Yoshikazu Aoki

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.

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.

Penetration twins of potassium chloride

Abstract A large number of penetration twins were formed during growth of KCl crystals from aqueous solution. All of them are interpenetrating octahedra or cuboctahedra with well defined rotation angles about the [100], [110] and rarely the [111] axis common to two individuals. Twin formation is favored by Pb 2+ and relatively high supersaturation. The maximum yield is obtained within the range 0.4–0.6 g Pb 2+ per liter H 2 O and σ=0.1–0.4. Both geometry and reticular aspects are discussed in terms of rotation twinning, on the ground of coincidence-site lattices. Good agreement is obtained between the rotation angles observed in the twins and those expected from the application of coincidence-site lattice theory.

Growth of KCI whiskers on KCI crystals including the mother liquid

Abstract Optical and scanning electron microscope observations were made of KCI whiskers grown on KCI crystals occluding liquid inclusions. Most of the whiskers were found to be hollow tubes which were connected with the liquid inclusions through narrow channels.

Dendritic diamonds synthesized by simple hot-filament-assisted chemical vapor deposition

Abstract Dendritic diamond crystals have been formed by using a simple method of hot-filament-assisted chemical vapor deposition. A dendritic single crystal consists of three square prisms elongated to the direction of [100], [010] and [001], and one to four triangular pyramids elongated to 〈111〉. Twins and aggregates attached to dendritic individuals are also found. Dendritic diamonds are formed under the conditions of higher filament temperature and substrate temperature than those for polyhedral diamond growth.

Arrowhead-like diamond crystals formed by hot-filament chemical vapor deposition

Abstract Arrowhead-like diamond crystals have been formed by using a simple method of hot-filament-assisted chemical vapor deposition. These are contact twins with {111} as the twin plane, of which each individual is composed of {100}, {110} and {111} faces. These twins flatten along {110} face and elongate parallel to {111} contact plane. The flattened {110} face consists of many {110} terraces sided by 〈110〉 and 〈112〉 steps. So the twinned crystal looks like an arrowhead. These twins are formed just underneath the uppermost substrate temperature for diamond growth.

Formation of tetrapod-like crystals of diamond formed by hot-filament chemical vapor deposition: effects of preformation of tungsten carbide on the substrate

Abstract A large number of diamond crystals with tetrapod-like form were obtained when a tungsten thin plate was used as the substrate of hot-filament-assisted chemical vapor deposition. In this case, the substrate was covered by hexagonal tungsten carbide (WC) thin films and subsequently diamond crystals grew on them by facing its own {111} to the substrate. The sites of carbon atoms on {111} of diamond are in good accord with those on (001) of WC. Hence WC microcrystals provided nucleation sites for subsequent diamond growth. Namely on (001) of WC, {111} of diamond grew epitaxially, constructing the coincidence site lattice (CSL).

Growth of twinned magnetic crystals in talc and talc-magnesite rock at Torika, Nagasaki Prefecture, Japan

Abstract Spinel-type twins of magnetite in a talc rock and a talk-magnesite rock at Torika, Nagasaki Prefecture, Japan have been studied by means of optical microscopy, differential interference microscopy, microprobe analysis and size distribution analysis. The growth processes are discussed in detail. The number of magnetite twins in the talc-magnesite rock is larger than in the talc rock, and the percentage of the frequency number increases rapidly with increase in grain size. It is suggested that magnetite crystals in the talc-magnesite rock have grown by rapid crystallization in the earlier stage and by a layer-growth mechanism in the later stage in the carbonation-dehydration reaction that occurred within the rock. As large number of twin nuclei formed by rapid crystallization in the earlier stage of magnetite formation. As the dehydration reaction proceeded, the number of twin nuclei gradually decreased with the lowering of supersaturation by addition of some water. Magnetite crystals in the talc rock formed after talc crystallization by silicification and dehydration reactions in the process of steatitization. The twin nuclei here must have formed with difficulty, governed by the distribution of talc which crystallized before the magnetite and at relatively low supersaturation.