X-Ray Diffraction Topography

The growth of crystals from solution〔邦文〕

In this paper, we present an experimental study of the interaction between gypsum (010) surfaces and aqueous solutions of Na2CO3 with different concentrations. This interaction leads to the carbonatation (i.e., the transformation into carbonate minerals) of gypsum crystals, which under ambient conditions shows the characteristics of a mineral replacement and leads to the formation of pseudomorphs consisting of an aggregate of calcite crystals. Carbonatation progress was monitored by scanning electron microscopy (SEM) and glancing incidence X-ray diffraction (GIXRD). The carbonatation advances from outside to inside the gypsum crystal and occurs through a sequence of reactions, which involves the dissolution of gypsum and the simultaneous crystallization of different polymorphs of CaCO3 [amorphous calcium carbonate (ACC), vaterite, aragonite, and calcite], as well as several solvent-mediated transformations between these polymorphs. The sequence in which CaCO3 phases form is interpreted taking into consideration nucleation kinetics and the qualitative evolution of several chemical parameters in the aqueous solution. The textural characteristics of the transformed regions are described. The degree of faithfulness of the pseudomorphs obtained is related to the kinetics of the carbonatation process, which in turn depends on the initial concentration of carbonate in the aqueous solutions. Finally, changes in the rate at which the transformation front advances are discussed on the basis of both textural and physicochemical considerations.

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The carbonatation of gypsum: Pathways and pseudomorph formation

Two complementary approaches are used to enhance the usefulness of X-ray topographies obtained from protein crystals. First, the use of thin plate-like crystals in conjunction with a high intensity, collimated and small source size synchrotron beam produces a large beneficial e⁄ect on the level of detail and contrast of topographies for the quantification of local misalignment in the crystal lattice. Second, the recording of topography series along the rocking curve of a di⁄raction peak is proposed as a technique to combine the benefits of both rocking curves and topographies and produce very detailed data (“rocking maps”) on the spatial distribution of lattice misalignments and mosaic spread (“local rocking curves”). The most important crystal features controlling the observed contrast are growth sectors and inter-sector boundaries, clearly observed in the topographies. Systems of parallel fringes are observed in many of the topographies. Two alternative explanations for these fringes are discussed: (a) as moire« interference fringes or (b) as Pendello‹ sung fringes in a wedge shaped crystal volume. In both cases, growth sectors play a central role in the physics of fringe generation. Many observations suggest the presence of a relatively large component of dynamical di⁄raction in these crystals; the consequences of this new scenario are discussed. ( 1999 Elsevier Science B.V. All rights reserved.

Topography and high resolution di⁄raction studies in tetragonal lysozyme

Protein crystallization in a magnetic field

Large single crystals of cesium-nickel sulfate hexahydrate Cs2Ni(SO4)2 · 6H2O of optical quality were grown for the first time. The crystal structure and the optical and thermogravimetric properties of this compound were investigated.

Cs2Ni(SO4)2 · 6H2O (CNSH) crystal: Growth and some properties

Crystals of the simple and complex nickel and cobalt sulfates as optical filters for the solar-blind technology

Phenomena and mechanisms of mixed crystal formation in solutions I. General concept on the example of the system KHC8H4O4–RbHC8H4O4–H2O

The results of studying crystallization in space are reviewed with focus on the growth of semiconductor and protein crystals. The history of the problem is considered, the influence of microgravity on the crystal growth is investigated, and the main experimental data on crystal growth in zero gravity are analyzed. The studies performed in this field at the Institute of Crystallography, Russian Academy of Sciences (IC RAS), are reviewed in detail.

Crystallization in space: Results and prospects

Optically homogeneous mixed K2Ni
 x
 Co(1 − x)(SO4)2 · 6H2O crystals are grown from solutions of different compositions by the temperature-reduction technique in static and dynamic regimes. The optical characteristics of the grown crystals are measured: transmittance reaches 80% in the wavelength range of 240–290 nm and no more than 9% in the visible spectral range. The thermal stability of the crystals is studied. It is established that the thermal stability of mixed K2Ni
 x
 Co1 − x
 (SO4)2 · 6H2O crystals is higher than that of K2Co(SO4)2 · 6H2O crystal. The defects of the mixed crystals grown in static and dynamic regimes are investigated by X-ray topography.

Alexey E. Voloshin

Papers

Cs2Ni(SO4)2 · 6H2O (CNSH) crystal: Growth and some properties

Crystals of the simple and complex nickel and cobalt sulfates as optical filters for the solar-blind technology

Phenomena and mechanisms of mixed crystal formation in solutions I. General concept on the example of the system KHC8H4O4–RbHC8H4O4–H2O

Crystallization in space: Results and prospects

Growth and properties of mixed K 2 Ni x Co 1−x (SO 4 ) 2 · 6H 2 O crystals