Katsuo Tsukamoto

Direct observations of pseudomorphism : compositional and textural evolution at a fluid-solid interface

Abstract Solid-fluid interactions often involve the replacement of one phase by another while retaining the morphology and structural details of the parent phase, i.e, pseudomorphism. We present in situ observations of the evolution of both the solid and fluid compositions at the interface during such a replacement reaction in the model system KBr-KCl-H2O, in which a single crystal of KBr is replaced by a single crystal of KCl. The pseudomorphism is initiated by epitaxial growth at the fluid-mineral interface, when the dissolution of the parent phase results in an interfacial fluid layer that is supersaturated with respect to a different solid composition. The subsequent evolution of the coupled dissolution and growth can be related to local equilibrium defined by a Lippmann diagram. The reaction features, including the development of porosity in the new solid phase, share many characteristics of replacement reactions in nature as well as in technical applications

Application of real time phase shift interferometer to the measurement of concentration field

Abstract A real time phase shift interferometer developed by Nakadate is applied to the measurement of the concentration distribution around a growing or dissolving crystal. Use of the polarized light interferometer allowed either a grey level picture depending on a two-dimensional phase distribution or a three-dimensional perspective profile of the concentration field to be displayed on a TV monitor in real time. The sensitivity of the interferometer is increased at least by a factor of 20 to 30 compared with the conventional two-beam interferometer. The time resolution was also improved so that succesive phase distribution could be obtained at the time resolution of 1/60 s. Using the Abel transformation method, a quasi-three-dimensional concentration profile of a sodium chlorate crystal was calculated, which made it possible to measure the actual surface concentration.

Activities of spiral growth hillocks on the (111) faces of barium nitrate crystals growing in an aqueous solution

In situ measurements of normal growth rates R, slopes p, and step advancing rates v = R / p of the spiral growth hillocks generated from two types of dislocations, screw (b = [111]) and mixed (b = 〈110〉), were made on the (111) faces of Ba(NO3)2 crystals growing from an aqueous solution at different flow velocity, u. These two types of dislocations were identified also in situ by stress birefringence microscopy. It was found that: (1) The growth hillocks originated from the screw dislocations grow faster than those from the mixed dislocations, and the tendency is more pronounced as u increases (Rs/Rm = 1.3 when u = 40 cm/s). (2) As u increases, the step advancing rates become equal for the two types, in spite of the difference of step heights (hs/hm = 1.5). (3) The growth hillocks generated from the screw dislocations are steeper under any growth conditions than those from the mixed dislocations. It was also demonstrated that the dislocations outcropped near the periphery of a growing face were twice more active as growth centres than those at the centre of the face, due to the higher supersaturation along the periphery of the face. It is concluded that the direct integration model explains the result on the step movement better than the surface diffusion model. It is also concluded that the increase of the interstep spacing and therefore the edge free energy of steps are not proportional to the increase of the step height.

In situ study of surface phenomena by real time phase shift interferometry

Abstract Real time phase shift interferometry is applied to the observation of a growing crystal surface. Detailed profiles of a growth hillock, such as local vibrations of slopes and height differences of growth steps, are clearly distinguished on a barium nitrate crystal, together with measurements of growth rate at each location. It was found that the height difference of 0.92 nm was directly detectable in this interferometry, indicating that the present method is a few ten times more sensitive than conventional two-beam interferometry, applicable to in situ study, such as Michelson interferometry. It was found that: (1) Step spacing gradually increases as a step approaches the edge of a crystal, which is inferred from the non-uniformity of surface supersaturation. (2) The observation of fluctuation of the growth rate under a constant condition was analyzed as due to the unequal separation of neighboring dislocations which produce the pertubation of steps.

In Situ observation of mono-molecular growth steps on crystals growing in aqueous solution. I

Abstract It is demonstrated that by combining optical phase contrast microscopy with a conventional TV system, mono-molecular spiral growth steps on crystals can be observed during the growth in aqueous solution. The image of the mono-molecular growth steps is stored either in a video tape recorder or through an A/D converter into the floppy disk in a computer. The minimal step height on CdI2 crystals measured by the in situ interferometry described in a forthcoming paper is about 1.4 nm, which satisfactorily agrees with the mono-molecular growth step height derived from the crystal structure. This observation method has a great advantage in understanding the growth mechanisms of crystals in more direct way when the growth rate measurement is coupled.

Stacking faults as self-perpetuating step sources

Abstract Atomic configurations of sub-steps created on a (111) growth surface of an fcc crystal by stacking faults with fault vectors 1 6 〈112〉 and 1 3 〈111〉 show that they can act as self-perpetuating step sources. Growth kinetics provided by such sub-steps have been analyzed, and it has been shown that the 2D heterogeneous nucleation barrier at the sub-steps is always smaller than that of conventional 2D nucleation. It has also been shown that the 2D heterogeneous mono-nuclear and birth-and-spread nucleation along the sub-steps should provide a growth rate exceeding the one provided by conventional 2D nucleation at low and high supersaturations.

Role of buoyancy driven convection in aqueous solution growth; A case study of Ba(NO3)2 crystal

Abstract Using Schlieren technique and Mach-Zehnder interferometry, the diffusion boundary layer and buoyancy driven convection around a growing barium nitrate crystal from the aqueous solution were visualized and their effect upon the growth kinetics of crystals was investigated in relation to the bulk supersaturation. It was demonstrated that buoyancy driven convection plumes behaved differently depending on the bulk supersaturation, and that their behavior gave a definitive effect upon the growth rates.

Transformation of α-glycine to γ-glycine

Transformation in a cell of the a form of glycine crystals to the γ form under high humidity was observed by an in situ observation method. The transformation of α-glycine to γ-glycine was found to be solvent-mediated phase transformation. The kinetic equation was obtained, and the calculated values were in good agreement with experimental values.

Measurements of surface supersaturations around a growing K-alum crystal in aqueous solution

Abstract Surface supersaturations, σ s , were directly measured by the Mach-Zehnder interferometer on K-alum crystals growing in the aqueous solution, at different flow velocities u , from 3 to 40 cm/s. The σ s is not linearly related to the bulk supersaturation, σ b , at smaller u , and is always smaller by 6 to 20% than σ b . The profile of σ s distribution over a growing face changes significantly and becomes more asymmetrical and shows a wider uniform σ s region as increasing u .

Clustering phenomenon and growth units in lysozyme aqueous solution as revealed by laser light scattering method

Abstract To analyse the clustering phenomenon, the diffusion coefficient in and the viscosity of the bulk supersaturated solutions were measured using quasi-elastic light scattering, and the concentration gradient in the diffusion boundary layer around a growing crystal interface was measured by means of Mach-Zehnder interferometry. The results obtained in case of tetragonal lysozyme crystals have demonstrated that (1) the solute particle size determined from values of both the diffusion coefficient and the viscocity indicated the presence of the solute clustering in the bulk supersaturated solutions, but (2) the major growth units controlling the growth rate were monomolecular entities. The growth kinetics for tetragonal lysozyme crystals were also analysed, based on the surface microtopographic observations, and it was shown that the growth was principally controlled by the surface kinetic process.