An AFM investigation of the mechanism of secondary nucleation induced by contact (original) (raw)
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Journal of Crystal Growth, 1996
Secondary nuclei of potash alum crystals may easily be produced by gentle crystal contact. In this investigation, crystal faces of the {100}, {110} and {111} families were identified in a parent crystal, and gentle contact between these and a solid surface in a slightly supersaturated solution of potash alum produced many secondary nuclei of the same orientation. Breeding of the large number of particles produced by contact between a parent crystal and a glass surface under supersaturated aqueous solution was directly observed by optical microscopy with an in situ, thermostatted cell. A strong correlation was found between the symmetry of the nuclei produced and that of the parent crystal face. Ex situ scanning (SEM) and transmission electron microscopic (TEM) measurements were also carried out to study this type of secondary nuclei, produced from a known surface geometry. In these cases, many small nuclei in the size range of 50 nm to 1 /xm were produced and studied. The larger crystals displayed morphologies commensurate with that of the parent face; the very small nuclei, whilst frequently showing very poorly ordered boundaries, nonetheless were highly ordered internally, as shown by electron diffraction, the symmetry observed reflecting that of the parent face.
Organic Process Research & Development, 2014
In the pharmaceutical industry, it is often desired to produce seed crystals with an appropriate narrow size distribution of the desired polymorph. This study describes a system that generates such crystals continuously in a small-scale tubular crystallizer at low supersaturation via contact secondary nucleation. A response surface model was constructed by conducting a statistical design of experiment that models the nucleation rate as a function of contact force, area, and frequency. This model reveals that within a certain range the nucleation rate is linearly related to all three factors in this system. A combination of in-line video analysis and off-line microscope image analysis was used to determine the particle size distribution of seed crystals obtained in this system, and the majority of the crystals were found to be under 20 μm. This seems to be a feature of contact secondary nuclei in general and does not vary significantly with contact force, area, and frequency. Furthermore, the seed crystals generated are of the same polymorph as the parent crystals as a result of the attrition process. This study shows that generating seed crystals with a narrow size distribution using contact secondary nucleation for a continuous tubular crystallizer can be realized at a controlled rate by quantitative variation of certain design parameters.
Journal of Crystal Growth, 1999
Contact of a potash alum crystal in a supersaturated solution with a solid surface may easily produce many secondary nuclei of the same orientation and crystal structure as the parent crystal contact faces. Previous studies have shown that, if this contact is sufficiently gentle, secondary nuclei may be produced by the transfer of ordered solute molecules without the need for microabrasion of the parent solid. In this investigation, crystal faces of the +1 0 0,, +1 1 0,, and +1 1 1, families were identified in a parent crystal, and gentle contact between these and a solid surface (glass slide) in a slightly supersaturated solution of potash alum produced many secondary nuclei, the external symmetry of which reflected that of the parent face. In situ atomic force microscopy (AFM) measurements were carried out to study the early stages of the growth of these new nuclei. A strong correlation was found between the symmetry of the nuclei produced and that of the parent crystal face. The topographies of the in situ growth of the (1 1 1) face of the parent crystal and those of the very small new nuclei produced were compared.
Crystallization mechanisms of acicular crystals
Journal of Crystal Growth, 2008
In this contribution, we present an experimental investigation of the growth of four different organic molecules produced at industrial scale with a view to understand the crystallization mechanism of acicular or needle-like crystals. For all organic crystals studied in this article, layer-by-layer growth of the lateral faces is very slow and clear, as soon as the supersaturation is high enough, there is competition between growth and surface-activated secondary nucleation. This gives rise to pseudo-twinned crystals composed of several needle individuals aligned along a crystallographic axis; this is explained by regular over-and inter-growths as in the case of twinning. And when supersaturation is even higher, nucleation is fast and random.
Chemical Engineering Science, 1993
AMmct-The rem&s of two series of cxpctients concerning, respectively, the breakage and the batch erystallimtion of Ks80, crystals suspended in liquids in the same apparatus are reported. A model, incorporattng erystnl breakage, to predict the performance of the seeded batch cooling crystallizer is also presented turd the ctkt of breakage on fine crystal distribution obtained is examined in detail. It is confirmed that f'ragments of potassium sulphate crystals arise by breakage over the whole size range up to the d size, and the generation rate by secondary nucleation is la&y dependent on magma density and supersaturation. In eonsequenee, a broadening of the product crystal size distribution is observed during seeded batch crystallization. This bchaviour Is well-simulated by the crystal breakage and growth model under modsrate cooling conditions; at high cooling rates, however, a significant deviation ia crystallimr fines dlstributlon occurs, implying a change in the mechanism of secondary nucleation on moving from slightly to highly supersaturated solutions.
Crystal Nucleation without Supersaturation
The Journal of Physical Chemistry Letters, 2012
Classical nucleation theory (CNT) has been extensively employed to 6 interpret crystal nucleation phenomena and postulates the formation of an ordered 7 crystalline nucleus directly from vapor or solution. Here, we provide the first experimental 8 demonstration of a two-step mechanism that facilitates deposition of crystals on solid 9 surfaces from vapor. Crucially, this occurs from saturated vapor without the need for 10 supersaturation, conditions that, according to CNT, cannot lead to direct deposition of 11 crystals from vapor. Instead, the process relies on condensation of supercooled liquid in 12 surface cavities below the melting point. Crystals then nucleate in this liquid, leading to 13 rapid deposition of more solid. Such a mechanism has been postulated for atmospheric 14 nucleation of ice on aerosol particles and may have analogies in the crystallization of 15 biominerals via amorphous precursor phases. 16 SECTION: Surfaces, Interfaces, Porous Materials, and Catalysis 17 C lassical nucleation theory (CNT) describes nucleation 18
Crystal Growth & Design, 2016
Experimental investigations of the batch seeded crystallisation of paracetamol in 2-propanol were carried at 200, 300 &375 RPM agitation rates, using a large seed size (355-500 µm) and a low level of initial supersaturation (S 0 =1.2) in a laboratory scale reactor. Such experiments are normally conducted for the indirect measurement of crystal growth, contingent on the assumption of negligible nucleation, agglomeration and breakage. In the present work a copious increase in crystals nuclei was noted shortly following seed addition. The formation of substantial numbers of new nuclei was substantiated through FBRM, laser diffraction and SEM. Secondary nucleation was proposed as the origin of the new crystals and a Secondary Nucleation Threshold (SNT) determined, with relative supersaturation between 1.09-1.11. Below this limit, crystal growth only was apparent. A study was undertaken to investigate the origin of secondary nucleation. Crystal nuclei breeding, as a mechanism of secondary nucleation, has being theorised for many years, however it is only very recently that definitive molecular dynamics simulations have provided mechanistic insight as to its action. The mechanically driven attrition and breakage mechanism of secondary nucleation remains prominent in literature. Stirred vessel experiments were conducted using paracetamol seed crystals suspended in a non-solvent indicated. Despite three hours of continuous agitation, no significant change in particle number or size was detected. Only after a threshold of four hours were significant crystal fatigue and fragmentation evident. Shadowgraphy investigations of crystal jet wall impingement revealed the squeeze film as a key protective element in preventing crystal attrition and breakage. A low temperature (283.15 K) crystallisation was conducted which indicated a significant temperature dependency, entirely inconsistent with the attrition and breakage mechanism of secondary nucleation. It was shown that through the use of smaller seed crystals (125-250 µm), a high agitation rate and elevated solution temperature that the rate of secondary nucleation could be enhanced thereby Page 2 of 38 ACS Paragon Plus Environment Crystal Growth & Design creating the potential for confounding rapid secondary nucleation with growth. The current work elucidates the potential impact of cluster breeding in laboratory scale crystallisations and furthermore, provides additional experimental support for the crystal breeding mechanism of secondary nucleation.
CRYSTALLIZATION-PART II - "Crystallization Processes
Industrial & Engineering Chemistry, 1969
Part 11. Crystallization Processes his second part of the Crystallization Review deals with T processes and techniques of crystallization as well as with the investigation of process operating parameters. The opening section of the review, page 86, October I&EC, was concerned with the transport phenomena involved in crystal growth and nucleation. Part I11 which follows in December is directed toward investigators whose interests lie in the crystallization of a particular product. (For details on subdivision, see Introduction and Outline in Part I.)