Growth hydrothermal

Low-temperature solid-state synthesis is preferred in most cases, where appropriate, for obvious reasons such as energy and cost economy and process safety or for critical concerns regarding the accessibility of compounds that are stable only at low temperatures or non-equilibrium phases, i.e., compounds thermodynamically unstable with respect to the obtained phase (e.g., a ternary instead of binary phase). The use of low-temperature eutectics as solvents for the reactants, hydrothermal growth... 

In hydrothermal growth, the materials usually grown as single crystals are those classified as insoluble at standard temperature and pressure (STP). 

Parameters Controlling Hydrothermal Growth of Single Crvstal.s-... 

For aU these reasons, purity of materieds is one of, if not the, most important of the parameters controlling hydrothermal growth. 

Ding, Y., Shen, X., Gomez, S., Luo, H., Aindow, M. and Suib, S.L. (2006) Hydrothermal growth of manganese dioxide into three-dimensional hierarchical nanoarchitectures. 

Another recent modification to the secondary growth method as applied to MFI-type zeolite membranes is to perform the hydrothermal growth on the seeded... 

M. Hosaka and S. Taki, Hydrothermal growth of quartz crystals in NaCl solu tion,... 

Hydrothermal Growth. Hydrothermal growth is used in the form of solution transport for the growth of synthetic quartz. Cmshed natural quartz is placed into the lower part of a high pressure steel vessel, called a bomb, and thin seed plates are located in the upper region, as seen in Figure 5. The vessel is filled, for example, to 80% capacity with a 4% NaOH [1310-73-2] solution the NaOH acts as a mineralizer to increase the solubility of Si02. 

Fig. 5. A small silver-lined hydrothermal growth vessel, 35-cm long, as used for synthetic quartz.

Thus, we felt it particularly worthwhile to try to improve the preparation of KTP since we were willing to make the bet that drastically improved new materials were not just around the comer. Two KTP preparation methods are in general use, anhydrous flux growth as described by Loiacono and his co-workers 40) and by Ballman 41) and relatively high temperature hydrothermal growth as perfected by Belt and his colleagues. 42) We will not attempt a historical review of the development of these methods. Instead we will outline some features and preparative improvements 43,45) which we discovered as a result of a preliminary study of the process physical chemistry of hydrothermal KTP growth. 

In the absence of KPO3, TiC>2 inclusions close to the seed resulted in poor growth. These studies were used by Belt and Gasharov et. al.(44 45 to scale up the process at lower temperatures than ever used previously resulting in excellent crystals at practical rates. The defect chemistry of KTP has been studied by Pat Morris(46) and is reported in a paper in this symposium. An important characteristic of KTP made by low temperature hydrothermal growth is that it is superior with respect to... 

Guo, M., Diao, P and Cai, S. M. (2005a). Hydrothermal growth of perpendicularly oriented ZnO nanorod array film and its photoelectrochemical properties. Appl. Surf. Sci. 249(1 1), 71-75. 

Key words ZnO synthesis, melt-growth, vapor-growth, solution-growth, hydrothermal-growth, electrical and structural properties... 

Hydrothermal-growth is usually defined as the use of an aqueous solvent at elevated temperature and pressure to dissolve a solute which would be insoluble under ordinary conditions. The advantages of the hydrothermal technique are a low growth temperature, a AT close to 0 at liquid/solid interface, an easily scalable technique, the reduction of most of the impurities from source. The disadvantages are the presence of intermediate products, the lithium or sodium or potassium incorporation when such solvents as LiOH, NaOH or KOH are used, the slow growth rates ( 10 mils per day), the inert liner needed, the occasional incorporation of OH and H2O. 

Some electrical and structural properties of crystals grown by various techniques, melt-growth, hydrothermal growth, SCVT and CVT are summarized in the following table. 

Characteristic red luminescence is observed for ZnO crystals doped with iron and then heat-treated in LizCOs (iron doping can be accomplished during hydrothermal growth, yielding black ZnO crystals) (see Fig. 3). 

Laudise, R.A., Hydrothermal Growth The Growth of Single Crystals, Prentice Hall, Englewood Cliffs, NJ, 275, 1970. 

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