Crystal cracking

Fe(btr)2(NCS)2]-H20 undergoes a complete ST centred at 134 Kwith a hysteresis loop of width 21 K. This derivative represents the first example of a 2D ST compound and has become a model material in SCO research. The presence of a crystallographic phase transition to account for the observed hysteresis was first proposed since crystal cracking was regularly observed when the sample was cooled through the temperature region of the spin transition [59]. Recent X-ray data recorded at 95 K, where the com-... 

If local stresses exceed the forces of cohesion between atoms or lattice molecules, the crystal cracks. Micro- and macrocracks have a pronounced influence on the course of chemical reactions. We mention three different examples of technical importance for illustration. 1) The spallation of metal oxide layers during the high temperature corrosion of metals, 2) hydrogen embrittlement of steel, and 3) transformation hardening of ceramic materials based on energy consuming phase transformations in the dilated zone of an advancing crack tip. 

Because the crystals were cooled from their edges, temperature gradients were significant. This problem was especially severe when a crystal cracked... 

When trying to determine the 3D structure of binary and ternary complexes of Drosophila alcohol dehydrogenase (DADH), researchers initial attempts to soak apo-form crystals with the oxidized coenzyme (NAD+) failed. The crystals cracked after several hours and became unusable. This suggested that the coenzyme, upon binding to the enzyme, induced a conformational change that seriously affected the crystal packing. The same phenomenon prevented solution of the HL-ADH 3D structure for many years. 

When a glass cracks, it shatters. When a crystal cracks, it cleaves along a flat plane. Explain why. 

On polymerization the C- C -COOH crystals crack parallel to the c-axis both in the bulk crystalline form and in multilayers, while the alcohol does not. (See Figure 3) This was attributed to the larger volume change upon phase transition. It also may well relate to the fact that hydrogen bonding is not three dimensional in the acid but is of the dimer type along the a-axis. ... 

An improved sodium silicate type mortar with greater water resistance and higher physical strength. Resistant to crystallization cracking, and vitrification to 1900°F. 

To minimize the damage that could occur to a furnace and danger to personnel in the event of a spill, the furnace floor was covered with a course sand to absorb as much of a spill as possible. A bed of sand was also maintained at the base of the furnace to trap any spillage, keeping it from flowing. Fortunately, this never became a problem. Several crucibles cracked during their use, but none catastrophically. Since crucibles were intentionally sacrificed upon the completion of crystallization, cracked crucibles presented no significant problems. 

Keep solid material wet or soaked with solvent as long as possible. In mixture with liquids explosives are normally desensitized (phlegmatized). Favoured solvents for this purpose are nonflammable solvents like water or halogenated hydrocarbons. Only highly sensitive compounds like primary explosives can detonate without obvious reason even when they are stored under water. It is supposed that these unexpected explosions are caused by internal stress of larger crystals leading to crystal cracks. 

Ferroelectric BaTiOj films prepared by sol-gel methods were first reported by Fukushima in 1975 [58], followed by lead titanate [60], lead zirconate titanate (PZT) [62,63] and lead, lanthanum, zirconate, titanate (PLZT) [64], Superconducting YBa2Cu307 j, and thallium-based films have been prepared using sol-gel methods by several groups [48-51]. Both ferroelectric and superconducting films share similar processing criteria with optoelectronic films described in the previous section, viz. precisely controlled stoichiometry combined with well-crystallized crack-free microstructures and absence of impurities. The possibility of orientation through physico-... 

An important recent catalyst development is related to the nondestructive framework substitution of Si for A1 in the Y zeolite, described above. Using this recently disclosed mild aqueous chemistry, silicon-enriched forms of the Y zeolite structure (called LZ-210) have been synthesized, greatly improving the thermal and hydrothermal stability of the Y crystal. Cracking catalysts prepared from these silicon-rich zeolites show substantially increased cracking activity retention, following severe steaming pretreatments. In addition. 

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