How is quartz grown?

Under normal conditions, crystals of those substances whose solubility is sufficiently high grow well from solutions. And what about substances that do not want to dissolve, for example, with quartz? So how then is quartz grown?

And what about substances that do not want to dissolve, for example, with quartz? So how then is quartz grown?

A quartz is perhaps the most common mineral on Earth. Flint, amethyst, jasper, opal, chalcedony are all types of quartz. Fine grains of quartz form sand. And the most beautiful, most wonderful form of quartz is rock crystal, that is, transparent quartz crystals. Rock crystal has a number of remarkable physical properties. First of all, it is transparent - transparent not only for visible light, but also for invisible ultraviolet. Therefore, lenses, prisms and other details of optical devices are made of transparent quartz. Particularly surprising are the electrical properties of quartz. If you compress or stretch a quartz crystal, electric charges appear on its faces. This is the piezoelectric effect in crystals. There is also an inverse piezoelectric effect: if an electric field is applied to a piezoelectric crystal, the crystal is compressed or stretched (depending on the direction of the field).

There is a lot of quartz on Earth, a lot, and yet natural quartz cannot provide the needs of technology. For optical, electrical, acoustic devices, highly perfect, perfectly homogeneous quartz crystals are needed, and such in nature are extremely rare. In the earth's crust, nature grows wonderful quartz crystals from hot mineral solutions. Is it possible in the laboratory to try to grow quartz from a solution? However, under normal conditions, quartz does not dissolve in water or in strong solvents, even in acids. From solutions it is possible to crystallize those substances that have a sufficiently high solubility.

To increase the solubility, you can choose the best solvent or increase the temperature. For most substances, solubility increases with increasing temperature. In aqueous solutions at normal pressures, it is impossible to raise the temperature above 100 - water boils and evaporates. However, boiling and evaporation can be prevented by increasing the pressure. So we come to the method of crystallization from solutions at elevated temperatures and pressures - to the hydrothermal synthesis of crystals.

Nowadays, quartz crystals of practically any size are grown by the hydrothermal method; they are ideally pure and homogeneous, incomparably purer, homogeneous and perfect than natural quartz.

In this method of growing quartz crystallizers are huge cylindrical vessels made of steel or special heat-resistant alloys that can withstand strong heat, high pressures, and corrosive effects of solvents. Crystallization is carried out in hermetically sealed vessels - autoclaves up to 56 meters high and up to 23 meters in diameter.

The autoclave is filled with an alkaline solvent, for example an aqueous solution of caustic soda. At the bottom of the autoclave is the raw material for crystallization. The raw material here is natural microcrystalline quartz, not suitable for any products. In the upper part of the autoclave, seeds are hung on steel frames - thin plates cut from a good quartz crystal, natural or artificially grown. The autoclave is hermetically sealed with special valves and heated, and between the bottom, where the raw material lies, and the upper part, where the seeds hang, create a temperature differential: the temperature at the bottom is higher than at the top. From heating the solution expands, its level rises, the pressure in the hermetically sealed vessel grows. At temperatures of 30035000C and pressures up to 2 thousand atmospheres, crushed quartz at the bottom of the vessel dissolves in a hot alkaline solvent and solution flows upwards; cooling down in the upper, less heated parts of the autoclave, the streams approach the seed already oversaturated, and crystals begin to grow on the seed.

The plate is freely suspended in the solution, neither neighboring crystals nor the walls of the autoclave do not interfere with it, and a perfectly faceted quartz crystal grows on the seed. It grows at a rate of about tenths of a millimeter per day. The whole cycle of growing such crystals lasts for months, up to six months!

And most importantly, in what a man surpassed nature, this is in perfect perfection of crystals grown by him. For homogeneity, transparency, and perfection of structure, they are much better than natural ones.

In recent years, crystals of very many substances have been grown by the hydrothermal method. For the needs of technology, not only quartz, but also sapphire, ruby, mica, grenades, emerald, topaz and many other crystals that did not exist previously in nature, grow in this way.

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