Crystal mistakes

Know your chemicals it can be very easy to confuse one chemical with another, especially if their names and packaging are similar. Also, the same compound may have different forms - for example it may be an anhydrous powder or hydrated crystals. Mistakes at this stage are wasteful of time and reagents and at worst may result in serious accidents. Always double check that you are using the right chemical. 

The solution is highly supersaturated, but it will remain so unless allowed to stand for an undue amount of time. It is also a mistake to add the quantity of concentrated hydrochloric acid specified to a suspension of the aminonaphthol, for this may initiate crystallization. 

In Ref [16] the terms fusion and crystallization are mixed up. The equation given here is corrected for this mistake. 

A point defect is a localized defect that consists of a mistake at a single atom site in a solid. The simplest point defects that can occur in pure crystals are missing atoms, called vacancies, or atoms displaced from the correct site into positions not normally occupied in the crystal, called self-interstitials. Additionally atoms of an impurity can occupy a normal atom site to form substitutional defects or can occupy a normally vacant position in the crystal structure to form an interstitial. Other point defects can be characterized in pure compounds that contain more than one atom. The best known of these are Frenkel defects, Schottky defects, and antisite defects. 

Figure 3.20 Planar defects in solids (a) boundaries between slightly misaligned regions or domains b) stacking mistakes in solids built of layers, such as the micas or clays (c) ordered planar faults assimilated into a crystal to give a new structure and unit cell (shaded).

There are a number of mechanisms by which twins can form. Growth twins are attributed to a mistake occurring when a crystal is nucleated, so that the orientation... 

The correction of mistakes is an important aspect of crystal nucleation and is achieved by the inherent weakness of most interactions in the typical molecular crystal. Such correction could be facile because only around 15 % of all crystal structures in the CSD are disordered. 

Free-radical polyolefin reactions form polymers with many mistakes in addition to the ideal long-chain alkanes because of chain-branching and chain-termination steps, as discussed. This produces a fairly heterogeneous set of polymer molecules with a broad molecular-weight distribution, and these molecules do not crystallize when cooled but rather form amorphous polymers, which are called low-density polyethylene. 

The crystals of this salt prepared by T. Thomson s process were formerly stated to be sodium octohydrated carbonate, Na2C03.8H20, but H. Lowel proved that this is a mistake the product is Bodium heptahydrated carbonate. The /8-hepta-hydrated carbonate is less soluble than the a-salt, and more soluble than the decahydrated carbonate, so that a soln. Bat. with the a-salt is supersaturated with respect to the j8-salt, and the decahydrated salt. The transformation of the a- into the /8-variety occurs while the salt is in contact with its mother liquid at very variable temp.—sometimes at 23°, more often below 10°. The /3-salt effloresces in dry air, and passes into the monohydrated carbonate at about 32°. An appreciable amount of heat is developed during the crystallization of a supersaturated soln., and this iB greater for the -heptahydrated carbonate than for the a-Balt but less than for the decahydrated carbonate. The temp, rose from 20 5° to 22 5° during the crystallization of the /3-salt from a sat. soln. 

Crystalline form,—Lithium nitrate crystallizes in rhombohedra (trigonal system).15 P. W. Bridgman observed no new form of lithium nitrate between 20° and 200°, and press, between 1 and 12,000 kgrms. per sp. cm. The older authorities—e.g. P. Kremers—supposed this salt to be trimorphic, but the supposed polymorphism is probably due to their mistaking hydrates for polymers of the anhydrous salt. It is doubtful if lithium nitrate is isomorphous with silver or sodium nitrate, although J. W. Retgers says that sodium and lithium nitrates are isomorphous. 

On a macroscopic scale, the adjustment of helical hand is an indisputable feature. Indeed, the very fact that different crystal structures (either con-formationally chiral or racemic) can be formed from the same initial melt (whether structured or not by, for example, spinodal decomposition) indicates that this selection of helical hand is operative. Even more demonstrative, the occurrence of mistakes in the adjustment of helical hands can have a profound impact on the growth process. For example, the formation of a sufficient patch of isochiral helices in the antichiral a phase of iPP may induce a growth transition to the chiral /3 phase. The rarity of such growth transi-... 

The hydrated cations that form when salts dissolve in water often remain hydrated if the solutions are evaporated to dryness thus, evaporation of an aqueous solution of ferric chloride yields solid Fe(H20)jj+(Cl )3. It is a mistake to consider the water merely as something extra thrown into ordinary solid FeCh. Not only does the hydrate have a different color and different crystal structure from the anhydrous chloride, but upon heat treatment, the Fe—O bonds survive while the chlorine will leave the lattice as IICL (Thus anhydrous FeCl3 cannot be made by simple dehydration of the hydrate.) Such water of hydration, fittingly called cation water, occurs frequently. 

With respect to the aggregation of vacancies in crystals to form CS planes, it is worth mentioning that this behaviour seems to hold in M0O3. However, the findings of Thoni and Hirsch, which apparently vindicated this mechanism, have been shown to be based upon a mistake in the interpretation of their electron microscope results. ... 

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