Hiromoto Nakazawa

Stepwise hydration of high-quality synthetic smectite with various cations

Smectites synthesized from experiments at 5.5 GPa and 1500°C are of high quality, crystals are large at >10 μm, and the 2:1 layers may have a homogeneous charge distribution. Smectite was exchanged with various cations (Na+, Li+, K+, Ca2+, and Mg2+) and the hydration behavior of each sample was observed by an in situ powder X-ray diffraction method under precisely controlled relative humidity (RH). The smectite showed distinct stepwise (discontinuous) hydration versus RH. During the transition between two hydration states, the coexistence of the two states was observed. Randomly interstratified structures with one and two planes of H2O are time-dependent phenomena and relate to hydration and dehydration processes.

Intercalation of N-alkyltrimethylammonium into swelling fluoro-mica

Trimethylammonium ions (TMA+) with formula CH3(CH2)n-1N+(CH3)3, with n = 4, 8, 12, 16, 18 and 22 were intercalated into synthetic Li-fluorotaeniolite (Li-FTN) and Li-fluorohectorite (Li-FHT) by cation exchange. The products were analyzed by thermogravimetric (TGA) and X-ray powder diffraction (XRD). XRD patterns exhibited variable (001) spacings of the TMA+/mica complexes depending upon the exchange ratio of TMA+/Li+ and the carbon number of TMA+. Detailed inspection of these XRD patterns clarified the structures of the complexes and also the intercalation mechanism, as follows: The fundamental structure of the complexes is the commonly known intercalation structure where the “paraffin-type bilayers” of TMA+ are in the mica interlayer and their long chains incline at approximately 30° to the silicate sheet. This structure appeared at the final stage of the intercalation reaction. During the intermediate stage of the reaction, units of this structure and those of hydrated mica formed randomly and regularly interstratified structures. Variable (001) spacings in XRD patterns showed the structural change of the complex with an increasing number of TMA+-intercalated units.

Flake-Shell Capsules: Adjustable Inorganic Structures

Structure-adjustable capsules are fabricated from inorganic components by using a self-template dissolution-regrowth mechanism to give flake-shell silica microcapsules. The capsules shrink under thermal stimulus and their structures can be adjusted by treatment at different pH values. Tuning of shell pore diameters leads to tailored drug release over prolonged periods.

Stability of Amino Acids and Their Oligomerization Under High-Pressure Conditions: Implications for Prebiotic Chemistry

The polymerization of amino acids leading to the formation of peptides and proteins is a significant problem for the origin of life. This problem stems from the instability of amino acids and the difficulty of their oligomerization in aqueous environments, such as seafloor hydrothermal systems. We investigated the stability of amino acids and their oligomerization reactions under high-temperature (180-400°C) and high-pressure (1.0-5.5 GPa) conditions, based on the hypothesis that the polymerization of amino acids occurred in marine sediments during diagenesis and metamorphism, at convergent margins on early Earth. Our results show that the amino acids glycine and alanine are stabilized by high pressure. Oligomers up to pentamers were formed, which has never been reported for alanine in the absence of a catalyst. The yields of peptides at a given temperature and reaction time were higher under higher-pressure conditions. Elemental, infrared, and isotopic analyses of the reaction products indicated that deamination is a key degradation process for amino acids and peptides under high-pressure conditions. A possible NH(3)-rich environment in marine sediments on early Earth may have further stabilized amino acids and peptides by inhibiting their deamination.

Crystal synthesis of smectite applying very high pressure and temperature

Abstract Single crystals of smectite have been obtained by quenching a hydrothermal product at very high pressures and temperatures (e.g. 5.5 GPa and 1600°C). The starting material was a glass with the composition of dehydrated montmorillonite. The phases coexisting with the smectite were coesite, jadeite, kyanite, and occasionally a very small amount of an unidentified phase. Smectite was identified by X-ray diffraction before and after intercalation of ethylene glycol. Thin fragments of smectite cleaved by water for electron microscopic observation were single crystals in the forms of extremely thin ribbons, lathes and plates having partly hexagonal edges. An electron microprobe analysis suggests that the smectite has a composition similar to that of montmorillonite.

ISOTHERMAL TREATMENTS OF REGULARLY INTERSTRATIFIED MONTMORILLONITE-BEIDELLITE AT HYDROTHERMAL CONDITIONS

A glass in the intermediate composition of montmorillonite and beidellite, 50/50 in mole ratio, was treated under a hydrothermal pressure of 100 MPa, in the temperature range from 250 to 500°C and durations from 2 to 129 days. The phases identified in the products were plotted in a time-temperature-transformation (TTT) diagram. The TTT diagram showed that the regularly interstratified montmorillonite-beidellite (r.i.M-B) was a metastable phase above the temperature of 350°C and changed to the assemblage of Na-rectorite + saponite + quartz, through the intermediate assemblage of beidellite + saponite + quartz. The TTT diagram suggested also that the r.i.M-B might be a stable clay mineral below the temperature of 300°C in the middle region of montmorillonite-beidellite pseudo-binary system, although the laboratory confirmation of the mineral stability was not easy for the sluggish reaction.

Compositional gap in dioctahedral-trioctahedral smectite system; beidellite-saponite pseudo-binary join

A series of hydrothermal experiments were performed to determine the phase relations on the beidellite-saponite pseudo-binary join. Quenched glasses with stoichiometric dehydrated compositions of an Na-rich smectite on the join were heated at 250–500°C for durations of 1–151 d at 100 MPa. Time-temperature diagrams showed that immiscibility occurs between dioctahedral smectite (beidellite) and trioctahedral smectite (saponite) below 400°C. Thus, smectite with intermediate chemical composition was considered as metastable in this system. Above 400°C the assemblage of regularly interstratified saponite-chlorite, quartz, and feldspar was recognized in the intermediate chemical compositional region of this join. On the beidellite side of this join, beidellite and mixed-layer phases of smectite and a regular interstratification of montmorillonite-beidellite, are possible phases that occur at <300°C. They readily reacted to form a mixture of dioctahedral rectorite plus quartz at 300°C. This assemblage then reacted to a dioctahedral “mica”, which can expand with glycol and quartz. On the saponite side of this join, a single phase, saponite, existed at <400°C, and transformed to saponite plus trioctahedral rectorite with aging and increasing temperature of synthesis. The alteration was affected strongly by the chemical composition of the binary system.

FORMATION OF SMECTITE CRYSTALS AT HIGH PRESSURES AND TEMPERATURES

Smectite single crystals of superior quality were synthesized at high pressures and temperatures using a modified belt type high pressure apparatus. Pressure-temperature conditions were established for smectite formation by quenching experiments in the pressure range from 2–5.5 GPa and temperatures of 700°–1000°C. Smectite crystals with extraordinary quality were formed beyond 3 GPa and 1000°C with coexisting phases of coesite, kyanite, jadeite, and in some cases with mica and glass. Smectite was confirmed from the XRD taken after intercalation of ethylene glycol. The smectite crystals were considered to be quenched crystals metastably from the hydrous silicate melts formed at high pressures and temperatures.

Porous clay-organic composites: Potential substitutes for polystyrene foam

Abstract Porous clay-organic composites have been prepared by lyophylization of mixtures of clay and organic sols. They are shown to have properties applicable for packing and for use as insulating buffer material. The organics which have been used are all naturally reproduceable in the biosphere. The relations between the organic:clay ratio, the pore size and the mechanical properties have been studied in detail for the porous composites, especially for those of clay and agar. The compressive strengths of the porous composites are comparable to, or higher than that of commercially available polystyrene foam. The porous composites, being solely composed of materials found in the biosphere, may be potential substitutes for polystyrene foam which is a petroleum product.

Hard X-ray Imaging Microscopy using X-ray Guide Tube as Beam Condenser for Field Illumination

An optical system for illumination of object in x-ray imaging microscopy is developed. The optical system is a beam condenser consisting of a single-bounce conical-shape mono-capillary (x-ray guide tube: XGT) made of Pyrex glass. The XGT condenser was tested at the beam line 47XU of SPring-8 using a Fresnel zone plate as an objective lens. Comparing with the microscope without beam condenser, the flux density is improved by a factor of 12–20 in the x-ray energy range of 6–8 keV. Test patterns with a 50 nm-structure are clearly resolved at 8 keV with an exposure time less than 1 s.