Qi Feng

Hydrothermal Soft Chemical Process for Synthesis of Manganese Oxides with Tunnel Structures

A soft chemical process is used for the synthesis of manganese oxides with tunnel structures. This process comprises two steps: the first step is the preparation of a precursor with layered structure and insertion of templates (structure-directing agents) into its interlayer space by a soft chemical reaction [1], and the second step is the transformation of the template-inserted precursor into a tunnel structure by hydrothermal treatment. The usefulness of this process was demonstrated by synthesizing six kinds of tunnel manganese oxides from a birnessite-type manganese oxide with layered structure. The transformation reactions from layered structure to tunnel structures were investigated by X-ray, DTA-TG, and chemical analyses, and IR spectroscopy. Spinel-, hollandite-, romanechite-, and todorokite-type manganese oxides, which have (1×3), (2×2), (2×3), and (3×3) tunnel structures, can be obtained by using Li+, K+, Ba2+, and Mg2+ ions as the templates, respectively. Pyrolusite- and ramsdellite-type manganese oxides with (1×1) and (1×2) tunnel structures can be obtained in acidic solutions. The size of the resulting tunnels correspond to the size of the templates.

Formation mechanism of fine anatase crystals from amorphous titania under hydrothermal conditions

Crystallization of amorphous titania prepared by hydrolysis of ethoxide was accelerated even by a small amount of water in the vapor phase. The existence of water promoted the change of localized structure of the amorphous titania to anatase structure, which resulted in acceleration of anatase nucleation. The anatase crystals grew in steam by solid-state epitaxial growth, but stopped growing in a short time. The growth of anatase crystals under hydrothermal conditions could be divided into the following two stages: the first stage with fast growth rate by the solid-state epitaxial growth and the second stage with slow growth rate by the dissolution and deposition process.

Hydrothermal single crystal growth of calcite in ammonium acetate solution

Abstract Calcite single crystals were successfully grown in newly discovered ammonium acetate solution, an organic salt solution, under mild hydrothermal conditions below 250°C at saturated vapor pressure. The growth rate increased with the increase in growth temperature, temperature difference, and concentration of ammonium acetate solution. Even in a dilute ammonium acetate solution of 0.07M with a pH of 7.0, the seed crystal grew at a growth rate of 57 μm/day at 235°C with a temperature difference of 15°C. The grown crystal under these conditions was optically transparent and not contaminated with the mineralizer. Ammonium acetate solution has a large difference as a mineralizer for crystal growth of calcite from other inorganic salt solutions; In ammonium acetate solution, new planes, the f and a planes, developed on the seed crystal bound by the r planes.

Hydrothermal synthesis of xonotlite whiskers by ion diffusion

Abstracts are not published in this journal

Improvement of quality of hydrothermally grown calcite single crystals

The effects of growth factors (nutrient and mineralizer) on the perfection of calcite single crystals grown under hydrothermal conditions in an organic salt solution were investigated. The increase of carbon number in alkyl group of the ammonium monocarboxylates as a mineralizer solution, showed a general trend of decreasing the growth rate. When Iceland spar was used as the nutrient instead of natural limestone, the dislocation density remarkably decreased. It was shown that Mg 2 and Mn 2+ ions in the nutrient caused the increase in the dislocation density in the grown calcite crystals.

Synthesis of LiAl2(OH)6+ intercalated montmorillonite by a hydrothermal soft chemical reaction

A LiAl2(OH)6+ intercalated montmorillonite was prepared from a montmorillonite by using a hydrothermal soft chemical process. As a first step, lithium aluminium hydroxide complex ions (LixAln(OH)mz+) were inserted into the interlayer space of the montmorillonite by an ion-exchange reaction. In the second step, the ion-exchanged montmorillonite was hydrothermally treated to polymerize the complex ions in the interlayer space, forming a sandwich-like layered compound. The mechanism of formation of the sandwich layered structure was investigated by XRD, TG–DTA, chemical analyses and FTIR spectroscopy. Na+ and Ca2+ ions in the interlayer space of the montmorillonite were first exchanged with LixAln(OH)mz+ complex ions, and during this process the basal spacing of the montmorillonite increased from 1.6 to 2.0xa0nm after the ion-exchange. Two types of reactions of the ion-exchanged montmorillonite were observed under the hydrothermal conditions. In the temperature range 100–150°C, the basal spacing changed from 2.0 to 1.7xa0nm, corresponding to polymerization of LixAln(OH)mz+ complex ions to LiAl2(OH)6+ layers between the silicate layers. At temperatures over 200°C, Li+ ions of LiAl2(OH)6+ layers probably migrated into the octahedral sheets of silicate layers, accompanied by a decrease of the basal spacing from 1.7 to 1.4xa0nm. The LixAln(OH)mz+ complex ion was also used for pillaring montmorillonite, and a pillared montmorillonite with a basal spacing of 1.5xa0nm was obtained by heat treatment of this LixAln(OH)mz+ ion-exchanged montmorillonite in air at 500°C.

Transformation of manganese oxides from layered structures to tunnel structures

Birnessite-type manganese oxide can be transformed to tunnel structures by hydrothermal treatment.

Morphology control of ATiO3 (A=Ba, Sr, Ca) by hydrothermal soft chemical process

Abstract A hydrothermal soft chemical process for controlling the morphology of ATiO3 (A = Ba, Sr, Ca) perowkites is proposed, and used for the synthesis of fibrous particles. In this process. a fibrous hydrous tetratitanate (H2Ti4O9 · nH2O) which has a layered structure was used as the precursor, and hydrothermally treated with Ba(OH)2, Sr(OH)2and Ca(OH)2 solutions. The hydrous tetratitanate was transformed to the perowkite structure, but retained the fibrous morphology after the hydrothermal reactions.

Preparation of ceramics by hydrothermal hot-pressing

Abstract The densification mechanism of borosilicate glass, silica gel and amorphous titania powders by hydrothermal hot-pressing is described. The glass powders were densified by a viscous flow mechanism, and fully dedfied compacts were obtained by hydrothermal hot-pressing. On the other hand, porous ceramics were produced from silica gel and amorphous titania. The pore size distribution of these ceramics could be controlled by hydrothermal hot-pressing conditions. In the case of silica gel, it remained amorphous, but amorphous titaaia was crystallized to anatase by hydrothermal hot-pressing. The pore diameter and mechanical strength of the compacts prepared from silica gel increased with reaction time. The densification of the amorphous titania was improved by increasing temperature and pressure.

Synthesis of Lithiophorite by Hydrothermal Soft Chemical Process

Publisher Summary This chapter discusses that lithiophorite has a sandwich layered structure that was prepared from birnessite-type manganese oxide by using hydrothermal soft chemical process. A birnessite-type sodium manganese oxide with layered structure was prepared as a precursor. The Na+ ions in the interlayer space of the birnessite-type manganese oxide were ion-exchanged with LixAln (OH)mz+ complex ions. The ion-exchanged birnessite was treated under hydrothermal conditions to transform the birnessite structure to the sandwich layered structure. The transformation reactions from the birnessite structure to the sandwich-layered structures were investigated by X-ray, DTA-TG, and chemical analyses, and IR spectroscopy. The lithiophorite can be obtained by hydrothermally treating the ion-exchanged birnessite at 150oC. A reaction model was proposed for the formation reaction of the sandwich-layered structure.