S. Veintemillas-Verdaguer

Growth habit and surface morphology of L-arginine phosphate monohydrate single crystals

The results of a study of the growth habit and the surface topography of L-arginine phosphate monohydrate (LAP) single crystals as a function of supersaturation are described and discussed. Apart from a change in the growth habit with supersaturation, it was observed that most of the as-grown faces of LAP exhibit isolated growth hillocks and macrohillocks and parallel bunched layers and that the formation of bunched layers is pronounced on faces showing macrohillocks. Observations of bunching of growth layers emitted by macrohillocks on the {100} faces revealed that, for the onset of bunching close to a macrospiral, there is a characteristic threshold distance whose value depends on the interstep distance and supersaturation, but is independent of step height. The theoretical habit of LAP deduced from PBC analysis showed that all faces exhibiting growth hillocks and macrohillocks are F faces. Analysis of the results on bunch formation revealed that growth of LAP takes place by the direct integration of growth entities at the growth steps, that the bunching is facilitated by an increasing value of the activation energy for their integration, and that the observed dependencies of threshold distance on interstep distance, supersaturation and step height are qualitatively in agreement with van der Eerden and Muller-Krumbhaars theory of bunch formation.

Surface microtopographic study of KDP crystals grown at the boiling point

Abstract The surface microtopography of prism and pyramidal faces of KDP crystals grown at the boiling point is investigated. Inclusions, block structures and isolated growth hillocks are observed. The origin of these growth structures and the mechanism of growth of the crystals are discussed. From an analysis of the results it is inferred that the formation of inclusions, block structures and growth hillocks (dislocations) is determined by the behaviour (i.e. association, dissociation and rearrangement) of growth steps and that the crystal grows by the pilling up of layers originated by two-dimensional nucleation, dislocation or other defects on the surface.

Metastability in drowning-out crystallisation : precipitation of highly soluble sulphates

In this paper we derive equations for evaluating the supersaturation, b, and the supersaturation rate, Rb, for the drowning-out crystallisation under isothermal conditions and assuming a constant rate of the addition of the co-solvent. Such equations are applied to the drowning-out crystallisation of single and double sulphates in theM2SO4±LiSO4±H2O (M=Na, Rb) ternary systems. A linear relationship between lnRb and ln bmax, similar to that reported for the crystallisation by cooling, evaporation and chemical reaction, has been found.

A thermodynamical approach to tetramethylsilane (TMS) pyrolysis : application to SiC coatings obtained by MOCVD

Tetramethylsilane is an organometallic precursor commonly used in the preparation of SiC layers by MOCVD. However, little is known about the chemical reactions involved in the deposition process. Thermal decomposition of TMS in the presence of H 2 used as carrier gas, has been thermodynamically modelled considering the byproducts detected in the exhaust gas and some others that theoretically could be present: C, Si, H 2 , mononuclear silanes and mononuclear methylsilanes, methane, ethane, ethene, acetylene and SiC vapour

On the formation of dislocation etch pits on L-arginine phosphate monohydrate single crystals

The results of the etching behaviour of different faces of L-arginine phosphate monohydrate (LAP) crystals in distilled water, methanol and ethanol are described. It was found that all the three solvents produce dislocation etch pits on different faces of LAP crystals, and that the capability of revelation of etch pits by a solvent on different faces depends on their crystallographic orientation. The observations are interpreted from the standpoint of Cabreras thermodynamic theory of dislocation etch-pit formation.

Crystal growth from boiling solutions

Abstract This paper reviews the present status of crystal growth from boiling solutions. The understanding of the peculiar characteristic of this technique: high rates of growth, restricted aplicability to substances presenting complexing phenomena in solution, high crystal perfection, etc, makes interesting to analyze the structure of saturated solutions and the nature of crystal growth units. After a discussion of the role of complex formation and solute association, metastable zone width, crystal solution interface and bubbling in boiling solutions in applying this technique, the experimental set-ups reported so far are narrated. Finally, the macro and micromorphology, the growth kinetics and the perfection of the obtained crystals are described and discussed.

Criteria for growing crystals from boiling solutions

Abstract The criteria for growing single crystals from boiling solutions are developed by analysing the dependence of the width of the metastable zone, the surface roughening and solution structure, with solution temperature and solute concentration, as well as the mechanical and kinetics effects of solution boiling.

Crystal growth of potassium hydrogen tartrate from aqueous solution

The morphology and the kinetics of growth of potassium hydrogen tartrate (KHT) crystals are investigated from aqueous solutions at 50 and 100°C. These results are then discussed in the light of the physical properties of saturated KHT solutions, and the processes of growth. The results suggest that KHT crystals grow by spiral growth mechanism and that the growth units are K+ and solvated HC4H4O-6 ions.

Growth of K2Mg2(SO4)3 and K2Mn2(SO4)3 from solution by solvent evaporation and diffusion-reaction methods

Abstract Crystals of K 2 Mg 2 (SO 4 ) 3 and K 2 Mn 2 (SO 4 ) 3 , have been grown by slow evaporation of solvent and by a diffusion-reaction technique in a gelified media at 85 and 80°C, respectively. The obtained crystals were characterized by inductively coupled plasma mass spectrometry (ICP-MS), UV-visible and IR spectroscopy. The morphologies observed were interpreted as a function of supersaturation.

Study of growth dislocations in L-arginine phosphate monohydrate single crystals by chemical etching

The results of a study of the distribution of growth dislocations revealed on different faces of L-arginine phosphate monohydrate (LAP) crystals by selective etching in relation to the growth conditions of the crystals are described. It was found that (1) the dislocation density, ϱ, on a face is the highest in its central regions and depends on the supersaturation used for growth, and that (2) ϱ on different faces is different. The observations are discussed from the standpoint of the mechanism of generation of dislocations at the seed-crystal interface in the initial stages of regeneration of the seed and at the crystal-medium interface due to the formation of bunches of growth layers on the growing crystal faces during their development.