Formation of mullite phase in diphasic gels consisting of TEOS and boehmite with and without dehydroxylation

1998 ◽  
Vol 18 (12) ◽  
pp. 1765-1769 ◽  
Author(s):  
P. Padmaja ◽  
G.M. Anilkumar ◽  
K.G.K. Warrier
Keyword(s):  
Mullite Phase ◽  
Diphasic Gels

scholarly journals F/OH ratio in a rare fluorine-poor blue topaz from Padre Paraíso (Minas Gerais, Brazil) to unravel topaz’s ambient of formation

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
N. Precisvalle ◽  
A. Martucci ◽  
L. Gigli ◽  
J. R. Plaisier ◽  
T. C. Hansen ◽  
...  
Keyword(s):  
Supercritical Fluids ◽  
Fluorine Content ◽  
Minas Gerais ◽  
Hydroxyl Groups ◽  
Exchange Reactions ◽  
Silicate System ◽  
Mullite Phase ◽  
Anomalous Water

AbstractTopaz [Al2SiO4(F,OH)2] is one of the main fluorine-bearing silicates occurring in environments where variably acidic (F)/aqueous (OH) fluids saturate the silicate system. In this work we fully characterized blue topaz from Padre Paraíso (Minas Gerais, Brazil) by means of in situ synchrotron X-Ray and neutron powder diffraction measurements (temperature range 298–1273 K) combined with EDS microanalyses. Understanding the role of OH/F substitution in topaz is important in order to determine the hydrophilicity and the exchange reactions of fluorine by hydroxyl groups, and ultimately to characterize the environmental redox conditions (H2O/F) required for mineral formation. The fluorine content estimated from neutron diffraction data is ~ 1.03 a.f.u (10.34 wt%), in agreement with the chemical data (on average 10.0 wt%). The XOH [OH/(OH + F)] (0.484) is close to the maximum XOH value (0.5), and represents the OH- richest topaz composition so far analysed in the Minas Gerais district. Topaz crystallinity and fluorine content sharply decrease at 1170 K, while mullite phase starts growing. On the basis of this behaviour, we suggest that this temperature may represent the potential initial topaz’s crystallization temperature from supercritical fluids in a pegmatite system. The log(fH2O/fHF)fluid (1.27 (0.06)) is coherent with the fluorine activity calculated for hydrothermal fluids (pegmatitic stage) in equilibrium with the forming mineral (log(fH2O/fHF)fluid = 1.2–6.5) and clearly different from pure magmatic (granitic) residual melts [log(fH2O/fHF)fluid < 1]. The modelled H2O saturated fluids with the F content not exceeding 1 wt% may represent an anomalous water-dominant / fluorine-poor pegmatite lens of the Padre Paraíso Pegmatite Field.

scholarly journals A Mechanism of Anti-Oxidation Coating Design Based on Inhibition Effect of Interface Layer on Ions Diffusion within Oxide Scale

Coatings ◽  
2021 ◽  
Vol 11 (4) ◽  
pp. 454
Author(s):  
Bo Yu ◽  
Ya Liu ◽  
Lianqi Wei ◽  
Xiaomeng Zhang ◽  
Yingchao Du ◽  
...  
Keyword(s):  
Oxide Scale ◽  
Energy Barrier ◽  
Tetrahedral Site ◽  
Interface Layer ◽  
Diffusion Behavior ◽  
Mullite Phase ◽  
Inhibition Effect ◽  
Coating Design ◽  
Oxidation Effect ◽  
Dynamics Method

In this paper, a mechanism of anti-oxidation coating design based on the inhibition effect of the interface layer on the diffusion of ions within oxide scale was introduced. The Fe2+ ions diffusion behavior in Fe3O4, Cr2FeO4, and FeAl2O4 were studied by molecular dynamics method of Nudged elastic bond. As the result shown, Fe2+ ions tended to diffuse through the vacancy at tetrahedral site in Cr2FeO4 and FeAl2O4, but diffuse through the octahedral vacancy in Fe3O4. When temperature ranged from 1073 to 1325 K, the energy barrier of Fe2+ ions diffusion in Cr2FeO4 was higher than that of FeAl2O4, and both of that were still obvious higher than that in Fe3O4. A new anti-oxidation coating was prepared based on the inhibition of interface layer consisted of FeAl2O4 to protect the carbon steel S235JR at 1200 °C for 2 h. The FeAl2O4 region was formed and observed at the interface between coating and Fe element diffusion area, and the mullite phase was distributed outside of the FeAl2O4 region. Comparing to the bare sample, the prepared coating exhibited an excellent anti-oxidation effect.

scholarly journals X-ray diffraction analysis of kaolin M1 and M2 via the Williamson–Hall and Warren–Averbach methods

2021 ◽  
pp. 174751982098472
Author(s):  
Lalmi Khier ◽  
Lakel Abdelghani ◽  
Belahssen Okba ◽  
Djamel Maouche ◽  
Lakel Said
Keyword(s):  
Grain Size ◽  
High Temperature ◽  
Low Temperature ◽  
Diffraction Analysis ◽  
Mechanical Resistance ◽  
X Ray Diffraction ◽  
Integral Breadth ◽  
X Ray ◽  
Mullite Phase

Kaolin M1 and M2 studied by X-ray diffraction focus on the mullite phase, which is the main phase present in both products. The Williamson–Hall and Warren–Averbach methods for determining the crystallite size and microstrains of integral breadth β are calculated by the FullProf program. The integral breadth ( β) is a mixture resulting from the microstrains and size effect, so this should be taken into account during the calculation. The Williamson–Hall chart determines whether the sample is affected by grain size or microstrain. It appears very clearly that the principal phase of the various sintered kaolins, mullite, is free from internal microstrains. It is the case of the mixtures fritted at low temperature (1200 °C) during 1 h and also the case of the mixtures of the type chamotte cooks with 1350 °C during very long times (several weeks). This result is very significant as it gives an element of explanation to a very significant quality of mullite: its mechanical resistance during uses at high temperature remains.

Mullite phase formation and reaction sequences with the presence of pentoxides

2003 ◽  
Vol 351 (1-2) ◽  
pp. 264-272 ◽  
Author(s):  
L.B. Kong ◽  
Y.B. Gan ◽  
J. Ma ◽  
T.S. Zhang ◽  
F. Boey ◽  
...  
Keyword(s):  
Phase Formation ◽  
Mullite Phase

scholarly journals Effect of the sintering temperature on the fabrication of alumina beads

2019 ◽  
Vol 16 (2) ◽  
pp. 125-135
Author(s):  
Ayse KALEMTAS
Keyword(s):  
Sintering Temperature ◽  
Sol Gel ◽  
Xrd Analysis ◽  
Liquid Phase Sintering ◽  
Sintered Ceramic ◽  
Mullite Phase ◽  
Commercial Grade ◽  
Composite Beads ◽  
Sintering Additive ◽  
Dta Analysis

In this study, kaolin bonded alumina-alginate composite beads were fabricated via a facile one-step sol-gel process by using sodium alginate. In order to achieve sintering of the beads at lower sintering temperatures a limited amount of CC31 commercial-grade kaolin was used as a sintering additive (Al2O3:CC31 commercial-grade kaolin=14:1). Produced composite beads were heat treated at 1300°, 1400° and 1500°C for 1 hour to achieve partial densification of the beads. TG-DTA analysis of the CC31 commercial-grade kaolin showed that mullite phase formation took place approximately at 1000°C. However, XRD measurements revealed that there is only alumina phase in the sintered ceramic beads. Due to the low amount of CC31 commercial-grade kaolin, mullite formation was not detectable via XRD analysis. No significant grain growth was observed at the sintered samples depending on the increasing sintering temperature. However, when the sintering temperature was increased, densification ratio and mechanical properties of the produced beads were enhanced significantly. Microstructural investigations of the sintered beads shown that with the help of the liquid phase sintering process, a good chemical bonding was achieved between the alumina particles.

scholarly journals Enhanced Performance of Fly Ash-Based Supports for Low-Cost Ceramic Membranes with the Addition of Bauxite

Membranes ◽  
2021 ◽  
Vol 11 (9) ◽  
pp. 711
Author(s):  
Wan Fan ◽  
Dong Zou ◽  
Jingrui Xu ◽  
Xianfu Chen ◽  
Minghui Qiu ◽  
...  
Keyword(s):  
Fly Ash ◽  
High Performance ◽  
Bending Strength ◽  
Ceramic Membrane ◽  
Sintering Temperature ◽  
Low Cost ◽  
Pure Water ◽  
Ceramic Membranes ◽  
Mullite Phase ◽  
Optimum Balance

Support is a necessary foundation for ceramic membranes to achieve high performance. Finding the optimum balance between high performance and low cost is still a significant challenge in the fabrication of ceramic supports. In this study, low-cost fly ash-based ceramic supports with enhanced performance were prepared by the addition of bauxite. The pore structure, mechanical strength, and shrinkage of fly ash/bauxite supports could be tuned by optimizing the bauxite content and sintering temperature. When the sintering temperature and bauxite content were controlled at 1300 °C and 40 wt%, respectively, the obtained membrane supports exhibited a high pure water permeance of approximately 5.36 m3·m−2·h−1·bar−1 and a high bending strength of approximately 69.6 MPa. At the same time, the optimized ceramic supports presented a typical mullite phase and excellent resistance to acid and alkali. This work provides a potential route for the preparation of ceramic membrane supports with characteristics of low cost and high performance.

scholarly journals Effect of reduced Al2O3 mole ratio on fabrication of cordierite ceramic by solid-state sintering method

2019 ◽  
Vol 51 (2) ◽  
pp. 189-197
Author(s):  
Ye Li ◽  
Hengze Zhao
Keyword(s):  
Silicon Dioxide ◽  
Magnesium Oxide ◽  
Crystallization Process ◽  
Raw Materials ◽  
Linear Shrinkage ◽  
Pore Connectivity ◽  
Mullite Phase ◽  
Cordierite Ceramic ◽  
Solid State Sintering ◽  
Sintering Method

Cordierite ceramic was fabricated by reducing Al2O3 mole ratio from 2.0 to 1.4 with kaolin, silicon dioxide and magnesium oxide as the raw materials. The effect of reduced Al2O3 mole ratio on the sintering behaviors, phase transition, main properties, and microstructure were characterized in detail. The results show that cordierite phase becomes the main crystallization phase at 1300?C, and mullite phase can be consumed to produce cordierite phase by reducing Al2O3 mole ratio. But additional quartz phase still exists until 1400?C. Moreover, the open porosity, pore connectivity and pore size increase as Al2O3 mole ratio reduces from 2.0 to 1.4 while the linear shrinkage percent and bulk density decrease with the reduced Al2O3. It is considered that the sintering activity of the raw materials at low temperature decreases due to the increase of chemically pure magnesium oxide and silica with the decrease of Al2O3 mole ratio, while the crystallization process, pore growth and cordierite phase rather than the liquid phase control the densification process at high temperature.

scholarly journals Chemical, Mineralogical, and Refractory Characterization of Kaolin in the Regions of Huayacocotla-Alumbres, Mexico

2018 ◽  
Vol 2018 ◽  
pp. 1-11
Author(s):  
L. M. Romero-Guerrero ◽  
R. Moreno-Tovar ◽  
A. Arenas-Flores ◽  
Y. Marmolejo Santillán ◽  
F. Pérez-Moreno
Keyword(s):  
Thermogravimetric Analysis ◽  
Decomposition Temperature ◽  
X Ray Diffraction ◽  
Polarization Optical Microscopy ◽  
Plagioclase Feldspar ◽  
X Ray ◽  
Mullite Phase ◽  
Significant Difference ◽  
The Stability

In the present work, the chemical, mineralogical, refractory, and microstructural characterizations of kaolinites from the Huayacocotla-Alumbres region, which is between Veracruz and Hidalgo border, by X-ray diffraction (XRD), polarization optical microscopy (POM), scanning electron microscopy (SEM), refractoriness proof (pyrometric cone equivalent), and thermogravimetric analysis (TGA) were carried out. The analysis by POM showed that the kaolinization degree in this region is variable due to the presence of primary minerals, such as plagioclase, feldspar, and quartz. Additionally, hydrothermal alteration of the epithermal type was determined by oxidation of sulfides (pyrite and galena) and chlorite association. With the X-ray diffraction technique, andalusite and kaolinite were identified as the majority phases in Huayacocotla and quartz was identified as the majority phase in Alumbres. The minority phases, such as dickite, kaolinite, and cristobalite, were observed in both zones. The SEM technique was useful in the determination of the morphology of kaolinite and impurities of Na, Mg, K, and Fe of the complex clay illite-andalusite-dickite group. Thermogravimetric analysis was useful to discover the decomposition temperature and reveal the significant difference between 400 and 800°C, which showcases the greatest mass loss due to dehydration and carbonates decomposition. The mullite phase was detected at approximately 1000°C in the kaolin samples. The refractoriness tests were important to determine the stability temperature of kaolin, which is between 1300 and 1600°C. This stability temperature makes it feasible to use the kaolin as a refractory material for both low and high temperatures. The variables that affect the kaolin stability temperature were determined by principal components with the XLSTAT free program.

In Situ Formation of Mullite-Al2O3 Refractory Ceramic from Al-Matrix Mixtures

2014 ◽  
Vol 602-603 ◽  
pp. 628-631
Author(s):  
Xing Yong Gu ◽  
Ping Li ◽  
Wei Xia Dong ◽  
Ting Luo
Keyword(s):  
Thermal Expansion ◽  
Bulk Density ◽  
Thermal Expansion Coefficient ◽  
Expansion Coefficient ◽  
Bending Strength ◽  
Potential Effect ◽  
Apparent Porosity ◽  
Mullite Phase ◽  
Two Samples

Two types of mullite-Al2O3 composites were designed and sintered in situ from different composition containing Al composites e.g. kaolin, alumina hydroxide and calcined bauxite etc, and auxiliary additives. The phase composition and microstructure were studied using X-ray diffraction (XRD) and scanning electron microscope (SEM) techniques. Bulk density, apparent porosity, thermal expansion coefficient and bending strength were also measured. The two samples exhibited XRD reflections characteristic of alumina and mullite phases. The amount of these phases depended on starting batch compositions, and reaction of starting and auxiliary materials together to form mullite. Because of in-situ formation of mullite fiber, the bulk density and bending strength were improved and apparent porosity was decreased for the composites with uniform microstructure. The presence of high mullite phase was found to decrease the thermal expansion coefficient. The potential effect of these morphologies and phase on properties was discussed. These mullite-Al2O3 composite was expected to have major applications in the areas of refractory material.

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