In situ crystal growth

Professor Norbert W. Mitzel is professor of inorganic and structural chemistry at the University of Bielefeld. After preparative work on phosphorus ylides and then volatile silicon hydrides and Si-N compounds for CVD purposes, he studied weak intramolecular Si- -N interactions, poly-Lewis acids of B, Al, Ga and In, and later also organometallic lithium and lanthanide chemistry. He was particularly involved in multinuclear NMR spectroscopy. X-ray crystallography, including in-situ crystal growth of low-melting substances, and gas electron diffraction. 

Zeolite membranes are generally synthesized as a thin, continuous film about 2-20 xm thick on either metallic or ceramic porous supports (e.g., alumina, zirco-nia, quartz, siHcon, stainless steel) to enhance their mechanical strength. Typical supported membrane synthesis follows one of two common growth methods (i) in situ crystallization or (ii) secondary growth. Figure 10.2 shows the general experimental procedure for both approaches. 

Fuss T., Ray C.S., Lesher C.E., and Day D.E. (2006) In situ crystallization of lithium disilicate glass effort of pressure on crystal growth rate. /. Non-Cryst. Solids 352, 2073-2081. 

Fig. 9 Initial rates of growth of C246H494 crystals normal to 110 and 100 planes, Gno and G10o, versus crystallization temperature from an initially 4.75% solution in oc-tacosane. The associated interference optical micrographs show typical crystal habits recorded in situ during growth from solution at selected temperatures. The experimental G values are averages over many crystals (from [29] by permission of American Chemical Society)...

Polycrystalline zeolite membranes consist of inter-grown zeolite crystals with no apparent cracks or pinholes (Fig. lA). These films are composed of only zeolite (i.e., there are no non-zeolite components such as amorphous silica or polymer). They are normally supported on a substrate although free-standing films have also been synthesized. Membranes can be prepared on different substrates such as silicon wafer, quartz, porous alumina, carbon, glass, stainless steel (SS), gold, etc. Polycrystalline films are primarily prepared by hydrothermal synthesis methods including in situ crystallization, seeded growth,and vapor transport, " and have potential use in all of the applications discussed in this entry. 

The measurement of bulk parameters of a synthesis mixture is one of the older methods to study silicalite-1 formation. These methods include in situ pH measurements and calorimetry [28, 29]. With calorimetry, the change in reaction enthalpy can be measured, in other words, whether and to what degree a reaction is endothermic or exothermic. In the case ofthe synthesis of silicalite-1, a set of two studies has shown that there are two regimes in the crystal growth mechanism [30,... 

Since the location and density of nucleation sites can be well controlled in the secondary growth method, the nature of the support is less important for membrane formation than in the in-situ crystallization synthesis method. Furthermore, the elimination of the in-situ nucleation... 

Unlike melting and the solid-solid phase transitions discussed in the next section, these phase changes are not reversible processes they occur because the crystal stmcture of the nanocrystal is metastable. For example, titania made in the nanophase always adopts the anatase stmcture. At higher temperatures the material spontaneously transfonns to the mtile bulk stable phase [211, 212 and 213]. The role of grain size in these metastable-stable transitions is not well established the issue is complicated by the fact that the transition is accompanied by grain growth which clouds the inteiyDretation of size-dependent data [214, 215 and 216]. In situ TEM studies, however, indicate that the surface chemistry of the nanocrystals play a cmcial role in the transition temperatures [217, 218]. 

Dunuwila, D. and Berglund, K.A. 1997. ATR FTIR spectroscopy for in situ measurement of supersaturation. Journal of Crystal Growth, 179, 185-193. 

Lincot D, Ortega-Borges R (1992) Chemical bath deposition of cadmium sulfide thin films. In situ growth and structural studies by Combined Quartz Crystal Microbalance and Electrochemical Impedance techniques. J Electrochem Soc 139 1880-1889... 

An early attempt for ordered growth of a chalcogenide simple compound has been the cathodic deposition of thin (3 p,m) CdTe films on n-type (100) GaAs single crystals from an acidic aqueous electrolyte at 95 °C, which contained Cd(II) and Te traces generated electrolytically in situ by using a pure Te anode [4]. The... 

Cement formation requires a continuous structure to be formed in situ from a large number of nuclei. Moreover, this structure must be maintained despite changes in the character of the bonds. These criteria are, obviously, more easily satisfied by a flexible random structure than by one which is highly-ordered and rigid. Crystallinity implies well-satisfied and rigidly-directed chemical bonds, exact stoichiometry and a highly ordered structure. So unless crystal growth is very slow a continuous molecular structure cannot be formed. 

Further advances in the interpretation of mineral data could come from in situ analyses (unfortunately only possible presently on U-Th rich accessory minerals like zircon), or from detailed studies of particularly large phenocrysts, whose successive growth zones could be sampled (e g., through microdrillings) and analyzed. Ra measurements in such crystals could allow a direct determination of their growth rates. A systematic study of successive, well-dated eruptions of a given volcano, combining U-series measurements in both whole rocks and minerals, should also help with the interpretation of mineral data. 

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