Satoru Ueda

Synthesis of new gallosilicate zeolite with sodalite structure

Abstract A sodium gallosilicate zeolite with the sodalite structure was synthesized from the silica-rich starting gel. This gallosilicate zeolite has a very low SiO 2 to Ga 2 O 3 molar ratio (less than 1.0), which means that it violates the Loewensteins rule. Moreover, against the expectations, the unit cell of this gallosilicate zeolite is smaller than that of an aluminosilicate with the sodalite structure.

The Synthesis of Zeolite NaA from Homogeneous Solutions and Studies of its Properties

The authors first synthesized zeolite NaA from homogeneous solutions at 100°, 90°, 80°, 60°C and room temperature, respectively. With the prolongation of crystallization, zeolite NaA was converted into NaX and NaHS type zeolites and into NaHS completely at last. We have studied the morphology, IR spectra, thermal stability, and 29 Si MAS-NMR measurements, and preliminarily investigated the mechanism of the formation of NaA type zeolite based on the results of 27 Al- and 29 Si-NMR spctra.

The stability and vibrational spectra of three-ring containing zeolitic silica polymorphs

Abstract Zeolitic silica polymorphs containing three-membered rings are modeled using three different atomistic potential sets for lattice energy minimization calculations of their structure and using a general valence force field to calculate vibrational spectra. In some cases, large deviations from the experimental symmetry occur upon energy minimization. The lattice energy calculations show that structures with tetrahedra that participate in one or two three-rings can exist in the pure silica form. A hypothetical structure in which all tetrahedrally coordinated atoms are part of a three ring, and with a corresponding very low framework density, is shown to be significantly less stable. The calculated vibrational spectra are very sensitive to small-scale structural features like bond lengths and bond angles. Because three-ring structures generally have small SiOSi angles compared with other zeolites, relatively low-frequency asymmetric stretch models are predicted. No specific spectral peak can be assigned to a three-ring mode. The differences in structural detail computed using the three potential sets for silica produce variations in predicted infrared spectra that are larger than found between different structural polymorphs. This indicates the need for further improvement of potential parameters applicable to structure relaxation.

Synthesis of Offretite-Erionite Type Zeolite from Solution Phase

Offretite, erionite, and offretite-erionite (OE) type zeolite analogous to zeolite ZSM-34 were synthesized from nearly homogeneous solutions and heterogeneous hydrogels in the system of Na2O-K2O-TMA2O-Al2O3-SiO2-H2O. Their crystal shapes are prismatic and the crystal sizes range from 0.5 to 5.0 μm. The SiO2/Al2O3 mole ratio in zeolite framework increased with increasing SiO2/Al2O3 ratio of initial gels, and was in the range of 5.4 to 8.5. Offretite was formed from reaction mixtures having low SiO2/Al2O3 ratio, and erionite crystallized in high SiO2/Al2O3 ratio, whereas OE type zeolite was formed in the intermediate ratio between the above ratios.

Synthesis of Fe-substituted Al-mordenites by hydrothermal method

Al-mordenite and Fe-mordenite were synthesized with the tetraethylammonium as atemplate by hydrothermal method at 150°C in the Na2O–Al2O3–SiO2–H2O and Na2O–Fe2O3–SiO2–H2O system, respectively. Synthesis of several Al-mordenites substituted with Fe, Al/Fe ratio = 75/25, 50/50, 25/75, were also attempted in the Na2O–Al2O3–Fe2O3–SiO2–H2O system under the same conditions by the hydrothermal method. The continuous solid solution of Fe in Al-mordenite was successfully obtained in mordenites with various Al-Fe molar ratios. Al-mordenite crystal was tablet-like with approximately 20–30 μm in diameter and 5–10 μm in thickness. Fiber-like Fe-mordenite grew up to 20–30 μm in length and 5 μm in diameter. The morphology of Fe-substituted Al-mordenite was cubic-like with 5–10 μm in size. The size of Fe-substituted Al-mordenite decreased with the increase of Fe-content.

Estimate of polytype fractions and dislocation density in SiC before and after sintering in Si3N4 matrix

A quantitative characterization of polytype fractions and dislocation morphology and density is presented for two α-SiC powders. The tools were X-ray diffraction (XRD) and etch-pit analysis carried out before and after hot-isostatic-press (HIP) sintering in an Si3N4 matrix at 2050 °C under 180 MPa. Results are compared with data from transmission electron microscopy and electron diffraction previously obtained on the same powders. To avoid overlapping of the major XRD peaks with that of the Si3N4 matrix and to make possible the observation of the Si plane during etch-pit analysis in the powders after sintering, a chemical etching procedure to separate nitride and carbide phases without damage was developed. The morphology and density of pits and dislocations were analysed to get quantitative information about the crystal structures of the SiC crystallites and their modifications after the HIP cycle. The polytype fractions were found to be unchanged after sintering. It was also determined that polytypes 6H, 4H and 15R generally share part of the surface in a single crystallite rather than existing as single crystallites themselves, the 15R polytype generally being a hosted structure by a 6H or 4H matrix. A high density of dislocations (1013–1014cm−2) was found in both the SiC powders after HIP sintering compared with the raw materials.

Studies on the Initial Product in the Synthesis of Zeolite A from Concentrated Solutions

Amorphous aluminosilicate, which is often referred to as the initial product in the synthesis of zeolite A, has been characterized as a possible detergent builder. Ion exchange capacity and crystallinity were evaluated. The crystallization process of amorphous aluminosilicate was studied by X-ray diffraction and selected area electron diffraction analyses. It is shown that the amorphous aluminosilicate has a short-range order of Si and Al atoms similar to the crystallized zeolite A, and that anionic surfactant AOS retards the crystallization of zeolite A without significant effects on the builder characteristics.

Synthesis and Microstructure of Fe-Substituted Mordenite.

Fe-substituted mordenite, Al-mordenite (Al end-member) and Fe-mordenite (Fe end-member) were synthesized in the Na2O-Al2O3-Fe2O3-SiO2-H2O system under TEA (tetraethylammonium) as a template by hydrothermal method. The hydrothermal process was performed in a stainless Morey bomb at 150°C. The continuous solid solution of Fe into Al-site in mordenite was obtained for mordenites with Al-Fe molar ratio (75/25, 50/50, 25/75). The mordenite crystal with Al-end member showed a tablet-like structure with 10μm diameter and 5μm thickness. The morphology of Fe-substituted mordenite was platelet shaped with 10μm in size. Fiber-like Fe-mordenite grew up to 30μm in length and 5μm in diameter. TEA was decomposed in air atmosphere at 440-450°C for Al-mordenite, Fe-mordenite, and Fe-substituted mordenites.