Crystal growth, hydrothermal

M.S. (1980) Hydrothermal crystal growth rate of goethite and hematite from amorphous ir-on(III) hydroxide investigated by x-ray diffraction and neutron diffraction. Acta Chem. Scand. A 34 771-776 Christensen, H. Norlund-Christensen, A. (1978) Hydrogen bonds of y-FeOOH. Acta Chem. Scand. 32 87-88... 

In recent years, more novel methods have been developed by chemists in order to hasten the reaction between solids or to grow single crystals of new and exotic solids. Among those included in the following syntheses are electrolysis of fused salts, chemical transport, and hydrothermal crystal growth. 

Hydrothermal crystal growth Hydrothermal treatment Hydrothermal alteration Hydrothermal dehydration Hydrothermal extraction Hydrothermal reaction sintering Hydrothermal sintering Corrosion reaction Hydrothermal oxidation... 

Crystal growth of low-temperature forms of materials requires its own specific processes. For examples, a-quartz is an interesting material because of its piezoelectric properties. The a- transition is close to 573 °C a high-pressure hydrothermal, crystal-growth method has been developed because the application of pressure increases the solubility of the nutrient. Such a process is shown in Fig. 7.15. The difference in temperature, AT, between the upper part of the reaction vessel (which contains the seeds) and the lower part (containing the nutrient) provides the driving force of the chemical transport for the crystal-growth process. 

Some work has been reported on deposition of hydroxyapatite under hydrothermal conditions, that is much above 100 °C. This includes a study by Liu, Savino and Yates (2011) who coated hydroxyapatite on titanium, stainless steel, aluminium and copper substrates by a seeded hydrothermal deposition method. The deposition strategy included an electrochemical reaction to form quickly a thin layer of HAp seed crystals. Subsequent hydrothermal crystal growth from the seed layer resulted in dense and durable HAp films. In a typical hydrothermal synthesis, a solution of Na2EDTA (0.20 M) and Ca(NOs)2 (0.20 M) was prepared in 15 ml water and a solution of (NH4)2HP04 (0.12 M) in 15 ml water was prepared in a second container. The two source solutions were mixed together after the pH of each solution was raised to 10.0 with ammonium hydroxide. The resulting combined solution was stirred at room temperature for about 20 min and then transferred to a Teflon-lined stainless steel pressure vessel of 40 ml internal volume. 

R.A Laudise, and J.W. Nielsen, ((1969), Hydrothermal Crystal Growth in Seitz and Turnbull (eds.), Solid State Physics Academic Press, N. Y. 

There are pressure apparatus that produce pressures up to 1.5 million PSI. Apparatus that produce artificial diamonds and gems operate in this pressure range. They are more technically presses and not pressure vessels, per se. Pressures in the range of 20,000 to 150,000 PSI are used for food sterilization. Isostatic pressing operates in the range from 15,000 to 100,000 PSI. Autoclave reactors for hydrothermal crystal growth or production of artificial quartz are used with pressures in the 15,000 to... 

Gelabert, M.C., Laudise, R.A., Riman, R.E. Phase stability, solubility and hydrothermal crystal growth of PbTiOs. J. Cryst. Growth 197, 195-203 (1999)... 

IkormkovaN.Y. (1975) Hydrothermal Crystal Growth in Chloride Systems (Russ.), Nauka, Moscow, USSR. 

Conditions Variation and Procedural Improvement for Hydrothermal Crystal Growth of Oxides Under Highly Oxidizing Conditions, M. McKelvy and L. Eyring, J. Cryst. 

In both cases one is dealing with condensed phases (in contrast, e.g., to the solubility of a gas in a solution), and therefore the volume difference is small. Therefore, the dependence of the solubility on pressure is usually very small. The reason for the application of an external pressure is therefore not to change the solubihty of the solute, instead it is to suppress the evaporation of the solvent, to increase its existence region as a hquid or to prevent the evaporation of volatile constituents from the melt This also holds true for hydrothermal crystal growth. The necessity of high pressure is only due to the high vapor pressure of the solvent at high temperatures, with the exceptions of diamond and GaN. 

Ishiwata S, Tokunaga Y, Taguchi Y, Tokura Y. High-pressure hydrothermal crystal growth and multiferroic properties of a perovskite YMnOs- Journal of American Chemical Society 2011 133 13818-13820. 

Mann M, Jackson S,KolisJ (2010) Hydrothermal crystal growth of the potassium niobate and potassium tantalate family of crystals. J Solid State Chem 183 2675-2680... 

Hydrothermal crystallisation processes occur widely in nature and are responsible for the formation of many crystalline minerals. The most widely used commercial appHcation of hydrothermal crystallization is for the production of synthetic quartz (see Silica, synthetic quartz crystals). Piezoelectric quartz crystals weighing up to several pounds can be produced for use in electronic equipment. Hydrothermal crystallization takes place in near- or supercritical water solutions (see Supercritical fluids). Near and above the critical point of water, the viscosity (300-1400 mPa s(=cP) at 374°C) decreases significantly, allowing for relatively rapid diffusion and growth processes to occur. 

Byrappa, K. and Adschiri, T. (2007) Hydrothermal technology for nanotechnology. Progress in Crystal Growth and Characterization of Materials, 53, 117-166. 

Moreira, M.L., Andres, J., Varela, J.A. and Longo, E. (2009) Synthesis of fine microsized BaZr03 powders based on a decaoctahedron shape by the microwave-assisted hydrothermal method. Crystal Growth and Design, 9, 833-839. 

Viswanathiah, M.N. Tareen, J.A.K. Krishna-murthy (1980) Low temperature hydrothermal synthesis of magnetite. J. Crystal Growth 49 189-192... 

In an alternative process, the starting material consists of needle-shaped particles of a-Fe203 instead of FeOOH pigments [5.9], [5.10]. The synthesis is carried out in a hydrothermal reactor, starting from a suspension of Fe(OH)3, and crystal growth is controlled by means of organic modifiers. 

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