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"Hydrothermal Crystal Growth - Quartz" - Roditi
In the period before and during World War II, Richard Nacken led an extensive German effort to grow quartz crystals; especially once the supply of natural crystals from Brazil was blocked. They used an isothermal growth process that relied on the higher solubility of the vitreous silica supply to supersaturate the solution.
Surprisingly, however, the dissolution curves of quartz were nearly identical for all samples with w/s from 1.7 to 9, indicating that the dissolution rate is predominated by surface area.
The hydrothermal synthesis of quartz - [PDF Document]
However, the composition (Ca/Si) of non-crystalline C–S–H at the start of tobermorite formation was identical regardless of the quartz dissolution rate.
We detected the first organic chemistry in quartz minerals of tectonic fault zones in Archean quartz dykes of Western Australia." 25 Mar 2015: Origin-of-life puzzle cracked How Earth's earliest life overcame a genetic paradox by Tim Wogan, Science News, 30 Jan 2015.
US3051558A - Hydrothermal synthesis of quartz - …
At operating conditions, the temperature is controlled such that a temperature difference is established between the internal temperature in the lower half of the autoclave, called the dissolving chamber, and the upper half, called the growing chamber. A temperature gradient in a closed cylinder of fluid in a gravitational field establishes a natural convection pattern called a closed themosyphon. In the warmer dissolving chamber, quartz dissolves in the solution. The warm, less dense fluid rises. In the growing chamber, the cooler temperature leads to supersaturation of the solution for quartz and the quartz precipitates on the seed crystals. The cool, dense fluid sinks into the dissolving chamber and the cycle continues.
The mineraliser is a compound added to the solution to increase the solubility of the compound of interest, in this case, quartz. Typically, alkali metal salts, particularly sodium hydroxide or sodium carbonate, are used. In natural systems, sodium chloride is believed to be the most common mineraliser.
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determined to grow quartz crystals at ..
With a melting point of 1670 °C and high chemical resistance, quartz crystals would be very difficult to form by either melt or flux techniques. Since cooling through the Curie point at 573 ° usually produces twins, any technique for production of single crystals must be done below the Curie temperature. The process used is a solution growth technique called hydrothermal growth. This technique is very similar to the processes by which natural quartz crystals are formed.
The Use of Hydrothermal Methods In the Synthesis of …
Hydrothermal growth is conducted in steel pressure vessels called autoclaves (see figure). A supply of nutrient material, usually natural clear or milky quartz, is placed in the bottom half of the autoclave. In the top half, seed crystals, cut from either cultured (synthetic) or natural crystals are hung. The baffle, a metal plate with one or more holes cut in it to provide a constant and controlled opening, is placed between the upper and lower halves. An aqueous solution, usually an alkali metal hydroxide or carbonate solution, is added to the autoclave so that the solution occupies a set percentage of the total free volume of the vessel. The alkali metal compound acts as a mineraliser, increasing the solubility of the quartz in the solution, through the formation of soluble silicate complexes.
The use of hydrothermal methods in the synthesis of ..
The development of superconductivity at a high enough temperature would revolutionize the electrical grid by creating highly efficient power lines. In addition to this extraordinary property, superconductors can create large, stable magnetic fields, which already have utility in medical technologies such as magnetic resonance imaging (MRI). To fulfill potential future applications, we must find compounds with optimal properties such as a high enough to make practical devices. Our group synthesizes transition metal chalcogenides with layered-type structures in order to prepare new superconductors or related physical properties. With advanced measurements that include synchrotron X-rays and neutrons, we study the key structure-property relationships of our superconducting materials. In addition, we find novel chemical route towards the preparation of single crystals of our materials. Common to all of our superconductors is the similarity in their crystal structures. In these chalcogenides, the M2+ ions are in tetrahedral coordination, and those MCh4 tetrahedra are edge-sharing. For the 2D materials, we are primarily interested in how to build new heterestructures to manipualte the magnetism and superoconductivity. For the 3D materials, we are interested in the fundamental interactions between the magnetism and itinerant electrons. In all cases, we are looking to find new synthetic routes towards new materials and single crystal growth. () to see our our latest papers on these materials. Below, a schematic of the topochemical reactions to achieve different phases of layered iron chalcogenides.
Hydrothermal synthesis - Wikipedia
There the cooler temperature causes the molten quartz to cool enough that the quartz comes out of its liquid state and attaches itself to a seed crystal of high quality quartz, natural or synthetic, that allows the seed crystal to grow.
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