used as a nutrient in the synthesis of zeolites and amorphous silica alumina (ASA). The objective of this research is to convert the Belitung kaolin into silica and alumina as nutrients for the synthesis of zeolites and amorphous silica alumina, which are required in the preparation of the catalysts. Silica and alumina contained in the kaolin were separated by leaching the active kaolin called as metakaolin, using HCL solution, giving a solid phase rich silica and a liquid phase rich alumina. The solid phase rich silica was synthesized to zeolite Y by adding seed of the Y Lynde type, through the hydrothermal process with an alkaline condition. While, the liquid phase rich alumina was converted into an amorphous silica alumina through a co precipitation method. Characterization of zeolite and ASA were done using XRD, surface area and pore analyzer and SEM. The higher of alumina in liquid phase as a result of the rising molar of HCL in the leaching process was observed, but it didn’t work for its rising time. Products of ASA and zeolite Y were obtained by using liquid phase rich alumina and solid phase rich silica, respectively, which resulted through leaching metakaolin in 2.5 M HCl at temperature of 100° C for 2 hours.

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2

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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3

Barthomeuf, D. "Amorphous silica alumina debris in zeolites and zeolitic-type clusters in amorphous silica-alumina catalysts." Zeolites 10, no. 2 (February 1990): 131–33. http://dx.doi.org/10.1016/0144-2449(90)90031-l.

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4

Hensen, Emiel J. M., Dilip G. Poduval, Volkan Degirmenci, D. A. J. Michel Ligthart, Wenbin Chen, Françoise Maugé, Marcello S. Rigutto, and J. A. Rob van Veen. "Acidity Characterization of Amorphous Silica–Alumina." Journal of Physical Chemistry C 116, no. 40 (October 2, 2012): 21416–29. http://dx.doi.org/10.1021/jp309182f.

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5

Maggard, Jeffrey G., N. David Theodore, and C. Barry Carter. "The behavior of an α-alumina twist grain-boundary in the presence of silica." Proceedings, annual meeting, Electron Microscopy Society of America 48, no. 4 (August 1990): 378–79. http://dx.doi.org/10.1017/s0424820100175028.

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Grain boundaries and polyphase boundaries can control the electrical, optical, and mechanical properties of many ceramic materials. The study of such boundaries is therefore essential for understanding these materials. Some studies of grain boundaries in alumina have reported a thin layer of amorphous intergranular material coating nearly all boundaries while others question this interpretation. The quality and structure (crystalline or amorphous) of an intentionally-added siliceous intergranular phase has been found to affect the mechanical properties of polycrystalline α-alumina and tetragonal zirconia. It is therefore of interest to examine the behavior of various α-alumina grain boundaries in the presence of controlled amounts of amorphous silica. A recent study characterized the behavior of low-angle [0001] twist boundaries in the presence of silica which had been intentionally incorporated during the course of grain boundary fabrication. The present study is aimed at characterizing the behavior of low-angle rhombohedral (102) twist boundaries under similar conditions.Single crystal wafers of α-alumina were mechanically polished parallel to the (102) plane. Silica was deposited to a thickness of 260Å on one of the wafers using plasma deposition. The silica-coated wafers were then placed face-to-face with clean, uncoated wafers and pressure-sintered at 1980°C for 3 hours. The temperature was chosen to lie above the melting point of silica and below that of alumina. A low pressure (∼50 psi) was used to hold the wafers together. The pressure and furnace heating and cooling cycles had to be carefully controlled to prevent fracture of the crystals.

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6

Triani, Desak Nyoman Deasi, Januarti Jaya Ekaputri, Triwulan, Setyo Hardono, and Tri Eddy Susanto. "Application of Pozzolan as Materials of Geopolymer Paste." Materials Science Forum 841 (January 2016): 111–17. http://dx.doi.org/10.4028/www.scientific.net/msf.841.111.

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This research use metakaolin and clay containing amorphous silica and alumina after calcination at 700°C. Mechanical properties and fire resistance of geopolymer paste increase as the ratio of silica to alumina. Mix design composition on this research based on the ratio of silica to alumina. The ratio of silica to alumina for metakaolin paste are 1.4 and 1.8. While for clay paste the ratio that used are 2.8 and 3.2. Na2SiO3 and NaOH with 10 M and 8 M were used as alkali activator at this research. Based on analysis the effect of increasing the ratio of silica to alumina increase fire resistance ability for both metakaolin and clay. However initial compressive strength is effected not only by ratio of silica to alumina but also the ratio of water to solid and SiO2/Na2O. The compressive strength decrease as the ratio of water to solid increases. Meanwhile compressive strength increase as the ratio of SiO2/Na2O increase.

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7

Beh, Gein Khai, Chang Ting Wang, Kyungduk Kim, Jiangtao Qu, Julie Cairney, Yun Hau Ng, Alicia Kyoungjin An, Ryong Ryoo, Atsushi Urakawa, and Wey Yang Teoh. "Flame-made amorphous solid acids with tunable acidity for the aqueous conversion of glucose to levulinic acid." Green Chemistry 22, no. 3 (2020): 688–98. http://dx.doi.org/10.1039/c9gc02567g.

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Composition-tunable mixed Brønsted/Lewis acids on silica-alumina and silica-alumina-phosphate prepared by the rapid flame spray pyrolysis produce exceptionally high glucose-to-levulinic acid yield, twice that of commercial ZSM-5 and Zeolite X.

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8

Freitas, A. A., R. L. Santos, R. Colaço, R. Bayão Horta, and J. N. Canongia Lopes. "From lime to silica and alumina: systematic modeling of cement clinkers using a general force-field." Physical Chemistry Chemical Physics 17, no. 28 (2015): 18477–94. http://dx.doi.org/10.1039/c5cp02823j.

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9

Wulandari, Futri, Eka Putra Ramdhani, Yatim Lailun Ni’mah, Ahmad Anwarud Dawam, and Didik Prasetyoko. "Synthesis of Amorphous Aluminosilicates from Bintan’s Red Mud as Alumina Source." Indonesian Journal of Chemistry 18, no. 4 (November 12, 2018): 580. http://dx.doi.org/10.22146/ijc.25184.

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Red mud is a generated by-product in alumina production from bauxite ore. In this study, Bintan’s red mud has been used as alumina and silica source to synthesize amorphous mesoporous aluminosilicates material. Alkali fusion method with a NaOH/red mud ratio 0.8; 1.0; 1.2; 1.4 and 1.5 followed by hydrolysis method was used to extract dissolved alumina and silica from red mud. Synthesis of amorphous aluminosilicates by hydrothermal method was conducted at 80 °C for 24 h. Cetyltrimethylammonium bromide (CTABr) was added as the structure directing agent. Aluminosilicate products were characterized using FTIR spectroscopy (Fourier Transform Infra-Red Spectroscopy), XRD (X-ray Diffraction), SEM (Scanning Electron Microscopy), and nitrogen adsorption-desorption. XRD and SEM result shows that the product was amorphous with low uniformity in terms of surface morphology and particle size. Nitrogen adsorption-desorption profile shows that all aluminosilicates products has a meso pore structure, confirmed by the highest pore distribution at 3.05–17.70 nm. The highest surface area and pore volume were obtained in ASM 0.8 (NaOH/red mud ratio = 0.8) i.e. 177.97 m2/g and 1.09 cm3/g, respectively.

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10

Chraska, T., J. Hostomsky, M. Klementova, and J. Dubsky. "Crystallization Kinetics of Amorphous Alumina-Zirconia-Silica Ceramics." Microscopy and Microanalysis 15, S2 (July 2009): 1000–1001. http://dx.doi.org/10.1017/s1431927609095397.

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11

Hensen, E. J. M., D. G. Poduval, P. C. M. M. Magusin, A. E. Coumans, and J. A. R. van Veen. "Formation of acid sites in amorphous silica-alumina." Journal of Catalysis 269, no. 1 (January 1, 2010): 201–18. http://dx.doi.org/10.1016/j.jcat.2009.11.008.

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12

Chráska, T., J. Hostomský, M. Klementová, and J. Dubský. "Crystallization kinetics of amorphous alumina–zirconia–silica ceramics." Journal of the European Ceramic Society 29, no. 15 (December 2009): 3159–65. http://dx.doi.org/10.1016/j.jeurceramsoc.2009.05.020.

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13

Shyu, Jiin-Jyh, and Yuan-Chieh Chen. "Zirconia-mullite ceramics made from composite particles coated with amorphous phase: I. Effect of zirconia addition." Journal of Materials Research 10, no. 1 (January 1995): 63–70. http://dx.doi.org/10.1557/jmr.1995.0063.

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Mullite-based ceramics added with 0–20 vol % stabilized zirconia have been prepared by alumina/zirconia particles coated with an amorphous silica layer. All samples can be densified through the viscous flow of the amorphous silica layer in the typical temperature range of 1100–1310 °C. For the ZrO2-free mullite ceramics, the viscous densification kinetics is inhibited by increasing the content of the alumina inclusion particles and by crystallization of the amorphous silica layer. However, for the zirconia-mullite ceramics, the addition of the zirconia inclusion particles accelerates the viscous densifcation kinetics. Mullitization kinetics is also enhanced by the addition of zirconia. As the sintering temeperature is high, a porous, duplex microstructure is observed in samples with or without zirconia. Zirconia addition enhances the development of this microstructure. As the sintering temperature and/or zirconia content is increased, ZrO2 particles tend to coarsen, resulting in a decreased tetragonal to monoclinic ratio. Fracture toughness KlC increases with the zirconia content. Mullite-20 vol % ZrO2 composite sintered at 1600 °C has a KlC of 3.8 MPa · m1/2.

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14

Mohammed, Al-Saudi Sarah Kareem, Emese Kurovics, Jamal-Eldin F. M. Ibrahim, Mohammed Tihtih, Andrea Simon, and Róbert Géber. "Preparation of an Aluminum Titania /Mullite Composite from the Raw Materials Alumina, Titania and Silica Fume." Revue des composites et des matériaux avancés 32, no. 5 (October 31, 2022): 223–28. http://dx.doi.org/10.18280/rcma.320502.

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The present work deals with the preparation of ceramic composites and the study of phase transformation. Three mixtures were prepared, the main mixture containing (80 wt%) alumina and (20 wt%) titania and the other two mixtures to which two amounts of silica fume were added at (5 and 10 wt%). The phase transformation was studied at two temperatures: 1200℃ and 1400℃. The X-ray diffraction results at 1200℃ show that the amorphous silica (silica fume) transformed into the crystalline phase cristobalite. At 1400℃, aluminum titanate formed by the reaction of alumina with titania, and mullite formed by the reaction of alumina with silica. The result of scanning electron microscopy shows that the addition of (5 wt%) silica leads to a microstructure with smaller grain size up to (500 nm), a lower porosity (20 vol%), a lower water absorption (7 wt%) and a thermal conductivity (1.514W/m.k).

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15

Chizallet, Céline, and Pascal Raybaud. "Density functional theory simulations of complex catalytic materials in reactive environments: beyond the ideal surface at low coverage." Catal. Sci. Technol. 4, no. 9 (2014): 2797–813. http://dx.doi.org/10.1039/c3cy00965c.

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16

Rahayu, Endang Sri, Gatot Subiyanto, Shoerya Shoelarta, Marvin Indi Hartono, and Hagai Elisafa. "The effect of the process condition on synthesis amorphous silica alumina from metakaolin on pore structure and crystallinity of product." MATEC Web of Conferences 268 (2019): 04002. http://dx.doi.org/10.1051/matecconf/201926804002.

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The objective of the research to study the effect of amorphous silica alumina (ASA) synthesis condition on pore structure and crystallinity. Synthesis of ASA was done by co-precipitation method, that preceded by neutralization to form a sol phase, followed by introducing a silica solution, and then aging to form an amorphous phase. Alumina solution is resulted by leaching of metakaolin from kaolin Belitung, Indonesia. The use of alumina source from this kaolin is a novelty method. Process conditions synthesis of ASA were varied on Si /Al ratio, time of neutralization and time of aging. While, a pH and temperature of neutralization are as independent process variable, of 7-8 and 50-55 °C, respectively. Characterization of ASA was performed using XRD, surface area and pore analyzer. The increasing of Si/Al ratio in starting material affects on the surface area of ASA, as well as with aging time. The best product of ASA with a specific surface area of 510 m2/g, average pore diameter of 85 Å, a total pore volume of 1.1 mL/g, and an amorphous phase of 53%-mass were observed.

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17

Harmel, Justine, Lars I. van der Wal, Jovana Zečević, Petra E. de Jongh, and Krijn P. de Jong. "Influence of intimacy for metal-mesoporous solid acids catalysts for n-alkanes hydro-conversion." Catalysis Science & Technology 10, no. 7 (2020): 2111–19. http://dx.doi.org/10.1039/c9cy02510c.

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Pt on both ordered mesoporous Al-SBA-15 and commercial amorphous mesoporous silica–alumina bi-functional catalysts were prepared and studied for n-heptane hydro-isomerization and n-hexadecane hydro-cracking.

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18

Olvianas, Muhammad, Mazaya Najmina, Bernardo Saktya Ludy Prihardana, Fransiskus A. K. G. P. Sutapa, Anis Nurhayati, and Himawan Tri Bayu Murti Petrus. "Study on the Geopolymerization of Geothermal Silica and Kaolinite." Advanced Materials Research 1112 (July 2015): 528–32. http://dx.doi.org/10.4028/www.scientific.net/amr.1112.528.

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Geothermal plant produces numerous kinds of possible side products. One of them is silica as a consequence of the existing silica scaling problem which causes geothermal power plant efficiency depletion. The silica recovery possesses a way to utilize it. Geopolymer concrete is a solution to utilize the abundance recovered geothermal silica with low energy consumption and green house gas emission. Thus, in this study, the geopolymerization of geothermal silica and kaolinite will be observed. Geopolymer was inorganic polymer consist of Si and Al atoms that formed through polymerization process. The raw materials being used are geothermal silica as amorphous silica source and kaolinite as alumina source, whereas the activator composed of sodium hydroxide and sodium silicate. Geothermal silica possesses amorphous structure which had been proven by X-Ray Diffraction (XRD) and X-Ray Fluorescence (XRF) analysis with 96.09% silica (SiO2) content and 18.92% alumina (Al2O3) content of kaolinite. The experiment conducted to determine geopolymerization rate of geothermal silica and kaolinite reaction in presence of alkali activator with certain composition and temperature variation ranged from 80°C up to 120°C. Study on geopolymerization rate was carried out by observing geopolymer bond along with the compressive strength as a function of curing time and temperature. As for geopolymer bonds for each sample with different curing temperatures, FTIR and SEM analysis were used to investigate.

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19

Perras, Frédéric A., Zichun Wang, Takeshi Kobayashi, Alfons Baiker, Jun Huang, and Marek Pruski. "Shedding light on the atomic-scale structure of amorphous silica–alumina and its Brønsted acid sites." Physical Chemistry Chemical Physics 21, no. 35 (2019): 19529–37. http://dx.doi.org/10.1039/c9cp04099d.

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Advanced solid-state NMR methods, using dynamic nuclear polarization (DNP), are applied to probe the atomic-scale bulk structure of amorphous silica–alumina catalysts prepared by flame-spray pyrolysis, and the structure of their Brønsted acid sites.

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20

Luu Thi, Hong, Long Luong Duc, Cham Trinh Thi, Luan Ta Van, and Qui Duong Thanh. "Effects of silicafume and fly ash on properties of alumina cement." MATEC Web of Conferences 251 (2018): 01015. http://dx.doi.org/10.1051/matecconf/201825101015.

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Alumina cement which was used in this investigation contains about 56% of Al2O3 in the component. Early compressive strength alumina cement at 1 and 3 days can be achieved of 85% compressive strength value at 28 days. After a long period of hydration, the compressive strength of alumina cement harder decreased due to the releasing process of aluminum hydroxide [Al(OH)3] to the outside environment [1, 4,11]. To improve and maintain the long lasting compressive strength of alumina cement harden, new binders would be created SiO2- Al2O3 and among CaO-SiO2-Al2O3. The new binders would exist sustainably in the cement harden as a result of the chemical reaction between the product of hydrated cement called gel [Al(OH)3] with micro silica (amorphous SiO2) [4]. This report demonstrates the result of the investigation which is about the effect of silica fume and fly ash on alumina cement.

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21

Snel, Ruud. "Control of the porous structure of amorphous silica—alumina." Applied Catalysis 33, no. 2 (September 1987): 281–94. http://dx.doi.org/10.1016/s0166-9834(00)83062-6.

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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

Abbot, J., and B. W. Wojciechowski. "Catalytic reactions of n-hexenes on amorphous silica-alumina." Canadian Journal of Chemical Engineering 63, no. 5 (October 1985): 818–25. http://dx.doi.org/10.1002/cjce.5450630518.

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24

Hahn, Maximilian W., John R. Copeland, Adam H. van Pelt, and Carsten Sievers. "Stability of Amorphous Silica-Alumina in Hot Liquid Water." ChemSusChem 6, no. 12 (October 7, 2013): 2304–15. http://dx.doi.org/10.1002/cssc.201300532.

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25

Snel, R. "Control of the Porous Structure of Amorphous Silica—Alumina." Applied Catalysis 36 (January 1988): 249–58. http://dx.doi.org/10.1016/s0166-9834(00)80119-0.

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26

Yin, Yanchao, Lihong Qin, Xiaofeng Wang, Genggeng Wang, Jun Zhao, Baijun Liu, and Yu Chen. "Preparation of a core–shell structured Y@ASA composite material and its catalytic performance for hydrocracking of n-decane." RSC Advances 6, no. 112 (2016): 111291–98. http://dx.doi.org/10.1039/c6ra24384c.

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A series of core–shell structure Y@ASA composites with different content of Y-type zeolite was synthesized in the small-crystal Y zeolite suspensoid by adding CTAB surfactant in the synthesis process of amorphous silica alumina (ASA).

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27

Rames, P. D., and K. J. Rao. "Preparation of β-SiAION from silica-alumina gel." Journal of Materials Research 9, no. 8 (August 1994): 1929–31. http://dx.doi.org/10.1557/jmr.1994.1929.

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Amorphous aluminosilicate gel powders have been subjected to carbothermal reduction and nitridation reaction at high temperature (1673 K). The influence of Al2O3 content in the gel powder on the nature and structure of the product phases has been examined. Between 5% and 9% Al2O3 in the gel powder, it is found that only β-SiAION is formed as the product of CTR/N reaction.

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28

Shyu, Jiin-Jyh, and Yuan-Chieh Chen. "Zirconia-mullite ceramics made from composite particles coated with amorphous phase: Part II. Effects of boria additions to the amorphous phase." Journal of Materials Research 10, no. 10 (October 1995): 2592–98. http://dx.doi.org/10.1557/jmr.1995.2592.

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Mullite and zirconia-mullite ceramics have been prepared by coating alumina/zirconia particles with an amorphous silica layer. The effect of composition change of the amorphous silica layer by adding B2O3 was investigated. For the zirconia-free compositions, the addition of B2O3 remarkably accelerates the kinetics of the crystallization of the amorphous coating layer, the viscous sintering, and the mullitization. For the zirconia-containing ceramics, the addition of B2O3 enhanced the viscous sintering kinetics and delayed the decomposition of the transient zircon phase and the subsequent t- to m ZrO2 transition, thus resulting in a higher ratio of t- to m-ZrO2. The B2O3-containing zirconia-mullite composites exhibit the same level of fracture toughness (Kic) as the B2O3-free zirconia-mullite composites.

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29

Wang, Zichun, Robert Buechel, Yijiao Jiang, Lizhuo Wang, Haimei Xu, Patrice Castignolles, Marianne Gaborieau, et al. "Engineering the Distinct Structure Interface of Subnano-alumina Domains on Silica for Acidic Amorphous Silica–Alumina toward Biorefining." JACS Au 1, no. 3 (February 19, 2021): 262–71. http://dx.doi.org/10.1021/jacsau.0c00083.

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30

Santoro, Federica, Matteo Mariani, Federica Zaccheria, Rinaldo Psaro, and Nicoletta Ravasio. "Selective synthesis of thioethers in the presence of a transition-metal-free solid Lewis acid." Beilstein Journal of Organic Chemistry 12 (December 6, 2016): 2627–35. http://dx.doi.org/10.3762/bjoc.12.259.

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The synthesis of thioethers starting from alcohols and thiols in the presence of amorphous solid acid catalysts is reported. A silica alumina catalyst with a very low content in alumina gave excellent results in terms of both activity and selectivity also under solvent-free conditions. The reaction rate follows the electron density of the carbinol atom in the substrate alcohol and yields up to 99% and can be obtained for a wide range of substrates under mild reaction conditions.

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31

Ma, Xianzheng, Katarzyna Janowska, Vittorio Boffa, Debora Fabbri, Giuliana Magnacca, Paola Calza, and Yuanzheng Yue. "Surfactant-Assisted Fabrication of Alumina-Doped Amorphous Silica Nanofiltration Membranes with Enhanced Water Purification Performances." Nanomaterials 9, no. 10 (September 24, 2019): 1368. http://dx.doi.org/10.3390/nano9101368.

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Surfactant-templated 5 mol% Al2O3-doped silica membranes nanofiltration membranes were synthesized via the sol-gel method, and afterward, were optimized, and tested with respect to the permeability and rejection rate. The disordered silica network was stabilized by doping 5 mol% alumina. Tetraethyl orthosilicate and aluminum isopropoxide were used as the silica and alumina precursors, respectively. Cetyltrimethylammonium bromide (CTAB) was used not only as a pore-forming agent, but also to control the reaction rate of the aluminum isopropoxide, thus obtaining highly homogeneous materials. The results about filtration of model solutions showed that the optimized membranes are featured by both a relatively high water permeability (1.1–2.3 L·m−2·h−1 ·bar−1) and a high rejection for salts (74% for NaCl, and >95% for MgSO4 and Na2SO4) and organic pollutants (e.g., about 98% for caffeine). High rejection of divalent ions and organic molecules was also observed when a real wastewater effluent was filtered. The influence of the synthesis conditions on the membrane performance is discussed.

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32

Poduval, Dilip G., J. A. Rob van Veen, Marcello S. Rigutto, and Emiel J. M. Hensen. "Brønsted acid sites of zeolitic strength in amorphous silica-alumina." Chemical Communications 46, no. 20 (2010): 3466. http://dx.doi.org/10.1039/c000019a.

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33

Lin, Yung-Jen, and Lee-Jen Chen. "Reaction synthesis of mullite–silicon carbide–yttria-stabilized zirconia composites." Journal of Materials Research 14, no. 10 (October 1999): 3949–56. http://dx.doi.org/10.1557/jmr.1999.0534.

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SiC/mullite/zirconia composites were fabricated by controlling the oxidation of powder compacts of SiC, alumina, and 3 mol% yttria-stabilized zirconia. The powder compacts were first oxidized in air at 1100 °C for various times to obtain proper amounts of amorphous silica. Subsequent reaction sintering at 1500 °C for 2 h combined the amorphous silica with alumina to form mullite with planned amounts. The incorporation of 3 mol% yttria-stabilized zirconia promoted mullite formation and enhanced the densification of the samples. With ≥10 vol% of 3 mol% yttria-stabilized zirconia in the samples, the temperature of mullite formation was lowered from 1400 to 1300 °C, and mullitization was near completion after sintering at 1500 °C for 2 h. The densification of the samples depended on the contents of SiC and 3 mol% yttria-stabilized zirconia. Samples with 20 vol% SiC and 10–20 vol% 3 mol% yttria-stabilized zirconia could be sintered to reach approximately 97% of theoretical density after sintering at 1500 °C for 2 h.

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34

Zhao, Yunlong, Yajie Zheng, Hanbing He, Zhaoming Sun, and An Li. "Silica extraction from bauxite reaction residue and synthesis water glass." Green Processing and Synthesis 10, no. 1 (January 1, 2021): 268–83. http://dx.doi.org/10.1515/gps-2021-0028.

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Abstract Bauxite reaction residue (BRR) produced from the poly-aluminum chloride (PAC) coagulant industry is a solid acidic waste that is harmful to environment. A low temperature synthesis route to convert the waste into water glass was reported. Silica dissolution process was systematically studied, including the thermodynamic analysis and the influence of calcium and aluminum on the leaching of amorphous silica. Simulation studies have shown that calcium and aluminum combine with silicon to form hydrated calcium silicate, silica–alumina gel, and zeolite, respectively, thereby hindering the leaching of silica. Maximizing the removal of calcium, aluminum, and chlorine can effectively improve the leaching of silicon in the subsequent process, and corresponding element removal rates are 42.81%, 44.15%, and 96.94%, respectively. The removed material is not randomly discarded and is reused to prepare PAC. The silica extraction rate reached 81.45% under optimal conditions (NaOH; 3 mol L−1, L S−1; 5/1, 75°C, 2 h), and sodium silicate modulus (nSiO2:nNa2O) is 1.11. The results indicated that a large amount of silica was existed in amorphous form. Precipitated silica was obtained by acidifying sodium silicate solution at optimal pH 7.0. Moreover, sodium silicate (1.11) further synthesizes sodium silicate (modulus 3.27) by adding precipitated silica at 75°C.

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35

Liu, Xiaoxu, Xiaowen Liu, and Yuehua Hu. "Investigation of the thermal behaviour and decomposition kinetics of kaolinite." Clay Minerals 50, no. 2 (June 2015): 199–209. http://dx.doi.org/10.1180/claymin.2015.050.2.04.

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AbstractPrevious work on the structural and thermal properties of various types of kaolinite have led to different conclusions, rendering comparison of analytical results difficult. The objectives of the present study were to investigate the thermal behaviour of kaolinite and to carry out a kinetic analysis of the decomposition of kaolinite at high temperatures. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and thermogravimetry-differential scanning calorimetry (TG-DSC) were used to study the mechanism of the thermal decomposition. The modified Coats–Redfern, Friedman, Flynn–Wall–Ozawa and Kissinger decomposition models were used to determine the decomposition mechanism of the kaolinite sample. The dehydroxylation of kaolinite occurred at ∼600°C with the formation of metakaolin, which then transformed into either γ-alumina or aluminium-silicon spinel together with amorphous silica. The results of the XRD and FTIR analyses indicated that the γ-alumina, or aluminium-silicon spinel and amorphous silica phases, transformed into mullite and α-cristobalite, respectively, after decomposition at 900°C. Good linearity was observed with the modified Coats–Redfern, Flynn–Wall–Ozawa and Kissinger models from room temperature to 1400°C and the range of the activation energy determined was 120–180 kJ/mol.

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36

Gun'ko, V. M., and O. K. Matkovsky. "Adsorption of various compounds onto nanooxides unmodified and differently pretreated." Himia, Fizika ta Tehnologia Poverhni 14, no. 4 (December 30, 2023): 474–94. http://dx.doi.org/10.15407/hftp14.04.474.

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Features of interfacial adsorbate/adsorbent phenomena depend on several factors: particulate morphology, texture, and structure of adsorbents, molecular weight, shape, and polarity of adsorbates; as well as prehistory of adsorbents pretreated under different conditions. All these factors could affect the efficiency of practical applications of not only adsorbents but also polymer fillers, carriers, catalysts, etc. Interactions of nonpolar nitrogen, hexane, benzene, weakly polar acetonitrile, and polar diethylamine, triethylamine, and water with individual (silica, alumina), binary (silica/alumina (SA)) and ternary (alumina/silica/titania, AST) nanooxides were studied using experimental and theoretical methods to elucidate the influence of the morphological and textural characteristics and surface composition of the materials on the adsorption phenomena. The specific surface area SX / ratio (X is an adsorbate) changes from 0.7 for hexane adsorbed onto amorphous silica/alumina SA8 with 8 wt. % Al2O3 (degassed at 200 °C) to 1.9 for acetonitrile adsorbed onto pure fumed alumina (treated at 900 °C). These changes are relatively large because of variations in orientation, lateral interactions, and adsorption compressing of organic molecules interacting with surfaces characterized by certain set and amounts of various active sites, as well as due to changes in the accessibility of pore surface for probe molecules of different sizes. Larger SX / > 1 values are observed for complex fumed oxides with larger primary nanoparticles, greater surface roughness, hydrophilicity, and Brønsted and Lewis acidity of a surface. Both polar and nonpolar adsorbates can change the morphology and texture of aggregates of oxide nanoparticles, e.g., swelling of structures, compacted during various pretreatments, upon the adsorption of liquids. The studied effects should be considered upon practical applications of adsorbents, especially “soft” fumed oxides.

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37

Leydier, Fabien, Céline Chizallet, Dominique Costa, and Pascal Raybaud. "CO adsorption on amorphous silica–alumina: electrostatic or Brønsted acidity probe?" Chemical Communications 48, no. 34 (2012): 4076. http://dx.doi.org/10.1039/c2cc30655g.

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de Klerk, Arno. "Oligomerization of Fischer−Tropsch Olefins to Distillates over Amorphous Silica−Alumina." Energy & Fuels 20, no. 5 (September 2006): 1799–805. http://dx.doi.org/10.1021/ef060169j.

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39

Xie, Yongbing, Hongbin Cao, Yuping Li, Yi Zhang, and John C. Crittenden. "Highly Selective PdCu/Amorphous Silica−Alumina (ASA) Catalysts for Groundwater Denitration." Environmental Science & Technology 45, no. 9 (May 2011): 4066–72. http://dx.doi.org/10.1021/es104050h.

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Moses, Anthony W., Naseem A. Ramsahye, Christina Raab, Heather D. Leifeste, Swarup Chattopadhyay, Bradley F. Chmelka, Juergen Eckert, and Susannah L. Scott. "Methyltrioxorhenium Interactions with Lewis Acid Sites of an Amorphous Silica−Alumina." Organometallics 25, no. 9 (April 2006): 2157–65. http://dx.doi.org/10.1021/om050962k.

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41

Villegas Brito, J. C., N. V. Gaponenko, K. S. Sukalin, T. F. Raichenok, S. A. Tikhomorov, Xiang Wang, Zhiqun Cheng, and N. I. Kargin. "Europium luminescence from amorphous yttrium alumina films on fused silica substrates." IOP Conference Series: Materials Science and Engineering 475 (February 18, 2019): 012019. http://dx.doi.org/10.1088/1757-899x/475/1/012019.

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42

Kuczynski, M., A. van Ooteghem, and K. R. Westerterp. "Methanol adsorption by amorphous silica alumina in the critical temperature range." Colloid and Polymer Science 264, no. 4 (April 1986): 362–67. http://dx.doi.org/10.1007/bf01418197.

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43

Shoppert, A. A., I. V. Loginova, L. I. Chaikin, and D. A. Rogozhnikov. "Alkali Fusion-Leaching Method For Comprehensive Processing Of Fly Ash." KnE Materials Science 2, no. 2 (September 3, 2017): 89. http://dx.doi.org/10.18502/kms.v2i2.952.

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<p>Fly ash, composed of mullite, hematite, amorphous silica and quartz, is a promising source for the recovery of alumina and silica. Desilication with help of NaOH and alkali fusion-leaching method and utilization of alumina and silica in the fly ash for preparation of sodalite and silica white were explored in this research. The samples were characterized by using wet chemical analysis and X-ray diffraction. The optimal extraction of SiO<sub>2</sub> from Reftinskaya power plant fly ash was 46.2% with leaching at 95 <sup>o</sup>C for 3 h. Sodalite was synthesized at 200 °C for 1 h followed water leaching at 95 °C for 1 h. Silica white with specific surface area 180-220 m2/g was prepared by carbonation of the Na<sub>2</sub>SiO<sub>3</sub> solution at 40 <sup>o</sup>C for 90-120 min. The as-prepared silica has a purity of 98,8%.</p><p>The proposed method is suitable for the comprehensive utilization of the fly ash.</p>

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Ratkovic, Sanja, Erne Kiss, and Goran Boskovic. "Synthesis of high-purity carbon nanotubes over alumina and silica supported bimetallic catalysts." Chemical Industry and Chemical Engineering Quarterly 15, no. 4 (2009): 263–70. http://dx.doi.org/10.2298/ciceq0904263r.

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Carbon nanotubes (CNTs) were synthesized by a catalytic chemical vapor deposition method (CCVD) of ethylene over alumina and silica supported bimetallic catalysts based on Fe, Co and Ni. The catalysts were prepared by a precipitation method, calcined at 600 ?C and in situ reduced in hydrogen flow at 700?C. The CNTs growth was carried out by a flow the mixture of C2H4 and nitrogen over the catalyst powder in a horizontal oven. The structure and morphology of as-synthesized CNTs were characterized using SEM. The as-synthesized nanotubes were purified by acid and basic treatments in order to remove impurities such as amorphous carbon, graphite nanoparticles and metal catalysts. XRD and DTA/TG analyses showed that the amounts of by-products in the purified CNTs samples were reduced significantly. According to the observed results, ethylene is an active carbon source for growing high-density CNTs with high yield but more on alumina-supported catalysts than on their silica-supported counterparts. The last might be explained by SMSI formed in the case of alumina-supported catalysts, resulting in higher active phase dispersion.

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Teles, U. M., and Fabiano A. N. Fernandes. "HYDROCRACKING OF FISCHER-TROPSCH PRODUCTS." Revista de Engenharia Térmica 6, no. 2 (December 31, 2007): 14. http://dx.doi.org/10.5380/reterm.v6i2.61685.

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The hydrocracking behavior the product of a Fischer-Tropsch synthesis consisting of a C4–C30 mixture of paraffins and olefins on a platinum/amorphous silica–alumina catalyst has been analyzed and optimized. The influence of temperature on the selectiveness of the hydrocracking has been investigated. Time and temperature optimization was performed in order to obtain the best operating conditions for the enhancement of gasoline and diesel cuts.

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46

Nuryanto, R., W. Trisunaryanti, and Triyono. "Variation of Gelatin Amount as Template for Mesoporous Silica-Alumina Synthesis based on Lapindo Mud." Asian Journal of Chemistry 32, no. 7 (2020): 1575–80. http://dx.doi.org/10.14233/ajchem.2020.22412.

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The synthesis of mesoporous silica-alumina from Na2SiO3 and NaAlO2 solutions extracted from lapindo mud using mesoporous gelatin templates from catfish bone extract has been performed. Mesoporous silica-alumina (MSA) synthesis was carried out by sol-gel method with a gelatin template of catfish bone for as much as 0.0; 0.5; 1.0 and 1.5 g, which produced MSA-G00, MSA-G05, MSA-G10 and MSA-G15, respectively. The obtained MSA was analyzed using FTIR, XRD, TEM and surface area analyzer (BET and BJH methods). The MSA-G00, MSA-G05, MSA-G10 and MSA-G15 showed a specific surface areas of 24.58, 41.73, 59.73, 89.82 m2/g and pore diameters of 10.20, 3.86, 9.97, and 7.31 nm, respectively. The XRD results proved that all the MSA were amorphous while the TEM analysis showed that all prepared MSAs using gelatin as a template were wormhole-like pores

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Sanchez Escribano, Vicente, Gabriella Garbarino, Elisabetta Finocchio, and Guido Busca. "γ-Alumina and Amorphous Silica–Alumina: Structural Features, Acid Sites and the Role of Adsorbed Water." Topics in Catalysis 60, no. 19-20 (August 14, 2017): 1554–64. http://dx.doi.org/10.1007/s11244-017-0838-5.

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Korányi, Tamás I., and and János B. Nagy. "27Al and 29Si NMR studies of alumina and amorphous silica-alumina supported NiW(Mo) HDS catalysts." Reaction Kinetics and Catalysis Letters 85, no. 1 (May 2005): 131–38. http://dx.doi.org/10.1007/s11144-005-0252-z.

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49

Taheraslani, Mohammadreza, and Han Gardeniers. "High-Resolution SEM and EDX Characterization of Deposits Formed by CH4+Ar DBD Plasma Processing in a Packed Bed Reactor." Nanomaterials 9, no. 4 (April 10, 2019): 589. http://dx.doi.org/10.3390/nano9040589.

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The deposits formed during the DBD plasma conversion of CH4 were characterized by high-resolution scanning electron microscopy (HRSEM) and energy dispersive X-ray elemental analysis (EDX) for both cases of a non-packed reactor and a packed reactor. For the non-packed plasma reactor, a layer of deposits was formed on the dielectric surface. HRSEM images in combination with EDX and CHN elemental analysis of this layer revealed that the deposits are made of a polymer-like layer with a high content of hydrogen (60 at%), possessing an amorphous structure. For the packed reactor, γ-alumina, Pd/γ-alumina, BaTiO3, silica-SBA-15, MgO/Al2O3, and α-alumina were used as the packing materials inside the DBD discharges. Carbon-rich agglomerates were formed on the γ-alumina after exposure to plasma. The EDX mapping furthermore indicated the carbon-rich areas in the structure. In contrast, the formation of agglomerates was not observed for Pd-loaded γ-alumina. This was ascribed to the presence of Pd, which enhances the hydrogenation of deposit precursors, and leads to a significantly lower amount of deposits. It was further found that the structure of all other plasma-processed materials, including MgO/Al2O3, silica-SBA-15, BaTiO3, and α-alumina, undergoes morphological changes. These alterations appeared in the forms of the generation of new pores (voids) in the structure, as well as the moderation of the surface roughness towards a smoother surface after the plasma treatment.

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50

Hidayat, Kukuh, Agus Wahyudi, and Husaini Husaini. "Making a synthetic zeolite from a residue of bauxite washing." Indonesian Mining Journal 23, no. 2 (November 2020): 99–104. http://dx.doi.org/10.30556/imj.vol23.no2.2020.1112.

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A zeolite synthetic of NaA type is generally prepared by mixing the alumina and silicate-containing materials (alkali alumino hydro-silicates). The used raw materials include the amorphous solids such as metakaolin, siliceous earth, coal ash, kimberlite waste, alumina trihydrate [Al(OH)3], bauxite, and aluminum metal. Residue of bauxite washing retains a fine texture and contains significant alumina and silica content, namely 30-36% Al2O3 and 10-15% SiO2. Both components are required for making the zeolite NaA . In this research, the zeolite NaA was made by extracting the alumina from residue of bauxite washing with caustic soda, and followed by reacting it with a water glass after through the flushing and washing process. The composition of zeolite NaA is as follows: 33.87% SiO2, 27.63% Al2O3, 16.31% Na2O, and 22.18% H2O with Na96Al96Si96O384.216H2O or Na12(AlO2)12(SiO2)12.27H2O as its mineral composition.

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