The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
Heriberto Pfeiffer - One of the best experts on this subject based on the ideXlab platform.
-
Synthesis of advanced ceramics by Hydrothermal Crystallization and modified related methods
Journal of Advanced Ceramics, 2012Co-Authors: José Ortiz-landeros, Carlos Gómez-yáñez, Rigoberto López-juárez, Iván Dávalos-velasco, Heriberto PfeifferAbstract:The present article aims to give a brief overview about the advantages of the Hydrothermal Crystallization method for the synthesis of advanced ceramics. Emphasis is given, not only on the conventional Hydrothermal Crystallization, but also on some of its variants; such as ultrasound-assisted, electrochemical-assisted, microwave-assisted and surfactant-assisted Hydrothermal methods which open up new opportunities for the synthesis of ceramic materials with novel properties demanded for advanced applications. In the current work the synthesis of barium titanate (BaTiO_3), lithium metasilicate (Li_2SiO_3) and sodium-potassium niobate (Na, K)NbO_3 powders are reported as cases of study.
-
surfactant assisted Hydrothermal Crystallization of nanostructured lithium metasilicate li2sio3 hollow spheres ii textural analysis and co2 h2o sorption evaluation
Journal of Solid State Chemistry, 2011Co-Authors: Jose Ortizlanderos, Carlos Gomezyanez, Heriberto PfeifferAbstract:Abstract In a previous work, the synthesis and structural-microstructural characterization of different nanocrystalline lithium metasilicate (Li 2 SiO 3 ) samples were performed. Then, in this work, initially, a textural analysis was performed over the same samples. Li 2 SiO 3 samples prepared with a non-ionic surfactant (TRITON X-114) presented the best textural properties. Therefore, this sample was selected to evaluate its water vapor (H 2 O) and carbon dioxide (CO 2 ) sorption properties. Sorption experiments were performed at low temperatures (30–80 °C) in presence of water vapor using N 2 or CO 2 as carrier gases. Results clearly evidenced that CO 2 sorption on these materials is highly improved by H 2 O vapor, and of course, textural properties enhanced the H 2 O–CO 2 sorption efficiency, in comparison with the solid-state reference sample.
-
surfactant assisted Hydrothermal Crystallization of nanostructured lithium metasilicate li2sio3 hollow spheres i synthesis structural and microstructural characterization
Journal of Solid State Chemistry, 2011Co-Authors: M E Contrerasgarcia, Jose Ortizlanderos, Carlos Gomezyanez, Heriberto PfeifferAbstract:Lithium metasilicate (Li2SiO3) was successfully synthesized using a Hydrothermal process in the presence of different surfactants with cationic, non-ionic and anionic characters. The samples obtained were compared to a sample prepared by the conventional solid-state reaction method. The structural and microstructural characterizations of different Li2SiO3 powders were performed using various techniques. Diffraction analyses revealed the successful Crystallization of pure Li2SiO3 single phase by Hydrothermal technique, even without further heat-treatments and independent of the surfactant used. Electron microscopy analyses revealed that Li2SiO3 powders were composed of uniform micrometric particles with a hollow sphere morphology and nanostructured walls. Finally, different thermal analyses showed that Li2SiO3 samples preserved their structure and microstructure after further thermal treatments. Specific aspects regarding the formation mechanism of the spherical aggregates under Hydrothermal conditions are discussed, and there is a special emphasis on the effect of the synthesis pathway on the morphological characteristics.
Jiaqi Zhang - One of the best experts on this subject based on the ideXlab platform.
-
mild Hydrothermal Crystallization of heavy rare earth chromite recro3 re er tm yb lu perovskites and magnetic properties
Inorganic Chemistry, 2019Co-Authors: Shan Wang, Jiaqi Zhang, Long Yuan, Tiesheng Wang, Chenyang Zhang, Xiaofeng Wu, Dayong LuAbstract:Crystallization of perovskite structure chromites (ACrO3) in aqueous conditions is difficult owing to the amphoteric nature of the Cr3+ in the alkaline-mediated reaction conditions. This is especia...
-
Mild Hydrothermal Crystallization of Heavy Rare-Earth Chromite RECrO3 (RE = Er, Tm, Yb, Lu) Perovskites and Magnetic Properties
2019Co-Authors: Shan Wang, Jiaqi Zhang, Long Yuan, Tiesheng Wang, Chenyang Zhang, Xiaoqiang CuiAbstract:Crystallization of perovskite structure chromites (ACrO3) in aqueous conditions is difficult owing to the amphoteric nature of the Cr3+ in the alkaline-mediated reaction conditions. This is especially true for the small metal cations at the A-site with large distortion angle of CrO6 octahedral and small Goldschmidt tolerance factors. Here, we performed a progressive dehydration Crystallization strategy to synthesize four RECrO3 with the smallest radii of rare earth elements (Er, Tm, Yb, Lu) in mild Hydrothermal conditions. Profile refinement of the high-resolution powder X-ray diffraction results indicated slightly longer unit cell parameters of a and c in our samples with a higher distorted angle of CrO6 octahedral units along ⟨010⟩ direction. All of the samples show rounded rectangle plate morphology with uniform distribution of particle sizes. These four RECrO3 crystals can only form in a very narrow mineralization temperature range, i.e., 260–280 °C and 4.45–6.24 M of KOH. HRTEM results indicated that the normal crystallographic direction is ⟨001⟩, and the lattice of steps at the edge of elliptic rounded crystal is consistent with the bulk, which demonstrated single crystalline nature of the as-obtained crystals. Room-temperature Raman and FT-IR spectra reveal a continuous symmetry mode shift-dependent on the radii of A-site rare-earth cations. Temperature-dependent magnetization curves of RECrO3 show typical antiferromagnetism to paramagnetism transition with Néel temperature of 93, 90, 86, and 83 K for ErCrO3, TmCrO3, YbCrO3, and LuCrO3, respectively. Samples of YbCrO3 and LuCrO3 show clear magnetization reversal and exchange bias phenomena below their Néel points. This paper indicates that the coupling of magnetic exchange in perovskite structure oxides could be tailorable in mild Hydrothermal condition, towards the exploration of new magnetic and other physical properties
-
mineralizer effect on facet controllable Hydrothermal Crystallization of perovskite structure ybfeo3 crystals
CrystEngComm, 2018Co-Authors: Jiaqi Zhang, Keke Huang, Long Yuan, Shouhua FengAbstract:Mineralizer is a key factor in the Hydrothermal Crystallization of most metal oxide materials. However, the effect of mineralizer on crystal facet growth is not well understood. Herein, YbFeO3 is taken as a model compound to determine the effect of mineralizer on its shape evolution during a mild Hydrothermal Crystallization process. By adjusting the concentration and ratio of NaOH and KOH, the shapes of YbFeO3 crystals showed two different facet formation routes: NaOH stabilizes {110} and {002} facets, while KOH stabilizes {101} facets. The percentage of each family of crystal facets could be tailored by changing the concentrations of mineralizer and NH4+. The shape formation mechanism of YbFeO3 was analyzed based on Bravais–Friedel–Donnay–Harker theory, in addition to their facet structures and interactions between crystal facets and Na+, K+ and NH4+. This study will not only improve understanding of the role of mineralizers in oxide Crystallization, but also provide a crystal facet controllable method for the Hydrothermal synthesis of oxide materials with potential anisotropy applications.
Jose Ortizlanderos - One of the best experts on this subject based on the ideXlab platform.
-
surfactant assisted Hydrothermal Crystallization of nanostructured lithium metasilicate li2sio3 hollow spheres ii textural analysis and co2 h2o sorption evaluation
Journal of Solid State Chemistry, 2011Co-Authors: Jose Ortizlanderos, Carlos Gomezyanez, Heriberto PfeifferAbstract:Abstract In a previous work, the synthesis and structural-microstructural characterization of different nanocrystalline lithium metasilicate (Li 2 SiO 3 ) samples were performed. Then, in this work, initially, a textural analysis was performed over the same samples. Li 2 SiO 3 samples prepared with a non-ionic surfactant (TRITON X-114) presented the best textural properties. Therefore, this sample was selected to evaluate its water vapor (H 2 O) and carbon dioxide (CO 2 ) sorption properties. Sorption experiments were performed at low temperatures (30–80 °C) in presence of water vapor using N 2 or CO 2 as carrier gases. Results clearly evidenced that CO 2 sorption on these materials is highly improved by H 2 O vapor, and of course, textural properties enhanced the H 2 O–CO 2 sorption efficiency, in comparison with the solid-state reference sample.
-
surfactant assisted Hydrothermal Crystallization of nanostructured lithium metasilicate li2sio3 hollow spheres i synthesis structural and microstructural characterization
Journal of Solid State Chemistry, 2011Co-Authors: M E Contrerasgarcia, Jose Ortizlanderos, Carlos Gomezyanez, Heriberto PfeifferAbstract:Lithium metasilicate (Li2SiO3) was successfully synthesized using a Hydrothermal process in the presence of different surfactants with cationic, non-ionic and anionic characters. The samples obtained were compared to a sample prepared by the conventional solid-state reaction method. The structural and microstructural characterizations of different Li2SiO3 powders were performed using various techniques. Diffraction analyses revealed the successful Crystallization of pure Li2SiO3 single phase by Hydrothermal technique, even without further heat-treatments and independent of the surfactant used. Electron microscopy analyses revealed that Li2SiO3 powders were composed of uniform micrometric particles with a hollow sphere morphology and nanostructured walls. Finally, different thermal analyses showed that Li2SiO3 samples preserved their structure and microstructure after further thermal treatments. Specific aspects regarding the formation mechanism of the spherical aggregates under Hydrothermal conditions are discussed, and there is a special emphasis on the effect of the synthesis pathway on the morphological characteristics.
Svetozar Music - One of the best experts on this subject based on the ideXlab platform.
-
the Crystallization process of hfo2 and zro2 under Hydrothermal conditions
Journal of Alloys and Compounds, 2005Co-Authors: Goran Stefanic, Svetozar Music, Kresimir MolcanovAbstract:Abstract Hydrothermal Crystallization of hydrous hafnia at 90 and 120 °C, was monitored at pH 3, 7, 9.5 and 13, using X-ray powder diffraction analyses. The obtained results showed that Hydrothermal Crystallization proceeded much more slowly in a neutral pH medium than in an acidic or alkaline medium. Phase analysis of the products of Hydrothermal treatment showed that, regardless of pH, hydrous hafnia crystallized into m-HfO2. Stabilization of a metastable cubic or tetragonal HfO2 occurred upon adding a sufficient amount of stabilizing Na+ ions. Similarities and differences between the Hydrothermal Crystallization of HfO2 and the Hydrothermal Crystallization reported for ZrO2 were discussed. It was concluded that in both cases Hydrothermal Crystallization proceeds via a dissolution/precipitation mechanism in the whole pH range.
-
Hydrothermal Crystallization of boehmite from freshly precipitated aluminium hydroxide
Materials Letters, 1999Co-Authors: Svetozar Music, đurđica Dragcevic, Stanko PopovicAbstract:Abstract Hydrothermal Crystallization of boehmite from freshly precipitated aluminium hydroxide was monitored using X-ray powder diffraction (XRD) and Fourier transform infrared (FT-IR) spectroscopy. Crystallite sizes and interplanar spacings for boehmite samples were determined. Changes in the crystallinity of boehmite influenced the corresponding FT-IR spectra. The maximum specific area for boehmite powder was 246 m2 g−1, as measured by the Brunauer–Emmet–Teller (BET) method. With an increase of the crystallinity of boehmite, the specific area decreased and for the best crystalline sample, was 91 m2 g−1. All boehmite samples contained particles of colloidal dimensions. For the best crystalline boehmite sample, hexagonal-like plates were observed and some of them were elongated.
-
influence of ph on the Hydrothermal Crystallization kinetics and crystal structure of zro2
Thermochimica Acta, 1997Co-Authors: Goran Stefanic, Stanko Popovic, Svetozar MusicAbstract:Abstract Differential scanning calorimetry was used to measure the heat evolved as zirconia samples are heated at constant rate. The data are used to deduce the kinetics of zirconia Crystallization during Hydrothermal treatments at pH 2, 7, 9.5 and 13. Hydrothermal Crystallization was found to proceed much more slowly in the neutral pH medium than in the acidic or alkaline medium. The analogy between the rate of the Hydrothermal Crystallization of ZrO 2 and solubility of zirconium hydroxide was discussed. The results of phase analysis showed that metastable cubic zirconia, c -ZrO 2 , could be produced by Hydrothermal Crystallization in the presence of NaOH as a stabilizing agent. The results of X-ray diffraction showed that, even at low pH, monoclinic zirconia, m -ZrO 2 , was not the only product of the dissolution/precipitation mechanism of Hydrothermal Crystallization. It is concluded that in situ Crystallization of amorphous zirconium hydroxide, if it occurs, is not a topotactic process.
Long Yuan - One of the best experts on this subject based on the ideXlab platform.
-
mild Hydrothermal Crystallization of heavy rare earth chromite recro3 re er tm yb lu perovskites and magnetic properties
Inorganic Chemistry, 2019Co-Authors: Shan Wang, Jiaqi Zhang, Long Yuan, Tiesheng Wang, Chenyang Zhang, Xiaofeng Wu, Dayong LuAbstract:Crystallization of perovskite structure chromites (ACrO3) in aqueous conditions is difficult owing to the amphoteric nature of the Cr3+ in the alkaline-mediated reaction conditions. This is especia...
-
Mild Hydrothermal Crystallization of Heavy Rare-Earth Chromite RECrO3 (RE = Er, Tm, Yb, Lu) Perovskites and Magnetic Properties
2019Co-Authors: Shan Wang, Jiaqi Zhang, Long Yuan, Tiesheng Wang, Chenyang Zhang, Xiaoqiang CuiAbstract:Crystallization of perovskite structure chromites (ACrO3) in aqueous conditions is difficult owing to the amphoteric nature of the Cr3+ in the alkaline-mediated reaction conditions. This is especially true for the small metal cations at the A-site with large distortion angle of CrO6 octahedral and small Goldschmidt tolerance factors. Here, we performed a progressive dehydration Crystallization strategy to synthesize four RECrO3 with the smallest radii of rare earth elements (Er, Tm, Yb, Lu) in mild Hydrothermal conditions. Profile refinement of the high-resolution powder X-ray diffraction results indicated slightly longer unit cell parameters of a and c in our samples with a higher distorted angle of CrO6 octahedral units along ⟨010⟩ direction. All of the samples show rounded rectangle plate morphology with uniform distribution of particle sizes. These four RECrO3 crystals can only form in a very narrow mineralization temperature range, i.e., 260–280 °C and 4.45–6.24 M of KOH. HRTEM results indicated that the normal crystallographic direction is ⟨001⟩, and the lattice of steps at the edge of elliptic rounded crystal is consistent with the bulk, which demonstrated single crystalline nature of the as-obtained crystals. Room-temperature Raman and FT-IR spectra reveal a continuous symmetry mode shift-dependent on the radii of A-site rare-earth cations. Temperature-dependent magnetization curves of RECrO3 show typical antiferromagnetism to paramagnetism transition with Néel temperature of 93, 90, 86, and 83 K for ErCrO3, TmCrO3, YbCrO3, and LuCrO3, respectively. Samples of YbCrO3 and LuCrO3 show clear magnetization reversal and exchange bias phenomena below their Néel points. This paper indicates that the coupling of magnetic exchange in perovskite structure oxides could be tailorable in mild Hydrothermal condition, towards the exploration of new magnetic and other physical properties
-
mineralizer effect on facet controllable Hydrothermal Crystallization of perovskite structure ybfeo3 crystals
CrystEngComm, 2018Co-Authors: Jiaqi Zhang, Keke Huang, Long Yuan, Shouhua FengAbstract:Mineralizer is a key factor in the Hydrothermal Crystallization of most metal oxide materials. However, the effect of mineralizer on crystal facet growth is not well understood. Herein, YbFeO3 is taken as a model compound to determine the effect of mineralizer on its shape evolution during a mild Hydrothermal Crystallization process. By adjusting the concentration and ratio of NaOH and KOH, the shapes of YbFeO3 crystals showed two different facet formation routes: NaOH stabilizes {110} and {002} facets, while KOH stabilizes {101} facets. The percentage of each family of crystal facets could be tailored by changing the concentrations of mineralizer and NH4+. The shape formation mechanism of YbFeO3 was analyzed based on Bravais–Friedel–Donnay–Harker theory, in addition to their facet structures and interactions between crystal facets and Na+, K+ and NH4+. This study will not only improve understanding of the role of mineralizers in oxide Crystallization, but also provide a crystal facet controllable method for the Hydrothermal synthesis of oxide materials with potential anisotropy applications.
