Lattice collapse

Thermal measurements such as DSC and DTA can be used to determine the crystal collapse temperature. The presence of the exothermic peak is associated with the lattice collapse. As shown in Figure 4.44 for a steamed and unsteamed faujasite, the thermal stability improves with increasing silica/alumina framework. 

Some metal oxide structures are unstable when over-delithiated, and as a consequence, the crystal lattice collapses to form a new phase that is electrochemically inactive. Examples are the so-called Jahn—Teller effect for spinel cathodes and similar behavior for LiNi02 and LiCo02 materials as well. These irreversible processes are considered to be caused by the intrinsic properties of the crystalline materials instead of electrolytes and are, therefore, beyond the scope of the current review. See ref 46 for a detailed review. 

To determine the character of the dislocations and the displacement vector b under dynamic reaction conditions, the g A criteria are used. The dislocation contrast is mapped in several reflections (g) by tilting the crystal, including the reflection in which the dislocation is invisible, i.e. = 0 when b is normal to the reflecting planes. Careful analysis (figure 3.25(f) and (g) of defects from the same crystal area (c)) shows that the displacement vector lies in the plane of shear (i.e. parallel to the shear plane), consistent with glide shear, with no lattice collapse. These criteria show the displacement vector to be 6 = (a/7, 0, c/4). 

X-ray diffractometry, spectrometric techniques ( Si high-resolution NMR, adsorbed 125Xe NMR, and electron paramagnetic resonance), and transmission electron microscopy (TEM) have been used to study solid-state reactions occurring between NaY zeolite and V205 at 700 K. When the ratio R (V atom number/[Al + Si] atom number) is 0.2, the zeolite lattice collapses. However, when R 0.05, the lattice remains. The interaction is interpreted in terms of sodium vanadate (containing Vv and atoms) formation. 

NaX (13X) zeolite is the catalyst of choice for benzylic chlorinations while zeolites with high Bronsted acidity (ZF520) affected ring chlorination, even though X-ray diffraction studies have later shown that the zeolite lattice collapses under the reaction conditions127. In both instances the mechanism involves active site outside the channel network of the microporous solid. Contradictory to the latter authors, Delude and Laszlo suggest that aluminum-rich zeolites would preferably initiate radical chain reaction via formation of siloxy radicals. Both the reaction medium and substituents on the aromatic substrate have a profound effect on the rate and selectivity of these reactions. Interestingly, the catalyst applied in the radical chlorinations can be easily recycled and reused. The opposite has been observed in the ionic chlorinations where the catalyst has rapidly lost its activity. 

During steaming, hydrolysis products of compounds (such as V2O5) generates acids (such as H4V2O7) that further promote Si-O-Al bond breakage, dealumination reactions, and therefore lattice collapse. 

Lipid—Lipid and Lipid—Protein Interactions. The DPL—cholesterol and the protein—DPL systems are particularly amenable to interpretation using our membrane model. The high viscosity lattice of DPL can be broken by cholesterol (Figure 9), and the lattice of BSA can be broken by a lipid (e.g., DPL, Figure 10), with a marked loss of surface viscosity. This lattice collapse means formation of independent membrane subunits whose lateral valences are saturated within the subunit, thereby producing a fluid system (Figure 1A) the subunit could be a lipid-lipid system, as with DPL and cholesterol, or a lipid-protein system. The phenomenon of lattice collapse with loss of surface viscosity is impressive in the DPL-albumin system since individually both components have a high surface viscosity. 

Preferential retention of K and NH4 by vermiculite and by weathered mica edges is sufficiently dramatic that a sizeable literature has accumulated on this so-called fixation reaction. Fixation generally decreases with soil acidification and increases with soil liming. This is attributed to the formation of Al and Fe hydroxide interlayers between mica and vermiculite layer lattices under acid conditions. Such interlayers prevent the lattices from collapsing completely. Lattice collapse is theoretically... 

TJirst studies (1, 2) of ion-exchanged forms of zeolite A reported that the exchange of Na for certain ions caused the breakdown of the zeolite lattice. However, Sherry and Walton (9) reported the existence of a hydrated BaA and concluded that the earlier reports of the nonexistence of this ion-exchanged form were based upon x-ray examination of calcined samples. Dyer, Gettins, and Molyneux (7) confirmed the existence of BaA and were able to measure Ba cation self-diffusion parameters in A. They also concluded that removal of water even at temperatures below 100 °C caused lattice collapse. Recently, Radovanov, Gacinovic, and Gal (8) have reported the preparation of Co(II)A in hydrated form, again contrary to the original studies. 

For the Na/BaA samples, the x-ray results indicate that the thermal stability of the A lattice is reduced considerably when there are >2 Ba p.u.c. That lattice collapse occurs on calcination of samples containing this Ba concentration is demonstrated also by a sudden decrease in the ability to recover 22Na by self-exchange and the appearance of an endo-therm on the DTA curve. However, the x-ray results show that up to a concentration of at least 4.5 Ba p.u.c. some structure is retained after calcination. The isotope experiments also demonstrate that above concentrations of about 3.7 Ba p.u.c. there is a relative increase in the amount of 22Na recoverable from calcined samples. These 2 points, taken in conjunction with the observed maximum in Figure 2 and the inability to prepare samples in the concentration range 2.7-3.7 Ba p.u.c., may indicate that the presence of 4 Ba ions p.u.c. is one of relative stability. Presumably, the first 2 divalent ions entering the crystal replace the 4 monovalent ions which are not located by x-ray structural analysis (3) and... 

A Dupont 160 differential thermal analyzer was used to detect the ciystal lattice collapse temperature. The measurement was conducted in 140 mL/min airflow at 10 K/min heating rate. 

Fig. 8. a Isothermal DTA trace showing the endotherm connected with the Na-Pl Na-P2 transformation b DTA curve of Ba-exchanged Linde A zeolite, showing the sharp endotherm connected with lattice collapse (reproduced by permission from [35])... 

Calcium sulfate dihydrate is stable only up to about 45 °C, and loses water at higher temperatures to be converted to hemihydrate. If the heating is done in air, in the absence of liquid water (that is, under dry conditions), three quarters of the water incorporated in its crystalline lattice escapes, the crystalline lattice collapses, and the dihydrate converts to hemihydrate, which possesses a highly distorted crystalline lattice. With more... 

Stoichiometric hydroxyapatite does not readily lose OH from its crystal lattice which remains stable up to at least 1000°C. In addition, a typical precipitated product may contain up to 3% HjO even after drying at 100°C, and will only expel it after heating to 800°C. Above 1000°C, a small proportion of the OH reacts to form O2 and water, without producing any lattice collapse (5.45). Above 1500°C, hydroxyapatite decomposes according to the reaction (5.46) ... 

The proportions of the two different ortho anions in mixed salts are sometimes variable over a wide range of composition without lattice collapse taking place, as with eulytite. On the other hand, the degree of variation may be more limited as in some naturally occurring sulphate and silicate-substituted apatites with formulae ... 

A particularly interesting and important development in recent years has been the use of organic compounds as templates when forming porous inorganic phosphate structures, for example, 2D pillared layer or 3D cavity structures. These organic templates dictate the shape and size of the pores which are formed, and they can usually be removed from the inorganic framework afterwards. If their removal results in lattice collapse, the lattice should not be regarded as truly microporous [3]. 

Figure 26 4 x4 DNA tile and lattices, (a) Schematic strand trace of a 4 x 4 tile, (b) AFM image of nanoribbons formed from tubules of 4 x 4 tile lattice collapsed flat onto mica surface, (c) AFM image of flat lattice nanogrid formed from 4x4 with corrugated tile orientations. 

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