Yoshihiro Kuwahara

In-situ AFM study of smectite dissolution under alkaline conditions at room temperature

Abstract An experimental study on smectite dissolution was carried out using in-situ TMAFM and CMAFM (tapping mode and contact mode atomic force microscopy, respectively) analyses at 25 °C under alkaline conditions. Smectite particles dissolved via the retreat of the edge surfaces without scratching by the AFM tip, except in a series of the dissolution experiment in CMAFM. The retreat of each straightened edge surface appeared to occur with a constant rate. In contrast, the basal surface was unreactive within the experimental duration. The dissolution rates normalized to the edge surface area (ESA) of smectite at a certain pH and temperature condition, therefore, had a constant value independent of the particle size, whereas the dissolution rates normalized to the total surface area (TSA) varied with the particle size. These dissolution rates were consistent with those derived from wet-chemical data in previous studies. The anisotropic dissolution behavior was also observed along the ESA, that is, the retreat of dissolution fronts along the {110} faces was much faster than that along {010} faces. This difference can be explained by smectite dissolution under alkaline conditions being controlled by OH- attack, which is catalyzed by protonated Al-OH groups, on the bridging O atoms of both Al-O-Si sites, which locate only on the {110} surfaces, and Al2-O-Si sites on the {010} and {110} surfaces. The bridging O atoms of Al2-O-Si sites on the {010} surfaces are buried more deeply in the structure than those of Al-O-Si sites on the {110} surfaces, which would be more difficult to attack on the {010} surfaces.

Surface microtopography of lath-shaped hydrothermal illite by tapping-mode™ and contact-mode AFM

Lath-shaped hydrothermal illite particles in Izumiyama pottery stone were examined by contact-mode atomic force microscopy (CMAFM) and tapping-mode AFM (TMAFM) in air. With CMAFM, the lath-shaped particles showed interlacing patterns on the (001) surface in deflection images, while in height images such patterns were unclear. Also, evidence of artifacts caused by frictional forces between the surface and tip and/or edge effects were found in the CMAFM height images of the particle and Si substrate surfaces. In contrast, TMAFM showed interlacing patterns clearly in both amplitude and height images, and artifacts were barely evident. The TMAFM height images permitted the accurate measurement of 1.0- or 2.0-nm height steps corresponding to single or double mica layers, as well.Many lath-shaped particles in the Izumiyama hydrothermal illite exhibit interlacing patterns on their (001) surface, as shown by these AFM observations. The interlacing patterns are characterized by polygonal spirals with comparatively wide spacings and steps having a height of 1.0 or 2.0 nm. Generally a single lath-shaped particle has a single spiral center on the (001) surface, and 2 mica layers rotated 120° originate from the dislocation point. These support the view that lath-shaped illites belong to the 2M1 polytype. It is likely that these illite particles were formed by a uniform process of development that is characterized by very slow growth, spiral mechanisms in that growth and low supersaturation conditions.

Dissolution process of phlogopite in acid solutions

The alteration experiments of phlogopite with 0.01 N HCl solution containing 0.1 M NaCl at 50°, 80° and 120°C have been carried out to aid in the understanding of the dissolution process of mica and the formation of secondary phases such as vermiculite and interstratified mica/vermiculite. Twenty milligrams of phlogopite samples were suspended in 20 ml or 100 ml of leaching solution.In these experiments, the dissolution ofphlogopite occurred incongruently, where the preferential release of K occurred in almost all stages of the alteration reaction. In the 100 ml experiments, the priority in dissolution in the initial stage was in the order; K > Fe > Mg, Al > Si. This supports that phlogopite leaching is controlled by the mineral structure. At 80° and 50°C in the 20 ml experiments, the release of all elements except for K was nearly congruent. At 120°C in the 20 ml experiments, the dissolution was outwardly incongruent, which Fe decreased remarkably after six days and Al was released most slowly compared with all other elements in phlogopite. This is probably due to the precipitation of secondary phases such as aluminum and iron oxides and/or hydroxides.Vermiculite and R1-type interstratified mica/vermiculite, containing 70 ∼ 50% mica, were formed in the alteration process of phlogopite. The following two processes were confirmed for the formation of interstratified structure: Interstratified structure was formed (1) directly from phlogopite or (2) from vermiculite which was produced earlier from phlogopite by regaining of K from the ambient solution. It may depend on the release rate of K from phlogopite whether mica-vermiculite layer sequences develop or vermiculite-vermiculite sequences do.

In situ observations of muscovite dissolution under alkaline conditions at 25-50 °C by AFM with an air/fluid heater system

Abstract Dissolution behavior of muscovite under alkaline conditions at 25-50 °C was investigated using in situ atomic force microscopy (AFM) with an air/fluid heater system to derive reliable dissolution rates and determine the dissolution mechanism and the effect of temperature on the dissolution rates. The muscovite dissolution took place only at the edge surfaces that are less than a few percent of the total surface area (TSA), while the basal surfaces were completely unreactive. During the initial stage of the experiments, some rough edge surfaces of muscovite dissolved much faster at the reactive site and appeared to straighten. The straightened edge surfaces seemed to retreat with a lower constant rate, which may correspond to the actual dissolution rate of muscovite, in the late stage. The edge surface area (ESA)-normalized dissolution rate at a certain pH and temperature condition, therefore, has a constant value independent of the size of etch pit or island (particle). The ESA-normalized dissolution rates derived from this AFM study were consistent with the dissolution rates renormalized to the estimated ESA of the earlier studies. In contrast, the TSA-normalized dissolution rates varied with the size of etch pit or island. The activation energy for muscovite dissolution under alkaline conditions was very close to that for montmorillonite and illite dissolution. A model dissolution rate equation, which simultaneously includes the effect of pH and temperature, was deduced from the effect of pH on the activation energy, the rate equation of muscovite dissolution at 25 °C, and the Arrhenius equation. The dissolution rates estimated from the model were in good agreement with the experimental rates from 25 to 70 °C. The dissolution reaction order with respect to hydroxyl activity (or pH) increases with temperature.

ATOMIC FORCE MICROSCOPY STUDY OF HYDROTHERMAL ILLITE IN IZUMIYAMA POTTERY STONE FROM ARITA, SAGA PREFECTURE, JAPAN

The surface microtopographic observations and analyses of Izumiyama hydrothermal illite particles were made by utilizing tapping-mode atomic force microscopy (TMAFM). The Izumiyama illite particles showed platy to lath shapes. Platy particles exhibited various spiral growth patterns, i.e. circular, malformed circular, or polygonal single unit-cell layer spirals, polygonal parallel step spiral, or interlaced spiral patterns. The polygonal parallel step spiral and interlaced spiral patterns are formed by two single unit-cell layers rotated by 180° and 120° arising from a single screw dislocation point, respectively. The spiral patterns indicate that the illite particles have 1M, 2O and 2M1 polytypes. Lath-shaped particles show only interlacing patterns supporting the formation of 2M1 structures.Particles showing circular or malformed circular spirals were found to be thinner and to have narrower step separations than particles showing polygonal spirals. Polygonal platy and lath-shaped particles showing interlaced patterns tended to be thicker and to have wider step separations than the other polygonal platy particles.These results suggest that the Izumiyama illites crystallize as the result of a mechanism involving solution-mediated polytypes and spiral-type transformations of illite. The mechanism involves the Ostwald ripening process, i.e. a transformation of the polytype and spiral shape. The sequence of crystallization of the Izumiyama illite is: 1M circular spirals → 1M, 2O polygonal spirals → 2M1 polygonal spirals occurring during crystal growth and sequentially overgrowing on the initial particle surfaces. The super-saturation of the hydrothermal solution probably decreases gradually during the transformation, and this decrease may cause not only the transformation from a circular to a polygonal crystal morphology but also the development of a lath habit due to the inhibition of the growth rate in the [010] direction of the particle.

In situ hot-stage AFM study of the dissolution of the barite (001) surface in water at 30–55 °C

Abstract This paper reports in situ observations of the dissolution behavior of the barite (001) surface in pure water at 30-55 °C using hot-stage atomic force microscopy (AFM). The dissolution at 30 and 40 °C occurred in three stages; however, at 55 °C, the dissolution behavior observed at the former temperatures started immediately after injecting water into the AFM fluid cell. The first stage of the dissolution was characterized by the retreat of the initial steps and continued for about 60 min at 30 °C and about 10 min at 40 °C. The second stage of the dissolution was characterized by the splitting of the initial one-layer step into two half-layer steps [fast (“f”) and slow (“s”) retreat steps] with different retreat rates and by the formation of etch pits. The large difference in the retreat rate of the “f” and “s” steps led to the formation of a new one-layer step, which showed slightly faster retreat rates than the “s” half-layer step at all temperatures. The splitting of the [010] one-layer step into two half-layer steps was observed only at 55 °C. During the third stage, the development of angular deep etch pits from an initial form with a curved outline differed at each temperature. The deep etch pits grew rapidly at higher temperature, but showed at least two different retreat rates for the (001) plane at each temperature, indicating the development of the pits along different dislocations (screw and edge dislocations). The activation energies (62-74 kJ/mol) for the step and face retreats in this study were significantly higher than those reported in earlier studies. Recalculations performed using only data obtained under similar conditions in previous studies led to activation energies of 66-79 kJ/mol. These results and the earlier report showing that the form of the deep etch pits changed from angular to bow-shaped at about 60 °C may indicate that the activation energy of barite dissolution in water is higher at lower temperatures as compared with higher temperatures, thus changing the rate-limiting step. Whether the vertical and lateral retreat rates of the barite (001) plane differ in dependence of temperature remains unclear; however, the activation energies of the retreat of the (001) face in deep etch pits tended to be slightly higher than that of the lateral retreat rates of steps or other faces in deep etch pits.

Apparent polytypism in the Ruiz Peak ferric phlogopite

An example of apparent polytypism in micas, i.e. twinning of a polytype giving a diffraction pattern which simulates that of a different polytype with longer periodicity, is reported from the Ruiz Peak ferric phlogopite, which is well known for the large number of polytypes and twins already found. The X-ray diffraction pattern, precession method, may correspond to a l M polytype twinned by reticular pseudo-merohedry, a 3 T polytype, untwinned or twinned by complete merohedry, or a 1 M -3 T allotwin. The morphological observation under the polarising microscope clearly shows the presence of twinning with composition plane (001) (rotation twinning), ruling out the case of untwinned 3 T polytype. The SPM observation of the surface reveals the presence of 10 A steps, without interlacing pattern or multiple steps, indicating that the sample is a twin of 1 M . The twin is law [310] π (or [310] π ), the twin index is 3, and the twin obliquity is 0.03°. The higher frequency of rotations twins, i.e. with composition plane (001), with respect to reflection twins, i.e. with composition plane (quasi) normal to (001), is discussed in terms of the crystal growth conditions.

AFM Study on Surface Microtopography, Morphology and Crystal Growth of Hydrothermal Illite in Izumiyama Pottery Stone from Arita, Saga Prefecture, Japan

Atomic force microscope (AFM) observation and analysis of Izumiyama hydrothermal illite (the weaker al- tered illite-kaolinite zone (IZ-1) and the higher altered illite zone (IZ-2)) were performed to understand the crystal growth mechanism and the relation between morphology and polytype of the illites. Our AFM results suggest that growth of the Izumiyama illite was controlled by a mechanism of solution-mediated polytype and spiral-type transformations, based on the Ostwald ripening process. The sequential variations could follow the changes in supersaturation and/or temperature of the solution. The paths of the thermal and supersaturation condition changes of the hydrothermal solutions for the two samples were estimated from the saturation state of the solution, which was evaluated by the step separation, polytype and mineral assemblage of the samples.

Archeointensity estimates of a tenth-century kiln: first application of the Tsunakawa–Shaw paleointensity method to archeological relics

Paleomagnetic information reconstructed from archeological materials can be utilized to estimate the archeological age of excavated relics, in addition to revealing the geomagnetic secular variation and core dynamics. The direction and intensity of the Earth’s magnetic field (archeodirection and archeointensity) can be ascertained using different methods, many of which have been proposed over the past decade. Among the new experimental techniques for archeointensity estimates is the Tsunakawa–Shaw method. This study demonstrates the validity of the Tsunakawa–Shaw method to reconstruct archeointensity from samples of baked clay from archeological relics. The validity of the approach was tested by comparison with the IZZI-Thellier method. The intensity values obtained coincided at the standard deviation (1σ) level. A total of 8 specimens for the Tsunakawa–Shaw method and 16 specimens for the IZZI-Thellier method, from 8 baked clay blocks, collected from the surface of the kiln were used in these experiments. Among them, 8 specimens (for the Tsunakawa–Shaw method) and 3 specimens (for the IZZI-Thellier method) passed a set of strict selection criteria used in the final evaluation of validity. Additionally, we performed rock magnetic experiments, mineral analysis, and paleodirection measurement to evaluate the suitability of the baked clay samples for paleointensity experiments and hence confirmed that the sample properties were ideal for performing paleointensity experiments. It is notable that the newly estimated archaomagnetic intensity values are lower than those in previous studies that used other paleointensity methods for the tenth century in Japan.

Millennial-Scale Interaction between Ice Sheets and Ocean Circulation during Marine Isotope Stage 100

Waxing/waning of the ice sheets and the associated change in thermohaline circulation have played an important role in global climate change since major continental ice sheets appeared in the northern hemisphere about 2.75 million years ago. In the earliest glacial stages, however, establishment of the linkage between ice sheet development and ocean circulation remain largely unclear. Here we show new high-resolution records of marine isotope stage 100 recovered from deep-sea sediments on the Gardar Drift, in the subpolar North Atlantic. Results of a wide range of analyses clearly reveal the influence of millennial-scale variability in iceberg discharge on ocean surface condition and bottom current variability in the subpolar North Atlantic during marine isotope stage 100. We identified eight events of ice-rafted debris, which occurred mostly with decreases in sea surface temperature and in current components indicating North Atlantic Deep Water. These decreases are interpreted by weakened deep water formation linked to iceberg discharge, similarly to observations from the last glacial period. Dolomite fraction of the ice-rafted events in early MIS 100 like the last glacial Heinrich events suggests massive collapse of the Laurentide ice sheet in North America. At the same time, our early glacial data suggest differences from the last glacial period: absence of 1470-year periodicity in the interactions between ice sheets and ocean, and northerly shift of the ice-rafted debris belt. Our high-resolution data largely improve the picture of ice-sheet/ocean interactions on millennial time scales in the early glacial period after major Northern Hemisphere glaciation.