Crystal nucleus

By scratching the inside of the vessel with a glass rod. The efifect is attributed to the breaking ofiF of small particles of glass which may act as crystal nuclei, or to the roughening of the surface, which facilitates more rapid orientation of the crystals on the surface. 

Randolph, A.D. and Sikdar, S.K., 1976. Creation and survival of secondary crystal nuclei. The potassium sulphate-water system. Industrial and Engineering Chemistry Fundamentals, 15, 64. 

These CaC03 crystal nuclei then provide seeding points for silicate precipitation. 

Phosphonates, especially aminotri(methylenephosphonic acid) (ATMP) and l-hydroxyethylidene-l,l-diphosphonic acid (HEDP). Organophosphonates have the ability to control both scaling and corrosion by a combination of chelation and crystal nuclei growth supression (threshold) mechanisms they also provide scale control by crystal distortion. 

The simplest case occurs when a number of nuclei is formed at the beginning of the process and does not change with time instantaneous nucleation). This is the case when the electrolysis is carried out by the double-pulse potentiostatic method (Fig. 5.18B), where the crystallization nuclei are formed in the first high, short pulse and the electrode reaction then occurs only at these nuclei during the second, lower pulse. A second situation in which instantaneous nucleation can occur is when the nuclei occupy all the active sites on the electrode at the beginning of the electrolysis. 

The initial transition of dissolved silicate molecules into solid nanoparticles is perhaps the least explored step in the synthesis of zeolites. One impediment to understanding this mysterious step is the poorly elucidated molecular composition of dissolved particles. The major mechanistic ideas for the formation of zeolites approach these structures differently i) many researchers believe that secondary building units (SBU) must be present to form initial nanoslabs [1,2] ii) some others prioritize the role of monomers to feed artificially introduced crystal nuclei or assume that even these nuclei form via appropriate aggregation of monomers [3] iii) silicate solutions are also frequently viewed as random mixtures of various siloxane polymers which condense first into an irregular gel configuration which can rearrange subsequently into a desired crystal nucleus at appropriate conditions [4,5],... 

Zinc chalcogenide thin hlms have been grown by ECALE using zinc sulphate as metal source and sodium sulphide and sodium selenite as chalcogenide precursors.145-148 The formation of the hrst layers of ZnS on (lll)Au has been analyzed by STM and XPS.145 HRSEM images showed that the him surface was very hat, even at an atomic level. On the other hand, thicker ZnS hlms were formed of well-separated crystal nuclei. The stoichiometry of a thicker ZnS him showed a slight excess of sulphur, with a Zn S ratio of 1 1.2. The band gap of a thicker him (deposition time 12 h) was 3.60eV.147... 

There will be some differences and it is a quantitative question, whether or not they can be tolerated or not. For a final decision, test runs in a pilot plant should be carried out with freshly frozen product and such which has been resting for 5 h before drying. These tests are recommended because the methods mentioned above use different sized samples in different configuration than are used in the production. The amount of product and its geometrical dimension will also influence the structure as well as the number of crystallization nuclei in the product, which can be very different in a normal laboratory and in a clean production area. 

All experiments up to this time employed only minute quantities of seed crystals. In investigating the variables affecting the growth of the dextrose crystals, Newkirk found that the operation could be controlled by using much greater proportions of seed crystals than had hitherto been employed.8 The excessive formation of crystal nuclei too small and numerous to be able to grow to satisfactory size could be avoided by this means. The operation was most economically carried out by leaving in the crystallizer 25 to 30% of a finished batch to act as seed for the... 

The fibers exhibit a fine structure consisting of large crystals separated by areas of poorly oriented, amorphous regions with many crystal nuclei at a pronounced skin/core character, which is a consequence of a complex structure formation mechanism. The nuclei grow into large crystals upon heating. 

Spontaneous resolution seems to be a general phenomenon, because it is also observed to occur from solutions of achiral sodium chlorate, which crystallizes into morphologically chiral crystals. In the same way as quartz, however, any given spontaneous crystallization produces nearly equal numbers of left- and right-handed sodium chlorate crystals. The explanation for this behavior is that the primary crystallization nuclei that form throughout a cooling concentrated solution must occur with a random distribution of the two morphological chiralities. 

This method requires the addition of a mixed M(II)/M(III) salt solution to an alkaline solution containing the desired interlayer anion. Preparations under conditions of high supersaturation generally give rise to less crystalline materials, because of the high number of crystallization nuclei. Because this method leads to a continuous change in solution pH, the formation of impurity M(0H)2 and/or M(OH)3 phases, and consequently an LDH product with an undesired M(II)/M(III) ratio, often results. Thermal treatment performed following coprecipitation may help increase the crystallinity of amorphous or badly crystallized materials. 

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